Empirical Data: Challenges and Future Directions

Transcription

1 Empirical Data: Challenges and Future Directions by Todd McAlary, Consultants, Inc. AEHS VI Workshop March 16, 2004

2 Challenges Temporal Variability Spatial Variability Sampling Variability Media which ones and how many? Chemical Data vs Physical Data Data Sufficiency

3 HCBD (ppbv) 4-Jun Jun Jun Jun-01 2-Jul-01 9-Jul Jul Jul Jul-01 6-Aug Aug Aug Aug-01 Temporal Variability Indoor air What is the driver? wind rain temperature sampling biases? Soil Gas How much data is enough? How do we minimize it? longer-term samples diffusive samplers

4 Spatial Variability Interpolation from distributed samples? 3 subslab samples per house? 4 soil gas samples around a house? House Folkes et al, 2004)

5 Sampling Variability Driven vs drilled probes Purging Procedures Vertical profiling vs depth-integrated Tracers to confirm absence of leaks

6 Soil Gas Probes: Driven vs Drilled Driven: Faster, no fluids or cuttings Smearing? Sealing? Drilled: Easier to place a seal May require more equilibration Geoprobe.com Slam-bar?

7 Purging and Sampling Field instruments: PID/FID O2/CO2/LEL He Draeger Pylon PY-AB5 Confirm steady readings

8 Monitor Flow and Vacuum Analagous to low-flow protocol Provides data to calculate permeability

9 Permeability Testing

10 Multi-Level Probes Bundle of probes in a single hole HDPE tubes around PVC pipe Nested installations of one probe/hole Geoprobe.com

11 Vertical Profiling in Groundwater DMLS, Hydropunch, Waterloo Profiler, PDBs Ground-Water Profile at Monitoring Well 214S Using Discrete Multi-Level Sampling (DMLS) System Ground-Water Concentration (ug/l) Specific Conductance (us/cm) Ground-Water Concentration (ug/l) water table water table MW-214 TCE (Q4, Q5 screening level = 5 ug/l) 1,1-DCE (Q4, Q5 screening level = 200, 280 ug/l) 1,1,1-TCA (Q4, Q5 screening level = 3300, 4700 ug/l) well sample = 55 ug/l well sample = 32 ug/l well sample = 21 ug/l 20 water table 1,1-DCE (ND) TCE = 0.6 ug/l 1,1-DCE=1.4 ug/l TCE = 2.2 ug/l Depth (m) (DiGiulio et al, 2004)

12 Tracers to Confirm Seals

13 Media which ones and how many? Soil data not recommended Groundwater available, but far removed Soil gas Can it meet DQOs for risk assessment? Subslab 3 per house adds up in a hurry Indoor air background issues every time Outdoor air necessary expense Pathway samples need a-priori identification Continuous monitoring TAGA, Field instruments

14 Chemical vs Physical Data ~30 inputs in the J&E Model only one is a concentration So why do we only measure concentrations? Other easy to measure and important parameters: Gas permeability, texture, moisture content, layering Pressure gradients, HVAC flows, barometric cycles O2/CO2, CH4, radon

15 Data Sufficiency Indoor Air Every house? Every Floor? Sub-Slab/Soil gas 3 per house? Seasonal? Longer-term? Statistics median, 95 UCL, max

16 Future Directions Toolbox approach Better to have more to select from Standardization Clarification

17 Representative Purge Volume Concentration (ppbv) ,1,1-TCA TCE 1,1-DCE c-1,2-dce Sampled Volume (L) (DiGiulio, 2004)

18 Putting Volume into Perspective Residential exposure scenario 20,000 L/day inhalation 350 days/yr, 30 years 210,000,000 litres of air inhaled

19 High Purge Volume Sampling

20 High Purge Volume Sampling PID = 1,000 ppmv over 1,700,000 L (3 days) indicates concentrations are spatially uniform Total mass removed ~ 10 kg (10E-6 risk needs only 0.005g) Combine with pneumatic testing double benefit!

21 Pressure Transducers / Data Loggers

22 Pneumatic Testing Drawdown 0.1 to 0.2 in-h2o (vs baseline drift of 0.1 in H2O)

23 Pneumatic Data 566 vacuum measurements in only a day of testing

24 Hantush Model Geometry

25 Hantush Type-Curve Fitting Calculates permeability and leakance

26 Continuous Multichannel Tubing Einarson and Cherry (2002) developed this for groundwater, but it can be used for soil gas too Up to 300 ft long tube with no joints, no leaks

27 CMT for Soil Gas Profiling

28 Draeger Chips

29 Standardization Standard Operating Procedures Dom DiGiulio sub-slab protocol DTSC/RWQCB Soil Gas Protocol Others for emerging methods Best Practices Manual

30 Clarity Data Presentation Consistency

31 Basic Charts

32 COC Correlations in Redfield PreRemediation Indoor Air (w/o 3 TCE outliers) 1,1,1-TCA (ug/m3) TCE vs. 1,1,1-TCA 1,1,1-TCA = * TCE Correlation: r =.301 (N=723) TCE (ug/m3) PCE (ug/m3) TCE vs. PCE PCE = * TCE Correlation: r =.227 (N=723) TCE (ug/m3) 1,1-DCE (ug/m3) TCE vs. 1,1-DCE 1,1-DCE = * TCE Correlation: r =.694 (N=723) TCE (ug/m3) Regression 95% confid. Folks, et al, 2004

33 10000 PCE-1/Alpha PCE-Alph /Alpha x 75th percentile subslab concentration Wertz and McDonald, 2004

34 Actual vs. Theoretical Theoretical alpha of % background x 100 PCE Theoretical 92 PCE Actual PCE theoretical 410 1/Alpha Subslab Concentration Wertz and McDonald, 2004

35 Consistency Units: ug/l, mg/m3, ppm, ppb, ppt, % Detection limits Magnitude relative to: MDL Background indoor Ambient outdoor Target concentration

36 Conclusions Current State of the Art Variability Cause and effect Limited tools, inconsistent methods Future directions Standardization of protocols Expansion of toolbox Reduction in variability (hopefully)