Archives - Page 12
-
Chemical Quality Series 4: Chemical Quality of Irrigation Waters in Hamilton, Kearny, Finney, and Northern Gray Counties
The utilization of irrigation waters in Kansas has increased dramatically since the drought period of the 1950's. With this development has come the need for information which can be used in the determination of compatibility of groundwaters with soils and crops and in the management of the groundwater systems tapped for agricultural purposes. An important component of this information is the chemical character of the waters under consideration.
The chemical quality data contained in this report show that groundwater presently in use from the Arkansas River valley in Kearny, Hamilton, and Finney counties and a band north of the river in Finney County is of sufficiently poor quality that it could produce adverse effects upon soils and crop yields with uncontrolled long-term usage. In most cases, poorer quality groundwater is associated with the presence of saline soils and shallow water tables.
Further efforts in this study are being directed toward correlating the chemistry of the groundwaters with natural variables such as soil association, bedrock types, depth to water, and surface and bedrock topography, and using these correlations to produce areal presentations of the chemical quality data. With these correlations and more complete coverage of western Kansas, positive policy recommendations concerning the conservation and proper use of the groundwater supplies of the state will be possible. This series of studies was begun on a limited scale in 1974 with that goal in mind. Greeley, Wichita, Scott, Lane, and southern Wallace counties were covered in that year; the results were reported in Kansas Geological Survey Chemical Quality Series 2. This report covers work done in 1975. In 1976, the rest of the southwest portion of the state was sampled; a report on that area is in preparation. This summer the Great Bend Prairie area will be sampled.
-
Chemical Quality Series 5: Ground Water from Lower Cretaceous Rocks in Kansas
Continuing declines in the water table in western Kansas due to the heavy demands of irrigation and municipalities have led to a search for additional supplies of water. Lower Cretaceous rocks (primarily the Cheyenne Sandstone and Dakota Formation) have long supplied water for irrigation and stock.
This survey of the available data on the quantity and quality of ground water available from Lower Cretaceous rocks indicates that an estimated 70-80 million acre-feet of fresh water containing less than 1,000 mg/l (milligrams per liter) dissolved solids and 10-15 million acre-feet of slightly saline water containing 1,000-3,000 mg/l dissolved solids could be obtained. The Kansas Department of Health and Environment recommends less than 500 mg/l dissolved solids for drinking water and will accept up to 1,000 mg/l. Thus, much of the available water could be used as is and even more would be available after desalinization. Water quality tends to be good to the south and the east along the Lower Cretaceous outcrop belt and to gradually decline towards the north and west.
The Lower Cretaceous rocks outcrop in a band from the southwest in a northeasterly direction across the center of the State and are present in the subsurface to the north and west. Their depth increases to 2,600 feet below land surface in the extreme northwest. The thickness of sandstone in the Lower Cretaceous rocks is less than 200 feet in most of Kansas, but is as much as 400 feet in Lane County. The movement of water in Lower Cretaceous sandstones is generally in an easterly or northeasterly direction. The rocks are directly overlain and hydraulically connected with Pliocene and Pleistocene aquifers in parts of southwestern Kansas. Although ground water from the Lower Cretaceous rocks has seen only moderate use to date, there are indications that, locally, pumpage already exceeds recharge.
The ground-water resources in the Lower Cretaceous rocks of western Kansas represent a significant resource for present and future. Additional studies are needed of the regional relationships of the Lower Cretaceous aquifers to overlying Pliocene and Pleistocene aquifers and underlying Jurassic and Permian aquifers with respect to head changes and water-quality changes that may result from water-level declines in the overlying aquifers and pumpage from large numbers of multi-aquifer irrigation wells. Careful planning could result in an extended lifetime for the aquifers.
-
Chemical Quality Series 12: A survey of organic carbon and trihalomethane formation potential
Drinking-water standards promulgated by the U.S. Environmental Protection Agency (EPA) underscore the importance of detailed water-quality data for sources used in conjunction with public water supplies. It has been recognized that reaction of the chlorine (used as a disinfectant) with organic matter present in surface waters can lead to formation of trihalomethanes (THMs) in concentrations which may exceed the 100 µg/L maximum contaminant level (MCL) established by the EPA. However, relatively little consideration has been given to ground-water sources with regard to the organic carbon content of the waters, the potential for THM formation, or the presence of ammonium ion (NH4+), which both consumes chlorine and serves to reduce THM formation. The successful operation of water-treatment plants for public supplies is dependent upon many factors, such as operator skill and the condition of the equipment, but of similar importance is a detailed knowledge of water quality for the sources being employed.
A survey of Kansas ground waters to determine their concentrations of total organic carbon (TOC) and trihalomethane-formation potential (TFP) was conducted in the spring of 1986. Wells were carefully selected, based on well logs made during construction, to represent particular geologic intervals. Thirty-four samples were collected from public water supply wells and 16 samples were collected from private water wells. Samples from 11 alluvial aquifers, four unconsolidated aquifers in Quaternary and Tertiary formations, and four consolidated aquifers in Cretaceous, Permian, Pennsylvanian, and Cambrian-Ordovician rocks were taken.
The mean and median TOC concentrations were 1.03 ± 0.76 and 0.84 mg/L, while the mean and median TFP concentrations were 46.7 ± 39.5 and 30.6 µg/L, respectively. The mean TFP yield was 0.242 ± 0.07 µmol per mg of TOC, and the TFP concentration in micromoles per liter was very strongly correlated (r = 0.953) with TOC. Only 8% of the samples had a TFP concentration exceeding the present MCL for THMs of 100 µg/L, but 56% exceeded 25 µg/L and 90% exceeded 10 µg/L, suggesting that many Kansas water-supply systems using ground water might have difficulty meeting a substantially lower THM standard.
The average instantaneous THM (ITHM) concentration was only 6.95 µg/L, while the average terminal (TTHM) concentration was 35.6 µg/L. Hence, only a small fraction of the THM concentration to which consumers might be exposed is formed prior to distribution. For the 21 TTHM samples having a free chlorine residual at the end of the incubation period, TTHM was strongly correlated with both TOC (r = 0.819) and TFP (r = 0.926), suggesting that either of these might be a good surrogate measure for TTHM.
TOC (and TFP) appeared to be unrelated to aquifer (well screen) depth, but both were clearly much higher in the alluvial aquifers, all of which were located at relatively shallow depths. TOC also appeared to be unrelated to the inorganic constituents present in the samples, with the exception of a subset of samples from alluvial aquifers having high concentrations of NH4+ (>0.1 mg/L) and Fe + Mn (>1.0 mg/L). For these samples, TOC was strongly correlated with both NH4+ (r = 0.676) and Fe + Mn (r = 0.991). These relationships merit further investigation, since all of the constituents involved pose problems for water-treatment plants.
In Kansas, efforts to control THMs in public water supplies from groundwater sources should focus primarily on alluvial aquifers, especially those having high concentrations of TOC, NH4+, Fe, and Mn. TOC and TFP may be useful surrogates for TTHM and could be used as a basis for exemptions from monitoring requirements. Use of combined chlorine appears to be the simplest and most effective means of limiting THM formation, but the necessary precautions must be taken to ensure that the microbial quality of the drinking-water supply is not compromised.
