Geology topics

Research about Iowa River alluvial aquifer

Source-linked reports with geographic coverage including Iowa River alluvial aquifer.

3 recordsLinked to original sources

USGS2025

Conceptual and numerical groundwater flow model of the Iowa River alluvial aquifer near Tama County, Iowa, 1980 through 2022

The Iowa River alluvial aquifer is an important source of water on the Meskwaki Settlement in Tama County, Iowa, which is land owned by the Sac & Fox Tribe of the Mississippi in Iowa (commonly known as the Meskwaki Nation). The U.S. Geological Survey constructed a groundwater flow model, including a conceptual and numerical model, of the Iowa River alluvial aquifer and underlying hydrogeologic units near the Meskwaki Settlement in Tama County, Iowa, for the period of January 1980–August 2022 to estimate the fraction of water pumped from the Iowa River alluvial aquifer by Meskwaki Settlement wells that is derived from streamflow depletion in the Iowa River and its tributaries. Streamflow depletion is a reduction in streamflow caused by groundwater pumping and includes the interception by groundwater production wells of water that otherwise would have been discharged to streams (called “captured groundwater discharge”) and induced infiltration of streamflow to the production wells. Calibrated model runs were performed with no simulated pumping and simulated pumping only at Meskwaki Settlement wells, and the change in simulated flow rates between the groundwater system and streams for the two model runs represents the amount of streamflow depletion in the Iowa River and tributary streams resulting from pumping at the Meskwaki Settlement wells. Streamflow depletion in the Iowa River and its tributaries as a percentage of simulated pumping at the Meskwaki Settlement wells was calculated by dividing this difference by the total simulated pumping rate for the Meskwaki Settlement wells. The model results demonstrate that the mean monthly streamflow depletion, including induced infiltration and captured discharge, in the Iowa River and its tributary streams as a percentage of mean monthly pumping at the Meskwaki Settlement wells was 97.4 percent and ranged from 65.4 to 112 percent. Of the total streamflow depletion, mean monthly induced recharge was 20.9 percent and ranged from 4.9 to 37.2 percent. Mean monthly captured discharge was 76.5 percent and ranged from 57.1 to 97.1 percent. These results indicate that most of the water pumped from the Meskwaki Settlement wells is the result of streamflow depletion, in the form of both induced infiltration and captured discharge.

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USGS1997

Herbicides and nitrates in the Iowa River alluvial aquifer prior to changing land use, Iowa County, Iowa, 1996

The Iowa River alluvial aquifer in Iowa County, Iowa (fig. 1), underlies an area of intensive agricultural activity where pesticides and nitrogen-based fertilizers are extensively used. The effects of changing land use on shallow ground-water quality in part of the Iowa River alluvial aquifer are currently being investigated as part of the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program. Approximately one-third of the cropland in the study area will be taken out of production over the next few years as part of wetland restoration. Over a three-week period in 1996, the USGS collected water samples from 23 observation wells completed in the Iowa River alluvial aquifer and analyzed the samples for selected agricultural chemicals. Four herbicides (alachlor, atrazine, cyanazine, and metolachlor) and one nutrient (nitrate) were selected for study on the basis of frequent usage in Iowa and high detection rates in ground water (Detroy and Kuzniar, 1988). Alachlor was not detected at concentrations greater than the method detection limit (MDL). Atrazine was detected at concentrations greater than the MDL in samples from 48 percent of the 23 wells, cyanazine from 13 percent, metolachlor from 26 percent, and nitrate from 91 percent. None of the four herbicides were detected at concentrations greater than the respective U.S. Environmental Protection Agency's (USEPA) Maximum Contaminant Level (MCL) for drinking water. Thirteen percent of the samples had nitrate concentrations above the USEPA's MCL of 10 mg/L (milligrams per liter). Relations between constituent concentration and well depth were observed for specific constituents at individual well nests.

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USGS1988

Occurrence and distribution of nitrate and herbicides in the Iowa River alluvial aquifer, Iowa: May 1984 to November 1985

From May 1984 to November 1985, the U.S. Geological Survey, in cooperation with the University of Iowa Hygienic Laboratory and the Iowa Department of Natural Resources, Geological Survey Bureau, investigated nitrate and herbicides in the Iowa River alluvial aquifer. The occurrence and distribution of nitrate and selected herbicides were determined in the Iowa River alluvial aquifer, a sand and gravel aquifer beneath agricultural land along the Iowa River in Iowa County, Iowa. Test drilling and water-quality sampling of the aquifer indicated that the areal distribution of nitrate in the aquifer is variable. Nitrate (as nitrogen) concentrations range from less than 0.10 to 79 milligrams per liter. Although nitrate distribution is variable, extensive aquifer contamination by nitrate is not apparent. Median nitrate concentrations were 5.9 milligrams per liter for municipal wells and 7.2 milligrams per liter for area streams, but were less than 2.0 milligrams per liter for test wells and domestic wells. Atrazine, cyanazine, metribuzin, alachlor, metolachlor, and trifluralin were detected in ground-water samples. Maximum concentration of atrazine in ground-water samples was 2.4 micrograms per liter; maximum concentration of metribuzin was 8.1 micrograms per liter. Area streams also contained herbicides in concentrations generally larger than concentrations in ground water. At a municipal well adjacent to a stream, similar seasonal concentrations of atrazine were detected for both ground- and surface-water samples. Surface water sometimes may be a source of nitrate and herbicides to adjacent ground water. Detailed sampling of vertical profiles using well nests indicated that the distribution of nitrate and selected herbicides is not vertically homogeneous. Generally, larger nitrate concentrations were detected at shallow depths in the aquifer; at greater depths, the nitrate concentrations were near the detection limit. Herbicides were detected in a pattern similar to that determined for nitrate. The true areal distribution of nitrate may be masked by inconsistent depths of sampling or incomplete vertical sampling. Variations in nitrate concentrations with depth possibly are because local aquifer flow is predominantly horizontal and may limit significant vertical dispersion of nitrate and herbicides, and because nitrate may not act conservatively in ground water and may be removed from the system by denitrification. For nested wells, the seasonal variations of nitrate and herbicides were greater at the shallower sampling depths for domestic and test wells. Seasonal variations of nitrate and herbicides illustrate that these constituents move quickly from surface application to shallow underlying aquifers. These constituents can be detected in ground water soon after chemical applications, usually within 6 weeks.

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