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Robert A. Evans, RWQCB <br />Page 2 <br />September 30, 1991 <br />APPROVAL OF CORRECTIVE ACTION PLAN (CAP). AUSTIN ROAD LANDFILL. CITY OF STOCKTON <br />Response <br />The pumping test conducted on June 24, 1991, did not affect the monitoring wells <br />which were attempted to be sampled in July. The pumping test data indicated that <br />the aquifer recovered within several hours of pump shutdown. The low water <br />levels in the aquifer are due to seasonal and drought conditions. If these low <br />water levels persist, the City will convert observation wells MW -8, and MW -9 into <br />monitoring wells by installing dedicated pumps. <br />Comment <br />Ground -water level measurements and hydrographs should be submitted either on a <br />monthly or quarterly basis. <br />Response <br />As indicated on page 2-4 of the CAP, ground -water elevations will be monitored <br />monthly. Hydrographs will be prepared on a quarterly basis. The City will <br />submit both the ground -water elevations and hydrographs with the quarterly <br />reports to the RWQCB. <br />Comment <br />The CAP implies that only VOCs are constituents of concern. Review of analytical <br />data indicates the pH, electrical conductivity (EC), and total dissolved solids <br />(TDS) should be included on the list of constituents of concern. The CAP did not <br />address elevated levels of TDS and EC in well MW -3 and trace levels of VOCs in <br />well MW -5. No further action has been proposed by the City. <br />Response <br />Samples collected from downgradient wells MW -1 and MW -4 have contained <br />concentrations of TDS and EC which have exceeded secondary maximum contaminant <br />levels (MCLS). These nonenforceable MCLs are not health -based standards, but <br />rather are based on aesthetic qualities of water. The pH levels in ground water <br />from well MW -1 fell below the secondary MCL range of 6.5 to 8.5 on two occasions. <br />Otherwise, the pH levels in ground water from these wells have not exceeded or <br />fallen below the secondary MCL range. Please note that the pH range of 5.01 to <br />6.92 reported on Table 5 of the CAP was incorrect. The correct range of pH <br />values for ground water at the site is actually 6.2 to 7.8. <br />The concentrations of TDS and EC in ground water from upgradient wells MW -2 and <br />MW -3 have also exceeded secondary MCLS. In addition, TDS and EC concentrations <br />in ground water from downgradient wells MW -1 and MW -4 are similar to the levels <br />observed in ground water from background well MW -3. For these reasons, we feel <br />