California Regional Water Quality Control Board, Santa Ana Region. 57 pp, 2018

The landfill is a closed, unlined Class III, non-hazardous municipal solid waste landfill that operated from August of 1963 to March of 1990. Site closure was implemented between 1992 and 1994. Since the mid-1980s, chlorinated VOCs (PCE, TCE, cDCE, and VC) have been detected in groundwater beyond the waste footprint of the landfill at concentrations exceeding the federal and State drinking water MCLs. To address the VOC release in groundwater, which is partially attributed to landfill gas diffusion, the Discharger is actively operating a landfill gas extraction and collection system and has completed a 2-yr (June 2015 - June 2017) enhanced in situ bioremediation pilot project. Conducted June 23-30, 2015, the pilot consisted of a network of five direct-push injection points that delivered 15,000 gal of substrate and dechlorinating microbes to the subsurface, plus three monitoring wells to assess treatment effectiveness. The pilot project has shown sequential breakdown of VOCs (reductions of 90% TCE, 61% cDCE, and 14% VC). Monitored natural attenuation is proposed as the final remedial measure to meet site cleanup objectives in addition to any necessary measures to control ongoing VOC release from the landfill. https://www.waterboards.ca.gov/santaana/board_decisions/tentative_orders/docs/2018/R8-2018-0009_tentative.pdf Follow up on the pilot's long-term biodegradation progress and other cleanup measures in the semi-annual groundwater monitoring reports at http://geotracker.waterboards.ca.gov/profile_report?global_id=L10004005233.