APPLICATION OF SUBSURFACE VAPOUR ASSESSMENT AT HYDROCARBON IMPACTED SITES

Transcription

1 APPLICATION OF SUBSURFACE VAPOUR ASSESSMENT AT HYDROCARBON IMPACTED SITES Mitch Kenaschuk, P.Eng. Peter Olmsted, M.Sc.,P.Eng. October 2004

2 OUTLINE Introduction Regulatory Framework and Methodology Vapour Inhalation Pathway Derivation of Vapour Monitoring Objectives Case Studies Conclusions

3 INTRODUCTION Soil Quality Guidelines Risk Based Consider Multiple Exposure Pathways Vapour Inhalation Pathway increasing importance in urban settings Subsurface Vapour Assessment

4 REGULATORY FRAMEWORK Alberta Guidelines PST Guidelines Upstream Guidelines CCME Canada Wide Standards PHC Fractions F1 to F4 Human Health Pathways Ecological Pathways

5 Vapour Migration Governing Processes Partitioning to vapour Vapour Transport Infiltration/dilution Johnson & Ettinger Vapour Model VAPOUR INHALATION

6 VAPOUR INHALATION Attenuation Factor (building conc)/(source vapour conc) Diffusive transport Advective transport Model Parameters Soil parameters Contaminant properties Building Parameters Distance to Impact

7 VAPOUR INHALATION CCME Tier I Criteria Dilution Factors CCME Published Values DF i = 1 α L T (cm) Residential slab-on-grade Fine-grained Coarse-grained

8 VAPOUR OBJECTIVES Derivation of vapour objectives C sgs = ( RfC C )( SAF)( DF ) a ET i Comparison with measured vapour levels BTEX F1 and F2 Use mass fraction

9 Case Study 1 BACKGROUND Operating Service Station Site: Located in a small Town in Southern Alberta Current facilities include service station building, USTs and pump islands Several Environmental Investigation Phases completed Tier 2 Approach recommended to derive soil and groundwater criteria

10 Case Study 1 INVESTIGATION Site Conditions: 18 boreholes drilled and 8 wells installed Stratigraphy consists of thin gravel fill overlying clay till Depth to groundwater from 2.5 m to 3 m

11 Case Study 1 INVESTIGATION Soil and Groundwater Impacts: Elevated vapours in soil Elevated Benzene and F1 in soil at 3 m to 3.75 m Elevated benzene in groundwater onsite and offsite On-site impacts south of pump islands and southeast corner of site

12 CASE STUDY 1 INVESTIGATION

13 Case Study 1 TIER 2 ASSESSMENT Approach: Install 2 soil vapour monitor wells (2 m) Complete in vadose zone above zone of highest impact Measure soil vapour BTEX, F1, F2 Compare measured levels with vapour objectives Agreement from regulatory agency

14 CASE STUDY 1 INVESTIGATION

15 Case Study 1 TIER 2 ASSESSMENT Soil Vapour Wells: Completed in clay till above soil with highest hydrocarbon impact Screened between 1.8 m and 2.1 m depth 9.5 mm drop tube to middle of screen Valve fitted in cap and connected to drop tube

16 Case Study 1 TIER 2 ASSESSMENT Well Locations:

17 Case Study 1 TIER 2 ASSESSMENT Soil Vapour Sampling: Pelican case and tedlar bags Connect pump to valve in well cap Purge 2 well volumes of air Collect vapour sample in tedlar bag

18 Case Study 1 TIER 2 ASSESSMENT

19 Case Study 1 TIER 2 ASSESSMENT Soil Vapour Objectives: Based on CCME methodology Derived for site based on the following: Residential scenario with slab-on-grade foundation Fine-grained soil conditions Dilution factors calculated for Lt = 150 cm Input parameters and chemical properties consistent with development of CWS PHC Tier I standards

20 Case Study 1 TIER 2 ASSESSMENT Soil Vapour Results (mg/m 3 ): Location Benzene Toluene Ethyl benzene Xylenes F1 F2 BH <3.8 <4.3 < <30 BH < <4.3 5,600 <30 Vapour Objectives ,406 75,232 13,437 84,284 44,870

21 Case Study 1 FUTURE WORK Future Work: Incorporate derived Tier 2 criteria into Remediation Plan for site Obtain agreement from stakeholders on Remediation Plan Complete site remediation to Tier 2 levels Confirm site remediation and complete any additional monitoring

22 CASE STUDY #2 Mitch Kenaschuk, P.Eng. October 2004

23 Case Study 2 BACKGROUND Former Service Station Site: Located in a major urban centre in Western Canada Operated between 1972 and 2002 Facilities included a service station building, office building, 3 USTs and 2 pump islands Historic tank bed below service station building

24 Case Study 2 EXCAVATION

25 Case Study 2 EXCAVATION Conditions Towards Building: Historic tank bed material underlying building

26 Case Study 2 EXCAVATION Conditions Towards Building: Elevated soil vapours and residual hydrocarbon impact above criteria towards building

27 Case Study 2 EXCAVATION

28 Case Study 2 RISK TO BUILDING Environmental Investigation: Conducted below building slab-ongrade foundation Four boreholes with monitor wells Two shallow soil vapour monitor wells Soil, groundwater and soil vapour sampling and analysis

29 Case Study 2 RISK TO BUILDING

30 Case Study 2 RISK TO BUILDING

31 Case Study 2 RISK TO BUILDING

32 Case Study 2 RISK TO BUILDING Soil and Groundwater Impact Conditions: Soil vapour concentrations between 75 ppm and 550 ppm Soil hydrocarbon conc. Below applicable criteria Groundwater hydrocarbon conc. Below applicable criteria

33 Case Study 2 RISK TO BUILDING Shallow Soil Vapour Wells: Completed in historic tank bed fill Completed in sand fill underlying kiosk floor slab Screened between 0.3 m and 0.6 m depth 9.5 mm drop tube to middle for screen Valve fitted in cap connected to drop tube

34 Case Study 2 RISK TO BUILDING

35 Case Study 2 RISK TO BUILDING

36 Case Study 2 RISK TO BUILDING Shallow Soil Vapour Well Sampling: Laboratory supplies pump and tedlar sampling bags Connect pump to valve in well cap Purge 2 wells volumes of air Collect vapour sample in tedlar bag (2 per well)

37 Case Study 2 RISK TO BUILDING

38 Case Study 2 RISK TO BUILDING Shallow Soil Vapour Analysis: Samples analyzed for BTEX, F1 and F2. Soil vapour from one tedlar bag per well analyzed directly from bag. Based on initial results, BTEX analysis conducted on the second soil vapour sample via a Carbotrap tube to obtain lower detection limits.

39 Case Study 2 RISK TO BUILDING Shallow Soil Vapour Objectives: Based on methodology discussed Derived for site based on the following: Commercial scenario with slab-on-grade foundation Coarse-grained soil conditions Published CCME dilution factors for Lt = 30 cm Input parameters and chemical properties consistent with development of CWS PHC Tier I standards

40 Case Study 2 RISK TO BUILDING Sample Name BH102 BH102 Carbotrap BH104 CASE STUDY #2 RESULTS VAPOUR ASSESSMENT COMMERCIAL SCENARIO COARSE GRAINED SOIL Date 1/1/2004 1/1/2004 1/1/2004 Benzene <3 <0.007 <3 Toluene <3 <0.007 <3 Ethylbenzene <4 <0.007 <4 Xylenes <4 <0.02 <4 F1 <30 NA <30 F2 <30 NA <30 BH104 Carbotrap 1/1/2004 <0.008 <0.008 <0.008 <0.02 NA NA Soil Vapour Objectives a ,950 78,522 11, ,692 41,880 Results consistent with expectations considering soil and groundwater analysis

41 Case Study 2 RISK TO BUILDING Shallow Soil Vapour Conclusions: Subsurface hydrocarbon conditions underlying the building are not considered a health risk to future commercial building occupants

42 Case Study 2 Property Transaction: PROPERTY SALE Provincial regulatory approval obtained Sale of property was finalized contingent upon on-going soil vapour sampling to confirm conditions over long-term

43 Case Study 2 Future Work: FUTURE WORK Semi-annual groundwater and soil vapour monitoring, sampling and analysis Re-assess site conditions annually Recent confirmatory sampling in June 2004 confirmed previous results Program to continue until long term conditions are confirmed

44 CONCLUSIONS Soil vapour measurements can be effective for assessing vapour intrusion pathway CCME methodology can be applied to develop remediation criteria for the vapour inhalation pathway

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