Updated J&E Model VIAModel.xls

Transcription

1 Updated J&E Model VIAModel.xls Helen Dawson, Ph.D. USEPA Region 8 AEHS Spring 2006

2 What s Different? Combines screening and advanced versions of the groundwater and soil gas spreadsheets. Provides default parameters for commercial buildings and commercial exposure scenarios. Uses default Q soil /Q building rather than default Q soil Incorporates reasonableness checks based on Johnson (2002).

3 What s Different, Cont d? Makes transparent the intermediate fate and transport calculations. Provides an estimate of subsurface soil gas profile under building. Provides both forward and reverse calculations: Soil gas and/or groundwater screening level concentrations Indoor air concentration estimate and corresponding cancer risk and/or hazard quotient Incorporates uncertainty calculations Provides results for multiple chemicals

4 What Hasn t Changed Same basic J&E (1991) algorithm Same conceptual assumptions

5 Intended Applications? Constrained applications: Tier 3: Exterior Site-Specific Screening No interior sampling needed Calibrated applications: Site-specific assessments Interior samples for comparison

6 J&E Model Input Constrained application:

7 J&E Model Input Constrained model input parameters Source characteristics Building characteristics Vadose zone characteristics Exposure parameters

8 J&E Model Input Source Characteristics Vapor source medium groundwater or soil gas not bulk soil Source medium concentration If groundwater: check < aqueous solubility for groundwater If soil gas: check < saturated vapor conc. for soil gas* Depth to source If groundwater: depth to water table If soil gas: depth to sample Average subsurface temperature

9 Source Characteristics

10 J&E Model Input Building Characteristics Building setting Residential Commercial/industrial Foundation type Basement w/ slab Basement w/ dirt floor Crawlspace w/ slab Crawlspace w/ dirt floor Slab-on-grade

11 Residential Building Parameters For Tier 3, default parameters for residential buildings should not be changed.

12 Commercial Building Parameters For Tier 3, default parameters for residential buildings may be changed.

13 Building Data Table

14 Residential Default Building Parameters Depth below grade to base of foundation Foundation thickness Enclosed space mixing height Fraction of foundation area with cracks Enclosed space floor area Indoor air exchange rate Qsoil/Qbuilding No Changes Typical or Mean Values Conservative

15 Residential Q soil /Q building = Sub-Slab Alpha 0.1 Filtered Sub-Slab Attenuation Factors Attenuation Factor Default Bonnie Brae Georgetown Orion Park Hppwell Precision Raymark Endicott Lowry AFB Sub-Slab Concentration (ug/m3)

16 Residential Q soil /Q building = Sub-Slab Alpha Filtered Sub-Slab Attenuation Factor Statistics Sub-Slab Attenuation Factor 1.0E E E E E E-05 Min Median 90% 95% Max Statistics DenverPCEBB Georgetown Orion Park Hopewell Precision Site Raymark Endicott LAFB Site Name Min Median 90% 95% Max DenverPCEBB 1.1E E E-03 Georgetown 1.3E E E E-03 Orion Park 5.0E E E E E-02 Hopewell Precision Site 1.5E E E E E-02 Raymark 6.3E E E E E-02 Endicott 2.6E E E E E-02 LAFB 3.5E E E E E-02

17 Model input? Q soil /Q building or Q soil? Q soil /Q building Issues: Empirical data substantial only for residential buildings with slabs Default value for commercial? Crawlspace? Dirt floors? Options: Default value Constrained range Q soil = Qbuilding ( A H ACH ) Allow Qs/Qb to vary when building parameters vary Q soil building building

18 Model input? Qsoil/Qbuilding or Qsoil? Qsoil Issues: Very limited empirical data Default values? Calculated Qsoil may yield unrealistic values. Function of soil properties and building properties Options: Default Qsoil Constrained range for Qsoil Constrain to ensure Qsoil/Qbuilding is within reasonable bounds

19 J&E Model Input Vadose Zone Characteristics Up to three soil layers 12 SCS soil types Default parameters (typical or mean values): Total porosity Water-filled porosity Bulk density

20 J&E Model Input Risk & Exposure Parameters Target risk for carcinogens Target hazard quotient for non-carcinogens Exposure scenario (tied to building type) Default Values:

21 J&E Model Output Attenuation factor Predicted indoor air concentration Critical parameters Risk based target screening levels Incremental risk estimates Soil gas profile* Uncertainty estimate* Propagation of error (coefficient of variation)

22 J&E Model Output

23 Mean = Mean = Mean = Mean = 1.03E E E E E E-2 Mean = Mean = Mean = Mean = Mean = Depth below grade to water table (m) Ls 6.7 Normal m (+_ ~1.0 ft) Average groundwater temperature ( o C) Ts 15 Normal; mean 15; stdev 1.5 Vapor concentration at water table (ug/m3) Cs Chemical Name - Chem Trichloroethylene CAS No. - CAS Chemical Properties Pure component water solubility (mg/l) S 1.472E+03 Henry's Law 25 o C (-) Hr 4.36E-01 Henry's Law system temperature (-) Hs 2.65E-01 Toxicity Factors Unit risk factor (ug/m 3-1 ) URF 2.00E-06 Reference concentration (mg/m 3 ) RfC 4.00E-02 Building setting Bldg_Setting Residential Foundation type Found_Type Basement Depth below grade to bottom of foundation (m) Lb 2.00 Foundation thickness (m) Lf 0.10 Fraction of foundation area with cracks (-) eta 2.22E-04 Enclosed space floor area (m2) Ab 100 Enclosed space height (m) Hb 3.66 Indoor air exchange rate (1/hr) ach 0.45 Lognormal; 10% 0.2, 90% 1.0 Building ventilation rate (m3/hr) Qb Average vapor flow rate into building (m3/hr) Qsoil 0.30 Lognorm; 10% 0.2; 90% 0.4; gstd same SwSA Check: Qsoil/Qbuilding C_Param Stratum A (soil below building foundation): Stratum A soil type - SCS_A Loamy Sand Stratum A thickness below foundation (m) hsa 4.70 Ls-Lb Stratum A total porosity (-) nsa Normal; mean 0.375, min 0.35 max 0.4 Stratum A water saturation (-) SwSA Lognormal, g mean 0.144; min 0.13, max 0.16 Stratum A water-filled porosity (-) nwsa Stratum A bulk density (g/cm 3 ) rhosa Stratum directly above the water table Select Stratum A, B, or C - wt_soil Stratum A Height of capillary fringe (m) hcz 0.19 Capillary zone total porosity (-) ncz Capillary zone water saturation Swcz Lognormal; gstc same as SwSA Capillary zone water filled porosity (-) nwcz Exposure Scenario Scenario Residential Uncertainty Analysis Cell: F7 Cgw Cell: F39 SwSA Cell: F8 Forecast: GW - IA Alpha Ls 10,000 Trials Frequency Chart 221 Outliers Cell: F30 Input Data Units Symbol Value Used Comments Source Characteristics: Groundwater concentration (ug/l) Cgw 140 Normal; mean 140, stdev 34 per LAFB ach Chemical: Cell: F9 Henry's Law 25 o C (atm-m 3 /mol) Hc 1.03E-02 Normal; mean 1.03E-3; stdev 2.5E Ts Building Characteristics: Cell: F Swcz Vadose zone characteristics: Cell: F Hc Cell: F38 Exposure Parameters: nsa 6.99E E E E E-3 Cell: F32 Qsoil INPUT PARAMETERS ATTENUATION FACTOR

24 Uncertainty Estimate Coefficient of variation assigned to each input parameter Propagation of error Estimate coefficient of variation for each predicted output parameter

25 Uncertainty Analysis Input

26 Uncertainty Analysis Output Uncertainty Estimate Frequency Median Estimate Mean Estimate Default Point Estimate Lifetime Cancer Risk

27 Proposed New Name for Spreadsheet Vapor Intrusion Assessment Guidance for Risk Assessment