by Robin V. Davis, P.G. Project Manager Utah Department of Environmental Quality Leaking Underground Storage Tanks rvdavis@utah.gov 801-536-4177

Evaluating Purging and Sampling Methods to Determine

Representativeness of Soil Vapor Data

Platform Session Wednesday March 25, 2015

1:30pm to 5:00pm

Association for Environmental Health & Sciences (AEHS) 25th Annual International Conference on Soil, Sediment, Water & Energy

San Diego, California

124/>1000

Perth Sydney

Tasmania

Australia

Davis, R.V., 2009-2011

McHugh et al, 2010

Peargin and Kolhatkar, 2011

Wright, J., 2011, 2012, Australian data

Lahvis et al, 2013

EPA Jan 2013, 510-R-13-001

REFERENCES

4/13

70/816

Canada

United States

MAP KEY

# geographic locations evaluated

# paired concurrent measurements

of subsurface benzene soil vapor

& source strength

70

Empirical Studies Petroleum Vapor Database, EPA 2013

Australian sites evaluated separately

816

Screening Distances

95%-100% Confidence

Dissolved Sources Benzene Vapors vs. Distance of Attenuation

LNAPL Sources (small sites) Benzene Vapors vs. Distance of Attenuation

5 ft 15 ft

High hydrocarbon and CO2 concentrations, low O2

Rebound of O2 and CO2 to atmospheric as hydrocarbons biodegrade

Measure O2 and CO2 when vapor sampling Multiple Lines of Evidence

1.E+00 1.E+02 1.E+04 1.E+06 1.E+08

0

5

10

15

0 5 10 15 20

Benzene (ug/m3)

O2 & CO2 (% V/V)

Coachella, CA COA-2 (Ririe, et al 2002)

LNAPL

1.E+00 1.E+02 1.E+04 1.E+06 1.E+08

0

5

10

15

0 5 10 15 20 25

Benzene (ug/m3)

De

pth

, fe

et

bls

O2 & CO2 (% V/V)

Santa Clara, UT VW-4 (UDEQ, 2009)

Benzene in GW 3180 ug/L

Signature Characteristics of Subsurface Aerobic Biodegradation

1.E+00 1.E+02 1.E+04 1.E+06 1.E+08

0

2

4

6

8

10

0 5 10 15 20

Benzene (ug/m3)

O2 & CO2 (% V/V)

Huntington Beach, CA HB-3 (Ririe, et al 2002)

O2%

CO2%

Occasional Anomalies

Co-existing high concentrations hydrocarbon/oxygen, low CO2

Co-existing low concentrations hydrocarbon/oxygen, high CO2

1.E+00 1.E+02 1.E+04 1.E+06 1.E+08

0

5

10

15

20

0 5 10 15 20

Benzene (ug/m3)

De

pth

be

low

gra

de

(fe

et)

O2 & CO2 (% v/v)

Hal’s UT VW-10 (UDEQ 9/1/09)

Oxygen

Carbon Dioxide

Benzene

Anomalies

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

1.00E+08

0 5 10 15 20 25Be

nze

ne

Vap

or

Co

nce

ntr

atio

ns,

ug

/m3

Oxygen Soil Gas %

Small UST/AST & Large Industrial Sites

Paired Measurements of Benzene Vapor & Oxygen in Soil Gas

Oxygen vs Benzene for Dissolved & LNAPL Sources

Anomalies represent small data population in database (4%)

No effect on overall observation of biodegradation

No effect on screening criteria

Anomalies

Case Study

• Large data population in EPA database, highly-studied site – UDEQ 1991-present – EPA ORD 2007, 2009, 2011 (Wilson, DiGuilio, Jewell, Paul, Adair, Ruybal)

– Sweeney 2014

• 11 multi-depth vapor probes, >50 monitoring wells

Hal’s Service, Green River, Utah

– 396 paired measurements of source strength and soil vapor – Vapor samples analyzed for petroleum constituents, O2, CO2, CH4 – Occasional anomalies of high hydrocarbons and O2 in same sample

– Understand anomalies – Improve practices of installing and completing vapor

points, and purging and sampling

• Objectives

Hal’s Service, Green River, UT, VW-7 Tubing, Sand Pack and Purge Volumes

v

v

Fee

t B

elo

w G

rad

e

0

15

10

5

v

v

v LNAPL

Clayey Silt

Silt

3 ft

Tubing+Sand Pack = 1.32 L

7 ft

Tubing+Sand Pack = 1.34 L

11 ft

Tubing+Sand Pack = 1.36 L

15 ft

Tubing+Sand Pack = 1.37 L

Standard practice Purge 1 tubing volume Sample with <1-Liter containers (except 2009, 6-L samples)

NOT ADVISED 1 Boring for Multiple Vapor Point Completions

v Fee

t B

elo

w G

rad

e

0

15

10

5

Cement

Bentonite

Sand

Tubing

Vapor Point, 6-inch stainless steel screen

v

v

LNAPL

High Potential for Leaks, Non-Representative Samples

• Full hydration of bentonite with each lift is difficult to achieve

• High potential for tubing to bend, tangle and kink

Bentonite Chips

Vapor Screen

Bentonite Crumbles

Bentonite Crumbles Bentonite

Chips

Sand Pack

A

B C

NOT ADVISED

Bentonite Crumbles

Optimal Method to Complete

Vapor Points

• Thick layers of

bentonite chips • Thin layers of

crumbles only

above and below

sand pack

0

5

10

15

20

0 5 10 15 20

De

pth

be

low

gra

de

(fe

et)

2006-2014 Oxygen

Over Time

O2 4/14/06 fixed lab

O2 8/26/06 fixed lab

O2 6/26/07 fixed lab

O2 9/1/09 fixed lab

O2 6/24/14 0.5 min purge (0.1L)(Sweeney field-measured)O2 6/24/14 2-min purge (0.4 L)(Sweeney field-measured)

O2 %

• 2014 high-purge data corresponds to 2009 high-volume sample data

• Over-purging/large sample volume= non-representative soil gas samples

1.E+00 1.E+02 1.E+04 1.E+06 1.E+08

0

5

10

15

20

0 5 10 15 20

Benzene (ug/m3)

De

pth

be

low

gra

de

(fe

et)

O2 & CO2 (% v/v)

VW-7 9/1/09

Oxygen

Carbon Dioxide

Benzene

TPH-gro

Anomalies

2009

Vapor Samples

6-L Container

VW-7

Conclusions of Studies

Sample soil gas within and around sand pack

EPA Petroleum Vapor Database results:

Analyze for hydrocarbons, O2 and CO2

Anomalies caused by:

Anomalies comprise only 4% of database

96% representative of in-situ conditions

Anomalies do not affect screening distances

Get the whole picture Multiple Lines of Evidence

Leaks in bentonite seal or sample train

Over-purging or high-flow purging

Sampling soil gas from non-representative areas