SITE INFORMATION AND CORRESPONDENCE_1998-2000

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March 1998 Page 2 continued from page 1 and analyzed to ev to the extent of dry cleaning con- tamination at or near suspected source areas. Source Area Investigation A Source Area Investigation is being conducted at the Site Results of the Source Area Investigation and recommenda- to identify and characterize suspected or known dry clean- tions for further source area activities will be presented in ing contamination release areas along portions of the the Source Area Report,which will be available for public sanitary sewer system where leaks are suspected. This review in April 1998 at the document depository, as investigation also focuses on areas around the former and described below. current dry cleaning facilities.The initial phase of the Plume Perimeter Investigation Source Area Investigation identified potential areas of dry A Plume Perimeter Investigation is being conducted cleaning contamination.Past dry cleaning waste-handling concurrently with the Source Area Investigation to identify practices included the customary and standard disposal of and characterize the extent to which dry cleaning contami- wastewater containing dissolved dry cleaning fluids into the nation has migrated in groundwater away from the source sanitary sewers. Considering past practices, a video survey areas. CPT borings were advanced to investigate the of sewer lines at Lincoln Center was performed.The video, lithologic conditions in the vicinity of Lincoln Center and which examined approximately 1,850 feet of the sanitary collect groundwater samples from the A- and B-zone sewer, revealed numerous areas of sags, offsets, and aquifers.Monitoring wells were installed at 10 targeted cracks in the lines that could have contributed to leakage of a q locations to further evaluate the extent of dry cleaning dry cleaning contamination from the sewer lines into soil contamination in these zones, as well as in the deeper C- ard groundwater surrounding those lines. zone aquifer. Additional CPT borings, groundwater After identifying potential source areas,a soil-vapor samples, and monitoring wells have been recommended as survey was conducted to analyze for the presence of dry part of the ongoing Plume Perimeter Investigation.Results cleaning contamination.A soil-vapor survey is a study of these additional activities will be summarized in the RI performed to analyze vapor samples collected from unsat- Report,tentatively scheduled to be available in the fall of urated soils to determine if chemicals are present below the 1998. These investigations to date have shown that ground surface. Soil-vapor probes were driven into the groundwater contamination has moved offsite, east of ground at over 600 locations at the Site and were used to Lincoln Center, and to a lesser extent, west of Lincoln obtain soil-vapor samples at depths ranging between 3 and Center along the sanitary sewer line. 40 feet below ground surface (bgs). Over 800 soil-vapor Monitoring Activities samples were analyzed for dry cleaning contamination and/ Periodic monitoring of groundwater elevations and ground- or petroleum hydrocarbon compounds. This investigation water quality in over 25 site monitoring wells continues on identified locations at Lincoln Center where dry cleaning a quarterly basis. A monitoring well integrity assessment contamination is present in unsaturated soil. was conducted on existing wells to evaluate their suitability Suspected source areas were further investigated using a for use in the periodic monitoring program. A survey of cone penetration testing (CPT) rig to push an instru- public and private wells was also conducted to identify mented probe into the ground to obtain data regarding the wells in the vicinity of the Site that could be potentially types of soils encountered and to collect groundwater affected by groundwater containing dry cleaning contami- samples.Numerous locations were investigated to depths nation.Results of periodic monitoring,the well integrity of 70 to 120 feet bgs within the source area. Groundwater assessment, and the public and private well survey are samples were obtained from selected intervals within the A- documented in reports available for public review at the zone aquifer,the A/B aquitard,and the B-zone aquifer, document depository, as described below. PHASE I IRA ACTIVITIES The Phase I IRA is designed to control migration of Detailed Plan.The Phase I IRA Detailed Plan is a compre- groundwater containing dry cleaning contamination off of hensive document that presents the results of data collected Lincoln Center.Phase I IRA activities initially included field during the Source Area and Plume Perimeter Investigations scoping work to collect data necessary to design a shallow (to date) and the Phase I IRA Investigation, and discusses A-zone groundwater extraction and treatment system. the analyses that were performed leading to design of the Phase I IRA scoping activities included advancing CPT Phase I IRA. The Phase I IRA system will consist of borings near the downgradient (eastern)boundary of multiple extraction and monitoring wells completed in the Lincoln Center to assess the type of soil and presence of A-zone aquifer, connected to a treatment system(Figure dry cleaning contamination in the A-zone aquifer along the 2).The line of extraction wells will act as a barrier, which proposed alignment of the Phase I IRA extraction system, is designed to prevent contamination from moving east of installing two monitoring wells and one piezometer,per- Lincoln Center. Groundwater removed from the A-zone forming aquifer tests, and developing a groundwater model aquifer will be pumped to the treatment system,to be to simulate groundwater extraction scenarios. located on the south side of Lincoln Center, via an under- ground conveyance pipeline where it will be treated to Data collected during the ongoing RI activities and Phase I remove dry cleaning contamination.Following treatment, IRA scoping activities were evaluated in the Phase I IRA the water will be discharged under an RWQCB permit to a