The U.S. Geological Survey, in cooperation with the city of Pella, Iowa, conducted a study of the ground-water resources in selected parts of Jasper,Mahaska, and Marion Counties near Pella, Iowa, during 2000?01. The purpose of the study was to describe the ground-water resources in the Pella, Iowa, area. Following a review of available hydrologic and geologic information, the study focused on investigating the alluvial deposits along the South Skunk River within a 10-mile radius of the city of Pella. Thickness, lithologic, and water-quality data for the alluvial deposits in the South Skunk
River Valley were collected at selected sites from
August 2000 through July 2001.
The South Skunk River alluvial aquifer near
Pella consists of stratified deposits of sand and
gravel of glacial and fluvial origin. The upper
15 to 20 feet of the alluvial deposits are interbedded
with flood-plain clay and silt lenses and are
overlain by a developed soil horizon. The alluvial
aquifer is underlain by a thin (less than 50 feet
thick) layer of glacial drift. Glacial drift, as it is
defined in the study area, is a heterogeneous,
unsorted, unstratified, unconsolidated, relatively
impermeable deposit consisting of clay, sand, and
gravel. The bedrock surface beneath the glacial
drift consists primarily of shale and limestone of
Pennsylvanian or Mississippian age. The alluvial
sand and gravel deposits along the South Skunk
River near Pella range from less than 30 to more
than 80 feet thick. Saturated thickness of the alluvial
aquifer ranges from 15 to about 70 feet.
Water-quality samples were collected from
four observation wells installed in the South
Skunk River alluvial aquifer in the study area.
Results of the water-quality sampling show that
the chemical quality of the ground water is generally
similar at all of the sampling sites. All
ground-water samples were low in dissolved oxygen,
which resulted in high concentrations of iron
and manganese and reduced forms of nitrogen.
Additional Publication Details
USGS Numbered Series
Ground Water near Pella and in Selected Parts of Jasper, Mahaska and Marion Counties, Iowa