ARCHIVED REPORTS_XR0013013 - Laserfiche WebLink

Home Browse Search

3-3 hydrocarbons as gasoline (TPHg), diesel (TPHd) and motor oil (TPHmo) following EPA Method 8015 modified. Analytical results of the soil samples collected during this investigation identified petroleum hydrocarbon constituents at varying depths beneath the former UST to a depth of 43 feet bgs. A summary of the soil sample analytical results is presented in Table 3-1. The complete analytical reports and chain-of-custody documentation are included as Appendix B of our July 27, 1993, letter report, which is included in this report as Attachment C. ` Four temporary groundwater monitoring wells were installed in Soil Borings TW-1 through TW-4 between May 11 and 14, 1993. Since these wells were temporary and were for the sole purpose of collecting grab groundwater samples, .permits for construction were not � required by the County. The well casings consisted of 2-inch-diameter polyvinyl chloride, flush- threaded, blank and slotted casing. The annulus surrounding the slotted interval of each well • casing was left open so that the casing could be removed from the ground after collecting a grab ground sample. During the time period the casings were left in the ground, rainfall did not occur, eliminating the possibility of water entering the boring from the ground surface. Groundwater samples were collected on May 14, 1993, and submitted to WEST laboratory for analysis of BTEX, TPHg, TPHd, and TPHmo following the methods described above. Analytical results of the groundwater samples collected as a part of this investigation are summarized in Table 3-2. The complete laboratory report is included as Appendix B of our July 27, 1993, report, included as Attachment C. Laboratory results of the groundwater sample collected from temporary well TW4 identified low concentrations of TPHg in groundwater. Petroleum hydrocarbons constituents were not identified in the remaining three groundwater samples. �1. Following the measurement of static water levels and collection of grab groundwater samples the casings were removed from the ground and the borings were backfilled to ground �— surface with neat cement grout containing approximately 5-percent powdered bentonite, using the tremie method. Static water level measurements were obtained to provide depth to groundwater i in the area, which was found to be approximately 80 feet below ground surface or 37 feet deeper than the deepest occurrence of petroleum hydrocarbons identified in the borings. The July 27, 1993, letter report prepared by BC recommended the further excavation of visibly affected soil. In this letter report BC questioned the origin of the TPHg in groundwater identified in the grab groundwater sample collected from TW4. Specifically, BC suggested that there may be an upgradient source for the TPHg, since gasoline range hydrocarbons (C7 to C12) have reportedly never been stored on-site. BC recommended the installation of three permanent groundwater monitoring wells to identify the groundwater flow direction, hydraulic gradient, and quality of the groundwater beneath the former UST. This recommendation is discussed in more detail in Chapter 6. Use or disclosure of data contained on this sheet is subject to tire restriction specified at the beginning of this document. Izr_:,v\F--v69"FPORIYrEN-OIL.CLO QMs-Psroo Yr