Ohio State University Extension Fact Sheet

Ohio State University Extension

Food, Agricultural and Biological Engineering

590 Woody Hayes Dr., Columbus, Ohio 43210

Marion County Ground-Water Resources


Donald J. Breece
James M. Raab, Hydrogeologist
Kristina M. Boone
Larry C. Brown

Water stored under the earth's surface is a plentiful, yet precious, resource in most areas of Ohio. Humans greatly affect ground water. However, the availability and quality of this resource are influenced directly by the properties of the geologic formation that holds 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 Marion County. Its purpose is to help the reader better understand the factors that influence the quantity and quality of ground water. Water resources terminology used in this publication is included in Surface and Ground Water Terminology, fact sheet AEX-460, which provides a listing of generally accepted water resource definitions. Fact sheet AEX-460 and the publication Marion County Water Resources, AEX-480.51, are available through your county Extension office.


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 types of geologic material from which the formation originally was made influence its ability to hold and transmit water. For example, sands and gravels 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 carbonate aquifer, which is composed of layers of limestone and dolomite, is the principal source of ground water in west central Ohio, including Marion County. Limestone consists of fossilized sea shells, shell fragments and consolidated limy mud. Its main mineral is calcium carbonate, CaCO3. Dolomite is similar to limestone, but has few recognizable fossils; its main mineral is calcium magnesium carbonate, (Ca,Mg)CO3. Both limestone and dolomite are commonly referred to as limestone or carbonate rocks. The limestone and dolomite formations, which underlie most of the western portion of Ohio, were deposited between about 400 and 500 million years ago. In most areas of this region, these formations are covered by a layer of glacial till, which is an unsorted mixture of clay, sand, gravel and boulders deposited by a glacier.

Limestone formations are good sources of ground water because of their naturally formed solution channels, joints and fractures. 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.

The aquifer for the extreme eastern portion of Marion County is shale. This type of sedimentary bedrock, originating from compacted layers of mud and clay, allows very little water to flow through. Another source of ground water in some areas in west central Ohio is lenses (or pockets) of sand and gravel, which were deposited by glacial activity. These sand and gravel deposits usually are interbedded in the glacial till.

Well Yield

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.

Ground-Water Availability

The Ohio Department of Natural Resources (ODNR), Division of Water, maintains a statewide data base of more than 700,000 well logs. The Ground-Water Resources Section of the Division manages this valuable data base, 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, and 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 Marion County (adapted from map by Crowell, 1979). This illustration is based on a hydrogeologic interpretation of the well log data from Marion County and surrounding areas. It should be used only as a guide to understanding the ground-water resources in the county. The remainder of this section provides a brief description of the types of aquifers illustrated on the map in Figure 1.

Figure 1. Ground-water resources of Marion County, Ohio (modified from K.S. Crowell, ODNR Division of Water, by R.A. Roberts).

AREA A: Limestone beneath Glacial Till

The limestone aquifer illustrated in Figure 1 as Area A is part of the regional carbonate aquifer that underlies west central Ohio. It is overlain by glacial till consisting principally of clay with intermittent deposits of sand and gravel. The majority of wells are drilled into the limestone, and yields generally are adequate for domestic and farm water supplies. Although yields in excess of 1,000 gpm have been obtained in wells less than 300 feet deep, regional yields are less than 500 gpm. Farm and domestic supplies of 10 to 15 gpm can usually be developed in wells less than 80 feet deep.

Because the minerals in limestone are water soluble, water from this formation may be excessively hard and mineralized, and may require treatment. Many wells contain an excess of iron. As raw water is exposed to air, iron oxide forms as a precipitate, which may cause "red water." Wells drilled into the limestone often produce water that contains hydrogen sulfide. Objectionable amounts of hydrogen sulfide generally increase with the depth drilled.

Area B: Clayey Till over Shale

The aquifer for the extreme eastern portion of Marion County is shale, as illustrated as Area B. This type of sedimentary bedrock produces extremely small yields of water. Generally, the sand or sand and gravel deposits within the clayey till above the non-water-bearing shale yields less than 4 gpm. Dry wells and cisterns are common. Wells drilled into shale often produce water charged with hydrogen sulfide. Wells developed in the limestone beneath the shale have produced yields in excess of 400 gpm.

Figure 2 (referenced in Figure 1 as line X-X') is a general west-to-east representation of the cross section through the upper three-fourths of Marion County, showing the relationship of the different aquifers. The "?" in Figure 2 indicates that sufficient data have not been collected to properly characterize these specific locations.

Figure 2. Generalized west-to-east cross section of Marion County, Ohio (modified from Underground Water Resources map, M-2, ODNR Division of Water).

Ground-Water Levels

The water level in any well typically does not remain constant, but changes depending upon the proximity of adjacent wells and surface streams, and natural rainfall. Ground-water discharge and recharge greatly effect water levels in wells. The ODNR Division of Water monitors ground-water levels in three observation wells in Marion County, noted as MN-1, MN-2 and MN-4 in Figure 1. These are three of a number of wells throughout west central Ohio used to monitor the natural seasonal fluctuation, or the effects of nearby pumping, on the water levels in the limestone.

Both observation wells MN-1 and MN-2 are completed in limestone and drilled to 100 and 67 feet, respectively. Observation well MN-4 is drilled 286 feet into a limestone-dolomite formation. Continuous water level measurements have been recorded at MN-1 since 1946, at MN-2 since 1959, and at MN-4 since 1973. The lowest level recorded on MN-1 (LaRue) was 14.9 feet below land surface in October 1988; the highest level recorded was 5.7 feet below land surface in January 1959. The data from MN-2 (west of Marion) indicate the lowest level recorded was 49.5 feet below land surface in February 1956; the highest level recorded was 7 feet below land surface in July 1987. MN-4, located in the Big Island Wildlife area, recorded its lowest level of 32.6 feet in August 1983, and its highest level of 0.6 feet in March 1974.

Ground-Water Quality

Various state and federal agencies have participated in programs to determine ground-water quality in Ohio. In Marion County, water-quality data for four wells were available from the ODNR Division of Water. In Figure 1, these wells are noted as Chemical Analysis Sites No. 1, 2 and 3. Data for observation well MN-4 were also available. The results from some of the chemical tests performed on these Marion County wells are given in Table 1. The chemical constituents listed include total dissolved solids, hardness (as CaCO3), hydrogen sulfide, sodium, iron, sulfate, chloride and iron. All concentrations are given in parts-per-million. For comparison purposes, drinking water-quality standards for these chemical constituents are also 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). There are no drinking water-quality standards for private wells.

The information in Table 1 can be used as a guide to what one might expect from an existing or new well. Even though all four of these wells were developed in the limestone underlying Marion County, and all are in the range of 210 to 310 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.

Table 1. Chemical constituents of selected Marion County wells.
Well No.MN-4123WQ Std1
Depth (feet)286310300210
Capacity (gpm)1,6001,0002,8001,800
Depth to Bedrock (feet)22763610
Water-Bearing Formation2LSLSLSLS
Chemical Constituents3
Total Dissolved Solids604497554501500
Hardness CaCO3445-1,500426470440None4
Hydrogen Sulfide (H2S)0.300.30.2None
Iron (Fe)0.751.
1 USEPA Secondary Water Quality Standard.
2 LS - Limestone.
3 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.
Hydrogen Sulfide: Presence of this unpleasant smelling gas is difficult to measure but not difficult to detect, even in small concentrations. Highly corrosive to pump parts and plumbing fixtures, but has no known harmful effects in humans.
Sodium: Major component of brine. High concentrations may impart a soda taste and be a dietary concern.
Sulfates: Concentrations in excess of 250 ppm may have laxative effect on persons unaccustomed to the water. Also affects the taste of water and will form a hard scale in boilers and heat exchangers.
Chloride: High concentrations may result in an objectionable salty taste to water and the corrosion of plumbing in the hot water system.
Iron: Concentrations greater than 0.3 ppm may cause rust-colored stains on laundry, plumbing fixtures and sinks. Metallic taste may be present and may affect the taste of beverages made from the water.
4 No USEPA Secondary Standard.
5 Data not available.


Marion 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. By understanding the physical and chemical nature of these resources, better decisions can be made about ground-water protection, management and use. This publication was designed to provide the reader with 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.

Where to Get More Information

The Marion County Extension office can provide other publications about the county's water resources. Your Extension agent, the Marion County Health Department and Ohio EPA Division of Drinking and Ground Water (1800 WaterMark Drive, Columbus, OH 43266) 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 Marion 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 Marion County. 1979. K.S. Crowell. 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.

Marion County Water Resources. 1992. D.J. Breece, K.M. Boone and L.C. Brown. AEX-480.51. Ohio Cooperative Extension Service, The Ohio State University.

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.

Surface and Ground Water Terminology. 1990. L.C. Brown and L.P. Black. AEX-460. Ohio Cooperative Extension Service, The Ohio State University.

Underground Water Resources (maps of various river basins). 1958-1962. ODNR Division of Water.

Water Testing. 1988. K. Mancl. AEX-314. Ohio Cooperative Extension Service, The Ohio State University.


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 Kristina M. Boone. Support for this publication was provided, in part, by: cooperating agencies; Marion County Extension office; Marion County Phosphorus Reduction Committee grant from Ohio EPA under provisions of Section 319 of the Clean Water Act as amended in 1987; Overholt Drainage Education and Research Program; and USDA Extension Service Grant No. 90-EWQI-1-9018. The project leaders acknowledge the following reviewers: John V. Fark and K. Troy Putnam (OSU Extension); David Cashell (ODNR Division of Water); John Brown (USDA-Soil Conservation Service); Scott Golden (Environmental Health, ODH); Randall Reeder (Agricultural Engineering, OSU); Steve Hindall (USGS, Ohio District); and Tim Fishbaugh (Ohio EPA Division of Drinking and Ground Water).

A special thanks to Michelle Roby and Ross A. Roberts (Agricultural Engineering Undergraduate Assistants) for help in manuscript and graphics preparation, and Judy Kauffeld and Tonya Ewing (Section of Information and Applied Communications, OSU Extension), 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 614-292-6181

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