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0 4� <br /> Mr Terry Tarditt <br /> April 10, 2000 <br /> Page 2 <br /> quarter (February,May,August, and November) Samples are required to be analyzed for the <br /> following constituents total petroleum hydrocarbons as gasoline (IPH-G), by EPA method 8015 <br /> Modified,benzene, toluene, ethylbenzene, and xylene (BTEC,and oxygenates by EPA method <br /> 8260B <br /> Groundwater Disposal: <br /> Purge water from this sampling event was placed into drums and disposed of properly <br /> Quarterly Results Summary <br /> Analytical laboratory Ki.ff Analytical, Inc,Davis, California <br /> (Cahfornia Department of Health Services <br /> Certification No 2336) <br /> Sample exceptions None <br /> Shallow groundwater gradient 0 002 <br /> Shallow groundwater flow direction South to Southeast <br /> Average depth-to-water 64 38 feet <br /> Average change in shallow groundwater elevation 3 feet decrease since 4/27/99 <br /> Field data sheets from the January 2000 quarterly groundwater sampling event are included as <br /> Attachment A Historical groundwater elevation data is summarized in Table 1 Table 2 <br /> summarizes groundwater flow direction and gradient Table 3 summarizes the historical analytical <br /> results for petroleum hydrocarbon constituents Laboratory reports for the groundwater samples <br /> collected for this sampling event is included as Attachment B A comparison of groundwater <br /> analytical results after the installation of wells MW-2 through MW-4 in August 1998 with this <br /> quarter's sampling is summarized in Table 4 <br /> Table 4 Comparison of Groundwater Analytical Results with Previous Sampling Event <br /> TPH-G Benzene MTBE (8260 B) <br /> 2nd qtr,`99 1 st qtr,`00 2nd qtr,`99 1 st qtr,`00 2nd qtr,`99 1 st qtr,100 <br /> Highest concentration,(P9/L) 8,500 2,600 1,200 620 1,300 2,300 <br /> Well vcnth}ugliest concentration MW-3 MW-3 MW-3 MW-3 MW-1 MW-1 <br /> Number of wells with detection 4/4 2/4 4/4 1 3/4 3/4 3/4 <br /> Discussion- <br /> Based on this quarter's data, groundwater flows south to southeast under a hydraulic gradient of <br /> approximately 0 002 Concentrations of TPH-G and benzene decreased in MW-1 through <br /> MW-4 Based on the groundwater chemical and gradient data, the extent of the petroleum <br /> hydrocarbon plume can be estimated to extend further to the south, west and east of MW-3 <br /> Use or 4 sclosm of data contrnxed on thts sheet is sxbject to the restriction speaf:ed at the beg:mmng of this document <br /> 04/10/OOP\16000\16771\Reports\1 sMgtr doc <br />