Kansas Geological Survey, Open-file Report 2008-4
Part of the Water-quality Effects of Stormwater Runoff into Sand Pits web site
Donald O. Whittemore
KGS Open File Report 2008-4
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 select the six sand pits to study in more detail. Four of the study sites are in northwest Wichita; three of these are in residential areas and the other is surrounded by cropland. Two of the sites are in southern Wichita; one is in a more densely populated residential (mainly apartments) and commercial area, the other is in a residential location with a golf course. The study group obtained assistance from the U.S. Bureau of Reclamation to install three monitoring wells around each of the six sites selected for study. Funds were obtained for the U.S. Geological Survey (USGS) to sample and analyze surface water from the pits, ground water from the monitoring wells, and pit bottom sediment at the four sites in northwest Wichita in 2006, and at the two sites in southern Wichita in 2007. 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 for the waters from the two pit sites in southern Wichita and for the sediments from all six sites. The report also includes a comparison of the water chemistry at all of the sites.
Surface waters sampled from the two sand pits in southern Wichita contained several different organic compounds of concern for drinking waters. However, none of the concentrations measured exceeded drinking water standards or recommended levels, and all of the organic compounds for which standards or health advisories exist for water consumption were present at levels substantially below the standards and advisories. The organics for which there are drinking water standards or health advisories and that occurred in the surface waters of both pits were the herbicides atrazine, metolachlor, and tebuthiuron, and the solvent isophorone. These compounds were also found in some of the well-water samples at the two sites. In comparison, surface waters from the three residential pits in northwest Wichita contained a wider range of pesticide compounds. Also, the concentrations of the triazine herbicides were greater in the pit waters from the residential sites in northwest Wichita than in the southern part of the city. Ground waters at the sand-pit site within a more densely populated area of southern Wichita that included commercial land use in the vicinity contained many volatile organic compounds (VOCs), and the concentrations of three of these (chlorinated ethenes) exceeded primary drinking water standards and the presence of five others (chlorinated hydrocarbons and benzene) exceeded the maximum contaminant level goal of zero for drinking water. None of these VOCs were detected in the surface or ground waters of the other five study sites. The source of these VOCs is not expected to have been runoff into the pit but surface infiltration of the chemicals to the ground water outside the immediate pit area.
The only inorganic constituent that exceeded a primary drinking water standard was arsenic, which was found at a level slightly above the standard in a well water downgradient of the pit in a more densely populated area of southern Wichita. An arsenic concentration at the same value of this standard was found in one of the well waters at one of the residential pits in northwest Wichita. Just as for the four study sites in northwest Wichita, the surface and ground waters at the two sites in southern Wichita had total dissolved solids (TDS) contents that exceeded the recommended drinking water standard. The high TDS 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 content exceeded the recommended drinking-water standard in two and dissolved manganese concentration exceeded the recommended standard in all of the samples from the six monitoring wells at the two sites in southern Wichita. Concentrations of these two constituents also exceeded the recommended levels in some of the waters of the northwest Wichita sites. All of the surface waters sampled from both pits in southern Wichita contained measurable or estimable contents of E. coli, fecal coliform, and total coliform bacteria but not at levels of concern to contact recreation. Similar to the study sites in northwest Wichita, the contents of these bacteria in the monitoring well samples for the southern Wichita sites were generally less than those in the surface waters.
The bottom sediments of the six sand pits did not have heavy or semi-metal concentrations that exceeded the assessment guidelines for probable toxic effects on freshwater ecosystems. However, the maximum concentrations of arsenic, cadmium, chromium, copper, lead, nickel, and zinc observed in some of the bottom sediments exceeded one or more of different threshold or possible toxic effects levels for ecosystems. The insecticide DDT, four of its degradates, and PCBs were found in the sediment at the sand pit in the more densely populated area of southern Wichita. The concentration of DDT, two of its degradates, and of PCBs exceeded threshold levels for exotoxicological effect on freshwater ecosystems. The presence of DDT and PCBs at this site and not at the other pits probably reflects the greater age of the pit and the residential development at this location compared to the other study sites, because these chemicals were no longer produced in the U.S. after 1972 and 1977, respectively. The insecticide chlordane was detected in the sediment of one of the residential pits in northwest Wichita even though this chemical was banned in the U.S. in 1988. The chlordane and DDT presence at two sand pits indicates the persistent nature of these insecticides.
The concentration distributions of pesticides and organics other than pesticides at the four northwest Wichita sites, 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. The evidence for connection between the surface and ground waters at the two southern Wichita sites is not as strong as for the four northwest Wichita sites, although the distribution of some compounds and chemical properties does support the movement of pit water to ground water. The entrance of contaminants from stormwater runoff into the ground water would be expected to occur most prominently when runoff into the pits increases the hydraulic gradient between the pit surface level and adjacent ground-water levels.
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Kansas Geological Survey, Geohydrology
Updated April 28, 2009
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