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iNTERiM REMEDIAL ACTIONS <br /> 13. During October and November 1985,300 cubic yards of TCA-contaminated soil was excavated and <br /> aerated onsite. After aeration, the soil was returned to the excavation once non-detectable levels of <br /> VOCs were reached. Soil remediation is complete and no further work is to be done. <br /> 14. Varian began operating a groundwater extraction trench INFL-I (Trench 1) in March 1986. <br /> Subsequent evaluation of Trench 1 showed that the downgradient extent of groundwater capture was <br /> insufficient and a second trench (Trench 2) was installed in August 1987. Extracted groundwater <br /> is treated using an air stripper and discharged into San Tomas Aquinas Creek. The discharge is <br /> authorized by NPDES Permit No. CA0029033, adopted (and renewed) by the Board on March 18, <br /> 1992, in Order No.92-026. Board staff gave approval to shut down.Trench I after monitoring data <br /> for Trench 1 and the upgradient weII &I showed VOC levels below MCL for several months <br /> Trench I was shut down in September 1992. <br /> IS. Additional investigations around Trench 2 showed that two shallow, hydraulically-connected <br /> permeable zones are present and together comprise the A-level aquifer. Trench 2 intercepts <br /> groundwater in the upper permeable zone but off-site migration is Iikely to occur in the lower zone <br /> Two groundwater extraction wells were installed in June 1993 to intercept groundwater in the Iower <br /> zone. Groundwater extraction from the two wells was never initiated because shortly after <br /> installation, monitoring data from the wells and other nearby wells showed VOC levels below <br /> MCLS. Varian requested to shut down Trench 2 on a pilot basis to evaluate the effect of the <br /> shutdown on groundwater quality and to assess whether groundwater extraction can be halted <br /> indefinitely. Previous groundwater monitoring data showed a decreasing trend in contaminant levels <br /> and the surrounding wells showed VOC levels below MCLS. Board staff gave approval to shut <br /> down Trench 2 in September 1994. <br /> 16 The treatment system began operating in March 1986 Except for a few months in 1991, the <br /> instantaneous total concentration of VOCs at any time measured in the effluent has been less than <br /> the permit limit daily maximum Approximately 7,600 gallons per day (gpd) of polluted <br /> groundwater were being extracted, treated and discharged in 1993. A total of about 41 million <br /> gallons of groundwater have been extracteid and treated since the system tvas activated <br /> RISK ASSESSMENT <br /> 17 Varian included a public health and environmental assessment in its 1993 Remedial <br /> Investigation/Feasibiiicy Study (RI/FS) One potential exposure pathway for chemicals remaining at <br /> this Site is through groundwater, by ingestion or other domestic use The chemicals of concern that <br /> were considered were TCA, DCE, and 1,1-DCA These chemicals are non-carcinogens (Class "C' <br /> or "D") The assessment on risk at the Site calculates a non-carcinogenic health hazard index of less <br /> than one, under a scenario of on-site residential exposure, potable water ingestion and vapor <br /> inhalation, and gsidential exposure, irrigation water, dermal contact, using VOC concentrations <br /> detected at the time the risk assessment was made <br /> 18 A second expoeure pathway, by volatil iz-ition from soil and/or groundwater, could exist if excay.!ticin <br /> Of sh ilklw soil occurred and was not properly identified, monitored, and controlled if necesS,iry <br /> 3 <br />