Biofouling of Injection Wells at 200 West Pump and Treat - 19252
Located on the U.S. Department of Energy's Hanford Site in Richland, Washington, the 200 West Pump and Treat Facility (200 West P and T) has a 9,464 L/min capacity designed to capture and treat an 8 km{sup 2} contaminated groundwater plume. The 200 West P and T system was designed and built by CH2M Hill Plateau Remediation Company to capture and treat contaminated groundwater to reduce the mass of carbon tetrachloride, chromium (trivalent and hexavalent), cyanide, nitrate, and trichloroethene. The system was constructed in calendar years 2010 and 2011 and started operation in 2012. Following treatment, the water is reinjected into the aquifer to serve as a recharge source and to provide flow-path control. Fouling of injection wells has occurred since system startup, characterized by reduced capacity and associated increases in dynamic water level during injection. In severe cases, the water level increases 30.5 m in the first 24 hours of injection. Video inspection of injection wells confirms that the accumulation of solids obstruct the well screens. Because replacement of treated groundwater to the aquifer is essential to the overall remedy, a comprehensive program was initiated to understand the nature/cause of well fouling and to identify mitigation strategies. As a result of this program, a sodium hypochlorite feed system was installed on the pipeline to one injection well to determine whether preventing biological growth would prevent well fouling. A residual of 0.5 to 1.0 mg/L as Cl{sub 2} not only halted fouling but also reversed fouling impacts. Current efforts focus on disinfecting the entire volume of injection water. (authors)