MTBE and TBA Groundwater Remediation Using Sulfate Enhanced Biodegradation

Transcription

1 Innovation with Integrity MTBE and TBA Groundwater Remediation Using Sulfate Enhanced Biodegradation 22nd National Tanks Conference & Expo September 19-22, 2010

2 Why Sulfate Enhancement? Accelerates site cleanup as a major electron acceptor for natural attenuation In-Situ and minimally disruptive to the site and surroundings Cost effective in achieving remediation goals Safe to the environment and people A Green Technology which enhances natural conditions and reduces carbon foot print when compared to conventional remediation a socially responsible approach to remediation Proven by case study results on numerous site types 2

3 Significance of Sulfate Sulfate reduction according to multiple studies accounts for more than 70% of natural attenuation sulfate reduction methanogenesis nitrate reduction aerobic oxidation iron reduction Relative Importance of Electron Acceptor Processes in Degrading Hydrocarbon Contamination in Groundwater. Graph derived from data by Kolhatkar (BP), Wilson (USEPA), and Dunlap (BP) (2000); Weidemeier, et.al. (1999) 3

4 Overview of Patented Process US Patent No. 7,138,060 Issued November 21, 2006 Patent issued for: A process that enhances the environmental conditions existing within a contaminant plume by replenishing a natural groundwater compound required by bacteria to degrade the contaminants. Sulfate solution in excess of 1,000 ppm Covers all pollutants that can be degraded by sulfate-reducing microorganisms 4

5 Technical Overview Sulfate Reduction Process Petroleum Hydrocarbon + MgSO4 + Dissolved Iron Iron Sulfide+H2O+MgCO3+ CO2 Byproducts: Iron/other metal Sulfides and Magnesium Carbonate are insoluble and immobile. Raw Materials = + 5

6 Technical Advantages of Sulfate No air discharge involved with process Exists naturally in most groundwater High solubility in comparison to other electron acceptors Easily applied as an aqueous solution Proper application of sulfate enhanced biodegradation will result in no adverse health effects Degradation rate is significantly increased In comparison to mechanical remediation systems, significantly reduced costs and no long term operation and maintenance 6

7 Site Feasibility Evaluation Not a solution for every site, but a likely candidate for many Applicable where the existing plume demonstrates a lack of electron acceptors relative to background Not applicable for significant thickness of liquid phase hydrocarbons, but potentially useful for sheens Effective within saturated zone. Residual soil impact in vadose zone may need to be addressed by other techniques Threatened receptors may warrant additional response actions 7

8 Common Misconceptions Efficient biodegradation requires aerobic conditions Anaerobic degradation is the predominant mechanism for natural attenuation at most sites Anaerobic Biodegradation is too slow Significant contaminant reduction can occur in as little as 3 months Addition of sulfate solution will result in increased plume migration The volume of sulfate solution is minimal in comparison to the volume of the aquifer being treated This technology will result in a lingering sulfate contaminant plume Sulfates are rapidly utilized after application Hydrogen Sulfide gas will be generated Delta has never detected this, but continues to monitor Sulfate enhancement is NOT in-situ oxidation (Persulfate Radical) Delta s process is bio-enhancement 8

9 MTBE Degradation Case Studies Four active petroleum retail LUST sites in Washington, D.C. Tight clays and silts with interbedded saturated sand seams (1-3 thick) A concentrated sulfate solution was applied by gravity flow to treat the source area Applied volumes ranged from 160 gallons to 505 gallons per event 9

10 MTBE Case Study Results Month Pre-App Avg 30 Days Post-App MTBE Concentration (ug/l) % (6,100) 69% (2,900) 60 Days Post-App 90 Days Post-App 180 Days Post-App 40% (4,600) 27% (660) MW-1 MW-4 MW-3 MW-2 Concentration vs. Time 10

11 MTBE Case Study Conclusions Post-application MTBE concentrations declined an average of 57% across the four test sites during six month test period Observed radius of influence was between 10 and 45 feet Similar reductions of post-application BTEX concentrations have been reported for each site Declining sulfate groundwater concentrations indicate stimulation of anaerobic degradation No adverse impacts observed from any application Two of the incidents have been closed as a result of the sulfate application Considerable cost-savings have been recognized by utilizing this approach when compared to other more traditional remedial technologies 11

12 Can TBA be Degraded Anaerobically? Excerpts from Monitored Natural Attenuation of Tertiary Butyl Alcohol (TBA) in Ground Water at Gasoline Spill Sites EPA/600/R-07/100 October 2007 anaerobic biodegradation of TBA at many particular field sites will be limited by the availability of sulfate and the rate of TBA biodegradation will be limited by the rate that sulfate is supplied to the plume The anaerobic biodegradation of TBA is most commonly carried out by sulfate reducing bacteria. Data on the availability of electron acceptors in ambient ground water and the concentrations of electron acceptors in the source area of plumes indicates that sulfate is the most important electron acceptor at fuel spill sites 12

13 TBA Case Study Active retail petroleum facility located in Silver Spring, Maryland Regulatory drivers are elevated BTEX, MTBE and TBA Remediation target area is approximately 100 feet by 100 feet Lithology consists of saturated coarse seams interbedded with saprolite 175 gallons of sulfate solution were gravity fed into each of 7 application points (IP-1 through IP-7) 13

14 TBA Case Study Results TBA Concentration (PPB) 70,000 60,000 50,000 40,000 30,000 20,000 Max 219,500 95% (12,000) 94% (2,700) 91% (1,800) 12 Month Pre-App Avg 1 Month Post-App 5 Months Post-App 8 Months Post-App 11 Months Post-App 14 Months Post-App 39% (3,100) 10,000 0 MW-13 RW-11 RW-10 MW-7 Concentration Vs. Time 14

15 TBA Case Study Conclusions Post-application TBA concentrations have declined an average of 80% across the test wells in a 14 month post-application time-frame Observed radius of influence was between 20 and 80 feet Similar reductions of post-application BTEX and MTBE concentrations have been reported from each test well Declining sulfate groundwater concentrations indicate stimulation of sulfate reduction anaerobic degradation No adverse impacts observed from the application Site incident closure request is pending Considerable cost-savings have been recognized by utilizing this approach when compared to other more traditional remedial technologies 15

16 Contact Information For additional information, please contact: Jim Cuthbertson, Delta Consultants ; Benjamin M. Hansen, Delta Consultants ; 16