Site Conditions Conducive for Potential Petroleum Vapor Intrusion...
Transcript of Site Conditions Conducive for Potential Petroleum Vapor Intrusion...
Site Conditions Conducive for Potential Petroleum Vapor
Intrusion (PVI) RiskRobert E. Sweeney, Ph.D., R.G.
Intrusion (PVI) Risk
E & P Geochemistry
AEHS 21st Annual West Coast International Conference on Soil, Sediment, Water & Energy
Mission Valley, San Diego, CaliforniaMarch 14-17, 2011
Evaluation of BiodegradationPVI approach using methane field data
• All Sites are not the same for PVI risk– Discrepancy in evaluation for benzene – ‘fast’ reaction for biodegradation vs
‘large’ exclusion distance for sites in database must reflect site conditionslarge exclusion distance for sites in database - must reflect site conditions.
• Site conditions:– 1) limited oxygen flux;1) limited oxygen flux; – 2) inefficient biodegradation (oxygen and benzene both present); – 3) enhanced oxygen demand – fresh gasoline and methane; – 4) unidentified shallow source; ) ;– 5) sample interval.
• Methane study:y– 1) oxygen measurements at 4 or 5 depths; – 2) 891 measurements of oxygen and methane;– 3) 142 methane measurements > oxygen demand than fresh gasoline; – 4) no shallow sources; – 5) sample interval at 2 feet from surface to 8 or 10 feet.
Diffusion Dominated Vapor TransportEBI Study Guadalupe Oil FieldDil t (di l) l U i F t R ti l l ti 75% O
Install vapor points – field meter can be used to measure oxygen and methane concentrations at limit 0.1 %-v. Need m ltiple samples in aerobic one to define o gen
0
EBI Study - Guadalupe Oil FieldDiluent (diesel) plume - Using Fast Reaction calculation – 75% Oxygen Flux used to oxidize methane
multiple samples in aerobic zone to define oxygen concentration gradient.
0 20 40 fe
et)
60 80
100
Dep
th (f
Aerobic Zone
100 120
0 2 4 6 8 10 12 14 16 18 20 22 24
Anaerobic Zone – clean soil – TPH measurements
0 6 8 0 6 8 0Concentration Soil Vapor (%-v)
Methane Oxygen
Gasoline/Diesel smear zone extending downgradient from source – 56 locations with soil and soil vapor measurements
Typical cross section – silt layer over smear zone (red) – confinedyp y ( )aquifer above - but usually unconfined with top of smear at about7 – 10 feet-bgs. TPH/BTEX at top, middle and bottom of smear.
Soil Vapor AnalysesBenefit of soil gas profile data – can evaluated data quality andand thickness of biodegradation zone
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Soil Vapor AnalysesSeasonal - 56 locations - 891 analyses
and thickness of biodegradation zone.
50
60 Biodegradation Zone – Oxygen & Methane
30
40
4 (%
-v) Bad Data ?
20
30
CH
4
No biodegradation
0
10
0 5 10 15 20 25 Oxygen (%-v)
Top of Contamination
Oxygen and Methane concentrations are valid.
Sample interval = 2 feetThickness biodegradation layer <= 4 feet
Oxygen Demand Methane 2 - 4 times fresh gasoline
0PZ-23Well #1 – soil vapor data from 1998; 2000; 2006
0
2
44
6
epth
(ft)
8
10
D Oxygen Flux 100 mg/m3-hr
Top of Contamination12
0 5 10 15 20 25 Soil Gas (%-v)
Top of Contamination
O2 (9/98) O2 (6/00) O2 (11/06)
CH4 (9/98) CH4 (6/00) CH4 (11/06)
0
PZ-23Well #1 – Methane Data Collected in 20090
2
4
6
epth
(ft)
8
10
De
12 0 1 2 3 4 5 6 7
Methane (%-v)Methane (%-v)
May 2009 August 11 2009y g
August 28 2009 November 2009
0PZ-23Well #1 – Benzene Data Collected in 2009
0
2
4
6
epth
(ft)
8
10
De
12 0 200 400 600 800 1,000 1,200
B ( / 3)Benzene (ug/m3)
May 2009 August 11 2009
August 28 2009 November 2009
Effectiveness of Biodegradation• Review of site with extensive gasoline/diesel smear zone. No near surface
contamination.
• 891 measurements made at 56 different locations and at 2 foot intervals from the surface to 8 or 10 feet depth.
• Methane measurements– 623 at < 0.1 %-v [all samples from < 6 feet] – 126 between 0.1 and 10 %-v [range for oxygen demand – gasoline in soil]
142 at 10 % v or greater [larger oxygen demand than for fresh gasoline]– 142 at 10 %-v or greater [larger oxygen demand than for fresh gasoline]
• Thickness of biodegradation zone (clean soil needed for attenuation) = 4 feet.– At 4 locations: < 0.1 %-v methane corresponded to benzene < 30 ug/m3p g– 0.1 %-v methane = 700,000 ug/m3 methane– How low does the methane concetration go in aerobic zone?
Low level methane measurement (FID) – Atmosphere = 1.7 ppm-v
- Roslev, et al. (1997) – Applied Envir Microbiology v 63 #3 p.874
- www.co2science.org/subject/m/summaries/methaneextract.php
Ohio Site - May 2009Soil Vapor Samples @ 2 foot Depth
2,500
Soil Vapor Samples @ 2-foot Depth
At h i M th L l2,000
b-v)
Atmospheric Methane Level
1,500
ne (p
pb
500
1,000
Met
han
0
500
. . .
PVI approaches to evaluate biodegradation i h dusing methane data
Th i di b bi d d i• There is no discrepancy between biodegradation models and exclusion rules.
• 891 measurements – all consistent with bi d d i d lbiodegradation model.
• Thickness of biodegradation layer is 4 feet for oxygen demand up to 4 times fresh gasoline.