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SENECA II-W RESPONSE TO COMMENTS 1986 ANNUAL HYDROLOGY REPORT 1. The report states that streamflow is perennial for Stations SG4, FG1 and SG5 and not intermittent as originally stated in the permit. As baseline data was collected during a period of low streamflow, and subsequent data have been collected in a high flow period, is this modification of the description of streamflow regime based on the more recent data, or does it include a consideration of the previous data as well? RESPONSE: The modification of the description of streamflow regime is based on a reconsideration of previous data after reviewing more recent data. For Site SG4, the only "no flow" on record is November, 1979. No flows were reported by the USGS at their continuous recorder, Site GS1, from July to November, 1979, August, 1980, and June to September, 1981. During visits to this site on June to September, 1981, Peabody personnel have observed flows. The USGS data appears to be in error, possibly due to problems with their stilling well arrangement. For Site DC7, Hayden Gulch Coal Company reported "no measurable flow" on June 1978. Although Peabody personnel did not visit the sites in question until after February, 1983, flows have observed every month since then to the present. It is therefore our conclusion that a no flow condition at that time of the year is highly unlikely as fall season flows have been observed after the most recent winter drought of 1986-1987. 2. On Page 91, the report states the mean TDS value is 701 mg/1 at FG1. This value is inconsistent with Table 27 which indicates the mean is 927 mg/1. Peabody Coal Company should clarify which value is the correct mean TDS concentration at Station FG1. RESPONSE: The mean TDS value of 701 mg/1 is for Site FG2. The correct mean TDS value for FG1 is 927 mg/1. Please substitute replacement Page 91 for the existing Page 91 in the AHR.