Magnesium Sulfate A METHOD TO ENHANCE THE BIODEGRADATION OF DISSOLVED PHASE-MTBE AND TBA IN ANAEROBIC ENVIRONMENTS

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1 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 2

3 Magnesium Sulfate How it works: stimulates biodegradation of dissolved phasehydrocarbons 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 3

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 4

5 Magnesium Sulfate Limitations Not effective if residual soil impacted in vadose zone Not applicable for LNAPL Anaerobic environments Favorable groundwater geochemistry 5

6 Injection Method Magnesium sulfate is mixed with water and injected into the plume via Geoprobe 6

7 New Jersey Case Study 7

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 8

9 Pipeline Release location 9

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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 11

12 Plume Dynamics/ Reaction Zones 12

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 and MW-10R is , 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. 13

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) 14

15 Baseline Groundwater Geochemistry Sulfate concentrations Ambient ranged from 13.3 to 78.9 ppm Inverse relationship 15

16 Baseline Groundwater Geochemistry Literature Value for anaerobic conditions DO (source of plume) < 1 mg/l 0.17 mg/l ORP <-50 mv -11 mv ph > Sulfate Concentration gradient from source to fringe of plume Site Concentrations 13 mg/l (source) 59 mg/l (plume fringe) 16

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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 ( gal/min and psi) 18

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20 Sulfate Concentration (mg/l) Sulfate Injection January 3, 2012 Sulfate Analytical Data MW-1 MW-3 MW-4 MW-10R MW-22 MW-31 MW Sampling Date 20

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23 MTBE and TBA Concentration (mg/l) Monthly Precipitation (inches) Monitoring Well MW-10R Precipitation (inches) TBA Concentrations MTBE Concentrations Injection January Ozone / Air Sparge Injection System Operation Period Sampling Date 23

24 MTBE and TBA Concentration (mg/l) Monthly Precipitation (inches) Monitoring Well MW Precipitation (inches) TBA Concentrations MTBE Concentrations Ozone / Air Sparge Injection System Operation Period Injection January Sampling Date 24

25 MTBE and TBA Concentration (mg/l) Monthly Precipitation (inches) Monitoring Well MW-31 Precipitation (inches) TBA Concentrations MTBE Concentrations 18 Injection January Sampling Date 25

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 dissolvedphase hydrocarbons Continued monitoring. 26