Monitoring Production of Methane From Spills of

Gasoline at UST Release Sites

Ken Jewell and John T. Wilson U.S. EPA/ORD/NRMRL

John SkenderR.S. Kerr Center, Ada, OK

22nd National Tanks Conference

Boston, Massachusetts

September 20-22, 2010

Background

• In 2008 The Oklahoma Legislature required that gasoline refineries reveal the content of ethanol in the gasoline being sold in Oklahoma.

• Until that time the tank owners and the UST regulators did not know whether ethanol was present in motor gasoline in Oklahoma.

Why Was This Study Done?

• Oklahoma Corporation Commission (OCC) had particular concern about older tanks that were upgraded by spraying an epoxy or polyester coating on the inside of the tank.

• Oklahoma state regulators (OCC) requested assistance from the EPA Office of Research Development concerning the effects of ethanol on the integrity of underground storage tanks, and the environmental consequences of a release of gasoline containing ethanol.

What Did EPA/ORD Tell OCC?

• We did not know what E10 would do to spray the spray lining. Other people are currently working on issues of materials compatibility. Storage tanks lined prior to 1980 may not be suitable for E-10.

• We do know that a release of E10 has a number of undesirable consequences associated with the biodegradation of ethanol.

• We told them look for the undesirable consequences of a release.

Consequences of E10 Release

Anaerobic biodegradation of ethanol produces methane. Methane leaves the ground water and enters soil gas where it can present an explosion hazard if it finds a confined space.

We found little evidence this has ever happened in Oklahoma.

30 CFR §57.22003

Mine Category or subcategory.

Table 1

See MSHA Illus. 27

Relation Between Quantitative Composition and

Explosibility of Mixtures of Methane and Air

Further Consequences of E10 Release

Aerobic biodegradation of methane in the soil gas will consume oxygen that would otherwise be available to degrade benzene and other gasoline constituents in soil gas.

Because methane inhibits benzene degradation in the unsaturated zone, there is greater risk of vapor intrusion of benzene.

Probably is a big deal, but we had not routinely looked for methane in soil gas.

CH4 + 2 O2 → CO2 + 2 H2O

One part methane will consume two parts oxygen.

Air is 20% oxygen.

Biodegradation of 10% methane by volume can consume all of the oxygen in soil gas, preventing aerobic biodegradation of benzene in soil gas.

Conventional Conceptual Model for Aerobic Biodegradation of Petroleum Vapors in the Vadose Zone

O2

O2O2

BTEX Vapor

How does Methane affect BTEX vapor intrusion?

BTEX Vapor plus Methane

O2

O2

Most conventional ground water monitoring wells are screened across the water table to sample free product.

BTEX Vapor plus Methane

Sampling Existing Monitoring Wells

EX-Cap

Pump

Is there methane in soil gas at confirmed release sites in Oklahoma?

Soil gas was sampled at 13 sites with recent confirmed releases.

Methane concentrations were determined by analysis on a Agilent Micro 3000 gas chromatograph.

0

10

20

30

40

50

60

0 2 4 6 8 10 12 14

Number of Sites

Hig

hes

t C

on

c. M

eth

ane

(% v

/v)

Highest concentration of methane in soil gas in the UST tank pit or the adjacent sediments at 13 confirmed release sites in Oklahoma

LEL

We need a screening method that is simple, that can be easily incorporated into existing sampling protocols, and that is inexpensive.

Can we use conventional field meters to measure methane in soil gas?

High concentrations of methane

have been found at these sites.

Sampling Tank Pit Air (Screening System)

EXHAUSTEXHAUSTEXHAUSTEXHAUST CO2CH4

O2

Monitoring Well

Precision of field meters and GC for analysis of pure methane

Determined against known standards 0.1

1

10

100

0.1 1 10 100

Standard (%v/v)

Ana

lysi

s (%

v/v)

Fixed labOrion field meterLandtec field meterLinear (Equivalent)

Methane

0

5

10

15

20

25

30

0 10 20 30 40 50

Time of Sampling (Minutes)

Met

er R

eadi

ng fo

r M

etha

ne (

% v

/v)

bypassed the activated carbon trap

Need for a Carbon Trap in front of the IR of the Field Meter

gasoline hydrocarbons fooled the meter

Tank Pit Well (Antlers, OK. GMW-5)

Concentration (% v/v)

Conc. Propane in standard 0.99

Lab GC as propane 1.02

Orion #1 as methane 6

Orion #2 as methane 11

Landtec as methane 37.5

Laboratory study to document interference of propane in analysis of methane by IR meters

Well GC at Lab Landtec Orion

Meters protected by GAC trap Methane (% v/v)

Antlers-MW-2-A 44.8 61.4 27.2

Henryetta NW-TP-1 10.0 18.4 9.9

Pauls Valley VPW-3 4.0 5.1 3.5

Pauls Valley VPW-3 10N 3.6 4.5 3.2

MW-1-Wapanuka-A 2.5 4.3 4.6

OKC S.E. 29th Street 1.3 2.3 1.8

Antlers GMW-5 0.8 1.9 1.6

Henryetta NW-TP-1E 0.5 0.7 0.8

Oklahoma City TMW-3-A 0.1 0.1 0.1

OKC N.E. 23rd Street TMW-1-A 0.1 0.0 0.1

Maysville N.E. Well 0.0 0.0 0.0

OKC N.E. 23rd Street TMW-2-A 0.0 0.0 0.0

Pickett-MW-2-4" 0.0 0.6 0.6

Is there benzene in soil gas at confirmed release sites in Oklahoma?

Benzene concentrations were also determined on the Agilent Micro 3000 gas chromatograph.

We did not use TO-15.

We used the same analytical run on the Agilent Micro 3000 gas chromatograph to determine methane and benzene. We wanted an affordable method to screenfor high concentrations of benzene.

So what does all that methane and benzene in soil gas mean for risk

management?

UGEConvenience Store

Diesel Dispenser

Diesel Dispenser

Gasoline Dispenser

UGE

Product Lines

100 feet

EPA-1

MW-2

GMW-3 GMW-1

Product Lines

UGEConvenience Store

Diesel Dispenser

Diesel Dispenser

Gasoline Dispenser

UGE

100 feet

CH4 8.5%, O2 2.2%

Benzene 43.2 ppm soil gas

0 .0008 ppm in H20

EPA-1

MW-2

CH4 1.2%, O2 4.1%

Benzene 13.7 ppm in H20CH4 51%, O2 0.8%

Benzene 0.077 ppb in H20

CH4 45%, O2 1.9% Benzene 406 ppm soil gas

1.7ppm in H20

GMW-1GMW-3

GMW-4 Benzene 0.078 ppm in H20

What to think about EPA-1 and MW-2?

The concentrations of methane are high enough to inhibit or preclude aerobic biodegradation of benzene.

0.1

1

10

100

1000

10000

0.01 0.1 1 10 100Methane (% v/v)

Ben

zene

(pp

m v

/v)

Benzene detected

Benzene not detected

The higher concentrations of benzene were associated with higher concentrations of methane.

EPA-1

MW-2

What does all that methane and benzene in soil gas mean for risk management and exposure pathways?

One method to calibrate the Johnson and Ettinger Model of vapor intrusion uses measured concentrations of benzene in water from wells to predict concentrations of benzene in soil gas.

How well does that work in our case sites in Oklahoma?

Product Lines

UGEConvenience Store

Diesel Dispenser

Diesel Dispenser

Gasoline Dispenser

UGE

100 feet

CH4 8.5%, O2 2.2%

Benzene 43.2 ppm soil gas

0 .0008 ppm in H20

EPA-1

MW-2

CH4 1.2%, O2 4.1%

Benzene 13.7 ppm in H20CH4 51%, O2 0.8%

Benzene 0.077 ppb in H20

CH4 45%, O2 1.9% Benzene 406 ppm soil gas

1.7ppm in H20

GMW-1GMW-3

GMW-4 Benzene 0.078 ppm in H20

0.001

0.01

0.1

1

10

100

1000

10000

0.001 0.01 0.1 1 10 100 1000 10000

Conc.of Benzene in Soil Gas (ppm v/v) calculated from Benzene in Ground Water

Con

c. B

enze

ne in

Soi

l Gas

(pp

m v

/v)

Benzene in Soil Gas or Tank Fill

EPA-1

MW-2

EPA Generic Screening Level

for Deep Soil Gas

This is a Session on Biofuels Remediation

Question:

Is the Methane from Ethanol or Petroleum?

Methane from ethanol made from corn should have the same 14C content as the atmosphere.

Methane from petroleum should have no detectable 14C content.

Some of the methane comes from dissolved inorganic carbon.

Percent modern carbon in methane

0

10

20

30

40

50

60

70

80

90

100

Henryetta Paul's Valley Antlers Wapanucka

Methane Produced Expected if from EthanolExpected if from Petroleum

Conclusions about what’s out there:

A significant fraction of spill sites had high concentrations ofmethane in soil gas.

At many of our sites, the methane is from petroleum and not biofuels.

A significant fraction of spill sites had high concentrations ofbenzene in soil gas.

Conclusions about monitoring:

Conventional monitoring wells were useful as a vapor probe for methane in soil gas.

Field meters provide convenient and affordable screening tool for methane in soil gas, with the following precautions:

•Must use a carbon trap to separate methane from other hydrocarbons.

•Must watch for leaks in the sampling system.

•Sometimes tank pits fill with water, and the water tables inundate the top of screen in the wells.

Suggestions:

If vapor intrusion is a concern at a spill site, portable field meters are a useful tool to screen existing monitoring wells to detect concentrations of methane in soil gas.

If methane concentrations exceed a few percent, sample vapors from existing monitoring wells for GC analyses to determine concentrations of methane and benzene in soil gas.

If concentrations of methane and benzene are of concern, initiate a formal evaluation of vapor intrusion. It is highly recommended that you use dedicated vapor probes installed for that purpose, if necessary.

Ken Jewell, U.S. EPA/ORD/NRMRLR.S. Kerr Center, Ada, OK

Jewell.ken@epa.gov

Ken Jewell, U.S. EPA/ORD/NRMRLR.S. Kerr Center, Ada, OK

Jewell.ken@epa.gov

Background Slides

Sub Slab Vapor Sampling Using a Peristaltic Pump

Sampling for Carbon14 Isotope Ration Analysis

Gas Sample Collected Using Water Displacement

Methane and Dissolved Inorganic Carbon (DIC) in ground water was analyzed for the ratio of carbon 14 to carbon 12, using accelerator mass spectrometry.

The ratio is presented as a percent of the ratio in carbon dioxide in air in 1955, before atmospheric testing of nuclear weapons.

This is termed the percent modern carbon or PMC.

CH3CH2OH + H2O → CH3COOH + 2 H2

CH3COOH → CO2 + CH4

2 H2 + ½ CO2 → ½ CH4 + H2O

2/3 of methane comes from ethanol

1/3 of methane comes from DIC

Ethanol Fermentation to Methane

2 CH + 2 H2O → CH3COOH + H2

CH3COOH → CO2 + CH4

H2 + 1/4 CO2 →1/4 CH4 + 1/2 H2O

4/5 of methane comes from Benzene

1/5 of methane comes from DIC

BTEX Fermentation to Methane

Location Methane% v/v

CO2

% v/v

PMCin

Methane

Center 21.9 9.07 <0.4

Paul’s Valley 5.32 7.06 6.5

Henryetta 16.95 6.09 9.1

Wapanucka 13.98 9.67 10.9

Antlers 34.9730.66

15.0314.82

27.030.8

LocationPMC

inDIC

PMCin

Methane

PMC expected inMethane if

from Petroleum

PMC expected inMethane if

from Ethanol

Methane from

Ethanol

Center <0.4 Natural Gas

Paul’s Valley 24.3 6.5 4.9 74.8 2.4%

Henryetta 27.4 9.1 5.5 75.8 5.1%

Wapanucka 73.2 10.9 14.6 91.1 Not Detected

Antlers 43.0 27.030.8

8.6 81.0 25%31%