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POWDERHORN COAL COMPANY 1993 ANNUAL HYDROLOGIC REPORT AND MZNE INFLOWS STUDY OCTOBER 1, 1992 THROUGH SEPTEMBER 30, 1993 Introduction Operations continued at Powderhorn's Roadside Mine and remained idle at the Cameo No. 1 Mine during the 1993 water year(the year). Production for the year was 337,139 clean tons. During the year management of Powderhorn changed from the Powder River Coal Company Division to the Peabody Western Coal Company Division. Along with this change came a transfer of the hydrologic data base to the PWCC computer system and associated orientation to this operation. As anticipated in last year's report, refinements were made in the preparation of graphs, tables and data submission. The general format of this report is the same as in the past. One addition was in response to correspondence from Erica Crosby on September 28, 1993, requesting more information on a Colorado River monitoring station above the mine site. Another addition to this year's report is information from the Whole Effluent Toxicity (WET) testing required by our CDPS permit. During renewal of our mining and reclamation permit in 1993, changes were made in the hydrologic monitoring requirements. An annual full suite quality analysis in now required on the mine discharge outfalls 001, 002 and 004, and another stream flow monitoring site, SWGS-O5, is now required. Information associated with these changes is incorporated in this report. Lowess Smooth Plots were used for several sites to assist in the analysis of data in this report. Lowess uses a moving median (non-parametric statistics) approach to fit a smooth line through time-series data. Lowess is resistant to outliers and allows more influence from the data near the middle of the overall data set. Lowess is not constrained by parametric statistical assumptions (ie, normal distribution) and has no significance tests associated with it. Another means of analysis used in this report are Trilinear Diagrams. This system was developed A. M. Piper as a geochemical interpretation of water quality. It uses a relative proportion of select cations and anion to indicate general water types. Significant changes in a water type may indicate outside influences. Another note in reviewing information in this report is that for the statistical average water quality reports, censored data is data that was below the analytical detection level of the lab.