ARCHIVED REPORTS_XR0007097 - Laserfiche WebLink

Home Browse Search

WEGE used historical groundwater elevations recorded at selected wells in the site vicinity by the California DWR, the San Joaquin County Flood Control District, and California Water Services to determine the historical groundwater elevation minimum at the site for the years 1965 -1999 The historical groundwater elevations for each well during this period are included as Appendix F of this report A review of this data shows the interval September 15 through October 15, 1977 to coincide with the lowest groundwater elevations for the majority of the wells The elevations at each well (in feet above mean sea level) for the period September 15 through October 15 1977 were plotted on a base map provided by the San Joaquin County Flood Control Distnct and used to establish five foot groundwater elevation contour intervals (See Figure 7) Figure 7 shows the site to be located between the -60 and —65 foot groundwater elevation contour intervals, indicating that the top of groundwater reached a maximum depth (minimum elevation) of 72 to 77 feet below ground surface (bgs) The groundwater flow direction for this period was to the northeast at a gradient of approximately 0 006 feet/linear foot RECOMMENDATIONS 1) Continue quarterly groundwater monitoring 2) Construct a workplan to further assess the lateral and vertical extent of soil and groundwater contamination originating from the former UST at the site The assessment should address the potential impact on soil and groundwater from possible releases during periods of reduced groundwater elevation WEGE has determined that the top of groundwater in site vicinity receded to its lowest recorded elevation (since 1965) in October 1977 of 60-65 feet below mean sea level (72-77 feet bgs) LIMITATIONS The discussion presented in this report is based on the following 1 The observations and data collected by field personnel 2 The results of laboratory analyses performed by a state certified analytical laboratory 3 Our understanding of the regulations of San Joaquin County and the State of California Changes in groundwater conditions can occur due to variations in rainfall, temperature, local and regional water use, and local construction practices in addition, variations in the soil and groundwater conditions could exist beyond the points explored in this investigation State Certified Laboratory analytical results are included in this report This laboratory follows EPA and State of California approved procedures, however, WEGE is not responsible for errors in these laboratory results 4 Arc Pump QM 10-12 1998