HomeMy WebLinkAbout10036_South End Transit_Southline VI Risk Evaluation Rpt Final 03-04-13-OCR
March 4,
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Vapor Intrusion Risk Evaluation Page 2
Transit-Oriented, Multi-Family Residential Project, Southline Apartments March 4, 2013
Based on these exceedences, PSI returned to the site in December 2012 to collect additional
samples at the locations showing exceedences. The results of the December 2012 sampling
indicated exceedences only in the sample collected at the Building 18 Lower location.
In the event of exceedences of IHSB VISLs for individual constituents, the Brownfields Program
Vapor Intrusion Guidelines (March 2012) specify that additional risk calculations can be
performed to further evaluate the data. ATC was contracted to perform additional risk
calculations, as detailed in this submittal. The primary goal of the calculations was to determine
whether the sub-slab soil gas data poses a sufficient risk to require active venting or additional
sampling to confirm the vapor mitigation system performance.
2.0 Risk Calculation Procedures
ATC performed calculations to evaluate the cumulative risk for the combined constituents of
concern for each sample showing exceedences of IHSB VISLs for residential soil gas for
individual constituents. The samples included Building 17 Upper, Building 18 Upper, and
Building 18 Lower collected in September 2012, as well as Building 18 Lower collected in
December 2012. Per the process specified in the Brownfields Program Vapor Intrusion
Guidelines (March 2012), ATC initially calculated the predicted indoor air concentration by
multiplying the sub-slab concentrations by a sub-slab to indoor air attenuation factor of 0.1
(1/10). ATC then calculated the cumulative carcinogenic risk and hazard index based on the
predicted indoor air concentrations.
Chloroform was removed from the cumulative risk calculation since the Brownfields Program
previously concurred that detection of this constituent was associated with city water rather than
vapor intrusion. Note that ATC considers it likely that additional detected constituents are also
associated with sources other than vapor intrusion. However, inclusion of these constituents
does not significantly impact the cumulative risk results. Therefore, all detected constituents
except for chloroform were included in the cumulative risk evaluation.
3.0 Risk Evaluation Results
The Brownfields Program requires mitigation for sites showing repeated exceedences of a
carcinogenic risk limit of 10-4 and hazard index limit of 1. The results of the risk calculations for
the subject site indicated no exceedences of carcinogenic risk limit of 10-4. Calculated hazard
index values were below the limit of 1 for all samples except the Building 18 Lower sample
collected in September 2012, which indicated a hazard index of 1.06. The risk calculations are
included in Attachment 1.
ATC does not consider the hazard index value for the Building 18 Lower sample to represent a
significant risk based on several lines of evidence. First, the risk calculations performed by ATC
were based on an extremely conservative sub-slab to indoor air attenuation factor of 0.1 (1/10).
If an attenuation factor of 0.094 (1/10.6) is applied, the calculated risk for the September 2012
Building 18 Lower sample would drop below the hazard index limit of 1. ATC considers it
likely that the actual attenuation factor at the subject site is substantially less than 0.094 based on
both published references and the building construction, as further discussed below.
Vapor Intrusion Risk Evaluation Page 3
Transit-Oriented, Multi-Family Residential Project, Southline Apartments March 4, 2013
The Environmental Protection Agency (EPA) originally recommended an attenuation factor of
0.1 (1/10) in their 2002 OSWER Draft Guidance for Evaluating the Vapor Intrusion to Indoor
Air Pathway from Groundwater and Soils. However, additional data collected over the past 10
years suggest that a lower attenuation factor is appropriate for even the most conservative
assessment (note that a lower attenuation factor represents less vapor intrusion through the slab).
The EPA released a report entitled EPA’s Vapor Intrusion Database: Evaluation and
Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds and
Residential Buildings on March 16, 2012. Based on an EPA database of over 400 samples, this
report calculated a median sub-slab soil gas attenuation factor of 0.003 (1/333), and the 95th
percentile was found to be 0.03 (1/33). The EPA is currently preparing an updated vapor
intrusion guidance document which has not yet been released. However, the draft guidance
reportedly recommends an attenuation factor of 0.03 (1/33). Other regulatory programs and
states are using even lower attenuation factors on the order of 0.01 (1/100). These data clearly
show that the calculated passing attenuation factor of 0.094 (1/10.6) for the subject site is very
conservative.
Furthermore, the building at the subject site is constructed with a vapor barrier and passive
venting system, as well as a newly installed concrete slab. A building with this construction is
expected to have a slab attenuation factor which is many orders of magnitude higher than the
most conservative EPA recommendations. Based on the building construction, ATC considers it
extremely unlikely that indoor air concentrations exceed applicable risk levels due to vapor
intrusion.
Lastly, the Brownfields Vapor Intrusion Guidelines specifically state that mitigation is required
if sampling shows “repeated” exceedences of the hazard index limit of 1. At the Building 18
Lower location, samples were collected on two occasions in September 2012 and December
2012. The September 2012 sample indicated a hazard index of 1.06, which only slightly exceeds
the limit of 1. The December 2012 sample indicated a hazard index of 0.524, which is
significantly below the limit of 1. The data do not show “repeated” exceedences, and therefore
mitigation does not appear to be required.
4.0 Conclusions and Recommendations
ATC has completed a vapor intrusion risk evaluation for the Southline Apartments site in
Charlotte, North Carolina. Previous sub-slab soil gas sampling indicated exceedences of IHSB
VISLs for residential soil gas at three locations (Building 17 Upper, Building 18 Upper, and
Building 18 Lower). ATC calculated predicted indoor air concentrations based on a conservative
slab attenuation factor of 0.1 (1/10), then calculated the cumulative risk for the combined
constituents of concern based on the predicted indoor air concentrations. The results of the
calculations indicated an exceedence of the hazard index limit of 1 in only one sample
(September 2012 Building 18 Lower). However, based on an evaluation of the data, ATC
concludes that this sample does not indicate a significant vapor intrusion risk because (1) the
calculated risk was based on an overly conservative slab attenuation factor, and (2) later
sampling at the same location indicated no exceedences of acceptable risk levels. Based on the
results of this risk evaluation, ATC recommends no further vapor intrusion investigation or
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ATTACHMENT 1
VAPOR INTRUSION RISK CALCULATIONS
RISK CALCULATIONS
Southline Apartments Project
140 Remount Road
Charlotte, Mecklenburg County, NC
Brownfields Project No. 10036-06-60
ATC Project No. 089.43337.1724
Page 1 of 5
Risk Equations
Step 1 - Calculation of predicted indoor air concentration.
Predicted Indoor Air Concentration = Sub-slab Soil Gas Concentration x Default Sub-slab to Indoor Air Attenuation Factor of 0.1
Step 2 - Calculation of cumulative risk based on predicted indoor air concentrations.
Carcinogenic Risk = [ concentration(x)/screening level(x) + concentration(y)/screening level(y) + concentration(z)/screening level (z) ] * 10-6
Hazard Index = [ concentration(x)/screening level(x) + concentration(y)/screening level(y) + concentration(z)/screening level (z) ]
References
Summary of Risk Calculation Results
Carcinogenic Risk Hazard Index
Exceedences of
Target Risk Levels?
Building 17 Upper BLDG-17-UPPER 9/28/2012 4.39E-06 4.71E-01 No
Building 18 Upper BLDG-18-UPPER 9/13/2012 1.38E-06 2.76E-01 No
Building 18 Lower BLDG-18-LOWER 9/28/2012 1.08E-05 1.06E+00 Yes*
Building 18 Lower BLDG-18-LOWER 12/14/2012 2.56E-06 5.24E-01 No
* - See discussion in report text. ATC recommends that this exceedence be disregarded based on more detailed data evaluation.
Risk Evaluation Results
Per the Brownfields Program Vapor Intrusion Guidance1, a default sub-slab soil gas to indoor air attenuation factor of 0.1 was used to calculate the predicted
indoor air concentration via the equation shown below.
The attached spreadsheets show cumulative risk calculations for each sample showing exceedences of IHSB VISLs for soil gas. Refer to Table 1 of the Sub-Slab
Vapor Sampling Results report prepared by PSI and dated January 24, 2013, for a comparison of analytical data for individual constituents to VISLs. Chloroform
was removed from the cumulative risk evaluation since the Brownfields Program has already concurred that this constituent is indicative of city water. It should
be noted that additional constituents are also likely indicative of sources other than vapor intrusion. However, removal of these constituents from the calculations
does not substantially affect the cumulative risk results. As such, all detected constituents except chloroform were included in the cumulative risk calculations.
1. NC Division of Waste Management. Draft Vapor Intrusion Guidelines of the Brownfields Program. March 2012.
2. Environmental Protection Agency, Mid-Atlantic Risk Assessment. Regional Screening Table - User's Guide. November 2012. http://www.epa.gov/reg3hscd/risk/human/rb-
concentration_table/usersguide.htm.
3. Environmental Protection Agency, Mid-Atlantic Risk Assessment. Regional Screening Level Resident Air Supporting Table. November 2012. http://www.epa.gov/reg3hscd/risk/human/rb-
concentration_table/Generic_Tables/pdf/resair_sl_table_run_NOV2012.pdf.
4. The DWM IHSB VISLs for indoor air are the lower of the EPA Carcinogenic RSL for a target risk of 10-6 or the EPA Noncarcinogenic RSL adjusted for a hazard quotient of 0.2. (The EPA
website reports Noncarcinogenic RSLs based on a hazard quotient of 1; the value is divided by 5 to adjust for a hazard quotient of 0.2.)
Per EPA protocol2, cumulative carcinogenic risk and non-cancer hazard index for multiple chemicals of concern (x, y, and z in the example below) in indoor air
were calculated via the equations shown below. The screening levels referenced in the equations are the EPA Carcinogenic and Noncarcinogenic Regional
Screening Levels (RSLs)3. For the subject site evaluation, the EPA RSLs for residential land use were used. Note that the EPA RSLs are the basis for the NC
Division of Waste Management (DWM) Inactive Hazardous Sites Program (IHSB) Vapor Intrusion Screening Levels (VISLs)4. As such, use of these screening
levels is in accordance with NC DWM protocol.
Building Location Sample ID Date Collected
RISK CALCULATIONS
Southline Apartments Project
140 Remount Road
Charlotte, Mecklenburg County, NC
Brownfields Project No. 10036-06-60
ATC Project No. 089.43337.1724
Page 2 of 5
Risk Calculations for Individual Samples
Sample ID:
Date:
Constituent Concentration (µg/m3) Slab Attenuation Factor Predicted Indoor Air
Concentration
Residential Carcinogenic
RSL3 Carcinogenic Risk
Benzyl Chloride 1.2 0.1 0.12 5.0E-02 2.40E-06
Carbon Tetrachloride 0.36 0.1 0.04 4.1E-01 8.78E-08
Chloroethane 0.34 0.1 0.03 NE NA
Chloromethane 0.91 0.1 0.09 NE NA
Dibromochloromethane 0.29 0.1 0.03 9.0E-02 3.22E-07
Dichlorodifluoromethane (Freon 12) 34 0.1 3.40 NE NA
1,1-Dichloroethane 0.71 0.1 0.07 1.5E+00 4.73E-08
Methylene Chloride 1.5 0.1 0.15 9.6E+01 1.56E-09
Tetrachloroethylene (PCE) 4.2 0.1 0.42 9.4E+00 4.47E-08
1,1,1-Trichloroethane 4.9 0.1 0.49 NE NA
Trichloroethylene (TCE) 6.4 0.1 0.64 4.3E-01 1.49E-06
Trichlorofluoromethane (Freon 11) 6.2 0.1 0.62 NE NA
1,1,2-Trichloro-1,2,2-trifluoroethane 0.69 0.1 0.07 NE NA
4.39E-06
NO
Constituent Concentration (µg/m3) Slab Attenuation Factor Predicted Indoor Air
Concentration
Residential
Noncarcinogenic RSL3 Hazard Index
Benzyl Chloride 1.2 0.1 0.12 1.0E+00 1.20E-01
Carbon Tetrachloride 0.36 0.1 0.04 1.0E+02 3.60E-04
Chloroethane 0.34 0.1 0.03 1.0E+04 3.40E-06
Chloromethane 0.91 0.1 0.09 9.4E+01 9.68E-04
Dibromochloromethane 0.29 0.1 0.03 NE NA
Dichlorodifluoromethane (Freon 12) 34 0.1 3.40 1.0E+02 3.40E-02
1,1-Dichloroethane 0.71 0.1 0.07 NE NA
Methylene Chloride 1.5 0.1 0.15 6.3E+02 2.38E-04
Tetrachloroethylene (PCE) 4.2 0.1 0.42 4.2E+01 1.00E-02
1,1,1-Trichloroethane 4.9 0.1 0.49 5.2E+03 9.42E-05
Trichloroethylene (TCE) 6.4 0.1 0.64 2.1E+00 3.05E-01
Trichlorofluoromethane (Freon 11) 6.2 0.1 0.62 7.3E+02 8.49E-04
1,1,2-Trichloro-1,2,2-trifluoroethane 0.69 0.1 0.07 3.1E+04 2.23E-06
4.71E-01
NO
Notes:
NE = No established RSL.
NA = Not applicable.
Exceeds Carcinogenic Risk Limit of 10-4?
Noncarcinogenic Hazard Index Calculations
Cumulative Hazard Index
Exceeds Hazard Index of 1?
Carcinogenic Risk Calculations
Cumulative Carcinogenic Risk
BLDG-17-Upper
9/28/2012
RISK CALCULATIONS
Southline Apartments Project
140 Remount Road
Charlotte, Mecklenburg County, NC
Brownfields Project No. 10036-06-60
ATC Project No. 089.43337.1724
Page 3 of 5
Risk Calculations for Individual Samples
Sample ID:
Date:
Constituent Concentration (µg/m3) Slab Attenuation Factor Predicted Indoor Air
Concentration
Residential Carcinogenic
RSL3 Carcinogenic Risk
Carbon Tetrachloride 0.31 0.1 0.03 4.1E-01 7.56E-08
Chloroethane 0.29 0.1 0.03 NE NA
Chloromethane 0.70 0.1 0.07 NE NA
Dichlorodifluoromethane (Freon 12) 8.4 0.1 0.84 NE NA
1,1-Dichloroethane 0.24 0.1 0.02 1.5E+00 1.60E-08
Methylene Chloride 1.5 0.1 0.15 9.6E+01 1.56E-09
Tetrachloroethylene (PCE) 3.2 0.1 0.32 9.4E+00 3.40E-08
1,1,1-Trichloroethane 2.7 0.1 0.27 NE NA
Trichloroethylene (TCE) 5.4 0.1 0.54 4.3E-01 1.26E-06
Trichlorofluoromethane (Freon 11) 7.3 0.1 0.73 NE NA
1,1,2-Trichloro-1,2,2-trifluoroethane 0.58 0.1 0.06 NE NA
1.38E-06
NO
Constituent Concentration (µg/m3) Slab Attenuation Factor Predicted Indoor Air
Concentration
Residential
Noncarcinogenic RSL3 Hazard Index
Carbon Tetrachloride 0.31 0.1 0.03 1.0E+02 3.10E-04
Chloroethane 0.29 0.1 0.03 1.0E+04 2.90E-06
Chloromethane 0.70 0.1 0.07 9.4E+01 7.45E-04
Dichlorodifluoromethane (Freon 12) 8.4 0.1 0.84 1.0E+02 8.40E-03
1,1-Dichloroethane 0.24 0.1 0.02 NE NA
Methylene Chloride 1.5 0.1 0.15 6.3E+02 2.38E-04
Tetrachloroethylene (PCE) 3.2 0.1 0.32 4.2E+01 7.62E-03
1,1,1-Trichloroethane 2.7 0.1 0.27 5.2E+03 5.19E-05
Trichloroethylene (TCE) 5.4 0.1 0.54 2.1E+00 2.57E-01
Trichlorofluoromethane (Freon 11) 7.3 0.1 0.73 7.3E+02 1.00E-03
1,1,2-Trichloro-1,2,2-trifluoroethane 0.58 0.1 0.06 3.1E+04 1.87E-06
2.76E-01
NO
Notes:
NE = No established RSL.
NA = Not applicable.
Exceeds Carcinogenic Risk Limit of 10-4?
BLDG-18-Upper
9/13/2012
Carcinogenic Risk Calculations
Cumulative Carcinogenic Risk
Noncarcinogenic Hazard Index Calculations
Cumulative Hazard Index
Exceeds Hazard Index of 1?
RISK CALCULATIONS
Southline Apartments Project
140 Remount Road
Charlotte, Mecklenburg County, NC
Brownfields Project No. 10036-06-60
ATC Project No. 089.43337.1724
Page 4 of 5
Risk Calculations for Individual Samples
Sample ID:
Date:
Constituent Concentration (µg/m3) Slab Attenuation Factor Predicted Indoor Air
Concentration
Residential Carcinogenic
RSL3 Carcinogenic Risk
Carbon Tetrachloride 0.38 0.1 0.04 4.1E-01 9.27E-08
Chloroethane 0.75 0.1 0.08 NE NA
Chloromethane 0.49 0.1 0.05 NE NA
Dibromochloromethane 4.9 0.1 0.49 9.0E-02 5.44E-06
Dichlorodifluoromethane (Freon 12) 3.0 0.1 0.30 NE NA
Tetrachloroethylene (PCE) 0.99 0.1 0.10 9.4E+00 1.05E-08
1,1,1-Trichloroethane 0.33 0.1 0.03 NE NA
Trichloroethylene (TCE) 22 0.1 2.20 4.3E-01 5.12E-06
Trichlorofluoromethane (Freon 11) 46 0.1 4.60 NE NA
1,1,2-Trichloro-1,2,2-trifluoroethane 0.63 0.1 0.06 NE NA
Vinyl Chloride 0.18 0.1 0.02 1.6E-01 1.13E-07
1.08E-05
NO
Constituent Concentration (µg/m3) Slab Attenuation Factor Predicted Indoor Air
Concentration
Residential
Noncarcinogenic RSL3 Hazard Index
Carbon Tetrachloride 0.38 0.1 0.04 1.0E+02 3.80E-04
Chloroethane 0.75 0.1 0.08 1.0E+04 7.50E-06
Chloromethane 0.49 0.1 0.05 9.4E+01 5.21E-04
Dibromochloromethane 4.9 0.1 0.49 NE NA
Dichlorodifluoromethane (Freon 12) 3.0 0.1 0.30 1.0E+02 3.00E-03
Tetrachloroethylene (PCE) 0.99 0.1 0.10 4.2E+01 2.36E-03
1,1,1-Trichloroethane 0.33 0.1 0.03 5.2E+03 6.35E-06
Trichloroethylene (TCE) 22 0.1 2.20 2.1E+00 1.05E+00
Trichlorofluoromethane (Freon 11) 46 0.1 4.60 7.3E+02 6.30E-03
1,1,2-Trichloro-1,2,2-trifluoroethane 0.63 0.1 0.06 3.1E+04 2.03E-06
Vinyl Chloride 0.18 0.1 0.02 1.0E+02 1.80E-04
1.06E+00
YES
Notes:
NE = No established RSL.
NA = Not applicable.
Exceeds Carcinogenic Risk Limit of 10-4?
Cumulative Carcinogenic Risk
Noncarcinogenic Hazard Index Calculations
Cumulative Hazard Index
Exceeds Hazard Index of 1?
BLDG-18-Lower
9/28/2012
Carcinogenic Risk Calculations
RISK CALCULATIONS
Southline Apartments Project
140 Remount Road
Charlotte, Mecklenburg County, NC
Brownfields Project No. 10036-06-60
ATC Project No. 089.43337.1724
Page 5 of 5
Risk Calculations for Individual Samples
Sample ID:
Date:
Constituent Concentration (µg/m3) Slab Attenuation Factor Predicted Indoor Air
Concentration
Residential Carcinogenic
RSL3 Carcinogenic Risk
Trichloroethylene (TCE) 11 0.1 1.10 4.3E-01 2.56E-06
2.56E-06
NO
Constituent Concentration (µg/m3) Slab Attenuation Factor Predicted Indoor Air
Concentration
Residential
Noncarcinogenic RSL3 Hazard Index
Trichloroethylene (TCE) 11 0.1 1.10 2.1E+00 5.24E-01
5.24E-01
NO
Notes:
NE = No established RSL.
NA = Not applicable.
Exceeds Hazard Index of 1?
Noncarcinogenic Hazard Index Calculations
Cumulative Hazard Index
BLDG-18-Lower
12/14/2012
Exceeds Carcinogenic Risk Limit of 10-4?
Carcinogenic Risk Calculations
Cumulative Carcinogenic Risk