ARCHIVED REPORTS XR0009998 - Laserfiche WebLink

Home Browse Search

CJeoCogicalTerfnirs Inc. Page 7 Soil Groundwater Investigation Report C&B Equipment Project No.: 336..2 December 22,1997 3.1.2 Groundwater Analytical Results The soil pore water sample taken with the SimulProbe sampling tool from MW-101 28-28.5 feet bgs tested positive for moderate levels of BTEX and TPH-G. After development of new monitoring wells, a groundwater monitoring was conducted on October 23, 1997 and samples were submitted for analysis for BTEX, TPH-G and the five oxygenates. The results of the groundwater analysis are included as Table 2 in Appendix A. _4 The analytical data reports are included in Appendix C. In summary, MW-1 tested negative for BTEX, TPH-G and the oxygenates. This is the second event where MW-1 was either completely non-detect or close to it. MW-2 was also non-detect for all analytes. MW-3 tested positive for Ethyl Benzene and Xylene, just above detection limits for the second time. MW-4 through MW-7 and the domestic well were non- detect for all analytes. MW-101 showed moderate levels of BTEX and TPH-G, these levels were very similar to those from the pore water sample collected at roughly the same interval. The highest levels of TPH-G detected during this monitoring was in MW-101. None of the wells tested positive for the oxygenates. 3.2 Site Hydrology On December 16, 1997 the top of casings were surveyed into a known elevation. A site specific groundwater gradient and bearing was calculated from the depth to water measurements taken during the groundwater monitoring. The gradient was 0.00356 ft/ft flowing N12°W. The average elevation of groundwater under the site was 39.32 feet above ==<= mean sea level. Monitoring wells 1, 2 and 3 were used to determine gradient. Table 3 in Appendix A is a summary of water level elevations, gradient slopes and bearings. Figure 2 is a groundwater gradient map for the site. 3.3 Geology and Field Observations =_ The following section discusses the subjective field observations and geology documented during this investigation based on the interpretations of the field geologist. A cross section, Figure 3, was generated-from the boring logs of MW-5, MW-1, MW-101 and MW-3. As !.a shown in the cross section the geology is not very consistent across the site. Primarily the geology consists of alternating layers of silts and clays with varying amounts of sand. As stated earlier while drilling MW-101 it was decided by the county regulator and the field geologist that the clays and silts encountered from 30 to 40 feet bgs provided a possible stratagraphic barrier to the vertical migration of contamination so the borehole was terminated at 40 feet bgs. J' Domestic Well Attempts were made to locate the well driller's log for the on site domestic well through the I DWR and San Joaquin County PHS/EHD to no avail. While on site for this drilling event the _3 total depth of the domestic well was measured and determined to be 93 feet bgs. It was not determined if the well had a screened interval or if it was opened bottom. f I 1