Legend- Lithology, Thickness and Yield
| LITHOLOGY |
DESCRIPTION |
| Note: |
T=till
S=sand
G=gravel
F=fines(undifferentiated)
C = confining Predominant material - Upper case letters, secondary material - lower case letters
eg. Tsg Till is predominant, sand and gravel is secondary. |
| T |
Predominantly till, water well logs typically lack indication of sand and gravel lenses. Wells are typically finished in the underlying bedrock. Wells commonly are developed at or near the drift/bedrock contact. Shallow dug wells may still be used on a limited basis. Shallow monitor wells may be completed in this unit. Many of these mapped areas are shallow to bedrock; mapping may include small areas where bedrock comes to ground surface.
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| Tsg |
Predominantly till, contains sand and gravel lenses of varying thicknesses. These lenses may or may not be interconnected. Wells are developed in these lenses. |
| F |
Fines, predominantly clay and silt, may be laminated. Commonly lacks sand or gravel lenses. Sedimentation occurred in quiet water bodies. Typically associated with lacustrine plains or larger slackwater deposits. |
| Fsg |
Predominantly fines with sand and gravel lenses. This setting is commonly found in valleys. Fines include alluvium, minor lacustrine (slackwater) deposits, till and colluvium. |
| SGf |
Predominantly sand and gravel with minor fines. Typically represents thick sequences of outwash/valley train deposits with minor alluvium, lacustrine deposits, etc. |
| SG |
Predominantly sand and gravel with minor, insignificant fines. Fines may not be reported in well log records. Most common in the Ohio River Valley and Hocking River Valley. |
| SGC |
Limited to portions of the Great Miami River Valley where the probability of encountering a confining or semi-confining zone within the aquifer is high. Such a confining layer would split the sand and gravel into upper and lower aquifers. The thickness and continuity of the confining layer may vary considerably in the mapped area. |
| SGt |
Predominantly sand and gravel with thin covering of till or thin interbedded layers of till. Commonly associated with ice-contact features, i.e. kames, eskers, some moraines, etc. It is also associated where thin beach ridges directly overly till. |
| THICKNESS |
DESCRIPTION |
| <25' |
Less than 25 feet of drift. May include areas where bedrock comes up to the ground surface. Area delineated by Div. of Geological Survey Bedrock Topography and Drift Thickness Maps, soils maps, and well log data. |
| 25'-100' |
25 to 100 feet of drift. |
| >100' |
Areas containing over 100' of drift. Thicknesses over 400' have been reported in isolated parts of the state. These areas are predominantly buried valleys, thick end moraine sequences, or thick drift complexes. |
| YIELD |
DESCRIPTION |
| *Note |
Yields refer to a typical or reasonable sustainable yield. In many areas a very large diameter, screened well or a well screened at multiple levels could produce higher yields. It is also possible that lower-yielding wells could be completed within the mapped area.
Yields also roughly correspond to lithology as well. For example, in an area mapped Tsg with a yield of 25-100 gpm, the sand and gravel layers are probably more numerous, thicker, or better interconnected than in a Tsg with a yield of 5-25 gpm. Also, wells completed in areas with sand and gravel lenses occurring at several elevations (i.e. "stacked" sand and gravel lenses) may be able to be screened at multiple depths. This would help to increase the overall yield of wells developed in the drift.
Maximum sustainable yields in the "lower" aquifers may be questionable in some areas. In such areas, well logs typically indicate thicker coarse deposits, but high-yielding wells are lacking in the vicinity. Test-drilling or geophysical techniques may be necessary to locate the higher-yielding units. The lateral extent of these units may also be unknown. Many of these units are not overlain by modern streams or may have an overlying aquiclude which inhibits recharge. In these situations, the long-term sustainable yield may be less than anticipated. |
| <5 gpm |
Typically corresponds to areas with thin drift, areas lacking sand and gravel lenses as reported by well logs, and areas where bedrock is almost exclusively the aquifer. |
| 5-25 gpm |
Aquifer is typically thin sand and gravel lenses interbedded in thicker sequences of till, finer-grained alluvial, or lacustrine deposits. |
| 25-100 gpm |
Transitional areas, typically along the margins of buried valley systems, in smaller tributary buried valleys, in coarser alluvial valleys, associated with some end moraines and kames, and in some of the thicker, coarser beach ridges. |
| >100 gpm |
Commonly associated with buried valley systems containing appreciable outwash sand and gravel, some kame complexes. |
| >500 gpm |
Limited to thick, continuous outwash (valley train) deposits within buried valley systems. These aquifers tend to be in hydraulic connection with surficial water and have higher recharge rates. These areas contain reported high-yielding, large diameter municipal or industrial wells. |
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| SETTINGS |
DESCRIPTION |
| Buried Valley |
Thick drift filling previously existing valley incised into bedrock. Drift thickness typically >100ft. Predominantly contains fines (silts, alluvium, lacustrine, etc.) and sand and gravel. Modern streams commonly overlie these features. Yields are typically 100 gpm or greater. |
| Ground Moraine |
Moderately thick drift (25-100ft) composed primarily of till. Yields are obtained from thin, interbedded lenses of sand and gravel. Commonly associated with broad uplands between stream valleys. |
| End Moraine |
Moderately thick (25-100ft) to thick (>100ft) drift primarily composed of till. Water is obtained from thin, interbedded lenses of sand and gravel. Commonly correspond with end moraines as mapped on the Glacial Map of Ohio and other Division Of Geologic Survey publications. These features are typically ridges with hummocky topography. They often function as local drainage divides. |
| Thin Upland |
Areas of thin drift (<25 ft). Drift typically is comprised of weathered till, commonly lacks sand and gravel lenses capable of sustaining yields. Underlying bedrock is close to surface and is usually the aquifer. Topography is commonly bedrock-controlled. |
| Alluvial |
Areas containing modern streams not associated with major buried valley systems. Includes primarily fines, water obtained from interbedded lenses or layers of sand and gravel. Drift is typically <100 ft. |
| Outwash/kame |
Areas containing mixture of sand, gravel, and till. Commonly associated with kames, eskers, and outwash areas not overlying major buried valleys. |
Thick Drift
Complex |
Areas of thick drift (usually >100ft). Drift typically comprised of thick accumulations of glacial till (and lacustrine). Water is obtained from thin, interbedded lenses of sand and gravel. Areas may consist of a combination of settings such as end moraine overlying a buried valley. |
| Valley Fill |
Limited to Ohio River Valley deposits only. Thickness varies, but is usually over 100 ft. Contains predominantly sand and gravel as well as finer alluvium. Yields are commonly over 100 gpm. |
| Lacustrine |
Includes areas of Lake Plain adjacent to Lake Erie. Commonly fine-grained silts and clays containing thin, interbedded lenses of sand and gravel. Also includes some areas where the underlying till was heavily eroded by wave activity. Inland, refers to settings containing fine-grained lacustrine and slackwater materials deposited in ponded areas. Ponded areas typically occur between end moraines in western Ohio or in alluvial valleys in eastern Ohio. |
| Beach |
Refers to typically thin, linear features found on the Lake Plain in northern Ohio. Includes dunes, deltas, and other coarse-grained shoreline deposits. Comprised primarily of sand and gravel. Locally, can be important shallow aquifers. |
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