## Technical Support Document for U.S. EPA’s Proposed Rule for Addition of a Subsurface Intrusion Component to the Hazard Ranking System 

# Appendix F : Ground Water Contaminant Intrusion

Page F-2: The Ground Water Intrusion Threat

Page F- 2: Evaluation as Part of Development of the draft HRS SsI Addition

Page F- 3: Methodology Used to Evaluate Ground Water Intrusion Sites

Page F-4: Reviews of Possible Ground Water Intrusion Sites

Page F-6: Example of Ground Water Intrusion Site with Sufficient Data for HRS Scoring

Page F -1The Ground Water Intrusion Threat

Ground water contaminant intrusion is a type of subsurface intrusion where contaminant s have entered a structure via infiltrating groundwater (e.g., metals precipitat ing from

-- or hazardous substances volatilizing out

-- of the ground water.) Ground water c ontaminant intrusion is an emerging issue that is being evaluated as part of the development of the Hazard Ranking System ( HRS ) Subsurface Intrusion (SsI) addition. The U.S. Environmental Protection Agency ( EPA ) regional site assessment programs have identified site s where intrusion of contaminated ground water is a potential issue and the related threat cannot be evaluated using the current HRS. T he proposed SsI addition would make ground water intrusion into regularly occupied structures eligible for evaluation and inclusion in an HRS evaluation. As EPA further explores this emerging issue, the agency considers it likely that additional ground water intrusion sites requiring evaluation will be identified.

Evaluation of Ground Water Contaminant Intrusion as Part of Development of the draft HRS SsI Addition

The addition of a subsurface intrusion component to the HRS would expand the number of available options for
EPA to evaluate hazardous substance releases that could endanger human health from ground wat er enter ing into regularly occupied structures from the subsurface. There is no mechanism within the current structure of the HRS that allows for the evaluation , or consideration, of ground water contaminant intrusion into a site’s HRS score. Therefore, ground water contaminant intrusion cannot currently factor into a site’s potential placement on the National Priorities List (NPL) via the HRS, regardless of any threat to human health it may pose.

During the development of th e proposed SsI addition to the HRS EPA considered both vapor intrusion and ground water contaminant intrusion (both of which are types of subsurface intrusion). T he draft SsI HRS addition includes the consideration of ground water contaminant intrusion in the evaluation criteria and , where needed, identifies any specific considerations for ground water contaminant intrusion because it occurs differently than the intrusion of vapors. It is proposed that s ubsurface intrusion be evaluated on the likelihood of exposure, wast e characteristics and targets based on current site conditions. EPA considered including the evaluation of the potential for ground water contaminant intrusion in the proposed HRS SsI componen t, similar to the included evaluation of the potential for vapor intrusion . However, the available science and methods for predicting the potential for ground water contaminant intrusion would likely be beyond the scope of a site inspection. Therefore, ground water contaminant intrusion can only be evaluated in the proposed HRS SsI addition if it meets HRS observed exposure criteria. The evaluation of ground water intrusion in the draft HRS SsI addition is specified in detail in several sections :

• Likelihood of Exposure (Draft HRS SsI Addition Section 5.2.1.1)

• Waste Characteristics (Draft HRS SsI Addition Section 5.2.1.2)

• Targets (Draft HRS SsI Addition Section 5.2.1.3)

EPA evaluated multiple sites with documented and potential groundwater contaminant intrusion a s part of the evaluation of including ground water cont aminant intrusion in the draft HRS SsI. One of these site s, Garfield Groundwater Contamination, is currently on the NPL [ based on an Agency for Toxic Substances and Disease Registry (ATSDR) evaluation, not on an HRS evaluation] . The other sites evaluated may have ground water contaminant intrusion issues , but the data currently available for these sites is not sufficient to support an HRS scoring evaluation . The sections below provide details about how the sites were evaluated given limited information

, and include site description s and the results of the evaluation based on the information available.

Page F -2EPA applied the draft HRS SsI addition to the Garfield site to further demonstrate the need to revise the current HRS by including a component for subsurfa ce intrusion.

Methodology Used to Evaluate Ground Water Intrusion Sites

S everal sites with possible ground water contaminant intrusion impacts were identified and reviewed using available information in order t o assess the scope of the threat from ground water contaminant intrusion. A methodology for review ing sites identified with p ossible g round water contaminant intrusion impacts was developed using the following parameters:

• Evidence of ground water contaminant intrusion into a regularly occupied structure

• Probability of ground water contaminant intrusion into a regularly occupied structure, based on the depth from the structure foundation to ground water



### o < 10 feet (high)



### o > 10 feet (low)

• Contaminants present in the gro und water (e.g., chlorinated solvents , dissolved metals )

• Number of Impacted Targets Including Residents and W orkers



### o Number of Residences Possibly Impacted

- >10 residences (high)

- 5- 10 residences (medium)

- < 5 homes (low)

- Unknown



### o Number of Workers Possibly Impacted

- 1,000 workers (high)

- 101 – 1000 workers (medium)

- 1-100 workers (low)

Based on the parameters above, a tiering methodology was developed to evaluate possible ground water intrusion sites in a similar manner to which the sites tiered in the compiled inventory of sites (see Appendix A) were evaluated. The definitions of the tiers assigned to ground water intrusion sites are listed below :

• Tier 1 – Evidence of ground water contaminant intrusion and a high number of targets; enough HRSrequired data to confirm that the site would not score sufficiently high to qualify for the NPL without the addition of a subsurface intrusion component to the HRS.

• Tier 2 – Either a high probability of ground water contaminant intrusion and a high number or targets or evidence of ground water contaminant intrusion and medium number or targets.

• Tier 3 – High probability of ground water contaminant intrusion and a low number of targets.

• Tier 4 – Low probability of ground water contaminant intrusion and a low or unknown number of targets.

Page F -3

### Reviews o f Possible Ground Water Intrusion Sites

The following sites were identified by EPA regional office s as having a possible ground water contamina nt intrusion issues.

• Ground Water Intrusion Site 1 (Region 1)

o Located in a residential and commercial area; TCE documented in ground water samples

o No evidence of actual ground water intrusion; however, high probability of occurrence based on depth to ground water of less than ten feet

o Low number of targets; four residential structures (including one multi-subunit residence)

o Tier 3; unlikely to score greater than or equal to 28.50 based on available information when evaluating ground water intrusion

• Ground Water Intrusion Site 2 (Region 1)

o Located in urban area; PCE residue documented in building materials and in the soil of one elevator shaft

o Data suggests documented contamination likely associated with an indoor source and may not represent subsurface intrusion

o Low number of targets; one commercial tenant space located on the lowest floor of the building that is eligible for evaluation

o Tier 4; unlikely to score greater than or equal to 28.50 based on available information when evaluating ground water intrusion; building includes eight floors of residential tenant space

• Ground Water Intrusion Site 3 (Region 1)

o Located in residential and commercial area; PCE documented in residential sumps.

o Evidence of contaminated ground water intrusion based on sample collected from residential
sumps

o Low number of targets; five commercial tenant spaces and one residential apartment

o Tier 3; unlikely to score equal to or greater than 28.50 based on available information when evaluating ground water intrusion

• Ground Water Intrusion Site 4 (Region 2)

o Located in rural area with homes and businesses within a half

- mile of the site; chromium was documented in ground water samples

o No evidence of actual ground water intrusion; however, high probability of occurrence based on depth to ground water of less than ten feet

o Low number of targets; less than five res idences and less than 100 estimated workers

o Tier 3; unlikely to score greater than or equal to 28.50 based on available information when evaluating ground water intrusion

• Ground Water Intrusion Site 5 (Region 2)

o Located in a residential and commercial ar ea

o No evidence of actual ground water intrusion; however, insufficient information to completely tier this site

• Ground Water Intrusion Site 6 (Region 3)

o Located in a residential and commercial area; TCE and PCE documented in ground water samples

o Insufficient information available to document whether ground water intrusion has occurred; to determine whether ground water intrusion has occurred additional research of the existing site file or further field work would need to be done

o Sufficient targets present to achieve a score equal to or greater than 28.50 using the 1990 HRS

Page F -4ground water migration pathway and the draft SsI component of the HRS addition

• Ground Water Intrusion Site 7 (Region 5)

o Located in a residential and industrial area; arsenic and cyanide documented in surface and subsurface samples; blue waste material documented to contain cyanide was found in foundational cracks and a sump in two residences

o Evidence of infiltration of blue waste material into basements

o Low number of targets; t wo residential structures

o Tier 3; unlikely to score greater than or equal to 28.50 based on available information when evaluating ground water intrusion

Page F -5

### Example of Ground Water Intrusion Site with Sufficient D ata for HRS S coring – Garfield Ground Water Contamination Site

The Garfield Ground Water Contamination Site demonstrates the need to revise the current HRS with the addition of a component for subsurface intrusion. The Garfield site had shallow (surficial) ground water contaminated with chromic ac id that intruded into residential basements . A fter the water receded, or evaporated, a precipitate of chromium remained in the basements as a residue. The presence of this residue posed a significant threat to public health; however, the site could not be evaluated using the current HRS due to the lack of a mechanism to evaluate human exposure resulting from intrusion of contaminated ground water (subsurface intrusion contamination). The only viable option to place the site on the NPL was to rely on ATSDR to make a determination that the exposure at the site posed a significant threat to public health. The decision to include sites on the NPL based on a determination by ATSDR is made infrequently because it requires ATSDR to issue a healthy advisory recommending dissociation of individuals from the release at a site

. EPA then determines whether the release poses a threat

. EPA will consider the cost

- effective ness to use remedial authority, rather than removal authority, to respond to the release.



### Garfield Ground Water Contamination (EPA ID NJN00020631)

Site Description

This site is located in a mixed area of commercial and residential structures in the state of New Jersey

, across the Hudson River from New York City, and is the result of a historical release of chromic acid from a commercial operation’s storage tank that failed, releasing chromic acid to the environment. Approximately 29% of the material released was thought to have been recovered, but the unclaimed s hare entered the subsurface environment beneath the facility, eventually entering shallow ground water and migrating into the basements of nearby hydraulically downgradient properties. Past investigations have identified chromium and hexavalent chromium contaminated ground water and precipitates intruding into occupied commercial and residential structures. Since 2005 EPA has identified approximately 288 residences in the study area with possible ground water infiltration issues. The available analytical data has identified chromium or hexavalent chromium contamination in a basement or basement sump at 10 occupied structures

. Key Scoring Limitations/Assumptions

• Available U.S. Census data is used to determine average number of persons per household residential targets in the AOE and ASC. Worker population data is assumed to be at least 1 full

- time worker per workplace if more specific information is not available.

• It is assumed that the data presented within the available reports, including sample values collected between 2000 and 2003 (basement and basement sump samples) and in April 2010 (ground water samples), are still representative of current conditions at the site. Additionally, the quality of analytical data is assumed to be sufficient and of known quality.

• It is assumed that all ground water sampling data used in this analysis represent a single surficial ground water layer.

• It is assumed that all contaminated samples considered as part of this evaluation are representative of a single contaminant plume associated with a single originating source and do not represent multiple, comingled contaminant plumes.

• P ublicly available ariel imagery was used to identify and estimat e types (e.g., single family residence, multi

tenant residence) of occupied structures for the purposes of this analysis. These images are assumed to

Page F -6Page F -7 represent current conditions and that all residences or commercial operations are occupied, unless evidence indicates otherwise. This information has not been validated.

• Sampl e locations presented are approximate and may not represent the actual extent of contamination at the site.

• A n assigned area value of 1,740 square feet is used in determining a waste quantity estimate for all regularly occupied structures (including multi

- subunit structures)

. • It is assumed that previous and current remedial or removal actions have not completely removed the threat to public health posed by this release under evaluation.

• A ground water migration pathway score of 50.77 was previously determined in historical site assessment reports and for purposes of this evaluation is assumed to be accurate and representative of current site condition. Supporting data for the ground water migration pathway evaluation was not available for review.

It should be noted that these figures and site scores are presented for the sole purpose of testing the proposed subsurface intrusion component. The presented HRS s ite scores are based on limited information and that additional evaluation and sampling would be necessary to determine if the site would qualify for listing using the HRS

.

## Garfield Ground Water Contamination (EPA ID NJN00020631)

Site Diagra m

Areas of Observed Exposure (AOEs) Delineated by Observed Exposure Indoor Basement/Sump Samples

Page F -8HRS T ABLE 5- 11

– S UBSURFACE I NTRUSION C OMPONENT S CORESHEET

Factor Categories and Factors Maximum

Value Value Assigned

Subsurface Intrusion Component

Likelihood of Exposure:

1. Observed Exposure Two areas of observed exposure have been delineated at the site, based on samples collected from the basements of several occupied structures (including sump samples). An observed exposure to chromium (total and/or hexavalent) by direct observation has bee n established at 10 regularly occupied structures. 550 550

2. Potential for Exposure Per the draft HRS, the potential for exposure factor was not evaluated based on the documentation of an observed exposure. 500 -

2a. Structure Containment 10 -
2b. Depth to C ontamination 10 -

2c. Vertical Migration 15 -
2d. Vapor Migration Potential 25 -

3. Potential for Exposure ( lines 2a * ( 2b + 2c + 2d ), subject to a maximum of 500) 500 -

4. Likelihood of Exposure ( higher of lines 1 or 3 ) 550 550

Waste Characteristics:

5. Toxicity /Degradation The highest toxicity value for the substances documented in the area of subsurface contamination and/or the areas of observed exposure documentation is 10,000 for hexavalent chromium. (a) 10,000

6. Hazardous Waste Quantity The footprint of the 43 regularly occupied structures located within the area of observed exposure is unknown. Therefore, as stated in the draft HRS, a value of 1,740 ft 2 per regularly occupied structure was used in calculating a hazardous waste quantity, which was used to select a hazardous waste quantity factor value using HRS Tables 5

- 18 (draft) and 2

- 6. (a) 100

7. Waste Characteristics (subject to a maximum of 100) The toxicity/degradation and hazardous waste quantity factor values were multiplied and the resulting value of 1x10 5 was used to select a waste characteristics factor category value of 32 from the draft HRS Table 2

- 7. 100 32

Targets:

8. Exposed Individual There is at least one individual present in a regularly occupied structure in the AOE that is exposed to Level II contaminant concentrations. Per the draft HRS, a value of 45 is assigned. 50 45

9. Population:

9a. Level I Concentrations (b) 0

Page F -9Factor Categories and Factors Maximum
Value Value Assigned
Analytical data for indoor air samples were not included in the information provided.

9b. Level II Concentrations In the two established AOEs, 34 single family homes, one duplex (i.e., two residences), one basement apartment and one commercial building were identified as exposed (or inferred to be exposed to) Level II concentrations. The number of people living or working within each regularly occupied structure is unknown, therefore, a county average of 2.69 was assumed for residential populations and at least one full

- ti me worker is assumed (1 full

- time worker divided by 3=.33). (U.S. Census Bureau). Based on this information, a Level II population of 99. 86 is assigned. (b) 99.86

9c. Population with in A rea (s) of S ubsurface C ontamination Population in the ASC was not evaluated for this site. (b) 0

9d. Total Population ( lines 9a + 9b + 9c ) (b) 99.86

10. Resources Based on the information available, one resource has been identified in the AOE. Per the draft HRS, a value of 5 is assigned. 5 5

11. Targets ( lines 8 + 9d + 10 ) (b) 149.86
Subsurface Intrusion Component Score

12. Subsurface Intrusion Component ( lines 4 x 7 x 11) / 82,500 c (subject to a maximum of 100) 100 31.97

Soil Exposure and Subsurface Intrusion Pathway Score

13. Soil Exposure Component + Subsurface Intrusion Component (subject to a maximum of 100) 100 31.97

HRS Site Score

14. √[ ( S gw 2 + S sw 2 + S sessi 2 + S a 2 )/4] = √ [( 50.77 2 + 0 2 + 31.97 2 + 0 2 ) /4] 100 29.99

a Maximum value applies to waste characteristics category.
b Maximum value not applicable.

c Do not round to nearest integer.

Page F

- 10