RIVERBANK FILTRATION AND THE IMPACT OF AN ALLUVIAL WETLAND ON WATER QUALITY
Induced infiltration from pumping is of concern to municipal water operators due to high nitrate concentrations (often greater than 10.0 mg/L nitrogen) in the Cedar River. The Cedar River upstream of Cedar Rapids is listed on the State of Iowa impared waters list for nitrate. A ground-water flowpath study through natural wetlands in the Cedar Rapids Seminole wellfield was conducted from the fall of 1998 through spring of 2003 to investigate the potential of reducing nitrate concentrations using existing wetland areas and to better understand riverbank filtration processes. Water samples from wells completed in the wetland area contained low nitrate concentrations (0.1 to 4.7 mg/L) compared to the Cedar River (8.0 to 18.4 mg/L) and to an up-gradient well (3.1 to 7.6 mg/L). Conversely, water samples from these wells contained higher iron concentrations (13 to 312 µg/L) and manganese concentrations (4.5 to 1080 µg/L) when compared to the Cedar River (iron2.0 to 25 µg/L , manganese1.6 to 37 µg/L). A recent assessment of denitrification potential of soil types in the Cedar River Basin suggests that soils of alluvial wetlands/bottomland forest may be the areas of highest denitrification potential in the basin. Natural wetland areas might provide improvements in ground water quality as pertains to nitrate, a constituent of concern for public water supply.