TMDL Salt Assessment and Analysis: Chloride Impairment in the Gar-Peace and Cow Subbasins of the Lower Arkansas River Basin
by Donald O. Whittemore
KGS Open File Report 2004-5
A report for the Kansas Department of Health and Environment
The State of Kansas, under the Clean Water Act of the United States, is establishing Total Maximum Daily Loads (TMDL) on all stream segments with designated uses to provide a quantitative basis for water-quality assessment. Chloride is one of the substances considered as a pollutant in the TMDL process. A key element of the Clean Water Act is the restoration of waters. Although there are chloride contributions from anthropogenic sources, the main chloride input to the waters of Kansas is from natural geologic sources. The former state of some of the streams and wetlands of Kansas before settlement was saline. Therefore, any restoration of Kansas streams must consider the natural conditions contributing chloride. The Kansas Department of Health and Environment (KDHE) requested the Kansas Geological Survey (KGS) apply knowledge concerning natural sources and procedures for differentiating salinity sources to assist in the process of developing TMDL's for chloride. The focus of this report is on the Arkansas River in the Gar-Peace Subbasin and the Cow Creek Subbasin where stream segments are listed by the KDHE as impaired by chloride with a high implementation priority. The project objectives for this report were to 1) quantify the sources, location, magnitude and variability of chloride concentrations in impaired stream segments of the Gar-Peace and Cow Creek subbasins of the Lower Arkansas River Basin, and 2) distinguish natural intrusion of chloride in the impaired segments from conditions aggravated by anthropogenic activities.
The Gar-Peace Subbasin of the Lower Arkansas River Basin includes the Arkansas River from its confluence with Rattlesnake Creek in southwest Rice County through Reno County to the confluence with the Little Arkansas River in Wichita in Sedgwick County. Tributaries entering the Arkansas River in the subbasin are, in downstream order, Peace Creek, Salt Creek, Cow Creek, and Gar Creek. The Cow Creek Subbasin includes Cow Creek and its tributaries from the headwaters in Barton County to its confluences with the Arkansas River. The drainage basin includes the watershed of Cheyenne Bottoms. Streamflow from Cow Creek splits into three different flow paths in the Hutchinson area before entering the Arkansas River: the Cow Creek diversion canal on the west side of Hutchinson, the Harsha canal in southwest Hutchinson, and the Cow Creek channel through Hutchinson and that enters the Arkansas River north-northeast of Yoder.
The chloride concentration of the Arkansas River exceeded 250 mg/L during the decade of May 1992 to April 2002 in 83% and 84% of the samples collected by the KDHE at sites 523 and 524 west and southeast of Hutchinson, respectively. The predominant chloride source in the Arkansas River in the Gar-Peace Subbasin is natural intrusion of saltwater derived from dissolution of rock salt in the Permian bedrock. The chloride concentration generally decreases and the chloride load increases with flow in the river. However, there is substantial scatter in the distribution of points on graphs of these data, indicating that there are complex relationships that govern the chloride content of streamflow in the subbasin. The main cause of the appreciable variation in chloride concentration and load relative to river flow is the presence or absence of flow from the upper Arkansas River in eastern Colorado. Flows from Colorado that are large enough to reach Hutchinson have a very high sulfate content (typically greater than 1,000 mg/L), a moderate chloride concentration (usually less than 100 mg/L), and a sulfate/chloride ratio of 15. In contrast, the saline ground water that is the main natural source of chloride in the Arkansas River contains a much greater concentration of chloride than sulfate. When the Arkansas River is flowing substantially past Dodge City during conditions when the flow in the Arkansas River near Hutchinson would ordinarily be low, as much as 50% of the chloride load in the river at water-quality monitoring site 523 can come from the upper Arkansas River water. However, the chloride in such conditions at that site would be expected to be less than 250 mg/L.
The main anthropogenic sources of chloride in the Arkansas River in the Gar-Peace Subbasin west of Hutchinson are probably the municipal wastewater treatment plant (MWTP) discharges from the cities along the river (from Great Bend to Nickerson). The largest sources of chloride related to anthropogenic activities that enter the Arkansas River in the Hutchinson area are the NPDES effluents from Morton Salt, the South Hutchinson MWTP, and the Hutchinson MWTP, which flow to the south side of the river, and the anthropogenic component of chloride in Cow Creek water, which flow to the north side of the river via the diversion canals west of Hutchinson and the creek channel southeast of Hutchinson. The wastewater discharges from Morton Salt and the South Hutchinson and Hutchinson MWTP's can comprise as much as about 20% of the chloride load in low flow of the Arkansas River passing between Hutchinson and South Hutchinson. The NPDES discharge from Morton Salt contributes the largest flow load of the three wastewaters inputs to the Arkansas River in the Hutchinson area. However, the source of most of the chloride in the Morton Salt wastewater is probably mainly natural chloride in the supply water pumped from wells between the salt plant and the river. The chemistry of river water samples downstream of the outfall suggests that some saltwater from past salt processing in the area could be mixed with the natural salinity in the ground water pumped by Morton Salt. The waste effluents from both the South Hutchinson and Hutchinson MWTP's contain chloride concentrations that are greater than the source water used by the municipalities. The probable sources of additional chloride in the municipal wastewaters are water-softener salt and saline industrial wastewaters input to the cities' sewage systems.
Water quality profiles during low flow of the Arkansas River in late winter and summer of 2002 showed that the chloride concentration of water on the south side of the river through Hutchinson downstream of the confluence with Salt Creek and of the Morton Salt outfall is greater than on the north side. The chloride contents both Salt Creek and the Morton Salt outfall that enter the south side of the river are usually greater than the chloride concentration of the Arkansas River just upstream, and the chloride content of flow from the Cow Creek diversion canal that enters the north side of the river is typically less than that of the Arkansas River. The river profiles indicate that a distance of about a mile or more is required for an inflow to one side of the Arkansas River to become relatively well mixed across the broad, shallow river channel
The main source of chloride in Cow Creek is natural chloride from ground-water discharge in the subbasin. The chloride concentration generally decreases and the chloride load increases with flow in Cow Creek. However, there is substantial scatter in the distribution of points on graphs of these data, indicating that there are complex relationships that govern the chloride content of the streamflow. The primary causes of the variations are the relative amounts of different tributary inflows that contain diverse natural and anthropogenic chloride sources, and the timing of sample collection relative to the rise and fall of high flow events.
Up to 80% of the chloride content of low flows in Cow Creek near Lyons is from natural sources. The tributary with the highest chloride concentrations and probably the single largest contribution to loads in Cow Creek during low flow in the fall of 1999 was Little Cheyenne Creek. The chloride content of this tributary was 678 mg/L near where it joined the upper part of Cow Creek, which contained only 261 mg/L above the confluence. The primary chloride source in the watershed of Little Cheyenne Creek appeared to be saline ground water affected by evapotranspiration concentration of dissolved solids. Water in the pools of Cheyenne Bottoms can have a chloride content of from several hundred to over 1,000 mg/L. If substantial outlet flows from the Cheyenne Bottoms pools occurred, the chloride content would be expected to be lower than this range but high enough to appreciably affect the chloride content and loads of Cow Creek.
The chloride contents of Cow Creek below the confluence with Little Cheyenne Creek during the fall 1999 low-flow profile were slowly diluted downstream to west of Hutchinson. Anthropogenic inputs increased the chloride load and kept the chloride concentration from being diluted at a greater rate downstream along the creek. Chloride concentrations exceeded 250 mg/L in Cow Creek near Lyons and at Willowbrook in 79% and 56%, respectively, of the samples collected by KDHE during the decade 1992-2002. The anthropogenic inputs upstream of Hutchinson included discharge of ground waters contaminated by oil-field brine, and wastewater discharges from MWTP's and a salt production plant. The largest anthropogenic source of chloride loads in Cow Creek south of Lyons is oil-field brine pollution. The oil brine contributes up to an estimated 10-20% of the chloride load during most low-flow conditions at this site. The brine pollution is primarily from past surface disposal of produced saltwaters and is being slowly diluted by natural recharge and is flushing. The wastewaters from the Lyons MWTP contributed approximately 7% of the chloride load of Cow Creek during low flow in the fall 1999 at the U.S. Geological Survey gaging station near Lyons (combined flow of Cow Creek and Little Cow Creek). The wastewater from other smaller MWTP's probably contributes a few to several percent of the chloride load of Cow Creek near Lyons. The three outfalls from the IMC plant, two of which enter Owl Creek and a third that flows into Cow Creek southeast of Saxman, comprised an estimated 14-15% of the total chloride load of Cow Creek during low flow in the fall of 1999.
Chloride concentrations exceeded 250 mg/L in 90% of the KDHE samples collected from Cow Creek southeast of Hutchinson during 1992-2002. Based on chloride concentrations and flow rates for NPDES effluents and low flows in Cow Creek for late winter and summer 2002, the wastewaters from Cargill and Cessna-Eaton can comprise most of the chloride load in Cow Creek southeast of Hutchinson during low-flow conditions. Discharge of ground water contaminated by saltwater from past salt-processing probably contributes to the chloride load of low Cow Creek flows southeast of Hutchinson. When the flow of Cow Creek past Willowbrook is high enough to provide substantial flows through Hutchinson, the anthropogenic sources from upstream of Willowbrook would contribute to the total chloride load of Cow Creek southeast of Hutchinson.
There are several feedlot operations with NPDES permits in the Gar-Peace and Cow Creek subbasins that might possibly contribute to the chloride load of streamflow, either through direct effluent flow or delayed, slow discharge from ground-water flow. Much of the chloride in the effluent is expected to come from supply waters; additional chloride derives from feed and and materials used in the operations. Long-term use of water for irrigation could lead to higher chloride concentrations in ground-water discharge through concentration of dissolved salts in the supply waters by evapotranspiration. The agricultural sources are not expected to add substantial amounts of extra anthropogenic chloride (beyond that in the supply waters) to the streamflows in either the Gar-Peace or Cow Creek subbasins compared to the additional chloride that comprises part of MWTP and some salt plant wastewaters and all of oil-brine pollution.
The study was partially supported by a contract with the Kansas Department of Health and Environment. Galen Worthington of the KGS assisted in the water sample collection for the second profile by sampling on the south side of the Arkansas River at the same time that the author of this report sampled on the north side of the river. Lawrence Hathaway and Michael Magnuson of the KGS analyzed the water samples. Tom Stiles and Chris Gnau provided electronic files of waste discharge flow and quality and provided information and comments for helping the author prepare and revise the report.