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Section No 6 • <br /> Revision No 1 <br /> Date January 13, 1992 <br /> Page 38 of 55 <br /> of centralizers is not required because the HSA will sufficiently center the <br /> casing strings in the hole <br /> For wells constructed using rotary wash methods, the annular space will <br /> be no less than 2-inches or the radius of the casing, whichever is greater <br /> The borehole will be lightly reamed to remove "mud cake" on the borehole <br /> walls prior to casing installation The casing string will be suspended from <br /> the ground surface Centralizers will be placed from the bottom of every 20 <br /> feet on the well screen greater than 20 -feet long Centralizers will be <br /> placed every 40 feet on the blank casing . Casing guides will be kept in a <br /> straight line so as not to interfere with the intersection of tremie lines <br /> for grouting and placing filter material 0 <br /> Overlying water-bearing units will be isolated by installing a conductor <br /> or-surface-casing—The-conductor-casing,willTbe-driven-into-a-competent-clay <br /> layer of thickness no less than 5 feet Conductor casing shall have a wall <br /> thickness of at least 1/4-inch and be made from corrosion-resistant steel <br /> Sections of casing will be joined by welding and will be fitted with welding <br /> collars The casing will be set into a borehole which provides at least four <br /> inches of annulus , it must be free in the borehole Once the casing has been <br /> freely set on top of the low permeability stratum it will be seated by <br /> pushing it into the stratum 12 to 14 inches The conductor casing will be <br /> pressure grouted using the methods described in Section 6 6 5 The methods <br /> and depths of conductor casing installation will be recorded in the well <br /> construction log <br /> - • <br /> 6-38 <br />