Historic USGS and KDHE data indicate that the actual conditions are rare during which the chloride concentration of the Solomon River at Beloit actually exceeds the secondary drinking water limit of 250 mg/L. The many days during which the river water apparently exceeded the 250 mg/L chloride value based on the City of Beloit measurements actually are the result of error in the analyses. Comparison of chloride measurements made by the KGS for this study (maximum error of 3%) with City analyses made on the same day indicate that the City values averaged 22% too high during 2002-2003. After adjustment of the chloride measurements and elimination of anomalously high values that are not consistent with the prior and following concentrations, there are only two periods, one 11 days and the other 3 days long, when the chloride content might have actually exceeded 250 mg/L during October 1988 to May 2003. The flow in the Solomon River during these two periods was generally in the 15-20 ft3/sec range at the USGS gaging station below Glen Elder Dam. None of the mean monthly values of adjusted chloride concentration during 1988-2003 exceeded 250 mg/L. The river flow below Glen Elder was <20 ft3/sec during eight out of the 12 days for which the KGS analyzed river samples from Beloit. The flow during the historic USGS and KDHE record when the chloride content exceeded 250 mg/L was <10 ft3/sec. Extrapolation of the best-fit power curve on a graph of river flow and mean monthly chloride concentration for the adjusted Beloit record to a chloride value of 250 mg/L gives a flow of 6-7 ft3/sec. Thus, the expected flow in the Solomon River when the chloride content exceeds 250 mg/L is <10 ft3/sec.
The range and mean chloride concentrations of the North Fork Solomon River at Downs, just upstream of Waconda Lake, were 55-78 mg/L and 66.5 mg/L, respectively, for the 12 monthly samples collected during 2002-2003 for this study. This period was relatively dry and represents conditions when the dissolved solids content of the river water would be expected to be greater than average. The range and mean chloride content of the South Fork Solomon River near Corinth, also just upstream of Waconda Lake, were 107-152 mg/L and 125 mg/L, respectively, for 2002-2003. The range and mean chloride concentration for water collected at the outlet of Glen Elder Dam, which represents Waconda Lake water, were 98-112 mg/L and 107 mg/L, respectively, for 2002-2003. Use of the average chloride concentration for the inflows from the North and South forks of the river to Waconda Lake instead of the outlet flow (lake) chloride content for the same date does not change the outlet release calculation significantly. Thus, limitations based on the bypass of natural flow principle (assuming that Waconda Lake were not present) are not expected to be an important consideration in the release of lake water to dilute high chloride content in the Solomon River at Beloit.
Increases in the outlet release from Waconda Lake needed to dilute chloride concentrations in the Solomon River at Beloit below 250 mg/L are expected to be small. An equation for calculating the outlet release includes the variables of 1) outlet flow from the lake before the added release, 2) chloride concentration of the Solomon river at Beloit before the release, 3) chloride concentration of the river desired at Beloit, and 4) chloride concentration of the lake water (outlet flow). The equation predicts that an increase of 2.6 ft3/sec in the outlet flow would dilute a chloride concentration of 270 mg/L in the river at Beloit to 240 mg/L, given an existing outlet release of 10 ft3/sec and a lake chloride content of 107 mg/L. If the lake chloride content were 140 mg/L, the increase in the outlet release would be 3.4 ft3/sec instead of 2.6 ft3/sec. A smaller existing outflow would require a smaller increase in the release needed for the chloride concentration dilution. The calculated flow increases for chloride dilution are well within the range that could be achieved by the City of Beloit using a portion of the 2,000 acre-ft that it has the right to accumulate in Waconda Lake. For example, a flow release of 3 ft3/sec for a 30-day month equates to 179 acre-ft.
The greatest uncertainty in the flow release equation is the change in Solomon River flow between Glen Elder Dam and Beloit due to increases from ground-water discharge and small tributary inflows, and decreases from bank storage related to a higher river-water level after an increased release and from lower ground-water levels in the alluvial aquifer caused by pumping. The maximum estimated uncertainty in the outlet release computation from this source and error in the chloride concentration analyses could cause the outlet release for the example above (2.6 ft3/sec) to be in the range 1.1-4.9 ft3/sec. Most likely, the uncertainties would not be this great but in the range of ±1 ft3/sec, which is probably about the accuracy of the flow release gage of Glen Elder Dam. An error of 5% in the chloride concentration used for the Solomon River at Beloit is ±12.5 mg/L at a chloride level of 250 mg/L. Thus, the chloride content of the river at Beloit should be based on an actual analysis of the water using a laboratory that can achieve an accuracy of <5%. Although estimates of chloride concentration of the dam outlet water based on specific conductance for use in the flow release equation would increase the error in the calculation, the increased uncertainty in the value would be relatively small.
The range and mean sulfate concentrations in the 12 samples collected from the Solomon River at Beloit during 2002-2003 and analyzed by the KGS were 263-310 mg/L and 289 mg/L, respectively. The average sulfate value for the weekly measurements by the City of Beloit, after downward adjustment for the 10% difference compared to KGS analyses, was 276 mg/L for the period of May 2002 through April 2003. Thus, the sulfate content of the river at Beloit can often exceed the secondary drinking water limit of 250 mg/L. The range and average sulfate concentration in the dam outlet flow that represents Waconda Lake water was 265-304 mg/L and 284 mg/L, respectively, during 2002-2003. Therefore, releases of lake water cannot be used to achieve dilution of the sulfate level in the river at Beloit based on recent data.
Evaluation of long-term records indicate that chloride and sulfate concentrations have been increasing at varying rates in the North Fork Solomon River at Portis, the South Fork Solomon River at or near Osborne, Waconda Lake, and the Solomon River below Glen Elder Dam and at Beloit. Short-term fluctuations in flow due to climatic variations produce a larger magnitude in the chloride and sulfate changes than the long-term trends. However, the long-term trend of increasing sulfate content has caused Solomon River water at Beloit to exceed the secondary drinking water limit much more often than in the past. If the long-term increase in chloride concentration continues at a similar rate as in the past, the frequency at which the river water at Beloit exceeds the secondary drinking water limit could increase.
The study was partially supported by contracts with the Kansas Department of Agriculture and the Kansas Department of Health and Environment. Mark Billinger of the DWR assisted in the study, including collecting most of the water samples and sending them to the KGS for analysis and obtaining water-quality data from the City of Beloit. Lawrence Hathaway and Michael Magnuson of the KGS analyzed the water samples. Bonnie Liscek and Chris Gnau provided electronic files of KDHE water-quality data for selected sites. Mark Billinger, Tina Alder, and Mindy Sieck of the DWR and Chris Gnau and Tom Stiles of the KDHE reviewed the report and provided valuable comments for its improvement.
Kansas Geological Survey, Geohydrology
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Placed online Jan. 18, 2006