Figure 1. Ground-water resources of Seneca County, Ohio (modified from Ground Water Resources of Seneca County map, J.J. Schmidt, 1982, ODNR Division of Water; illustration prepared by Carlos Lopez).
Christopher D. Penrose
Chris L. Bruynis
A. Wayne Jones
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 depth and formations. This publication contains information about the ground-water resources underlying Seneca County. Its purpose is to help the reader better understand the factors which influence the quantity and quality of ground water. An overview of the county's water resources is provided in the publication Water Resources of Seneca County, AEX-480.74.
Much of the water-resource and water-quality terminology used in this publication is described in Extension Fact Sheets AEX 460 and AEX 465. Ohio Extension publications are available through the Seneca 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 carbonate aquifer, which is composed of layers of limestone and dolomite, is the principal source of ground water in northwest Ohio, including Seneca County. Limestone consists of fossilized seashells, shell fragments, calcareous sands, 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, silt, sand, gravel, and boulders deposited by glacial activity.
Located in the southeastern part of Seneca County is non-water bearing shale bedrock lying underneath a relatively thin layer of clayey till. Dry wells are not uncommon and additional sources, such as cisterns and ponds, may be needed to meet water needs.
Limestone formations are usually good 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.
In Thompson Township, the fractures and solution channels are so numerous that sinkholes have developed. Sinkholes allow surface water to move directly to the ground water, thus there is a great potential for the ground water to become polluted when polluted surface water is introduced. This type of condition forms when the bedrock is primarily composed of CaCO3 and is very near the land surface. Landforms of this type are called karst topography.
Ground water also occurs in lenses (or pockets) of sand and gravel deposited by glacial activity. These deposits occur above the carbonate bedrock and may be imbedded in the glacial till or deposited in layers.
The 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 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 (since the early 1950's, well drillers have been required by State law to file a construction log of each new well). 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 (each county has a published, county-specific, ground-water map).
Estimates of the size, shape, geologic make-up, and yields of aquifers are being mapped for Seneca County. The map presented in Figure 1 is a generalized representation of the water-bearing formations underlying Seneca County (adapted from map by J. J. Schmidt, 1982). This illustration is based on a hydrogeologic interpretation of the well-log data from Seneca 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 Seneca County, Ohio (modified from Ground Water Resources of Seneca County map, J.J. Schmidt, 1982, ODNR Division of Water; illustration prepared by Carlos Lopez).
The limestone aquifer illustrated in Figure 1 as Area A is part of the regional aquifer which underlies much of northwest Ohio. The limestone is overlain by an average of 25 feet of glacial till, consisting primarily of clay with intermittent deposits of sand and gravel. Proven yields of as much as 500 gpm have been developed at depths of less than 300 feet. Farm and domestic supplies of 10 to 25 gpm are often encountered at depths of less than 125 feet.
Deposits of sand and gravel interbedded in thick layers of clayey till partially fill buried valleys in the area denoted as Area B. Yields of up to 25 gpm may be developed for domestic and farm supplies. Industrial water users rely on the underlying carbonate formation for larger yields.
Although the water-bearing aquifer illustrated as Area C is composed of limestone and dolomite, yields are not known to be as large as those from Area A. At depths of less than 200 feet, yields of 25 to 50 gpm have been obtained. Domestic supplies are usually developed at depths of less than 100 feet.
The glacial till illustrated as Area D is thicker than the till covering the rest of the county. This thick layer of till is the result of the end of a glacial movement that created a ridge of deposited clay, silt, sand, and gravel. Sand and gravel lenses are interbedded in these glacial deposits. Domestic and farm water supplies may be developed from these thin lenses of sand and gravel.
Non-water bearing shale is found beneath the moraine in the eastern part of the county (Area D3). The limestone which underlies the moraine in the central and western portions of the county, Areas D1 and D2, respectively, is the principal aquifer described as Areas A and B above. Area D1 denotes locations where the moraine overlays limestone with high-yield potential, while D2 denotes locations where the underlying limestone has moderate-yield potential.
The shale aquifer in southeastern Seneca County, denoted as Area E, does not have the potential to produce the volume of water as the carbonate aquifer in other parts of the county. In addition, this shale lies beneath a relatively thin layer of clayey till. At depths of less than 45 feet in the till, yields of less than two gpm can be expected. Dry wells are not uncommon, and wells that are extended deeper into the shale may yield a black sulfurous and brackish water. In the extreme southeastern corner of Venice Township, is a small area (not shown in Figure 1) within Area E where limited amounts of fine-grained sand and silt overlie the non-water bearing shale. These materials generally contain water, but it is very difficult to recover. Yields are less than 1 gpm.
The water level in any well usually 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-table 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, in cooperation with the USGS, manages a statewide network of water level observation wells. The network currently consists of 102 State-operated sites equipped with continuous water-level recorders. Water-level data are collected to provide a database for scientists and water resources managers to learn about short- and long-term water-level fluctuations.
The ODNR Division of Water monitors ground-water levels in one well in Seneca County, located in Tiffin (at Tiffin State Hospital). This well is designated as Observation Well SE-2 on Figure 1. Observation Well SE-2 is 250 feet deep and the depth to limestone is approximately eight feet. It is representative of many limestone wells in the region. Continuous water level measurements have been recorded at SE-2 since July 1962. The lowest level recorded on SE-2 was 23.8 feet below land surface in November 1964; the highest level recorded was 14.1 feet below land surface in January 1991.
Various state and federal agencies have participated in programs to determine the ground-water quality in Ohio. For seven wells in Seneca 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 7. These sites are test wells or municipal wells.
The results from some of the chemical tests performed on these Seneca County wells are given in Table 1. The chemical constituents listed are total dissolved solids, hardness (as CaCO3), iron, sulfate, and hydrogen sulfide (H2S). 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 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., hardness) in concentrations greater than 180 ppm, and iron concentrations exceeding 0.3 ppm may require treatment for some purposes (see notes in Table 1). Generally, water produced from wells in the carbonate aquifer is highly mineralized, and the unconsolidated aquifer may contain high levels of iron. Wells drilled into shale or limestone may produce water that contains objectionable quantities of hydrogen sulfide gas (rotten egg odor). Hydrogen sulfide concentrations as small as 1 ppm can result in an offensive, rotten egg odor and taste. In general, the probability of obtaining sulfur in objectionable amounts increases with the depth drilled.
Bacteria and nitrate concentrations may be of concern in some wells in the northeast portion of Seneca County (Thompson Township). In a 1990 well-water testing program conducted in the county, 87 wells in Thompson Township were tested for nitrate, and 85 for coliform bacteria (used as indicators of water pollution by human or animal wastes). The average nitrate level was 3.8 ppm in Thompson Township compared to the county average of 1.67 ppm. Eleven of these Thompson Township wells (over 12%) had nitrate concentrations that exceeded the drinking water standard of 10 ppm; the largest concentration was 16.9 ppm. Twenty of the Township wells had nitrate concentrations in the range of 0.0 to 0.3 ppm, 31 wells in the range of 0.3 to 3.0 ppm, and 25 in the range of 3.0 to 10.0 ppm. Of the 85 bacterial samples taken, 30 contained excessive coliform bacteria levels indicating the water was unsafe, and there was great potential that the water may be polluted by human or animal wastes. The more than 200 sinkholes found throughout the township are the primary reason for these undesirable results. Sinkholes allow poor quality surface water and subsurface drainage to move directly to the ground water.
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 all seven of these wells were developed in the limestone and shale bedrock underlying Seneca County, and all are in the range of 169 to 395 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 Seneca County, Ohio, wells.1 | ||||||||
|---|---|---|---|---|---|---|---|---|
| Well No. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | WQ Std2 |
| Well Depth (feet) | 355 | 375 | 342 | 200 | 169 | 310 | 395 | |
| Capacity (gpm) | 50 | 300 | 100 | 1 | 10 | 250 | 500 | |
| Depth to Bedrock (feet) | 54 | 32 | 14 | 25 | 24 | 45 | 48 | |
| Water Bearing Formation3 | LS | LS | LS | SH/LS | LS | LS | LS | |
| Chemical Constituents4 | ||||||||
| Total Dissolved Solids | 600 | 1300 | 571 | 3120 | na5 | 1410 | 775 | 500 |
| Hardness (as CaCO3) | 459 | 784 | 454 | 2010 | 0.0 | 863 | 620 | none6 |
| Iron | 0.86 | 1.6 | 2.6 | na | na | 2.3 | 0.88 | 0.3 |
| Sulfate | 181 | 716 | 140 | 1780 | na | 780 | 302 | 250 |
| Hydrogen Sulfide (H2S) | 0.3 | na | na | 3.4 | 82 | 0.7 | 1.1 | none |
| 1. Data on these wells taken from map by J. J. Schmidt, 1982; general location of each well is shown on Figure 1. | ||||||||
| 2. USEPA Secondary Water Quality Standard. | ||||||||
| 3. LS--limestone; SH--shale. | ||||||||
| 4. 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 scale may form in boilers and water heaters, and on cooking utensils. Iron: Concentrations greater than 0.3 ppm 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. Sulfate: Concentrations in excess of 250 ppm may have a 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. 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 at the concentrations found in water supplies. | ||||||||
| 5. Data not available, or constituent not tested. | ||||||||
| 6. No USEPA Secondary Standards. | ||||||||
Seneca 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 formations that underlie much of Seneca 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 provides 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 Seneca County office of Ohio State University Extension can provide other publications on the county's water resources. Your Extension agent, the Seneca County Department of Health, and Ohio EPA (Northwest District Office, 347 North Dunbridge Road, Bowling Green, OH 43402) can provide information on well-water testing and drinking-water quality. Your local health department and county Extension office also will be able to provide information about proper well construction and requirements for private water systems. For example, State law requires that each new well constructed must be cased to a minimum depth of 25 feet. The health department issues permits and inspects new well construction.
The ODNR Division of Water--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 Seneca County, and other information available through the Division. This map is much more detailed than that given in Figure 1, and the Water Resources Section can provide detailed information on ground-water availability and wells. The Water Resources Section also has conducted a ground-water pollution potential study for the county. This information was published in 1994 (see Bibliography). In regard to constructing a new well, the Division maintains a list of the State's registered and bonded well drillers. Hydrogeologists in the Division may be able to provide you with a list of well drillers who are familiar with geological conditions in your area, and provide technical assistance on proper well construction.
An additional excellent source of Ohio ground-water information is the USGS, Ohio District (975 W. Third Ave., Columbus, OH 43212). The USGS has conducted and published a number of ground- and surface-water investigations in Ohio. Additional information on Ohio's geological formations can also be obtained through the USGS, and through ODNR's Division of Geological Survey.
Geology of Seneca Caverns, Seneca County, Ohio. 1990. L. C. Ruedisili, G. E. Kihn, R. C. Bell and Seneca Caverns. Ohio Journal of Science 90(4):106-111.
Ground- and Surface-Water Terminology. 1994. L. C. Brown and L. P. Black. AEX 460. Ohio State University Extension.
Ground Water Pollution Potential of Seneca County Ohio. 1994. Report No. 9. ODNR Division of Water.
Ground-Water Resources of Seneca County. 1982. J. J. Schmidt. ODNR Division of Water. (map).
Impact of Best Management Practices on Surface Runoff and Ground Water Quality in a Solutioned Limestone Area, Thompson Township, Seneca County, Ohio. 1994. J. Raab, W. Jones, R. Petty, M. Angle, J. Kreglow, M. Zimmerman, A. Walton, L. A. Drane and R. J. Kocher. ODNR Division of Water (misc. report to Ohio EPA Nonpoint Source Program).
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. 1996. R. P. Leeds, L. C. Brown and N. L. Watermeier. 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.
Thompson Township Water Quality--Special Project. 1992. Seneca Soil and Water Conservation District.
Time of Travel of Solutes in Selected Reaches of the Sandusky River Basin, Ohio, 1972 and 1973. 1976. A. O. Westfall. U.S. Geological Survey Water-Resources Investigations Report 76-50.
Underground Water Resources (maps of various river basins). 1958-1962. ODNR Division of Water.
Water Resources Data, Ohio, Water Year 1995. Volume 1. St. Lawrence River Basin and Statewide Project Data. 1996. U.S. Geological Survey Water-Data Report OH-95-2.
Water Resources of Seneca County. 1995. C. D. Penrose, C. L. Bruynis, K. T. Ricker and L. C. Brown. AEX-480.74. 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, Seneca County; Seneca County Commissioners; USDA Water Quality Initiative Funds; Overholt Drainage Education and Research Program; and the Ohio Management Systems Evaluation Area project (USDA CSREES Grant No. 94-EWQI-1-9057).
The project leaders acknowledge the following reviewers: Scott Miller (USDA NRCS, Crawford, Seneca, and Wyandot counties); Ada Jahns (Seneca Soil and Water Conservation District); David Cashell (ODNR Division of Water); Scott Golden (Environmental Health, ODH); Steve Hindall (USGS, Ohio District); and Tim Fishbaugh (NWDO Ohio EPA).
A special thanks to Carlos Lopez and Kate Weber (Undergraduate Engineering Assistants) for illustration preparation, and Kim Wintringham (Associate Editor, Section of Communications and Technology, Ohio State University 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.
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