ARCHIVED REPORTS XR0012690 - Laserfiche WebLink

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�-. WESTERN GER-ENGINEERS { The annular space between the outside of the slot-Led well casing and the borehole will be filled with a clean sand pack (medium aq;arium sand) to variable dept.hs, but not less than 4 feet above the slotted pipe section. 1 1 foot neat cement seal followed by a 1 foot bentonite seal will be placed above the sand pack to form an impermeable . stationary plug. A grout mixture of Portland cement and bentonite (5:1 mixture) will be placed above the bentonite plug up to a depth of approximately 4 feet below the ground surface. Concrete will be poured, t:o slightly above the paving surface, incorporating the protective well box. The groundwater monitoring wells will be sealed with ;sight fitting caps which can be locked to prevent tampering. A typical groundwater monitoring well design proposed for this site is illustrated on Figure 5. A 2 inch casing (ID) will be used for all wells to enable necessary equipment installation and use. z The minimum thickness of the sand/gravel pack placed between the 3 slotted casing interval and aquifer formation material (the annulus) F will be at least 2.5 inches. The minimum thickness of the formation/sanitary seal will be at least 2.5 inches also. The minimum thickness of the reinforced concrete slab used for surface protection will be 4 inches and will slope away from the casing and the protective box. Elevations and top-of-casing measurements will be accurately surveyed ' and recorded to within 4.01 vertical foot and surveyed location will be accurate to within 0.5 horizontal foot with respect to established reference point(s). Well Development Because a monitoring well must be properly constructed and developed to avoid subsequent sampling problems, the design criteria for the intake Part of the well ahould allow for easy inflow of water from the i geological formation. T's:e casing slot width should be small enough to 's i keep the gravel pack sand and the natural formation materials out,' The well will be cleaned of drilling debris and properly developed as indicated by a consistently clean water sample during the development Process. To remove any silts which may be caked on the sides of the borehole and reduce the amount of naturally occurring fine material in the vicinity Of the well screen, a high--velocity water jet or other similar device will be used to wash this material from the formation walls into the wells. Air lift pumping, surging and/or bailing of the wells will later remove this material. Well development will continue until completely depleating well of water and/or when water H,_tem ------ ---- ---- -p p i---------- T_resistivity have itabilized and the groundwater is. consistently clean with no visible turbidity. The well will then be allowe d to equilibrate for a minimum of 48 hours before sampling.