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Chemical Quality of Ground Water

The chemical character of ground water in Pratt County is indicated by analyses of 64 water samples from 46 wells and 11 test holes (table 4). The results in table 4 are given in milligrams per liter of mineral constituents and can be expressed in milliequivalents per liter by multiplying milligrams per liter by conversion factors given in table 5. Except near Cairo, ground water in Pratt County is chemically suitable for most uses.

Table 4--Chemical analyses of water from selected wells and test holes. [Chemical constituents reported in milligrams per liter. Analyses by Kansas State Department of Health.]

Well or test-hole number1	Sample number (fig. 11)	Date of collection	Temp. (° C)	Dissolved solids (residue at 180° C)	Silica (SiO2)	Iron (Fe)	Manganese (Mn)	Calcium (Ca)	Magnesium (Mg)	Sodium and potassium2 (Na+K)	Bicarbonate (HCO3)	Sulfate (SO4)	Chloride (Cl)	Fluoride (F)	Nitrate (NO3)	Hardness as CaCO3		Specific conductance (micromhos at 25° C)	PH	Remarks3
																Calcium, Magnesium	Noncarbonate
26-11W-8aaa	1	29-Nov-1951	14	260	18	0.24		66	6.4	18	222	8.6	19	0.2	15	190	9
-13daa	2	23-Nov-1951	16	404	7			111	13	14	312	31	21	0.4	53	330	74
-29cbc	3	29-Nov-1951	14	152	10	0.3		18	4.2	24	57	30	10	0.8	27	62	16
-30add1	4	6-Aug-1964		348	19	0	0	83	6.1	34	271	26	23	0.3	23	232	10	540
26-12W-2aac		1-May-1964											83					670
-34cdd	5	7-Aug-1964		381	3.5	0.46	0.06	51	8.8	83	144	22	140	0.6	0.4	165	45	690		TH, 50
26-13W-2ccc	6	29-Nov-1951	15	215	11			49	5.8	18	167	11	10	0.3	28	146	9
26-15W-6baa	7	28-Nov-1951	16	739	8.2	0.07		123	16	95	321	52	52	0.2	235	373	110
-26bda	8	28-Nov-1951	15	138	19	0.06		27	4.8	8.5	85	2.9	9	0.2	25	87	17
-32cbb	9	28-Nov-1951	14	144	17			27	5.4	17	138	2.5	6	0.4	0.7	90	0
27-11W-18cbb	10	6-Aug-1964	18	325	18	0.01	0	68	8.4	37	268	15	15	0.3	32	204	0	510
-19bbc		20-Jul-1964		150				43	2.1	8.2	139	7	9			116		260		TH, 65
-25cdb	11	23-Nov-1951	16	375	12	0.19		62	8.2	66	200	18	100	0.3	10	188	24
-30bcb	12	19-Sep-1956		229	20	0.47		55	4.2	19	188	7	13	0.2	18	154	0			TH, 56
-30bcb	13	19-Sep-1956		2,230	20	0.39		59	9.5	787	227	119	1,120	0.3	8	186	0			TH, 116
-30ccc	14	18-Sep-1956		2,480	21	0.34		107	16	817	226	155	1,240	0.2	8	333	147			TH, 45
-30ccc	15	18-Sep-1956		10,200	19	0.54		261	76	3,536	207	720	5,480	0.3	13	964	794			TH, 95
-32cba	16	29-Nov-1951	15	283	14	0.04		74	7	17	239	12	14	0.3	27	214	18
-35dad	17	19-Sep-1951	15	685	15			170	14	63	210	6.2	307	0.2	6.6	482	310
27-12W-9aaa	18	22-Jul-1964		8,860	14	0.28	0	152	41	3,240	220	451	4,845	0.3	5.3	548	368	15,000		TH, 106
-13add	19	21-Jul-1964	21	19,360	1	0.26	0	448	112	6,835	73	1,202	10,700	0.6	3.6	1,578	1,518	29,100		TH, 210
-14adb	20	21-Jul-1964	18	805	17	0.01	0	119	17	155	232	33	336	0.2	14	367	177	1,410
-25daa	21	20-Jul-1964		1,460	4			131	13	404	178	96	720	0.3	2	380	234	2,660		TH, 41
-25daa	22	20-Jul-1964	17	3,060	5.5		0.38	119	18	1,034	215	170	1,600	0.2	6.2	371	195	5,480		TH, 90
-26dda	23	17-Jul-1964	23	336	21			52	3.5	61	188	26	65	0.6	14	144	0	550		TH, 27
-26dda	24	17-Jul-1964	18	2,270	12		0	93	12	749	222	134	1,150	0.3	6.6	282	100	4,150		TH, 116
-35aab		17-Jul-1964		276				69	2.9		215	11	11			184		420
-36bcb	25	20-Jul-1964	17	298	14	0.23	0	64	6	33	210	21	20	0.3	37	184	12	450		TH, 32
-36bcb	26	20-Jul-1964	16	271	17		0	52	4.5	41	202	20	25	0.3	12	148	0	410		TH, 69
-36daa	27	21-Sep-1956		275	26			54	6.2	32	195	23	25	0.3	12	160	0			TH, 26
-36daa	28	21-Sep-1956		242	22	0.12		47	6.6	29	185	13	24	0.3	8.4	144	0			TH, 105
27-13W-21aca1		1-May-1964											40					440
-32bbb	29	28-Nov-1951	15	158	17	0.37		40	5.2	7.4	144	4.5	7.5	0.2	4.9	122	4
-33dcb	30	3-Sep-1964	17	323	17			66	7.4	30	190	14	50	0.2	14	195	39	510	7.2
-34cad	31	3-Sep-1964	17	321	16			58	1.8	59	181	17	72	0.2	11	152	4	550	7.4
-34dab	32	3-Sep-1964	16	355	15			66	3.8	57	195	25	72	0.2	16	180	20	600	7.4
27-15W-6ddd	33	10-Jul-1964	17	218		0.67	0	38	3.2	32	144	18	8	0.4	30	108	0	320		TH, 59
-6ddd	34	10-Jul-1964	19	213	16			51	3.2	21	181	14	5	0.6	14	140	0	330		TH, 128
-34ccc		1-May-1964											6					230
-35cdc	35	27-Nov-1951	16	155	19	0.26		38	5.2	7.6	144	1.6	5	0.2	7.5	116	0
28-11W-18bdc		1-May-1964											18					430
28-12W-14bbd		1-May-1964											240					1,110
-21bad		1-May-1964											22					390
28-13W-1bdb		1-May-1964											48					500
-3aca	36	3-Sep-1964	16	349	20	0.01	0	62	8.2	48	178	33	57	0.1	20	188	22	570	8.3
-3bad		2-Sep-1964		317		0.09	0	57	8.8		185	24	45		24	178		510
-4dbd	37	3-Sep-1964	16	378	16			54	5	82	200	28	84	0.3	15	155	0	640	7.3
-26dcb1	38	14-Jul-1964	16	230	19	0	0	48	3.9	28	181	15	21	0.3	5.8	136	0	360
28-14W-7bbb	39	1964		207	22	0.08	0	38	7.6	25	161	7.4	20	0.3	7.5	126	0	340	7.6
-11bba	40	30-Nov-1951	15	207	17	0.1		51	5.6	16	190	3.3	14	0.2	5.8	150	0
-11bbd		1-May-1964		253				49	5.4		166	7	41		6.2			410
-22ccc		9-Jul-1964	17	196				50	5.1		185	4	9			146		320
28-15W-25cdd	41	2-Sep-1964	16	185	19			44	1.2	18	161	3.2	8	0.2	4	115	0	280	7.1
29-11W-4aaa		1-May-1964											16					500
-29bbb	42	7-Aug-1964	16	287	17			74	2.3	23	254	7.8	13	0.2	13	194	0	460	7.3
-34baa	43	29-Nov-1951	14	171	12	0.14		40	6.8	14	167	4.5	10	0.3	1.5	128	0
29-13W-6baa	44	8-Jul-1964	18	223	21			51	3.2	22	181	8	15	0.3	8.9	140	0	350	7.6
-24ddd	45	1-Sep-1964	16	275	15			67	3.2	18	210	12	10	0.2	23	180	8	420	7.3
29-14W-4cdd	46	27-Nov-1951	16	176	15	0.4		46	5.6	8.5	163	6.2	7.5	0.2	6.6	138	4
-19ddc	47	2-Sep-1964	16	148	19	0.03	0	28	4.4	15	107	5.8	10	0.2	12	88	0	230	8.1
-23bba1	48	2-Sep-1964	20	237	16			54	6.7	18	195	9.1	13	0.2	10	162	2	370	7.6
-23bba2	49	27-Nov-1951	16	209	9.8	0.56		54	6.8	13	196	7.8	8	0.2	12	162	2
29-15W-2dab	50	28-Nov-1951	15	203	15			51	6.2	13	186	8.6	9	0.2	8.4	152	0
-16aaa	51	28-Nov-1951	16	87	14	0.25		17	3.4	4.8	56	6.2	5	0.2	8.8	56	10
1. Well- and test-hole numbering system described in text. 2. Includes potassium reported as sodium. 3. TH, test hole; number (such as 50) designates depth below land surface, in feet, from which water sample was collected for chemical analysis.

Table 5--Factors for converting milligrams per liter to milliequivalents per liter.

Mineral constituent	Chemical symbol	Multiply by
Calcium	Ca++	0.04990
Magnesium	Mg++	.08226
Sodium	Na+	.04350
Bicarbonate	HCO3-	.01639
Sulfate	SO4--	.02082
Chloride	Cl-	.02821
Fluoride	F-	.05264
Nitrate	NO3-	.01613

The chemical analyses in table 4 do not indicate the sanitary quality of the water, although a large amount of certain mineral constituents, such as nitrate or chloride, may indicate pollution. Water containing mineral matter that imparts an objectionable taste or odor may be free from harmful bacteria and safe for drinking. Conversely, water that is clear and pleasant to the taste may contain harmful bacteria. Great care should be taken to protect domestic and public water supplies from pollution. To guard against contamination, a well must be sealed to keep out dust, insects, vermin, debris, and surface water. Wells should not be placed where runoff or leakage from barnyards, privies, or cesspools are possible sources of pollution.

Water from private wells may be tested for bacteriological content by the Division of Environmental Health of the Kansas State Department of Health at little or no cost to the well owner. This service can be obtained by the County Health Officer.

Water to be used for drinking should not contain excessive amounts of iron, magnesium, chloride, sulfate, or nitrate. Water to be used for cooking should have neither an excessive hardness nor a high bicarbonate content. The quality of water in relation to use is described in table 6.

Table 6--Quality of water in relation to use, Pratt County.

Constituent	Principal characteristics	Recommended maximum concentration1(mg/l)
Dissolved solids	Water high in dissolved-solids concentration may have a disagreeable taste or a laxative effect. When water is evaporated the residue consists mainly of the minerals listed in table 4.	500
Hardness	Hardness is caused by calcium and magnesium. Forms scale in vessels used in heating or evaporative processes. Hardness is commonly noticed by its effect when soap is used with the water. Carbonate hardness can be removed by boiling, non-carbonate hardness cannot.	120 (easily detected) 200 (sometimes softened for household use)
Iron (Fe)	Stains cooling utensils, plumbing fixtures, and laundry. Water may have a disagreeable taste.	0.3
Fluoride (F)	Fluoride concentrations of about 1 mg/l in drinking water used by children during the period of calcification of teeth prevent or lessen the incidence of tooth decay. However, concentrations in excess of 1.5 mg/l may cause mottling of the tooth enamel (Dean, 1936). Bone changes may occur with concentrations of 8 to 20 mg/l.	1.5
Nitrate (NO3)	Comly (1945) states that concentrations of 45 mg/l may be harmful to infants. Adverse effects from drinking water high in nitrate concentration are also possible in older children and adults.	45
Sulfate (SO4)	Derived from solution of gypsum and oxidation of iron sulfides (pyrite, etc.). Concentrations of magnesium sulfate (Epsom salt) and sodium sulfate (Glauber's salt) may have a laxative effect on some persons.	250
Chloride (Cl)	Chloride in ground water may be derived from connate marine water in sediments, surface contamination, or solution of minerals containing chloride. Causes water to taste salty and, in high concentrations, increases the corrosiveness of the water.	250
1 Concentration recommended by the U.S. Public Health Service (1962).

The modified Piper diagram (Piper, 1953; Hem, 1959) shown on figure 10 illustrates the chemical type of ground water from 34 wells and 10 test holes in Pratt County. Milliequivalents per liter of cations or anions are plotted as percentages of total milliequivalents per liter of all cations or anions; thus, the position of the analysis on the diagram reflects the predominant anions and cations. The analyses plot in three general groups. The group in the upper left represents waters of the sodium chloride type. All these waters are from the Cairo area. Calcium and bicarbonate are the predominant ions for the analyses in the lower right, which are typical of ground water in the High Plains. The middle grouping of analyses represents mixed waters that probably result from the influx of saline water from Permian rocks.

Figure 10--Modified Piper diagram showing grouping of analyses of water from wells. Numbers by symbols are sample identification numbers from table 4.

The numerical values of these water analyses can be shown graphically by the Stiff technique (Stiff, 1951; Hem, 1959) as an aid in classifying and correlating the water types. The patterns produced by plotting the data are useful for quick comparison of water types. Stiff diagrams representing the three water types found in Pratt County are illustrated on figure 11.

Figure 11--Stiff diagrams of selected analyses of water. A, Calcium bicarbonate water, typical of ground water in Pratt County. B, Mixed calcium bicarbonate and sodium chloride water. C, Sodium chloride water, typical of ground water in the Cairo area. Units are milliequivalents per liter.

Suitability for Irrigation

This discussion of the suitability of water for irrigation is based on Agriculture Handbook 60, U.S. Department of Agriculture (U.S. Salinity Laboratory Staff, 1954).

In areas of sufficient rainfall and ideal soil conditions, soluble salts in the soil or salts added to the soil by water are carried downward by percolation and ultimately reach the potentiometric surface. Soil that was originally nonsaline and nonalkaline may become unproductive if an excess of soluble salts or exchangeable sodium is allowed to accumulate as a result of improper irrigation and soil management. If the amount of water applied to the soil is less than that needed by plants, water will not percolate below the root zone, and mineral matter will accumulate in the zone. Likewise, impermeable soil zones near the surface can retard the downward movement of water and cause waterlogging of the soil and deposition of salts.

The characteristics that seem to be most important in determining the suitability of water for irrigation are the concentration of sodium ion and dissolved solids. For diagnosis and classification, the dissolved solids concentration of irrigation water can be estimated from specific conductance, which is a measure of the capacity of the inorganic salts in solution to conduct an electrical current. The specific conductance can be measured accurately in the laboratory, or it can be approximated by multiplying the total milliequivalents per liter of cations (calcium, magnesium, sodium, and potassium) by 100 or by dividing the dissolved-solids content in milligrams per liter by 0.64.

Salt-sensitive crops such as strawberries, green beans, and red clover may be affected adversely by irrigation water having a specific conductance exceeding 250 micromhos per centimeter, but water having a specific conductance below 750 micromhos per centimeter generally is satisfactory for irrigation, insofar as salt content is concerned. Water in the range of 750 to 2,250 micromhos per centimeter is widely used, and satisfactory crop growth is obtained under good management and favorable drainage conditions, but saline conditions will develop if leaching and drainage are inadequate. Use of water having a conductivity of more than 2,250 micromhos per centimeter is the exception, although a few cases can be cited where such water has been used successfully.

When the sodium-adsorption ratio and the electrical conductivity of a water are known, the suitability of the water for irrigation can be determined graphically by plotting these values on the diagram shown on figure 12. The sodium-adsorption ratio (SAR) is determined by dividing the concentration of sodium, expressed in milliequivalents per liter, by the square root of one-half the sum of the concentrations of calcium and magnesium, also expressed in milliequivalents per liter, as shown below:

Figure 12--Classification of water used for irrigation. Hatchured area includes analyses of water from Holdrege and Grand Island Formations given in table 7.

Low-sodium water (S1) can be used for irrigation on almost all soils with little danger that harmful levels of exchangeable sodium will develop. Medium-sodium water (S2) may be used safely on coarse-textured or organic soils having good permeability, but S2 water will present an appreciable sodium hazard in certain fine-textured soils, especially under poor leaching conditions. High-sodium water (S3) may produce harmful levels of exchangeable sodium in most soils and will require special soil management such as good drainage, leaching, and additions of organic matter. Very high sodium water (S4) generally is unsatisfactory for irrigation unless special action is taken, such as addition of gypsum to the soil.

Low-salinity water (C1) can be used for irrigation of most crops on most soils with little likelihood that soil salinity will develop. Medium-salinity water (C2) can be used if a moderate amount of leaching occurs. Crops that tolerate moderate amounts of salt, such as potatoes, corn, wheat, oats, and alfalfa, can be irrigated with C2 water without special practices. High-salinity water (C3) cannot be used on soils having restricted drainage. Very high-salinity water (C4) can be used only on certain crops and then only if special practices are followed.

Chemical analyses of water from wells in the two major aquifers in the county were selected for determining irrigation suitability (table 7). Specific conductance ranged from 230 to 1,410 micromhos, with the latter value probably being caused by contamination. The analysis of this high-salinity water sample from an irrigation well (27-12W-14adb) in the Cairo area is plotted separately on figure 12. All the other samples are classified as low-sodium (S1) and low- to medium-salinity (C1-C2) water, because they plot within the hatchured area shown on figure 12.

Table 7--Sodium-adsorption ratios and specific conductances of water samples from selected wells and test holes.

Well or test-hole number	Sodium adsorption ratio	Specific conductance micromhos per centimeter at 25° C)
26-11W-30add1	0.91	540
27-11W-18cbb	1.06	510
27-12W-14adb 1	3.40	1,410
27-12W-36bcb	1.35	410
27-13W-34dab	1.68	600
27-15W- 6ddd	1.17	320
28-13W-26dcb1	.97	360
28-15W-25cdd	.48	280
29-11W-29bbb	.62	460
29-13W- 6baa	.73	350
29-13W-24ddd	.51	420
29-14W-19ddc	.60	230
1Analysis plotted separately on figure 12.

The Cairo Area

An investigation of the chemical quality of water in the South Fork Ninnescah River basin is being made currently as part of the cooperative program between the Kansas State Department of Health and the U.S. Geological Survey. The principal objectives are to (1) determine the chemical quality of the water resources, (2) determine the relation between water quality and the major hydrologic and cultural factors that influence water quality, and (3) identify the principal sources and extent of natural and man-made pollution. Such information is essential to wise planning for development of the water resources of the basin.

A. M. Diaz (1965) stated: "The deterioration of water quality in the South Fork Ninnescah River by the inflow of saline waters has been known for many years. Parker and Bailey of the U.S. Geological Survey reported in 1911 that the concentration of chloride in the water of the South Fork Ninnescah increased considerably in the area between Pratt and Kingman [Kingman County]. However, the increase was attributed to inflow from salt mines near Kingman. The occurrence of saline inflow to the river from the slough area between Cairo and Cunningham was reported by the U.S. Bureau of Reclamation in administrative reports of low-flow studies made in 1956."

Water samples are collected during periodic discharge measurements of the South Fork Ninnescah River. The measuring and sampling stations along the river are designated by the number of river miles the station is upstream from the confluence with the North Fork Ninnescah River; thus, station 60.8 is near Cunningham in Kingman County, and station 70.3 is near Cairo. Sampling stations pertinent to the Cairo area are shown on figure 13.

Figure 13--Locations of water-sampling stations and selected wells in the Cairo area.

The discharge of chemical constituents and of the stream at stations in the Cairo area is shown on figure 14. The discharge values increase at a relatively low and uniform rate to station 76.8, which is about 5 river miles east of Pratt. From there to station 66.1, which is 2.5 river miles upstream from the county line, the discharge values increase markedly. The rate of increase is greatest in the 7.7-mile reach between stations 73.8 and 66.1. The dissolved-solids discharge in this reach increases from 30 to 185 tons per day and streamflow increases from 32 to 60 cfs. The increased discharge of chemical constituents is attributed to inflow of saline water in the reach. The increase in streamflow is attributed partly to the saline-water inflow, but primarily to discharge of ground water from the Holdrege Formation. The Fullerton Formation contains a confining layer of silt and clay in the, Cairo area, and water in the underlying deposits of Nebraskan age is under hydraulic pressure. The confining layer has been breached in the South Fork Ninnescah Valley by Wisconsinan erosion, and alluvium and terrace deposits in the river valley are hydraulically connected to the lower Fullerton and to the Holdrege Formations (fig. 15). Ground water from these Nebraskan deposits moves through the alluvium and terrace deposits to the stream. The increased streamflow in the Cairo area is indicated also by the sharp upstream bend of the potentiometric contours shown on plate 1.

Figure 14--Relation of stream and chemical discharge to distance upstream from mouth, South Fork Ninnescah River, April 1963 (A.M. Diaz, written comun., 1965). Locations of water sampling stations are shown on figure 13.

Figure 15--Geologic section showing the hydraulic connection between the alluvium and terrace deposits and the Holdrege and Fullerton Formations in the Cairo area. Trace of section is shown on figure 13.

A limited amount of test drilling and collection of ground-water samples for chemical analysis was done in an attempt to determine the source of the saline water. The sources considered were (1) leakage of oil-field brine from evaporation ponds or through faulty oil-well casing, and (2) inflow of saline water from rocks of Permian age that underlie the South Fork Ninnescah Valley.

Test holes were drilled and cased along a north-northwesterly trend from Cairo toward the oil-producing area near Natrona and Carmi (fig. 13). Water samples for chemical analysis were collected from these test holes and from wells in the area. The samples were collected from various depths and from both the Holdrege and Grand Island Formations. The analyses showed that saline water is present along the trend and that it occurs on the north side of the river only. However, the upper aquifer (Grand Island) did not contain saline water, so leakage from brine-evaporation ponds on the land surface is not considered a likely source of the contamination.

Leonard (1964) has shown that the ratio of sodium concentration to chloride concentration in Kansas oil-field brines is less than 0.60. This value has been confirmed by analyses of 24 brine samples from 18 oil wells in eastern Pratt County in which the sodium to chloride ratio ranged from 0.43 to 0.59 (A. M. Diaz, written commun., 1967). Saline-water contamination was found in seven of the samples collected from test holes drilled in the Cairo area. The sodium to chloride ratios in these samples ranged from 0.64 to 0.70, which is typical of water from Permian rocks, not oil-field brine from rocks of pre-Permian age (A. M. Diaz, written commun., 1967). The chemistry of the water, therefore, indicates that the contamination is by upward leakage of saline water from rocks of Permian age that underlie the South Fork Ninnescah Valley. The conclusion of a natural rather than a man-made source is further supported by the fact that the contamination was known many years before oil production began in Pratt County.

Further study of the Cairo area is needed to determine whether (1) saline water moves upward along a geologic fault in eastern Pratt County (fig. 5), or (2) the ancesteral South Fork Ninnescah River has eroded the Permian rocks sufficiently to permit direct movement of saline water into the Holdrege Formation. Hydraulic pressure that would cause movement of the water, by either path, is known to exist. Parker (1911, p. 160) reported that salt water rose to within 15 feet of land surface in an 800-foot deep well drilled at Pratt. Pressure sufficient to raise water this high would cause saline water to move into the Holdrege Formation, into the alluvium and terrace deposits, and, eventually, into the river.

Summary and Conclusions

Ground water is an important factor in the economy of Pratt County. The future population and economic growth of the area depend largely on the availability and extent of development of the ground-water resource.

Pratt County is fortunate in being underlain by extensive aquifers from which good-quality water can be withdrawn by wells. Well yields of 500 gpm are possible almost anywhere in the county, and yields of 2,000 gpm are possible in much of the area. Even though ground water in the Holdrege Formation near Cairo is contaminated by upward leakage of saline water from Permian rocks, good-quality water is available from wells completed in the shallower Grand Island Formation.

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Kansas Geological Survey, Geology
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