Technology Application Manager
Dan Leigh is the Technology Application Manager for biological and reductive technologies and Department of Defense programs for PeroxyChem Soil and Groundwater Remediation. He has over 30 years of experience in contaminated site evaluation and remediation and has over 100 publications in the areas of groundwater hydrology, natural attenuation, bioaugmentation, aerobic, anaerobic, and cometabolic bioremediation, biogeochemical degradation and in situ chemical reduction for treatment of chlorinated and non-chlorinated organics and metals. He has conducted site investigations and remediation at projects across the United States and Internationally. He is a California registered geologist and certified hydrogeologist located in Walnut Creek, CA. He can be contacted at email@example.com
FLASH POSTER PRESESNTER - Oxidative and Reductive Treatments
Combining ZVI and Organic Substrates for Full-Scale Treatment of TCE in Aerobic Aquifer at Concord Naval Weapons Station
Background/Objectives. A trichloroethene (TCE) plume at the Concord Naval Weapons Station (CNWS) extends approximately 700 feet down gradient from the source area and up to 100 feet below ground surface. The aquifer consists of unconsolidated silt, sands and clays. Groundwater in the treatment area is highly aerobic. An Enhanced Anaerobic Bioremediation (EAB) pilot test conducted by CB&I demonstrated complete degradation the CE concentration from approximately 5,000 microgram per liter (µg/L) to less than 1 µg/L in approximately 500 days. The Navy wanted to evaluate a more aggressive approach to achieve site cleanup. CB&I conducted a second pilot test to evaluate enhancement of the biological approach by In Situ Chemical Reduction (ISCR). The ISCR approach was demonstrated to treat the CEs substantially quicker than the EAB alone.
Approach/Activities. Based on the successful application of ISCR, the Navy applied the ISCR process to the remainder of the plume. The ISCR process applied abiotic processes by distribution of zero valent iron (ZVI) to provide a long lasting substrate which degrades TCE while minimizing the generation of daughter products. The treatment process incorporated biological degradation processes by amending the ZVI with long lasting organic substrates (Emulsified Lecithin Substrate®; ELS (PeroxyChem). Lactate was added to the amendment water to create reducing conditions prior to injection and to help establish the bioaugmentation culture in the aerobic aquifer. Bioaugmentation was conducted using SDC-9™ (CB&I Federal Services LLC). Substrate distribution was conducted using direct push technology (Vironex). At each interval, the aquifer was first primed by fracturing the aquifer with the injection solution (ELS bioaugmentation culture and conditioned groundwater). Following confirmation of fracture development, ZVI in guar was injected into the interval followed immediately by the remaining injection solution. The injection was conducted to depths of up to 100 feet below ground surface.
Results/Lessons Learned. The injection process distributed substrates a minimum of 15 feet from the injection point. The ISCR process rapidly degraded TCE, dichloroethene (DCE) and vinyl chloride (VC) to below MCLs in the majority of the plume during the first injection event. Small area of the plume in which substrate was not effectively distributed was effectively treated with a second injection event. The reduced treatment time in the ISCR approach is attributed to β-elimination of DCE compared to the hydrogenolysis pathway in the EAB approach. This aggressive approach was demonstrated to effectively treat a laterally and vertically extensive CE plume in an aerobic aquifer.