Soil Vapor Installation

Transcription

1 Soil Vapor Installation and Sampling Procedures In general accordance with 2012 DTSC Active Soil Gas Investigations Advisory H&P Mobile Geochemistry, Inc. Irvine Marriott Sept 25, 2012

2 To Be Discussed Installation of Soil Vapor Probes Construction Specifications and Installation Methods Sampling Soil Vapor Probes Procedures for Quality Samples, Purge Volumes, etc. Specialized Services for Multiple Lines of Evidence Diffusion Coefficient, Soil Permeability, Oxygen Testing, etc. Training and Experience Quality Samples start with Quality Sampling

3 Installation of Soil Vapor Probes Installation Methods Direct Push Temporary or Permanent Probes in Sand Through the Rod with PRT (Post Run Tubing) Hand Probe or Drive Point Sampling Sub-slab Manual Drill Auger Hand Auger Hollow Stem Auger

4 Installation of Soil Vapor Probes Construction Materials Sand Pack Dry Bentonite Hydrated Bentonite Tubing Type Filter Type Probe Termination

5 PRT and Drive Point PRT (Post Run Tubing) No introduction of foreign material Hard to test tubing connection Not recommend for consolidated lithologies Hand Probe/Drive Point Tubing connected prior to insertion Should be discussed with regulatory agency prior to inclusion in work plan

6 Sampling Soil Vapor Probes Equilibration Period Direct Push 120 minutes PRT not specified, other CA Guidance documents (SD DEH) suggest 60 minutes Hand Probe / Drive Point not specified; SD DEH suggests 30 minutes Hand or Hollow Stem Auger 48 hours Shut-In Test Minimum 100 water for 60 sec. Not a replacement for leak check

7 Sampling Soil Vapor Probes Purge Volumes Tubing and Filter Porosity of Materials Sand Dry Bentonite Purge Test Steps Pre-2012 = 1, 3, 7 Current = 1, 3, 10 Sand Pack To Purge or not to Purge? If you are not sure, conduct a multi-step purge test

8 Sampling Soil Vapor Probes Flow Rate and Probe Vacuum Recommended: <200mL/minute during purging and sampling activities Flow Rate does not matter as much as applied vacuum to the probe! Probe Vacuum <100 Water (or <8 Mercury) Faster Flow Rates may be necessary and are completely ACCEPTABLE

9 Sampling Soil Vapor Leak Check Liquid: 1,1-Difluoroethane Saturated cloth method Full strength chemical Leak Threshold ~10x the analytical reporting limit, EXTREMELY conservative Excellent for mobile lab sampling and acceptable for summa sampling with experience.

10 Sampling Soil Vapor Leak Check Gaseous: Helium Shroud method Measure amount of helium before and after sample collection Leak threshold ~5% leak Excellent for summa canister sampling and acceptable for mobile lab sampling.

11 Soil Vapor Sample Containers Glass Syringes Simple to collect, small volumes Summa Canisters The smaller 400mL and 1L size are preferred for soil vapor/sub slab Tedlar Bags Helpful for sites with moisture, large sites that require travel time between probe and lab, helium leak testing, etc. DTSC recommends 6 hour holding time for VOCs (other states up to 5 days) Sorbent Tubes TO-17 for diesel and naphthalene Two volumes collected for reporting limit purposes Very simple to collect with a syringe

12 Multiple Lines of Evidence Diffusion Coefficient Measurements let H&P Help Inject a known volume of a compound into the subsurface, then measure amount recovered over time to determine the diffusion coefficient Soil Permeability Testing Multiple vacuum readings at varying flow rates Site Specific Attenuation Factors with Radon Testing Below slab and above slab radon measurements (tedlars) Low Threat Closure Policy: Oxygen Data and Soil Sampling/Analysis for evidence of bioattenuation zone

13 Training and Experience Hire a company that has experience with soil vapor sampling. Before working with a new company, don t be afraid to ask about their experience and training program for field technicians. The 2012 ASGI Guidance encourages innovations. Be sure that your sampling team is experienced enough to react to varying site conditions by making necessary adaptations to procedures while remaining within general accordance with the recommended protocols.