Treatability Study in Support of Remediation by Natural Attenuation (RNA) for CCFTA-2 (FT-17), Cape Canaveral Air Station, Florida

摘要

This report presents the results of a treatability study (TS) performed by Parsons Engineering Science, Inc. (Parsons ES) at CCFTA-2 (FT-17), Cape Canaveral Air Station, Florida to evaluate remediation by natural attenuation (RNA) of chlorinated aliphatic hydrocarbons (CAHs) dissolved in the site groundwater. The TS focused on the fate and transport of dissolved CAHs, particularly trichloroethene (TCE), dichloroethene (DCE), and vinyl chloride (VC); however, petroleum hydrocarbons including benzene, toluene, ethylbenzene, and xylenes (BTEX) are present in site groundwater. Residual and mobile light nonaqueous-phase liquid (LNAPL) present in the vadose zone and phreatic soils serves as a continuing source for the dissolved CAHs and BTEX. Site history and the results of previous investigations are summarized in this report. The use of RNA has been evaluated with consideration to additional remedial actions at CCFTA-2 (FT-17), including source remediation via excavation and soil washing, and a horizontal air sparging system (HASS) that has been installed to reduce CAH concentrations in groundwater that discharges to surface water. Comparison of CAH, BTEX, electron acceptor, and biodegradation byproduct isopleth maps for CCFTA-2 (FT-17) provides strong qualitative evidence of biodegradation of dissolved CAHs. These geochemical data strongly suggest that reductive dehalogenation of dissolved CAHs is occurring at the site as microbes utilize natural organic carbon, BTEX, and other fuel hydrocarbons as substrates. Despite the presence of mobile LNAPL, BTEX concentrations in groundwater are low and will likely continue to drop as fuel compounds are consumed as substrates. Patterns observed in the distribution of CAHs, daughter products of CAHs, electron acceptors, and biodegradation byproducts further indicate that biodegradation is reducing the concentration of CAHs dissolved in site groundwater.