The Soil Category S-3 standards are based on a short but intense construction/excavation exposure scenario in which the potential receptor may come into contact with the contaminated soil through direct contact (ingestion and dermal absorption) and through the inhalation of airborne particulates.

General Methodology

The sequential approach taken to develop the MCP S-3 Soil standards is as follows:

Step

Description

1.

A noncancer risk-based concentration associated with 20% of an allowable daily intake is identified.

2.

A cancer risk-based concentration associated with an excess lifetime cancer risk of one-in-one million (10-6) is identified.

3.

A leaching-based concentration (a level in soil considered protective of the applicable groundwater standard) is identified. (Workbook: MCP Leach.xls, Sheet: Leaching, columns: H-J)

4.

A ceiling concentration is identified. The ceiling concentration varies by category, as described below. (Workbook: MCP Toxicity.xls, sheet: Toxicity, columns BJ - BQ)

5.

The lowest of the concentrations identified in steps 1 through 4 is carried through the process.

6.

A Practical Quantitation Limit (PQL) for an appropriately sensitive analytical method is identified (Workbook: MCP Toxicity.xls, sheet: Toxicity, column: AP).

7.

A background concentration is identified, if available (Workbook: MCP Toxicity.xls, sheet: Toxicity, column: AD).

8.

The highest of the three values identified in steps 5, 6 and 7 is chosen.

9.

The value identified in step 8 is rounded to one significant figure. This value is adopted as the Method 1 Soil Standard for the specified soil category.

 

This process is diagramed:

Diagram of S-1 Development Methodology

Equations

Noncancer Risk-Based Soil Concentrations

The noncancer risk-based concentration of a chemical in soil is a function of the direct contact exposure (ingestion, dermal contact) and inhalation of particulates. Inhalation of particulates can result in both an inhalation exposure (through the lungs), as well as an ingestion exposure when heavier particulates are deposited in the upper respiratory tract and subsequently swallowed (MADEP, 2002).

Ingestion & Dermal Exposures

The noncancer risk-based concentration associated with ingestion and dermal contact with contaminated soil is calculated using the following equation:

equation 14 (equation 14)

Workbook: MCP Soil.xls, Sheet: S-3, column: B

parameter
 
description

[OHM]nc-id
=

Target noncancer risk-based concentration in soil, based on direct contact (ingestion and dermal exposure) with the soil and ingestion of inhaled particulates, (mg/kg)

HI
=
Target Hazard Index level (unitless)
RfDoral
=
chronic oral Reference Dose or equivalent toxicity value, (mg/kg/day)
ADSIR
=
Average Daily Soil Ingestion Rate, (1/day)
ADSIGIE=

Average Daily Soil Inhalation - GI Exposure, (1/day)

RAFnc-ing
=
Relative Absorption Factor for noncancer, oral exposures (unitless)
ADSDCR
=
Average Daily Soil Dermal Contact Rate, (1/day)
RAFnc-dermal
=
Relative Absorption Factor for noncancer, dermal exposures (unitless)
 

The exposure terms, ADSIR, ADSIGIE, and ADSDCR, are compilations of exposure assumptions that are not chemical-specific. They are calculated as follows.

S1 Equation 2 (equation 15)

Workbook: MCP Soil.xls Sheet: S-3 Assumptions cell: J22

And,

equation 16 (equation 16)

Workbook: MCP Soil.xls Sheet: S-3 Assumptions cell: O87

And,

S1 Equation 3 (equation 17)

Workbook: MCP Soil.xls Sheet: S-3 Assumptions cell: K44

parameter
 
description
 

ADSIR
=
Average Daily Soil Ingestion Rate, (1/day)
ADSIGIE
=
Average Daily Soil Inhalation-GI Exposure, (1/day)
ADSDCR
=
Average Daily Soil Dermal Contact Rate, (1/day)
IRsoil
=
Soil Ingestion Rate, (mg/day)
PM10=

Concentration of Particulate Matter of diameter 10 microns or less in air, (µg/m3)

Fing=

Fraction of PM 10 material ingested, (unitless)

VRw=

Ventilation Rate for a worker, (liters/minute)

SSA
=
Average Daily Skin Surface Area Exposed, (cm2/day)
SAF
=
Soil Adherence Factor, (mg/cm2)
EF1
=
Exposure Frequency (days/week)
EF2
=
Exposure Frequency, (weeks/year)
EF3=

Exposure Frequency, (hours/day)

EP
=
Exposure Period, (years)
BW=Body Weight (kg)
AP=Averaging Period (years)
C1=Conversion Factor (365 days/year)
C2
=
Conversion Factor (106 mg/kg)
C4=Conversion Factor (10 -9 kg/µg)
C8=Conversion Factor (0.143 weeks/day)
C9=Conversion Factor (0.001 m3/liter)
C10=Conversion Factor (60 minutes/hour)
 

Inhalation of Airborne Particulates

Typical residential (S-1) exposure scenarios generate little dust from outdoor soil. The risk associated with dust inhalation in a residential setting is insignificant in both an absolute sense and relative to the high direct contact exposures assumed for residents. In contrast, the relative risk from inhalation exposure is higher for a construction/excavation scenario because (a) the activities at the site actively generate dust, increasing the magnitude of this exposure, and (b) the shorter exposure period for construction workers results in a smaller direct contact risk. The noncancer risk-based concentration associated with the inhalation of airborne particulates is calculated using the following equation:

equation 18 (equation 18)

Workbook: MCP Soil.xls, Sheet: S-3, column C

parameter
 
description
 

[OHM]nc-part
=
Target noncancer risk-based concentration in soil, based on inhalation of airborne particulates, (mg/kg)
HI
=
Target Hazard Index level (unitless)
RfCsub
=
Subchronic inhalation Reference Concentration or equivalent toxicity value, (mg/m3)
ADSIE
=
Average Daily Soil Inhalation Exposure, (kg/m3)
 

The exposure term, ADSIE, is a compilation of exposure assumptions that are not chemical-specific. The factor is calculated:

equation 19 (equation 19)

Workbook: MCP Soil.xls, Sheet: S-3 Assumptions, cell N66

parameter
 
description
 

ADSIE
=
Average Daily Soil Inhalation Exposure, (kg/m3)
PM10
=
Concentration of Particulate Matter of diameter 10 microns or less in air, (µg/m3)
Finh
=
Fraction of PM10 material inhaled, (unitless)
VRw
=
Ventilation Rate for a worker, (liters/minute)
VRd
=
Default Ventilation Rate, (liters/day)
EF1
=
Exposure Frequency (days/week)
EF3
=
Exposure Frequency, (hours/day)
EP
=
Exposure Period, (weeks)
AP=Averaging Period (weeks)
C3=Conversion Factor (0.006 weeks/hour)
C4=Conversion Factor (10-9 kg/µg)
C5
=
Conversion Factor (1440 minutes/day)
 

Cumulative Noncancer Risk-Based Soil Concentration

Having calculated the target soil concentrations for indirect contact (ingestion, dermal contact and ingestion of inhaled particulates) and inhalation of particulates separately, a target soil concentration protective of both exposure pathways is calculated using a harmonic mean:

equation 20 (equation 20)

Workbook: MCP Soil.xls, sheet: S-3, column D

parameter
 
description
 

[OHM]soil-nc
=
Target noncancer risk-based concentration in soil (mg/kg)
[OHM]nc-id
=
Target noncancer concentration in soil based on ingestion and dermal contact (mg/kg)
[OHM]nc-part
=
Target noncancer concentration in soil based on inhalation of particulates (mg/kg)
 

Cancer Risk-Based Soil Concentrations

The cancer risk-based concentration of a chemical in soil is a function of the direct contact exposure (ingestion, dermal contact) and inhalation of particulates. Inhalation of particulates can result in both an inhalation exposure (through the lungs), as well as an ingestion exposure when heavier particulates are deposited in the upper respiratory tract and subsequently swallowed (MADEP, 2002).

Ingestion & Dermal Exposures

The cancer risk-based concentration associated with ingestion and dermal exposure of contaminated soil is calculated using the following equation:

equation 21 (equation 21)

Workbook: MCP Soil.xls, Sheet: S-3, column: E

parameter
 
description
 

[OHM]ca-id
=
Target cancer risk-based concentration in soil, based on direct contact (ingestion and dermal exposure) with the soil, (mg/kg)
ELCR
=
Target Excess Lifetime Cancer Risk level (unitless)
LADSIR
=
Lifetime Average Daily Soil Ingestion Rate, (1/day)
LADSIGIE=

Lifetime Average Daily Inhalation-GI Exposure, (1/day)

RAFca-ing
=
Relative Absorption Factor for cancer, oral exposures (unitless)
LADSDCR
=
Lifetime Average Daily Soil Dermal Contact Rate, (1/day)
RAFca-dermal
=
Relative Absorption Factor for cancer, dermal exposures (unitless)
CSForal
=
Oral Cancer Slope Factor, (mg/kg/day)-1
 

The exposure terms, LADSIR, LADSIGIE and LADSDCR, are compilations of exposure assumptions that are not chemical-specific. They are calculated as follows.

equation 22 (equation 22)

Workbook: MCP Soil.xls Sheet: S-3 Assumptions cell: J30

And,

equation 23 (equation 23)

Workbook: MCP Soil.xls Sheet: S-3 Assumptions cell: O95

And,

equation 24 (equation 24)

Workbook: MCP Soil.xls Sheet: S-3 Assumptions cell: K44

parameter
 
description
 

LADSIR
=
Lifetime Average Daily Soil Ingestion Rate, (1/day)
LADSIGIE
=
Lifetime Average Daily Soil Inhalation-GI Exposure, (1/day)
LADSDCR
=
Lifetime Average Daily Soil Dermal Contact Rate, (1/day)
IRsoil,x
=
Soil Ingestion Rate, specific to each age group, (mg/day)
PM10=

Concentration of Particulate Matter of diameter 10 microns or less in air, (µg/m3)

Fing=

Fraction of PM10 material ingested, (unitless)

VRw=Ventilation Rate for a worker, (liters/minute)
SSAx
=
Average Daily Skin Surface Area Exposed, specific to each age group (cm2/day)
SAFx
=
Soil Adherence Factor, specific to each age group (mg/cm2)
EF1,x
=
Exposure Frequency specific to each age group (days/week)
EF2,x
=
Exposure Frequency specific to each age group (weeks/year)
EF3=

Exposure Frequency, (hours/day)

EPx
=
Exposure Period specific to each age group (years)
BWx
=
Body Weight specific to each age group (kg)
AP=Averaging Period (years)
C1=Conversion Factor (365 days/year)
C2=Conversion Factor (106 mg/kg)
C4=Conversion Factor (10-9 kg/µg)
C9=Conversion Factor (0.001 m3/liter)
C10=Conversion Factor (60 minutes/hour)
C11=

Conversion Factor (365 days/years)

C12=Conversion Factor (0.0027 years/day)
 

Inhalation of Airborne Particulates

As described previously, the relative risk from inhalation exposure is higher for a construction/excavation scenario because (a) the activities at the site actively generate dust, increasing the magnitude of this exposure, and (b) the shorter exposure period for construction workers results in a smaller direct contact risk. The cancer risk-based concentration associated with the inhalation of airborne particulates is calculated using the following equation:

equation 25 (equation 25)

Workbook: MCP Soil.xls, Sheet: S-3, column F

parameter
 
description
 

[OHM]ca-part
=
Target cancer risk-based concentration in soil, based on inhalation of airborne particulates, (mg/kg)
ELCR
=
Target Excess Lifetime Cancer Risk level (unitless)
URinh
=
Inhalation Unit Risk value, or equivalent toxicity value, (µg/m3)-1
LADSIE
=
Lifetime Average Daily Soil Inhalation Exposure, ((µg/m3)/(mg/kg))
 

The exposure term, LADSIE, is a compilation of exposure assumptions that are not chemical-specific. The factor is calculated:

equation 26 (equation 26)

Workbook: MCP Soil.xls, Sheet: S-3 Assumptions, cell N74

parameter
 
description
 

LADSIE
=
Lifetime Average Daily Soil Inhalation Exposure, ((µg/m3)/(mg/kg))
PM10
=
Concentration of Particulate Matter of diameter 10 microns or less in air, (µg/m3)
Finh
=
Fraction of PM10 material inhaled, (unitless)
VRw
=
Ventilation Rate for a worker, (liters/minute)
VRd=Default Ventilation Rate, (liters/day)
EF1=Exposure Frequency (days/week)
EF2=Exposure Frequency (weeks/year)
EF3
=
Exposure Frequency, (hours/day)
EP
=
Exposure Period, (years)
AP
=
Averaging Period (years)
C5
=
Conversion Factor (1440 minutes/day)
C6=Conversion Factor (1.1E-04 years/hour)
C7
=
Conversion Factor (10-6 kg/mg)
 

Cumulative Cancer Risk-Based Soil Concentration

Having calculated the target soil concentrations for indirect contact (ingestion, dermal contact and ingestion of inhaled particulates) and inhalation of particulates separately, a target soil concentration protective of both exposure pathways is calculated using a harmonic mean:

equation 27 (equation 27)

Workbook: MCP Soil.xls, sheet: S-3, column D

parameter
 
description
 

[OHM]soil-ca
=
Target cancer risk-based concentration in soil (mg/kg)
[OHM]ca-id
=
Target cancer concentration in soil based on ingestion and dermal contact (mg/kg)
[OHM]ca-part
=
Target cancer concentration in soil based on inhalation of particulates (mg/kg)
 

Input Parameters

The Method 1 S-3 Soil Standards are based on a short-term adult construction/excavation exposure to soil.

Factor

Age

Value

Units

Comment


Body Weight (BW)

 

22

58

kg

Median (50th %-tile) body weight, ages 18-25 years (females).
Soil Ingestion Rate (IRsoil)
 22100mg/day

Enhanced soil ingestion rate for construction/excavation workers (MADEP 2002a)

Skin Surface Area (SSA)
 223,473cm2

Average of median values of the face, hands, forearms, lower legs and feet for adult females. (EPA, 1997)

Soil Adherence Factor (SAF)

 

22

0.29

mg/cm2

Weighted average of adherence factors for specific body parts exposed (MA DEP 2002)

Particulate Concentration in Air (PM10)
(PM10)
2260µg/m3Default PM 10 concentration for excavation scenario (MADEP 1995, Appendix B)
Fraction of Particulates Inhaled (Finh)
(Finh)
220.5unitlessAssumed half of the PM 10 material reaches the lung and is available as an inhalation exposure (MADEP, 2002)
Fraction of Particulates Ingested (Fing)
(Fing)
221.5unitlessAssumed half of the PM 10 material and all of the PM 10-30 is deposited in the GI tract and is swallowed (MADEP, 2002)
Exposure Frequency (EF)
EF1
225days/weekEF reflects an occupational exposure over a 6-month construction project.
EF2
2226weeks/year
EF3
228hours/day
Exposure Period (EP)
Noncancer
2226weeks

Note that for cancer risk, the combination of EF2 and EP calculate to be a 26 week exposure.

Cancer
221year
Averaging Period (AP)
Noncancer
2226weeks

Equal to EP for noncancer risk, a lifetime for cancer risk.

Cancer

22

70

years