Ground Water Monitoring
The majority of ground water information used for analysis is generated from three monitoring activities:
- Ambient Ground Water Quality Monitoring Program (AGWQMP)
- Public water system compliance data and raw water samples
- Special studies
The data from these monitoring activities are used to characterize the water quality in Ohio’s major aquifers, to identify site-specific threats to local aquifers, and to help evaluate potential threats to public drinking water systems.
Ohio's Ambient Ground Water Monitoring Network
Ohio EPA Division of Drinking and Ground Waters maintains the Ambient Ground Water Monitoring Network as part of an effort to characterize general water quality conditions in Ohio. This program was established in 1967 to measure seasonal and annual water quality changes in the State's major aquifers. The network initially consisted of 12 large production wells, and was expanded to 60 wells in 1972. In 1986, the network was further expanded to around 90 wells. A large number of public water supply wells were added to the network in the late 1980's and early 1990's to provide better representation of the major aquifers in Ohio.
The program currently includes over 200 wells (stations). Of the total stations, roughly 85 percent are public water systems and 15 percent are industrial or commercial enterprises or residential. Raw water is analyzed for a suite of inorganic parameters every six or eighteen months depending on the total number of samples that have been collected and the stability of the geochemistry of major elements at the site. Samples are also analyzed for volatile organic compounds once every eighteen months. Some ambient sites have historical semi-volatile organic compounds and pesticide data.
Locational and lithologic information have been compiled for all of the more than 200 ambient wells for effective geochemical and Geographical Information System (GIS) analysis. Two-thirds of the wells in the ambient network are developed in unconsolidated deposits, and the remaining produce from bedrock aquifers systems.
A central goal of the Ambient Ground Water Monitoring Program is to provide reliable ground water quality data to enhance water resource planning and protection on a state-wide basis. This is consistent with Ohio EPA-DDAGW mission to protect human health and the environment by characterizing and protecting ground water quality and ensuring that Ohio's public water systems provide adequate supplies of safe drinking water.
Ambient Ground Water Monitoring Locations and Water Quality Data
An interactive map of the Ambient monitoring well locations has been developed. This application allows the user to zoom into an area in Ohio and click on a monitoring location. Information such as water quality summary reports and time series analyses for each monitoring location can be obtained from this site.
Publications on Special Ground Water Investigations in Ohio
- Unsafe Water Supply Investigation, Putman Community Water Association, Devola, Washington County, Ohio (June 2011)
- Investigation of Total Coliform in Public Water System Compliance Monitoring Samples, Village of Buckeye Lake, Licking County, Ohio (July 2008)
- Ground Water Quality Impacts of Infiltration of Partially Treated Wastewater at Catalina Mobile Home Park, Butler County, Ohio (October 2007)
- Report of Findings: Unsafe Water Supply Investigation, Wooster Township, Wayne County (December 2006)
General Ground Water Quality in Ohio
Several factors influence ground water quality in Ohio, including the composition of the soil and vadose zone, the composition of the aquifer material, and the residence time of the ground water. Although the vadose zone material is variable and influences the quality of water infiltrating to the major aquifers, the composition and solubility of the aquifer material exerts the greatest control on the local ground water quality. The more soluble the aquifer material, the greater the influence it has on water quality. For instance, carbonate rocks are more soluble than sandstones and, consequently, the calcium concentration in limestone aquifers is greater than in sandstone aquifers. The residence time of the ground water is also a major factor, with longer residence time leading to higher total dissolved and greater mineralization.
These differences are illustrated in the piper diagram (at left, click to enlarge), which provides a summary of cation data (left triangle), anion data (right triangle), and a composite diamond (center) to visually distinguish waters of different chemical composition and origin. The small symbols are the individual mean concentrations for each ambient station, and the squares are the average concentrations for the major aquifer type.
GREEN POINTS: The carbonate ground waters in the piper diagram trend toward a more magnesium- and sulfate-rich composition, reflecting the dissolution of dolomite and gypsum minerals within the carbonate stratigraphic section. Carbonate ground waters also demonstrate higher concentrations of calcium than water from sandstones and sand and gravel aquifers.
RED POINTS: The sandstone water chemistry reveals a higher mean sodium, potassium, and chloride contents than the other two systems, indicating a probable natural source for these ions from deeper formation waters. Most of the higher sodium concentrations are associated with deeper wells supporting the influence of deep formation waters.
BLUE POINTS: The overlap in water chemistry between the carbonate aquifer and the sand and gravel aquifer is due to the fact that much of the aquifer material in the unconsolidated sand and gravel units is carbonate bedrock that was eroded and transported by the glaciers and deposited within the buried valley aquifers. The concentrations of many constituents in the ground water from the sand and gravel aquifers is intermediate between the carbonate and sandstone due to the mixing of local bedrock into the buried valley sand and gravel deposits.
Accessing Water Quality Data
Downloads of the complete Ambient Ground Water database for both inorganic and organic ground water data may be accessed through the links below. Two data formats for each dataset are provided: .xlsx (Microsoft Open Office XML) and .csv (comma-separated values). The .xlsx format was chosen because it lacks the worksheet size limits of earlier Excel versions. The .csv is a standard text format which can be imported to wide variety of software products. Readers needing alternative formats are encouraged to direct email requests to email@example.com
Fluoride Distribution in Ohio's Ground Water
Fluoride is the naturally-occurring stable form of the gaseous element fluorine (F). Fluoride is among the top 15 most abundant components of the Earth’s crust and is naturally found in very small amounts in most aquifers. An aquifer is an underground unit of saturated earth materials that can provide usable quantities of ground water to a well.
The map on this page (click on them to enlarge) shows that the limestone aquifers in western Ohio have the highest fluoride concentrations in Ohio. Limestone aquifers contain the most fluoride-bearing minerals and dissolution of these minerals releases fluoride into ground water in the limestone aquifers. The sand and gravel aquifers found throughout the state may contain some fluoride-bearing carbonate material from local erosion. Thus, the fluoride concentrations in some sand and gravel aquifers falls between the higher concentrations found in the limestone aquifers and the lower concentrations in the sandstone aquifers.
Manganese Distribution in Ohio's Ground Water
Manganese solubility is controlled redox reactions. If ground water is oxidized, manganese is not soluble and, consequently, manganese concentrations are low. In reduced conditions, manganese is soluble and the concentrations of dissolved manganese increase. The figure illustrates that redox conditions in the sandstones and particularly buried valley aquifers are the best for elevated manganese. This is confirmed by the fact that many public water systems using buried valley aquifers need to remove manganese.
Sodium Distribution in Ohio's Ground Waters
The map of sodium concentrations in Ohio does not exhibit associations of sodium with a major aquifer. Plotting box plots of sodium concentrations against major aquifer types confirms the lack of strong associatiosn, but the higher concentrations of sodium are associated with sandstone aquifers, probably associated with deep formation waters.
Sulfate Distribution in Ohio's Ground Waters
The map of sulfate concentrations exhibits a strong correlation between elevated sulfate and carbonate bedrock in northwest Ohio. Much of the sulfate is derived from the dissolution of gypsum (CaSO4 2H2O), which is present in the Devonian Salina Group.
Total Dissolved Solids Distribution in Ohio's Ground Waters
Total dissolved solids (TDS) are variable across the state, but limestone bedrock aquifers consistently demonstrate elevated TDS. The high solubility of limestone and the presence of gypsum interbedded with limestone contributes to the elevated TDS in northwest Ohio.
Major Aquifers in Ohio
Ohio's aquifers can be divided into three major types: Sand and Gravel, Sandstone, and Carbonate.
The sand and gravel valley aquifers are distributed through the state (click on the map at left to enlarge). The valleys these sands fill are cut into sandstone and shale in eastern Ohio and into carbonate aquifers in western Ohio. The sandstone and carbonate aquifers generally provide sufficient production for water wells except where dominated by shale, as in southeast Ohio.
Sole Source Aquifers in Ohio
U.S. EPA defines a Sole Source Aquifer (SSA) as an aquifer that supplies at least 50 percent of the drinking water consumed in the area overlying the aquifer. These areas may have no alternative drinking water source(s) that could physically, legally and economically supply all those who depend on the aquifer for drinking water.
The Sole Source Aquifer designation protects an area's ground water resource by requiring U.S. EPA to review certain proposed projects within the designated area. All proposed projects receiving federal funds are subject to review to ensure that they do not endanger the water source.
GREATER MIAMI SOLE SOURCE AQUIFER
ALLEN COUNTY SOLE SOURCE AQUIFER
CATAWBA ISLAND SOLE SOURCE AQUIFER
PLEASANT CITY SOLE SOURCE AQUIFER
For more information on Sole Source Aquifers, visit U.S. EPA's web site.
Ground Water Resources in Ohio
Related Ohio EPA Links
Here are a few links outside of Ohio EPA that may be of interest if you want to know more about Ohio's geology or ground water resources:
Contact Ground Water Quality Staff
To get more information about ground water quality in Ohio, contact the Ground Water Quality Characterization Program staff at:
Ohio Environmental Protection Agency
Ground Water Quality Characterization Program
Division of Drinking and Ground Waters
P.O. Box 1049
50 West Town Street
Columbus, OH 43215-1049
Phone: (614) 644-2752