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�_. VI'm <br /> IN RUM, <br /> WE <br /> III U <br /> 76 <br /> �, '^,^T" r -.+6^ {mak. x,;:, ,�,;, �:a"w -„' _�� '•- °iN-., k"t �k^ s; �, .F.7r, <br /> a <br /> i <br /> Mr. Kyle Christie <br /> July 18, 1989 <br /> Page 5 <br /> Al <br /> Groundwater Flow <br /> Groundwater levels at the site are being measured in each well on a weekly basis. The levels <br /> are measured with an electronic water level indicator to determine groundwater elevations <br /> relative to top of casing elevations. Since late April 1988, the groundwater flow direction has <br /> been influenced by the recovery system. Sometime in April 1989, the recovery pump stopped <br /> operating. The malfunction was not detected until June 1989. Figure 2 is a groundwater <br /> contour map for May 30, 1989. The figure shows that groundwater has almost returned to - - <br /> true static conditions. During true static conditions, groundwater flows to the northwest. <br /> Conclusions <br /> Groundwater samples collected d+wring the spring quarter 1989, show that benzene concentra- <br /> tions are increasing in wells E-2, E-5, E-10, and E-11. This increase could be the result of <br /> two factors: (1)residual contamination that was pulled by the recovery system toward the site <br /> from another source. Though the, recovery system has not been operating since April 1989, <br /> and groundwater has returned to static conditions; the groundwa!er gradient is relatively flat <br /> and contamination pulled from another source during recovery system operation could still <br /> remain. Also, a Chevron station, located north of the site, across Benjamin Holt Drive, has <br /> a confirmed soil contamination and suspected groundwater contamination problerl and could <br /> potentially have affected the site during recovery operators; a,id (2) continued solubilization <br /> of product from the soil. The aforementioned C76vron station was under construction recently, <br /> and the entire station was demolished and the asphalt covering the lot was removed. Although <br /> the asphalt has subsequently been replaced,' the period of time wizen the soil was exposed <br /> allowed for increased rain water access to contaminated soi!, and therefore, possibly caused <br /> the solubilization of product from the soil into the groundwater. <br /> Recommendations <br /> Continued quz�terly monitoring of the site is recommended. Repair or replace the recovery <br /> system pump. <br /> Very truly yours, - <br /> BROWN AND CALDWEU <br /> Phillips <br /> Pra�jec anager <br /> LEP:PYD;mrp <br /> Enclosure <br /> cc/enc: Ms. Laurie Cotulla, San Joaquin County Health Department <br /> Mr. John Randall. Chevron <br /> Mr. Chris Winsor, ARCO, Products Company <br /> BROWN AND CALDWELL _ <br /> 733s5TREET SACRA MENTO,GAUFORNIA95E14-?M.(..),14-M3 <br />