SR2500864 - Laserfiche WebLink

Home Browse Search

Geospte& consultants The LTCP includes media-specific criteria for groundwater, for vapor intrusion to indoor air, and for direct contact with soil and outdoor air exposure. Groundwater and soil vapor samples collected during the subject investigation will determine if the Site meets the media-specific criteria, as described further below. • The petroleum hydrocarbon plume in groundwater has been monitored since 1999 in groundwater wells 917-01 through 917-14 (Figures 4 and 5). The most recent data collected from the wells suggests that the groundwater plume (specifically benzene and TPH-g) is not laterally delineated to the east, west, or south. To determine if the site meets one of the five groundwater-specific criteria in the LTCP, the lateral extent of the petroleum hydrocarbon groundwater plume will be delineated through the collection of grab groundwater samples and the collection of low-flow groundwater samples from all monitoring wells in the network. Groundwater analysis will include TPH-g, BTEX, and methyl tert-butyl ether(MTBE). As shown in Figure 6, the most recent MTBE concentrations from existing monitoring wells suggest that MTBE concentrations have attenuated and are likely no longer a contaminant of concern. • Soil vapor samples collected in 2019 (SVP-1 and SVP-3) contained elevated concentrations of BTEX that present a potential inhalation risk(Figure 7). Shallow soil vapor probes will be installed as part of the subject investigation to delineate the area of impact and to determine the potential health risk to nearby receptors. Additionally, data collected for the subject investigation will be used to determine if corrective action measures may be appropriate to achieve closure under the LTCP. For example, soil sample data will be used to assess the extent of TPH-g and may be used to evaluate the potential need for further excavation. 3. SUMMARY OF INVESTIGATION ACTIVITIES A total of 16 borings (817B-08 through 817B-23)will be advanced in order to meet the objectives outlined above. Some of the borings advanced will serve multiple purposes, including collection of soil and/or grab-groundwater samples, followed by installation and sampling of soil vapor probes. Additionally, all groundwater monitoring wells within the current monitoring well network will be sampled. Soil samples will be collected from the vadose zone at depths of 2, 4, and 6 feet below ground surface (bgs) from borings 817B-08, 817B-09, 817B-10, 817B-12, 817B-13, 817B-15, 817B-17, 817B-20, 817B-21, 817B-22, and 817B-23. Borings 817B-13, 817B-20, 817B-21, and 817B-23 will be advanced around the former UST excavation area to delineate elevated concentrations of petroleum hydrocarbons detected in soil during the 2022 investigation. Borings 817B-08, 817B- 09, 817B-10, 817B-12, 817B-15, 817B-17 and 817B-22 will be advanced around the perimeters of the presumed 2010 excavation area to evaluate residual soil contamination. All soil sample data will be used to develop the CSM. Soil vapor probes will be installed at a depth of approximately 5 feet bgs in borings 817B-08 through 817B-18 to delineate the soil vapor plume and to evaluate the potential inhalation risk to human receptors. Soil vapor sample data will be used to evaluate LTCP media-specific criteria Investigation Work Plan—UST 817B 5 December 2024