PROTECTING URBAN WATER SUPPLIES IN SOUTH-CENTRAL KANSAS BY
INTEGRATED GROUNDWATER-SURFACE WATER MANAGEMENT TO MEET
MUNICIPAL, AGRICULTURAL AND ECOSYSTEM WATER NEEDS
Robert W. Buddemeier*, Hillel Rubin**, and David P. Young
*
*Kansas Geological Survey, The University of Kansas, Lawrence, Kansas 66047, U.S.A. Email: buddrw@kgs.ukans.edu
and young@kgs.ukans.edu
.
**
Faculty of Civil Engineering, Technion – Israel Institute of Technology, Haifa 32000,
Israel. E-mail: hrubin@techunix.technion.ac.il
ABSTRACT
A key area of south-central Kansas depends heavily on groundwater for a mixture of municipal, agricultural, and environmental needs. Groundwater quality is threatened by natural salt intrusion that is being enhanced and expanded by groundwater pumping. Municipal water supplies face an uncertain long-term future. A regional water management structure is proposed that would make effective use of treated municipal wastewater to modify groundwater flow patterns, mitigate salt intrusion, and meet presently unsatisfied demands for water in a major wildlife refuge. Implementation of a regional water management system designed to address the problems of all users over hydrologicallyappropriate scales of time and space would have additional benefits, such as increasing the feasibility of using advanced waste treatment or desalination techniques to augment the regional water supply.
KEYWORDS
Multiple use, regional management, salinity, wastewater injection
BACKGROUND
This study develops the conceptual design of an integrated regional water management system. Its objective is to provide a range of options to stabilize and protect long-term urban water supplies in an area where the primary water source is an aquifer subject to a variety of threats and demands, and the primary uses are non-urban. The region considered is the eastern portion of the High Plains aquifer in south-central Kansas (Figure 1). Critical characteristics of this region include:

A west-to-east transition from predominantly agricultural to largely urban water demands, and (at the state-wide scale) from semi-arid to sub-humid conditions.

Dependence on groundwater extraction and on surface flow that results from groundwater discharge for most of the water use in the region.

Fully-appropriated groundwater in most areas (no new water rights are available), with some areas exhibiting groundwater depletion.

Geologic bedrock formations that are a natural source of salt contamination to portions of the overlying High Plains aquifer.

Two major wildlife refuges (one state, one federal) that have significant water requirements and rights.

A wide range of human threats to water quality, including enhancement of natural contamination processes, agricultural contamination (primarily nitrates) and irrigationinduced salinization, urban and industrial wastes, brine wastes from salt mining and oil production, and the possible introduction of high-density livestock production facilities.

Figure 1: Study area, showing the locations of the major communities, the groundwater salt sources, the wildlife refuge, and the possible saltwater and wastewater distribution and injection or extraction systems proposed in this paper.
The agencies responsible for groundwater management in the region operate under a policy of
"safe yield" (i.e., withdrawal should not exceed long-term recharge, with allowance for stream baseflow needs). However, groundwater resources are fully appropriated in most areas, water demands are either stable or increasing, and gradual deterioration of water quality has the effect of further limiting the available resources. The varieties of problems, the varieties of water use, and the existence of both governmental and non-governmental bodies committed to avoiding conflicts due to competing water demands, make this region an ideal test-bed for innovative integrated management approaches.

PROBLEM STATEMENT
The proposed integrated solution developed in the framework of this research arises from studies of mineral intrusion into the freshwater aquifers of the region. The most recent investigations addressed potential long-term threats to the municipal wells of the cities of
Hutchinson and Nickerson (see Figure 1) due to encroachment of natural salinity underneath the Arkansas River from the south (Young et al. 1998, 2000; Rubin et al., 2000). The salt is of natural origin, originating in unconfined Permian bedrock deposits that underlie and are hydraulically connected with the alluvial freshwater aquifer system (Layton & Berry, 1973;
Fader & Stullken, 1978; Young, 1993). Salt intrusion is greatest in the western part of the region (north-central Stafford county -- Figure 1), but it occurs sporadically throughout the region, probably associated with low points, paleochannels, and fractures in the bedrock surface (Gillespie & Hargadine, 1993; Rubin & Buddemeier, 1997; Young et al., 1998).
Salt transport is a critical factor in regional water quality problems, and is also the aspect of the problem that is most susceptible to deliberate or inadvertent modifications by humans.
Some salt is brought into the region from the west by Arkansas River flow, but far more leaves the area in surface flow after discharge from the deep aquifer source (Quinodoz &
Buddemeier, 1997). The balance between discharge to surface water and groundwater transport is a critical factor in the salt balance of the area, with salt remaining in the groundwater being redistributed both vertically and horizontally by regional groundwater flow (Rubin & Buddemeier, 1997) and probably by more rapid and concentrated transport in paleochannels (Rubin & Buddemeier, 1997; Rubin et al., 2000). The groundwater in the area south of the Arkansas River and southwest of the Hutchinson-Nickerson corridor (Figure 1) is largely unusable because of its salinity, which preliminary budget estimates suggest is from a combination of salt transported from source areas in Stafford county to the west and from local bedrock discharge within the region.
Water quality in the freshwater portion of the shallow aquifer is affected by water table changes resulting primarily from large-volume pumping. Irrigation pumping in the
Rattlesnake Creek basin has been shown to result in upconing of salt and subsequent dispersion into the freshwater aquifer (Young, 1995; Ma & Sophocleous, 1996). Pumping in this area also has the potential to reduce streamflow, which is a critical water supply for the
Quivira National Wildlife Refuge, and is an important outlet for discharged salt that helps to mitigate the effect of bedrock discharge on groundwater salinity (Quinodoz & Buddemeier,
1997).
In the Hutchinson-Nickerson region, combined agricultural, industrial and municipal pumping has lowered the water table north of the river to the point where saline water intrusion beneath the river has been observed (Young et al., 2000). Combined with the potential for long-term increases in the groundwater salinity (see preceding paragraph), this implies serious threats to the municipal water supplies on a scale of decades. At the same time, application of federal standards for surface water quality has caused heightened awareness of contamination issues and requirements for resource protection and wastewater treatment and discharge throughout the region.
PROPOSED MANAGEMENT SYSTEM

The fundamental assumptions are that problems of regional origin are best addressed by regional solutions, and that such solutions will be practical only if all of the water-user communities in the region perceive the necessary changes as beneficial. The proposed overall conceptual design is therefore composed of components that could be assembled in various combinations, or implemented over time. A key aspect is the use of treated municipal wastewater (presently discharged to the Arkansas River) for beneficial modification of the groundwater regime to optimize the quantity and quality of water available for various uses.
The volumes and qualities of these resources are comparable to those of some of the critical components of the natural system (see Table 1).
Table 1: Inventory/Flux Comparisons -- Approximate Annual Volumes
Q Q [Cl ]
Wastewater:
Hutchinson
Pop.
40000 acre-ft/yr
6300 m3/yr
7.8E+06 mg/L
~400
Nickerson
Great Bend
Total
1000
15000
56000
100
1800
8200
1.2E+05
2.2E+06
1.0E+07
~370
Water use:
Hutchinson-
Nickerson Area
N Stafford Co.
Permian Saltwater Inflow:
N Stafford Co.
Quivira NWR water right
16000
10000
2400
14600
2.0E+07
1.2E+07
2.9E+06
1.8E+07
40,000
Wastewater as a Resource
Notes
Mostly groundwater not incl. QNWR
Surface water
The city of Hutchinson generates approximately 7.7 million m
3
of treated wastewater per year; Great Bend generates about 2.2 million m
3
, and the other communities of the region produce individually smaller amounts that are cumulatively significant. Budget model estimates indicate that the volume of the Great Bend wastewater is comparable to that of the high-salinity brine discharged at the base of the aquifer between Great Bend and Rattlesnake
Creek, and the treated municipal wastes are generally of better water quality than the saltaffected groundwater or the Arkansas River. Figure 1 illustrates some of the possible components of a regional management program, including:

Injection of treated wastewater along the Arkansas River corridor to create a local barrier to salt penetration beneath the river, with or without modification of the irrigation regime.

Use of treated wastewater to replace groundwater extraction for irrigation or industrial use in the Hutchinson-Nickerson corridor. This could reduce or eliminate the gradient enabling northward flow of saline water.

Use of treated wastewater for augmentation of the freshwater supply not available to the wildlife refuge, mitigating the effects of groundwater pumping.

Injection of treated wastewater into the aquifer to replace a similar amount of saltwater extracted, and dilution of the extracted saltwater to a quality suitable for enhancing the wildlife refuge supply from Rattlesnake Creek.
The last option is by far the most elaborate, but it promises the greatest benefits. By pumping saltwater from the deep aquifer in primary saltwater intrusion areas and injecting wastewater

to replace it, the salinity of the aquifer water will be reduced over time even if irrigation pumping continues at present levels. By managing the relative volumes of groundwater and wastewater discharged to Rattlesnake Creek as a function of flow and salinity, the water supply to the refuge could be increased while keeping it within acceptable salinity limits.
Enhancing salt extraction and stream discharge in the Stafford county area will also protect and improve the quality of the groundwater flowing eastward into the region of concern for the municipal supplies.
As a result of agricultural practices, much of the fresh groundwater in northern Stafford county exceeds the drinking water standard for nitrate concentration. Injection of treated wastewater there, or its direct diversion to the Quivira National Wildlife Refuge, will thus not result in degradation of the water or environmental quality in this regard (Rubin et al., 2000).
Future opportunities
Continued consumptive use of water in the region, particularly in view of the high salt loads already present, will result in some continued deterioration of water quality. Water demands, particularly in the larger urban areas, can be expected to increase. A regional water management program will be necessary to implement the approach described above, and it will also expand the resource base available to address other problems. Further aspects of the proposed management plan include:

Extension of public water supplies to the rural areas and small communities, which are presently ill-equipped to deal with the extensive non-point nitrate contamination associated with irrigated agriculture;

Waste stream management and segregation to enhance the quality and recycling effectiveness of the treated municipal waste water; and

Selective use of desalination to maintain the overall quality of the public water supplies as a long-term option.
Waste stream segregation and desalination are both practical because the region already has deep waste injection wells, which permit brine disposal without contaminating surface resources. Although these are rather expensive options, they can be applied as part of a largescale management system because of the potential for wide distribution of both costs and benefits. The region has a large supply of marginal-quality water available; complete desalination would not be required, as a relatively small proportion of high-quality water could be blended to make a much larger volume of water comply with (for example) standards for municipal use.
SUMMARY AND OVERVIEW
Municipal water supplies are faced with combined problems of quality deterioration, increasing demand, and extremely limited options for additional supplies of good-quality water. Agricultural and environmental needs continue to be high, and present patterns of use are probably not sustainable. Enhancing surface flow and groundwater quality in the major salt source region will address the underlying salinity problems on time scales of decades, while local water table manipulation closer to the cities can mitigate problems on shorter time scales. Municipal wastewater is an unused resource in the area, and is available in volumes that would make it effective for high-leverage applications like brine replacement or local flow modification. Agricultural demands are highly seasonal and the surface relief of the

region is too low to provide good opportunities for surface storage of water. This also serves to make aquifer injection of the wastewater an attractive option for environmentally effective use to protect against the salinity transport induced by transient water table reduction due to irrigation pumping.
ACKNOWLEDGMENTS
The authors wish to acknowledge the cooperation and assistance of GMD5, GMD2, the
Bureau of Reclamation, the US Geological Survey, the Kansas Water Office, and cooperating landowners in the study area. Dr. D. O. Whittemore contributed to the project as a coinvestigator. Mark Schoneweis, Melany Miller, and Sharon Vaughn provided staff support.
The Mineral Intrusion studies were funded in part by the Kansas Water Plan Fund.
REFERENCES
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Kansas . Kansas Geological Survey Irrigation Series 4, Lawrence: Kansas Geological
Survey.
Gillespie, J.B. & Hagadine, G.D. (1993). Geohydrology and saline ground-water discharges to the South Fork Ninnescah River in Pratt and Kingman Counties, south-central
Kansas.
Report 93-4177 Water Resources Investigations, U.S. Geological Survey,
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Layton, D.W. & Berry, D.W. (1973). Geology and ground-water resources of Pratt County, south-central Kansas , Kansas Geological Survey Bulletin 205, Lawrence: Kansas
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