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-- <br />COLORADO DIVISION OF RECLAMATION, MINING, AND SAFETY <br />Prospecting Drill Hole Abandonment Suggestions <br />These guidelines recommend procedures for adequate abandonment of prospecting drill holes, in accordance with <br />Rule 5.4 of the Rules and Regulations of the Colorado Mined Land Reclamation Board, and CRS 34-32-113(5.5). <br />These suggestions are not intended to limit the options of the prospector, but may be used as guidelines for drill hole <br />abandonment. <br />(1) Pennanent abandonment of any drill hole which evidences flow of ground water to the <br />surface. <br />(a) The drill hole should be filled with neat cement grout from a point not less than 50 <br />feet below the bottom of the artesian zone to a point not less than 50 feet above the top of the artesian zone or <br />to a minimum depth of two feet below either the original land surface or the collar of the hole, whichever is <br />the lowest elevation. The remaining portions of the hole should be abandoned in accordance with the <br />provisions of Sections 5.4.2(2), 5.4.2(3), 5.4.2(4), or 5.4.2(5), whichever is appropriate. <br />(b) If the operator so elects, any drill hole may be filled with neat cement grout from the <br />bottom of the hole to two feet below either the original land surface or the collar of the hole, whichever is the <br />lowest elevation. Material representative of the undisturbed surface material should be tamped into the <br />remaining portion of the drill hole. <br />(c) Neat cement grout should be a mixture of Portland cement, drilling-grade bentonite <br />and clean water in the proportions of 1 bag of cement (94 lbs) to a minimum of 6 pounds of bentonite (to <br />reduce shrinkage) and between 9 and 17 gallons of water. Sulfate-resistant cement (ASTM type II, II <br />modified to IV) should be used, if appropriate to prevent deterioration of the grout plug. Cement additives, <br />such as calcium chloride or fly ash may be used. <br />(2) Permanent abandonment of any drill hole which encounters an aquifer in volcanic or <br />sedimentary rock. <br />(a) Drill holes should be sealed with a high quality sodium bentonite abandonment mud <br />having a marsh funnel viscosity of at least 55 seconds per quart, or at least 20 seconds per quart greater than <br />that of the drilling mud used in drilling the hole, whichever viscosity is greater. Holes should be filled with <br />abandonment mud to 10 feet below either the original land surface or the collar of the hole, whichever is the <br />lower elevation. <br />(b) The abandonment mud should have the following characteristics: <br />(i) It should be thoroughly mixed and uniform in consistency,