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ABOUT KANSAS WSCUSGS IN YOUR STATEUSGS Water Science Centers are located in each state. 
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U.S. Geological Survey
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| Multiply | By | To obtain |
| cubic foot per second (ft³/s) | 0.02832 | cubic meter per second |
| foot (ft) | 0.3048 | meter |
| gallon per minute (gal/min) | 0.06309 | liter per second |
| inch (in.) | 2.54 | centimeter |
| mile (mi) | 1.609 | kilometer |
| million gallons (Mgal) | 3.785 | cubic meter |
| square mile (mi²) | 2.590 | square kilometer |
Temperature can be converted to degrees Celsius (°C) or degrees
Fahrenheit (°F) by the equations:
°C = 5/9 (°F - 32)
°F = 9/5 (°C) + 32.
Milliequivalnets per liter (meq/L) can be calculated with the following equation:
meq/L=(concentration in milligrams per liter)(1/molecular weight in grams)(valence).
Sea level: In this report, "sea level" refers to the National Geodetic
Vertical Datum of 1929--
a geodetic datum derived from a general adjustment of the first-order level nets of the
United States and Canada, formerly called Sea Level Datum of 1929.
To investigate the feasbility of artificial recharge as a method of meeting future water-supply needs and to protect the Equus Beds aquifer from saltwater intrusion from natural and anthropogenic sources to the west, the Equus Beds Ground-Water Recharge from Demonstration Project was begun in 1995. The project is a cooperative effort between the city of Wichita and the Bureau of Reclamation, U.S. Department of the Interior. During the project, high flows from the Little Arkansas River are captured and recharged into the Equus Beds aquifer through recharge basins, a trench, or a recharge well, located at two recharge sites near Halstead and Sedgwick, Kansas. To document baseline concentrations and compatibility of stream (recharge) and aquifer water, the U.S. Geological Survey collected water samples from February 1995 through August 1998. These samples were analyzed for dissolved solids, total and dissolved inorganic constituents, nutrients, organic and volatile organic compounds, radionuclides, and bacteria.
Results of baseline sampling indicated that the primary constituents of concern for recharge were sodium, chloride, nitrite plus nitrate, iron and manganese, total coliform bacteria, and atrazine. Chloride and atrazine were of particular concern because concentrations of these constituents in water from the Little Arkansas River frequently exceeded regulatory criteria. The Little Arkansas River is used as the source water for recharge. The U.S. Environmental Protection Agency Secondary Maximum Contaminant Level for chloride is 250 mg/L (milligrams per liter), and the Maximum Contaminant Level for atrazine is 3.0 µg/L (micrograms per liter) as an annual mean. Baseline concentrations of chloride in surface water ranged from 8.0 to 400 µg/L. Baseline concentrations of atrazine in surface water ranged from less than 0.10 to 46 µg/L.
Concentrations of chloride and atrazine have increased in water from some of the wells at both the Halstead and Sedgwick recharge sites after recharge began, although concentrations remained within the range of baseline values in the Equus Beds aquifer and are considerably less than U.S. Environmental Protection Agency drinking-water criteria. However, a substantial quantity of water has not been recharged at the Sedgwick site to determine the overall effects of artificial recharge on aquifer quality. Continued monitoring is necessary to determine long-term effects at both sites.
Major ion and trace element concentrations in source water and receiving water were analyzed to determine the compatibility of recharge and receiving ground water for artificial recharge. Stiff diagrams of major ions were used to show the similarity or differences between source surface water and receiving ground water. The water from both sources, for the most part, was chemically compatible to the receiving aquifer water at both recharge sites.
It may be possible to decrease the monitoring frequency at the Halstead recharge site because water-quality changes in receiving water at this site are very gradual. However, real-time water-quality monitoring of surrogates needs to be site specific for the determination of chloride and atrazine. Real-time water-quality monitoring potentially can be used to more effectively manage the artificial recharge process, enabling project officials to respond more rapidly to changes in water quality.
The Wichita well field, initiated in the 1940's and completed in the 1950's in the Equus Beds aquifer, is one of the primary sources of water for the city of Wichita and the surrounding area in south-central Kansas. Historical water use for municipal supply and irrigation caused water levels in the Equus Beds aquifer to decline as much as 30 ft by 1993 (Aucott and others, 1998). Lower water levels not only represent a diminished water supply but also encourage saltwater intrusion from the Burrton oil field to the northwest and from the Arkansas River to the southwest into the freshwater of the beds (Myers and others, 1996).
Cheney Reservoir was first used in 1965 to supplement Wichita's water supply. In 1994, city officials changed water-policy practices and began to use the reservoir for a larger percentage of water supply for the area. Since 1993, ground-water levels have risen by more than 10 ft in some areas of the Wichita well field, primarily because of increased use of water from Cheney Reservoir and decreased pumping in the well field area (Aucott and others, 1998). However, an expected increase in demand from both water sources could cause supply shortages in the near future (2010) (Warren and others, 1995).
The Equus Beds Ground-Water Recharge Demonstration Project was begun in 1995 to investigate the feasibility of artificially recharging the Equus Beds aquifer as one alternative to meet future water-supply needs and to protect the aquifer from saltwater intrusion from natural and anthropogenic sources. Throughout the project, high flows from the Little Arkansas River are captured and recharged into the aquifer through various techniques, including recharge basins, a trench, and a recharge well. Before artificial recharge can be determined to be a viable alternative, the water-quality effect of artificially recharging the Equus Beds aquifer needs to be assessed.
The Equus Beds Ground-Water Recharge Demonstration Project is a cooperative effort between the city of Wichita and the Bureau of Reclamation, U.S. Department of the Interior. Additional participants in the project are the U.S. Geological Survey (USGS), Equus Beds Groundwater Management District No. 2 (Halstead, Kansas), and the U.S. Environmental Agency (USEPA). Project work is coordinated with the Kansas Department of Health and Environment (KDHE), the Kansas Water Office, and the Kansas Department of Agriculture, Division of Water Resources. Burns and McDonnell Engineering Consultants (Kansas City, Missouri) and Mid-Kansas Engineering Consultants (Wichita, Kansas) provide engineering expertise and project management. The maintenance and operation of the recharge facilities are performed by the city of Wichita.
The Equus Beds Ground-Water Recharge Demonstration Project is a part of the High Plains States Ground-Water Recharge Demonstration Program, which is a cooperative effort among the Bureau of Reclamation, USGS, and USEPA to study the potential for artificial recharge and its effects in 17 Western States. The USGS also has worked cooperatively with the city of Wichita for many years in evaluating the ground-water system and interaction with streams in the area to further the understanding of the entire hydrologic system and to provide information to improve local decisionmaking.
The purposes of this report are: (1) to describe baseline water quality of the Little Arkansas River and the Equus Beds aquifer for the Equus Beds Ground-Water Recharge Demonstration Project and (2) to describe preliminary effects of artificial recharge from April 1996 through August 1998 on ground-water levels and water quality of the aquifer at two locations--the Halstead recharge site and the Sedgwick recharge site. The compatibility of recharge source water with the receiving ground water and constituents of concern for artificial recharge as related to monitoring frequency and future recharge operations are also discussed.
Preliminary effects of artificial recharge on water levels in the Equus Beds aquifer were determined by comparing baseline water levels (measurements made prior to any recharge activities) to water-level measurements made after artificial recharge began. Preliminary effects of artificial recharge on water quality of the Equus Beds aquifer were determined by comparing baseline concentrations and artificial recharge concentrations of selected constituents in water collected from ground-water monitoring wells.
Compatibility of recharge source water with receiving ground water was determined by comparing major-ion chemistry for water from various data-collection sites during baseline and artificial recharge conditions. Also, an examination of water temperatures, turbidity, dissolved oxygen, iron, and manganese were used as measures of whether source water, when combined with receiving ground water, could cause plugging of aquifer material and thus inhibit artificial recharge activities.
Constituents of concern were identified as those water-quality constituents that frequently exceeded USEPA water-quality criteria and had the potential to affect artificial recharge operations. The benefits of continued monitoring of these constituents during future recharge operations are also outlined.
Information in this report may be used to evaluate the effects of artificial recharge to date (1999) and to adjust future monitoring frequency and (or) scope. The methodology described in this report can be applied to similar recharge studies in other parts of the United States and foreign lands with similar hydrologic conditions.
The study area for the Equus Beds Ground-Water Recharge Demonstration Project encompasses approximately 165 mi² and extends northwest of Wichita across parts of Harvey and Sedgwick Counties in south-central Kansas (fig. 1). The study area is bounded by the Arkansas River on the southwest and includes the Little Arkansas River on the northeast. The Wichita well field encompasses 55 mi² and is located within the study area. The drainage area for the Little Arkansas River Basin is about 1,200 mi². Land use in the basin is primarily agricultural and includes the production of livestock (pasture and rangeland) and field crops. Field crops produced include corn, sorghum, soybeans, and wheat (Kansas Department of Agriculture and U.S. Department of Agriculture, 1997). Agricultural chemicals applied to enhance crop production in the area include fertilizers (such as nitrate, ammonia, and phosphorus) and pesticides (primarily alachlor and atrazine).
The Equus Beds aquifer, a part of the larger High Plains aquifer, consists of alluvial deposits of sand and gravel interbedded with clay or silt. In the study area, the general direction of ground-water movement in the Equus Beds aquifer is to the east (Aucott and others, 1998). However, in the vicinity of the well field and the Little Arkansas River, ground-water movement has been altered by pumping wells and a low-head dam on the river (fig. 2). The Little Arkansas River is primarily a gaining stream within the study area as indicated by higher water levels in wells adjacent to the stream (Myers and others, 1996; Aucott and others, 1998). This is not the case, however, near the Halstead monitoring site (07143680, fig. 1) where a low-head dam about 1 mi downstream causes higher water levels in the stream than in the adjacent aquifer, resulting in stream-water recharge of the aquifer in this vicinity (fig. 2).
The McPherson channel is a trough of unconsolidated deposits about 200 ft thick within the Equus Beds aquifer that extends from Lindsborg (about 30 mi north of the study area) to Halstead (Spinazola and others, 1985). This buried alluvial valley is a major flow path for ground-water movement within the Equus Beds aquifer (Leonard and Kleinschmidt, 1976) and is important as it relates to the movement of chemical constituents. Flow of ground water in the vicinity of the McPherson channel is towards the center of the channel and southward. The towns of Lindsborg and McPherson are upgradient from the study area, and wastewater discharge from these towns may be sources of chemical constituents, such as chloride, in the aquifer water.
The encroachment of saltwater into the Equus Beds aquifer has been a concern in the area for many years. The sources of this saltwater include mineralized water from the Arkansas River (Spinazola and others, 1985; Myers and others, 1996), oil-field brines from the Burrton area west of the study area and northwest of the Wichita well field, and mineralized water in the underlying Wellington aquifer (Leonard and Kleinschmidt, 1976; Spinazola and others, 1985). Other possible sources of saltwater are municipal waste and industrial discharges from upgradient urban areas in McPherson and Newton (Donald Whittemore, Kansas Geological Survey, oral commun., January 1999).
Artificial recharge began at the Halstead recharge site on May 29, 1997. The Halstead recharge system consists of the USGS streamflow-gaging station on the Little Arkansas River at Highway 50 near Halstead (station 07143672, fig. 2), the Halstead diversion well site (fig. 2), and the Halstead recharge site (fig. 2). Water for the demonstration project may be diverted from the well completed in the alluvium adjacent to the Little Arkansas River only when flow in the river exceeds 42 ft³/s at the gaging station from April 1 through September 30 and 20 ft³/s from October 1 through March 31 in accordance with the Kansas Department of Agriculture, Division of Water Resources, permit conditions (Burns and McDonnell, 1998). The flow requirements at this site did not apply to aquifer tests conducted from April through July 1996. By pumping the diversion well, the ground water stored in the bank deposits of the Little Arkansas River is withdrawn, thereby decreasing the water levels surrounding the diversion well and causing surface water from the Little Arkansas River to be induced into the alluvium. The water quality and quantity at the diversion well site are monitored through samples from five shallow monitoring wells, a deep monitoring well, and the diversion well, which has a pumping capacity of about 1,000 gal/min (fig. 3).
Discharge from the diversion well then is pumped about 2 mi through an underground pipeline to the Halstead recharge site (fig. 3) where it is recharged into the aquifer using one of three methods-recharge basins, a recharge trench, or a recharge well. There are two recharge basins at the Halstead site that are each capable of recharging 50 to 120 gal/min to the aquifer.
At the Halstead recharge site, a clay layer occurs approximately 30 ft below land surface (fig.4) and impedes the vertical flow of recharge water into the Equus Beds aquifer. This impediment creates a "mounding" of water that rises to the level of the basin bottom and results in slowed percolation. A recharge trench was installed by the city of Wichita to promote vertical movement of recharge water into the aquifer (fig. 3). The recharge trench is 100 ft long, 3 ft wide, and approximately 15 ft deep and has been tested at recharge rates of 100 to 120 gal/min (Burns and McDonnell, written commun., 1998). In addition, a recharge well is used to inject water into the lower parts of the Equus Beds aquifer. The recharge well is deep (225 ft) and is capable of recharging about 900 gal/min to the aquifer. The vertical-flow problems associated with recharge water at this site do not affect the recharge well because the recharge water is injected beneath the clay layer (fig.4).
Artificial recharge at the Sedgwick recharge site began in April 1998. Unlike the Halstead recharge system, where water is withdrawn from the alluvium, the water in the Sedgwick recharge system is diverted directly from the Little Arkansas River for recharge. In the Sedgwick recharge system, water may be withdrawn from the river near USGS streamflow-gaging station 07144100 (fig. 1) at all times when streamflow exceeds 40 ft³/s (Burns and McDonnell, 1998). At the intake site, a polymer is added as a coagulant aid to reduce turbidity as water passes through a parallel plate separator (Burns and McDonnell, 1998). Next, powdered activated carbon (PAC) is added to remove atrazine and other organic compounds from the water. The treated source water then is pumped about 2 mi by underground pipeline to the Sedgwick recharge site.
Once the treated source water reaches the Sedgwick recharge site (fig. 5), it is pumped to a settling basin to allow the remaining suspended sediment and PAC to settle out of the water. From the settling basin, treated source water is pumped to one of three recharge basins and allowed to infiltrate into the aquifer. A hydrogeologic section across the Sedgwick recharge site between deep monitoring wells DMW-S10 and DMW-S14 is shown in figure 6. Clay layers could impede recharge to the Equus Beds aquifer; however, at this location, the water table is usually above the uppermost clay layer, and therefore, flow of recharge water to the water table occurs rapidly. The water levels from the shallow and deep monitoring wells shown in figure 6 are the same. This is an indication of hydraulic connection between the upper sand-and-gravel layers and the lower layers at this site. Infiltration rates as high as 950 gal/min have been observed (Burns and McDonnell, written commun., 1998). High permeability of the sand-and-gravel layer at the site also contributes to rapid infiltration.
The potential for water-quality degradation of an aquifer is a major concern for any artificial recharge project. For the Equus Beds Ground-Water Recharge Demonstration Project, surface- and ground-water quality are monitored frequently throughout the study area according to a monitoring plan established in consultation with State and Federal agencies. Surface-water quantity and quality are monitored at two USGS streamflow-gaging stations on the Little Arkansas River--Little Arkansas River at Highway 50 near Halstead (station 07143672, fig. 1) and Little Arkansas River near Sedgwick (station 07144100, fig. 1). Flow at both stations is affected by ground-water withdrawals, surface-water diversions, and return flow from irrigated areas (Putnam and others, 1997, p. 288 and 290).
Monitoring wells used in this study were installed by the city of Wichita and constructed of polyvinyl chloride pipe. Wells typically are screened in the lowermost 10 ft of the casing. For dates of completion, type of drill rig, development methods, and other information on individual monitoring wells, refer to Burns and McDonnell (1996).
Ground-water quality is monitored throughout the study area at the following data-collection sites: the Halstead diversion well site, consisting of five shallow monitoring wells (43-70 ft deep) and one deep monitoring well (120 ft deep); the Halstead recharge site, consisting of two shallow (27 and 29 ft deep) and two deep (220 ft deep) monitoring wells; the Sedgwick recharge site, consisting of two shallow (34.5 and 59 ft deep) and two deep (190 and 195 ft deep) monitoring wells; 12 background monitoring wells (40-59 ft deep) located immediately adjacent to the Little Arkansas River; and 10 domestic wells near the Halstead and Sedgwick recharge sites (generally less than 100 ft deep).
Background and domestic wells were used to provide baseline water-quality information on the shallow part of the Equus Beds aquifer in the study area. The background wells were designed to monitor water quality. However, domestic wells were designed to provide water supply to landowners and were not installed with the same specifications as the monitoring wells. This should be considered when comparing constituent concentrations for water samples from domestic wells to water samples from monitoring wells. Both shallow and deep wells were sampled during the demonstration project because the shallow and deep zones are geologically different and thus may react differently with the source water artificially recharged to the aquifer. Additional information about these wells, including altitude and screened interval, is given in table 1a and 1b.
Sample collection began in February 1995 and continued at most data-collection sites through September 1997 to document baseline water quality in the Little Arkansas River and the Equus Beds aquifer. Samples to determine the preliminary effects of artificial recharge on the Equus Beds aquifer were collected from October 1997 through August 1998. Analysis of surface and ground water was performed for dissolved solids, total and dissolved inorganic constituents, nutrients, organic compounds, volatile organic compounds (VOC's), radionuclides, and bacteria. Table 2 defines the time periods for baseline conditions and artificial recharge conditions for each of the data-collection site groupings. A complete list of constituents analyzed is given in table 3a, 3b, 3c, and 3d. Further information related to the data-collection sites, constituents analyzed, data-collection methods, sample frequency, preservation, holding times, and reporting limits can be found in Ziegler and Combs (1997). A preliminary determination of compatibility of recharge source water and receiving ground water was made through the examination of major-ion chemistry and comparison of particular constituents such as dissolved oxygen, iron, and manganese.
Most of the surface-water samples collected for analysis of triazine herbicides were obtained using automated samplers. Results of analyses of surface-water samples collected by automated samplers were compared to results of analyses of samples collected using depth- and width-integrating techniques (Ward and Harr, 1990). Ground-water samples were collected with a submersible pump, using methods described in Wood (1976), Koterba and others (1995), and Puls and Barcelona (1996).
Triazine herbicides were analyzed by enzyme-linked immunosorbent assay (ELISA) (Thurman and others, 1990). Selected samples were verified by gas chromatography/mass spectrometry (GC/MS). A previous study (Christensen and Ziegler, 1998a) indicated a good relation between ELISA-determined triazine concentrations and the GC/MS-determined atrazine concentrations in the artificial recharge study area. In fact, the slope of the regression line, 0.81, indicates that the results of the two analyses are similar for surface water (Christensen and Ziegler, 1998b). Therefore, triazine herbicide concentrations determined by ELISA are referred to as atrazine concentrations in this report. However, the relation between triazine herbicide concentrations determined by ELISA and atrazine concentrations determined by GC/MS is not acceptable for ground-water samples because concentrations of atrazine are more frequently equal to or less than the reporting limit for ELISA (0.10 mg/L, microgram per liter). Therefore, in figures 20, 27, and 28, atrazine concentrations determined by ELISA are reported for surface-water samples, whereas atrazine concentrations determined by GC/MS are reported for ground-water samples.
Information on the water quality of the Equus Beds aquifer and the Little Arkansas River before artificial recharge began was established as a basis for determining what effects, if any, artificial recharge would have on existing ground-water conditions. Baseline water-quality monitoring also was done to establish the constituents of concern for artificial recharge in the study area.
Surface- and ground-water samples were collected from February 1995 through September 1997 to document baseline concentrations of selected chemical constituents, except at the Halstead diversion well site where baseline water-quality monitoring ended in March 1996 because an aquifer test began in April 1996. At the Sedgwick recharge site, baseline water-quality monitoring was extended through February 1998 because recharge operations did not begin at this site until April 1998. In addition, baseline water-quality monitoring of domestic wells near Sedgwick continued until August 1998.
Summary results of baseline water-quality sampling are presented in tables 4-10. Summary tables give the range in detected concentrations, the number of samples analyzed, and the median concentrations (where applicable) for physical properties and selected constituents (table 4a, 4b, and 4c), filtered major ions (table 5a, 5b, and 5c), nutrients (table 6a, and 6b), selected trace elements (table 7a, 7b, and 7c), total organic carbon (table 8), and total coliform bacteria (table 9) in samples from surface- and ground-water data-collection sites. Table 10a, 10b, 10c, 10d, 10e, 10f, 10g, 10h, 10i, 10j, 10k, and 10l displays the range in detected concentrations, number of samples analyzed, and the median concentrations (where applicable) for all organic compounds in filtered samples. Individual data values for all samples collected are on file at the USGS office in Lawrence, Kansas.
Filtered constituents were reported because Ziegler and others (1997) found that in an artificial recharge study it was more appropriate and cost effective to analyze samples for filtered rather than total-recoverable concentrations. In this recharge study, sediment is removed from surface water before it is recharged through basins or trenches. In addition, onsite turbidity measurements in ground-water samples are required to be less than 10 NTU (nephelometric turbidity units), making analysis of total-recoverable concentrations unnecessary for inorganic and most organic compounds (Ziegler and Combs, 1997). However, total concentrations are used for total organic carbon, VOC's, acid and base/neutral organic compounds, and total coliform bacteria.
Although human activities can affect the concentrations of an inorganic constituent, natural concentrations may be large. Therefore, not all detected inorganic constituents are reported in tables 4a, 4b, 4c, 5a, 5b, 5c, 6a, 6b, 7a, 7b, 7c, 8), and 9. Inorganic constituents are listed in those tables if the concentration in any sample was larger than 20 percent of the USEPA's Maximum Contaminant Level (MCL), the Secondary Maximum Contaminant Level (SMCL), the Drinking-Water Equivalent Level (DWEL), or the Health Advisory Level (HAL) for that constituent. In addition, some properties and constituents with no MCL, SMCL, DWEL, or HAL are included in tables 4-9 if they are of particular interest for operation or design of recharge facilities and (or) are needed to describe the water chemistry.
Table 10a, 10b, 10c, 10d, 10e, 10f, 10g, 10h, 10i, 10j, 10k, and 10l reports organic compounds that were detected in any sample. Different reporting guidelines were used for these tables because many organic compounds, such as pesticides, do not occur naturally in the environment but result from human activity. VOC's, acid, or base/neutral organic compounds, were not detected in any samples from any data-collection site.
Selected constituents from tables 4-10 are discussed in the following sections. Each selected constituent is examined in terms of the concentations in surface water and ground water. Constituents of concern for artificial recharge activities are defined, especially as related to frequent large concentrations, relative to the regulatory criteria for dringing water, (MCL, SMCL, DWEL, or HAL), in surface water-the source water for recharge.
Physical properties and selected constituents summarized in table 4a, 4b, 4c for baseline water-quality conditions are specific conductance, pH, water temperature, turbidity, dissolved oxygen, total hardness, alkalinity, suspended solids, and dissolved solids. It is important to consider the physical properties of a water sample because these properties are unique in a number of respects and sometimes are affected by other properties. For example, dissolved ions have a tendency to increase specific conductance (Hem, 1992).
The only physical properties or constituents that have a regulatory criterion are pH, laboratory turbidity, and dissolved solids. The range in pH for all sites during baseline monitoring was 4.4 to 8.6 (standard units). The SMCL's acceptable range is 6.5 to 8.5 (U.S. Environmental Protection Agency, 1999).
Both onsite turbidity and laboratory turbidity are reported in table 4a, 4b, 4c. Onsite turbidity, which is typically smaller than laboratory turbidity, is measured because a ground-water sample is required to have an onsite turbidity not greater than 10 NTU for water-quality analyses (Ziegler and Combs, 1997). There were four instances when onsite turbidity exceeded 10 NTU. Two of these occurred at the Sedgwick recharge site in wells that were recently drilled (wells SMW-S13 and SMW-S11), one occurred in domestic well DW-10 near Sedgwick, and one occurred in the first sample collected from background well TH-08-A1. Laboratory turbidity was measured at greater than the MCL for drinking water of 0.5 to 1.0 NTU in water from some data-collection sites. The range in laboratory turbidity in baseline surface water was 0.30 to 1,200 NTU. The range in water from wells was 0.13 to 1,300 NTU. These larger laboratory turbidities in ground water probably are a result of iron precipitates being formed after sampling. The value of 1,300 NTU occurred in water from a shallow well at the Sedgwick recharge site (well SMW-S13) shortly after the well was drilled. The well may not have been completely developed, which also may account for the larger laboratory turbidity.
Dissolved solids concentrations exceeded regulatory criteria at most sites. Dissolved solids concentration is the total amount of dissolved material in the water and can be attributed to the dissolved major ions present. In the study area, the large dissolved solids concentrations detected during baseline conditions were associated with large sodium, bicarbonate, and chloride concentrations. These and other major ions are discussed in the following section.
Major ions result primarily from the dissolution of rocks and minerals or from discharges of municipal or industrial sources. Excessively large concentrations of major ions are objectionable in drinking water because of possible physiological effects, unpalatable mineral tastes, and greater costs because of corrosion or the need for additional treatment (U.S. Environmental Protection Agency, 1986). Regulatory criteria have been assigned for sodium, sulfate, chloride, and fluoride(table 5a, 5b, 5c).
Fluoride did not exceed its MCL of 4.0 mg/L in any baseline sample. However, sodium, sulfate, and chloride exceeded their respective regulatory criteria at some data-collection sites during baseline sampling. Sodium and chloride were detected at values greater than their DWEL and SMCL of 20 and 250 mg/L, respectively, during baseline water-quality monitoring. The range of sodium in surface-water samples was 4.4 to 200 mg/L; the range in water from wells was 14 to 150 mg/L. Figure 7 shows the ranges in sodium concentrations of the baseline samples. Individual data points were used when there were less than six water samples from the site. The concentration of sodium in water is closely related to the concentration of chloride. Chloride concentrations in surface-water samples ranged from 8.0 to 400 mg/L; in water from ground-water wells, the range was less than 5.0 to 290 mg/L (fig. 7). In both cases, the range of concentrations is larger in the surface-water samples than in the ground-water samples. Sources for sodium and chloride in the Little Arkansas River may be related to past oil and gas activities near McPherson and Burrton or from wastewater-treatment and industrial discharges from McPherson and Newton (Donald Whittemore, Kansas Geological Survey, oral commun., 1999). Additional sources include seepage from ground water affected by the dissolution of marine sediment, concentration by irrigation, and seepage from sewage lagoons, which tend to be enriched in sodium and chloride (Kemmer, 1979).
Because baseline monitoring was limited to one sample from each of the four monitoring wells, seasonal variation of sodium and chloride concentrations could not be documented at the Halstead recharge site. However, water samples collected in April 1998 from domestic wells near Halstead were used to help define the baseline conditions in that part of the study area.
Nutrients, including species of nitrogen and phosphorus, are required for the growth and reproduction of plants. Agricultural activities, sewage-treatment plants, and domestic sewage lagoons are sources of nutrients in surface and ground water. Large nutrient concentrations in drinking water may have undesirable health effects in humans. For example, nitrate concentrations greater than 10 mg/L as nitrogen in drinking water can cause methemoglobinemia in infants 6 months and younger (U.S. Environmental Protection Agency, 1986); consequently, KDHE has set the MCL for nitrite plus nitrate at 10 mg/L (Kansas Department of Health and Environment, 1994). No other nutrient has regulatory criteria for drinking water.
The nitrite plus nitrate as nitrogen (referred to as nitrite plus nitrate in the remainder of this report) concentration in surface water during baseline water-quality monitoring ranged from less than 0.02 to 3.0 mg/L (table 6a, and 6b, fig. 8.). In water from wells, the range was less than 0.01 to 15 mg/L (table 6a, and 6b, fig. 8.). The larger concentrations occurred in water from shallow wells at the Halstead and Sedgwick recharge sites. The disposal of sewage on the land surface can cause nitrate contamination in ground water (Freeze and Cherry, 1979), and there is a sewage lagoon east of the Halstead recharge site (fig. 3). Although ground-water flow is generally to the east, mounding beneath the sewage lagoon could result in local radial flow that could affect the water in the monitoring wells at the Halstead recharge site. At the Sedgwick site, fertilizer application on nearby fields may have an effect on nitrate concentrations in shallow wells because a significant portion of the nitrogen applied to crops like corn may not be used by the plants and the nitrogen may percolate to the ground water (Hammer, 1986). None of the water samples from deep wells had nitrite plus nitrate concentrations larger than 3.0 mg/L; in fact, nitrite plus nitrate was not detectable in most samples from deep wells.
Trace elements refer to solutes in natural water that nearly always occur in concentrations less than 1.0 mg/L (Hem, 1992, p. 129). Of particular concern in this study are the concentrations of iron and manganese. Iron and manganese can precipitate and cause plugging of plumbing and stain laundry. In addition, the tendency of these trace elements to form a precipitate could affect the recharge process by plugging aquifer materials or equipment. During baseline water-quality monitoring, iron was detected at concentrations larger than the USEPA SMCL of 300 mg/L in water samples from both surface-water monitoring sites (table 7a, 7b, and 7c). In fact, iron occurred at concentrations as large as 860 mg/L in samples from the Halstead surface-water site and is associated with suspended sediment (Ziegler and others, 1997). Iron was detected in water from all wells except the deep monitoring wells at the Sedgwick recharge site. The range of iron concentrations in water from wells was less
