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will be done to drill out probable large cobbles or <br /> boulders . Nominal 10" to 12" diameter holes are plan- <br /> ned. Casing of nominal 5" to 6" ID will be grouted in <br /> the holes . The casing should be 20 ft . long . This <br /> will remove influence from surface runoff and protect <br /> the well screen from possible severe frost action. <br /> The screens themselves should go to bedrock. The pull- <br /> back method of installation is called for in these <br /> formations . To account for probable clay and silt <br /> lenses along the hole , a No . 10 ( 0 .010" ) screen is <br /> recommended for the entire well screen . This will <br /> allow free waterflow from the alluvial sands and <br /> cobbles , but restrict silting of the well from the <br /> finer lenses . A fairly coarse formation stabilizer , <br /> such as a USGS Class D curve material , would be best <br /> for the alluvium. <br /> Modifications in the above specified drilliing and <br /> casing techniques will be allowed for cost and <br /> expediency . Certain contractors may be able to <br /> mobilize self-advance casing rigs at a rate competitive <br /> with conventional rotary units . <br /> The permit calls for pumping prior to sampling . If a <br /> suitable pump can be obtained , inert to the trace <br /> levels of metals being monitored , that will be used <br /> also as the sampling device . In lieu of that , either <br /> double check value or syringe bailers can be used to <br /> obtain the actual samples . The bailers are commonly <br /> constructed of PVC and/or glass , which assures no me- <br /> tallic contamination of any samples . <br /> 04 <br /> �i <br /> R. Sacrison <br /> Geological Engineer <br /> �.S�'••�R•SAC <br /> . F <br /> # 22043 Z. = <br />