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City of Stockton A68104 01A October 25, 1995 Page A-3 registered geologist or certified professional engineer Soil borings for monitoring wells are drilled and sampled according to Twining's "Standard Operating Procedures for Drilling and Soil Sampling" Equipment used for drilling, ' sampling, and constructing wells, and well construction materials are thoroughly cleaned according to Twining's "Standard Operating Procedures for Equipment Decontamination" Groundwater monitoring wells are constructed of minimum Schedule 40 polyvinyl chloride (PVC), stainless steel, or other material casing. Screen may be machine-slotted or wire- wrapped Casing and well screen specifications will depend upon project objectives, site conditions, and project budgets The well screen and casing sections are joined by factory- made flush-threaded connections rThe well filter pack material consists of appropriately-sized pre-washed sand The filter material is placed in the annulus between the boring wall, from the bottom of the boring to approximately 2 feet above the top of the screen Subsequent to filter pack emplacement, preliminary development may be performed to provide a uniform filter pack about the casing Above the filter pack, a 3- to 4-foot thick bentonite seal is installed The bentonite may consist of 1/4- or 1/2-inch pellets, or may be in the form of a slurry If pellets are used, they are hydrated prior to grouting the well, by adding at least one gallon of water for every bucket of pellets The thickness of the bentonite seal depends upon local regulatory requirements The remainder of the well annulus is sealed with a 6-sack sand-cement, or cement grout slurry in one continuous operation from the bottom of the interval to be filled to the top For wells with a seal more than 15 feet deep, the grout is emplaced through the hollow augers, which will extend to within 15 feet of the bentonite seal if required by the local regulatory agency, the grout is emplaced by pumping through a tremie pipe which extends to within 15 feet of the seal The tremie pipe or augers are withdrawn from the boring in 10-foot increments as the boring fills with grout A watertight well cap is placed on top of each groundwater monitoring well, and a 3-foot steel standpipe with locking cover or a traffic-rated box is installed around the wellhead Monitoring wells are locked to restrict access to unauthorized personnel Monitoring well construction details are recorded on the field well construction form Construction information is transferred to Monitoring Well construction schematics for presentation in final reports A-3 Standard Operating Procedures for Groundwater Monitoring_Well Development When possible, initial well development is performed during installation of the sand pack A minimum of 48 hours following installation, groundwater monitoring wells are developed in order to remove sediment that may accumulate in the well during installation, and to settle the filter pack Groundwater monitoring well development is performed using a combination of either bailing, pumping, and surging