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~ iii iiiiiiiii~iuii~ <br />999 <br />MINED LAND RECLAMATION DIVISION <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, CO 80203 <br />303 866-3567 <br />FA%:303 832-8106 <br />• <br />STATE OF COLORADO <br />OF CO(O <br />.~`~ - 'P <br />9 <br />w "/ ~ <br />• in.. 8 n a <br />• r <br />Ala 76 ~ <br />Foy Romet <br />Governor <br />Fred R. Banta, <br />Division Drrecmr <br />DATE: April 22, 1991 <br />70: Gregg R. Squire <br />FROM: John T. Doerfer U Iii <br />RE: Hydrologic Adequacy Review, Amendment No. 2, Nahcolite Solution Mine, <br />NaTec Minerals, Inc., File No. M-83-194 <br />I have reviewed the hydrologic aspects of the above-referenced permit <br />amendment. The proposal is to expand the permit area by 30 acres to a total <br />of 73 acres. The amendment consolidates previous information describing the <br />in-situ method of mining sodium bicarbonate using hot water dissolution. I <br />reviewed the mine plan, reclamation plan, water resources, and monitoring plan <br />and provide you the following comments: <br />1. The ground water monitoring plan states that the monitoring frequency <br />will increase to once per week if the effects from the mining operations <br />are recorded (page 37 ). In the Appendix under Item 1.2.7 of the BLM <br />requirements, leakage from cavities is defined as exceeding State of <br />Colorado Standards (Table 3-2, Final EIS) for total dissolved solids. A <br />review of this table in the EIS indicates a 25 percent increment above <br />855 mg1L for the upper aquifer and 2,210 mg1L for the lower aquifer, or <br />1,070 mg1L and 2,7Ei0 mg1L, respectively, as the standards. The use of <br />TDS as an indicator of contamination may be appropriate, however, it also <br />may be difficult to distinguish between natural variability and man-made <br />effects due to mining. Have other indicators been considered? Please <br />confirm the criteria proposed to be used to determine the effects of <br />mining on ground water quality. <br />2. The ground water monitoring plan includes a network of upgradient and <br />davngradient monitoring wells, referred to as dedicated monitors, as well <br />as a number of wells within the area to mined, The Division is currently <br />in the process of developing proposed rules which will identify criteria <br />to be used in estatllishing appropriate "point of compliance" for ground <br />water standards, 1'he discussion on page 8 states that the distance to <br />the two groups of wells is appropriate, in that wells closer could <br />potentially "miss" the effect and wells at a greater distance could <br />result in too long of a time between development of a problem and <br />detection of that problem. <br />If you were to propose an appropriate "point of compliance" for ground <br />water from the proposed operation, which location would you choose? If <br />the more distant set of wells was selected, where would new wells be <br />located as the operation extends laterally? <br />