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UOlu87 Hr. Leon A. Wurl Page Three 2. Stream Flow vs. Diversion As poor as the stream flow conditions are in Coal Creek, the demand for water in the reach of the river between the Plainview Gauge and the Louisvi I Ie Wastewater Treatment Plant would appear to cause an even more detrimental environment for aquatic 1 ife. Table II shows the flows of Coal Creek as recorded at the U.S.G.S. Plainview Gauge versus the diversions (see Figure 2) in the reach of the river between the gauge and the Louisvi lie Wastewater Treatment Plant. Water year 1965 was chosen since the 3610 A.F. which flowed in that year most nearly represents the 17 year average of 3175 A.F. shown in Table I. Table II is a rough hydrology of Coal Creek, but is nevertheless enlightening since it reveals that in addition to the 43 days of zero flow in October and November of 1965, Coal Creek has zero flows for certain reaches and survives on return flows from irri9ated farmland, particularly during June, July and September. It has also been suggested by staff of the CWQCD that Coal Creek flows below Highway 93 are essentially sub-surface and create pools wherein fish habitat may survive. However, it should be noted that the U.S.A. Water and Power Resources Service is studying the feasibil ity of a dam and reservoir on Coal Creek. If built, such a facility would have a positive cutoff to bedrock. Consequently, sub-surface flows would essentially be eliminated below the dam. In contrast, the City of Louisville derives all of its water from S. 80ulder Creek and returns over 50 percent of said water to Coal Creek. Table III shows the City of Louisvi lie's current and projected water requirements along with return flows which have been estimated at 50 percent of the raw water requirement. This table shows that if the City does not 90 to some type of Land Application, the majority of the flow in Coal Creek wi II be the wastewater discharges of Louisvi lie, Lafayette and Erie. From the above data, it may be concluded: (A) That Coal Creek is defini tely an intermi ttent stream, (e) That non-point return flows are significant, particularly when contrasted with initial stream flows. (Although it cannot be concluded from the above data it is intuitive that return flows of the ma9nitude noted must certainly have a detrimental effect on the quality of the water carried in the channel bed), (C) That sub-surface flows wi II be essentially eliminated below the Coal Creek dam, when this facility is built. 3. Costs Insufficient data is currently avai lable to ascertain a firm cost for the City of Louisville to treat its wastewater discharges to meet the proposed stream standard level. Accordingly the following assumptions had to be made: (A) Influent Ammonia Levels Prior to Hay 1980, the State of Colorado and the Ci ty of Louisvi J Ie had not tested the influent ammonia levels of the City's wastewater (Apparently this condi tion is true for most ci ties in Colorado.)