Silurian-Devonian Aquifer

The Silurian-Devonian aquifer is composed mainly of porous dolomite of Silurian age, and limestone and shale of Devonian age. The aquifer is usually described as a single unit because the rocks making up the individual units are similar in hydrogeologic properties and are hydraulically connected.  In eastern and northern Iowa, where the aquifer ranges from 200 to 400 feet thick and may yield 150 to 400 gpm, it is an important source of water for many users.  Locally, differences in rock types cause the Silurian and Devonian to behave as separate aquifers with different water quality properties.  Although significantly thicker toward the southwest water quality rapidly deteriorates in that direction, especially where the aquifer is overlain by shales.   In western and southwestern Iowa, where the aquifer is deeply buried beneath younger rocks the well-developed fracture systems found in the eastern subcrop area are proportionately fewer and the yields are smaller.  Recharge??  The regional flow of groundwater in the Silurian-Devonian aquifer is to the southeast. Natural discharge from the aquifer toward valleys contributes significantly to the amount of water flowing in the some northern Iowa rivers. The aquifer thus serves as an important source of baseflow to these streams.

Silurian Devonian Aquifer

• Geology
  Overview
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  Borehole data
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Groundwater Quantity
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Modeling
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Pump test data


• Groundwater Quality
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  For further information:  Iowa’s Groundwater Basics by Jean C. Prior, et al, Iowa Dept. of Natural Resources, Iowa Geological Survey Educational Series 6, 83 pages.