Enhanced In Situ Anaerobic Bioremediation of Chlorinated VOC’s: Technical Feasibility Pilot Demonstration

Problem

The DOE is working to accelerate the acceptance and application of innovative technologies that improve the way the nation manages its environmental remediation problems. DOE established the Innovative Treatment Remediation Demonstration (ITRD) Program to accelerate the adoption and implementation of innovative soil and groundwater remediation technologies. In September 1993 the ITRD initiated a project at the Pinellas STAR Center in Largo, Florida. The site is characterized by chlorinated volatile organic compound (CVOC) contamination (i.e., TCE, DCE’s, Vinyl chloride) of soil and groundwater in a shallow, sandy, surficial aquifer.

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Solution

Pelorus is a member of an advisory group composed of DOE, EPA, State regulators and, industry experts in In-situ bioremediation technologies. The in-situ bioremediation technology chosen was, In-Situ Anaerobic Bioremediation. As a member of the advisory group, Pelorus was involved in the development of the in-situ system design, operational implementation plan and data review and interpretation. The in situ bioremediation system involved enhancing the natural biodegradative process by using infiltration trenches to deliver organic substrates (i.e., electron donors) required to stimulate and enhance reductive dechlorination of the CVOC’s to ethene and ethane. Horizontal extraction wells were installed and alternately operated at two depth intervals to enhance the in situ mixing of nutritional supplements. Groundwater extracted through the horizontal wells was supplemented with the nutritional amendments and reintroduced through the infiltration trenches.

Pelorus also performed on-site support by providing specialized mobile analytical methodologies required to monitor system performance. Periodic monitoring of groundwater samples for dissolved hydrogen levels, methane, ethane and ethene were performed using highly specialized sampling and analysis techniques that must be performed in the field. Pelorus mobilized a field gas chromatograph specially equipped with a reducing gas detector (RGD2) and PID/FID. Low flow groundwater sampling at discrete depth intervals was required using a specially developed down well sampling apparatus and a bubble-strip methodology. Headspace gas samples were collected from the bubble strip chamber and analyzed on site for hydrogen, methane, ethane, ethene, and CVOC’s. A total of 4 wells were analyzed at four discrete depth intervals, representing a total of 60 analyses over a time period of 4-days.

The system was operated for six months. During this period, groundwater was recirculated at a rate of 1.5 gpm, representing 250,000 gallons of water or 2 pore volumes. Tracer and nutrient analyses indicated that nutrients reached approximately 90% of the central treatment area. Where nutrient breakthrough was observed, significant declines in total CVOC concentrations (70-99 %) were documented. Degradation rates as high as 1 – 2 ppm per day were observed in areas where CVOC exceeded 100 ppm. No degradation product build-up was observed. Many wells with initial CVOC levels below 10 ppm showed reduction to regulatory levels.

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