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FINAL Offsite Remediation Report Former Madera Manufactured Gas Plant Site Madera, California

January 2013 Prepared for PACIFIC GAS AND ELECTRIC COMPANY 3401 Crow Canyon Road San Ramon, California 94583 Prepared by AECOM Technical Services, Inc. 2101 Webster Street, Suite 1900 Oakland, California 94612

i FINAL REMEDIATION CLOSURE REPORT January 2013

Table of Contents

Abbreviations and Acronyms .................................................................................................................... x

Acknowledgment and Signature Page ................................................................................................... xiv

Disclaimer .................................................................................................................................................. xv

Executive Summary ................................................................................................................................. xvi

1.0 Introduction ......................................................................................................................................... 1 1.1 OVERVIEW .................................................................................................................................... 1 1.2 SITE HISTORY AND DESCRIPTION ................................................................................................... 1 1.3 INVESTIGATION AND REMEDIATION ACTIVITIES ................................................................................ 2 1.4 PURPOSE OF THE REPORT ............................................................................................................. 2

2.0 Remedial Activities ............................................................................................................................. 3 2.1 OVERVIEW .................................................................................................................................... 3

2.1.1 Alley Area ......................................................................................................................... 3 2.1.2 Offsite Arsenic Area ......................................................................................................... 4 2.1.3 Offsite TPH Area .............................................................................................................. 4 2.1.4 Other Offsite Area ............................................................................................................ 4

2.2 PRELIMINARY ACTIVITIES ............................................................................................................... 4 2.2.1 Permitting ......................................................................................................................... 5 2.2.2 Site Preparation ............................................................................................................... 5

2.3 SITE DEMOLITION .......................................................................................................................... 5 2.3.1 Fencing 5 2.3.2 MGP Related Pipes ......................................................................................................... 5

2.4 EXCAVATION AND BACKFILL ........................................................................................................... 6 2.4.1 Excavation Procedures .................................................................................................... 6 2.4.2 Loading of Soil ................................................................................................................. 7 2.4.3 Backfill and Compaction .................................................................................................. 8

2.5 ENVIRONMENTAL CONTROL............................................................................................................ 8 2.6 RESTORATION ............................................................................................................................... 8 2.7 SUMMARY OF MATERIAL QUANTITIES RELATED TO OFFSITE WORK .................................................. 9

3.0 Offsite Confirmation Sampling and Analyses................................................................................ 10 3.1 INTRODUCTION ............................................................................................................................ 10 3.2 SUMMARY OF EXCAVATION ACTIVITIES ......................................................................................... 10 3.3 CONFIRMATION SAMPLING AND ANALYSES .................................................................................... 11

3.3.1 Additional Offsite Investigations..................................................................................... 12 3.3.2 Abandoned Pipe in Alley ................................................................................................ 12

Table of Contents (Continued)

ii FINAL OFFSITE REMEDIATION REPORT January 2013

3.3.3 Results .......................................................................................................................... 13

4.0 Post Remediation Health Risk Assessment ................................................................................... 15 4.1 INTRODUCTION AND OBJECTIVES .................................................................................................. 15 4.2 DATA EVALUATION AND SELECTION OF CHEMICALS OF POTENTIAL CONCERN ................................. 16

4.2.1 Data Evaluation.............................................................................................................. 17 4.2.2 Selection of Chemicals of Potential Concern ................................................................ 17

4.3 EXPOSURE ASSESSMENT ............................................................................................................. 19 4.3.1 Identification of Potentially Exposed Populations and Complete Exposure Pathways . 19 4.3.2 Human Intake Assumptions ........................................................................................... 19 4.3.3 Estimation of Representative Exposure Point Concentrations ...................................... 20

4.4 TOXICITY ASSESSMENT ................................................................................................................ 21 4.4.1 Toxicity Assessment for Carcinogenic Effects ............................................................... 22 4.4.2 Toxicity Assessment for Noncarcinogenic Effects ......................................................... 22 4.4.3 Toxicity Assessment for Lead ........................................................................................ 23

4.5 RISK CHARACTERIZATION .................................................................................................... 24 4.5.1 Comparison of CPAH Concentrations in Offsite row Area Soil to Ambient

Concentrations ............................................................................................................... 24 4.5.2 Estimated Cancer Risks and Noncancer Hazards ........................................................ 25 4.5.3 Findings and Conclusions .............................................................................................. 30

4.6 RECOMMENDATIONS .................................................................................................................... 31

5.0 References ......................................................................................................................................... 32


iii FINAL OFFSITE REMEDIATION REPORT January 2013

List of Tables

Table 2-1 Summary of Onsite Cleanup Goals

Table 3-1 Summary of Confirmation Offsite Soil Analytical Results for PAHs and B(a)P Equivalent Concentrations

Table 3-2 Summary of Confirmation Offsite Soil Analytical Results for VOCs and TPH

Table 3-3 Summary of Confirmation Offsite Soil Analytical Results for Metals and Cyanide

Table 4-1 Summary of Chemicals Included in the Risk Assessment: Offsite Rights-Of-Way Area Soil (0-10 feet bgs)

Table 4-2 Exposure Parameters

Table 4-3 Equations Used to Calculate Exposure Concentrations and Chronic Daily Intakes: Intrusive Worker Scenario

Table 4-4 Exposure Point and Predicted Outdoor Air Concentrations for Chemicals of Potential Concern in Offsite ROW Area Soil: Offsite Intrusive Worker Scenario

Table 4-5 Chemical Properties for Chemicals of Potential Concern

Table 4-6 Carcinogenic and Noncarginogenic Toxicity Values for Chemicals of Potential Concern

Table 4-7 Summary of Representative Post-Excavation CPAH Data for Offsite ROW Area Soil (0-10 feet bgs)

Table 4-8 Summary Statistics of Representative Post-Excavation CPAH Dataset for Offsite ROW Area Soil (0-10 feet bgs)

Table 4-9 Summary Statistics of Northern California

Table 4-10 Exposure Concentration and Chronic Daily Intake for Carcinogens in Offsite ROW Area Soil: Offsite Intrusive Worker Scenario

Table 4-11 Exposure Concentration and Chronic Daily Intake for Noncarcinogens in Offsite ROW Area Soil: Offsite Intrusive Worker Scenario

Table 4-12 Cancer Risks from Offsite ROW Area Soil: Offsite Intrusive Worker Scenario

Table 4-13 Noncancer Hazard Indices from Offsite ROW Area Soil: Offsite Intrusive Worker Scenario


iv FINAL OFFSITE REMEDIATION REPORT January 2013

List of Figures

Figure 1-1 Former Madera MGP Site Vicinity Map

Figure 1-2 Former Madera MGP Site Assessor’s Parcel Map

Figure 1-3 Former Madera MGP Site Historical Operations

Figure 1-4 Confirmation Sample Locations

Figure 2-1 Initial Proposed Excavation Areas

Figure 2-2 Offsite Areas including Maximum Excavation Extents and Depth Contours

Figure 3-1 In-Place Offsite Sampling Locations, B(a)P Equivalent Concentrations and Other Select Soil Analytical Results

Figure 3-2 Post-Remediation Samples Showing Arsenic in the Right of Way

Figure 3-3 Post-Remediation Samples Showing TPH in the Right of Way List of Appendices

Appendix A Correspondence

Appendix B Permits

Appendix C Alley Roadbed Analysis

Appendix D Data Statistical Evaluation

Appendix E Uncertainties in the Risk Assessment

x FINAL REMEDIATION CLOSURE REPORT January 2013

Abbreviations and Acronyms

‘ Foot

< less than

> greater than

~ Approximately

% Percent

µg/dL micrograms per deciliter

µg/kg micrograms per kilogram

(µg/m3)-1 per microgram of chemical per cubic meter of air

AECOM AECOM Technical Services, Inc.

AETL American Environmental Testing Laboratory

AF attenuation factor

ASTM American Society for Testing and Materials

atm-m3/mol atmospheres cubic feet per mole

B(a)P benzo(a)pyrene

bgs below ground surface

BTEX benzene, toluene, ethylbenzene and xylenes

Cal/EPA California Environmental Protection Agency

CDI chronic daily intake

CEQA California Environmental Quality Act

CFR Code of Federal Regulations

COC chain of custody

COPCs chemicals of potential concern

CPAHs carcinogenic polycyclic aromatic hydrocarbons

CSF cancer slope factor

DTSC Department of Toxic Substances Control

EC exposure concentration

EPC exposure point concentration

g/m2-s grams per squared meter per second

HEAST Health Effects Assessment Summary Tables

HERO Office of Human and Ecological Risk

HHRA Human Health Risk Assessment

Abbreviations and Acronyms (Continued)

xi FINAL OFFSITE REMEDIATION REPORT January 2013

HI hazard index

HQ hazard quotient

IRIS Integrated Risk Information System

kg Kilogram

kg/mg kilogram per milligram

kg/m3 kilogram per cubic meter

MDL method detection limit

mg/kg milligrams per kilogram

mg/kg-day-1 milligram of chemical per kilogram body weight per day

mg/L milligrams per liter

mg/m3 milligrams per cubic meter

MGP manufactured gas plant

mm Hg millimeters of mercury

NA not applicable

NAAQS National Ambient Air Quality Standard

NCP National Contingency Plan

ND non-detect

ng/m3 nanograms per cubic meter

OEHHA Office of Environmental Health Hazard Assessment

PAHs polycyclic aromatic hydrocarbons

PCB polychlorinated biphenyl

PCE tetrachloroethene or perchloroethene

PDR personal dust monitor

PEA Preliminary Endangerment Assessment

PEF particulate emissions factor

PID photoIonization detector

ppm parts per million

PPRTV Provisional Peer Reviewed Toxicity Values

PQL practical quantitation limit

PUF polyurethane foam

QASR Quality Assurance Summary Report

Abbreviations and Acronyms (Continued)

xii FINAL OFFSITE REMEDIATION REPORT January 2013

RAW Removal Action Workplan

RBCG Risk-based cleanup goals

RCRA Resource Conservation and Recovery Act

REL reference exposure level

RfC reference concentration

RfD reference dose

RI remedial investigation

RSL Regional Screening Level

STSC Superfund Health Risk Technical Support Center

SVOC semi-volatile organic compound

SWPPP Storm Water Pollution Prevention Program

TF transfer factor

™ trade mark

TPH total petroleum hydrocarbons

TPH-D total petroleum hdrocarbons as diesel

TPH-G total petroleum hydrocarbons as gasoline

TPH-H total petroleum hydrocarbons as heavy hydrocarbons

UCL upper confidence limit

URF unit risk factor

USEPA United States Environmental Protection Agency

UTL upper tolerance limit

VCA Voluntary Cleanup Agreement

VOCs volatile organic compounds

xv FINAL OFFSITE REMEDIATION REPORT January 2013

Disclaimer

This Offsite Remediation Report (Report) was prepared by AECOM Technical Services, Inc. (AECOM), for the sole use and benefit of Pacific Gas and Electric Company (Client) and for the specific Site known as the Former Madera Manufactured Gas Plant (MGP) site, at corner of Clinton Street and South E Street, located in the city of Madera, California “Site.” Neither this Report, nor any of the information contained herein, shall be used or relied upon for any purpose by any person or entity other than the Client and for the Site.

This Report was prepared based partially on information supplied to AECOM from outside sources and other information which is in the public domain, and partially on the information and data AECOM generated during investigation and remediation of the Site. Documentation for the statements made in this Report is on file either at the Client’s offices or at AECOM’s office located in Oakland, California. AECOM makes no warranty as to the accuracy of statements made by others that are contained in this Report, nor are any other warranties or guarantees, expressed or implied, included or intended in this Report with respect to information supplied by outside sources or conclusions or recommendations substantially based on information supplied by outside sources. This Report has been prepared in accordance with the current generally accepted practices and standards consistent with the level of care and skill exercised under similar circumstances by other professional consultants or firms performing the same or similar services. Since the facts forming the basis for this Report are subject to professional interpretation, differing conclusions could be reached. AECOM does not assume responsibility for the discovery and elimination of hazards that could possibly cause accidents, injuries, or damage unless those hazards were apparent, and should have been discovered, as a result of the services AECOM performed for the Client. This Report represents the best professional judgment of AECOM. However, compliance with submitted recommendations or suggestions does not assure elimination of hazards or the fulfillment of the Client's obligations under local, State, or Federal laws, or any modifications or changes to such laws.

None of the work performed hereunder shall constitute or be represented as a legal opinion of any kind or nature, but shall be a representation of findings of fact from records examined.

xvi FINAL OFFSITE REMEDIATION REPORT January 2013

Executive Summary

This Final Offsite Remediation Report (Report) was prepared by AECOM Technical Services, Inc. (AECOM), on behalf of the Pacific Gas and Electric Company (PG&E), for the remediation of the offsite areas in the public right-of-way adjacent to the Former Madera Manufactured Gas Plant (MGP) site (the Site) which are referred as “offsite ROW areas”. This Report presents a summary of the work conducted in performing the soil remediation for offsite ROW areas. The offsite ROW remediation was an extension of the on-site remediation which was completed in October, 2011 and was documented in the Final Onsite Remediation Closure Report [AECOM, 2012b].

Site History and Description

The Site is an approximately 1-acre parcel located at the corner of 9th and South E Streets in Madera, Madera County, California (Figure 1-1).

Beginning in 1913 and until sometime in 1930, the Madera Gas Company operated a MGP facility at the Site. The Site was subsequently acquired by PG&E in 1931 and between 1931 and 1935 the MGP facility was dismantled and removed when natural gas was introduced into the area.

The Site is currently used as an open space storage facility for power poles, transformers, and miscellaneous gas and electrical hardware and as a field mobilization yard by PG&E.

The offsite ROW areas include: an unpaved sidewalk beyond which is Clinton Street (8th Street); an unnamed, unpaved alley to the northeast; an unpaved sidewalk beyond which are South E Street and a Southern Pacific railroad spur to the southwest; and an unpaved sidewalk beyond which is 9th Street to the southeast. The offsite ROW areas are covered with crushed rock, concrete, or asphalt pavement.

Summary of Site Investigations

Several investigations were conducted at the Site to identify and delineate potential environmental impacts due to the historical MGP operations. These investigations were designed to evaluate the extent of impacts at the Site and included analysis of soil, groundwater and soil vapor samples. These investigations are summarized in the Remedial Investigation/Human Health Risk Assessment (RI/HHRA) [MSE/Earth Tech, 2008]. Based on the investigation results, a Removal Action Work Plan (RAW) [AECOM, 2011a] was prepared to address the remediation of the soils that were impacted with carcinogenic polyaromatic hydrocarbons (CPAHs), arsenic, naphthalene, benzene, ethylbenzene, acenaphthene, benzo(g,h,i)perylene, fluoranthene, pyrene, and/or lead. The RAW recommended the excavation of the soil with concentrations of contaminants of concerns (COCs) above the risk-based clean up goals (RBCGs) developed as part of the HHRA. The RBCGs are set to restore the site soil to ambient-like conditions. The remedy recommended in the RAW was approved by the Department of Toxic Substances Control (DTSC) on January 28, 2011. A supplemental investigation for offsite areas was conducted concurrently with the subject onsite and offsite remediation to delineate the extent of impact.

Remedial Activities

A detailed evaluation of remedial alternatives was conducted for the Site, as part of the RAW. The selected remedial alternative for soil remediation at the Site was excavation and disposal. The HHRA identified an initial remediation target of 0.9 milligrams per kilogram (mg/kg), in benzo(a)pyrene (B(a)P) equivalents, to reduce the concentrations of CPAHs to ambient-like levels. The HHRA also identified an initial remediation target of 16 mg/kg for arsenic to remediate arsenic concentrations at the Site to ambient-like levels such that the upper bound average (i.e., 95 percent upper confidence level [UCL] of the arithmetic mean concentrations) of post-excavation arsenic concentrations is at or below 6 mg/kg. Moreover, the RAW set a target cleanup level for total petroleum hydrocarbons in diesel range (TPH-d)

xvii FINAL OFFSITE REMEDIATION REPORT January 2013

of 4,000 mg/kg. Naphthalene, benzene, ethylbenzene, acenaphthene, benzo(g,h,i)perylene, fluoranthene, pyrene, and lead concentrations above residential RBCGs were collocated with soil which displayed high concentrations of CPAHs; thus, planned removal of CPAHs would remove these constituents to levels below their RBCGs.

The RAW did include the removal of impacted soil beyond the property boundary, however, during the on-site excavation, it was decided (between DTSC and PG&E) to extend the on-site remediation into the public right of way where the soil impacts exceeded onsite clean up goals. In general, excavations were continued until 1) all contamination was removed; 2) adjacent private property was reached; or 3) continued removal of soil would have necessitated the closure of either Clinton Avenue or South E Street. This report discusses the four offsite ROW areas where soil was removed 1) along the unnamed alley east of the site referred as “The Alley” where PAHs and lead were detected above onsite cleanup goals; 2) the arsenic-impacted area near the intersection of Clinton Avenue and South E Street, referred to as the “Offsite Arsenic Area”; 3) the total petroleum hydrocarbon (TPH)-impacted area along South E street, referred to as the “Offsite TPH Area; and 4) the PAH-impacted sidewalk area along 9th street. Of these areas, only the arsenic offsite is not suitable for residential use with residual arsenic concentrations that are above ambient-like levels.

A total of 14,820 tons of non-hazardous impacted soil (PAH, VOCs, TPH, and arsenic) were excavated from the onsite and offsite areas and transported to Forward Landfill in Manteca, California for disposal. A total of 84 tons of soil that meet the criteria as non-Resource Conservation Recovery Act (RCRA) hazardous soil (lead and PAH) were excavated from the onsite and offsite ROW areas and transported to Clean Harbor’s Buttonwillow Landfill in Buttonwillow, California for disposal. Of these totals, 2,530 tons of non-hazardous impacted soil and 14 tons of non RCRA hazardous soil were removed from the offsite ROW areas.

During the excavation, confirmation soil samples were collected and analyzed for PAHs and metals. Selected samples were also analyzed for TPH, and VOCs, as required. In general concentrations of arsenic exceeding ambient-like levels were left in place in the public ROW near the intersection of South “E” Street and Clinton Avenue due to limited accessibility. Concentrations of TPH along South E Street also exceeded the target cleanup goal for TPH (not a risk based level). Concentrations of lead and PAHs were left in place along the southeastern edge of the alley (closer to 9th avenue), but these concentrations appear to be unrelated to site activities and are on neighboring properties (i.e. not the ROW). A post-remediation Human Health Risk Assessment was conducted by Iris Environmental using the offsite soil confirmation data.

Conclusions

Remediation activities were extended to the offsite ROW areas and were completed to the practical extent possible and the extent of soil impact beyond offsite remediation areas was delineated. The overall objective of the offsite investigation and remedial activities was to minimize potential future exposure of humans (intrusive workers, residents and visitors) to CPAHs, TPH, naphthalene, benzene, ethylbenzene, acenaphthene, benzo(g,h,i)perylene, fluoranthene, pyrene, lead, and arsenic in soil through inhalation, dermal absorption and/or ingestion. Offsite investigation and remediation activities were successful in removing accessible CPAHs, TPH, lead and arsenic, except in areas where access to the impacted soil was limited. Where the offsite soil remediation was limited by site access, delineation of the impacted soil was achieved instead. Based upon the concentrations of COC left in-place in the offsite ROW area along Clinton Avenue and South “E” Street, the post-remediation HHRA for the offsite ROW area supports the following findings:

Future Residential and Commercial Land-Use Scenario

∑ CPAH concentrations in soil from the offsite ROW areas along South E Street and Clinton Avenue are similar to ambient levels. Thus, the potential risks from residual CPAHs in the offsite

xviii FINAL OFFSITE REMEDIATION REPORT January 2013

ROW area soil from these areas would be no different than the risks posed by ambient levels of CPAHs. As such, the residual levels of CPAHs remaining in offsite ROW area soil are consistent with concentrations that would be considered acceptable for unrestricted land use (i.e., residential land-use).

∑ Residual concentrations of other PAHs, lead, and VOCs in offsite ROW area were below their respective cleanup goals. However, residual levels of arsenic remain in offsite ROW area soils above the respective cleanup goal established to reduce the residual arsenic concentrations to ambient levels for the protection of a hypothetical future residential population. Note that the level of arsenic developed in the HHRA for the protection of future commercial populations is the same level as that developed for the protection of future residential populations ; i.e., ambient level. As such, soils within the offsite ROW area that are not suitable for future residential or commercial land use would require some form of risk management such as capping. In addition, a Soil Management Plan [AECOM, 2012c] was prepared and should be followed for any intrusive work in these areas.

Offsite ROW Intrusive Worker Scenario ∑ As described above, CPAH concentrations in soil from the offsite ROW areas along South E

Street and Clinton Avenue are similar to ambient levels. Thus, the potential risks from residual CPAHs in the offsite ROW area soil from these areas would be no different than the risks posed by ambient levels of CPAHs. As such, the residual levels of CPAHs remaining in offsite ROW area soil are consistent with concentrations that would be considered acceptable for unrestricted land use (i.e., residential land-use), and therefore, are protective of potential receptor populations under all land uses, including intrusive worker populations.

∑ The cumulative cancer risks posed by other residual chemicals (other than CPAHs) and noncancer hazards posed by all residual chemicals remaining in the offsite ROW area soil along the northern portion of South E Street and along Clinton Avenue which are adjacent to the Site are well within levels considered acceptable for worker populations performing intrusive activities in the offsite public ROW. Furthermore, lead concentrations in offsite ROW area soil are not expected to result in an increase in the blood lead level for the fetus of the offsite intrusive worker of more than 1 microgram per deciliter (mg/dL). As such, the residual levels of chemicals in the offsite ROW area soil would be considered safe and protective of the current use under an intrusive worker scenario. In addition, a Soil Management Plan [AECOM, 2012c] was prepared and should be followed for any intrusive work in these areas.

Recommendations

Arsenic concentrations in soils that remain in some of the offsite ROW areas are above levels considered suitable for residential or commercial land use. As such, the land use of these offsite ROW areas should not change without additional remediation (e.g. soil removal) or other form of risk management (e.g. capping). In addition, excavation activities should be properly conducted, and soils removed from these areas should be properly managed and disposed of. Accordingly, a Soil Management Plan [AECOM, 2012c] was prepared and should be followed for any intrusive work conducted in these offsite ROW areas.

1 FINAL OFFSITE REMEDIATION REPORT January 2013

1.0 Introduction

1.1 Overview

This Final Offsite Remediation Report (Report) was prepared by AECOM Technical Services, Inc. (AECOM), on behalf of the Pacific Gas and Electric Company (PG&E), for the remediation of the offsite public right-of-way areas (offsite ROW areas) adjacent to the Former Madera Manufactured Gas Plant (MGP) site (the Site). The Site is located in Madera, California (Figures 1-1 and 1-2). The remediation of the offsite ROW areas was completed in October 28, 2011.

The remediation was conducted by Pivox Corporation (Pivox) and overseen by AECOM to assure general compliance with the Removal Action Work Plan (RAW), prepared by AECOM [AECOM 2011a] and, approved by California Department of Toxic Substances Control (DTSC) on January 28, 2011. The RAW did not specify removal of materials beyond the Site boundary; however, during the onsite remedial excavation, it was decided (based on discussions between PG&E, DTSC, and AECOM) to remove materials in the public right of way which exceeded the onsite clean up goals. In general, the on-site excavations were continued until: 1) all contamination was removed; 2) adjacent private property was reached; or 3) continued removal of soil would have necessitated the closure of either Clinton Avenue or South E Street. This report focuses on the four offsite ROW areas where soil contamination, associated with the former MGP site activities, were found above the onsite cleanup goals; these included: 1) the unnamed alley east of the site referred as “The Alley”; 2) the arsenic-impacted area near the intersection of Clinton Avenue and South E Street, referred to as the “Offsite Arsenic Area”; 3) the total petroleum hydrocarbon (TPH)-impacted area along South E street, referred to as the “Offsite TPH Area”; and 4) the PAH-impacted sidewalk area along 9th Street.

The impacted soil was removed from the accessible offsite ROW areas, under the oversight of the DTSC. This report was prepared to comply in part with the Voluntary Cleanup Agreement (VCA), Docket No. HAS-A 05/06-160, agreed upon by California Environmental Protection Agency, DTSC, and PG&E [DTSC, 2006]. Supporting agencies included the Central Valley Regional Water Quality Control Board and the Madera County Environmental Health Department.

1.2 Site History and Description

The former MGP site is an approximately 1-acre parcel located at 9th and South E Streets in Madera, Madera County, California (Figure 1-1).

Beginning in 1913 and until sometime in 1930, the Madera Gas Company operated a MGP facility at the Site. The Site was subsequently acquired by PG&E in 1931 and between 1931 and 1935 the MGP facility was dismantled and removed when natural gas was introduced into the area.

The former MGP site is currently used as an open space storage facility for power poles, transformers, and miscellaneous gas and electrical hardware and as a field mobilization yard by PG&E.

A detailed history of the MGP site and the activities conducted there is included in the Onsite Remediation Closure Report by AECOM [2012b].

The offsite ROW areas include: the unpaved sidewalk area, northwest of the Site, beyond which is Clinton Street (8th Street); an unnamed alley, northeast of the Site; the unpaved sidewalk area, southwest of the Site, beyond which is South E Street and a Southern Pacific railroad spur; and another unpaved sidewalk area, southeast of the Site, beyond which is 9th Street. The alley is paved in the southern portion while unpaved in the northern half. Several above ground and underground utilities are present within the alley. Beyond the alley on the north side are two residences and on the south side is an automobile repair shop. The offsite ROW areas are covered with crushed rock, concrete, or asphalt pavement.


1.3 Investigation and Remediation Activities

Below is a summary of the investigations and remedial activities conducted at the Site which led to the offsite remediation discussed in this report. A more detailed description of the on-site remediation is included in the Onsite Remediation Closure Report (AECOM 2012).

Several investigations were conducted at the Site to identify and delineate potential environmental impacts due to the historical MGP operations. These investigations were designed to evaluate the extent of impacts at the Site and included analysis of soil, groundwater and soil vapor samples. These investigations are summarized in the Remedial Investigation/Human Health Risk Assessment (RI/HHRA) [MSE/Earth Tech, 2008]. Based on the investigation results, a Removal Action Work Plan (RAW) [AECOM, 2011a] was prepared to address the remediation of the soils that were impacted with carcinogenic polyaromatic hydrocarbons (CPAHs), arsenic, naphthalene, benzene, ethylbenzene, acenaphthene, benzo(g,h,i)perylene, fluoranthene, pyrene, and/or lead. The RAW recommended the excavation of the soil with concentrations of contaminants of concerns (COCs) above the risk-based clean up goals developed as part of the HHRA.

Residential risk-based cleanup goals (RBCGs) were established based upon data collected during the RI and evaluated in the HHRA. In addition, ambient-like levels were developed for CPAHs and arsenic as the RBCGs are below the ambient levels for these constituents. Nine onsite areas were targeted for remediation based upon the established RBCGs or ambient-like levels. In August through October 2011, the Site was remediated by excavating the soils that were impacted with CPAHs, arsenic, naphthalene, benzene, ethylbenzene, acenaphthene, benzo(g,h,i)perylene, fluoranthene, pyrene, TPH, and/or lead as identified in the RAW. The excavated soil was transported offsite for disposal.

Based on confirmation sampling results, the boundaries of the excavation were expanded to include offsite ROW areas. Soil was excavated across most of the offsite area to depths ranging from 2 feet below ground surface (bgs) to 16 feet bgs. A total of 14,820 tons of soil was removed from both onsite and offsite ROW areas and replaced with clean imported fill material which meets the criteria established by the DTSC’s fact sheet entitled “Import Advisory, Clean Imported Fill Material” [DTSC, 2001]. Additionally, certain areas were excavated in a slot trench method and filled with cement slurry to maintain the structure integrity of the street side walls. As shown on Figure 1-4, soil confirmation samples were collected throughout the excavated areas.

1.4 Purpose of the Report

The purpose of this Report is to document the remedial actions which occurred in the offsite ROW areas adjacent to the former Madera MGP Site. Although these activities were not explicitly delineated in the RAW [AECOM, 2011a], the procedures and techniques outlined in the RAW were followed in these offsite excavations. In general, impacted soil in the offsite area was removed until concentrations below the overall remedial action objectives were achieved or until direct access to the impacted soil was blocked (such as by paved ROW or by the property lines of a neighboring property).

The overall remedial action objective for the offsite ROW areas was to minimize potential future exposure of humans (onsite workers, hypothetical future residents, and visitors) to CPAHs, TPH, naphthalene, benzene, ethylbenzene, acenaphthene, benzo(g,h,i)perylene, fluoranthene, pyrene, lead, and arsenic in soil through inhalation, dermal absorption and/or ingestion.


2.0 Remedial Activities

2.1 Overview

The remedial activities in the offsite ROW areas at the Site included excavation of soil impacted by PAHs, volatile organic compounds (VOCs), total petroleum hydrocarbons (TPH), and various metals including arsenic and lead in accordance with the general recommendations for onsite areas as per the RAW [AECOM, 2011a]. Mobilization and remediation activities began on July 25, 2011 and were completed on October 28, 2011. In general, onsite areas with impacted levels above the remedial clean up goals, presented on Table 2-1, were targeted for excavation. Figure 2-1 presents the initial clean up areas that were proposed for the site based upon the RI data. However, confirmation samples along the Site boundary indicated that in several areas cleanup goals were not achieved. Therefore, several excavations were extended beyond the Site boundary to remove soil with impacted concentrations exceeding these cleanup goals. In general, these excavations continued until removal would have required closing of the public right of way (i.e., Clinton Avenue or South E Street) or until private property was reached (i.e., across the alley). The extent and depth of the offsite excavations are shown on Figure 2-2. These areas are listed below and discussed in more detail in the following sections.

∑ Alley Area – Adjacent to Initial Excavation Areas 8 and 9 ∑ Offsite Arsenic Area – Adjacent to Initial Excavation Areas 1 and 2 ∑ Offsite TPH Area – Adjacent to Initial Excavation Areas 4 and 6 ∑ Other Offsite ROW areas – Adjacent to Initial Excavation Areas 7 and 8

During the excavation activities, confirmation soil samples were collected and submitted to American Environmental Testing Laboratory Inc. (AETL) for chemical analyses. In some cases, the PAH-impacted soil was found in visibly identifiable layers in the field, consisting of discolored soil which extended both laterally and vertically. Removal of the discolored soil generally resulted in removal of PAH-impacted soil. Therefore, in addition to the results of the previous investigations, the excavation was guided by visual observation. If a discrete discolored layer was observed during the excavation, the excavation was extended until the layer was removed. Upon obtaining satisfactory confirmation soil sample results, the excavation limits were terminated, and the excavation was backfilled with clean soil or sand/cement slurry, compacted, and restored. As shown in Figure 2-2, these excavations often extended from the original targeted excavation areas as specified in the RAW. Permits relating to additional offsite work are presented in Appendix B.

2.1.1 Alley Area

PAH-, lead-, and arsenic-impacted soil was removed from onsite Areas 8 and 9 in the eastern portion of the Site as well as within the Alley Area adjacent to the Site. The excavations were approximately 2 to 4 feet in depth and extended the entire length of the alley from 9th Street to Clinton Street. Approximately 658 tons of non-hazardous impacted soil and 1.46 tons of non RCRA hazardous soil were removed from the Alley Area. The Alley Area remedial excavations were completed in two sections discussed below.

2.1.1.1 Southern Alley Excavations

The southern alley excavations extended into the southern portion of the alley where soil discoloration was observed within the upper 1 foot of soil and where confirmation samples show contaminant concentrations above cleanup goals in the sidewall of the on-site excavation. The excavation terminated at or near the neighbor’s property line; however, residual impact in the soil was observed and soil samplings were collected. Elevated concentrations above action levels for PAHs, lead and arsenic were


found for selected soil samples within the eastern sidewall. Detailed analyses of soil concentrations in a sidewall dark layer indicate that the contamination present was not related to past MGP processes and most likely was from a past roadbed based upon forensic samples collected from this layer. Discussion of these forensic findings is included in Appendix C. Elevated lead concentrations were observed in the eastern sidewall, which were an order of magnitude higher than any concentrations of lead detected on Site. Based on visual inspection of the excavated soil in this layer, the forensics evaluation of this layer, and the higher concentrations of lead in this layer, it was determined that contaminants detected in this soil were not related to former MGP processes and arose from an offsite source. Detailed discussions of these findings are presented in Section 3.3.3.

2.1.1.2 Northern Alley Excavations

Excavation in the northern portion of the Alley was guided by the removal of identifiable layers of discolored soil as well as the removal of an abandoned clay pipe that was filled with discolored soil. Removal of the clay pipe is discussed further in Section 3.2.2.

2.1.2 Offsite Arsenic Area

Arsenic-impacted soil was removed from onsite Areas 1 and 2 in the northwestern portion of the Site. During the onsite excavation, confirmation samples from the sidewalls indicated that the arsenic extended offsite from these areas into the sidewalk areas along Clinton Street and South E Street. A letter work plan was submitted to and approved by DTSC to extend the investigation into the offsite ROW areas for further delineating the extent of offsite arsenic impact [AECOM, 2011e]. To delineate the arsenic extent in the ROW, additional hard auger borings, which are further discussed in Section 3.3.1.1, were installed in areas beyond the extent of the excavations. Prior to collecting the hand-auger samples, a City of Madera encroachment permit for drilling at Clinton St and South E Street was secured by AECOM and a copy of the permit is included in Appendix B. Figure 3-2 presents the additional hand auger locations. Excavations adjacent to the city streets were accomplished by stabilization of the excavation sidewalls using the ABC trench method (discussed further in Section 2.4.1.1). Approximately 877 tons of non-hazardous impacted soil and 11.6 tons of non RCRA hazardous soil were removed from the Offsite Arsenic Area.

2.1.3 Offsite TPH Area

TPH-impacted soil was removed from onsite Areas 4 and 6 and a portion of sidewalk area along South E Street in the western portion of the Site. Impacted soil was observed along an abandoned subsurface pipe that paralleled the property line along the western portion of the Site. Hand-auger samples (as discussed in Section 3.3.1.2) were collected within and beyond the excavation sidewalls to delineate the TPH-impact extent. Approximately 469 tons of non-hazardous impacted soil was removed from the Offsite TPH Area. The excavations adjacent to the city streets were accomplished by using the ABC trench method (discussed further in Section 2.4.2.1).

2.1.4 Other Offsite ROW Area

PAH-impacted soil was removed from onsite Areas 7 and 8. Confirmation sampling indicated that the PAH-impacted soil extended into the sidewalk areas along South E Street and 9th Street in the southern portion of the Site. The excavations performed adjacent to the city streets in these areas were accomplished by benching at a 1:1 (vertical to horizontal ratio) slope. Approximately 526 tons of non-hazardous impacted soil was removed from these excavations.

2.2 Preliminary Activities

Preliminary activities of the excavations included permitting, Site preparation, and the demolition/destruction of some Site features. Each of these subtasks is discussed in the following subsections.


2.2.1 Permitting

Prior to remediation, the remedial contractor (Pivox) obtained an encroachment permit for traffic control and temporary closure of the eastern alley and surrounding sidewalk areas, a grading permit, and a business license. Copies of the Erosion Control Plan and permits are included in Appendix B. Pivox also contacted Underground Services Alert of Northern California for underground utility locating services and Division of Occupational Safety & Health for excavation and trenching notification. An encroachment permit was obtained by AECOM to conduct additional drilling for delineating impacted areas along Clinton and South E Streets as previously discussed.

2.2.2 Site Preparation

Site preparation for the offsite remediation was conducted concurrently with onsite remediation activities and included the following:

∑ Marking underground utilities at the Site;

∑ Erecting temporary fencing and installing a visual barrier on the temporary and existing fence around the perimeter of the work area. A portion of the eastern and southern fence line was affixed with sound panels to mitigate the noise emissions.

∑ Setting up three air-monitoring stations around the work area, located in the northern, southern and eastern corners of the Site;

∑ Connecting a water meter to an offsite fire hydrant so that the water could be used for dust and odor control;

∑ Setting up access and egress paths for equipment;

∑ Mobilizing construction equipment to the Site;

∑ Installation of temporary power including power pole and electrical panel;

∑ Mobilizing a construction trailer, and connecting to the temporary power supply;

∑ Collecting 24-hour background air samples for PAH, lead, and arsenic analyses; and

∑ Setting up decontamination stations, work areas, and traffic control.

2.3 Site Demolition

Surface features at the Site, perimeter fencing were removed. Subsurface features encountered during the excavations included underground abandoned piping. Demolished and/or removed features are further discussed in Sections 2.3.1 and 2.3.2.

2.3.1 Fencing

To access offsite impacted soil, approximately 783 linear feet of 6-foot high chain-link fence were removed during remediation. Three rolling gates, one in the northern portion of the Site and two in the southern portion of the Site were also removed. The fence and gates were replaced during Site restoration activities. The removal and replacement of the fencing and gates are discussed further in the Onsite Closure Report [AECOM, 2012b].

2.3.2 MGP Related Pipes

During excavation activities in the western and eastern portions of the Site, a number of subsurface pipes were encountered. The western pipes appeared to be associated with conveyance of raw products on the western portion of the Site and the eastern pipes related to the gas holder and former MGP


operations located in that area. Approximately 220 linear feet of piping varying in diameter from 3 to 4 inches were removed.

∑ During excavation activities in the southern portion of the alley, an abandoned 3-inch diameter vitreous clay pipe was encountered approximately 2 feet bgs. The pipe was found to originate from onsite areas near Area 9 and extended to the center of the alley and northward to Clinton Street. The pipe was found to be filled with various stained soil and appeared to be abandoned once MGP Plant operations ceased. Soil samples collected at three locations along this pipe route determined that that infill soil within the pipe was Cal-hazardous and was removed and disposed of appropriately.

∑ A 4-inch diameter steel pipe was encountered in the western portion of Area 4 and extended offsite to the west. The pipe was found to be about 2 feet bgs and contained residual heavy oil. Excavations in the offsite area adjacent to Area 4 removed the pipe which was found to have a welded end cap. The pipe was included with steel waste material at the site and recycled.

2.4 Excavation and Backfill

2.4.1 Excavation Procedures

Impacted soil was typically removed from open excavations using an excavator or backhoe. The excavated soil was loaded directly onto trucks, or when necessary, temporarily stockpiled. At the end of the day, the remaining impacted soil stockpile, if any, was covered with visqueen sheeting. Where appropriate, impacted soil exposed in the open excavation area was covered with plastic sheeting at the end of the day to minimize potential emissions. The excavation adjacent to active subsurface utilities or adjacent to sensitive aboveground structures was conducted using a mini-excavator or accomplished by hand. The type of excavation equipment used is provided in the Onsite Closure Report [AECOM, 2012b].

Soil excavation during the remediation was conducted within the guidelines and specifications provided in the RDIP [AECOM, 2011c]. The procedures included the following:

∑ Prioritizing areas to be excavated to ensure that access and egress were available for other Site activities;

∑ Developing staging and access paths for equipment to be used during remediation;

∑ Selecting locations for stockpiles and developing loading procedures;

∑ Developing dust and odor control procedures to be used at each excavation area;

∑ Identifying locations for air monitoring stations in addition to the perimeter air monitoring stations; and,

∑ Pre-planning sequencing of slot trenches for stabilization of temporary excavations near streets and structures.

Aggressive dust and odor control measures were applied throughout the remediation period. Upon completion of the excavation, confirmation soil samples were collected and analyzed. If it was determined that further excavation was required, then additional soil was excavated and additional confirmation samples were collected and analyzed. Section 3.0 of this Report provides a detailed discussion of confirmation sampling results.

Petroleum hydrocarbon odors were encountered during excavation in a number of offsite ROW areas around the Site, predominantly in the western TPH area. As planned, extra efforts were implemented to control and monitor the emission of vapors. Odex©, a highly concentrated odor suppressant made by Kuma Corporation, was mixed into the water truck and constantly applied to the soil during excavation using a fire hose and/or a garden hose. Additional odor suppressant application included the addition of Simple Green® additives to the water truck. In some cases, soil with a petroleum odor was directly


loaded into trucks for immediate offsite disposal. The excavation was monitored using a photoionization detector (PID) to confirm that VOC concentrations in the worker breathing zone did not exceed action levels set in the Health and Safety Plan.

Excavation sidewalls greater than 4 feet bgs were sloped or benched at a minimum of 1:1 (horizontal to vertical) slope. Prior to backfilling, the completed excavation areas were inspected by Moore Twinning Associates (MTA), an independent geotechnical and soil engineering firm located in Fresno, California. The responsibilities of MTA included:

∑ Observing the bottom of the excavations to verify that the loosened soil was removed and approving placement of the imported fill;

∑ Conducting compaction tests in accordance with applicable American Society for Testing and Materials (ASTM) methods; and,

∑ Selecting the number, location, and depth of field density tests.

2.4.1.1 ABC Trenching

Several areas were excavated using the ABC trenching method including sensitive areas such as along the streets. As part of this method, each trench was excavated to approximately three to six feet wide and as much as 16feet deep. All trenches were parallel to each other. Excavation started with the first trench designated as “A”. After removal of the impacted soil to the desired depth, confirmation samples were collected from the bottom and the sides and the trench was backfilled with two-sack cement slurry. Then, the second “A” trench (normally six to 12 feet away from the first “A” trench) was excavated and backfilled, as discussed before. Excavation of “B” trenches started after the backfill in the adjacent “A” trench had solidified overnight. Then the excavation of “C” trenches continued accordingly. The ABC trenching method proved to be very effective in areas where deeper excavation was required adjacent to the streets, beneath the gas regulator station and at the deeper TPH-impacted area, where sloping of the excavation was not possible. Use of the two-sack cement slurry eliminated the necessity of compaction of the backfill material; however, the solidified cement slurry backfill is considered rippable if removal is required in the future for other construction purposes. In addition, ABC trenching method helped prevent the collapse of the excavations.

2.4.2 Loading of Soil

Excavated soil was typically either loaded directly into trucks or temporarily stockpiled in a designated area by an excavator and/or loader. Stockpiled soil was loaded into end-dump trucks primarily with a loader and in some cases an excavator.

Soil stockpiles were periodically sprayed with water. The temporary soil stockpiles that remained onsite overnight were covered with visqueen sheeting at the end of each workday. Soil excavation and loading operations were conducted in a manner to reduce the volume of stockpiles remaining overnight.

Excavated PAH-, TPH-, VOC-, arsenic-, and lead-impacted offsite soil that was classified as non-hazardous was profiled and transported, under California non-hazardous waste manifests, to Forward Landfill. A total of approximately 2,530 tons of offsite soil was transported to the Forward Landfill for disposal. Copies of the job summaries, manifests and the weighmaster certificates are included in the Onsite Closure Report [AECOM, 2012b].

Excavated lead impacted soil that was classified as non-RCRA hazardous waste was profiled and transported, under hazardous waste manifests to Clean Harbors Class I Landfill. A total of approximately 13 tons of offsite soil was transported to Clean Harbors. Copies of the manifests and the weighmaster certificates are included in the Onsite Closure Report [AECOM, 2012b].


2.4.3 Backfill and Compaction

Following the completion of excavation and the testing of confirmation samples, the excavation areas were backfilled with slurry or soil. The soil backfill consisted of imported crushed quarry fines from Cemex Quarry, located in Friant, California. Weighmaster certificates for imported soil are included in the Onsite Closure Report [AECOM, 2012b]. Clean backfill was placed within the excavation directly from the transport trucks. As discussed later, the backfill soil was sampled and analyzed prior to placing it into the excavation. The backfill soil was spread and compacted using the front-end loader or compaction wheel attached to the excavator. Water was applied to the backfill using handheld hoses or the water truck during compaction.

Compaction testing was performed periodically by MTA, at locations and depths selected by MTA. The compaction tests met backfill densities of 90 percent or better and 95 percent or better in the upper 1 foot beneath the driveway approaches and alleyway. A total of 202 compaction tests were performed on the import soil for onsite and offsite ROW areas. Copies of the compaction test results are included in the Onsite Closure Report [AECOM, 2012b]. A total of approximately 747 cubic yards of sand-cement slurry and 1,115 tons of clean backfill soil were placed in the excavation during the remediation.

Additional information on the backfill materials and procedures are provided in the Onsite Closure Report [AECOM, 2012b].

2.5 Environmental Control

Safety and protection of the general public and the environment were given the highest priority when performing the remedial activities. The environmental measures implemented at the Site included the following:

∑ Implementation of the Site-Specific Health and Safety Plan;

∑ Noise monitoring and control,

∑ Dust monitoring and control;

∑ Air emissions monitoring and control, and

∑ Traffic Control

Data generated as a result of the implementation of the above measures were recorded daily. Additional information on each of these measures is provided in the Onsite Closure Report [AECOM, 2012b]. Copies of the daily field logs, tailgate safety meetings, and dust and air emission monitoring records are kept on file at the AECOM office in Oakland, California, Pivox Corporation office in Irvine, California and at PG&E’s office in San Ramon, California.

2.6 Restoration

After fill placement and compaction, the restoration was completed by grading the fill area to 6-inches minus previous existing grade. Six inches of Class II aggregate base, imported from San Joaquin Sand and Gravel, was placed and compacted to better than 90% compaction. A total of approximately 275 tons of Class II aggregate base was placed in the offsite ROW areas. Asphalt pavement section was placed in the southern portion of the alley that consisted of 4-inches of asphalt over 6-inches of Class II aggregate base. The final grade generally matched the original ground level at the Site. Weighmaster certificates for the imported aggregate are presented in the Onsite Closure Report [AECOM, 2012b].


2.7 Summary of Material Quantities Related to Offsite Work

Quantities from offsite ROW areas of the impacted soil exported from the Site, clean backfill imported to the Site, cement slurry used at the Site, and recycled waste materials (asphalt and concrete) exported from the Site are listed in the table below.

Material Quantities

Description Source/Destination Approximate Quantity

Total Non-Hazardous Exported Soil – Alley Area Forward Landfill in Manteca, CA 658 tons

Total Non-Hazardous Exported Soil – Offsite Arsenic Area Forward Landfill in Manteca, CA 877 tons

Total Non-Hazardous Exported Soil –Off site TPH Area Forward Landfill in Manteca, CA 469 tons

Total Non-Hazardous Exported Soil – Other Off site ROW Areas Forward Landfill in Manteca, CA 526 tons

Total Non RCRA-Hazardous Exported Soil – Alley Clean Harbors, LLC in Buttonwillow, CA 1.46 tons

Total Non RCRA-Hazardous Exported Soil – Offsite Arsenic Area

Clean Harbors, LLC in Buttonwillow, CA 11.6 tons

Imported Soil Cemex Quarry in Friant, CA 1,115 tons

Imported Class II Aggregate Base San Joaquin Sand and Gravel in Madera, CA 275 tons

2-Sack Cement-Sand Slurry – Offsite TPH Area Builders Concrete, Inc. in Fresno, CA 300 cubic yards

2-Sack Cement –Sand Slurry – Offsite Arsenic Area Builders Concrete, Inc. in Fresno, CA 447 cubic yards

Exported Recyclable Waste (asphalt )

Triangle Rock Products, Inc. in Madera, CA (asphalt) San Joaquin Sand and Gravel in Madera, CA

40 tons


3.0 Offsite Confirmation Sampling and Analyses

3.1 Introduction

The overall remedial action objective for the Site was to minimize potential future exposure of humans (onsite workers, residents and visitors) to CPAHs, TPH, naphthalene, benzene, ethylbenzene, acenaphthene, benzo(g,h,i)perylene, fluoranthene, pyrene, lead, and arsenic in soil through inhalation, dermal absorption and/or ingestion. The remedial goal was to reduce the residual concentrations of contaminants at the Site to levels that would require no land use restrictions (i.e., to a point that the area could be used for hypothetical, future residential purposes).

During the course of the onsite remediation, offsite ROW areas to the north, south, west and east of the Site were also remediated. A summary of onsite remediation was submitted under a separate cover. This report focuses on the offsite ROW areas.

Following excavation, confirmation soil samples were collected and analyzed for PAHs, metals and select samples were also analyzed for TPH, VOCs and cyanide. The concentrations of CPAHs were converted into B(a)P equivalent concentrations using the potency equivalency factors shown in the table below.

Factors to Calculate CPAH expressed in Benzo(a)Pyrene Equivalent Concentration

Compound Potency Equivalency Factor(a)

Benzo(a)pyrene 1.0

Benzo(a)anthracene 0.1

Benzo(b)fluoranthene 0.1

Benzo(k)fluoranthene 0.1

Chrysene 0.01

Dibenzo(a,h)anthracene 0.34

Indeno(1,2,3-c,d)pyrene 0.1

(a) Cal/EPA, 1994a Appendix 1 The results obtained from the offsite remediation confirmation sampling, combined with previous offsite soil sampling results representing the in-place offsite soil were compared to remedial cleanup goals and used to assess the residual risk to future offsite intrusive workers working in ROW areas.

3.2 Summary of Excavation Activities

A combination of previous soil analytical results and visual observations during remediation were used to direct the excavations at the Site. In areas where confirmation samples detected elevated results or visual observations showed impacted soil extending beyond the excavated area, the area was further excavated, if possible, and additional confirmation samples were collected. Planned excavations extended in some areas beyond what was originally proposed in the RAW [AECOM, April 2011a] to include offsite ROW areas. The Onsite Closure Report describes the excavation activities on site and some of these details are described below.

Figures 2-1 and 2-2 present the planned and actual excavated areas, respectively. Figure 2-2 also presents depth contours of the excavation including the offsite excavations, and Figure 1-4 shows the


locations of the onsite and offsite confirmation soil samples and the samples collected during previous Site investigations. Figure 3-1 shows the location, depth, B(a)P equivalent, select VOC, TPH, arsenic and lead concentrations for samples representing offsite soil left in-place following remediation.

Figures 3-2 and 3-3 show the residual concentrations of arsenic and TPH above cleanup goals and extent of impacted soils in the offsite ROW areas of interest to the HHRA. In general, the area in the ROW at the intersection of South E Street and Clinton Avenue had concentrations of arsenic exceeding the cleanup goal for unrestricted use. In addition, an area along South E Street had concentration of TPH exceeding the cleanup goal established in the RAW.

3.3 Confirmation Sampling and Analyses

The primary objective of the confirmation sampling program was to characterize the residual levels of PAHs, arsenic, lead, TPH, and VOCs that remain on and off site. Confirmation sampling was conducted in general accordance with the approved RAW [AECOM, 2011a] and the Post-Remediation Soil Gas Work Plan [AECOM, 2012a]. These documents describe the protocol and specifications for sample collection, processing, detection limits, holding times and appropriate documentation.

The confirmation soil sampling program was comprised of a systematic triangular grid sampling pattern for samples to be collected from the bottom of the excavation. For collection of an adequate number of samples for the Site, the spacing between the sampling points was approximately 30 feet. The triangular grid was supplemented, as necessary, to obtain adequate coverage from the bottom of each excavation area. Excavation sidewall samples were collected at horizontal intervals of approximately 20 to 30 feet to confirm that the horizontal boundaries of the impacted soil had been adequately defined and removed. At each wall locations, several depth intervals were collected to facilitate targeted waste removal.

Soil samples from the bottom of the excavation areas were generally collected by the direct insertion of laboratory-supplied, 4-ounce glass sample jars into the soil. When necessary, the soil was first slightly dislodged with a decontaminated shovel, hand-auger or excavator bucket.

Excavation sidewall samples were collected by methods utilizing either decontaminated shovel, hand-auger or excavator bucket. In areas with no remaining evidence of impacted soil, sidewall samples for PAH analyses were collected by direct insertion into laboratory-supplied 4-ounce glass jars, along a typically 1.5-foot interval of the exposed excavation sidewall. In this report, these samples are referred to as interval samples. This process was repeated to sample the entire vertical interval of the sidewall. For example, if the depth of the excavation was 5 feet, three interval samples were collected from the sidewall to represent the top 2 feet, the middle 2 to 3.5 feet and the lower 3.5 to 5-foot intervals. In areas that a discolored layer had existed and was subsequently removed, a discrete sample was also collected at the same depth from the sidewall, in addition to the interval samples.

Sample jars were filled fully with soil and sealed with threaded, Teflon®-lined lids. The samples were appropriately labeled, placed in re-sealable plastic bags, and stored on ice in a cooler until being delivered to the analytical laboratory.

Soil samples for VOC analysis were collected from the undisturbed soil in accordance with USEPA SW-846, Method 5035. An EasyDraw Syringe™ and PowerStop Handle™ were used to collect 5-gram soil cores which were transferred to pre-weighed 40 milliliter VOA vials in the field. Four soil cores were collected at each sample location; two were placed in VOA vials preserved with sodium bisulfate for potentially low level (200 µg/kg) VOC analysis, and one was placed in a blank VOA vial with no preservative for either low level or high level analysis as needed by the laboratory. A new EasyDraw Syringe™ was used at each sample location and discarded after each sample had been collected.


Soil samples collected from the offsite ROW areas were labeled and submitted under chain of custody to AETL, a California-certified analytical laboratory based in Burbank, California. Copies of the analytical laboratory reports for confirmation soil samples and the Quality Assurance Summary Report (QASR) are provided in the Onsite Closure Report [AECOM, 2012b].

Confirmation soil samples collected from the Site were analyzed for PAHs by USEPA Method 8310 and metals by USEPA 6010B. The results of offsite confirmation sample analyses for PAHs are reported in B(a)P equivalent concentrations and are listed in Table 3-1. Samples from selected areas, including the former wastewater pit were analyzed for TPH by USEPA Method 8015 (modified) and VOCs including benzene, toluene, ethylene, and xylenes (BTEX) by USEPA Method 8260B. In addition, in areas that PID measurements were recorded and/or hydrocarbon odors were detected, additional samples were collected for VOC and TPH analysis. The TPH and VOCs results are summarized in Table 3-2. Analytical results for metals including arsenic and lead analyses are summarized in Table 3-3.

3.3.1 Additional Offsite Investigations

During the completion of the soil excavation activities, additional drilling and hand augering was required to determine extent of contamination in the offsite ROW areas. Prior to advancing the hand auger borings, an encroachment permit was obtained by AECOM from the City of Madera. These investigations are described below:

3.3.1.1 Arsenic Area Investigation

A total of 31 hand auger borings were advanced to depths up to 5 feet bgs to collect soil samples in South E Street and Clinton Street. Due to the weathered nature of the asphalt in these streets, asphalt was removed using a heavy steel bar in about a 5-inch diameter circular area for each boring. Soil samples were collected from a clean stainless steel hand auger bit. Soil was directly placed into clean laboratory supplied 4-oz glass jars and analyzed for total arsenic. The borings were backfilled with a concrete mix and the surface was dyed to match the surrounding asphalt pavement.

3.3.1.2 TPH Area Investigation

A total of 4 hand auger borings were advanced to depths up to 16.5 feet bgs to collect soil samples in South E Street in the TPH stained area. Due to the weathered nature of the asphalt in these streets, asphalt was removed using a heavy steel bar in about a 5-inch diameter circular area for each boring. Soil samples were collected from a clean stainless steel hand auger bit. Soil was directly placed into clean laboratory supplied 4-oz glass jars and analyzed for TPH-gas/diesel/heavy hydrocarbons. The borings were backfilled with a concrete mix and the surface was dyed to match the surrounding asphalt pavement.

3.3.2 Abandoned Pipe in Alley

A 3-inch diameter clay pipe was discovered approximately 2 feet bgs while excavating soil in the alley. The pipe was full of a mixture of clean and stained soil. Soil samples were collected from the end of the pipe using a clean stainless steel spade and placed in clean laboratory-supplied, 4-ounce glass jars. A pothole trench was excavated by Pivox laborers in the alley at the alley terminus with Clinton Street to locate the pipe. The pipe was uncovered at about 2 feet bgs. A small hole was opened in the top of pipe and found to be partially filled with soil. A soil sample was collected and placed in a 4-ounce glass jar. Soil samples from the pipe were submitted to the laboratory and analyzed for PAHs and Metals. The pipe was removed from the alley and transported as Cal-hazardous material to Clean Harbors. The remainder of the soil was removed from the pipe by hand-augering horizontally approximately 10 feet laterally where the pipe apparently terminated on another subsurface utility. The pipe was removed from the alley and capped at the curbside of Clinton Street. Capping of the pipe was witnessed by the city of Madera inspector.


3.3.3 Results

The following sections summarize the results from the investigation/confirmation samples collected in the offsite ROW areas.

3.3.3.1 PAHs

Offsite concentrations of B(a)P equivalents in ROW areas ranged from non-detect to 1.131 mg/kg. Only one sample, V-A4-W10-2-3.5, had concentration of B(a)P detected that slightly exceeded the cleanup goal of 0.9 mg/kg B(a)P equivalents. The samples collected along South E Street and Clinton Avenue were used in the offsite HHRA described in Section 4.

In addition to the samples collected in the ROW, six wall samples (locations V-C1-W10 through V-C1-W12) were collected from a layer in the excavation wall along the alley at the neighboring property line which had concentrations of CPAH exceeding clean up goals for CPAHs. These six samples ranged from 1.403 to 55.4 mg/kg. However, it should be noted that split samples from these locations were sent for forensic analysis. These forensic samples suggest that the soil in this layer is related to a previous road bed and not to former MGP activities (Appendix C). Therefore, the concentration of PAHs from this area were not used in the offsite HHRA.

3.3.3.2 Metals

Arsenic and lead were the primary metal COCs. Arsenic was detected in confirmation samples in the ROW at concentrations ranging from non-detect to 87.2 mg/kg with 19 samples exceeding the cleanup goal of 16 mg/kg arsenic. The samples exceeding the 16-mg/kg arsenic criterion are primarily located along the edge of the excavation that borders South E Street and Clinton Avenue.

Additional arsenic samples were collected via hand auger along South E Street and Clinton Avenue as shown on Figure 3-2. Concentrations of arsenic in these samples ranged from non-detect to 56.9 mg/kg arsenic with 14 samples exceeding the arsenic cleanup goal of 16 mg/kg. Arsenic concentrations in this area are above the criteria for unrestricted use.

Lead concentrations in the ROW ranged from non-detect to 13.3 mg/kg well below the 150 mg/kg cleanup goal. Additional lead samples were collected from the side wall of the excavation of the alley along the neighboring property line (locations V-C1-W10 through V-C1-W12 and V-C2-W5 through V-C2-W10). These concentrations ranged from an estimated detection of 3.08 to 54,000 mg/kg lead. Nine of the samples from this area exceeded the clean up goal for lead. However, these samples appear to be on the neighboring property and do not appear to be mixed with MGP products. Moreover this samples have concentrations of lead that are up to an order of magnitude higher than any concentrations detected on site indicating that they are not related to the site activities.

Additionally, several samples collected from the alley excavation wall from the side wall of the excavation of the alley along the neighboring property line were analyzed for arsenic (locations V-C1-W10 through V-C1-W12, V-C2-W5, V-C2-W6, and V-C2-W10). These concentrations are collocated with lead samples that appear to unrelated to the site. Concentrations of arsenic in this area ranged from non-detect to 288 mg/kg with 7 samples exceeding the arsenic cleanup goal of 16 mg/kg.

Concentrations of lead and arsenic from the Alley Area were not used in the HHRA discussed in Section 4 as this soil appears unrelated to site activities.

3.3.3.3 VOCs

In general, samples collected in the ROW that were analyzed for VOCs were non-detect for all constituents. However, one set of sample (locations V-C1-W10 through V-C1-W12) collected from a layer in the excavation wall along the alley at the neighboring property line had detectable concentrations of benzene ranging from an estimated detection of 1.71 to 11.6 µg/kg. These samples are collocated with


PAH materials that appear to be unrelated to MGP activities. Therefore, these samples were not used in the HHRA.

3.3.3.4 TPH

Total TPH as diesel and gasoline was detected in confirmation samples in the ROW at concentrations ranging from non-detect to 10,300 mg/kg with 6 samples exceeding the cleanup target of 4,000 mg/kg TPH. The samples exceeding the 4,000-mg/kg TPH criterion are primarily located along the edge of the excavation that borders South E Street in the vicinity of a pipeline that appeared to connect the MGP operation with the rail service.

Additional TPH samples were collected via hand auger along South E Street as shown on Figure 3-3. Concentrations of TPH in these samples ranged from non-detect to 6,170 mg/kg TPH with 1 sample exceeding the TPH cleanup target of 4,000 mg/kg.

3.3.4 Risk-Based Evaluation of Offsite Confirmation Samples

As discussed in Section 3.3.3, residual concentrations of PAHs, arsenic, lead, and VOCs in offsite ROW areas were below their respective cleanup goals with the exception of arsenic in soils in South E Street and Clinton Street as shown on Figure 3-2. Further, residual concentration of TPH in offsite ROW areas were below the target cleanup level of 4,000 mg/kg with the exception of concentrations in soils in South E Street as shown on Figure 3-3. As such, remediation activities have been successful in attaining the remedial action goals for the majority of chemicals in the offsite area. However, residual levels of arsenic remain in offsite soils above the respective cleanup goal established to reduce the residual arsenic concentrations to ambient levels. Note that the level of arsenic developed in the HHRA for the protection of a hypothetical future commercial population is the same level as that developed for the protection of a hypothetical future residential population; i.e. ambient level. As such, soils within the offsite arsenic area are not suitable for future residential or commercial land use and would require some form of risk management such as capping and following the guidance in the Soil Management Plan [AECOM, 2012c]. Furthermore, soils with TPH above the target cleanup level would require some form of risk management. A post-remediation Human Health Risk Assessment, as presented in Section 4.0 of this Report, was conducted by Iris Environmental using the analytical results of the samples representing the in-place soil at the offsite arsenic and TPH areas to confirm that impacted soils remaining in the offsite ROW area along Clinton Avenue and South E Street would not adversely impact human health under the current land use.


4.0 Post Remediation Health Risk Assessment

4.1 Introduction and Objectives

This section of the report describes the post-remediation human health risk assessment (HHRA) conducted to confirm that impacted soils remaining in the offsite ROW (i.e., the offsite arsenic and TPH areas along Clinton Avenue and South E Street discussed in previous sections) would not adversely impact human health.

As stated in the RAW [AECOM, 2011a], the overall remedial action objective for the Site was to minimize potential future exposure of humans (such as Site workers, hypothetical residents, and visitors) to the chemicals of potential concern (COPCs) via inhalation, dermal absorption and/or ingestion. Specifically, the removal action goal is to remediate to the point that minimizes the need for any future land use restrictions, to the extent feasible and practicable. To meet the stated remedial objectives, remedial activities were focused on reducing the concentrations of COPCs present in soils at the Site to levels that would be protective of potential future onsite residential land use, and accordingly, protective of all future land uses. Onsite remediation extended beyond the boundaries of the Site into the adjacent offsite public ROW to the extent feasible and practicable to remove impacted soil above the numerical remedial goals set forth in the RAW (AECOM, 2011.

As discussed previously in Section 3.3.3, concentrations of COPCs in in-place confirmation and previous investigation soil samples representative of offsite soil in the adjacent public ROWs were below their respective numerical remedial goals set forth in the RAW [AECOM, 2011a] with the exceptions of in-place samples representative of offsite soil in the (offsite ROW area). Concentrations of primarily arsenic 1in in-place samples representative of offsite ROW area soil were above the initial remediation target of 16 mg/kg set forth in the RAW [AECOM, 2011a], developed for the protection of future residential population. Note that the level of arsenic developed in the HHRA for the protection of future commercial populations is the same level as that developed for the protection of future residential populations; i.e. ambient levels. As such, soils with arsenic concentrations in the offsite ROW area above the initial remediation target would not be suitable for residential or commercial land use and would require some form of risk management such as capping and following the guidance provided in the Soil Management Plan [AECOM, 2012c]. It should be noted that although concentrations of TPH in the offsite ROW area also are present in soils in excess of their remedial goal, this goal is not risk-based. Thus, exceeding this goal is not considered to represent a health risk to current or future site receptors.

It is highly unlikely that the offsite ROW area along Clinton and South E Street will change from its current use as a street. In order to confirm that impacted soils remaining in the offsite ROW area along Clinton Avenue and South E Street would not adversely the health of populations who would be most likely to come into contact with these soils, this post-remediation HHRA evaluates risks to workers who could potentially become exposed to these soils (i.e., a worker who may be involved in a one-time subsurface digging activity).

Additionally, concentrations of select COPCs in in-place confirmation soil samples representative of offsite soil in the adjacent property to the east of the Site were above their respective numerical cleanup goals set forth in the RAW [AECOM, 2011a]. However, as previously discussed, impacted soils at the 1 CPAH in only one sample, V-A4-W10-2-3.5, with a B(a)P equivalents of 1.1 mg/kg slightly exceeded the initial remediation target of 0.9 mg/kg (expressed in B(a)P equivalents). However, this concentration is with the range of concentrations in the CPAH background study dataset for Northern California urban soils.


adjacent property to the east of the alley are not related to the former MGP operations at the Site and therefore are not addressed in this report.

Therefore, to confirm that impacted soils remaining in the offsite ROW area would not adversely impact human health, the post-remediation risk assessment is conducted to:

∑ Confirm that soil remediation efforts have effectively reduced the concentrations of CPAH in the offsite ROW area to concentrations that are similar to ambient concentrations and therefore, would be protective of potential receptor populations under all land uses, including intrusive worker populations 2;

∑ Confirm that the cumulative cancer risks posed by all other residual chemicals posed by all other residual chemicals and noncancer hazards posed by all residual chemicals remaining in offsite ROW area soil are acceptable and protective of intrusive worker populations.

The post-remediation HHRA is conducted in a manner consistent with the approach set forth in the RAW, and in accordance with State and Federal risk assessment guidance documents.

The remaining sections of the post-remediation HHRA are organized according to the typical steps in a risk assessment, as outlined below.

∑ Section 4.2 summarizes the analytical data and chemicals included in the post-remediation HHRA;

∑ Section 4.3 presents the exposure assessment, including the identification of the potentially exposed populations, the specific pathways through which populations could become exposed to chemicals in soil and air, and the magnitude of the potential chemical exposures;

∑ Section 4.4 presents the toxicity values used in the calculation of the incremental cancer risks and noncancer hazard indices. Section 4.4 also presents the methodology for evaluating health effects associated with the lead detected in soil;

∑ Section 4.5 presents a comparison of the residual levels of CPAHs remaining in offsite ROW area soil to ambient concentrations, as well as a characterization of residual risks associated with all other chemicals remaining in offsite ROW area soil.

4.2 Data Evaluation and Selection of Chemicals of Potential Concern

This section discusses the environmental data evaluated for use in the post-remediation HHRA and the methodology used to select COPCs for inclusion in the post-remediation HHRA.

2 The B(a)P equivalent concentration in only one out of 42 samples representative of offsite ROW area soils in the top 10 feet was slightly above the initial remediation target of 0.9 mg/kg (i.e., 1.1 mg/kg in V-A4-W10-2-3.5), but within the range of concentrations included in the Northern California CPAH ambient dataset (i.e., the maximum concentration of 2.8 mg/kg). The next highest B(a)P equivalent concentration representative of offsite ROW area soil is 0.23 mg/kg which is below the 95% UCL of the mean of the Northern California CPAH ambient dataset of 0.40 mg/kg. Therefore, concentrations of CPAH in the offsite ROW area are compared to concentrations in the ambient dataset to confirm that concentrations of CPAH in off-site ROW area soil are similar to ambient concentrations.


4.2.1 Data Evaluation

The analytical results for all samples representative of soil remaining in the offsite ROW area following the implementation of the remedial activities that are used in the post-remediation HHRA (i.e., samples from locations and/or depths that have not been remediated), are presented in Tables 3-1 through 3-3. This includes data obtained during the RI/HHRA [MSE/AECOM Team, 2008] and post-remediation confirmation sampling. In summary, all soil analytical results considered representative of post-remedial conditions in the offsite ROW area are used in the quantitative post-remediation HHRA. A list of samples considered to be representative of post-remedial conditions in the offsite ROW area that are included in the quantitative post-remediation HHRA is provided in Appendix D.

Overall, the depths of the remedial excavations conducted in the offsite ROW area ranged from 2 feet bgs to 16 feet bgs. Intrusive subsurface work in the offsite ROW area such as repair or maintenance of underground utilities would likely not extend beyond the top 10 feet of soil. As such and to be consistent the general assumption of the depth of soil that could potentially be brought up and mixed with surface soils during site development, all offsite ROW area soil samples remaining in-place down to a depth of 10 feet bgs are considered in the dataset used to evaluate direct exposures to soils that

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