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EPA/ROD/R07-05/040 2005 EPA Superfund Record of Decision: RAILROAD AVENUE GROUNDWATER CONTAMINATION SITE EPA ID: IA0001610963 OU 01 WEST DES MOINES, IA 09/19/2005
Transcript
Page 1: RECORD OF DECISION (RODS) · RI Remedial Investigation ROD record of decision SARA Superfund Amendments and Reauthorization Act START Superfund Technical Assistance and Response Team

EPA/ROD/R07-05/040 2005

EPA Superfund

Record of Decision:

RAILROAD AVENUE GROUNDWATER CONTAMINATION SITE EPA ID: IA0001610963 OU 01 WEST DES MOINES, IA 09/19/2005

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Ciher

RECORD OF DECISION

for the

Northern Plume

Operable Unit 1

Railroad Avenue Groundwater Contamination SiteWest Des Moines, Iowa

Prepared by:

U.S. Environmental Protection Agency

Region VII

Kansas City, Kansas

September 2005

40221019

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Contents

Abbreviations and Acronyms i

I. Declaration D-1

II. Decision Summary 1

1.0 Site Name, Location, and Description 1

2.0 Site History and Enforcement Activities 2

3.0 Community Participation .': 3

4.0 Scope and Role of Interim Response Action 4

5.0 Site Characteristics 45.1 Physical Characteristics 55.2 Nature and Extent of Contamination 75.3 Contaminant Migration and Conceptual Site Model 8

6.0 Current and Potential Future Site and Resource Uses 12

7.0 Summary of Site Risks 137.1 Human Health Risk Assessment 137.2 Ecological Risk Assessment 167.3 Risk Assessment Summary and Conclusion 16

8.0 Remedial Action Objectives 17

9.0 Description of Alternatives 189.1 Alternative 1: No Action ; 199.2 Alternative 2: Monitored Natural Attenuation 20

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9.3 Alternatives: Extraction with Recovery Wells/On-site Tray Aeration/Surface

Water Discharge 229.4 Alternative 4: In-Situ Stripping Wells 24

10.0 Comparative Analysis of Alternatives 2610.1 Overall Protection of Human Health and the Environment 26

10.2 Compliance with Applicable or Relevant and AppropriateRequirements (ARARs) 27

10.3 Long-Term Effectiveness and Permanence 2710.4 Reduction of Toxicity, Mobility, and Volume Through Treatment 27

10.5 Short-Term Effectiveness 28

10.6 Implementability 2810.7 Cost 2910.8 State/Support Agency Acceptance 2910.9 Community Acceptance 30

11.0 Principal Threat Wastes 30

12.0 Selected Remedy 3012.1 Summary of the Rationale of Selected Remedy 3012.2 Description of Selected Remedy 31

12.3 Summary of Estimated Costs 3512.4 Expected Outcomes of the Selected Remedy 36

13.0 Statutory Determinations 3613.1 Protection of Human Health and the Environment 37

13.2 Compliance with ARARs 3713.3 Cost Effectiveness 38

13.4 Utilization of Permanent Solutions and Innovative Treatment Technologiesto the Maximum Extent Practicable 38

13.5 Preference for Treatment which Reduces Toxicity, Mobility, orVolume 39

14.0 Documentation of Significant Changes 39

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III. Responsiveness Summary RS-1

Tables

Table 1 VOC Data Summary (Monitoring Wells)Table 2 VOC Data Summary (Water Supply Wells)Table 3 Medium-Specific Exposure Point Concentration SummaryTable 4 Selection of Exposure PathwaysTable 5 Non-Cancer Toxicity DataTable 6 Cancer Toxicity DataTable 7 Summary of Cancer Risk for Each Population EvaluatedTable 8 Summary of Hazard Indices for Each Population EvaluatedTable 9 Risk SummaryTable 10 Comparative Analysis of AlternativesTable 11 Metals, Geochemical, and Biochemical Data SummaryTable 12 Monitored Natural Attenuation Screening Step 1Table 13 Present Worth Cost EstimateTable 14 Final Cleanup Levels

Figures

Figure 1 Site Vicinity MapFigure 2Contaminant Contour Map

Figure 3 Conceptual Site ModelFigure 4Plot of TCE, DCE, and VC vs. Distance Downgradient from Source Area

May 2004Figure 5 Plot of TCE, DCE, and VC vs. Distance Downgradient from Source Area

November 2004

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Abbreviations and Acronyms

ARARs applicable or relevant and appropriate requirements

BCF bioconcentration factor

bgs below ground surface

BTEX benzene, toluene, ethylbenzene, and xylene

CERCLA Comprehensive Environmental Response, Compensation, and

Liability Act

cis-1,2-DCE cis-1,2-dichloroethene

CFR Code of Federal Regulations

cfs cubic feet per second

COC contaminant of concern

COPC contaminant of potential concern

DNAPL dense non-aqueous phase liquid

DO dissolved oxygen

EPA U.S. Environmental Protection Agency

EPC Exposure Point Concentration

ESD explanation of significant difference

ESI expanded site inspection

FS feasibility study

ft feet

gpm gallons per minute

HI hazard index

HQ hazard quotient

IAC Iowa Administrative Code

IDNR Iowa Department of Natural Resources

MCL maximum contaminant level

mg/kg milligram per kilogram

MNA monitored natural attenuation

msl mean sea level

Railroad Avenue Groundwater Contamination SiteNorthern Plume Record of Decision

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MTBE methyl tert-butyl ether

MW monitoring well

NAPL non-aqueous phase liquid

NCP National Contingency Plan

NPDES National Pollutant Discharge Elimination System

NPL National Priorities List

O&M operation and maintenance

ORP oxidation-reduction potential

OSHA Occupational Safety and Health Administration

OU Operable Unit

PA/SI preliminary assessment and site investigation

PCB polychlorinated biphenyl

PCE Tetrachloroethene

PCOPEC preliminary contaminant of potential ecological concern

POTW publicly owned treatment works

PRP potentially responsible party

RAC Response Action Contract

RAO remedial action objective

RBC risk based concentration

RCRA Resource Conservation and Recovery Act

RD remedial design

RfD reference dose

RI/FS remedial investigation/feasibility study

RI Remedial Investigation

ROD record of decision

SARA Superfund Amendments and Reauthorization Act

START Superfund Technical Assistance and Response Team

SVOC semivolatile organic compounds

TBC to-be-considered

Railroad Avenue Groundwater Contamination SiteNorthern Plume Record of Decision

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TCE Trichloroethene

TCLP Toxicity Characteristic Leaching Procedure

Aig/L micrograms per liter

VC vinyl chloride

VOC volatile organic compound

WDM West Des Moines

WDMW West Des Moines Well

Railroad Avenue Groundwater Contamination SiteNorthern Plume jjj Record of Decision

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I. Declaration for the Record of Decision

Northern Plume

Operable Unit 1

Railroad Avenue Groundwater Contamination Site

West Des Moines, Iowa

Site Name and Location

The Railroad Avenue Groundwater Contamination site, Comprehensive

Environmental Response, Compensation, and Liability Information System (CERCLIS)

identification number IA0001610963, is located in West Des Moines, Iowa, a suburb of

Des Moines, Iowa, in southwest Polk County in south central Iowa. Two separate source

areas and their respective contaminant plumes have been identified at the Railroad

Avenue site. Because there are two separate and distinct plumes, the site has been

separated into two operable units (OUs): OU 1 - Northern Plume, and OU 2-Southern

Plume. This Record of Decision (ROD) addresses the Northern Plume (OU 1) of the

Railroad Avenue Groundwater Contamination site.

Statement of Basis and Purpose

This decision document presents the Selected Remedy for the Northern Plume OU

of the Railroad Avenue Groundwater Contamination site in West Des Moines, Iowa. The

Selected Remedy was chosen in accordance with the Comprehensive Environmental

Response, Compensation, and Liability Act of 1980 (CERCLA), as amended by the

Superfund Amendments and Reauthorization Act of 1986 (SARA), and to the extent

practicable, the National Oil and Hazardous Substances Pollution Contingency Plan

(NCP). This decision is based on the Administrative Record for this site.

The state of Iowa concurs with the selected remedy.

Dl

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Assessment of the Site

The remedial action selected in this ROD is necessary to protect the public health or

welfare and the environment from actual or threatened releases of hazardous substances

into the environment.

Description of Selected Remedy

This ROD addresses groundwater contaminants of the Northern Plume. The

Southern Plume and Northern Plume contaminants that are captured by the West Des

Moines well field were addressed in a separate ROD approved September 26, 2003. The

Northern Plume contaminants that are not captured by the West Des Moines well field are

addressed in this ROD.

The principal threat at this site is chlorinated volatile organic compounds (VOCs)

contamination in groundwater. The source materials for the VOCs in the Northern Plume

are currently unknown despite thorough investigative efforts. However, concentrations of

VOC contaminants in suspected Northern Plume source areas appear to be diminishing

through natural attenuation processes. The specific VOCs which have been identified as

contaminants of concern (COCs) are tetrachloroethene (PCE), trichloroethene (TCE), cis-

1,2-dichloroethene (cis-l,2-DCE), and vinyl chloride (VC).

The selected remedy will permanently and significantly reduce the toxiciry, mobility,

and volume of the site COCs through natural attenuation processes as the principalelement of remediation. The major components of the selected remedy for groundwater

include the following:

• Institutional controls including local or state well restrictions and public

education to prevent use of contaminated groundwater

• Restoration of the aquifer by reduction of the COCs through natural attenuation

processes

• Performance of monitoring at the site to confirm the effectiveness of the

attenuation processes

D2

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Statutory Determinations

The selected remedy is protective of human health and the environment, complies

with federal and state requirements that are legally applicable or relevant and appropriate

to the remedial action, is cost effective, and utilizes permanent solutions and alternative .

treatment (or resource recovery) technologies to the maximum extent practicable. This

remedy also satisfies the statutory preference for remedies that employ treatment as a

principal element (i.e., this remedy reduces the toxicity, mobility, or volume of

contaminants through treatment). Because hazardous substances above health-based

levels are expected to be onsite in five years, a review will be conducted within five years

after completion of the remedial action to ensure that the remedy continues to provide

adequate protection of human health and the environment. . ;

Data Certification Checklist

The following information is included in the Decision Summary Section of the ROD.

Additional information can be found in the Administrative Record for this site.

• COCs and their respective concentrations

• Baseline risk represented by the COCs

• Cleanup levels established for COCs and the basis for the levels

• How source materials constituting principal threats are addressed

• Current and future land use assumptions from the baseline risk assessment

• Groundwater use that will be available at the site as a result of the selected

remedy

• Estimated capital, operation and maintenance (O&M), and total present worth

costs; discount rate; and the number of years over which the remedy cost

estimates are projected

D3

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Decisive factors that lead to selecting the remedy

Authorizing Signature

Date

D4

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II. Decision Summary

1.0 Site Name, Location, and Description

The Railroad Avenue Groundwater Contamination site is in West Des Moines, Iowa,

which is a suburb of Des Moines, Iowa, in southwest Polk County in south central Iowa,

(Comprehensive Environmental Response, Compensation, and Liability Information

System [CERCLIS] identification number IA0001610963). This Record of Decision

(ROD) was developed by the U.S. Environmental Protection Agency (EPA), as lead

agency, with support from the Iowa Department of Natural Resources (IDNR). Costs for

remedial efforts at the Northern Plume portion of the site are being paid by the Superfund

trust fund.

The Railroad Avenue site consists of the West Des Moines water treatment plant

well field, the areas of groundwater contamination, and the potential source areas of the

contamination (Figure 1). The site is approximately 1,000 acres in size. The West Des

Moines well field contains 22 West Des Moines municipal water supply wells

(WDMWs) that currently supply water to the West Des Moines water treatment plant.

Historically, five municipal wells had been taken offline as a result of the volatile

organic compounds (VOCs) contamination: WDMW-6, -7, -12, -13, and -21. However,

interim response actions completed at the site in November 2004 have allowed these

wells to be returned to service. Wells WDMW-2, -10, and -11 were abandoned because

of well production problems.

Two separate and distinct source areas and respective contaminant plumes have been

identified through the EPA Expanded Site Inspection (ESI) and remedial investigation

(RI) sampling efforts. Because of the two plumes, the site has been separated into two

operable units (OUs): OU 1 - Northern Plume, and OU 2 - Southern Plume.

The EPA is the lead agency for the Northern Plume. The Northern Plume lies along

Railroad Avenue in West Des Moines, Iowa, approximately between First and Thirteenth

Street, east of wells WDMW-5, -6, 12, and -13 (Figure 1). The source area for the

Northern Plume has not been identified. Several suspected source areas for the Northern

Plume were investigated during the ESI. The ESI included collecting and analyzing

sediment, surface water, groundwater, surface soil, and subsurface soil samples from

targeted industrial business properties and surrounding areas.

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The Southern Plume is located northwest of wells WDMW-19, -20, and -21 where a

release of trichloroethylene (TCE) has occurred (Figure 1). Further investigation and

remediation of the Southern Plume are being performed by the potentially responsible

party (PRP) with the IDNR as the lead agency.

2.0 Site History and Enforcement Activities

The Railroad Avenue Groundwater Contamination site was first identified in 1993

when a routine water distribution sample collected by the city of West Des Moines was

found to contain cis-l,2-dichloroethene (cis-l,2-DCE) at 1.2 micrograms per liter (ug/L).

The drinking water standard for DCE is 70 ug/1. Subsequent sampling of well WDMW-

13 detected cis-l,2-DCE at significantly higher concentrations than the water distribution

sample, once at a level higher than the drinking water standard in 1996.

The contamination in the West Des Moines municipal wells was formally brought to

the attention of the EPA after a site investigation was conducted by the IDNR at a

potential source area in 1996.

The EPA performed a Preliminary Assessment/Site Investigation (PA/SI) under the

Superfund Technical Assessment and Response Team (START) program for well

WDMW-13 in October 1997. Results of the PA/SI identified two potential groundwater

contaminant plumes at locations along Railroad Avenue between West Des Moines wells

WDMW-12 and WDMW-13 and 10th Street. While contaminants were found in wellsWDMW-6 and -7, a distinct groundwater contaminant plume near these two wells was

not identified. Soil sampling conducted at five potential source areas could not determine

a primary source area. However, due to the variable groundwater flow gradients induced

by the water supply wells adjacent to the site, additional source areas south of the

investigated areas along Railroad Avenue were proposed for investigation.

An ESI was conducted by EPA in November and December 1999. Groundwater,

surface soil, subsurface soil, sediment, sewer, and surface water samples were collected

to confirm the results of the PA/SI and to investigate additional areas. Results from the

ESI confirmed that there were two source areas and separate groundwater contaminant

plumes in the southern and northern portions of the study area. Results also indicated a

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need for further investigation east of the Northern Plume and south of the Southern Plume

to further delineate the plume areas and to locate any other potential source 'areas.

The EPA held a community meeting on October 24,2000, in West Des Moines,

Iowa, to present a review of the results of the ESI. Questions from the public concerning

the site were answered.-

In December 2000, IDNR used direct-push sampling techniques to collect

ground water samples at the water table and at equipment refusal (i.e., at bedrock) at three

locations along Railroad Avenue. The samples confirmed results of the ESI.

The EPA performed the RI and Feasibility Study (FS) under the Remedial Action

Contracts (RAC) program in several phases. Characterization efforts were typically

performed on a semi-annual basis beginning in April 2001 and continuing through at least

May 2005.

A previous interim remedial action that addressed those portions of the Northern and

Southern Plumes which is captured by the West Des Moines well field was authorized in

a ROD dated September 26, 2003. The interim remedial action construction was

completed in November 2004. The previous interim remedial action included increasing

the treatment capacity of the West Des Moines water treatment plant by constructing new

aerators.

3.0 Community Participation

The Community Relations Plan, the Administrative Record of Activity, the Baseline

Risk Assessment, the RI Report, the Focused FS Report, and supporting documentation

were made available to the public for a public comment period which began on July 11,

2005, and was continued until August 10, 2005. The documents were available at EPA

Region VII Headquarters in Kansas City, Kansas, and the West Des Moines Public

Library, West Des Moines, Iowa. The notice of the availability of these documents and

the time and location of the public meeting were published in the Des Moines Register on

July 10, 2005. A fact sheet summarizing the Proposed Plan and preferred alternative was

mailed to residents and local administrators on July 12,2005. A public meeting was held

during the public comment period at West Des Moines, Iowa, on July 25, 2005. At this

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public meeting the Proposed Plan was presented to a broader community audience than

those that had already been involved at the site. At the public meeting, representatives

from EPA and the IDNR answered questions about the conclusions of the RI/FS, the

remedial alternatives, and the proposed remedial action. The EPA's response to the

comments received at the public meeting, as well as written comments received during

the comment period, are included in the Responsiveness Summary (Section III), which is> •

part of this ROD.

4.0 Scope and Role of the Action

This ROD addresses groundwater contaminants of the Northern Plume that are not

captured by the West Des Moines well field. Contaminants of the Southern Plume and

Northern Plume: that are captured by the West Des Moines well field were addressed in a

separate ROD approved September 26, 2003. The Southern Plume is being addressed by

the PRP with the IDNR as the lead agency. This ROD includes previous remedial action

efforts and presents the final action selected for the Northern Plume.

Several potential source areas for the Northern Plume were investigated; however, a

specific source area for the Northern Plume was not identified. During the RI, it was

determined that the western portion of the Northern Plume has adversely affected nearby

municipal water supply wells. As a result, the EPA conducted a focused FS to address

contaminated groundwater in close proximity to the municipal water supply wells,

specifically wells WDMW-5, -6, -12, and -13 in the northern West Des Moines well field

area. Therefore, EPA pursued an interim action remedy in September 2003 for theSouthern Plume and the northern West Des Moines well field area of the Northern Plume

which included increasing the treatment capacity of the West Des Moines water treatment

plant by constructing new aerators. In this ROD, EPA will address the final remedy for

the Northern Plume OU.

5.0 Site Characteristics

The physical characteristics of the site, the nature and extent of contamination, and

migration of contaminants are discussed in this section. Physical characteristics

discussed include topography and surface hydrology, regional hydrogeology and soils,

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and site geology and hydrogeology. The location of contaminant sources and distribution

of the contaminants of concern (COCs) are discussed.

5.1 Physical Characteristics

The Railroad Avenue site lies within the flood plain of the Raccoon River and glacial

terrain of the Central Lowland Plains. The topography of the site area is relatively flat

with a gentle south-southeasterly slope toward the Raccoon River. The local relief of the

site vicinity is about 150 feet. The elevation ranges from approximately 800 feet mean

sea level (msl) along the Raccoon River to about 950 feet msl on the higher bluffs.

Surface drainage in the site vicinity flows south-southeast via storm drains to a retention

pond or a flooded gravel pit (Gravel Pit Lake) and eventually discharges into the Raccoon

River, which is located along the southeast edge of the site area (Figure 2). Jordan Creek,

which flows eastward along the north side of the Raccoon River Park and drains much of

southeast West Des Moines, also discharges into the Raccoon River. The perennial

Raccoon River flows easterly and has an annual mean discharge of about 2,770 cubic feet

per second (cfs) in the West Des Moines area. Approximately 10 miles downstream of

the site, the Raccoon River discharges into the Des Moines River. The Des Moines River

flows to the east and has a mean annual discharge of 6,790 cfs. The site is situated within

the 25-year flood plain of the Raccoon River, which last flooded the site area in July

1993.

The site lies above the alluvial aquifer of the Raccoon River. The site is underlain

with alluvial sediments consisting of unconsolidated clay, silt, sand, and gravel whichoverlay shale and coal of the Cherokee Group of the Pennsylvanian System. Boring logs

for the twelve monitoring wells (MW-1 through MW-12) and six observation wells (OB-

1 through OB-6) installed as part of the Phase 3 RI indicate the thickness of the

unconsolidated material to be thinnest in the western portion of the site, grading thicker

toward the east. The alluvial aquifer is unconfined and consists of permeable, sorted, and

stratified sand and gravel deposits. Depth to bedrock in the western portion of the site is

approximately 37 feet; depth to bedrock at the eastern portion of the site is approximately

52 feet.

The upper portion of the unconsolidated sediments is characterized by 0 to 7 feet of

fill material consisting of clay, silt, sand, and miscellaneous materials. The fill material is

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underlain by silty clay to depths ranging from 5 to 19 feet below ground surface (bgs).

Underlying the silty clay are relatively thick units of sand and gravel interbedded with

localized clay and silt lenses containing natural organics. The natural organics

encountered include wood fragments and lignite lenses up to four inches thick. The

thickest silty clay lens encountered was ten feet thick and was encountered in well MW-3.

Depth to groundwater across the site area ranged from approximately 9 to 14 feet

bgs. Groundwater table contour maps were developed from the groundwater elevations.

The groundwater flow direction on November 4, 2004, is illustrated on Figure 2. As

illustrated, the flow direction for groundwater is to the east-southeast. Water levels

measured on other dates confirmed this groundwater flow direction. On the basis of the

groundwater contours, it appears that groundwater is recharged from upgradient flow and

infiltration of precipitation. Groundwater flows toward, and discharges into; the Gravel

Pit Lake and Raccoon River south and southeast of the site. The average horizontal

hydraulic gradient at the site varies seasonally from approximately 0.0006 foot per foot

(ft/ft) to 0.0015 ft/ft.

A pump test was performed at West Des Moines Water Supply well WDMW-13 as

part of the RI efforts. Results of the pump test indicate the hydraulic conductivity of the

alluvial aquifer to be approximately 193 feet per day. Assuming an effective porosity of

25 percent for the aquifer, the groundwater seepage velocity across the site is estimated to

be approximately 222 feet per year (ft/yr) to the east-southeast in the summer and

approximately 139 ft/yr to the east-southeast in the fall.

The alluvial aquifer is underlain by the Cherokee Group of the Pennsylvanian

system, which is approximately 400 feet thick and consists primarily of shale with thin

layers of clay, siltstone, sandstone, limestone, and coal. Bedrock encountered in

monitoring wells drilled during the Phase 3 RI was shale and coal. Although the shaleunits of the Cherokee Group will most likely act as an aquitard, preventing further

downward vertical migration of contaminants, sandstone layers within the Cherokee

Group provide groundwater to some wells in the southern half of Polk County with yields

from 5 to 25 gallons per minute (gpm). The thicknesses of these sandstone units are quite

variable and the depth of wells drilled into them varies between 75 and 100 feet.

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The bedrock aquifer used as a water supply at the Railroad Avenue site consists of

the Jordan Aquifer (wells WDMW-1, -3, and -4). The Jordan Aquifer consists of

fractured and porous sandstone and dolostone of the Cambrian-Ordovician System which

can yield significant amounts of water. The Jordan Aquifer is approximately 2,500 feet

bgs. Because of the considerable depth of the Jordan Aquifer, it is extremely unlikely to

be affected by contaminants in the alluvial aquifer. . . . .

The site lies within the northeast part of the Forest City Basin bedrock structure. No

major faults have been mapped at the surface in the site vicinity, and none are known to

be active within the Holocene Epoch.

5.2 Nature and Extent of Contamination

The nature and extent of contamination in the groundwater at the Railroad Avenue

site was evaluated from the ESI and RI sampling events. The monitoring wells and the

water supply wells were sampled and analyzed for the presence of VOCs, semi-volatile

organic compounds (SVOCs), pesticides, and polychlorinated biphenyls (PCBs). The

majority of the analytical results for all wells were non-detect. Data validation efforts

qualified results where necessary and screened out contaminants identified as potential

laboratory contaminants. Because of the frequency of detection and elevated

concentrations, the contaminants tetrachloroethene (PCE), TCE, cis-l,2-DCE, and vinyl

chloride (VC) were determined to be the COCs for the Railroad Avenue Groundwater

Contamination site. The analytical results are summarized in Table 1 for the monitoring

wells and Table 2 for the West Des Moines water supply wells. Also presented in Table1 and Table 2 are the maximum contaminant levels (MCLs) for the analytes.

The concentrations of TCE, cis-l,2-DCE, and VC in groundwater have been

contoured in Figure 2 to illustrate the horizontal extent of contaminants in the aquifer.

PCE was not included in the figure because PCE was consistently detected in only one

well (MW-6) during the RI sampling events.

The surface water samples were only analyzed for VOCs. The analytical results for

the surface water samples were all non-detect for VOCs.

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Diffusion bag samplers were used to evaluate the vertical stratification of VOCs at

the site. Diffusion samplers were located at depths correlating to the five most granular

zones of wells MW-3, MW-7, and MW-10. The diffusion bag results indicate a slight

trend for higher concentrations of contaminants in the lower part of the aquifer.

However, significant vertical stratification of contaminants is not indicated so that

targeting vertical zones for remedial efforts will not be beneficial.

5.3 Contaminant Migration and Conceptual Site Model

Several years of site data have been collected to evaluate site conditions. Results of

the ESI and RI indicate the primary migration pathway of contaminants at the Railroad

Avenue site is through groundwater. The conceptual model of the site is illustrated in

FigureS.

The source area or source areas for the Northern.Plume contaminants at the Railroad-

Avenue site have not been specifically identified despite thorough investigation efforts.

However, the source areas for the site contaminants are most likely a single, or several,

local businesses which improperly managed production and/or waste solvents. Several

historical and active local businesses in the site area were evaluated during the ESI.

The COCs for the site are PCE, TCE, cis-l,2-DCE, and VC which are halogenated

aliphatic compounds. PCE is widely used in the dry cleaning industry and as a solvent

for degreasing. TCE is a common solvent used for degreasing of metals, textile

processing, gas purification, and in the manufacturing of Pharmaceuticals. Cis-l,2-DCEis occasionally used in the production of solvents; however, its presence in the

environment is usually as a result of the degradation of PCE and TCE. VC is also used to

a limited extent in manufacturing processes, but as with cis-l,2-DCE, VC in the

environment is usually a result of the degradation of PCE or TCE to cis-l,2-DCE which

degrades to VC.

The migration of the COCs in groundwater is complex and subject to several

physical and chemical processes including biochemical processes and groundwater

transport. Initially, the COCs leach vertically downward into groundwater from

contaminated subsurface soils in the source area where the contaminants were originally

released. As the COCs enter the groundwater, diffusion and advection processes control

8

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the migration of the contaminants. Diffusion causes the contaminants to spread in all

directions within groundwater; adsorption processes cause the COCs to remain sorbed to

the aquifer matrix. At this site, advective flow is a dominant migration process and

causes contaminants to migrate along with groundwater in the direction of groundwater

flow. Once in the groundwater, biodegradation processes reduce the persistence of the

site contaminants. The COCs typically degrade into daughter compounds through the -

loss of chlorine atoms. For example, PCE typically degrades to TCE, TCE typically

degrades to cis-l,2-DCE, cis-l,2-DCE typically degrades to VC, and VC can degrade to

ethene. Finally, ethene (which is not chlorinated) can degrade to carbon dioxide and

water.

While advective flow processes cause contaminants to migrate along with

groundwater in the direction of groundwater flow, biodegradation processes, including

reductive dechlorination, will simultaneously degrade the site contaminants.

Biodegradation is a preferred natural attenuation process because hydrocarbons are

eventually reduced to more stable, less toxic compounds. Studies have determined that

chlorinated aliphatic hydrocarbons including PCE, TCE, and cis-l,2-DCE readily degrade

in anaerobic environments.

Biodegradation of PCE and TCE is occurring at the Northern Plume area as

evidenced by the low concentrations of PCE and TCE and the relatively elevated

concentrations of cis-l,2-DCE and VC which are degradation products of PCE and TCE.

The extent of TCE, cis-l,2-DCE, and VC are illustrated in Figure 2. Figure 2 shows that

the highest concentrations of the suspected source contaminant TCE are located near thesuspected release area, whereas down gradient of the source area, the concentrations of

TCE are lower and the daughter contaminants (cis-l,2-DCE and VC) are higher.

Other indicators of biodegradation may be identified by the evaluation of site

geochemical data. Analytical results show the absence of electron acceptors such as

dissolved oxygen (DO) and nitrate within the plumes. However, sulfate, another less

easily consumed electron acceptor, is present indicating the aquifer is not at the optimal

reducing condition for reduction of the cis-l,2-DCE plume. The presence of VC

indicates that the cis-l,2-DCE plume is reducing, although at a slower rate than PCE and

TCE. The presence of electron donors, such as carbon sources, also supports the

occurrence of reductive dechlorination processes. Natural organic carbon was

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encountered in borings drilled in the area which indicates the availability of a carbon

source to support reductive dechlorination. The presence of reductive dechlorination by-

products such as ferrous iron and methane also indicates the occurrence of reductive

dechlorination processes.

-Site data indicate PCE, TCE, and cis-lj2-DCE may be biodegrading at-an optimal

rate and that expansion of these plumes may not occur. However, site data indicate that

biodegradation of the VC plume may not be occurring. The aquifer is anaerobic which

does not easily allow biodegradation of VC. The VC plume continues to expand toward

the Gravel Pit Lake and Raccoon River; however, the VOC contaminants that eventually

reach these surface water bodies appear to be attenuating through natural processes as

indicated by the absence of VOCs above detection limits in the surface water samples.

The COCs are also adsorbing to the aquifer matrix which will impede contaminant

: extraction. Studies at other sites contaminated with chlorinated hydrocarbons indicate

that two to four times the dissolved concentrations can be expected to be sorbed to the

aquifer matrix. Significant amounts of chlorinated solvents can result in accumulations

of non-dissolved phase contaminants (i.e., dense nonaqueous phase liquids [DNAPL]).

However, to date DNAPL has not been identified at the site.

The groundwater flow direction at the Railroad Avenue site is primarily to the east-

southeast toward the Gravel Pit Lake and the Raccoon River. The distribution of the

plumes also shows evidence of an east-southeasterly groundwater flow trend. The

migration rates and paths for the Northern Plume contaminants have been evaluated usinggroundwater flow and contaminant transport computer models and are discussed in the

Technical Memorandum: Groundwater Model Northern West Des Moines Well Field,

July 8, 2003. A MODFLOW groundwater flow model was developed and calibrated to

site water level measurements and pump test data. A contaminant transport model was

developed to simulate contaminant migration in groundwater in the Northern West Des

Moines well field. Assumptions used in development of the model included establishing

no-flow boundaries where the bedrock forms boundaries of the alluvial aquifer and that

the WDMWs south of well WDMW-9 would not significantly affect migration of the

Northern Plume.

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The model shows that the contaminant plumes will continue to be captured by wells

in the West Des Moines well field and will also eventually reach Gravel Pit Lake and the

Raccoon River. The VOC contaminants that eventually reach the surface water bodies

will most likely attenuate through natural processes.

Initial concentrations of the TCE, cis-1 j2-DCE, and VC contaminant plumes in the

model were the levels reported in the RI Report for the November 2002 sampling event in

combination with the ESI data. Together, these data were used as the starting point for

predictive modeling of contaminant transport.

The scenarios that were evaluated in the model include: Scenario 1 - No Action (all

wells pumping); Scenario 2 - Current Response Action (wells WDMW-5, WDMW-8, and

WDMW-9 pumping); and Scenario 3 - Potential Response Action (all wells pumping,

except well WDMW-7).

Model results for Scenario 1 (before shutting down any of the north pumping wells)

estimate that the MCL for cis-l,2-DCE is exceeded at well WDMW-13 within

approximately one year. Although, as with any transport contaminant modeling effort,

estimating the actual time of plume arrival is uncertain, it does appear that the MCL for

cis-l,2-DCE will be exceeded fairly quickly if well WDMW-13 was returned to

operation. The TCE plume is reduced to below the MCL in nearly one year, the VC

plume is reduced to below the MCL in less than ten years, and the cis-l,2-DCE plume is

nearly gone at forty years with only a small fraction (within the error of the model)

remaining.

Model results for Scenario 2 indicate that MCLs will not be exceeded in the

extraction wells that are operating under this scenario (i.e., pumping wells WDMW-5,

WDMW-8, and WDMW-9 without pumping wells WDMW-6, WDMW-7, WDMW-12,

and WDMW-13). The TCE plume is estimated to be reduced to below the MCL in less

than one year, the VC plume is reduced to below the MCL in less than ten years, and the

cis-1,2-DCE plume is reduced to below the MCL in nearly thirty years. However, the

capture zone is reduced, which would allow migration of the plumes toward Gravel Pit

Lake and the Raccoon River.

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Scenario 3 evaluates contaminant capture with aggressive pumping at recovery wells

WDMW-5, WDMW-6, WDMW-8, WDMW-9, WDMW-12, and WDMW-13. The

modeled maximum pumping rates under Scenario 3 were 20 percent of the historical

daily average. Aggressive pumping would accelerate removal of contaminants from the

capture zone of the extraction wells. The TCE plume is estimated to be reduced to below

the MCLin less than one. year, the VC plume is reduced to below the MCL in nearly ten

years, and the cis-l,2-DCE plume is reduced to below the MCL in less than thirty years.

Bioaccumulation of halogenated aliphatic compounds is not expected to be

significant, based on the low octanol-water partition coefficients and low

bioconcentration factor values of the COCs.

6.0 Current and Potential Future Site and Resource Uses

The Railroad Avenue Groundwater Contamination site is in West Des Moines, Iowa,

which is a suburb of Des Moines, Iowa. The Northern Plume site lies along Railroad

Avenue between First Street and Thirteenth Street. The western portion of the Northern

Plume site contains a softball field complex, light industrial and commercial areas, and

single-family dwellings. Further to the east, the site is mostly commercial and residential.

The Valley Junction shopping district is located in the 100- to 300-block area along Fifth

Street. The Valley Junction shopping area has been renovated with brick sidewalks and

ornamental street fixtures. The eastern portion of the site is a residential area consisting

primarily of single-family dwellings. The southern part of the North Plume site consists

of light industrial businesses and a surface water detention basin. Future use of the site isanticipated to be similar to current uses.

Groundwater in the Railroad Avenue site and vicinity is currently used as the

primary water source for the city of West Des Moines and local industries. It is

anticipated to continue to be used as the city's water source indefinitely. Water supply

wells used by the city of West Des Moines have been impacted by the North Plume

contaminants. Surface water in the Railroad Avenue site is used recreationally.

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7.0 Summary of Site Risks

The baseline risk assessment estimates what risks the site poses if no action was

taken. It provides the basis for taking action and identifies the contaminants and

exposure pathways that need to be addressed by the remedial action. This section of the

ROD summarizes the results of the baseline risk assessment for this site.

7.1 Human Health Risk Assessment

A human health baseline risk assessment was prepared for the Railroad Avenue

Groundwater Contamination site for drinking water. This summary presents an overview

of the risk assessment prepared for the site. The complete risk assessment may be

consulted in the Administrative Record file for a more detailed evaluation of the site

risks. The human health risk assessment qualitatively evaluated soils at the site and

quantitatively evaluated groundwater at the site. Contaminants identified in the soil were

found to be at acceptable health risk levels and will require no further action.

Contaminants identified in the groundwater, however, were found to be at unacceptable

health risk concentrations.

7.1.1 Identification of Contaminants of Concern

Risk assessment is an analysis of the potential adverse health effects that may result

from human exposure to chemical contaminants present at the site. The risk assessmentidentified several contaminants of potential concern (COPCs) in groundwater. Risk

management evaluation of the COPCs relative to natural occurrence, prevalence, and site

history determined the COCs for the Railroad Avenue site. The COCs at the Railroad

Avenue site are PCE, TCE, cis-l,2-DCE, and VC in groundwater. These VOCs may pose

adverse health effects at relatively high concentrations or exposures. Tables 3.1 through

3.8 summarize the COPCs and the Exposure Point Concentrations used in the human

health risk assessment.

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7.1.2 Exposure Assessment

The exposure pathways evaluated in the risk assessment are presented in Figure 3

which shows the conceptual site model for the site. Table 4 summarizes all of the

scenarios and pathways considered in the risk assessment. As shown, health risks to both

current and future residents and workers from exposure (ingestion, dermal contact, and

inhalation) to groundwater were evaluated. The exposure pathways are also included in

Tables 3.1 through 3.8.

7.1.3 Toxicity Assessment

The human health risk assessment evaluated exposures to carcinogenic and non-

carcinogenic contaminants at the site. Tables 5.1 and 5.2 summarize the non-cancer

toxicity data and Tables 6.1 and 6.2 summarize the cancer toxicity data.

7.1.4 Risk Characterization

For carcinogens, risks are generally expressed as the incremental probability of an

individual's developing cancer over a lifetime as a result of exposure to the carcinogen.

Excess lifetime cancer risk is calculated from the following equation:

Risk = GDI x SF

where: risk = a unitless probability (e.g., 2 x 10"5) of an individual's developing

cancer

GDI = chronic daily intake averaged over 70 years, milligrams per

kilogram-day (mg/kg-day)

SF = slope factor, expressed as (mg/kg-day)"1

These risks are probabilities that usually are expressed in scientific notation (e.g., 1 x

10~6). An excess lifetime cancer risk of 1 x 10~6 indicates that an individual experiencing

the reasonable maximum exposure estimate has a 1 in 1,000,000 chance of developing

cancer as a result of site-related exposure. This is referred to as an "excess lifetime

cancer risk" because it would be in addition to the risks of cancer individuals face from

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other causes such as smoking or exposure to too much sun. The chance of an individual's

developing cancer from all other causes has been estimated to be as high as one in three.

The EPA's generally acceptable risk range for site-related exposures is 10"4 to 10"6.

The potential for noncarcinogenic effects is evaluated by comparing an exposure

level over a specified time period (e.g., lifetime) with a reference dose (RfD) derived for a

similar exposure period. A RfD represents a level that an individual may be exposed to

that is not expected to cause any deleterious effect. The ratio of exposure to toxicity is

called a hazard quotient (HQ). A HQ less than 1 indicates that a receptor's dose of a

single contaminant is less than the RfD and that toxic noncarcinogenic effects from that

chemical are unlikely. The Hazard Index (HI) is generated by adding the HQs for all

COCs that affect the same target organ (e.g., liver) or that act through the same/

mechanism of action within a medium or across all media to which a given individual

may reasonably be exposed. A HI less than 1 indicates that, based on the sum of all HQs

from different contaminants and exposure routes, toxic noncarcinogenic effects from all

contaminants are unlikely. A HI greater than 1 indicates that site-related exposures may

present a risk to human health.

The HQ is calculated as follows:

Non-cancer HQ = CDI/RfD

where:

GDI = Chronic daily intake

RfD = reference dose.

The GDI and RfD are expressed in the same units and represent the same exposure

period (i.e., chronic, subchronic, or short term).

A summary of carcinogenic risks for each population is presented hi Table 7; a

summary of non-carcinogenic risks for each population is presented in Table 8.

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As indicated in Table 7, unacceptable cancer risks resulted for the hypothetical future

resident at locations MW-6, MW-8, and well WDMW-13. There were also unacceptable

cancer risks for the hypothetical future industrial worker at MW-8. The carcinogenic

risks are associated with the COCs - TCE and VC, and the COPCs - bis(2-ethylhexyl)

phthalate and arsenic.

As indicated in Table 8, six exposure scenarios had total HI values that were above

1: the hypothetical future child and adult residents at well locations MW-6, MW-8, and

well WDMW-13. The non-carcinogenic risks are associated with the COCs - TCE and

VC, and the COPCs - manganese, arsenic, and l,2-dibromo-3-chloropropane.

Tables 9.1 through 9.11 present risk information for COPCs and media/exposure

points that could hypothetically trigger the need for remedial action. Risk management

evaluation of the COPCs relative to natural occurrence, prevalence, and site history

determined the COCs for the Railroad Avenue site. The COCs at the Railroad Avenue

site are PCE, TCE, cis-l,2-DCE, and VC in groundwater.

7.2 Ecological Risk Assessment

The Screening-Level Ecological risk assessment evaluated analytical data as they

relate to ecological risks at the Railroad Avenue Groundwater Contamination site. The

risk assessment identified several preliminary contaminants of potential ecological

concern (PCOPECs). Risk management evaluation of the PCOPECs relative to natural

occurrence, prevalence, current and future site use, and site history determined thatcurrent and future ecological risks posed by site contaminants are at acceptable levels.

7.3 Risk Assessment Summary and Conclusion

The excess carcinogenic risks to current lifetime residents (adult and child) were

calculated to be 6 x 10~6 to 2 x 10~5 and excess carcinogenic risk to current industrial

workers was calculated to range from 1 x 10"6 to 3 x 10"6. The excess carcinogenic risk to

future lifetime residents (adult and child) was calculated to range from 1 x 10^ to 7 x 10~3

and excess carcinogenic risks to future industrial workers were calculated to range from

8 xlO'5 to 3x10" (Table 7).

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The non-carcinogenic risk (expressed as HQs) to current lifetime resident adults,

current lifetime resident children, and industrial workers was calculated to be 0.5, 1, and

0.2, respectively. The maximum noncarcinogenic risks to future lifetime resident adults,

future lifetime resident children, and industrial workers were calculated to be 4, 11, and 1,

respectively (Table 8).

The remedial action selected in this ROD is necessary to protect the public health or

welfare or the environment from actual or threatened releases of hazardous substances

from this site. However, no current unacceptable risk exists since no one is drinking

contaminated water.

8.0 Remedial Action Objectives

The Comprehensive Environmental Response, Compensation, and Liability Act

(CERCLA), as amended by Section 121(b) of the Superfund Amendments and

Reauthorization Act of 1986 (SARA), requires selection of remedial actions which ensure

protection of human health and the environment, attain applicable or relevant and

appropriate requirements (ARARs), are cost effective, use permanent solutions and

alternative treatment technologies or resource recovery technologies to the maximum

extent practicable, and satisfy the preference for treatment that reduces the toxicity,

mobility, or volume of contaminants or provide an explanation as to why they do not. To

satisfy CERCLA requirements, remedial action objectives (RAOs) were developed for

the Railroad Avenue site. General response actions were then developed to attain the

RAOs.

The RAOs developed for the contaminated groundwater at the Railroad Avenue site

within the West Des Moines well field area are identified below.

• Prevent ingestion of groundwater having concentrations of the site COCs in

excess of current regulatory drinking water standards. The current regulatory

drinking water standards for the COCs are the MCLs. The MCLs are the

maximum permissible levels established by the Safe Drinking Water Act

[40 Code of Federal Regulations (CFR) 141] for a contaminant in water that is

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delivered to any user of a public water system. The MCLs are discussed in further

detail in the following section.

• Comply with Iowa Surface Water Criteria for COCs.

The primary focus,of the remedial action is to address remediation of the

contaminated groundwater which is the primary risk posed from the site.

9.0 Description of Alternatives

CERCLA requires that the selected site alternative be protective of human health and

the environment, be cost effective, comply with other environmental laws, and use

permanent solutions, alternative treatment technologies, and resource recovery

alternatives to the maximum extent practicable. In addition, the statute includes a

preference for the use of treatment as a principal element for the reduction of toxicity,

mobility, or volume of the hazardous substances.

The Focused FS Report prepared for the Northern Plume dated February 25, 2005,

evaluated in detail four remedial alternatives (including the no action alternative, which

EPA is required to consider by law) for addressing the contamination associated with the

Northern Plume at the Railroad Avenue Groundwater Contamination site. As part of the

process of choosing a remedy, the remedial alternatives from the FS are compared and

evaluated using nine criteria that appear in the National Oil and Hazardous Substances

Pollution Contingency Plan (NCP). (These criteria and evaluations are discussed in

Section 10 below.)

For the purpose of analyzing and comparing the remedial alternatives, EPA

estimated costs of the alternatives by making certain assumptions, such as estimating the

remediation time for pumping and treating groundwater. The EPA Superfund policy is to

try to estimate costs with "+50/-30 percent" accuracy.

The present worth of each alternative was calculated for all alternatives assuming a 7

percent discount rate for up to 30 years. The present worth is a summary measure of cost

that, for comparison purposes, turns a stream of payments or costs over a future period of

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years into the equivalent of a single lump sum in the present. The cost estimates, as

discussed above, are conceptual, with an estimated +50 percent to -30 percent level of

accuracy. The alternatives from the Focused FS Report are described in the remainder of

Section 9. Section 10 compares the alternatives. Section 12 discusses the selected

alternative; Section 12 also discusses several additional measures that will be taken as

part of the selected remedy, including-remedial design activities.

All of the alternatives, except the no further action alternative, include institutional

controls as a common element. The institutional controls include the following:

• Implementation of well permitting requirements to limit use of groundwater at the

site. The permitting requirements would consist of an ordinance passed by the

city of West Des Moines, Iowa, prohibiting the installation of new wells if city

water is available. If a local ordinance could not be passed, a protected water

source designation at the state level would be sought. In a protected water source

area, new well installation would be restricted.

• Public education would inform local officials on well drilling restrictions and be

used to inform citizens of the potential health hazards associated with exposure to

contaminated groundwater. Public education would be implemented through

informational meetings and flyers.

9.1 Alternative 1: No Action

Estimated Capital Cost: $0

Estimated Annual Operation & Maintenance (O&M) Cost Range: $0 to $50,500Estimated Present Worth Cost: $111,300

Estimated Construction Timeframe: 0 months

Estimated Time to Achieve RAOs: Indeterminate

The NCP requires that the EPA considers a no further action alternative as a baseline

against which other remedial alternatives can be compared. Under this alternative, no

further action would be taken to monitor, control, or remediate groundwater

contamination. Alternative 1 would not meet the RAOs because it does not minimize any

future potential exposure at the site. The costs for this alternative are for the required

five-year review.

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9.2 Alternative 2: Monitored Natural Attenuation

Estimated Capital Cost: $24,000

Estimated Annual O&M Costs Range: $15,300 to $90,300

Estimated Present Worth Costs: $430,000

Estimated Construction Timeframe: 1 month - - - •

Estimate Time to Achieve RAOs: Greater than 30 years

Alternative 2 would rely on the aquifer's ability to lower contaminant concentrations

through monitored natural attenuation (MNA) processes. This alternative includes

groundwater and surface water monitoring to confirm continued efficiency of the natural

attenuation of contaminants and institutional controls to minimize potential health risks

associated with groundwater contaminants still undergoing attenuation.

As discussed in Section 5.3, several years of site data have been collected to evaluate

site conditions. Advective flow processes cause contaminants to migrate along with

groundwater in the direction of groundwater flow while biodegradation processes

simultaneously degrade the site contaminants. Biochemical processes at sites include

biodegradation where chlorinated hydrocarbons are eventually reduced to more stable,

less toxic compounds.

Biodegradation of PCE and TCE is occurring at the Northern Plume site as

evidenced by the low concentrations of PCE and TCE and the relatively elevated

concentrations of cis-l,2-DCE and VC which are degradation products of PCE and TCE.Figure 2 illustrates that the highest concentrations of a potential source contaminant,

TCE, are located near the suspected release area, whereas downgradient of the suspected

source area, the concentrations of TCE are lower and the concentrations of daughter

contaminants (cis-l,2-DCE and VC) are higher.

The EPA has developed site screening criteria for identifying sites where efficient

biodegradation is occurring. The site data were evaluated using the screening criteria and

indicate evidence of an adequate biodegradation rate for PCE, TCE, and cis-1,2-DCE.

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Site data indicate PCE, TCE, and cis-l,2-DCE may be biodegrading at an optimal

rate and that expansion of these plumes may not occur. However, site data indicate that

biodegradation of the VC plume may not be occurring. The aquifer is anaerobic which

does not easily allow biodegradation of VC. The VC plume continues to expand toward

the Gravel Pit Lake and Raccoon River; however, the VOC contaminants that eventually

reach these surface water bodies appear to be attenuating through natural processes as

indicated by the absence of VOCs, including VC, above detection limits in the surface

water samples.

This alternative would include implementation of local or state well permit

restrictions and public education. In addition, groundwater monitoring would be included

to evaluate the effectiveness of the natural attenuation processes. A detailed sampling

and quality assurance plan would be written before the groundwater monitoring activities

began. The sampling and quality assurance plan would include sample locations,

sampling frequency, sampling procedures, sample analysis methods, and sample

documentation procedures.

For the purpose of developing this alternative, it was assumed that one new

monitoring well would be installed downgradient of the VC plume along First Street.

The final location of the well would be determined during remedial design and would be

contingent upon access agreements with the property owners.

It was assumed that the groundwater monitoring would consist of sampling the newmonitoring well, the twelve existing monitoring wells, three surface water sample

locations, and four WDM water supply wells (WDMW-5, WDMW-6, WDMW-12, and

WDMW-13) quarterly for years one and two; semiannually for years three, four, and five;

and annually after year five until RAOs are attained. The frequency of the monitoring

may be re-evaluated and modified after the five-year reviews or after review of the

monitoring data by the EPA and IDNR. The groundwater samples would be analyzed for

VOCs.

It was assumed that the surface water monitoring would consist of collecting two

samples from the Gravel Pit Lake and one sample from the Raccoon River at the same

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frequency of the groundwater samples. The surface water samples would also be

analyzed for VOCs.

The results of the sample analysis would be used to confirm the rate and direction of

groundwater contaminant migration. If the monitoring results indicate that the plume is

•migrating towards new receptors, further.remedial actions would be initiated.

9.3 Alternative 3: Extraction with Recovery Wells/Onsite Tray Aeration/Surface Water

Discharge

Estimated Capital Cost: $532,000

Estimated Annual O&M Costs Range: $44,500 to $145,000

Estimated Present Worth Costs: $1,343,000

Estimated Construction Timeframe: 17 to 18 months

Estimated Time to Achieve RAOs: Greater than 30 years

Alternative 3 would include extraction of contaminated groundwater using recovery

wells followed by onsite tray aeration treatment and discharge of the treated groundwaterto Gravel Pit Lake. The recovery wells would be pumped at a rate to hydraulically

control the groundwater flow which would provide containment of the groundwater

contaminant plume.

Groundwater would be extracted using three new recovery wells. Groundwater flow

equations were used to estimate the location and extraction rate of the recovery wells that

would prevent migration of contaminants to surface water bodies. It is estimated that

each recovery well would be pumped at 70 gpm to achieve a 1,380-foot-wide capturezone for each well. Strategically placing three recovery wells would achieve plume

containment and prevent migration of contaminants to the Gravel Pit Lake and Raccoon

River.

The water would be piped to an onsite treatment plant and treated by air stripping

with tray aerators. The groundwater would be pumped through a tray aeration system to

remove the contaminants. In a tray aeration system, the contaminated groundwater enters

the top of the treatment system and flows across a series of aeration trays. Air passes

upward through openings in the trays and bubbles up through the water. The bubbles and

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water form a very turbulent mixture that is excellent for stripping the COCs from the

water and volatilizing them into the air. The vapor/contaminant mixture is removed from

the system and released to the atmosphere or treated. The system can be readily expanded

to accommodate an increase in influent flow or contaminant concentration by addition of

additional trays.

Based on available information from air stripping tray aeration vendors and the Iowa

Air Quality Standards, it is anticipated that the air stripper off-gas would not have to be

treated. Further evaluation of emission rates would be evaluated during the engineering

design.

Once collected and treated, the extracted groundwater from the recovery wells would

be discharged directly to Gravel Pit Lake through a newly constructed discharge line.

Treatment plant operation efficiency would be evaluated by collecting and analyzing

influent, effluent, and emission samples.

The final location of the recovery wells, onsite treatment system, and discharge

piping would be determined during the remedial design.

This alternative would include implementation of local or state well permit

restrictions and public education. In addition, groundwater monitoring would be included

to evaluate the effectiveness of plume containment by the recovery well. A detailed

sampling and quality assurance plan would be written before the groundwater monitoring

activities began. The sampling and quality assurance plan would include samplelocations, sampling frequency, sampling procedures, sample analysis methods, and

sample documentation procedures.

It was assumed that monitoring would consist of sampling the twelve existing

monitoring wells, three surface water sample locations, the three new recovery wells, and

four WDM water supply wells (WDMW-5, WDMW-6, WDMW-12, and WDMW-13)

quarterly for years one and two; semiannually for years three, four, and five; and annually

after year five until RAOs are attained. The frequency of the monitoring could be re-

evaluated and modified after the five-year reviews or after review of the monitoring data

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by the EPA and IDNR. The groundwater and surface water samples would be analyzed

for VOCs.

It was assumed that the surface water monitoring would consist of collecting two

samples from the Gravel Pit Lake and one sample from the Raccoon River at the same

frequency of the groundwater samples. The surface water samples would also be

analyzed for VOCs.

The results of the sample analysis would be used to evaluate the rate and direction of

groundwater contaminant migration and determine if adjustments in recovery well flow

ratios are needed. If the monitoring results indicate that the plume is migrating towards

new receptors, further remedial actions would be initiated.

9.4 Alternative 4: In-situ Stripping Wells

Estimated Capital Cost: $670,000

Estimated Annual O&M Costs Range: $66,900 to $171,900

Estimated Present Worth Costs: $1,844,000

Estimated Construction Timeframe: 17 to 18 months

Estimated Time to Achieve RAOs: Greater than 30 years

Under Alternative 4, two lines of in-situ stripping wells would be placed along theeastern and southern edges of the plume to treat the contaminated groundwater as it

migrates towards the Gravel Pit Lake and Raccoon River. Based on information from

vendors, it is estimated that the in-situ stripping wells would have a radius of influence ofapproximately 150 feet. Therefore, it is estimated that ten in-situ stripping wells would

be required to act as a barrier between the plume and the surface water bodies.

In-situ stripping wells are double-screened wells that re-circulate groundwater in the

aquifer by pulling groundwater in through the lower well screen and recharging the

aquifer through the upper screen using air lift pumping. The air lift pumping would

simultaneously strip the VOCs from the contaminated groundwater that is pulled in

through the lower well screen.

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The stripped VOCs are then discharged from the in-situ stripping well to the air.

Based on available information, it is not anticipated that treatment of the VOC-laden air

would be required. Further evaluation of emission rates would be conducted during the

engineering design.

This alternative would include implementation of local or state well permit

restrictions and public education. In addition, groundwater monitoring would be included

to evaluate the effectiveness of the in-situ stripping wells protection of the Gravel Pit

Lake and Raccoon River. A detailed sampling and quality assurance plan would be

written before the groundwater monitoring activities began. The sampling and quality

assurance plans would include sample locations, sampling frequency, sampling

procedures, sample analysis methods, and sample documentation procedures. Wells from

the existing monitoring well network would be used as much as possible to avoid

duplication of effort and to minimize the number of new monitoring wells installed. One

new monitoring well would be added to the existing monitoring well network to allow

evaluation of the effectiveness of the in-situ stripping wells..

It was assumed that the groundwater monitoring would consist of sampling the new

monitoring well, the twelve existing monitoring wells, the shallow and deep piezometer

at each in-situ treatment well, three surface water sample locations, and four WDM water

supply wells (WDMW-5, WDMW-6, WDMW-12, and WDMW-13) quarterly for yearsone and two; semiannually for years three, four, and five; and annually after year five

until RAOs are attained. The frequency of the monitoring could be reevaluated and

modified after the five-year reviews or after review of the monitoring data by the EPAand IDNR. The groundwater and surface water samples would be analyzed for VOCs.

It was assumed that the surface water monitoring would consist of collecting two

samples from the Gravel Pit Lake and one sample from the Raccoon River at the same

frequency of the groundwater samples. The surface water samples would also be

analyzed for VOCs.

The results of the sample analysis would be used to evaluate the rate and direction of

groundwater contaminant migration. If the monitoring results indicate that the plume is

migrating towards new receptors, further remedial actions would be initiated.

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10.0 Comparative Analysis of Alternatives

Nine criteria are used to evaluate the different alternatives individually and against

each other in order to select a remedy. The nine evaluation criteria are: (1) overall

protection of human health and the environment; (2) compliance with ARARs; (3) long-

term effectiveness and permanence; (4) reduction of toxicity, mobility, or volume of

contaminants through treatment; (5) short-term effectiveness; (6) implementability; (7)

cost; (8) state/support agency acceptance; and (9) community acceptance. This section of

the ROD profiles the relative performance of each alternative against the nine criteria,

noting how it compares to the other options under consideration. The nine evaluation

criteria are discussed below and are summarized in Table 10.

10.1 Overall Protection of Human Health and the Environment

Overall protection of human health and the environment determines whether an

alternative eliminates, reduces, or controls threats to public health and the environmentthrough institutional controls, engineering controls, or treatment.

Human health and the environment would be adequately protected by Alternatives 2,

3, and 4. Alternatives 3 and 4 would provide the highest overall protection of human

health and the environment since groundwater contaminants are contained. Alternative 3

collects and treats the extracted groundwater before contaminants migrate to

downgradient surface water bodies. Similarly, Alternative 4 would provide treatment ofthe groundwater that passes through the line of in-situ treatment wells before

contaminants migrate to downgradient surface water bodies. Alternative 2 would provide

the next best overall protection of human health and the environment through observed

and documented natural attenuation processes. Alternative 1 would provide the least

overall protection of human health and the environment since Alternative 1 provides no

means of control to prevent public exposure to contamination and no monitoring of

plume changes.

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10.2 Compliance with Applicable or Relevant and Appropriate Requirements (ARARs)

All the alternatives except Alternative 1 would comply with chemical-specific and

action-specific ARARs. No location-specific ARARs were identified for any alternative.

Alternatives 2, 3, and 4 would meet chemical-specific ARARs in the long term through

•MNA processes. Alternatives 3 and 4 contain the groundwater plume above cleanup

levels (i.e., MCLs) in addition to MNA processes reducing onsite contaminant levels.

10.3 Long-Term Effectiveness and Permanence

Long-term effectiveness and permanence consider the ability of an alternative to

maintain protection of human health and the environment over time.

Biodegradation of COCs at the site would be effective and permanent under

Alternatives 2, 3, and 4. Alternatives 3 and 4 would provide best long-term effectiveness

and permanence because the groundwater plume containing COCs above cleanup levels

(i.e., MCLs) would be contained. Because no remedial actions would occur,

Alternative 1 would provide the lowest long-term effectiveness and permanence.

10.4 Reduction of Toxicity, Mobility, or Volume of Contaminants Through Treatment

Reduction of toxicity, mobility, or volume of contaminants through treatment

evaluates an alternative's use of treatment to reduce the harmful effects of principal

contaminants, their ability to move in the environment, and the amount of contaminationpresent.

Alternatives 2, 3, and 4 would be effective in reducing the toxicity and volume of

contaminants at the completion of the remedial actions. However, under Alternative 2

the reduction of the toxicity of contaminants would occur through natural processes rather

than treatment efforts in the last phases of the chemical reduction process as the COCs

eventually degrade to non-toxic compounds. Alternatives 3 and 4 meet the statutory

preference for treatment as a principal element of the alternative and also reduce mobility

of contaminants. Because groundwater monitoring would not be conducted under

Alternative 1, there would be no mechanism to evaluate or demonstrate the reduction in

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the toxicity, mobility, or volume of contaminants through natural attenuation processes.

Therefore, reduction in the toxicity, mobility, and volume of contaminants under

Alternative 1 cannot be presumed.

10.5 Short-Term Effectiveness

Short-term effectiveness considers the length of time needed to implement an

alternative and the risks the alternative poses to workers, residents, and the environment

during implementation.

Alternatives 2, 3, and 4 would reach cleanup goals in a similar timeframe which is

estimated to be in excess of thirty years. However, Alternative 3 may reach cleanup goals

slightly sooner because the recovery wells would increase the hydraulic gradient at the

site, resulting in an increased migration rate of the plume. Short-term risk would exist to

the community from onsite groundwater contaminants which are relatively slower to

attenuate. However, the short-term risks would be mitigated through institutional

controls. Alternatives 3 and 4 would contain the plume. The containment efforts may

need to operate in excess of thirty years. Alternative 1 would not include any action and

may not meet RAOs.

There would be no increase in short-term risks to workers under Alternative 1;

however, there would be a continued risk to the community because contaminants above

cleanup levels (i.e., MCLs)s would remain onsite unmanaged and unmonitored.

Alternative 2 would have minor, controllable increased risk to the community duringconstruction, and worker protection would be required during monitoring well

installation. Alternatives 3 and 4 would have the greatest short-term risks, although still

moderately low, from construction of the new onsite treatment plant, associated pipelines,

and in-situ stripping wells.

10.6 Implementability

Implementabiliry considers the technical and administrative feasibility of

implementing the alternative such as the relative availability of goods and services.

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Alternative 1 would be the easiest alternative to implement because no construction

or operation would be required. Alternative 2 would be the next easiest alternative to

implement because the only construction required would be installation of one

monitoring well, and only periodic monitoring would be required. Alternative 4 would be

more difficult to implement because it would require installation and O&M often in-situ

stripping wells. Alternative 3 would be the most difficult to implement, requiring

construction of a new onsite treatment plant, installation of collection and discharge

piping, installation of recovery wells, as well as more extensive O&M.

10.7 Cost

Cost includes estimated capital and O&M costs as well as present worth costs. The

present worth cost is the total cost of an alternative over time in terms of today's dollar

value. Cost estimates are expected to be accurate within a range of+50 percent to -30

percent.

Cost estimates were prepared for each alternative. These estimates are approximate

and made without detailed engineering data. The actual cost of the project would depend

on the final scope of the remedial action and other unknowns. The total present worth of

Alternative 1 would be the lowest at a cost of $111,300. The total present worth cost of

Alternative 4 would be the greatest at a cost of $1,844,000. The total present worth costs

of Alternatives 2 and 3 are estimated to be $430,000 and $1,343,000, respectively.

10.8 State/Support Agency Acceptance

State agency acceptance considers whether the state agrees with the EPA's analyses

and recommendations of the RI/FS and the Proposed Plan.

The IDNR supports the preferred alternative, Alternative 2: Monitored Natural

Attenuation, as proposed by the EPA.

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10.9 Community Acceptance

Community acceptance considers whether the local community agrees with the

EPA's analyses and preferred alternative. Comments received on the Proposed Plan are

important indicators of community acceptance.

During the public comment period, the community expressed its support for

Alternative 2: Monitored Natural Attenuation, as proposed by the EPA.

11.0 Principal Threat Wastes

The "principal threat" concept is applied to the characterization of "source materials"

at a Superfund site. A source material is material that includes or contains hazardous

substances, pollutants, or contaminants that act as a reservoir for migration of

contamination to groundwater, surface water, or air, or acts as a source for direct

exposure. Contaminated groundwater generally is not considered to be a source material;

however, non-aqueous phase liquids (NAPLs) in groundwater may be viewed as source

material.

The source materials for the VOCs in the Northern Plume are currently unknown

despite reasonable investigation efforts. However, the source materials for the Northern

Plume appear to be diminishing.

12.0 Selected Remedy

This section expands upon the details of the selected remedy from that which is

presented in the Description of Alternatives Section (Section 9) of this ROD.

12.1 Summary of the Rationale for the Selected Remedy

The selected remedy for the Northern Plume of the Railroad Avenue Groundwater

Contamination site will consist of Alternative 2: Monitored Natural Attenuation to be

performed simultaneously with the previous interim action that included expansion of the

stripping capacity at the West Des Moines drinking water plant as documented in the

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September 26, 2003, ROD. This previously implemented interim remedial action is

intended to protect the West Des Moines water supply from contamination, leaving the

selected remedy to address only the remaining contaminants that do not impact the water

supply system. This alternative will provide the best balance of trade-offs among

alternatives with respect to the evaluating criteria. The EPA believes Alternative 2 in

conjunction with the previous interim action will be protective of human health-and the ,

environment, will comply with ARARs, will be cost effective, and will utilize permanent

solutions and alternative treatment technologies or resource recovery technologies to the

maximum extent practicable.

The main factors influencing EPA in its selection of Alternative 2 as the remedy

include:

• Institutional controls will eliminate or minimize the chance of a receptor being

exposed to the contaminated groundwater at OU 1.

• Site data indicate that significant amounts of source material or NAPLs no longer

remain at OU 1; hence, there is no evidence of principal threat wastes at OU 1.

• Monitoring of OU 1 is warranted because of the levels of COCs detected in the

groundwater at OU 1.

• Current monitoring data at the site indicate that natural attenuation is actively

occurring at the site.

12.2 Description of Selected Remedy

Alternative 2 will rely on the aquifer's ability to lower contaminant concentrations

through MNA processes. The alternative will include groundwater and surface water

monitoring to confirm continued efficiency of the natural attenuation of contaminants and

institutional controls to minimize potential health risks associated with groundwater

contaminants still undergoing attenuation. The estimated timeframe required to attain

cleanup levels is greater than thirty years, which is similar to the other proposed

alternative timeframes. The long timeframe is appropriate for the site since the

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previously implemented interim action remedy addresses contaminated groundwater that

is collected by the West Des Moines drinking water plant.

Several years of site data have been collected to evaluate site conditions and are

summarized in Tables 1, 2, and 11. Results of the evaluation indicate that migration of

contaminants in groundwater is complex and subject to several physical and chemical

processes. However, contaminant migration at the Railroad Avenue site is strongly

affected by two primary site conditions: groundwater transport, and biochemical

processes.

The groundwater flow direction and current extent of the COCs at the Northern

Plume are illustrated in Figure 2. The groundwater flow direction at the Northern Plume

is primarily to the east-southeast toward Gravel Pit Lake and the Raccoon River. The

distribution of the contaminant plumes also shows evidence of an east-southeasterly

groundwater flow trend. However, distribution of the contaminants indicates that the

groundwater capture zone created from historical periodic pumping of WDM water wells

WDMW-5, WDMW-6, WDMW-12, and WDMW-13 has caused contaminants to migratewest toward these water supply wells.

While advective flow processes cause contaminants to migrate along with

groundwater in the direction of groundwater flow, biodegradation processes

simultaneously degrade the site contaminants. Biochemical processes at sites include

biodegradation which is where hydrocarbons are eventually reduced to more stable, less

toxic compounds. Studies show that chlorinated hydrocarbons such as PCE and TCEand, to a lesser degree, cis-l,2-DCE, can degrade naturally via reductive dechlorination

under anaerobic conditions. Biodegradation of PCE and TCE is occurring at the Northern

Plume site as evidenced by the low concentrations of PCE and TCE and the relatively

elevated concentrations of cis-l,2-DCE and VC, which are degradation products of PCE

and TCE. The extent of TCE, cis-l,2-DCE, and VC are illustrated in Figure 2. Figures 4

and 5 illustrate that the highest concentrations of the source contaminant TCE are located

near the suspected release area, whereas downgradient of the source area, the

concentrations of TCE are lower and the daughter contaminants (cis-l,2-DCE and VC)

are higher.

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Other indicators of biodegradation include evaluation of materials within the plumes

which act as electron acceptors and electron donors in the reductive dechlorination

process and the presence or absence of by-products of the process within the plumes.

The absence of electron acceptors indicates the occurrence of reductive

dechlorination.processes. -The site geochemical data show the absence of electron

acceptors such as dissolved oxygen and nitrate within the plumes. However, sulfate,

another less easily consumed electron acceptor, is also present indicating the aquifer is

not at the optimal reducing condition for reduction of the cis-l,2-DCE plume. The

presence of VC indicates that the cis-l,2-DCE plume is reducing, albeit at a slower rate

than PCE and TCE.

The presence of electron donors, such as carbon sources, also supports the

occurrence of reductive dechlorination processes. Natural organic carbon was

encountered in borings drilled in the area which indicates the availability of a carbon

source to support reductive dechlorination.

The presence of reductive dechlorination by-products also indicates the occurrence

of reductive dechlorination processes. Site geochemical data show the presence of

reductive dechlorination by-products within the plumes including ferrous iron and

methane.

The EPA has developed site screening criteria for identifying sites where reductive

dechJorination is occurring (Technical Protocol for Evaluating Natural Attenuation ofChlorinated Solvents in Ground Water, EPA /600/R-98/128, USEPA, September 1998).

The site data from May and November 2004 were evaluated using the screening criteria.

Results of the screening evaluation are presented in Table 12 and indicate adequate

evidence for reductive dechlorination of PCE, TCE, and cis-l,2-DCE.

Site data indicate PCE, TCE, and cis-l,2-DCE may be biodegrading at an optimal

rate and that expansion of these plumes may not occur. However, site data indicate that

biodegradation of the VC plume may not be occurring. The aquifer is anaerobic which

does not easily allow biodegradation of VC. The VC plume continues to expand toward

the Gravel Pit Lake and Raccoon River; however, the VOC contaminants that eventually

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reach these surface water bodies appear to be attenuating through natural processes as

indicated by the absence of VOCs above detection limits in the surface water samples.

The migration rates and paths for site contaminants were further evaluated by

groundwater flow and contaminant transport computer models and are discussed in the

Groundwater Model Technical Memorandum prepared for the site. Results of the

computer groundwater modeling show that the contaminant plumes will continue to be

captured by wells in the West Des Moines well field and will also eventually reach the

Gravel Pit Lake and Raccoon River.

This alternative will include implementation of local or state well permit restrictions

and public education. The alternative will include implementation of well permitting

requirements to limit use of groundwater at the site. The permitting requirements will

consist of an ordinance passed by the city of West Des Moines, Iowa, prohibiting the

installation of new wells if city water is available. If a local ordinance could not be

passed, a protected water source designation at the state level will be sought. In a

protected water source area new well installation will be restricted.

Public education efforts will be performed which will include informing local

officials on well drilling restrictions and informing citizens of the potential health hazards

associated with exposure to contaminated groundwater. Public education will be

implemented through informational meetings and flyers.

Groundwater monitoring will be included to evaluate the effectiveness of the naturalattenuation processes. A detailed sampling and quality assurance plan will be written

before the groundwater monitoring activities begin. The sampling and quality assurance

plan will include sample locations, sampling frequency, sampling procedures, sample

analysis methods, and sample documentation procedures.

One new monitoring well will be installed down gradient of the VC plume along

First Street. The final location of the well will be determined during remedial design and

will be contingent upon access agreements with the property owners.

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Groundwater monitoring will consist of sampling the new monitoring well, the

twelve existing monitoring wells, the three surface water sample locations, and four

WDM water supply wells (WDMW-5, WDMW-6, WDMW-12, and WDMW-13)

quarterly for years one and two; semiannually for years three, four, and five; and annually

after year five until RAOs are attained. The frequency of the monitoring could be re-

evaluated and modified after the five-year reviews or-after review of monitoring data-by

the EPA and IDNR. The groundwater samples will be analyzed for VOCs.

Surface water monitoring will consist of collecting two samples from the Gravel Pit

Lake and one sample from the Raccoon River at the same frequency of the groundwater

samples. The surface water samples will be analyzed for VOCs.

The results of the sample analysis will be used to confirm the rate and direction of

groundwater contaminant migration. If the monitoring results indicate that the plume is

migrating towards new receptors, further remedial actions will be initiated. •

12.3 Summary of Estimated Costs

The detailed cost summary of the capital and O&M costs associated with the

implementation of Alternative 2 is presented in Table 13. The information in the cost

estimate is based on the best available information regarding the anticipated scope of the

remedial alternative. Changes in the cost elements are likely to occur as a result of new

information and data collected during the engineering design of the remedial alternative.

Major changes may be documented in the form of a memorandum in the AdministrativeRecord file, an Explanation of Significant Difference, or a ROD amendment. This is an

order of magnitude engineering cost estimate that is expected to be within +50 percent to

-30 percent of the actual project cost.

The capital costs include both direct and indirect capital costs. The direct capital

costs include efforts to install one additional monitoring well and legal fees to provide

assistance to the city of West Des Moines or the state of Iowa to implement permitting

requirements. With the addition of indirect costs, the total capital cost is estimated to be

$24,000. The capital costs for this alternative may be assumed by others.

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The O&M costs associated with implementing this alternative include groundwater

monitoring and five-year reviews. The O&M costs are divided into two types, yearly and

intermittent costs. Yearly costs are those items that do not change over the life of the

alternative. Examples of yearly costs are the annual newsletters for public education.

Intermittent costs are those periodic costs that differ over the life of the alternative.

Examples of intermittent costs are the costs for groundwater monitoring and five-year

reviews.

Annual O&M costs for the first year are estimated to be $56,700 and are estimated to

be between $15,300 and $90,300 for every year thereafter. The total O&M cost for the

life of the project for Alternative 2 is $921,000. The total present worth of the O&M

costs for Alternative 2 is $406,000. The total present worth of Alternative 2 is estimated

to be $430,000.

12.4 Expected Outcomes of the Selected Remedy

The site aquifer is expected to be available as a drinking water resource as a result of

successful completion of the remedy. The selected remedy will require an extensive

period of time (greater than thirty years) to attain final cleanup levels.

Final cleanup levels were established for groundwater at the site based on the MCLs

established under the Safe Drinking Water Act. The final cleanup levels for groundwater

are presented in Table 14. The cleanup level for groundwater will restore the

groundwater to drinking water quality, with respect to VOC contamination.

13.0 Statutory Determinations

Under CERCLA Section 121, EPA must select remedies that are protective of

human health and the environment, comply with ARARs (unless a statutory waiver is

justified), are cost effective, and utilize permanent solutions and alternative treatment

technologies or resource recovery technologies to the maximum extent practicable. In

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addition, CERCLA includes a preference for remedies that employ treatment that

permanently and significantly reduces the volume, toxicity, or mobility of hazardous

wastes as a principal element. The following sections discuss how the selected remedy

meets these statutory requirements.

• 13.1 Protection of Human Health and the Environment - - -

The selected remedial action will protect human health and the environment. Active

biodegradation processes identified at the site will eliminate the groundwater pathways

through which contaminants pose risks. Restricting future use of groundwater at the site

through institutional controls will prevent inadvertent use of groundwater contaminated

above cleanup levels.

13.2 Compliance with ARARs

Section 121(d)(2) of CERCLA, 42 USC §9621(d)(2), requires that cleanup actions

conducted under CERCLA achieve a degree or level of cleanup which, at a minimum,attains "any standard, requirement, criteria or limitation under any Federal environmental

law...or any promulgated standard, requirement, criteria, or limitation under a State

environmental or facility siting law that is more stringent than any Federal

standard...[which] is legally applicable to the hazardous substance or pollutant or

contaminant concerned or is relevant and appropriate under the circumstances of the

release or threatened release of such hazardous substance or pollutant of contaminant...."

The identified standards, requirements, criteria, or limitations thus adopted from otherenvironmental laws, which govern onsite cleanup activities at this site, are referred to as

ARARs.

For onsite cleanup activities, under Section 121(e)(l) of CERCLA, EPA is not

required to obtain any federal, state, or local permits for actions conducted onsite,

complying only with the substantive (non-administrative) requirements of the identified

federal and state laws. On the other hand, for cleanup activities that will occur offsite,

both the substantive as well as the administrative requirements of such laws will apply to

cleanup activities.

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This section identifies the ARARs which will apply to the remedy selected for this

site. (The many laws and regulations which apply to offsite cleanup or disposal activities

are not called "ARARs" and are not enumerated here.)

• National Primary Drinking Water Standards-Safe Drinking Water Act (40 CFR

Part 141) and Iowa Water Sources (Iowa Administrative Code (IAC) 567 Chapter

41, 133, & 137): Establishes MCLs for a number of common organic and

inorganic contaminants including the site COCs. These levels regulate the

concentrations of contaminants in public drinking water supplies and are

considered relevant and appropriate for groundwater aquifers potentially used for

drinking water.

• Iowa Protected Water Sources-Purposes-Designation Procedures-Information in

Withdrawal Applications-Limitations-List of Protected Sources (IAC 567

Chapter 53): Provides for designating a protected water source.

• Iowa Water Quality Standards (IAC 567 Chapter 61): Provides for the

maintenance and protection of surface water for aquatic life, agricultural,

domestic, industrial water supply, and recreation.

In addition, all remedial activities for the site would need to comply with

Occupational Safely and Health Administration requirements.

13.3 Cost Effectiveness

The selected remedial action is cost effective, providing overall effectiveness

proportional to its costs. The selected remedy will be effective in the long term,

providing a significant and permanent reduction of the toxicity, mobility, and volume ofcontaminated groundwater contaminants.

13.4 Utilization of Permanent Solutions and Innovative Treatment Technologies to the

Maximum Extent Practicable

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The EPA has determined, and the state of Iowa has concurred with EPA's

determination, that the selected remedy represents the maximum extent to which

permanent solutions and treatment technologies can be utilized in a practicable manner

for the Northern Plume at the Railroad Avenue Groundwater Contamination site even

though the selected remedy does not satisfy the statutory preference for treatment as a

principal element of-the remedy. Of.those alternatives that are protective of human health

and the environment and comply with ARARs, EPA and the state have determined that

this selected remedy provides the best balance of trade-offs in terms of the five balancing

criteria, while also considering the statutory preference for treatment as a principal

element and considering state and community acceptance. The selected remedy treats the

primary threats posed by VOC-contaminated groundwater, achieving VOC reduction,

although the source material for the contaminants appears to be reduced through

attenuation processes.

The selected remedy will permanently and significantly reduce the toxicity, mobility,

and volume of the site COCs through natural attenuation processes rather than through

treatment as a principal element. The most significant difference among the proposed

groundwater alternatives that met overall protection and ARARs was with regard to the

cost and implementability.

13.5 Preference for Treatment which Reduces Toxicity, Mobility, or Volume

The selected remedy does not satisfy the statutory preference for treatment as a

principal element of the remedy; however, the toxicity, mobility, and volume of the siteCOCs will be permanently and significantly reduced through natural attenuation

processes. Observed active bioremediation processes of the selected remedial action

addresses the primary threat posed by VOC-contaminated groundwater, achieving VOC

reductions, although the source material for the contaminants appears to be reduced

through attenuation processes.

14.0 Documentation of Significant Changes

The selected remedy has not been significantly changed from the preferred

alternative presented in the Proposed Plan.

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RAILROAD AVENUE SUPERFUND SITEWEST DES MOINES, IOWA

RESPONSIVENESS SUMMARYTO

COMMENTS FROM PUBLIC MEETING

Comment 1: One commenter raised no objection to the proposal, but noted that if humanskeletal remains are uncovered during construction, work should stop immediatelyand proper authorities notified.

Response 1: The EPA will follow the noted steps if excavation uncovers such remains, but wenote that very little excavation will occur on this project.

Comment 2: Two commenters expressed concern about an existing monitoring station on thecorner of 11th and Railroad Avenue and whether it could be removed.

Response 2: As was noted at the meeting, this monitoring station is not for the EPA RailroadAvenue project. An IDNR representative at the meeting agreed to check with thestate's leaking underground storage tank program to ascertain if this station wasfor one of their projects and whether it could be removed.

Comment 3: Another commenter asked about any impacts from the project on futuredevelopment in the area.

Response 3: As we explained at the meeting, we foresee no impact on future developmentfrom our project. There is no surface impact from the contaminated groundwaterin the area, and only one additional monitoring well will be installed during theproject. No impacts to any future development should arise from this project.

Comment 4: A commenter asked if the new aerators at the water works had significantlyreduced contamination in the water supply.

Response 4: Based on data from the operation of the new aerators, they are successfullytreating any volatile organic compounds (VOCs) drawn into the municipal wellsystem. All data following aerator treatment have shown no detections for thesecontaminants.

Comment 5: The same commenter asked if any of this contamination was caused by the floodof 1993.

Response 5: We do not believe the contamination came as a result of the flood of 1993. Thecontamination in the water supply was first discovered in that year, but likely tookseveral years to travel to the well where it was first detected.

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Comment 6: A commenter asked if the plume could get into the Des Moines water supplysystem.

Response 6: The remedy specifies monitoring of the plume to make sure it is annuating, andtherefore, we will be watching for this possibility during the remediation period.Based on current data, however, we believe the plume will never reach the Des

.Moines well field area and will be attenuated before it reaches the Raccoon Riverand Gravel Pit Lake.

Comment 7: The same commenter asked if there was anything citizens and businesses need todo now to protect themselves.

Response 7: Since there is no surface impact from the contamination, there is very little thatcitizens and businesses need to do. The only thing they should not do would be todrink groundwater from a private well in the area of the contamination plume.We do not know of any drinking water wells in the area, but if there are, theyshould not be used for drinking. Watering yards or gardens would not be aproblem with such wells, just do not drink it regularly.

RS2

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TABLES

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Table 1VOC Data Summary (Monitoring Wells)

Railroad Avenue Groundwater Contamination Site

Monitoring

Well

MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12

AnalytePCEPCEPCEPCEPCEPCEPCEPCEPCEPCEPCEPCETCETCETCETCETCETCETCETCETCETCETCETCE

MCL*

W

5

5

Concentration

July 2002

0.5 U0.5 U0.5 U0.5 U0.5 U

'-• 5 . ' •0.5(0.5) U

0.5 U0.5 U0.5 U0.5 U0.5 U

0.960.5 U0.5 U0.5 U6.7 :2.5

0.5(0.5) U2.80.5 U0.5 U0.5 U0.5 U

Nov. 2002

0.5 U0.5(0.5) U

0.5 U0.5 U0.5 U120.5 U0.5 U0.5 U0.5 U0.5 U0.5 U1.5

1.3(1.2)0.510.5 U6.6 :•4.70.5 U2.70.5 U1.10.5 U0.5 U

May 2003

0.5 U0.5 U0.5 U0.5 U0.5 U4.30.5 U

0.5(0.5) U0.5 U0.5 U0.5 U0.5 U1.4

0.830.5 U0.5 U2.12.60.5 U

0.5 (0.5) U0.5 U1.10.5 U0.5 U

Nov. 20031 U1 U

1.0(1.0) U1 U1 U

1.61 U1 U1 U1 U1 U1 U1 U

1.11 .0(1 .0) U

1 U' .7.3 ' ; • ; •

1 U1 U

1.71 U1 U1 U1 U

May 20040.5 U0.5 U0.5 U0.5 U0.5 U6.7 :.:•'".

0.5(0.5) U10 U0.5 U0.5 U0.5 U0.5 U

0.900.930.500.50 U

' : 5.6 • ' , ' . ' , -. 5.5 '• • .0.5(0.5) U

10 U0.50 U0.890.50 U0.50 U

Nov. 2004

NA0.5 UNA

0.5(0.5) U0.5 U

.; 5.2 -•' •0.5 U0.5 U

• 6.5. ••..-.NA0.5 U0.5 UNA0.5 UNA

0.5(0.5) U-6:12.50.5 U

0.983.3NA0.5 U0.5 U

Units

ug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/L

Railroad Avenue Groundwater Contamination SiteNorthern Plume I of 4 Record of Decision

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Table 1 (Continued)VOC Data Summary (Monitoring Wells)

Railroad Avenue Groundwater Contamination Site

MonitoringWell

MW-01MW-02MW-Q3MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12

Analytecis-1 ,2-DCEcis-1 ,2-DCEcis-1, 2-DCEcis-1 ,2-DCEcis-1,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1, 2-DCEcis-1, 2-DCEcis-1 ,2-DCEcis-1 ,2-DCE

VCVCVCVCVCVCVCVCVCVCVCVC

MCL*

(ufi/L)

70

2

Concentration

July 200215

:%>iio '••'200.0.5 U147.3

490(500), 3 7 0

0.5 U4.B5.20.5 U0.5 U0.5 U

0.510.5 U0.5 U0.5 U12(11)290.5 U172.72.3

Nov. 2002

10270(240)2200.5 U1112

4104200.57

46

0.5 U0.5 U

0.5(0.5) U0.5 U0.5 U0.5 U0.5 U171100.5 U8.1116.7 ...

May 200319

' ..• :. 140' •:>;1800.5 U1318

.830220(250)

0.5 U3.64.40.5 U0.5 U

0.830.550.5 U0.5 U0.5 U34

110(120)0.5 U4.321

.12 .

Nov. 200312

'•!•-',• .-V-liBO!'1. '210(220)

1 U1611

820^ 280

1 U4.45.71 U2 U2 U

2.0(2.0) U2 U2 U2 U15 J92 J2 U

' 12 J12 J.12 :J

May 200424

-'2201900.5 U199.1

-;110(130)370;0.5 U4.66.60.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U

2.4(2.0)670.5 U7.6131.2

Nov. 2004NA0.5 UNA

0.5(0.5) U144.8

v 170290 :6.6NA3.60.5 UNA1.7NA

0.5(0.5) U0.5 U0.5 U2.8370.5 UNA5.80.66

Unitsug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/L

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Table 1 (Continued)VOC Data Summary (Monitoring Wells)

Railroad Avenue Groundwater Contamination Site

MonitoringWell

MW-01

MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09

MW-10MW-11

MW-12MW-01

MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11

MW-12

Analyte

1,1 -DCE1,1 -DCE1,1 -DCE1,1 -DCE

1,1 -DCE1,1 -DCE

1,1 -DCE

1,1 -DCE1,1 -DCE

1,1-DCE1,1 -DCE

1,1-DCE

MTBEMTBEMTBEMTBEMTBEMTBEMTBEMTBEMTBEMTBEMTBEMTBE

MCL*

<PSM

7

None

Concentration

July 2002

0.5 U0.5 U0.60.5 U

0.5 U0.5 U

1.6(1.6)1.20.5 U

0.5 U

0.5 U0.5 U1

0.5 U0.99

0.5 U12

0.5 U

1.5(1.5)1.92.23.2

0.5 U3.2

Nov. 2002

0.5 U0.5(0.5) U

0.5 U

0.5 U0.5 U

0.5 U

0.5 U

1.0

0.5 U

0.5 U

0.5 U0.5 U1.1

1.1(0.9)1.2

0.5 U11

0.5 U1.5

2.37.6

6.3

0.5 U4.1

May 2003

0.5 U0.60.70.5 U0.5 U0.5 U2.5

0.9(0.9)

0.5 U

0.5 U

0.5 U0.5 U0.5 U

0.5 U0.5 U

0.5 U1.1

0.5 U

0.5 U0.5(0.5) U

0.5 U

0.5 U

0.5 U0.5 U

Nov. 2003

1 U1 U

1.0(1.0) U1 U

1 U

1 U

1.31 U

1 U

1 U1 U

1 U--

-

--

-

-

--

-

-

-

May 2004 | Nov. 2004

0.5 U0.690.690.5 U0.5 U0.5 U

0.5(0.5) U10 U0.5 U0.5 U0.5 U0.5 U0.670.750.88

0.5 U13

0.5 U

0.5(0.5) U10 U1.9

3.0

0.5 U4.1

MA

0.5 UNA

0.5(0.5) U0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

NA

0.5 U0.5 U.NA

2.6NA

0.5(0.5) U8.90.5 U

0.5 U1.1

0.5 UNA

0.5 U1.7 J

Units

ug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/L

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Table 1 (Continued)VOC Data Summary (Monitoring Wells)

Railroad Avenue Groundwater Contamination Site

Monitoring

Well

MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12

Analytetrans-1,2-DCEtrans-1 ,2-DCEtrans-1 ,2-DCEtrans-1 ,2-DCEtrans-1 ,2-DCEtrans-1 ,2-DCEtrans-1 ,2-DCEtrans-1 ,2-DCEtrans-1 ,2-DCEtrans-1 ,2-DCEtrans-1 ,2-DCEtrans-1 ,2-DCE

MCL*

<w/u

100

Concentration

July 2002

0.5 U0.5 U1.30.5 U0.5 U0.5 U

4.7(4.5)3.10.5 U0.5 U0.5 U0.5 U

Nov. 20020.5 U

2.1(1.7)1.30.5 U0.5 U0.5 U3.2

3.90.5 U0.5 U0.5 U0.5 U

May 20031.11.31.30.5 U0.5 U0.5 U4.2

1.9(1.9)0.5 U0.5 U0.5 U0.5 U

Nov. 2003

1 U1.3

1.1(1.1)1 U1 U1 U321 U1 U1 U1 U

May 20040.632.11.30.5 U0.5 U0.5 U

1.2(1.1)10 U0.5 U0.5 U0.5 U0.5 U

Nov. 2004NA0.5 UNA

0.5(0.5) U0.5 U0.5 U1

1.60.5 UNA0.5 U0.5 U

Units

ug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/L

* Maximum contaminant levels established under 40 CFR 141

ug/L = micrograms per liter

U = Not detected at or above the reportable level shown.

J = The associated numerical value is an estimated quantity.

Duplicate result in parentheses.

NA = not available

Shaded results indicate where contaminant was detected above respective MCL.

Other VOCs detected infrequently at low concentrations include 2-butanone at 0.76 ug/L in well MW-7 in July 2002, toluene at 0.76 ug/Lin well MW-1 in July 2002, and 1,2-dibromo-3-chloropropane at 1.4 ug/L in well MW-8 in July 2002.

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Table 2VOC Data Summary (Water Supply Wells)

Railroad Avenue Groundwater Site

WellWDMW-01WDMW-03WDMW-04WDMW-05WDMW-06WDMW-07WDMW-08WDMW-09WDMW-12WDMW-13WDMW-14WDMW-15WDMW-16WMDW-17WDMW-18WDMW-19WDMW-20WDMW-21WDMW-22WDMW-23WDMW-24WDMW-25WDMW-01WDMW-03WDMW-04WDMW-05WDMW-06WDMW-07WDMW-08WDMW-09WDMW-12WDMW-13WDMW-14WDMW-15WDMW-16WMDW-17WDMW-18WDMW-19WDMW-20WDMW-21

WDMW-22

WDMW-23

WDMW-24

WDMW-25

AnalyteTCETCETCETCETCETCETCETCETCETCETCETCETCETCETCETCETCETCETCETCETCETCE

cis-1,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCECis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCEcis-1 ,2-DCECis-1 ,2-DCE

cis-1 ,2-DCE

cis-1 ,2-DCE

cis-1 ,2-DCE

cis-1, 2-DCE

MCL*

(ug/L)

5

5

Concentration

July 2002

0.5 U0.5 UNA0.5 U0.5 U

0.5(0.5) U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U1

0.5 U1.40.5 U0.5 U0.5 U

0.5(0.5) U0.5 U0.5 UNA3

4.50.5(0.5) U

0.5 U0.5 U2.20.540.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.960.5 U

0.5 U0.5 U

0.5(0.5) U

Nov. 2002NANA0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U1.40.5 U1.90.5 U

0.5(0.5) U0.5 U0.5 UNANA0.5 U2.86

0.5 U0.5 U0.5 U2.31.50.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.660.5 U

0.5(0.5) U

0.5 U0.5 U

May 20030.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U1.50.5 U

1.8(1.8)0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U1.35.80.5 U0.5 U0.5 U3.10.540.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U

1.7(1.7)

0.5 U

0.5 U0.5 U

0.5 U

Nov. 20031.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 ul1.0 U1.0 U

1.0(1.0) ul1.41.0 U2.41.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U2.03.81.0 U1.0 U1.0 U1.81.0 U1.0 U1.0 U1.0 U1.0 U

1.0(1.0) U1.0 U1.0 U3.1

1.0 U

1.0 U1.0 U

1.0 U

Nov. 20040.5 U0.5 U0.5 UlNA ~l

0.5(0.5) U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 UNA0.5 U0.5 U

0.950.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 U0.5 UNA I

1.9(2.4)0.5 U0.5 U0.5 U2.10.5 U0.5 U0.5 UNA0.5 U0.5 U0.5 U0.5 U2.6

0.5 U

0.5 U0.5 U0.5 U

Feb. 20051.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U

2.1 (2.0)1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.11.41.0 U1.0 U1.0 U1.5

1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U1.0 U

1.8(1.8) U

1.0 U

1.0 U1.0 U1.0 U

Unitsug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/L

ug/Lug/Lug/L

Railroad Avenue Groundwater Contamination SiteNorthern Plume I o f 2 Record of Decision

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Table 2 (Continued)VOC Data Summary (Water Supply Wells)

Railroad Avenue Groundwater Site

Well

WDMW-01

WDMW-03

WDMW-04

WDMW-05

WDMW-06

WDMW-07

WDMW-08

WDMW-09

WDMW-12

WDMW-13

WDMW-14

WDMW-15

WDMW-16

WMDW-17

WDMW-18

WDMW-19

WDMW-20

WDMW-21

WDMW-22

WDMW-23

WDMW-24

WDMW-25

Analyte

VCVCVCVCVCVCVC

VC

VC

VC

VC

VC

VC

VC

VC

VC

VC

VC

VC

VC

VC

VC

MCL*

(ug/L)

2

Concentration

July 2002

0.5 U0.5 U

NA

0.5 U

0.5 U

0.5(0.5) U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5(0.5) U

Nov. 2002

NA

NA

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5(0.5) U

0.5 U

0.5 U

May 2003

0.5 U0.5 U

NA

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5(0.5) U

0.5 U

0.5 U

0.5 U

0.5 U

Nov. 2003

2.0 U2.0 U

2.0 U

2.0 U

2.0 U

2.0 U

2.0 U

2.0 U

2.0 U

2.0 U

2.0 U

2.0 U

NA

2.0 U

2.0(2.0) U

2.0 U

2.0 U

2.0 U

2.0 U

2.0 U

2.0 U

2.0 U

Nov. 2004

0.5 U

0.5 U

0.5 U

NA

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

0.5 U

NA

0.5 U

0.5 U

0.5 U

0.5 U

5.1

0.5 U

0.5 U

0.5 U

0.5 U

Feb. 2005

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

1.0 U

Units

ug/Lug/Lug/L

ug/L

ug/L

ug/L

ug/Lug/L

ug/Lug/Lug/Lug/L

ug/L

ug/Lug/Lug/Lug/L

ug/Lug/Lug/Lug/Lug/L

* MCLs established under 40 CFR 141

ug/L = micrograms per liter

U = Not detected at or above the reportable level shown.

J = The associated numerical value is an estimated quantity.

Bolded results indicate contaminant detected above MCL

NA = not availableDuplicate result in parentheses.

Other VOCs detected infrequently at low concentrations include xylene (total) at 3.7 ug/L and 1.5 ug/L in well WDMW-21 in November 2002and November 2003, respectively; chloromethane at 0.51 ug/L in well WDMW-7 in May 2003; chloroethane at 2.9 ug/L in well WDMW-19 inNovember 2003; chloroform at 19 ug/L and xylene (total) at 9 ug/L in well WDMW-9 in November 2004; and chloroform at 1.0 ug/L, ethylbenzene at 2.9 ug/L, m and/or p-xlyene at 4.9 ug/L, and o-xylene at 14 ug/L in well WDMW-7 in February 2005.

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Table 3.1Medium-Specific Exposure Point Concentration Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timeframe: CurrentMedium: GroundwaterExposure Medium: Groundwater

Exposure Point

Aquifier 1

Tap Water

WDMW*

Chemicalof

Potential

Concern

Trichloroethene

bis(2-Ethylhexyl)phthalate

Manganese

Units

ug/L

ug/L

ug/L

ArithmeticMean

(D

N/A

N/A

266

95% UCL(Distribution)

N/A

N/A

N/A

MaximumConcentration

1.4

27

664

Exposure Point Concentration (2)

Value

1.4

27

266

Units

ug/L

ug/L

ug/L

Statistic

Max

Max

Arith Mean

Rationale

1 Arithmetic mean was not calculated due to only one detection for each chemical.2 The wells used in determining the EPCs were WDMW18, WDMW05, WDMW15, WDMW16, WDMW17, WDMW14, WDMW19, WDMW20.* WDMW - West Oes Moines Municipal Supply WellsN/A - Not ApplicableArith Mean - Arithmetic MeanMax - Maximum Detected Concentrationug/L - Micrograms per liter

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Northern Plume

Record of Decision

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Table 3.2Medium-Specific Exposure Point Concentration Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timeframe:Medium:Exposure Medium:

CurrentGroundwaterAir

Exposure Point

Water Vapors

from Showerhead

WDMW

Chemicalof

Potential

Concern

Trichloroethene

bis(2-Ethylhexyl)phthalate

Units

ug/L

ug/L

ArithmeticMean

(1)

N/A

N/A

95% UCL(Distribution)

N/A

N/A

MaximumConcentration

1.4

27

Exposure Point Concentration (2)

Value

1.4

27

Units

ug/L

ug/L

Statistic

Max

Max

Rationale

1 Arithmetic mean was not calculated due to only one detection for each chemical.2 The wells used in determining the EPCs were WDMW18, WDMW05, WDMW15, WDMW16, WOMW17, WDMW14, WDMW19, WDMW20.' WDMW - West Des Moines Municipal Supply WellsN/A - Not ApplicableMax - Maximum Detected Concentrationug/L - Micrograms per liter

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Scenario Timeframe: FutureMedium: GroundwaterExposure Medium: Groundwater

Table 3.3Medium-Specific Exposure Point Concentration Summary

Railroad Avenue Groundwater Contamination Site

Exposure Point

Aquifer 1Tap Water

MW-06

Chemicalof

Potential

Concern

cis-1 ,2 DichloroetheneTetrachloroethene

Trichloroethene

Arsenic

Manganese

Units

ug/Lug/L

ug/Lug/L

ug/L

ArithmeticMean

(D

1212

4.7

5.23

1,290

95% UCL

(Distribution)

N/AN/A

N/A

N/A

N/A

MaximumConcentration

1212

4.7

5.23

1,290

Exposure Point Concentration (2)

Value

1212

4.7

5.23

1,290

Units

ug/Lug/L

ug/L

ug/L

ug/L

Statistic

MaxMax

MaxMax

Max

Rationale

1 This column contains the arithmetic average of detected concentrations.2 The groundwater exposure point concentration is the maximum detected concentration at well location MW-06.N/A - Not ApplicableMax - Maximum Detected Concentrationug/L - Micrograms per liter

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Scenario Timeframe:Medium:Exposure Medium:

FutureGroundwaterAir

Table 3.4Medium-Specific Exposure Point Concentration Summary

Railroad Avenue Groundwater Contamination Site

Exposure Point

Water Vapors fromShowerhead

MW-06

Chemical

ofPotential

Concern

cis-1,2 DichloroetheneTetrachloroethene

Trichloroethene

Units

ug/Lug/L

ug/L

Arithmetic

Mean

(D

1212

4.7

95% UCL

(Distribution)

N/AN/A

N/A

Maximum

Concentration

1212

4.7

Exposure Point Concentration (2)

Value

1212

4.7

Units

ug/Lug/L

ug/L

Statistic

MaxMax

Max

Rationale

1 This column contains the arithmetic average of detected concentrations.

2 The groundwater exposure point concentration is the maximum detected concentration at well location MW-06.

N/A - Not Applicable

Max - Maximum Detected Concentration

ug/L - Micrograms per liter

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Table 3.5Medium-Specific Exposure Point Concentration Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timeframe:Medium:Exposure Medium:

FutureGroundwaterGroundwater

Exposure Point

Aquifer 1Tap Water

MW-08

Chemicalof

Potential

Concern

1 ,2-Dibromo-3-Chloropropanolcis-1,2 Dichloroethene

Trichloroethene

Vinyl Chloride

Manganese

Units

ug/Lug/L

ug/L

ug/L

ug/L

ArithmeticMean

(1)

1.4420

2.7

110

872

95% UCL(Distribution)

N/AN/A

N/A

N/A

N/A

MaximumConcentration

1.4420

2.7

110

872

Exposure Point Concentration (2)

Value

1.4420

2.7

110

872

Units

ug/Lug/L

ug/L

ug/L

ug/L

Statistic

MaxMaxMaxMaxMax

Rationale

1 This column contains the arithmetic average of detected concentrations.

2 The groundwater exposure point concentration is the maximum detected concentration at well location MW-08.

N/A - Not Applicable

Max - Maximum Detected Concentration

ug/L - Micrograms per liter

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Table 3.6Medium-Specific Exposure Point Concentration Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timeframe:Medium:Exposure Medium:

FutureGroundwaterAir

Exposure Point

Water Vapors fromShowerhead

MW-08

Chemicalof

Potential

Concern

1 ,2-Dibromo-3-Chloropropanolcis-1 ,2 Oichloroethene

Trichloroethene

Vinyl Chloride

Units

ug/Lug/L

ug/L

ug/L

ArithmeticMean

(D

1.4.

420

2.7

110

95% UCL

(Distribution)

N/A

N/A

N/A

N/A

MaximumConcentration

1.4

420

2.7

110

Exposure Point Concentration (2)

Value

1.4

420

2.7

110

Units

ug/Lug/L

ug/L

ug/L

Statistic

MaxMax

Max

Max

Rationale

1 This column contains the arithmetic average of detected concentrations.2 The groundwater exposure point concentration is the maximum detected concentration at well location MW-08.N/A - Not ApplicableMax - Maximum Detected Concentration

ug/L - Micrograms per liter

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Scenario Timeframe:Medium:Exposure Medium:

FutureGroundwaterGroundwater

Table 3.7Medium-Specific Exposure Point Concentration Summary

Railroad Avenue Groundwater Contamination Site

Exposure Point

Aquifer 1

Tap Water

WDMW13

Chemicalof

Potential

Concern

cis-1 ,2 Dichloroethene

Arsenic

Barium

Manganese

Units

ug/L

ug/L

ug/L

ug/L

ArithmeticMean

d)

1.5

14.3

124

1,300

95% UCL(Distribution)

N/A

N/A

N/A

N/A

MaximumConcentration

1.5

14.3

124

1,300

Exposure Point Concentration (2)

Value

1.5

14.3

124

1,300

Units

ug/L

ug/L

ug/L

ug/L

Statistic

Max

Max

Max

Max

Rationale

1 This column contains the arithmetic average of detected concentrations.2 The groundwater exposure point concentration is the maximum detected concentration at well location WDMW13.N/A - Not ApplicableMax - Maximum Detected Concentration

ug/L - Micrograms per liter

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Scenario Timeframe: FutureMedium: GroundwaterExposure Medium: Air

Table 3.8Medium-Specific Exposure Point Concentration Summary

Railroad Avenue Groundwater Contamination Site

Exposure Point

Water Vapors from

Showerhead

WDMW13

Chemical

ofPotential

Concern

cis-1 ,2 Dichloroethene

— -- - —

Units

ug/L

Arithmetic

Mean

(D

1.5

95% UCL(Distribution)

N/A

Maximum

Concentration

1.5

Exposure Point Concentration (2)

Value

1.5

Units

ug/L

Statistic

Max

Rationale

1 This column contains the arithmetic average of detected concentrations.

2 The groundwater exposure point concentration is the maximum detected concentration at well location WDMW13.

N/A - Not Applicable

Max - Maximum Detected Concentration

ug/L - Micrograms per liter

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Table 4Selection of Exposure Pathways

Railroad Avenue Groundwater Contamination Site

1Scenario

Ttmeframe

Current/Future

Medium

Soil

Groundwater

Exposure

Medium

Surface toll

Subsurface soil

Air

Groundwster

Mr

Exposure

Point

Onslte

Onslte

Onstta

Tap Water

Water Vapors at Showertiaad

Receptor

Population

Industrial Worker

Resident

Resident

Industrial Worker

Resident

Resident

Industrial Worker

Resident

Receptor

Age

Adult

Adult

Child

Adult

Child

Adult

Adult

Child

Adult

Child

Adult

Adult

Exposure

Route

Ingestton

Dermal

Ingestion

Dermal

Ingestion

Dermal

Ingestion

Dermal

Ingestion

Dermal

Inhalation

Inhalation

Inhalation

Ingestion

Dermal

Ingestion

Dermal

Ingestion

Dermal

Inhalation

Onslte/

Offslte

Onslte

Onslte

Onslte

Onslte

Onstta

Onslte

Onslte

Onslte

Onslte

Onslte

Onslte

Onslte

. . _

Type of

Analysis

Qua!

Qual

dual

Qual

Qual

Qual

Qual

Qual

Qual

Qual

Qual

Qual

Qual

Quant

Quant

Quant

Quant

Quant

None

Quant

Rationale for Selection or Exclusion

of Exposure Pathway

Workers may be exposed to soil across the site.

Current and future adult residents may be exposed to contaminants In on-slte soil.

Current and future child residents may be exposed to contaminants In on-slte soil.

Current and future adult resident may be exposed to contaminants In subsurface soilbrought to the surface during construction activities.

Current and future child resident may be exposed to contaminants In subsurface soilbrought to the surface during construction activities.

Workers possibly exposed to airborne contaminants via Inhalation of VOCs or fugitivedust emissions.

Adults possibly exposed to airborne contaminants via Inhalation of VOCs or fugitive dustemissions.

Children possibly exposed to airborne contaminants via Inhalation of VOCs or fugitivedust emissions.

Residents currently obtain water from the West Des Molnes Municipal Supply Wells andmay obtain water from offline wells and other monitoring wells In the future.

Residents currently obtain water from the West Des Molnes Municipal Supply Wells andmay obtain water from offline wells and other monitoring wells In the future.

Workers currently obtain water from the West Des Molnes Municipal Supply Wells andmay obtain water from offline wells and other monitoring wells In the future.

Residents currently obtain water from the West Des Molnes Municipal Supply Wells andmay obtain water from offline wells and other monitoring wells In the future.

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Table 5.1

Non-Cancer Toxicity Data ~ Oral/Dermal

Railroad Avenue Groundwater Contamination Site

Chemical

of Potential

Concern

1 ,2-Dibromo-3-Chloropropane

cis-1,2 Dichloroethene

Tetrachloroethene

Trichloroethene

Vinyl ChlorideArsenic

bis(2-Etnylhexyl)phthalate

bis(2-Ethylhexyl)phthalate

Manganese (water)

Chronic/

Subchronic

NA

Chronic

Chronic

Chronic

Chronic

Chronic

Chronic

Subchronic

Chronic

Oral RfD

Value

NA1E-002

1E-002

3E-004

3E-003

3E-04

2E-002

2E-002

2E-02

Units

NAmg/kg-day

mg/kg-day

mg/kg-day

mg/kg-day

mg/kg-day

mg/kg-day

mg/kg-day

mg/kg-day_

Oral Absorbtion

Efficiency for

Dermal (1)

NA

100%

100%

100%

100%

95%

55%

55%

20%

Absorbed RFD for Dermal (2)

L Value

NA

1E-002

1E-002

3E-004

3E-003

2.9E-004

1E-002

1E-002

4E-003

Units

NA

mg/kg-day

mg/kg-day

mg/kg-day

mg/kg-day

mg/kg-day

mg/kg-day

mg/kg-day

mg/kg-day

Primary

Target

Organ(s)

NA

Blood

Liver

Liver/Kidney/Fetus

Liver Cell Polymorphum

Skin

Liver

Liver

Central Nervous system

Combined

Uncertainty/

Modifying

Factors

NA

3000

1000

3000

30

31000

1000

1

RfD:1

Source(s

NA

HEAST

IRIS

NCEA

IRIS

IRIS

IRIS

HEAST

IRIS

N/A = Not Applicable

IRIS = Integrated Risk Information System

HEAST = Health Effects Assessment Summary Tables

NCEA = National Center for Environmental Assessment

(1) Source: Risk Assessment Guidance for Superfund. Volume 1: Human Health Evaluation Manual (Part E, Supplemental Guidance for dermal risk Assessment) Interim. Section 4.2 and Exhibit 4-1.

(2) See Risk Assesment text for the derivation of the "Absorbed RfD for Dermal."

Railroad Avenue Groundwater Contamination Site

Northern Plume

Date(s)

NA

07/01/1997

03/11/2003

03/11/2003

03/11/2003

03/11/2003

03/11/2003

07/01/1997

03/11/2003

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Table 5.2

Non-Cancer Toxicity Data ~ Inhalation

Railroad Avenue Groundwater Contamination Site

Chemical

of Potential

Concern

1 ,2-Dibromo-3-Chloropropane

cis-1,2 Dichloroethene

Tetrachloroethene

Trichloroethene

Vinyl ChlorideArsenic

bis(2-Ethylhexyl)phthalateManganese (water)

Chronic/

Subchronic

Chronic

N/A

Chronic

Chronic

Chronic

N/A

N/A

Chronic

Value

Inhalation

RfC

2.4E-004

N/A

4.0E-001

4.0E-002

1.0E-001

N/A

N/A

5.0E-005

Units

mg/m3

N/A

mg/m3

mg/m3

mg/m3

N/A

N/A

mg/m3

Adjusted

Inhalation

RfD(1)

5.7E-005

N/A

1.7E-001

1.1E-002

2.8E-002

N/A

N/A

1.4E-05

Units

mg/kg/day

N/A

mg/kg/day

mg/kg/day

mg/kg/day

N/A

N/A

mg/kg-day

Primary

Target

Organ

Testicular

N/A

Liver/Kidney

CNS/Liver/Endocrine

Liver Cell Polymorphism

N/A

N/A

Central Nervous System

Combined

Uncertainty/

Modifying

Factors

1E+003

N/A

3E+002

1E+003

3E+001

N/A

N/A

1,000

Source of

RfC:RfD

Target Organ

IRIS

N/A

NCEA

NCEA

IRIS

N/A

N/A

IRIS

Dates (2)

(MM/DD/YY)

03/11/2003

N/A06/20/1977

08/01/2001

03/11/2003

N/A

N/A03/11/2003

N/A = Not Applicable

IRIS = Integrated Risk Information System

HEAST = Health Effects Assessment Summary Tables

NCEA = National Center for Environmental Assessment

(1) See Risk Assessment text for the derivation of the "Extrapolated RfD."

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Table 6.1Cancer Toxicity Data -- Oral/Dermal

Railroad Avenue Groundwater Contamination Site

Chemicalof Potential

Concern1 ,2-Dibromo-3-Chloropropane

cis-1 ,2 Dichloroethene

Tetrachloroethene

Trichloroethene

Trichloroethene

Vinyl Chloride

Arsenic

bis(2-Ethylhexyl)phthalate

Manganese (water)

Oral Cancer Slope Factor

N/A

N/A

5.2E-002

2.0E-02 to 4.0E-01

6.0E-03

1.4E+OOV7.2E-Q1"

1.5E+000

1.4E-002

N/A

Oral to DermalAdjustment

FactorN/A

N/A

100%

100%

100%

100%

85%

55%

4%

Adjusted DermalCancer Slope Factor (1)

N/A

N/A

5.2E-002

2.0E-02 to 4.0E-01

6.0E-03

1.4E+00'/7.2E-01"

1.6E+000

2.5E-002

N/A

Units

N/A

N/A

(mg/kg-day)-1

(mg/kg-<iay)-1

(mg/kg-day)-1

(mg/kg-dayH

(mg/kg-day)-1

(mg/kg-day)-1

N/A

Weight of Evidence/Cancer Guideline

DescriptionN/A

N/A

B2

B2

B2

A

A

B2

N/A

I

Source

N/A

N/A

NCEA

NCEA

NCEA

IRIS

IRIS

IRIS

N/A

Date (2)(MM/DD/YY)

N/A = Not Available.

IRIS = Integrated Risk Information System.

NCEA - National Center for Environmental Assessment.

(1) RAGs Subpart A (1989); RAGs Subpart E (2001); see explanation in text.

(2) For IRIS, last revision date as provided in IRIS.

• Lifetime exposure from birth (child).

~ Lifetime exposure during edullhood (adult).

EPA Group:

A - Human carcinogen

B2 - Probable human carcinogen - indicates sufficient evidence in animals and

Inadequate or no evidence in humans.

N/A

N/A

12/01/2001

08/01/2001

1987

03/11/2003

03/11/2003

03/11/2003

N/A

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Table 6.2

Cancer Toxicity Data - Inhalation

Railroad Avenue Groundwater Contamination Site

Chemicalof Potential

Concern1 ,2-Dibromo-3-Chloropropane

cis-1,2 Dichloroethene

Tetrachloroethene

Trichloroethene

Tricnloroethene

Vinyl Chloride

Arsenic

bis(2-EUiylhexyl)phthalate

Manganese (water)

Unit Risk

N/A

N/A

3.1E-006

1.1E-004

1.1E-004

8.8E-06V4.4E-06"

4.3E-003

4.2E-006

N/A

Units Adjustment

(1)

Inhalation CancerSlope Factor

Units

r N/A | N/A T A T IRIS

N/A

(ug/m3)-1

(ug/m3)-1

(ug/m3)-1

(ug/m3M

(ug/m3)-1

(ug/m3)-1

N/A

N/A

3,500

3.500

3,500

3,500

3,500

3,500

N/A

N/A

1.0E-002

2.0E-02 to 4.0E-01

6.0E-03

3.1E-02V1.5E-02"

1.5E+001

1.4E-002

N/A

N/A

(mg/kg-day}-1

(mg/kg-day)-1

(mg/kg-day)-1

(mg/kg-day)-1

(mg/kg-day)-1

(mg/kg-day)-1

N/A

Weight of Evidence/Cancer Guideline

Description

Source

N/A | N/A

N/A

B2

B2

B2

C

A

B2

N/A

N/A

NCEA

NCEA

NCEA

NCEA

IRIS

NCEA

N/A

Date (2)(MM/DD/YY)

N/A

N/A

12/21/2001

08/01/2001

1987

08/01/2001

03/11/2003

09/20/1995

N/A

N/A= Not Available.

IRIS = Integrated Risk Information System.

NCEA = National Center for Environmental Assessment.

~(1) ExptanatTon^of derivation provided In text.

(2) For IRIS, last revision date as provided in IRIS.

• Lifetime exposure from birth (child).

~ Lifetime exposure during adulthood (adult).

Railroad Avenue Groundwater Contamination Site

Northern Plume

EPA Group:

A - Human carcinogen.

B2 - Probable human carcinogen - indicates sufficient evidence In animals and

inadequate or no evidence in humans.

C - Possible human carcinogen.

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Table 7

Summary of Cancer Risk for Each Population Evaluated

Railroad Avenue Groundwater Contamination Site

Timeframe

Current

Future (MW-6)

Future (MW-8)

Future (WDM W- 13)

Receptor Population*

Resident

Industrial Worker

Hypothetical Resident

Hypothetical IndustrialWorker

Hypothetical Resident

Hypothetical Industrial

Worker

Hypothetical Resident

Hypothetical Industrial

Worker

Carcinogenic

Risks**

6E-06 to 2E-05

!E-06to3E-06

i

1E-04to.2E-04

3E-05to4E-05i1

7E-03 i

3E-04 !1i

3E-04 1t

8E-05 |

1

Chemicals of PotentialConcern

B is(2-ethylhexyl)phthalate

and TCE

Bis(2-ethylhexyl)phthalate,

and TCE

PCE, TCE, and arsenic

PCE, TCE, and arsenic

Vinyl chloride, TCE

Vinyl chloride, TCE

Arsenic

Arsenic

* The cancer risk results for the child and adult were combined to obtain an excess cancer risk for aresident (30-year exposure) (EPA, 1989a).

** A range of cancer risks is provided for the current scenario and future (MW-6). The EPArecommended calculating cancer risks for TCE using a range of draft values, dated August 2001, andthe original provisional value dated 1987. Although TCE was detected in well MW-8, a range wasnot presented since the cancer risks were the same for all cancer slope factors used.

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Table 8Summary of Hazard Indices for Each Population Evaluated

Railroad Avenue Groundwater Contamination Site

Timeframe

Current

Future (MW-6)

Future (MW-6)

Future (WDMW-1 3)

ReceptorPopulation

Adult Resident

Child Resident

Industrial Worker

Hypothetical AdultResident

Hypothetical ChildResident

HypotheticalIndustrial Worker

Hypothetical AdultResident

Hypothetical ChildResident

HypotheticalIndustrial Worker

Hypothetical AdultResident

Hypothetical ChildResident

HypotheticalIndustrial Worker

HazardIndex

0.5

1

0.2

3

7

1

4

11

1

3

7

1

Chemicals of PotentialConcern

Manganese, TCE

Manganese, TCE

Manganese

Manganese, arsenic, TCE

Manganese, arsenic, TCE

Manganese, arsenic, TCE

Manganese, vinyl chloride,TCE,1 ,2-dibromo-3-chloropropane

Manganese, vinyl chloride,TCE,1 ,2-dibromo-3-chloropropane

Manganese, vinyl chloride,TCE,1 ,2-dibromo-3-chloropropane

Manganese, arsenic

Manganese, arsenic

Manganese, arsenic

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Table 9.1

Risk Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timetrame: Future

Receptor Population: Resident

Receptor Age: Adult

Medium

Groundwater

Exposure

Medium

Groundwater

Exposure

Point

Aquifer 1- Tap Water

MW-06

Chemical of

Potential Concern

TrlcMoroetfrane

Arsenic

Manganese

Chemical Total

Radionudide Total

Carcinogenic Risk || Non-Carcinogenic Hazard Risk

Ingestion Inhalation Dermal External

Radiation

Exposure || Primary

Routes Total || Target Organ(s)

Liver/Kidney/Fetus

Skin

Central Nervous System

Ingestion

0.4

0.5

2

3

Inhalation Dermal

0.0005

0.00002

0.04

0.04

Exposure

Routes Total

0.4

0.5

2

3 I~l

Exposure Point Total II II II 3

Exposure Medium Total Jl jl II 3

I

I

Exposure Point Total || ||

Exposure Medium Total II It II

Groundwater Total || || IL 3 1

Receptor Total || || || 3 |

Total Risk Across All Media Total Hazard Across All Media =

Total Liver/Kidney/Fetus HI Across All Media =

Total Skin HI Across All Media =

Total Central Nervous System HI Across All Media =

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Table 9.2Risk Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timeframe: Future

Receptor Population: Resident

Receptor Age: Child

Medium

Groundwater

Exposure

Medium

Groundwater

Exposure

Point

Aquifer 1- Tap Water

MW-06

Chemical of

Potential Concern

Trichloroethene

Arsenic

Manganese

Chemical Total

Radionudide Total

Carcinogenic Risk ]) Non-Carcinogenic Hazard Risk

Ingestlon Inhalation Dermal External

Radiation

Exposure 1 1 Primary

Routes Total j| Target Organ(s)

Liver/Kidney/Fetus

Skin

Central Nervous System

Ingestlon

1.0

1.1

4

6

Inhalation Dermal

0.0010

0.00006

0.12

0.12

Exposure

Routes Total

1.0

1.1

4

6

Exposure Point Total || I || 6

Exposure Medium Total || || || 6 |

Exposure Point Total || ||

Exposure Medium Total

Groundwater Total

"1

[ .

II II I

I II II 6 |Receptor Total [| || || 6

Total Risk Across All Media = Total Hazard Across All Media =

Total Liver/Kidney/Fetus HI Across All Media =

Total Skin HI Across All Media =

Total Central Nervous System HI Across All Media =

1 1-0

I 1.1I 4

I

I

I

Railroad Avenue Groundwater Contamination Site

Northern Plume Record of Decision

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Table 9.3Risk Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timeframe: Future

Receptor Population: Resident

Receptor Age: Adult

Medium

Groundwater

Exposure

Medium

Groundwater

Exposure

Point

Aquifer 1- Tap Water

MW-08

Chemical of

Potential Concern

cis-1,2 Dichloroethene

Trlchloroothene

Vinyl Chloride

Manganese

Chemical Total

Radionudide Total

Carcinogenic Risk || Non-Carcinogenic Hazard Risk

Ingestion

7E-004

7E-004

Inhalation Dermal

3E-006

3E-006

External

Radiation

Exposure || Primary

Routas Total || Target Organ(s)

7E-004

7E-004

Blood

Liver/Kidney/Fetus

Liver Cell Polymorphum

Central Nervous System

Ingestion

1.13

0.2

1.0

1

4

Inhalation Dermal

0.01

0.0003

0.004

0.03

0.04

Exposure

Routes Total

1.1

0.2

0.99

1.2

« I

._ I" 1

Exposure Point Total || 7E-004 ]|~ II 4 |

Exposure Medium Total _J| 7E-004 || _JL 4 I

Air Water Vaporsfrom Showerhead

MW-08Vinyl Chloride

Chemical Total

Radionudide Total

2E-006

2E-006

2E-006

2E-006

I

Exposure Point Total || 2E-006 |P II

Exposure Medium Total || 2E-006 || ||

| Groundwater Total || 7E-004 || [_"" 4 1

| Receptor Total || 7E-004 || || 4

Total Risk Across All Media = Total Hazard Across All Media

Total Blood HI Across All Media =

Total Liver/Kidney/Fetus HI Across All Media =

Total Liver Cell Polymorphum HI Across All Media =

Total Central Nervous System HI Across All Media =

Railroad Avenue Groundwater Contamination Site

Northern Plume Record of Decision

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Table 9.4

Risk SummaryRailroad Avenue Groundwater Contamination Site

Scenario Timeframe: Future

Receptor Population: Resident

Receptor Age: Adult

Medium

Groundwater

Exposure

Medium

Groundwater

Exposure

Point

Aquifer 1- Tap Water

MW-08

Chemical of

Potential Concern

Trichlorotthem

Chemical Total

Radionudide Total

Carcinogenic Risk || Non-Carcinogenic Hazard Risk

Ingestion

1E-005

1E-005

Inhalation Dermal

1E-008

1E-008

External

Radiation

Exposure || Primary

Routes Total || Target Organ)*)

1E-005

|_ 1E-005

Ingestlon Inhalation Dermal Exposure

Routes Total

Exposure Point Total 1 1 1E-005 || 1 1

Exposure Medium Total || 1E-005 ||

Air Water Vaporsfrom Showerhead

MW-08

Tr/c/i/oTDet/iene

Chemical Total

Radionudide Total

1E-006

1E-006

1E-006

1E-006

Exposure Point Total || 1E-006

1

1

CL";_iExposure Medium Total || 1E-006 || I

Groundwater Total || 1E-005 || ||

Receptor Total || 1E-005 || ||

Total Risk Across All Media = Total Hazard Across All Media

Railroad Avenue Groundwater Contamination Site

Northern Plume Record of Decision

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Table 9.5

Risk Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timeframe: Future

Receptor Population: Resident

Receptor Age: Child

Medium

Groundwater

Exposure

Medium

Groundwater

Exposure

Point

Aquifer 1- Tap Water

MW-08

Chemical of

Potential Concern

cis-1.2Dichloroethene

Trichloroethene

Vinyl Chloride (1 ) *

Vinyl Chloride (1) "

Manganese

Chemical Total

Radionudide Total

Carcinogenic Risk || Non-Carcinogenic Hazard Rlak

Ingestion

4E-004

5E-003

6E-003

Inhalation Dermal

2E-006

2E-CM

2E-004

External

Radiation

Exposure I Primary

Routes Total || Target Organ(a)•' '

4E-004

5E-003

6E-003

Blood

Liver/Kidney/Fetus

Liver Cell Polymorphum

Liver Cell Polymorphum

Central Nervous System

Ingestion

2.69

0.6

2.3

2.3

3

11

Inhalation Dermal

0.02

0.0006

0.009

0.009

0.08

0.1

Exposure

Routes Total

2.7

0.6

2.4

2.4

2.9; "ii ~l

. ^"~ I

Exposure Point Total \\~ 6E-003 |[ ]| 11

Exposure Medium Total |[ 6E-003 || || 11 |

Air Water Vaporsfrom Showertiead

MW-08

Vinyl Chloride (1 ) '

Vinyl Chloride (1) "

Chemical Total

Radionudide Total

2E-006

8E-006

1E-005

2E-006

8E-006

1E-005 H

Exposure Point Total || 1E-OOS || ||

Exposure Medium Total 1 1 1E-OOS | 1 1

Groundwater Total || 6E-003 || || 11

Receptor Total || 6E-003 || ||_ 11

Total Risk Across All Media =

(1) The child risk calculation for vinyl chloride has a two-part equation (one is pio-raied and the other is not).

• Pro-rated equation was used to do the risk calculation. Adult Cancer Slope Factor has been used.

" Non-prorated equation was used to do the risk calculation. Adult Cancer Slope Factor has been used.

Railroad Avenue Groundwater Contamination Site

Northern Plume

Total Hazard Across All Media =

Total Blood HI Across All Media =

Total Liver/Kidney/Fetus HI Across All Media =

Total Liver Cell Polymorphum HI Across All Media =

Total Central Nervous System HI Across All Media =

11

2.7

0.6

__47.| 2.9

Record of Decision

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Table 9.6

Risk Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timeframe: Future

Receptor Population: Resident

Receptor Age. Child

Medium

Groundwater

ExposureMedium

Groundwater

Exposure

Point

Aquiferl -Tap Water

MW-08

Chemical of

Potential Concern

Trtchloroethene

Chemical Total

Radionudide Total

Carcinogenic Risk ]| Non-Carcinogenic Hazard Risk

Ingestion

IE-DOS

6E-006

Inhalation Dermal

IE-009

6E-009

External

Radiation

Exposure || Primary

Routes Total ||_ Target Organ(s)

6E-006

6E-006

Ingestion Inhalation

"

Dermal Exposure

[ Routes Total

J

Exposure Point Total || 6E-006 || II

Exposure Medium Total |[ 6E-006 | |

~ 1..... _ ̂

Exposure Point Total II II II

Exposure Medium Total || || ||

Groundwater Total |j 6E-006 || [|

Receptor Total || 6E-006 || ||

Total Risk Across All Media = 6E-006 Total Hazard Across All Media =

(1) The child risk calculation for vinyl chloride has a two-part equation (one is pro-rated and the other is not).

* Pro-rated equation was used to do the risk calculation. Adult Cancer Slope Factor has been used.

" Non-prorated equation was used to do the risk calculation. Adutt Cancer Slope Factor has been used.

Railroad Avenue Groundwater Contamination Site

Northern Plume Record of Decision

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Table 9.7

Risk SummaryRailroad Avenue Groundwater Contamination Site

Scenario Timeframe: Future

Receptor Population: Resident

Receptor Age: Child

Medium

Groundwater

Exposure

Medium

Groundwater

Exposure

Point

Aquifer 1- Tap Water

MW-08

Chemical of

Potential Concern

Trfc/i/oroefliene

Chemical Total

Radionudide Total

Carcinogenic Risk

Ingestlon

BE-ooe

6E-006

Inhalation Dermal

6C-009

6E-009

External

Radiation

Exposure

Routes Total

6E-OOB

6E-006

Non-Carcinogenic Hazard Risk

Primary

Target Organ(s)

Ingestlon Inhalation Dermal Exposure

Routes Total

_ I

I

Exposure Point Total || 6E-006 || || |

Exposure Medium Total IP 6E-006 )f J ]|

... ]

I

Exposure Point Total || || || |

Exposure Medium Total II 11 II

Groundwater Total || 6E-006 || ||

Receptor Total || 6E-006 || ||

Total Risk Across All Media = Total Hazard Across All Media

(1) The child risk calculation for vinyl chloride has a two-part equation (one is pro-rated and the other is not).

• Pro-rated equation was used to do the risk calculation. Adult Cancer Slope Factor has been used.

" Non-prorated equation was used to do the risk calculation. Adult Cancer Slope Factor has been used.

Railroad Avenue Groundwater Contamination Site

Northern Plume Record of Decision

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Table 9.8Risk Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timeframe: FutureReceptor Population: Industrial WorkerReceptor Age: Adult

Medium

Groundwater

ExposureMedium

'

Groundwater

ExposurePoint

Aquifer 1- Tap Water

MW-08

Chemical ofPotential Concern

Vinyl Chloride

Chemical Total

Radionudide Total

Carcinogenic Risk || Non-Carcinogenic Hazard Risk

Ingestion

3E-004

3E-004

Inhalation Dermal ExternalRadiation

Exposure || PrimaryRoutes Total || Target Organ(s)

3E-004

3E-004

Ingestion Inhalation Dermal ExposureRoutes Total

""""I

r " ~iExposure Point Total If 3E-004 ||~~ If"

Exposure Medium Total || 3E-004 || iGroundwater Total _|| 3E-OM J|_ ||

[Receptor Total || 3E-OM |[ |1~~ 1

Total Risk Across All Media Total Hazard Across All Media =

Railroad Avenue Groundwater Contamination Site

Northern Plume Record of Decision

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Table 9.9

Risk Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timeframe: Future

Receptor Population: Industrial Worker

Receptor Age: Adult

Medium

Groundwater

ExposureMedium

Groundwater

ExposurePoint

Aquifer 1- Tap Water

MW-08

Chemical of

Potential Concern

Trichloroethene

Chemical Total

Radionudide Total

Carcinogenic Risk || Non-Carcinogenic Hazard Risk

Ingeation

4E-000

4E-006

Inhalation Dermal Extemil

Radiation

Exposure 1 1 PrimaryRoutes Total || Target Organ(s)

4E-006

4E-006 J

I

Ingestlon Inhalation Dermal ExposureRoutes Total

_.n_ . .j

Exposure Point Total || 4E-006 ~~|l II I

Exposure Medium Total 1 1 4E-006 || II

Groundwater Total || 4E-006 || || |

| Receptor Total || 4E-006 ||_ 1 1

Total Hazard Across All Media =

Railroad Avenue Groundwuer Contamination Site

Northern Plume Record of Decision

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Table 9.10

Risk Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timeframe: Future

Receptor Population: Resident

Receptor Age: Adult

Medium

Groundwater

Exposure

Medium

Groundwater

Exposure

Point

Aquifer 1- Tap Water

WDMW13

Chemical of

Potential Concern

Arsenic

Manganese

Chemical Total

Radiomidide Total

Carcinogenic Risk ||_ Non-Carcinogenic Hazard Risk

Ingestion

2E-004

2E-004

Inhalation Dermal

9E-009

9E-009

External

Radiation

Exposure || Primary

Routes Total H Target Organ(s)

2E-004

2E-004

Skin

Central Nervous System

Ingestion

1.3

2

3

Inhalation Dermal

0.00006

0.04

0.04

Exposure

Routes Total. .

1.3

2

3

I

Exposure Point Total || 2E-004 HP II 3

Exposure Medium Total ||_ 2E-004 ||_ Jl 3

Exposure Point Total If If"

I

:_]L_ .. . .....

c '"":::Exposure Medium Total || || II

Groundwater Total ]| 2E-004 || || 3

Receptor Total || 2E-004 |] || 3

Total Risk Across All Media = Total Hazard Across All Media =

Total Skin HI Across All Media =

Total Central Nervous System HI Across All Media =

Railroad Avenue Groundwater Contamination Site

Northern Plume Record of Decision

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Table 9.11Risk Summary

Railroad Avenue Groundwater Contamination Site

Scenario Timeframe: Future

Receptor Population: Resident

Receptor Age: Child

Medium

Groundwater

ExposureMedium

Groundwater

Exposure

Point

Aquifer 1- Tap Water

WDMW13

Chemical of

Potential Concern

Arsenic

Manganese

Chemical Total

Radionudide Total

Carcinogenic Risk

Ingestlon Inhalation Dermal External

Radiation

Exposure

Routes Total

Non-Carcinogenic Hazard Risk

Primary

Target Organ(s)

Skin

Central Nervous System

Ingestlon

3.1

4

7

Inhalation Dermal

0.00017

0.12

0.12

Exposure

Routes Total

3.1

4

...7... .

rExposure Point Total || || || 7

Exposure Medium Total ]| || || 7 ]

Exposure Point Total II II IP 1

Exposure Medium Total || || ||

Groundwater Total II II II 7

Receptor Total II II II 7

Total Risk Across All Media Total Hazard Across All Media =

Total Skin HI Across All Media =

Total Central Nervous System HI Across All Media =3

Railroad Avenue Groundwater Contamination Site

Nonhem Fiume Record of Decision

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Table 10Comparative Analysis of Alternatives

Railroad Avenue Groundwater Contamination Site/Northern Plume

Evaluation CriteriaAlternative 1

No Action

Alternative 2

Monitored Natural Attenuation(MNA)

Alternative 3Extraction with Recovery

Wells/Treatment by On-site TrayAeration/Surface Water Discharge

(Containment)

Alternative 4

In-situ Stripping Wells(Containment)

OVERALL PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT

HumanHealthProtection

GroundwaterIngestion forCurrent Users

No current groundwaterusers within OU1 area.

No current groundwater userswithin OU1 area.

No current groundwater userswithin OU1 area.

No current groundwater userswithin OU1 area.

GroundwaterIngestion forPotentialFuture Users

Current risks posed fromcontaminants at the sitewould remainunmitigated, uncontrolled,and unmanaged.

Institutional controls wouldcontrol exposure to potentialfuture users.

Institutional controls wouldcontrol exposure to potentialfuture users.

Institutional controls wouldcontrol exposure to potentialfuture users.

Environmental ProtectionCurrent risks posed fromcontaminants at the sitewould remainunmitigated, uncontrolled,and unmanaged.

Protects environmental receptorsthrough attenuation processes.Monitoring would allowidentification of non-attenuatedCOCs.

Migration of the contaminatedgroundwater would be controlledby pumping. Monitoring wouldallow detection of non-capturedCOCs.

Migration of the contaminatedgroundwater would be controlledby treatment as it passed throughthe in-situ stripping wells placedas a barrier. Monitoring wouldallow detection of non-treatedCOCs.

COMPLIANCE WITH ARARS

Chemical-Specific ARARs Groundwater exceedsPRGs. Time necessary toreduce groundwatercontamination to belowPRGs is unknown.

Groundwater would meetchemical-specific ARARs in thelong term through naturalattenuation processes and wouldbe confirmed throughmonitoring.

Groundwater would meetchemical-specific ARARs in thelong term through naturalattenuation processes and wouldbe confirmed through monitoring.

Groundwater would meetchemical-specific ARARs in thelong term through naturalattenuation processes and wouldbe confirmed through monitoring.

Location-Specific ARARs No location-specificARARs.

No location-specific ARARs. No location-specific ARARs. No location-specific ARARs.

Railroad Avenue Groundwater Contamination SiteNorthern Plume I o f 6

Record of Decision

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Table 10 (Continued)Comparative Analysis of Alternatives

Railroad Avenue Groundwater Contamination Site/Northern Plume

Evaluation CriteriaAlternative 1

No Action

Alternative 2

Monitored Natural Attenuation(MNA)

Alternative 3Extraction with Recovery

Wells/Treatment by On-site TrayAeration/Surface Water Discharge

(Containment)

Alternative 4

In-situ Stripping Wells(Containment)

COMPLIANCE WITH ARARS (Continued)

Action-Specific ARARs No action-specificARARs.

Would meet Iowa water qualitystandards and Iowa wellpermitting requirements.

Would meetNPDES dischargerequirements, air release standards,Iowa water quality standards, andIowa well permitting requirements.

Would meet air release standardsfor the in-situ stripping wells,noise control requirements, Iowawater quality standards, and Iowawell permitting requirements.

Other Criteria and Guidance Would allow ingestion ofgroundwater exceedingPRGs.

Institutional controls wouldprotect against ingestion ofgroundwater with contaminationexceeding PRGs.

Institutional controls wouldprotect against ingestion ofgroundwater with contaminationexceeding PRGs.

Institutional controls wouldprotect against ingestion ofgroundwater with contaminationexceeding PRGs.

LONG-TERM EFFECTIVENESS AND PERMANENCE

Magnitude of Residual Risk

Groundwater Ingestion forCurrent Users

No current groundwaterusers within OU1 area.

No current groundwater userswithin OU1 area.

No current groundwater userswithin OU1 area.

No current groundwater userswithin OU1 area.

Groundwater Ingestion forPotential Future Users

Risk from exposure isincreased becausemanagement andmonitoring of plume is notperformed.

Risk would be reduced byimplementing institutionalcontrols.

Risk would be reduced bycontrolling plume migration,accelerated VOC removal, andimplementing institutionalcontrols.

Risk would be reduced bycontrolling plume migration andimplementing institutionalcontrols.

Adequacy and Reliability ofControls

No monitoring of thegroundwater would beimplemented.Groundwatercontaminants wouldremain above PRGs.

Institutional controls at the Cityor State level would be reliable.

Groundwater extraction wouldcontrol contaminant plumemigration and accelerated VOCremoval. Institutional controls atthe City or State level would bereliable.

Barrier of in-situ stripping wellswould control contaminant plumemigration. Institutional controls atthe City or State level would bereliable.

Railroad Avenue Groundwater Contamination SiteNorthern Plume 2 of 6

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Table 10 (Continued)Comparative Analysis of Alternatives

Railroad Avenue Groundwater Contamination Site/Northern Plume

Evaluation CriteriaAlternative 1

No Action

Alternative 2

Monitored Natural Attenuation(MNA)

Alternative 3Extraction with Recovery

Wells/Treatment by On-site TrayAeration/Surface Water Discharge

(Containment)

Alternative 4

In-situ Stripping Wells(Containment)

REDUCTION OF TOXICITY. MOBILITY OR VOLUME THROUGH TREATMENT

Treatment Process Used Would not providetreatment.

Would not provide treatment. Groundwater would be treated at anew on-site plant with airstripping/tray aeration.

Groundwater would be treated byin-situ stripping wells.

Amount Destroyed orTreated

None. None. 90 percent of the volatiles wouldbe removed from the groundwatertreated at the on-site treatmentplant.

Approximately 50 percent ofvolatile mass in the groundwaterthat passes through the line of in-situ stripping wells would beremoved.

Reduction of Toxicity,Mobility, or Volume

None. None. Would reduce mobility ofcontaminated groundwater bypumping.

Would reduce mobility ofgroundwater contamination byproviding a treatment barrier.

Irreversible Treatment None. None. Air stripping would be irreversible. In-situ stripping would beirreversible.

Type and Quantity ofResiduals Remaining AfterTreatment

None. None. None. None.

SHORT-TERM EFFECTIVENESS

Community Protection Continued risk tocommunity through noaction.

Controllable, minor increase inrisk to community duringinstallation of monitoring wells.

Controllable, minor increase inrisk to community duringtreatment plant construction,installation of recovery wells, andinstallation of pipelines.

Controllable, minor increase inrisk to community duringinstallation of in-situ strippingwells and monitoring well.

Worker Protection No risk to workers. Protection required during wellinstallation.

Protection required duringtreatment plant construction,installation of recovery wells, andinstallation of pipelines.

Protection required during in-situtreatment well installation andmonitoring well installation.

Railroad Avenue Groundwater Contamination SiteNorthern Plume 3 of 6

Record of Decision

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Table 10 (Continued)Comparative Analysis of Alternatives

Railroad Avenue Groundwater Contamination Site/Northern Plume

Evaluation CriteriaAlternative 1

No Action

Alternative 2

Monitored Natural Attenuation(MNA)

Alternative 3Extraction with Recovery

Wells/Treatment by On-site TrayAeration/Surface Water Discharge

(Containment)

Alternative 4

In-situ Stripping Wells(Containment)

SHORT-TERM EFFECTIVENESS (Continued)

Environmental Impacts Continued impacts fromexisting conditions.

Plume exposure controlledthrough institutional controls.

Migration of the plume would becontrolled by pumping.

Migration of the plume would becontrolled by treatment barrier.Vapors from in-situ stripping wellsmight produce slight odors butwould meet emission standards.

Time Until Action isComplete

Not applicable. In excess of 30 years. The recovery wells, treatmentplant, and pipeline could beinstalled and startup completedwithin 17 to 18 months. Estimatedrun time is in excess of 30 years.

In-situ treatment wells could beinstalled and startup completewithin 17 to 18 months. Estimatedrun time is in excess of 30 years.

IMPLEMENT ABILITY

Ability to Construct andOperate

No construction oroperation would berequired.

Easy to construct onemonitoring well.

Would require significantequipment and controls and wouldbe complex to operate.

Would require equipment andcontrols and would be equallycomplex to operate as Alternative3.

Ease of Doing AdditionalRemedial Action, if Needed

May require RODamendment if futureproblems arise.

May require ROD amendment iffuture problems arise. Wouldnot interfere with additionalremedial actions implemented inthe remaining portion of theNorth Area Plume, if required.

Would be moderately easy toexpand tray aeration groundwatertreatment plant. Would notinterfere with additional remedialactions implemented in theremaining portion of the NorthArea Plume, if required.

Would be easy to extend thebarrier of in-situ treatment wells.Would not interfere withadditional remedial actionsimplemented in the remainingportion of the North Area Plume, ifrequired.

Railroad Avenue Groundwater Contamination SiteNorthern Plume 4 of 6

Record of Decision

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Table 10 (Continued)Comparative Analysis of Alternatives

Railroad Avenue Groundwater Contamination Site/Northern Plume

Evaluation CriteriaAlternative 1

No Action

Alternative 2

Monitored Natural Attenuation(MNA)

Alternative 3Extraction with Recovery

Wells/Treatment by On-site TrayAeration/Surface Water Discharge

(Containment)

Alternative 4

In-situ Stripping Wells(Containment)

IMPLEMENTABILITY (Continued)

Ability to MonitorEffectiveness

No monitoring. Failure tomonitor the plume wouldnot allow effectiveevaluation and necessaryresponse to potentialfuture risks.

Monitoring would alloweffective evaluation andnecessary response to potentialfuture risks.

Monitoring and maintenanceinspections would give notice offailure before significant exposurewould occur.

Monitoring and maintenanceinspections would give notice offailure before significant exposurewould occur.

Ability to Obtain Approvalsand Coordinate with OtherAgencies

No approvals necessary. Would need to demonstratecompliance with Iowa surfacewater standards.

Would need to demonstratecompliance with air standards,NPDES permit requirements, andIowa surface water standards.

Would need to demonstratecompliance with air standards andIowa surface water standards.

Availability of Equipment,Specialists, and Materials

None required. No special equipment, materials,or specialist required. Iowalicensed well drillers are readilyavailable.

No special equipment, materials,or specialist required. Iowalicensed well drillers andconstruction contractors arereadily available. Personnel toprovide operation andmaintenance of treatment plantand recovery wells are readilyavailable.

Contractors that specialize in in-situ stripping wells are available.Personnel to provide operationand maintenance of systems arereadily available.

Availability of Technologies None required. MNA evaluation technologyreadily available.

Extraction well technology readilyavailable. Air strippingtechnology developed andcommercially available.

In-situ stripping well technologydeveloped and commerciallyavailable.

Railroad Avenue Groundwater Contamination SiteNorthern Plume 5 of 6

Record of Decision

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Table 10 (Continued)Comparative Analysis of Alternatives

Railroad Avenue Groundwater Contamination Site/Northern Plume

Evaluation CriteriaAlternative 1

No Action

Alternative 2

Monitored Natural Attenuation(MNA)

Alternative 3Extraction with Recovery

Wells/Treatment by On-site TrayAeration/Surface Water Discharge

(Containment)

Alternative 4

In-situ Stripping Wells(Containment)

COSTS

Capital Costs

Present Worth of O&MCosts

Total Costs of O&M Costs

Total PresentWorth*

$0

$111,300

$321,000

$111,300

$24,000

$406,000

$921,000

$430,000

$532,000

$811,000

$1,899,000

$1,343,000

$670,000

$1,174,000

$2,702,000

$1,844,000

Notes:State and community acceptance will be evaluated during preparation of the ROD.* Present worth calculated at a discount rate of 7 percent.

Railroad Avenue Groundwater Contamination SiteNorthern Plume 6 of 6

Record of Decision

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Table 11Metals, Geochemical, and Biochemical Data Summary (Monitoring Wells)

Railroad Avenue Groundwater Contamination Site

MonitoringWell

MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12

Analyte

Alkalinity, bicarbonateAlkalinity, bicarbonateAlkalinity, bicarbonateAlkalinity, bicarbonateAlkalinity, bicarbonateAlkalinity, bicarbonateAlkalinity, bicarbonateAlkalinity, bicarbonateAlkalinity, bicarbonateAlkalinity, bicarbonateAlkalinity, bicarbonateAlkalinity, bicarbonate

Chemical Oxygen DemandChemical Oxygen DemandChemical Oxygen DemandChemical Oxygen DemandChemical Oxygen DemandChemical Oxygen DemandChemical Oxygen DemandChemical Oxygen DemandChemical Oxygen DemandChemical Oxygen DemandChemical Oxygen DemandChemical Oxygen Demand

ChlorideChlorideChlorideChlorideChlorideChlorideChlorideChlorideChlorideChlorideChlorideChloride

Concentration

July 2002

398352387340379298

428(427)460300342329343MANANANANANANANANANANANA12696.954.213484.8109

32(32)58.794.714244.172

Nov. 2002424

370(376)390346397327383525324320425346NANANANANANANANANANANANA125

94(93)53.113182.599.355.460.610315453.188.5

May 2003NANANANANANANANANANANANANA10 UNANANANANA10 UNA10.785.1NANANANANANANANANANANANANA

Nov. 2003

NANANANANANANANANANANANA10.4 U10.4 U

10.4(10.4) U10.4 U10.4 U10.4 U10.4 U261116

10.4 U10.4 UNANANANANANANANANANANANA

May 2004NANANANANANANANANANANANA20 U20 U20 U20 U20 U20 U

20(20) U20 U20 U20 U20 U20 UNANANANANANANANANANANANA

Nov. 2004

NANANANANANANANANANANANANANANANANANANANANANANANANA96.6NA

99.5(103)39.795.990.644.9104NA75.794.0

Unitsmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmgrt.mg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/L

Railroad Avenue Groundwaler Contamination SiteNorthern Plume l o f ? Record Of Decision

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Table 11 (Continued)Metals, Geochemical, and Biochemical Data Summary (Monitoring Wells)

Railroad Avenue Groundwater Contamination Site

Monitoring

Well

MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12

Analyte

ConductivityConductivityConductivityConductivityConductivityConductivityConductivityConductivityConductivityConductivityConductivityConductivity

Dissolved Organic CarbonDissolved Organic CarbonDissolved Organic CarbonDissolved Organic CarbonDissolved Organic CarbonDissolved Organic CarbonDissolved Organic CarbonDissolved Organic CarbonDissolved Organic CarbonDissolved Organic CarbonDissolved Organic CarbonDissolved Organic Carbon

Dissolved OxygenDissolved OxygenDissolved OxygenDissolved OxygenDissolved OxygenDissolved OxygenDissolved OxygenDissolved OxygenDissolved OxygenDissolved OxygenDissolved OxygenDissolved Oxygen

Concentration

July 2002

1390930105711301043NA

104511001220118364011581.51.11.61 U

1.42.31(1) U2.11 U

1.51.91 U

5.450.40.1NA0.1NA0.40.1NA0.20.12.2

Nov. 2002

11821009125711241148142512691189126514729961477

1 U1(1) U1.41 U1 U2

1.52.31 U

1.52.81.10.20.10.10.10.10.10.10.10.10.10.10.1

[ May 2003

NA1155NANANANANA

1404NA

1395961NANANANANANANANANANANANANANA1.7NANANANANA3.4NA0.31.2NA

Nov. 2003

160213001174127615151447149716081335139510541461NANANANANANANANANANANANA0.60.40.40.50.40.50.40.40.50.40.50.5

May 2004

168113131292139813811436167314661392153111101318NANANANANANANANANANANANA0.10.10.10.10.10.10.10.10.10.10.30.1

Nov. 2004NA

1134NA

103011691284115612701075NA9971250NANANANANANANANANANANANANA0.5NA0.50.30.80.40.10.5NA0.50.6

Units

umhos/cmumhos/cmumhos/cmumhos/cmumhos/cmumhos/cmumhos/cmumhos/cmumhos/cmumhos/cmumhos/cmumhos/cmmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/L

Railroad Avenue Groundwater Contamination SiteNorthern Plume 2 of 7 Record Of Decision

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Table 11 (Continued)Metals, Geochemical, and Biochemical Data Summary (Monitoring Wells)

Railroad Avenue Groundwater Contamination Site

Monitoring

Well

MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12

Analyte

EhEhEhEhEhEhEhEhEhEhEhEh

EthaneEthaneEthaneEthaneEthaneEthaneEthaneEthaneEthaneEthaneEthaneEthaneEthaneEtheneEtheneEtheneEtheneEtheneEtheneEtheneEtheneEtheneEtheneEthene

Concentration

July 2002

-16-18-108NA-54NA-38-60NA-97

-135-61NA

NA

NA

NANA

NANANANA

NANA

NANA

NANANA

NANA

NA

NA

NA

NA

NA

NA

Nov. 2002

180 R121 R28 R255 R157 R160 R122 R157 R161 R180 R63 R128 RNA

NA

NA

NANA

NA

NANA

NANANA

NANANANA

NA

NANA

NA

NA

NA

NA

NA

NA

May 2003

NA-30NA

NANA

NANA

-60NA

-33-117NANA

NA

NA

NANA

NA

NANA

NA

NANANANANANA

NA

NANA

NA

NA

NA

NA

NA

NA

Nov. 2003

122-33-6431-64

-5-54

-71

-3527

-€0

-19

2 U2 U

2(2) U2 U2 U2 U2 U2

2 U2 U2 U2 U3 U3 U

3(3) U3 U3 U3 U3 U3 U3 U3 U3 U3 U

May 2004

54-0.6-76

21-35

60153

-1875

23

-85-35

2 U2 U2 U2 U2 U2 U

2(2) U2 U2 U2 U2 U2 U3 U3 U3 U3 U3 U3 U

3(3) U3 U3 U3 U3 U3 U

Nov. 2004

NA

-74NA

-135-9

736

-51NA

-98-63NA

2 UNA

2(2) U2 U2 U2 U4

2 UNA2 U2 U

NA3 U

NA

3(3) U3 U3 U3 U3 U3 U

NA

3 U3 U

Units

mvmvmvmvmvmvmvmvmvmvmvmvug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/L

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Table 11 (Continued)Metals, Geochemical, and Biochemical Data Summary (Monitoring Wells)

Railroad Avenue Groundwater Contamination Site

Monitoring

Well

MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12

AnalyteIron (total)Iron (total)Iron (total)Iron (total)Iron (total)Iron (total)Iron (total)Iron (total)Iron (total)Iron (total)Iron (total)Iron (total)Iron (+2)Iron (+2)Iron (+2)Iron (-1-2)Iron (+2)Iron (+2)Iron (+2)Iron (+2)Iron (+2)Iron (+2)Iron (+2)Iron (+2)MethaneMethaneMethaneMethaneMethaneMethaneMethaneMethaneMethaneMethaneMethaneMethane

Concentration

July 2002

14601370829054914002240

5840(6070)2030674317028904220NANANANANANANANANANANANANANANANANANANANANANANANA

Nov. 2002

9662280(2130)

8510376

32301330161066503900816393054701.62.42.70.83.31.41.71.97.51.32.45.0NANANANANANANANANANANANA

May 2003NA

1680NANANANANA

4010NA

17904140NANA

2200NANANANANA

2600NA

16004400NANANANANANANANANANANANANA

Nov. 2003

8581080

8900(9050)1780405044604320563063701180445062300.51.13.82.13.43.13.63.43.21.63.33.51 U4

3(4)1 U2215190 J1 U

39638

May 2004

9723230901023304240666

453(892)34704242130466047301.02.84.52.23.20.40.03.20.81.23.22.81441

141 U

KD110 J1 U71 U10

Nov. 2004

NA3700NA

1920(1960)337098463743702130NA

47204620NA3.2NA2.43.71.10.83.82.5NA4.43.4NA5

NA

1(1) U71 U3

2101 U

NA1 U2

Units

ug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/Lug/L

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Table 11 (Continued)Metals, Geochemical, and Biochemical Data Summary (Monitoring Wells)

Railroad Avenue Groundwater Contamination Site

Monitoring

Well

MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12

Analyte

Nitrate as NitrogenNitrate as NitrogenNitrate as NitrogenNitrate as NitrogenNitrate as NitrogenNitrate as NitrogenNitrate as NitrogenNitrate as NitrogenNitrate as NitrogenNitrate as NitrogenNitrate as NitrogenNitrate as Nitrogen

PHPHPHpHpH

PHPHPHpHPHPHPH

SulfateSulfateSulfateSulfateSulfateSulfateSulfateSulfateSulfateSulfateSulfateSulfate

Concentration

July 2002

1.160.310.03 U0.03 U0.10.03 U

0.03(0.03) U0.1

0.050.03 U0.03 U0.03 U7.236.86.9NA6.8NA6.96.8NA7

7.17

229164300200224308

332(335)26021224746.5358

Nov. 2002

1.860.18(0.14)

0.03 U0.03 U0.03 U0.340.390.210.03 U0.03 U0.03 U0.03 U6.97

7.16.86.96.96.96.977

7.26.9210

213(206)29620528033531224827326042.5358

May 2003

NANANANANANANANANANANANANA7

NANANANANA6.9NA7.07.2NANANANANANANANANANANANANA

Nov. 2003

0.03 U0.28

0.03(0.3) U0.03 U0.03 U0.03 U0.03 U0.03 U0.050.03 U0.03 U0.03 U6.77.16.96.57

6.76.97

6.76.86.86.7236163

221(221)20327934233923923623072.5322

May 2004

1.100.030.03 U0.03 U0.03 U0.07

0.63(0.64)0.03 U0.590.03 U0.03 U0.03 U7.07.07.16.96.97.06.97.07.07.07.27.0202178211205244253

224(233)28025623263.4288

Nov. 2004

NA0.25NA

0.03(0.03) U0.03 U0.260.520.03 U0.03 UNA0.03 U0.03 UNA6.9NA6.86.96.86.86.96.9NA7.16.9NA291NA

243(236)206387245389230NA54.5311

Units

mg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/LSUSUSUSUSUSUSUSUSUSUSUSUmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/L

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Table 11 (Continued)Metals, Geochemical, and Biochemical Data Summary (Monitoring Wells)

Railroad Avenue Groundwater Contamination Site

MonitoringWell

MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12

AnalyteSulfideSulfideSulfideSulfideSulfideSulfideSulfideSulfideSulfideSulfideSulfideSulfide

TemperatureTemperatureTemperatureTemperatureTemperatureTemperatureTemperatureTemperatureTemperatureTemperatureTemperatureTemperature

Total Organic CarbonTotal Organic CarbonTotal Organic CarbonTotal Organic CarbonTotal Organic CarbonTotal Organic CarbonTotal Organic CarbonTotal Organic CarbonTotal Organic CarbonTotal Organic CarbonTotal Organic CarbonTotal Organic Carbon

Concentration

July 2002

MANANANANA

NANANA

NA

NANA

NANA

1314.414.813.5NA

15

13.815.515.112.814.5

1 U7.41.2

1.3

1.2

1.5

7.1(7.2)1.8

1 U1.9

2.7

1 U

Nov. 2002NANANANANANANANANANANANA15

14.314.315.414

15.815.813.714.214.312.213.4

1 U1(1) U1.31 U1 U1 U1 U

1.91.85.131 U

May 2003NANANANANA

NANANA

NA

NANA

NANA

13.5NA

NANANA

NA

13.9NA

14.612.6NANA

NANA

NA

NA

NA

NA

NANA

NANA

NA

Nov. 2003NANA

NANA

NA

NANA

NANA

NANA

NA

14.813.614

14.713.515.215

13.514.114.212.113.5NANANA

NA

NA

NA

NA

NA

NA

NANA

NA

May 2004NANANANA

NA

NANA

NANA

NANA

NA13.413.014.211.713.614.814.813.814.114.312.713.7NA

NANA

NA

NA

NANA

NANA

NANA

NA

Nov. 2004NA

0.033NA

0.075(0.079)0.010 U0.010 U0.010 U0.1051.64NA

0.0350.010 U

NA14.3NA

14.713.415.716.313.414.0NA12.413.4NA1 U

NA1. 1(1.0 U)

1.71 U1 U

1.71 U

NA2.71 U

Units

mg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/LDegCDegCDegCDegCDegCDegCDegCDegCDegCDegCDegCDegCmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/Lmg/L

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Table 11 (Continued)Metals, Geochemical, and Biochemical Data Summary (Monitoring Wells)

Railroad Avenue Groundwater Contamination Site

Monitoring

Well

MW-01MW-02MW-03MW-04MW-05MW-06MW-07MW-08MW-09MW-10MW-11MW-12

Analyte

TurbidityTurbidityTurbidityTurbidityTurbidityTurbidityTurbidityTurbidityTurbidityTurbidityTurbidityTurbidity

Concentration

July 2002

5.92.49.1MA2

NA5.12.8NA3.71.81.5

Nov. 2002

0000

0.1000

5.2000

May^2003

NA0

NANANANANA0

NA2.40.8NA

Nov. 2003

00

1.30

0.10.40.81.45000

May 2004

2.14.18.53.54.75.02.65.033

14.33.94.5

Nov. 2004

NA0.2NA-1.75.5-0.83.77.03.5NA4.2-0.6

Units

NTUNTUNTUNTUNTUNTUNTUNTUNTUNTUNTUNTU

NA = Not Available

mg/L = milligrams per liter

ug/L = micrograms per liter

U = Not detected at or above the reportable level shown.

J = The associated numerical value is an estimated quantity.

umhos/cm = micromhos per centimeter

mv = millivolt

SU = standard units (pH)

deg C = degrees Celsius

NTU = Nephelometric turbidity units

R = rejected

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Analvte

Table 12

Monitored Natural Attenuation Screening Step 1

Railroad Avenue Groundwater Contamination Site

Northern Plume

Average Concentration in

Most Contaminated Zone

(May and November 2004^) Points Awarded1

Dissolved Oxygen

Nitrate

Iron (II)

Sulfate

Sulfide

Methane

ORP (Eh)

pH

Total Organic Carbon

Temperature

Chloride

PCE (source product)

TCE (source/daughter product)

cis-1,2-DCE (daughter product)

Vinyl Chloride (daughter product)

Ethene/Ethane (daughter product VQ

0.1 mg/L

<0.03 mg/L

3.5 mg/L

335 mg/L

0.11 mg/L

0.16 mg/L

-6mv

7.0 SU

1.7 mg/L

13.6 degrees C

45 mg/L

< 0.5 ug/L

lug/L

330 ug/L

47 ug/L

4 ug/L (maximum')

Total Screening Points

3

2

3

0

0

I2

1

0

0

0

0

0

I2

2

2

1!

163

Total screening points of 16 indicate adequate evidence3 for anaerobic biodegradation of chlorinated

organics.

Note 1 = Table 2.3 (Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground

Water, EPA/600/R-98/128, USEPA, September 1998)

Note 2 = Partial points Table 2.3 (Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents

in Ground Water, EPA /600/R-98/128, USEPA, September 1998)

Note 3 = Table 2.4 (Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground

Water, EPA/600/R-98/128, USEPA, September 1998)

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Table 13Present Worth Cost Estimate

Alternative 2 - Monitored Natural Attenuation

Cost Estimate ComponentCAPITAL COSTSMonitoring Well (1 well installed to depth of 50 with 25-foot screen, locking well cap)Assist City Drafting of Well Permitting Requirements

Quantity

50

1

Units Unit Cost Capital Cost | Annual Cost

VLF

LS

$200

$5,000DIRECT CAPITAL COST SUBTOTAL

Bid Contingency (15%)Scope Contingency (15%)

TOTAL DIRECT CAPITAL COSTPermitting and Legal (5%)Construction Services (10%)

CONSTRUCTION COSTS TOTALEngineering Design (8%)

TOTAL CAPITAL COST

$10,000

$5,000$15,000$2,300$2,300

$19,600$1,000$2,000

$22,600$1,800

$24,000

Cost Estimate Component Quantity Units Unit Cost Capital Cost Annual CostANNUAL O&M COSTSGROUNDWATER and SURFACE WATER MONITORING (Analysis Only) +

Years 1 and 2Quarterly sampling of 13 monitoring wells, 4WDM wells, and 3 surface water locations forVOCs (standard turnaround)Years 3 through 5Semi-annual sampling of 13 monitoring wells, 4WDM wells, and 3 surface water locations forVOCs (standard turnaround)Years 6 through 30Yearly sampling of 13 monitoring wells, 4WDM wells, and 3 surface water locations forVOCs (standard turnaround)

88

44

22

EA

EA

EA

$159

$159

$159

$14,000

$7,000

$3,500

GROUNDWATER MONITORING (Labor only)Years I and 22 Level PI persons for 2 - 8 hour days persampling event and 4 - 8 hour days per dataevaluation reportExpenses (including per diem)Years 3 through 52 Level PI persons for 2 - 8 hour days persampling event and 4-8 hour days per dataevaluation reportExpenses (including per diem)Years 6 through 302 Level PI persons for 2 - 8 hour days persampling event and 4-8 hour days per dataevaluation reportExpenses (including per diem)

384

16192

896

4

EA

DAYHR

DAYHR

DAY

$75

$150$75

$150$75

$150

$28,800

$2,400$14,400

$1,200$7,200

$600PLAN PREPARATION / INSTITUTIONAL CONTROLS

Preparation of Health and Safety Plan (Year 1only)Preparation of QA/Sampling Plan (Year 1 only)

40

60

HR

HR

$75

$75

$3,000

$4,500

Railroad Avenue Groundwater Contamination Siie

Northern Plume 1 of 3 Record of Decision

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Table 13 (Continued)Present Worth Cost Estimate

Alternative 2 - Monitored Natural Attenuation

Cost Estimate ComponentPrepare Annual NewsletterAnnual Newsletter Publication in Local Newspaper andDirect MailingPublic Informational Meeting @ 5, 10, 15, 20, 25, and30yrsFive- Year Review @ 5, 10, 15, 20, 25, and 30 yrsAbandon Monitoring Wells (13 wells) Year 30 only

Quantity40

1

1

113

UnitsHR

LS

LS

LSEA

Unit Cost$75

$1,000

$5,000

$50,500$1,500

TOTAL PRESENT WORTH O&M COSTTOTAL PRESENT WORTH

Capital Cost

$406,000$430,000

Annual Cost$3,000

$1,000

$5,000

$50,500$19,500

7 percent discount rate used to calculate present worth.+ For each sampling event, includes one duplicate per 20 primary samples and one trip blank.

Railroad Avenue Groundwaler Contamination Site

Northern Plume 2 of 3 Record of Decision

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Table 13 (Continued)Present Worth Cost Estimate

Alternative 2 - Monitored Natural Attenuation

Year

123456789101112131415161718 j192021222324252627282930

Yearly O&MCost*

$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000$4,000

IntermittentO&M Costs

$52,700$45,200$22,600$22,600$78,100$11,300$11,300$11,300$11,300$66,800$11,300$11,300$11,300$11,300$66,800$11,300$11,300$11,300$11,300$66,800$11,300$11,300$11,300$11,300$66,800$11,300$11,300$11,300$11,300$86,300

Total Costs of Annual O&MPresent Worth of Annual O&M

Total AnnualO&M Costs

$56,700$49,200$26,600$26,600$82,100$15,300$15,300$15,300$15,300$70,800$15,300$15,300$15,300$15,300$70,800$15,300$15,300$15,300$15,300$70,800$15,300$15,300$15,300$15,300$70,800$15,300$15,300$15,300$15,300$90,300

$921,000$406,000

Intermittent O&M Costs Include:

Year 1 (plans, monitoring)

Year 2 monitoring

Years 3-5 monitoring

Years 3-5 monitoring

Years 3-5, 5-yr review, informational meeting

Years 6-30 monitoring

Years 6-30 monitoring

Years 6-30 monitoring

Years 6-30 monitoring

Years 6 - 30, 5-yr review, informational meeting

Years 6-30 monitoring

Years 6-30 monitoring

Years 6-30 monitoring

Years 6-30 monitoring

Years 6 - 30, 5-yr review, informational meeting

Years 6-30 monitoring

Years 6-30 monitoring

Years 6-30 monitoring

Years 6-30 monitoring

Years 6 - 30, 5-yr review, informational meeting

Years 6 - 30 monitoring

Years 6-30 monitoring

Years 6-30 monitoring

Years 6-30 monitoring

Years 6 - 30, 5-yr review, informational meeting

Years 6-30 monitoring

Years 6-30 monitoring

Years 6-30 monitoring

Years 6-30 monitoring

Years 6 - 30, 5-yr review, informational meeting

* Yearly O&M costs include: annual newsletter.

Railroad Avenue Groundwater Contamination Site

Northern Plume 3 of 3 Record of Decision

Page 104: RECORD OF DECISION (RODS) · RI Remedial Investigation ROD record of decision SARA Superfund Amendments and Reauthorization Act START Superfund Technical Assistance and Response Team

Table 14Final Cleanup Levels

Railroad Avenue Groundwater Contamination Site

Contaminant

PCE

TCE

cis-1,2-DCE

VC

Final GroundwaterCleanup Levels1

5^g/L

5/^g/L

70/ug/L

2//g/L

Basis for CleanupLevel2

Federal MCL

Federal MCL

Federal MCL

Federal MCL

Notes1 /^g/L - micrograms per liter2 40 CFR Part 141

Railroad Avenue Groundwater Contamination SiteNorthern Plume Record of Decision

Page 105: RECORD OF DECISION (RODS) · RI Remedial Investigation ROD record of decision SARA Superfund Amendments and Reauthorization Act START Superfund Technical Assistance and Response Team

FIGURES

Page 106: RECORD OF DECISION (RODS) · RI Remedial Investigation ROD record of decision SARA Superfund Amendments and Reauthorization Act START Superfund Technical Assistance and Response Team

!

i!

Milfit

IOWA

2000

LEGEND

^ ALLUVUL AQUIFER WELLS

* JORDAN AQUIFER WELLS

MAP LOCATION WDMW#2, 10. AND 11 HAVE BEEN ABANDONEDBECAUSE OF WELL PRODUCTION PROBLEMSWDMW#2, 10. AND 11 HAVE BEEN ABANDON*BECAUSE OF WELL PRODUCTION PROBLEMSAND ARE NOT SHOWN.

BLACK &VEATCH

FIGURE 1SITE VICINITY MAP

RAILROAD AVENUE GROUNDWATER CONTAMINATION SITE

REV0

Page 107: RECORD OF DECISION (RODS) · RI Remedial Investigation ROD record of decision SARA Superfund Amendments and Reauthorization Act START Superfund Technical Assistance and Response Team

o

JO »•O ra

If!iZO ra

Page 108: RECORD OF DECISION (RODS) · RI Remedial Investigation ROD record of decision SARA Superfund Amendments and Reauthorization Act START Superfund Technical Assistance and Response Team

PRIMARYSOURCES

PRIMARYRELEASE

MECHANISM

SECONDARYSOURCES

SECONDARYRELEASE

MECHANISMS

PATHWAY RECEPTOR

EXPOSUREROUTE

Current/Future

Industrial

Current/FutureAdult

Resident

Current/FutureChild

Resident

Onsite IndustrialOperations

ImproperSolvent

Management

-> Soil Infiltration/Percolation

Groundwater

Ingestion

Inhalation

Dermal

• •

This pathway is quantitatively evaluated.

Figure 3Conceptual Site Model

Railroad Avenue Groundwater Contamination Site

Page 109: RECORD OF DECISION (RODS) · RI Remedial Investigation ROD record of decision SARA Superfund Amendments and Reauthorization Act START Superfund Technical Assistance and Response Team

Plot of TCE, DCE, and VC vs. Distance Downgradient fromSuspected Source Area May 2004

1000

S«O >.O 5S2

m

'5o

TCEcis-1,2-DCE

0.1500 1000 1500 2000 2500 3000

Approximate Distance Downgradient (feet)

3500 4000

Railroad Avenue Groundwater Contamination SiteNorthern Plume

Figure 4Plot of TCE, DCE, and VC vs.

Distance Downgradient from Source AreaMay 2004

Page 110: RECORD OF DECISION (RODS) · RI Remedial Investigation ROD record of decision SARA Superfund Amendments and Reauthorization Act START Superfund Technical Assistance and Response Team

Plot of TCE, DCE, and VC vs. Distance Downgradient fromSuspected Source Area November 2004

1000

O)32. 100o*= *•re ot oC CM0) »-o o>C £1O PO £

x2Q.a

•TCE-cis-1,2-DCEVC

500 1000 1500 2000 2500 3000

Approximate Distance Downgradient (feet)

3500 4000

Railroad Avenue Groundwater Contamination SiteNorthern Plume

Figure 5Plot of TCE, DCE, and VC vs.

Distance Downgradient from Source AreaNovember 2004


Recommended