1993-11-15_PERMIT FILE - C1981017 (2)

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Mid-Continent Report; Nov. 15, 1993 Steve Renner/Harry Posey Page 3 3. Examine Cond, TSS, and TDS values that are more than one standard deviation above the mean of the regression curve (line) and determine whether these outliers bear any relation to time of sampling. The question is whether recently-collected samples record perturbations in the system, and whether such perturbations can be linked to on-site activities. RESULTS The results are discussed in terms of flow, conductivity (and TDS), TSS, and date of sampling. All of the following discussion refers to data collected at Station #20, the furthest downstream sampling point on Coal Creek. 1. Date of Sampling A fairly complete set of samples was collected in 1978 and 1979. Sampling took place, in most instances, in 2-3 week intervals during that period. From 1980 through 1992, flows were measured and samples were collected 2 to 4 times per year. 2. Flow. At station #20, the flow ranges from 2 cfs to 222 cfs. Data for 1978-1979 indicate clearly that the peak flow occurs in May. (This fits the general trend in Colorado whereby peak flows occur about 4-6 weeks after the initiation of snowmelt at high altitudes.) For the years following 1979, the rate of flow was interpolated for the May peak based on adjacent samplings. Provided these interpolations are correct, high flows occurred in 1979, 1980, 1982, 1983, and 1991. Flows for these years are nearly two times greater than the other years. Peak flow measurements were collected in 7 out of the 15 years of data collection. 3a. Conductivity and TDS. Conductivity and TDS behave in nearly identical ways (see later sections). High conductivities and TDS occur during low flow, probably for two reasons. First, spring melt dilutes the water relative to the dissolved species because melt water is relatively free of dissolved species. About the only material available for dissolution by snowmelt is dust. Second, water produced during low flow periods spends a greater amount of time in contact with available soluble species, so higher portions of soluble minerals are able to be dissolved. About half of the low flow season occurs in warm weather, and warm water generally increases the solubility of solids. The effect of temperature on solubility is probably minor relative to the effects of time that the water spends in contact with the minerals.