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Y �J KIKLEI N FELDER March 26, 1990 File: 24 -220002 -BOO r Mr. Tom Horton San Joaquin County Department of Public Works P. O. Box 1810 Stockton, California 95201 Subject: Subchapter 15 Monitoring Program Implementation Foothill Landfill Dear Mr. Horton: The following information addresses the questions and concerns expressed by Mr. Jeffery Tucker, in a letter to you dated October 18, 1989 (Attachment 1). 1. The Kleinfelder report on Subchapter 15 Monitoring Program Implementation, Foothill Landfill, San Joaquin County, California, dated September 14, 1989 does contain a map of ground water elevation contours, see Plate 3 of that report. 2. At the time of the September Subchapter 15 implementation report, Kleinfelder did not have well construction details for LW -1. This resulted in errors in Table 1 of that report concerning LW -1. Since then we have contacted Purviance Drilling, and they have provided us with well construction details. The driller's log for LW -1 is attached (Attachment 2). The correct information is contained on Table 1 of the Monitoring Reports for October 1989 and January 1990, both dated March 7, 1990. We have included a copy of this table (Attachment 3) showing the correct well construction details for all three wells with this letter. For LW -1, the TOP is -1.6 feet, and the BOP is -131.6 feet. Both of these elevations are referenced to mean sea level. The screened interval for this well is 130 feet. 3. Pumping from LW -1 may affect ground water flow in the area around LW -1, but it appears to be a local effect. LW -1 appears to be pumping water from the Mehrten Formation. This aquifer is generally very transmissive, and provides a substantial amount of ground water for the east side of San Joaquin Valley. A DWR study on San Joaquin County groundwater resources (Bulletin No. 146, 1967) indicates that the average regional capability of the Mehrten formation is approximately 1,000 gallons per minute. LW -1 pumps only approximately 1500 gallons every 15 minutes, an average of 100 gallons per rmnute. Table 1 shows depth of water in the three wells for the Foothill Landfill. On July 5 and 10, 1989, water levels were recorded during the day while LW -1 was being heavily used by Foothill Landfill. On July 27, 1989, water levels were recorded early in the morning before Foothill Landfill began usin& LW -1. The water levels in MW -1 and MW -2 were ap roximately equal at the times when LW -1 was drawing water (7/5/89 and 7/10/89, and when it was not (7/27/89). Therefore, pumping in LW -1 does not appear to affect the ground water gradient at MW -1 and MW -2. Previously we assumed that the depth -to -ground water in LW -1 on July 10, 1989 exceeded 300 feet due to pumping. It now appears that an obstruction, which prevented ground water depth to be measured ;in LW -1 during January 1990 (see KLEINFELDER 9795 Business Park Drive, Sacramento, CA 95827 (916) 366-1701