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Geothermal Rules <br />Statement of Basis and Purpose <br />Vinyl coated copper tubing is commonly used in the construction of direct exchange <br />(DX) loop fields in a geoexchange system. The Rule requires that the material must be <br />specifically designed for use in geothermal applications. <br />To ensure that all buried pipe is joined to prevent leakage of the circulating fluid/vapor <br />and loss of operating pressure, Rule 8.3.1.1 requires that HDPE pipe be joined by heat <br />fusion in accordance with the pipe manufacturer's specifications and that copper tubing <br />be brazed using the nitrogen brazing technique, unless otherwise specified by the <br />manufacturer. Rule 8.3.1.2 allows the use of threaded connections or clamps only <br />above ground level or at a service outlet where the connection can be visually inspected <br />for leaks and accessed for repair if necessary. <br />In terms of protecting the public health, ground water resources, and the environment, <br />grout (and its proper mixing and placement) is the most important component of a <br />vertical closed -loop geoexchange system. Rule 8.3.2 provides a list of materials <br />approved for use in grouting boreholes constructed for loop fields in a geoexchange <br />system. The selection of a grout material that is suited for loop fields in geoexchange <br />system design and the subsurface environment into which it is placed is the <br />responsibility of the certified individual. Grouting of the loop field boreholes should be <br />viewed as permanent emplacement of a low permeability material that will endure for <br />the life of the loop fields in a geoexchange system and maintain its integrity as a <br />component of the abandoned structure. <br />Sodium bentonite should not be used to grout boreholes that have encountered ground <br />water with a high concentration of calcium or magnesium, or when the borehole has <br />penetrated an extended interval of dry, porous sand and/or gravel where fluid loss to the <br />formation is likely. <br />Rule 8.3.2.1 expresses the importance of proper mixing of grout materials to achieve <br />maximum effectiveness as a sealing agent. It is the responsibility of the certified <br />individual to ensure that the grout mixture is produced in accordance with the <br />manufacturer's specifications. Use of excess water in a grout mixture is a common <br />temptation when it appears that a grout material is too viscous to be easily pumped. <br />However, the Rule specifically prohibits using water in excess of the amount specified in <br />the directions for mixing provided by the manufacturer. Excess water in the mixture can <br />diminish the sealing properties of the grout. An accurate report of the grout mix must be <br />provided on the construction report. <br />Approved circulating fluids are listed in Rule 8.3.3. The fluids stated in the Rule are <br />approved based on their potential for causing minimum impacts to public health and the <br />environment should they leak from the system or be spilled during construction <br />activities. Use of a circulating fluid or vapor not specifically approved in Rule 8.3.3 <br />requires obtaining a variance from the State Engineer. <br />Rule 8.4 addresses construction of Type A-CLH geothermal wells (horizontal closed - <br />loop geoexchange systems that do not encounter geothermal fluids with temperatures <br />E:3 <br />