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jeo(ogicafTechnks 2w. ..,'�, Page 4 y &B Equipment Additional Site Characterization WP Addendum Project No. 336.2 April 7, 1997 All sampling equipment is decontaminated using a steam cleaner before and between uses. .. The effectiveness of the decontamination procedure is ensured by using the following quality control measures: • Disposable gloves will be used while collecting all samples and will be changed with each sampling event. • A blank will be collected prior to sampling by filling the decontaminated sample chamber �. with water (provided by the laboratory) and then filling a VOA vial (provided by the laboratory)using the same procedures for actual sample collection. ,., Bailer blanks for each sample, along with a field blank (prepared from water provided by the laboratory poured into a VOA vial on site), will accompany the samples to the laboratory and serve as checks against cross contamination. A chain of custody document, listing all samples collected, accompanies the samples from field to laboratory, thereby providing a means to track their movement and insure their integrity. V 3.3 Well Construction We propose that the deep well target a screened interval between 40-45 feet below grade. The on site geologist will confer with the supervising registered professional geologist to finalize well construction based on the geologic record. The well will be constructed using 2.0 inch diameter schedule 40 PVC casing with flush threads. A 5 foot screened interval will extend from 40 feet to 45 feet below surface grade (Figure 3 - Deep Well Construction Schematic). A #3 sand filter pack will surround and extend two feet above the 0.020" screened interval. Due to the extended depth below the water table we have discovered it useful to install a short sump at the bottom of the screened interval which allows incidental slough material and suspended sediments to be packed in .� below thus allowing the engineered filter pack to be installed at the screened interval. A decontaminated surge block will be used to achieve a maximum density filter pack. A retarded hydration granular bentonite transition seal will be installed and allowed to hydrate �- for one hour. A surface seal will be achieved by pumping a neat cement grout (augmented with < 4% bentonite) via a tremie tube. The well will be secured with a locking watertight cap encased in flush mounted traffic rated well box. After the well sealing materials have set (>24 hours) the well will be developed (using mechanical surging and pumping methods) until a clear stream of water is obtained. The well will be purged and groundwater samples collected no sooner than 24 hours after well development. All development and purge water will be containerized in 55 gallon DOT approved containers and stored on site until their disposition can be arranged. In the event that a clay layer is encountered that is non-fractured and continuous for 25 feet,it will be assumed that the layer acts as an affective barrier to verticle migration of contaminants and the boring will be terminated. The borehole will be grouted with a neat cement grout, with a 4% bentonite mix, and a tremie pipe from the bottom up in order to displace all groundwater from the hole. A concrete cap will be added to bring the borehole to