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 Metal
Leeds Metal NPL Listing Support Document September 2012

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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 20460 
Leeds Metal NPL Listing Support Document September 2012

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Table of Contents

Executive Summary...................................................................................................................................... iv

Introduction ................................................................................................................................................... v

Background of the NPL ........................................................................................................................... v

Development of the NPL ........................................................................................................................ vi

Hazard Ranking 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 Level 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

Attachment 3: Excerpt of Petroleum Hydrocarbons And Chlorinated Hydrocarbons Differ In Their Potential For 

Vapor Intrusion, EPA Office of Underground Storage Tanks, March 2012 ............................................... 58
Leeds Metal NPL Listing Support Document September 2012

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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 September 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 September 2012. 
Leeds Metal NPL Listing Support Document September 2012 

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Introduction

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 on 

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 hazardous 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 Pollution 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 emergency 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 placing sites on the NPL, which makes them eligible for remedial actions financed by the Trust Fund 

established under CERCLA, were included 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 since then, most recently on May 10, 2012 (77 

FR 27368). 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 (77 FR 515344).
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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 and 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 assign 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 informational 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 nature 

and 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 responsible 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 threatened 

release of hazardous substances, pollutants, or contaminants, and Section 105(a)(8)(A) directs the EPA to 

consider certain enumerated and other appropriate 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 CERCLA 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 response 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 some 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 analysis approach to scoring sites. This approach assigns numerical values to 

factors that relate to or indicate risk, based 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; 
Leeds Metal NPL Listing Support Document September 2012 

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• 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 (Sgw) 

- drinking water 

• Surface Water Migration (Ssw) 

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 (Ss) 

- resident population

- nearby population 

- sensitive environments

• Air Migration (Sa) 

- 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 score is low. However, the HRS score can be relatively high even if only 

one pathway score is high. This is an important requirement for HRS scoring because some extremely dangerous 

sites pose threats 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 40 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

gw
Leeds Metal NPL Listing Support Document September 2012 

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• 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 Federal Regulations

CLP Contract Laboratory Program

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 Register

ft Feet

ft bgs Feet below ground surface
Leeds Metal NPL Listing Support Document September 2012 

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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 Milligrams 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 dose

RI/FS Remedial investigation/feasibility study 

SARA Superfund Amendments and Reauthorization Act 

SI Site inspection

START Superfund Technical Assessment and Response Team

TCA Trichloroethane

TCE Trichloroethene or trichloroethylene

TPH Total petroleum hydrocarbons 

TDL Target distance limit

VOC Volatile organic compound 
Leeds Metal NPL Listing Support Document September 2012 

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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 Priorities 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), a 

degradation 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 this 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 property by various entities. 

Included in the scrap metal recovery operations was an automobile shredding plant, which operated on the 

property until 1978. Lead batteries and other auto parts were also cleaned for resale. Metal from the shredded cars 

was salvaged, and upholstery was piled in former gravel excavation pits. Such 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 property boundary. The Leeds and Monmouth Fire Departments 

responded to fires at the property; gasoline tanks would ignite, causing oil-saturated soil to burn. 
Leeds Metal NPL Listing Support Document September 2012 

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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 feet below 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 flow direction was based 

on the bedrock topography at the Site. The 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 Figure 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 Maine Department of Environmental Protection 

(ME DEP).

Subsurface investigations and ground water monitoring 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 

five 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 for 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 Site to the observed release monitoring wells and downgradient 

residential drinking water wells; 
Leeds Metal NPL Listing Support Document September 2012 

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• 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 and 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 significantly 

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 the HRS 

toxicity factor value and the ground water pathway 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. The HRS toxicity factor value for TCE has changed from 10,000 to 1,000; however the toxicity factor 

value for PCE remains the same at 100. The TCE benchmark value for drinking water based 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 potential 

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. 
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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 Metal 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 site 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 wells 

evaluated for the HRS package are not all locations recommended for treatment by ME DEP. MEC also 

concluded 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 that 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 definitively 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. 
Leeds Metal NPL Listing Support Document September 2012 

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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 concentrations, 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 regarding 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 geohydrologic 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 fractures 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 should 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 wells 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 hydraulically 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 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.” 

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, further 
Leeds Metal NPL Listing Support Document September 2012 

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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 closure 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 

National 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 ME 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 another statutory authority.
Leeds 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 Footprint. 

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 best 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 document 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 sites 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 extent 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 Decision 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 during 

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 wells 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 recommended 
Leeds 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 signatures “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 Maine regulatory levels, the 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 

regulatory 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

boundaries. Further, CERCLA Section 101(a) defines a "facility" as the "site" where a hazardous substance has been 

"deposited, stored, placed, or otherwise come to be located." The "come to be located" language gives EPA broad authority to 

clean up contamination 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) where 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, until the site investigation process has been completed and a remedial action (if any) 

selected, EPA can neither estimate the extent of contamination at the Site, nor describe the ultimate dimensions of the Site.
Leeds 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 frequently 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 proposal 

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, Aquifer 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 scoring purposes if aquifer 
Leeds 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 establishing 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: 

Surficial 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 conducted 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, pp. 3, 14-26; 32, 

Narrative Chronology (pp. 4-6), Table 1]. Overburden 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, quartzo-feldspathic biotite granofels, and finegrained 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 faulting in the area is 

almost entirely lacking 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 approximately 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 feet bgs (Well 

location DW-02), while the depth to bedrock immediately south of the Leeds Metal property on 
Leeds 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, pp.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 overburden 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 from 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, the 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 vertical 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]. Subsurface investigations to date have not identified any continuous 

aquitards in the vicinity of the Leeds Metal property [21; 24; 25; 28]. Furthermore, as noted 

above, the fine-to-coarse sand overburden deposits and moderately permeable fracture 

metamorphic bedrock do not demonstrate 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-site 

shallow 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 Release Data Tables – Tables 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 Shallow Overburden, 

Deep 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 discontinuity 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 

significance” to the agency’s decision).
Leeds 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 creating 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 the 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 direction. 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, and 
Leeds 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 aquifer 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 high 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 

conducted at the Site, stating on pages 99-: 

The ground water flow direction in the shallow overburden, deep overburden, and bedrock 

aquifers 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 consultants [24, p. 3; 25, p. 5]. Interpretation of the shallow overburden data, by ME 

DEP personnel, 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 vertical 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, 
Leeds Metal NPL Listing Support Document September 2012 

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p. 16]. Furthermore, no monitoring well data exists to indicate flow direction at depths greater 

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 boundary [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 release contaminants to sink through the ground water 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 

drainage 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 throughout the Leeds Metal 

property [24, pp. 1-2, 7, 11]. The intent of the temporary ground water monitoring well points 

was to provide a preliminary evaluation of on-site ground water quality [24, p. 2]. ERM advanced 

the temporary monitoring wells 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]. 

ERM determined that in general, ground water elevations were highest in the north and northeast 

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 ground water monitoring wells at soil boring locations on the Leeds Metal property 

[25, pp. 2-3, 12]. Four sets of monitoring well clusters 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 feet bgs [25, p. 3]. Deep overburden wells were installed to a maximum 

depth of 47 feet 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 sample [25, p. 3]. The soil at the site consists primarily of brown-to-gray, 

medium-to-fine sand with some medium-to-coarse 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, utilizing 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 gradient measured between the shallow and the deep wells [141, p. 2]. ME DEP noted 

that all of the wells have downward vertical gradients [141, p. 2]. In addition, ME DEP noted that 

the flow direction in the deeper aquifer appears to be much different from the shallow ground 
Leeds 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 the 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 role 

in one or both [141, p. 3]. ME DEP concluded that further off-site investigation and site 

characterization 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 monitoring 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 presented 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 demonstrate 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 from ~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 (identified 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 high 
Leeds 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 Map, 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 direction 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.” MEC 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 shallow ground water flow direction 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 increases 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 has 
Leeds Metal NPL Listing Support Document September 2012 

23 

been identified that is likely to be significantly contributing to the hazardous 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 attribution 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 documentation 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 substances in the ground water is 

attributable to the site as is required by the HRS and explained above.
Leeds 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 detail 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 and 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 Other 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 automotive 

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 lubricants (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 record 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. 
Leeds 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 pages 

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 water 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 low 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 

conveyances. 

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 formations 
Leeds Metal NPL Listing Support Document September 2012 

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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 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 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 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 μg/L and 140 μg/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 μg/L PCE in new wells and a 

maximum of 46 μg/L in previously existing well samples; laboratory results detected maximum 

concentrations of PCE and 1,1,1-trichloroethane at 120 μg/L and 2.8 μg/L, respectively.
Leeds Metal NPL Listing Support Document September 2012 

27 

• A June 1, 2009 EPA sampling of the wells installed in 1999 on Leeds Metal property found PCE at a 

maximum of 15 μg/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 

μg/L; 1,1,1-trichloroethane was found in one sample at 1.0 μg/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 Monitoring 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 μg/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 

these 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 information 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 potential 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 one 
Leeds 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 Spill 

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 SafetyKleen 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 the 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 shallow 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 shallow 

ground water flow is occasionally interrupted by surfical depressions, which are ground water 
Leeds 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 facility, 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 concentration 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 sporadically 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 

generally 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 of 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 conducted 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 the 
Leeds Metal NPL Listing Support Document September 2012 

30 

former 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 Site, consistent with the 

HRS.

The following subsections of this support document address comments regarding chemical signatures/distribution 

in ground water, and ground water flow/discontinuities 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 water 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 water 

flow direction in the shallow overburden appears to locally flow toward the north/northwest, the downward 
Leeds 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 property. 

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, Likelihood 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 

Site, consistent with the HRS (including documentation of the historical operations conducted on site, which 

could include solvents containing PCE and TCE; the documentation of PCE in on-site source samples; 

documentation of chemical breakdown processes of PCE to 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 commented 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 residential 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 residential 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 detections 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 elevation 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. 
Leeds 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 concentrations 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 wells 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 commented 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 impacts 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 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 can be explained as due to differential 

migration rates and degradation 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 Site 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 Site, 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 hazardous 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 and 
Leeds Metal NPL Listing Support Document September 2012 

33 

at this site including that both TCE 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 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 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 impermeable 

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 horizontally 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 microorganisms 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 the 
Leeds Metal NPL Listing Support Document September 2012 

34 

dichloroethene (DCE) isomers (cis-DCE or 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 sulfates 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 residential 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 deeper 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 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 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 is 
Leeds 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. Research 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 documentation 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 the Leeds 

Metal property (the total depth of these wells was 13.9 and 26.3 ft bgs, respectively). Further recent evidence of 

the possible presence of PCE breakdown products on the Leeds Metal property includes the following: 

• 52 J μg/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 μg/L TCE detected in November 2010 SI field duplicate of sample GW-07, ground water sample 

collected from monitoring 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 generally 

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-TCA 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 ERM4D.) 
Leeds 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 μg/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 migrating 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 wells
Leeds 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, which 

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 elevation 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 measurements 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 the 

decreasing concentration gradient with depth at the facility, this also does not disprove the attribution of offproperty residential drinking water well contaminants to the Site. 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-chlorinated 
Leeds 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 gasolinerelated 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 

necessarily 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 aerobic 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 consistent 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 gasoline has been reduced well below 1% by volume, the historic concentrations of 
Leeds 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 dug 

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 residential 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 alone include the following:

Concentration Sample Sample Description

HRS 

Documentation 

Record at Proposal 

Reference

11 J μg/kg ethylbenzene

7 J μg/kg o-xylene

24 J μg/kg m,p-xylene

SS-16 November 2010 SI sample, surface 

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 μg/kg o-xylene

19 J m,p-xylene

SS-20 November 2010 SI sample, surface 

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 

property

11, pp. 14, 33, 55

26 EB μg/kg toluene

16 J μg/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 μg/kg ethylbenzene

9.3 J μg/kg o-xylene

21 J μg/kg m,p-xylene

6.7 J μg/kg MTBE

SS-25 November 2010 SI sample, surface 

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 μg/kg toluene SS-27 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, 34, 60
Leeds Metal NPL Listing Support Document September 2012 

40 

Concentration Sample Sample Description

HRS 

Documentation 

Record at Proposal 

Reference

16 J μg/kg ethylbenzene

9.4 J μg/kg o-xylene

23 J μg/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 μg/kg ethylbenzene 

30 JEB μg/kg toluene

22 J μg/kg o-xylene

37 J μg/kg m,p-xylene

SS-35 November 2010 SI sample, surface 

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 μg/kg ethylbenzene

15 J μg/kg m,p-xylene

SS-44 November 2010 SI sample, Field 

Duplicate of SS-20

11, pp. 14, 39, 73

14 J μg/kg ethylbenzene

10 J μg/kg o-xylene

37 J μg/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 μg/kg ethylbenzene

21 JEB μg/kg toluene

38 J μg/kg o-xylene

55 J μg/kg m,p-xylene

SB-34 November 2010 SI sample, Subsurface 

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 μg/kg 

ethylbenzene

2,000 EB μg/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

EB2 = 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 at 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 affected 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 represent estimated results, the presence of the analyte is not in 

question.
Leeds 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 gasolinerelated 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 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)].

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 where 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 rather than sink as DNAPLs do4

. 

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 than 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.”
Leeds 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, 

respectively5

. 

• 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, respectively6

. 

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) conditions7

. As previously mentioned, page 2 of HRS documentation record at proposal Reference 

165, produced by a ME DEP certified environmental hydrogeologist stated 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 shallower 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 drinking 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 related 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 Attachment 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), ethylbenzene (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. 
Leeds 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 contains 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 the geologic 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 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 consideration 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 Section 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.
Leeds 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 evaluated 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 Appendix 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 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. 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 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 population 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 and 
Leeds 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 purposes (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 

weighted (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 wells 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 the 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 commented 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 impacts 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, in 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].
Leeds Metal NPL Listing Support Document September 2012 

46 

HRS Section 3.3.2.2, Level I concentrations, 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)

SampleAdjusted 

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 
Leeds Metal NPL Listing Support Document September 2012 

47 

Sample ID Hazardous 

Substance

Concentration 

(μg/L)

SampleAdjusted 

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 the 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 the 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 2.5.1 
Leeds 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 identifies 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 correctly 

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 Section 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 migration rates and degradation rates of the 

contaminants as they travel in the aquifer.
Leeds 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 concentrations, 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 concentration 

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 DW13, 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-
Leeds 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

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 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.
Leeds 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 documentation 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, DW23, 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 confirmed [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 the 
Leeds 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 wells 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 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-13, DW-16, DW18, 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 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. 

Therefore, all of the wells identified as Level II 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 

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 also 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 
Leeds Metal NPL Listing Support Document September 2012 

53 

geographic data. MEC went on to explain that the geologic material 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: The potential target population within the 4-mile DL for this site is correctly included in the HRS 

evaluation. 

HRS Section 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.

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. [Emphasis 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:
Leeds 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 document 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 became 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 conclusion 
Leeds 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 the 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: 32.25 
Leeds Metal NPL Listing Support Document September 2012 

56 

Attachment 1: Select Physical Properties Pages from the United States 

National Library of Medicine ChemIDplus Lite Database
8/10/12 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.

U.S. Na tional Library o f Medicine, 8600 Rockville Pike , Be the sda , MD 20894,

Na tional Institute s o f Health, Departm ent o f Health & Hum an Service s

Copyright and Privacy Policy, Freedom o f Inform a tion Act, Acce ssibility

Custom er Service: tehip@teh.nlm .nih.gov.
8/10/12 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

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.

U.S. Na tional Library o f Medicine, 8600 Rockville Pike , Be the sda , MD 20894,

Na tional Institute s o f Health, Departm ent o f Health & Hum an Service s

Copyright and Privacy Policy, Freedom o f Inform a tion Act, Acce ssibility

Custom er Service: tehip@teh.nlm .nih.gov.
8/10/12 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

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.

U.S. Na tional Library o f Medicine, 8600 Rockville Pike , Be the sda , MD 20894,

Na tional Institute s o f Health, Departm ent o f Health & Hum an Service s

Copyright and Privacy Policy, Freedom o f Inform a tion Act, Acce ssibility

Custom er Service: tehip@teh.nlm .nih.gov.
8/10/12 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

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.

U.S. Na tional Library o f Medicine, 8600 Rockville Pike , Be the sda , MD 20894,

Na tional Institute s o f Health, Departm ent o f Health & Hum an Service s

Copyright and Privacy Policy, Freedom o f Inform a tion Act, Acce ssibility

Custom er Service: tehip@teh.nlm .nih.gov.
8/10/12 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

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.

U.S. Na tional Library o f Medicine, 8600 Rockville Pike , Be the sda , MD 20894,

Na tional Institute s o f Health, Departm ent o f Health & Hum an Service s

Copyright and Privacy Policy, Freedom o f Inform a tion Act, Acce ssibility

Custom er Service: tehip@teh.nlm .nih.gov.
8/10/12 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

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, Departm ent o f Health & Hum an Service s

Copyright and Privacy Policy, Freedom o f Inform a tion Act, Acce ssibility

Custom er Service: tehip@teh.nlm .nih.gov.
8/10/12 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

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.

U.S. Na tional Library o f Medicine, 8600 Rockville Pike , Be the sda , MD 20894,

Na tional Institute s o f Health, Departm ent o f Health & Hum an Service s

Copyright and Privacy Policy, Freedom o f Inform a tion Act, Acce ssibility

Custom er Service: tehip@teh.nlm .nih.gov.
Leeds 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 ofPure Compounds: Datanillipascal 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 11 ' . 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 ofLiquids 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 

(i1mpomuls 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,HFp2 Trifluoroacetic acid 0.808 0.571 

C,H,Ct2 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,Cl4 1,1,1,2-Tetrachloroethane 3.660 2.200 1.437 1.006 0.741 0.570 

C,H 3 CIF2 1-Chloro-1, 1-difluoro-ethane 0.477 0.376 

c,H,c1o Acetyl chloride 0.368 0.294 

C,H,ct3 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,Br2 1,2-Dibromoethane 1.595 1.116 0.837 0.661 

6-231 
6-232 Viscosity 

Molecular Viscosi!}: in mPa s

formula Name -25'C O'C 25'C 50'C 75'C 

c,H4Cl 1,1-Dichloroethane 2 0.464 0.362 

c,H4Cl 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 

C2

H5Br Bromoethane 0.635 0.477 0.374 

C H5Cl 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 H5N02 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 

C2

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 

C2H S Ethanethiol 0.364 0.287 6 

C H N Dimethylamine 0.300 0.232 2 7 

C 2H NO Ethanolamine 7 21.1 8.560 3.935 1.998

C3H5Br 3-Bromopropene 0.620 0.471 0.373 

C3

H5Cl 3-Chloropropene 0.408 0.314 

C3H5

Cl0 Epichlorohydrin 2.492 1.570 1.073 0.781 0.597 0.474 

C H3 5N 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,H60 Prop anal 0.321 0.249 

c,H 0 Ethyl formate 0.506 0.380 0.300 6 2 

C3H 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 H3 7Br 1-Bromopropane 0.645 0.489 0.387 

C3

H7Br 2-Bromopropane 0.612 0.458 0.359 

C H Cl 1-Chloropropane 0.436 0.334 3 7

C3H,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 3H7l 2-Iodopropane 0.883 0.653 0.506 

C H NO 3 7 N,N-Dimethylformamide 1.176 0.794 0.624 

C3

H7N02 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 

C3

H80 2-Propanol 4.619 2.038 1.028 0.576 

C 1,2-Propylene glycol 4.770 2.750 3

H80 2 248 40.4 11.3 

C3H80 3 Glycerol 934 152 39.8 14.8 

C S 1-Propanethiol 3H8 0.503 0.385

C3

H8S 2-Propanethiol 0.477 0.357 0.280 

C3

H9N Propylamine 0.376 

C H3 9

N Isopropylamine 0.454 0.325 

C H 0 Furan 0.661 0.475 0.361 4 4 

C4H5N Pyrrole 2.085 1.225 0.828 0.612 

0.377 C4H60a Acetic anhydride 1.241 0.843 0.614 0.472 

0.268 C4H,N Butanenitrile 0.553 0.418 0.330 

C4H,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 4H,o, 1.177 0.787 0.569 

c,H,o, Ethyl acetate 0.578 0.423 0.325 0.259 

C4H,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 C4H,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 H4 8o,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

C4

H9Cl 1-Chlorobutane 0.556 0.422 0.329 0.261 

C4

H 0.512 9N Pyrrolidine 1.914 1.071 0.704 

C4

H9NO 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 Diacetone 28.7 6.621 alcohol C6H,2o2 1.079 0.692 0.485

C6H,20, Paraldehyde 0.36?.

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·

C6H,40 Dipropyl ether

4.578 2.271 1.270 0,7gl C6H,40 1-Hexanol

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

C6H,,N Diisopropylamine

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 

C7H, Toluene

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

C7H,40 2-Heptanone 1.488 3.840 2.282 l.Ooll

Heptanoic acid C7H,•Oz 0.523 0.387 ·0.301 0.243

Heptane 0.757 C7Hl6 0.350 3-Methylhexane C7Hl6 5.810 2.603' 1.389 0.849 

C7H,60 1-Heptanol 0,987 0.615 3.955 1.799

C7H,60 2-Heptanol 1.957 0.976 0.584 

C7H,60 3-Heptanol 0.882 0.539 4.207 1.695 

C7H,60 4-Heptanol 0,600 0.43•1 1.314 0.865

C7H,7N Heptylamine 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,H1P 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,)118 

trans-Decahydronaphthalene 6.192 3.243 1.948 1.289 0.917 0.689 c,..H18 

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" 

CH,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 C11 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

,,,
Leeds Metal NPL Listing Support Document September 2012 

58 

Attachment 3: Excerpt of Petroleum Hydrocarbons And Chlorinated 

Hydrocarbons Differ In Their Potential For Vapor Intrusion, EPA Office 

of Underground Storage Tanks, March 2012
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

Office 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 For 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 guidance (EPA, 2002), which specifically states that it is not recommended for 

Subtitle I underground storage tank (UST) sites. EPA’s Office of Underground Storage Tanks (OUST) is thus 

currently developing guidance to address petroleum vapor intrusion (PVI) at UST sites. OUST has consulted on 

several occasions with experts in the field of vapor intrusion 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 UST PVI guidance. This information paper1 describes how petroleum 

compounds behave differently in the subsurface 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 

aerobic3 biodegradation is substantial and can limit the potential for PVI. In contrast, 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 contamination 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 are 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 concepts of petroleum vapor intrusion. 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 automotive gasoline, diesel fuel, lubricating oils, and the like. 3 Aerobic means that the process requires oxygen. In contrast, anaerobic means the process does not require oxygen. Anoxic 

refers to the absence of oxygen.
 

1 
 

 

Introduction 

This paper discusses the impact on the inhalation exposure pathway from vapor intrusion (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 primarily on the latter concern, although the reader 

should recognize that in high enough concentrations, petroleum compounds and methane (a 

biodegradation product) can collect in buildings, leading 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 hydrocarbon contamination. 

There are two classes of VOCs4

 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 tetrachloroethylene (perchloroethylene, 

or PCE) and the degreasing solvents trichloroethylene (TCE), 1,1,1-trichloroethane (TCA), and 

PCE 

This information paper discusses and compares petroleum 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 buildings and other confined spaces as well as some implications for 

addressing PVI. 

The foremost difference between PHC and chlorinated solvent vapors in the subsurface is that PHCs 

biodegrade readily under aerobic (oxygenated) environmental conditions, whereas chlorinated solvents5 

typically biodegrade much more slowly and under anaerobic conditions (Howard, 1991). Because PHC 

biodegradation is relatively rapid when oxygen is present, aerobic biodegradation can typically limit the 

concentration and subsurface migration of petroleum vapors in unsaturated soils. In addition, 

biodegradation of chlorinated solvents can produce toxic degradation products, such as dichloroethylene 

and vinyl chloride, while petroleum degradation usually produces carbon dioxide, water, and sometimes 

methane or other simple hydrocarbons. A second primary difference is density: PHC liquids (e.g., 

gasoline, diesel fuel) are lighter (less dense) than water and when released from a leaking UST, can float 

on the groundwater surface (water table), whereas chlorinated 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 for PHCs and chlorinated solvents 

under commonly observed subsurface conditions. The conceptual scenarios in these figures are simplified 

4 A third class of volatile chemicals is inorganics, of which radon is probably the most identifiable and problematic from a VI 

perspective.

5

 Vinyl chloride, which is itself a product of the degradation of chlorinated solvents, has been observed to biodegrade relatively 

rapidly in the presence of very low concentrations of oxygen; concentrations so low that it is not possible to measure in the field 

with standard instruments (Bradley, 2011; Bradley and Chapelle, 2011; and Gossett, 2010). 

2 
 

many 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 inhalation 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 controlling diffusion and sorption in the vapor phase; 

advection, in contrast, is unaffected by chemical 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 vapors in many situations (McHugh et al., 2010). 

Biodegradation Of Petroleum Hydrocarbons 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 for adequate populations of active microorganisms. If 

oxygen is present, these organisms will generally consume available PHCs. Furthermore, aerobic 

biodegradation of petroleum compounds can occur relatively 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 important and generally much slower than aerobic 

biodegradation. 

Figure 1 (page 3) depicts key processes for the biodegradation of PHCs in the unsaturated zone under 

common conditions: downward oxygen transport from the atmosphere, upward hydrocarbon vapor 

migration from the contaminant source, and aerobic 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 oxygen 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 dioxide concentrations increase with depth. The characteristic vertical profile, 

which will vary in shape depending on site-specific 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 high enough, available oxygen 

may be depleted, which in turn limits aerobic biodegradation. When oxygen is limited, anaerobic 

biodegradation of LNAPL or other organic sources can produce methane. Significant anaerobic 

biodegradation and methane generation can occur in some situations within anoxic zones of the plume 

interior and adjacent to the LNAPL source. Methane readily biodegrades under aerobic conditions and, 

6