SR0085423 (3) - Laserfiche WebLink

Home Browse Search

Geocon Project No. S2170-07-12 - 3 - June 6, 2022 • Retain Ground Penetrating Radar Services (GPRS), a private utility locator of Sacramento, California, to clear drilling locations for utilities. • Mark each proposed boring location with white paint and provide a minimum of 72-hour notice to the local public utilities via Underground Service Alert prior to commencement of the subsurface excavations as required by law. Task 2 – Field Activities Soil Vapor Well Installation We will install seven nested (or fourteen side-by-side) temporary soil vapor wells to depths of 5 feet and 15 feet (Figure 3) to collect soil vapor samples following guidelines in Advisory-Active Soil Gas Investigation (California Environmental Protection Agency [Cal-EPA] et al., 2015). Soil vapor wells will be located in the southwestern portion of the Site primarily under the proposed building footprints and near the 2019 soil vapor locations SV4 and SV5 (Figure 2). We will adjust proposed locations as needed to avoid any conflicts with identified utilities. To install each nested temporary soil vapor well, we will: • Use a truck-mounted, direct-push rig to advance a 1.5-inch-diameter boring to an approximate depth of 15 feet. • Insert a 1.75-inch-long, polyethylene, screened vapor probe tip connected to 0.25-inch- diameter Nylaflow® tubing into the boring. • Place the vapor probe tip at a depth of approximately 14.5 feet and a 1-foot-thick filter pack (deep filter pack) consisting of #30 silica sand around the vapor probe tip and the tubing. • Place a 0.5-foot-thick layer of dry granular bentonite clay on top of the deep filter pack. • Place hydrated bentonite gel clay from the top of the dry granular bentonite to a depth of approximately 5 feet 9 inches to create a seal to separate the vapor probe tip from atmospheric air and the 5-foot vapor well. • Place a 3-inch-thick layer of dry granular bentonite then place the vapor probe tip of the second vapor well at a depth of approximately 5 feet and a 1-foot-thick filter pack (shallow filter pack) consisting of #30 silica sand around the vapor probe tip and the tubing. • Place a 0.5-foot-thick layer of dry granular bentonite clay on top of the shallow filter pack. • Place hydrated bentonite gel clay from the top of the dry granular bentonite to the surface to create a seal to separate the vapor probe tip from atmospheric air. • Extend the Nylaflow® tubing for both wells approximately 2 feet above the ground surface to connect to sample collection equipment and cap each well with a polypropylene ball valve (well valve) in the closed position. We may adjust the depth of the temporary soil vapor wells and amount of filter pack placed around the vapor well tip as needed based on the permeability of the soil encountered. Field personnel may decide side-by-side well installation of the vapor wells is preferred to nested wells in the same hole. If side-by- side well construction is used, the wells will be placed approximately 5 feet apart and constructed in the same manner described above except the 15 foot wells will be sealed with hydrated bentonite gel clay from the top of the dry granular bentonite to the surface. The typical temporary soil vapor well detail for nested and side-by-side wells in depicted on Figure 3.