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


# Appendix C : Conceptual Site Modeling

Tabl e C-1: Initial Conceptual Site Scenario Evaluation

Table C-2: Sample HRS Site Scores Based on Potential Exposures Only and Actual Hazardous Waste Quantity Values

Table C-3: Sample HRS Site Scores Based on Potential Exposures Only and Minimum Hazardous Waste Quant ity Values

Table C-4: Sample HRS Site Scores Based on Potential Exposures Only with Consideration of Subslab Sampling Data

Table C-5: Sample HRS Site Scores Based on Different Population Densities and Actual and Potential Exposures

Table C-6: Sample HRS Site Scores Based on a Combination of the Ground Water Migration Pathway and the Subsurface Intrusion Component of the Soil Exposure and Subsurface Intrusion Pathway

Table C-7a: Proposed Conceptual Site Scenario Evaluation

Table C-7b: Sample HRS Site Sc ore s Based o n P otential E xposures Only with C

onsideration o

f D ifferent Population Densities and Varying Types of Ss I S ampling D ata

Tabl e C- 7c: Sample HRS Site Scores Based on Different Population Densities, a Mix of Actual and Potential Exposures and Differen t Types of SsI Sampling Data

Table C-7d: Minimum Populations Needed to Achieve an HRS Site Score of 28.50 with Different Likelihood of Exposure, Waste Characteristics and Different Types of SsI Samples

Table C- 7e: Minimum Actually Exposed Population Needed to Achieve an HRS Site Score of 28.50 Based on Varying Waste Characteristic Factor Values

Table C- 7f: Minimum Potentially Exposed Population Needed to Achieve an HRS Site Score of 28.50 Based on Varying Waste Characteristic Factor Values

Table C-7g: Minim um Population Needed to Achieve an HRS Site Score of 28.50 Based on

Varying Likelihood of Exposure and Waste Characteristics Factor Values and no ASC

T

able C- 7h: Minimum Populations needed Based on a Combination of the Evaluation of a Second HRS Pathway and the Subsurface Intrusion Component of the Soil Exposure and Subsurface Intrusion Pathway

Table C- 7i: Minimum Residents and Wo rke rs N

eeded to A chieve a n H

RS S ite Score of

2 8.50 Based

on Weighting b

y Level o f E xposure and Sample Type

Page C-1

# Conceptual Site Modeling

A sensitivity analysis was performed during development of the proposed Hazard Ranking System ( HRS ) addition to test the proposed HRS addition, identify and establish the relative magnitude of the factors that hav e the greatest impact on the HRS site score , and ensure that the factors driving the score are similar to those of existing pathways and components. The analysis illustrates the types of sites that may qualify for the National Priorities List ( NPL ) considering vapor intrusion (VI) contamination under various scenarios based on different

site characteristics and different factor value weightings

. These scoring models are presented in Tables C -2 through C-6 of this appendix. Table C- 1 presents the in itial conceptual site scenario evaluation with varying likelihood of intrusion levels, zone of contamination, waste characteristics and levels of contamination. The tables included below were used in the development of the proposed HRS Subsurface Intrusion (SsI) addition, and as a result of changes to the rule, weighting factors and values may not be representative of the current proposed HRS

addition. Table C -7 present s scoring simulations using the proposed HRS addition methodology and identif ies

various factors impacting the HRS site score. Additional information regarding conceptual site modeling completed as a part of the development of the proposed HRS addition is included in Section 8.1.b of the Technical Support Document ( TSD ).

Page C-2

# Table C-1

Initial Conceptual Site Scenario Evaluation

Factor Categories Impacting Potential Site Scores Potential Number
of V I Sites Eligible for Listing on the
NPL Population Density/Individual
Risk Balance Minimum Level of Impact Required to Score a Site (i.e., Greater than EPA Removal action) ( Assumes 3 people per residence )

Likelihood of Intrusion

Scenario 1

– Consider only releases above health based
benchmarks (Score only Level I Exposed People)

• Observed Release Score = 550

• Need 23 Level I exposed people to reach 28.5

• Assumes Waste Characteristics Value of 32 Low Places emphasis on populations with high individual risk; minimizes impact on population density Minimum population needed to qualify fo r the NPL

• 23 People exposed to contamination above a health

based benchmark, or

• 8 Homes with documented contamination above a health

based benchmark, or

• 1 Multi

- story building with 8 lower

- floor contaminated

apartments, or

• 1 Daycare facility with 23 attendees

Scenario 2

– Consider all releases greater than background (Score Level I and II Exposed People)

• Observed Release Score = 550

• Need 23 Level I exposed people; or

• Need 231 Level II exposed people; or

• Combination of Level I / II exposed people to reach 28.50

• Assumes Waste Characteristics Value of 32 Medium Places emphasis on populations with high and medium individual risk; equal balance on population
and risk Minimum number of people exposed to contamination, but below a health based benchmark, to qualify for the NPL

• 231 People exposed to contamination, but below a

health based benchmark

• 1 Ten story building with 8 apartments per floor , or

• 1 Daycare facility with 231 attendees

Scenario 3

– Consider all releases or potential releases (Score Level I, II and Potential Exposed People)

• Potential Intrusion Score = 500

• Need 2,850 potential targets; or

• Combination of Level I / II and Potential exposed people to

reach 28.50

• Assumes Waste Character istics Value of 32 High Places emphasis on populations with high, medium and low individual risk; maximizes impact of population density Minimum number of potentially contaminated people to qualify for the NPL

• 2,850 Potential exposed people, or

• 950 Potentially contaminated homes, or

• 4 Twenty story buildings with 12 apartments per floor

and documented contamination only in the unoccupied

basement



### Page C-3

# Table C

- 1 (cont.)

Initial Conceptual Site Scenario Evaluation

Factor Categories Impacting Potential Site Scores Potential Number of VI Sites Eligible for Listing on the
NPL Population Density/Individual
Risk Balance Minimum Level of Impact Required to Score a Site (i.e., Greater than EPA Removal action) ( Assumes 3 people per residence )

Waste Characteristics / Waste Quantity

Scenario 1

– Use a minimum waste quantity value of 10 (Consistent with existing soil exposure pathway)

• Need 41 Level I exposed people; or

• Need 446 Level II exposed people; or

• Need 5,210 Potential exposed people; or

• Combination of Level I / II and Potential exposed people to

reach 28.50

• Assumes Toxicity Value of 10,000 (e.g., Vinyl Chloride)

• Assumes Waste Characteristics Value of 18 Low Places same emphasis on population and individual risk as the soil exposure pathway Increases the number of exposed people required for a site to qualify for the NPL

• 14 Homes with documented contamination above a

health based benchmark, or

• 149 Homes with documented contamination, but below

a health based benchmark, or

• 1,737 Potentially contaminated ho mes

Scenario 2

– Use a minimum waste quantity value of 100 (Consistent with existing ground water, surface water and air migration pathways)

• Need 23 Level I exposed people; or

• Need 231 Level II exposed people; or

• Need 2,850 Potential exposed people; or

• Combination of Level I / II and Potential exposed people to

reach 28.50

• Assumes Toxicity Value of 10,000 (e.g., Vinyl Chloride)

• Assumes Waste Characteristics Value of 32 Medium Places same emphasis on population and individual risk as the ground water, su rface water and air pathways Decreases the number of exposed people required to score 28.50 relative to the existing soil exposure pathway; however, maintains the number of exposed people required relative to the other existing pathways

• 8 Homes with documented contamination above a health

based benchmark, or

• 77 Homes with documented contamination, but below a

health based benchmark, or

• 950 Potentially contaminated homes



### Page C-4

# Table C

- 1 (cont.)

Initial Conceptual Site Scenario Evaluation

Factor Categories Impacting Potential Site Scores Potential Number of VI Sites Eligible for Listing on the NPL Population Density/Individual Risk
Balance Minimum Level of Impact Required to Score a Site (i.e., Greater than EPA Removal action) ( Assumes 3 people per residenc e )

Zones of Contamination

Scenario 1

– Consider only people within the Area of Contamination (AOC)

• Use weighting factors of 10 and 1 Low Places emphasis on populations with high individual risk; minimizes impact on population density Minimum population needed to qualify for the NPL

• 23 People exposed to contamination above a health based

benchmark, or

• 8 Homes with documented contamination above a health based

benchmark, or

• 1 Multi

- story building with 8 lower

- floor contaminated apartments,

or

• 1 Daycare fa cility with 23 attendees

Scenario 2

– Consider people within the AOC and Zone of Subsurface Contamination (ZOC)

• Use weighting factors of 10, 1, 0.1 Medium Places emphasis on populations with high and medium individual risk; equal balance on population
and risk Minimum number of people exposed to contamination, but below a health based benchmark, to qualify for the NPL

• 231 People exposed to contamination, but below a health based

benchmark

• 77 Contaminated homes, but below a health based benchmark, or

• 1 Ten story building with 8 apartments per floor , or

• 1 Daycare facility with 231 attendees

Scenario 3

– Consider people within the AOC, ZOC and Potential Exposure Zone (PEZ)

• Use weighting factors 10, 1, 0.1 and Dispersion

Weighted / 10 High Places emphasis on populations with high,
medium and low individual risk; maximizes impact of population density Minimum number of potentially contaminated people to qualify for the
NPL

• 950 Potentially contaminated homes, or

• 2,850 Potential exposed people, or

• 4 Twenty story buildings with 12 apartments per floor and

documented contamination only in the unoccupied basement

• Requires greater amounts of sampling to identify to qualify for the

NPL

Scenario 4

– Do not infer contamination Low Increases emphasis on population with measured high individual risk



### Page C-5

# Table C

- 1 (cont.)

Initial Conceptual Site Scenario Evaluation

Factor Categories Impacting Potential Site Scores Potential Number of VI Sites Eligible for Listing on the NPL Population Density/Individual Risk
Balance Minimum Level of Impact Required to Score a Site (i.e., Greater than EPA Removal action) ( Assumes 3 people per residence )

Levels of Contamination

Scenario 1

– Only count Level I exposed people Low Places emphasis on populations with high individual risk; minimizes impact on population density Minimum population needed to qualify for the NPL

• 23 People exposed to contamination above a health based

benchmark, or

• 8 Homes with documented contamination above a health based

benchmark, or

• 1 Multi

- story building with 8 lower

- floor contaminated apartments,

or

• 1 Daycare facility with 23 attendees

Scenario 2

– Only Count Level I and II exposed people Medium Places emphasis on populations with high and medium individual risk; equal balance on population
and risk Minimum number of people exposed to contamination, but below a health based benchmark, to qualify for the NPL

• 231 People exposed to contamination, but below a health based

benchmark

• 77 Contaminated homes, but below a health based benchmark, or

• 1 Ten story building with 8 apartments per floor , or

• 1 Daycare facility with 231 attendees

Scenario 3

– Count Level I / II and Potential exposed people High Places emphasis on populations with high,
medium and low individual risk; maximizes impact of population density Minimum number of potentially contaminated people to qualify for the
NPL

• 2,850 Potential exposed people, or

• 950 Potentially contaminated homes, or

• 4 Twenty story buildings with 12 apartments per floor and

documented contamination only in the unoccupied basement

Assumptions/ Explanations 1. Several of the weighting factors presented in Table C

- 1 were preliminary considerations only, and were revised as part of the second phase of conceptual site testing as discussed in

Section 8.0 of th e TSD

.



### Page C-6

### Page C-7 

# Table C-2

Sample HRS Site Scores Based on Potential Exposures Only and Actual Hazardous Waste Quantity Values

Assumptions / Explanations
1. People per square mile 2. Number of Homes = Population density / 2.6 (average people per household; Source: US Census 2005

- 2009 http://quickfacts.census.gov/qfd/states/00000.html ); rounded up to nearest whole integer
3. Total Volume = [Number of homes x 1300sf (average basal footprint) x 8ft (average ceiling height)] / 27 (cubic feet to cubic yard conversion)
4. Source Waste Quantity = Total Volume / 2.5
5. Pathway Waste Quantity: Referenced from HRS Table 2 -6
6. Contaminant: Sample contaminants chosen based on varying volatility/mobility factors
7. Toxicity: Referenced from HRS Section 2.4.1.1
8. Mobility: Referenced from Proposed Rule Table 5

- 17 (Based on Contaminant Vapor Pressure)

9. Waste Characteristics Factor Category Value: Referenced from HRS Table 2

- 7 (Subject to a Maximum of 100)
10. Exposed Individual: Assumes all targets are located within the ASC (i.e., no Level I or II targets)
11. Target Weighting Factor
- Assumes entire population within the ASC (1 square mile) are subject to the same contamination concentration and therefore the same weightin g factor
12. Population Score = Population Density x 1 square mile x Target Weighting Factor
13. Total Target Points = Exposed In dividual + Population Score (Assumes no worker targets and no resources present)

14. Site Score
- Assumes only SsI component is being scored

• Italicized indicates subject to a maximum score of 50 (Based on a pathway score of 100)

• B oldface indicates a site score greater than 28.50
ASC = area of subsurface contamination

### Page C-8 

# Table C-3

Sample HRS Site Scores Based on Potential Exposures Only and Minimum Hazardous Waste Quantity Values

### Page C-9 

# Table C-3 (cont.)

Sample HRS Site Scores Based on Potential Exposures Only and Minimum Hazardous Waste Quantity Values

Assumptions / Explanations
1. People per square mile 2. Number of Homes = Population density / 2.6 (average people per household; Source: US Census 2005

- 2009 http://quickfacts.census.gov/qfd/states/00000.html); rounded up to nearest whole integer

3 . Pathway Waste Quantity: Subject to a minimum of 10 or 100

4 . Contaminant: Sample contaminants chosen based on varying volatility/mobility factors

5 . Toxicity: Referenced from HRS Section 2.4.1.1

6 . Mobility: Referenced from Proposed Rule Table 5

- 17 (Based on Contaminant Vapor Pressure)

7 . Waste Characteristics Factor Category Value: Referenced from HRS Table 2

- 7 (Subject to a Maximum of 100)

8 . Exposed Individual: Assumes all targets are located within the ASC (i.e., no Level I or II targets)

9 . Target Weighting Factor
- Assumes entire population within the ASC (1 square mile) are subject to the same contamination concentration and therefore th e same we ighting factor

10 . Population Score = Population Density x 1 square mile x Target Weighting Factor

11 . Total Target Points = Exposed Individual + Population Score (Assumes no worker targets and no resources present)
12 . Site Score
- Assumes only SsI component is being scored (i.e., soil exposure component, ground water migration pathway, surface water migration pathway and air migration pathway are not scored)

• Italicized indicates subject to a maximum score of 50 (Based on a pathway score of 100 )

• Boldface indicates a site score greater than 28.50

ASC = area of subsurface contamination

### Page C- 10 

# Table C-4

Sample HRS Site Scores Based on Potential Exposures Only with Consideration of Subslab Sampling Data

Assumptions / Explanations
1. People per square mile, assuming one square mile
2. Number of Homes = Population density / 2.6 (average people per household; Source: US Census 2005

- 2009 http://quickfacts.census.gov/qfd/states/00000.html); rounded up to nearest whole integer
3. Pathway Waste Quantity: Subject to a minimum of 10 or 100
4. Toxicity: Referenced from HRS Section 2.4.1.1
5. Mobility: Referenced from Proposed Rule Table 5

- 17 (Based on Contaminant Vapor Pressure)
6. Waste Characteristics Factor Category Value: Referenced from HRS Table 2

- 7 (Subject to a Maximum of 100)
7. Exposed Individual: Assumes all targets are located within the area of subsurface contamination ( ASC ) (i.e., no Level I or II targets)
8. Level I Target Points: Number of people subject to Level I concentrations x 10
9. Level II Target Points: Number of people subject to Level II concentrations x 1
10. Subslab Target Points: Number of people in the ASC with subslab concentrations 10x great than an appropriate benchmark x 0.75

11. Non

- Subslab T arget Points: All other individuals in the ASC x 0.1
12. Total Target Points = Exposed Individual + Population Score (Assumes no worker targets and no resources present)

13. Site Score
- Assumes only SsI component is being scored (i.e., soil exposure component, ground water migration pathway, surface water migration pathway and air migration pathway are not scored)

• Italicized indicates subject to a maximum score of 50 (Based on a pathway score of 100) • Boldface indicates a site score greater than 28.50

# Table C -5

Sample HRS Site Scores Based on Different Population Densities and Actual and Potential Exposures

Subslab Target

Points 10


### (Weighting Factor = 0.75) Non-Subslab
Target Points 11



### (Weighting Factor = 0.1)

500 192 100 10,000 1 1.00E+06 32 50 40 0 0 50 140 14.89

1,000 385 100 10,000 1 1.00E+06 32 50 40 0 0 100 190 20.22

5,000 1,923 100 10,000 1 1.00E+06 32 50 40 0 0 500 590 50 (62.89)

500 192 100 10,000 1 1.00E+06 32 50 40 0 74 40 204 21.77

1,000 385 100 10,000 1 1.00E+06 32 50 40 0 149 80 319 34.04

5,000 1,923 100 10,000 1 1.00E+06 32 50 40 0 749 400 1,239 50 (132.17)

500 192 100 10,000 1 1.00E+06 32 50 40 0 50 198 338 36.05

1,000 385 100 10,000 1 1.00E+06 32 50 40 0 100 398 588 50 (62.72)

5,000 1,923 100 10,000 1 1.00E+06 32 50 40 0 500 1,998 2,588 50 (276.05) Scenario Population
Density 1 

### Targets

Site Score (SsI
Only) 13


### (Likelihood of Exposure = 550) Pathway

Waste
Quantity 3 

### Toxicity 4 

### Mobility 5 

### Pathway WQ x Toxicity x Mobility Waste
Characteristics

Factor Value 6 

### Exposed

Individual 7



### 2. Four Level I homes within the AOE with the remaining homes located in the ASC where 20% have subslab contaminant concentrations 10x greater than an appropriate benchmark.

3. Four Level I homes within the AOE with the remaining homes located in the ASC where 50% have subslab contaminant concentrations 10x greater than an appropriate benchmark. Population

Total Target

Points 12 

### Level I Target

Points 8


### (Weighting Factor = 10) Level II Target

Points 9


### (Weighting Factor = 1) Population on ASC

1. Four Level I homes within the AOE with the remaining homes located in the

ASC where no subslab data is available. Number of

Homes 2 

### Waste Characteristics (WC)

Assumptions / Explanations
1. People per square mile, assuming one square mile
2. Number of Homes = Population density / 2.6 (average people per household; Source: US Census 2005

- 2009 http://quickfacts.census.gov/qfd/states/00000.html); rounded up to nearest whole integer
3. Pathway Waste Quantity: Subject to a minimum of 10 or 100
4. Toxicity: Referenced from HRS Section 2.4.1.1
5. Mobility: Referenced from Proposed Rule Table 5

- 17 (Based on Contaminant Vapor Pressure)
6. Waste Characteristics Factor Category Value: Referenced from HRS Table 2

- 7 (Subject to a Maximum of 100)
7. Exposed Individual: Assumes all targets are located within the ASC (i.e., no Level I or II targets)
8. Level I Target Points: Number of people subject to Level I concentrations x 10
9. Level II Target Points: Number of people su bject to Level II concentrations x 1
10. Subslab Target Points: Number of people in the ASC with subslab concentrations 10x great than an appropriate benchmark x 0.75

11. Non

- Subslab Target Points: All other individuals in the ASC x 0.1
12. Total Target Points = Exposed Individual + Population Score (Assumes no worker targets and no resources present)

13. Site Score

- Assumes only SsI component is being scored (i.e., soil exposure component, ground water migration pathway, surface water migr ation pathwa y and air migration pathway are not scored)

• Italicized indicates subject to a maximum score of 50 (Based on a pathway score of 100)

• Boldface indicates a site score greater than 28.50
ASC = area of subsurface contamination



### Page C- 11

# Table C -6 Sample HRS Site Scores Based on a Combination of the Ground Water Migration Pathway and the Subsurface Intrusion Component of the Soil Exposure and Subsurface Intrusion Pathway

Nearest
Individual Level I Target

Points Level II Target
Points Potential Target
Points Pathway

Waste Quantity 6 WC Factor

Value 6 Subslab Target

Points 10
(Weighting Factor = 0.75) Non-Subslab
Target Points 11

(Weighting Factor = 0.1)

50 - - 550 32 50 104 0 36 40.53 20.26 0 0 0 0 0 0 0 0 0 0 0 20.26

100 - - 550 32 50 104 0 53 44.07 22.03 0 0 0 0 0 0 0 0 0 0 0 22.03

250 - - 550 32 50 104 0 171 69.35 34.67 0 0 0 0 0 0 0 0 0 0 0 34.67

500 - - 550 32 50 104 0 360 100 (110) 50 .00 (55.00) 0 0 0 0 0 0 0 0 0 0 0 50.00 (55.00)

50 - - 550 32 45 0 10.4 36 19.49 9.74 0 0 0 0 0 0 0 0 0 0 0 9.74

100 - - 550 32 45 0 10.4 53 23.04 11.52 0 0 0 0 0 0 0 0 0 0 0 11.52

250 - - 550 32 45 0 10.4 171 48.32 24.16 0 0 0 0 0 0 0 0 0 0 0 24.16

500 - - 550 32 45 0 10.4 360 88.64 44.32 0 0 0 0 0 0 0 0 0 0 0 44.32

50 19 50 550 32 50 104 0 36 40.53 20.26 500 10 18 20 0 0 0 5 25 2.72 1.36 20.31

100 38 100 550 32 50 104 0 53 44.07 22.03 500 10 18 20 0 0 0 10 30 3.27 1.63 22.09

250 96 250 550 32 50 104 0 171 69.35 34.67 500 10 18 20 0 0 0 25 45 4.90 2.45 34.76

500 192 500 550 32 50 104 0 360 100 (110) 50 .00 (55.00) 500 10 18 20 0 0 0 50 70 7.63 3.81 50.15 (55.13)

50 19 50 550 32 45 0 10.4 36 19.49 9.74 500 10 18 20 0 0 0 5 25 2.72 1.36 9.83

100 38 100 550 32 45 0 10.4 53 23.04 11.52 500 10 18 20 0 0 0 10 30 3.27 1.63 11.63

250 96 250 550 32 45 0 10.4 171 48.32 24.16 500 10 18 20 0 0 0 25 45 4.90 2.45 24.28

500 192 500 550 32 45 0 10.4 360 88.64 44.32 500 10 18 20 0 0 0 50 70 7.63 3.81 44.48

50 19 50 550 32 50 104 0 36 40.53 20.26 500 100 32 20 0 0 8 4 32 6.10 3.05 20.49

100 38 100 550 32 50 104 0 53 44.07 22.03 500 100 32 20 0 0 15 8 43 8.33 4.16 22.42

250 96 250 550 32 50 104 0 171 69.35 34.67 500 100 32 20 0 0 38 20 78 15.03 7.51 35.48

500 192 500 550 32 50 104 0 360 100 (110) 50 .00 (55.00) 500 100 32 20 0 0 75 40 135 26.18 13.09 51.69 ( 56.54)

50 19 50 550 32 50 104 0 36 40.53 20.26 500 100 32 20 0 0 19 3 41 8.00 4.00 20.65

100 38 100 550 32 50 104 0 53 44.07 22.03 500 100 32 20 0 0 38 5 63 12.12 6.06 22.85

250 96 250 550 32 50 104 0 171 69.35 34.67 500 100 32 20 0 0 94 13 126 24.48 12.24 36.77

500 192 500 550 32 50 104 0 360 100 (110) 50 .00 (55.00) 500 100 32 20 0 0 188 25 233 45.09 22.54 54.85 (59.44)

50 19 50 550 32 50 104 0 36 40.53 20.26 550 100 32 50 104 0 0 0 154 32.85 16.42 26.08

100 38 100 550 32 50 104 0 53 44.07 22.03 550 100 32 50 104 0 0 0 154 32.85 16.42 27.48

250 96 250 550 32 50 104 0 171 69.35 34.67 550 100 32 50 104 0 0 0 154 32.85 16.42 38.36

500 192 500 550 32 50 104 0 360 100 (110) 50 .00 (55.00) 550 100 32 50 104 0 0 0 154 32.85 16.42 52.63 (57.40)

50 19 50 550 32 50 104 0 36 40.53 20.26 550 100 32 50 104 0 0 5 159 33.92 16.96 26.42

100 38 100 550 32 50 104 0 53 44.07 22.03 550 100 32 50 104 0 0 10 164 34.98 17.49 28.13

250 96 250 550 32 50 104 0 171 69.35 34.67 550 100 32 50 104 0 0 25 179 38.18 19.09 39.58

500 192 500 550 32 50 104 0 360 100 (110) 50 .00 (55.00) 550 100 32 50 104 0 0 50 204 43.52 21.76 54.53 (59.15)

50 19 50 550 32 50 104 0 36 40.53 20.26 550 100 32 50 104 0 8 4 166 35.30 17.65 26.87

100 38 100 550 32 50 104 0 53 44.07 22.03 550 100 32 50 104 0 15 8 177 37.76 18.88 29.01

250 96 250 550 32 50 104 0 171 69.35 34.67 550 100 32 50 104 0 38 20 212 45.12 22.56 41.36

500 192 500 550 32 50 104 0 360 100 (110) 50 .00 (55.00) 550 100 32 50 104 0 75 40 269 57.38 28.69 57.65 ( 62.03)

50 19 50 550 32 50 104 0 36 40.53 20.26 550 100 32 50 104 0 19 3 175 37.38 18.69 27.56

100 38 100 550 32 50 104 0 53 44.07 22.03 550 100 32 50 104 0 38 5 197 41.92 20.96 30.41

250 96 250 550 32 50 104 0 171 69.35 34.67 550 100 32 50 104 0 94 13 260 55.52 27.76 44.41

500 192 500 550 32 50 104 0 360 100 (110) 50 .00 (55.00) 550 100 32 50 104 0 188 25 367 78.18 39.09 63.47 (67.48) Population on ASC

1. Four homes subject to Level I ground water concentrations, potential ground water targets and NO SsI component evaluated.

2. Four homes subject to Level II ground water concentrations, potential ground water targets and NO SsI component evaluated.

3. Four homes subject to Level I ground water concentrations, potential ground water targets and SsI component evaluated for ASC only. Assumes none of the ASC homes have subslab contaminant concentrations 10x greater than an appropriate benchmark and WQ minimum of 10 for SESsI pathway.

4. Four homes subject to Level II ground water concentrations, potential ground water targets and SsI component evaluated for ASC only. Assumes none of the ASC homes have subslab contaminant concentrations 10x greater than an appropriate benchmark and WQ minimum of 10 for SESsI pathway.

5. Four homes subject to Level I ground water concentrations, potential ground water targets and SsI component evaluated for ASC only. Assumes 20% of ASC homes have subslab contaminant concentrations 10x greater than an appropriate benchmark and WQ minimum of 100 for SESsI pathway. Targets

7. Four homes subject to Level I ground water concentrations, potential ground water targets, four homes subject to Level I SsI concentrations and no ASC

evaluated.

8. Four homes subject to Level I ground water concentrations, potential ground water targets, four homes subject to Level I SsI concentrations and ASC evaluated assuming none of the ASC homes have subslab contaminant concentrations 10x greater than an appropriate benchmark and WQ minimum of 100 for SESsI pathway.

9. Four homes subject to Level I ground water concentrations, potential ground water targets, four homes subject to Level I SsI concentrations and ASC evaluated assuming 20% of ASC homes have subslab contaminant concentrations 10x greater than an appropriate benchmark and WQ minimum of 100 for SESsI pathway.

10. Four homes subject to Level I ground water concentrations, potential ground water targets, four homes subject to Level I SsI concentrations and ASC evaluated assuming 50% of ASC homes have subslab contaminant concentrations 10x greater than an appropriate benchmark and WQ minimum of 100 for SESsI pathway.Number of Homes in ASC2

6. Four homes subject to Level I ground water concentrations, potential ground water targets and SsI component evaluated for ASC only. Assumes 50% of ASC homes have subslab contaminant concentrations 10x greater than an appropriate benchmark and WQ minimum of 100 for SESsI pathway. Ground Water Pathway 13Site Score (GW Only)

Total Target

Points 12Site Score (Combined GW andSESsI)

ScenarioPopulation Density1,1ALikelihood of ReleaseWaste Characteristics4Number of People in ASC3GW Pathway ScoreSite Score (SESsI Only) Soil Exposure and Subsurface Intrusion Pathway Score 14Likelihood of Exposure5 Waste Characteristics (WC)SESsI Pathway Score

Level II Target

Points 9
(Weighting Factor = 1) Targets

Level I Target

Points 8
(Weighting Factor = 10) Exposed

Individual 7 Population



### Page C- 12Assumptions / E xplanations

1. People per square mile

1A. Assumes ground water (GW) pathway potential population density is uniform for entire TDL and all individuals are on private wells

2. Number of Homes = Population density / 2.6 (average people per household; Source: US Census 2005

- 2009 http://quickfacts.census.gov/qfd/states/00000.html); rounded up to nearest whole integer

3. Population in ASC assuming one square mile

4. GW Waste Characteristics: Assumed to be 32 (i.e., Toxicity = 10,000)

5. SsI Likelihood of Exposure: Assumed to be 500 for scenarios where SESsI Pathway is evaluated except where Level I concentrations are present when WC = 55 0

6. SsI Waste Characteristics Factor Value: Referenced from HRS Table 2

- 7 (Subject to a Maximum of 100) Assumes Waste Quantity of 10 or 100)

7. Exposed Individual: Assumes all targets are located within the ASC (i.e., no Level I or II targets)

8. Level I Target Points: Number of people subject to Level I concentrations x 10

9. Level II Target Points: Number of people subject to Level II concentrations x 1

10. Subslab Target Points: Number of people in the ASC with subslab concentrations 10x great than an appropriate benchmark x 0.75

11. Non

- Subslab Target Points: All other individuals in the ASC x 0.1

12. Total Target Points = Exposed Individual + Population Score (Assumes no worker targets and no resources present)

13. Ground Water Pathway = Assumes only drinking water threat is evaluated

14. SESsI Pathway Score: Assumes only SsI Component is being scored

• Italicized indicates subject to a maximum

• Boldface indicates a site score greater than 28.50

ASC = area of subsurface contamination



### Page C- 13

# T able C -7a

Proposed Conceptual Site Scenario Evaluation

Factor Categories Impacting Potential Site Scores Potential Number of VI Sites Eligible for Listing on the
NPL Population Density/Individual
Risk Balance Minimum Level of Impact Required to Score a Site (i.e., Greater than EPA Removal action) ( Assumes 3 people per residence )

Likelihood of Exposure
Proposed Option

S coring all Actual and Potential Exposures at site

A ctually Exposed People



### • Level I (actually exposed people at levels above health
based benchmarks)



### • Level II (actually exposed people but sampling does not

show levels above health

- based benchmarks)

P otentially Exposed People



### • P eople living or working above a soil gas or ground water

plume High Places emphasis on populations with high, medium and low individual risk; maximizes impact of population density Population n eed ed to qualify for the NPL



### • 23 Level I exposed p eople, ( e.g., 8 homes

, a daycare

center with 23 students and staff

, 69 full

- time workers

, or 138 part

- time workers ), or



### • 230 Level II exposed p eople , or



### • 371 people living or working above a soil gas plume , or

various combinations of Level I exposed people , Level
II exposed people, and p otential ly exposed people



### • (Assumes a toxicity of 10,000 and a Hazardous Waste

Quantity score of 100 for actually exposed people and 10,000 for potentially exposed people)

Waste Characteristics / Waste Quantity
Proposed Option



### • Use a minimum waste quantity value of 100 and an

estimate of 1,740 square feet per regularly occupied

structure or subunit unless actual square footage available Medium P laces similar emphasis on population and individual risk as the ground water, surface water and air pathways 

### • Decreases the number of exposed people required to score 28.50 relative to the existing soil exposure pathway; however, maintains the number of exposed people required relat ive to the other existing pathways.



### • Based on an area of 1,740 sq u are feet per residence, need

1 home to reach a Hazardous Waste Quantity score of
100 and 75 regularly occupied structures or subunits to reach a Hazardous Waste Quantity score of 10,000

Zones of Exposure
Proposed Option Consider people within the AO E and ASC



### • AOE: area of observed exposure (area delineated by regularly

occupied structures with actual contamination)



### • ASC: area of subsurface contamination (area delineated by

regularly occupied structures above soil gas or ground water contamination)



### • (Uses weighting factors of 10, 1 and between 0.1 and 0.9 for

Level I, Level II and potentially exposed people) Medium Places emphasis on populations with high and medium individual risk; equal balance on population
and risk 

### • Includes all people exposed to contamination, above or
below a health

- based benchmark, and those where intrusion is considered to be presently possib le (potentially exposed)

Levels of Exposure

Proposed Option

C ount Level I, Level II and Potentially Exposed people

A ctually Exposed People:



### • Level I (actually exposed people at levels above health

- based

benchmarks),



### • Level II (actually exposed people but sampling does not show

levels above health

- based benchmarks)

P otentially Exposed People



### • P eople living or working in regularly occupied structures

above a soil gas or ground water plume H igh Places emphasis on pop ulations with high, medium and low individual risk; maximizes impact of population density 

### • Maximum number of people needed in each Level to
reach a score of 28.50



### • 23 People exposed to contamination above a health

based benchmark (Level I)



### • 223 People exposed to contamination but sampled levels

not above a health

- based benchmark (Level II)



### • 225 Potentially Exposed People in structures with crawl

space contamination or subslab contamination



### • 371 Potentially Exposed People in structures above

shallow soil gas contamination



### • 741 Potentially Exposed People in structures above a

ground water plume



### Page C- 14

# Table C -7b

Sampl e HRS S ite Scores Based o n P otential E xposures Only with C

onsidera tion o

f D ifferent Population D ensities and Varying T ypes of SsI Sa mpling Data

D ata

Scenario Population Density 1 Number of Homes 2 Waste Characteristics (WC) Targets Site Score (SsI Only) 11Pathway Waste Quantity3Toxicity4Biodegradation5Pathway WQ x Toxicity xBiodegradationWaste Characteristics Factor Value6Exposed Individual7 PopulationTotal Target Points10If Likelihood of Exposure = 180If Likelihood of Exposure = 320If Likelihood of Exposure = 500Level I Target Points8(Weighting Factor = 10)Level II Target Points9(Weighting Factor = 1) Population on ASCCrawl Space samples(Weighting Factor= 0.09)Subslab samples(Weighting Factor = 0.4)Soil Gas samples(Weighting factor = 0.2)Ground Water Samples(Weighting Factor = 0.1)

1. All targets located within the ASC (No Level I or II Concentrations). All crawl space samples (Assumes WQ of 10,000) 100 38 100 1,000 1 1.00E+05 18 20 0 0 90 0 0 0 110 2.16 3.84 6.00

500 192 10,000 1,000 1 1.00E+07 56 20 0 0 450 0 0 0 470 28.71 51.04 79.76

1,000 385 10,000 1,000 1 1.00E+07 56 20 0 0 900 0 0 0 920 56.20 99.92 156.12

5,000 1,923 10,000 1,000 1 1.00E+07 56 20 0 0 4500 0 0 0 4,520 276.13 490.90 767.03

2. All targets located within the ASC (No Level I or II Concentrations). All subslab samples (Assumes WQ of 10,000) 10 0 38 100 1,000 1 1.00E+05 18 20 0 0 0 40 0 0 60 1.18 2.09 3.27

500 192 10,000 1,000 1 1.00E+07 56 20 0 0 0 200 0 0 220 13.44 23.89 37.33

1,000 385 10,000 1,000 1 1.00E+07 56 20 0 0 0 400 0 0 420 25.66 45.61 71.27

5,000 1,923 10,000 1,000 1 1.00E+07 56 20 0 0 0 2000 0 0 2,020 123.40 219.38 342.79

3. All targets located within the ASC (No Level I or II Concentrations). All soil gas samples (Assumes WQ of 10,000) 100 38 100 1,000 1 1.00E+05 18 20 0 0 0 0 20 0 40 0.79 1.40 2.18

500 192 10,000 1,000 1 1.00E+07 56 20 0 0 0 0 100 0 120 7.33 13.03 20.36

1,000 385 10,000 1,000 1 1.00E+07 56 20 0 0 0 0 200 0 220 13.44 23.89 37.33

5,000 1,923 10,000 1,000 1 1.00E+07 56 20 0 0 0 0 1000 0 1,020 62.31 110.78 173.09

4. All targets located within the ASC (No Level I or II Concentrations). All ground water samples (Assumes WQ of 10,000) 100 38 100 1,000 1 1.00E+05 18 20 0 0 0 0 0 10 30 0.59 1.05 1.64

500 192 10,000 1,000 1 1.00E+07 56 20 0 0 0 0 0 50 70 4.28 7.60 11.88

1,000 385 10,000 1,000 1 1.00E+07 56 20 0 0 0 0 0 100 120 7.33 13.03 20.36

5,000 1,923 10,000 1,000 1 1.00E+07 56 20 0 0 0 0 0 500 520 31.77 56.48 88.24

Assumptions / Explanations

1. People per square mile, assuming one square mile

2. N umber of Homes = Population density / 2.6 (average people per household; Source: US Census 2005

- 2009 http://quickfacts.census.gov/qfd/states/00000.html); rounded up to nearest whole integer

3. Pathway Waste Quantity: 10,000 based on number of homes and default tier D square footage

4. Toxicity: Referenced from HRS Section 2.4.1.1 for TCE

5. Biodegradation for non

- readily biodegradable substance

6. Waste Characteristics Factor Category Value: Referenced from HRS Table 2

- 7 (Subject to a Maximum of 100)

7. Exposed Individual: Assume s all targets are located within the ASC (i.e., no Level I or II targets)

8. Level I Target Points: Number of people subject to Level I concentrations x 10

9. Level II Target Points: Number of people subject to Level II concentrations x 1

10. Total Target Points = Exposed Individual + Population Score (Assumes no worker targets and no resources present)

11. Site Score
- Assumes only SsI component is being scored (i.e., soil exposure component, ground water migration pathway, surface water migr ation path way and air migration pathway are not scored)
ASC = area of subsurface contamination



### Page C- 15

# Table C

- 7c

Sample HRS Site Scores Based on Different Population Densities, a Mix of Actual and Potential Exposures and D ifferent Types of SsI Sampling Data

Scenario Population Density 1 Number of
Homes 2 Waste Characteristics (WC) Targets Site Score (SsI Only) 11 (Likelihood of Exposure = 550)

Pathway

Waste Quantity 3 Toxicity 4 Pathway WQ x Toxicity Waste Characteristics
Factor Value 6Exposed Individual7 Population Total Target
Points 10Level I Target Points8(Weighting Factor = 10)Level II Target Points9(Weighting Factor = 1) Population on ASC

Biodegradation 5CrawlSpaceSamples(WeightingFactor = 0.9)SubslabSamples(WeightingFactor = 0.4)Soil Gas Samples(Weighting = 0.2)Ground Water Samples(Weighting = 0.1)

1. Three Level I homes within the AOE with the remaining homes located in the ASC with crawl space samples 100 38 100 1,000 1 1.00E+05 18 50 78 0 87.30 0.00 0.00 0.00 215 12.92

250 96 10,000 1,000 1 1.00E+07 56 50 78 0 222.30 0.00 0.00 0.00 350 65.39

500 192 10,000 1,000 1 1.00E+07 56 50 78 0 447.30 0.00 0.00 0.00 575 107.39

2. Three Level I homes within the AOE with the remaining homes located in the ASC with subslab samples. 100 38 100 1,000 1 1.00E+05 18 50 78 0 0.00 38.80 0.00 0.00 167 10.01

250 96 10,000 1,000 1 1.00E+07 56 50 78 0 0.00 98.80 0.00 0.00 227 42.34

500 192 10,000 1,000 1 1.00E+07 56 50 78 0 0.00 198.80 0.00 0.00 327 61.00

3. Three Level I homes within the AOE with the remaining homes located in the ASC with soil gas sam ples. 100 38 100 1,000 1 1.00E+05 18 50 78 0 0.00 0.00 19.40 0.00 147 8.84

250 96 10,000 1,000 1 1.00E+07 56 50 78 0 0.00 0.00 49.40 0.00 177 33.11

500 192 10,000 1,000 1 1.00E+07 56 50 78 0 0.00 0.00 99.40 0.00 227 42.45

3. Three Level I homes within the AOE with the remaining homes located in the ASC with ground water samples 100 38 100 1,000 1 1.00E+05 18 50 78 0 0.00 0.00 0.00 9.70 138 8.26

250 96 10,000 1,000 1 1.00E+07 56 50 78 0 0.00 0.00 0.00 24.70 153 28.50

500 192 10,000 1,000 1 1.00E+07 56 50 78 0 0.00 0.00 0.00 49.70 178 33.17

Assumptions / Explanations

1. People per square mile, assuming one square mile

2. Number of Homes = Population density / 2.6 (average people per household; Source: US Census 2005

- 2009 http://quickfacts.census.gov/qfd/states/00000.html); rounded up to nearest whole integer

3. Pathway Waste Quantity: 10,000

4. Toxicity: Referenced from HRS Section 2.4.1.1

5. Biodegradation for a non

- readily biode gradable substance.

6. Waste Characteristics Factor Category Value: Referenced from HRS Table 2

- 7 (Subject to a Maximum of 100)

7. Exposed Individual: Assumes all targets are located within the ASC (i.e., no Level I or II targets)

8. Level I Target Points: Number of people subject to Level I concentrations x 10

9. Level II Target Points: Number of people subject to Level II concentrations x 1

10. Total Target Points = Exposed Individual + Population Score (Assumes no worker targets and no resources present)

11. Site Score
- Assumes only SsI component is being scored (i.e., soil exposure component, ground water migration pathway, surface water migration pathway and air migration pathway are not scored) AOE = area of observed exposure
A SC = area of subsurface contamination



### Page C- 16

# Table C -7d

Minimum Population s Needed to Achieve an HRS Site Score of 28.50 with Different Likelihood of Exposure, Waste Characteristics and Different Types of SsI Samples

Scenario Likelihood of Exposure Waste Characteristics (WC) Targets

Pathway Score Site Score Exposed Individual AOE ASC

Target Score Waste Quantity Toxicity Biodegradation WC
Product WC Factor Value # Level I Targets # Level II Targets # Crawl Space Targets # Subslab Targets # Shallow Soil Gas Targets # GW/Other

Targets



### 1 550 100 1000 1 1.00E+05 18 50 43 0 0 0 0 0 480.00 57.60 28.80

2 550 10000 1000 1 1.00E+07 56 50 11 0 0 0 0 0 160.00 59.73 29.87

3 550 10000 10000 1 1.00E+08 100 50 4 0 0 0 0 0 90.00 60.00 30.00

4 550 10000 1000 1 1.00E+07 56 45 0 108 0 0 0 0 153.00 57.12 28.56

5 550 10000 10000 1 1.00E+08 100 45 0 41 0 0 0 0 86.00 57.33 28.67

6 500 10000 1000 1 1.00E+07 56 20 0 0 165 0 0 0 168.50 57.19 28.59

7 500 10000 1000 1 1.00E+07 56 20 0 0 0 370 0 0 168.00 57.02 28.51

8 500 10000 1000 1 1.00E+07 56 20 0 0 0 0 740 0 168.00 57.02 28.51

9 500 10000 1000 1 1.00E+07 56 20 0 0 0 0 0 1480 168.00 57.02 28.51

10 550 10000 1000 1 1.00E+07 56 50 10 0 0 0 100 0 170.00 63.47 31.73



### Assumptions/Explanations

1. H azardous waste quantity: Assigns a value of 100 or 10000

2. T oxicity: Assigns a value of 100, 1000 or 10000

3. B iodegradation: Assumes that a biodegradation facto r value of 1 is assigned

4. Was te Characteristics Factor Category Value: Reference H RS Table 2 -7 (Subject to a Maximum of 100)

5. E xposed Individual: Reference H RS Section 5.2.1.3 .1

6. L evel I Targets: Reference HRS Section 5.2.1.3.2.1 (multiply by 10)

7. L evel II Targets: Reference HRS Section 5.2.1.3.2.2 ( multiply by 1)

8. A SC Targets: Reference HRS Table 5

- 20 (multiply by a weighting factor assigned from Table 5 -20)
9. T ar get Score = Exposed Individual + Level I targets + Level II targets + Crawl Space targets + Subslab targets + Shallow Soil Gas targets + GW/Other targets (multiplied by appropriate weighting factors)

10. S ite Score: Assumes only SsI component is being scored (i.e., soil exposure component, ground water migration pathway, surface water migration pathway and air migration pathway are not scored)

11. A OE = area of observed exposure, ASC = area of subsurface contamination, GW = ground water
12. Subslab samples are assumed to be at or within 5 feet of a structure’s foundatio n 13. S hallow soil gas are assumed to be greater than 5 feet from a structure’s foundation and at a depth less than or equal to 30 feet below ground surface
14. G round water samples are assumed to be greater than 5 feet from a structure’s foundati on

Page C- 17

# Table C -7e

Minimum Actually Exposed Population Needed to Achieve an HRS Site Score of 28.50 Based on Varying Waste Characteristic Factor Values

Scenario Likelihood of Exposure Waste Characteristics (WC) Targets

Pathway Score Site Score Exposed Individual AOE ASC

Total Target Value Waste Quantity Toxicity Biodegradation WC Factor Value # Level I Targets # Level II Targets # Targets (Crawl Space Samples) # Targets (Samples
≤ 5 ft) # Targets (Samples

≤ 30 ft) # Targets (GW/Other Samples)



### 1 550 100 100 1 10 50 81 0 0 0 0 0 860.00 57.33 28.67

2 550 100 1000 1 18 50 43 0 0 0 0 0 480.00 57.60 28.80

3 550 100 10000 1 32 50 22 0 0 0 0 0 270.00 57.60 28.80

4 550 10000 100 1 32 50 22 0 0 0 0 0 270.00 57.60 28.80

5 550 10000 1000 1 56 50 11 0 0 0 0 0 160.00 59.73 29.87

6 550 10000 10000 1 100 50 4 0 0 0 0 0 90.00 60.00 30.00

7 550 10000 100 1 32 45 0 223 0 0 0 0 268.00 57.17 28.59

8 550 10000 1000 1 56 45 0 225 0 0 0 0 270.00 100.80 50.40

9 550 10000 10000 1 100 45 0 225 0 0 0 0 270.00 180.00 90.00



### Assumptions /

E xplanations

1. Li kelihood of exposure : Assigns a value of 5 50
2. H azardous waste quantity: Assigns a value of 100 or 10000
3. Biodegradation: Assumes that a biodegradation facto r value of 1 is assigned
4

. Toxicity: Assigns a value of 100, 1000 or 10000

5

. Waste Characteristics Factor Category Value: Reference HRS Table 2 -7 (Subject to a Maximum of 100) 6. Exposed Individual: Reference HRS Section 5.2.1.3.1
7 . ASC targets: Assumes only actually exposed populations are present 8. AOE = area of observed exposure, ASC = area of subsurface contamination, GW = ground water
9. Site Score: Assumes only SsI component is being scored (i.e., soil exposure component, ground water migration pathway, surface water migration

pathway and air migration pathway are not scored)

Page C- 18

# Table C -7f

Minimum Potentially Exposed Population Needed to Achieve an HRS Site Score of 28.50 Based on Varying Waste Characteristic Factor Values

Scenario Likelihood of Exposure Waste Characteristics (WC) Targets

Pathway Score Site Score Exposed Individual AOE ASC

Total Target Value Waste Quantity Toxicity Biodegradation WC Factor Value # Level I Targets # Level II Targets # Targets (Crawl Space Samples) # Targets (Samples
≤ 5 ft) # Targets (Samples

≤ 30 ft bgs) # Targets (GW/Other Samples)



### 1 500 10000 100 1 32 20 0 0 305 294.50 57.12 28.56

2 500 10000 1000 1 56 20 0 0 225 222.50 75.52 37.76

3 500 10000 10000 1 100 20 0 0 225 222.50 134.85 67.42

4 500 10000 100 1 32 20 0 0 685 294.00 57.02 28.51

5 500 10000 1000 1 56 20 0 0 370 168.00 57.02 28.51

6 500 10000 10000 1 100 20 0 0 225 110.00 66.67 33.33

7 500 10000 100 1 32 20 0 0 1370 294.00 57.02 28.51

8 500 10000 1000 1 56 20 0 0 740 168.00 57.02 28.51

9 500 10000 10000 1 100 20 0 0 371 94.20 57.09 28.55

10 500 10000 10000 1 100 20 0 0 741 94.10 57.03 28.52



### Assumptions /

E xplanations

1. Assumes the maximum potential for exposure factor value of 500 2. Assumes a hazardous waste quantity factor value of 10000 and a biodegradation factor value of 1 3. Toxicity: Assigns a value of 100, 1000 or 10000 4. Waste Characteristics Factor Category Value: Reference HRS Table 2

- 7 (Subject to a Maximum of 100) 5. Exposed Individual: Assumes all targets are located within the ASC (i.e., no Level I or II targets) ; see HRS Section 5.2.1.3.1 6. ASC targets: Reference HRS Table 5

- 20 (multiply by a weighting factor assigned from Table 5

- 20) 7. # Targets Samples ≤ 5 ft: r eferences subsu rface samples located at or within 5 feet vertically or horizontally from a regularly occupied structure's foundation 8. # Targets Samples ≤ 30 ft: r eferences subsurface samples located less than or equal to a depth of 30 feet below ground surface 9. AOE = area of observed exposure, ASC = area of subsurface contamination, GW = ground water 10. Site Score: Assumes only SsI component is being scored (i.e., soil exposure component, ground water migration pathway, surface water migration pathway and air migration pathway are not scored)

Page C- 19

# Table C -7g

Minimum Population Needed to Achieve an HRS Site Score of 28.50 Based on Varying Likelihood of Exposure and Waste Characteris tics Factor Values and no ASC

Scenario Likelihood of Exposure Waste Characteristics (WC) Targets

Pathway Score Site Score Exposed Individual AOE ASC

Total Target Value Waste Quantity Toxicity Biodegradation WC Factor Value # Level I Targets # Level II Targets # Targets (Crawl Space Samples) # Targets (Samples ≤ 5 ft) # Targets (Samples

≤ 30 ft) # Targets (GW/Other Samples)



### 1 550 100 1000 1 18 50 43 0 0 0 0 0 480.00 57.60 28.80

2 550 10000 1000 1 56 45 0 225 0 0 0 0 270.00 100.80 50.40

3 500 10000 1000 1 56 20 0 0 225 0 0 0 222.50 75.52 37.76

4 400 10000 1000 1 56 20 0 0 225 0 0 0 222.50 60.41 30.21

5 300 10000 1000 1 56 20 0 0 289 0 0 0 280.10 57.04 28.52

6 200 10000 1000 1 56 20 0 0 450 0 0 0 425.00 57.70 28.85

7 100 10000 1000 1 56 20 0 0 911 0 0 0 839.90 57.01 28.51

8 500 10000 10000 1 100 20 0 0 225 0 0 0 222.50 134.85 67.42

9 400 10000 10000 1 100 20 0 0 225 0 0 0 222.50 107.88 53.94

10 200 10000 10000 1 100 20 0 0 239 0 0 0 235.10 56.99 28.50



### Assumptions/Explanations

1. W aste quantity is assigned based on the following assumptions: 3 people per regularly occupied structure, an area of 1740 square f eet per structure

2. T oxicity: A ssigns a value of 1000 or 10000

3. B iodegradation: Assumes a biodegradation facto r value of 1

4. Was te Characteristics Factor Category Value: Reference H RS Table 2 -7 (Subject to a Maximum of 100)

5. E xposed Individual: Reference H RS Section 5.2.1.3 .1

6. L evel I Targets: Reference HRS Section 5.2.1.3.2.1 (multiply by 10)

7. L evel II Targets: Reference HRS Section 5.2.1.3.2.2 ( multiply by 1)

8. A SC Targets: Reference HRS Table 5

- 20 (multiply by a weighting factor assigned from Table 5 -20)

9. T ar get Score = Exposed Individual + Level I targets + Level II targets + ASC targets (each multiplied by appropriate weighting factors)

10. S ite Score - Assumes only SsI component is being scored (i.e., soil exposure component, ground water migration pathway, surface water migration pathway and air migration pathway are not scored)
1 1. A ssumes there are no workers or resources present
12. A OE = area of observed exposure, ASC = area of subsurface contamination, GW = ground water

13. S ite Score: Assumes only SsI component is being scored (i.e., soil exposure component, ground water migration pathway, surface water migration pathway and air migration pathway are not scored)

Page C- 20

# Table C -7h

Minimum Populations needed Based on a Combination of the Eva luation of a Second HRS Pathway and the Subsurface Intrusion Component of the Soil Exposure and Subsurface Intrusion Pathway

Scenario Likelihood of Exposure Waste Characteristics (WC) Targets

SsI Component Score 2nd Pathway

Score SsI Component Score Site Score Exposed Individual AOE ASC

Target Score Waste Quantity Toxicity Biodegradation WC Product WC Factor Value # Level I Targets # Level II Targets # Crawl Space Targets # Subslab Targets # Shallow Soil Gas Targets # GW /Other Targets

1 550 100 1000 1 1.00E+05 18 50 43 480.00 57.60 0 57.60 28.80

2 550 100 1000 1 1.00E+05 18 50 41 460.00 55.20 15 55.20 28.60

3 550 100 1000 1 1.00E+05 18 50 38 430.00 51.60 25 51.60 28.67

4 550 100 1000 1 1.00E+05 18 50 18 230.00 27.60 50 27.60 28.56

5 550 10000 1000 1 1.00E+07 56 50 11 160.00 59.73 0 59.73 29.87

6 550 10000 1000 1 1.00E+07 56 50 10 150.00 56.00 15 56.00 28.99

7 550 10000 1000 1 1.00E+07 56 50 9 140.00 52.27 25 52.27 28.97

8 550 10000 1000 1 1.00E+07 56 50 3 80.00 29.87 50 29.87 29.12

9 550 10000 10000 1 1.00E+08 100 50 4 90.00 60.00 0 60.00 30.00

10 550 10000 10000 1 1.00E+08 100 50 1 60.00 40.00 50 40.00 32.02



### Assumptions /

E xplanations

1. Waste quantity is assigned based on the following assumptions: 3 people per regularly occupied structure, an area of 1740 square feet per structure 2. Toxicity: Assigns a value of 1000 or 10000 3. Biodegradation: Assumes a biodegradation factor value of 1 4. Waste Characteristics Factor Category Value: Reference HRS Table 2 -7 (Subject to a Maximum of 100) 5. Exposed Individual: Reference HRS Section 5.2.1.3.1 6. Level I Targets: Reference HRS Section 5.2.1.3.2.1 (multiply by 10)
7 . Assumes the re are no workers or resources present 8. AOE = area of observed exposure, ASC = area of subsurface contamination, GW = ground water
9. 2 nd 

### pathway scores were chosen because they represent a range from little or no significant threat to almost enough to score the site based on the 2 nd 

### pathway alone

Page C- 21

# Table C

- 7i

Minimum Residents and Workers Needed to Achieve an HRS Site Score of 28.50 Based on Weighting by Level of Exposure and Sample Type

Scenario Likelihood of Exposure Waste Characteristics (WC) Targets

Pathway Score Site Score Exposed Individual AOE ASC

Target Score Waste Quantity Toxicity Degradation WC
Product WC Factor Value # Level I Residents # Level I Workers Level I Value #Level II Residents # Level II Workers Level II Value #Crawl Space Residents # Crawl Space
Workers Crawl Space
Value # Shallow Soil Gas
Workers Shallow Soil Gas

Value

1 550 100 1000 1 1.00E+05 18 50 20 68 426.67 0 0 0.00 0.00 476.67 

### 57.20 28.60

2 550 100 1000 1 1.00E+05 18 50 35 23 426.67 0 0.00 0.00 476.67 

### 57.20 28.60

3 550 100 1000 1 1.00E+05 18 50 40 8 426.67 0 0.00 0.00 476.67 

### 57.20 28.60

4 550 10000 1000 1 1.00E+07 56 45 0 40 205 108.33 0.00 0.00 153.33 

### 57.24 28.62

5 550 10000 1000 1 1.00E+07 56 45 0 50 175 108.33 0.00 0.00 153.33 

### 57.24 28.62

6 550 10000 1000 1 1.00E+07 56 45 0 60 145 108.33 0.00 0.00 153.33 

### 57.24 28.62

7 550 10000 10000 1 1.00E+08 100 45 0 25 47 40.67 0.00 0.00 85.67 

### 57.11 28.56

8 500 10000 1000 1 1.00E+07 56 20 0 0 100 195 148.50 0.00 168.50 

### 57.19 28.59

9 500 10000 1000 1 1.00E+07 56 20 0 0 0.00 0.00 168.00 

### 57.02 28.51

10 500 10000 1000 1 1.00E+07 56 20 0 0 0.00 1925 148.33 168.33 

### 57.13 28.57



### Assumptions / Explanations 1. Waste quantity is assigned based on the following assumptions: 3 people per regularly occupied structure, an area of 1740 square feet per structure
2. Toxicity: Assigns a value of 1000 or 10000
3. Degradation: Assumes a degradation factor value of 1
4. Waste Characteristics Factor Category Value: Reference HRS Table 2-7 (Subject to a Maximum of 100)
5. Exposed Individual: Reference HRS Section 5.2.1.3.1
6. Level I Targets: Reference HRS Section 5.2.1.3.2.1 (number of workers divided by 3 before being added to number of residents and the sum multiplied by 10)
7. Assumes there are no resources present
8. AOE = area of observed exposure, ASC = area of subsurface contamination, GW = ground water

Page C- 22