United States
Environmental Protection Agency 1200 Pennsylvania Avenue, N.W

. Washington, D.C. 20460 September 2012

Office of Solid Waste and Emergency Response



# Support Document for the
Revised National Priorities List
Final Rule

– Leeds MetalLeeds Metal NPL Listing Support Document September 2012

ii 

# Support Document for the
Revised National Priorities List
Final Rule
Leeds Metal September 2012

Site Assessment and Remedy Decisions Branch Office of Superfund Remediation and Technology Innovation Office of Solid Waste and Emergency Response U.S. Environmental Protection Agency Washington, DC 20460Leeds Metal NPL Listing Support Document September 2012

iii 

## Table of Contents

Executive Summary

................................................................................................ ...................................... iv

Introduction ................................................................................................................................................... v
Background of the NPL ........................................................................................................................... v
Development of the NPL ........................................................................................................................ vi

Hazard Ran king System

.......................................................................................................................... vi
Other Mechanisms for Listing

............................................................................................................... vii
Organization of this Document ............................................................................................................. viii
Glossary

................................................................................................................................................ viii

1.0 List of Commenters and Correspondence ............................................................................................. 1

2.0 Site Description ..................................................................................................................................... 1

3.0 Summary of Comments ...................................................................................................................... 10

3.1 Support for Listing and Other Non-opposition Comments .......................................................... 11

3.2 State Deferral ............................................................................................................................... 12

3.3 Consistency with EPA Draft Methodology ................................................................................. 13

3.4 Consistency with State Treatment Recommendations ................................................................. 13

3.5 Aquifer Description ..................................................................................................................... 15

3.5.1 Ground Water Discontinuities ............................................................................................... 18

3.5.2 Ground Water Flow Direction ............................................................................................... 19

3.6 Likelihood of Release: Attribution .............................................................................................. 22

3.6.1 Shallow Ground Water Flow Direction and Aquifer Continuity ........................................... 30

3.6.2 Chemical Signatures/Distribution .......................................................................................... 31

3.7 Eligible Targets ............................................................................................................................ 43

3.7.1 Level I Targets ...................................................................................................................... 45

3.7.2 Lev el II Targets ..................................................................................................................... 49

3.7.3 Potential Targets .................................................................................................................... 52

4.0 Conclusion .......................................................................................................................................... 55
Attachment 1: Select Physical Properties Pages from the United States National Library of Medicine ChemIDplus Lite Database ............................................................................................................................................... 56
Attachment 2: Excerpt of CRC Handbook of Chemistry and Physics, 92nd Edition, 2011-2012 .............. 57

A ttachment 3: Excerpt of Petroleum Hydrocarbons And Chlorinated Hydrocarbons Differ In Their Potential For Vapor Intrusion, EPA Office of Underground Storage Tanks, March 2012 ............................................... 58Leeds Metal NPL Listing Support Document September 2012

iv 

## Executive Summary

Section 105(a)(8)(B) of CERCLA, as amended by SARA, requires that the EPA prepare a list of national priorities among the known releases or threatened releases of hazardous substances, pollutants, or contaminants throughout the United States. An original National Priorities List (NPL) was promulgated on Se ptember 8, 1983 (48 FR 40658). CERCLA requires that the EPA update the list at least annually.

This document provides responses to public comments received on the Leeds Metal site, proposed on September 16, 2011 (76 FR 57702) and amended on July 9, 2012, (77 FR 40318 ). This site is being added to the NPL based on an evaluation under the EPA’s Hazard Ranking System (HRS) in a final rule published in the Federal Register in September2012.Lee ds Metal NPL Listing Support Document September 2012

v 

## I ntroduction

This document explains the rationale for adding the Leeds Metal site in Leeds, Maine

, to the National Priorities List (NPL) of uncontrolled hazardous waste sites and also provides the responses to public comments received o n this site. The EPA proposed this site on September 16, 2011 (76 FR 57702 ). A Notice of Data Availability (NODA) was published on July 9, 2012, (77 FR 40318) to amend the proposed HRS documentation record. This site is being added to the NPL based on an evaluation under the Hazard Ranking System (HRS) in a final rule published in the Federal Register in September 2012.



### Background of the NPL

In 1980, Congress enacted the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), 42 U.S.C. Sections 9601 et seq . in response to the dangers of uncontrolled hazar dous waste sites. CERCLA was amended on October 17, 1986, by the Superfund Amendments and Reauthorization Act (SARA), Public Law No. 99-499, stat., 1613 et seq. To implement CERCLA, the EPA promulgated the revised National Oil and Hazardous Substances Poll ution Contingency Plan (NCP), 40 CFR Part 300, on July 16, 1982 (47 FR 31180), pursuant to CERCLA Section 105 and Executive Order 12316 (46 FR 42237, August 20, 1981). The NCP, further revised by the EPA on September 16, 1985 (50 FR 37624) and November 20, 1985 (50 FR 47912), sets forth guidelines and procedures needed to respond under CERCLA to releases and threatened releases of hazardous substances , pollutants, or contaminants. On March 8, 1990 (55 FR 8666), the EPA further revised the NCP in response to SARA.

Section 105(a)(8)(A) of CERCLA, as amended by SARA, requires that the NCP include

criteria for determining priorities among releases or threatened releases throughout the United States for the purpose of taking remedial action and, to the extent practicable, take into account the potential urgency of such action, for the purpose of taking removal action.

Removal action involves cleanup or other actions that are taken in response to eme rgency conditions or on a short-term or temporary basis (CERCLA Section 101). Remedial action is generally long -term in nature and involves response actions that are consistent with a permanent remedy for a release (CERCLA Section 101 ). Criteria for placin g sites on the NPL, which makes them eligible for remedial actions financed by the Trust Fund established under CERCLA, were includ ed in the HRS. The EPA promulgated the HRS as Appendix A of the NCP (47 FR 31219, July 16, 1982). On December 14, 1990 (56 FR 51532), the EPA promulgated revisions to the HRS in response to SARA, and established the effective date for the HRS revisions as March 15, 1991.

Section 105(a)(8)(B) of CERCLA, as amended, requires that the statutory criteria provided by the HRS be used to prepare a list of national priorities among the known releases or threatened releases of hazardous substances, pollutants, or contaminants throughout the United States. The list, which is Appendix B of the NCP, is the NPL.

An original NPL of 406 sites was promulgated on September 8, 1983 (48 FR 40658). At that time, an HRS score of 28.50 was established as the cutoff for listing because it yielded an initial NPL of at least 400 sites, as suggested by CERCLA. The NPL has been expanded several times sinc e then, most recently on May 10 , 2012 (7 7 FR 2 7368 ). The Agency also has published a number of proposed rulemakings to add sites to the NPL. The most recent proposal was on March 15, 2012 (7 7 FR 515344 ).Lee ds Metal NPL Listing Support Document September 2012

vi 

### Development of the NPL

The primary purpose of the NPL is stated in the legislative history of CERCLA (Report of the Committee on Environment and Public Works, Senate Report No. 96-848, 96th Cong., 2d Sess. 60 [1980]).

The priority list serves primarily informational purposes, identifying for the States a nd the public those facilities and sites or other releases which appear to warrant remedial actions. Inclusion of a facility or site on the list does not in itself reflect a judgment of the activities of its owner or operator, it does not require those persons to undertake any action, nor does it a ssign liability to any person. Subsequent government actions will be necessary in order to do so, and these actions will be attended by all appropriate procedural safeguards.

The NPL, therefore, is primarily an i nfo rmational and management tool. The identification of a site for the NPL is intended primarily to guide the EPA in determining which sites warrant further investigation to assess the natureand extent of the human health and environmental risks associated with the site and to determine what CERCLAfinanced remedial action(s), if any, may be appropriate. The NPL also serves to notify the public of sites the EPA believes warrant further investigation. Finally, listing a site may, to the extent potentially r esponsible parties are identifiable at the time of listing, serve as notice to such parties that the Agency may initiate CERCLA -financed remedial action.

CERCLA Section 105(a)(8)(B) directs the EPA to list priority sites among the known releases or threat ened release of hazardous substances, pollutants, or contaminants, and Section 105(a)(8)(A) directs the EPA to consider certain enumerated and other ap propriate factors in doing so. Thus, as a matter of policy, the EPA has the discretion not to use CERCLA to respond to certain types of releases. Where other authorities exist, placing sites on the NPL for possible remedial action under CERCLA may not be appropriate. Therefore, the EPA has chosen not to place certain types of sites on the NPL even though CERC LA does not exclude such action. If, however, the Agency later determines that sites not listed as a matter of policy are not being properly responded to, the Agency may consider placing them on the NPL.



### Hazard Ranking System

The HRS is the principle mechanism the EPA uses to place uncontrolled waste sites on the NPL. It is a numerically based screening system that uses information from initial, limited investigations

-- the preliminary assessment and site inspection

-- to assess the relative potential of sites to pose a threat to human health or the environment. HRS scores, however, do not determine the sequence in which the EPA funds remedial response actions, because the information collected to develop HRS scores is not sufficient in itself to determine either the extent of contamination or the appropriate r esponse for a particular site. Moreover, the sites with the highest scores do not necessarily come to the Agency's attention first, so that addressing sites strictly on the basis of ranking would in s ome cases require stopping work at sites where it was already underway. Thus, the EPA relies on further, more detailed studies in the remedial investigation/feasibility study that typically follows listing.

The HRS uses a structured value analy sis approac h to scoring sites. This approach assigns numerical values to factors that relate to or indicate risk, ba sed on conditions at the site. The factors are grouped into three categories. Each category has a maximum value. The categories are:

• likelihood that a site has released or has the potential to release hazardous substances into the environment;Lee ds Metal NPL Listing Support Document September 2012

vii • characteristics of the waste (toxicity and waste quantity); and

• people or sensitive environments (targets) affected by the release.

Under the HRS, four pathways can be scored for one or more threats as identified below:

• Ground Water Migration (S gw ) - drinking water

• Surface Water Migration (S
sw ) The following threats are evaluated for two separate migration components, overland/flood migration and ground water to surface water. - drinking water - human food chain

- sensitive environments

• Soil Exposure (S
s )

- resident population - nearby population

- sensitive environments

• Air Migration (S
a ) - population

- sensitive environments

After scores are calculated for one or more pathways according to prescribed guidelines, they are combined using the following root

- mean -square equation to determine the overall site score (S), which ranges from 0 to 100 :

If all pathway scores are low, the HRS sc ore is low

. However, the HRS score can be relatively high even if o nly one pathway score is high. This is an important requirement for HRS scoring because some extremely dangerous sites pose thr eats through only one pathway. For example, buried leaking drums of hazardous substances can contaminate drinking water wells, but

-- if the drums are buried deep enough and the substances not very volatile

-- not surface water or air.



### Other Mechanisms for Listing

There are two mechanisms other than the HRS by which sites can be placed on the NPL. The first of these mechanisms, authorized by the NCP at 40 CFR 300.425(c)(2), allows each State and Territory to designate one site as its highest priority regardless of score. The last mechanism, authorized by the NCP at 4 0 CFR 300.425(c)(3), allows listing a site if it meets the following three requirements:

• Agency for Toxic Substances and Disease Registry (ATSDR) of the U.S. Public Health Service has issued a health advisory that recommends dissociation of individuals from the release;

• EPA determines the site poses a significant threat to public health; and 

### 4 S + S + S + S = S 2

a 2

s 2

sw 2
gwLee ds Metal NPL Listing Support Document September 2012

viii • EPA anticipates it will be more cost

- effective to use its remedial authority than to use its emergency removal authority to respond to the site.



### Organization of this Document

The following section contains the EPA responses to site-specific public comments received on the proposal of the Leeds Metal site on September 16, 2011 (76 FR 57702) and the amendment of the HRS documentation record on July 9, 2012, (77 FR 40318). The site discussion begins with a list of commenters, followed by a site description, a summary of comments , and Agency responses to each comment. A concluding statement indicates the effect of the comments on the HRS score for the site.



### Glossary

The following acronyms and abbreviations are used throughout the text:

Agency U.S. Environmental Protection Agency

AMSL Above mean sea level

ATSDR Agency for Toxic Substances and Disease Registry
bgs Below ground surface

BMP Best Management Practice

BTEX Benzene, toluene, ethylbenzene, and xylene

oC Degrees Celsius

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act of 1980, 42 U.S.C. Sections 9601 et seq ., also known as Superfund

CFR Code of F ederal R egulations

CLP Contract L aboratory P rogram
cm/s Centimeters per second

CRQL Contract- required quantitation limit

CVOC Chlorinated volatile organic compound

DCA Dichloroethane

DCE Dichloroethene

DNAPL Dense non- aqueous phase liquid

DO Dissolved oxygen

DRO Diesel range organics

Eh Reduction potential

EPA U.S. Environmental Protection Agency , also USEPA

ERM Environmental Resources Management

FR Federal R egister

ft Feet ft bgs Feet below ground surfaceLee ds Metal NPL Listing Support Document September 2012

ix GIS Geographic information system

HRS Hazard Ranking System, Appendix A of the NCP

HRS score Overall site score calculated using the Hazard Ranking System; ranges from 0 to 100

LNAPL Light non- aqueous phase liquid

ME Maine

MEC Maine Central Railways

ME DEP Maine Department of Environmental Protection

MEG Maximum exposure guideline

MEK Methyl ethyl ketone (2 -butanone) μg/ L Micrograms per liter mg/L Milligram s per liter
mmHg Millimeters of mercury

mPa s Millipascal seconds

MTBE Methyl

- tert -butyl-ether

mV Millivolts

NCP National Oil and Hazardous Substances Pollution Contingency Plan, 40 C.F.R. Part 300

NODA Notice of data availability

NPL National Priorities List, Appendix B of the NCP

PA/SI Preliminary assessment/site investigation

PCB Polychlorinated biphenyl

PCE Tetrachloroethene or tetrachloroethylene

RfD Reference d ose
RI/FS Remedial investigation/ f easibility s tudy

SARA Superfund Amendments and Reauthorization Act

SI Site inspection

START Superfund Technical Assessment and Response Team

TCA Trichloroethane

TCE Trichloroethene or t richloroethylene

TPH Total petroleum hydrocarbons

TDL Target distance limit

VOC Volatile o rganic compoundLee ds Metal NPL Listing Support Document September 2012

1 

## 1. 0 List of Commenters and Correspondence

EPA -HQ- SFUND -2011-0647-0004 State Concurrence Letter
– Leeds Metal (September 2011).

EPA

- HQ

- SFUND -2011-0647-0005 Comment and attachments submitted by John C. Drobinski, P.G., LSP and Lyndsey Colburn, P.G., Environmental Resources Management (ERM) on behalf of Maine Central Railways (MEC), November 15, 2011.

EPA

- HQ

- SFUND -2011-0647-0006 U.S. Environmental Protection Agency, Federal Register Notice, Availability of Addendum to Documentation Supporting the Proposal of the Leeds Metal Site to the National P riorities List

, 77 FR 40318, July 9, 2012.

EPA

- HQ

- SFUND -2011-0647-0007 U.S. Environmental Protection Agency, Notice of Data Availability (NODA) - HRS Documentation Record Revisions - Leeds Metal (July 2012)

.

EPA

- HQ

- SFUND -2011-0647-0008 Comment and attachments regarding Leeds Metal proposed scoring changes ( EPA

- HQ

- SFUND -2011-0647-0006) submitted by John C. Drobinski, P.G., LSP and Lyndsey Colburn, P.G., Environmental Resources Management (ERM) on behalf of Maine Central Railways (MEC), August 8, 2012

.



## 2. 0 Site Description

The Leeds Metal site (the Site) as proposed in September 2011 includes five sources on the Leeds Metal property— four debris piles and one area of contaminated soil

— all of which are contaminated with various hazardous substances including tetrachloroethene (PCE), Aroclor -1254, Aroclor-1260, arsenic, chromium, and lead. The Site also includes the releases of hazardous substances, including PCE , and trichloroethylene (TCE), adegradation product of PCE, to ground water identified in samples from on-property monitoring wells and offproperty residential drinking water wells (see Figure 2, Ground Water Sample Location Map, and Figure 3, Drinking Water Sample Location Map, of this support document). Targets scored in the HRS documentation record at proposal consisted of the population served by the seven residential drinking water wells in which releases were identified.

The Leeds Metal property is located along Blue Rock Road in Leeds, Androscoggin County, Maine (ME) (see Figure 1 , Property Map, of th is support document). Prior to 1969, the Leeds Metal property, then known as Libby’s Pit, was mined for sand and gravel. According to information compiled by the State of Maine, from approximately 1969 to 1984, scrap metal recovery processes were conducted on the prop erty by various entities

. Included in the scrap metal recovery operations was an automobile shredding plant, which operated on the property until 1978. L ead batteries and other auto parts were also cleaned for resale. M etal from the shredded cars was salva ged, and upholstery was piled in former gravel excavation pits. S uch materials as gasoline, diesel, transformer oil, brake fluid, oils, battery acid, and antifreeze were dumped on the ground, and approximately 100 ‘barrels’ were staged along the southern p roperty b oundary. The Leeds and Monmouth Fire Departments responded to fires at the property; gasoline tanks would ignite, causing oil -saturated soil to burn.Lee ds Metal NPL Listing Support Document September 2012

2 The eastern and southern portions of the Leeds Metal property contained car shredding waste both on the ground surface and in piles, including Source Nos. 1- 4 (Debris Piles A -D) (see Figure 1, Property Map, of this support document). The material that comprises Debris Piles A -D was observed to include rubber, plastic, and metal debris. In addition, Source No. 5 consists of contaminated soil in the location of the former automobile reclamation operations (see Figure 1, Property Map, of this support document for source locations). Sampling conducted by the EPA during its November 2010 Leeds Metal Site Inspection documented PCE, Aroclor-1254, Aroclor -1260, arsenic, chromium, and lead in some or all of Sources 1-5.

The aquifer being evaluated at the Leeds Metal site has three different depth intervals (zones): the shallow overburden at approximately 15-22 f ee t b elow ground surface (ft bgs), the deep overburden at approximately 25- 47 ft bgs, and the bedrock at approximately 200 ft bgs (see Figure 4, Site Cross-Section, and Figure 5, Cross Section Profile Map, of this support document). No physical barriers to horizontal ground water flow, such as mountains or large rivers, have been identified within a 4- mile radius of the Leeds Metal property. Subsurface investigations to date have not identified any continuous aquitards in the vicinity of the Leeds Metal property that would retard vertical ground water flow.

The HRS documentation record at proposal used water elevation data in monitoring wells to evaluate the shallow and deep overburden flow directions while the evaluation of the bedrock ground water flo w direction was based on the bedrock topography at the Site . T he data show that ground water flow direction in the shallow overburden

zone is towards the north/northwest and the deep overburden ground water flow direction is toward the southwest (see Figur e 4, Site Cross -Section, and Figure 5, Cross Section Profile Map, of this support document). The relatively low overall topographical gradient at the property is not supportive of high horizontal ground water flow rates but is supportive of vertical ground water movement from the surface (shallow overburden wells) toward the bedrock (deep overburden wells) as observed by the M aine Department of Environmental Protection ( ME DEP ).

Subsurface investigations and ground water mo nitoring well installation on the Leeds Metal property were conducted to a maximum depth of 47 ft bgs within the overburden zone. Ground water samples collected from the monitoring wells documented releases of PCE in four monitoring wells at levels significantly above background (see Figure 2, Ground Water Sample Location Map, of this support document for monitoring well sample locations). TCE, which is a breakdown product of PCE, was detected in two ground water samples (GW-06 (a shallow overburden well) and GW-07 (a deep overburden well)).

Ground water samples collected from private drinking water wells screened in the bedrock and south of the Leeds Metal property documented concentrations of PCE and TCE significantly above background concentrations in f ive wells (DW -12, DW-13, DW-18, DW-23, and DW -24). Concentrations of TCE were identified significantly above background concentrations in two additional wells (DW-16 and DW-25) (see Figure 3, Drinking Water Sample Location Map, of this support document fo r residential drinking water well sample locations).

The significant increase in PCE and TCE found in monitoring wells and residential drinking water wells was attributed to the Site based on several lines of evidence, including:

• documentation of the historical operations conducted on site, which could include solvents containing PCE and TCE;

• identification of PCE in on

- site source samples;

• documentation that the vertical and horizontal ground water flow directions provide a clear path for hazardous substances to migrate from the S ite to the observed release monitoring wells and downgradient residential drinking water wells ;Lee ds Metal NPL Listing Support Document September 2012

3 • an explanation of the behavior of chlorinated solvents, and that they may exist as dense non -aqueous phase liquids (DNAPLs), which tend to sink through the subsurface and aquifers;

• documentation of chemical breakdown processes of PCE to TCE;

• the documentation of PCE in on-site “shallow” and “deep” overburden monitoring wells;

• the documentation of PCE an d TCE in residential drinking water well samples ; and

• a review of available information to identify other potential sources of PCE and TCE contamination in the area of the Leeds Metal property , which indicated that there is no other likely source significa ntly contributing to the hazardous substances found in observed release samples established for the Site.

At the time of proposal, 17 people were documented to use the water from the 7 contaminated private drinking water wells; based on PCE and TCE levels, this population was evaluated as targets subject to contamination above heath- based benchmarks in the HRS documentation record at proposal.

On July 9, 2012, revisions to the Leeds Metal HRS package in a notice of data availability (NODA) were announced in the Federal Register: Availability of Addendum to Documentation Supporting the Proposal of the Leeds Metal Site to the National Priorities List (77 FR 40318, July 9, 2012). The NODA explained that t he HRS toxicity factor value and the ground water pathw ay drinking water benchmark values for PCE and TCE used in HRS scoring at proposal were updated to reflect the EPA’s most recent health effects evaluations on these two substances . T he HRS toxicity factor value for TCE has changed from 10,000 to 1,000; how ever the toxicity factor value for PCE remains the same at 100. The TCE benchmark value for drinking water bas ed on the cancer slope screening concentrations has changed from 0.21 mg/L to 1.0 mg/L. The drinking water benchmark for PCE has changed from 1.6 mg/L to 5.0 mg/L.

Based on the changes to the TCE and PCE benchmarks, two drinking water wells have TCE concentrations above an HRS benchmark and no well has PCE concentrations above a benchmark. The evaluation of the threat to other ground water users in the vicinity of the Site was updated to reflect those people utilizing drinking water not currently found to be contaminated due to this site, but that for HRS purposes are considered subject to poten tial contamination

.
As explained in the NODA (77 FR 40318), the toxicity values and drinking water benchmarks have been revised, and the evaluation of the targets have been updated. As a result of these updates, the HRS ground water migration pathway score changes from 100.00 to 64.512; and the HRS site score changes from 50.00 to 32.25 . The NPL listing decision is not changed by this updated information and scoring.Lee ds Metal NPL Listing Support Document September 2012

4Lee ds Metal NPL Listing Support Document September 2012

5Lee ds Metal NPL Listing Support Document September 2012

6Lee ds Metal NPL Listing Support Document September 2012

7Lee ds Metal NPL Listing Support Document September 2012

8Lee ds Metal NPL Listing Support Document September 2012

9Lee ds Metal NPL Listing Support Document September 2012

10 

## 3. 0 Summary of Comments

The following comments were received by the EPA regarding the Leeds Metal HRS package proposed on September 16, 2011.

Paul R. LePage, Governor of the State of Maine, wrote on June 6, 2011, that “[d]ue to the apparent scope of contamination and potential clean

- up cost at the former Leeds Metal Site in Leeds, Maine, the State of Maine concurs with EPA’s proposed listing of this Site on the National Priorities List.”

Environmental Resources Management submitted comments on behalf of Maine Central Railways (MEC) objecting to the addition of the proposed Leeds Metal site to the National Priorities List (NPL). These comments
dealt with deferral of the Site to the State of Maine, the inclusion of wells in the HRS evaluation for which the State did not call for remediation, the description of the aquifer below the Leeds facility, and the attribution of the contamination in drinking water wells to releases from the Leeds Meta l site.

MEC expressed a preference to have this site deferred to the state of Maine, commenting that remediation and regulatory closure of this site under ME DEP’s regulatory program would be more timely, expedient, and cost effective than placing the si te on the NPL. In addition, MEC pointed out that deferring the Site to the state would also be in alignment with EPA’s draft Methodology for Understanding and Reducing a Project’s Environmental Footprint

.

MEC commented that the EPA was not consistent with state treatment recommendations because, according to MEC, concentrations of volatile organic compounds (VOCs) in monitoring wells located on the Leeds Metal property are within ME DEP maximum exposure guidelines, and some of the private drinking water we lls evaluated for the HRS package are not all locations recommended for treatment by ME DEP. MEC alsoconcluded that the chemical signature of the monitoring wells on the Leeds Metal property is different than offproperty residential drinking wells, thus questioning the attribution of the ground water release to the Site.

MEC commented that the aquifer contaminated by releases from the Leeds Metal site was mischaracterized in the HRS documentation record at proposal. Aspects of the aquifer description tha t MEC claimed were mischaracterized or excluded altogether included the discussion of ground water flow direction and discussion of an alleged ground water discontinuity between the Site sources and the drinking water wells scored as targets for
the Leeds Metal HRS package. Thus, MEC reasoned in its comments that any contamination found in private drinking water wells south

- southwest of the sources could not be attributed to the Leeds Metal site because those drinking water wells, according to MEC, are not downgradient of the sources and even if ground water did flow from the sources towards those private drinking water wells, a ground water divide, according the MEC, blocks the flow of ground water between the sources and drinking water wells.

MEC asserted that based on its review of data available to date, the chemical signatures of the contaminants in the monitoring wells on-site (i.e., on the Leeds Metal property) differ from those found in residential drinking water wells, and thus, it cannot be definit ively concluded that PCE impacts to private drinking water wells originated from the Leeds Metal site. MEC further concluded that this difference in chemical signatures represents two differing sources of impacts to ground water quality.Lee ds Metal NPL Listing Support Document September 2012

11 MEC commented that the concentrations of substances (including VOCs) in the deep monitoring wells, which are screened in the overburden section of the aquifer, located on the Leeds Metal facility are different compared to the residential drinking water well substance conce ntrations, which were drawn from the deeper bedrock section of the aquifer. MEC surmised that these concentrations are not consistent with the decreasing concentration gradient with depth at the facility.

The comments below were received by the EPA regard ing the revised HRS score sheet for the Leeds Metal site made available for comment in the Notice of Data Availability published July 9, 2012.

MEC submitted additional comments on August 8, 2012, in response to the July 9, 2012, NODA (77 FR 40318). In addition to repeating its earlier comments, MEC asserted that the ground water migration pathway score should be revised, thereby dropping the HRS score significantly and perhaps not triggering NPL listing.

MEC challenged the assumption that populations using ground water as a water supply within four miles of the Site should be included in the HRS evaluation. MEC commented that using the “4- radial mile” [target distance limit (TDL)] approach to identifying eligible populations threatened by the releases for the Site assumes the Site releases flow radially. MEC disputed this approach as valid based on its interpretation of ground water flow direction. Additionally, MEC disputed including the entire population within the 4- mile TDL because MEC claims that geohy drologic data was not taken into consideration. MEC argued that geologic mapping by the State of Maine demonstrates that the area is underlain by a heterogeneous geologic material making the nature and extent of the interconnectivity of the bedrock fractur es uncertain, and that the hydraulic connection between the overburden and bedrock flow systems is not proven. MEC commented that to conclude the entire “4- radial mile” population is a “Potential population Target” is overly conservative and the scoring sh ould be re

- evaluated because it does not reflect the geohydrologic data but only the geographic data, and because its data indicated that the area comprises at least two separate watershed basins.

MEC commented that the contamination documented in the we lls with contaminant levels above drinking water benchmarks (Level I wells) is not attributable to the Site because these wells are, according to MEC, hydraulically upgradient of the facility, and because the contaminants’ geochemical signature at these wells does not match the contaminant geochemistry under the facility property.

MEC commented that the contamination documented in other contaminated wells (Level II wells) is not attributable to the Site because these wells are, according to MEC, also hydra ulically upgradient of the facility.



### 3.1 Support for Listing and Other Non-opposition Comments

Comment : Mr. Paul R. LePage, Governor of the State of Maine, wrote on June 6, 2011, that “[d]ue to the apparent scope of contamination and potential clean -up co st at the former Leeds Metal Site in Leeds, Maine, the State of Maine concurs with EPA’s proposed listing of this Site on the National Priorities List.”

Response : The Leeds Metal site (the Site) is being added to the NPL. Listing makes a site eligible for remedial actions under CERCLA, and the EPA will examine the Site to determine what response, if any, is appropriate. Actual funding may not necessarily be undertaken in the precise order of HRS scores, however, and upon more detailed investigation may not be necessary at all in some cases. The EPA will determine the need for Superfund
monies for remedial activities on a site -by- site basis, taking into account the NPL ranking, State priorities, furtherLee ds Metal NPL Listing Support Document September 2012

12 site investigation, other response alternatives and other factors as appropriate. Work will not be stopped at some sites to begin work at other higher- scoring sites added to the NPL more recently

.



### 3.2 State Deferral

Comment : MEC commented that remediation and regulatory clos ure of this site under ME DEP’s regulatory program would be more timely, expedient, and cost effective.

Response : In the case of the Leeds Metal site , the EPA has decided that deferral to the State of Maine is not appropriate because, on January 23, 2008, ME DEP wrote to the EPA and requested assistance in investigating the Leeds Metal property due to lack of cooperation from the property owner [Reference 30, pp. 1-2 of the HRS documentation record at proposal]. Furthermore, Mr. Paul R. LePage, Governor of the State of Maine, wrote on June 6, 2011, that “[d]ue to the apparent scope of contamination and potential clean- up cost at the former Leeds Metal Site in Leeds, Maine, the State of Maine concurs with the EPA’s proposed listing of this Site on the
Nation al Priorities List” (see Section 3.1, Support for Listing and Other Non-opposition Comments, of this support document).

Regarding MEC ’s argument that remediation and regulatory closure of this site under the ME DEP’s regulatory program would be more cost- effective than listing the Site on the NPL, listing the site does not dictate or preclude any particular strategy for handling the site, including under the ME DEP’s regulatory program. EPA will defer to
the M E DEP’s regulatory program if that proves to be appropriate. The cost discussion in the Federal Register clearly states that including a site on the NPL does not cause the EPA necessarily to undertake remedial action, or that any action is required by, nor liability for site response costs assigned to, a private party (56 FR 21462, May 9, 1991). The cost discussion then outlines the Agency's perception of average potential costs per site that may occur in association with events generally following the proposed listing of a site. Any Agency actions that may impose costs on firms are based on discretionary decisions and are made on a case

- by

- case basis. Also, responsible parties may bear some or all the costs of the remedial investigation/feasibility study (RI/FS) and subsequent work, or the costs may be shared by the EPA and the States. Therefore, expenditures cited by the commenter are associated with events that generally follow listing the site, not with the listing itself. The EPA has
not allocated costs for this site at this time.

As to MEC’s recommendation to defer the remediation of this site to ME DEP’s regulatory program because it would be more timely and expedient, nothing in CERCLA or any other environmental laws limits the EPA’s authority to place eligible sites on the NPL where appropriate. EPA places eligible sites on the NPL pursuant to the Agency’s authorities under CERCLA and its associated regulations. As set out in the HRS documentation record and in these responses to comments, the Site in this case is eligible for listing and placing it on the NPL is
consistent with EPA’s authorities. In particular, because placing a site on the NPL is only an identification that a site warrants further investigation and not an identification of what remedial actions will be taken, it is not relevant at this stage to address which statutory authorities will be used to conduct remedial activities and whether a certain statutory authority would be able to implement those yet undetermined remedial activities more timely and expediently than an other statuto ry authority.Lee ds Metal NPL Listing Support Document September 2012

13 

### 3.3 Consistency with EPA Draft Methodology

Comment : MEC commented that addressing this site under ME DEP’s regulatory program would be in alignment
with the EPA’s draft Methodology for Understanding and Reducing a Project’s Environmental Foo tprint

.

Response : The EPA’s Office of Superfund Remediation and Technology Innovation document, Methodology for Understanding and Reducing a Project’s Environmental Footprint (finalized in February 2012) does not preclude a site from being placed NPL, and in fact, the b est management practices (BMPs) that the document describes are in place under a range of cleanup programs including Superfund, RCRA, federal facility, brownfield, and state voluntary actions (see http://www.epa.gov/oswer/greenercleanups/examples.html). Further, he document states that it does not, “. . . impose legally binding requirements, nor does it confer legal rights, impose legal obligations, implement any statutory or regulatory provisions, or change or substitute for any statutory or regulatory provisions” (see p. i of Methodology for Understanding and Reducing a Project’s Environmental Footprint, February 2012). Instead, “[t]his document presents [the] EPA’s metrics and methodology for conducting an environmental footprint analysis of site cleanup activities and describes common approaches to reduce that footprint” (see p. 1 of Methodology for Understanding and Reducing a Project’s Environmental Footprint

, February 2012). That is, this docum ent provides suggestions that are applicable to the remedy selection/clean -up part of the site assessment process, which follows the listing process as described below.

Consistent with CERCLA, the Agency has in place an orderly procedure for identifying s ites where releases of substances addressed under CERCLA have occurred or may occur, placing such sites on the NPL, evaluating the nature and extent of the threats at such sites, responding to those threats, and deleting sites from the NPL. The purpose of the initial two steps is to develop the NPL, which identifies for the States and the public those sites that appear to warrant remedial action (56 FR 35842, July 29, 1991). The evaluation or RI/FS phase involves onsite testing to assess the nature and exte nt of the public health and environmental risks associated with the site and to
determine what CERCLA -funded remedial actions, if any, may be appropriate. After a period of public comment, the Agency responds to those threats by issuing a Record of Decisio n which selects the most appropriate alternative. It is at this point that the EPA document, Methodology for Understanding and Reducing a Project’s Environmental Footprint (February 2012) is applicable and relevant. The selected remedy is implemented durin g the remedial design/remedial action phase. Finally, the site may be deleted from the NPL when the Agency determines that no further response is appropriate.



### 3.4 Consistency with State Treatment Recommendations

Comment : MEC questioned the inclusion of w ells in the HRS evaluation of the Site for which the ME DEP did not previously recommend treatment. Some these wells had concentrations below State guidelines or had different chemical signatures. MEC pointed out that concentrations of chlorinated volatile organic compounds (CVOCs) in “deep” wells at the Leeds property are consistently below the Maine maximum exposure guidelines (MEGs); however, drinking water wells not on the Leeds property had detections of CVOCs above the ME DEP action
levels. MEC stated , “[e]xcluding DW- 05, all drinking water wells where treatment systems were recommendedLee ds Metal NPL Listing Support Document September 2012

14 by MEDEP are located southwest of the Leeds Metal site.” 1 MEC stated that private drinking water wells directly downgradient of MW- 4D exhibit different chemical sign atures “and are also not locations recommended for
treatment.”

Response : The wells identified by the ME DEP as not recommended for treatment were correctly included in the HRS evaluation for this site consistent with the HRS. The HRS documentation record at proposal demonstrates that all the evaluated residential drinking water wells downgradient of the facility property were appropriately
characterized as contaminated due to releases from the Leeds Metal site.

Regarding the wells that did not exceed Main e regulatory levels, t he wells in question in MEC’s comments appear to be monitoring wells located on the Leeds Metal facility and residential drinking water wells located off of the Leeds Metal facility. The wells in question were used to document the likelihood that hazardous substances released from the Site entered ground water (i.e., these wells were identified as observed release wells) or to document users of the wells as a source of drinking water as actually contaminated targets associated with the
Leeds Metal site.

That drinking water standards of certain hazardous substances were not exceeded, or certain wells were not originally designated by ME DEP as locations recommended for treatment under the state program, does not eliminate the releases associated with these wells from consideration when evaluating a site using the HRS.

As first explained on July 16, 1982, when responding to public comments on the proposed (original) HRS (47 FR 31188), and again on September 8, 1983 (48 FR 40665), the Agency rejected the idea that releases within regul atory limits should not be considered "observed releases" under the HRS. As the Agency noted in 1982:

1 Please note that the commenter commonly uses the term “site” when referring to the Leeds Metal facility property rather than the “site” as defined by the HRS. CERCLA Section 105(a)(8)(A) requires EPA to list national priorities among the known "releases or threatened releases" of hazardous substances; thus, the focus is on the release, not precisely delineated
bound aries. Further, CERCLA Section 101(a) defines a "facility" as the "site" where a hazardous substance has been "deposited, stored, placed, or other wise come to be located." The "come to be located" language gives EPA broad authority to clean up contaminatio n when it has spread from the original source. On March 31, 1989 (54 FR 13298), EPA stated:

HRS scoring and the subsequent listing of a release merely represent the initial [emphasis added] determination that a certain area may need to be addressed under CERCLA. Accordingly, EPA contemplates that the preliminary description of facility boundaries at the time of scoring will need to be refined and improved as more information is developed as to where the contamination has come to be located; this refining step generally comes during the RI/FS
stage.

The revised HRS (55 FR 51587, December 14, 1990) elaborates on the "come to be located" language, defining "site" as "area(s) wh ere a hazardous substance has been deposited, stored, disposed, or placed, or has otherwise come to be located. Such areas may include multiple sources, and may include the area between the sources."

As discussed in the proposed rule, u ntil the site inves tigation process has been completed and a remedial action (if any) selected, EPA can neither estimate the extent of contamination at the S ite, nor describe the ultimate dimensions of the S ite.Lee ds Metal NPL Listing Support Document September 2012

15 [E]mission or effluent limits do not necessarily represent levels which cause no harm to public health or the environment. These limitations are frequen tly established on the basis of economic impacts or achievability.

By contrast, an observed release represents a 100 percent likelihood that substances can migrate from the site (47 FR 31188, July 16, 1982). The actual degree of contamination and its effects are more fully determined during the Remedial Investigation.

Section 3.6, Likelihood of Release: Attribution

, of this support document, contains a discussion of observed release requirements in the HRS and observed release documentation in the Leeds Metal HRS documentation record at proposal, and establishes that the wells in question were correctly identified as observed release wells.

Regarding that contamination in some wells might have different chemical signatures (that is, different mixtures of chemicals at different concentrations), Section 3.6.2, Chemical Signatures/Distribution, of this support
document identifies that the contaminants in these wells are also attributable to the Leeds Metal site and thus also correctly included in the Leeds Metal site HRS evaluation.



### 3.5 Aquifer Description

Comment : MEC provided several comments stating that the aquifer scored as part of this site contains ground water flow that has been mischaracterized in the HRS documentation record at proposal

. MEC presented a summary of data that shows ground water flow in the shallow overburden beneath the Site to be toward the north/northwest and away from the eligible targets; similarly, MEC commented that a basin divide is present southwest of the facility that makes it unlikely that ground water would flow toward the eligible targets.

Response : The aquifer being evaluated at the Leeds Metal site was properly delineated in the HRS documentation record at proposal to extend throughout the TDL for the Site with no aquifer discontinuities. For HRS purposes, an aquifer is one or more strata of rock or sediment that is saturated and sufficiently permeable to yield economically significant quantities of water to wells or springs. The HRS documentation record at proposa l correctly identifies that the aquifer being evaluated is a single aquifer system composed of three zones and all of the wells identified at the Site draw water from the same aquifer system.

The HRS presents the requirements to be met to establish the extent of the aquifer being evaluated at a site. HRS Section 3.0.1.1, Ground water target distance limit , contains the requirements to establish the TDL:

The target distance limit defines the maximum distance from the sources at the site over which targets are evaluated. Use a target distance limit of 4 miles for the ground water migration pathway, except when aquifer discontinuities apply (see section 3.0.1.2.2). Furthermore, consider any well with an observed release from a source at the site (see section 3.1.1) to lie within the target distance limit of the site, regardless of the well's distance from the sources at the site.

HRS Section 3.0.1.2, Aquife r boundaries, contains the requirements for establishing the continuity of the aquifer within the TDL and which individual aquifers underlying the site are considered part of the site aquifer :

Combine multiple aquifers into a single hydrologic unit for s coring purposes if aquiferLee ds Metal NPL Listing Support Document September 2012

16 interconnections can be established for these aquifers. In contrast, restrict aquifer boundaries if aquifer discontinuities can be established.

HRS Section 3.0.1.2.2, Aquifer discontinuities, presents the requirements establish ing the extent of the aquifer within the TDL :

Evaluate whether aquifer discontinuities occur within the 4- mile target distance limit. An aquifer discontinuity occurs for scoring purposes only when a geologic, topographic, or other structure or feature entirely transects an aquifer within the 4

- mile target distance limit, thereby creating a continuous boundary to ground water flow within this limit. If two or more aquifers can be combined into a single hydrologic unit for scoring purposes, an aquifer discontinuity occurs only when the structure or feature entirely transects the boundaries of this single hydrologic unit. When an aquifer discontinuity is established within the 4

- mile target distance limit, exclude that portion of the aquifer beyond the discontinuity in evaluating the ground water migration pathway. However, if hazardous substances have migrated across an apparent discontinuity within the 4

- mile target distance limit, do not consider this to be a discontinuity in scoring the site.

The HRS documentation record at proposal outlines the aquifer composition and characteristics of the ground water for the Leeds Metals site in Section 3.0.1, Regional Geology/Aquifer Description, and states on page 101 of the HRS documentation record at proposal:

Sur ficial deposits beneath the Leeds Metal property are classified as Island Pond Marine Delta, which were formed under glacial-marine deltaic conditions and are composed of sorted and stratified sand and gravel [69; 69a; 70; 70a]. On

- site investigations cond ucted to date indicate the subsurface geology consists of fine

- to

- coarse sand , with some fine- to

- coarse gravel and inconsistent inclusions of silt and clay on the property [21, Appendix G; 25, p p. 3, 14 -26; 32, Narrative Chronology (pp. 4-6), Table 1]. Ove rburden material thickness in the area around the Leeds Metal property is approximately 97 feet northwest

, along Plains Road

, and between 148 and 188 feet to the south and southwest of the property [72; 72a; 73, pp. 1-2]. The hydraulic conductivity of fine- to

- coarse sand deposits such as this is approximately 10 -4 centimeters per second (cm/s) [1, p. 51601 (Table 3-6)].

The Leeds Metal property is underlain by meta- sedimentary bedrock of the Sangerville Formation, Patch Mountain Member [7; 8; 63, pp. 1-2; 63a; 64, pp. 1-4; 65, p. 3, 66; 66a; 67, p. 10]. The Patch Mountain Member is characterized by ‘thin well- bedded alternations of light to medium greenish

- gray calc

- silicate granofels, quartz o-feldspathic biotite granofels, and finegrain ed impure granoblastic marble’ [64, p. 2]. In places, the Patch Mountain Member is composed of massive marble only [64, p. 2 ]. Bedding is frequently accentuated on weathered surfaces by the differential solution of marble beds [64, p. 2 ]. Evidence of fault ing in the area is almost entirely lack ing and the metamorphic rocks, as a rule, are poorly jointed [64, p. 9]. The hydraulic conductivity of low to moderate permeable fracture metamorphic bedrock such as this is from appro ximately 10 -4 to 10 -6 cm/s [ 1, p. 51601 (Table 3 -6) ].

Depth to bedrock northwest of the Leeds Metal property, along Plains Road, is 97 f ee t bgs (Well location DW-02), while the depth to bedrock immediately south of the Leeds Metal property onLee ds Metal NPL Listing Support Document September 2012

17 the adjacent property (Town of Leeds, ME Tax Assessors Office Map No. 4, Lot No. 39) is 148
feet bgs (Well location DW-09) [72; 72a; 73, p p.1-2; 144 p. 1].

Based on GPS data collected by START in November and December 2010, local residential well information regarding the depth to bedrock, and overb urden thickness in the area of the Leeds Metal property, the bedrock surface elevation (topography) in the vicinity of the Leeds Metal property, generally slopes from north to south along ME Route 106 [144, p. 1,]. The bedrock
surface topography slopes fro m 267.4 ft above mean sea level (amsl) northwest of the site along Plains Road (Background drinking water well location DW-02, 0.51 miles northwest of Debris
Pile D ), to 180.9 ft amsl adjacent the southwestern corner of the site along ME Route 106 (Sample DW -09 location, 0.1 miles southwest of Debris Pile D), to 160. 9 ft amsl south of the southwestern corner of the site along ME Route 106 (Sample DW -23 location, 0.3 miles
southwest of Debris Pile D) [144].

According to ME DEP, t he hydrogeologic environment is very complex and the limited sampling completed to date had been inadequate to understand the temporal and spatial complexities and variations [142, p. 1; 165, p. 3]. There is insufficient data to determine the location, size or relative strength of the source areas or v ertical and horizontal distribution of VOCs in the subsurface [142, p. 1]. However, no physical barriers to ground water flow, such as mountains or large rivers , have been identified within a 4- mile radius of the Leeds Metal property ( See Figure 6) [7; 8 ; 150 ; 151 ; 152]. S ubsurface investigations to date have not identified any continuous aquitards in the vicinity of the Leeds Me tal property [21; 24; 25; 28]. Furthermore, as noted above, the fine

- to -coarse sand overburden deposits and m oderately permeable fracture metamorphic bedrock do not demon strate any significantly lower hydraulic conductivity layers that separate aquifers throughout a 2

- mile radius of the site sources [1, Table 3 -6]. Therefore the hydrogeology beneath the site is characterized by a single aquifer consisting of the on- siteshallow and deep glacial overburden aquifer and the hydraulically connected underlying metasedimentary bedrock aquifer. The aquifer interconnection is also demonstrated by a downward migration of hazardous substances (PCE) from the Leeds Metal sources into the on

- site shallow and deep overburden aquifers, and then to the bedrock aquifer, which supplies nearby residential wells within 1 mile of the site sources (See Observed R elease D ata T ables – T ables 41 and 45). Therefore, an aquifer interconnection occurs within 2 miles of the sources at the site and the combined aquifer constitutes the aquifer being evaluated that is used for scoring the site [1, p. 51595 (Section 3.0.1.2.1)]. For the purposes of this evaluation, since the S hallow Overburden,

D eep Glacial and underlying Meta- sedimentary Bedrock Aquifers are interconnected the combined aquifer (Leeds Aquifer) constitutes the aquifer being evaluated.

While MEC claimed that the aquifer underneath the facility includes a basin divide that influences the ground water to flow toward the north/northwest, MEC did not present any new evidence beyond that presented and discussed in the HRS documentation record at proposal to demonstrate that an aquifer d iscontinuity is present at
the Site. See Northside Sanitary Landfill, Inc. v. Thomas , 849 F.2d 1516, 1520 (D.C. Cir. 1988) (commenter “cannot merely state that a particular mistake was made,” rather it must show “why the mistake was of possible significanc e” to the agency’s decision).Lee ds Metal NPL Listing Support Document September 2012

18 As presented above in this section, the HRS documentation record at proposal outlines the underlying geological conditions at the Site. These conditions support that no aquifer discontinuities exist at the Site that entirely transect the aquifer to influence the ground water flow direction and affect the eligibility of wells used in the scoring of the Site. The following subsections address MEC’s specific comments about establishing the TDL in the aquifer underlying the Site:

• 3.5.1 Ground Water Discontinuities

• 3.5.2 Ground Water Flow Direction

3. 5.1 Ground Water Discontinuities

Comment : MEC stated that the Leeds Metal property is located northeast of a basin divide, indicating it is unlikely that ground water from the facility is flowing to the southwest. MEC based this assertion on a review of the Maine Geological Survey geologic map for the vicinity of the Site, which was provided as Appendix A of the public comments (Docket ID: EPA- HQ

- SFUND -2011-0647-0005). MEC also asserted (citing Figures 1 through 3 of these public comments) that this information is consistent with ground water gauging and ground water flow direction determined for the Site. Additionally in its review of the revised scoring presented in the NODA (77 FR 40318, July 9, 2012), MEC commented that the geological materials at the surface are “a heterogeneous mixture of sand and gravel, silt, clay, peat, and till (Appendix A [map of Surficial Deposits]).” MEC asserted that this heterogeneous mixture calls into question the interconnectivity of the aquifer throughout the TDL.

Response : The aquifer being evaluated at the Leeds Metal site was properly established in the HRS documentation record at proposal and contains no documented aquifer discontinuities. The HRS documentation record at proposal correctly identified that the aquifer being evaluated is a single aquifer system and is continuous throughout the TDL. The heterogeneous soil mixture (presented in a map titled “Surficial Deposits” in Appendix
A of the public comments (Docket ID: EPA

- HQ

- SFUND -2011-0647-0008)) does not act as an aquifer discontinuity and MEC does not present any evidence to show that this heterogeneous soil mixture should be considered an aquifer discontinuity at the Site. Additionally, the Basin divide does not physically entirely transect the aquifer being evaluated and in fact appears to only influence ground water flow direction in the uppermost zone of the aquifer and thus is not an aquifer boundary.

As quoted above in Section 3.5, Aquifer Description, of this support document, the HRS only considers an aquifer discontinuity to be present when “a geologic, topographic, or other structure or feature entirely transects an aquifer within the 4

- mile target distance limit, thereby cr eating a continuous boundary to ground water flow within this limit.” Based on a review of the Maine Geological Survey geological map (attached in Appendix A of MEC’s public comments), MEC stated that a basin divide is present southwest of the Leeds Metal site and implied that the divide acts as an aquifer discontinuity.

While the geological map shows that a “surface

- water drainage -basin boundary” is present to the south and west of the Site, this boundary does not constitute an aquifer discontinuity at t he Site as it does not act as a barrier to ground water flow that transects the entire aquifer. A surface water drainage basin boundary illustrates the general direction that overland water will flow, but does not necessarily dictate ground water flow dire ction. While the map legend to Appendix A of MEC’s comments explains that “surface water divides generally correspond to ground water divides,” surface water flow direction does not always correlate to the ground water flow direction.
Site -specific ground water data (monitoring well ground water elevation data presented in References 14, 24, andLee ds Metal NPL Listing Support Document September 2012

19 44 of the HRS documentation record at proposal, as well as in MEC’s figure 2 and figure 3 of its submitted public comments) shows that this surface boundary does not act as an aquifer discontinuity; ground water located more than 25 feet below the Leeds Metal property is documented to flow toward the southwest, which is across this surface water boundary. The HRS documentation record at proposal documents that the local ground water flow direction in the aquifer beneath the Leeds Metal site is toward the south/southwest. As stated in Section 3.5.2, Ground Water Flow Direction, of this support document, MEC agreed with and presented additional evidence to
show that the ground water flow in the deep overburden is toward the southwest across the surface water boundary. Additionally, MEC presented no data or evidence to support the presence of an aquifer discontinuity
within the 4

- mile TDL that completely transects the aqu ifer being evaluated.

This comment results in no change to the HRS score and no change in the decision to place the Site on the NPL.

3.5.2 Ground Water Flow Direction

Comment : In questioning whether the contamination in wells located south/southwest of the Site could be attributed to the Site, MEC stated that the ground water beneath the Site flows toward the north/northwest across the Leeds Metal property.

Response : The ground water in the shallow and deep overburden aquifer zones flows in different directions. While the flow is generally toward the north/northwest in the shallow overburden zone, in the deeper zones the flow is toward the south/southwest. The HRS documentation record at proposal, as cited below, stated that it is
known that there is a h igh vertical gradient in the monitoring wells as well as documented portions of the underlying aquifer that support ground water flow toward the west/southwest. The aquifer being evaluated at the Leeds Metal site has been evaluated at three different depth intervals within the same aquifer at proposal: shallow overburden (~15-22 ft bgs), deep overburden (~25-47 ft bgs), and bedrock (~200 ft bgs). The HRS documentation record at proposal used water elevation data in monitoring wells to evaluate the shallow and deep overburden flow directions while the evaluation of the bedrock ground water flow direction was based on the bedrock topography at the Site.

The HRS documentation record at proposal outlines the evaluation of the ground water and flow direction

co nducted at the Site , stating on pages 99 -:

The ground water flow direction in the shallow overburden, deep overburden, and bedrock aquife rs is not fully characterized. As discussed below, the ground water in the “shallow overburden” was originally interpreted to flow in a southerly direction and later in a north to northwest direction (as indicated by wells with a maximum depth of 22 ft bgs) by the property
owner’s con sultants [24, p. 3; 25, p. 5]. Interpretation of the shallow overburden data, by ME DEP p ersonnel, concluded that the ground water flow direction was in a more westward direction than noted in the property owner’s report [9; 141, p. 2, Figure 3]. In addition, as noted by the ME DEP, the investigation reports prepared on behalf of the property owner do not discuss the ground water flow direction in the “deeper overburden” (maximum depth of 47 feet bgs) [141, p. 2]. ME DEP further noted that, based on the property owner’s data, the monitoring well couplets on the property exhibit a downward verti cal gradient [141, p. 2]. In addition, Roux, working on behalf of the property owner, noted that a ground water recharge condition exists on property based on the comparison of ground water elevations in the shallow and deep overburden monitoring wells [21

,Lee ds Metal NPL Listing Support Document September 2012

20 p. 16]. Furthermore, no monitoring well data exists to indicate flow direction at depths great er than 47 ft bgs [141, p. 2]. According to ME DEP and the ME Geological Survey, the overburden material in the area is estimated to exceed 100 ft in thickness, based on boring logs from a private well in the immediate vicinity of the property bo undary [72; 72a; 73, pp. 1-2]. Moreover, as discussed below, the slope of the bedrock surface will influence contaminant flow direction due to tendency of the observed re lease contaminant s to sink through the ground wa ter column and travel downward along impermeable surfaces due to their densities being greater than that of

water

. MEDEP notes that deeper ground water flow will likely follow the regional surface water
drain age pattern towards the Dead River, located to the southwest of the site [163, pp. 4-5; 164; 165, p.3].

On 16 and 17 September 1998, ERM, on behalf of Maine Central Railroad, installed 11 temporary ground water monitoring wells at various locations thro ughout the Leeds Metal
property [24, pp. 1 -2, 7, 11]. The intent of the temporary ground water monitoring well points

w as to provide a preliminary evaluat ion of on

- site ground water quality [24 , p. 2]. ERM advance d the temporary monitoring well s to a maximum total depth of 28 feet bgs and gauged the depth to water within each well point [24 , p. 2]. Depth to water ranged from 5.5 to 22 feet bgs [24 , p. 3].

ER M determined that in general, ground water elevations were highest i n the north and northe ast areas of the site [24 , p. 3]. ERM further stated that ground water flow directions are generally
from north to south across the site [24, pp. 3, 12].

On 1 through 3 November 1999, ERM, on behalf of Maine Central Railroad, installed nine
overburden gr ound water monitoring wells at soil boring locations on the Leeds Metal property [25, pp. 2 -3, 12]. Four sets of m onitoring well cluster s were installed whose design involved installing one shallow water table well and one deep overburden well [25, pp. 3, 13 ]. In addition,
ERM installed one shallow water table well on the central portion of the site to provide data for ground water flow determination [25, pp. 3, 13]. Shallow water table wells were installed to a maximum depth of 22 f ee t bgs [25 , p. 3]. Deep overburden wells were installed to a maximum depth of 47 f ee t bgs [25, p. 3]. Split spoon soil samples were collected at approximate five -foot intervals in each boring of the deep overburden wells [25, pp. 3, 5]. An ERM geologist
characterized each soil s ample [25 , p. 3]. The soil at the site consists primarily of brown

- to

- gray, medium- to -fine sand with some medium- to

- co a rse gravel [25 , p. 5, Appendix A]. Bedrock was not encountered at any of the four deep overburden wells [25, p. 5]. ERM conducted ground

water gauging at the monitoring well locations [25, p. 5]. Ground water elevation ranged from 90.00 feet to 92.44 feet as measured with respect to an arbitrary survey datum [25 , p. 5]. In general, ERM found that ground water elevations for shallow overburden wells are highest in the south and southeast areas of the site [25 , p. 5]. ERM stated that ground water flow directions are generally from southeast to the northwest [25, p. 5]. In response comments to the ERM Investigation Report, ME DEP personnel, uti lizing the ERM data, noted that ground water flow appears to be directed west, towards lot 43 and 44 [9; 141, p. 2, Figure 3]. ME DEP also pointed out that the ERM report did not discuss the ground water flow in the deeper overburden or the vertical gradie nt measured between the shallow a nd the deep wells [141, p. 2]. ME DEP noted
that all of the wells have downward v ertical gradients [141, p. 2]. In addition, ME DEP noted that the flow direction in the deeper aquifer appears to be much different from the s hallow groundLee ds Metal NPL Listing Support Document September 2012

21 water flow direction [141, p. 2]. The water levels measured in ground water monitoring wells

ERM -3D and ERM-4D have the same elevation of 90.00 (90.01 is within the accuracy of the measurement) [141, p. 2]. ME DEP suggested that the flow in t he deep overburden has a more westerly component than the shallow ground water flow direction [141, p. 2]. ME DEP declared that looking at the hydrogeology setting, the stratigraphy will influence ground water flow and contaminant distribution [141, p. 3]. ME DEP stated that it was not clear if the stratigraphy will dominate both ground water flow and contaminant distribution, but it is likely to play a major ro le in one or both [141, p. 3]. ME DEP concluded that further off- site investigation and site
char acterization was needed [141, p. 3]. . . .

On 11 May 2004, ground water elevation data for the accessible existing wells (shallow and deep well pairs ERM -1 through ERM-4, and ERM- 5) located on the Leeds Metal Area and the newly installed ground water moni toring wells RX -1S through RX-3S located on the Site was completed [21, p. 16]. The Leeds Metal Area was defined by Roux as the area of historical automobile storage and metal recycling operations [21, p. 3]. Based on the gauging data combined with the survey results produced by Guilford Rail, it was concluded that the direction of ground water flow beneath the site in the shallow overburden aquifer is in a north to northwesterly direction [21, p. 16]. Roux also noted that a comparison of ground water elevations in the shallow and deep overburden monitoring wells located in the Leeds Metal Area indicates that ground water recharge conditions (i.e., downward vertical flow) exist in this portion of the Guilford Rail property [21, p. 16].

As discussed previously in this response, the aquifer has been evaluated at three different depth zones (the shallow overburden, deep overburden, and bedrock). Although MEC presented November 2011 sampling data that had been collected after Site proposal, the data pres ented leads to the same conclusion as the data collected by EPA START in 2010 and presented in Reference 44 of the HRS documentation record at proposal; the data show ground water flow in the shallow overburden aquifer toward the north/northwest and deep overburden ground water flow toward the southwest. The HRS documentation record at proposal discusses these results, as quoted above, and also discusses that the three different zones evaluated all make up one aquifer and present sufficient
evidence to demo nstrate that contaminated ground water from the Leeds Metal facility will flow down into the aquifer and follow the bedrock topography toward the south.

The shallow overburden aquifer zone referred to in the HRS documentation record at proposal ranges fro m ~15

- 22 ft bgs and is established based on the presence of local shallow monitoring wells at these depths. These wells were interpreted in the HRS documentation record at proposal to have ground water flow toward the north to northwest (toward the lagoons identified on Figure 2 of the HRS documentation record at proposal). While the surface topography in the general vicinity of the Leeds Metal property is flat as indicated in Figures 1 and 6 of the HRS documentation record at proposal, the Leeds Metal property itself contains a depression in the northwest portion of the property that, according to Figure 1 of the HRS documentation record at proposal, is more than 20 feet in elevation below all four borders of the identified property boundary. Two ponds (ide ntified as lagoons in Figure 2 of the HRS documentation record at proposal) are located in the center of the depression in the northwest portion of the property. These local topographical features likely account for the ground water flow direction
observed in the shallow overburden monitoring well water elevations that indicate flow toward the north/northwest. The relatively low overall topographical gradient at the property is not supportive of highLee ds Metal NPL Listing Support Document September 2012

22 horizontal ground water flow rates and is supportive of vertical ground water movement from the surface (shallow overburden wells) toward the bedrock (deep overburden wells) as observed by ME DEP and presented in the HRS documentation record at proposal (see Figures 1, 4 and 5, Property Map, Site Cross -Section M ap, and Cross Section Profile Map, respectively , of this support document).

The deep overburden aquifer zone referred to in the HRS documentation record at proposal ranges from ~25-47 ft bgs and is established based on the presence of local “deep” monitoring wells at these depths. As quoted above, the HRS documentation record states that these wells have a more westerly component than the shallow ground water flow direction. Additionally, MEC submitted comments that concur with the HRS documentation record at proposal and state that the “groundwater elevation data for the deep overburden Site wells suggest flow to the southwest.” Finally, bedrock topographical information as presented in the HRS documentation record at proposal
demonstrates that the bedrock slopes from the north to the south toward the Dead River. As cited in Section 3.5, Aquifer Description, of this support document, the HRS documentation record at proposal states that the bedrock consists of a geological substrate that contains a different hydraulic conductivity (between 10 -4 to 10 -6 cm/s) than the surficial overburden deposits, which are documented to consist of sand, gravel, and silt (10 -4 cm/s). While the hydraulic conductivities do not differ by greater than two orders of magnitude (which would suggest a hydrological barrier) the different geological materials exhibit different flow rates. The slower bedrock flow rate coupled with the downward vertical gradient observed by the ME DEP in the overburden causes the ground water
flow directi on to follow the local bedrock topography towards the south.

Thus, while the ground water flow direction in the shallow overburden appears to locally flow toward the north/northwest, the downward vertical gradient observed in the monitoring wells transports the ground water below 25 ft. bgs and into the deep overburden and bedrock aquifer zones of the aquifer, which exhibit a south/southwest ground water flow direction. Therefore, the ground water flow direction was properly evaluated
beneath the Site at proposal.

This comment results in no change to the HRS score and no change in the decision to place the Site on the NPL.



### 3.6 Likelihood of Release: Attribution

Comment : Based on the arguments presented below, MEC asserted that it cannot be definitively concluded that PCE impacts to private drinking water wells originated from the Leeds Metal site. MEC suggested they may have originated “in the locus of the well head.” M EC stated that the dramatically different geochemical signature observed between residential drinking water target wells and monitoring wells located on the facility property represents two differing sources of impacts to ground water quality. The basis for this rationale includes
differences in the s hallow ground w ater f low d ir ection and aquifer continuity, and chemical signatures/distribution.

Response : Some portion of the significant increase in concentrations of PCE and TCE established in downgradient drinking water wells is attributed to the Site. The HRS documentation record at proposal shows that site sources contain hazardous substances (including PCE), that monitoring wells and residential drinking water well ground water exhibit significant incre ases of PCE and TCE (a degradation product of PCE), that a clear transport route exists from the sources to these wells via ground water flow, and that no other off

- site source hasLee ds Metal NPL Listing Support Document September 2012

23 been identified that is likely to be significantly contributing to the haza rdous substances found in release samples
from these wells.

HRS Requirements for Attributing a Release to the Site

The HRS requirement of attribution of contamination in the aquifer below a site to a release from a site is part of assigning the likelihood of release category value for the site. HRS Section 3.1, Likelihood of release , and its subsections provide the specific requirements for assigning a likelihood of release factor category value based on an observed release for the ground water migration pathway:

For an aquifer, evaluate the likelihood of release factor category in terms of an observed release factor or a potential to release factor.

An observed release may be established by direct observation and/or by chemical analysis. At this site, only an observed release by chemical analysis was established at proposal. HRS Section 3.1.1, Observed release , states in relevant part:

Establish an observed release to an aquifer by demonstrating that the site has released a hazardous
substance to the aquifer. Base this demonstration on either:

• Direct observation . . . .

• Chemical analysis

— an analysis of ground water samples from the aquifer indicates that the concentration of hazardous substance(s) has increased significantly above the background concentration for the site (see section 2.3). Some portion of the significant increase must be attributable to the site to establish the observed release , except: when the source itself consists of a ground water plume with no identified source, no separate at tribution is required. [emphasis added]

HRS Section 2.3, Likelihood of release

, presents the basic requirements for identifying an observed release by chemical analysis :

The minimum standard to establish an observed release by chemical analysis is analytical evidence of a hazardous substance in the media significantly above the background level

. Further, some portion of the release must be attributable to the site. [emphasis added]

HRS Documentation Record Establishment of Attribution

The HRS docu mentation record at proposal establishes a likelihood of release factor category value by documenting:

• A significant increase in the concentration of hazardous substances to the ground water and

• That some portion of the significant increase in hazardous s ubstances in the ground water is attributable to the site as is required by the HRS and explained above.Lee ds Metal NPL Listing Support Document September 2012

24 Attribution of some portion of the significant increase of hazardous substances in the ground water was
established as such and described in more deta il below in the following subsections:

• Documentation of Significant Increase,

• Documentation of Historical Activities and Use of PCE as a Cleaning Solvent,

• Documentation of PCE in Sources,

• Degradation Process of PCE to TCE,

• Physical Nature of PCE and TCE a nd their Existence as DNAPLs,

• Ground Water Flow Direction and Hydrogeology at the Site,

• Documentation of On- property Monitoring Wells and Off

- property Drinking Water Wells Sampling Used to Establish Observed Releases to Ground Water, and

• Efforts to Find Ot her Possible Off -site Sources of Chlorinated Solvent Ground Water Contamination.

Documentation of Significant Increase

Pages 103 -114 of the HRS documentation record at proposal list results from the November 2010 EPA SI sampling event to establish a significant increase in concentrations of PCE and TCE in monitoring wells on the facility property and to private drinking water wells south of the property.

Documentation of Historical Activities and Use of PCE as a Cleaning Solvent

Pages 114 -115 of the HRS documentation record at proposal presented information, which is summarized below, on processes conducted at the facility that the hazardous substance PCE was associated with:

[F] rom approximately 1969 to 1984, scrap metal recovery processes were conducted on the Leeds Metal property. According to a former Town of Leeds official, cars were transported to the property for “shredding”; however, lead batteries and other auto parts were salvaged and cleaned for resale [26]. Automotive part cleaners, rust removers (penetrating oils), and lubricants commonly contain large amounts of PCE [156]. Many common aerosol and liquid auto motive part cleaners contain high percentages of PCE; these include brake cleaners (greater than 90% PCE), carburetor cleaners (15-20% PCE), non- flammable Penetrating Oils (60 -65% PCE), automotive wire drying products (45- 55% PCE), and multipurpose lubrica nts (65- 80% PCE) [156]. A former town official also stated that materials such as “gasoline, diesel, transformer oil, brake fluid, oils, battery acid, and antifreeze” were dumped on the ground and that approximately 100 “barrels” were staged along the southern property boundary [26]. This same official noted that the Leeds and Monmouth Fire Departments responded to fires at the property, and that gasoline tanks would ignite and cause oil-saturated soil to burn [26].

Pages 116 -117 of the HRS documentation r ecord at proposal describe common uses of PCE and TCE. This discussion noted that TCE is used as a solvent to degrease metal parts, and an ingredient in adhesives, paint removers, typewriter correction fluids, and spot removers; PCE is used for degreasing, dry cleaning, and is an ingredient in part cleaners and rust removers.Lee ds Metal NPL Listing Support Document September 2012

25 Documentation of PCE in Sources

Pages 115 and 116 of the HRS documentation record at proposal associate PCE with Sources 4 and 5 at the site.

Pages 115 -116 of the HRS documentation record at proposal detail the hazardous substances found at the Site in recent investigations, including PCE, arsenic, cadmium, chromium, and lead detected in site soils collected in June 2009 EPA Removal Program Preliminary Assessment/Site Investigation (PA/SI) activities. These pages also listed where PCE has been detected in site piles and soil evaluated as HRS sources above background levels:

• Debris Pile D (Source 4): 9 VOCs, 4 PCBs, and 16 metals (HRS documentation record at proposal pag es 72-77 show these Source 4 VOCs included PCE)

• Contaminated Soil (Source 5): 10 VOCs, 4 PCBs, and 23 metals (HRS documentation record at proposal pages 84 -92 show these Source 5 VOCs included PCE)

Physical Nature of PCE and TCE and their Existence as DNAPLs

Pages 116 -118 of the HRS documentation record at proposal discuss the behavior of PCE and TCE in the environment. Pages 116-117 of the HRS documentation record at proposal noted:

TCE is a colorless, highly volatile liquid that is miscible with wa ter and a number of organic
solvents . . . TCE dissolves a little in water, but can remain in ground water for a long time

. . . PCE is a colorless, highly volatile liquid with a limited tendency to mix with or dissolve in water

.

. . As a result of its lo w solubility and high density, liquid PCE tends to “sink” through water and can exist in the ground water environment as a separate dense non

- aqueous phase liquid (DNAPL) that will collect or pool at or along low points in water containing vessels or

conve yances

.

Given the high vapor pressure of PCE, much of it that enters into the environment evaporates into the air [148, pp. 1-3]. In the air, PCE is broken down by sunlight or brought back to the soil and water by rain [148, pp. 1-3]. Small amounts of PCE (roughly 0.012 % by volume) can dissolve in ground water or surface water [148, pp. 1-3]. This PCE will move as a dissolved phase along with the water [148, pp. 1- 3]. Releases of larger amounts of PCE can exist as a separate DNAPL

. . . . Both TCE and PCE can exist as DNAPLs

.

Regarding the behavior of DNAPL in general, pages 117-118 of the HRS documentation record at proposal
stated:

DNAPLs are denser than water and are relatively immiscible in water, allowing them to remain in a nonaqueous phase [145, Appendix B (pp. B-1 – B-8)]. DNAPLs are difficult to detect in the environment and can act as a source for dissolved contamination in ground water over time [148, pp. 1-3]. While these are defining features of DNAPLs, there are a number of other physical and chemical properties that influence actual migration in the subsurface and their physical/geochemical behavior [145, Appendix B (pp. B-1 – B8)]. Their behavior is determined by complex interactions between the DNAPL chemicals and the hydrogeological formationsLee ds Metal NPL Listing Support Document September 2012

26 through which the DNAPLs move [145, Appendix B (pp. B-1 – B- 8)]. DNAPL chemicals are subject to several processes, including downward migration by gravity; absorption and adsorption on soil; volatilization into soil gas; dissolution and dispersion in ground water; preferential solution of components; phase separation or the formation of emulsions; and transformation into other chemicals by microbiological and/or chemical processes (when chemicals are in solution or air) [145, Appendix B (pp. B-1 – B-8 )]. Given relatively equal viscosities, the greater the specific gravity, the greater the tendency of the substance to migrate under the influence of gravity through the subsurface [145, Appendix B (pp. B-1 – B-8)].

Provided there is sufficient mass to d rive the movement, the DNAPL will continue to move downward through preferential pathways (i.e., coarser grained materials that provide less capillary resistance) until it meets a zone of low permeability, where it will tend to pool or, if the
zone has a d ip, will move across the surface to lower areas [145, Appendix B (pp. B-1 – B-8)]. DNAPLs will tend to move vertically downward and collect in low spots or along impermeable
barriers.

Ground Water Flow Direction and Hydrogeology at the Site

Pages 118 and 123 of the HRS documentation record at proposal describe historical information related to ground water flow. As further explained in section 3.5.2, Ground Water Flow Direction, of this support document, while the ground water flow direction in the shallow overburden appears to locally flow toward the north/northwest, the downward vertical gradient observed in the monitoring wells will take the ground water below 25 ft bgs and into the deep overburden and bedrock aquifer zones of the aquifer, which exhibit a south/southwest ground water flow direction. Additionally, section 3.5.1, Ground Water Discontinuities, of this support document explains that the aquifer being evaluated at the Leeds Metal site was properly established in the HRS documentation record a t proposal and contains no documented aquifer discontinuities. The HRS documentation record at proposal correctly identified that the aquifer being evaluated is a single aquifer system and all of the wells identified at the Site are located in the same aquifer system.

Pages 118 -120 of the HRS documentation record at proposal presents results from several historical ground water sampling events:

• A September 1998 ERM sampling of several temporary ground water wells on the Leeds Metal property (installed to a maximum depth of 28 ft bgs) found PCE at 0.27 mg/L in sample MW-8 and 0.13 in sample MW -9 along the eastern property boundary.

• A November 1999 ERM sampling of overburden aquifer wells on the Leeds Metal property found 1,1,1-
trichloroethane and PCE at 2.6 μ g/L and 140 μ g/L, respectively (cited HRS documentation record at proposal Reference 25 pages 6, 11, and 12 show that these detections were in well ERM-4S/D in the south-central portion of the property).

• A November 2000 ERM sampling of 12 newly installed temporary monitoring wells (installed from 8 to 24 ft bgs) and five samples from previously existing wells found chlorinated solvents in several of the wells. Field screening results detected a maximum concentration of 4.3 μ g/L PCE in new wells and a
maxi mum of 46 μ g/L in previously existing well samples; laboratory results detected maximum concentrations of PCE and 1,1,1

- trichloroethane at 120 μ g/L and 2.8 μ g/L, respectively.Lee ds Metal NPL Listing Support Document September 2012

27 • A June 1, 2009 EPA sampling of the wells installed in 1999 on Leeds Metal proper ty found PCE at a
maximum of 15 μ g/L (again at well location ERM -4).

• A June 17-18, 2009 EPA sampling of 8 newly installed temporary well points throughout the Leeds Metal property, as well as re-sampling of well location ERM-4 found PCE in all samples at a maximum of 86

μ g/L; 1,1,1- trichloroethane was found in one sample at 1.0 μ g/L (cited HRS documentation record at proposal Reference 32 pages 39 and 56 show this 1,1,1- trichoroethane was detected in well WP -08A near the southeast corner of the property).

• From 2000 to 2005, ME DEP sampled residential drinking water from wells south and southwest of the Leeds Metal property. Analytical results indicated the presence of several VOCs, including cis -1,2- DCE, PCE, and TCE.

Documentation of On

- property Monitori ng Wells and Off

- property Drinking Water Wells Sampling Used to
Establish Observed Releases to Ground Water

Pages 120 -121 of the HRS documentation record at proposal summarize the results of on-property monitoring wells and off-property drinking water wells sampling collected as part of the November 2010 EPA investigation (the results used to establish observed releases to ground water in the HRS documentation record at proposal), noting the following:

• During the November 2010 EPA Site Inspection (SI), 12 ground water samples were collected from 11 monitoring wells on the property. Four of these samples showed observed release levels of PCE (with a maximum concentration of 19 μ g/L). In addition, although not present at observed release levels, TCE

was detected in two of these samples (GW -06 and GW-07).

• Also during the November 2010 EPA SI, 31 drinking water samples were collected from 29 drinking water wells northwest, west, southwest, south, southeast, and east of the Leeds Metal property. Seven of the se samples exhibited observed release levels of TCE and/or PCE.

Efforts to Find Other Possible Off -site Sources of Chlorinated Solvent Ground Water Contamination

Pages 121 -124 of the HRS documentation record at proposal discuss the efforts to identify other possible off- site
sources of PCE and concluded that none were found.

Pages 121 -123 of the HRS documentation record at proposal discuss efforts to find other potential off- site sources
of the chlorinated solvent contamination:

A review of available in formation was conducted to identify other potential sources of PCE and TCE contamination in the area of the Leeds Metal property. As part of the review effort, a search of the Hazardous & Oil Spill System for Maine was conducted. . . . As part of the poten tial source search, the database was queried for the following spill criteria: Reported Date Range equal to 1 January 1961 (the earliest possible search date within the system) to 30 November 2010 (the last day of sampling conducted as part of the EPA SI); Municipality equal to Town of “Leeds”; and Keywords equal to “Hazardous” [161, pp. 1-5]. The database search identified 64 spill records based on these criteria [161, pp. 1

- 5]. The majority (52 records) were listed as “hazardous material incidents”, while 12 were listed as “non -oil, non-hazardous incidents” [161, pp. 1-5]. A review of the online documentation of the 52 hazardous material incident spills identified oneLee ds Metal NPL Listing Support Document September 2012

28 spill in which PCE or TCE was identified: Spill Number A -708-1998 [161, pp. 1- 7]. The Spi ll Report for Spill Number A-708- 1998 summarized that “a leaking gasket on a drum caused a minor perchloroethylene spill inside a truck. It was picked up using sorbents” [161, p. 7]. The documentation further noted that 0.10 gallons of PCE were spilled and recovered at the Safety

Kleen facility located along Route 202, Leeds, Maine, at the corner of Goldrup Road (see Figure 1) [161, p. 7]. The Safety- Kleen facility is located approximately 1.1 miles southwest of the Leeds Metal site [7]. The other hazardous material incident spills identified by the database query either were not located with 4 radial miles of the Leeds Metal site, or were not identified as spills containing PCE or TCE contamination [158; 161, pp. 1 -5].

As part of the review effort, Weston START personnel also queried the Maine Hazardous & Oil Spill System database by the following spill criteria: Reported Date Range equal to 1 January 1961 to 30 November 2010; Municipality equal to Town of “Monmouth”; and Keywords equal to “Hazardous” [161, pp. 8- 10]. The database search identified 27 records based on these criteria [161, pp. 8-10]. Only four of the spills were listed as “hazardous material incidents”, while the majority of the spills (23 records) were listed as “non- oil, non -hazardous incidents” [161, pp. 8- 10]. A review of the online documentation of the four hazardous material incident spills identified no hazardous material incidents involving PCE or TCE [161, pp. 8-10].

In addition, a former Concrete Manufacturing Facility was observed during field activities along Route 106, which was comprised of a large warehouse and garage buildings [14, pp. 12-13; 158]. Database reviews did not identify any PCE and/or TCE releases at the former Concrete Manufacturing Facility [158; 159; 160; 161].

In the effort to identify other potential sources of PCE and TCE contamination, reviews of the
EPA RCRA and CERCLIS databases were conducted. These database reviews identified three RCRA and one CERCLIS (Leeds Metal) sites in Leeds, Maine, and zero RCRA or CERCLIS sites in Monmouth, Maine [159; 160]. One of the three RCRA sites identified in Leeds, Maine was identified as containing known PCE and TCE contamination: the Safety

- Kleen Systems Inc. (Safety -Kleen) facility (EPA Facility ID Number MED980667810), located on a 5.8- acre lot identified on the Town of Leeds Tax Assessors Map No. 1 as Lot 47 -1, along Route 202 [corner of Goldrup Road (also known as Sumner Road)] [10; 159; 162; 175, p. 9]. The other RCRA sites identified were two gravel pits located to t he north of the Leeds Metal property, which were not identified as containing PCE or TCE contamination.

Pages 122 -124 of the HRS documentation record at proposal detail historical investigations involving the SafetyKleen facility. Page 123 of the HRS documentation record at proposal describes movement of ground water in the area of the Safety

- Kleen facility:

Based on topography, and on ground water elevation observations in monitoring wells between 1987 and 1989, the on

- site shall ow ground water radiates from the facility and the predominant flow direction is to the south [169, p. 25]. Generally, the regional topographic slope to the south causes the shallow ground water to flow southerly from the facility [169, pp. 25- 26]. The sha llow ground water flow is occasionally interrupted by surfical depressions, which are ground waterLee ds Metal NPL Listing Support Document September 2012

29 discharge zones during wet seasons [169, p. 26]. Therefore, some of the shallow ground water flow is discharged to the surface relatively close to the facili ty, and does not continue to the south [169, p. 26]. Additional variations in shallow flow direction are apparent to the northwest, west and east [169, p. 26]. These variations are the result of the seasonal influences on recharge and the physical characteristics of the site

.

Page 124 of the HRS documentation record at proposal concludes that:

[A]vailable ground water monitoring data indicates that PCE was detected sporadically in both
on- and off- site wells associated with the facility, at a maximum con centration of 0.056 mg/L in ground water monitoring well MW-9D (on 8/10/2004) located southeast of the facility [169, p. 18 (Table II); 170 Figure 2, Table 2 (pp.196); 171, Table 2 (pp.1-12); 173, Table 4 (pp. 1-27)]. In addition, TCE was detected sporadic ally in both on-and off- site wells, at a maximum concentration of 0.009 mg/L in ground water monitoring well MW-10M (on 8/23/2005 and 4/23/2008) located southwest of the facility [169, p. 18 (Table II); 170, Figure 1, Table 1; 171, Table 2; 173, Table 4]. Based on the above information, a release of PCE has been documented at the Safety

- Kleen facility; however, the recent hydrogeologic investigations have shown that the resulting impacts are to ground water to the south -southeast of the facility, and do not extend in
the direction of the PCE - and TCE-contaminated drinking water wells along Route 106 investigated as part of the Leeds Metal SI.

Thus, the Safety-Kleen facility, located approximately 1.1 miles southwest of the Site, from which ground water

gene rally moves south is unlikely to contribute hazardous substances to the drinking water observed release wells (the farthest of which is less than 0.5 mile south of the Site, about 0.75 mile northeast of the Safety- Kleen facility, and therefore upgradient o f the Safety

- Kleen facility [see Figures 1 and 5 of the HRS documentation record at proposal]).

Page 124 of the HRS documentation record at proposal also discusses other small isolated automobile repair operations in the area:

During field activities con ducted in 2010 in the area of the Leeds Metal site, small

- scale automobile and small engine repair operations were observed at several of the residential properties near the Leeds Metal property [158]. These operations included, but were not limited to, the following: small engine repairs conducted at the residence depicted on the Town of Leeds, ME Tax Assessor’s Office Map No. 4 as Lot No. 48 (location of drinking water sample DW -03); automobile repairs conducted at residences depicted on the Town of Leeds , ME Tax Assessor’s Office Map No. 1 as Lot No. 66 (location of drinking water sample DW-14 and field duplicate
DW -33), Lot No. 59-2 (location of drinking water sample DW-29), and Lot No. 59 (location of
DW -30); and automobile repairs conducted at the residence depicted on the Town of Leeds, ME Tax Assessor’s Office Map No. 4 as Lot No. 49 [9; 10; 158]. Based on these observations, automobile parts cleaners potentially containing PCE or TCE may be used during operations on these residential properties, resulting in a potential point source for a release of these contaminants to the environment [156; 158]. However, due to the limited scale of the operations conducted on the residential properties, compared to the relatively significantly larger scale of theLee ds Metal NPL Listing Support Document September 2012

30 f ormer recycling operation at the Leeds Metal property, it is presumably unlikely that these potential residential point sources could contribute a significant volume of PCE and/or TCE to the environment [158].

Page 124 of the HRS documentation record at proposal concludes:

PCE has been documented within the source areas on the Leeds Metal site and within on- site ground water wells; therefore, at least partial attribution has been demonstrated (see Source Section and Table 41 of this HRS Documentation Record).

Therefore, there is no other likely source significantly contributing to the hazardous substances found in observed release samples established for the Site; and the HRS documentation record at proposal correctly documented that some portion of the significant increase in hazardous substances is attributable to the S ite , consistent with the
HRS.

The following subsections of this support document address comments regarding chemical signatures/distribution in ground water, and ground water flow/discon tinuities as they impact the attribution of the observed release to
the Site:

• 3.6.1 Shallow Ground Water Flow Direction and Aquifer Continuity

• 3.6.2 Chemical Signatures/Distribution

3.6.1 Shallow Ground Water Flow Direction and Aquifer Continuity

Comment : MEC argued that ground water flow direction and aquifer discontinuities call into question the ability of hazardous substances to migrate from the Site to the residential drinking water wells. MEC presented a summary of data that shows shallow ground wat er flow to be north/northwest across the Leeds Metal property. It indicated that all of the scored target wells are southwest of the property, and therefore, concluded that “off- Site” private wells are not impacted by contaminants originating from the Site

.

MEC stated that “the Leeds Metal site is located northeast of a basin divide, while most of the off

- Site private drinking water wells sampled are located southwest of the basin divide, indicating it is unlikely that groundwater from the Site is flowing to the southwest.” MEC based this assertion on a review of the Maine Geological Survey geologic map for this region, which was provided as Appendix A of MEC’s comments. MEC also asserted (citing Figures 1 through 3 of its comments) that this information is consistent with ground water gauging and ground
water flow direction determined for the Site.

Response : The private wells identified as contaminated due to a release from the Site (i.e., observed release wells) are indeed downgradient of the sources at the Site and draw water from the same aquifer as that below the Leeds Metal property. A clear path for hazardous substances to migrate from the Site to the observed release monitoring wells and residential drinking water wells exists; and the attribution of the significant increase in PCE and TCE concentrations detected in those wells was correctly established in the HRS documentation record at proposal.

As explained in section 3.5.2, Ground Water Flow Direction, of this support document, while the ground w ater flow direction in the shallow overburden appears to locally flow toward the north/northwest, the downwardLee ds Metal NPL Listing Support Document September 2012

31 vertical gradient observed in the monitoring wells takes the ground water below 25 ft bgs and into the deep overburden and bedrock aquifer zones of the aquifer, which exhibit a south/southwest ground water flow direction. Thus, there is a clear path for contaminants migrating via ground water from the Leeds metal property to take toward the residential drinking water wells to the south of the prope rty.

As explained in Section 3.5.1, Ground Water Discontinuities , of this support document, the aquifer being evaluated at the Leeds Metal site was properly established in the HRS documentation record at proposal and contains no documented aquifer discontinuities. The HRS documentation record at proposal correctly identifies that the aquifer being evaluated is a single aquifer system and all of the wells identified at the Site are located in the same aquifer system.

And, as explained in Section 3.6, Like lihood of Release: Attribution , of this support document, there is no other likely source significantly contributing to the hazardous substances found in observed release samples established for the Site; and the HRS documentation record at proposal has provided ample evidence that some portion of the significant increase in hazardous substances found in the residential drinking water wells is attributable to the
S ite, consistent with the HRS (including documentation of the historical operations conducted o n site, which
could include solvents containing PCE and TCE; the documentation of PCE in on

- site source samples;
documentation of chemical breakdown process es of PCE t o TCE; the documentation of PCE in on

- site “shallow” and “deep” overburden monitoring wells; and the documentation of PCE and TCE in residential drinking water well samples).

This comment results in no change to the HRS score and no change in the decision to place the Site on the NPL.

3.6.2 Chemical Signatures/Distribution

Comment : MEC co mmented that a comparison of the pattern/distribution of chlorinated and non-chlorinated VOCs in residential drinking water wells versus that in monitoring wells on the Leeds Metal property did not support the attribution of hazardous substances in the res idential drinking water wells to the Site.

MEC asserted that based on its review of data available to date, the chemical signatures of the contaminants in the monitoring wells on site [i.e., on the Leeds Metal property] differ from those found in resident ial drinking water wells. It asserted that monitoring wells at the facility where chlorinated solvents were detected only show concentration of PCE, and PCE breakdown products were generally absent; however, the residential drinking
water wells showed dete ctions of PCE breakdown products: cis-1,2-DCE, TCE, and 1,1-DCA. MEC, therefore, surmised that the chemical signatures of the ground water contaminants in the monitoring wells versus the chemical signatures in drinking water wells are not consistent.

MEC argued that the “on-Site” ground water chemistry in deep overburden monitoring wells does not support the
conclusion that “off- Site” [off -property] wells are impacted by contaminants originating from the “Site.” It argued that although ground water elevati on data for deep overburden “site wells” suggest flow to the southwest, PCE was generally not detected above the laboratory reporting limit in these “on- site” wells, with the exception of deep monitoring well MW-4D. MEC also pointed out that the farthest downgradient deep overburden monitoring well,
MW -3D, showed no detections of CVOCs in either the June 2009 or November 2010 sampling events.Lee ds Metal NPL Listing Support Document September 2012

32 MEC pointed out that the “deep” wells at the Leeds Metal property [in this case referring to wells screened in the “deep overburden aquifer” zone, not the bedrock aquifer zone], which range “from 27 feet” bgs to “47 feet bgs” have CVOC concentration generally below laboratory reporting limits and are consistently below the Maine MEG. MEC pointed out that the some conce ntrations present in the drinking water wells, which are significantly deeper “ranging from 127 feet bgs to 400 feet bgs” [in the bedrock aquifer zone] were detected above the ME DEP action levels. MEC argued that therefore, these concentrations “are not consistent with the decreasing concentration gradient observed with depth” at the facility.

MEC made a point similar to that above regarding the lack of similarity of the chemical signatures between the

on- facility monitoring wells and the drinking water w ells of non

- chlorinated compounds. MEC commented that gasoline constituents (such as benzene, ethylbenzene, toluene, xylene, and gasoline additive MTBE) were detected in the drinking water wells and not in the on-facility monitoring wells. MEC also comment ed that 2

- butanone was documented in on-facility monitoring wells and not in the drinking water wells. MEC concluded that “[g]roundwater chemistry data indicate the impacts to off

- Site [off

- property] drinking water wells is different than the groundwater i mpacts originating from the Leeds Metal Site.”

Response : The distribution of chlorinated solvents, their breakdown products, and non

- chlorinated volatile organic compounds (VOCs) is consistent with the scenario in which ground water in on-property monitor ing wells and off-property drinking water wells have been contaminated by hazardous substances migrating from the Site. Although the chemical signature varies, the changes in the signature can be explained as due to differential migration rates and degrada tion rates of the contaminants as they travel in the aquifer.

As explained in Section 3.6, Likelihood of Release: Attribution , of this support document, HRS Section 3.1.1,
Observed release , requires that some portion of the significant increase in hazardous substances must be
attributable to the S ite to establish an observed release. The HRS documentation record at proposal provided ample evidence that this is the case —consistent with the HRS—including that, apart from the Si te, there are no other feasible significant sources of the ground water contamination found in the observed release. Specific comments regarding the distribution of hazardous substances and its effect on attribution are addressed in the following subsections:

• Chlorinated Solvent Breakdown Product Distribution

• Distribution of PCE in Deep Overburden On- Property Wells and Residential Drinking Water Wells

• Non

- Chlorinated VOCs Distribution

Chlorinated Solvent Breakdown Product Distribution

Regarding MECs comments about chemical signatures, MEC commented that the chemical signatures of the ground water chlorinated contaminants in the monitoring wells and the chemical signatures in drinking water wells are not consistent, and thus do not support attribution of h azardous substances in the residential drinking water wells to the Site. As explained below, the distribution of chlorinated solvents and their breakdown products is consistent with the attribution of PCE and TCE in observed release samples to the Site.

As discussed above in Section 3.6, Likelihood of Release: Attribution , of this support document, pages 116-117 of the HRS documentation record at proposal discuss behavior of PCE and TCE in the environment in general andLee ds Metal NPL Listing Support Document September 2012

33 at this site including that both TC E and PCE can exist as DNAPLs [see page 8 of Reference 149 of the HRS documentation record at proposal].

Regarding the behavior of DNAPLs in general, pages 117-118 of the HRS documentation record at proposal state:

DNAPLs are denser than water and are relatively immiscible in water, allowing them to remain in a nonaqueous phase [145, Appendix B (pp. B-1 – B-8)]. DNAPLs are difficult to detect in the environment and can act as a source for dissolved contamination in ground water over time [148, pp. 1-3]. While these are defining features of DNAPLs, there are a number of other physical and chemical properties that influence actual migration in the subsurface and their physical/geochemical behavior [145, Appendix B (pp. B-1 – B8)]. Their behavior is determi ned by complex interactions between the DNAPL chemicals and the hydrogeological formations through which the DNAPLs move [145, Appendix B (pp. B-1 – B- 8)]. DNAPL chemicals are subject to several processes, including downward migration by gravity; absorption and adsorption on soil; volatilization into soil gas; dissolution and dispersion in ground water; preferential solution of components; phase separation or the formation of emulsions; and transformation into other chemicals by microbiological and/or chemical processes (when chemicals are in solution or air) [145, Appendix B (pp. B-1 – B- 8)]. Given relatively equal viscosities, the greater the specific gravity, the greater the tendency of the substance to migrate under the influence of gravity through the subsurface [145, Appendix B (pp. B-1 – B-8)].

Provided there is sufficient mass to drive the movement, the DNAPL will continue to move downward through preferential pathways (i.e., coarser grained materials that provide less capillary resistance) until it meets a zone of low permeability, where it will tend to pool or, if the zone has a dip, will move across the surface to lower areas [145, Appendix B (pp. B-1 – B-8)]. DNAPLs will tend to move vertically downward and collect in low spots or along impermeab le
barriers.

Thus, the behavior and movement of PCE and TCE through the soil and aquifers can involve PE and TCE existing as DNAPLs, which have a tendency to sink through an aquifer (in addition to the downward vertical component to ground water flow discussed in Section 3.6.1, Shallow Ground Water Flow Direction and Aquifer Continuity, of this support document); it is expected that PCE and TCE would tend to migrate downward toward the bedrock aquifer

— and residential drinking water wells

— as they migrate ho rizontally south with ground water
flow.

Page 117 of the HRS documentation record at proposal also discusses the common chemical breakdown processes
related to PCE and TCE:

Under reducing conditions in soil and/or ground water, naturally occurring microo rganisms can break PCE down (through a process known as anaerobic reductive dechlorination) [51, Section 1.4.4 (pp. 1-10 - 1-11, Figure 1.4); 148, pp. 1-3]. Under oxygenated conditions in soil and/or ground water, PCE tends to be environmentally persistent [148, pp. 1-3]. TCE is a common degradation product of PCE through biotic anaerobic reductive dechlorination [51, Section 1.4.4 (pp. 1-10 - 1-11, Figure 1.4)]. Degradation of TCE continues and breaks down TCE to theLee ds Metal NPL Listing Support Document September 2012

34 dichloroethene (DCE) isomers (cis

- DCE o r trans

- DCE)

. . . . ME DEP staff notes that anaerobic, reduced ground water in Maine bedrock is common, especially under this hydrogeologic setting where deeper ground water is not in contact with the atmosphere [165, p. 2]. The presence of dissolved arsenic, iron, and sulfa tes in many of the water supply wells drilled into bedrock suggests that the ground water in the bedrock is reduced and anaerobic [165, p. 2]. PCE degradation is a relatively slow and complex process even under reducing conditions [165, p. 2].
This allows the compound to travel greater distances before attenuation can reduce it below levels capable of producing daughter compounds that exceed safe levels for human consumption.

As explained above, PCE breaks down to TCE, then to cis- DCE and/or trans

- DCE via reductive dechlorination; and, the reducing conditions favorable to this process are common in Maine bedrock at the Site, especially in deeper ground water. Therefore, the presence of relatively more PCE breakdown products in the residential drinking water wells than the on-property monitoring wells is expected because:

• Facility operations on the Leeds Metals property that are the likely origin of source and observed release hazardous substances began as early as 1969. There has been time for chlorinated solvent degradation to have occurred.

• The residential drinking water wells are farther downgradient (south) from the Site than on-property monitoring wells (see Figures 4 and 5 of the HRS documentation record at proposal). Chlorinated solvents in these wells may represent earlier releases at the property, which have had more time to migrate farther from their point of origin, and therefore would have had more time to undergo degradation from a more chlorinated form (e.g., PCE) to less chlorinated forms.

• On -property monitoring wells are screened in the shallow and deep overburden aquifers from approximately 15-47 ft bgs. The residential drinking water wells, on the other hand, are located in the deeper bedrock aquifer at approximately 200 ft bgs. The resident ial drinking water wells are thus likely in an aquifer under anaerobic reduced conditions more conducive to the reductive dehalogenation degradation process; it is to be expected that the incidence of PCE degradation products would be higher in these deepe r wells.

This scenario is further supported by page 2 of Reference 165 of the HRS documentation record at proposal, cited
in the above- quoted HRS documentation record text. This reference, produced by a ME DEP certified environmental hydrogeologist states :

It is my opinion that the chemical signatures between the monitoring wells and the drinking water supplies are directly related. Research has shown that PCE degrades under reducing conditions and does not degrade under oxidized conditions. The field par ameters collected during monitoring well sampling completed in June 2009 (see below) indicates that the monitoring wells on-site reflect oxidized conditions. ERM-4S and ERM-4D were the only monitoring wells with dissolved oxygen (DO) concentrations below 1ppm, indicating an anaerobic environment. However, the corrected Eh measurements exceed 500 mV in the two wells, indicating an oxidized environment. It appears that even though there is an anaerobic environment at ERM- 4, it is not a reducing environment capable of supporting PCE degradation. Given the thickness of saturated overburden present in the area (approximately 150- feet based on driller records) it is likely that Eh of the groundwater present in the deep overburden or underlying bedrock off- site is indicative of a reduced environment. Anaerobic, reduced groundwater in Maine bedrock groundwater isLee ds Metal NPL Listing Support Document September 2012

35 common, especially under this hydrogeologic setting where deeper groundwater is not in contact with the atmosphere. The presence of dissolved arsenic, iron, and sulfate in many of the area water supply wells drilled into the bedrock suggests that the groundwater in the bedrock is reduced and anaerobic. PCE degradation is a relatively slow and complex process even under reducing conditions, which allows the compound to travel greater distances before attenuation can reduce it below levels capable of producing daughter compounds that exceed safe levels for human consumption. The conceptual model is further supported by the lack of vinyl chloride present. Researc h has shown that degradation of 1,2- DCE to vinyl chloride is an aerobic process. It appears that oxygen is not present in the bedrock groundwater at sufficient levels to support the generation of vinyl chloride.

The multiple lines of evidence suggest that the reason why the chemical signatures are different between the on-site monitoring wells and off- site drinking water supply wells is due to natural changes in geochemistry.

In addition, there is some evidence of possible limited PCE degradation even in shallow and deep overburden aquifer ground water collected from on- property wells. Regarding observed release samples GW -06 and GW-07, page 120 of the HRS documentation record at proposal notes:

TCE was detected in two ground water samples (GW -06 and GW-07) at concentrations above CLP laboratory reporting limits, but below the sample-adjusted CRQL, and were therefore not evaluated for scoring in this HRS documentation record . . . TCE is a common breakdown product of PCE.

Page 106 of the HRS documentatio n record at proposal explains that samples GW -06 and GW- 07 were collected from monitoring wells ERM-4S and ERM-4D, respectively, located on the southern- central portion of th e Leeds Metal property (the total depth of these wells was 13.9 and 26.3 ft bgs , r espectively). Further recent evidence of the possible presence of PCE breakdown products on the Leeds Metal property includes the following:

• 52 J μ g/kg TCE detected in November 2010 SI sample SB-35, subsurface soil boring, northeastern portion of Debris Pile B, on the southeastern corner of the Leeds Metal property (see HRS documentation record at proposal Reference 11, pages 87, 103, 108).

• 0.062 μ g/L TCE detected in November 2010 SI field duplicate of sample GW-07, ground water sample collected from monit oring well ERM-4D, in the southern portion of the Leeds Metal property (see HRS documentation record at proposal Reference 11, pages 126, 130, 132).

Regarding the commenter’s reference to 1,1

- DCA in downgradient residential wells, that substance is genera lly not a degradation product of chlorinated ethenes (PCE, TCE, etc.), but rather the reductive dechlorination degradation product of 1,1,1

- TCA (see HRS documentation record at proposal Reference 51, page 1 -11). And, there is historical evidence of 1,1,1-T CA at the Leeds Metal property:

• Page 28 of the HRS documentation record at proposal notes that a November 1999 ERM overburden ground water sample showed the presence of 1,1,1-TCA. (Page 6 of Reference 25 of the HRS documentation record at proposal cited on that page explains that 1,1,1- TCA was detected in well ERM

4D.)Lee ds Metal NPL Listing Support Document September 2012

36 • Page 29 of the HRS documentation record at proposal notes that a November 2000 ERM overburden ground water sample showed the presence of 1,1,1-TCA. (Page 4 of Reference 28 of the HRS documentation record at proposal cited on that page explains that 1,1,1- TCA was again detected in well
ERM -4D.)

• Pages 32 -33 of the HRS documentation record at proposal notes that a June 2009 EPA Removal Program PA/SI overburden ground water sample exhibited 1,1,1-TCA at 1.0 μ g/L. (Page 27 of Reference 32 of the HRS documentation record at proposal cited on those pages explains that this was from sample location WP -08A.)

Therefore, the presence of 1,1 -DCA in downgradient residential wells may also be explained by degradation of a hazardous substance (1,1,1

- TCA) migrating from the Site.

Distribution of PCE in Deep Overburden On

- Property Wells and Residential Drinking Water Wells

Regarding the comment that on-property deep overburden wells only contained PCE at MW-4D, and that MW3D exhibited no chlorinated solvents, these findings do not disprove the attribution of off-property residential drinking water well contaminants to the Site.

Note that wells MW -4D and MW- 3D are identified as ERM -4D and ERM-3D in the HRS documentation record at proposal, respectively. ERM-4D is located just northeast of Debris Pile D (Source 4), in the south- central portion of the Leeds Metal property. ERM -3D is located near the southern property line (see Figures 1, 4 and 5, Property Map, Cross Section and Cross Section Profile Map, respectively, of this support document).

First, as discussed above, pages 117 -118 of the HRS documentation record at proposal mention that PCE (and TCE) can exist as DNAPL, and that:

DNAPLs are difficult to detect in the environment and can act as a source for dissolved contamination in ground water over time . . . there are a number of other physical and chemical properties that influence actual migration in the subsurface and their physical/geochemical behavior [145, Appendix B (pp. B-1 – B8)]. Their behavior is determined by complex interactions between the DNAPL chemicals and the hydrogeological formations through which
the DNAPLs move

.

Therefore, no guarantee exists that every well downgradient of migrat ing chlorinated solvents will precisely intercept that migration path and exhibit detectable concentrations.

Additionally, page 4 of Reference 165 (produced by an ME DEP certified hydrogeologist) of the HRS documentation record at proposal addresses this subject, explaining why chlorinated solvents migrating from the
Site could miss well MW

- 3D (ERM

- 3D):

ERM -3 is located south, southeast of ERM-4 (approximately 200-degrees) and did not detect any chlorinated VOCs. The conceptual site model presented in my April 7 memo [Reference 163 of the HRS documentation record at proposal] states that it is unclear if the VOCs enter the bedrock on the eastern portion of the site or further west. The fact that ERM-3D did not detect any VOCs is not surprising based on the vertical component of flow measured between the S and D wellsLee ds Metal NPL Listing Support Document September 2012

37 [shallow and deep couplets at each well location] and the elevation of ERM-4D and ERM-3D. [See Figure 4, Site Cross -Section, and Figure 5, Cross Section Profile Map, of this support
document showing these wells in a site cross

- section.] The vertical component of flow is consistently downward at ERM-2 and ERM- 3 and within the error of measurement at ERM -1 and

ERM -4. [See also page 16 of Reference 21 of the HRS documentation record at proposal, wh ich discusses the vertical component.] This indicates that the combination of the physical parameters of PCE and the hydraulic gradient would cause the plume to migrate downward through the aquifer as groundwater and the plume migrate laterally. The elevat ion of the bottom of ERM- 4D is approximately 69

- feet (based on ERM assumed elevation survey). The elevation of the bottom
of ERM -3D is approximately 64- feet, five vertical feet below ERM

- 4D. This small vertical difference may allow the plume to pass under the bottom of ERM -3D without being detected by the well. According to drillers logs the bedrock surface in the Hilliard drinking water well [location of sample DW-09], located 170- feet south west of ERM -3D, is 148- feet below the ground surface. [See HRS documentation record at proposal Figures 2 and 5; Reference 73, pages 1-2; and Reference 144 pages 1-2.] ERM -3D is drilled to a depth of 42- feet, leaving 106

- feet of saturated overburden below the bottom of ERM-3D for the plume to migrate undetected, not to mention the possibility that the plume may be entirely in the bedrock as it passes under ERM

- 3D.

Furthermore, there were indeed historical indications of PCE in deeper overburden aquifer samples. PCE was detected in June 2009 field screening m easurements of samples from WP -01 (in a sample at 26 ft bgs), and WP02, WP-03, WP-04, WP-05, and WP-06 (in samples at 26 and 30 ft bgs at each), all in the southwest portion of the property near Source 4 Pile D (see HRS documentation record at proposal Reference 32, pages 26, 39, and 56).

Thus, the pattern of PCE distribution in deep overburden wells on the Leeds Metal property is consistent with the attribution of PCE and TCE in residential drinking water wells to the Site.

Regarding the comment that concentrations in deep overburden and bedrock wells are not consistent with thedecreasing concentration gradient with depth at the facility, this also does not disprove the attribution of offproperty residential drinking water well contaminants to the Si te. As discussed above, PCE may sink through aquifers as DNAPL, as well as being drawn downward via vertical ground water movement. It is consequently reasonable that some deeper wells in the bedrock aquifer may exhibit higher PCE concentrations than deep overburden wells closer to the surface, because much of the PCE released at the Leeds Metal property has likely migrated downwards in the decades since the original releases may have occurred (page 26 of the HRS documentation record at proposal noted that scrap metal recovery operations on the property began in approximately 1969).

Therefore, these comments do not invalidate attribution of observed release hazardous substances to the Site.

Non

- Chlorinated VOCs Distribution

Regarding MEC’s point concerning the lack of similarity of the chemical signatures between the on

- facility monitoring wells and the drinking water wells of non- chlorinated compounds, the distribution of non -chlorinatedLee ds Metal NPL Listing Support Document September 2012

38 VOCs also does not contradict the attribution of PCE/TCE in observed release samples to the Site. As explained
below:

• 2- butanone may degrade before it makes its way from the Site to downgradient residential drinking water wells.

• Some toluene found in residential drinking water wells may be due to adhesives on tapes commonly used to secure wiring to well waterlines.

• Due to the historical automobile storage and recycling operations at the Leeds Metal property, it is expected that gasoline

- related contaminants may be associated with the Site and could be tied to gasoline

rela ted contaminants in downgradient residential drinking water wells; indeed, there has been evidence of gasoline- related contaminants in Site soils.

• Because migration behaviors of PCE/TCE and these gasoline constituents could be different, there is not

neces sarily a direct link between the distribution of non-chlorinated VOCs and the distribution of chlorinated VOCs.

• Gasoline- related contaminants may be relatively absent in samples from on -property wells and shallow wells due to conditions favorable to aerobi c degradation of petroleum hydrocarbons.

First, the subject of non-chlorinated VOCs distribution was addressed by an ME DEP certified hydrogeologist on pages 5 -6 of Reference 165 of the HRS documentation record at proposal, which states:

The detection of butanone on -site is likely related to the poor handling of various chlorinated and

non- chlorinated solvents as well as petroleum products during the metal recycling practices.
Research has indicated that 2 -butanone (MEK) degrades under aerobic conditions in groundwater. Given the conditions at the site, it appears that there is sufficient DO present in the shallow portion of the overburden aquifer to degrade 2- butanone before it reaches the bedrock aquifer. This would explain why 2-butanone has been detected in the shallow portion of the aquifer on-site, but not in the deep bedrock wells or shallow dug wells off- site.

The detection of chloroform in ERM- 3S is likely related to chloroform bacteria present in the shallow monitoring well. Bacterial contamination may have taken place at the time of well
installation or at a later time. Bacterial contamination in wells is not uncommon in Maine.

The only non-chlorinated VOC reported in Table 12 of the Draft Site Inspection Report [the final version of this report is included as Reference 11 of the HRS documentation record at proposal] is
toluene at DW -25 (19 ug/L), DW- 26 (0.81 ug/L), and DW -30 (0.58 ug/L). Low detections of toluene in a water supply can be from many sources, but is most often attributable to the glue on black electrical tape. Often times, electrical tape is used to secure pump wires to the waterline within a well. Such usage can contribute low levels of toluene to the water in a water supply well. The levels of toluene reported in Table 12 are cons istent with the use of electrical tape within the
well.

It would not be surprising to find low detections of MTBE, BTEX, or methylene chloride reported in water samples collected from the water supply wells in the future. While the presence of MTBE in gas oline has been reduced well below 1% by volume, the historic concentrations ofLee ds Metal NPL Listing Support Document September 2012

39 MTBE in gasoline formulation in Maine exceeded 35% by volume and small releases of older gasoline could result in low levels of MTBE and the other BTEX compounds. The shallow du g wells located in the area are more susceptible to these small quantity releases. Methylene Chloride can be detected in water samples and is often attributable to contaminated glassware or
from cross

- contamination in the laboratory as it is a solvent used regularly in water analyses. The low level detections of such compounds do not discount the relationship between PCE detections on-site and the PCE and daughter products detected in the drinking water wells off- site.

Second, due to the historical automobile storage and recycling operations at the Leeds Metal property, it is expected that gasoline

- related contaminants may be associated with the Site and could be tied to gasoline

- related contaminants in downgradient resi dential drinking water wells. Although not used for HRS scoring purposes, there is historical evidence of related contaminants on the property; detections of BTEX ( benzene, toluene, ethylbenzene and xylenes )/ MTBE on the property from the November 2010 SI a lone include the following:

Concentration Sample Sample Description HRS
Documentation Record at Proposal
Reference

11 J μ g/kg ethylbenzene

7 J μ g/kg o

- xylene

24 J μ g/kg m,p

- xylene SS

- 16 November 2010 SI sample, s urface soil/source sample collected from a soil boring adjacent to (west) of the concrete pad on the central

- eastern portion of the
Leeds Metal property 11, pp. 14, 31, 50;

6 J μ g/kg o

- xylene 19 J m,p

- xylene SS

- 20 November 2010 SI sample, s urface soil/source sample collected from a soil boring adjacent to the north

- northwest

toe

- slope of Debris Pile D 11, pp. 14, 32, 53

9.5 J m,p

- xylene SS

- 22 November 2010 SI sample, Surface soil/source sample collected from a soil boring adjacent to Debris Pile D on the
southern portion of the Leeds Metal

prop erty 11, pp. 14, 33, 55

26 EB μ g/kg t oluene

16 J μ g/kg m,p

- xylene SS

- 23 November 2010 SI sample, surface soil/source sample collected from a soil boring adjacent to Debris Pile D on the southern portion of the Leeds Metal
property 11, pp. 14, 33 , 56,

9. 1 J μ g/kg ethylbenzene

9.3 J μ g/kg o

- xylene

21 J μ g/kg m,p

- xylene

6.7 J μ g/kg MTBE SS

- 25 November 2010 SI sample, s urface soil/source sample collected from a soil boring approximately 20 feet northwest of
the bottom toe

- slope of Debris Pile D on the Leeds Metal property 11, pp. 14, 34, 58

16 EB μ g/kg toluene SS

- 2 7 November 2010 SI sample , s urface soil/source sample collected from a soil boring adjacent to Debris Pile D on the
southern portion of the Leeds Metal
property 11, pp. 14, 34, 60Lee ds Metal NPL Listing Support Document September 2012

40 Concentration Sample Sample Description HRS
Documentation Record at Proposal
Reference

16 J μ g/kg ethylbenzene

9.4 J μ g/kg o

- xylene

23 J μ g/kg m,p

- xylene SS

- 31 November 2010 SI sample, Surface soil/source sample collected from a soil boring from the northern slope of Debris
Pile D 11, pp. 14, 36, 64,
65

34 J μ g/kg ethylbenzene

30 JEB μ g/kg toluene

22 J μ g/kg o

- xylene

37 J μ g/kg m,p

- xylene SS

- 35 November 2010 SI sample , s urface soil/source sample collected from a soil boring from the surface of the northeastern portion of Debris Pile B, on
the southeastern corner of the Leeds Metal
property 11, pp. 14, 37, 68

6.4 J μ g/kg ethylbenzene

15 J μ g/kg m,p

- xylene SS

- 44 November 2010 SI sample, Field Duplicate of SS

- 20 11, pp. 14, 39, 73

14 J μ g/kg ethylbenzene

10 J μ g/kg o

- xylene

37 J μ g/kg m,p

- xylene SB

- 31 November 2010 SI sample, Subsurface soil/source sample collected from a soil boring from the northern slope of Debris
Pile D on the Leeds Metal property 11, pp. 14, 86, 98

62 J μ g/kg ethylbenzene

21 JEB μ g/kg toluene

38 J μ g/kg o

- xylene

55 J μ g/kg m,p

- xylene SB

- 34 November 2010 SI sample, S ubsurface soil/source sample collected from a soil boring from the surface of the western portion of Debris Pile B 11, pp. 14, 87, 101

1,900 μ g/kg ethylbenzene 2,000 EB μ g/kg toluene 1,200 o

- xylene 2,000 m,p

- xylene SB

- 35 November 2010 SI sample, Subsurface soil/source sample collected from a soil boring from the surface of the northeastern portion of Debris Pile B, on
the southeastern corner of the Leeds Metal
property 11, pp. 14, 87, 103

EB 2 = The compound was identified in an aqueous equipment blank used to assess field contamination associated with soil/source samples.

J 3 = The associated numerical value is an estimated quantity. MTBE = methyl tert

- butyl ether

And, the HRS documentation record a t proposal points out several instances in which other fuel- related analytes have been found in detectable levels on the property:

• May 1998 ME DEP Site Discovery analysis of surface soil samples found diesel range organics (DROs) and total petroleum hydrocarbons (TPHs) (see page 27 of the HRS documentation record at proposal).

2 Although the results associated with EB qualifiers may be aff ected by high bias, the presence of the analyte is not in question, and the concentrations detected in the field samples cannot be explained by the concentrations found in related equipment blanks.

3 Although the results associated with J qualifiers may re present estimated results, the presence of the analyte is not in question.Lee ds Metal NPL Listing Support Document September 2012

41 • The November 2000 ERM investigation detected DRO in a sediment sample on the central portion of the property (see page 29 of the HRS documentation record at proposal).

• The 2004 Roux and Associates Targeted Environmental Investigation found DRO in onsite well ground water samples and soil samples (see pages 31 -32 of the HRS documentation record at proposal).

Third, the behavior and migration of DNAPL through the subsurface is complex and can depend on many factors, and therefore the pattern of PCE/TCE distribution may not necessarily correlate with the pattern of gasoline

related contaminants. As described on pages 117 -118 of the HRS documentation record at proposal:

Their [DNAPL] behavior is determined by complex interactions between the DNAPL chemicals and the hydrogeological formations through which the DNAPLs move [145, Appendix B (pp. B-1

– B- 8)]. DNAPL chemicals are subject to several processes, including downward migration by gravity; absorption and adsorption on soil; volatilization into soil gas; dissolution and dispersion in ground water; preferential solution of components; phase separation or the formation of emulsions; and transformation into other chemicals by microbiol ogical and/or chemical processes (when chemicals are in solution or air) [145, Appendix B (pp. B-1 – B- 8)]. Given relatively equal viscosities, the greater the specific gravity, the greater the tendency of the substance to migrate under the influence of gr avity through the subsurface [145, Appendix B (pp. B-1 – B- 8)].

Non

- chlorinated VOCs such as the gasoline constituents mentioned by the commenter (benzene, toluene, ethylbenzne, xylene, and MTBE) may behave and migrate differently in the environment than chlorinated VOCs such as PCE and TCE. There are many factors that can affect migration of PCE and TCE as DNAPL, as described on page B-1 of Reference 145 of the HRS documentation record at proposal:

[t] he physical/chemical properties of a DNAPL mass most important to subsurface migration are specific gravity and dynamic viscosity. Factors, such as vapor pressure, Henry’s Law constant, and solubility in water, contribute to the dissolution of the DNAPL chemicals into dissolved or soil gas vapor phases wher e they may undergo biodegradation and chemical transformation.

For instance, because the abovementioned gasoline constituents have densities less than that of water, they may exist as light non- aqueous phase liquids (LNAPLs), which can float on water rat her than sink as DNAPLs do 4

. Also, there are differences in other physical parameters that can impact the rate of migration in ground water and through aquifer matrices:

• PCE and TCE have water solubility values of approximately 206 and 1280 mg/L at 25 ° C, respectively; benzene, toluene, ethylbenzene, xylenes, and MTBE have solubility values of approximately 1790, 526, 169, 106, 51,000 mg/L at 25 ° C.

• PCE and TCE have vapor pressures of 18.5 and 69 mm Hg at 25 ° C, respectively; benzene, toluene, ethylbenzene, xylenes, and MTBE have vapor pressures of approximately 94.8, 28.4, 9.6, 7.99, and 250

4 See HRS documentation record at proposal Reference 149, page 5, which notes that “[u]nlike light non

- aqueous phase liquids (LNAPLs) such as petrol and heating oil (which are less dense than water), DNAPLs (which are denser th an water) have the ability to migrate to significant depths below the water table where they slowly dissolve into flowing groundwater, giving rise to aqueous phase plumes.”Lee ds Metal NPL Listing Support Document September 2012

42 mm Hg at, 28 mm Hg at 25 ° C, 7 mm Hg at 20 ° C, 6.61-8.84 mm Hg at 25 ° C, and 245 mm Hg at 25 ° C, respectively 5

.

• PCE and TCE have viscosities of approximately 0.844 and 0.545 millipascal seconds (mPa s) at 25 ° C, respectively; benzene, toluene, ethylbenzene, and xylenes have viscosities of approximately 0.604, 0.560, 0.631, and 0.760 (o-xylene), 0.581 (m-xylene), and 0.603 (p- xylene) mPa s, respectively 6

.

Thus, because physical nature and migration behaviors of PCE/TCE and these gasoline constituents could be different, there is not necessarily a direct link between the distribution of non- chlorinated VOCs and the
distribution of chlorinated VOCs.

Finally, petroleum hydrocarbons such as gasoline constituents can quickly undergo biodegradation in aerobic (oxygenated) conditions 7 . As previously mentioned, page 2 of HRS documentation record at proposal Reference 165, produced by a ME DEP certified environmental hydrogeologist stat ed that:

The field parameters collected during monitoring well sampling completed in June 2009 (see below) indicates that the monitoring wells on

- site reflect oxidized conditions. ERM -4S and ERM4D were the only monitoring wells with dissolved oxygen (DO) concentrations below 1ppm, indicating an anaerobic environment. However, the corrected Eh measurements exceed 500 mV in the two wells, indicating an oxidized environment. It appears that even though there is an
anaerobic environment at ERM- 4, it is not a reducing environment capable of supporting PCE degradation.

Therefore, part of the reason for the relative absence of gasoline-related contaminants in on-property monitoring wells may be that remnants of historical spills of these contaminants in the shal lower oxidized environment of the overburden aquifer at the Leeds Metal property have been broken down by aerobic biodegradation over time since the original spills took place.

Consequently, some of the fuel-related contaminants found in downgradient drin king water wells may indeed have originated at the Leeds Metal property; the distribution of those contaminants may not be directly linked to the distribution of PCE and TCE; and, those contaminants’ relative abundance in drinking water wells compared to on-site overburden wells could again be a product of the complexities described above associated with organic contaminant migration and degradation through aquifers, and the time which has elapsed since the original release(s) occurred. Thus, the gasoline r elated contamination found in downgradient residential drinking water wells may be explained as an effect of the Site, and does not contradict the attribution of PCE/TCE in observed release samples to the Site.

This comment results in no change to the HRS score and no change in the decision to place the Site on the NPL.

5 See pages ChemID

- 1 through -7 of At tachment 1

, Select Physical Properties Pages from the United States National Library of Medicine ChemIDplus Lite Database , of this support document, for water solubility and vapor pressure values

. 6 See Attachment 2 of this support document, Excerpt of CRC Handbook of Chemistry and Physics, 92nd Edition, 2011

- 2012 for PCE (p. 6

- 231), TCE (p. 6

- 231), benzene (p. 6

- 233), toluene (p. 6

- 234), ethylbenze ne (p. 6

- 234), and xylenes (p. 6- 234) viscosity values

. 7 See pages 2 and 6 of Attachment 3

, Excerpt of Petroleum Hydrocarbons And Chlorinated Hydrocarbons Differ In Their Potential For Vapor Intrusion, EPA Office of Underground Storage Tanks, March 2012, of this support document.Lee ds Metal NPL Listing Support Document September 2012

43 

### 3.7 Eligible Targets

Comment : MEC questioned the validity of using the entire “4- radial mile ” population as “a Potential population Target” in the target scoring in the revised target scoring presented in the NODA (77 FR 40318, July 9, 2012). MEC commented that the EPA included the entire population within the 4- radial mile area of the site as potential population targets without considering geohydrologic data and only considering geographic data. MEC asserted that this approach is overly conservative because using the 4- radial mile approach assumes that site releases to ground water flow radially from the facility . Instead

, MEC claimed that site

- specific data

, as well as State of
Maine data

, show the area co ntains at least two separate watershed basins with the majority of the “Site” flowing northeast and the other flowing southwest and southeast toward the higher population densities. MEC also
commented that th e geol ogic material in the area, based on the map provided in Appendix A of its comments, is composed of a heterogeneous mixture of sand and gravel, silt, clay, peat, and till, which overlies a complex sequence of bedrock making the interconnectivity of the bedrock fractures unproven throughout the 4- radial mile

area.

MEC also claimed in its comments on the original proposed Leeds Metal HRS documentation record dated September 2011 that “the Leeds Metal site is located northeast of a basin divide, while most of the off

- Site private drinking water wells sampled are located southwest of the basin divide, indicating it is unlikely that groundwater from the Site is flowing to the southwest.” MEC pointed to the Maine Geological Survey geologic maps for this region in support, which were provided as Appendix A of its comments. MEC a lso asserted (citing Figures 1 through 3 of its comments) that this information is consistent with ground water gauging and ground water flow
direction determined for the Site.

Response : The considerat ion of all targets within the 4

- mile TDL of the site is as required by the HRS. Specifically

, flow direction is not considered in identifying eligible targets.

HRS S ection 3.0.1.1, Ground water target distance limit, identifies which targets at a site are to be included in an
HRs evaluation:

[t]he target distance limit defines the maximum distance from the sources at the site over which targets are evaluated . Use a target distance limit of 4 miles for the ground water migration pathway, except when aquifer discontinuities apply (see section 3.0.1.2.2). Furthermore, consider any well with an observed release from a source at the site (see section 3.1.1) to lie within the target distance limit of the site, regardless of the distance limit of the site, regardless of the well’s
distance from the sources at the site.

Section 3.5.1, Ground Water Discontinuities, of this support document identifies that there are no discontinuities restricting the extent of the TDL for this site.

HRS Section 3.3.2, Population, explains that people using these wells make up the eligible target population:

In evaluating the population factor, include those persons served by drinking water wells within the target distance limit specified in section 3.0.1.1.Lee ds Metal NPL Listing Support Document September 2012

44 As explained in Section 2.0, Site Description, of this support document, the HRS documentation record at proposal was updated by the NODA (77 FR 40318, July 9, 2012) to reflect the most current and accurate population factor values within the 4- mile TDL available at this time.

As explained above, all targets within the TDL are correctly considered eligible to be included in the Target Factor Category score independent of ground water flow direction unless an aquifer discontinuity completely transects the aquifer.

In addition, as explained in Sections 3.5 and 3.5.1, Aquifer Description and Ground Water Discontinuities, respectively, of this support document, the aquifer being evalua ted at the Leeds Metal site was properly established in the HRS documentation record at proposal and contains no documented aquifer discontinuities even when considering the heterogeneous soil mixture (presented in a map titled “Surficial Deposits” in Appe ndix A of MEC’s comments). The HRS documentation record at proposal correctly identifies that the aquifer being evaluated is a single aquifer system and all of the wells identified at the Site are located in the same aquifer
system.

Furthermore, as expla ined in Section 3.5.2, Ground Water Flow Direction , of this support document, while the ground water flow direction in the shallow overburden locally flows toward the north/ northwest, the downward vertical gradient observed in the monitoring wells will ta ke the ground water below 25 ft bgs and into the deep overburden and bedrock aquifer zones of the aquifer, which exhibit a south/southwest ground water flow direction. Thus, there is a clear path for contaminants in ground water to migrate from the Leeds M etal property to the residential drinking water wells.

Therefore, all of the wells identified as target wells in Section 3.3 of the HRS documentation record at proposal remain eligible for evaluation in the Leeds Metal HRS package.

Furthermore, the HRS does not specifically take into account such level of detail as ground water flow gradients to determine target populations under the HRS (55 FR 51551, December 14, 1990).

In responding to public comments on the proposed (original) HRS on July 16, 1982 (47 FR 31190), the EPA explained that it is generally not practicable to determine the population actually exposed or threatened by using ground water flow information. In many instances, the information is not available, and in others the flow direction varies over time. Even where there is extensive knowledge of geohydrology, interpretation is nearly always subject to dispute. Requiring a precise measure of the affected popul ation would add inordinately to the time and expense of applying the HRS. EPA decided not to use ground water flow information, even when available, because of the need to develop a nationally uniform system for scoring a large number of sites expeditiously with commonly available data. EPA reconsidered this issue when revising the HRS, and determined that the decision not to directly consider ground water flow direction in evaluating targets was still appropriate (55 FR 51551).

Instead, the HRS considers flow direction indirectly in the method used to evaluate target populations by weighting target populations based on actual and potential contamination of drinking water wells. The HRS uses a radius of 4 miles around the site when determining the distance to the nearest well in the contaminated aquifer andLee ds Metal NPL Listing Support Document September 2012

45 the population at risk due to actual or potential contamination, provided there is no discontinuity that completely transects the aquifer of concern between the site and the well being scored for HRS purp oses (55 FR 51595).

In addition, if wells have not been contaminated by the site, as would be typical of upgradient wells, the wells are considered potentially rather than actually contaminated, and the population drawing from those wells is distance weig hted (55 FR 51603). Conversely, if wells have been contaminated, a likelihood for downgradient wells, the wells are considered actually contaminated and given higher weight in scoring.

Therefore, as detailed above, all of the wells identified as target w ells in Section 3.3 of the HRS documentation record at proposal are eligible for evaluation in the Leeds Metal HRS scoring.

This comment results in no change to the HRS score and no change in the decision to place the Site on the NPL.

MEC’s comments on t he eligibility of targets for HRS scoring are further discussed in the following sections of this support document:

• Section 3.7.1 Level I targets,

• Section 3.7.2 Level II targets and

• Section 3.7.3 Potential targets.

3.7.1 Level I Targets

Comment : MEC co mmented that the geochemical signature of the two wells scored as Level I target wells presented in the HRS documentation record as modified by the NODA (77 FR 40318, July 9, 2012)

, wells DW -12 and DW-24, do not match “Site” geochemistry and thus the impac ts to these receptors appear unrelated to the site. In addition, MEC commented that these two wells are not within the “Leeds site” aquifer and are, i n fact, upgradient of the Site.

Response : Wells DW -12 and DW- 24 were correctly scored as eligible Level I targets wells in the revised HRS documentation record at the time of the NODA (77 FR 40318, July 9, 2012). HRS Section 3.3.2.1, Level of

contamination , presents the requirements for identifying Level I targets:

Evaluate the population served by water from a point of withdrawal based on the level of contamination for that point of withdrawal. [Emphasis added]. Use the applicable factor: Level I concentrations, Level II concentrations, or potential contamination.

If no samples meet the criteria for an observed release for a point of withdrawal and there is no observed release by direct observation for that point of withdrawal, evaluate that point of withdrawal using the potential contamination factor in section 3.3 .2.4. If there is an observed release by direct observation, use Level II concentrations for that point of withdrawal. However, if one or more samples meet the criteria for an observed release for the point of withdrawal, determine which factor (Level I or Level II concentrations) applies to that point of withdrawal as specified in sections 2.5.1 and 2.5.2. Use the health- based benchmarks from
Table 3

- 10 in determining the level of contamination. [Emphasis added].Lee ds Metal NPL Listing Support Document September 2012

46 HRS Section 3.3.2.2, Level I concentration s , explains how to assign a targets score for Level I targets:

Sum the number of people served by drinking water from points of withdrawal subject to Level I concentrations. Multiple this sum by 10. Assign this product as the value for this factor. Enter this
value in Table 3 -1.

The HRS documentation record on pages 113-114 as revised at the time of the NODA (77 FR 40318, July 9, 2012) documents that TCE and PCE were found at concentrations significantly above background levels in wells
DW -12 and DW-24:

Of the seven drinking water samples presented, PCE was detected at a maximum concentration of 3.9 μg/L in drinking water sample DW -12 [16, pp.22-23; 34, pp. 25; 46, Table 1 (p. 1 of 3); 74, pp. 1- 2]. PCE was detected in five of the selected drinking water samples (DW -12, DW-13, DW18, DW-23, and DW- 24) at concentrations greater than or equal to the background sample concentration (DW

- 02, concentration 0.5 U μg/L) [14, pp. 23 -25, 44-45; 15, pp. 16-17; 16, pp. 7- 10, 22-23; 34, pp. 8, 12, 15, 22-23, 25; 45, Table 1 (pp. 1-2 of 3); 46, Table 1 (pp. 1-2 of 3); 47, Table 1 (p. 1 of 3); 74, pp. 1 -2].

Table 45 - Hazardous Substances Associated with Drinking Water Samples

Sample ID Hazardous
Substance Concentration (μg/L) Sample

Adjusted

CRQL (μg/L) References

DW

- 12 PCE 3.9 0.5 16, pp. 22

- 23; 34, p. 25; 46, Table 1 (p. 1 of 3) ); 74, pp. 1

- 2; 153, pp.
17

- 18
TCE 18 0.5 16, pp. 22

- 23; 34, p. 25; 46, Table 1 (p. 1 of 3) ); 74, pp. 1

- 2; 153, pp.
17

- 18

DW

- 13 PCE 0.91 0.5 14, pp. 23

- 25; 34, p. 8; 45, Table 1 (p. 1 of 3); 153, pp. 19

- 20
TCE 0.96 0.5 14, pp. 23

- 25; 34, p. 8; 45, Table 1 (p. 1 of 3); 153, pp. 19

- 20

DW

- 16 TCE 0.63 0.5 14, pp. 37

- 38; 34, p. 11; 45, Table 1 (p. 2 of 3); 153, pp. 21

- 22

DW

- 18 PCE 1.1 0.5 15, pp. 16

- 17; 34, p. 15; 47, Table 1 (p. 1 of 3); 153, pp. 23

- 24
TCE 0.52 0.5 15, pp. 16

- 17; 34, p. 15; 47, Table 1 (p. 1 of 3); 153, pp. 23

- 24

DW

- 23 PCE 0.61 0.5 16, pp. 9

- 10; 34, pp. 22

- 23; 46, Table 1 (p. 2 of 3); 153, pp. 25

- 26
TCE 0.91 0.5 16, pp. 9

- 10; 34, pp. 22

- 23; 46, Table 1 (p. 2 of 3); 153, pp. 25

- 26

DW

- 24 PCE 0.77 0.5 14, pp. 44

- 45; 34, p. 12; 45, Table 1 (p. 2 of 3); 153, pp. 27

- 28
TCE 1.5 0.5 14, pp. 44

- 45; 34, p. 12; 45, Table 1Lee ds Metal NPL Listing Support Document September 2012

47 Sample ID Hazardous
Substance Concentration (μg/L) Sample

Adjusted

CRQL (μg/L) References

(p. 2 of 3); 153, pp. 27

- 28

DW

- 25 TCE 0.65 0.5 14, pp. 35

- 36; 34, p. 10; 45, Table 1 (p. 2 of 3); 153, pp. 29

- 32 PCE = Tetrachloroethene. TCE = Trichloroethene. μg/L = Micrograms per liter. CRQL = Contract Required Quantitation Limit.

Section 3.6, Likelihood of Release: Attribution, of this support document, documents that at least some portion of the contamination in wells DW -12 and DW- 24 is attributable to t he Leeds metal site.

The HRS documentation record on page 127 as revised at the time of the NODA (77 FR 40318, July 9, 2012) and presented in Section 3.3 of the errata document in the NODA (see docket number EPA

- HQ

- SFUND -2011-0647- 0007), establishes that levels of TCE in wells DW -12 and DW-24 document are at Level I concentrations:

Level I Concentrations

Of the seven drinking water samples presented, TCE was detected at a concentration above the
health

- based benchmarks for hazardous substances in drinking water (screening concentration for
cancer corresponding to that concentration that corresponds to the 10 -6 individual cancer risk for oral exposures) in two drinking water samples (DW -12 and DW-24) [1, pp. 51593 (Section 2.5.1 and Section 2.5.2), 51603 (Table 3 -10); 14, pp. 44-45; 16, pp. 22-23; 34, pp. 12, 25; 45, Table 1 (pp. 2 of 3); 46, Table 1 (pp. 1 of 3); 74, pp. 1-2; 176, pp. A-1-2; 177 pp. BII-23; 178; 179].

Sample
ID Hazardous
Substance Hazardous
Substance
Concentration (μg/L) Benchmark
Concentration (μg/L) Benchmark References for
Benchmark

DW

- 12 TCE 18 1.0 Cancer Risk 176, pp. A

- 1

- 2; 177 pp. BII

- 23.
A- 1, A

- 2; 178;
179

DW

- 24 TCE 1.5 1.0 Cancer Risk 176, pp. A

- 1

- 2; 177 pp. BII

- 23; 178; 179

TCE = Trichloroethene. μg/L = Micrograms per Liter.

The HRS documentation record on page128-129 as revised at the time of the NODA (77 FR 40318, July 9, 2012), documents the number of people using drinking water from observed release wells DW-12 and DW-24 and the
determination of t he Level I concentration factor value:

Level I Population Targets

Based on TCE analytical results of drinking water samples, a release to two drinking water supply wells has been documented, and Level I concentrations confirmed [1, pp. 51593 (Section 2.5.1Lee ds Metal NPL Listing Support Document September 2012

48 and Section 2.5.2), 51603 (Table 3-10); 14, pp. 44-45; 16, pp. 22-23; 34, pp.12, 25; 45, Table 1 (pp. 2 of 3); 46, Table 1 (pp. 1 of 3); 74, pp. 1-2; 176, pp. A-1-2; 177 pp. BII-23; 178; 179]. Information provided by the residents served by the drinking water supply wells indicate that a total of five Level I Actual Contamination Targets have been documented [1, pp. 51593 (Section 2.5.1 and Section 2.5.2), 51603 (Table 3-10); 14, pp. 44-45; 16, pp. 22-23; 34, pp.12, 25; 45,Table 1 (pp. 2 of 3); 46, Table 1 (pp. 1 of 3); 74, pp. 1-2; ; 117; 129; 176, pp. A-1-2; 177 pp. BII23; 178; 179].

Level I Well Aquifer No. Population References
DW

- 12 1 3 117; 16, p. 22
DW

- 24 1 2 129; 14, p. 44

Sum of Population Served by Level I Wells: 5

Sum of Population Served by Level I Wells x 10: 50

Level I Concentrations Factor Value: 50 [1, p. 51603, Section 3.3.2.2]

As explained above, the HRS documentation record as revised at the time of the NODA (77 FR 40318, July 9, 2012) , correctly identifie s wells DW -12 and DW- 24 as Level I wells based on documentation of a significant increase of TCE concentrations, which are attributable to the site, and documentation of TCE concentrations above the lowest health-based benchmark of 1.0 μg/L for the cancer screening concentration. Additionally, as explained above, the HRS documentation record as revised at the time of the NODA (77 FR 40318, July 9, 2012), correctly associates a sum of five people as drinking water users of wells DW -12 and DW-24, and correctl y multiplies the sum of Level I population by 10, as required by the HRS, to assign a 50 as the Level I concentration
factor value.

Regarding MEC’s comment that wells DW -12 and DW- 24 are upgradient of the Leeds Metal site sources, as explained in Section 3.5.2, Ground Water Flow Direction, of this support document, while the ground water flow direction in the shallow overburden locally flows toward the north/northwest, the downward vertical gradient observed in the monitoring wells will take the ground water below 25 ft bgs and into the deep overburden and bedrock aquifer zones of the aquifer, which exhibit a south/southwest ground water flow direction. Wells DW-12
and DW- 24 are screened in the bedrock aquifer zone and are located south/southwest of the site sources, which is the downgradient direction for this aquifer zone (see Figures 1 and 3, Property Map and Drinking Water Sample Location Map, respectfully, of this support document). Thus, there is a clear path for contaminants in ground water to migrate from the Leeds Metal property to the residential drinking water wells.

Regarding MEC’s comment that the chemical signature of these wells is different that the chemical signature of contamination directly under the facility property, as discussed in Sec tion 3.6.2, Chemical Signatures/Distribution, of this support document, the distribution of chlorinated solvents, their breakdown products, and non -chlorinated volatile organic compounds (VOCs) is consistent with the scenario in which ground
water in on -property monitoring wells and off-property drinking water wells have been contaminated by hazardous substances migrating from the Site. Although the chemical signature varies, the changes in the signature are within the range expected due to differential mig ration rates and degradation rates of the contaminants as they travel in the aquifer.Lee ds Metal NPL Listing Support Document September 2012

49 Therefore, all of the wells identified as Level I target wells in Section 3.3 of the HRS documentation record as revised at the time of the NODA ( 77 FR 40318, July 9, 2012 ) are eligible for evaluation in the Leeds Metal HRS scoring as Level I wells.

This comment results in no change to the HRS score and no change in the decision to place the Site on the NPL.

3.7.2 Level II Targets

Comment : MEC commented that the Level II targets wells, DW -13, 16, 18, 23 and 25, presented in the NODA (77 FR 40318, July 9, 2012) are “clearly” upgradient of the site and are not within the same watershed. MEC indicated that thus this scoring element should be re-evaluated.

Response : Wells DW -13, 16, 18, 23, and 24 were correctly scored as eligible Level II targets wells in the HRS documentation record as revised at the time of the NODA (77 FR 40318, July 9, 2012).

HRS Section 3.3.2.1, Level of contamination , presents the requirements for identifying Level II targets:

Evaluate the population served by water from a point of withdrawal based on the level of contamination for that point of withdrawal. [Emphasis added

. ] Use the applicable factor: Level I concentrations, Level II concentrations, or potential contamination.

If no samples meet the criteria for an observed release for a point of withdrawal and there is no observed release by direct observation for that point of withdrawal, evaluate that point of withdrawal using the potential contamination factor in section 3.3 .2.4. If there is an observed release by direct observation, use Level II concentrations for that point of withdrawal. However, if one or more samples meet the criteria for an observed release for the point of withdrawal, determine which factor (Level I or Level II concentrations) applies to that point of withdrawal as specified in sections 2.5.1 and 2.5.2. Use the health- based
benchmarks from Table 3 -10 in determining the level of contamination. [Emphasis added.]

HRS Section 3.3.2.3, Level II concentratio ns , explains how to assign a targets score for these Level II targets:

Sum the number of people served by drinking water from points of withdrawal subject to Level II concentrations. Do not include those people already counted under the Level I concentrat ion factor. Assign this product as the value for this factor. Enter this value in Table 3 -1.

Pages 113 -144 of the HRS documentation record as revised at the time of the NODA (77 FR 40318, July 9, 2012) document that TCE and/or PCE were found at concentrations significantly above background levels in wells DW

13, DW -16, DW -18, DW

- 23 , and DW -24:

Of the seven drinking water samples presented, PCE was detected at a maximum concentration of 3.9 μg/L in drinking water sample DW -12 [16, pp.22-23; 34, pp. 25; 46, Table 1 (p. 1 of 3); 74, pp. 1- 2]. PCE was detected in five of the selected drinking water samples (DW -12, DW-13, DW-Lee ds Metal NPL Listing Support Document September 2012

50 18, DW-23, and DW- 24) at concentrations greater than or equal to the background sample concentration (DW

- 02, concentration 0.5 U μg/L) [14 , pp. 23 -25, 44-45; 15, pp. 16-17; 16, pp. 7- 10, 22-23; 34, pp. 8, 12, 15, 22-23, 25; 45, Table 1 (pp. 1-2 of 3); 46, Table 1 (pp. 1-2 of 3); 47, Table 1 (p. 1 of 3); 74, pp. 1 -2].

Table 45 - Hazardous Substances Associated with Drinking Water Samples

Sa mple ID Hazardous
Substance Concentration (μg/L) Sample

- Adjusted CRQL (μg/L) References

DW

- 12 PCE 3.9 0.5 16, pp. 22

- 23; 34, p. 25; 46, Table 1 (p. 1 of 3) ); 74, pp. 1

- 2; 153, pp. 17

- 18
TCE 18 0.5 16, pp. 22

- 23; 34, p. 25; 46, Table 1 (p. 1 of 3) ); 74, pp. 1

- 2; 153, pp. 17

- 18

DW

- 13 PCE 0.91 0.5 14, pp. 23

- 25; 34, p. 8; 45, Table 1 (p. 1 of 3); 153, pp.
19

- 20
TCE 0.96 0.5 14, pp. 23

- 25; 34, p. 8; 45, Table 1 (p. 1 of 3); 153, pp.
19

- 20

DW

- 16 TCE 0.63 0.5 14, pp. 37

- 38; 34, p. 11; 45, Table 1 (p. 2 of 3); 153, pp. 21

- 22

DW

- 18 PCE 1.1 0.5 15, pp. 16

- 17; 34, p. 15; 47, Table 1 (p. 1 of 3); 153, pp. 23

- 24
TCE 0.52 0.5 15, pp. 16

- 17; 34, p. 15; 47, Table 1 (p. 1 of 3); 153, pp. 23

- 24

DW

- 23 PCE 0.61 0.5 16, pp. 9

- 10; 34, pp. 22

- 23; 46, Table 1 (p. 2 of 3); 153, pp. 25

- 26
TCE 0.91 0.5 16, pp. 9

- 10; 34, pp. 22

- 23; 46, Table 1 (p. 2 of 3); 153, pp. 25

- 26

DW

- 24 PCE 0.77 0.5 14, pp. 44

- 45; 34, p. 12; 45, Table 1 (p. 2 of 3); 153, pp. 27

- 28
TCE 1.5 0.5 14, pp. 44

- 45; 34, p. 12; 45, Table 1 (p. 2 of 3); 153, pp. 27

- 28

DW

- 25 TCE 0.65 0.5 14, pp. 35

- 36; 34, p. 10; 45, Table 1 (p. 2 of 3); 153, pp. 29

- 32 PCE = Tetrachloroethene. TCE = Trichloroethene. μg/L = Micrograms per liter. CRQL = Contract Required Quantitation Limit.Lee ds Metal NPL Listing Support Document September 2012

51 Section 3.6, Likelihood of Release: Attribution, of this support document, documents that at least some portion of the contamination in wells DW -13, DW -16, DW -18, DW -23, and DW -24 is attributable to the Leeds Metal site.

Pages 127 -128 of the HRS documenta tion record as revised at the time of the NODA (77 FR 40318, July 9, 2012)
establish that levels of TCE in wells DW -13, DW -16, DW -18, DW -23, and DW -24 are documented at Level II
concentrations:

Level II Concentrations

Of the seven drinking water samples presented, TCE was detected at a concentration greater than or equal to the relevant background sample concentration but below the health- based benchmarks for hazardous substances in drinking water (screening concentration for cancer corresponding to
that concentration that corresponds to the 10 -6 individual cancer risk for oral exposures) in five drinking water samples (DW-13, DW-16, DW-18, DW-23, and DW-25) [1, pp. 51593 (Section 2.5.1 and Section 2.5.2), 51603 (Table 310); 14, pp. 23-25, 35-38, 44-45; 15, pp. 16-17; 16, pp. 9- 10, 22-23; 34, pp. 8, 10-12, 15, 22-23, 25; 45, Table 1 (pp. 1-2 of 3); 46, Table 1 (pp. 1-2 of 3); 47, Table 1 (p. 1 of 3); 74, pp. 1-2; 176, pp. A-1-2; 177 pp. BII-23; 178; 179].

Sample ID Hazardous Substance Hazardous Substance Concentration (μg/L) Benchmark Concentration (μg/L) Benchmark References for Benchmark

DW

- 13 TCE 0.96 1.0 Cancer Risk 176, pp. A

- 1

- 2; 177 pp. BII

- 23; 178; 179
DW

- 16 TCE 0.63 1.0 Cancer Risk 176, pp. A

- 1

- 2; 177 pp. BII

- 23; 178; 179
DW

- 18 TCE 0.52 1.0 Cancer Risk 176, pp. A

- 1

- 2; 177 pp. BII

- 23; 178; 179
DW

- 23 TCE 0.91 1.0 Cancer Risk 176, pp. A

- 1

- 2; 177 pp. BII

- 23; 178; 179
DW

- 25 TCE 0.65 1.0 Cancer Risk 176, pp. A

- 1

- 2; 177 pp. BII

- 23; 178; 179 TCE = Trichloroethene. μg/L = Micrograms per Liter.

Pages 128 -129 of the HRS documentation record as revised at the time of the NODA (77 FR 40318, July 9, 2012) document the number of people using drinking water from observed release wells DW -13, DW -16, DW -18, DW

23, and DW -24, and the determination of the Level II concentration factor value:

Level II Population Targets

Based on TCE analytical results of drinking water samples, a release to five drinking water supply wells has been documented, and Level II concentrations conf irmed [1, pp. 51593 (Section 2.5.1 and Section 2.5.2), 51603 (Table 3-10); 14, pp. 23-25, 35-38, 15, pp. 16-17; 16, pp. 9-10; 34, pp. 8, 10-11, 15, 22-23; 45, Table 1 (pp. 1-2 of 3); 46, Table 1 (pp. 1-2 of 3); 47, Table 1 (p. 1 of 3); 74, pp. 1-2; 176, pp . A -1-2; 177 pp. BII-23; 178; 179 ]. Information provided by theLee ds Metal NPL Listing Support Document September 2012

52 residents served by the drinking water supply wells indicate that a total of 12 Level II Actual Contamination Targets have been documented [1, pp. 51593 (Section 2.5.1 and Section 2.5.2), 51603 (Table 3-10); 14, pp. 23-25, 35-38; 15, pp. 16-17; 16, pp. 9-10; 34, pp. 8, 10-11, 15, 22-23; 45, Table 1 (pp. 1-2 of 3); 46, Table 1 (pp. 1-2 of 3); 47, Table 1 (p. 1 of 3); 74, pp. 1-2; 114; 119; 121, p. 2; 122; 124, p. 4; 127; 131; 176, pp. A-1-2; 177 pp. BII-23; 178; 179].

Level II Well Aquifer No. Population References DW

- 13 1 2 119; 14, p. 23
DW

- 16 1 2 121, p. 2; 122; 14, p. 37
DW

- 18 1 2 124, p. 4; 15, pp. 16

- 17
DW

- 23 1 3 127; 16, p. 9
DW

- 25 1 3 131; 14, pp. 35

- 36

Sum of Population Served by Level II Wells: 12

Level II Concentrations Factor Value: 12 [1, p. 51603, Section 3.3.2.3]

As explained above, the HRS documentation record as revised at the time of the NODA (77 FR 40318, July 9, 2012) correctly identifies we lls DW -13, DW -16, DW -18, DW -23, and DW -24 as Level II wells based on documentation of a significant increase of TCE concentrations, which are attributable to the Site, and
documentation that none of the TCE concentrations in wells DW -13, DW -16, DW -18, DW -23, and DW -24 are above the lowest TCE health -based benchmark of 1.0 μg/L for the cancer screening concentration. Additionally, as explained above, the HRS documentation record as revised at the time of the NODA (77 FR 40318, July 9, 2012), correctly associates a sum of 12 people as drinking water users of wells DW -13, DW -16, DW -18, DW -23,
and DW -24 , to assign a 12 as the Level II concentration factor value.

Regarding MEC’s comment that these wells are upgradient of the Leeds Metal site sources, as explaine d in Section 3.5.2, Ground Water Flow Direction, of this support document, while the ground water flow direction in the shallow overburden locally flows toward the north/northwest, the downward vertical gradient observed in the monitoring wells will take t he ground water below 25 ft bgs and into the deep overburden and bedrock aquifer zones of the aquifer, which exhibit a south/southwest ground water flow direction. Wells DW -13, DW -16, DW

18, DW -23, and DW -24 are screened in the bedrock aquifer zone and are located south/southwest of the site sources, which is the downgradient direction for this aquifer zone (see Figures 1 and 3, Property Map and Drinking Water Sample Location Map, respectfully, of this suppor t document). Thus, there is a clear path for contaminants in ground water to migrate from the Leeds metal property to the residential drinking water wells.

Therefore, all of the wells identified as Level II target wells in Section 3.3 of the HRS document ation record as revised at the time of the NODA ( 77 FR 40318, July 9, 2012 ) are eligible for evaluation in the Leeds Metal HRS package.

This comment results in no change to the HRS score and no change in the decision to place the Site on the NPL.

3.7.3 Potential Targets

Comment : MEC commented that to conclude the entire “4- radial mile ” [TDL] population is “a Potential population Target” is overly conservative and the scoring presented in the NODA (77 FR 40318, July 9, 2012),
should be re

- evaluated. MEC a lso commented that the EPA included the enti re population within the 4- radial mile area of the site as potential population targets without considering geohydrologic data and only consideringLee ds Metal NPL Listing Support Document September 2012

53 geographic data. MEC went on to explain that the geologic materi al in the area is composed of a heterogeneous mixture of sand and gravel, silt, clay, peat, and till which overlies a complex sequence of bedrock making the interconnectivity of the bedrock fractures unproven throughout the 4- radial mile area.

Response : T he potential target population within the 4- mile DL for this site is correctly included in the HRS
evaluation.

HRS S ection 3.0.1.1, Ground water target distance limit, identifies which targets at a site are to be included in an
HRS evaluation:

[t]he tar get distance limit defines the maximum distance from the sources at the site over which targets are evaluated. Use a target distance limit of 4 miles for the ground water migration pathway, except when aquifer discontinuities apply (see section 3.0.1.2.2). Furthermore, consider any well with an observed release from a source at the site (see section 3.1.1) to lie within the target distance limit of the site, regardless of the distance limit of the site, regardless of the well’s
distance from the sources at the site.

Section 3.5.1, Ground Water Discontinuities, of this support document identifies that there are no discontinuities restricting the extent of the TDL for this site.

HRS Section 3.3.2, Population, explains that people using these wells make up th e eligible target population:

In evaluating the population factor, include those persons served by drinking water wells within the target distance limit specified in section 3.0.1.1.

HRS Section 3.3.2.1, Level of contamination , presents the requirements for identifying potential targets:

Evaluate the population served by water from a point of withdrawal based on the level of contamination for that point of withdrawal. [Emphasis added

. ] Use the applicable factor: Level I concentrations, Level II concentrations, or potential contamination.

If no samples meet the criteria for an observed release for a point of withdrawal and there is no observed release by direct observation for that point of withdrawal, evaluate that point of withdrawal using the potential contamination factor in section 3.3.2.4. [E mphasis added .] If there is an observed release by direct observation, use Level II concentrations for that point of withdrawal. However, if one or more samples meet the criteria for an observed release for the point of withdrawal, determine which factor (Level I or Level II concentrations) applies to that point of withdrawal as specified in sections 2.5.1 and 2.5.2. Use the health- based benchmarks
from Table 3

- 10 in determining the level of contamination

.

HRS Section 3.3.2.4, Potential contamination, explains how to assign a score to the potential targets . It states in relevant part:Lee ds Metal NPL Listing Support Document September 2012

54 Determine the number of people served by drinking water from points of withdrawal subject to potential contamination. Do not include those people already counted under the Level I and Level
II concentrations factor.

Assign distance -weighted population values from Table 3–12 to this population as follows: . . .

The HRS documentation record on pages 129a through 129c as revised at the time of the NODA (77 FR 40318, July 9, 2012) presents the method used to calculate the potential population targets. Additionally, see Figure 6, Active Public Ground Water Supplies Within 4 Mile Target Distance Limit Map , of this support doc ument for an
illustration of where in the 4- mile TDL the public ground water supply wells are located.

The calculation of Potential Population Targets was evaluated as part of this HRS Documentation Record utilizing two separate techniques. Method 1 utilized the 1990 and 2000 census data to estimate the populations relying upon both private and public ground water supplies presented in the SI report (Reference 11) [11, pp. 112-115; 180].

. . . Method 2 utilized the most recent census data (2010), which bec ame available after completion of the SI report (Reference 11), and discussions with local personnel knowledgeable of the public and private ground water resource
within 4

- radial miles of the site. The discussions with local personnel were used to validate the drinking water supply of the entire population presented in the 2010 census within 4- radial miles of the site [11, pp. 112-115; 180].

. . . This HRS Documentation Record reports the method resulting in the minimal Potential Population Targets for determining the Potential Contamination Factor Value [1, Table 3 -12; 11, pp. 112

- 115; 180 ]. The listing decision will remain the same using the Method 1 data utilized at proposal or using the newer 2010 census data, reflecting current site conditions; conversely the new data confirms the listing decision. . . .

Population per Distance Category (see Section 3.3.2.4 of the errata document [ see docket
number EPA- HQ

- SFUND -2011-0647-0007 ])

Distance Category Population References Distance

- Weighted Population Value (Ref. 1, Table 3

- 12)
0 to 1/4 mile 21* 11, pp. 112

- 115; 180 17
>1/4 to 1/2 mile 169* 11, pp. 112

- 115; 180 102
>1/2 to 1 mile 184 11, pp. 112

- 115; 180 52
>1 to 2 miles 574 11, pp. 112

- 115; 180 94
>2 to 3 miles 2,921** 11, pp. 112

- 115; 180 212
>3 to 4 miles 1,832 11, pp. 112

- 115; 180 131

. . . . Sum of Distance

- Weighted Population Values: 608 Sum of Distance

- Weighted Population Values/10: 60.8 Potential Contamination Factor Value: 60.8 (1, p. 51603-51604, Section 3.3.2.4)

As explained above and in Sections 3.5 and 3.5.1, Aquifer Description, and Ground Water Discontinuities, respectively, of this support document, the HRS documentation record as revised at the time of the NODA (77 FR 40318, July 9, 2012), carefully considers the hydrogeology at this site and correctly concludes that the entire population within the 4-mile TDL should be included as part of the potential targets factor value. This conclusionLee ds Metal NPL Listing Support Document September 2012

55 is based on the conclusion that there is no evidence of the existence of an aquifer discontinuity that completely transects the aquifer.

Additionally, as explained above, the HRS documentation record as revised at the time of the NODA (77 FR 40318, July 9, 2012), correctly associates a Distance -Weighted Population value sum of 608, and correctly divides the sum of the Distance-Weighted Population value by 10, as required by the HRS, to assign a 60.8 as the potential contamination factor value.

Therefore, all of the wells identified as potential target wells in Section 3.3 .2.4 of the HRS documentation record
as revised at the time of the NODA (77 FR 40318, July 9, 2012) remain eligible for evaluation in the Leeds Metal HRS package.

This comment results in no change to the HRS score and no change in the decision to place th e Site on the NPL.



## 4. 0 Conclusion

The original HRS score for this site was 50.00. Based on the changes presented in the NODA published July 9, 2012, in the Federal Register (77 FR 40318), the HRS documentation record is revised at promulgation and the
Site score has been adjusted accordingly

. The final HRS scores for the Leeds Metal site are:

Ground Water: 64.512
Surface Water: NS Soil Exposure: NS Air Pathway: NS
HRS Score: 32.25Lee ds Metal NPL Listing Support Document September 2012

56 

## Attachment 1: Select Physical Properties Pages from the United States National Library of Medicine ChemIDplus Lite Database8/10/12 C hemIDplus Lite

chem.sis.nlm.nih.gov /chemidplus/jsp/common/Phy sicalProperties.jsp?calledFrom=lite News SIS Home | Site | About Us | Contact 

## Physical Properties

Tetrachloroethylene RN: 127-18-4

Physical Property Value Units Temp (deg C) Source

Melting Point -2.23E+01 deg C EXP

Boiling Point 121.3 deg C EXP

log P (octanol-water) 3.4 (none) EXP

Water Solubility 206 mg/L 25 EXP

Vapor Pressure 18.5 mm Hg 25 EXP

Henry's Law Constant 0.0177 atm-m3/mole 24 EXP

Atmospheric OH Rate Constant 1.67E-13 cm3/molecule-sec 25 EXP

Phyiscal property data is provided to ChemIDplus by Syracuse Research Corporation

. See all available property data for this compound , including references.

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Custom er Service: tehip@teh.nlm .nih.gov

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## Physical Properties

Trichloroethylene [INN] RN: 79-01-6

Physical Property Value Units Temp (deg C) Source

Melting Point -8.47E+01 deg C EXP

Boiling Point 87.2 deg C EXP

log P (octanol-water) 2.42 (none) EXP

Water Solubility 1280 mg/L 25 EXP

Vapor Pressure 69 mm Hg 25 EXP

Henry's Law Constant 0.00985 atm-m3/mole 25 EXP

Atmospheric OH Rate Constant 2.36E-12 cm3/molecule-sec 25 EXP

Phyiscal property data is provided to ChemIDplus by Syracuse Research Corporation

. See all available property data for this compound , including references.

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ChemID-2 of 78/10/12 C hemIDplus Lite

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## Physical Properties

Benzene RN: 71-43-2

Physical Property Value Units Temp (deg C) Source

Melting Point 5.5 deg C EXP

Boiling Point 80 deg C EXP

log P (octanol-water) 2.13 (none) EXP

Water Solubility 1790 mg/L 25 EXP

Vapor Pressure 94.8 mm Hg 25 EXP

Henry's Law Constant 0.00555 atm-m3/mole 25 EXP

Atmospheric OH Rate Constant 1.23E-12 cm3/molecule-sec 25 EXP

Phyiscal property data is provided to ChemIDplus by Syracuse Research Corporation

. See all available property data for this compound , including references.

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ChemID-3 of 78/10/12 C hemIDplus Lite

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## Physical Properties

Toluene RN: 108-88-3

Physical Property Value Units Temp (deg C) Source

Melting Point -9.49E+01 deg C EXP

Boiling Point 110.6 deg C EXP

log P (octanol-water) 2.73 (none) EXP

Water Solubility 526 mg/L 25 EXP

Vapor Pressure 28.4 mm Hg 25 EXP

Henry's Law Constant 0.00664 atm-m3/mole 25 EXP

Atmospheric OH Rate Constant 5.96E-12 cm3/molecule-sec 25 EXP

Phyiscal property data is provided to ChemIDplus by Syracuse Research Corporation

. See all available property data for this compound , including references.

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ChemID-4 of 78/10/12 C hemIDplus Lite

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## Physical Properties

Ethylbenzene RN: 100-41-4

Physical Property Value Units Temp (deg C) Source

Melting Point -9.49E+01 deg C EXP

Boiling Point 136.1 deg C EXP

log P (octanol-water) 3.15 (none) EXP

Water Solubility 169 mg/L 25 EXP

Vapor Pressure 9.6 mm Hg 25 EXP

Henry's Law Constant 0.00788 atm-m3/mole 25 EXP

Atmospheric OH Rate Constant 7.10E-12 cm3/molecule-sec 25 EXP

Phyiscal property data is provided to ChemIDplus by Syracuse Research Corporation

. See all available property data for this compound , including references.

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ChemID-5 of 78/10/12 C hemIDplus Lite

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## Physical Properties

Xylenes RN: 1330-20-7

Physical Property Value Units Temp (deg C) Source

Boiling Point 138.5 deg C EXP

log P (octanol-water) 3.16 (none) EXP

Water Solubility 106 mg/L 25 EXP

Vapor Pressure 7.99 mm Hg 25 EXP

Henry's Law Constant 0.00663 atm-m3/mole 25 EXP

Atmospheric OH Rate Constant 1.87E-11 cm3/molecule-sec 25 EXP

Phyiscal property data is provided to ChemIDplus by Syracuse Research Corporation

. See all available property data for this compound , including references.

U.S. Na tional Library o f Medicine , 8600 Rockville Pike , Be the sda , MD 20894, Na tional Institute s o f Health
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ChemID-6 of 78/10/12 C hemIDplus Lite

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## Physical Properties

t-Butyl methyl ether RN: 1634-04-4

Physical Property Value Units Temp (deg C) Source

Melting Point -1.09E+02 deg C EXP

Boiling Point 55.2 deg C EXP

pKa Dissociation Constant -3.70E+00 (none) 23 EXP

log P (octanol-water) 0.94 (none) EXP

Water Solubility 5.10E+04 mg/L 25 EXP

Vapor Pressure 250 mm Hg 25 EXP

Henry's Law Constant 5.87E-04 atm-m3/mole 25 EXP

Atmospheric OH Rate Constant 2.94E-12 cm3/molecule-sec 25 EXP

Phyiscal property data is provided to ChemIDplus by Syracuse Research Corporation

. See all available property data for this compound , including references.

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ChemID-7 of 7Lee ds Metal NPL Listing Support Document September 2012

57 

## Attachment 2: Excerpt of CRC Handbook of Chemistry and Physics, 92nd Edition, 2011

- 2012-------------------------

## -~

VISCOSITY OF LIQUIDS

. sity of some common liquids at temperatures 

### References ·**~~lute~~~~** 'C is given in this table. Values were**deri~ed** an< ental data to suitable expressions for the tern­ 1. Viswanath, D. S. and Natarajan, G.,. Data Book on the Viscosity of

1 New York, 1989. · The substances are arranged by molecular Liquids, Hemisphere Publishing Corp.,
Jp!'lrJlOCJICC• 2. Daubert, T. E., Danner, R. P., Sibul, H., M., and C. C., odified Hill**S~ebbins,** order (see Preface). All values are , f m d ( p ) h'

.. 'd . I Physical and Thermodynamic Properties of Pure Compounds: Data nillipascal secon s m a s i t 1s umt 1s 1 entlca cHJiillS 0 I Compilation, extant 1994 (core with 4 supplements), Taylor & Francis, (cp).

. . Bristol, PA (also available as database). values correspond to a n111mmal pressure of 1 atmos- 3. Ho, C. Y., Ed., CINDAS Data Series on Material Properties, Vol. V-1, is given at a temperature above the normal boiling Properties of Inorganic and Organic Fluids, Hemisphere Publishing

• cable pressure is understood to be the vapor pres- Corp., New York, 1988. ,1pp 1 1 '

. li uid at that temperature. A few values are giVen at a 4. Stephan, K. and Lucas, K., Viscosity ofDense Fluids, Plenum Press,

### ~lightly New York, 1979. · below the normal freezing point; these refer 5. Vargaftik, N. B., Tables of Thermophysical Properties of Liquids and 'llfl!'fCOOied liquid. •. ' 

## ,c Gases, 2nd ed., John Wiley, New York, 1975. ·**~"uracy** ranges from 1% in the best cases to 5 to 10% in the

· Additional significant figures are included in the table

11 ,M interpolation.

Viscosity in mPa s .llulccular fonuula Name -25'C O'C 25'C 50'C 75'C 100'C

(i 1

mpomuls uot coutai11i11g carho11

, HI, Bromine 1.252 ·0.944 0.746
CI,HSI Trichlorosilane 0.415 0.326
<1,1' Phosphorous trichloride 0.870 0.662 0.529 0.439

< I,Si Tetrachlorosilane 99.4 96.2 11,0 Water 1.793 0.890 0.547 0,378 0.282
II,N, Hydrazine 0.876 0.628 0.480 0.384 llg Mercury 1.526 1.402 1.312 1.245; NO, Nitrogen dioxide 0.532 0.402

CiiiiiJIOIII/ds colttaillillg carbon
I CCI F

1 Trichlorofluoromethane 0.740 0.539 0.421 CCI '

1 Tetrachloromethane 1.321 0.908 0.656 0.494 

### cs, Carbon disulfide 0.429 0.352 Cllllr 3 Tribromomethane 1.857 1.367 1.029 CIICI 3 Trichloromethane 0.988 0.706 0.537 0.427 CIIN Hydrogen cyanide 0.235 0.183 CII,Br,**Dibromom~thane** 1.948 1.3.20 0.980 0.779 0.652 Cll,cJ 2 Dichloromethane 0.727 0.533 0.413 CII,O, Formic acid 1.607 1.030 0.724 0.545 CII,I lodomethane 0.594 0.469 CII,NO Formamide 7.114 3.343 1.833 CH,N0
2 Nitromethane 1.311 .0.875 0.630 0.481 0.383 0.317 CHp Methanol 1.258 0.793 0.544 CHIN Methylamine 0.319 0.231 c,cll, 1,1,2- Trichlorotrifluoro-ethane**1.~65** '0.945 0.656 0.481 C,CI, Tetrachloroethylene ' 1.114 0.844 0.663 0.535 0.442. C,HCI '.

3 Trichloroethylene 0.703 0.545 0.444 0.376 C,Hct, Pentachloroethane '3.761 2.254 1.491 1.061 C,HFp
2 Trifluoroacetic acid 0.808 0.571 C,H,Ct 2 cis-1,2-Dichloroethylene 0.786 0.575 0.445 C,H,ct, trans-1,2- Dichloroethylene 0.522 0,398 0.317 0.261 C,H,Cl
4 1,1,1,2- Tetrachloroethane 3.660 2.200 1.437 1.006 0.741 0.570 C,H 3 CIF
2 1-Chloro-1, 1-difluoro-ethane 0.477 0.376 c,H,c1o Acetyl chloride 0.368 0.294 C,H,ct
3 1,1,1- Trichloroethane 1.847 1.161 0.793 0.578 0.428 C,H,N Acetonitrile 0,400 0.369 0.284 0.234 C,H,Br 2 1,2- Dibromoethane 1.595 1.116 0.837 0.661

6-2316-232 Viscosity

Viscosi!}: in mPa s Molecular
formula Name -25'C O'C 25'C 50'C 75'C
c,H 4 Cl 1,1- Dichloroethane 2 0.464 0.362
c,H 4 Cl 1,2- Dichloroethane 1.125 0.779 0.576 0.447 

# -----­ 100'C

2 C 2 H 4 0 Acetic acid 1.056 0.786 2 0.599 0.464 C H 0 Methyl formate 0.424 0.325

2 4 2 C 2 H 5 Br Bromoethane 0.635 0.477 0.374

C H 5 Cl Chloroethane 0.416 0.319

2 C H l

2 5 Iodoethane 0.723 0.556 0.444 0.365

C H NO N- Methylformamide 2.549 1.678 1.155

2 5 ·0.824 0.606 C H 5 N0 2 Nitro ethane 1.354 0.940 0.688 0.526 0.415

2 0.337 c,H 0 Ethanol 3.262 1.786 1.074 0.694 0.476 6 C 2 HpS Dimethyl sulfoxide 1.987 1.290
c,H 0 Ethylene glycol 16.1 6.554 3.340 6 2 1.975 C H S Dimethyl sulfide 0.356 0.284

2 6 C 2 H S Ethanethiol 0.364 0.287 6 C H N Dimethylamine 0.300 0.232

2 7 C 2 H NO Ethanolamine 7 21.1 8.560 3.935 1.998 C 3 H 5 Br 3- Bromopropene 0.620 0.471 0.373

C 3 H 5 Cl 3-Chloropropene 0.408 0.314

C 3 H 5 Cl0 Epichlorohydrin 2.492 1.570 1.073 0.781 0.597 0.474 C H

3 5 N Propanenitrile 0.294 0.240 0.202
c,H 0 Acetone 0.540 0.395 0.306 0.247 6 C,Hp Allyl alcohol 1.218 0.759 0.505
c,H 6 0 Prop anal 0.321 0.249
c,H 0 Ethyl formate 0.506 0.380 0.300 6 2 C 3 H 0 Methyl acetate 0.477 0.364 0.284 6 2 C H 0 Propanoic acid 1.499 1.030 0.749 0.569

3 6 2 0.449
C H

3 7 Br 1-Bromopropane 0.645 0.489 0.387

C 3 H 7 Br 2- Bromopropane 0.612 0.458 0.359

C H Cl 1-Chloropropane 0.436 0.334

3 7 C 3 H,Cl 2-Chloropropane 0.401 0.303

C H I 1- Iodopropane

3 7 0.970 0.703 0.541 0.436 0.363

C 0.407

3 H 7 l 2- Iodopropane 0.883 0.653 0.506

C H NO

3 7 N,N- Dimethylformamide 1.176 0.794 0.624

C 3 H 7 N0 2**1-Nitropr~pane** 1.851 1.160 0.798 0.589 0.460 0.374
c,H,o 1-Propanol 8.645 3.815 1.945 1.107 0.685

C 3 H 8 0 2-Propanol 4.619 2.038 1.028 0.576

C 1,2-Propylene glycol 4.770 2.750

3 H 8 0 2 248 40.4 11.3

C 3 H 8 0 3 Glycerol 934 152 39.8 14.8

C S 1- Propanethiol

3 H 8 0.503 0.385

C 3 H 8 S 2-Propanethiol 0.477 0.357 0.280

C 3 H 9 N Propylamine 0.376

C H

3 9 N Isopropylamine 0.454 0.325

C H 0 Furan 0.661 0.475 0.361

4 4 C 4 H 5 N Pyrrole 2.085 1.225 0.828 0.612 0.377 C4H60a Acetic anhydride 1.241 0.843 0.614 0.472 0.268 C

4 H,N Butanenitrile 0.553 0.418 0.330

C 4 H,o 2-Butanone 0.720 O.S33 0.405 0.315' 0.249
c,H,O Tetrahydrofuran 0.849 0.605 0.456 0.359

C 1,4-Dioxane

4 H,o, 1.177 0.787 0.569
c,H,o, Ethyl acetate 0.578 0.423 0.325 0.259

C 4 H,o, Methyl propionate 0.581 0.431 0.333 0.266

C H 0 2 formate 0.669 0.485 0.370 0.293

4 8 Propyl 0.542 C 4

H,o, Butanoic acid 2.215 1.426 0.982 0.714 0.491 C H,O, 2-Methylpropanoic acid 1.857 1.226 0.863 0.639

4 2.559 C H

4 8 o,s Sulfolane 6.280 3.818
c,H.s Tetrahydrothiophene 0.973 0.912

C H,Br 1- Bromobutane 0.815 0.606 0.471 0.379

4 C 4 H 9 Cl 1-Chlorobutane 0.556 0.422 0.329 0.261

C 4 H 0.512 9 N Pyrrolidine 1.914 1.071 0.704

C 4 H 9 NO N,N- Dimethylacetamide 1.927 /\



# ......6-234 Viscosity of

Viscosi9:: in mPa s Molecular -25'C O'C 25'C 50'C 75 'C

--------­

formula Name 1.648 I(){)'( 2.798 1.829 28.7 6.621 Diacetone alcohol C6H,2o2 1.079 0.692 0.485 Paraldehyde 0.36?. C6H,20, 1.944 1.169 0.782 C H N Cyclohexylamine 0.565

6 13 0.405 0.300 0.240 Hexane C6H,. 0.372 0.286 0.226 C H 2- Methylpentane

6 14 0.395 0.306 3- Methylpentane C6H14 0.542 0.396 0.304 0.242· Dipropyl ether C6H,40 4.578 2.271 1.270 0,7gl 1-Hexanol C6H,40 0.347 0.273 0.221 0.455 C H N Triethylamine

6 15 0,751 0.517 0.377 0.288 0.22R C6H,,N Dipropylamine 0.393 0.300 0.237 Diisopropylamine C6H,,N 609 114 31.5 11.7 C H NO, Triethanolamine

6 15 1.267 0.883 0.662 0.52·1 C H N Benzonitrile

7 5 '1.390 0.964 0.710 0.547 O.<l:l7 C H CI a-Chlorotoluene

7 7 0.823 0.616 0.482 1.165 0.391 C H CI m-Chlorotoluene

7 7 0.837 0.621 0.483• 0.390 C H CI p-Chlorotoluene

7 7 0.778 0.560 0.424 0.333 1.165 0.270 Toluene C7H, 3.035 1.562 0.961 C H,0 a-Cresol

7 12.9 4.417 2.093 1.207 C H,O m-Cresol

7 5.474 2.760 1.618 1.055 C H 0 Benzyl alcohol

7 8 1.056 0.747 0.554 

### o,m C H 0 Anisole

7 8 2.042 1.222 0.825 4.120 0.606 C H N N-Methylaniline

7 9 10.3 3.823 1.936 1:198 0.839 C H N a- Methyl aniline

7 9 3.306 1.679 1.014 0.699 8.180 C H N m-Methyl aniline

7 9 1.624 1.080 0.769 0.577 C H N Benzylamine

7 9 0.501 0.390 0.316 0.991 0.679 Methylcyclohexane C7Hl4 0.273 0.226 0.441 0.340 1-Heptene C7Hl4 0.714 0.407 0.297 2-Heptanone C7H,40 1.488 3.840 2.282 l.Ooll Heptanoic acid C7H,•Oz 0.523 0.387 ·0.301 0.243 0.757 Heptane C7Hl6 0.350 3-Methylhexane C7Hl6 5.810 2.603' 1.389 0.849 1-Heptanol C7H,60 0,987 0.615 3.955 1.799 2-Heptanol C7H,60 1.957 0.976 0.584 3-Heptanol C7H,60 0.882 0.539 4.207 1.695 4-Heptanol C7H,60 0,600 0.43•1 1.314 0.865 Heptylamine C7H,7N 0.310 0.695 0.507 0.390 1.050 C,H, Styrene 0.634 1.681 Acetophenone

· c,H,O 1.857 C,H 0 Methyl benzoate 8 2 1.102 0.815 C H,0 Methyl salicylate

8 3 0.304 0.631 0.482 0,380 0.872 C,H Ethylbenzene 10 0.345 0.561 0.432 1.084 0.760 C H a-Xylene

8 10 0.289 0.795 0,581 0.445 0.353 C,H m-Xylene 10 0.457 0.359 0.290 0.603 C H p-Xylene

8 10 0.453 1.197 0.817 0.594 C H 0 Phenetole

8 10 0.523 0.911 0.675 1.996 1.300 C H N N,N- Dimethylaniline

8 11 0.596 3.981 2.047 1.231 0.825 C H N N- Ethylaniline

8 11 1.139 0.784 0.579 c,H Ethylcyclohexane 16 1.147 5.020 2.656 1.654 C,H 0 Octanoic acid 16 2 0.243 0.385 0.302 0.700 0.508 c,H,, Octane 0.991 7.288 3.232 1.681 C,H 0 1-0ctanol 18 0.375 1.085 0.702 0.497 1.904 C H 0 4-Methyl-3-heptanol

8 18 0.401 0.762 0.536 2.052 1.178 C H 0 5-Methyl-3-heptanol

8 18 0.810 1.360 20.7 6.271 2.631 C H 0 2- Ethyl-1-hexanol

8 18 0.281 0.637 0.466 0.356 C,H 0 Dibutyl ether 1.417 0.918 18 0.345 0.918 0.619 0.4,.49 1.509 C H N Dibutylamine

8 19 0.303 1.115 0.723 0.511 0.384 C,H N Diisobutylamine 19 0.833 3.337 1.892 1.201 C H N Quinoline

9 7 0.545 2.230 1.357 0.931 0.692 Indane' C9HIO 0.737 0.547 1.075 Cumene c.H,z /\'t)' of Liquids 6-235

<111

Viscosi!Y in mPa s ,\lolcctdar Name -25'C O'C 25'C 50'C 75'C 100'C formula ]sopborone 4.201 2.329 1.415 0.923 0.638 C)!"O 5-Nonanone 1.199 0.834 0.619 0.484 C)l,P Nonanoic acid 7.011 3.712 2.234 1.475 C)!,p, Nonane 0.964 0.665 0.488 0.375 0.300 C)IM 1-Nonanol 9.123 4.032 c,H 1 

### P 63.2 14.4 5.309 2.824 1.980 c,,H,p, Dimethyl phthalate Butylbenzene 0.950 0.683 0.515 C,)l 11 cis- Decahydronaphthalene 12.8 5.645 3.042 1.875 1.271 0.924 c,)1 18 trans- Decahydronaphthalene 6.192 3.243 1.948 1.289 0.917 0.689 c,

.. H 18 Decanoic acid 4.327 2.651 c,)l,,,o, Decane 2.188 1.277 0.838 0.598 0.453 0.359 c,,11,, 1-Decanol 10.9 4.590 c,)I"O Undecane 1.707 1.098 0.763 0.562 0.433 <)I" C H,p Diphenyl ether 2.130 1.407 1.023

11 Dodecane 2.277 1.383 0.930 0.673 0.514 C"ll" Diphenylmethane 1.265 0.929 <)I"
C 11, Tridecane 2.909 1.724 1.129 0.796 0.594

11 Tetradecane '2.128 1.376 0.953 0.697 C

11 11"' Dibutyl phthalate 483 66.4 16.6 6.470 3.495 2.425 c,H"O' c,,H Hexadecane 3.032 1.879 1.260 0.899
11 C)l" Octadecane 2.487 1.609 1.132 ,,,Lee ds Metal NPL Listing Support Document September 2012

58 

## Attachment 3: Excerpt of Petroleum Hydrocarbons And Ch lorinated Hydrocarbons Differ In Their Potential For Vapor Intrusion, EPA Office of Underground Storage Tanks, March 2012Office of Underground Storage Tanks, Washington, D.C. 20460 March 2012 www.epa.gov/oust



## Petroleum Hydrocarbons And Chlorinated Hydrocarbons Differ In Their Potential For Vapor Intrusion

Contents Page Background And Purpose 1 Introduction 2 Differences Under Common Subsurface Scenarios 2

Effect Of Biodegradation 3

Influence Of Density 4 Fate And Transport Processes For Vapor-Phase Contaminants 5 Biodegradation Of Petroleum Hydrocarbons In The Unsaturated Zone 6 Conditions With Greater Potential Fo r Petroleum Vapor Intrusion 7 Considerations For Petroleum Site Investigation And Screening 10

Site Investigation Considerations 10 Site Screening Considerations 11 References 11



### Background And Purpose

In November 2002, the U.S. Environmental Protection Agency ( EPA), Office of Solid Waste and Emergency Response issued draft vapor intrusion guida nce (EPA, 2002), which specifically st ates that it is not recommended for Subtitle I underground storage tank (UST) sites. EPA’s Office of Undergrou nd Storage Tanks (OUST) is thus currently developing guidance to address petroleum vapor in trusion (PVI) at UST sites. OUST has consulted on several occasions with experts in the field of vapor in trusion and petroleum releases from EPA, state regulatory agencies, private consultants, and industry groups to obtain their individual input on technical and practitioner issues for EPA to consider in developing the US T PVI guidance. This information paper 1 describes how petroleum compounds behave differently in the subs urface from other volatile chemicals, in particular chlorinated solvents, and how these behaviors can be considered when evaluating the potential for vapor intrusion at sites contaminated by leaking Subtitle I USTs or other sources of petroleum hydrocarbons (PHCs). 2

PHCs typically degrade biologically in groundwater as well as in unsaturated soil zones. In many cases, this aerobic 3 biodegradation is substantial and ca n limit the potential for PVI. In cont rast, biodegradation of chlorinated solvents is anaerobic (under anoxic conditions), which is generally slower than aerobic biodegradation of PHCs. This limited biodegradability is to some degree responsible for the greater observed prevalence of chlorinated solvent vapor intrusion when compared with PVI.

During the 1980s and 1990s, a better understanding of PHC biodegradation in groundwater led to the development of monitored natural attenuation, a remediation approach that involves no external inputs and has now been used successfully to address groundwater contam ination at many leaking UST sites (Wilson et al.,1986; Bedient et al., 1994). Based on a review of current literature (e.g., Sanders and Hers, 2006; Davis et al., 2009; McHugh et al., 2010), EPA recognizes that analogous aerobic biodegradation processes ar e active in the unsaturated zone and that these processes can limit the potential for PVI.

1 This information paper is intended to communicate the overall c oncepts of petroleum vapor intrus ion. It is not intended to be interpreted as either a technical guidance document or statement of regulatory policy.

2 Petroleum hydrocarbons are chemical compounds made up of hydrogen and carbon that are constituents of petroleum and various refined products of petroleum, including automotiv e gasoline, diesel fuel, lubr icating oils, and the like.

3 Aerobic means that the process requires oxygen. In contrast, anaerobic means th e process does not require oxygen. Anoxic refers to the absence of oxygen.

1

### Introduction

This paper discusses the impact on the inhalation ex posure pathway from vapor in trusion (VI) of volatile organic chemicals (VOCs). VI occurs when vapor-phase contaminants migrate from subsurface sources into buildings. The primary concerns regarding VI are immediate threats to safety (e.g., explosive concentrations of petroleum vapors or methane) and possible adverse health effects from inhalation exposure to toxic chemicals. This paper focuses pr imarily on the latter concern, although the reader should recognize that in high enough concentr ations, petroleum compounds and methane (a biodegradation product) can collect in buildings, lead ing to imminent explosive hazards. The information in this paper focuses on small-scale Subtitle I UST sites as opposed to sites with large sources (e.g., refineries and tank farms); however, you can use this information to inform decisions at non-Subtitle I petroleum releases. In addition, this paper does not address sites with comingled plumes such as mixed chlorinated and petroleum hy drocarbon contamination.

There are two classes of VOCs 4 that together account for a large number of soil and groundwater contamination sites in the United States:

 Petroleum hydrocarbons (PHCs) such as gasoline, diesel, and jet fuel

 Chlorinated solvents such as the dry cleaning chemical te trachloroethylene (perchloroethylene, or PCE) and the degreasing solvents trichloroeth ylene (TCE), 1,1,1-trichloroethane (TCA), and PCE

This information paper discusses and compares petrol eum vapor intrusion (PVI) and chlorinated solvent vapor intrusion with respect to processes that influence whether and how vapors can migrate through vadose zone materials into build ings and other confined spaces as well as some implications for addressing PVI.

The foremost difference between PHC and chlorinated solvent vapors in the su bsurface is that PHCs biodegrade readily under aerobic (oxygenated) environmental conditions, whereas chlorinated solvents 5 typically biodegrade much more slowly a nd under anaerobic conditions (Howard, 1991). Because PHC biodegradation is relatively rapid when oxygen is pr esent, aerobic biodegradation can typically limit the concentration and subsurface migration of petrol eum vapors in unsaturated soils. In addition, biodegradation of chlorinated solvents can produce to xic degradation products, such as dichloroethylene and vinyl chloride, while petroleum degradation us ually produces carbon dioxide, water, and sometimes methane or other simple hydrocarbons. A second prim ary difference is density: PHC liquids (e.g., gasoline, diesel fuel) are lighter (less dense) than wa ter and when released from a leaking UST, can float on the groundwater surface (water table), whereas chlori nated solvents (e.g., TCE, PCE) are heavier than water and sink through the groundwater column to the bottom of the aquifer. These key differences (biodegradability and density) lead to very different subsurface behavior that often reduces the potential for human exposure.



### Differences Under Common Subsurface Scenarios

Figures 1 and 2 illustrate differences in subsurface transport behavior fo r PHCs and chlorinated solvents under commonly observed subsurface conditions. The c onceptual scenarios in these figures are simplified

4 A third class of volatile chemicals is in organics, of which ra don is probably the most identifia ble and problemat ic from a VI perspective.

5 Vinyl chloride, which is itself a product of the degradation of chlorinated solvents, has been observed to biodegrade relative ly rapidly in the presence of very low concentr ations of oxygen; concentrations so low th at it is not possible to measure in the f ield with standard instruments (Bradley, 2011; Bradley and Chapelle, 2011; and Gossett, 2010).

2many homes and attached garages; examples include glues, cleaners, solvents, dry-cleaned clothes, and gasoline (EPA, 2011). Although EPA (2011) presents information on typical background levels of both PHCs and chlorinated solvents 

### in indoor air resulting from sources other than vapor intrusion, this information should not substitute for site-specific data.

The chemicals that pose the most significant potential i nhalation risks (sometimes called risk drivers) in PVI (i.e., benzene) and vapor intrusion of chlorinated solvents (e.g., TCE, PCE), respectively, generally have similar physical-chemical properties contro lling diffusion and sorption in the vapor phase; advection, in contrast, is unaffected by chemi cal properties. Fundamentally though, these processes (diffusion, sorption, and advection) have a similar influence on the subsurface distribution of vapor-phase contaminants for both PHC and chlorinated solvents. If biodegradation is excluded, one generally would expect PHC and chlorinated solvent vapors to behave similarly. However, investigations from sites across the United States and other countries have shown that vapor plumes of PHCs are typically less extensive than vapor plumes of chlorinated solvents, providing empirical evidence that aerobic biodegradation can effectively limit the migration of petroleum va pors in many situations (McHugh et al., 2010).



### Biodegradation Of Petroleum Hydro carbons In The Unsaturated Zone

Scientific research and site investigations going back decades have demonstrated conclusively that microorganisms capable of aerobically degrading PHCs are present in nearly all subsurface soil environments (Zobell, 1946; Atlas, 1981; Wilson et al., 1986; Leahy and Colwell, 1990; Bedient et al., 1994; EPA, 1999). Effective aerobic biodegradation of PHCs depends on the soil having sufficient oxygen and enough soil water to provide a habitat fo r adequate populations of active microorganisms. If oxygen is present, these organisms will generally consume available PHCs. Furthermore, aerobic biodegradation of petroleum compounds can occur relativ ely quickly, with degradation half lives as short as hours or days under some conditions (DeVaull, 2007). Some petroleum compounds can also biodegrade under anaerobic conditions; however, above the water table, where oxygen is usually available in the soil zone, this process is less im portant and generally much slower than aerobic biodegradation.

Figure 1 (page 3) depicts key processes for the biodeg radation of PHCs in the unsaturated zone under common conditions: downward oxygen transport from the atmosphere, upward hydrocarbon vapor migration from the contaminant source, and aer obic biodegradation along the perimeter of the contamination zone where PHCs are consumed by microbial activity. Important factors influencing aerobic biodegradation in the vadose zone include source concentration, oxygen demand (the oxygen required to biodegrade the available hydrocarbons and any ambient soil organic matter that is present), distance between the source and the building, and soil type.

Aerobic biodegradation consumes oxyg en and generates carbon dioxide and water. This leads to a characteristic vertical concentration profile (Figure 3) in the unsaturated zone in which oxygen concentrations decrease with depth and VOCs (including PHCs and methane from anaerobic biodegradation) and carbon di oxide concentrations increase with depth. The characteristic vertical profile, which will vary in shape depending on site-sp ecific conditions (Roggemans et al., 2002).

PHC vapor concentrations will almost always be much greater adjacent to a LNAPL hydrocarbon source than adjacent to a dissolved hydrocarbon plume. If PHC concentrations are hi gh enough, available oxygen may be depleted, which in turn limits aerobic bi odegradation. When oxygen is limited, anaerobic biodegradation of LNAPL or other organic sources can produce methane. Significant anaerobic biodegradation and methane generation can occur in so me situations within anoxic zones of the plume interior and adjacent to the LNAPL source. Meth ane readily biodegrades under aerobic conditions and,

6