Vapor Intrusion: Lesson Learned on Sampling and Data Interpretation G. Todd Ririe BP La Palma, CA March 12, 2008 AEHS Meeting, SD G. Todd Ririe BP

Outline of Presentation Avoid indoor air sampling whenever possible ‹ Oxygen levels above 4% are an effective barrier to HC vapors ‹ Slabs are well oxygenated ‹ Methane is a good surrogate for benzene ‹ Do preview sampling and analysis in field ‹ Use the right tubing ‹ Tips on QA/AC ‹

G. Todd Ririe BP

Always Collect Outdoor Air Sample Before Collecting Indoor Air ‹ Bldgs

designed to exchange indoor air for outdoor air every hour ‹ Average ambient outdoor benzene concentration is 2 ug/m3 ‹ USEPA risk-based target indoor air concentration is 0.23 ug/m3 ‹ CA residential screening level for indoor air is 0.084 ug/m3 G. Todd Ririe BP

One Way to Start Collecting Indoor Air Samples

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Goal is avoid having to do this type of indoor sampling

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Subslab Sampling in DrivewayBetter than in the House

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Case StudyHome Over Former Oil Field Sump Sandy to silty sandy soils-Central Coast ‹ Perched Water 4 ft (Groundwater >60 feet) ‹ Predominantly crude oil ‹ Affected soil 4-15 feet bgs ‹

– TPH 100 to 10000 mg/kg – Benzene < 0.1 mg/kg – BTEX < 30 mg/kg (mostly < 1 mg/kg)

Slab under house ‹ Non-slab area formerly irrigated ‹

G. Todd Ririe BP

Home over Sump •Single Story •Slab on grade •Heating only (no AC)

Bare Sand 17

4

20

14

11

21

15

22

12

3m 18

19

13

Garage Sample Locations Grass Concrete

Nested probes Sub-slab probe

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0

0

1

1

2

2

3

3 Depth (feet)

Depth (feet)

Vertical Profile of Soil Gases at House over Sump

4

5

4

5

6

6

7

7

SG-4 No Slab

8

SG-12 Sub-Slab

8

9

9 0

4

0 0

8 12 O2 Concentration (%)

16

2 4 CO2 Concentration (%) 40000

80000 120000 CH4 Concentration (ppm)

0

20

160000

6

0

200000

0

G. Todd Ririe BP

4

8 12 O2 Concentration (%) 1

2 3 CO2 Concentration (%)

16

20 4

40000 80000 120000 CH4 Concentration (ppm)

5 160000

Case Study Building Over Oil Field ‹ Clay-rich

soils-Orange County ‹ Deep groundwater- 120 feet ‹ Clean Soils ‹ Shallow oil field (several thousand ft) ‹ New construction forced soil gas analysis ‹ Slab under buildings over 50 yrs old G. Todd Ririe BP

Location of Building on Edge of Oil Field

Approximate Scale

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N

Vertical Profile of Soil Gases-Building over Oil Field 0 1 2 3

Depth (feet)

4

No Slab

5

Sub-Slab

6 7 8 9 10 11 12 0

5

10 15 O2 Concentration (%)

20

25

0

0.2

0.4 0.6 CH4 Concentration (ppmv)

0.8

1

G. Todd Ririe BP

Case StudyFree Product Under Active Distribution Facility ‹ Sandy

Soil ‹ Groundwater at 10 feet ‹ Free Product (gasoline and diesel) ‹ Clean Soils (where soil gas collected) ‹ Large Asphalt Slab ‹ Non slab area little vegetation no irrigation G. Todd Ririe BP

Case Study #1-Comparison of field data to modeled data for benzene

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Vertical Profile of Soil Gases at Distribution Facility 0

0

1

1

2

2

3

3

COA-2 No Cover

4 Depth (feet)

Depth (feet)

4 5 6 7

5 6 7

8

8

9

9

10

10

11

11

12

12

0 0 0

0

4

8 12 O2 Concentration (%) 4

8 12 CO2 Concentration (%)

20000

20000

40000 CH4 Concentration (ppm)

40000 60000 Benzene Concentration (ppb)

16

0

20 16

60000

80000

COA-3 Asphalt Cover

20 80000

100000

0 0

0

4

8 12 O2 Concentration (%) 4 20000

20000

Free product is at 10 feet G. Todd Ririe BP

8 12 CO2 Concentration (%) 40000 CH4 Concentration (ppm)

40000 60000 Benzene Concentration (ppb)

16

20 16

60000

80000

20 80000

100000

Field Data vs. Alpha Values for Distribution Facility Site Depth in feet

Benzene concentration in ppmv G. Todd Ririe BP

Comparison of model predictions with field data for distribution facility-semi-log plot of data. 0

Case 2 Slab

Distance (feet)

2

No Slab

4 6 8 10 0.01

0.1

1.0

10

100

Benzene content (ppm soil gas)

= field data COA-3 under asphalt = field data COA-2 no asphalt G. Todd Ririe BP

Model Case 1 - No slab Model Case 2 - With Slab

1000

Summary of Case Studies Oxygen levels above 4% are an effective barrier ‹ Sub-slab environment contains oxygen above 4% ‹ Methane and benzene degrade at similar rates ‹ Vertical profile data needed to evaluate pathway ‹ Models without bioattenuation do not match field data ‹

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Procedures Which Influence Reported Soil Vapor Data ‹ Sample

spacing ‹ Collection depth ‹ Purge volume ‹ Excessive vacuums during collection ‹ Probe seals ‹ Probe decontamination ‹ Systems with vacuum pumps ‹ Sample containers & storage of samples G. Todd Ririe BP

Dedicated Soil Gas Probes

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Soil gas sampling probe down the borehole

Collecting soil gas sample through the probe

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Clay and Sand in Drill Cuttings

Collecting Soil Sample G. Todd Ririe BP

50 Ft Tubing Test

Tygon

Polyethylene G. Todd Ririe BP

NylaFlow

Teflon

1-

he

xe

ne

ne xa

n-

he

en

1-

pe

nt

nt

an

e

e

e pe n-

bu

1-

n-

bu

ta

en op

t en

ne

e

e pr

pr

op

an

ne

Et

he

ne

Et

ha

e an et h M

%

1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20

Vinyl

Delta D CH4 per mil

Isotopes can ID Source of Methane -100 -120 -140 -160

Thermogenic Gas

-180

Sub-Surface Microbial Gas

-200 -220 -240 -260 -280 -300

SG4-3

-320 -340 -360

-90

-80

-70

Near Surface Microbial Gas -60

-50

-40

Delta 13C CH4 per mil

-30

Sources of gases as defined in Coleman (1994) G. Todd Ririe BP

Summary of Some Lessons Learned High concentrations of CH4 can be generated quickly in soils ‹ Isotopes can be used to determine source of methane ‹ Use the right tubing-Tygon ok for fixed gases; NylaFlow best for BTEX ‹ Do preview sampling in field to determine vertical profile ‹ Use dedicated soil gas sample points at correct depths to evaluate VI pathway ‹

G. Todd Ririe BP