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SOP No. 5.0 Monitoring Well Installation <br />• All requirements for casing, except for strength requirements, apply to well screens. <br />• Well screens will be 15 feet to 20 feet in length or the length specified by the Field Geologist <br />in specific cases. <br />• Screens shall be machine-slotted (No hack saw slotting), or installed with an approved <br />manufactured screen. <br />• Screen slot openings shall be 0.010 inches or 0.020 inches depending on subsurface material <br />sizes and groundwater flow rates. Screen slot sizes will be selected using methods <br />recommended by the manufacturer. <br />• The bottom of the screen will be capped with a threaded cap. <br />• The top of the well screen will be placed at least 5 feet above the static water level, if <br />possible (except for the deep bedrock wells). <br />5.2.1.2 Well Filter Pack <br />The purpose of the well filter pack is to provide lateral support for the well screen, increase yield <br />by improving the hydraulic conductivity in the immediate vicinity of the well, and retain the <br />formation to prevent natural materials from entering the well. The filter pack material will be <br />clean, inert, and well rounded, and will contain less than 2 percent flat particles. The filter pack <br />material will be certified free of contaminants by the vendor or contractor. The filter pack will <br />consist of 12/20 or 20/40 mix or equivalent of clean silica sand and will be placed from the <br />bottom of the hole to at least 2 feet, but not more than 4 feet, above the top of the well screen (5 <br />to 7 feet in the bedrock water table wells). The size of the filter pack material used will be <br />selected as appropriate for the well screen slot size installed so that no more than 10% of the <br />filter pack material is smaller than the slot size (ASTM 1996, EPA 1990). For auger boreholes, <br />the filter pack will be placed in the hole by pouring the sand through the augers and slowly <br />raising the augers out of the hole. For bedrock monitoring wells installed in open boreholes (by <br />air rotary drilling), the screen and riser casing will be suspended at least one foot above the <br />bottom of the borehole as the filter pack is poured directly into the borehole. The volume of the <br />filter pack placed in the well will be recorded. <br />After the filter pack is placed, the well will be surged with a surge block or bailer for 30 minutes <br />to ensure that the filter pack is settled so that the grout in the annular seal does not come into <br />contact with the well screen. The top of the sand pack will be sounded using a weighted tape <br />during placement to verify its depth. Additional filter pack material will be placed as required to <br />return the level of the pack to at least 2 feet above the screen and the well will be surged for an <br />additional 5 minutes. Again, additional filter pack material will be placed, as required, to bring <br />the level to at least 2 feet above the screen, or as specified by the Field Geologist. <br />5.2.1.3 Well Seal <br />The materials used to seal the annulus between the borehole wall and casing must: prevent <br />potential contaminant migration from ground surface or intermediate zones; isolate a discrete <br />monitoring zone; preserve confining conditions; prevent intrusion of the overlying grout into the <br />filter pack; and prevent cross-contamination between strata. The bentonite seal will consist of at <br />7/28/08 Page 5 of 7 R Squared Inc. <br />Attachment A