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v kT C A S S O C I A T E S I N C . Groundwater was encountered at a depth of approximately 50 feet. Visibility was initially fair but cleared after 60 feet. Suspended particles that appeared to be organic matter were present in the groundwater. The total depth of the facility well borehole was observed to be 133 feet below top of casing. The bottom 25 feet of the borehole was open. Based on observations from the bottom 25 feet of F the boring, the borehole diameter was estimated to be 18 to 24 inches. The well casing was constructed of steel pipe with a diameter of approximately 1 foot and Ft extended to a depth of 108 feet from the top of casing. The well. was vertically perforated beginning at a depth of 67 feet below top of casing and extended to the bottom of the casing. The casing was in fair condition. A one-half inch diameter pipe extending from the top of casing to a depth of 100 feet was present F'" inside the casing. It is unknown what the smaller pipe was used for. A three-foot long disposable bailer was observed at the bottom of the borehole. Don Pedro Pump was not able to retrieve the bailer. A copy of the video log on VHS tape is available upon request. 6.0 CONCLUSIONS • Hexavalent chromium is present in groundwater at very low concentrations in the deeper water-bearing zone. Based on the analytical results from samples collected from well MW9 and the CPT borings, it does not appear to be significantly impacted. Well MW9 is located immediately downgradient from the former source and from well MW3. Well MW3 is screened in the shallow water bearing zone and historically has contained the highest concentrations of hexavalent chromium. • The reported concentration of hexavalent chromium and total chromium from well MW9 were each below the California Primary MCL for total chromium of 0.05 mg/l. Hexavalent chromium does not have an established MCL or Action Level. • The video log of the facility.well indicates that the well borehole is a total depth of 133 feet. t . The well casing has perforations from 67 feet to 108 feet, and the borehole is open from 108 feet to 133 feet. The facility well appears to be screened in more than one water-bearing Fzone and is a potential conduit for migration of groundwater between aquifers. 7.0 RECOMMENDATIONS ` F Based on the results of this investigation, current regulatory guidelines, and the judgement of ATC, the following recommendations are presented for consideration: f w:lwordpro%23831reportsldeep well inst.doc 6 I