SR2500864 - Laserfiche WebLink

Home Browse Search

Geosyntec° consultants be placed from approximately 9 to 14 feet bgs, which will correlate to the bottom half of the well screen for the shallow monitoring wells (screened 4 to 14 feet bgs). Once the target grab groundwater sample interval is achieved, and sample tooling installed, the groundwater will be allowed to equilibrate within the casing. It will be assumed that equilibration has been achieved when the depth to groundwater difference between two successive readings is less than or equal to 0.1 feet. A grab groundwater sample will then be collected from the temporary casing using an inertial pump or peristaltic pump with dedicated polyethylene tubing, a check-valve attached to dedicated polyethylene tubing, or a dedicated bailer. The grab groundwater sample will be collected directly into laboratory-supplied containers. Although not anticipated based on the results of the 2022 Limited Investigation(Geosyntec 2024), if LNAPL is encountered, Geosyntec field personnel will attempt to measure the relative thickness of the LNAPL. A sample of the LNAPL will also be collected using by lowering a clean, disposal bailer into the casing to retrieve a LNAPL sample and placed into an appropriate laboratory supplied container. 4.2.3 Groundwater Monitoring Well Sampling Groundwater samples will be collected from the existing monitoring well network(i.e. wells 917-01 through 917-14) as shown in Figure 8. Well screen intervals are provided in Table 1. Groundwater monitoring wells will be sampled by low-flow methods with a bladder pump and dedicated tubing. The intake of the bladder pump will be placed at the mid-point of saturated portion of the well screen interval. Groundwater sampling will be performed in general accordance with the SOP for low-flow sampling provided in Appendix A. Based on the 2023 groundwater monitoring activities described in the 2023 Annual Groundwater Monitoring Report(Geosyntec 2023), 13 of the 14 groundwater monitoring wells are accessible and available for sampling. Monitoring well 917-14 was not able to be located during the 2023 monitoring event. If the well is not able to be located during the subject investigation, or if field conditions have changed and one or more of the monitoring wells is not able to be located, a grab groundwater sample boring will be advanced adjacent to the well location(approximately five feet away), and a grab groundwater sample will be collected from the depth that corresponds to the mid-point of the well screen. 4.2.4 Soil Vapor Probe Installation Soil vapor probes will be installed by a C-57 licensed driller and in general accordance DTSC guidance, including the Advisory-Active Soil Gas Investigations (DTSC 2015) (Advisory) and the Supplemental Guidance: Screening and Evaluating Vapor Intrusion(DTSC 2023) (Supplemental Guidance). A total of I I soil vapor probes will be installed at locations shown on Figure 8 and as outlined in Table 1. As groundwater is anticipated to be encountered as shallow as approximately 7 feet bgs, only one soil vapor probe depth is proposed to be installed at each location. Soil vapor probes will be constructed in borings using '/2 - inch diameter, 1-inch long stainless steel screen attached to a 1/4-inch Nylaflow tubing. Soil vapor probes will be installed at Investigation Work Plan—UST 817B 8 December 2024