Magnesium Sulfate A METHOD TO ENHANCE THE BIODEGRADATION OF

DISSOLVED PHASE-MTBE AND TBA IN ANAEROBIC

ENVIRONMENTS

Samantha Sheer Clark

and

Richard A. Jasaitis C.P.G

2

Magnesium Sulfate

What is it:

A salt commonly known as Epson Salt (MgSO4)

Most favorable electron acceptor in anaerobic

microbial biodegradation

Naturally more abundant in groundwater making

sulfate the dominant degradation process

Soluble in water, which allows easy introduction

through injection into a plume

3

Magnesium Sulfate

How it works:

stimulates biodegradation of dissolved phase-

hydrocarbons in anaerobic conditions

magnesium sulfate is an electron acceptor that

increases microbial activity similar to adding dissolved

oxygen in aerobic environments

Sulfate has twice the electron acceptor capacity of

oxygen

4

Magnesium Sulfate

Benefits:

Non-Hazardous, safe handling

Cost effective (.75/lb)

Highly soluble (1 lb/gal = 46,000 ppm)

Easily applied as an aqueous solution

No documented adverse health effects

No permanent structures or long term operation and

maintenance needed

5

Magnesium Sulfate

Limitations

Not effective if residual soil impacted in vadose zone

Not applicable for LNAPL

Anaerobic environments

Favorable groundwater geochemistry

6

Injection Method

Magnesium sulfate is mixed with water and

injected into the plume via Geoprobe

7

New Jersey Case Study

8

New Jersey Case Study

Site History

A 1996 release of an unknown quantity of gasoline

Pipeline located 5 feet below grade

Spill response solely by client personnel

Road moratorium/source uncertainty

Site Description

Southwestern New Jersey

Close proximity to the Delaware River

Pipeline runs through a residential neighborhood

Medical rehabilitation facility

9

Pipeline Release

location

10

11

Baseline Investigation

Site Conceptual Model

MIP/EC Logs, onsite lab

Temp. groundwater sampling points

Complete plume delineation (2 weeks)

Rock works

Geology/Hydrogeology

Thin sandy unit overlying a regional clay formation

Depth to water 5 feet, depth to clay 15 feet

Discontinuous sand distribution/silty lenses

Former wetland areas

12

Plume Dynamics/ Reaction Zones

13

Baseline Groundwater Geochemistry

Compound Specific Isotope Analysis of MTBE

Manufactured MTBE del o/oo value of -27 to -33

del o/oo of MW-3 is -25.36 and MW-10R is -18.54, which

are less negative then for manufactured MTBE indicating

degradation is occurring.

Dissolved Methane Analysis:

MW-3 = 740 µg/l and MW-10R = 99 µg/l, which indicates

that anaerobic degradation is the primary mechanism.

14

Baseline Groundwater Geochemistry

Dissolved Carbon Dioxide Analysis:

MW-3 = 460 mg/l and MW-10R = 300 mg/l, indicates

anaerobic conditions are occurring

Dissolved Iron and Manganese Analysis:

Dissolved iron concentrations are higher in the source

area, which suggests biodegradation is occurring (120 µg/l

vs. 20 µg/l)

Dissolved manganese concentrations are highest down

gradient of the release area, suggesting biodegradation is

occurring (2.2 µg/l vs. 0.8 µg/l)

15

Baseline Groundwater Geochemistry

Sulfate concentrations

Ambient ranged from 13.3 to 78.9 ppm

Inverse relationship

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Baseline Groundwater Geochemistry

Literature Value for

anaerobic conditions

Site Concentrations

DO (source of plume) < 1 mg/l 0.17 mg/l

ORP <-50 mv -11 mv

pH >6.5 5.94

Sulfate Concentration gradient

from source to fringe of

plume

13 mg/l (source)

59 mg/l (plume fringe)

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Injection Plan Cost-constraint

Two week field effort

Injection Solution Ratio

12% solution for “source areas” (1 lb/gal)

6% solution for “diffuse areas” (0.5 lb/gal)

Injection Grid and Quantity

87 points

5,800 lbs. MgSO4 in 7,000 gallons water

Modified 30 foot grid plan

Variable volume and concentration

Injection flow and pressure (18-30+ gal/min and 18-30+ psi)

19

20

0

50

100

150

200

250

300

350

400

450

500

Su

lfa

te C

once

ntr

ation

(m

g/L

)

Sampling Date

Sulfate Analytical Data

MW-1 MW-3 MW-4 MW-10R

MW-22 MW-31 MW-36

Sulfate Injection

January 3, 2012

21

22

23

0

2

4

6

8

10

12

14

16

18

1

10

100

1000

10000

100000

Mo

nth

ly P

recip

ita

tion

(in

che

s)

MT

BE

and

TB

A C

once

ntr

ation

(m

g/L

)

Sampling Date

Monitoring Well MW-10R

Precipitation (inches)

TBA Concentrations

MTBE Concentrations

Ozone / Air Sparge Injection

System Operation Period

Injection January 2012

24

0

2

4

6

8

10

12

14

16

18

1

10

100

1000

10000

100000

Mo

nth

ly P

recip

ita

tion

(in

che

s)

MT

BE

and

TB

A C

once

ntr

ation

(m

g/L

)

Sampling Date

Monitoring Well MW-16

Precipitation (inches) TBA Concentrations MTBE Concentrations

Ozone / Air Sparge Injection

System Operation Period

Injection January 2012

25

0

2

4

6

8

10

12

14

16

18

1

10

100

1000

10000

Mo

nth

ly P

recip

ita

tion

(in

che

s)

MT

BE

and

TB

A C

once

ntr

ation

(m

g/L

)

Sampling Date

Monitoring Well MW-31

Precipitation (inches) TBA Concentrations MTBE Concentrations

Injection January 2012

26

Conclusions

The extent of the dissolved-phase MTBE and

TBA plume has decreased

Sulfate concentrations are stable to increasing

Sulfate concentrations indicated sulfate is

present in the groundwater and continuing to

enhance natural degradation of the dissolved-

phase hydrocarbons

Continued monitoring.