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Mc Michacl R. Neumann Montgomery Watson Americas, Inc. October 20, 1998 Page 2 b) Although a data set of four samples is too sparse for a rigorous statistical analysis, the Division considers that the narrow range of the four pre-mining values gives the data set some value as a basis for comparison with post-mining TDS values. c) The post-mining site that can be compazed to the pre-mining S-3 site is LHG, located 0.6 miles upstream from S-3. Hydrologic features are fairly uniform along the 0.6-mile distance between the two sites; therefore, it is unlikely TDS values aze significantly altered in that stretch of Hayden Gulch. d) TDS concentrationsat the post-mining LHG site averaged 1937 mg/1 in the seven samples taken over the last two yeazs (1996-1997). It appears that since mining began, TDS levels in Hayden Gulch downstream from the mine have increased at least several hundred mg/I from the pre- mining level of azound 1000 mg/1 (see Figure 1). The timing and location of the TDS degradation indicate that mining operations at Hayden Gulch Mine caused [he degradation. e) Based on Wyoming DEQ's 2000 mg/1 use suitability standard for irrigation water (referenced in H-G Coal's bond release submittal's hydrologic impact analysis), mining at Hayden Gulch Mine has caused Hayden Gulch water to approach the unsuitability limit for irrigation use immediately downstream from the mine. TDS levels at site LHG have regulazly exceeded the 2000 mg/1 limit in recent years in both fall and spring sampling. f) Section 3.03.1(4) of the Regulations specifies that no bond shall be fully released until all reclamation requirements of the Regulations and the Act aze fully met. One requirement is that surface mining activities shall be conducted to prevent material damage to the hydrologic balance outside the permit azea in order to prevent long-term adverse changes in the hydrologic balance (Section 4.05.1(1) of the Regulations). g) The permittee has previously cited a lack of irrigable land and insufficient summer stream flow as reasons why Hayden Gulch water would never be used for irrigation. Now that mining has degraded surface water to near the imgation suitability limit, it would be appropriate to re- evaluate the potential for material damage to imgation users. Please verify that Hayden Gulch surface water could not be used for irrigation even if it had it not been degraded. h) Please submit a calculation of the TDS increase in the East Fork of the Williams Fork River, during baseflow conditions, caused by the increased TDS levels at surface water site LHG.