SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

` Trom:STANTEC • 9168610421 09/2812 10:51 #386 P.004/004 stantet Corrective Action Plan Stockton Charter Way Commingled Plume No. CP0057 June 19,2012 North and 811, a private utility locating company will be utilized for clearing proposed well boring locations for underground utilities. 4.1.2 Welllnstatlation Prior to well installation, depth to groundwater will be gauged in monitoring wells closest to the location of the proposed wells. Ten sparge wells will be screened below the water table at varying screen intervals as summarized in Figure 3. Five vapor extraction wells will be screened immediately above the water table approximately from 11 to 16 feet bgs. Stantec will contract a California-licensed (C-57) driller to first air knife the borehole locations to approximately 8.1 feet bgs and then to advance the soil borings to different borehole depths. The proposed well locations may change slightly due to aboveground structures or the presence of utilities. Stantec policy prohibits drilling closer than 10 feet from overhead utilities and 5 feet from underground utilities. A hollow-stem drill rig with 10-inch diameter augers will be used to advance each borehole. Drilling will be performed under the direction of a State of California Professional Geologist. Detailed field records of all activities will be recorded by Stantec field personnel and will include Site conditions, names of field personnel, pertinent dates and times, etc. The sparge wells will be constructed as 2-inch diameter wells within 10-inch diameter boreholes. The sparge well screens will be set at varying screen intervals as described in Figure 3. The sparge well screen section will be constructed with 2-inch flush-threaded, Schedule 40 polyvinyl chloride (PVC) casing perforated with 0.020-inch slots. The vapor extraction wells will be constructed as 4-inch diameter well within 10-inch diameter boreholes. The vapor extraction well screen will be set from 11 to 16 feet bgs, which will be constructed with 4-inch flush-threaded, Schedule 40 PVC casing perforated with 0.020-inch slots. All well screen casings will be flush threaded to the necessary length of schedule 40 PVC blank casing to complete the well casing to ground surface. Figure 3 presents the vapor extraction and air sparge well details. The well screen filter pack will be constructed by pouring #3-graded sand from the bottom of each borehole to top of well screen casing or one foot above the top of the well screen casing. A minimum one foot interval of fine-grained bentonite will be placed in the annular space above the sand filter pack. The bentonite will be hydrated and allowed to swell for one hour to verify saturation. The remaining annular space to approximately 0.5 feet bgs will be filled with a neat cement grout containing approximately five percent bentonite powder. A V-notch will be placed on the top of the north facing portion of each well casing for use as a surveying reference point. A 12-inch diameter, traffic-rated, bolt-down well vault box will be placed around the top of the wells and will be secured in place with concrete. 4.1.3 Waste Handling and Disposal Soil cuttings, drilling fluids, purge water, decontamination water and personal protective equipment generated during drilling operations will be containerized in DOT-approved 55-gallon drums and temporarily stored on the subject property pending characterization and disposal. Stockton Charter Way Commingled Plume Corrective Action Plan,doc 10