Laserfiche WebLink
S MEMORANDUM • <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION <br /> 3443 Routier Road, Suite A Phone: (916) 361-5600 <br /> Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 <br /> TO: Antonia K. J. Vorster� FROM: Camilla Williams <br /> Senior WRC Engineer Engineering Geologist <br /> DATE: 16 October 1991 SIGNATURE: tGl(,(> ^��C,[�y�� <br /> SUBJECT: SECOND QUARTER 1991 MONITORING REPORT, DEFENSE DISTRIBUTION REGION WEST <br /> (DDRW), SNARPE SITE, SAN JOAQUIN COUNTY <br /> I have review the Second Quarter 1991 Monitoring Report for the DDRW, Sharpe Site <br /> (Sharpe) submitted on 25 September 1991. The Second Quarter 1991 Monitoring Report <br /> includes the trichloroethylene (TCE) concentration contour maps for the A, B and C <br /> Zones. These maps reveal that the extent of the TCE plumes have spread laterally and <br /> vertically much further than previously depicted on plume maps. <br /> Of great concern is the off-site lateral extent of Plumes 1&3, 4&5, 6 and 7&8 in the <br /> A and B Zones and Plumes 3, 4&5 and 7&8 in the C Zone. Due to the location and yield <br /> of the off-site agricultural supply wells, it is apparent that the pumpage of these <br /> wells has accelerated the movement and exacerbated the extent of the volatile organic <br /> constituent (VOC) plumes. <br /> For example, the concentrations of TCE in samples from MW-503 and MW-510 are 7.6 and <br /> 5.1 micrograms per liter (µg/1 ) in the A Zone, are 7.5 and 6.4 Ag/1 in the B Zone and <br /> are 7.6 and 14.3 µg/1 in the C Zone. The TCE concentrations in all of these well <br /> samples are above the Primary Drinking Water Standard (DWS) of 5 ug/l . These are the <br /> furthest monitor wells to the west and are less than 1000 feet east of Harlan Road. <br /> The lateral extent of Plume 4&5, as well as the other plumes, remains undefined. In <br /> addition, the sample from MW-509C, approximately a third of a mile east of Harlan Road <br /> near Squires Road, has a concentration of 80.8 mg/1 of TCE, which is an order of <br /> magnitude greater than the Primary DWS. This indicates that the Plume 4&5 has extended <br /> to a depth of at least 150 feet below ground surface. The location of these monitor <br /> wells are depicted on the attached map. <br /> The continued use of agricultural supply wells, particularly of AGW-6, AGW-7, AGW-9 and <br /> AGW-10, will cause the VOC concentrations of the off-site plumes to increase, and will <br /> also be counter productive to any remedial action to cleanup the aquifer, causing it <br /> to be ineffective. The continued unabated use of these wells will further spread the <br /> ground water contamination and will threaten the water quality of the potable supply <br /> wells along Harlan Road. <br /> CKW:cw <br /> Attachment <br />