Geological Survey Water-Supply Paper 1475-Q Present and Future Water Supply for Mammoth Cave National Park, Kentucky

GREEN RIVER

The Green River is the largest potential source of water supply for Mammoth Cave National Park. It drains 1,983 square miles of central Kentucky. The runoff from 444 square miles of this area does not reach the river through surface streams but drains into limestone sinks.

QUANTITY

Flow-duration curves for Green River at Mammoth Cave (fig. 74) show the percentage of time during which specified discharges are equaled or exceeded in a given period. For example, in the period 1916-22, 1928-31, 1938-61 (water years), the daily mean flow of Green River (fig. 74) was at least 205 cfs, or 132 mgd, during 90 percent of the time. The curve for this period was obtained from the curve for the actual period of gaging-station operation, 1939-50 (water years) and from records for the gaging station at Munfordville,

FIGURE 74.—Duration curves of daily flow, Green River at Mammoth Cave, Ky. (click on image for an enlargement in a new window)

Figure 75 shows low-flow frequency curves for Green River at Mammoth Cave. A low-flow frequency curve is defined (Langbein, 1960, p. 13) as a graph showing the magnitude and frequency of minimum flows for a period of given length. For example, the minimum 7-day flow is expected to be less than 150 cfs (97 mgd) at average intervals of 2 years (fig. 75).

FIGURE 75.—Magnitude and frequency of low flows, Green River at Mammoth Cave, Ky. (click on image for an enlargement in a new window)

The curves in figure 75 were obtained from the records at Mammoth Cave for the period 1939-49 (climatic years) and were extended to the longer period 1915-21, 1928-30, 1938-60 (climatic years) on basis of records at Munfordville.

Flow-duration and low-flow frequency analysis thus shows that there is an ample quantity of water in the Green River at all times without storage for any present or future needs of Mammoth Cave National Park.

A frequency curve of annual floods is shown in figure 76. The curve was obtained from a regional flood-frequency analysis by McCabe (1962). The right ordinate scale is expressed in feet above the zero of the gage at Mammoth Cave Ferry and the left ordinate scale is expressed as discharge in cubic feet per second. For example, a flood having a recurrence interval of 20 years can be expected to reach a gage height of at least 51.0 feet and a discharge of at least 70,400 cfs. This in no way implies that once a flood having a stage of 51.0 feet and a discharge of 70,400 cfs occurs that it will not recur for another 20 years. The curve merely shows that on the basis of past flood experiences at gaging stations in this flood region and hydrologic area of Kentucky, a flood of 70,400 cfs, or higher, can be expected to occur on a long-term average of once every 20 years. This curve can be used for location and planning of water-supply structures above floods of selected frequencies.

FIGURE 76.—Frequency of annual floods, Green River at Mammoth Cave, Ky. (click on image for an enlargement in a new window)

Two reservoirs on the Green River are being considered by the U.S. Army Corps of Engineers. Green River Reservoir, 108 miles upstream from Mammoth Cave, is presently (1962) in the design stage. The reservoir is to be a flood control and water-quality control project. When built, the reservoir will augment low flows and reduce flood peaks in the Green River at Mammoth Cave. The other project, Mining City Reservoir, 93 miles downstream from Mammoth Cave, has been deferred for further study. Details of the design of the Mining City Reservoir are not known to the authors, but magnitude of flood flows or low flows at Mammoth Cave would not be affected.

QUALITY

Water in the Green River in the vicinity of Mammoth Cave prior to 1958 was suitable for nearly all uses with little or no treatment. From 1958 to 1961, however, the water was polluted by oil-field brine. Enforcement of pollution-control regulations and a decline in oil production has resulted in a marked improvement in water quality since that time. Since November 1961, the water in the Green River has met U.S. Public Health Service drinking-water standards every day in the year.

Since October 1, 1950, the U.S. Geological Survey, in cooperation with the Commonwealth of Kentucky, has maintained a daily sampling station on Green River at Munfordville, Ky., about 29 miles upstream from the ferry at Mammoth Cave National Park. The sampling station is operated to provide chemical-quality, water-temperature, and sediment data for the upper Green River basin. The basic assessment of water-quality conditions of the Green River in the park is made primarily on the data collected at the Munfordville station. Data collected from the Green River in the park shows local conditions and dilution effects in the 29-mile reach, The reliability of the data collected from the Green River in the park is increased greatly by the long daily record collected at Munfordville.

The quality of water in the Green River is normally good. However, waste brine from oil production in the Greensburg field in Green and Taylor Counties was discharged into the Green River in large quantities and drastically changed the quality of the river. Later, these practices were corrected. Some oil production also occurred in Metcalfe County, but it never reached the boom conditions characteristic of the Greensburg field. A summary of the chemical quality of Green River water is given in table 2. The 13 years of record summarized in the table are divided into four periods to show the drastic change in the quality of Green River water due to the increase and decrease in brine pollution. The effects of brine pollution were revealed principally in the analyses for dissolved solids, hardness, and chloride. Brine had little or no effect on the amount of bicarbonate (alkalinity), pH, color, or suspended sediment in the Green River.

TABLE 2.—Chemical quality of Green River at Munfordville, Ky., October 1, 1950-January 31, 1963
[Chemical analyses in parts per million]

The key to the potability of the Green River is the number of days each year the chloride concentration is within or exceeds U.S. Public Health Service drinking-water standards of 250 ppm (parts per million) chloride. Table 3 gives these days for both the long-term water-quality station at Munfordville and the short-term station at Mammoth Cave.

TABLE 3.—Oil production in the upper Green River and its effect on the potability of Green River water

Chloride measurements at Mammoth Cave Ferry and at Munfordville show considerable dilution caused by ground-water flow into Green River within the 29-mile reach. Consequently, the quality of water at Green River at Mammoth Cave was always better than at Munfordville. The dilution not only reduced the concentration of chloride but also reduced the number of days in which the water exceeded drinking-water standards for chloride at Mammoth Cave. The chloride content at Munfordville (fig. 77) has not exceeded 250 ppm any day since December 1961 and at Mammoth Cave, since November 1961. Even the unusually low flows of the Green River in July-September 1962 did not produce chloride concentrations at Munfordville or at Mammoth Cave in excess of 250 ppm. Much of the brine currently appearing in Green River probably is due to drainage of residues of brine that polluted fresh-water aquifers previously. The data show that some oil production with proper disposal of waste oil brine does not seriously affect the quality of Green River water. There is every reason to believe that Green River water could be used to augment the water supply of Mammoth Cave National Park. Use of the river water would require chlorination and the removal of suspended sediment, which could be done with commercially available water-treatment systems.

FIGURE 77.—Chemical composition of water of highest salinity during July-September, Green River at Munfordville, Ky. Number at top of bar is concentration of dissolved solids, in parts per million, of composite sample. Date at top of bar shows days in composite sample.

The Green River basin upstream from Mammoth Cave National Park contains only eight towns having a combined population in 1960 of 18,137. Not all of these towns have adequate sewage collection and treatment systems; however, this condition is being corrected rapidly. Columbia, Campbellsville, and Greensburg have modern sewage-treatment plants. Munfordville began construction of a collection system and treatment plant in the summer of 1963. Horse Cave, Cave City, Edmonton, and Liberty have plans and construction grants approved or pending. It appears that collection and treatment of sewage in the upper Green River basin will be adequate in the near future. However, any surface water source would need chlorination to be acceptable for public use.

SUSPENDED SEDIMENT

In contrast to ground-water sources, the Green River contains appreciable amounts of suspended sediment. Sediment characteristics of the river have been studied by the Geological Survey at the Munfordville sampling station for more than 12 years. The sediment in the Green River is almost entirely suspended because there is very little bed load. The sediment is fine, as shown by the following table. Consequently, the Green River carries a smaller volume of sediment than its muddy appearance would indicate.

Suspended-sediment characteristics of the Green River since April 1950

Suspended-sediment concentration varies widely during the year. On the basis of the measurements at Munfordville, concentrations of suspended sediment in the Green River are distributed as follows:

Surprisingly, the period of July-September contains about the same proportion of days of low concentration as the entire year.

NOLIN RIVER

The Nolin River drains 727 square miles of central Kentucky. Water from about 223 square miles of this area does not drain into the Nolin River through surface streams but into limestone sinks. The Nolin River flows into the Green River near the western edge of Mammoth Cave National Park and 8 miles west of Mammoth Cave. Above Nolin River Dam, 8 miles upstream from the mouth of the river and 10 miles northwest of Mammoth Cave, the river drains 707 square miles (of which about 223 square miles does not contribute directly to surface runoff). Storage of water in the reservoir behind the dam started in March 1963. Minimum releases from the reservoir will probably be about 150 to 200 cfs (97 to 129 mgd).

The Nolin River water is moderately hard to very hard but is generally well within the limits of drinking-water standards. A summary of chemical quality is given in table 4. Nolin River water would require chlorination and probably removal of sediment or turbidity.

TABLE 4.—Chemical quality of water in Nolin River, Wet Prong Buffalo, Dog, Bylew, and Beaver Dam Creeks
[Chemical analyses in parts per million]

WATER FROM SMALL STREAMS

A reconnaissance of small streams was made in the Mammoth Cave National Park area during the period August-November 1961. Measurements or estimates of flow and observations of no flow were made at many points. Additional measurements of flow were made at selected locations during the period June-December 1962. The results are summarized in table 5.

TABLE 5.—Discharge measurements made in Mammoth Cave National Park area excluding Green and Nolin Rivers, Flint Ridge springs, and Pike Spring

(click on image for an enlargement in a new window)

Many streams in the area are wet-weather streams; that is, they carry storm runoff only and are dry most of the time, However, an observation of no flow at one point on a stream does not necessarily mean that the stream does not have flow in it somewhere upstream or downstream. (See below.) Therefore, the results of the reconnaissance made in 1961 are not complete. A complete reconnaissance would necessitate observing each stream channel from the divide to the mouth; however, it is believed that the most important perennial surface flows have been observed. All references to streamflow are under dry-weather conditions.

Wet Prong Buffalo Creek is probably the best potential supply from a small stream. A discussion of the perennial streams and information not included in table 6 follows. Because of its importance remaining small Buffalo Creek is discussed first, followed by the streams.

TABLE 6.—Chemical quality of Styx River, Echo River, and Pike Springs
[Chemical analyses in parts per million]

DESCRIPTION AND DISCHARGE

Buffalo Creek.—Wet and Dry Prongs of Buffalo Creek are aptly named. The flow of several small springs in the Dry Prong Buffalo Creek basin is suitable for small local supplies, but the flow disappears into the streambed at some point downstream. Wet Prong Buffalo Creek is fed by springs in the headwater tributaries. The Wet Prong is a perennial stream to some point between Pigeon Hollow and the confluence with Dry Prong. At the confluence both prongs are dry. Flow from two springs (see table 5) enters Buffalo Creek between the confluence of the two prongs and the mouth of the creek. Presumably the flow that disappeared into the streambed of Wet Prong downstream from Pigeon Hollow reappears in the larger of the two springs tributary to Buffalo Creek. However, the Buffalo Creek tributary springs are near Green River level. Data collected to date indicates that the minimum flow to be expected in Wet Prong is probably about 300,000 gpd. This supply is ample for present or future needs of Mammoth Cave. Most of the drainage area of Wet Prong lies within the park, which will assist pollution control of the watershed. The principal disadvantage of this source is that it is 5 miles from Mammoth Cave and on the north side of the Green River.

Three Sisters Hollow.—The interruption of streamflow is evident in Three Sisters Hollow. On September 7, 1961, no flow was observed in the westernmost tributary and in the main stem throughout its length, but Blair Spring, a tributary of Three Sisters Hollow, was undoubtedly discharging some water that never reached the main stem.

Big Spring Hollow.—The flow of Big Spring Hollow was 1.49 cfs (963,000 gpd) September 8, 1961. However, this flow was from a spring on the right bank of the hollow about 200 feet upstream from the mouth of the hollow. Because the spring is at Green River level and the hollow is on the north side of the Green River, its potential as a source of water supply for Mammoth Cave National Park is negligible.

Ugly Creek.—A small tributary spring of Ugly Creek is near the north boundary of the park. Flow on August 22, 1961, was less than 3,000 gpd. The spring could be used as a small local supply but is too small to be considered for any other purpose. The discharge from the spring disappeared into the streambed at some point upstream from a ford over Ugly Creek, 1.3 miles upstream from its mouth. On September 6, 1961, a discharge of 0.5 cfs (323,000 gpd) was estimated at the mouth of Ugly Creek, but most of this flow was from a spring on the right bank 800 feet upstream from the mouth of Ugly Creek and near Green River level.

Big Hollow.—The flow was 0.025 cfs (16,200 gpd) November 2, 1961, in the headwaters of Big Hollow. This water disappeared into the streambed a short distance downstream, and the streambed was dry from this point to the mouth. This water could be a local source, but the supply is too small and the distance too far to be a source for Mammoth Cave.

Floating Mill Hollow.—Several local people reported the existence of a "large" spring in the upper part of the drainage basin of Floating Mill Hollow. No spring was found except at a point 150 feet upstream from time mouth of the hollow and below Green River flood level; thus its potential as a source of water supply is negligible.

Styx and Echo Rivers.—Discharge measurements made since 1953 are listed in table 5. These streams are discussed on page 631.

Closed basin near Pig.—A closed basin of about 4 square miles north west of Pig has a well-defined drainage pattern. The runoff from this basin probably enters the Green River through underground passages at or near Turnhole Bend. A total of about 0.5 cfs (323,000 gpd) was estimated in several branches of this tributary about 1 mile northwest of Pig on October 30, 1961. However, this combined flow disappeared into the streambed a short distance downstream, and the tributary was dry from this point to its end at a sinkhole. Its distance from Mammoth Cave (about 5 miles) and its location outside the boundary of the park precludes considering the tributary as a potential source of water supply.

Sal, McCoy, and Dry Hollows.—Small flows were observed at or near the mouths of Sal, McCoy, and Dry Hollows. However, these supplies are below Green River flood level.

Dog Creek.—The drainage area of Dog Creek, a tributary of the Nolin River, lies outside the park to the north. Quantity and quality of the water are satisfactory, but the distance of the tributary from Mammoth Cave and its location outside the park and north of the Green River probably precludes its use for a source of water supply for Mammoth Cave. Results of measurements of flow of Dog and Little Dog Creeks are shown in table 5.

Bylew, First, and Second Creeks.—Three streams—Bylew, First, and Second Creeks—tributary to the Nolin River are perennial, but their distance from Mammoth Cave and proximity to the Nolin River with its larger flow would dictate that the Nolin River be used as a possible source. However, these smaller streams might be used to supply local areas within the undeveloped part of the park. Discharge measurements or estimates are listed in table 5.

Beaver Dam Creek.—Beaver Dam Creek, a tributary of the Green River, is 6-8 miles southwest of Mammoth Cave. It is a perennial stream, but its distance from Mammoth Cave and location outside the park probably preclude its use as a potential source of water supply for Mammoth Cave. See table 5 for results of discharge measurements.

QUALITY

A summary of the chemical quality of water from four of the small streams is given in table 4. Water from the four small creeks is of better quality and very similar to that from Three Springs. Water from Wet Prong Buffalo Creek is soft, and that from the other three small creeks is moderately hard. The small creeks usually are clear except after a storm. These small streams would probably require only chlorination most of the time.

WATER IN ALLUVIUM ADJACENT TO GREEN RIVER

Ground water in the alluvium adjacent to the Green River is a potential source of water supply for Mammoth Cave National Park. However, the permeability and water-yielding capacity of the alluvial material is low, and the potential is probably small. The development of a municipal supply of adequate yield from sand and gravel in the Green River alluvium at Brownsville, about 18 miles downstream from Mammoth Cave, prompted the exploration of this source at Mammoth Cave. Eight exploratory test holes were angered into the alluvial terrace on the bank of the Green River between the Styx and Echo Rivers in October 1961. All test holes were bottomed on resistant material, probably limestone, at depths ranging from 25 to 35 feet below land surface. All penetrated compact yellowish-brown silt and clay but no sand or gravel.

The alluvium in the bed of the river in this area, as at Cave Island upstream from the mouth of Styx River, may be coarser and more permeable, but it was not tested. If found to consist of coarse sand and gravel, this alluvium, which undoubtedly would have hydraulic continuity with the river, could yield substantial supplies of water to properly constructed wells. Development of this source by vertical wells or a horizontal collector well would necessitate that the well be constructed to a level above the highest flood stage of the river.

Water obtained from wells in the alluvium would consist, in part, of water infiltrated from the Green River, and thus would be similar in quality to the river water. Water pumped from the aforementioned well at Brownsville, for example, contains an undesirable concentration of iron and, during the period when the Green River was contaminated by oil-field brines, contained a high concentration of chloride.

GROUND WATER IN BEDROCK

BASAL GROUND WATER

GENERAL CONSIDERATIONS

The basal ground water in the Mammoth Cave area is contained in, and moves through, a thick sequence of limestones, the Ste. Genevieve and St. Louis Limestones. The occurrence of water in these limestones is described in detail by Brown. (See footnote 1, p. 606.)

The storage and movement of ground water in limestone in the Mammoth Cave area is confined to numerous openings along interconnected joints and bedding planes. Most openings have been enlarged by solution, and large quantities of ground water move through them at relatively high velocities. The body of basal ground water, although confined to random openings, is continuous and is controlled by the Green River. The upper surface is continuous with the level of the Green River, and all openings below this level are completely saturated.

Recharge to the basal ground-water body comes from several sources: (1) The sinking streams that drain the surface of the Pennyroyal plain and disappear into sinkholes before they reach the Dripping Springs escarpment, (2) local precipitation on the Mammoth Cave plateau, which moves rapidly downward through sinkholes or vertical shafts or percolates slowly downward along innumerable conduits of different diameters and shapes, and (3) recharge from the Green River in time of flood. No information on the total amount of recharge or the amounts from the several sources is available. Except for the part that is lost by evapotranspiration (about 50 percent), most of the precipitation ultimately reaches the basal water body. Thus, 24 inches of the annual precipitation, or an equivalent of about 420 million gallons per year for each square mile, recharges this body.

Recharge from the Pennyroyal plain is continuous throughout the year and is greatest in the winter. Recharge from the Mammoth Cave plateau is intermittent; it is large in winter but is negligible during the late summer and fall.

The general movement of basal ground water in the area is northwestward from the Pennyroyal plain to the Green River. The water table slopes in this general direction from an altitude of about 570 feet on the Pennyroyal to 420 feet at Green River level. The water probably moves in several large conduits or drains trending generally northwestward. Large conduits probably underlie the Mill Hole-Cedar Sink area and the Mammoth Cave plateau. Their specific location and the location of other large conduits will have to await the results of further exploration and tests. The large conduits are adjoined by numerous smaller cross conduits of many diameters and shapes.

The large and small conduits discharge to the Green River through such springs and underground streams as Pike and Sand Cave Springs and the Echo and Styx Rivers. The magnitude of the low flow from these points of discharge is indicated by flow data of the Echo and Styx Rivers listed in table 5.

DEVELOPMENT

Basal ground water in the Mammoth Cave area can be developed by deep drilled wells or by direct pumping from known large conduits, such as the underground parts of Echo River in Mammoth Cave. The basal ground water in the vicinity of the developed area of the park is contained in the Ste. Genevieve and St. Louis Limestones.

The success of a drilled well depends on its intersecting a trunk conduit or one of the numerous cross conduits at an altitude equivalent to that of the basal water table. The conduits are controlled by the systems of joints and by bedding planes, and their locations are difficult to predict in advance of drilling. In fact, drilling into the larger water-filled conduits requires considerable luck. The few wells in the area of Mammoth Cave plateau that have been drilled to the basal ground water all yielded water, but none yielded significantly large supplies. The test well in Eaton Valley, pumped for 8 hours at an average rate of 36 gpm, is probably the largest-yielding well penetrating the basal water in the plateau area. The well at Bransford Spring was pumped throughout the summer of 1962 at an average rate of 14 gpm. The depth to water is usually great; wells on the Mammoth Cave plateau generally reach water at about 400 feet below land surface.

Basal ground water also can be developed by pumping it directly from known flooded underground passages, such as Echo River in Mammoth Cave and the flooded passage in the lower level of Great Onyx Cave. The dry-weather yield of these sources, if no water is taken from storage, is probably equal to the low-flow data of Echo River and Pike Spring given in table 5. Withdrawals greater than the low flows would be from storage in the submerged passages below the water level. Little is known of the configuration and volume of the submerged parts of the passages, and no estimate can be made of the amount of water in storage, but the amount is probably large. However, withdrawals greater than the low flow at known points of outflow would cause a lowering of the water surface. Such lowering may induce recharge of water from the Green River, which would maintain the yield but would probably change the quality of the water.

QUALITY

Styx River, Echo River, and Pike Springs drain the basal water table at about the same level as the Green River. They become flooded whenever the Green River is in flood, and consequently can yield water that is either basal ground water or Green River water and at times a mixture of the two waters. Sediment concentration, chloride, and pollution depend to a large extent on the stage of the Green River, but these effects are usually diluted by the normal water of the springs. The Green River seems to back up into Pike Spring and Styx River Spring more readily and frequently than into Echo River Spring. The daily analyses of Echo River and Styx River Springs show that the quality of water flowing from Echo River Spring is not influenced by the Green River nearly as much as the other two springs. A summary of the quality of water from the three springs is shown in table 6. With the improvement in quality of the Green River water, the three springs are acceptable sources of water. Echo River Spring, however, is the best of the three. In Mammoth Cave, suspended-sediment concentrations are usually less than 20 ppm at low flows of the Green River. At higher flows concentrations of 40 ppm have been measured several times, and much higher concentrations probably occur.

The chemical quality of water from wells tapping the basal ground water body generally is similar to that from Echo, Styx, or Pike Springs when the latter are draining into the Green River (see table 7). Because the wells tap the basal water distant from the Green River, the chemical quality and turbidity are not affected by Green River flooding. However, the water from the Eaton Valley well (table 7), is of poor and contrastingly different quality from the average quality of the basal ground water. This well was drilled considerably below the basal water table in an effort to increase its yield. It is believed that it penetrated deeper water of a poorer quality, and that this water is now moving upward in the bore and mixing with the upper basal ground water. To insure that it will yield good quality basal ground water, a well should not be drilled more than 20 to 30 feet below the basal water table in the Mammoth Cave area.

TABLE 7.—Chemical analyses of water from wells and springs, Mammoth Cave National Park
[Dissolved constituents given in parts per million]

(click on image for an enlargement in a new window)

PERCHED GROUND WATER IN BEDROCK

The geology and topography of the Mammoth Cave plateau area combine to create conditions favorable to the formation of several zones of perched ground water. These zones are: (1) a generally continuous body of ground water in the Haney Limestone Member of the Golconda Formation (fig. 73) perched above shale beds in the lower part of the Haney, (2) a generally continuous body of ground water in the Big Clifty Sandstone Member of the Golconda Formation perched above a shale at the base of the Big Clifty, and (3) discontinuous bodies of ground water perched above local shale beds near the top of the Girkin Formation.

PERCHED GROUND WATER IN HANEY LIMESTONE MEMBER OF THE GOLCONDA FORMATION ON FLINT RIDGE

The following discussion is concerned only with the occurrence of perched ground water in the Haney Limestone Member of the Golconda Formation on Flint Ridge. Similar conditions may occur elsewhere, as east of Rhoda and north of the Green River, but all are distant from the area of present use.

GENERAL CONSIDERATIONS

The Haney Limestone Member and the overlying Hardinsburg Sandstone and the underlying Big Clifty Sandstone Member are the so-called caprocks that form Flint Ridge. The thick Big Clifty forms the cliffs around the margin of Flint Ridge. The Haney, only about 40 feet thick in this area, is exposed in places above the Big Clifty along the margin of the ridge at an altitude of about 740-760 feet. The caprocks are broken by numerous joints. The openings along joints in the Hardinsburg Sandstone and Big Clifty Sandstone Member are small. The openings along joints in the Haney are enlarged by solution, and the limestone is cavernous.

Almost all the precipitation on Flint Ridge either sinks into the permeable surface rocks or runs off in short intermittent streams to the edge of the ridge and is diverted downward in underground drainage channels in the Girkin Formation to the basal water table. Probably more than 50 percent of the precipitation is disposed of in this manner; the remainder is evaporated or transpired. Water penetrating the permeable surface rocks on Flint Ridge moves downward until it reaches the relatively impermeable shale at the base of the Haney Limestone Member and then moves laterally in solution channels in the limestone to emerge as seeps or springs along the margin of the ridge. This outflow also sinks to the basal water table via the solution channels in the Girkin Formation. Some of the lateral flow probably never appears at the surface along the margin but is abruptly diverted downward in places where the impermeable shale is breached by joints.

The solution openings in the Haney may have considerable reservoir capacity, and thus may sustain the flow of the visible springs during dry periods longer than those previously experienced. Several test wells drilled in April 1961 on the surface of Flint Ridge to the base of the Haney penetrated a body of ground water, the upper surface of which was in the overlying Hardinsburg Sandstone. Thus, at these locations in April 1961 the Haney Limestone Member was completely saturated. At the lowest observed decline of this water surface in October 1962, about 20 feet of the Haney was saturated.

Part of the outflow probably emerges as slow seepage, along the margin of the ridge at the outcrop of the lower part of the Haney Limestone Member and is rarely seen. However, part of the outflow emerges as visible springs having flows ranging from several hundred gallons per minute in early spring to less than 10 gpm in late fall. Seven such springs are known on Flint Ridge. In addition to the springs already mentioned in the section on present water supply (Three Springs and Bransford, Blair, and Adwell Springs), there are also Cooper and Collins Springs and a spring at CCC No. 1. Typically, these springs emerge from small caverns in the Haney at the head of deep reentrants on the sides of Flint Ridge, flow down the surface of the Big Clifty Sandstone Member for short distances, and sink into openings in the surface.

DEVELOPMENT

The perched ground water in the Haney Limestone Member can be developed by collecting the flow from the seven springs, as has been done in part, or by means of wells drilled from the top of the ridge to solution channels near the base of the limestone.

The flow of CCC No. 1 Spring is small, 4 gpm or less, and the flow of Bransford and Blair Springs decreases to 7 gpm or less near the end of the dry season. The flow of the rest of the springs is remarkably similar, the dry-weather flow being about 14-16 gpm. The graph of the flow of a typical spring is shown in figure 78. All observed flows from the seven springs are furnished the Park Service in monthly reports. Minimum flows during the critical period in August 1962 and minimum observed flows of all springs are summarized in the following table.

FIGURE 78.—The flow of Three Springs, Mammoth Cave National Park, is lowest in September and October. (click on image for an enlargement in a new window)

During the critical week of August 19-25, 1962, the developed supply of 45 gpm, or 64,800 gpd (includes Bransford well), could have been supplemented by an additional flow of 57 gpm or 82,000 gpd, had the minimum August flow of the additional springs been utilized. If it is assumed that the minimum flows observed later in 1962 represent the August flows of an extremely dry year, this supplemental supply would be reduced by 11.5 gpm to a supply of 45.5 gpm, or 65,500 gpd. Thus, during an extreme year, if the flow of the seven springs were collected and Bransford well were pumped 24 hours per day, the total available supply in August would be 84.5 gpm, or 121,700 gpd.

It is possible that the flow of one or more springs could be diverted or captured by natural means and the spring dried up. An enlargement of an underground opening by solution or a slight shifting and opening of a previously tight joint could cause this change. However, the chance of this happening is remote, and long-time residents remember that these springs have always flowed at their present locations.

Wells drilled to water-bearing solution channels in the limestone from the top of Flint Ridge are a potential means of developing the perched water. The test wells drilled in April 1961 provide information on the feasibility of this method of development. Because the solution channels are controlled by joints, one might assume that the flow of water would he concentrated along these channels and could not be found elsewhere. Of the four test wells, all penetrated solution channels in the limestone immediately below the base of the Hardinsburg Sandstone, and all but one channel contained water. The yield from these wells was small, less than 10 gpm, and all wells had difficulty with sand and silt particles washing out from the channels or caving from the bottom of the Hardinsburg Sandstone. Thus, it is probable that ground water in the Haney Limestone Member would be difficult to obtain in sufficient quantity to be useful as a supply. Wells too close to existing springs might decrease the flow of the springs if pumped heavily.

QUALITY

Perched ground water in the Haney has the best quality and is the most suitable for use of all water in the Mammoth Cave area.

The chemical quality of 37 samples of water from Three Springs obtained during the period October 1954-May 1962 is summarized in the following table. Analyses are shown in table 7.

Water from Adwell, Bransford, Blair, Collins and Cooper Springs, and the spring at CCC No. 1 is similar in quality to water from Three Springs. Water from most of the springs seems to have a low iron content, but this may not always be true because all water shows some variation in quality.

PERCHED GROUND WATER IN BIG CLIFTY SANDSTONE MEMBER OF THE GOLCONDA FORMATION AND GIRKIN FORMATION

A potential water supply is contained in a continuous body of ground water in the Big Clifty Sandstone Member and in discontinuous bodies in the underlying Girkin Formation.

GENERAL CONSIDERATIONS

The Big Clifty Sandstone Member caps a major part of the Mammoth Cave plateau and crops out in many places on the surface of the plateau and along the sides of many of the valleys. On Flint Ridge it is overlain by beds of shale, limestone, and sandstone. Where the Big Clifty is the surface rock, it absorbs large amounts of water from precipitation through pore spaces and openings along numerous joints. Where it is overlain by other rocks on Flint Ridge, the Big Clifty is largely protected from water infiltration and probably receives water only where the overlying rocks are breached by joints, principally near the margin of the ridge.

Percolating water from precipitation moves downward to the relatively impermeable shale at the base of the sandstone. A perched body of ground water which is nearly continuous throughout the formation is supported in the sandstone by this shale. Part of the water drains laterally to points of discharge along the sides of valleys and the Dripping Springs escarpment, and part drains downward and recharges the Girkin Formation where the shale bed is locally absent or where it is broken by joints. In the Girkin Formation water flows downward through solution channels of different sizes and shapes to the basal water table. In some places this water is perched in small solution depressions or above local thin beds of shale.

DEVELOPMENT

Perched water in the Big Clifty Sandstone Member and the Girkin Formation is developed by drilled wells; some water in the Big Clifty is obtained by dug wells. Most wells on the Mammoth Cave plateau obtain water from the Big Clifty. The depth from the surface to the water table in the perched body of water in the sandstone ranges from about 2 to 20 feet. Yields of wells are not large but are reported to be adequate for domestic use. Dug wells 2 to 3 feet in diameter yield adequate quantities for domestic and stock use.

Wells drilled into the Girkin Formation obtain small supplies of water at numerous levels. Water levels in these wells change rapidly with heavy rains and dry spells, and some wells go dry. In some wells the water supply may be only a gallon or two a day; in others it may, with normal precipitation, be adequate for a domestic supply, although it will likely fail in dry summers. Commonly, none of the perched water bodies in the Girkin Formation are adequate for year-round domestic supplies with pressure systems installed.

QUALITY

The chemical quality of water from the Big Clifty Sandstone Member is suitable for most uses. It is soft and slightly acid but sometimes contains objectionable amounts of iron. Because of its widespread occurrence at the surface, water in the Big Clifty is subject to pollution from barnyard and other agricultural wastes. No samples of water were taken from wells obtaining water exclusively from the Girkin Formation. The water is probably similar in quality to that from the Haney Limestone Member, but it may be harder.