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(11 r groundwater surface beneath the site, possibly due to the heterogeneous nature of the soils and/or the varying well depths On December 6, 1996, groundwater samples were collected from wells MW1R, MW2, MW3, MW4, MW5R2, and MW6, after purging at least three casing volumes of water Monitoring wells were purged and sampled In accordance with the field methods included In Attachment 1 Well purge logs are included as Attachment 2 LABORATORY ANALYSIS Groundwater samples were transported under chain of custody protocol to Sequoia Analytical Laboratory In Redwood City, California (ELAP #1210) for analysis of benzene, toluene, ethylbenzene, and xylenes (BTEX) utilizing EPA method 8020, total petroleum hydrocarbons as gasoline (TPHg) and as diesel (TPHd) utilizing EPA method 8015 modified, and halogenated volatile organics (HVOCs) utilizing EPA method 8010 An unidentified hydrocarbon in the TPHd range was detected at concentrations ranging from 96 parts per billion (ppb) to 770 ppb In wells MW-3, MW-4, MW-5R2, and MW-6 BTEX and TPHg were not detected in any of the samples Analytical results of petroleum hydrocarbon constituents are summarized in Table 2 Laboratory data sheets and chain-of-custody documentation are included In Attachment 3 HVOCs 1,2-dichlorobenzene and 1,4-dichlorobenzene were detected in the sample collected from monitoring well MW5R2 at concentrations of 5 1 ppb and 2 7 ppb, respectively Both HVOCs were detected at concentrations below their respective maximum contaminant levels Analytical results of HVOCs are summarized in Table 3 Laboratory data sheets and chain-of-custody documentation are included in Attachment 3 RECOMMENDATIONS During the last two quarters of monitoring, HVOCs, BTEX, and TPHg concentrations have steadily decreased BTEX and TPHg have not been detected since June 1995 HVOC concentrations have not exceeded the State of California Drinking Water Maximum Contaminant Levels (MCLs) since June 1995 Based on this data, Smith Technology believes that site closure activities are warranted After regulatory approval has been received, a closure report requesting site closure will be prepared in accordance with the guidelines outlined by CRWQCB correspondence dated October 7, 1993 (Addendum to Appendix A of the Tri-Regional Recommendations) The closure report will also contain a workplan for the abandonment of the onsite monitoring wells i w 1943311quarllyl4gr--1996 doe 2 • SMITH