Figure 1. Ground-water resources of Darke County, Ohio (adapted from Ground-Water Resources of Darke County map, J. M. Raab, 1993, ODNR Division of Water; illustration prepared by J. Humphreys).
James R. Sutherly
James M. Raab
Larry C. Brown
Karen T. Ricker
Water stored under the earth's surface is a plentiful, yet precious, resource in most areas of Ohio. Many human activities may affect the quality and quantity of this resource. However, the availability and quality of this resource are influenced directly by the properties of the geologic formations that hold water. The chemical and physical nature of these formations varies from area to area, creating a wide range of water yields and quality at different depths. This publication contains information about the ground-water resources underlying Darke County. Its purpose is to help the reader better understand the factors that influence the quantity and quality of ground water. An overview of the county's water resources is provided in the publication Water Resources of Darke County, AEX-480.19.
Much of the water resource and water quality terminology used in this publication is described in Extension Fact Sheets AEX 460 and 465. Extension publications are available through the Darke County office of Ohio State University Extension.
Geologic formations (e.g., sand, gravel, limestone, sandstone) have the ability to receive, store and transmit water. In general, if a formation is capable of yielding enough water to support a well or spring, it is called an aquifer. The material from which the formation originally was made influences its ability to store and transmit water. For example, sand and gravel allow water to flow through easily. By comparison, shale, which originated from compacted layers of mud and clay, generally allows very little water to flow through it unless the shale is highly fractured.
The regional carbonate aquifer, which is composed of layers of limestone and dolomite, is the principal source of ground water in west-central Ohio, including Darke County. Limestone is consolidated limy mud or calcareous sand, with fossil shells and shell fragments. The main mineral in limestone is calcium carbonate, CaCO3. Dolomite is similar to limestone; its main mineral is calcium magnesium carbonate, (Ca,Mg)CO3. Limestone and dolomite are technically carbonate rocks, though both are commonly referred to as limestone. The limestone and dolomite formations, which underlie most of the western portion of Ohio, were deposited about 400 to 450 million years ago. These formations are covered by a layer of glacial till, which is an unsorted mixture of clay, silt, sand, gravel and boulders, deposited by glacial processes that occurred approximately 10,000 to 20,000 years ago.
Limestone formations usually are adequate sources of ground water because of their naturally formed solution channels, joints and fractures, which provide water storage capacity and pathways for water movement. The number of fractures and other openings in limestone varies greatly from one location to another and affects the amount of water that may be encountered when drilling a well. The position of such openings rarely can be determined from the land surface; therefore, there is always some uncertainty as to the production capability of a proposed well. Ground water also occurs in lenses (or pockets) of sand and gravel deposited by glacial processes. These deposits occur above the carbonate bedrock and may be interbedded in the glacial till or deposited in stratified layers. Glacial till generally does not provide enough water to support a well.
Contact the Ohio Department of Natural Resources (ODNR), Division of Geological Survey, for information on Ohio's geologic formations (Fountain Square, Columbus, OH 43224-1362).
The actual yield of a well, in gallons per minute (gpm), will vary considerably depending on the age and depth of the well, the diameter of the casing, well construction, pump capacity and age, and most importantly, properties of the geologic formation. The exact yield and depth of each well will depend on the properties of the geologic formation at the specific location of the well.
To support the development of ground-water availability assessments in Ohio, the Ohio Department of Natural Resources (ODNR), Division of Water, maintains a statewide database of more than 700,000 well logs. The Ground-Water Resources Section of the Division manages this valuable database, which includes some information collected by the U.S. Geological Survey (USGS) and the Ohio Environmental Protection Agency (Ohio EPA). Since 1948, well-log information has been collected to increase the understanding of the ground-water resources in Ohio. Geologists and hydrogeologists continue to study the state's ground-water resources. As a result, Ohio is one of only a few states that has been completely mapped for ground-water availability (mapped by river basin, from 1959 to 1962).
Estimates of the size, shape, geologic make-up and yields of aquifers are being mapped county by county. Most of Ohio's counties have a completed map. The map presented in Figure 1 is a generalized representation of the water-bearing formations underlying Darke County (adapted from map by J. M. Raab, 1993). This illustration is based on a hydrogeologic interpretation of the well-log data from Darke County and surrounding areas. It should be used only as a guide to understanding the ground-water resources in the county. The section below provides a brief description of the types of aquifers illustrated on the map in Figure 1.
Figure 1. Ground-water resources of Darke County,
Ohio (adapted from Ground-Water Resources of Darke
County map, J. M. Raab, 1993, ODNR Division of Water;
illustration prepared by J. Humphreys).
Figure 2 is a generalized cross section (referenced in Figure 1 as the line X-X') of the majority of Darke County. This cross section shows the range of depth to bedrock as well as the variation in composition of the glacial till. Notice the large deposits of sand and gravel that exist above the underlying bedrock.
Figure 2. Generalized cross section of Darke County, Ohio (adapted
from Underground Water Resources map H-6 and 7, ODNR Division of Water;
illustration prepared by R. Roberts).
Area A in Figure 1 denotes one of the most productive aquifers in Darke County. Yields of 500 gpm or more may be obtained from properly screened wells constructed in these sand and gravel deposits at depths ranging from 50 to 70 feet. This aquifer type is located in the vicinity of both Greenville and Versailles, and is part of the major buried river valley in Darke County. The underlying bedrock is relatively non-water-bearing shale and thin limestone of lower Silurian and upper Ordovician age (425 to 400 million years ago). Lenses of sand and gravel interbedded with clayey till may serve as a source of water supply at depths ranging from 25 to 75 feet.
Located in the north and northwest sections of the county, including parts of Washington and Greenville townships, thick layers of limestone and dolomite are delineated as Area B. Yields of up to 100 gpm or more can be obtained from wells that penetrate the entire thickness of these Silurian-aged carbonate rocks. Generally, most wells are 38 to 180 feet in depth and produce 10 to 100 gpm.
Area C is located throughout the southern two-thirds of Darke County. Yields in this region are lower than those obtained in the northern one-third of the county due to thinning of the more productive Silurian-aged carbonate bedrock in the southerly direction. Yields typically do not exceed 100 gpm.
Permeable deposits of sand and gravel, denoted as Area D, are located within buried river valleys. Yields ranging from 25 to 100 gpm can be obtained. In the northern one-third of the county, yields from the underlying carbonate bedrock are similar to those from the sand and gravel deposits. The carbonate bedrock in the southern two-thirds of the county is very thin and typically yields only up to 25 gpm.
Area E delineates areas where yields adequate for domestic purposes can be obtained from interbedded sand and gravel deposits. Yields generally do not exceed 25 gpm due to excessive amounts of clay. Drilling into the underlying bedrock is not recommended because of the non-water-bearing nature of the shaly limestone formations.
Meager domestic yields can be obtained from discontinuous layers of sand and gravel in the areas denoted as Area F. Wells drilled in this relatively small formation in Monroe Township will yield little more than 10 gpm at depths of 115 feet. Drilling into the underlying bedrock is not recommended in this area because the underlying shaly limestone is generally non-water-bearing. Area F is the poorest yielding area in Darke County.
The water level in any well does not remain constant, but changes in response to several factors. Rainfall distribution and amount may affect ground-water recharge and discharge, and subsequently may affect the water level in area wells. Also, wells that are hydraulically connected to a stream may show fluctuations in the water level as the stream level changes. In some cases, depending upon the hydraulic properties of the geologic formation, the intense pumping of a well, or number of wells, may cause the water level in some nearby wells to be lowered.
The ODNR Division of Water monitors one well in Darke County. Located at the Greenville Industrial Park, this well is denoted as Observation Well D-2 on Figure 1. This well, along with other wells throughout west-central Ohio, is used to monitor the natural seasonal fluctuation of water levels in various aquifers. Observation Well D-2 was completed in the sand and gravel aquifer at a depth of 70 feet. The depth to limestone is approximately 110 feet. Continuous water-level measurements have been recorded at D-2 since August 1977. The lowest level recorded at D-2 was 20.9 feet below land surface in April 1992; the highest level recorded was 16.7 feet below land surface in March 1991.
Various state and federal agencies have participated in programs to determine the ground-water quality in Ohio. For three wells in Darke County, water-quality data were available from the ODNR Division of Water. In Figure 1, these wells are noted as Chemical Analysis Sites 1 through 3. These sites are municipal wells located at Union City, Versailles, and Arcanum.
The results from some of the chemical tests performed on these Darke County wells are given in Table 1. The chemical constituents listed are total dissolved solids, hardness (as CaCO3), iron, sulfate and pH. For comparison purposes, secondary drinking water-quality standards for these chemical constituents also are shown. These standards are established by the U.S. Environmental Protection Agency (USEPA) for public water systems for aesthetic reasons (taste, odor, appearance, etc.), and are not enforceable. These chemical constituents do not pose a risk to human health (see notes in Table 1). For private wells, there are no legally enforceable drinking water-quality standards other than total coliform, which is an indicator of bacteriological quality.
Ground water, whether obtained from bedrock or glacial deposits, may require some treatment. In some areas, water containing calcium carbonate (CaCO3, i.e. hard water), and iron concentrations greater than 0.3 ppm, may require treatment for some uses (see notes in Table 1). Wells drilled into shale or limestone may produce water that contains objectionable quantities of hydrogen sulfide (rotten egg or sulfur odor). In general, the probability of obtaining sulfur in objectionable amounts increases with the depth drilled.
The information in Table 1 can be used as a guide to what one might expect from an existing or new well developed in similar geologic material in the county. This information provides a general representation of the quality of the water at the time of sampling, which was not the same for all wells. In most cases, the data provided in Table 1 was taken from a water sample obtained just after the well was put into operation. Even though two of these wells were developed in the limestone underlying Darke County, and these wells are in the range of 72 to 230 feet deep, some variation exists in the concentrations of each of these chemical constituents. Just as well yields differ, water quality will vary depending on aquifer properties at the specific location of each well. One should not forget that many human activities also affect the quality of ground water (see AEX 465).
| Table 1. Chemical constituents of selected Darke County wells.1 | ||||
|---|---|---|---|---|
| Well No. | 1 | 2 | 3 | WQ Std2 |
| Well Depth (feet) | 230 | 72 | 170 | |
| Capacity (gpm) | 300 | 200 | 80 | |
| Depth to Bedrock (feet) | 95 | ne3 | 38 | |
| Water-Bearing Formation4 | LS | SG | LS | |
| Chemical Constituents5 | ||||
| Total Dissolved Solids | 567 | 537 | 587 | 500 |
| Hardness (as CaCO3) | 450 | 440 | 394 | none6 |
| Iron | 5.8 | 1.2 | 2.4 | 0.3 |
| Chloride | 7 | 7 | 7 | 250 |
| pH | 7.2 | 7.6 | 7.7 | none |
| 1 Data on these wells taken from Underground Water Resources map H-6 and 7; general location of each well is shown on Figure 1. | ||||
| 2 USEPA Secondary Water Quality Standard. | ||||
| 3 ne = well constructed in this formation did not encounter bedrock. | ||||
| 4 SG-Sand and Gravel; LS-Limestone. | ||||
| 5 Units are parts-per-million, ppm; Comments as per
Interpreting Your Water Test Report (1988); Total Dissolved Solids: Concentrations above 500 ppm may cause adverse taste and deteriorate domestic plumbing and appliances. Use of water containing 500 ppm is common. Hardness: Primary concerns are that more soap is required for effective cleaning, a film may form on fixtures, fabrics may yellow, and scales may form in boilers, water heaters, and cooking utensils. Iron and Manganese: Iron concentrations greater than 0.3 ppm and manganese concentrations greater than 0.03 may cause brown or black stains on laundry, plumbing fixtures and sinks. Metallic taste may be present which may affect the taste of beverages made from the water. Chloride: High concentrations may result in an objectionable, salty taste to water and the corrosion of plumbing in the hot water system. pH: Is expressed on a scale of 1 (acidic) to 14 (basic). A pH of 7.0 is neutral. | ||||
| 6 No USEPA Secondary Standard. | ||||
Darke County's ground-water resources are valuable assets to the county's citizens and industry. The availability and quality of these resources are directly influenced by the properties of the geologic formations underlying the county. The productive limestone, dolomite, and sand and gravel formations that underlay much of Darke County have the potential to provide excellent water adequate for domestic, agricultural, industrial and many municipal uses. By understanding the physical and chemical nature of these resources, better decisions can be made about ground-water protection, management and use. This publication provided an overview of the county's ground-water resources. It should be used as a guide, and not as a substitute for detailed information and professional advice when drilling a well.
The Darke County office of Ohio State University Extension can provide other publications on the county's water resources. Your Extension agent, the Darke County Health Department, and Ohio EPA Southwest District Office-SWDO 40 South Main St., Dayton, OH 45402) can provide information on well-water testing and drinking-water quality. The ODNR Division of Water-Ground-Water Resources Section (Fountain Square, Columbus, OH 43224) is an excellent source of information on ground water. Some of the information in this publication was summarized from the map, Ground-Water Resources of Darke County, and other information available through the Division of Water. This map is much more detailed than that given in Figure 1, and the Ground-Water Resources Section can provide detailed information on ground-water availability and wells. The USGS, Ohio District (975 W. Third Ave. Columbus, OH 43212), also provides information concerning ground water in Ohio.
Ground-Water Resources of Darke County. 1993. J. M. Raab. ODNR Division of Water. (map).
Interpreting Your Water Test Report. 1988. D. Lundstrom and S. Fundingsland. AE-937, No. 13-AENG-10. North Dakota State University Extension Service.
Nonpoint Source Pollution: Water Primer. 1993. R. Leeds and L. C. Brown. AEX 465. Ohio State University Extension.
Ohio Ground-Water Quality. USGS National Water Summary-Ohio. 1986. U.S. Geological Survey Water-Supply Paper 2325.
Ohio Ground-Water Resources. USGS National Water Summary-Ohio. 1984. U.S. Geological Survey Water-Supply Paper 2275.
Southwest Ohio Water Plan. 1976. ODNR Division of Water.
Surface and Ground Water Terminology. 1990. L. C. Brown and L. P. Black. AEX 460. Ohio State University Extension.
Underground Water Resources (maps of various river basins). 1958-1962. ODNR Division of Water.
Water Resources of Darke County. 1994. J. R. Sutherly, K. T. Ricker and L. C. Brown. AEX-480.19. Ohio State University Extension.
Water Testing. 1988. K. Mancl. AEX 314. Ohio State University Extension.
This publication was produced through the Ohio Water Resources Education Project, in cooperation with: ODNR Division of Water; Ohio EPA; USGS, Ohio District; and Ohio Department of Health (ODH). Project leaders are Larry C. Brown and Karen T. Ricker. Partial support for this publication was provided by these cooperating agencies and programs: Ohio State University Extension, Darke County; Darke County Commissioners; Overholt Drainage Education and Research Program; and the Ohio Management Systems Evaluation Area Project (USDA Extension Service Grant No. 90-EWQI-1-9018).
The project leaders acknowledge the following reviewers: Dennis Baker (Ohio State University Extension, Darke County); Jim Bennett (USDA-Soil Conservation Service, Darke County); Scott Golden (Environmental Health, ODH); and Steve Hindall (USGS, Ohio District).
A special thanks to Michelle Roby, Ross Roberts, and John Humphreys (Agricultural Engineering Undergraduate Assistants) for help in graphic and manuscript preparation, and Kim Wintringham, Associate Editor (Section of Communications and Technology, The Ohio State University), for editorial and graphic production.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868