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.