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GeoStrategies Inc. April 20, 1990 <br /> Soil Sam ling - cont <br /> Soil borings not converted to monitoring wells will be backfilled <br /> (sealed) to ground surface using either a neat cement or <br /> cement-bentonite grout mixture Backfilling will be tremied by <br /> continuously pumping grout from the bottom to the top of the boring <br /> where depth exceeds 20' or as required by local permit requirements <br /> All field and office work, including exploratory boring logs, are <br /> prepared under the direction of a registered geologist. <br /> MonitOring Well Installatign <br /> Monitoring well casing and screen will be constructed of Schedule 40, <br /> flush-point threaded polyvinylchloride (PVC) The well screen will be <br /> factory mill-slotted unless additional open area is required (eg <br /> conversion to an extraction well in a low-yield aquifer) The screen <br /> length will be placed adjacent to the aquifer material to a minimum of <br /> 2-feet above encountered water No screen shall be placed in a <br /> borehole that potentially creates hydraulic interconnection of two or <br /> 10 more aquifer units Screen slot size and well sand pack will be <br /> compatible with encountered aquifer materials, as confirmed by sieve <br /> analysis <br /> Monitoring wells will be completed below grade (Figure 2) unless <br /> special conditions exist that require above-grade completion design <br /> In the event a monitoring well is required in an aquifer unit beneath <br /> an existing aquifer, the upper aquifer will be sealed off by <br /> installing a steel conductor casing with an annular neat cement or <br /> cement-bentonite grout seal This seal will be continuously trcmie <br /> pumped from the bottom of the annulus to ground surface <br /> The monitoring well sand pack will be placed adjacent to the entire <br /> screened interval and will extend a recommended minimum distance of <br /> 2-feet above the top of the screen No sand pack will be placed that <br /> interconnects two or more aquifer units A minimum 2-foot bentonite <br /> pellet or bentonite slurry seal will be placed above the sand pack <br /> Sand pack, bcntonite, and cement seal levels will be confirmed by <br /> sounding the annulus with a calibrated weighted tape The remaining <br /> annular space above the bcntonite seal will be grouted with a <br /> bentonite-cement mixture and will be tremie-pumped from the bottom of <br /> the annular space to the ground surface The bentonite content of the <br /> grout will not exceed S percent by weight A field log of boring and <br /> a field well completion form will be prepared by GSI for each well <br /> installed <br />• Decontamination of drilling equipment before drilling and between <br /> wells will consist of steam cleaning, and/or Alconox wash <br /> Page 3 <br />