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increases; 2) the volumetric flow rates of the injection fluid and production fluid aze roughly <br />equal (after accounting for additional fluids having been left in cavity as it grows); 3) the cavity <br />temperature increases as a result of an increase in injection fluid temperature; 4) the <br />concentration of nahcolite in the production fluid increases as cavity temperature increases; and <br />5) cavity pressures remain stable. <br />Based on these relationships and a close examination ofthe monitoring data, American <br />Soda has recommended that the following criteria be used to determine if action should be taken <br />on an individual well to assure compliance either: 1) the pressure differential (difference between <br />inlet and discharge pressure) increases, but the concentration of nahcolite in the production fluid <br />does not increase; 2) the volumetric flow rates of the injection fluid and pt~oduction fluid differ <br />by greater than 15 percent; 3) the cavity temperature does not increase as the injection fluid <br />temperature increases; 4) the cavity temperature increases, but the concentration of nahcolite in <br />the production fluid does not increase; or 5) the pressure in the cavity decreases with a <br />corresponding decrease in production fluid flow. <br />EPA agrees with these recommendations and has prepazed Minor Permit Modification <br />No. 6 that adds criteria for determining if certain investigations and actions aze needed to assure <br />compliance at an individual well. Minor Modification No. 6 and an Addendum to the Statement <br />of Basis are enclosed. All other provisions and conditions of the Finat Permit for the Yankee <br />Gulch Site, EPA Area Permit C030858-00000 Rio Blanco County, Colorado remain in effect. <br />If you have any questions regarding the changes to this Permit or any future requests , <br />please contact either Dan Jackson 1-800-227-8917 Ex.6155 or Paul Osborne at 1-800-227-8917 <br />Ex. 6125. <br />Sincerely, <br />.,, <br />~' ~~~ Stephen S. Tuber <br />~, Acting Assistant Regional Administrator <br />Office of Partnerships and Regulatory Assistance <br />Enclosures: Minor Permit Modification: No. 6 <br />Addendum to the Statement of Basis: No. 6 <br />cc: Mr. Kent Walters <br />White River Resource Area <br />Bureau of Land Management <br />73544 Highway 64 <br />Meeker, CO 81641 <br />Page 2 of 3 <br />