Tuolumne Service Station Soil Gas Survey

The purpose of the soil gas survey at the Tuolumne Meadows Service Station (TMSS) is to characterize the presence or lack of Volatile Organic Compounds (VOC) within the shallow soil zone to support underground clean-up activities related to the 1998 removal and replacement of underground fuel tanks. The Regional Water Quality Control Board is interested in this characterization because remediation at the site is nearing conclusion and the agency requires this type of data at sites such as this before they will grant official closure. The data can be used to determine if there is any potential health risk to humans or the environment in multiple scenarios, including the scenario of future buildings constructed at the site. Soil gas collection is contained in a vacuum Summa canisters following appropriate Department of Toxic Services sample collection protocol. The canisters are sent to a lab and tested for VOC levels occurring in the soil. The samples are compared to previous background samples to quantify the clean-up effort. The data may be helpful for future TM planning efforts.

DNC has hired a consultant and proposes to collect six soil gas samples at a depth of 5 feet below ground surface at each location. The locations are noted on the map provided (SG1-6). Soil gas borings will be advanced using a truck-mounted direct-push drilling rig to a depth of 5 feet, with a diameter of 2 inches. Two of the six soil gas samples (SG1 & SG2) will be collected near monitoring wells 2A, 2B, 2C which are located approximately 20 feet off the roadway on the meadow side of the Hwy 120 North. Direct push technology is not invasive and creates minor disruption to the sample location (2" hole, 5' deep). The remaining samples (SG 3 – 6) will be collected in previously disturbed areas with in the TMSS land assignment.