ARCHIVED REPORTS_XR0004215 - Laserfiche WebLink

Home Browse Search

r.. performed, including a plate count and bench scale study, to further establish that the t bioremediation would be successful without negative side effects. Slug testing was performed at the site by Black & Veatch in January 1994 to facilitate extraction and injection well design. A CAP was prepared as an addendum to the ASA/RO, Addendum No. Y to the Additional Site Assessment and Remedial Options Report: L' Remedial Action Plan, Black & Veatch, September 1994, and was submitted in September 1994 to the SJCPHS and RWQCB. to Because reinjection was proposed, a waste discharge permit was required by the RWQCB. The RWQCB raised several concerns regarding the addition of nitrogen t`, to the aquifer and the hydraulic capture of the bioremediation system. A bench scale study was performed to evaluate residual nitrogen levels and a short duration step draw down test was conducted to further estimate the range of transmissivity in the aquifer. The step draw down test was used in place of a constant rate pump test to minimize the amount of water extracted and requiring disposal. The groundwater w• extraction and injection system was then modeled to determine optimum extraction and injection rates while achieving hydraulic control. An extraction and injection system was designed and presented in Addendum No. Y to the Remedial Action Plan, Black & Veatch, April 1995. The SJCPHS approved the CAP and addendum and the RWQCB issued a general waste discharge permit in May 1995. Additional groundwater data gathered during the lengthy permitting process indicated that the plume was stable and passive bioremediation was occurring at the +� site. In March 1996, the concentration of benzene in MW-8 was determined to be 3.3 ppb. The chemical was not detected in wells MW-1 and MW-9. Although it is possible to treat benzene at this low concentration to meet California MCLS, treatment options are not cost-effective. Since initiating the groundwater monitoring program in September 1993, benzene concentrations in groundwater have decreased almost 50-fold through natural degradation. The benzene concentration in well MW- 8 is approaching the drinking water standard using no treatment within 2-1/2 years. Also during this time, research conducted by a team of scientists from University of California institutions and Lawrence Livermore National Laboratory for the State Water Resources Control Board recommended that passive bioremediation be the remedial alternative and "unless there is a compelling reason otherwise, close cases after source removal to the point of residual FHC (fuel hydrocarbon) saturation" L. (Recommendation to Improve LUFTs, pg 19). Due to the low-risk nature of residual hydrocarbons in groundwater and the effectiveness thus far of passive bioremediation, 96R7 Fast Bay Municipal Utility District 40429700.fcr 8 Final Closure Report ;r