ARCHIVED REPORTS_XR0011373 - Laserfiche WebLink

Home Browse Search

at the subject site was terminated at a depth of 35 5 fbg Thus, ground water would occur at a depth of 40 5 fbg according to SJCPHS Cambria is not aware of any site specific depth to ground water information for this site Because of the discrepancies in depth to ground water information for the subject site, Cambria contacted the San Joaquin County Flood Control and Water Conservation District (SJCFCWCD) to find out what information they may have for depth to ground water in the vicinity of the subject site The closest well to the subject site that SJCFCWCD monitors is a well at Gianone County Park, approximately 3/4 of a mile north of the subject site The depth to water in this well as of March 1998 is 49 fbg It remains unclear at this point what the actual depth to ground water is beneath this site Cost-Effective Approach SJCPHS commented that the investigative approach outlined in Cambria's Work Plan is not a cost- effective approach for this case The most cost-effective approach for dealing with a case where soil has been impacted by hydrocarbons but ground water is not know to be impacted, is to investigate the vertical extent of hydrocarbons in the soil Should it be found that hydrocarbons do not extent to the depth where ground water occurs then the case should be considered a soils-only case Not only is this a cost-effective approach, it is also a common investigative technique based on a scientifically defensible methodology To install ground water monitoring wells only to find out that ground water has not been impacted and then to close the case as a soils-only case is not a cost-effective approach Well installation could be avoided by focusing the initial investigation on the vertical extent of petroleum hydrocarbons beneath the source area This is the approach used in Cambria's work plan Work Plan Addendum Cambria agrees with SJCPHS that if ground water occurs five feet below the depth where Boring SB-2 was terminated it is possible ground water has been impacted by petroleum hydrocarbons and at ground water monitoring well installation is warranted However, due to the discrepancy in depth to water information for the vicinity of the site, Cambria proposes the following alteration to our February 28, 1998 Work Plan I One soil boring_will be drilled adjacent to the northern-most dispenser island to define the vertical extent of_petroleumhydrocarbons in the soil and to determine the depth at which ground water occurs beneath the site Should ground water be encountered at 40 fbg, the boring will be converted to a ground water monitoring well and two additional ground water monitoring wells will be installed at the site as proposed in Cambria's February 28, 1998 Work Plan If during the drilling of this boring ground water is encountered at a depth &MsLter than 40 fb and field evidence indicates that petroleum hydrocarbon impacted soil_extends_to the_deoth where around water occurs, the boring will be converted to a ground water monitoring well and two additional 240-0797 2