Document Type



Groundwater contamination; Well water contamination


Two hundred wells in the northeastern Iowa counties of Winneshiek and Allamakee were analyzed for nitrate concentration and coliform bacteria. The degree of well water contamination was found to correlate with aquifer tapped, type of well construction, and proximity to barnyards. Wells which terminated in the Galena Limestone aquifer usually showed evidences of surface pollution. Deeper wells which terminated in St. Peter Sandstone were found to produce consistently good water when cased into the sandstone. However, the water quality from a group of St. Peter Sandstone wells in which the overlying limestone was not cased out was not better than that in the Galena wells. Nitrates and coliform bacteria were tested periodically during the calendar year 1973 and summer 1974, in a group of seven wells. The water in the two deeply cased wells from this group consistently tested safe for drinking. The other five wells in which the overlying limestone was not cased out showed fluctuating nitrate levels 10- to 200- fold greater than the deeply cased wells and exhibited intermittant coliform contamination. These data are interpreted as evidence that surface contamination enters the fractured and cavernous Galena Limestone and is drawn into wells in response to pumping. This condition also occurs in deeper wells finished in the St. Peter Sandstone in which the Galena interval is left uncased. It indicates that when the wells are idle the water from the Galena, having a higher static head than the water from the St. Peter, probably moves down-hole into the St. Peter and contaminates the sandstone in that vicinity. This study supports a recommendation that new wells drilled through the upper cavernous limestone to deeper aquifers should be cased from the surface into the top of the St. Peter Sandstone with the pipe grouted in place with cement for its full length. This will protect the sandstone from contamination and insure high quality well water. Old wells extending to the St. Peter Sandstone that are to be abandoned should be properly plugged.

Publication Date

March 1977

Journal Title

Proceedings of the Iowa Academy of Science





First Page


Last Page



©1977 Iowa Academy of Science, Inc.



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