ARCHIVED REPORTS_XR0013116 - Laserfiche WebLink

Home Browse Search

As referenced in Figures 9 and 11, each soil sample was named using the alphanumeric grid location along with the boring number within that grid, and the sample depth. The suffix of a soil sample number indicates the depth in feet bgs from which the sample was collected. For example, sample number AI-1-3 designates a soil sample collected from alphanumeric grid A1, from the first sample location (1) at a depth of three feet, and sample number Al-1-5 designates a soil sample collected from the same sample location at a depth of five feet. Additionally, background soil samples were collected at the designated locations in Figure 10. Samples were collected using a hand trowel to a depth of approximately 0.5 feet bgs. Samples were packed into clean, laboratory supplied 4-ounce glass jars with Teflon®-lined lids. Samples were labeled, placed in sealable baggies and placed immediately in a cooler filled with ice to preserve the sample prior to transport. The sample identification was placed on the chain-of- custody(COC) form and noted in the field notebook. 3.2.3 Soil Gas Sampling Procedures Soil gas samples were collected from soil gas probes installed during the RI and SSI. Soil gas probe construction and sampling was conducted in accordance with the Cal/EPA Advisory — Active Soil Gas Investigations (DTSC, 2003). Leak test procedures in the Advisory were in the process of being revised in between the RI and SSI sampling events. As such, the RI soil gas sampling procedures followed the 2003 guidance (using isobutane as the leak detection compound) and the SSI soil gas sampling procedures used helium as the leak detection compound. The following subsections describe in detail the procedures implemented at the Site during the RI/SSI. 3.2.3.1 Soil Gas Probe Construction Soil gas probes were positioned at five feet bgs at each sample location. Due to shallow groundwater (8-10 feet bgs), a second probe could not be installed at 15 feet bgs as typically recommended by the Cal/EPA Advisory. Soil gas borings were advanced using hand auger techniques. Soil gas probe construction began by positioning a 9-inch stainless steel or PVC soil gas sampling implant connected to 0.25 inch Teflon® or Teflon® lined tubing at 5 feet bgs. The annulus around the implant and tubing was backfilled with sand pack to approximately nine inches above the top of the implant (approximately 1.5 feet of sand pack). The boring was then backfilled with granular bentonite to approximately 0.5 feet bgs. Finally, a traffic rated soil gas well box was placed over the probe and sample tubing to protect the sampling equipment and to prevent the soil gas boring from becoming a conduit to groundwater. The well box was secured in cement and the granulated bentonite was brought up inside the well box. As required by the San Joaquin County Environmental Health Department, the bentonite was hydrated as it was being placed in the annulus and, at the surface, standing water was allowed to sit atop the granulated bentonite for a minimum of 10 minutes to ensure that the bentonite was properly hydrated. The Teflon tubing from each soil gas probe was trimmed to a distinct length for identification and capped with a threaded 3-way valve that was shut to seal the tubing upon completion. PARSONS 21 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010