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Seneca II-w. PIi~' February 26, 1999 Paec ~ should continue to be monitored. Please incorporate [his site into the current surface water monitoring program. 28.-32. Responses accepted. 33. To verify the projected impacts to the Wadge overburden and coal seam aquifers. groundwater monitoring down gradient of the proposed pit areas in the II-W South area will be required. This may be accomplished by installing and monitoring one overburden groundwater well down gradient of the proposed pit areas in the II-W South extension area, and by continuing to monitor existing wells 4W and 4WC in the II-W South area. Please refer to item nos. 23. and 26. above. 34. Based on the information presented in Table 17-42a, it appears that the projected dissolved solids concentration will result in exceedances of the Division's material damage suspect levels. The salinity suspect level for the Yampa River Basin is I.0 millimhos/cm for specific conductance. Postmining TDS concentrations as high as 1, 888 mg/1 are predicted for Hubberson Gulch. This would equate to specific conductance concentrations in excess of 2.0 millimhos/cm. A postmining TDS concentration of 1,650 mgll is shown for Site WSWTF2 located on Watering Trough Gulch. It appears that this site is located upstream on Watering Trough Gulch outside of any potential impacts from mining. Please explain how the postmining concentration of 1,650 mg/1 was calculated for this location. Please also provide an explanation of how the postmining TDS concentration of 1,336 was determined for site WSDS on Dry Creek. An evaluation of crop productivity declines is presented. In the discussion, SCC explains that the grass hay fields were not included in the vegetation survey, yet SCC concludes that since most hay fields in Routt County produce a mixture of smooth brome, timothy, orchard grass and barley, this field must also. Please verify the crops grown with the landowner. Crop verification is critical, because the data presented by SCC shows that there will be material damage to the hay field from the mining operation. Different crops have different salt tolerances that will impact the productivity and resulting material damage assessment . Based on SCC's calculations, the decline in crop productivity will be 3.3%. This is based on salinity threshold values and yield decrease values for barley and orchard crass from the D~IG's 1988 Material Damage Assessment Process (page 4). Where did the values For smooth brome come from? No values for timothy are presented in Table 17-43a, yet the text on page 112a indicates "experimental" values were used. Threshold ranges and yield decrease ranges for these species are presented in a study titled, "Crop Salt Tolerance Study -Phase II". I can provide a copy of this document for SCC if necessary. It will be important to determine the actual crops grown and ttse acceptable values for those crops to assess potential material damage. 35. Response accepted.