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M e m o r a n d u m CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD • CENTRAL VALLEY REGION 3443 Routier Road Phone: (916) 361-5600 Sacramento, CA 95827-3098 ATSS: 8-495-5600 TO: FROM: Antonia K. J. Vorster Gary A. Reents, P.E. Senior Engineer Project Engineer 412 l� i AUG 198@ DATE: 4 August 1988 SIGNATURE: I �t 1��r';l5 ENVIROMENTAL 11EALfh St 'ICE% SUBJECT: SOUTHWEST HIDE COMPANY REMEDIAL INVESTIGATION, SAN JOAQUIN COUNTY Moldenhauer Engineering Company, on behalf of Southwest Hide Company, submitted an "Interim Report for Ground Water Study" dated June 1988. The Interim Report contains descriptions and results from the latest (second) phase of monitoring well installation on-site. My comments are as follows: 1. It is not clear how the proposed additional monitoring well locations were selected . No discussion, interpretation, or conclusions of the sampling or water level data were included in the report. I plotted the three sets of water level (13 May, 20 May and 9 June) data included in the report for the new and old monitoring wells. Data from all three dates indicate a north- easterly ground water flow direction. The recent sampling data from the monitoring wells, however, indicate contamination is moving (has moved) to the northwest (regional ground water flow is generally to the west-northwest) of the pond area, the apparent contamination source. Thus it appears that probable ground water flow direction varies from northwest to at least northeast, and additional monitoring wells should be placed accordingly. Comparing the proposed monitoring well locations to the above conditions/ assumptions, I recommend that: a. an additional well is located to the east-southeast of location #12 to determine if contamination, plume has moved to the northeazt; b. Well location #13 ( assumed to be background) is moved to the southwest so as to be upgradient of the ponds based on a northwest or northeast ground water flow direction. I realize movement of this well may be limited by access due to the vineyard south of the ponds. However, it appears that there exists open land southeast of proposed location #13 to better locate this well ; c. Proposed deep well location #9A be reassessed. This location is not contaminated, thus placing a deeper well here will not aid in vertical plume definition; and d. Investigate additional potential sources in the area of the hide processing building. This work is necessary to confirm that contami- nation in wells ;"6 and 7 is resulting only from the pond area,