Soil Vapor Installation
and Sampling Proceduresand Sampling ProceduresIn general accordance with
2012 DTSC Active Soil Gas Investigations Advisory
H&P Mobile Geochemistry, Inc.
Irvine Marriott – Sept 25, 2012
To Be Discussed
• Installation of Soil Vapor Probes▫ Construction Specifications and Installation Methods
• Sampling Soil Vapor Probes• 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
Installation of Soil Vapor Probes
• Installation Methods
▫ Direct Push� Temporary or Permanent Probes in Sand� 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
Installation of Soil Vapor Probes
• Construction Materials
▫ Sand Pack▫ Sand Pack
▫ Dry Bentonite
▫ Hydrated Bentonite
▫ Tubing Type
▫ Filter Type
▫ Probe Termination
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
Sampling Soil Vapor Probes
• Equilibration Period
▫ Direct Push – 120 minutes
▫ PRT – not specified, other CA
Guidance documents (SD DEH)
suggest 60 minutes 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
Sampling Soil Vapor Probes
Purge Volumes
▫ Tubing and Filter
▫ Porosity of Materials
� Sand
� Dry Bentonite� 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…
Sampling Soil Vapor Probes
• Flow Rate and Probe Vacuum
▫ Recommended:
<200mL/minute during purging
and sampling activitiesand 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
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.
Sampling Soil Vapor – Leak Check
Gaseous: Helium▫ Shroud method
▫ Measure amount of helium
before and after sample before and after sample
collection
▫ Leak threshold ~5% leak
▫ Excellent for summa canister
sampling and acceptable for
mobile lab sampling.
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▫ 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
Multiple Lines of Evidence
• Diffusion Coefficient Measurements
▫ Inject a known volume of a compound into the subsurface, then
measure amount recovered over time to determine the diffusion
…let H&P Help
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
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.