Ohio State University Extension

Food, Agricultural and Biological Engineering

590 Woody Hayes Dr., Columbus, Ohio 43210

Delaware County Ground-Water Resources

AEX-490.21

K. Troy Putnam
A. Wayne Jones
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 Delaware 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 Delaware County Water Resources, AEX-480.21, are available through your county Extension office.

Aquifers

An aquifer is a geologic formation capable of yielding enough water to support a well or spring. The type of earth material composing a formation influences its ability to store 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.

Delaware County is underlain with four distinct aquifer systems. These are: sand and gravel deposits in buried valleys, limestone and dolomite, sandstone and shale.

Buried valley aquifers, in southern Delaware County, consist of thin lenses of sand and gravel interbedded with thick layers of clay. The carbonate aquifer, which is composed of layers of limestone and dolomite, is the principal source of ground water in the western half of the 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. Sandstone aquifers are found in the eastern third of the county. Sandstone aquifers, as the name implies, are massive to thin-bedded formations of fine-grained to conglomerate, cemented sands. The poorest aquifer that may be encountered in the county is shale, which can be found in the central third of the county. As mentioned earlier, the movement of water through layers of shale is minimal.

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 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 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 of their ground-water resources. The map presented in Figure 1 is a generalized representation of the water-bearing formations underlying Delaware County (adapted from map by Schmidt, 1979). This illustration is based on a hydrogeologic interpretation of the well log data from Delaware 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 Delaware County, Ohio (modified from J.J. Schmidt, ODNR Division of Water, by R.A. Roberts).

AREAS A and B: Limestone beneath Glacial Till

The principal aquifer shown in Figure 1 as Area A consists of limestone bedrock overlain by sand and gravel, and clay-rich glacial till. The glacial deposits are generally less than 100 feet thick. Although yields in excess of 1,000 gpm have been proven at depths of less than 300 feet, regional yields are less than 500 gpm. Farm and domestic supplies of 10 to 15 gpm are usually encountered at depths of less than 85 feet.

Water from this formation is generally hard, and may be highly mineralized with calcium and magnesium sulfates. Hydrogen sulfide gas (H2S; rotten egg or sulfur odor) can be a problem in some areas. Water can be saline below 500 feet. Despite quality problems, this aquifer is an important source of water for a large geographic area. Area B is very similar to A except that wells are often cased to as deep as 180 feet to seal off poor quality water from the shale, shaley limestone and surface limestone formations.

AREA C: Shallow Buried Valley

The aquifers found in Area C are the smallest in the county in terms of occupied area. They are permeable layers of sand and gravel deposited in the relatively shallow buried valleys adjacent to the Olentangy River and Little Walnut Creek. Water may be found from 30 to less than 75 feet, and wells can yield in excess of 100 gpm.

AREA D: Sandstone beneath Clayey Till

Area D is a sandstone aquifer made up of massive to thin-bedded formations of fine-grained to conglomerate sandstone, mostly quartz cemented by calcite, silica, iron and clay. The aquifer is located beneath 10 to 60 feet of clayey glacial till. Wells are seldom deeper than 95 feet and yields average 15 to 25 gpm. Hydrogen sulfide is often encountered in water from the sandstone. Water could be saline below 300 feet.

AREA E: Buried Valley

The buried valleys of Area E are partially filled with thin lenses of sand and gravel interbedded with thick layers of clay. Domestic and farm well yields in these areas average 5 to 15 gpm. Wells penetrating as much as 175 feet of glacial till (unconsolidated mixture of clay, sand, gravel and boulders) in the western portion of the county can develop excellent water supplies. In the eastern portion of the county, a sandstone bedrock aquifer can be found below as much as 240 feet of till deposits. However, wells should not be drilled deeper into the non-water-bearing shale.

AREA F: Glacial Moraine above Bedrock

Areas illustrated as F1, F2 and F3 are glacial moraines overlying limestone, shale and sandstone, respectively. Moraines are formed from an accumulation of boulders, stones or other debris carried and deposited by glaciers. The glacial moraines of Delaware County are found in three distinct paths as illustrated by F1, F2 and F3. Moraine deposits range from 30 to more than 80 feet thick. Again, thin lenses of water-bearing sand and gravel interbedded with fairly thick layers of clayey till are the only source for domestic supplies above the non-water-bearing shale bedrock. Wells should not be drilled deeper into the non-water bearing shale. If a permeable sand and gravel deposit is not encountered above the limestone or sandstone formations, wells may be deepened into the bedrock to develop adequate supplies in the range of 3 to 10 gpm.

AREAS G and H: Clayey Till above Shale

The poorest well yields of the county are found in Areas G and H. Clayey glacial till above non-water-bearing shale bedrock yields on average less than 3 gpm, and dry wells are common. Homeowners rely upon additional storage and/or cisterns, or public supplies to maintain daily requirements. In Area G, wells seldom exceed 75 feet. Deeper drilling often encounters salty, poor-tasting water.

In Area H, wells yielding in excess of 400 gpm have been developed in limestone formations beneath the thick layers of shale. However, water quality is a problem, and specialized methods of well construction used to seal off water from the shale and surface limestone have not been successful. Shallow domestic wells, usually less than 50 feet deep, yield minimal supplies of water containing sulfur.

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 affect water levels in wells. The ODNR Division of Water monitors ground-water levels in one well in Delaware County. Located north of Delaware, the well is designated as DL-3 on Figure 1. This is one of a number of wells throughout central Ohio used to monitor the natural seasonal fluctuation or the effects of nearby pumping on the water levels in the carbonate aquifer.

Observation well DL-3 is 135 feet deep and the depth to limestone is approximately 55 feet. This is representative of many wells in the region in this type of aquifer. Continuous water level measurements have been recorded at DL-3 since 1948. The lowest level recorded on DL-3 was 37.0 feet below land surface in November 1948; the highest level recorded was 20.4 feet below land surface in January 1954.

Ground-Water Quality

Various state and federal agencies have participated in programs to determine ground-water quality in Ohio. In Delaware County, data for seven test wells were available from the ODNR Division of Water. In Figure 1, these wells are noted as Chemical Analysis Sites 1 through 7. These are either industrial or domestic wells.

The results from some of the chemical tests performed on these Delaware County wells are given in Table 1. The chemical constituents listed are total dissolved solids, hardness (as CaCO₃), hydrogen sulfide, iron and sulfate. All concentrations are given in parts-per-million (ppm). 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 seven of these wells were developed in Delaware County, and all are in the range of 62 to 494 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 Delaware County wells.
Well No.	1	2	3	4	5	6	7	WQ Std1
Well Depth (feet)	350	370	494	62	62	65	75
Capacity (gpm)	2,500	800	-2	60	-	5	-
Depth to Bedrock (feet)	12	20	25	NE3	NE	46	35
Water-Bearing Formation4	LS	LS-SH	LS	SG	SG	SH	SS
Chemical Constituents5
Total Dissolved Solids	684	494	1,600	788	1,070	2,800	1,410	500
Hardness (as CaCO3)	550	440	4,100	649	881	2,160	866	None6
Hydrogen Sulfide (H2S)	0.2	0	0.3	-	-	-	12	None
Iron	0.58	0.4	8.8	4	9.4	16	2.3	0.3
Sulfate	250	130	22	348	470	1,740	549	250
1. USEPA Secondary Water Quality Standard.
2. Data not available.
3. Well constructed in this formation did not encounter bedrock.
4. LS--Limestone; SG--Sand and Gravel; SH--Shale; SS--Sandstone.
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. 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. 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. Sulfate: 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.
6. No USEPA Secondary Standard.

Summary

Delaware 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 Delaware County Extension office can provide other publications about Delaware County's water resources. Your Extension agent, the Delaware County Department of Health, and the 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 Delaware 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 about ground water in Ohio.

Bibliography

Delaware County Water Resources. 1992. AEX-480.21. K.T. Putnam, K.M. Boone and L.C. Brown. Ohio Cooperative Extension Service, The Ohio State University.

Ground-Water Resources of Delaware County. 1979. J.J. Schmidt. 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.

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.

Acknowledgments

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; Delaware County Extension office; Overholt Drainage Education and Research Program; and USDA Extension Service Grant No. 90-EWQI-1-9018. The project leaders acknowledge the following reviewers: Ralph Jordan and Donald Breece (OSU Extension); David Cashell (ODNR Division of Water); Larry Ufferman (Delaware Soil and Water Conservation District); Tom Edwards (USDA-Soil Conservation Service); Scott Golden (Environmental Health, ODH); Randall Reeder (Agricultural Engineering, OSU); Steve Hindall (USGS, Ohio District); and Linnea Saukko (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.