Soil Gas Sampling MethodsSoil Gas Sampling Methods

Todd McAlaryTodd McAlaryGeoSyntecGeoSyntec Consultants, Inc.Consultants, Inc.

“Soil Gas Sampling Workshop”“Soil Gas Sampling Workshop”Midwestern States Risk Assessment SymposiumMidwestern States Risk Assessment Symposium

Indianapolis, INIndianapolis, INAugust 21, 2006August 21, 2006

RepresentativeRepresentativeNo leaks, no adsorption/No leaks, no adsorption/desorptiondesorption or reactionsor reactions

ReproducibleReproducibleConsistent for different events, Consistent for different events, geologysgeologys, samplers, samplers

ReliableReliableMinimal opportunity for errorsMinimal opportunity for errors

Able to meet Data Quality ObjectivesAble to meet Data Quality ObjectivesTarget levels ~1ug/m3, roughly 1,000 times lower Target levels ~1ug/m3, roughly 1,000 times lower than than hydrogeologistshydrogeologists meet with groundwatermeet with groundwater

Soil Gas Sampling GoalsSoil Gas Sampling Goals

MSRAS Field MethodsMSRAS Field Methods

Different types of probesDifferent types of probesSubSub--slabslabNested insertsNested insertsPost Run Tubing (PRT)Post Run Tubing (PRT)Continuous MultiContinuous Multi--Channel TubingChannel TubingSoil gas monitoring wellsSoil gas monitoring wells

Different Sampling ContainersDifferent Sampling ContainersSumma canistersSumma canistersTedlarTedlar bagsbagsAutomatic thermal Automatic thermal desorptiondesorption (ATD) tubes(ATD) tubes

Assorted Supplemental MethodsAssorted Supplemental MethodsField screeningField screeningTracer testingTracer testingBarometric pressure monitoringBarometric pressure monitoringDifferential pressure monitoringDifferential pressure monitoringGas permeability testingGas permeability testing

SubSub--Slab Soil Gas SamplingSlab Soil Gas Sampling

(DiGiulio, 2004)

SubSub--Slab SamplingSlab Sampling

EPA, 2006

Sample Depth and DistanceSample Depth and Distance

-8-7-6-5-4-3-2-10

0.90.8

g

0.3 0.2 0.1 0.011E-41E-51E-6

0.5

0.6

0.4 1E-3

α = 7.1Ε−5

Hydrocarbon @ 200 mg/L

Abreu and Johnson, 2005

Potential for many orders of magnitude differences in concentrations, depending on depth and distance

Active Soil Gas SamplingAnd

Selecting Direct Push (D-P) Techniques To Achieve Data Quality Objectives

VOCs??

Wes McCall, Geologist KS28

Geoprobe Systems

Select the Probe unit to “fit” your needs

Sample Collection MethodDownholeSampling System Syringe Tedlar

BagGlass Bulbs

Summa Canister

Increase Quality

Direct Sampling

Low/Low Low/High

PRT System

Implants

Gas Wells High/Low High/High

Matrix for Guidance on Selection of Methods with Compatible DQO Results

Direct Sampling Through D-P Rods

Grab SampleAdvantages:

• Quickest method

• Minimal parts/expendables

Disadvantages:

• Possible leaks along outside of casing

• Decontaminate every rod (X-contamination?)

• Possible reactions on metal surfaces

• Potential leaks at rod couplings

Post-Run Tubing Sampling

Grab SamplesAdvantages:

• Eliminate rod joint leaks

• Eliminate metal surface reactions

• Expendable tubing

Disadvantages:

• Potential leaks along outside of tubing

• Expendable tubing

Single Level Implants with Small Rods

Long Term MonitoringAdvantages:

• Specific Interval

• Moderate Integrity

• Sample over time

Disadvantages:

• Without pre-coring = compression/loss of permeability?

• Not easy to place a slurry seal – possible leaks

• Slower than grab sampling

Single Level Implants with Large Rods

Long Term MonitoringAdvantages:

• Highest Sample Integrity

• Sample over time

• Specific Depth Interval

Disadvantages:

• Without pre-coring = compression/loss of permeability?

• Slower than small rod method

Slurry seal throughout annulusSlurry seal throughout annulus

Multi Level Implants

Long Term MonitoringAdvantages:

• Multiple Discrete Intervals

• Good Integrity

• Sample over time

Disadvantages:

• Without coring = compression/loss of permeability?

• Labor intensive

Slurry seal throughout annulusSlurry seal throughout annulus

Sand filter pack around insert tipsSand filter pack around insert tips

Long Term MonitoringAdvantages:

• Defined sample interval

• Custom screen lengths

• Very High Integrity

• Sample over time

Disadvantages:

• Without coring = compression/loss of permeability?

• Installation/construction more rigorous and time consuming

Gas Wells with Pre-pack Screens

ASTM D6725

Abandonment

DP Grouting techniques allow for proper abandonment of borings to assure that contaminant migration does not occur across lithologic boundaries when conducted appropriately.

Bentonite slurries of 20+% solids and neat cement can be injected.

Don’t create additional problems …

grout it out !!!

Continuous MultiContinuous Multi--Channel TubingChannel Tubing

Continuous MultiContinuous Multi--Channel TubingChannel Tubing

Soil Gas Monitoring WellsSoil Gas Monitoring Wells

Annular SealsAnnular Seals

Powder Granular Chips

Whole Air Whole Air vsvs Adsorptive SamplingAdsorptive Sampling

Summa canisters

Sorbent tubes

Direct Summa Canister CollectionDirect Summa Canister Collection

EPA, 2006

TedlarTedlar Bag SamplingBag Sampling

Data Quality Control MethodsData Quality Control Methods

Pneumatic testing-flow-vacuum-permeability

Leak testing-shut-in-helium tracer

Field Screening

Ratio of flow/vacuum Ratio of flow/vacuum should be constant (Q/s)should be constant (Q/s)Calculate permeabilityCalculate permeabilityFlow >100 Flow >100 mLmL/min at /min at vacuum <100 invacuum <100 in--HH22OO

Never leave a probe Never leave a probe unsealed! They breathe…unsealed! They breathe…

Pneumatic Testing

Add 10% to 50% helium Add 10% to 50% helium to shroudto shroudFill Fill TedlarTedlar bag via Lung bag via Lung Box and screen for Box and screen for helium readinghelium readingRealReal--time verification of time verification of absence of leaksabsence of leaks

Can also use alcohols, Can also use alcohols, fuels, fluorocarbons, fuels, fluorocarbons, with various pros and with various pros and conscons

Tracer Testing

VOCsVOCs

Field ScreeningField Screening

O2/CO2/CH4/H2S

Helium detector

Optional compound specific analysis (Draeger chips)

LowLow--Level ScreeningLevel Screening

RAE Systems ppbRAE

Foxboro TVA 1000 FID/PIDFoxboro TVA 1000 FID/PID

From Thermo ElectronicsFrom Thermo Electronics

SorbentSorbent Tube SamplingTube Sampling

Sample VolumeSample Volume

Courtesy of Severn Trent Laboratories

SAMPLE VOLUME TO ACHIEVE OSWER TABLE 2C SUB-SLAB TARGET CONCENTRATION

0.01

0.1

1

10

100

1000

10000

100000

1000000

Acena

phthe

neAce

tonitri

leBenz

aldehy

de

Benzo

(b)flu

oranthe

ne

Bis(2-c

hloro

ethyl)

e ther

Chlorop

heno

l; 2-

Chryse

ne

Fluore

ne

HCH; alpha

- (alp

ha-B

HC)

HCH; gam

ma- (L

indane

)

Hexac

hloroc

yclope

ntadie

neHex

achlo

roeth

ane

Methac

rylon

itrile

Methyln

aphth

alene

; 2-

Nitrobe

nzen

eNitro

propan

e; 2-

Nitroto lue

ne;o-

Propy

lbenz

ene;

n-

Pyrene

Sam

ple

Volu

me

(L)

Barometric Pressure ChangesBarometric Pressure Changes

Differential Pressure MonitoringDifferential Pressure Monitoring

TimeTime--Integrated SamplesIntegrated Samples

Up to 7Up to 7--day flow controllers for Summa canistersday flow controllers for Summa canisters

Slower flowSlower flow--rates and longer time for ATD tubesrates and longer time for ATD tubes

Larger Larger sorbentsorbent tubes (VOST tubes) and larger volume samplestubes (VOST tubes) and larger volume samples

Scope SummaryScope Summary

CMTs

Nested Inserts

Scope SummaryScope Summary

SubSub--slab via slab via TedlarTedlar/TAGA /TAGA –– ArcadisArcadisNested Probes inside Nested Probes inside vsvs outside outside –– OEPAOEPAGrab Grab vsvs timetime--integrated integrated –– EnviroGroup/NewfieldsEnviroGroup/NewfieldsSyringe Syringe vsvs lunglung--box box vsvs Summa Summa –– H&P labs & STLH&P labs & STLTime after installation Time after installation –– H&P/OEPAH&P/OEPATOTO--17 17 vsvs whole gas whole gas –– GeoSyntecGeoSyntec/STL/STLCMT CMT vsvs nested probes nested probes –– Solinst/BoartSolinst/Boart LongyearLongyear/STL/STLPassive Passive vsvs Active sampling Active sampling –– W.L. Gore & Assoc.W.L. Gore & Assoc.ppbRAEppbRAE and TVA1000 and TVA1000 vsvs TAGA TAGA –– Thermo ElectronicsThermo ElectronicsHelium Tracer, Gas K & pressure testing Helium Tracer, Gas K & pressure testing –– GeoSyntecGeoSyntecVideo Documentary Video Documentary -- OEPAOEPA