Technical Support Document for U.S. EPA’s Proposed Rule for Addition of 

a Subsurface Intrusion Component to the Hazard Ranking System

Appendix D: Site Summaries and Scoring Information 

for Test Sites (Tier 1)

Test Site 001: District of Columbia 

Test Site 002: Maryland 

Test Site 003: District of Columbia 

Test Site 004: Maryland 

Test Site 005: Pennsylvania 

Test Site 006: Texas 

Test Site 007: District of Columbia

Test Site 008: Montana 

Test Site 009: Wisconsin

Test Site 010: Missouri

Test Site 011: Minnesota

Page D-1 
Scoring Information for Test Sites (Tier 1)

As part of the evaluation of the need for the proposed subsurface intrusion (SsI) addition to the Hazard 

Ranking System (HRS), efforts to identify and classify sites with suspected impacts from SsI were 

undertaken. The sites identified and classified as a part of this effort are identified and classified in further 

detail in appendix A. Eleven of the identified sites were determined to have a subsurface threat and 

sampling data sufficient to indicate that these sites would not result in a significant HRS site score with 

the inclusion of the proposed SsI addition. These sites were classified as Tier 1 sites in the SsI Inventory 

of Sites. Using available sampling data, these 11 sites were used to test and evaluate the proposed HRS 

SsI addition. 

The following evaluations of the 11 test sites contain summaries of the sites with brief introductions on 

the sites, outlines of the scoring approach for each site and annotated scoresheets indicating the rationale 

for the calculated HRS site score using the SsI component and other current HRS pathways, as applicable, 

with available data. Due to limited information available, these site summaries include the key-site 

specific scoring limitations and assumptions used in the evaluation of these sites with the proposed SsI 

addition. The summaries provided below are intended for testing purposes are not intended to justify the 

placement of these sites on the National Priorities List. 

Page D-2 
Page D-3 

Subsurface Intrusion Test Site 001

(January 2016)

Site Description

Test site 001 consists of a chlorinated solvents release from an operating drycleaner situated adjacent to a 

daycare and a private school. The U.S. Environmental Protection Agency (EPA) determined that exhaust 

from the drycleaner was causing elevated levels of tetrachloroethylene (PCE) and trichloroethylene (TCE) 

to be taken into nearby building ventilation systems. EPA has collected indoor air samples from the 

drycleaner, daycare, and private school and has also collected soil gas samples from beneath the 

foundations (i.e., subslab) of surrounding residential and commercial buildings, including the drycleaner, 

daycare and private school. Additionally, EPA has also collected outdoor air samples. 

The site includes an area of observed exposure (AOE) delineated by indoor air samples meeting observed 

exposure criteria. Tetrachloroethene was documented to be present in the AOE in the daycare facility and 

private school. 

The site additionally includes an area of subsurface contamination (ASC) delineated by subslab samples 

meeting observed release criteria. The structures within the ASC include two commercial buildings, one 

residential home and a church. 

 

Scoring Limitations/Assumptions 

Besides the assumptions made for all test sites listed at the beginning of this appendix, the following sitespecific limitations and assumptions were identified for scoring this site:

• It is assumed that all regularly occupied structures within the AOE and the ASC have a non-zero 

structure containment value.

• The online databases (i.e., http://www.privateschoolreview.com and http://www.childcarecenter.us/ ) 

used to estimate the number of students and workers at the nearby contaminated daycare and school 

represents current conditions. The buildings comprising the contaminated daycare and school are 

structurally interconnected. 

• Indoor air samples meeting the observed exposure criteria are not due to anthropogenic sources (e.g.,

potential indoor sources of vapor-forming chemicals, such as household cleaners) and the significant 

increase in hazardous substance concentrations are attributable at least in part to the release(s) being 

evaluated.

• Outdoor contaminated air (measured during one of the three sampling events when the drycleaner 

was in operation) is not the source of the indoor air contamination. 

• Data quality is sufficient for use in testing the draft subsurface intrusion component.

• Sampling locations presented are approximate and may not represent the actual extent of 

contamination at the site.

• 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. 
Page D-4 

• An indoor air temperature of 25 °C and 1 standard atmosphere were assumed when converting indoor 

air sampling data provided in units of parts per billion by volume (ppbv) for comparison to healthbased benchmarks (i.e., from ppbv to micrograms per cubic meter [μg/m3

]).

• Per the draft HRS addition, An 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).

• Information used in the scoring of the test sites (including aerial imagery) is representative of current 

conditions. 

• The contamination evaluated in the site scoring is either from a single release or from commingled 

plumes resulting from multiple releases. 

• The HRS scoring does not include people residing in what appears to be apartments located above or 

behind the school, daycare and drycleaner facilities, as there was not sufficient information available 

to evaluate them.

• The depth below ground surface at which the subslab sample was collected at the regularly occupied 

residential structure identified within the ASC is unknown. It is assumed for evaluation purposes that 

the sample was collected within five feet of the structure.

The figure and site score presented for this test site are for the purpose of testing the draft subsurface 

intrusion component addition to the HRS. The presented HRS site score and associated figure are not 

intended to justify placement on the National Priorities List (NPL) and it is likely that additional data 

collection, evaluation and sampling would be necessary to determine if the site would qualify for listing.

As part of this limited assessment, test site 001 was evaluated using only the draft HRS subsurface 

intrusion component. While additional threats may exist at this site, sufficient data was not provided to 

evaluate the ground water migration pathway, surface water migration pathway, air migration pathway or 

the soil exposure pathway of the 1990 HRS. 
Page D-5

Subsurface Intrusion Test Site 001 (Figure 1) 

Site Diagram
Page D-6

Table 5-11 Subsurface Intrusion Component Scoresheet

Factor Categories and Factors Maximum

Value

Value

Assigned

Subsurface Intrusion Component

Likelihood of Exposure:

1. Observed Exposure

An observed exposure by chemical analysis for PCE was documented in two 

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.

2a. Structure Containment 10 -

2b. Depth to contamination 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 an ASC or the area 

of observed exposure (AOE) is 1,000 for TCE. Per the draft HRS, although TCE 

was not found in a sample that met observed exposure criteria, as the depth to 

contamination = is less than 10 feet, a degradation factor of one is assigned. The 

degradation factor is multiplied by the toxicity factor value to calculate the 

toxicity/degradation factor value of 1,000, which is the highest combined value of 

all eligible substances.

(a) 1,000

6. Hazardous Waste Quantity

The actual basal area footprints of the six regularly occupied structures in the

AOE and ASC are unknown. Therefore, as stated in the draft HRS, a value of 

1,740 ft2 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 1x105 was used to select a waste 

characteristics factor category value of 18 from the draft HRS Table 2-7.

100 18

Targets:

8. Exposed Individual

There is at least one individual present in a regularly occupied structure in the 

AOE that is exposed to Level I contaminant concentrations. Per the draft HRS, a 

value of 50 is assigned.

50 50

9. Population:

 9a. Level I Concentrations

The estimated population attending the daycare and school is 169 and 

approximately 10 full-time staff at the daycare facility and 19 full-time staff at the 

(b) 1786
Page D-7

school located within the within the AOE, which contain PCE concentrations 

greater than the applicable health-based benchmark of 9.3 μg/m3 (Cancer Risk 

Screening Concentration), is 169. Per the draft HRS, the total number of workers 

are divided by 3(29/3=9.6) and summed with the population attending the school 

and day care, which is 9.6 + 169 = 178.6. This value is then multiplied by a 

weighting factor of 10.

 9b. Level II Concentrations

No regularly occupied structures subject 

within the AOE.

to Level II concentrations are present (b) 0 

9c. Population within Area(s) of Subsurface Contamination 

The actual population present within the three regularly occupied structures (one 

commercial facility, one religious facility and one residence) located within the 

ASC is unknown. Per the draft HRS, for a residence, an average of 2.17 persons 

per household associated with the area in which the site is located results in an 

estimate of 2.17 people; Worker population is assumed to be at least 1 full-time 

worker per facility, resulting in a worker population of 2 workers divided by 3 (.7)

in the ASC. The populations are summed (2.87). A subslab sample meeting 

observed release criteria was taken at the residence; therefore, this population 

estimate was multiplied by a weighting factor of 0.4 using the draft HRS Table 5-

20. This results in a population estimate of 1.15 for the ASC.

(b) 1.15

 9d. Total Population (lines 9a + 9b + 9c) (b) 1,787.15

10. Resources

There is one religious facility (a place of potential 

are unknown) within the ASC. Per the draft HRS, 

worship, but building activities 

a value of 5 is assigned.

5 5 

11. Targets (lines 8 + 9d + 10) (b) 1,842.1 

Subsurface Intrusion Component Score

12. Subsurface Intrusion Component 

maximum of 100)

(lines 4 x 7 x 11)/82,500c (subject to a 100 100.00

Soil Exposure and Subsurface Intrusion Pathway Score

13. Soil Exposure Component 

maximum of 100)

+ Subsurface Intrusion Component (subject to a 100 100.00

a Maximum value applies to waste characteristics category.

b Maximum value not applicable.

c Do not round to nearest integer. 

HRS Site Score Maximum 

Value 

Value 

Assigned

√[ ( Sgw2 + Ssw2 + Ssessi2 + Sa

2 )/4] = √ [( 02

 + 02 + 1002 +02 )/4] 100 50
Page D-8

Subsurface Intrusion Test Site 002 

(January 2016)

Site Description

Test site 002 is located in central Maryland, within an area of commercial and residential land use types. 

The subject property consists of an L-shaped shopping center strip and three pad sites consisting of multisubunit structures. Historical operations have resulted in a release of chlorinated solvents to shallow 

ground water and soils immediately surrounding the facility. Dry cleaning facilities are documented to 

have been ongoing for approximately 40 years – the current tenant ceased on-site dry cleaning operations 

in 2004. This site has been investigated on multiple occasions that have included indoor air sampling in 

January, July and November of 2013. Additionally, ground water samples have been collected on 

multiple occasions dating back to November 2007. 

The site includes an area of observed exposure (AOE) delineated by indoor air samples meeting observed 

exposure criteria. The hazardous substances documented to be present in the AOE were tetrachloroethene 

(PCE), trichloroethene (TCE), and cis-1, 2-dichloroethene. The structures within the AOE include 17 

multi-subunit structures and 29 residential homes. 

The site additionally includes an area of subsurface contamination (ASC) delineated by ground water 

samples meeting observed release criteria. Additional structures within the ASC include 8 multi-subunit 

structures. 

Scoring Limitations and Assumptions

Besides the assumptions made for all test sites listed at the beginning of this appendix, the following sitespecific limitations and assumptions were identified for scoring this site:

• For the soil gas and indoor air sampling events, no appropriate background sample was available;

it was assumed that the background level to compare against release contaminant concentrations

was non-detect for manufactured substances (e.g., PCE/TCE). Therefore, per the draft HRS

Subsurface Intrusion (SsI) Addition (draft HRS addition), an observed exposure or observed

release was documented when a release contaminant concentration equaled or exceeded its

appropriate reporting limit.

• It is assumed that all regularly occupied structures within the AOE and ASC have a non-zero

structure containment value.

• Indoor air samples meeting the observed exposure criteria are not due to the presence of potential

indoor sources of vapor-forming chemicals, such as household cleaners, and the significant

increase in hazardous substance levels are attributable at least in part to the release(s) being

evaluated.

• Data quality is sufficient for use in testing the draft subsurface intrusion component.

• Sampling locations presented are approximate and may not represent the actual extent of

contamination at the site.

• 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 fulltime worker per workplace if more specific information is not available.
Page D-9

• Per the draft HRS addition an 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)..

• Information used in the scoring of the test sites (including aerial imagery) is representative of

current conditions.

• The contamination evaluated in the site scoring is either from a single release or from

commingled plumes resulting from multiple releases.

• It is assumed that all ground water sampling data used in this analysis, including samples

collected at the water table and from ten feet below the water table, represent a single surficial

ground water layer.

• Hazardous Waste Quantity: Each apartment and townhouse building is assumed to be comprised

of either 4 or 5 separate building sub units. This evaluation includes 14 building sub units in three

buildings. Each sub unit is assumed to contain 4 separate apartments. The high-rise apartment is

assumed as one building unit with 13 apartments per floor (468 units, 12 floors per building, three

buildings).

• As part of this evaluation, it is assumed that the high-rise apartment floors are interconnected

within a building and therefore all 13 apartments per floor are considered. The apartment and

townhouse building is assumed to be interconnected at the sub unit level where each sub unit

contains 2 ground level apartments.

The figure and site score presented for this test site are for the purpose of testing the draft subsurface 

intrusion component addition to the HRS. The presented HRS site score and associated figure are not 

intended to justify placement on the National Priorities List (NPL), and it is likely that additional data 

collection, evaluation and sampling would be necessary to determine if the site would qualify for listing. 

As part of this limited assessment, the test site 002 was evaluated using only the draft HRS subsurface 

intrusion component. While additional threats may exist at this site, sufficient data was not provided to 

evaluate the ground water migration pathway, surface water migration pathway, air migration pathway or 

the soil exposure pathway of the 1990 HRS. 
Page D-10

Subsurface Intrusion Test Site 002 (Figure 2) 

Site Diagram
Page D-11

Table 5-11 Subsurface Intrusion Component Scoresheet 

Factor Categories and Factors Maximum

Value

Value 

Assigned

Subsurface Intrusion Component

Likelihood of Exposure:

1. Observed Exposure

An observed exposure by chemical analysis for tetrachloroethene, 

trichloroethene (TCE), and cis-1,2-dichloroethene has been documented in eight 

regularly occupied structures.

550 550

2. Potential for Exposure

Per the draft HRS addition, the potential for exposure factor was not evaluated 

based on the documentation of an observed exposure.. 

2a. Structure Containment 10 NS

2b. Depth to contamination 10 NS

2c. Vertical Migration 15 NS

2d. Vapor Migration Potential 25 NS

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

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

Waste Characteristics: - 

5. Toxicity/Degradation

The highest toxicity value for any of the substances documented in the AOE or 

ASC is 10,000 for Vinyl Chloride. Per the draft HRS addition, although Vinyl 

Chloride was not found in a sample that met observed exposure criteria, as the 

depth to contamination is less than 10 feet a degradation factor value of one is 

assigned. The degradation factor is multiplied by the toxicity factor value to 

calculate the toxicity/degradation factor value of 10,000, which is the highest 

combined value of all eligible substances. 

(a) 10,000

6. Hazardous Waste Quantity

The actual basal area footprints of the 54 regularly occupied structures in the 

AOE and ASC are unknown. Per the draft HRS addition, for Tier D, Area, a value 

of 1,740 ft2 per regularly occupied structure was used in calculating a hazardous 

waste quantity. These values were used to select a hazardous waste quantity 

factor value using HRS Tables 5-18 (draft addition) 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 1x105 was used to select a waste 

characteristics factor category value of 18 from the draft HRS Table 2-7.

100 32

Targets:
Page D-12

Factor Categories and Factors Maximum

Value 

Value

Assigned

8. Exposed Individual

There is at least one individual present in a regularly occupied structure in the 

AOE that is exposed to Level I contaminant concentrations for PCE. Per the draft 

HRS addition, a value of 50 was assigned.

50 50

9. Population:

9a. Level I Concentrations

The actual population living in the three regularly occupied structures containing 

concentrations above the applicable health-based benchmark of 9.3 μg/m3 

(Cancer Risk Screening Concentration) for PCE is unknown. Per the draft HRS 

addition, using the average of 2.79 persons per household for the county in 

which the site is located results in a total population estimate of 8.37 people 

exposed to Level I concentrations. This value is then multiplied by a weighting 

factor of 10 per the draft HRS addition.

(b) 83.7

9b. Level II Concentrations

The actual population living in the 43 regularly occupied structures (26 

residential homes; one multi-subunit apartment with 13 units; 8 multi-subunit 

apartments with 2 units each; 8 multi-subunits with at least one full-time worker – 

total of 63 structures) containing concentrations above the sample quantitation 

limit for PCE is unknown. Per the draft HRS addition, the total number of full-time 

workers are divided by 3 (8/3=2.6) and summed with the population residing in 

the remaining structures. Using the average of 2.79 persons per household for 

the county in which the site is located results in a total population estimate of 

156.0 (153.4+2.6=156.0) people exposed to Level II concentrations in the 

remaining 35 structures. 

(b) 156.0 

9c. Population within Area(s) of Subsurface Contamination

There are 8 regularly occupied structures (6 multi-subunit apartments and 2 

multi-subunits with at least one full time worker) within the ASC that are 

delineated with soil gas samples as well as with ground water samples 

approximately eight to ten feet bgs.

Per the draft HRS addition, the total number of full-time workers are divided by 3 

(2/3=0.6) and summed with the population residing in the remaining structures. 

The actual population living in the remaining structures is unknown. Per the draft 

HRS addition, using the average of 2.79 persons per household for the county in 

which the site is located results in a population estimate of 33.48 (based on 

ground water samples) (33.48+0.6 = 34.08). These population estimates were 

multiplied by a weighting factor of 0.1 (ground water) using the draft HRS 

addition Table 5-20.This results in a population estimate of 3.4 for the ASC.

(b) 3.4

9d. Total Population (lines 9a + 9b + 9c) (b) 243.1 

10. Resources

No resources were identified within the AOE or ASC. Per the draft HRS addition, 

a value of 0 is assigned. 

5 0 
Page D-13

Factor Categories and Factors Maximum

Value 

Value

Assigned

11. Targets (lines 8 + 9d + 10) (b) 293.1

Subsurface Intrusion Component Score

12. Subsurface Intrusion Component 

maximum of 100)

(lines 4 x 7 x 11)/82,500c (subject to a 100 62.52

Soil Exposure and Subsurface Intrusion Pathway Score

13. Soil Exposure Component 

maximum of 100)

+ Subsurface Intrusion Component (subject to a 100 62.52

a

Maximum value applies to waste characteristics category.

b

Maximum value not applicable.

c

Do not round to nearest integer. 

HRS Site Score Maximum

Value 

Value 

Assigned

√[ 2 ( Sgw + 2 Ssw + 2 Ssessi + Sa

2 )/4] = √ [(02 + 02 + 62.522 +02

)/4] 100 31.26
Page D-14

Subsurface Intrusion Test Site 003

(January 2016)

Site Description

Test site 003 is located in the District of Columbia, within an area of residential homes and a church. 

Previous investigations to assess a gasoline spill from a service station have identified ground water 

contaminated with tetrachloroethylene (PCE) and other chlorinated and non-chlorinated volatile organic 

analytes. The contamination appears to be traceable to a dry cleaning operation. The PCE contamination 

was first detected in 2002 and subsequent investigations in 2003 and 2004 were conducted to determine 

the extent of the PCE contamination and to evaluate the extent of vapor intrusion into overlying 

residential structures. 

The site includes an area of observed exposure (AOE) delineated by indoor air samples meeting observed 

exposure criteria. The hazardous substance documented to be present in the AOE was tetrachloroethylene 

(PCE). The structures within the AOE include 57 multi-subunit regularly occupied structures. 

The site additionally includes an area of subsurface contamination (ASC) delineated by ground water 

samples meeting observed release criteria. Additional structures within the ASC include two regularly 

occupied structures and 63 multi-subunit regularly occupied structures. 

Scoring Limitations/Assumptions

Besides the assumptions made for all test sites listed at the beginning of this appendix, the following sitespecific limitations and assumptions were made in the scoring of this site:

• It is assumed that all regularly occupied structures within the AOE and ASC have a non-zero

structure containment value.

• Indoor air samples meeting the observed exposure criteria are not due to the presence of potential

indoor sources of vapor-forming chemicals, such as household cleaners, and the significant

increase in hazardous substance levels are attributable at least in part to the release(s) being

evaluated.

• Data quality is sufficient for use in testing the draft subsurface intrusion component.

• Sampling locations presented are approximate and may not represent the actual extent of

contamination at the site.

• 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 fulltime worker per workplace if more specific information is not available.

• Per the draft HRS addition, an 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).

• Information used in the scoring of the test sites (including aerial imagery) is representative of

current conditions.

• The contamination evaluated in the site scoring is either from a single release or from

commingled plumes resulting from multiple releases.
Page D-15

• It is assumed that all ground water sampling data used in this analysis, including samples

collected at the water table and from ten feet below the water table, represent a single surficial

ground water layer.

• Aerial imagery, obtained through the maps.google.com online database was used to identify

occupied structures for the purposes of this analysis. These images are assumed to represent

current conditions and that all residences are occupied. In several instances, structures were

classified as duplex units based on these images and this information has not been validated. It is

also assumed that each structure and/or duplex unit identified is currently occupied.

• Although some reports indicate the presence of vapor mitigation systems, it is assumed that

cracks and/or preferential pathways into a structure still exist and that all structures have a

containment value greater than zero.

The figure and site score presented for this test site are for the purpose of testing the draft subsurface 

intrusion component addition to the HRS. The presented HRS site score and associated figure are not 

intended to justify placement on the National Priorities List (NPL) and it is likely that additional data 

collection, evaluation and sampling would be necessary to determine if the site would qualify for listing. 

As part of this limited assessment, test site 003 was evaluated using only the draft HRS subsurface 

intrusion component. While additional threats may exist at this site, sufficient data was not provided to 

evaluate the ground water migration pathway, surface water migration pathway, air migration pathway or 

the soil exposure pathway of the 1990 HRS. 
Page D-16

Subsurface Intrusion Test Site 003 (Figure 3) 

Site Diagram
Page D-17

Table 5-11 Subsurface Intrusion Component Scoresheet

Factor Categories and Factors Maximum

Value

Value

Assigned

Subsurface Intrusion Component

Likelihood of Exposure:

1. Observed Exposure

An observed exposure by chemical analysis for PCE was documented in six

regularly occupied structures.

550 550

2. Potential for Exposure

Potential for exposure was not evaluated based on the documentation of an

observed exposure per the HRS.

2a. Structure Containment 10 -

2b. Depth to contamination 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 the area of observed exposure is 100 for PCE. 

Per the HRS, the degradation factor is assigned a value of one due to the

documentation of an observed exposure to PCE. The degradation factor is 

multiplied by the toxicity factor value to calculate the toxicity/degradation factor 

value of 100, which is the highest combined value of all eligible substances.

(a) 100

6. Hazardous Waste Quantity

The area footprints of the 116 multi-subunit structures and two occupied 

structures (241 occupied units) in the areas of observed exposure and 

subsurface contamination are unknown. Therefore, a value of 1,740 ft2 per 

regularly occupied unit was used in calculating a hazardous waste quantity, which 

was used to select a hazardous waste quantity factor value using HRS Tables 2-

5 and 2-6.

(a) 10,000

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 1x106 was used to select a waste 

characteristics factor category value of 32 from HRS Table 2-7.

100 32

Targets:

8. Exposed Individual

As there is at least one individual in a regularly occupied structure that is exposed 

to Level I contaminant concentrations, a value of 50 is assigned.

50 50

9. Population:

 9a. Level I Concentrations

The population living in the six regularly occupied structures containing 

(b) 130.2
Page D-18

concentrations of PCE above the applicable health-based benchmark of 9.3

μg/m3 (Cancer Risk Screening Concentration) is unknown; using an average of 

2.17 persons per household for the area in which the site is located results in 

13.02 people exposed to Level I concentrations, which are then multiplied by a 

weighting factor of 10.

9b. Level II Concentrations

The population living in the 106 regularly occupied structures and multi-subunit 

structures (i.e., 43 duplex structures, 3 triplex structures, 6 units from duplex 

structures not scored as Level I, and 5 units from duplex structures where only 

one tenant space is located above an AOE) located within the area of observed 

exposure with inferred Level II contamination is unknown; using an average of 

2.17 persons per household for the area in which the site is located results in a 

population of 230.02.

(b) 230.02

9c. Population within Area(s) of Subsurface Contamination

There are 125 regularly occupied structures and multi-subunit structures (54 

duplexes, 4 triplexes, 2 single family homes, and 3 units in duplex structures 

where only one tenant space is located above an ASC) within the ASC that are 

delineated with ground water samples. In addition to these regularly occupied 

structures, there are two multi-unit structures (4 units) that have documented 

levels of PCE meeting HRS observed release criteria in subslab samples within 

five feet of the structure. 

Per draft HRS addition Table 5-20, samples delineated by ground water samples 

receive a weighting factor of 0.1 and samples with documented levels of PCE 

meeting HRS observed release criteria in subslab samples within five feet of the 

structure receive a weighting factor of 0.4. The actual population living in these 

structures is unknown. Per the draft HRS addition, using the average of 2.17

persons per household for the area in which the site is located results in a 

population estimate of 30.59.

(b) 30.59

9d. Total Population (lines 9a + 9b + 9c) (b) 390.81

10. Resources

One church was 

5 is assigned.

identified within the ASC. Per the draft HRS addition, a value of 5 5 

11. Targets (lines 8 + 9d + 10) (b) 445.81

Subsurface Intrusion Component Score

12. Subsurface Intrusion Component 

maximum of 100)

(lines 4 x 7 x 11)/82,500d (subject to a 100 95.10

Soil Exposure and Subsurface Intrusion Pathway Score

13. Soil Exposure Component 

maximum of 100)

+ Subsurface Intrusion Component (subject to a 100 95.10

a

Maximum value applies to waste characteristics category.

b

Maximum value not applicable.

c

No specific maximum value applies to factor.

d

Do not round to nearest integer. 

HRS Site Score

2 2 2 02 02 √[ ( Sgw + Ssw + Ssessi + Sa

2 )/4] = √ [( + + 95.102

 +02 ) /4] 100 47.55
Page D-19

Subsurface Intrusion Test Site 004 

(January 2016)

Site Description

Test site 004 is located in central Maryland, within an area containing a mixture of residential, 

commercial and industrial land use types. Historical operations at a former precious metal recovery 

operation resulted in a release of chlorinated solvents to shallow ground water and soils immediately 

surrounding the facility. The site includes a residential area comprised of row houses located between two 

noncontiguous property parcels. The two noncontiguous property parcels were previously the location of 

a former precious metal recovery operation. In 1981, the State of Maryland reported the property parcels 

to the U.S. Environmental Protection Agency (EPA) and requested assistance after discovering 

deteriorating and damaged tanks, containers and drums that were leaking their contents to the 

environment. EPA assessed the site and commenced an emergency response action, which was completed 

in December 1981. In 2002 the Maryland Department of the Environment (MDE) collected air samples 

from locations on or adjacent to the two noncontiguous property parcels. Results of these samples 

indicated the presence of volatile organic compounds (VOCs) inside the building located at the stateowned parcel. Further air testing at the site in November 2003 confirmed this finding and indicated the 

presence of VOCs in the air inside a building adjacent to the vacant property parcel. In November and 

December 2005, MDE conducted a more detailed investigation of the ground water and soil vapor 

beneath the homes separating the two noncontiguous property parcels. Results of this investigation 

showed that ground water contamination from the parcels was migrating beneath many of the intervening 

homes. Soil gas and indoor air testing conducted for MDE between June 2007 and August 2008 in six of 

the twenty row houses indicated vapor intrusion has occurred in all six tested houses. As of 2010 

installation of vapor intrusion mitigation systems in three homes had begun. 

The site includes an area of observed exposure (AOE) delineated by indoor air samples meeting observed 

exposure criteria. The hazardous substances documented to be present in the AOE include 

tetrachloroethylene (PCE), trichloroethylene (TCE) and vinyl chloride. The structures within the AOE 

include 17 occupied structures and 1 multi-subunit structure.

The site additionally includes an area of subsurface contamination (ASC) delineated by ground water and 

soil gas samples meeting observed release criteria. There are no additional structures within the ASC.

Scoring Limitations and Assumptions

Besides the global limitations and assumptions made for all test sites listed at the beginning of this 

appendix, the following site-specific limitations and assumptions were made in the scoring of this site: 

• For sampling events where no appropriate background sample was available, it was assumed that the

background level to compare against release contaminant concentrations was non-detect for

manufactured substances (i.e., PCE, TCE and vinyl chloride). Therefore, per the draft HRS

Subsurface Intrusion (SsI) Addition (draft HRS addition), an observed exposure or observed release

was documented when a release contaminant concentration equaled or exceeded its appropriate

reporting limit.

• It is assumed that all regularly occupied structures within the AOE have a non-zero structure

containment value.
Page D-20

• Indoor air samples meeting the observed exposure criteria are not due to the presence of potential

indoor sources of vapor-forming chemicals, such as household cleaners, and the significant increase

in hazardous substance levels are attributable at least in part to the release(s) being evaluated.

• Data quality is sufficient for use in testing the draft subsurface intrusion component.

• Sampling locations presented are approximate and may not represent the actual extent of

contamination at the site.

• 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.

• Per the draft HRS addition an 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)

• Based on the definitions provided for qualified data, it is assumed that the J-qualified data used to

identify observed exposure samples were above their applicable reporting limit.

• Information used in the scoring of the test sites (including aerial imagery) is representative of current

conditions.

• The contamination evaluated in the site scoring is either from a single release or from commingled

plumes resulting from multiple releases.

• It is assumed that all ground water sampling data used in this analysis, including samples collected at

the water table and from ten feet below the water table, represent a single surficial ground water layer.

• Although some reports indicate the presence of vapor mitigation systems, it is assumed that cracks

and/or preferential pathways into a structure still exist and that all structures have a containment value

greater than zero.

• It is assumed that any vapor intrusion mitigation systems present in an occupied structure do not

represent a permanent remedial action.

• Every regularly occupied residential structure within the AOE and ASC is occupied with the average

number of persons per household (2.48) for the city in which the site is located; with one exception,

one residence is documented as having four occupants based on a 2009 In-home Sampling Home

Survey Form. The city average number of persons per household is used as the city in which the site

is located is classified as an independent city. This value is assumed to be sufficiently close to an

appropriate county average to not significantly impact the HRS site score.

The figure and site score presented for this test site are for the purpose of testing the draft subsurface 

intrusion component addition to the Hazard Ranking System (HRS). The presented HRS site score and 

associated figure are not intended to justify placement on the National Priorities List (NPL) and it is likely 

that additional evaluation and sampling would be necessary to determine if the site would qualify for 

listing.

As part of this limited assessment, Test Site 004 is evaluated using only the draft HRS subsurface 

intrusion component. While additional threats may exist at the site, sufficient data was not provided to 

evaluate the ground water migration pathway, surface water migration pathway, air migration pathway or 

the soil exposure component of the draft soil exposure and subsurface intrusion pathway. 
Page D-21

Subsurface Intrusion Test Site 004 (Figure 4) 

Site Diagram
Page D-22

Table 5-11 Subsurface Intrusion Component Scoresheet

Factor Categories and Factors Maximum

Value

Value

Assigned

Subsurface Intrusion Component

Likelihood of Exposure:

1. Observed Exposure

An observed exposure by chemical analysis for multiple hazardous substances, 

including PCE, TCE and vinyl chloride, was documented in seven regularly 

occupied structures.

550 550

2. Potential for Exposure

Per the draft HRS, the potential for exposure factor 

the documentation of an observed exposure.

was not evaluated based on 

2a. Structure Containment 10 -

2b. Depth to contamination 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 ASC and the 

AOE is 10,000 for vinyl chloride. Per the draft HRS, as vinyl chloride was found 

in a sample that met observed exposure criteria, a degradation factor value of 

one is assigned. The toxicity factor value is multiplied by the degradation factor 

value to calculate the toxicity/degradation factor value of 10,000, which is the 

highest combined value of all eligible substances. 

(a) 10,000

6. Hazardous Waste Quantity

The actual basal area footprints of the 17 regularly occupied structures in the 

AOE and ASC are unknown. Per the draft HRS addition, for Tier D, Area, a value 

of 1,740 ft2 per regularly occupied structure was used in calculating a hazardous 

waste quantity. These values were used to select a hazardous waste quantity 

factor value using HRS Tables 5-18 (draft addition) 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 1x106 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 I contaminant concentrations. Per the draft HRS,

value of 50 was assigned.

a 

50 50

9. Population:

 9a. Level I Concentrations

The actual population living in the six regularly occupied structures and one multi-

(b) 151.8
Page D-23

unit structure (with at least one full time worker) containing TCE and/or PCE 3 above their respective health-based benchmarks of 0.43 μg/m3 and 9.3 μg/m

(Cancer Risk Screening Concentrations) is unknown. Per the draft HRS addition, 

the total number of workers are divided by 3 (1/3 = 0.3) and summed with the 

population residing in the remaining structures. Using the average of 2.48

persons per household for the city in which the site is located results in a 

population estimate of 15.18 (14.88+0.3 = 15.18) people exposed to Level I 

concentrations. This value is then multiplied by a weighting factor of 10 per the 

draft HRS addition. 

9b. Level II Concentrations

The actual population living in nine of the 10 regularly occupied structures 

located within the AOE, and not subject to Level I concentration levels, is 

unknown. One of the regularly occupied structures was documented in a survey 

to contain 4 persons. Per the draft HRS, applying the city average of 2.48 

persons per household to each of the aforementioned nine structures and 

including the four residents documented in the final occupied structure results in 

a population estimate of 26.32 people being exposed to Level II concentrations. 

(b) 26.32

9c. Population within Area(s) of Subsurface Contamination

No populations within the ASC not already evaluated as subject to Level I or 

contaminant concentrations were identified.

II (b) 0 

9d. Total Population (lines 9a + 9b + 9c) (b) 178.12

10. Resources

No resources were identified 

a value of 0 is assigned. 

within the AOE or ASC. Per the draft HRS addition, 5 0 

11. Targets (lines 8 + 9d + 10) (b) 228.12

Subsurface Intrusion Component Score

12. Subsurface Intrusion Component 

maximum of 100)

(lines 4 x 7 x 11)/82,500c (subject to a 100 48.66

Soil Exposure and Subsurface Intrusion Pathway Score

13. Soil Exposure Component 

maximum of 100)

+ Subsurface Intrusion Component (subject to a 100 48.66

a

Maximum value applies to waste characteristics category. b

Maximum value not applicable.

c

Do not round to the nearest integer.

HRS Site Score Maximum

Value

Value 

Assigned

2 √[ ( Sgw + 2 Ssw + 2 Ssessi + Sa2 )/4] = √ [( 02 + 02 + 48.662 +02 )/4] 100 24.33
Page D-24

Subsurface Intrusion Test Site 005 

(January 2016)

Site Description

Test Site 005 is located in southeastern Pennsylvania, within an area of mixed residential, commercial and 

industrial use. Historical operations at nearby facilities have resulted in a release of chlorinated solvents to 

shallow ground water and soils surrounding commercial and residential properties. The Environmental 

Protection Agency (EPA) initiated a removal assessment at the Site in September 2003 and continued 

investigations at the site through January 2006. The results of the removal assessment revealed the 

presence of trichloroethylene (TCE) in ground water, soil gas vapor and indoor air at both commercial 

and residential properties in the area of investigation. EPA Removal Program installed indoor air 

mitigation systems at three private residences which are impacted by the Site. The site was originally 

scored using only the ground water migration pathway, but would not score high enough to be considered 

National Priorities List (NPL) eligible based on this score alone. 

The site includes an area of observed exposure (AOE) delineated by indoor air samples meeting observed 

exposure criteria. The hazardous substances documented to be present in the AOE were 

tetrachloroethylene (PCE), TCE and cis-1,2-dichloroethylene (DCE). The structures within the AOE 

include three regularly occupied structures.

The site additionally includes an area of subsurface contamination (ASC) delineated by soil vapor and 

ground water samples meeting observed release criteria. The additional structures within the ASC include 

45 regularly occupied structures. 

Key Scoring Limitations/Assumptions

Besides the assumptions made for all test sites listed at the beginning of this appendix, the following sitespecific limitations and assumptions were made in the scoring of this site: 

• For sampling events where appropriate background samples were not collected, it is assumed that

the background level to compare release contaminant concentrations against is non-detect for the

manmade substances.

• Data obtained from multiple sampling events were used to delineate subsurface contaminant

plumes. Therefore, a minimal approach was used when delineating areas of subsurface

contamination based on the available information. However, it is likely that with additional data

the areas of subsurface contamination could be larger than shown in this evaluation.

• Based on the information available, it was not possible to determine if occupied structures

identified within the areas of observed exposure and subsurface contamination contained multiple

tenant spaces.

• Sampling locations presented are approximate and may not represent the actual extent of

contamination at the site.

• It is assumed that all regularly occupied structures within the AOE and ASC have a non-zero

structure containment value.

• Indoor air samples meeting the observed exposure criteria are not due to the presence of potential

indoor sources of vapor-forming chemicals, such as household cleaners, and the significant
Page D-25

increase in hazardous substance levels are attributable at least in part to the release(s) being 

evaluated.

• Data quality is sufficient for use in testing the draft subsurface intrusion component.

• 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 fulltime worker per workplace if more specific information is not available.

• Worker population at the commercial facility is determined to be 96 employees. Per the draft

Hazard Ranking System (HRS) addition, workers are considered full time unless information is

available identifying the number of full-time and part-time workers.

• An indoor air temperature of 25 °C and 1 standard atmosphere were assumed when converting

indoor air sampling data provided in units of parts per billion by volume (ppbv) for comparison to

health-based benchmarks (i.e., from ppbv to micrograms per cubic meter [μg/m3

]).

• Per the draft Hazard Ranking System (HRS) addition, an 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).

• Information used in the scoring of the test sites (including aerial imagery) is representative of

current conditions.

• The contamination evaluated in the site scoring is either from a single release or from

commingled plumes resulting from multiple releases.

• It is assumed that all ground water sampling data used in this analysis, including samples

collected at the water table and from ten feet below the water table, represent a single surficial

ground water layer.

• In several instances, structures were classified as duplex units based on aerial imagery and this

information has not been validated. It is also assumed that each structure and/or duplex unit

identified is currently occupied.

• Although some reports indicate the presence of mitigation systems, it is assumed that these

systems are not a permanent remedy and that preferential pathways into a structure still exist (i.e.,

all structures have a containment value greater than zero).

The figure and site score presented for this test site are for the purpose of testing the draft subsurface 

intrusion component addition to the HRS. The presented HRS site score and associated figure are not 

intended to justify placement on the NPL and it is likely that additional data collection, evaluation and 

sampling would be necessary to determine if the site would qualify for listing. 

As part of this limited assessment, test site 003 was evaluated using only the draft HRS subsurface 

intrusion component. While additional threats may exist at this site, sufficient data was not provided to 

evaluate the ground water migration pathway, surface water migration pathway, air migration pathway or 

the soil exposure pathway of the 1990 HRS. 

. 
Page D-26

Subsurface Intrusion Test Site 005 (Figure 5) 

Site Diagram
Page D-27

Table 5-11 Ground Water Migration Pathway Scoresheet

Factor Categories and Factors

Maximum

Value

Value

Assigned

Ground Water Migration Pathway 

Likelihood of Release to an Aquifer:

1. Observed Release

Observed release concentrations of cis-1,2-DCE and TCE attributable to the source 

were documented in the interconnected aquifers based on monitoring wells and one 

public supply well (TCE only).

550 550

2. Potential to Release:

Potential to release was not evaluated based on observed exposure per the HRS.

500 - 

2a. Containment 10 - 

2b. Net Precipitation 10 - 

2c. Depth to Aquifer 5 - 

2d. Travel Time 35 - 

2e. Potential to Release [ lines 2a * ( 2b + 2c + 2d ) ] 500 - 

3. Likelihood of Release ( higher of lines 1 and 2e ) 550 550

Waste Characteristics:

Concentrations of TCE, cis-1,2-DCE, and vinyl chloride were documented in the unconfined contaminated soil 

source.

4. Toxicity/Mobility

The highest toxicity/mobility value for the hazardous substances documented in the 

ground water observed release documentation and the contaminated soil source 

documentation is 10,000 for vinyl chloride.

(a) 10,000

5. Hazardous Waste Quantity

The quantity of the contaminated soil source is unknown but greater than zero. 

Because there are no drinking water wells subject to actual contamination and the 

hazardous constituent quantity cannot be adequately determined, a default of 10 may 

be assigned.

(a) 10

6. Waste Characteristics 100 18

Targets: 

7. Nearest Well

The closest drinking water well to the contaminated soil source is a public supply well, 

which is located between 0.5 and 1 mile from the source.

50 9 

8. Population:

8a. Level I Concentrations

No population subject to Level I concentrations was identified. (b) 0 

8b. Level II Concentrations

No population subject to Level II concentrations was identified. (b) 0 
Page D-28

8c. Potential Contamination

One public supply well is located between 0.5 and 1 mile from the contaminated soil 

source and serves a population of 1,141. Two public supply wells are located between 

1 and 2 miles of the contaminated soil source and serve a combined population of 

2,282. Four public supply wells are also located between 1 and 2 miles of the 

contaminated soil source and serve a combined population of 11,000. Five public 

supply wells are located between 2 and 3 miles from the source and serve a combined 

population of 7,000. One public supply well is located between 3 and 4 miles from the 

source and serve a population of 1,400 people. Using HRS Table 3-12 a distanceweighted population value of 4,271 is calculated. 

(b) 427.1

8d. Population ( lines 8a + 8b + 8c ) (b) 427.1

9. Resources

Insufficient information exists to determine a score for resources.

5 0 

10. Wellhead Protection Area

Insufficient information exists to determine a score for a wellhead protection area.

20 0 

11. Targets ( lines 7 + 8d + 9 + 10 ) (b) 436.1

Ground Water Migration Score For An Aquifer:

12. Aquifer Score [ ( lines 3 * 6 * 11 ) / 82,500 ]c 100 52.33

Ground Water Migration Pathway Score:

13. Pathway Score (Sgw),

(highest value from line 12 for all aquifers evaluated)c 100 52.33

a Maximum value applies to waste characteristics category.

b Maximum value not applicable.

c No specific maximum value applies to factor.

d Do not round to nearest integer.
Page D-29

Table 5-11 Subsurface Intrusion Component Scoresheet

Factor Categories and Factors Maximum

Value

Value

Assigned

Subsurface Intrusion Component

Likelihood of Exposure:

1. Observed Exposure

An observed exposure by chemical analysis for TCE was documented in three

regularly occupied structures.

550 550

2. Potential for Exposure

Potential for exposure was not evaluated based on the documentation of an

observed exposure per the HRS.

2a. Structure Containment 10 -

2b. Depth to contamination 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 area of observed exposure is 10,000 for 

vinyl chloride. Per the draft HRS, although vinyl chloride was not found in a 

sample that met observed exposure criteria, as the degradation half-life of Vinyl 

Chloride is greater than100 days, a degradation factor value of one is applied. 

The degradation factor is multiplied by the toxicity factor value to calculate the 

toxicity/degradation factor value of 10,000, which is the highest combined value 

of all eligible substances.

(a) 10,000

6. Hazardous Waste Quantity

The area footprints of the approximately 48 regularly occupied structures in the 

areas of observed exposure and subsurface contamination are unknown. 

Therefore, a value of 1,740 ft2 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 2-6 and 5-18.

(a) 100

7. Waste Characteristics (subject to a maximum of 100)

The toxicity/biodegradation and hazardous waste quantity factor values were 

multiplied to calculate a value of 1x106

, which was used to select a waste 

characteristics factor category value of 32 from HRS Table 2-7. 

100 32

Targets:

8. Exposed Individual

As there is at least one individual present in a regularly occupied structure in the 

AOE that is exposed to Level I contaminant concentrations, a value of 50 is 

assigned.

50 50

9. Population:

9a. Level I Concentrations

The actual population living in the three regularly occupied structures containing 

TCE above the applicable health-based benchmark of 0.43 μg/m3 (Cancer Risk 

Screening Concentration) is unknown; using a county average of 2.62 persons 

(b) 78.60 
Page D-30

per household results in 7.86 people exposed to Level I 

then multiplied by a weighting factor of 10. 

concentrations, which are 

9b. Level II Concentrations

No occupied structures subject to Level II 

this evaluation. 

concentrations was identified as part of (b) 0 

9c. Population within Area(s) of Subsurface Contamination

There is one regularly occupied structure within the ASC that is delineated with a 

subslab sample located within five feet of the structure. There are 29 regularly 

occupied structures within the ASC that are delineated with soil vapor samples 

approximately eight feet bgs (one of these structures includes the commercial

facility with 96 full-time workers and another eight of these structures contain at 

least one full-time worker); additionally, 15 regularly occupied residential 

structures within the ASC that are delineated with ground water samples 

approximately 10 feet bgs (three of these structures contain at least one full-time 

worker). 

Per the draft HRS, where worker population is unknown, it is assumed that at 

least 1 full-time worker per facility is present.

The actual population living in these structures is unknown. Per the draft HRS 

addition, using the borough average of 2.62 persons per household results in a 

population estimate of 1.048 people (based on a subslab sample located within 5 

feet of the structure); 17.4 (10.48+6.93 = 17.4) (based on soil gas samples); and 

3.24 (3.14+0.1 = 3.24) (based on ground water samples). These population 

estimates were multiplied by respective weighting factors of 0.4 (subslab within 5 

feet of an occupied structure),0.2 (soil gas) and 0.1 (ground water) using the draft 

HRS. These three values were then summed to calculate the total population of 

14.67 within an area of subsurface contamination

(b) 21.68

9d. Total Population (lines 9a + 9b + 9c) (b) 100.28

10. Resources

No resources were identified within the established areas of observed exposure 

and subsurface contamination.

5 0 

11. Targets (lines 8 + 9d + 10) (b) 150.28

Subsurface Intrusion Component Score

12. Subsurface Intrusion Component 

maximum of 100)

(lines 4 x 7 x 11)/82,500c (subject to a 100 32.05

Soil Exposure and Subsurface Intrusion Pathway Score

13. Soil Exposure Component

maximum of 100)

+ Subsurface Intrusion Component (subject to a 100 32.05

a

Maximum value applies to waste characteristics category. b

Maximum value not applicable.

c

Do not round to nearest integer. 

HRS Site Score

√[ ( Sgw2 + Ssw2 + Ssessi

2

 + Sa

2 )/4] = √ [(52.332

 + 02 + 32.052 +02 )/4] 100 30.68
Page D-31

Subsurface Intrusion Test Site 006 

(January 2016)

Site Description

Test site 006 is located in north-central Texas within an area of mixed residential, commercial and 

industrial use. Test Site 006 consists of a release of hazardous substances from a facility that historically 

conducted machining and metal forging operations and regularly occupied structures within documented 

areas of observed exposure (AOE) and an area of subsurface contamination (ASC) surrounding the AOE. 

Trichloroethylene (TCE) contamination was first identified at the facility during an environmental 

property assessment in 2002. Additional investigations identified ground water contaminated 

predominantly with TCE underlying the facility and adjacent residential areas. In 2008, the U.S. 

Environmental Protection Agency (EPA) conducted a vapor intrusion sampling event at 18 structures 

overlying the ground water plume, which documented indoor air samples containing levels of TCE and 

tetrachloroethylene (PCE) meeting observed exposure criteria. 

Additionally, based on the available information, sufficient data to evaluate the Hazard Ranking System 

(HRS) air and surface water migration pathways and the soil exposure pathway was not available. 

However, given the presence of contaminated soil and ground water documented at the facility and site 

during previous investigations, the site could be evaluated using the soil exposure and ground water 

migration pathways if additional information became available. 

Scoring Limitations/Assumptions 

Besides the assumptions made for all test sites listed at the beginning of this appendix, the following sitespecific limitations and assumptions were identified for scoring this site:

• It is assumed that the different structure types present in the areas of observed exposure and

subsurface contamination are sufficiently similar to each other for HRS scoring purposes.

• A single indoor air sample collected within an occupied structure outside the AOE and ASC can be

used as a background level to compare against release samples.

• Data obtained from multiple sampling events were used to delineate subsurface contaminant plumes.

Therefore, a minimal approach was used when delineating areas of subsurface contamination based

on the available information. However, it is likely that with additional data the areas of subsurface

contamination could be larger than shown in this evaluation.

• Based on the information available, it was not possible to determine if occupied structures identified

within the areas of observed exposure and subsurface contamination contained multiple tenant spaces.

• All sample locations are approximate and estimated based on figures identifying those sample

locations in relation to streets and industrial facilities.

• It is assumed that all regularly occupied structures within the AOE and ASC have a non-zero

structure containment value.

• Indoor air samples meeting the observed exposure criteria are not due to the presence of potential

indoor sources of vapor-forming chemicals, such as household cleaners, and the significant increase

in hazardous substance levels are attributable at least in part to the release(s) being evaluated.

• Data quality is sufficient for use in testing the draft subsurface intrusion component.

• 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.
Page D-32

• An indoor air temperature of 25 °C and 1 standard atmosphere were assumed when converting indoor

air sampling data provided in units of parts per billion by volume (ppbv) for comparison to healthbased benchmarks (i.e., from ppbv to micrograms per cubic meter [μg/m3

]).

• Per the draft HRS addition, an 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).

• Information used in the scoring of the test sites (including aerial imagery) is representative of current

conditions.

• The contamination evaluated in the site scoring is either from a single release or from commingled

plumes resulting from multiple releases.

• The depths at which the ground water samples were collected is unknown; however, it is assumed that

the wells were screened in the same relative portion of the surficial ground water and are sufficiently

similar to not cause a significant difference in contaminant levels. It is also assumed that the samples

were collected at a distance greater than five feet from a regularly occupied structure’s foundation

when assigning target weightings to ASC populations.

• As data for all identified wells in the site area were not available, with additional data, the area of

subsurface contamination could be larger in size.

The figure and site score presented for this test site are for the purpose of testing the draft subsurface 

intrusion component addition to the HRS. The presented HRS site score and associated figure are not 

intended to justify placement on the National Priorities List (NPL), and it is likely that additional data 

collection, evaluation and sampling would be necessary to determine if the site would qualify for listing. 

As part of this limited assessment, the Test site 002 was evaluated using only the draft HRS subsurface 

intrusion component. While additional threats may exist at this site, sufficient data was not provided to 

evaluate the ground water migration pathway, surface water migration pathway, air migration pathway or 

the soil exposure pathway of the 1990 HRS. 
Page D-33

Subsurface Intrusion Test Site 006 (Figure 6) 

Site Diagram
Page D-34

Table 5-11 Subsurface Intrusion Component Scoresheet

Factor Categories and Factors Maximum

Value

Value

Assigned

Subsurface Intrusion Component

Likelihood of Exposure:

1. Observed Exposure

An observed exposure by chemical analysis for TCE was documented in seven 

regularly occupied structures and for PCE in two regularly occupied structures.

550 550

2. Potential for Exposure

Potential for exposure was not evaluated based on the documentation of an

observed exposure per the HRS.

2a. Structure Containment 10 -

2b. Depth to contamination 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 ASC and/or the 

AOE is 10,000 for vinyl chloride. Per the HRS, although vinyl chloride was not 

found in a sample that met observed exposure criteria, as the degradation halflife of Vinyl Chloride is greater than100 days, a degradation factor value of one is 

applied. The degradation factor is multiplied by the toxicity factor value to 

calculate the toxicity/degradation factor value of 10,000, which is the highest 

combined value of all eligible substances.

(a) 10,000

6. Hazardous Waste Quantity

The actual basal area footprints of the 104 regularly occupied structures in the 

AOE and ASC are unknown. Therefore, as stated in the HRS, a minimum value 

of 1,740 ft2 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 and 2-6.

(a) 10,000

7. Waste Characteristics (subject to a maximum of 100)

The toxicity/biodegradation and hazardous waste quantity factor values were 

multiplied to calculate a value of 1x108

, which was used to select a waste 

characteristics factor category value of 100 from HRS Table 2-7. 

100 100

Targets:

8. Exposed Individual

There is at least one individual in a regularly occupied structure in the AOE that 

is exposed to Level I contaminant concentrations. Per the HRS, a value of 50 is 

assigned.

50 50

9. Population:

9a. Level I Concentrations

The population living in the seven regularly occupied structures containing TCE 

above the applicable health-based benchmark of 0.43 μg/m3 (Cancer Risk 

Screening Concentration) is unknown. Per the HRS, using the county average of 

2.77 persons per household results in a population estimate of 19.39 people 

(b) 193.9 
Page D-35

exposed to Level I 

of 10. 

concentrations, which are then multiplied by a weighting factor 

9b. Level II Concentrations

The population living in the two regularly occupied structures with documented 

exposure to Level II concentrations of PCE and the 14 regularly occupied 

structures inferred to be exposed to contamination is unknown. Per the HRS, 

using the county average of 2.77 persons per household results in a population 

estimate of 44.32 people exposed to Level II concentrations. 

(b) 44.32

9c. Population within Area(s) of Subsurface Contamination

The population living in the 81 regularly occupied residential structures within the 

ASC, is unknown (77 regularly occupied structures and 4 multi-subunit structures 

with at least one full-time worker). Per the draft HRS addition, the total number of 

full-time workers are divided by 3 (4/3 = 1.3) and summed with the population 

residing in the remaining structures. Using the county average of 2.77 persons 

per household results in a population estimate of 214.5 (213.2+1.3 = 214.5)

people in the ASC. As the depths of the ground water samples used to delineate 

the ASC are unknown and assumed to be greater than five feet from all structure 

foundations, this population estimate was multiplied by a weighting factor of 0.1 

using HRS Table 5-20. This results in a population estimate of 21.4. 

(b) 21.4 

9d. Total Population (lines 9a + 9b + 9c) (b) 259.62

10. Resources

One religious facility

assigned.

is located within the ASC. Per the HRS, a value of 5 is 5 5 

11. Targets (lines 8 + 9d + 10) (b) 314.62

Subsurface Intrusion Component Score

12. Subsurface Intrusion Component 

maximum of 100)

(lines 4 x 7 x 11)/82,500c (subject to a 100 100

Soil Exposure and Subsurface Intrusion Pathway Score

13. Soil Exposure Component

maximum of 100)

+ Subsurface Intrusion Component (subject to a 100 100

a

Maximum value applies to waste characteristics category.

b

Maximum value not applicable.

c

Do not round to nearest integer. 

HRS Site Score Maximum 

Value

Value 

Assigned

√[ ( Sgw2 + Ssw2 + Ssessi2 + Sa

2 )/4] = √ 02

 + 02 + 1002 +02 )/4] 100 50
Page D-36

Subsurface Intrusion Test Site 007 

(January 2016)

Site Description

Test site 007 is located in the District of Columbia, within an area of commercial and residential land use 

types and is immediately adjacent to the hospital complex. Dry cleaning operations have reportedly been 

ongoing for approximately 60 years at the facility. These historical operations have resulted in a release of 

chlorinated solvents to shallow ground water and soils immediately surrounding the facility, as has been

documented in several environmental investigations conducted in 2013 and 2014. 

The site includes an area of observed exposure (AOE) delineated by indoor air samples meeting observed 

exposure criteria. The hazardous substances documented to be present in the AOE were 

tetrachloroethylene (PCE), trichloroethylene (TCE) and cis-1,2-dichloroethene among other volatile 

organic compounds (VOCs). The structures within the AOE include one single-tenant occupied structure, 

a daycare facility with an estimated 48 enrolled children and the dry cleaning facility. Although 

subsurface samples meeting observed release criteria are present at the site, an area of subsurface 

contamination (ASC) is not delineated as no additional targets were identified, and its inclusion would not 

alter the subsurface intrusion (SsI) component score.

Scoring Limitations and Assumptions

Besides the assumptions made for all test sites listed at the beginning of this appendix, the following sitespecific limitations and assumptions were identified for scoring this site:

• For sampling events where no appropriate background sample was available, it was assumed that

the background level to compare against release contaminant concentrations was non-detect for

manufactured substances (e.g., PCE). Therefore, per the draft Hazard Ranking System (HRS)

Subsurface Intrusion (SsI) Addition, an observed exposure or observed release was documented

when a release contaminant concentration equaled or exceeded its appropriate reporting limit.

• It is assumed that all regularly occupied structures within the AOE have a non-zero structure

containment value.

• Indoor air samples meeting the observed exposure criteria are not due to anthropogenic sources

(e.g., potential indoor sources of vapor-forming chemicals, such as household cleaners) and the

significant increase in hazardous substance concentrations are attributable at least in part to the

release(s) being evaluated.

• Data quality is sufficient for use in testing the draft subsurface intrusion component.

• Sampling locations presented are approximate and may not represent the actual extent of

contamination at the site.

• The regularly occupied residential structure within the AOE is occupied with the applicable

average number of persons per household for the District of Columbia (based on available U.S.

Census data). At least one full-time employee works at the dry cleaning and daycare facilities

included in the evaluation.

• For the purposes of population scored, the daycare is assumed to be at capacity.
Page D-37

• An indoor air temperature of 25 °C and 1 standard atmosphere were assumed when converting

indoor air sampling data provided in units of parts per billion by volume (ppbv) for comparison to

health-based benchmarks (i.e., from ppbv to micrograms per cubic meter [μg/m3

]).

• An 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).

• Information used in the scoring of the test sites (including aerial imagery) is representative of

current conditions.

• The contamination evaluated in the site scoring is either from a single release or from

commingled plumes resulting from multiple releases.

The figure and site score presented for this test site are for the purpose of testing the draft subsurface 

intrusion component addition to the HRS. The presented HRS site score and associated figure are not 

intended to justify placement on the National Priorities List (NPL) and it is likely that additional data 

collection, evaluation and sampling would be necessary to determine if the site would qualify for listing. 

As part of this limited assessment, test site 007 was evaluated using only the draft HRS subsurface 

intrusion component. While additional threats may exist at this site, sufficient data was not provided to 

evaluate the ground water migration pathway, surface water migration pathway, air migration pathway or 

the soil exposure pathway of the 1990 HRS. 
Page D-38

Subsurface Intrusion Test Site 007 (Figure 7) 

Site Diagram
Page D-39

Table 5-11 Subsurface Intrusion Component Scoresheet

Factor Categories and Factors Maximum

Value

Value 

Assigned

Subsurface Intrusion Component

Likelihood of Exposure:

1. Observed Exposure

An observed exposure by chemical analysis for PCE has been documented in 3 

regularly occupied structures. 

550 550

2. Potential for Exposure

Per the draft HRS addition, the potential for exposure factor was not evaluated 

based on the documentation of an observed exposure.

2a. Structure Containment 10 -

2b. Depth to contamination 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 AOE is 1,000 for 

TCE. 

Per the draft HRS addition, as TCE was found in a sample that met observed 

exposure criteria, a degradation factor value of one is assigned. The toxicity 

factor value is multiplied by the degradation factor value. The 

toxicity/degradation factor value of 1,000, which is the highest combined value of 

all eligible substances, is assigned.

(a) 1,000

6. Hazardous Waste Quantity

The actual basal area footprints of the three regularly occupied structures in the 

AOE are unknown. Per the draft HRS addition, for Tier D, Area, a value of 1,740

ft2 per regularly occupied structure was used in calculating a hazardous waste 

quantity. These values were used to select a hazardous waste quantity factor 

value using HRS Tables 5-18 (draft addition) 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 1x105 was used to select a waste 

characteristics factor category value of 18 using HRS Table 2-7. 

100 18
Page D-40

Factor Categories and Factors Maximum

Value 

Value

Assigned

Targets:

8. Exposed Individual

There is at least one individual present in a regularly occupied structure in the 

AOE that is exposed to Level I contaminant concentrations. Per the draft HRS

addition, a value of 50 was assigned.

50 50

9. Population:

9a. Level I Concentrations

There are a reported total of 48 children attending the daycare facility, which 

contains concentrations above the applicable health-based benchmark of 9.3 

μg/m3 (Cancer Risk Screening Concentration) for PCE. There are two 

workplaces located within the AOE. The actual number of employees associated 

with these workplaces is unknown. Therefore, a minimum of one full-time worker 

per workplace is assumed to be present for estimation purposes. Per the draft 

HRS addition the total number of full-time workers are divided by 3 (2/3=0.6) and 

summed with the population estimate. Additionally, the actual population living in 

the one regularly occupied structure with documented exposure to Level I 

concentrations of PCE is unknown. Per the draft HRS addition, using the 

Washington, D.C. average of 2.2 persons per household results in a total 

population estimate of 50.8 people exposed to Level I concentrations which was

then multiplied by a weighting factor of 10. 

(b) 508.0

9b. Level II Concentrations

No population subject to Level II contaminant concentrations was identified as 

part of this evaluation.

(b) 0 

9c. Population within Area(s) of Subsurface Contamination

No ASC was established as part of this evaluation. (b) 0 

9d. Total Population (lines 9a + 9b + 9c) (b) 508.0

10. Resources

No resources were identified within the AOE or ASC. Per the draft HRS addition, 

a value of 0 is assigned. 

5 0 

11. Targets (lines 8 + 9d + 10) (b) 558.0

Subsurface Intrusion Component Score

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

maximum of 100) 100 66.96

Soil Exposure and Subsurface Intrusion Pathway Score

13. Soil Exposure Component + Subsurface Intrusion Component (subject to a

maximum of 100) 100 66.96

a

Maximum value applies to waste characteristics category.

b

Maximum value not applicable.
Page D-41

c

Do not round to nearest integer. 

HRS Site Score Maximum

Value 

Value 

Assigned

√[ ( Sgw2 + Ssw2 + Ssessi

2

 + Sa

2 )/4] = √ [(02

 + 02 + 66.962 +02 )/4] 100 33.48
Page D-42

Subsurface Intrusion Test Site 008

(January 2016)

Site Description

Test site 008 is located in south-central Montana within an area of residential and commercial land use 

types. Historical releases possibly associated with two nearby dry cleaning operations have resulted in a 

release of chlorinated solvents to ground water in the area; the plume encompasses about 140 acres (1,000 

ft wide by 8,000 ft long). State-lead preliminary assessments (PA), site inspections (SI) and expanded site 

inspections (ESI) were conducted at this site in Montana from 1993 to 2002 under the direction of the 

U.S. Environmental Protection Agency (EPA) Removal program since 2006. 

The site includes an area of observed exposure (AOE) delineated by indoor air samples meeting observed 

exposure criteria. The hazardous substances documented to be present in the AOE were 

tetrachloroethylene (PCE), trichloroethylene (TCE), 1,2-dichloroethane (1,2-DCA) and methylene 

chloride. The structures within the AOE include approximately 221 regularly occupied structures. 

Although, the site includes a large, well documented ground water plume that exceeds the boundaries of 

the established area of exposure, No area of subsurface contamination (ASC) was established as part of 

this evaluation and no population subject to potential contamination was identified as part of this 

evaluation. 

Scoring Limitations and Assumptions

• It is assumed that all regularly occupied structures within the AOE have a non-zero structure

containment value.

• Indoor air samples meeting the observed exposure criteria are not due to anthropogenic sources

(e.g., potential indoor sources of vapor-forming chemicals, such as household cleaners) and the

significant increase in hazardous substance concentrations are attributable at least in part to the

release(s) being evaluated.

• Data quality is sufficient for use in testing the draft subsurface intrusion component.

• Sampling locations presented are approximate and may not represent the actual extent of

contamination at the site.

• Available U.S. Census data is used to determine average number of persons per household

residential targets in the AOE. Worker population data is assumed to be at least 1 full-time

worker per workplace if more specific information is not available.

• An indoor air temperature of 25 °C and 1 standard atmosphere were assumed when converting

indoor air sampling data provided in units of parts per billion by volume (ppbv) for comparison to

health-based benchmarks (i.e., from ppbv to micrograms per cubic meter [μg/m3

]).

• An 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).

• Information used in the scoring of the test sites (including aerial imagery) is representative of

current conditions.

• The contamination evaluated in the site scoring is either from a single release or from

commingled plumes resulting from multiple releases.
Page D-43

• It is assumed that all ground water sampling data used in this analysis, including samples

collected at the water table and from ten feet below the water table, represent a single surficial

ground water layer.

• Each structure identified was considered as a single occupied structure. Many of these structures

might include apartments or duplex units, but for the purpose of this evaluation each structure

was only evaluated as one occupied structure. (Garage structures were not counted as part of this

evaluation even though some of them may contain apartments).

• Although some reports indicate the presence of vapor mitigation systems, it is assumed that

cracks and/or preferential pathways into a structure still exist and that all structures have a

containment value greater than zero.

• For indoor air samples, no unqualified background data were available. A qualified background

sample result was used, and the EPA November 1996 Factsheet Using Qualified Data to

Document an Observed Release and Observed Contamination (EPA 540-F-94-028) was

employed; an adjustment factor of 10 was applied to the qualified background result prior to its

use in setting observed exposure criteria.

The figure and site score presented for this test site are for the purpose of testing the draft subsurface 

intrusion component addition to the Hazard Ranking System (HRS). The presented HRS site score and 

associated figure are not intended to justify placement on the National Priorities List (NPL) and it is likely 

that additional data collection, evaluation and sampling would be necessary to determine if the site would 

qualify for listing.

As part of this limited assessment, test site 008 was evaluated using only the draft HRS subsurface 

intrusion component. While additional threats may exist at this site, sufficient data was not provided to 

evaluate the ground water migration pathway, surface water migration pathway, air migration pathway or 

the soil exposure pathway of the 1990 HRS. 
Page D-44

Subsurface Intrusion Test Site 008 (Figure 8) 

Site Diagram
Page D-45

Table 5-11 Subsurface Intrusion Component Scoresheet

Factor Categories and Factors Maximum

Value

Value 

Assigned

Subsurface Intrusion Component

Likelihood of Exposure:

1. Observed Exposure

An observed exposure by chemical analysis for PCE, TCE, 1,2-DCA and 

Methylene Chloride was documented in approximately 71 regularly occupied 

structures. 

550 550

2. Potential for Exposure

Potential for exposure was not evaluated based on the documentation of an

observed exposure per the HRS.

2a. Structure Containment 10 -

2b. Depth to contamination 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 

observed exposure is 1,000 for TCE. Per the draft HRS addition, as TCE has 

been documented in an observed exposure, a degradation factor value of one is 

applied. The degradation factor is multiplied by the toxicity factor value to 

calculate the toxicity/degradation factor value of 1,000, which is the highest 

combined value of all eligible substances.

(a) 1,000

6. Hazardous Waste Quantity

Approximately 228 Residential Structures and 7 businesses in the AOE have 

been identified based on a review of aerial images. Although several of the 

regularly occupied structures may include multi-subunit structures (e.g., separate 

basement apartments), for the purpose of scoring this site using the proposed 

subsurface intrusion component, each unique structure has been counted only a 

single time in determining the hazardous waste quantity factor value. The actual 

basal footprint area of the 235 regularly occupied structures in the AOE is 

unknown. Per the draft HRS addition, for Tier D, Area, a value of 1,740 ft2 per 

regularly occupied structure was used in calculating a hazardous waste quantity. 

These values were used to select a hazardous waste quantity factor value using 

HRS Tables 5-18 (draft addition) and 2-6.

(a) 10,000

7. Waste Characteristics (subject to a maximum of 100)

The toxicity/degradation and hazardous waste quantity factor values were

100 56
Page D-46

multiplied to calculate a value of 1x106, which was used to select a waste 

characteristics factor category value of 32 from HRS Table 2-7. 

Targets:

8. Exposed Individual

As there is at least one individual present in a regularly occupied structure in the 

AOE that is exposed to Level I contaminant concentrations for TCE. Per the draft 

HRS addition, a value of 50 is assigned.

50 50

9. Population:

9a. Level I Concentrations

The actual population living in the 26 regularly occupied structures containing 

concentrations above the applicable health-based benchmark of 9.3 μg/m3 

(Cancer Risk Screening Concentration) for PCE is unknown. There are 

approximately 7 apparent businesses located within the AOE. The actual number 

of employees associated with these workplaces is unknown. However, a 

minimum of one full-time worker per workplace is assumed to be present. Per the 

draft HRS addition the total number of full-time workers are divided by 7 (7/3=2.3) 

and summed with the population estimate. Per the draft HRS addition, using the

county average of 2.40 persons per household results in a total population 

estimate of 62.40 people exposed to Level I concentrations. This value is then 

multiplied by a weighting factor of 10, per the draft HRS addition. 

(b) 647.0

9b. Level II Concentrations

The actual population living in the 195 (11 documented occupied structures and 

184 inferred contamination) regularly occupied structures in the AOE containing 

concentrations below the applicable health-based benchmark of 9.3 μg/m3 

(Cancer Risk Screening Concentration) for PCE or with inferred Level II 

contamination is unknown. Per the draft HRS addition, using the county average 

of 2.40 persons per household results in a total population estimate of 484.8 

people exposed to Level II concentrations. 

(b) 468.0

9c. Population within Area(s) of Subsurface Contamination

Although, the site includes a large, well documented ground water plume that 

exceeds the boundaries of the established area of exposure, No ASC was 

established as part of this evaluation and no population subject to potential 

contamination was identified as part of this evaluation.

(b) NS

9d. Total Population (lines 9a + 9b + 9c) (b) 1115.0

10. Resources

No resources were identified within the AOE. Per the draft HRS addition, a value 

of 0 is assigned.

5 0 

11. Targets (lines 8 + 9d + 10) (b) 1165.0

Subsurface Intrusion Component Score

12. Subsurface Intrusion Component (lines 4 x 7 x 11)/82,500d (subject to a

maximum of 100) 100 100
Page D-47

Soil Exposure and Subsurface Intrusion Pathway Score

13. Soil Exposure Component

maximum of 100)

+ Subsurface Intrusion Component (subject to a 100 100

a

Maximum value applies to waste characteristics category.

b

Maximum value not applicable.

c

No specific maximum value applies to factor.

d

Do not round to nearest integer. 

HRS Site Score

√[ ( Sgw2 + Ssw2 + Ssessi

2

 + Sa

2 )/4] = √ [(02

 + 02 + 1002 +02 )/4] 100 50
Page D-48

Subsurface Intrusion Test Site 009 

(January 2016)

Site Description

Test site 009 is located in south central Wisconsin within an area of commercial, industrial and residential 

land use types. It consists of an area of observed exposure (AOE) delineated by indoor air samples 

meeting observed exposure criteria and an area of subsurface contamination (ASC) delineated by samples 

from multiple media meeting observed release criteria. Among the hazardous substances documented to 

be present in the AOE and ASC were tetrachloroethylene (PCE), trichloroethylene (TCE), vinyl chloride 

and cis-1,2-dichloroethene. 

The areas within the AOE and ASC include multiple regularly occupied structures and one industrial 

facility. Manufacturing-related activities have occurred on the industrial property since 1902, which is 

currently operated as a metal die casting facility. Environmental investigations of the industrial facility 

and the surrounding area have identified PCE contamination in shallow ground water, potentially 

originating from a former aboveground storage tank and two historic vapor degreasers which used PCE as 

a solvent. Remediation efforts in the area have included soil remediation (e.g., a soil vapor extraction 

system), installation of an ozone sparge system to remediate ground water and the installation of multiple

vapor mitigation systems in nearby occupied structures. 

Scoring Limitations and Assumptions

Besides the assumptions made for all test sites listed at the beginning of this appendix, the following sitespecific limitations and assumptions were identified for scoring this site:

• 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 fulltime worker per workplace if more specific information is not available.

• The depths at which the subslab samples used in the evaluation were collected are unknown. It

was assumed for evaluation purposes that they were located within a distance less than or equal to

five feet from a structure’s foundation.

• For sampling events where no appropriate background sample was available, it was assumed that

the background level to compare against release contaminant concentrations was non-detect for

manufactured substances (e.g., PCE). Therefore, per the draft HRS addition, an observed

exposure or observed release was documented when a release contaminant concentration equaled

or exceeded its appropriate reporting limit.

• Although vapor mitigation systems are present in some occupied structures, it is assumed that

these systems are not a permanent remedy and that all regularly occupied structures within the

AOE and ASC have a non-zero structure containment value.

• It is assumed that area remediation projects have not completely removed or remediated the

subsurface contamination.

• An 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).

• Per the draft Hazard Ranking System (HRS) addition, a ceiling height of 8 feet was assumed in

determining a waste quantity estimate for the industrial facility.
Page D-49

The figure and site score presented for this test site are for the purpose of testing the draft subsurface 

intrusion component addition to the HRS. The presented HRS site score and associated figure are not 

intended to justify placement on the National Priorities List (NPL) and it is likely that additional data 

collection, evaluation and sampling would be necessary to determine if the site would qualify for listing. 

As part of this limited assessment, Test site 009 was evaluated using only the draft HRS subsurface 

intrusion component. While additional threats may exist at this site, sufficient data was not provided to 

evaluate the ground water migration pathway, surface water migration pathway, air migration pathway or 

the soil exposure pathway of the 1990 HRS. For example, although multiple municipal wells are present

in the vicinity, such information as the numbers of people served by these wells or sampling data 

describing their condition were not available. Additionally, no sensitive species or habitat systems, 

including wetlands, were identified in the site’s vicinity. 
Page D-50

Subsurface Intrusion Test Site 009 (Figure 9) 

Site Diagram
Page D-51

Table 5-11 Subsurface Intrusion Component Scoresheet

Factor Categories and Factors Maximum

Value

Value 

Assigned

Subsurface Intrusion Component

Likelihood of Exposure:

1. Observed Exposure

An observed exposure by chemical analysis for PCE has been documented in 

18 regularly occupied structures.

550 550

2. Potential for Exposure

Per the draft HRS addition, the potential for exposure factor was not evaluated 

based on the documentation of an observed exposure.

2a. Structure Containment 10 -

2b. Depth to contamination 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 AOE and/or 

ASC is 10,000 for vinyl chloride. 

Per the draft HRS addition, as vinyl chloride was not found in a sample that met 

observed exposure criteria, as the depth to contamination below an area of 

subsurface contamination is less than 10 feet, a degradation factor value of one 

is assigned. The toxicity factor value is multiplied by the degradation factor value 

to calculate the toxicity/degradation factor value of 10,000, which is the highest 

combined value of all eligible substances.

(a) 10,000

6. Hazardous Waste Quantity

The actual basal area footprints of the 74 regularly occupied structures in the 

AOE and ASC are unknown. Per the draft HRS addition, a value of 1,740 ft2 per 

regularly occupied structure was used in calculating a hazardous waste quantity. 

The one industrial facility identified in the AOE and ASC has been identified as 

being 130,000 ft2 in size. Per the draft HRS addition, an assumed ceiling height 

of 8 feet and the known size of 130,000 ft2, was used to calculate a volume for 

the industrial building. These values were used to select a hazardous waste 

quantity factor value using HRS Tables 5-18 (draft addition) and 2-6.

(a) 10,000
Page D-52

Factor Categories and Factors Maximum

Value 

Value

Assigned

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 1x108 was used to select a waste 

characteristics factor category value of 100 from the draft HRS addition Table 2-

7. 

100 100

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 

addition, a value of 45 was assigned.

50 45

9. Population:

9a. Level I Concentrations

No population subject to Level I contaminant concentrations was identified as 

part of this evaluation.

(b) 0 

9b. Level II Concentrations

The actual population living in the 42 (19 with documented exposure to Level II 

concentrations of PCE and the 23 with inferred contamination) regularly 

occupied structures in the AOE containing concentrations below the applicable 

health-based benchmark of 9.3 μg/m3 (Cancer Risk Screening Concentration) for 

PCE or with inferred Level II contamination is unknown. There is one workplace

located within the AOE. The nature and number of employees associated with 

this workplace is unknown. Therefore, a minimum of one full-time worker is 

assumed to be present. Per the draft HRS addition the total number of full-time 

workers are divided by 3 (1/3=0.3) and summed with the population estimate. 

Per the draft HRS addition, using the county average of 2.33 persons per 

household results in a population estimate of 98.19 (97.86+0.3=98.19) people 

exposed to Level II concentrations.

(b) 98.19

9c. Population within Area(s) of Subsurface Contamination

The actual population living in the 32 regularly occupied structures within the 

ASC is unknown. Per the draft HRS addition, for the 13 regularly occupied 

structures with subslab samples meeting HRS observed release criteria, using 

the county average of 2.33 persons per household results in a population 

estimate of 30.29 people. This population estimate was then multiplied by a 

weighting factor of 0.4 using the draft HRS addition Table 5-20. For the 19 

regularly occupied structures where contamination is inferred to be present 

based on surrounding samples meeting HRS observed criteria, using the county 

average of 2.33 persons per household results in a population estimate of 44.27. 

This population estimate was then multiplied by a weighting factor of 0.2 using 

the draft HRS addition Table 5-20. Per the draft HRS addition, the weighted 

population values are summed, resulting in a factor value of 20.97. 

(b) 20.97

9d. Total Population (lines 9a + 9b + 9c) (b) 119.16
Page D-53

Factor Categories and Factors Maximum

Value 

Value

Assigned

10. Resources

No resources were identified 

a value of 0 is assigned. 

within the AOE or ASC. Per the draft HRS addition, 5 0 

11. Targets (lines 8 + 9d + 10) (b) 164.16

Subsurface Intrusion Component Score

12. Subsurface Intrusion Component 

maximum of 100)

(lines 4 x 7 x 11)/82,500c (subject to a 100 100

Soil Exposure and Subsurface Intrusion Pathway Score

13. Soil Exposure Component

maximum of 100)

+ Subsurface Intrusion Component (subject to a 100 100

a

Maximum value applies to waste characteristics category.

b

Maximum value not applicable.

c

Do not round to nearest integer. 

HRS Site Score Maximum

Value

Value 

Assigned

2 √[ ( Sgw + 2 Ssw + 2 Ssessi + Sa

2 )/4] = √ [(02 + 02 + 1002

 +02 )/4] 100 50.00
Subsurface Intrusion Test Site 010

(January 2016)

Site Description

Test site 010 is located in eastern Missouri within an area of occupied structures. The U.S. Environmental 

Protection Agency discovered a ground water plume in a neighborhood and delineated the extent over 

multiple sampling events beginning in the summer of 1998. Two hazardous waste facilities are known to 

exist in the immediate vicinity of the ground water plume, including a former metal shaping facility and a 

life insurance facility where small scale dumping historically occurred in the mid 1960’s. The ground 

water plume consists of chlorinated solvents (TCE, PCE, CIS-1,2-DCE, Vinyl Chloride) and underlies a 

neighborhood consisting of a mix of regularly occupied structures and several single-story, multi-subunit 

structures. Indoor air sampling has identified volatile organic compounds (VOCs) within the living space 

of numerous structures, including several contaminant concentrations exceeding cancer/non-cancer 

benchmarks. In addition, subslab sampling has been conducted and elevated concentrations have been 

documented to be underlying several of structures. 

The site includes an area of observed exposure (AOE) delineated by indoor air samples meeting observed 

exposure criteria. The hazardous substances documented to be present in the AOE were TCE, PCE and 

CIS-1,2-DCE. The structures within the AOE include 29 occupied structures. The site additionally 

includes an area of subsurface contamination (ASC) delineated by subslab samples meeting observed 

release criteria. The structures within the ASC include 9 occupied structures. 

Scoring Limitations and Assumptions

Besides the assumptions made for all test sites listed at the beginning of this appendix, the following sitespecific limitations and assumptions were made in the scoring of this site:

• It is assumed that all regularly occupied structures within the AOE and ASC have a non-zero

structure containment value.

• Indoor air samples meeting the observed exposure criteria are not due to anthropogenic sources

(e.g., potential indoor sources of vapor-forming chemicals, such as household cleaners) and the

significant increase in hazardous substance concentrations are attributable at least in part to the

release(s) being evaluated.

• Data quality is sufficient for use in testing the draft subsurface intrusion component.

• Sampling locations presented are approximate and may not represent the actual extent of

contamination at the site.

• 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 fulltime worker per workplace if more specific information is not available.

• An 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).

• Information used in the scoring of the test sites (including aerial imagery) is representative of

current conditions.

Page D-54
• The contamination evaluated in the site scoring is either from a single release or from

commingled plumes resulting from multiple releases.

• It is assumed that all ground water sampling data used in this analysis, including samples

collected at the water table and from ten feet below the water table, represent a single surficial

ground water layer.

• Aerial imagery, obtained through the maps.google.com online database was used to identify

occupied structures for the purposes of this analysis. These images are assumed to represent

current conditions and that all residences are occupied. In several instances, structures were

classified as duplex units based on these images and this information has not been validated. It is

also assumed that each structure and/or duplex unit identified is currently occupied.

• Although some reports indicate the presence of vapor mitigation systems, it is assumed that

cracks and/or preferential pathways into a structure still exist and that all structures have a

containment value greater than zero.

The figure and site score presented for this test site are for the purpose of testing the draft subsurface 

intrusion component addition to the Hazard Ranking System (HRS). The presented HRS site score and 

associated figure are not intended to justify placement on the National Priorities List (NPL) and it is likely 

that additional data collection, evaluation and sampling would be necessary to determine if the site would 

qualify for listing.

As part of this limited assessment, test site 010 was evaluated using only the draft HRS subsurface 

intrusion component. While additional threats may exist at this site, sufficient data was not provided to 

evaluate the ground water migration pathway, surface water migration pathway, air migration pathway or 

the soil exposure pathway of the 1990 HRS. 

Page D-55
Subsurface Intrusion Test Site 010 (Figure 10) 

Site Diagram

Page D-56
Table 5-11 Subsurface Intrusion Component Scoresheet

Factor Categories and Factors Maximum

Value

Value 

Assigned

Subsurface Intrusion Component

Likelihood of Exposure:

1. Observed Exposure

An observed exposure by 

structures. 

chemical analysis was documented in 24 regularly occupied 550 550

2. Potential for Exposure

Potential for exposure was 

exposure per the HRS.

not evaluated based on the documentation of an observed 

2a. Structure Containment 10 - 

2b. Depth to contamination 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 area of observed exposure is 10,000 for vinyl chloride. Per the 

HRS, as the degradation half-life of vinyl chloride is greater than 100 days, a 

degradation factor value of one is applied. The degradation factor value is multiplied by 

the toxicity factor value to calculate the toxicity/degradation factor value of 10,000, 

which is the highest combined value of all eligible substances.

(a) 10,000

6. Hazardous Waste Quantity

The area footprints of the 38 regularly occupied structures in the areas of observed 

exposure and subsurface contamination are unknown. Therefore, a value of 1,740 ft2

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 

6 and 5-18.

2-

(a) 100

7. Waste Characteristics (subject to a maximum of 100)

The toxicity/degradation and hazardous waste quantity factor values were multiplied to 

calculate a value of 1x106

, which was used to select a waste characteristics factor 

category value of 100 from HRS Table 2-7. 

100 32

Targets:

8. Exposed Individual

As there is at least one individual in the area of observed exposure

Level I contaminant concentrations, a value of 50 is assigned.

that is exposed to 50 50

Page D-57
9. Population:

9a. Level I Concentrations

The population living in the 19 regularly occupied structures containing TCE and/or PCE 

above the applicable health-based benchmark of 0.43 and/or 9.3 μg/m3 respectively is

unknown; using a county average of 2.43 persons per household results in 46.17 people 

exposed to Level I concentrations, which are then multiplied by a weighting factor of 10. 

(b) 461.7

9b. Level II Concentrations

The population living in the 5 regularly occupied structures with documented exposure to 

Level II concentrations of PCE and/or TCE and the 5 regularly occupied structures 

inferred to be exposed to contamination is unknown; using a county average of 2.43 

persons per household results in 24.3 people exposed to Level II concentrations. 

(b) 24.3 

9c. Population within Area(s) of Subsurface Contamination

The 6 regularly occupied structures with documented subslab contamination meeting 

observed release criteria for PCE, TCE and/or Vinyl Chloride are assigned a weighting 

factor of 0.4 using HRS Table 5-20. The 3 regularly occupied structures inferred to be 

overlying a subsurface soil gas plume based on their location within the area of 

subsurface contamination are assigned a weighting factor of 0.2 using HRS Table 5-20.

The 9 structures within the area of subsurface contamination were multiplied by a county

average of 2.43 persons per household and their appropriate weighting factor to 

calculate a value of 7.26. 

(b) 7.29 

9d. Total Population (lines 9a + 9b + 9c) (b) 493.29

10. Resources

No resources were identified within the established areas of observed exposure and 

subsurface contamination.

5 0 

11. Targets (lines 8 + 9d + 10) (b) 543.29

Subsurface Intrusion Component Score

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

of 100) 100 100

Soil Exposure and Subsurface Intrusion Pathway Score

13. Soil Exposure Component + Subsurface Intrusion Component (subject to a

maximum of 100) 100 100

a

Maximum value applies to waste characteristics category. b

Maximum value not applicable.

c

No specific maximum value applies to factor.

d

Do not round to nearest integer. 

HRS Site Score

2 2 2 02 √[ ( Sgw + Ssw + Ssessi + Sa

2 )/4] = √ + 02

 + 1002 +02 )/4] 100 50

Page D-58
Page D-59

Subsurface Intrusion Test Site 011 

(January 2016)

Site Description

Test site 011 is located southwest of Minneapolis, Minnesota within a primarily residential neighborhood. 

It consists of an area of observed exposure (AOE) delineated by indoor air samples meeting observed 

exposure criteria and an area of subsurface contamination (ASC) delineated by sub-slab samples meeting 

observed release criteria. The hazardous substance trichloroethylene (TCE) was documented to be present 

in the ASC. 

In 2009, the Minnesota Pollution Control Agency (MPCA) conducted an investigation to identify 

potential sources for a large contaminant ground water plume. Part of one study area, Area A, was

documented to have elevated concentrations of chlorinated solvents in ground water surrounding an 

occupied structure. Although this residential area with elevated contaminant ground water concentrations 

was determined not to be a likely source of the contamination, subsequent soil gas and indoor air 

sampling events detected contaminants within 11 of the surrounding structures that were sampled.

Sufficient information to identify the originating source of contamination for this area is not available. 

Extensive sampling within the region has identified a larger subsurface contaminant plume; however, for 

purposes of this analysis, the AOE and ASC were limited to the areas surrounding the property since it is 

not apparent that the larger subsurface contaminant plume is continuous and associated with the release(s) 

being scored. 

Scoring Limitations and Assumptions

Besides the assumptions made for all test sites listed at the beginning of this appendix, the following sitespecific limitations and assumptions were identified for scoring this site:

• Indoor air samples meeting the observed exposure criteria are not due to anthropogenic sources (e.g.,

potential indoor sources of vapor-forming chemicals, such as household cleaners) and the significant

increase in hazardous substance concentrations are attributable at least in part to the release(s) being

evaluated.

• Indoor air samples with concentrations exceeding residential indoor air screening levels are assumed

to meet Hazard Ranking System (HRS) observed exposure criteria and are sufficient to identify Level

I contamination.

• Data quality is sufficient for use in testing the draft subsurface intrusion component.

• Observed release/exposure samples and background samples are of sufficient similarity as to not

cause the significant difference in contaminant levels observed.

• Selected background sample locations and sample concentrations accurately represent background

levels of the released substances.

• Sample locations presented are approximate and may not represent the actual extent of contamination

at the site.

• Information used in the scoring of the test sites (including aerial imagery) is representative of current

conditions.
Page D-60

• 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. The

contamination evaluated in the site scoring is either from a single release or from commingled plumes

resulting from multiple releases.

• It is assumed that all regularly occupied structures within the AOE and the ASC have a non-zero

structure containment value.

The figure and site score presented for this test site are for the purpose of testing the draft subsurface 

intrusion component addition to the HRS. The presented HRS site score and associated figure are not 

intended to justify placement on the National Priorities List (NPL) and it is likely that additional data 

collection, evaluation and sampling would be necessary to determine if the site would qualify for listing. 

As part of this limited assessment, test site 011 was evaluated using only the draft HRS subsurface 

intrusion component. While additional threats may exist at this site, sufficient data was not provided to 

evaluate the ground water migration pathway, surface water migration pathway, air migration pathway or 

the soil exposure pathway of the 1990 HRS. 
Page D-61

Subsurface Intrusion Test Site 011 (Figure 11) 

Site Diagram
Page D-62

Table 5-11 Subsurface Intrusion Component Scoresheet

Factor Categories and Factors Maximum

Value

Value 

Assigned

Subsurface Intrusion Component

Likelihood of Exposure:

1. Observed Exposure

An observed exposure by chemical analysis 

regularly occupied structures. 

has been documented in 11 550 550

2. Potential for Exposure

Per the draft HRS addition, the potential for exposure factor 

based on the documentation of an observed exposure.

was not evaluated 

2a. Structure Containment 10 -

2b. Depth to contamination 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 an ASC or the area 

of observed exposure (AOE) is 1,000 for TCE. Per the draft HRS, although TCE 

was not found in a sample that met observed exposure criteria, as the depth to 

contamination below an area of subsurface contamination is less than 10 feet, a 

degradation factor of one is applied. The degradation factor is multiplied by the 

toxicity factor value to calculate the toxicity/degradation factor value of 1,000, 

which is the highest combined value of all eligible substances.

(a) 1,000

6. Hazardous Waste Quantity

Seventy-two regularly occupied structures have been identified in the AOE and 

ASC, including one church with a minimum area of 11,700 ft2

. The actual basal 

footprint area of each regularly occupied structure is unknown. Per the draft HRS 

addition, a value of 1,740 ft2 per regularly occupied regularly occupied structure

and a conservative value of 11,700 ft2 was applied to the church to calculate a 

hazardous waste quantity, which was used to select a hazardous waste quantity 

factor value using HRS Tables 5-18 (draft addition) and 2-6.

(a) 10,000

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 1x107 was used to select a waste 

characteristics factor category value of 56 from draft HRS addition Table 2-7. 

100 56

Targets:
Page D-63

Factor Categories and Factors Maximum

Value 

Value

Assigned

8. Exposed Individual

There is at least one individual present in a regularly occupied structure in the 

AOE that is exposed to Level I contaminant concentrations. Per the draft HRS 

addition, a value of 50 was assigned.

50 50

9. Population:

 9a. Level I Concentrations

The actual population living in the 11 regularly occupied structures with 

documented exposure to Level I concentrations is unknown. Per the draft HRS 

addition, using the county average of 2.38 persons per household results in a 

population estimate of 26.18 people exposed to Level I concentrations. This 

value is then multiplied by a weighting factor of 10 per the draft HRS addition. 

(b) 261.8 

 9b. Level II Concentrations

The actual population living in the 11 regularly occupied structures inferred to be 

exposed to Level II contamination is unknown. Per the draft HRS addition, using 

the county average of 2.38 persons per household results in a population 

estimate of 26.18 people exposed to Level II concentrations.

(b) 26.18

9c. Population within Area(s) of Subsurface Contamination

The actual population living in the 49 regularly occupied structures within the 

ASC is unknown. Per the draft HRS addition, for the 20 regularly occupied 

structures with subslab samples meeting HRS observed release criteria, using 

the county average of 2.38 persons per household results in a population 

estimate of 47.6 people. This population estimate was then multiplied by a 

weighting factor of 0.4 using the draft HRS addition Table 5-20 to get a value of 

19.04. 

For the 29 regularly occupied structures where contamination is inferred to be 

present based on surrounding samples meeting HRS observed criteria, using the 

county average of 2.38 persons per household results in a population estimate of 

69.02. There is one workplace located within the ASC. The nature and number 

of employees associated with this workplace is unknown. Therefore, a minimum 

of one full-time worker is assumed to be present. Per the draft HRS addition the 

total number of full-time workers are divided by 3 (1/3=0.3) and summed with the 

population estimate (69.02+0.3=69.32). This population estimate was then 

multiplied by a weighting factor of 0.2 using the draft HRS addition Table 5-20 to 

get a value of 13.86. 

(b) 32.90

The weighted population values are summed, resulting in a factor value of 32.90.

 9d. Total Population (lines 9a + 9b + 9c) (b) 321.5 

10. Resources

A church was identified within the ASC. 

is assigned.

Per the draft HRS addition, a value of 5 5 5 

11. Targets (lines 8 + 9d + 10) (b) 376.5
Page D-64

Factor Categories and Factors Maximum

Value 

Value

Assigned

Subsurface Intrusion Component Score

12. Subsurface Intrusion Component (lines 4 x 7 x 

maximum of 100)

11)/82,500c (subject to a 100 100

Soil Exposure and Subsurface Intrusion Pathway Score

13. Soil Exposure Component + Subsurface Intrusion Component (subject to a

maximum of 100) 100 100

a

Maximum value applies to waste characteristics category.

b

Maximum value not applicable.

c

Do not round to nearest integer.

HRS Site Score Maximum

Value 

Value 

Assigned

2 √[ ( Sgw 2 + Ssw 2 + Ssessi + Sa2 )/4] = √ [(02

 + 02 + 1002 +02 )/4] 100 50.00