An Empirical Approach to Site Assessment for Vapor Intrusion

Size: px
Start display at page:

Download "An Empirical Approach to Site Assessment for Vapor Intrusion"

Transcription

1 An Empirical Approach to Site Assessment for Vapor Intrusion Presented by: Helen Dawson, Hydrogeologist Susan Griffin, Toxicologist USEPA Region 8 Denver, CO NSAS Conference 2007

2 An Empirical Approach to Site Assessment for Vapor Intrusion Outline Vapor Intrusion Assessment Issues EPA s Empirical Vapor Intrusion Database Billings PCE Site Case Study

3 Vapor Intrusion Assessment Issues Multiple potential subsurface and exposure scenarios Spatial and temporal variability Indoor and ambient air sources

4 Vapor Intrusion Pathway Potential Scenarios Generic CSM T. McAlary

5 Indoor Air Spatial Variability REDFIELD 1478 & 1488 SO. KRAMERIA µg/m 3 4 µg/m

6 Spatial (and Temporal) Variability Groundwater Soil Gas Sub-Slab

7 Background Indoor Air Conc. Literature Review th Percentile 10E-6 RBC Carbon tetrachloride Chloroform 1,1- Dichloroethylene Methylene chloride Tetrachloroethylene 1,1,1- Trichloroethane Trichloroethylene Vinyl chloride Indoor Air Conc. (ug/m3) 21 studies compiled Dawson, 2007

8 H. Dawson (2007) Background Indoor Air Concentrations Tetrachloroethylene (ug/m 3 ) Reference Sample Dates N %Detect RL 25% 50% 75% 90% 95% 98% Max Sheldon et al, Clayton et al < US EPA Sexton et al Foster et al (2002); Kurtz (PC 2005) < Kurtz & Folkes < NYSDOH < Zhu et al, Median

9 EPA s Empirical Database of Vapor Intrusion Sites 43 Total sites (33 CHC, 12 PHC) 36 sites with paired indoor air / groundwater 14 sites with paired indoor air / subslab 19 sites with paired indoor air / soil gas 2570 paired measurements (2500 CHC, 70 PHC) 1143 paired indoor air / groundwater 1549 paired indoor air / subslab 186 paired indoor air / soil gas

10 Filterable Spreadsheet Database Site Characteristics: Site, chemical, medium, building type, foundation type, soil type, etc... Data quality: > DL, source strength, data consistency

11 What does the database show us? Sub-slab indoor air attenuation Groundwater indoor air attenuation

12 Sub-Slab / Indoor Air Attenuation 1.E+04 Indoor Air vs Sub-Slab Concentration Subslab Attenuation Factors Subslab Attenuation Stat Database Min 3.5E-05 Indoor Air Concentration (ug/m3) 1.E+03 1.E+02 1.E+01 1.E+00 EPA Data (IA>DL) Alpha = E-01 Alpha = 0.1 EPA Data Alpha = 95% EPA Data Alpha = 75% 1.E-02 EPA Data Alpha = 50% EPA Data Alpha = 25% 1.E-03 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 Sub-Slab Concentration (ug/m3) Subslab AF 1.0E E E E E E E-05 Database Max 95th % Mean 50th % Min 25% 1.4E-03 50% 2.8E-03 75% 7.2E-03 95% 2.9E-02 Max 2.3E+00

13 Groundwater / Indoor Air Attenuation Indoor Air Concentration (ug/m3) Indoor Air vs Groundwater Vapor Concentration 1.E+04 1.E+03 1.E+02 1.E+01 1.E+00 EPA Data (IA>DL) Alpha = E-01 Alpha = EPA Data Alpha = 95% 1.E-02 EPA Data Alpha = 75% EPA Data Alpha =50% 1.E-03 EPA Data Alpha = 25% 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 Groundwater Vapor Concentration (ug/m3) Groundwater AF Groundwater Attenuation Factors 1.0E E E E E E E E-07 Database Max 95th % Mean 50th % Min Grounwater Attenuation Stat Database Min 4.8E-07 25% 2.6E-05 50% 8.5E-05 75% 2.3E-04 95% 1.1E-03 Max 2.1E-02

14 What does the database show us? Typical range of attenuation factors: Groundwater/indoor air: ~ (95%); ~ (50%) Sub-slab/indoor air: ~ 0.03 (95%); ~ (50%) For a given source concentration (groundwater or subslab) indoor air concentrations vary over two to three orders of magnitude. Indoor source (background concentration) influence is significant. For a given pair of indoor and subsurface samples, attenuation factors for the chemicals analyzed are similar. Coarser-grained vadose zone materials lead to generally higher indoor air impacts.

15 Case Study: Billings PCE Site Billings PCE Site Boundary

16 Adverse Health Effects of PCE Depression of respiration and cardiac arrhythmias (> 1,000,000 ppb) Reproductive and developmental effects (>300,000 ppb) Liver and kidney toxicity (>100,000 ppb for exposures ranging from days to months, > 10,000 ppb for exposures lasting several years or more) Neurological effects such as dizziness, mood changes, sleepiness (> 10,000 ppb)

17 Adverse Health Effects of PCE PCE exposure is associated with liver and kidney tumors in mice and rats after a lifetime of exposure EPA considers PCE to be a probable carcinogen in humans EPA assumes that there is no threshold for a carcinogen and assesses risk based on the probability of a person coming down with cancer (e.g., a 1 in 100,000 chance). EPA evaluates the potential for both cancer and noncancer effects in a community and selects the most sensitive endpoint

18 Groundwater Investigation

19 Sub-Slab & Indoor Air Investigation B A B A

20 Center Line of Plume A Depth of Basement Sand and gravel A 23,

21 2 nd Street B Depth of Basement Sand and gravel B

22 How does Billings compare to other vapor intrusion sites? Subslab AF Subslab Attenuation Factors 1.0E E E E E E E-05 Database Billings Max 95th % 50th % Min Subslab Attenuation Stat Database Billings Min 4E-05 3E-05 25% 1E-03 4E-04 50% 3E-03 7E-04 75% 7E-03 1E-03 95% 3E-02 3E-03 Max 2E+00 3E-03 Count Groundwater Attenuation Stat Database New Data Min 5E-07 1E-06 25% 3E-05 2E-05 50% 8E-05 4E-05 75% 2E-04 7E-05 95% 1E-03 6E-04 Max 2E-02 8E-04 Count Groundwater AF Groundwater Attenuation Factors 1.0E E E E E E E E-07 Database Billings Max 95th % Mean 50th % Min

23 OSWER VAPOR INTRUSION GUIDANCE Generic Screening Level Concentrations ( Revised November 2006) Selected Parameters Value Symbol Enter Exposure Scenario Residential Scenario Enter Target Risk for Carcinogens 1.00E-04 CR_G Enter Target Hazard Quotient for Non-Carcinogens 1 HQ_G Enter Average Groundwater Temperature ( o C) 15 Tgw Target Target Indoor Air Conc. for Indoor Air Conc. for Non- Unit Risk Reference Carcinogen Carcinogen Factor Conc. s s URF RfC Cia,c Cia,nc (µg/m 3 ) -1 (mg/m 3 ) (ug/m 3 ) (ug/m 3 ) 5.90E E Target Target Indoor Air R= or HQ=1 Toxicity Basis Sub-Slab or Soil Gas R= or HQ=1 Target Ground Water R= or HQ=1 Target Ground Water Conc. < MCL? Cia, target Csg Cgw Cgw<MCL? CASN Chemical Name (ug/m 3 ) C/NC (ug/m 3 ) (ug/l) Yes/No (MCL) Tetrachloroethylene 41 C No (5) Notes: (1) Inhalation Pathway Exposure Parameters (RME): Units Symbol Value Symbol Value Exposure Scenario Residential Commercial Averaging time for carcinogens (yrs) Atc_R 70 Atc_C 70 Averaging time for non-carcinogens (yrs) Atnc_R 30 Atnc_C 25 Exposure duration (yrs) ED_R 30 ED_C 25 Exposure frequency (days/yr) EF_R 350 EF_C 250 Exposure time m3/day ET_R 24 ET_C 8 (2) Generic Attenuation Factors: Source Medium of Vapors Groundwater ( - ) AFgw_R AFgw_C Sub-Slab or Soil Gas ( - ) Afss_R 0.1 Afss_C 0.1

24 Bilings PCE Site: Subslab Attenuation 1.E+03 Indoor Air vs Sub-Slab Concentration Indoor Air Concentration (ug/m3) 1.E+02 1.E+01 1.E+00 Building Alpha Alpha = 1.0 Alpha = 0.1 EPA 95% Alpha = 0.03 Billings 95% Alpha = RBC 10E-4 1.E-01 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 Sub-Slab Concentration (ug/m3)

25 Billings PCE Site: Groundwater Alpha 1.E+03 Indoor Air vs Groundwater Concentration Sand/ cobbles under building Silt/clay under building Indoor Air Concentration (ug/m3) 1.E+02 1.E+01 Building Alpha EPA 95% Alpha = EPA 50% Alpha ~ RBC 10E-4 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 Groundwater Concentration (ug/l)

26 Billings PCE Site Data Analysis & Interpretation Multiple lines of evidence Groundwater plume defined Indoor air and sub-slab sampling indicate vapor intrusion pathway is complete Paired indoor air and subslab data attenuation factors fall within the range of attenuation factors in EPA s vapor intrusion database. Site specific attenuation factors used to define area with unacceptable risks. Evaluate remedial options.