Kansas Geological Survey, Open-file Report 2007-9
Part of the Water-quality Effects of Stormwater Runoff into Sand Pits web site
Donald O. Whittemore
KGS Open File Report 2007-9
A report for Groundwater Management District No. 2 Task Force on Sand Pits, Kansas Department of Agriculture, Division of Water Resources Kansas Department of Health and Environment and Sedgwick County
In December 2002, Equus Beds Groundwater Management District No. 2 and representatives of the Wichita Area Builders Association formed a Groundwater Quality Task Force to address issues regarding use of sand pits for stormwater flow management. In April 2004, the Kansas Legislature passed and the Governor approved Senate Bill 364 that amended laws on the appropriation of water in sand and gravel pits. The bill introduced a new section that included studying and developing recommendations regarding the pollution control and flood control impacts of diverting water runoff into sand and gravel pits. State and local agencies already involved in the sand pit task force developed a plan of study on the impacts of runoff into sand pits. Sedgwick County Department of Environmental Resources organized and conducted much of the efforts to determine which sand pits to study in more detail. The study group obtained assistance from the U.S. Bureau of Reclamation in drilling and installing three monitoring wells around each of the six sites selected for study. Funds were obtained for the U.S. Geological Survey to sample and analyze surface water from the pits, ground water from the monitoring wells, and pit bottom sediment at four sites located at the northwest edge of Wichita. The USGS analyzed the water samples for 18 physical and chemical properties, five bacteriological values, 40 inorganic constituents, 118 pesticide and degradate compounds, and 134 organic compounds other than pesticides. The USGS analyzed the sediments for five physical and chemical properties, 45 inorganic constituents, and 32 organic compounds. This report discusses the results of the chemical analyses.
Surface waters sampled from the four sand pits contained many organic compounds of concern for drinking waters. However, none of the concentrations measured exceeded drinking water standards or recommended levels, and essentially all of the organic compounds for which standards exist were present at levels substantially below the standard. The most common organics of interest relative to drinking water that were detected were the herbicides atrazine and two of its degradates (deethylatrazine and hydroxyatrazine), metolachlor, and simazine. These compounds occurred in the greatest percentage of the pit and well water samples and generally in the highest concentrations. The concentrations of these five compounds were usually greater in the surface and ground waters at the three sand pits located in residential areas than at a control site in a cropland area. This could be partly related to the design of the residential sites to allow stormwater runoff entry, whereas no storm drains are directed into the control pit. In addition, there were fewer pesticides and organics other than pesticides detected at the control site than at the residential pit sites. The generally greater occurrence and concentration of organic compounds at the residential sites reflect the use of selected organics in urban areas, for example, weed control in lawns.
Nearly all of the surface and ground waters at the pit sites contained total dissolved solids (TDS) and chloride contents that exceeded the recommended drinking water standard. The high TDS and chloride levels are primarily natural and result from the interaction of saline Arkansas River water, and possibly deeper saline ground water, with the alluvial aquifer and sand-pit water. Dissolved iron and manganese concentrations also exceeded recommended drinking water levels in some of the pit and well waters. None of the pit or well waters sampled at the study sites had concentrations of inorganic constituents that exceeded a primary drinking water standard. All of the surface waters sampled contained measurable or estimable contents of E. coli and total coliform bacteria and all but one of the pit water samples contained fecal coliform bacteria. One sample of residential pit water contained E. coli bacteria that exceeded the KDHE geometric mean criterion for primary contact recreation during the spring and summer. However, additional samples for E. coli measurement would have been needed to compute the geometric mean necessary for determination of a regulatory exceedance. All of the monitoring well samples contained measurable total coliform bacteria indicating that they would need to be treated if used for drinking water.
The bottom sediment samples of the four sand pits did not contain heavy metal concentrations high enough to be of concern to aquatic ecosystems. The only organic compounds detected in the sediments were three chemicals in the persistent insecticide chlordane, which was banned in the U.S. in 1988. The detections were for two samples from one of the residential pits.
The concentration distributions of pesticides and organics other than pesticides, as well as the general pattern in iron, manganese, and ammonium ion concentrations in the downgradient well waters relative to the upgradient well and pit waters, indicate that surface water in the sand pits enters the ground water in the southeast to south-southeast direction of the ground-water flow at the study sites. This would be expected to occur most prominently when surface runoff into the pits increases the hydraulic gradient between the pit surface and ground-water levels. Thus, stormwater runoff containing contaminants can enter ground water through the sand pits and impact the ground-water quality.
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Kansas Geological Survey, Geohydrology
Updated April 28, 2009
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