2011-08-09_REVISION - M1981185 (56)

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SOP No. 5..0 Monitoring Well Installation 5,2.1.1 Casing and Screen Requirements The casing requirements will be as follows (EPA 1990): • All casing will be new, unused, and as necessary decontaminated according to the specifications of Section 5.1. • All PVC will conform to the ASTM Standard F- 480 -88A or the National Sanitation Foundation Standard 14 (Plastic Pipe System). • The casing will be straight and plumb. Well screen requirements include: All requirements for casing, except for strength requirements, apply to well screens. • Well screens will be 15 feet to 20 feet in length or the length specified by the Field Geologist in specific cases. • Screens shall be machine- slotted (No hack saw slotting), or installed with an approved manufactured screen. • Screen slot openings shall be 0.010 inches or 0.020 inches depending on subsurface material sizes and groundwater flow rates. Screen slot sizes will be selected using methods recommended by the manufacturer. • The bottom of the screen will be capped with a threaded cap. 5.2.1.2 Well Filter Pack The purpose of the well filter pack is to provide lateral support for the well screen, increase yield by improving the hydraulic conductivity in the immediate vicinity of the well, and retain the formation to prevent natural materials from entering the well. The filter pack material Will be clean, inert, and well rounded, and will contain less than 2 percent flat particles. The filter pack material will be certified free of contaminants by the vendor or contractor. The filter pack will consist of 8/12 mix or equivalent of clean silica sand and will be placed from the bottom of the hole to at least 2 feet, above the top of the well screen. The size of the filter pack material used will be selected as appropriate for the well screen slot size installed so that no more than 10% of the filter pack material is smaller than the slot size (ASTM 1996, EPA 1990). For auger boreholes, the filter pack will be placed in the hole by pouring the sand through the augers and slowly raising the augers out of the hole. For bedrock monitoring wells installed in open boreholes (by air rotary drilling), the screen and riser casing will be suspended at least one foot above the bottom of the borehole as the filter pack is poured directly into the borehole. The volume of the filter pack placed in the well will be recorded. After the filter pack is placed, the well will be surged with a surge block, air, or bailer for 30 Minutes to ensure that the filter pack is settled so that the grout in the atmular seal does not come into contact with the well screen. The top of the sand pack will be sounded using a weighted tape during placement to verify its depth. Additional filter pack material will be placed as required to return the level of the pack to at least 2 feet above the screen and the well will be 7/28/08 5 -5 R Incorporated