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I BCR & Associates, Ltd. R.,pj 12193 Standard Procedure 4 Constructing and Developing Groundwater Monitoring Wells With Hollow Stem Auger Equipment 1 See Also Soil Classification, Advancing Soil Borings and Sample Collection From Hollow Stem Augers, Site Health and Safety and Equipment Decontamination Well Construction The well is constructed inside the soil boring in accordance with California Department of Water Resources Bulletin 74-90 . The boring diameter shall provide a minimum of two inches of annulus around the well pipe. For two-inch diameter wells, six inch I.D. augers are the minimum; for four-inch diameter wells, eight-inch I.D. augers are the minimum. If exisiting wells are not available to determine static water levels, the stabilized water level in the boring should always be determined. This may warrant the delay of additional construction. Flush-thread factory cleaned schedule #40 or #80 PVC well pipe and screen is utilized. A screw-on cap is secured to the bottom well screen piece and the well is constructed inside the boring according to design specification. This typically warrants that the well screen extends at least 10 feet into first groundwater, and five feet above it. If the wells screen will not reach total depth, this condition is noted on the boring /well construction log, or the well is pulled and re-drilled. Cleansed factory sand is utilized for filter pack of the well screen. Typically #3 L.onestar sand is used with 0.020 inch machine slot pipe, and #12 or #16 sand with 0.010 inch slot well screen. The sand is emplaced inside the augers to fill the annulus around the well screen as the augers are slowly withdrawn. Care is required to keep sand in the augers, and to prevent the hole from bridging. The sand will extend a minimum of two feet above the top of the well screen. Prior to any further well construction, the well is developed (see below) to settle the sand pack. Subsequent to well development, the top of the sand is measured and sand is added if required. Compressed, expansive bentonite pellets are added through the augers to form a seal between the filter pack and the grout sanitary seal. The pellets are hydrated with potable water and allowed to expand. Neat cement/bentonite grout is emplacElfrom the bentonite seal to the surface. Before the well head is constructed, the grout is checked for settling and additional grout is added, if necessary. Well Development Subsequent to filter pack placement, but prior to bentonite pellet seal emplacement, the well is developed by the surge and bail method. A