WORK PLANS - Laserfiche WebLink

Home Browse Search

Cleanup in Vulnerable Communities'Initiative Final Project Reference:Bobson Cleaners Discovery and Enforcement Discovery Project Number:60688620-5.1 Investigation Work Plan 3. Two screened intervals will be installed within one borehole with screens set at 5 and 15 feet.A bentonite plug will be set in each borehole to pneumatically isolate the screens. Deeper soil vapor probe implants will be installed to a depth of at least 10 feet bgs where possible. However, if shallow groundwater is encountered at a depth less than 16 feet bgs,deeper probe implant depths will be adjusted to approximately 3 feet above groundwater to prevent capillary fringe from interfering with the collection of soil vapor. 4. The sand pack around the screen will extend 6 inches below and 6 inches above the screened interval. 5. The annular space will be filled with hydrated bentonite.The bentonite clay will be hydrated prior to placement in the borehole annular space. 6. An equilibration time (waiting time)of 48 hours will occur between probe completion and probe sampling to allow for the re-establishment of subsurface equilibrium. 7. The probe will be constructed with high-density polyethylene tubing. 8. Each probe will be completed with a well box,and each tubing will be clearly labeled. 9. Post-run sampling methods will not be used for this project. Sub-Slab Soil Gas Probe Installation Permanent sub-slab soil gas probes will be installed in accordance with the method described in Section 3.6 of the DTSC Advisory and with the following: 1. Three permanent sub-slab soil vapor pins will be installed along the middle of the dry-cleaner retail space, away from the edges of the building. 2. All sub-slab utilities will be located and clearly marked on the slab prior to drilling.All cuttings will be removed from the borehole. 3. Depending on the sub-slab probe construction, a sand pack may be installed to minimize disruption of airflow to the sampling tip.The probe will be placed midway in the sand pack. 4. Dry granular bentonite will be used to fill the borehole annular space to above the base of the concrete foundation. 5. Hydrated bentonite will be placed above the dry granular bentonite.The bentonite for this portion of construction will be hydrated at the surface prior to placement to ensure proper sealing. 6. The remainder of the hole will be filled with neat cement mixed with bentonite. Prior to the introduction of this material,the concrete surfaces in the borehole will be cleaned with a damp towel to increase the potential of a good seal and, ideally, all concrete dust will be removed from the borehole. 7. All water used in the construction of the probe will be deionized,the cement will be contaminant-free and quick drying, and all metal probe components will be thoroughly cleaned to remove manufacturer-applied cutting oils. 8. Each probe will be constructed with a gas-tight fitting and flush-mounted well box so that the probe completion is not a tripping hazard. Soil Gas Sample Collection Protocols for collecting soil gas samples from the soil gas probes and sub-slab soil vapor pins will generally follow Section 4.0 of the DTSC Soil Gas Advisory. In addition, the following items will be performed. 1. Three purge volumes will be removed prior to sample collection. 2. Shut-in testing will be conducted. 3. Leak checking will be conducted with liquid tracers, such as isopropyl alcohol. Shrouding is not necessary.Any detection of the tracer compound above a concentration of 5 micrograms per cubic meter(pg/m3)is considered a leak and re-sampling is warranted. 4. A soil gas field sampling sheet,for the recording of all field parameters upon sampling,will be completed for each soil gas sample collected. Prepared for: Department of Toxic Substances Control AECOM 13