Download - RECORD OF DECISION (RODS)EPA/ROD/R03-06/009 2006 € EPA Superfund Record of Decision: € € DOVER AIR FORCE BASE EPA ID: €DE8570024010 OU 23 DOVER, DE 05/05/2006

EPA/ROD/R03-06/0092006

EPA Superfund

Record of Decision:

DOVER AIR FORCE BASEEPA ID: DE8570024010OU 23DOVER, DE05/05/2006

RECORD OF DECISION LAND USE CONTROLS AT MULTIPLE SITES DOVER AIR FORCE BASE, DELAWARE March 2006 Prepared by: Oak Ridge National Laboratory Environmental Sciences Division for the U.S. Department of Energy Under Contract DE-AC05-00OR22725 and URS GROUP INC. 200 Orchard Ridge Drive, Suite 101 Gaithersburg, Maryland 20878 Prepared for: United States Department of the Air Force Dover Air Force Base 436 CES/CEVR 600 Chevron Avenue Dover AFB, Delaware 19902-5600

Table of Contents LUCs ROD i

TABLE OF CONTENTS ACRONYMS AND ABBREVIATIONS..........................................................................v PART I: DECLARATION........................................................................................... I-1 1.0 SITE NAMES AND LOCATION........................................................................I-1 1.1 STATEMENT OF BASIS AND PURPOSE ........................................................I-1 1.2 ASSESSMENT OF SITES ...................................................................................I-1 1.3 DESCRIPTION OF SELECTED REMEDY........................................................I-2 1.4 STATUTORY DETERMINATION.....................................................................I-4 1.5 ROD DATA CERTIFICATION CHECKLIST....................................................I-5 1.6 AUTHORIZING SIGNATURES AND SUPPORT AGENCY CONCURRENCE.................................................................................................I-6 PART II: DECISION SUMMARY ............................................................................II-1 2.0 SITE NAMES, LOCATIONS, AND DESCRIPTIONS .................................... II-1 2.1 SITE HISTORY AND ENFORCEMENT ACTIVITIES .................................. II-4

2.1.1 LF22..................................................................................................... II-5 2.1.2 LF23..................................................................................................... II-5 2.1.3 WP29 ................................................................................................... II-5 2.1.4 OT56 .................................................................................................... II-5 2.1.5 ST58..................................................................................................... II-6 2.1.6 LF16..................................................................................................... II-6 2.1.7 LF19..................................................................................................... II-6 2.1.8 WP32 ................................................................................................... II-6 2.1.9 OT55 .................................................................................................... II-7 2.1.10 FT02..................................................................................................... II-7 2.1.11 LF24..................................................................................................... II-7 2.1.12 LF26..................................................................................................... II-7 2.1.13 WP33 ................................................................................................... II-8 2.1.14 WP38 ................................................................................................... II-8 2.1.15 OT42 .................................................................................................... II-8 2.1.16 OT43 .................................................................................................... II-8 2.1.17 OT45 .................................................................................................... II-9 2.1.18 OT46 .................................................................................................... II-9 2.1.19 OT47 .................................................................................................... II-9 2.1.20 OT49 .................................................................................................... II-9 2.1.21 OT57 .................................................................................................... II-9

2.2 COMMUNITY PARTICIPATION .................................................................. II-10 2.3 SCOPE AND ROLE OF OPERABLE UNIT OR RESPONSE ACTIONS..... II-10

2.3.1 Past Actions Associated with Sites Included in this ROD................. II-10 2.3.2 Ongoing and Planned Groundwater Actions ..................................... II-11 2.3.3 Actions Addressed in this ROD......................................................... II-12

ii LUCs ROD Table of Contents

TABLE OF CONTENTS (cont'd)

2.4 SITE CHARACTERISTICS............................................................................. II-12

2.4.1 Conceptual Site Model....................................................................... II-12 2.4.2 Topographical and Hydrogeologic Information ................................ II-13 2.4.3 Ecology .............................................................................................. II-14 2.4.4 Archaeological or Historical Significance......................................... II-14 2.4.5 Sampling Strategy.............................................................................. II-14 2.4.6 Nature and Extent of Contamination ................................................. II-15

2.4.6.1 OT56 ................................................................................ II-16 2.4.6.2 LF16................................................................................. II-16 2.4.6.3 FT02................................................................................. II-16 2.4.6.4 OT43 ................................................................................ II-16 2.4.6.5 LF22................................................................................. II-17 2.4.6.6 WP29................................................................................ II-17 2.4.6.7 ST58................................................................................. II-17

2.5 CURRENT AND POTENTIAL FUTURE LAND AND WATER USES....... II-18 2.5.1 Land Use ............................................................................................ II-18 2.5.2 Surface Water Use ............................................................................. II-18 2.5.3 Groundwater Use ............................................................................... II-19

2.6 SUMMARY OF SITE RISKS.......................................................................... II-19 2.6.1 Summary of Human Health Risk Assessment ................................... II-19

2.6.1.1 Identification of COCs..................................................... II-19 2.6.1.2 Exposure Assessment....................................................... II-20 2.6.1.3 Toxicity Assessment ........................................................ II-21 2.6.1.4 Risk Characterization....................................................... II-23

2.6.2 Summary of Vapor Intrusion Risks ................................................... II-29 2.6.3 Summary of Ecological Risk Assessment (ERA).............................. II-31

2.6.3.1 Tier I: Problem Formulation/Scoping Assessment ......... II-31 2.6.3.2 Tier II: Analysis .............................................................. II-31 2.6.3.3 Tier III: Risk Characterization ........................................ II-31 2.6.3.4 ERA Results..................................................................... II-32

2.6.4 Basis for Action ................................................................................. II-33 2.7 REMEDIAL ACTION OBJECTIVES (RAOs)................................................ II-34 2.8 DESCRIPTION OF ALTERNATIVES ........................................................... II-35

2.8.1 Description of Remedy Components ................................................. II-35 2.8.1.1 Remedy 1—No Action .................................................... II-35 2.8.1.2 Remedy 2—LUCs............................................................ II-35 2.8.1.3 Remedy 3—Groundwater Pump & Treat/Soil Dig & Haul....................................................................... II-35

2.8.2 Common Elements and Distinguishing Features of Each Alternative ......................................................................................... II-36 2.8.3 Expected Outcomes of Each Alternative ........................................... II-36

2.9 SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES........ II-37 2.9.1 Overall Protection of Human Health and the Environment............... II-38

Table of Contents LUCs ROD iii

TABLE OF CONTENTS (cont'd)

2.9.2 Compliance with ARARs .................................................................. II-38 2.9.3 Long-Term Effectiveness and Permanence ....................................... II-39 2.9.4 Reduction in Toxicity, Mobility, and Volume of Contaminants Through Treatment ............................................................................ II-39 2.9.5 Short-Term Effectiveness .................................................................. II-39 2.9.6 Implementability................................................................................ II-40 2.9.7 Cost .................................................................................................... II-40 2.9.8 State Agency Acceptance .................................................................. II-40 2.9.9 Community Acceptance..................................................................... II-40

2.10 PRINCIPAL THREAT WASTES .................................................................... II-41 2.11 SELECTED REMEDY..................................................................................... II-41

2.11.1 Summary of the Rational for the Selected Remedy........................... II-41 2.11.2 Description of the Selected Remedy.................................................. II-42 2.11.3 Summary of the Estimated Remedy Cost .......................................... II-48 2.11.4 Expected Outcomes of the Selected Remedy .................................... II-48

2.12 STATUTORY DETERMINATIONS .............................................................. II-48 2.12.1 Protection of Human Health and Environment.................................. II-48 2.12.2 Compliance with ARARs .................................................................. II-49

2.12.2.1 Chemical-Specific ARARs .............................................. II-49 2.12.2.2 Action-Specific ARARs................................................... II-49 2.12.2.3 Location-Specific ARARs ............................................... II-49

2.12.3 Cost Effectiveness.............................................................................. II-50 2.12.4 Use of Permanent Solutions and Alternative Treatment Technologies and Preference for Treatment as a Principal Element .............................................................................................. II-50 2.12.5 Five-Year Review Requirements....................................................... II-50

2.13 DOCUMENTATION OF SIGNIFICANT CHANGES TO THE SELECTED REMEDY FROM THE PREFERRED ALTERNATIVE OF THE PROPOSED PLAN............................................................................ II-52 PART III: RESPONSIVENESS SUMMARY......................................................... III-1 List of Figures Figure 1 Site Locations............................................................................................. II-2 Figure 2 LUCs in the EMU .................................................................................... II-44 Figure 3 LUCs in the SMU .................................................................................... II-45 Figure 4 LUCs in the WMU................................................................................... II-46

iv LUCs ROD Table of Contents

TABLE OF CONTENTS (cont’d) List of Tables Table 1 Site List ........................................................................................................I-2 Table 2 Groundwater COC Summary................................................................... II-15 Table 3 Human Health COC Summary ................................................................ II-21 Table 4 Cancer Toxicity Data Summary............................................................... II-22 Table 5 Non-Cancer Toxicity Data Summary ...................................................... II-22 Table 6 Risk Characterization Summary Highlights ............................................ II-24 Table 7 Risk Characterization Comprehensive Summary .................................... II-26 Table 8 ATSDR Summary Results, Base Housing............................................... II-30 Table 9 Remedy Evaluation Criteria..................................................................... II-37 Table 10 Cost Summary.......................................................................................... II-40 Table 11 Cost and Effectiveness Matrix ................................................................. II-51 Attachments ATTACHMENT 1 REFERENCES ATTACHMENT 2 ARARs

Table of Contents LUCs ROD v

LIST OF ACRONYMS AND ABBREVIATIONS AFI Air Force Instruction ARAR Applicable or relevant and appropriate requirement ATSDR Agency for Toxic Substances and Disease Registry bgs Below ground surface CAP Corrective Action Plan CDI Chronic daily intake CERCLA Comprehensive Environmental Response, Compensation and Liability

Act CFR Code of Federal Regulations cis-1,2-DCE cis-1,2-Dichloroethene COC Contaminant of concern COPC Contaminant of potential concern DAFB Dover Air Force Base 1,1-DCE 1,1-Dichloroethene DNREC Department of Natural Resources and Environmental Control EMU East Management Unit EPC Exposure point concentration ERA Ecological Risk Assessment ERP Environmental Restoration Program FFA Federal Facilities Agreement FFS Focused Feasibility Study FS Feasibility Study ft Feet GMZ Groundwater management zone HAZWRAP Hazardous Waste Remedial Actions Program HEAST Health Effects Assessment Summary Tables HI Hazard index HQ Hazard quotient HSCA Hazardous Substance Cleanup Act IRIS Integrated Risk Information System IRP Installation Restoration Program LECR Lifetime excess cancer risk LUCs Land use controls µg/L Micrograms per liter MCL Maximum contaminant level mg/kg-day Milligrams per kilogram-day MOA Memorandum of Agreement MRL Minimal risk level msl Mean sea level NA Not applicable or Not available NCP National Contingency Plan ND Not detected NPL National Priorities List

vi LUCs ROD Table of Contents

LIST OF ACRONYMS AND ABBREVIATIONS (cont’d) NQR No quantifiable risk NW/SE Northwest/southeast O&M Operation and maintenance ORNL/ESD Oak Ridge National Laboratory/Environmental Sciences Division PCE Tetrachloroethene RAO Remedial action objective RBC Risk-based concentration RBSC Risk-based screening criterion RCRA Resource Conservation and Recovery Act RfD Reference dose RI Remedial Investigation ROC Receptor of concern ROD Record of Decision SAIC Science Applications International Corporation SARA Superfund Amendments and Reauthorization Act SF Slope factor SI Site Investigation SLERA Screening Level ERA SMU South Management Unit TCE Trichloroethene TRV Toxicity reference value TSV Toxicity screening value UCL Upper confidence limit UF Uncertainty factor USACE U.S. Army Corps of Engineers USAF United States Air Force USEPA U.S. Environmental Protection Agency UST Underground storage tank VOC Volatile organic compound WMU West Management Unit

Part I: Declaration LUCs ROD I-1

PART I: DECLARATION 1.0 SITE NAMES AND LOCATION Sites: LF22, LF23, WP29, OT56, ST58, LF16, LF19, WP32, OT55, FT02, LF24,

LF26, WP33, WP38, OT42, OT43, OT45, OT46, OT47, OT49, and OT57 Dover Air Force Base Kent County, Delaware CERCLIS ID: DE8570024010 1.1 STATEMENT OF BASIS AND PURPOSE This Record of Decision (ROD) presents the selected remedy for 21 contaminant release sites at Dover Air Force Base (DAFB or Base) in Kent County, Delaware. It addresses all media at these sites. The U.S. Air Force (USAF), as the lead agency for Superfund activities at DAFB, has prepared this ROD to fulfill the requirements of the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA) as amended by the Superfund Amendments and Reauthorization Act of 1986 (SARA) 42 USC § 9601 et seq., and the National Oil and Hazardous Substances Pollution Contingency Plan, 40 Code of Federal Regulations (CFR) Part 300 (National Contingency Plan [NCP]). This decision is based on the Administrative Record file for these sites. The USAF and the U.S. Environmental Protection Agency (USEPA) Region 3 have made the final remedy selection for the sites addressed in this ROD. The State of Delaware, through the Department of Natural Resources and Environmental Control (DNREC), Division of Air and Waste Management, concurs with the selected remedy. 1.2 ASSESSMENT OF SITES As a result of past industrial activities at DAFB, residual contaminants are present in varying small amounts at each of the 21 sites. Although none of the sites pose an unacceptable health or environmental risk under their current use, the response action selected in this ROD is necessary to ensure the continued protection of public health and welfare from actual or threatened releases of hazardous substances into the environment at these sites. The 21 Environmental Restoration Program (ERP) sites addressed in this ROD are located in three of the four management units at DAFB and are listed in Table 1.

I-2 LUCs ROD Part I: Declaration

Table 1. Site List Site ID Description East Management Unit (EMU) LF22 Landfill LF23 Landfill WP29 Sludge Spreading Area OT56 Oil/Water Separator at Fire Training Area 3 ST58 Engine Test Facility South Management Unit (SMU) LF16 Landfill LF19 Landfill WP32 Hobby Shop Waste Oil Tank at Building 124 OT55 Hobby Shop Oil/Water Separator at Building 124 West Management Unit (WMU) FT02 Fire Training Area 2 LF24 Landfill LF26 Landfill WP33 Underground Waste Liquid Storage Tank at Industrial Waste Basins WP38 Entomology Shop at Building 921 OT42 Oil/Water Separator at Building 583 Aircraft Wash Rack OT43 Oil/Water Separator at Building 635 Vehicle Maintenance OT45 Oil/Water Separator at Building 725 Jet Engine Shop OT46 Oil/Water Separators at Industrial Waste Basins OT47 Oil/Water Separator at Building 613 Jet Engine Test Facility OT49 Oil/Water Separator at Building 945 Fuel Cell Dock OT57 Oil/Water Separator at Building 914 Grounds Maintenance Storage

1.3 DESCRIPTION OF SELECTED REMEDY Since its listing on the Superfund National Priorities List (NPL) in March 1989, DAFB has conducted Site Investigations (SIs), a Basewide Remedial Investigation (RI), and Feasibility Studies (FSs) under the Air Force ERP. As part of the overall site cleanup strategy for the Base, DAFB was divided into four management units for the purpose of conducting these studies. The 21 sites addressed in this ROD are in the EMU, SMU, and WMU. There are no unacceptable surface water or sediment related risks at any of these sites. The RI determined that there are no source materials constituting principal threats at any of the 21 sites. During the RI, ecological risks were assessed and contaminants at the sites were found to pose no unacceptable risks to the environment. Risks to human health resulting from exposure to contaminants at the 21 sites were evaluated assuming commercial/industrial uses (such as utility or maintenance work). At LF26, which is in the Base housing area, residential risks were also evaluated, with the assumption that the landfill soil cap would remain and current use would continue. The RI determined that no contaminants of concern (COCs) were present in soil at any of the 21 sites based on commercial/industrial land uses (U.S. Army Corps of Engineers [USACE], 1994 and 1997a). Several COCs


were identified in groundwater at a number of the sites based on an assumption of hypothetical future use of groundwater. However, the all of these groundwater contaminants are attributable to other upgradient or nearby ERP sites that are being addressed separately from this ROD. Groundwater from the contaminated aquifer is not used at DAFB, and groundwater use prohibitions prevent exposure to these contaminants. There are no unacceptable human health risks at any of the 21 sites included in this ROD as long as groundwater use prohibitions remain in place and as long as the land use assumptions used to assess risk at the sites remain valid. The Air Force has identified the following land use control (LUC) performance objectives:

• Prohibit the development and use of all the sites for residential housing, elementary or secondary schools, day care centers, and playgrounds until concentrations of hazardous substances at the site are at levels allowing for unrestricted use and unlimited exposure. At LF26 land use is restricted to commercial/industrial uses or to its current recreational use as a baseball field.

• Prohibit the use of on-Base groundwater from the Columbia Aquifer (first

shallow, unconfined aquifer) near any of the 21 sites until risks from groundwater use are shown to be at levels that allow for unrestricted exposure and unlimited use.

• Prevent non-industrial exposure to landfill contents at Sites LF16, LF19, LF22,

LF23, LF24, and LF26.

• Prevent drilling of wells or other ground-disturbing activities that could penetrate or otherwise disturb the landfill contents at Sites LF16, LF19, LF22, LF23, LF24, and LF26.

• Prohibit digging and other ground-disturbing activities at all of the sites in this

ROD that are inconsistent with the objectives listed above.

• Maintain the integrity of any nearby current and future remedial or monitoring system.

The major provisions of the LUCs remedy, which apply to all 21 sites, are summarized as follows:

• Restrict land use to industrial/commercial/non-residential purposes at all sites except LF26. Residential uses, housing, schools, daycare centers, and recreation areas are prohibited at the sites until concentrations of hazardous substances at the site are at levels allowing for unrestricted exposure and unlimited use. LF26 is restricted to commercial/industrial or its current recreational use as a baseball field.

• Maintain the turf cover over LF16, LF19, LF22, LF23, LF24, and LF26. LF26 is restricted to commercial/industrial or its current recreational use.

I-4 LUCs ROD Part I: Declaration

• Prohibit the use of on-Base groundwater from the Columbia Aquifer (first shallow, unconfined aquifer) in the EMU, WMU, and SMU until risks from groundwater use are shown to be at levels allowing for unrestricted exposure and unlimited use.

• Prohibit digging and other ground-disturbing activities at all sites that are inconsistent with the objectives listed above.

• Use the Base General Plan as the implementation plan for LUCs. DAFB will update the Base General Plan to include the LUC requirements for these sites.

• Comply with Air Force administrative procedures for review and prior approval by environmental personnel of proposed construction or subsurface soil disturbing activities (Base digging permit process).

• Conduct visual site inspections and report on an annual basis to verify compliance with LUC requirements, and promptly notify regulators of any LUC deficiencies.

• Comply with the notification requirements of CERCLA Section 120(h) prior to any transfer or sale of property at the sites.

• Enforce well installation restrictions on-Base and at nearby off-Base properties per the Groundwater Management Zone (GMZ) established by the Delaware DNREC.

• Maintain the integrity of any nearby current and future remedial or monitoring system.

The USAF, represented by the 436th Airlift Wing Commander at DAFB, is responsible for implementing, monitoring, reporting on, and enforcing the LUCs at each site with the exception of the GMZ, which is the responsibility of DNREC. All of the use and activity restrictions and controls set forth in this ROD shall remain in place until concentrations of hazardous substances at the sites are shown to be at levels allowing for unrestricted exposure and unlimited use. The USAF shall not modify or terminate LUCs, implementation actions, or modify land use without prior approval by USEPA and the State. The USAF shall seek prior concurrence before any anticipated action that may disrupt the effectiveness of the LUCs or any action that may alter or negate the need for LUCs. Part II Section 2.11.2 provides a detailed description of each of the above listed components of the LUCs remedy. 1.4 STATUTORY DETERMINATION The selected remedy (LUCs) is protective of human health and the environment, complies with federal and state applicable or relevant and appropriate requirements (ARARs), and is cost-effective. The remedy for the 21 sites does not use permanent solutions or alternative treatment technologies, nor does it satisfy the statutory preference for treatment as a principal element of the remedy for the following reasons: (1) site contaminants do not result in unacceptable human health risks under industrial land use scenarios (or recreational scenarios for LF26), (2) no unacceptable ecological risks exist, and (3) there are no source materials at any of the 21 sites that constitute principal threat


wastes. Although the remedy does not provide irreversible or permanent destruction of contaminants, this remedy does offer restrictions that mitigate and control exposure with a high degree of confidence and is an effective long-term solution. Because this remedy will result in hazardous substances remaining on-site above levels that allow for unlimited use and unrestricted exposure, a statutory review will be conducted within five years after initiation of the remedy to ensure that the remedy is protective of human health and the environment. 1.5 ROD DATA CERTIFICATION CHECKLIST The following information appears in the Part II: Decision Summary section of this ROD. Additional information regarding the 21 sites can be found in the DAFB Administrative Record.

1. COCs as identified in the human health risk assessment are summarized with their detected concentration ranges and detection frequencies in Table 3.

2. Baseline human health risks due to the COCs are summarized in Tables 6 and 7. 3. Results of the Basewide Ecological Risk Assessment (ERA) are outlined in

Section 2.6.2. 4. The remedial action objectives (RAOs) established for the 21 sites are detailed in

Section 2.7. 5. Principal threat wastes are not present at any of the 21 sites (Section 2.10). 6. Current and reasonably anticipated future land and groundwater use assumptions

used in the risk assessment and ROD are outlined in Section 2.5. 7. Potential land uses available at the completion of the remedy are described in

Section 2.11.4. 8. Section 2.11.3 summarizes the estimated capital, annual operation and

maintenance (O&M), and total present worth costs; discount rate; and the number of years over which the remedy costs are projected.

9. The key factors that led to the selection of the LUC remedy are detailed in Section 2.9 and summarized in Section 2.11.1.

Part II: Decision Summary LUCs ROD II-1

PART II: DECISION SUMMARY 2.0 SITE NAMES, LOCATIONS, AND DESCRIPTIONS Site Names: LF22, LF23, WP29, OT56, ST58, LF16, LF19, WP32, OT55, FT02,

LF24, LF26 WP33, WP38, OT42, OT43, OT45, OT46, OT47, OT49, and OT57

Location: West, East, and South Management Units, DAFB, Delaware National Superfund Electronic Database Identification Number: DE8570024010 Lead Agency: U.S. Air Force (USAF) Lead Regulatory Agency: U.S. Environmental Protection Agency (USEPA) Support Agency: Delaware Department of Natural Resources and Environmental Control (DNREC) Funding Source: Air Force Environmental Restoration Account Site Type: various, see descriptions of the 21 sites below Site Description: DAFB is located in Kent County, Delaware, about 3.5 miles southeast of the city of Dover (Figure 1 inset) and is bounded to the southwest by the St. Jones River. DAFB encompasses approximately 4,000 acres of land, including annexes, easements, and leased property. The surrounding area is primarily cropland and wetlands. DAFB began operations in December 1941. Since then, various military services have operated out of DAFB. The present host organization is the 436th Airlift Wing, a part of the USAF Air Mobility Command. Its mission is to provide global airlift capabilities, including transport of cargo, troops, equipment, and relief supplies. The Base also serves as the joint services port mortuary, designed to accept casualties in the event of war. On March 13, 1989, DAFB was placed on the USEPA NPL for Superfund. In August 1989, the USAF entered into a Federal Facility Agreement (FFA) with USEPA Region 3 and the State of Delaware to facilitate environmental cleanup activities at DAFB. Subsequently, investigations were conducted under the Air Force ERP (formerly the Installation Restoration Program [IRP]). For purposes of conducting these investigations, the Base was divided into four management units, known as the North, South, East, and West Management Units (Figure 1). Twenty of the 21 sites discussed in this ROD are located in the industrial area of the Base, northeast of U.S. Route 113 (Figure 1). This portion of the Base is enclosed by a

II-2 LUCs ROD Part II: Decision Summary

Figure 1. Site Locations


security fence and is only accessible through manned entry gates. LF26 is located in the Base housing area. These sites, grouped by management unit, are briefly described below. The EMU forms the eastern quadrant of the Base (Figure 1) and is primarily comprised of open grassy fields with some wooded and wetland areas along the eastern boundary. It is completely within the fenced area of the Base, and is not accessible to the general public. There are five EMU sites included in this ROD. They are:

• LF22 A former landfill used to dispose of rock, hard fill, empty drums, and paint cans. The site is currently an open, grassy field.

• LF23 A small trench used briefly for the disposal of general refuse. It is

currently an open, grassy field. • WP29 Former spreading area for sludge from the former wastewater

treatment plant. It is currently an open, grassy field. • OT56 A former oil/water separator located at a former fire training area

(ERP Site FT03). It is currently an open, grassy field. • ST58 A former engine testing and repair facility that was later used for

storage of pesticides. A jet fuel spill also reportedly occurred at the site. The facility was demolished at an unknown date. The site is currently leveled with areas of concrete pavement and grass.

A portion of the SMU lies northeast of U.S. Route 113 and is inside the security fence that surrounds this industrial area of the Base. The four SMU sites included in this ROD are inside this fenced area (Figure 1), and are not accessible to the general public. They are:

• LF16 A former landfill used for disposal of general refuse. The site is currently an open, grassy field.

• LF19 A former landfill used for disposal of construction rubble.

Currently, most of the site is an open, grassy field; the northwest portion of the site is partially paved.

• WP32 A former 1,000-gallon underground storage tank (UST) used for

waste oil at Building 124. The tank was removed in 1994.

• OT55 Three former oil/water separators and associated USTs located at Building 124. The separators and USTs were removed in 1995.

The WMU of DAFB is heavily industrialized northeast of U.S. Route 113. Eleven of the 12 sites included in this ROD are located in this area of the Base, which is inside the security fence and inaccessible by the general public (Figure 1). One site, LF26, is located in the Base housing area southwest of U.S. Route 113. The 12 sites are:


• FT02 A former fire training area. Currently Building 582 is situated on top of this site.

• LF24 A former landfill currently underneath one end of the northwest/

southeast (NW/SE) runway.

• LF26 A former landfill used for disposal of general refuse, clearance debris, and construction rubble. This site is currently underneath the ball fields behind the Base dependants’ school.

• WP33 A former 15,000-gallon UST used to store waste oil from various

operations. The UST was removed in 1984.

• WP38 A former paint shop that was later converted to the entomology shop where pesticides and herbicides are still currently stored.

• OT42 An existing oil/water separator housed within Building 583, and

servicing aircraft maintenance facilities.

• OT43 An existing oil/water separator supporting Building 635, a motor vehicle maintenance facility.

• OT45 An existing oil/water separator supporting Building 725, a jet

engine maintenance facility.

• OT46 Two former oil/water separators located at the former industrial waste lagoons (ERP Site WP21). They were removed in 1998.

• OT47 A former oil/water separator and attached holding tank at Building

613, a jet engine testing facility. It was replaced in 1997.

• OT49 An existing oil/water separator supporting Building 945, an aircraft maintenance facility.

• OT57 An existing oil/water separator supporting Building 914, a grounds

maintenance facility. 2.1 SITE HISTORY AND ENFORCEMENT ACTIVITIES This section summarizes information on activities that caused releases to the environment at each of the 21 sites, and the history of environmental investigations at each site. A list of all documents referenced in this section and throughout the ROD is included as Attachment 1. Based on the investigations conducted at these sites, no COCs were identified in soil at any of the sites included in this ROD. A few groundwater COCs were identified at a number of these sites as discussed in Section 2.6 of this ROD; however, all the contaminants are related to other upgradient or nearby ERP sites that are being


addressed separately from this ROD. There are no unacceptable surface water or sediment related risks at any of these sites. There have been no CERCLA or other enforcement activities associated with any of the sites in this ROD. 2.1.1 LF22 This former landfill in the EMU was used to dispose of rock, hard fill, empty drums, and paint cans from the early 1950s to the late 1960s. When disposal activities ceased, it was covered with soil and seeded with grass. It is currently maintained as an open grassy field. An SI (Hazardous Waste Remedial Actions Program [HAZWRAP], 1991a) was conducted in 1991 at this site, and RI field work was conducted in 1993-1994 (USACE, 1997a). No removal or remedial actions have been conducted at this site. 2.1.2 LF23 LF23 was a small trench (35 feet [ft] x 100 ft x 6 ft deep) in the EMU used for about 6 weeks in the 1960s for disposal of general refuse. The site is covered with soil and grass. An SI was completed in 1991 (HAZWRAP, 1991b), and RI field work was conducted in 1993-1994 (USACE, 1997a). No removal or remedial actions have been conducted at this site. 2.1.3 WP29 WP29 is a former sludge spreading area in the EMU where sewage sludge from the former wastewater treatment plant was spread and tilled into the soil. This activity occurred from 1969 to 1975. The site is currently an open, grassy field. An SI was completed in 1991 (HAZWRAP, 1991c), and RI field work was conducted in 1993-1994 (USACE, 1997a). No removal or remedial actions have been conducted at this site. 2.1.4 OT56 This site is a former oil/water separator located in the EMU at Site FT03, a former fire training area. OT56 and FT03 were initially investigated during a 1988 IRP Stage 2 Investigation (Science Applications International Corporation [SAIC], 1989). A Focused Feasibility Study (FFS) was conducted in 1990 (HAZWRAP, 1990). Based on the FFS, a ROD for FT03 was signed in December 1990 (DAFB, 1990). The selected remedy in the ROD was decontamination, removal, and off-Base disposal of piping and structures, soil sampling, and installation of a soil cover over the fire training area. A Remedial Action Work Plan was prepared in 1991 (HAZWRAP, 1991d), and the remedial action was conducted in 1992. Site structures, including the OT56 oil/water separator, an underground storage tank, dumpsters, and underground piping were removed, decontaminated, and sent off-site for disposal. A top layer of gravel, and 6 inches of soil underneath the gravel were excavated, tested, and sent off-site to a treatment and disposal facility. The site was backfilled with clean soil and seeded with grass.


Site OT56 was again investigated as an integral part of Site FT03 during the 1993-1994 Basewide RI (USACE, 1997a). The soil samples collected during the RI showed that contaminant levels had been significantly reduced as a result of the 1992 remedial action. However, several contaminants were detected in groundwater at levels requiring action. This groundwater contamination is being addressed under a second ROD for Site FT03 signed in 1997 (HAZWRAP, 1997). Monitored natural attenuation is the selected remedy to address groundwater contamination, and periodic groundwater monitoring and reporting is ongoing. Because groundwater contamination at this location is being addressed under the remedial action for Site FT03, it is not addressed in this ROD. 2.1.5 ST58 This 2- to 3-acre site in the EMU was used as an engine testing and repair facility in the 1960s. After this, pesticides were stored at the site and a jet fuel (JP-4) spill reportedly occurred in the 1970s at an UST. However, the facility was demolished at an unknown date, probably during the late 1970s, and investigations at the site have been unable to locate an UST. It is unknown whether an UST was removed at the time the facility was demolished. Currently the site is partially paved and is sometimes used to stockpile construction materials. The site was investigated during the 1993-1994 RI (USACE, 1997a). No removal or remedial actions have been conducted at this site. 2.1.6 LF16 Two trenches approximately 6 ft deep were used for disposal of general refuse at this site in the SMU during the late 1960s. The area was covered with soil and seeded with grass. It is currently a grassy area with a ball field nearby. The site was first investigated during a 1988 IRP Stage 2 Investigation (SAIC, 1989), and again during the 1993-1994 Basewide RI (USACE, 1997a). No removal or remedial actions have been conducted at this site. Fuel contamination detected in groundwater at this site is attributable to upgradient fuel release Site OT53. This fuel contamination is being addressed under a Corrective Action Plan (CAP) for OT53 (USACE, 1997b), and is therefore not addressed in this ROD. 2.1.7 LF19 This 4-acre site in the SMU was used in the 1960s for disposal of construction rubble. The area was covered with several feet of soil and seeded with grass. At the present time, it is mostly an open, grassy area, but is partially paved on its northwest end. The site was first investigated during a 1988 IRP Stage 2 Investigation (SAIC, 1989), and later during the 1993-1994 Basewide RI (USACE, 1997a). No removal or remedial actions have been conducted at this site. 2.1.8 WP32 A former 1,000-gallon UST was located near the western corner of Building 124, an automotive hobby shop in the SMU. It stored waste oil from the automotive shop located


in the building until mid-1991. An SI was conducted at the site in 1991 (HAZWRAP, 1991e), and RI field work was conducted in 1993-1994 (USACE, 1997a). The tank and associated contaminated soil were removed per a 1994 ROD (DAFB, 1994). Post-excavation soil samples met the industrial cleanup standards of the Delaware Regulations Governing Underground Storage Tank Systems. In September 1995, USEPA issued a closeout report for the UST and soil at WP32 (USEPA, 1995). 2.1.9 OT55 OT55 is also at the automotive hobby shop at Building 124, and comprises three former oil/water separators and associated USTs. The separators collected the liquid wastes that were discharged to floor drains in the building. An SI was conducted at the site in 1991 (HAZWRAP, 1991f), and RI field work was conducted in 1993-1994 (USACE, 1997a). The oil/water separators and USTs were removed in 1995 under the Base’s Environmental Compliance Program. 2.1.10 FT02 This former fire training area in the WMU is underneath Building 582, a large warehouse. Fire training exercises were held from 1956 to 1958 in a pit approximately 60 ft long and 40 ft wide, surrounded by a 6-inch-high soil berm. Contaminated waste oils, waste solvents, paint thinners, and jet fuel were stored onsite and used in the training exercises. An SI was conducted at the site in 1991 (HAZWRAP, 1991g), and RI field work was conducted in 1993-1994 (USACE, 1997a). No removal or remedial actions have been conducted at this site under the ERP. 2.1.11 LF24 LF24 is a former landfill in the WMU underneath the northwestern end of the NW/SE runway. General refuse was disposed of in the landfill during the 1970s. About 5,000 tons of general refuse along with approximately 30 5-gallon cans of aircraft and traffic paint were unearthed in 1987. This material was removed and disposed of offsite when the runway was extended in 1987. A few fuel and solvent contaminants were detected in soil samples collected after excavation of the landfill. However, during the 1993-1994 RI (USACE, 1997a) no COCs were identified in soil or groundwater at this site. The major portion of LF24 that is currently underneath the NW/SE runway was removed in 1987. If any residual portion of the landfill contents remain, they are underneath the soil and grass cover next to the runway. 2.1.12 LF26 Site LF26 is approximately 2 acres in size and was used in the early 1960s for the disposal of general refuse, clearance debris such as trees/branches, and construction rubble. Earlier, it had been a sand and gravel pit which was later filled with refuse to a depth of about 8 ft. When disposal activities ceased, the site was covered with local soil and seeded with grass. The site is currently maintained as grass-covered baseball playing


fields. An SI was conducted at the site in 1991 (HAZWRAP, 1991h), and RI field work was conducted in 1993-1994 (USACE, 1997a). No removal or remedial actions have been conducted at this site under the ERP. During the excavation of an RI test pit, two 5-gallon buckets containing an oily substance were found that apparently had been carefully placed upright within a void between concrete slabs and blocks. The contents of the buckets were sampled, and then the buckets and their contents were removed and disposed of. 2.1.13 WP33 This former 15,000-gallon UST in the WMU was used to store oils separated from industrial wastewater at the industrial waste lagoons (ERP Site WP21), oils pumped from various oil/water separators, and other hazardous wastes. The UST was removed in 1984 and the site is currently covered with grass. An SI was conducted at the site in 1991 (HAZWRAP, 1991i), and RI field work was conducted in 1993-1994 (USACE, 1994). 2.1.14 WP38 Building 921 in the WMU was initially built as an aircraft support center and was a paint shop from 1969-1970. In 1971, it was converted to an entomology shop and now houses quantities of pesticides and herbicides. An SI was conducted at the site in 1991 (HAZWRAP, 1991j), and RI field work was conducted in 1993-1994 (USACE, 1997a). No removal or remedial actions have been conducted at this site. 2.1.15 OT42 This site is an oil/water separator that services Buildings 582 and 706, aircraft maintenance facilities. It is housed within Building 583 and is constructed of reinforced concrete and measures 13 ft wide by 24 ft long by 12 ft deep. Separated oil is held in a 500-gallon tank, and processed water is discharged to the sanitary sewer. An SI was conducted at the site in 1991 (HAZWRAP, 1991k), and RI field work was conducted in 1993-1994 (USACE, 1997a). No removal or remedial actions have been conducted at this site. 2.1.16 OT43 The oil/water separator at this site in the WMU supports operations at Building 635, a motor vehicle maintenance facility. It is a below-ground structure 5 ft wide by 6.5 ft long by 12 ft deep. Processed water had historically been discharged to the industrial waste collection drain (ERP Site OT41) but now discharges to the sanitary sewer. An SI was conducted at the site in 1991 (HAZWRAP, 1991l), and RI field work was conducted in 1993-1994 (USACE, 1997a). No removal or remedial actions have been conducted at this site.


2.1.17 OT45 The oil/water separator at this site supports Building 725, a jet engine maintenance facility. Separated waste oils accumulate in a 275-gallon underground holding tank located outside the building. Separated water is discharged to the sanitary sewer. An SI was conducted at the site in 1991 (HAZWRAP, 1991m), and RI field work was conducted in 1993-1994 (USACE, 1994). No removal or remedial actions have been conducted at this site. 2.1.18 OT46 Two former oil/water separators, installed in 1985, were located at the northern and western corners of the concrete industrial waste basins at ERP Site WP21 in the WMU. An SI was conducted at the site in 1991 (HAZWRAP, 1991n), and RI field work was conducted in 1993-1994 (USACE, 1994). During the SI and RI, residual petroleum-related contaminants were detected in low concentration at shallow depths in the soil, and were likely due to minor spillage or surface runoff. In 1998, a ROD was signed for removal of the concrete industrial waste basins (WP21), oil/water separators (OT46), associated structures, and contaminated soil (HAZWRAP, 1998). The remedial action was carried out during the summer of 1998 in accordance with the approved Closure Plan (DAFB, 1998). The OT46 oil/water separators and associated contaminated soil were removed at that time. 2.1.19 OT47 This site was an oil/water separator located at Building 613, a jet engine testing facility in the WMU. Separated oils were stored in a 275-gallon holding tank at the southeast side of the oil/water separator. An SI was conducted at the site in 1991 (HAZWRAP, 1991o), and RI field work was conducted in 1993-1994 (USACE, 1994). No COCs were identified at this site during the SI and RI. The oil/water separator and its holding tank were replaced around 1997. A new oil/water separator with grit chamber was installed in its place as part of a sewer upgrade project. 2.1.20 OT49 This site is an oil/water separator on the west side of Building 945, an aircraft maintenance facility in the WMU. A 400-gallon storage tank is attached to the oil/water separator. An SI was conducted at the site in 1991 (HAZWRAP, 1991p), and RI field work was conducted in 1993-1994 (USACE, 1997a). No removal or remedial actions have been conducted at this site. 2.1.21 OT57 This site is an oil/water separator located at the northwestern side of Building 914, a grounds maintenance facility in the WMU. Processed wastewater is discharged to the sanitary sewer, separated oil is collected in a 500-gallon holding tank. An SI was


conducted at the site in 1991 (HAZWRAP, 1991q), and RI field work was conducted in 1993-1994 (USACE, 1997a). No removal or remedial actions have been conducted at this site. 2.2 COMMUNITY PARTICIPATION DAFB actively encourages public participation at all phases of environmental restoration work, and operates under a Community Relations Plan that is periodically updated. In accordance with NCP §300.430(f)(3), the Proposed Plan for LUCs at Multiple Sites at DAFB (Oak Ridge National Laboratory/Environmental Sciences Division [ORNL/ESD], 2005) and supporting documentation were made available to the public in July 2005. They can be found in the Administrative Record file and the Information Repository maintained at the 436th Civil Engineer Squadron DAFB and the Dover Public Library, 45 S. State Street, Dover, DE. The notice of availability for the proposed plan was published in the Delaware State News on July 3, 2005. A public comment period was held from July 10 to August 24, 2005. A public meeting was held on July 19, 2005 at the DNREC auditorium, 89 Kings Highway, Dover, Delaware. No questions or comments from the public were received. This is documented in Part III, the Responsiveness Summary, in this ROD. 2.3 SCOPE AND ROLE OF OPERABLE UNIT OR RESPONSE ACTIONS For the 21 sites included in this ROD, the Basewide RI determined that no cleanup action is required at any of these sites based on the commercial/industrial exposure scenarios (and a residential scenario at LF26) used to evaluate risk at the sites. Final remedy selection for all 21 sites is being documented in this one ROD. This section describes past removal or remedial actions that have taken place at these sites, ongoing and planned groundwater actions, and actions addressed in this ROD. This ROD addresses all media and all remaining response actions required at these 21 sites. For purposes of consistency with the RI documentation, the sites are grouped by the management unit (i.e., South, East, or West) within which they are located. 2.3.1 Past Actions Associated with Sites Included in this ROD Past Actions at EMU Sites:

• OT56: As described in Section 2.1.4, the oil/water separator at OT56 was removed in 1992 under a 1990 ROD for Site FT03 (DAFB, 1990). This action is listed as Operable Unit #1 in the USEPA’s CERCLIS database.

Past Actions at SMU Sites:

• WP32: As described in Section 2.1.8, the UST and associated soil at WP32 were removed in 1994 per a ROD (DAFB, 1994). This action is listed as Operable Unit #4 in the USEPA’s CERCLIS database. In 1995, USEPA issued a closeout report for the UST and soil (USEPA, 1995).


• OT55: As described in Section 2.1.9, the three oil/water separators and associated USTs at OT55 were removed in 1995 under the Base’s Environmental Compliance Program.

Past Actions at WMU Sites:

• LF24: Most of the material from the LF24 landfill was removed in 1987 during a runway extension project. The landfill material was transported to an off-site disposal facility.

• WP33: The UST at WP33 was removed in 1984 as part of routine Base

operations.

• OT46: As described in Section 2.1.17, the two oil/water separators at OT46 were removed in 1998 per a ROD for removal of the concrete industrial waste basins (ERP Site WP21), associated structures, and contaminated soil (HAZWRAP, 1998). This action is listed as Operable Unit #14 in the USEPA’s CERCLIS database.

• OT47: The oil/water separator and its holding tank at OT47 were replaced around

1997 as part of a sewer upgrade project. 2.3.2 Ongoing and Planned Groundwater Actions Groundwater Actions in the EMU

• OT56: Groundwater contamination detected in this area is being addressed under a 1997 ROD for Monitored Natural Attenuation at Site FT03 (HAZWRAP, 1997). Periodic groundwater monitoring is ongoing at this location. The groundwater action at this location is Operable Unit #6 in the USEPA’s CERCLIS database.

Groundwater Actions in the SMU

• LF16: As described in Section 2.1.6, fuel contamination detected in groundwater underneath LF16 is associated with an upgradient fuel release at ERP Site OT53, a petroleum exclusion site. This groundwater contamination is being addressed under the State of Delaware’s Tank Management Branch per a 1997 CAP for OT53 (USACE, 1997b). Monitored natural attenuation was implemented in 1998 and periodic groundwater monitoring is ongoing.

• WP32/OT55: With the exception of the petroleum-related contamination

associated with Site OT53, groundwater contamination within the entire SMU is being addressed in a single ROD. Although no unacceptable risk was associated with the tetrachloroethene (PCE) detected in groundwater at WP32/OT55 under commercial/industrial exposure scenarios (see Section 2.6.1), it is being addressed


in the SMU ROD in association with a large groundwater plume known as Area 9.

Groundwater Actions in the WMU

• FT02 and OT46: Groundwater contaminants detected underneath these two sites emanate from other nearby sites associated with a large multi-source groundwater plume known as Area 6. Two interim actions are ongoing within the Area 6 plume: 1) an accelerated anaerobic bioremediation remedy (USEPA CERCLIS Operable Unit #11) per an interim ROD signed in 1995 (DAFB, 1995a); and 2) a monitored natural attenuation remedy (USEPA CERCLIS Operable Unit #10) per an interim ROD signed in 1995 (DAFB, 1995b). Final actions for the Area 6 groundwater contaminant plume, including contaminants detected underneath Sites FT02 and OT46, will be addressed in a single ROD for Area 6.

• OT43: Groundwater contaminants detected at OT43 likely emanate from other

nearby sites associated with a large multi-source groundwater plume known as Area 5. Actions for the Area 5 groundwater contaminant plume, including contaminants detected at OT43, will be addressed in a single ROD for Area 5.

2.3.3 Actions Addressed in this ROD The remedy selected in this ROD addresses all remaining response actions required at Sites LF22, LF23, WP29, OT56, ST58, LF16, LF19, WP32, OT55, FT02, LF24, LF26, WP33, WP38, OT42, OT43, OT45, OT46, OT47, OT49, and OT57. There is no surface water or sediment at any of these sites. For soil and groundwater, this ROD selects LUCs as the final remedy for all 21 sites. The LUCs remedy is described in detail in Section 2.11.2. 2.4 SITE CHARACTERISTICS Twenty of the sites addressed in this section are all located in the industrial area of the Base. One site, LF26, is located in the Base housing area. Specific details, i.e., size, site features, and sampled media, were outlined for each site in Section 2.1. This section focuses on a generalized conceptual site model for the 21 sites, topographical and geographical information for the Base, ecological and archaeological issues, and the nature and extent of contamination at each site. 2.4.1 Conceptual Site Model Many of the 21 ERP sites discussed in this ROD appear to have released small quantities of contaminants to the subsurface. Subsurface contamination at the sites appears to exist at only residual levels. Exposure to residual soil contamination is a possible exposure route for Base maintenance or utility workers at these sites and for residents at site LF26 which is located in the Base housing area.


For groundwater, some of the sites may have had minor effects on water quality. Although a few isolated detections of contaminants in groundwater were observed, no migrating plumes originate from any of the 21 sites. At five sites (OT56, LF16, FT02, OT43, and OT46), groundwater quality is affected by contaminants migrating from other upgradient or adjacent sites. Groundwater from the Columbia Aquifer is not used for any purpose on Base at this time, and there are no off-Base users of the Columbia Aquifer currently affected by groundwater contamination from DAFB. Thus there are no current exposures to this medium. Surface contamination is not a problem at any of the sites, thus transport via runoff is not a migration route. Vapor intrusion was generally not recognized as a human health exposure pathway that could be reliably quantified during the time (mid 1990s) that the RI risk assessments were conducted for DAFB. Thus, this pathway was not evaluated during the RI/FS process for the 21 sites. One assessment of risks from this potential pathway at DAFB occurred later. Risks were assessed in 2003 for the Base residential area during a public health assessment conducted by the Agency for Toxic Substances and Disease Registry (ATSDR). Specific potential risks represented by the vapor intrusion pathway will be reviewed for the sites covered by this ROD using the vapor intrusion evaluation developed for the sites in the WMU and SMU. This is discussed in more detail in Section 2.6.2. 2.4.2 Topographical and Hydrogeologic Information The surface topography of DAFB is relatively flat, with elevations ranging from 10 to 30 ft above mean sea level (msl). Areas of lower elevation (10 ft above msl or less) are located adjacent to the St. Jones River and Pipe Elm Branch (a tributary to the Little River). Elevations of 30 or more feet above msl occur in the housing area, which is located south of U.S. Route 113, in the western portion of the Base. Surface water runoff is handled by an extensive storm drainage network of open ditches and pipe culverts. The storm drainage network discharges primarily to the St. Jones River to the west, the Pipe Elm Branch to the east, and the Morgan Branch to the north of the Base. There are four groundwater aquifers underlying DAFB. They are, in descending order: the Columbia, the Frederica, the Cheswold, and the Piney Point. The water table aquifer at DAFB is the Columbia Aquifer. The water table is usually encountered at 10 to 15 ft below ground surface (bgs), but varies according to surface topography from 30 ft bgs to within a few feet of the ground surface. The Pleistocene sediments occupied by the Columbia Aquifer underlying DAFB consist of medium- to coarse-grained sand with gravelly sand, gravel, silt, and clay lenses common throughout. The upper portion of the Columbia Formation is finer grained and contains more silt and clay lenses than the deeper portions. The deeper portion of the Columbia Formation is typically fine- to coarse-grained sand with occasional lenses of fine to medium sand and discontinuous gravel lenses interpreted as channel lag deposits. The overall trend from coarser to finer material represents a change in depositional environment from higher to lower energy.


The saturated thickness of the Columbia Aquifer ranges from 15 to 20 ft in the northern portion of the Base to 70 ft in the southeastern portion. Underlying the Columbia Aquifer is a dense Miocene clay layer known as the upper confining unit of the Calvert Formation. It ranges from 8.5 to 32 ft thick, although it is very thin or missing in at least one localized area near the center of the Base. The contact between the Columbia and Calvert Formations forms a hummocky erosional surface. The upper confining unit of the Calvert Formation generally consists of gray to dark gray, firm, dense clay, with thin laminations of silt and fine sand. This unit separates the Columbia Aquifer from the Frederica Aquifer, acting as a barrier to prevent the vertical migration of contaminants from the Columbia Aquifer to the Frederica Aquifer. The Frederica Aquifer is the upper sand unit of the Calvert Formation and underlies the upper clay and silt unit. The potentiometric surface of the Frederica Aquifer is generally 4 to 6 ft lower than the groundwater levels of the Columbia Aquifer except near groundwater discharge points such as the St. Jones River where the levels are reversed. Below the Frederica Aquifer, the next two deeper aquifers are the Cheswold and Piney Point. 2.4.3 Ecology DAFB is located on a broad, low coastal plain in the Atlantic Coastal Plain Physiographic Province know as the Delmarva Peninsula. This area is characterized by low desiccated hills and sandy plains and includes mature streams and wetland areas. Ecological habitat at DAFB is comprised of open grassy fields and areas adjacent to three main surface drainages: Pipe Elm Branch, St. Jones River, and Morgan Branch. These areas, where not covered by parking lots, buildings, or regularly mown grass, consist of low seral (dry, withered) vegetation, non-tidal emergent wetlands, mesic (moderate moisture) and wet hardwood forests, tidal swamp forests, and freshwater and brackish marshes. The best quality habitats (and the least disturbed) are found along the Pipe Elm Branch drainage in the EMU. 2.4.4 Archaeological or Historical Significance There are no areas of archaeological or historical significance at any of the 21 sites. 2.4.5 Sampling Strategy Investigations that have been conducted at each site were discussed in Section 2.1. Environmental investigations were conducted at many of the 21 ERP sites prior to the Basewide RI. However, the Basewide RI is the most recent and comprehensive evaluation of each site. During the Basewide RI (1993-1994), soil and groundwater were sampled and analyzed for environmental contaminants at all 21 sites (USACE, 1994 and 1997a). Environmental problems were not found in soil at any of the 21 sites. The RI identified minor, isolated detections of contaminants in the groundwater at eight of the sites, although in five cases these contaminants are known to originate at other upgradient or adjacent ERP sites. As discussed in Section 2.4.6 below, data collected for the RI


were combined with data from previous studies to provide the basis for the contamination and risk assessments. 2.4.6 Nature and Extent of Contamination No COCs were found in soil at any of the 21 sites based on the commercial/industrial exposure scenarios used to evaluate the sites. Under the residential land use scenario at LF26 only, one COC (arsenic) was identified in soil. This metal, however, was found in site surface soil at levels that are naturally occurring. This is discussed in more detail in Section 2.6.1.4. For groundwater, several COCs were identified during the risk assessment based on commercial/industrial exposure scenarios. None were identified based on the residential exposure scenario for LF26. Groundwater COCs were identified at eight of the 21 sites. COCs were not identified at the other 13 sites described in Section 2.1, and therefore these 13 sites are not discussed in this section. Contaminants are identified as COCs for one of two reasons: 1) their calculated risk values equaled or exceeded the federal comparison criteria for carcinogenic or non-carcinogenic risk, or 2) detected concentrations exceeded drinking water maximum contaminant levels (MCLs). Section 2.6.1 discusses the risk assessment results in more detail. Table 2 lists the groundwater COCs identified based on the risk assessment for each of these eight sites, with their maximum detected concentrations and MCLs. Table 2. Groundwater COC Summary

Site ID COC Maximum

Concentration (µg/L)

MCL (µg/L)

Number of MCL

Exceedances OT56 Arsenic1

Benzene2 Manganese1 Vinyl chloride1

10.4 150

1,800 21

10 5 -- 2

1 1 -- 1

LF16 Benzene1 410 5 1 FT02 cis-1,2-DCE2

TCE2 Antimony1

82 48

66.5

70 5 6

1 2 1

OT43 Benzene1 N-nitrosodipropylamine1

150 2

5 --

1 --

ST58 Arsenic1 10.9 10 1 OT46 1,1-DCE1

TCE2 7

15 7 5

1 1

WP32/OT55 PCE2 48 5 2 1COC identified based on Basewide RI risk assessment. 2COC identified based on federal drinking water MCL exceedance. The following paragraphs discuss the nature and extent of contamination in more detail for each site, starting with the sites listed in Table 2, where groundwater COCs were identified.


2.4.6.1 OT56 Sites OT56 and FT03 in the EMU were investigated as a unit since OT56 is located within the boundaries of Site FT03, a former fire training area. As shown in Table 2, two metals (arsenic and manganese), and one volatile organic compound (VOC) (vinyl chloride), were identified as COCs in groundwater based on exceedance of federal risk criteria. Additionally, although it did not contribute significantly to the total risk values for the site, benzene, a fuel constituent, was detected in groundwater at a maximum concentration of 150 micrograms per liter (µg/L), which exceeds its MCL of 5 µg/L. As discussed previously in Section 2.1.4, all of these groundwater contaminants are currently being addressed under a remedial action for Site FT03, per a ROD signed in 1997. Consequently, remediation of these COCs is not addressed in this ROD for Site OT56. 2.4.6.2 LF16 Benzene was the only groundwater COC detected at Site LF16 as shown in Table 2. However, as discussed in Section 2.1.6, this groundwater contaminant originates at an upgradient fuel spill site, OT53. Site OT53 is a petroleum exclusion site that is being addressed under the State of Delaware’s Tank Management Branch. A remedial action for groundwater contamination from OT53 was implemented in 1998 per a CAP (USACE, 1997b) in accordance with the Delaware Regulations Governing Underground Storage Tank Systems. The benzene detected underneath LF16 is being addressed per the OT53 CAP; therefore, remediation of this COC is not addressed in this ROD for Site LF16. 2.4.6.3 FT02 At Site FT02, antimony, a metal, was the only COC identified in groundwater based on the risk assessment. It was found in only one sample above its MCL and was not detected in the other five groundwater samples collected at the site. In addition to antimony, two VOCs, cis-1,2-dichloroethene (cis-1,2-DCE) and trichloroethene (TCE), were detected at maximum concentrations of 82 and 48 µg/L, respectively. These two VOCs were detected in the deeper portion of the Columbia Aquifer and were not detected in site soils, indicating that FT02 is not the source of these contaminants. The presence of cis-1,2-DCE and TCE underneath Site FT02 is likely related to nearby ERP Sites OT48 and WP31 which are associated with a large groundwater plume known as Area 6. These contaminants are being addressed under a separate ROD for Area 6, and are, therefore, not addressed in this ROD for Site FT02. 2.4.6.4 OT43 Groundwater COCs identified at Site OT43 are the VOC benzene and one semivolatile organic compound (n-nitrosodipropylamine) as shown in Table 2. The latter was present at only an estimated 2 µg/L and was not found in site soil. Nearby ERP Sites OT41 and OT44, associated with an industrial waste collection drain, are likely the source of these groundwater contaminants. OT41, OT44, and other upgradient sites have all contributed


to a groundwater contaminant plume known as Area 5. Groundwater remediation for Area 5 contaminants will be addressed under a separate ROD for Area 5, and is therefore not addressed in this ROD for Site OT43. 2.4.6.5 ST58 At ST58, arsenic was identified as a groundwater COC due to its detection in one sample slightly exceeding its current MCL. At the time the RI risk assessment was accomplished for this site, the MCL for arsenic was 50 µg/L. Since then the arsenic MCL has been lowered to 10 µg/L, and now the maximum concentration detected at Site ST58 slightly (10.9 versus 10 µg/L) exceeds the new MCL. Soil data for arsenic suggest that its presence in groundwater at ST58 is not site related. No other COCs were identified at ST58. 2.4.6.6 OT46 At OT46 in the WMU, 1,1-DCE was detected in groundwater in one of two samples at 7 µg/L (equal to its MCL). TCE was also reported in one sample at a concentration of 15 µg/L (above its MCL of 5 µg/L). However, the TCE did not contribute to an elevated risk. Soil data indicate that these VOCs are not likely related to the oil/water separators at OT46, but are more probably related to the adjacent former industrial waste basins (ERP Site WP21). As discussed in Section 2.1.17, the OT46 oil/water separators, WP21 concrete industrial waste basins, associated structures, and contaminated soil were removed in 1998 per a ROD (HAZWRAP, 1998). Sites OT46 and WP21 are located within a large multi-source groundwater contaminant plume known as Area 6. Groundwater contamination at this location will be addressed under a separate ROD for Area 6, and is therefore not addressed in this ROD for Site OT46. 2.4.6.7 WP32/OT55 Groundwater was evaluated for the combined area of WP32/OT55 in the SMU since the sites are so close together. One solvent, PCE, was detected in two geoprobe groundwater samples at concentrations (28 and 42 µg/L) above the MCL of 5 µg/L. No other VOCs were reported in the three groundwater samples collected at the site, nor was PCE detected in downgradient wells or in site soil. Because these results are from geoprobe samples, there is some uncertainty concerning the results. PCE did not cause an elevated health risk during the RI risk assessment. Three geoprobe groundwater samples were collected in 2005 along the downgradient side of WP32/OT55. None contained any VOC above an MCL. Thus, the solvents found during the RI appear to have degraded.


2.5 CURRENT AND POTENTIAL FUTURE LAND AND WATER USES 2.5.1 Land Use Current On-site Land Use. Current land use at DAFB includes both industrial and residential areas. The largest portion of the Base is the industrial area which includes taxiways and runways, aircraft hangars, maintenance and support facilities. The industrial portion of the Base is completely enclosed by a security fence. It is only accessible to authorized personnel through manned security gates; it is not accessible to the general public. All of the sites included in this ROD are located in the industrial portion of the Base. The residential area of the Base is on the southwest side of U.S. Route 113 (Figure 1) and includes a military family housing area, golf course, and military dependents school. Current Adjacent/Surrounding Land Use. Land uses in the vicinity of DAFB include single and multifamily residential areas, industrial zones, commercial land located along major highways, and extensive areas of agricultural and open land. There are two large concentrations of industrial areas located just north of DAFB. A privately owned sand and gravel quarry is located adjacent to and southwest of the Base (Figure 1). Reasonably Anticipated Future Land Use. The Base has operated as an airport since 1941. Due to its mission of providing critical air lift capabilities and serving as the joint services port mortuary, the projected land use of DAFB is to remain an active airfield for the foreseeable future. The 20 sites in the industrial area are unlikely to be developed for non-industrial purposes for the foreseeable future. Similarly, LF26 will likely remain recreational since the site is located at the river’s edge where more permanent development is very unlikely. 2.5.2 Surface Water Use Current Surface Water Use. There are no surface water bodies directly associated with any of the 21 sites in this ROD except for LF26 which is adjacent to the St. Jones River. There are two main surface water bodies to which stormwater runoff from the Base drains. Runoff from the northeast side of the Base drains through a series of ditches and culverts into the Pipe Elm Branch of the Little River. Similarly, runoff from the southwest side of the Base drains to the St. Jones River. The Pipe Elm Branch and the St. Jones River are used for recreational purposes, primarily fishing, but are not used for potable water. Potential Beneficial Surface Water Use. The anticipated future uses of the Pipe Elm Branch and the St. Jones River are recreational. They are not expected to be used as potable water sources because the Base and surrounding communities derive their drinking water from groundwater. Consequently, the beneficial uses of the Pipe Elm Branch and the St. Jones River are not expected to change from current recreational uses.


2.5.3 Groundwater Use Current Groundwater Use. Groundwater from the surficial (Columbia) aquifer is not used at DAFB. DAFB obtains potable water from several deep supply wells installed either in the Cheswold or Piney Point Aquifers (see Section 2.4.2). However, the State of Delaware considers all aquifers potential sources of drinking water and the Columbia Aquifer is used by the surrounding community. Moreover, the Columbia Aquifer would be considered a Class IIa aquifer, currently used source of drinking water, based on Guidelines for Ground-Water Classification under USEPA Groundwater Protection Strategy. Off-Base, the Columbia Aquifer is used predominantly for irrigation and domestic supply. In 2003, DNREC established a GMZ encompassing DAFB, the region between the Base and the St. Jones River, and a small area next to the Base near the Pipe Elm Branch. The GMZ prohibits unauthorized use of the Columbia Aquifer in these areas and is enforced through DNREC’s well permitting process. Potential Beneficial Groundwater Use. Potential beneficial use of groundwater from the Columbia Aquifer is as a drinking water source. 2.6 SUMMARY OF SITE RISKS This section presents the assessment methods and results for both human health and ecological risk assessments. 2.6.1 Summary of Human Health Risk Assessment As part of the Basewide RI a Baseline Risk Assessment was conducted. The Baseline Risk Assessment estimates what risks sites pose if no action is taken. It provides the basis for taking action and identifies what contaminants and exposure pathways, if any, need to be addressed by a remedial action. The risk assessment focused on potential pathways in which Base personnel (maintenance and construction workers) could be exposed to contaminated materials originating at each site. Base residents were also considered for the assessment of LF26. The risk assessment is summarized below. 2.6.1.1 Identification of COCs Human health risks from exposure to soil and groundwater were assessed in the Basewide RI (USACE, 1997a). Contaminants of potential concern (COPCs) were identified using both the historic and the Basewide RI data by comparing the maximum detected concentration of a chemical in each media to its risk-based screening criterion (RBSC) in accordance with USEPA Region 3 guidance (USEPA, 1993). Any chemical whose concentration either exceeded its RBSC, or for which no RBSC was available, was identified as a site-related COPC for that medium and was retained for further evaluation during the risk assessment. The RBSCs were developed according to USEPA Region 3 protocols using standard exposure pathways and available toxicity criteria. The COPCs


identified during this initial screening process were then evaluated for human health risks as described in sections 2.6.1.2 through 2.6.1.4. As a result of this risk evaluation, contaminants found to contribute to an elevated human health risk were identified as COCs. Table 3 is the initial list of COCs identified for each site and medium, their detected concentration ranges, detection frequencies, and exposure point concentrations (EPCs). No COCs were identified in soil at any of the 21 sites based on the commercial/industrial exposure scenarios used to assess the sites. One soil COC was identified in soil at LF26 under the residential land-use scenario. The development and use of EPCs in the exposure assessment portion of the risk assessment is discussed in the following section. 2.6.1.2 Exposure Assessment The exposure assessment is a process of characterizing the exposure setting, identifying exposure points and pathways (i.e., routes by which COPCs pass from contaminated media to human receptors), and quantifying exposure. The Site Conceptual Model (Section 2.4.1) is used to determine reasonable exposure scenarios and pathways of concern. Routes of exposure are based on the current, future, and, in some cases, hypothetical land and groundwater uses (see Section 2.5). Identification of Exposure Scenarios. It is assumed that current Base workers can be exposed to residual contaminants in the surface and subsurface soil during regular maintenance activities (e.g., utility installation or repair). Potential risks associated with the current workers' exposure to contaminants in groundwater are not calculated, because groundwater from the Columbia Aquifer is not being used anywhere on Base. It is assumed that future on-site workers can be exposed to residual contaminants in soil through construction or excavation activities. For DAFB, a hypothetical future commercial/industrial groundwater use was assumed such that: (1) there are commercial/industrial users located on Base who will use the Columbia Aquifer in the future as a source of water for drinking and showering, and (2) concentrations detected during the Basewide RI on or near the site represent the concentrations to which these users may be exposed (USACE, 1994 and 1997a). For the one site located in the Base housing area, a residential scenario was also evaluated. For all other sites, future residential groundwater use and soil exposure were not evaluated. Thus, the following scenarios were used in the Baseline Risk Assessment:

• Current and future commercial/industrial exposure to an on-Base worker through inhalation and ingestion of soil during construction or excavation.

• Hypothetical future commercial/industrial exposure to an on-Base worker through inhalation and ingestion of groundwater.

• Residential exposure through ingestion and inhalation of soil and groundwater by children and adults at Site LF26. Hypothetical future residential use was not evaluated at any of the other sites


Table 3. Human Health COC Summary

Pathway: Hypothetical Future Commercial/Industrial Exposure to GroundwaterEPC (µg/L);

Concentration Detection 95% UCL unlessSite ID COC Range (µg/L) Frequency noted otherwise

OT56 Arsenic ND - 10.4 3/6 7.99Manganese 2.8 - 1,800 6/6 1,150Vinyl chloride ND - 21 1/8 9.03

LF16 Benzene ND - 410 2/9 335FT02 Antimony ND - 66.5 1/6 45.6OT43 Benzene 150 1/1 150 (max)

N-nitrosodipropylamine 2 1/1 2 (max)LF22 Arsenic 5 - 6.4 2/10 3.46WP29 Arsenic 5.4 1/1 5.4 (max)ST58 Arsenic 3.5 -10.9 2/8 8.64OT46 1,1-DCE ND - 7 1/2 7 (max)

Pathway: Residential Exposure to Soil, LF26 only (units of measure are mg/kg)LF26 Arsenic 2 - 35.4 15/15 6.2

Pathway: Residential Exposure to Groundwater, LF26 only - No COCs identified

(max) - EPC is the maximum detected concentration.mg/kg - milligrams per kilogram.ND - not detected above laboratory detection limit.

Pathway: Current Commercial/Industrial Exposure to Soil - No COCs identified

Pathway: Future Commercial/Industrial Exposure to Soil - No COCs identified

Dermal exposures to soil and groundwater were not evaluated during the Basewide RI risk assessment for two reasons. (1) Chemical-specific absorption data were not available; and (2) The uptake models were inadequate. Quantification of EPCs. EPCs are calculated by estimating the 95 percent upper confidence limit (UCL) on the arithmetic mean for each COPC. Where the calculated EPC exceeds the COPC’s maximum concentration or there is a limited number of samples, the maximum concentration is used as the EPC in the risk assessment. EPCs for the COCs are listed in Table 3. 2.6.1.3 Toxicity Assessment The objectives of the toxicity assessment are to evaluate available information regarding the potential for COPCs to cause adverse health effects in exposed individuals, and to provide the analytical framework for the characterization of human health impacts. The toxicity assessment summarizes published data on human health effects. This includes quantitative slope factors (SF) for carcinogenic (cancer) effects and reference doses (RfD) for noncarcinogenic effects (health problems other than cancer). SFs are quantitative estimates of the increased probability of cancer developing in an exposed individual. SFs are expressed as the lifetime cancer risk per milligram of chemical per


kilogram of body weight per day (mg/kg/day). RfDs represent the maximum acceptable uptake of noncarcinogens by humans, expressed in milligrams of chemical per kilogram of body weight per day. Tables 4 and 5 summarize the cancer and non-cancer toxicity data for the COCs, respectively. Table 4. Cancer Toxicity Data Summary

Ingestion Inhalation Ingestion InhalationA, skin, IRIS A, lung, IRIS 1.75 15.1

NA NA NA NAA, leukemia, IRIS A, leukemia, IRIS 0.029 0.029C, kidney, IRIS C, kidney, IRIS 0.6 0.175

D, IRIS D, IRIS NA NAN-nitrosodipropylamine NA NA 7 0.006

Vinyl chloride A, liver & lungs, HEAST A, liver, HEAST 1.9 0.3(1) Weight of Evidence/Cancer Guideline Code, primary affected organ(s), data sourceCodes: A-Human carcinogen

B2- Probable human carcinogen, sufficient evidence in animals, inadequate or no evidence in humansC-Possible human carcinogenD-Not classifiable as a human carcingen

Data Sources:IRIS, Integrated Risk Information Management System (USEPA, 1993)HEAST, Health Effects Assessment Summary Tables (HEAST, 1993)Region III, USEPA Region III Risk-Based Concentration (RBC) Table, Third Quarter 1994.

Manganese

NA - Data not available(2) Units: (mg/kg)/day

AntimonyBenzene1,1-DCE

Cancer Effects (1) Slope Factors (2)COCArsenic

Table 5. Non-Cancer Toxicity Data Summary Non-Cancer Effects (1) Reference Doses (2)

COC Ingestion Inhalation Ingestion Inhalation

Arsenic

Chronic. Hyperpigmentation, keratosis, vascular complications,

UF = 300, IRIS NA 3 x 10-4 NA

Antimony Chronic. Increased mortality,

UF = 1000, IRIS NA 4 x 10-4 NA

Benzene NA Subchronic. Toxicity

to blood NA 0.00171 1,1-DCE Chronic. Liver, UF = 1,000, IRIS NA 0.009 NA

Manganese Chronic. Nervous system,

UF = 1, IRIS

Chronic. Respiratory and psychomotor

effects, UF = 300, IRIS 0.005 1.43 x 10-5

N-nitrosodipropylamine NA NA NA NA Vinyl chloride NA NA NA NA (1) Chronic or Subchronic, primary affected organ(s), UF, data source UF = uncertainty factor, listed where available. The higher this value, the greater the uncertainty in the estimation of toxic effects on human health. NA - Data not available (2) Units: mg/(kg x day) Data sources: IRIS, USEPA, 1993; HEAST, 1993; Region 3, USEPA Region 3 RBC Table, Third Quarter 1994


2.6.1.4 Risk Characterization The final step of the baseline risk assessment, risk characterization, consists of quantitative estimates of carcinogenic risk and noncarcinogenic hazard, which are derived by relating estimated intakes to toxicity criteria. Carcinogenic risks and noncarcinogenic hazards are quantified for each contaminant. The terms “lifetime excess cancer risk” (LECR) and “hazard index” (HI) are used to refer to carcinogenic and noncarcinogenic health effects, respectively. 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:

LECR = CDI x SF where: LECR = a unitless probability (e.g., 2 x 10-5) of an individual developing cancer CDI = chronic daily intake averaged over 70 years (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 1x10-6 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 other causes such as smoking or exposure to too much sun. The chance of an individual developing cancer from all other causes has been estimated to be as high as one in three. According to USEPA guidance, the generally acceptable LECR range for site-related exposures is 10-4 to 10-6. The risk characterization for the carcinogenic COCs for each exposure scenario is summarized in Table 6. The potential for noncarcinogenic effects is evaluated by comparing an exposure level over a specified time period (e.g., life-time) with a reference dose (RfD) derived for a similar exposure period. An 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). An HQ


Table 6. Risk Characterization Summary Highlights Scenario/Receptor(1): Hypothetical, future commercial/industrial groundwater exposure to Base workers Non-Cancer Risk (HI) Cancer Risk (LECR)

Site ID Contaminant Ingestion Inhalation Total(2) Ingestion Inhalation Total(2)

OT56 Arsenic 0.3 NA 0.3 5 x 10-5 NA 5 x 10-5 Manganese 2 NA 2 NA NA -- Vinyl chloride NA NA -- 6 x 10-5 1 x 10-5 7 x 10-5

Total 2 -- 2 1 x 10-4 1 x 10-5 1 x 10-4

LF16 Benzene NA 2 2 3 x 10-5 4 x 10-5 7 x 10-5

FT02 Antimony 1 NA 1 NA NA -- OT43 Benzene NA 1 1 2 x 10-5 2 x 10-5 4 x 10-5 N-nitrosodipropylamine NA NA -- 5 x 10-5 NA 5 x 10-5

Total -- 1.0 1 7 x 10-5 2 x 10-5 9 x 10-5

LF22 Arsenic 0.1 NA 0.1 2 x 10-5 NA 2 x 10-5

WP29 Arsenic 0.2 NA 0.2 3 x 10-5 NA 3 x 10-5

ST58 Arsenic 0.3 NA 0.3 5 x 10-5 NA 5 x 10-5 OT46 1,1-DCE 0.008 NA 0.008 2 x 10-5 5 x 10-6 2 x 10-5 Scenario/Receptor(1): Residential soil exposure to Base residents (LF26 only)

LF26 Arsenic (adult receptor) 0.08 NA 0.08 2 x 10-5 3 x 10-9 2 x 10-5

(1) Only those exposure scenarios for which COCs were identified are listed in this table.

(2)Total risks and hazard values are the sum of all COPCs that were retained from the initial screening and for which toxicity data were available. This table lists only those contaminants that contributed significantly to the total. Thus, the total may not precisely match the sum of the COCs due to the omission of low level COPCs and to rounding the total to one significant figure. Additionally, although listed here, some contaminants are not COCs. The various reasons for this are discussed in the text for each site.

NA - not applicable, no toxicity data available.

Part II: Decision Summa