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a1 � Sot] Borin Abandonment Soil borings which are not to be converted into monitoring"ells are sealed to the ground surface using neat cement or sand-cement slurry m accordance with federal, state and local regulations Native sots may be used to fill the top two to three feet for cosmetic purposes, as permitted Monitoring Well installation Well Casing. Screen and Filter Pack onstr ictlo All well construction is performed m accordance with Department of Water Resources "California Well Standards" and all requirements of local oversight agencies Soil borings to be converted into single-cased monitoring wells are a minimum of eight inches in diameter for 2-inch diameter wells and a minimum of ten inches in diameter for 4-inch diameter wells Monitoring wells are constructed with schedule 40, threaded, polyvinyl chloride (PVC) casing unless site geochemistry or contamination necessitates an alternative material The wells are constructed with factory-slotted screen and threaded end caps The screened interval is placed such that it extends approximately ten feet into the water bearing zone, and at least five feet above the expected maximum water level The screened interval may extend less than five feet above the maximum water leVwhere y to prevent the water tabletis too shallow to allow thisersection of the screened nconstru titerval t nthe top of the confining layer of a confined aquifer, or A graded sand filter pack is placed in the annular space across the screened interval and extended approximately one to two feet above the screen, as site conditions permit, so as to prevent extension of the sand pack into an overlying water-bearing unit The well screen slot size is the maximum size capable of retaining 90% of the filter pack e the ion is predominantly clay Typically,. lt or poorly-graded fine 020-in 0-0 ch screen is used where the 0- ch screen is used rformat on stpredomin predominantly well-graded or moedii sand 0 020 mum to coarse sand and/or gravel The filter pack grade(mean grant size)is selected according to native sediment type as follows a)for poorly graded fine sand or silt/clay -4 times the 70% retained grain size of the formation b) for medium to coarse sand, gravel or well graded sediments - b times the 70% retained gram size Since results of particle size analysis are not always available,Clearwater often selects screen size and filter pack on the basis of general site stratigraphy, and specifically the finest significantly withick layer of sediment to 0 020 m h slotted screen and Lone St r® 1120 with 0 010-inch screened Commonly grades slottedone screenr® 3, 2112 or 2115(or equivalent) _dell Seal and Cgmpletion A minimum two foot seal of bentonite is placed above the sand pack The bentonite seal is hydrated by either formation water or potable water Neat cement or a cement/bentonite grout mixture seals the remaining annular space to the surface 1f bentonite is used in the grout mixture, it does not exceed 5% by weight The grout is placed using a tremie pipe, if the top of the bentonite is more than 20 feet below grade, or if water is present in the ,ht locking cap and protective traffic-rated vault box is installed on top of boring above the bentonite seal A waterti each well Well construction details are presented on the Field Exploratory Soil Boring Log Following to completion of a well, Clearwater completes and submits, or ensures that the driller has sufficient information to complete and submit, the state-required Well Completion Report or equivalent document Well Development All newly installed wells are developed prior to sampling to remove fine grained sediments from the well and stabilize the filter pack and the disturbed aquifer materials Development takes place prior to or at least 24 hours after setting the seal on the well unless otherwise directed by a local oversight agency Well development consists of surging with a surge block and removing water from the well with either a pump or bailer, until the ell is free of v4 rm no sediment, or until at least 10 well casing volumes have been removed Depth to bottom is me surespeciidC t odete a i e casing volume if the well is sample immediately following development, temperature, p and turbidity (qualitative) are monitored during-well development (see section "Groundwater Sampling") All een n AlconoxO • development ain tere All data collected during development are vrecorded son the with aWell De e opmt quipment is cleaned entDatahrinsed if potable necessary, the Purging Data Sheet 2 re,�isec4 Juni- 29 2001