1993-11-15_GENERAL DOCUMENTS - C1981017 (2)

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Mid-Continent Report; Nov. 15, 1993 Steve Renner/Harry Posey Page 4 3b. Conductivity and TDS versus time. Conductivity averages about 500 and TDS averages about 250. However, the highest conductivity and the highest TDS occur from late 1987 through late 1992. 3c. Conductivity and TDS versus flow. Conductivity and TDS both show an inverse exponential relationship with flow. High Cond and TDS correlate with low flow. 4a. TSS. Most of the high TSS concentrations occurr during lowest flows. The cause is not perfectly known, but is probably related to the installation of sediment retention ponds around the mid-1980s. The most plausible explanation is that slow flowing streams carried only suspended clay sediment whereas the fast-flowing streams carried both sand, silt and clay. The sediment retention ponds probably allowed fine clays to pass through the system, whereas prior to their installation, all of the sediment passed through. Another contributing factor may be that waters during the high-flow season are purer than those of the low flow season, but this is probably only a minor component, and probably not dicipherable from the data. 4b. TSS versus time. TSS concentrations were highest during the first two years of data collection and decreased, progressively, through the end of 1984. After 1984, TSS fell to very low values, and remained low through 1992. It appears that mining had a positive impact on the sediment load; site management practices, particularly the installation of sediment retention ponds, caused the sediment load to diminish. Samp ractices may have had some control over TSS concentra ' Unless the J sampling events we ed, it is likely that samples we ed during good weather (i.e. locally low flow), and that were not , routinely, during or immediately �,Q following storms. Samples collec 1 years were collected at closely spaced intervals, and thus ve recorded more of Its of storms. Sampling in later years, which rred only twice yearly, probably took place durin�g� goo her, which would n during low flow when sediment loads consisted only of clays. 4c. TSS versus flow. TSS shows a-slight positive exponential relationship with flow. However, virtually all of the high TSS measurements were taken during lower flow. 5a. Evaluation of outliers. Data for Conductivity, TDS, and TSS were plotted relative to flow, and curves were fit to the data. A one standard deviation range was established in order to highlight the samples above (or below) one standard deviation from the mean for any given rate of flow. The choice of one standard deviation was selected arbitrarily. There is no reason to believe that this method is any more valid than other, more or less empirical methods for