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•r J <br /> 4 HEALTH <br /> ❑0� GROUNDWATER '.ERVIC <br /> E]LID <br /> 11 k L 1 1. Y4 <br /> TECHNOLOGY, INC. 4057 Port Chicago Highway Concord,CA 94520(415)6712387 <br /> FAX (415)685 9148 <br /> October 18, 1993 <br /> Project No 020702819 <br /> Mr Harlin Knoll <br /> San Joaquin County Public Health Services <br /> 445 N San Joaquin Street <br /> Stockton, CA 95201 <br /> Subject Request for a Reduction in Monitoring Well Sampling <br /> for the Former Manna Pro Corporation Facility Located at <br /> 4004 S EI Dorado Street, Stockton, California <br /> Dear Mr Knoll <br /> This letter is a request to reduce the sampling frequency of the monitoring wells at the above referenced <br /> facility on behalf of Manna Pro Corporation <br /> Historical groundwater levels and petroleum hydrocarbon concentrations were graphed to determine the <br /> relationship, if any, between groundwater levels and concentrations Copies of the graphs for wells <br /> MW-1 through MW-10 are presented in Attachment 1 The graphs for wells MWA through MW-4 and <br /> MW-7 though MW-10 show little change in concentrations with large changes in water levels <br /> Concentrations of benzene, toluene, ethylbenzene, and xylenes (BTEX) and total petroleum <br /> hydrocarbons (TPH)-as-gasoline decreased from November 1992 to April 1993 in wells MW-4, MW-5 and <br /> MW-6, which coincides with rising water levels during the rainy season These decreases may be due to <br /> dilution of groundwater concentrations No significant increases in the concentrations has occurred in <br /> the two years of quarterly monitoring and sampling during the rainy or dry seasons <br /> Groundwater Technology requests permission from San Joaquin County Public Health Services to j <br /> reduce the frequency of monitoring and sampling from wells MW-1 through MW-10, from quarterly to <br /> twice a year as long as concentrations remain the same or decrease We recommend that sampling <br /> occur in April and October of each year to evaluate petroleum hydrocarbon concentrations during the <br /> periods of highest and lowest groundwater elevations, respectively We consider this request to be <br /> reasonable and cost effective, and will help Manna Pro focus their efforts and funds on remedial action <br /> Offices throughout the US Canada and Overseas <br />