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I I <br /> °- Engineers :j <br /> Planners I <br /> Economists:,! - <br /> Scientists <br /> A ri13 <br /> p 0, 1996 <br /> E E <br /> i <br /> Mr.Richard Fish <br /> Del Monte Foods <br /> 205 N. Wiget Lane <br /> P.O. Box 9004 <br /> Walnut Creek, CA 94598 <br /> Dear Mr. Fish: <br /> Subject: Disco Site, 110 North Filbert Street, Stockton, California <br /> I <br /> Response to Letter from PHS/EHD to Del Monte dated February 20, 1996 <br /> t <br /> This letter summarizes CH2M HILL's response to the letter from San Joaquin County Public Health <br /> Services, Environmental Health Division(PHS/EHD)to Del Monte dated February 20, 096. The <br /> paragraph and page number iheadings that follow correspond with the PHS/EHD letter. <br /> Paragraph 2 - Page 1 <br /> The toluene,total xylenes, and total petroleum hydrocarbons(TPH)concentrations in MW-DIS-2 <br /> show a declining trend over,Iihe period of record. The analytical results from this most recent <br /> sampling event for some constituents show an unexpected deviation from this trend. This <br /> observation is noted in the reportto call attention to the possibility that errors could have been made <br /> and to provide some measure of data validation. <br /> Sample dilution is required in the analytical procedure EPA 602, as the instrument is only valid <br /> within a certain concentration range. Reported concentrations are always corrected for dilution, <br /> therefore accurate concentrations can be reported and results from different events can b'e compared. <br /> Paragraph 3 - Page 1 <br /> Under greater than 60 feet of head, small diameter groundwater pumps are limited to a minimum <br /> flow rate condition. Belowithat flow rate, pumps dead head and flow stops completely. A flow of <br /> less than 100 milliliters per minute is not physically possible under the hydraulic conditions present <br /> at the Disco site with readily available sampling equipment. <br /> k <br /> Even at a flow rate of 1,600 milliliters per minute,the purge rate is much slower than the flow rate of <br /> the rapid well purge technique that has been used on site for all previous sample collection. The <br /> wells were normally purgedl(rapid purge)at 2 to 5 gallons per minute or 7,500 to 18,750 milliliters <br /> per minute. It is logical to expect that at higher purge flow rates,more turbulence is generated and <br /> the water level in the well is'drawn down more significantly. Turbulence and draw down would <br /> PHSLETI.DOC <br /> CH2M HILL 1111 Broadway,P.O.Box 12681,Oakland,CA 94604-2681 510251-2426 Fox 510 893-8205 <br />