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• MEMORANDUM • CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION Phone: (916) 255-3000 3443 Routier Road, Suite A CALNET: 8-494-3000 Sacramento, CA 95827-3098 TO: GORDON L. BOGGS FROM: ELIZABETH A. THAYER UGT Program Coordinator Associate Engineer DATE: 9 March 1993 SIGNATURE: SUBJECT: MONITORING PROGRAM, 16 S. CHEROKEE LANE, LODI, SAN JOAQUIN COUNTY The existing Monitoring and Reporting Program No. 90-702 is inadequate. MW4, in the center of the plume, and several other wells have been dry for several quarters in the past several years and have not been adequately sampled. In addition, Geweke has not analyzed ground water samples for all required constituents. Therefore, I proposed in the draft C&A, that Geweke sample all 14 wells for all constituents quarterly. We had a meeting 18 February 1993, with Jeff Werner, of Geweke, and Bob Marty, of GeoAudit, Geweke's consultant, to discuss the draft C&A. During the meeting we required that Geweke submit rationale, by 23 February 1993, for sampling fewer than 14 wells quarterly as proposed. On 23 February 1993, Bob Marty submitted a proposal "that a total of 7 wells be monitored on a quarterly basis: EW1 , MW2, MW6, MW7, MW9, MW10, and MW13% "Monitoring wells 1, 3, 4, 5 will not be monitored because these wells are all located at or near the center of the contamination plume", and "MW11 and MW12 have not shown any detectable contamination in more than one year and may be located beyond the down-gradient extent of the contamination plume. Therefore, we do not recommend that these wells be monitored" . Board staff comments on GeoAudit's proposal : 1. Wells MW6, MW7, and MW10 are common to both the existing monitoring program and Geweke's proposed program. I have no disagreement with monitoring these three wells quarterly. MW6 and MWIO are the most upgradient wells and MW7 helps delineate the eastern edge of the plume. 2. No rationale was given for including EW1 in the monitoring program. However, I concur with its inclusion because it will allow monitoring of the area of high ground water contamination and provide comparison with monitoring wells at the edge of the plume. 3. No rationale was given for including MW2 in the monitoring program. I do not object to its inclusion, however, it appears that the eastern edge of the plume may be adequately monitored by sampling MW7 quarterly. 4. No rationale was given for including MW9 in the monitoring program. I do not object to its inclusion, however, MW9 is not adequate as the downgradient monitoring point. In the past, when the ground water level was higher, MW9 contained up to 300 ppb benzene. It is possible that contamination has been adsorbed to the soil and it may desorb back into the ground water if the water rises. The current downgradient zero line