First Pilot Test on the Integration of GCW (Groundwater Circulation Well) with ENA (Enhanced Natural Attenuation) for Chlorinated Solvents Source Remediation.

Abstract

The remediation of aged source zone affected by residual chlorinated aliphatic hydrocarbons (CAHs) represents one of the main challenges in contaminated aquifers. Groundwater Circulation Wells (GCWs) could be considered a strategy for the progressive source zone remediation; this in situ remediation technology is designed to create an in situ vertical groundwater circulation cells by drawing groundwater from an aquifer through one screened section of a multi-screened well and discharging it through another screened section. The pressure gradient between the two hydraulically separated screen sections in the well induces a circulation flow in the aquifer forcing water through less permeable layer where usually CAHs residual source are located. The groundwater moves through the treatment zone both horizontally and vertically and as a consequence the low permeable layer is constantly penetrated by the vertical flow of the GCWs. We tested the possibility to use GCW to enhance in-situ bioremediation (ISB) in an operative industrial site heavily contaminated by different chlorinated solvents (at concentration up to 100 mg/L) in a complex hydrogeological saturated zone. A 30 mts deep GCW, with three screen sections, was designed and installed at the site for a pilot testing. Groundwater is pumped towards two screen sections of the GCW and is reinjected into the aquifer by another screen section after passing through an external unit treatment. External treatment unit is composed of a sand filter tank and two reactors: one reactor was filled with a biodegradable polymer (poly- hydroxy-butyrrate, PHB) and the other one with a mixture of zero-valent iron (ZVI) and PHB. Results from the first eight months of operation clearly demonstrated how groundwater recirculation through the PHB reactor allowed delivering continuously electron donors in the contaminated aquifer enhancing the mobilization of CAHs and stimulating Natural Attenuation biological processes.