WORK PLANS - Laserfiche WebLink

Home Browse Search

Central Valley Regional Water Quality Control Board June 30, 2025 Page 3 mark each drilling location and notify Underground Service Alert at least 72 hours prior to the start of fieldwork. Each location will be screened for utilities by a private utility locator prior to any ground disturbance and will be manually cleared to a minimum depth of 5 feet bgs using a hand auger or other soft digging techniques. DRILLING AND WELL CONTRUCTION METHODS Haley&Aldrich will subcontract a California C-57 licensed drilling contractor to advance the proposed borings using sonic drilling methods. Each location will be continuously cored, and soil will be logged by a field geologist under the supervision of a California Professional Geologist in general accordance with ASTM International Standard D2488 (Standard Practice for Description and Identification of Soil, Visual-Manual Procedure). Soil cores will also be screened for organic vapors using a photoionization detector.The target depths and construction details for the proposed monitoring wells and piezometers are as follows: • North Area Treatment System Piezometers:Two piezometers (PZ-01 and PZ-02) will be constructed of 2-inch, Schedule 40 polyvinyl chloride (PVC), with approximately 5 feet of PVC machine-slotted screen (with 0.010-inch slots).The target screen intervals will intercept the first coarse-grained unit encountered within the screened interval for each injection well. For IW-1 (PZ-01),the approximate interval expected is 65 to 70 feet bgs and for IW-2 (PZ-02),the approximate interval expected is 60 to 65 feet bgs. Note that these screen intervals are estimated based on the lithology observed during the installation of the injection wells;the actual screen intervals will be determined in the field based on the subsurface lithology encountered. Each well will be capped at the bottom with a threaded stainless-steel endcap. • Monitoring Well M-57C1: Groundwater monitoring well M-57C1 will be constructed of 2-inch, Schedule 80 PVC, with up to 10 feet of PVC machine-slotted screen (with 0.010-inch slots). Based on previously drilled and sampled nearby locations, it is likely that the C1 Zone will be encountered between 115 and 140 feet bgs. Monitoring well M-59C1,which is located approximately 100 feet north of the Walnut Avenue System extraction wells, is screened from 125.1 to 130.1 feet bgs.The proposed screen interval for M-57C1 will target between 130 and 140 feet bgs; however, the final constructed depth will be determined based on the lithology observed in the field. Once drilling has reached the desired depth for each proposed well,the wells will be constructed inside the sonic drill casing. For both piezometer and monitoring well locations, the annular space around the well will be backfilled with#2/12 filter sand (or equivalent)to approximately 2 feet above the top of the screen interval. A 2-foot transition seal of bentonite will then be placed above the filter sand. Finally, a sanitary seal of neat cement grout will be placed up to just below the ground surface. For deeper monitoring well locations, neat cement grout will be placed in multiple lifts to reduce the potential for damage to the casing. All annular materials will be placed while incrementally retracting the sonic drill casing from the ground.The wells will then be completed with flush-mounted well boxes set in concrete and finished to match the existing surface conditions.The proposed locations for PZ-01, PZ-02, and M- 57C1 are shown on Figure 2. RICH