FINAL INDOOR AIR / VAPOR INTRUSION ASSESSMENT FOR SILRESIM SUPERFUND SITE Lowell, Massachusetts

December 2004

Contract Number: DACW33-03-D-0006 Task Order 3

Prepared by: Tetra Tech FW, Inc. 133 Federal Street Boston, MA 02110

Submitted by Tetra Tech FW, Inc. on Behalf of: Jacobs – Tetra Tech FW Joint Venture 2 Center Plaza Boston, MA 02108-1906

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TABLE OF CONTENTS

1.0 INTRODUCTION...........................................................................................................................1-1 1.1 Objectives ........................................................................................................................1-1 1.2 Report Organization.........................................................................................................1-2

2.0 BACKGROUND ............................................................................................................................2-1 2.1 Description of the Source and Pertinent Site Features....................................................2-1 2.2 Prior Air Sampling and Assessments of Volatile Contaminant Migration ........................2-2

2.2.1 Air Surveys..........................................................................................................2-2 2.2.2 Results of the Prior Risk Assessments...............................................................2-3

2.2.2.1 Results for the Administration Building Basement ..............................2-4 2.2.2.2 Results for the Operations Building Basement....................................2-5 2.2.2.3 Results for the Operations Building First Floor....................................2-6

2.2.3 Recommendations from the Previous Risk Assessments ..................................2-7

3.0 RECENT REGULATORY DEVELOPMENTS...............................................................................3-1 3.1 MADEP’s Indoor Air Sampling and Evaluation Guide .....................................................3-1 3.2 EPA’s Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway

from Groundwater and Soils (Subsurface Vapor Intrusion Guidance) ............................3-2

4.0 CURRENT PERSPECTIVES ON VAPOR INTRUSION ASSESSMENT .....................................4-1 4.1 Recent Developments......................................................................................................4-1 4.2 Comparison of the Currently Recommended Vapor Intrusion Evaluation

Approach to Existing Analyses for the Silresim Site ........................................................4-3

5.0 SITE-SPECIFIC APPLICATION OF EPA SUBSURFACE VAPOR INTRUSION GUIDANCE.....5-1 5.1 Tier 1 – Primary Screening ..............................................................................................5-1 5.2 Tier II – Secondary Screening .........................................................................................5-5 5.3 Tertiary Screening Tier III – Site-Specific Assessment..................................................5-16

6.0 SUMMARY AND RECOMMENDATIONS.....................................................................................6-1 6.1 Existing Site Inhalation Evaluations .................................................................................6-1 6.2 EPA Subsurface Vapor Intrusion Results ........................................................................6-1

6.2.1 Primary Screening ..............................................................................................6-1 6.2.2 Secondary Screening..........................................................................................6-2 6.2.3 Tertiary Screening...............................................................................................6-3 6.2.4 Overall Results....................................................................................................6-3

6.3 Recommendations ...........................................................................................................6-3

7.0 REFERENCES..............................................................................................................................7-1

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LIST OF TABLES

Table 2-1

Table 2-2

Table 5-1

Table 5-2

Table 5-3

Calculated Carcinogenic Risk and Non-Carcinogenic Hazard Indices for the Indoor Air Exposure Pathway for Areas Within the Operations and Administration Buildings...........................................................................................................................2-5

Comparison of the Maximum Detected COC Concentrations in the Indoor Air of the Operations Building Basement and First Floor (April 17, 2002 Sampling Event) ...............................................................................................................................2-6

Principal Volatile Compounds Detected in Groundwater at the Silresim Site and Their Henry’s Law Constants...........................................................................................5-2

Summary of Vapor Screening..........................................................................................5-8

Groundwater VOC Concentrations ................................................................................5-12

LIST OF FIGURES

Figure 2-1

Figure 5-1

Figure 5-2

General Schematic of the Key Components of the Vapor Intrusion Exposure Pathway Associated with the Silresim Superfund Site and the Adjacent Lowell Iron and Steel Facility ......................................................................................................2-2

Shallow Groundwater Total Volatiles 100-Foot Footprints ..............................................5-4

100-Foot Monitoring Well Footprints..............................................................................5-10

LIST OF APPENDICES

Appendix A Selected EPA Subsurface Vapor Intrusion Guidance Tables and Figures

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ACRONYMS AND ABBREVIATIONS

BAV Baseline Assessment Value BTEX benzene, toluene, ethyl benzene, and xylene BWSC Bureau of Waste Site Cleanup COCs contaminants of concern CSM conceptual site model CT Central Tendency CUGs cleanup goals DQO Data Quality Objective EI Environmental Indicator EPA U.S. Environmental Protection Agency ERH Electrical Resistance Heating Guidance EPA Subsurface Vapor Intrusion Guidance GWTP groundwater treatment plant LIS Lowell Iron & Steel MADEP Massachusetts Department of Environmental Protection MCP Massachusetts Contingency Plan mg/Kg milligrams per kilogram NAPL non-aqueous phase liquid NIOSH National Institute for Occupational Safety and Health OSHA Occupational Safety and Health Administration OSWER Office of Solid Waste and Emergency Response ppbv parts per billion by volume QA/QC quality assurance and quality control QAPP Quality Assurance Project Plan RAGS Risk Assessment Guidance for Superfund RI Remedial Investigation RME Reasonable Maximum Exposure SVOCs semi-volatile organic compounds TCE trichloroethene TERC Total Environmental Restoration Contract TtFW Tetra Tech FW, Inc. TVO total volatile organic ug/L micrograms per liter USACE U.S. Army Corps of Engineers VOC volatile organic compounds

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1.0 INTRODUCTION

Tetra Tech FW, Inc. (TtFW), formerly known as Foster Wheeler Environmental, has prepared this technical memorandum for the Silresim Superfund Site (the Site) under Task Order No. 03 of the U.S. Army Corps of Engineers (USACE) Total Environmental Restoration Contract (TERC) No. DACW33-03-D-0006.

In recent years, the intrusion of volatile organic vapors into buildings located on or near hazardous waste sites (including Superfund Sites), and the associated risks to human health, have received increased regulatory scrutiny. This issue has recently been examined by both the U.S. Environmental Protection Agency (EPA) and the Massachusetts Department of Environmental Protection (MADEP). It is now recognized that at certain hazardous waste sites, this contaminant migration route may, in fact, be an important contributor to overall site risk concerns. At the Silresim Site, high residual concentrations of volatile contaminants in site environmental media continue to raise certain current and future site use questions regarding vapor intrusion.

This memorandum summarizes the principal results and risk implications of indoor air analyses conducted, to date, at the Silresim Site. This memorandum subsequently presents the results of a detailed examination of the vapor intrusion migration and exposure pathway evaluation for the Site, developed in accordance with the recent Draft EPA Subsurface Vapor Intrusion Guidance (Guidance).

1.1 Objectives

The principal objective of this work effort has been to perform an evaluation of the vapor intrusion migration and exposure pathway and the potential health impacts associated with the inhalation of volatile organic compounds (VOCs) in indoor air that may have originated in subsurface contamination from the Silresim Site. This memorandum has been developed to assist the USACE, EPA, and MADEP in assessing vapor migration and intrusion at the Silresim Site and to evaluate the potential impacts on overall site remediation decisions and activities.

The specific technical objectives of this memorandum are as follows:

• To summarize the overall rationale and basis for existing vapor migration concerns at Silresim; • To assess the results of existing indoor air analyses and their implications regarding current

human health risks; • To consider the existing Silresim indoor air/vapor migration database in terms of recent EPA and

MADEP Vapor Intrusion Guidance; • To formally evaluate the Silresim Site in terms of the recent EPA Subsurface Vapor Intrusion

Guidance; and • To develop recommendations regarding further consideration of subsurface vapor intrusion at

Silresim (as appropriate).

Each of these objectives is discussed in greater detail in the following sections.

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1.2 Report Organization

This report is presented in six sections.

Section 1.0, Introduction, presents the objectives of this report and the organization.

Section 2.0, Background, discusses site background and summarizes existing indoor air sampling data.

Section 3.0, Recent Regulatory Developments, discusses recent MADEP and EPA guidance related to

indoor air and vapor intrusion.

Section 4.0, Current Perspectives on Vapor Intrusion Assessment, compares existing Silresim air

investigation efforts with the recent EPA and MADEP guidance.

Section 5.0, Site-Specific Application of EPA Subsurface Vapor Intrusion Guidance, presents a step by

step application of the recent EPA guidance to the Silresim Site.

Section 6.0, summarizes the investigation results and presents recommendations regarding possible

data gaps.

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2.0 BACKGROUND

This section presents a description of the subsurface contamination at the Silresim Site, the exposure points of most immediate concern relative to potential inhalation exposures, and a summary of the past air sampling activities and risk assessments performed in relation to the Silresim Site.

2.1 Description of the Source and Pertinent Site Features

A plume of contaminated groundwater originates at the Silresim Superfund Site on the former Silresim property and flows generally to the north and northwest. The plume contains a variety of dissolved volatile organic and semi-volatile organic compounds (SVOCs) at a wide range of concentrations. The concentrations of many of these contaminants are relatively high in relation to the most common published risk-based screening criteria for groundwater relative to possible vapor intrusion and inhalation exposure. A non-aqueous phase liquid (NAPL) material also has been periodically observed in the subsurface soil at some locations in association with the groundwater plume. Additionally, a smear zone of contamination exists in the subsurface soil at a depth just above the water table (which fluctuates 2 to 3 feet over the course of the year).

There are a number of commercial and industrial businesses downgradient of the Silresim property situated above the groundwater plume, with residential properties farther to the north. The downgradient facility most directly at risk from the existing plume currently (i.e., located above the portions of the plume with the highest concentrations of VOCs) is the Lowell Iron and Steel (LIS) industrial facility adjacent to the Silresim property.

The LIS facility includes an outdoor steel gantry crane, storage and fabrication area, two active and occupied buildings, and an area used primarily for vehicle parking and storage. A schematic of these features and the other key components of the vapor intrusion exposure pathway for the Silresim Site and the LIS property are presented in Figure 2-1. The Operations Building is where the bulk of the industrial activities of LIS are performed (e.g., metal cutting, cleaning, and handling). These activities are conducted primarily on the upper level of this building, whose floor is approximately four feet above the outside ground surface. The lower level of this building (which is mostly below ground and has a dirt floor) is used primarily for long-term storage. The construction of this older building would suggest that the floor and walls of the lower level would not be an effective barrier to vertical and horizontal migration of vapors originating beneath the building. There also are many openings in the floor and walls of the upper level that would allow a great deal of air exchange between the lower and upper levels, and between the upper level and the outside ambient air. Large doors in the upper level are often open during working hours, even in colder weather.

The Administration Building on the LIS property is a newer, more conventional structure where clerical and administrative work is performed on the first (ground) floor. A single stairway allows access to a basement with concrete walls and a poured concrete floor. The basement appears to be used primarily for document and file storage. The floor and walls are relatively competent and are believed to provide an effective barrier to vapor migration. A groundwater sump exists in the floor of the basement of the Administration Building. This opening, which is approximately 30 inches square in size, would represent a preferential migration pathway for the vertical migration of vapors into the building. The sump has a cover that is usually positioned to effectively seal the opening.

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Ground Surfac Basemen

Figure 2-1 General Schematic of the Key Components of the Vapor Intrusion Exposure Pathway

Associated with the Silresim Superfund Site and the Adjacent Lowell Iron and Steel Facility

Other Facilities LIS LIS and

Residences Administration

Building Operations

Building Vehicle Storage

Area

Basement

First Floor

Storage Yard and Crane

Vadose Zone

“Smear” Zone

Groundwater Table NAPL Pocket

Groundwater Plume

Sump Underground

Utility

Vapor Migration

2.2 Prior Air Sampling and Assessments of Volatile Contaminant Migration

2.2.1 Air Surveys

Given the presence of volatile contamination in the groundwater and subsurface soil in areas beneath and adjacent to buildings near the Silresim property where people work and live, questions were raised about the possible migration of volatile contaminants up through the soil and into the indoor air of these buildings. There was a concern that these migrating contaminants might create concentrations in the indoor air that may pose a health risk due to inhalation by the people using these buildings. In response to this concern, an air sampling survey was designed and performed in relation to the Operations Building and the Administration Building on the LIS property. These two buildings were selected for the survey since they are located above a portion of the contaminated groundwater plume.

The survey ultimately consisted of sampling indoor and ambient air at these two LIS buildings on July 21, 1999, April 26, 2000, April 20, 2001, and April 17, 2002. Further details of these sampling events are presented in the document entitled Indoor Air Sampling – Silresim Superfund Site, Lowell, Massachusetts, July 2001; prepared by Foster Wheeler Environmental. This report also includes information relative to a similar prior sampling survey conducted by the EPA on October 5 and December 6, 1988.

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The objectives of the air sampling survey were to collect representative, high quality data from the sampling locations in the occupied LIS buildings that could be used to determine if the groundwater and subsurface soil contaminants were influencing the air quality in these spaces and to determine if additional sampling and/or other actions were required to ensure that the people utilizing these buildings were being adequately protected. Another objective, added after the start of the survey, was to collect representative indoor air samples from the first floor of the Operations Building in order to determine if the industrial activities performed there may be influencing the indoor air within the building. In order to collect samples that represented as close to “worst-case” exposure conditions as possible, the sampling events were conducted at the time of year when groundwater levels were usually at their highest. The potential flux of volatile vapors and the risk associated with their migration from contaminated groundwater into a basement is usually greatest (all other factors being equal) when the water table is highest (i.e., the contaminated water is closest to the floor of the occupied space). Based on monitoring, the groundwater table was seen to generally be at its highest beneath the LIS property during the month of April.

The sampling methods were consistent with many of the recommendations contained in the recent MADEP (2002) guidance. The indoor air samples were collected using 6-liter Summa canisters. The stainless steel canisters were cleaned at the laboratory to prevent cross-contamination. Each canister was placed at the sampling location, the valve was opened, and the sample was allowed to collect for a period of approximately eight hours. The canisters were equipped with vacuum gauges that were monitored during the sampling period to ensure that the canister was operating properly.

In addition to the samples collected in the two LIS buildings, upwind and downwind ambient air samples were collected concurrently to see if off-site or on-site sources of airborne contaminants were influencing the air within the occupied spaces being sampled. Ambient air samples were not collected during the previous sampling performed by the EPA in 1988.

2.2.2 Results of the Prior Risk Assessments

In January 2000, TtFW completed a risk assessment to evaluate the magnitude of potential inhalation risk from indoor concentrations of the contaminants detected during the survey conducted in July 1999. The results of the risk assessment indicated that the calculated carcinogenic risk for both LIS buildings and exposure scenarios (assuming Reasonable Maximum Exposure (RME) and Central Tendency (CT) exposure scenarios) were below the EPA target risk range (1x10-4 to 1x10-6). The non-carcinogenic hazard index for the Operations Building basement was calculated to be higher than the EPA target value of 1.0. Due to the non-carcinogenic exceedance and because of the belief that the air concentrations in these basements could be possibly higher at times of higher groundwater, additional sampling and risk assessment was planned for April 2000.

In order to determine the additional risk associated with the high groundwater scenario, a risk assessment, similar to that performed for the July 1999 survey, was performed using the data collected during the sampling survey performed in April 2000. The results of this second risk assessment indicated that the calculated carcinogenic risk for the Administration Building basement exceeded the acceptable target risk range (1x10-4 to 1x10-6) for the RME exposure scenario. Also, the non-carcinogenic hazard index for both building basements exceeded the EPA target level of 1.0 for the RME exposure scenario.

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Similar sampling was conducted in April 2001. Accordingly, the data collected during the April 2001 survey was used to reassess potential inhalation risks. The results of this risk analysis indicated that the calculated carcinogenic risk and hazard index for the Administration Building basement were lower than the previous calculations from 2000 for both exposure scenarios. However, the hazard index calculated for the Operations Building basement exceeded the EPA target value of 1.0 and was significantly higher than the previously calculated hazard indices for both exposure scenarios. The contaminant levels measured in the Operations Building basement indicated a potential for long-term concern, due to the increase in the number of organic compounds detected and the increasing time trend of calculated risk and hazard index values under the RME and CT assumptions.

The data subsequently collected in April 2002 also was used to reassess the risk. The reassessment was undertaken as a follow-up to the three earlier events to evaluate the magnitude of potential inhalation risks from indoor air levels under a best estimate of the current exposure conditions and for reasonable maximum future exposure conditions. During the April 2002 sampling round, air monitoring was also performed on the first floor of the Operations Building to characterize the air quality in that area which was more actively used and occupied on a regular basis. Carcinogenic risks and non-carcinogenic hazard indices were calculated relative to potential inhalation exposures to the indoor air in the basements of the Operations and Administration Buildings and in the first floor of the Operations Building using the Risk Assessment Guidance for Superfund (RAGS) relationships.

2.2.2.1 Results for the Administration Building Basement

The total projected risk for each scenario was compared to the EPA target carcinogenic risk range of 1x10-4 to 1x10-6, while the cumulative hazard index was compared to the EPA target value of 1.0. As can be seen from Table 2-1, the carcinogenic risk projected for the Administration Building basement under the RME exposure scenario in April 2002 exceeded the carcinogenic risk range (risk = 3.18x10-4). This was the highest estimated carcinogenic risk level that had been projected for this area up to that time.

The contaminants of concern (COCs) that caused this exceedance were 1,4-dichlorobenzene (risk = 1.28x10-4) and trichloroethene (TCE) (risk = 1.43x10-4). The CT scenario carcinogenic risk results for this location were within the target risk range. The non-carcinogenic hazard indices projected under both the CT and RME exposure scenarios using the 2002 measurements were below the target value of 1.0. The time trend of the risk results for the Administration Building basement is also presented in Table 2-1. As shown in Table 2-1, the projected hazard index levels for the Administration Building basement based on the April 2002 sampling results were lower than the April 2000 results, but were still higher than the April 2001 and July 1999 results for both the CT and RME scenarios. The calculated carcinogenic risk was slightly higher in the Administration Building during the April 2002 sampling event than for previous events for both the RME and CT scenarios. All (14) compounds measured in the air samples in April 2002 were formerly detected in April 2000, eight of the compounds measured in April 2002 were also detected in April 2001, and ten were also detected in July 1999.

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Table 2-1 Calculated Carcinogenic Risk and Non-Carcinogenic Hazard Indices for the Indoor Air Exposure

Pathway for Areas Within the Operations and Administration Buildings

OPERATIONS BUILDING BASEMENT July 1999 April 2000 April 2001 April 2002

RME Scenario Risk 5.22E-05 2.78E-05 1.99E-05 3.34E-05

Hazard Index 2.05 1.44 8.99 3.35 Contributors to HI Benzene Benzene Benzene Benzene

- 1,2,4-Trimethylbenzene 1,2,4-Trimethylbenzene 1,2,4-Trimethylbenzene - 1,3,5-Trimethylbenzene 1,3,5-Trimethylbenzene -- Bromomethane - -

Methyl Ethyl Ketone - - -CT Scenario

Risk 6.53E-06 3.48E-06 2.49E-06 4.18E-06 Hazard Index 0.256 0.180 1.12 0.42

Contributors to HI - - 1,2,4-Trimethylbenzene -- - 1,3,5-Trimethylbenzene -

OPERATIONS BUILDING FIRST FLOOR July 1999 April 2000 April 2001 April 2002

RME Scenario Risk Not Sampled Not Sampled Not Sampled 6.38E-06

Hazard Index Not Sampled Not Sampled Not Sampled 4.65 Contributors to HI 4-Methyl-2-Pentanone (MIBK)

CT Scenario Risk Not Sampled Not Sampled Not Sampled 7.97E-07

Hazard Index Not Sampled Not Sampled Not Sampled 0.58

ADMINISTRATION BUILDING BASEMENT July 1999 April 2000 April 2001 April 2002

RME Scenario Risk 7.53E-05 1.58E-04 8.67E-05 3.18E-04

Contributors to Risk - 1,4-Dichlorobenzene - 1,4-Dichlorobenzene - - - Trichloroethene

Hazard Index 0.699 2.617 0.156 0.88 Contributors to HI - Benzene - -

- 1,2,4-Trimethylbenzene - -- 1,3,5-Trimethylbenzene - -- Tetrahydrofuran - -

CT Scenario Risk 9.41E-06 1.97E-05 1.08E-05 3.97E-05

Hazard Index 0.087 0.327 0.0195 0.11 Note: - = Not Applicable

Bold risk or hazard index estimates exceed the EPA target carcinogenic risk range or hazard index criterion, respectively

2.2.2.2 Results for the Operations Building Basement From Table 2-1, it also can be seen that the carcinogenic risk projected for the Operations Building basement under both the CT and RME exposure scenarios did not ever exceed the EPA target carcinogenic risk range of 1x10-4 to 1x10-6 in any of the assessments. The hazard index projected under the CT exposure scenario using the April 2002 data did not exceed the EPA target value of 1.0, but the projected hazard index for the RME exposure scenario did (HI = 3.35). The COCs contributing most to this exceedance were benzene (HQ = 1.84) and 1,2,4-trimethylbenzene (HQ = 1.11). The projected risk levels based on the April 2002 sampling results were comparable to all of the previous sampling results for both the CT and RME scenarios. However, the projected hazard index results for the Operations

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Building basement were higher than both the April 2000 results and the July 1999 results for both the CT and RME scenarios, and lower than the April 2001 results for both exposure scenarios. All (10) of the compounds measured in the air samples in April 2002 were formerly detected in both the April 2001 and April 2000 samples.

2.2.2.3 Results for the Operations Building First Floor The carcinogenic risk projected for the first floor of the Operations Building under both the CT and RME exposure scenarios did not exceed the carcinogenic risk range of 1x 0-4 to 1x10-6 in the April 2002 assessment. The hazard index projected under the CT exposure scenario did not exceed the target value of 1.0 but the projected hazard index for the RME exposure scenario did (HI = 4.65). The COCs contributing most to this exceedance were 4-methyl-2-pentanone (MIBK) (HQ = 4.31) and, to a lesser extent, benzene (HQ = 0.30). The first floor air of the Operations Building was only sampled and assessed in April 2002.

Table 2-2 shows the maximum concentration of each COC detected in the basement and the first floor of the Operations Building. Questions arose as to whether the source of any of the detected COCs might be the ongoing activities or residues from the past activities on the first floor, rather than the groundwater. Activities in the first floor production area have included metal cleaning, cutting, and machining operations, although no systematic or formal survey of current or past practices had been performed. A cutting oil that was commonly used in the Operations Building first floor and that had been spilled on occasion was identified to be Power-CutTM 390, a water-soluble oil cutting fluid. The ingredients of this product include a hydro-treated naphthemic oil and other hydro-treated middle petroleum distillates.

Table 2-2 Comparison of the Maximum Detected COC Concentrations in the Indoor Air of the Operations Building Basement and First Floor

(April 17, 2002 Sampling Event)

Chemical of Concern Operations Building

Basement (ug/m3)

Operations Building First Floor

(ug/m3) Acetone 22 25

Benzene 16 2.6

Dichlorofluoromethane ND 3.7

Ethanol 30 150

Hexane 34 ND

Methylene Chloride 8.7 9.6

4-Methyl-2-Pentanone (MIBK) ND 440

Methyl tert-butyl Ether 31 16

Toluene 160 16

1,2,4-Trimethylbenzene 9.6 ND

Xylenes (total) 57 14.3

Note: ND = Not Detected

Of the 11 COCs listed in Table 2-2, five of them were detected with a maximum concentration higher on the first floor than in the basement (i.e., acetone, dichlorodifluoromethane, MIBK, ethanol, and methylene chloride). Two of these, MIBK and ethanol, are compounds of the type possibly associated with the water soluble cutting oil. Acetone and methylene chloride levels, while slightly higher on the first floor, were

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fairly comparable, and the dichlorodifluoromethane was measured at a low concentration near its detection limit. As such, it appeared that some of the measured COCs in the Operations Building were coming from sources other than the groundwater. Lacking a specific survey of past and current material uses in the production area, it could not be definitively stated whether the chlorinated and halogenated compounds were associated with the Operations Building activities. The lighter weight BTEX compounds did not appear to be related to the cutting oil. Once again, no systematic review was undertaken of past operations to identify other possible products or sources of volatile compounds.

2.2.3 Recommendations from the Previous Risk Assessments

The RME exposure scenario risk projection exceeded the target range in the Administration Building basement and RME exposure scenario hazard index projection exceeded that target criterion in the Operations Building basement. These results indicated a basis for some concern relative to possible future routine, long term use of these areas should the measured conditions persist. While use of the maximum air concentrations of the volatile COCs and the RME exposure parameters was considered to be conservative for the basement areas (i.e., assuming occupancy of the basement for 8 hours per day for 5 days per week), the results indicated that any plans for intensive utilization of the basement spaces in either building in the future by workers should be preceded by verification air monitoring and (if needed) additional ventilation or engineering measures to block or reduce the migration of volatiles into these spaces.

Also, the RME exposure scenario exceedance of the hazard index for the first floor of the Operations Building raised a potential issue. The only significant contributor to the hazard index exceedance was 4-methyl-2-pentanone (also known as methyl isobutyl ketone [MIBK]), which had not been detected in any of the other prior sampling rounds. The MIBK was believed to be present as the result of the use or spillage of the identified cutting oil. While flagging a potential concern relative to possible chronic, long term exposure to a member of the public to MIBK at the levels detected in the indoor air on the first floor of the Operations Building that day, the maximum measured concentration of MIBK was well below the current occupational (OSHA and NIOSH) limits for this compound. Since this was the first (and ultimately the only) sampling performed on the first floor, it was recommended that an additional round of sampling be performed on the first floor in order to verify and confirm the presence of these contaminants in this area. This sampling would also possibly better establish what contaminants may be related to the groundwater and which may be attributable to other past or current sources associated with the Operations Building. It should be noted that MIBK has been detected at elevated concentrations in certain portions of the Silresim groundwater plume.

Because of the exceedance of the target risk range in the Administration Building basement, and the fact that the estimate was the highest that had yet been calculated for this basement, it was recommended that the indoor air on the first floor of the Administration Building also be sampled to ensure that unacceptable levels of the COCs were not migrating up to the first floor (an area that was more routinely occupied). In the interim, it also was recommended that the cover over the sump in the basement of the Administration Building be replaced such that the opening would be more effectively sealed relative to the migration of volatiles, and that any doors or means of separation between the basement and the first floor be kept closed whenever possible to minimize the possible transfer of volatiles between the two spaces.

Further sampling of the indoor air in the basement of either building and the associated outdoor ambient air monitoring was not indicated to be warranted at that time.

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3.0 RECENT REGULATORY DEVELOPMENTS

Since the LIS air surveys and assessments were completed, two relatively recent regulatory developments have occurred with relevance to the Silresim Site indoor air/vapor intrusion issue. The first was a guidance document published by the MADEP Bureau of Waste Site Cleanup (BWSC), and the second was a draft guidance document published by the EPA’s Office of Solid Waste and Emergency Response (OSWER). Both of these recent guidance documents are briefly described below, along with their potential relevance to the Silresim Site.

3.1 MADEP’s Indoor Air Sampling and Evaluation Guide

Nearly concurrent with the April 2002 survey and associated risk assessment, the MADEP BWSC published WSC Policy #02-430, “Indoor Air Sampling and Evaluation Guide” (MADEP, 2002). This seminal state guide was the first of a number of similar guidance documents published subsequently by other states on the topic of vapor intrusion analysis and sampling.

This guidance was developed in response to an increasing number of questions directed to the MADEP concerning what methodologies would be appropriate to use to conduct sampling and analysis of chemical contaminants in indoor air. MADEP had developed a growing understanding of the fate and transport of volatile chemicals in groundwater and how they could impact indoor air. This understanding led to the MADEP’s recognition of the importance of including consideration of this pathway when evaluating the impacts of a hazardous waste site on human health. Consideration of potential impacts of contaminated groundwater and subsurface soil on indoor air is now a common component of risk characterizations conducted under the Massachusetts Contingency Plan (MCP).

WSC Policy #02-430 provides an overview of the considerations involved in planning and executing an indoor air sampling study and evaluating its results. It is considered an essential reference for those conducting indoor air evaluations under the MCP. The guidance is not written as a prescriptive “cookbook”, but includes a fair amount of flexibility and allows for interpretation of results and management decisions to be made using a case-specific practical approach. The guidance presented applies principally to indoor air concentrations caused by the emission of volatile contaminants emitted from other environmental media (e.g., groundwater and soil). However, the guidance also has applicability to indoor air contamination originating from indoor sources (e.g., consumer products, building materials). The document mainly focuses its discussion on the indoor air evaluation at residential buildings. However, the concepts, practices and sampling and analysis principles discussed would be applicable to any single or multiple story non-residential buildings where the goal is to evaluate the health impacts of indoor air quality.

The MADEP guidance states that the design of an indoor air sampling plan should vary with the objectives of the study, and presents a number of components that should be addressed in the planning stages of the study so that those objectives will be met. These components include: developing a list of the target volatile compounds and parameters to be analyzed; determining the required sampling duration; choosing a sampling and analytical method and detection capability consistent with the study objectives; establishing representative sampling conditions; and ensuring adequate quality assurance and quality control (QA/QC) practices are in place throughout the sampling and analytical process.

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The guidance defines a 10-step sequential process to be used to design and conduct an indoor air study:

1. Define Study Objectives; 2. Identify Chemicals of Concern; 3. Identify Required Sampling Duration and Frequency; 4. Choose Sample Method 5. Check Limits of Detection are Adequate; 6. Define QA/QC Indicators for Sampling and Analysis; 7. Do a Pre-Sampling Investigation; 8. Establish Appropriate Sampling Conditions and Conduct Sampling; 9. Analyze Samples; and 10. Evaluate Data and Calculate Health Risks.

A corresponding checklist is provided that helps the user of the guidance through each step and cross-references the various topical sections of the guide.

While this guide was not available when the sampling and analysis plan for the indoor air study was conducted for the Operations Building and the Administration Building at LIS was developed, the process and procedures used during the sampling and analysis adhere quite well to the recommendations presented in the guide for the conditions present at LIS. No pre-sampling investigation was performed relative to the operations within the two buildings prior to the sampling, but a limited post-sampling investigation was performed in the Operations Building in response to the detection of MIBK (a chemical not associated with the Silresim Site) at levels that drove the risk results. All of the other steps and components were considered in some manner in the Silresim indoor air evaluation effort.

3.2 EPA’s Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Subsurface Vapor Intrusion Guidance)

Shortly after the MADEP guide was published, the EPA’s Office of Solid Waste and Emergency Response published EPA530-F-02-052, “Draft Guidance For Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (also referred to as the “Subsurface Vapor Intrusion Guidance”) (EPA, 2002). This draft federal guidance was widely disseminated and quickly adopted by a number of the EPA Regions and programs within EPA. EPA Region 1 also has adopted this draft document as guidance “to be considered” at its Superfund sites within the region.

The draft guidance specifically addresses only the evaluation of the vapor intrusion pathway. The intent of the draft guidance is to provide a tool for conducting a screening evaluation as to whether or not the vapor intrusion exposure pathway is complete, and (if so) whether it poses an unacceptable risk to human health. The evaluation process presented in the draft guidance begins with a simple and generally reasonable conservative screening approach and progresses toward a more complex assessment involving increasingly greater use of site-specific data. If a site is determined to have an incomplete vapor intrusion exposure pathway, further consideration of the current site situation is not recommended. For those sites determined to have a complete exposure pathway, recommendations are provided as to how to evaluate whether the vapor intrusion pathway does or does not pose a significant risk to the potentially affected people. However, the guidance does not address how to delineate the extent of the risk or how to mitigate or eliminate the risk.

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The draft guidance is clear in stating that it is not a regulation. The draft guidance represents OSWER’s technical and policy recommendations. EPA personnel are explicitly free to use or accept other technically sound approaches for an evaluation. In addition, persons who use the draft guidance are free to modify the approach recommended in the document. The draft guidance does not impose any requirements or obligations on the EPA, states, or the regulated community. Despite these statements, many federal and state regulators across the country quickly adopted and applied this draft guidance more-or-less as written.

The framework forming the foundation of the draft guidance is the EPA’s Data Quality Objective (DQO) step-wise process. For the case of possible vapor intrusion, this DQO process includes the development of a conceptual site model (CSM). A CSM is a graphical or tabular “picture” of site conditions that illustrates the contaminant sources, their movement in the environment, their exposure pathways and the potential human receptors who may breathe the volatile contaminants in indoor air.

The draft guidance recommends a tiered assessment approach that involves increasing levels of complexity and specificity:

• Tier 1 – Primary Screening is designed to be used with general knowledge of a site and the chemicals known or reasonably suspected to be present in the subsurface; it does not require media-specific concentration measurements for each constituent of concern;

• Tier 2 – Secondary Screening is designed to be used with some limited site-specific information about the contamination source and subsurface conditions (e.g., measured or reasonably estimated concentrations of target chemicals in groundwater or soil gas, the depth of contamination, and soil type); and

• Tier 3 – Site-Specific Pathway Assessment involves collecting more detailed site-specific information for possible modeling and conducting confirmatory sub-slab and/or indoor air sampling.

The evaluation process presented in the draft guidance follows a logical and linear progression designed to screen out sites that ordinarily do not need further consideration so that greater focus and attention can be placed on the sites that generally do need further consideration. It is recommended that the assessment begin with Tier 1 and progress on to Tiers 2 and 3, as needed. However, the assessment may begin immediately at Tiers 2 or 3.

The process associated with the draft guidance involves a comparison of site groundwater or soil gas measurements to conservatively established screening levels in the Tier 1 assessment. The Tier 2 assessment involves incorporating a limited amount of site-specific information about the depth to groundwater and soil type to select “semi-site-specific” attenuation coefficients and corresponding screening levels for the comparison. The Tier 3 assessment involves sampling and/or modeling tailored specifically to the conditions and circumstances at the Site.

The draft guidance is structured around a series of questions that take the analysis from the beginning of a Tier 1 assessment step-by-step to either a decision that no further assessment is needed or that a Tier 2 or Tier 3 assessment may be warranted. The questions also direct the assessment through a Tier 2, and then potentially to a Tier 3 assessment. A detailed application of this process and consideration of these questions is presented for the Silresim Site in Section 5.0.

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4.0 CURRENT PERSPECTIVES ON VAPOR INTRUSION ASSESSMENT

4.1 Recent Developments

A considerable effort and quantity of resources has been applied to the issue of how to assess the potential contribution of contaminated groundwater to indoor air quality and the possible associated risks due to the inhalation of indoor air. The two guidance documents described in some detail in Section 3.0 are but two of the foremost examples of guidance and technical studies produced in the last three to four years on the topic. The components common to the approaches described in these recent works reflect some changes in thinking regarding the evaluation of groundwater vapor migration and intrusion into buildings relative to the previous standard practices. A few of the more significant of these changes are identified and discussed below.

• The inhalation of VOCs in indoor air is now recognized as an exposure pathway that can represent a significant and, at times, the predominant contributor to the total risk of receptors at hazardous waste sites where VOCs are among the site contaminants.

• Recent reassessments of the toxicity of a number of VOCs via the inhalation route of exposure (as reflected in the contaminant’s cancer slope factor or reference concentration) have resulted in many of these VOCs now being considered to be more potent in causing cancer or other health effects than they were previously thought to be (e.g., trichloroethene).

• The direct measurement of the concentrations of various volatile contaminants in indoor air can lead to confounded conclusions with respect to the probable contribution of contaminated groundwater, subsurface soil or subsurface waste material as the source of the measured levels. This is because the concentrations of the VOCs measured in the air sampled inside an occupied structure may reflect contributions from: (1) outside ambient air; (2) vapors being released and migrating from below; (3) releases from consumer or industrial products (e.g., paints, dry cleaning, hobbies, solvents); and (4) out-gassing from the building construction materials (e.g., adhesives, coatings). Direct measurements of indoor air concentrations may be evaluated to determine what level of risk may be associated with inhalation exposure to those conditions, but these measurements alone usually can tell little about where the contaminants may have been released.

• The ability to model volatile chemical release from contaminated groundwater or subsurface soil up through the soil and into a building has been continually refined and improved, but also continues to be viewed with some skepticism when this modeling is applied without due consideration being given to the assumptions and limitations of the model and the quality and representativeness of the input values. The Johnson and Ettinger Model is the leading model for this type of analysis, and is the model recommended for use in the draft EPA guidance and the model that was used in the development of the MADEP’s MCP GW-2 groundwater standards (i.e., the standards associated with screening groundwater relative to it’s potential human health impact due to indoor air inhalation). This model has been in use for the purpose of evaluating the vapor intrusion pathway for over 10 years. However, a number of changes and refinements have been made to the modeling within the past three years with regard to the recommended default input parameters, enabling the explicit consideration of modeling with soil gas or NAPL as the

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source of the VOCs, and requiring a more focused attention on the inappropriateness of the modeling approach when preferential pathways are present at a site.

• Little or no evidence has emerged that suggests that the potential for indoor vapor intrusion from subsurface contamination can be predicted by the concentrations of the volatile contaminants in the subsurface soil. As such, sampling of the subsurface soil for purposes of evaluating a possible vapor intrusion exposure pathway is not currently recommended.

• Continued analysis of indoor air and associated groundwater data over the last few years has led to a greater understanding of the limits of using groundwater measurements to predict indoor air VOC concentrations. While still viewed as a reasonable indicator of whether there may be an indoor air issue at a site located above a contaminated groundwater plume, groundwater monitoring is no longer viewed as a stand alone best indicator. The ability of other site conditions and features to mask or override the role of the groundwater concentration is now better recognized than it had been. As such, groundwater monitoring is still recommended as one piece of information to be used in a weight-of-evidence evaluation of the potential contribution of the vapor intrusion pathway.

• Soil gas measurements (particularly subslab sampling) have become the preferred measurements for purposes of evaluating the vapor intrusion pathway in most cases. Strategically-placed, high quality soil gas measurements are now frequently viewed as the best empirical evidence for determining whether or not vapor migration from subsurface contamination and intrusion into a building is occurring. Soil gas measurements are now typically recommended to be taken: from the vertical soil column between the subsurface contamination and the building foundation; from just beneath the foundation slab/floor of the occupied building space; and from within or along possible preferential pathway routes or vapor accumulation points along those routes. These soil gas measurements add direct presence/absence information to the recommended weight-of-evidence evaluation.

• Considerably more attention is now given to collecting high quality and representative air and soil gas samples for use in these analyses so that they will support the decisions that follow from them. The MADEP guidance discussed in Section 3.1 above is primarily focused on sampling design to achieve well-conceived DQOs. Sampling plans for indoor air evaluations must specify the number and timing of the samples to be collected; the manner in which the samples will be collected; where the samples will be collected; how much sample will be collected; what the sample will be contained in; what methods will be used to prepare and analyzed the samples; what detection limits are required to be met; and what other measurements or other media samples should be collected concurrent with the air measurements. In many cases, air sampling must be preceded by a survey of the materials and activities conducted within the indoor space.

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4.2 Comparison of the Currently Recommended Vapor Intrusion Evaluation Approach to Existing Analyses for the Silresim Site

As seen from the descriptions of the most recent MADEP and EPA guidance on evaluating and assessing potential indoor air risks from subsurface contamination, a number of the recommended actions and assessment components have been performed in some manner:

• Indoor air measurements have been made over a three year period (on an annual basis) within the Operations Building and the Administration Building and in the ambient air. These measured concentrations have been used to estimate the inhalation risks to workers in these buildings assuming conservative, but reasonable exposure assumptions. The projected risks were generally at or just exceeding EPA risk goals for long-term public exposure. A few of the volatile contaminants measured in the indoor air that were associated with the highest projected risks were indicated to likely be associated with the current operations within the building and not the subsurface contamination (e.g., MIBK). Because of confounding influences like these, indoor air measurements are not now recommended to be made at the beginning of a vapor intrusion assessment, but later in the evaluation sequence and in accordance with a number of specific planning and sampling requirements.

• Groundwater concentrations have been compared to the MADEP MCP GW-2 standards and found to exceed these standards for a number of volatile compounds at various locations and depths within the groundwater contaminant plume.

• The groundwater-to-indoor air exposure pathway was explicitly incorporated into the development of the risk-based Baseline Assessment Values (BAVs) and the 2002 revisions to the cleanup goals (CUGs). This assessment was made using the Johnson and Ettinger Model (and the previous guidance and default parameters) with a selection of site-/property-specific modeling inputs. Many of these revised CUGs (some of which were driven by consideration of the vapor intrusion pathway), are currently not being met.

• A “worst case” assessment was made of the risks to a utility worker who may be working on the LIS property to repair or replace an existing buried utility line or to install a new one. This assessment considered the utility worker’s potential exposure to subsurface soil contamination or migrating volatiles. The projected risks associated with these relatively short duration and infrequent exposures did not exceed target risk levels.

Overall, the existing evaluations for the Silresim Site indicate that the exposures to volatile contaminants in the indoor air in the currently occupied buildings closest to the site source are associated with levels of risk close to or slightly exceeding the EPA target levels. In addition, the generic MADEP MCP groundwater standards and the site-specific CUGs considering the vapor intrusion pathway are currently exceeded in many locations. Therefore, further evaluation of this exposure pathway was considered to be warranted. It was also concluded that this further evaluation should be performed according to the draft EPA guidance and in consideration of the MADEP guidance described in Section 3.0 above.

Accordingly, additional evaluation of the vapor intrusion pathway has been undertaken for the Silresim Site in conformance with the draft EPA guidance and is presented in the following section.

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5.0 SITE-SPECIFIC APPLICATION OF EPA SUBSURFACE VAPOR INTRUSION GUIDANCE

As discussed in Sections 3.0 and 4.0, existing air analyses indicate some possible concerns related to vapor intrusion pathways at the Silresim Site. In light of this, a detailed assessment of vapor intrusion at Silresim has been undertaken following the specific approach recommended in the recent Draft EPA Subsurface Vapor Intrusion Guidance. It should be noted that the Guidance evaluation approach has been applied not only to the LIS property, but also across the remainder of the Silresim Site. This evaluation considers not only the potential inhalation exposures to persons currently working in or using buildings near the groundwater plume, but also on individuals who may be exposed in the future should the neighboring properties be modified, redeveloped, or reused for other purposes.

This section presents the results of the site-specific application of the EPA Subsurface Vapor Intrusion Guidance tiered screening approach described in Section 3.2. This approach includes three sequential tiers of evaluation including: 1) Tier I - Primary Screening; 2) Tier II - Secondary Screening; and 3) Tier III - Site-Specific Assessment. The following discussion presents the specific evaluation steps associated with each tiered level of screening as they apply to the Site.

5.1 Tier 1 – Primary Screening

The Primary Screening process is designed to assist in quickly screening out any site where the vapor intrusion pathway should not be a concern and should not require further consideration. The focus of Primary Screening is to identify whether the potential exists for vapor intrusion to result in unacceptable indoor inhalation risks.

Application of the Tier 1 Primary Screening process to the Silresim Site requires consideration of the following three principal criteria (as specifically identified in the Guidance):

• Are volatile and toxic chemicals present? • Are (or could) inhabited buildings be located near subsurface contaminants? • Does evidence suggest that immediate action may be warranted to mitigate current risks?

Question 1 – Are Volatile and Toxic Chemicals Present?

Answer – Yes, for the Silresim Site.

As indicated in Table 5-1, numerous volatile and toxic chemicals identified in the Subsurface Vapor Intrusion Guidance are present at the Silresim Site. The Guidance suggests that chemicals that possess Henry’s Law Constants >10-5 atm m3 /mol should be considered volatile. A wide variety of organic solvents with Henry’s Law constants in excess of 10-5 have been detected in relatively high concentrations at the Site.

Table 5-1 includes 27 of the most common volatiles detected in groundwater at the Silresim Site. It should be noted that several other VOCs have also been detected sporadically and/or at low concentration. These additional compounds are not anticipated to significantly impact vapor intrusion evaluations at the Site.

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Table 5-1 Principal Volatile Compounds and

Henry’s Law Constant Detected at Silresim

Volatile Compounds Henry’s Law Constant

Acetone 1.59x10-3

Benzene 2.28x10-1

2-Butanone 2.29x10-3

Carbon Tetrachloride 1.25x100

Chlorobenzene 1.52x10-1

Chlorodibromomethane 3.21x10-2

Chloroethane 4.52x10-1

Chloroform 1.50x10-1

1,1-Dichloroethane 2.30x10-1

1,2-Dichloroethane 4.01x10-2

1,1-Dichloroethene 1.07x100

1,2-Dichloroethene (total) -cis-1,2-Dichloroethene 1.67x10-1

trans-1,2-Dichloroethene 3.85x10-1

1,2-Dichloropropane 1.15x10-1

Ethylbenzene 3.23x10-1

Methylene Chloride 8.98x10-2

m-Xylene 3.01x10-1

o-Xylene 2.13x10-1

p-Xylene 3.14x10-1

Styrene 1.13x10-1

Tetrachloroethene 7.54x10-1

1,1,2,2-Tetrachloroethane 1.41x10-2

Toluene 2.72x10-1

Trichloroethene 4.22x10-1

1,1,1-Trichloroethane 7.05x10-1

1,1,2-Trichloroethane 3.74x10-2

Vinyl Chloride 1.11x100

Question 2 – Are (or Could) Inhabited Buildings be Located Near Subsurface Contaminants?

Answer – Yes

Under the EPA Subsurface Vapor Intrusion Guidance, “inhabited buildings” are defined as “structures with enclosed air space that are designed for human occupancy.” The Guidance also suggests that determining whether a building may be potentially affected by subsurface contamination, a distance of approximately 100 feet may be reasonable for primary screening evaluation purposes. That is, in general, structures more than 100 feet laterally and/or 100 feet vertically from volatile subsurface contamination should be sufficiently removed from contamination areas. The guidance does, however, note that the possibility of significant preferential vapor transport path ways resulting from site-specific stratigraphic conditions, should be considered in identifying potentially affected structures and areas. Factors potentially influencing vapor transport include soil fractures, utility conduits, and subsurface drains.

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At the Silresim Site, occupied buildings do exist within or near the existing footprint of the groundwater VOC plume. Figure 5-1 presents an outline of the groundwater plume footprint at the Silresim Site. In Figure 5-1, two groundwater footprint traces are presented. The first footprint trace is for the total volatile organic (TVO) 10 ug/L plume contour and the second is for the TVO 1,000 ug/L foot-print contour. (The plume contours are based upon the groundwater data presented in the Status Report #23 (Watermark, Inc., 2004) for the Silresim Site.)

Figure 5-1 also includes the respective vapor intrusion contour lines generated from 100 foot horizontal step outs from the 10 and 1,000 ug/L TVO groundwater contours. Both the areas within the two contours and the respective 100-foot step out contours represent the site areas within which vapor intrusion might impact existing buildings or buildings that may be constructed in the future. This 100 foot distance of potential vapor intrusion impact is based upon the distance suggested in the EPA Guidance as discussed above.

As is indicated in Figure 5-1, currently the only occupied structure that falls within approximately 100 lateral feet of the groundwater plume 1,000 ug/L TVO contour is the groundwater treatment plant (GWTP). However, structures that fall within approximately 100 feet of the 10 ug/L contour include two LIS buildings; the Administration Building and the Operations Building. In addition, the two B&L Auto Parts buildings located across Tanner Street; portions of the Scannell building; portions of the Ideas and Waldbert Plastics building and two buildings on the Lowell Used Auto Parts (Tucci) property also fall within this footprint.

The remaining buildings at or surrounding the Silresim Site fall outside of both of these 100 foot vapor intrusion contours. As such, the vapor migration pathway is considered to be incomplete and vapor intrusion should not be a concern for these buildings.

Question 3 – Does Evidence Suggest that Immediate Action may be Warranted to Mitigate Current Risks?

Answer – No, based upon an overall assessment of existing data.

As part of the primary screening process an evaluation should be performed to determine if available evidence suggests that immediate action may be warranted to mitigate current risks. Immediate actions are considered those that may be necessary to “verify or abate” imminent or substantial threats to human health.

Qualitative criteria that would indicate a need for immediate action include the following:

• Odors (e.g., chemical, solvent, or gasoline) reported by occupants; • Physiological effects (dizziness, nausea, vomiting, confusion, etc.) reported by occupants; • Wet basements, in areas where target VOCs are known to be present in groundwater and the

water table is shallow enough that the basements are prone to groundwater intrusion or flooding; or

• Short-term safety concerns (e.g., explosive or acutely toxic concentrations) are known or reasonably expected to exist.

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At the Silresim Site, there have been no reports of odors in the occupied buildings on the LIS property. Nor have there been any potential physiological effects reported by building occupants. The LIS Operations Building does possess an earthen floor in the basement. In addition, the Operations Building does possess a sump. However, LNAPL has not been observed in the basement. In addition, the basements of the two LIS buildings currently do not see extensive human use. Therefore, no short-term safety concerns are known to exist.

As summarized in Section 2.2, indoor air monitoring has been conducted within the LIS buildings on several occasions (see Section 2.2). While inhalation risks were indicated to be a potential concern assuming long-term exposures, no immediate action was indicated to be needed to ensure the safety or health of the current users of the LIS buildings over the short term.

Based upon this information, immediate action does not appear to be necessary to mitigate current risks at the Silresim Site.

5.2 Tier II – Secondary Screening

The EPA Guidance considers the vapor intrusion pathway to be potentially complex at many sites and recommends that a detailed assessment of all available data be conducted as part of the screening process. The Secondary Screening Guidance recommends a sequential evaluation of: 1) vapor sources including groundwater and unsaturated soils; 2) soil gas in the unsaturated zone; 3) exposure point concentrations in subslab areas; and finally, 4) indoor air concentrations.

Under the sequential Secondary Screening approach measured or “reasonably estimated” volatile constituents of potential concern, in groundwater or soil gas, should be compared to generic target concentrations developed by EPA. (The volatile constituents of potential concern at Silresim are those identified in the Primary Screening process [Section 5.1].) The media specific target concentrations are based on a generic conceptual model for vapor intrusion under which vapors diffuse upwards from groundwater or contaminants in the unsaturated zone toward the surface. Media specific target concentrations are presented in the EPA Guidance. The detailed Secondary Screening comparison process is incorporated into Guidance evaluation questions #4 and #5, discussed as follows.

Question 4 – Generic Screening

The initial phase of the recommended Tier II Secondary Screening process involves a screening of the available groundwater, soil gas, and indoor air data (if available). Question #4 uses data comparison tables containing conservative generic attenuation factors to evaluate “generally reasonable worst-case conditions” for initial screening of groundwater and soil gas data.

The EPA Guidance (Guidance Tables 2a, 2b, and 2c) presents target (threshold) concentrations for 10-4, 10-5, and 10-6 risk levels. At the Silresim Site, most of the existing CUGs have been developed for a 10-5 risk level. Therefore, for screening with respect to vapor intrusion at the Silresim Site, target concentrations corresponding to a 10-5 risk level (Guidance Table 2b; see Appendix A) were utilized.

Indoor Air Data

The initial component of the Tier II Secondary Screen involves a consideration of any available indoor air data.

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Question 4a – Are indoor air quality data available?

Answer – Yes, some indoor air data is available for the Silresim Site.

Indoor air measurements have been collected in the basements of the LIS Operations Building and Administration Building (see Section 2.2). Samples have been collected by the EPA twice in 1988 and by Tetra Tech FW, Inc. (dba Foster Wheeler Environmental Corporation) a total of four times in 1999, 2000, 2001 and 2002. Samples collected in 1988 and 1999 were completed using sorbent tubes and in line pumps. Beginning in 2000, the samples were collected using time regulated summa canisters. Samples were collected from different locations in the basements of the two buildings including from the location of a sump in the Administration Building. Quality control and ambient background samples were also collected during the sampling events. This sampling was described in Section 2.2.1.

Question 4b – Do measured indoor air concentrations of constituents of potential concern identified in Question 1 exceed the target concentrations given in Guidance Table 2b (10-5 risk level).

Indoor air samples, last collected in April, 2002 at the Silresim Site had detections of trichloroethene and benzene that exceed the generic target indoor air concentrations associated with a 10-5 risk level. The exceedance of trichloroethene, 0.93 ppbv (0.041 ppbv target level) was in a sample collected from the basement of the Lowell Iron and Steel Administration Building, and the exceedances for benzene, 1.2 ppbv and 2.4 ppbv (0.98 ppbv target level) from the basement of the LIS Operations Building, and 1.1 ppbv from the sump of the Administration Building basement. Note that the two ambient air samples collected in April 2002 had detections for benzene of 0.96 ppbv and 1.5 ppbv.

Subsurface Source Identification

In conjunction with the overall Tier II screening process, unsaturated zone soil contamination should be evaluated at any depths above the water table. If there is a contaminant source in the unsaturated zone, soil gas data are needed to evaluate the vapor intrusion pathway.

Question 4c – Is there potential contamination (source of vapors) in the unsaturated zone at any depth above the water table?

Answer – Yes, unsaturated zone contamination exists in some portions of the Silresim Site.

Unsaturated zone soil contamination is definitely present at the Silresim Site, on both the Silresim and LIS properties. However, the buildings of principal concern from a vapor intrusion perspective (aside from the groundwater treatment plant) are the buildings on the LIS property and the building(s) on the B&L Auto Parts property. The buildings on the LIS property have been impacted by the groundwater plume but are believed to be somewhat downgradient of unsaturated zone VOC contamination. In the area of the most contaminated part of the LIS property (the Gantry area) there is likely a zone of the unsaturated layer where a “smear” of VOC contamination is present. The depth of the “smear” is across the water table fluctuation. It is believed that most of this contamination currently resides at a distance of >100 feet from the LIS buildings. Studies to date indicate diminishing soil VOC concentrations in unsaturated zone soils as distances increase from the Silresim property. However, the number of soil samples collected from within 100 feet of the LIS buildings, that have been analyzed for VOCs, is limited.

It is currently not believed that unsaturated zone soil contamination has migrated to within 100 feet of the primary building on the B&L Auto Parts property.

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Groundwater Assessment

As part of the overall evaluation of vapor intrusion at a given site, groundwater concentrations and distributions for the volatile compounds should be evaluated and compared to the appropriate target concentrations. This has been done for the Silresim Site as follows.

Question 4d – Do measured or reasonably estimated groundwater concentrations exceed the generic target media-specific concentrations given in Guidance Table 2b (10-5 risk level)?

Answer – Yes, across certain properties intersected by the groundwater plume, including the portions of the Silresim, LIS properties, B&L Auto Parts, Scannell and Tucci properties.

For the Silresim Site, an evaluation of recent groundwater data has been performed to assess possible exceedances of the generic target media-specific concentrations. Specifically, groundwater concentrations for shallow monitoring wells have been examined. Attention has been focused on downgradient and cross-gradient shallow wells. Shallow wells have been defined as these wells screened in the upper most strata at a given monitoring well location. For many locations at the Silresim Site, wells in well clusters are screened at different depths. At these locations, groundwater data has only been examined for the shallowest well in the cluster. This approach is consistent with the EPA Guidance which emphasizes that the shallow groundwater layer is most likely to impact the unsaturated zone or overlying buildings. At locations where individual (single) monitoring wells exist, this well was considered to be the “shallowest” at that location, regardless of the actual screen depth.

The shallow wells that have been examined are summarized in Table 5-2. As indicated therein, the screen intervals of the wells that have been examined vary considerably, although most of the well screens are within 30 feet of ground surface. For each shallow well, Table 5-2 indicates whether or not any VOCs (as identified in Table 5-1) were reported. As is indicated, no VOCs were reported in recent groundwater data for wells MW-311B and MW-410B.

If VOCs are reported for a given shallow well, Table 5-2 subsequently indicates whether any buildings are located within a 100 foot horizontal distance of that well. The distribution of shallow wells containing VOCs is depicted in Figure 5-2. This figure indicates both those shallow wells containing any VOC contamination and also those wells containing one or VOC contaminants whose concentration exceeds the Guidance generic target groundwater concentrations (Table 2b).

As indicated in Figure 5-2, most of the shallow wells containing one or more VOCs whose concentrations exceed the generic target groundwater concentrations are on the LIS property or near Tanner Street. However, target concentrations are also exceeded in several wells on or along the Tucci property. If no buildings are within a 100 foot distance of a given well, the vapor intrusion pathway is considered to be incomplete based upon current site and exposure conditions. Therefore, the groundwater contamination in this well is not a current concern although it could be a concern with respect to possible future building construction in this area.

Following the identification of VOC contamination and the contamination footprint results, Table 5-2 identifies which if any specific VOC contaminants exceed the EPA 10-5 risk level for each individual well, based upon Guidance Table 2b. As is indicated, a number of shallow wells contain one or more VOCs at concentrations that exceed the generic target groundwater concentrations. Table 5-2 demonstrates that several specific VOCs repeatedly dominate the list of compounds that exceed the generic target groundwater concentrations at most of the wells. In particular, benzene, trichloroethene, dichloroethene, dichloroethane and vinyl chloride exceed target levels in four or more wells each.

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Table 5-2 Summary of Vapor Screening

Location Property Ground Surface (ft msl)

Screen Depth Interval (ft msl)

Screen depth Interval (ft bgs)

VOCs in Table 1

detected?

Building within 100 ft

of Well?

VOCs Exceeding Risk Thresholds Risk = 1x10-5

Table 2b Table 3b (a=1x10-4)

MW-105B LIS 104.7 93.7 88.7 11 16 y n MW-310A LIS 104.7 56.5 51.5 48.2 53.2 y n methylene chloride methylene chloride

1,2-dichloroethane 1,2-dichloroethane benzene benzene trichloroethene trichloroethene cis-1,2-dichloroethene cis-1,2-dichloroethene acetone 1,1-dchloroethane

MW-311B B&L/River 106.9 99.7 89.7 7.2 17.2 n Bond2 MW-315B Tanner St 104 94.3 89.3 9.7 14.7 y LIS1 ethylbenzene ethylbenzene

LIS2 benzene benzene SCAN1 chlorobenzene vinyl chloride

vinyl chloride cis-1,2-dichloroethene

MW-316A LIS 105.4 80.23 75.23 25.17 30.17 y LIS1 1,2-dichloroethane benzene benzene vinyl chloride vinyl chloride cis-1,2-dichloroethene

MW-408B B&L 103.9 98 88 5.9 15.9 y B&L1 MW-410B RT 109.3 106.1 96.1 3.2 13.2 n n MW-501B LIS 105.3 95.31 85.31 9.99 19.99 y LIS1 trichloroethene trichloroethene MW-702C LIS 104.7 100.5 90.5 4.2 14.2 y LIS1 trichloroethene trichloroethene MW-703C LIS 104.6 100.6 90.6 4 14 y LIS1 trichloroethene trichloroethene

LIS2 B&L1

MW-706B RT 109.6 79.55 69.55 30.05 40.05 y n MW-707B LIS 105.6 75.74 65.74 29.86 39.86 y LIS1 1,2-dichloroethane trichoroethene

benzene trichloroethene vinyl chloride

MW-708C B&L 104.9 89.82 79.82 15.08 25.08 y B&L1 benzene B&L2

MW-711C LIS 105.07 85.77 75.77 19.3 29.3 y LIS1 1,2-dichloroethane vinyl chloride LIS2 benzene

SCAN1 vinyl chloride cis-1,2-dichloroethene

Table 5-2 - cont’d Summary of Vapor Screening

VOCs Exceeding Risk Thresholds Risk = 1x10-5 Location Property

Ground Surface (ft msl)

Screen Depth Interval (ft msl)

Screen depth Interval (ft bgs)

VOCs in Table 1

detected?

Building within 100 ft

of Well? Table 2b Table 3b (a=1x10-4)

MW-713C LUAP 103.9 86.61 76.61 17.29 27.29 y n 1,2-dichloroethane trichloroethene benzene vinyl chloride trichloroethene vinyl chloride

MW-714 B&L/River 102.8 85.21 75.21 17.59 27.59 y B&L2 MW-719C Bond 103.54 85.54 75.54 18 28 y Bond1 MW-701B SIL 112.7 78.7 68.7 34 44 y Tucci1 chlorobenzene MW-701C LUAP 106.8 103.3 93.3 3.5 13.5 y n benzene benzene

chloroform chloroform cis-1,2-dichloroethene cis-1,2-dichloroethene 1,1-dichloroethene 1,1,2,2-1,1,2,2-tetrachloroethane tetrachloroethane tetrachloroethene tetrachloroethene toluene trichloroethene 1,1,2-trichloroethane 1,1,1-trichloroethane trichloroethene

MW-503B Res 106.2 104.8 94.8 1.4 11.4 n Tucci1 Tucci2 Res1

MW-705B Res 106.2 78.11 68.11 28.09 38.09 y Tucci1 Tucci2 Res1

Notes: Groundwater data collected in November 2002 and June 2003 Bond1 - building 1 Bond property Table 1, Table 2b, Table 3b – EPA Draft Vapor Intrusion Guidance (2002) Bond2 - building 2 Bond property SIL - Silresim B&L1 - building 1 B&L Auto Parts LIS - Lowell Iron and Steel B&L2 - building 2 B&L Auto Parts LUAP - Lowell Used Auto Parts LIS1 - building 1 Lowell Iron & Steel B&L - B&L Used Auto Parts LIS2 - building 2 Lowell Iron & Steel Bond - Bond property SCAN1 - building Scannel Res - Residence on corner of Main St and Canada St Tucci1 - building 1 Tucci property River - River Meadow Brook Tucci2 - building 2 Tucci property RT - Area between railroad tracks East of LIS ft msl - feet mean sea level ft bgs - feet below ground surface y - yes n - no

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Table 5-3 summarizes the individual groundwater concentrations for the key VOCs of concern at the individual monitoring wells under consideration. It can seen that individual VOC concentrations vary widely as do the magnitude of the exceedances of the vapor intrusion threshold levels.

Question 4e – Is the nature and extent of groundwater contamination adequately characterized?

Answer – Yes, with a few limitations.

An extensive network of monitoring wells is currently in place at the Silresim Site. Overall, this well network does provide adequate characterization of the groundwater plume. The monitoring well network on the B&L Auto Parts property is, however, somewhat more limited. Therefore, groundwater data with which to assess impacts to the existing building on this property and possible future buildings at other locations on this property is somewhat limited. However, at least one well is located within 100 feet of the two existing B&L Auto Parts buildings.

Also, due to the presence of very high concentrations of certain VOCs, the VOC detection limits for many groundwater samples are quite high. Therefore, in these samples, many VOC contaminants are probably present at lower although still potentially significant concentrations, but are reported as non-detects due to the elevated reporting limits and required sample dilutions. Also due to the heterogeneous stratigraphy and presence of preferential groundwater flow and migration pathways, a complete detailed description of plume migration is not possible for the Site.

Question 4f – Are there site conditions and/or data limitations that make the use of the generic groundwater attenuation factors inappropriate?

Answer – Yes, at some site locations.

At certain site locations on the Silresim Site generic groundwater attenuation factors may not be appropriate. In particular, on portions of the LIS property groundwater is relatively shallow (~10 feet or less) at a number of locations. In addition, the Operations Building possesses a basement with an earthen floor. The generic attenuation factors assume a basic concrete slab foundations (basement or slab-on-grade) and are potentially not representative of existing conditions and the actual resistance of vapor intrusion for the Operations Building. Also, a sump exists in the LIS Administration Building.

From the stratigraphic perspective, the silty sand/clay soil at the Site as well as the heterogeneous nature of the lithology make the use of generic attenuation factors uncertain and possibly inappropriate. Preferential pathways throughout the area characterize the groundwater plume migration across the Site. These features may also influence vapor migration.

In addition, in a few locations proximate to more contaminated components of the groundwater plume, significant subsurface utility corridors (primarily sewer lines) exist which might provide preferential pathways for groundwater and/or vapor migration. This is particularly true along Tanner Street, and also portions of the LIS property.

Finally, at many monitoring well locations on the Silresim Site, the very high groundwater VOC concentrations have resulted in highly elevated analytical detection limits. In these samples, potentially significant concentrations of key vapor intrusion VOCs (such as vinyl chloride) may be present below the elevated detection limits. Therefore, generic vapor intrusion calculations would potentially underestimate the actual risks for these samples.

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Monitoring Well/

Compound Table 2b (1 x 10-5)

GW

50 x Table 2 GW

value

Table 3b (attn:1 x 10-4

risk:1 x 10-5)

MW- 105B

MW- 310A

MW-311B

MW- 315B

MW- 316A

MW-408B

MW-410B

MW-501B

MW-503B

MW- 701A

MW-701B

MW- 701C

MW-702C

MW- 703C

MW- 705B

MW- 706B

MW- 707B

MW- 708C

MW-711C

MW-713C

MW-714

Table 5-3 Groundwater VOC Concentrations

MW-719C

Acetone 220000 11000000 2200000 390000 a 190 510 4 1400 110 12

Benzene 14 700 140 9100 abc 320 ac 1900 abc 120 a 4900 abc 20 a 110 a 22 66 a 3

Carbon Tetrachloride 5 250 13

Chlorobenzene 390 19500 3900 2200 a 210 200 150 10 21 79 13 1

Chlorodibromomethane 32 1600 320

Chloroethane 28000 1400000 280000 710 12

Chloroform 80 4000 80 43 270 ac 7 2

Cis-1,2-dichloroethene 210 10500 2100 4 57000 abc 250 a 800 a 1 3 1100 a 4800 ac 1 3 19 4 1500 a 170 1

1,1-dichloroethane 2200 110000 22000 10 13000 a 180 110 4 570 2 2 1 44 64 63 100 3

1,2-dichloroethane 23 1150 230 120000 abc 260 ac 4 43 a 20 46 a 62 a 2

1,1-dichloroethene 190 9500 1900 18 1 1200 a 920 a 38 100

1,2-dichloropropane 35 1750 350 26 2 4

Ethylbenzene 700 35000 700 9100 ac 96 230 210 3 2 230 65

Methylene chloride 67 3350 670 1100000 abc 9 1600 ac

2-butanone 440000 22000000 4400000 160 140 430

m-xylene 23000 1150000 - 1100 140 1000 220 25 3

o-xylene 33000 1650000 - 330 35 320 97 7 1

p-xylene 22000 1100000 - 1100 140 1000 220 25 3

Styrene 8900 445000 89000

1,1,2,2-tetrachloroethane 30 1500 300 1400 ac 390 ac 3

Tetrachloroethene 11 550 110 5 2 17 a 330 ac 610 abc 15 a 10 4

Toluene 1500 75000 15000 1200 280 3100 a 1600 a 34 4

Trans-1,2-dichloroethene 180 9000 1800 19 100 14 4

1,1,2-trichloroethane 41 2050 410 2 110 a 1 1 5

1,1,1-trichloroethane 3100 155000 31000 9 4 4000 a 4600 a 9 2

Trichloroethene 5 250 5.3 20 ac 76000 abc 2 18 ac 2100 abc 8700 abc 31 ac 10 ac 21 ac 1 3 19 ac

Vinyl chloride 2.5 125 25 31 ac 65 ac 13 a 81 ac 44 ac

Notes: Results and screening values are in ug/L Results are from groundwater sampling conducted in November 2002 and June 2003 a - results >Table 2 (GW) value for additional risk 10-5

b - results >50 x Table 2 (GW) screening value c - results >Table 3b (GW) with attenuation factor of 10-4

Blank cells - compound not detected in sample

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Soil Gas Assessment

Following evaluation of site-specific groundwater data, it is necessary to assess site-specific soil gas data. However, at the Silresim Site no soil gas data exists with which to assess unsaturated zone soil contamination.

Question 4g – Do measured or reasonably estimated soil gas concentrations exceed the generic target media-specific concentrations given in Guidance Tables 2a, 2b, or 2c?

Answer – Soil gas data is not available.

There is no soil gas data available for the Silresim Site. However, given the relatively high volatile concentrations in the groundwater plume, the absence of soil gas data represents a potential data gap with respect to the evaluation of vapor intrusion for existing buildings on the LIS and B&L Auto Parts properties.

Question 4h – Is the nature and extent of soil contamination adequately characterized?

Answer – Yes, although soil sampling data within 100 feet of the two LIS buildings is limited.

Extensive soil sampling has been conducted in the unsaturated zone on both the Silresim Site and the LIS properties. A number of soil sampling investigations have been performed on these properties during and since the Remedial Investigation. Soil VOC contamination sampling has not been conducted across Tanner Street. However, it is assumed based on historical evidence, that spillage from the Silresim operations did not occur across Tanner Street on the B&L Auto Parts and Bond properties.

Most recently, soil data collected in 1999 from across the Site along with data collected in 2003 from a more limited area have been reviewed. The soil data collected in 1999 was part of a comprehensive site sampling to delineate the VOC source term and to provide data for revising the site CUGs. The data collected in 2003 were from an area of the Site with significant VOC contamination where a remedial pilot test was conducted. The data reviewed was limited to subsurface soil samples collected from the Silresim and LIS properties. Most historic site activities took place on the Silresim property and the most significant VOC contamination source is also located on the Silresim and LIS properties. It should be noted that recent soil sampling events have focused on LIS areas under the gantry and near the Silresim property. Soil data within 100 feet of the LIS buildings is limited.

In assessing the potential for vapor intrusion, the results for source term delineation and CUG assessment completed in May 2001 were reviewed since this is the most recent site-wide data set and represents a relatively complete set of soil data. Chlorinated ethenes (trichloroethene) and ethanes (tetrachloroethene) along with aromatic VOCs (benzene) were frequently found to exceed the subsurface soil CUGs by several orders of magnitude. Tetrachloroethene had a maximum concentration detected of 5,800 mg/Kg with a CUG established for the Site of 0.85 mg/Kg, benzene had a maximum concentration of 11 mg/Kg with a CUG of 0.04 mg/Kg. It is noted that due to the high concentrations of some analytes, the reporting limits for other analytes in samples were often greater than the respective cleanup goals. Trichloroethene, methylene chloride and 1,1-dichloroethene data demonstrated numerous exceedances of their respective CUGs. These three compounds were found to be significant contributors to the soil contamination in the comprehensive sampling for the Electrical Resistance Heating (ERH) Pilot Test. This is primarily due to their relatively low CUG values.

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Question 4i – Are there site conditions and/or data limitations that may make use of the generic soil gas attenuation factors inappropriate?

Answer – Yes, in certain locations.

At certain site locations on the Silresim Site generic soil gas attenuation factors may not be appropriate. In particular, on portions of the LIS property groundwater is relatively shallow (~10 feet or less) at a number of locations. In addition, the Operations Building possesses a basement with an earthen floor. The generic attenuation factors assume a basic concrete slab foundation (basement or slab-on-grade) and are potentially not representative of conditions and the actual resistance of vapor intrusion for the Operations Building. Also, a sump exists in the LIS Administration Building.

The flooring beneath the buildings on the B&L Auto Parts property is believed to be both concrete slab and earthen floor. However, this information should be confirmed prior to making final assessments.

Question 5 – Semi-Site-Specific Screening

The objective of Question #5 is to further evaluate the potential vapor intrusion pathways considered in Question #4, using tables of generally recommended generic target media-specific concentrations that incorporate some limited Silresim site-specific information. This question factors a consideration of Silresim soil type and depth to source in screening available groundwater and soil gas data. In support of Question #5, attenuation factors based, in part, on the Johnson and Ettinger Model are incorporated into the assessments.

Question 5a – Do groundwater and/or soil gas concentrations for any constituents of potential concern exceed target media specific concentrations by a factor of >50?

Answer – Yes

Individual groundwater VOC concentrations at several shallow monitoring wells exceed the generic target groundwater concentrations for 10-5 by a factor > 50. See Table 5-3 for summary of these exceedances. As indicated, concentrations of one or more individual VOCs in wells MW-310A, MW-316B, MW-701A and MW-701C exceed threshold values by 50 times or more.

[Note - If observed concentrations are greater than 50 times the generic target concentrations, then the Subsurface Vapor Intrusion Guidance recommends expeditious site-specific evaluation.]

Question 5b – Are there site conditions and/or data limitations under which the use of semi-site-specific attenuation factors based upon the Johnson-Ettinger Model would not be recommended?

Answer – Yes

Factors that typically make the use of semi-site-specific attenuation factors inappropriate include:

• Very shallow vapor sources (e.g., depths less than 5 ft. below foundation level); or • Relatively shallow vapor sources (e.g., depths less than 15 ft. below foundation level), and one or

more of the following: � Buildings with significant openings to the subsurface (e.g., sumps, unlined crawlspaces,

earthen floors); or

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� Significant preferential pathways, either naturally occurring and/or anthropogenic; or � Buildings with very low air exchange rates (e.g., <0.25/hr) or very high sustained

indoor/outdoor pressure differentials (e.g., >10 Pascals); or � Soil types outside the range shown in EPA Guidance Table 4; or � Any other situation for which the Johnson-Ettinger Model is deemed inappropriate.

As previously noted, at the Silresim Site, an earthen floor exists in the basement of the Operations Building on the LIS property and a sump exists in the Administration Building basement. The earthen floor coupled with the relatively shallow water table on the LIS property would potentially make use of the Johnson-Ettinger Model inappropriate for these areas and not conservative. That is, actual rate of flow of VOC contaminated vapor up into the buildings could be higher than what may be predicted by the model.

Question 5c – Are the depth to vapor source and the overlying unsaturated zone soil type adequately characterized in areas with inhabited buildings?

Answer – Yes, for most of the Site.

The depth to volatile groundwater contamination is relatively well known for the Silresim and LIS properties. The depth to contamination is also relatively well known for most of the B&L Auto Parts property.

Soil stratigraphic types are relatively well characterized across the Silresim, LIS and B&L Auto Parts properties, although investigations of soil chemical contamination have not been performed on the B&L Auto Parts property.

Subsurface Source Identification

Question 5d – Is there any potential contamination (source of vapors) in the unsaturated zone at any depth above the water table?

Answer – Yes on the Silresim property and portions of the LIS property.

Volatile contamination is present in the unsaturated zone at the Silresim Site. Unsaturated zone VOC contamination is widespread on the Silresim property.

No substantive zones of unsaturated zone contamination are believed to be present in the soil immediately beneath the two LIS buildings. However, unsaturated zone or NAPL contamination is believed to be present in the gantry area of the LIS property. Evidence indicates that this contamination is >100 feet from the two LIS buildings. There is no current evidence to indicate that this contamination is within 100 feet of the LIS buildings. It should be noted that this does not preclude indirect contamination of the unsaturated zone beneath the LIS buildings from the contaminated groundwater below.

No bulk soil or soil gas measurements have been made on the B&L Auto Parts property immediately across Tanner Street from the Silresim Site. However, there is no site-related historical information to suggest that site contamination could have migrated beneath Tanner Street, in the unsaturated zone to this property.

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Question 5e – Do measured or reasonably estimated groundwater concentrations exceed the target media-specific concentrations given in Guidance Table 3b?

Answer – Yes

The soil at the Site, sandy silt, silty sand with clay, is determined to be loam according to the U.S. Soil Conservation Service system. Generally the depth from the basements to the groundwater well screen intervals is 5 feet - 25 feet for the monitoring wells located near existing buildings. Using the EPA Guidance Figure 3b for vapor attenuation factors - groundwater to indoor air pathway, an attenuation factor of 10-4 is determined across the area of interest for the Site. Use of EPA Guidance Table 3b (a risk level of 10-5) and an attenuation coefficient of 10-4 based on some of the site-specific attenuation parameters (depth and soil type) provides for a semi-site-specific screening. An evaluation of the groundwater VOC concentrations to the groundwater screening levels for the scenario-specific vapor attenuation factors are shown in Table 5-3.

As indicated in Table 5-3, several VOCs exceed the semi-site-specific screening for 10-5 risk.

Question 5f – Do measured or reasonably estimated soil gas concentrations exceed the target media-specific concentrations given in Tables 3b.

Answer – Soil gas data is not available.

5.3 Tertiary Screening Tier III – Site-Specific Assessment

Vapor Intrusion Pathways that cannot be screened out using primary and secondary screening warrant Tier III Site-Specific Assessment. Tier III assessment emphasizes the use of direct measurement. In particular, it is recommended that evaluation approaches be prioritized as follows:

1. Direct measurement of foundation (subslab) air concentrations before any indoor air measurements.

2. Direct measurements of indoor air concentrations coupled with a building surveys, as appropriate. 3. Complementary site-specific mathematical modeling, as appropriate.

Emphasis is placed on performing subslab soil gas sampling prior to indoor air sampling in order to minimize the detection of volatiles associated with sources other than the site-related contaminant plume.

In conjunction with the Guidance, the following questions have been incorporated into this Tier III evaluation for the Silresim Site.

Question 6a – Have the nature and extent of contaminated soil vapor, unsaturated soil, and/or groundwater as well as preferential pathways and overlying building characteristics been adequately characterized to identify the most-likely-to-be-impacted buildings at the Silresim Site?

Answer – Groundwater volatile contaminant distributions are relatively well characterized. However, contaminated soil vapor distributions are not well characterized.

As previously discussed, extensive groundwater monitoring data exists for the Site, which is considered to be well characterized with the exception of a few relatively limited areas, including some on the B&L Auto Parts property.

2004-JV03-0030 5-16 12/20/04

As previously noted, Figure 5-1 identifies those site buildings that are within the 100 foot footprints of the 10 ug/L and 1,000 ug/L groundwater total volatile organic contours. Also, as noted, preferential pathways for vapor migration do exist around certain portions of the buildings on the LIS property and along Tanner Street. Therefore, the possibility of preferential soil gas migration may exist.

As previously noted, no soil gas data currently exists for the Silresim Site. Therefore, the nature and extent of contaminated soil vapor beneath and around the LIS and B&L Auto Parts buildings is unknown.

Question 6b – Is an Environmental Indicator (EI) determination being conducted and is an appropriate and applicable model being used?

Answer – An EI determination has not been conducted at the Site to date.

No modeling has been performed specifically in response to the current EPA Guidance and a Tier III Site-Specific Pathway Assessment. No projections of risk associated with measured subsurface contaminant levels and modeled contaminant diffusion and migration have been developed. However, the Johnson and Ettinger Model was used to establish the relationships between groundwater and subsurface soil VOC contaminant levels and potential indoor inhalation exposure and intake during the calculation of the revised cleanup goals.

Question 6c – Does the model predict an unacceptable risk?

Answer – Modeling has not been conducted to date, with respect to the Tertiary Screening Guidance. However, modeling approaches were utilized in developing site CUGs.

Question 6d – Are subslab soil gas data available?

Answer – Subslab soil gas data are not currently available.

Question 6e – Do measured subslab soil gas concentrations exceed the target shallow soil gas concentrations given in Tables 2(a), 2(b), or 2(c)?

Answer – Subslab soil gas data are not currently available.

Question 6f – Is the subslab sampling data adequate?

Answer – No, subslab soil gas data is not available but is needed.

Subslab soil gas data is currently not available. This is of some concern given the results of the vapor intrusion Guidance evaluations performed under Questions #4 and #5 above and the risk assessment evaluations discussed in Section 2.2. In order to better assess possible vapor intrusion issues, particularly those pertaining to the buildings on the LIS and potentially B&L Auto Parts properties, subslab sampling data is warranted.

In addition, subslab soil gas data represents the link between groundwater VOC concentrations and potential indoor air VOC concentrations. Subslab data is considered necessary to support any future efforts to correlate groundwater VOC concentrations with potential indoor air VOC levels for designing possible future monitoring programs.

2004-JV03-0030 5-17 12/20/04

Question 6g – Do measured indoor air concentrations exceed the target concentrations given in Table 2(b)?

Answer – Yes, for a few VOC compounds.

As indicated in the response to Question 4(b), indoor air samples collected in April 2002 did have detections of trichlorethene and benzene that exceeded the indoor air 10-5 target concentrations identified in Guidance Table 2(b).

Question 6h – Do indoor air concentrations adequately account for seasonal variability and represent the most impacted buildings or area?

Answer – No, available indoor air concentrations do not adequately account for seasonal variability.

The available indoor air data is limited to the Operations and Administration Buildings on the LIS property. These two buildings probably do represent the most impacted area of the Silresim Site with respect to vapor intrusion. However, data is not available with which to evaluate possible seasonal fluctuations in the VOC vapor concentrations such as might result from changes in soil temperature and/or changes in water table levels.

Question 6i – Have background sources of vapor in indoor air and ambient (outdoor) air been adequately accounted for?

Answer – No, not fully.

Some limited background air samples to support the indoor air sampling programs have been collected. This has typically been one upgradient and one downgradient sample during each indoor sampling round. The data is not considered adequate to either confirm or eliminate non-site-related sources as potentially impacting indoor air in the LIS buildings.

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6.0 SUMMARY AND RECOMMENDATIONS

This section summarizes the results of the assessment of the Silresim Site with respect to the recent EPA Subsurface Vapor Intrusion Guidance.

6.1 Existing Site Inhalation Evaluations

As part of the ongoing Silresim environmental monitoring program, indoor air data was collected during several sampling events conducted at the LIS Operations and Administration buildings. Indoor air sampling data collected at the LIS buildings during four sampling events conducted between July 1999 and April 2002. Overall field sampling protocols were relatively consistent with those suggested in general guidelines published by MADEP (2002), near the end of the Silresim sampling effort.

Indoor air results were used to estimate the inhalation risks to workers in the LIS buildings using conservative but reasonable exposure assumptions. The projected risks were generally at or just exceeding EPA risk goals for long term public exposure. However, certain VOCs whose concentrations exceeded risk goals may have been associated with operations within the buildings themselves.

In addition to indoor air measurements, the groundwater-to-indoor air pathway was also explicitly incorporated into the development of the risk-based Baseline Assessment Values and the 2002 revisions to the Silresim Cleanup Goals. Results of these assessments indicated that some of the revised site CUGs for VOCs, which were primarily driven by the vapor intrusion pathway were not currently being met.

Overall, the results of the indoor air evaluation, considered in conjunction with certain site VOC concentrations exceeding both MADEP groundwater standards and site-specific CUGs based on the vapor intrusion pathway, suggest that further evaluation of this pathway was appropriate. As such, the issue of vapor intrusion at Silresim was evaluated following the guidelines of the recent draft EPA Subsurface Vapor Intrusion Guidance.

6.2 EPA Subsurface Vapor Intrusion Results

The results of the application of the three tier EPA Subsurface Vapor Intrusion Guidance to the Silresim Site indicate that given the relatively high residual volatile organic concentrations remaining in site soils and groundwater, some potential current and/or future health concerns related to vapor intrusion may exist.

6.2.1 Primary Screening

As identified in Table 5-1, the results of the Tier I Primary Screening Process confirm that numerous volatile and toxic chemicals are present at the Silresim Site and, therefore, are of possible concern from a vapor intrusion standpoint.

The Tier I assessment also confirmed that inhabited buildings are currently (and could in the future) be located near volatile subsurface contamination. As indicated in Figure 5-1, several currently occupied buildings are within the 100 feet of the 10 ug/L TVO contour for the groundwater plume. Those buildings that are of potentially greatest concern with respect to vapor intrusion reside on the Lowell Iron and Steel property. However, as depicted in Figure 5-1, other buildings such as those on the B&L Auto Parts and Scannell properties might conceivably be affected. In addition, the potential construction of future

2004-JV03-0030 6-1 12/20/04

buildings on several properties including the LIS, B&L Auto Parts, Tucci and Bond properties could potentially be impacted by the existing subsurface volatile contamination.

Based on the Tier I assessment, it does not appear that any immediate actions are warranted to address or mitigate current risks. This conclusion is based, in part, on the fact that some air monitoring has been conducted in the LIS buildings of greatest current concern. An assessment of the results of this monitoring effort indicates that immediate actions should not be necessary.

6.2.2 Secondary Screening

The results of Tier II Secondary Generic Screening confirm that some vapor intrusion concerns do, in fact, exist at the Silresim Site. Certain indoor air results for the most recent sampling round (April 2002) for LIS buildings do exceed the threshold results for trichloroethene and benzene. It should again be noted that these EPA Guidance target concentrations are primarily intended for application to residential buildings.

Tier II Secondary Screening results also clearly indicate that at a number of shallow well locations groundwater VOC concentrations exceed generic target concentrations associated with the 10-5 risk levels established in the Guidance. As indicated in Table 5-2, the magnitude of the exceedances varies depending upon the individual VOC contaminant and monitoring well in question. As indicated in Tables 5-2 and 5-3, VOC contaminants that exceed their respective VOC threshold levels at multiple shallow well locations include benzene, trichloroethene, cis 1,2-dichloroethene, 1,2-dichloroethane and vinyl chloride.

Groundwater VOC concentrations in excess of the threshold levels are observed for several shallow wells located within 100 feet of several site buildings. As indicated in Figure 5-2, the footprints of groundwater wells containing VOC contaminant levels in excess of the 10-5 threshold level intersect the two Lowell Iron and Steel buildings, as well as portions of the two B&L Auto Parts buildings, the Scannell building and the Tucci building. It should also be noted that undeveloped portions of the LIS, B&L Auto Parts, Bond and Tucci properties are potentially impacted by the contaminated groundwater vapor intrusion footprints.

In subsequent secondary screening evaluations (Question #5), results indicate that certain VOC contaminants in several shallow monitoring wells also exceed 50 times the target concentrations associated with the 10-5 risk level and/or the site-specific Guidance model (Table 3b) levels. Wells exceeding these criteria for one or more contaminants include several on the LIS property including MW-105B, MW-316A, MW-501B, MW-702C, MW-703C, MW-707B, and MW-711C. In addition, wells MW-315B in Tanner Street, and wells MW-713C and MW-701C on the Tucci property also exceed at least one of these criteria.

As noted in Section 5.0, substantial bulk soil VOC contamination exists in the unsaturated zone in certain portions of the Silresim Site. Data indicates extensive soil contamination on the Silresim property and on certain portions of the LIS property in the vicinity of the gantry. An examination of available LIS soil data suggests that most of unsaturated zone soil contamination on the LIS property resides more than 100 feet from the two LIS buildings and therefore should not pose a significant concern with respect to vapor intrusion in these buildings. However, it is noted that soil sampling data from within 100 feet of the LIS buildings is limited. It is also noted that the possibility of some preferential pathway migration of vapors from these deposits through the unsaturated zone to the buildings in question can not be ruled out.

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As discussed in Section 5.0, there is no soil gas data available for the Silresim Site. This applies to both open areas of the Site underlain by VOC contamination and unsaturated zone soils near the occupied buildings of potential concern. The absence of any soil gas data is considered to represent a substantive data gap for the Site. Soil gas data (including subslab vapor data) represents the key link in attempting to assess the potential relationship between the groundwater VOC contamination exceedances discussed above and indoor air VOC concentrations in buildings within their respective footprints.

6.2.3 Tertiary Screening

The EPA Guidance recommends that priority be given toward the collection of soil gas and/or subslab sampling data, in part, to avoid the complexities associated with performing indoor air sampling. However, the absence of soil gas and subslab soil gas data at the Silresim Site currently limits the applicability of tertiary screening.

Due to the complexity of the stratigraphy at the Silresim Site, the high VOC concentrations in groundwater, and the potential existence of preferential migration pathways, mathematical modeling is not considered to be an adequate substitute for the collection of soil gas/subslab sampling data. Basic modeling may, however, be an appropriate complement to the collection of actual field data.

6.2.4 Overall Results

The overall results of the application of the vapor intrusion screening guidance to the Silresim Site support existing site analyses and indicate that some potential exceedances of target concentration values currently exist. The Guidance target concentration values utilized in this assessment are primarily intended for residential buildings. Since the buildings at the Silresim Site are commercial/industrial, the extent of concern regarding the screening results may be somewhat reduced. Nonetheless, it is recommended that some additional site investigation related to vapor intrusion be considered.

6.3 Recommendations

In developing recommendations with respect to the Silresim Site, the results of the vapor intrusion screening have been considered in conjunction with future sampling objectives currently being considered for longer term application at the Site. Specifically, from the site management perspective it would be ideally preferred to minimize the need for long term monitoring programs, other than for groundwater. Therefore, it would be potentially advantageous to be able to use groundwater data as a potential indicator tool for possible indoor air concerns.

Consistent with the EPA vapor intrusion screening results, it is recommended that additional vapor intrusion investigation at the Silresim Site be focused on the collection of some soil gas/subslab vapor analytical data at the two buildings on the LIS property and potentially the primary building on the B&L Auto Parts property. Currently, these appear to be the buildings likely to be most significantly impacted by vapor intrusion at the Silresim Site. It is felt that soil gas/subslab data gathered at these locations would be indicative of potential vapor intrusion trends at other existing site buildings. As previously discussed, from the EPA Guidance perspective, the absence of soil gas/subslab vapor data is considered to be a substantive data gap at the Silresim Site. In addition, soil gas/subslab data is also the information considered most appropriate to try to establish a link between groundwater VOC contamination and possible indoor air vapor intrusion impacts. Therefore, this type of data is needed to develop analytical

2004-JV03-0030 6-3 12/20/04

correlations to support the potential future use of groundwater VOC data, as a surrogate, in place of routine indoor air monitoring.

The detailed field sampling and laboratory analysis methods to be used for any soil gas/subslab sampling effort (or other field efforts) should be summarized in a Quality Assurance Project Plan Addendum (QAPP Addendum) prepared prior to implementation of a field effort. QAPP components should reflect recent MADEP and EPA guidance. The recommended principal components of a vapor intrusion sampling program designed to achieve the objectives discussed above, are summarized as follows:

• Performance of a few (2-3) sampling events over a one year period at the LIS buildings and possibly one B&L Auto Parts building;

• Collection of multiple soil gas/subslab samples (3-4) from beneath each building during each sampling event;

• Laboratory analysis of vapor phase samples using methods and detection limits compatible with the EPA Guidance concentrations;

• Evaluation and correlation of vapor phase data for individual VOCs with available data for relevant groundwater monitoring wells;

• Extrapolate results for the LIS buildings to assess possible impacts at other existing site buildings; and

• Utilize basic modeling tools (if warranted) to assist in developing potential correlations to allow future use of groundwater data to preliminarily screen for any potential vapor intrusion concerns.

The rationale for the conceptual sampling approach identified above is briefly summarized as follows: First, multiple subslab vapor intrusion sampling events are necessary in order to evaluate the impacts of seasonal changes relating to groundwater levels and soil temperatures on soil gas VOC concentrations and vapor intrusion. Therefore, a minimum of two sampling events and possibly a third event are recommended to reflect high and low groundwater levels and higher and lower soil temperatures at the Silresim Site. (The third sampling event may be desirable to confirm the data ranges identified in the first two sampling rounds and also to resolve any discrepancies.)

Due to the variability inherent in soil gas VOC concentrations, multiple soil gas samples should be collected from beneath each building. Specifically, it is recommended that a minimum of three samples should be collected from beneath each building. One sample should be collected from beneath the center of each building, and a second sample from along the periphery of the building. A third sample should be collected from any area where preferred vapor migration may occur. Depending on the building size and location, an optional fourth sample might be warranted for certain buildings.

If the soil gas sampling program results reveal any VOC hot spots, the installation of a small diameter shallow well might warrant future consideration in the hot spot area(s). Such a well can provide refined information on VOC contamination at the top of the water table. The desirability for any such wells can be determined following the completion of the subslab soil gas sampling.

In conclusion, a conceptual program of this nature should provide a solid basis with which to address current and potential future vapor intrusion issues at the Silresim Site.

2004-JV03-0030 6-4 12/20/04

7.0 REFERENCES

FWENC, 2002. Final Additional Site Investigation and Revision of Site Clean-Up Goals, Silresim Superfund Site, Volume I: Report, Foster Wheeler Environmental Corporation, January.

MADEP, 2002. Indoor Air Sampling and Evaluation Guide, WSC Policy #02-430, Massachusetts Department of Environmental Protection, Office of Research and Standards, April.

USEPA, 2002. Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils (Subsurface Vapor Intrusion Guidance), Draft Guidance, EPA530-F-02-052, November.

Watermark Environmental Inc., 2004. Groundwater Status Report No. 22, August 5 – February 5, 2003, Silresim Superfund Site, Lowell, MA.

Watermark Environmental Inc., 2004. Groundwater Status Report No. 23, February 6 – August 5, 2003, Silresim Superfund Site, Lowell, MA.

2004-JV03-0030 7-1 12/20/04

Appendix A Selected EPA Subsurface Vapor Intrusion

Guidance Tables and Figures

2004-JV03-0030 12/20/04

Table 1: Question 1 Summary Shcel

1s Chemical Is Chemical Sufficiently

Volatile?' YES YES VCC

YES YES "CC

YES YES

NO YES NO YES YES NO

"CC

YES NO

YES YES YES NO YES YES "CC

' YES NO

NO YES YES VF9

Y t S YES YES YES "C'.

YES YES YES YES YES YES YES YES NO

YES NO NO

YES YES YES YES YES Nn

Y t S

Check Here if Known or

Reasonably Suspected To . Be Present

NA NA NA

NA

NA NA NA

NA

NA

NA NA NA

NA

NA NA

NA

Table 1 DRAFT November 20.2002

Table 1: Question 1Summary Sheet

1s Chemical Sufficientlv Volatila?'

YES YES YES NO YES YES YES NO NO NO NO NO NO NO NO

YES YES NO

YES YES YES YES YES YES YES YES YES YES YES NO

YES YES YES YES YES YES NO

YES NO

YES YES YES YES YES YES YES YES YES YES YES YES YES YES NO NO NO NO

YES YES YES YES

Check Hcre If Known or

Reasonably Suspected To Be Present '

Table '1 DRAFT November 20,2002

Table 1: Question 1Summary Shoct

' A Chemical is considered suficienUy toxic if the vapor concentration of the pure component (seeAppendix D) poser an incremental lifetime cancer risk greater than lo4 ora non-cancer hazard index greater than 1.

' A chemical is considered sufficiently volatile it its Henry's Law Constant is 1 x 105 atm-m3/molor greater (US EPA. 1991).

Users should check off mmpoundr that meet the criteria for toxicily andvolatilityand are known or reasonably suspected to be present.

Table f DRAFT November 20.2002

. .. .-... .. C=a"~ernrX liliirililablsl I f available] I lsva8lalsl Illavaiiablsl

CAS NO. chomicai so~rces ~ c = n ~ ~ d n ~ e r * k~(usrrn~) I loowl ~oedn(unt$ 1uarm~1 I i o ~ b v 1 ~ p a m u n i w i w h n ~ l I IOOW ~ r m c ~ n ( u n ~ ~ r l imtl ~ r p a d hu n i ~ F ~ ~ ~ o ~ Crw~ c- cap, %

I I YC I 23E*OI I

' *F = 0.1 b r ShalhSoil Our TamelCmc~nmlion I I

NC

C I 0 6E.01

2 SE.00 I AF i0.01 loiDIIp SoliesrTamDlConcm,mtion AF =OW1 ,or OroYndCllsrisrgelConCBnirafln 'Hei,m.barsd ,awe,breamlngconren,a,'an errssdr maximumpoSdb!8 *omira, vrpormnr~nlraisn@,!wry i"rnrnPbf~) ' 'TargetrolgorCM~eImYmcX~Bedim s i i m Y m p o r d b l s u a ~ r m n r e n ~ U ~ ~ ~ p a ~ y i n m m p l ~ ~ l t Tha ~rgelpmund~taimnronvltimir 19 Vle MCLlor blalXylCnsr1iha MCL. (me MCLforchDrnfonnis Ulo L!CLloilalslTnMbmsthansr,~@MCLii,lPdfor mXpano,o-Xpans,andp.Xl(ano ni h BtaRJOtmnr~nira~ion baradoo iho upper hundcansors!opo,sn~!dent~fi~din slops kcforis baredons~ate.af.~laanmsthdohy, srsorrmni is SIII v n d n l g o ! ~for tnch~omawfianeir EPNS dmnnsr srrrrrmmntror lnsonroelhrtene(usE P A . Z W ~ . T ~ ~ h a e v e i ~ l o ~ c ~ rsvisv As a rsluil. Ihssiopslaolar and ma !amalmnronlntionualu*r loriCE may bereriedlvnhsr 15eeAP~BndixO.l

Compoundf with 01 = 7x10.' m = 5x10' m = 3x10' a - 2x10.' a - ~xlo.'Pmvisianai~oxidty Baris of T a m s l C o n ~ ~ n ~ t i o n

Dale ExUapolated C=cancer tisX Cm cw Cw cw Cw chemical from oal savrcer C ~ ( u g u ~ I u m l u g 4CAS NO. N = risk ~ ~ ~ ~ ~ W L )~ W L I

Table 3bGW Nwember 20,2002

I

Table 3b. GW: Querllon 5 Groundwatsr Ssreenlng Lsvslr for Scsnarlo.SpsdRo Vapor Altsnuatlan Factors (aJ Risk. 1 x 1 0 5

Target Groundwater Concentrations at Different Attenuation Factors I I

cmpaundr wilh a = ~ x d a- 5x10' c1 = 3x10.' a = zxlv4 a 1 ~ 1 0 ~ Pravlrlmal Toxldly Basis ofTargei CancDnfraUon Data Extrapalaled C=cancernrk Cw Cw %A Cw Cw

CAS NO. chemical ~ m m ~cinancancerdrk ( u g u ( W L ) I'JgiL) (UglL) ( U Woral sources

Table 3b-GW November 20.2002

Tab!* 3b - OW: Quertion 5 Grovnduatsr Screening Levslr for Scenario.SpecificVapor Anenuatlon Fac1016 (01

Risk= 1 x 10d

Target Gmundwatar Concentrations at Different Attenuation Factors I II

DRAFT

Figure 3a- DRAFT Vapor Attenuation Factors -Soil Vapor to Indoor Air Pathway

Basement Foundations

Depth to Contamination from Foundation (m)

-Sand -Sandy Loam -Loamy Sand +-Loam - I Figure 3b-DRAFT

Vapor Attenuation Factors -Ground Water to Indoor Air Pathway Basement Foundations

1 .OE-05015 20 25 300 5 10

Depth to Contamination from Foundation (m)

+Sand +Sandy Loam tLoamy Sand +Loam