WORK PLANS - Laserfiche WebLink

Home Browse Search

Glogica[Technics Inc. Page 4 C&B Equipment Additional Site Characterization Work Plan Project No. 336.2 s July 15, 1996 (Figure 2), the nearby domestic well, and in consideration of compiled project information (Summary Tables-Appendix A). 3.2 Drilling and Sampling Because of the proximity to the point of release the following modified' well construction technique will be used to minimize the potential for cross contaminating the deeper zones. i The well boring will be drilled using a 12.25 inch outside diameter continuous flight hollow C stem auger owned and operated by a licensed well drilling contractor to a depth of 30 feet or into the top of the silty clay unit that is expected to begin at a depth of about 25 feet. This will be about 10 feet deeper than the initial monitoring wells (MW-1 - 3). An 8 inch diameter auger will be used to advance from the top of the possible aquatard to the total C depth. In this manner we can reduce the possibility for dragging contaminated soil from the vadose zone into the deeper zone. C In this boring soil samples will be collected continuously for geological and possible analytical evaluation. Soil samples for possible laboratory analyses will also be collected using the SimulProbe sampling device from beneath the water table. The design of the SimulProbe reduces the possibility for borehole waters entering into the sample chamber before the soil sample is collected thus "cross contaminating" the sample. In this manner, based on analytical data we will be able to judge the effectiveness of the screened interval of r the vertical definition groundwater monitoring well. GGA i 3.3 Well Construction We propose that the deep well target a screened interval of 2.5 feet placed between 40-50 feet below grade, depending on geology. The on site geologist will confer with the supervising registered professional geologist to finalize well construction based on the geologic record. w i LThe well will be constructed using 2.0 inch diameter schedule 40 PVC,casing with flush threads (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. i !, C 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. i C 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.