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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
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
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
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
16
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)
18
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)
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
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.
Recommended