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1.0 BACKGROUND Applied Hydrology Associates (AHA) were retained by Colorado Yampa Coal Company (CYCC) and Twentymile Coal Company (TCC) to recommend a program that would lead to complience with NPDES permit requirements. Primarily, this involved the evaluation of the water quality of inflows into, and discharge from sediment pond D located on CYCC mine property. The discharge point from the pond is defined .as point 005 in NPDES permit ,NCO-0027154. The discharge from the point is required to meet the limitations imposed by the NPDES permit which are based on stream standards for Segment 13 of the Yampa River (Table 1). The reason for these limitations is that the receiving stream, Foidel Creek, is defined as an intermittent stream on the basis of historical 10 year, 7 day minimum flow data of zero. Since late 1984, water quality data from the monitoring program required under the NPDES permit has indicated several exceedences, mostly for total silver and total zinc concentrations. The major objectives of the recommended program are to: 1) Determine the nature and source of the exceedences. 2) Evaluate alternatives for maintaining compliance with PIPDES limitations. 3) Evaluate the potential far submission of a petition to the Colorado Water Quality Control Commission to amend the water quality standards for Segment 13 of the Yampa River. 4) Determine whether the indicated exceedences are "real", and not due to analytical or sampling error. The last objective was added to the overall program at a later stage after examination of analytical results indicated that significant analytical errors had been made which raised serious questions as to the validity of the exceedences. This report fulfills the first objective of the program and presents recommendations for achieving the other objectives.