WORK PLANS - Laserfiche WebLink

Home Browse Search

0 The following are the details of abandonment for each of the groundwater monitoring/remediation features. Monitoring Wells The groundwater monitoring wells remaining onsite (TP-1, TW-1 through TW-4, TW-5R, and TW-6 through TW-14)will be destroyed via overdrilling to the total depth of each well. Wells TP-1, and TW-1 through TW-4 are constructed of 4-inch diameter, Schedule 40 PVC casing, and wells TW-5R through TW-14 are constructed of 4-inch diameter Schedule 80 PVC casing. All monitoring well surface completions consist of flush-mount, traffic-rated 12-inch well boxes set in concrete, with the exception of TW-13 and TW-14, which are installed in pre-cast 24-inch by 36-inch concrete vaults with steel lids. The monitoring wells are screened to total depths ranging from 11.5 to 28.5 feet bgs. Table 1 presents a summary of well construction details. The wells will be abandoned via overdrilling using a hollow stem auger. All field activities will be conducted consistent with the Site-specific Project Safety, Health and Environmental Plan (PSHEP), which will be amended to include the scope of work for well abandonment. In addition, the breathing zone and borehole will be monitored for the presence VOCs using a photoionization detector(PID) as is required by the PSHEP. The well abandonment process will consist of the following steps: • All remaining well materials (well casing, grout column, seal, and sand pack) will be removed by over-drilling the well with a hollow-stem auger drill rig. The hollow-stem auger diameter will be 10 inches (i.e., 120% greater than the 8-inch diameter of the original borings (Table 1). A guide rod ("stinger") will be attached to a center rod inside of the hollow stem auger during the over-drilling activities, to help the drilling to stay centered on the monitoring well casing. • The resulting borehole will be completely filled (to approximately 2 feet bgs) with neat cement grout. The grout mixture will consist of a cement mixture comprised of approximately 5 gallons of water per 47 pound bag of neat cement. Grout will be emplaced into the borehole from bottom to top using a tremie pipe or the augers to prevent air pockets or void spaces. At all times during the grouting procedure, the bottom of the tremie pipe or augers will be maintained below the top of the slurry to avoid creating any voids during grout emplacement. • Grout will be allowed to set up for approximately 10 minutes to identify whether grout settlement will occur; if any settlement is observed, additional grout will be added to the borehole. The uppermost 1.5 feet of each borehole will then be backfilled with bentonite chips. • The remaining void space at each boring will be filled with concrete to ground surface, which will be finished flush with and dyed to match the surrounding ground surface. 4