ARCHIVED REPORTS_XR0004281 - Laserfiche WebLink

Home Browse Search

sampling results are consistent with the Third Quarter 1993 and previous results However, a trace concentration [0 5 micrograms per liter (µg/]L)] of benzene was detected in the groundwater sample collected from MW-9 TPH-g, toluene, ethylbenzene, and total xylenes were not detected at MW-9 The low benzene concentration found in MW-9 was considered ambiguous, and warranted further investigation Tables 1 and 2 summarize the results of the Third and Fourth Quarter 1993 groundwater sampling events On January 26, 1994, at the direction of the District and SJCPHS, BVWST conducted a slug testing of the upper aquifer in MW-1, MW-8, and MW-9 Rising and falling head slug tests are used to determine hydraulic conductivities based on data derived from Huorslev (1965) Using best professional judgment, rising head ' and falling head slug test results the three wells were used to derive an average hydraulic conductivity of the aquifer on site based on existing data A complete description of the test and its results is presented in Appendix A In addition to the ' slug test work, SJCPHS also requested the development of geologic cross sections for the Stockton site These cross sections and a cross section location map are provided as Appendix B 4.0 First Quarter 1994 Groundwater Monitoring and Sampling ' 4.1 Monitoring ' The First Quarter 1994 groundwater monitoring data were collected on February 24, 1994 Monitoring activities included measuring the groundwater elevation in nine onsite monitoring wells shown on Figure 4-1 Groundwater ' measurements were taken using an electronic oil/water interface probe Free product was not detected in any of the onsite monitoring wells First Quarter 1994 depth to ' groundwater and well depth measurements were recorded for each monitoring well and are listed in Table 3 Data collected were used to determine groundwater flow direction (to the southwest) and average hydraulic gradient (0 002 foot/foot) across the site as shown on Figure 4-2 An average aquifer velocity of 0 00594 ft/day (2 17 ft/yr) was calculated by multiplying the slug test derived hydraulic conductivity by the ' gradient across the site 94128 East Bay Municipal Utility District 404296001stgtrgw 3 Stockton Service Center-Fust Quarter 1994