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`~- The major concern associated with surface water at the mine site is that salt laden ground water will be pumped from tl~e pit to Pond N4 and thereby enter the surface water system. Monitoring done by [oFC for baseline definition of the pre-mining environment has shown that surface water is of a much higher quality than ground water. This concern is mitigated by the extremely Iow water yield expected from the pit (less than I gpm), the large storage capacity of the pond without discharge (1.25 acre-ft.) allowing for a high evaporation potential, and the fact that the majority of water generated by the mining process will be used for dust suppression at the site. However, there is no guarantee that no discharge will ever occur frofq the pond, and in the event of a discharge, the Division is concerned about tracking any potential salt problems. The Division imposes the following stipulation: WYOMING FUEL COMPANY MUST PROVIDE MEAS UREPIENT OF TOTAL DISSOLVED SOLIDS (MG/L), AND SODIUM ADSORPTION RATIOS, AS WELL AS ALL REQUIREMENTS OF THE NP DES SYSTEM FOR EACH DISCHARGE EVENT AT POND H4. THESE REPORTS MUST BE SUBMITTED TO THE DIVISION QUARTERLI'. The applicant has already committed to similar monitoring of the Pond kl effluent (see page 54, Appendix C). As the structure identified as Temporary Impoundment NS is capable of storing over two acre-feet of water without any means of discharge, the acquisition of a water storage right is required. The purpose of the pond is to serve as a receptical for undisturbed waters from a diversion system and to develop an elevation gradient for passing this water around the pit. The need for this pond could be eliminated by providing a ditch capable of passing the IO-year, 24-hour storm peak flow around the pit. In order to assure compliance with State water law, the Division imposes the following stipulation: WITHIN 30 DAYS OF PERMIT ISSUANCE, WYOh1ING FUEL COMPANY MUST PROVIDE: 1. PROOF THAT STORAGE RIGHTS HAVE BEEN APPLIED FOR IN STATE DIVISION 6 WATER COURT AND PROVIDE A MEANS OF DE[JATERING TEMPORARY IMPOUNDMENT NO. 1 TO A VOLUME LESS THAN TWO ACRE-FEET IN THE EVENT OF A DOWNSTREAM CALL, OR 2, DESIGN FOR A DITCH COLLECTION SYSTEM, [dHICH WILL ELIh1INATE THE NEED FOR TEMPORARY IMPOUNDMENT NO. 1. THIS DESIGN SHALL INCLUDE ALL ASS Uh1PTZONS, METHODS AND CALCULATIONS NECESSARY TO ASSURE COMPLIANCE WITH 4.05.3. Three ditches exist at the site and four others are proposed. During the course of the review, several concerns were raised with respect to these ditches. AlI of these ditches were examined for compliance with 4.05.3 and were found to be acceptable, with the exception of the proposed ditch which will carry undisturbed flow from Temporary Impoundment H1 to an unaffected channel of the North Fork of Bolton Draw, Ditch E. This ditch has been found to have an erosive velocity during passage of estimated 25-year, 24-hour storm peak flow. The use of the 25-year, 24-hour storm for design pusposes, instead of the 10-year, 24-hour storm event, was required by the fact that this ditch serves as a conveyance for flow from the emergency spillway of Temporary Impoundment b1, which is designed for the 25-year, 24-hour storm as required by 9.05.6(3)(d). The replacement of Temporary Impoundment kl by a diversion ditch system would reduce the required design flow and would thereby reduce the design flow velocity. For this reason, the Division imposes the following stipulation: