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P1r. Richard Mills - 2 - April l7, 1986 This corresponds to a 1,000 umhos/cm irrigation water suspect level based on a 1.5 conversion factor (literature values ranged from 1.5-3 ). Since the standard applies to irrigated crops, we looked at average 1985 July-September EC values. On Foidel Creek the upstream (undisturbed) EC averaged below the 1,000 umhos/cm suspect level at only 650 umhos/cm. However, the EC values adjacent to the Eckman Park and Mine No. 1 ranged from 1735 umhos/cm at Pond A to almost 2,000 umhos/cm below Mine No. 2. Since backfilled spoils discharges have EC's that range from 2,640 umhos/cm to 3,990 umhos/cm (MLRD 1985 July-August inspection field data) it is probable that the surface mines are having an effect on the stream. Data from Mine No. 3 shows average summer EC ranges from 1,670 umhos/cm upstream on Foidel Creek to 1,160 umhos/cm downstream from Mine No. 3 on Middle Creek. Mine No. 3 may be having an effect on EC in the stream but it is being diluted to an extent by Middle Creek. The Fish Creek data shows that during the summer of 1985 the average stream quality stayed below our suspect level of 1,000 umhos/cm. EC. However, the alluvial monitoring well downstream from Mine No. 2 showed an average EC above the suspect level at 1,500 umhos/cm. For the Fish Creek drainage it is not known whether the stream would exceed the suspect level during a low flow event. Nor is it known whether the alluvial well contamination can be attributed solely to the mine. Both of these questions need to be looked into further. In summary, the Division is concerned that salt loading from Colorado Yampa Coal Company's (CYCC) Mines may have the potential to affect irrigated crops grown on Foidel Creek, Lower Middle Creek, and possibly portions of Fish Creek. The low flow effects on these streams and even Trout Creek are also not known. The Division finds that it is necessary for CYCC to investigate several issues to evaluate whether there is in fact a problem. Since evidence indicates that the potential for an impact is real, the Division requires that CYCC conduct a reevaluation of the probable hydrologic consequences (PHC) of mining. The original PHC completed by CYCC did not predict the existence or effects of spoils discharges to the surface water system in the basin. Therefore the PHC must be reevaluated for our findings of compliance to be valid. The Division cites the authority in Rule 2.08.3, periodic review of permits; the hydrologic performance standards of Rule 4.05.1; the alluvial valley floor performance standards of Rule 4.24, and the PHC requirements of Pule 2.05.6(3)(b)(iv) in making such a request. Our recommended approach in addressing the issue is as follows. First, CYCC should determine whether the elevated TDS could be attributed in whole or in part to natural conditions, other land uses, or other mines. If CYCC is causing some or all of the salt load to the streams, an investigation should be made as to whether any AVF's or other crop production