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Re-Revised Groundwater Monitoring Well Construction Workplan August 2023 intervals may range from 10 to 20 feet long, depending upon the thickness of the aquifer,but will at no time will cross multiple aquifers. -A copy of the final design will be provided to SJEHD prior to construction for approval as long as the review and approval. A 24-hour notice will be provided when the geophysical log may be run and a final well design. The borehole cannot sit idle for long periods of time and construction must continue to prevent borehole collapse. The geophysical log will be used to select the screen and filter pack intervals. The well screen intervals will be selected such that they are only screened opposite a single aquifer and will range from 10 to 20 feet in length. The geophysical log may show thin clay layers (2 to 10 foot thick) that are unlikely to be laterally continuous and therefore not considered to be indicative of separating two different aquifers. Clay Igyers ,greater than 30 feet will be considered to isolate individual aquifers. Bentonite clay seals will be placed across these intervals. Bentonite clay will be used for annular seals. Bentonite clay is available in the form of granular (installed as a shirty), chips (angular and uncoated) and pellets (typically rounded and coated with a polymer to delahydration). Bentonite pellets will be used for seals greater than 750 feet bgs. Bentonite chips will be used for seals shallower than 750 feet bgs. The wells will be constructed with 2.5-inch-diameter, Schedule 80 polyvinyl chloride (PVC) casings and PVC well screens. The well casing and screens for each monitoring well will be installed into the borehole separately (deepest monitoring well first) and surrounded with, suitable sand filter packs,with bentonite chip or pellet annular seals placed between the filter packs, opposite a4 the bottom and top off confining beds_- Each monitoring well casing will be equipped with centralizers (three per interval equally paced around the well casing). Three sets of centralizers will be placed below the screen, immediately above the screen and at 100-foot intervals with at least one centralized placed mid-way within confining beds. The centralizers will have a minimum spacing between the well casing and the expanded centralizers of 2-inches. The bentonite chips will be placed using a tremie pipe after the drilling muds have been thinned down (having a viscosity of 32 seconds or less). A maximum 5 foot thickness will be place' o top of the sand filter stiffounding the top well screen interval to prevent concrete from intmdi into the filter„aek. The bentonite chips used shall be NSF approved. The bentonite chips seals will be allowed to hydrate for I hour after placement, prior to proceeding with construction. After placement of the deepest monitoring well and filling of the annular space with either bentonite chip or filter pack, the next shallowest monitoring well casing and screen will be placed using the procedures described above until all monitoring well casing and screens are installed and surrounded with annular materials. Construction of all wells may take 2 to 3 das to complete, working 24 hours per day. Volumes of the annular space will be calculated for each bentonite and sand interval using the caliper survey of the reamed borehole. It should be expected with this deep of monitoring well construction and duration, that the calculated volume may be different than the actual volume placed due to swelling of native clays into the borehole and raveling of sediments that mqy occur over a several day period as the construction is being,per formed. GEI Consultants, Inc. 19