Preliminary Results from a New Ground-Water Network in Northeastern Mississippi

Author(s): Manning, M.; Rose, C.; Welch, H.; Coupe, R.

In 2010, the U.S. Geological Survey established a new groundwater network to better understand the influence of agricultural land use on shallow groundwater quality. The areal extent of the study spans from southwestern Tennessee southward through the middle of northern Mississippi. A 30 well network overlays the basic recharge area that conforms along the eastern outcrop boundary of the Middle Claiborne Group, (Sparta Sand) within Tennessee and Mississippi. Well locations were randomly selected using a grid of 30 polygons generated by a geographical information system (GIS) model. Monitoring- well locations were then selected for each GIS-generated polygon that best fit both agricultural land use, and location to the outcrop area. These areas of outcrop for the Sparta Sand provide a hydrologic connection between the aquifer, and surface-water sources such as rivers, lakes, and rainfall runoff. This study will investigate the shallow groundwater quality of the Sparta waters on the eastern edge of the formation that could be altered by agricultural land use and will document any unfavorable compounds that may be carried into the aquifer.

During the fall of 2010, 15 of the new 30 well network were drilled and established on private properties located in northeastern Mississippi. These new monitoring wells were installed using a rotary drilling-type rig until the first water was identified. Using historical data, potentiometric surfaces were estimated to range from zero (land-surface) to about 30 feet below land surface. During the initial well drilling, the first water was encountered anywhere from 12 to 40 feet below land surface. All of the wells were screened at a 10 foot interval from the bottom of the well. Each well screen was set within mixed marine/deltaic facies consisting mostly of sand to sandy silty clays which are considered consistent with most Sparta Sands. Most of the wells were drilled within an area consisting of a least 60 percent or more local agricultural land-use. The locations were selected because the landowners were interested in the study, allowed accesses to their property, and they possessed land that had active agricultural activities that included corn, cotton, and /or soybeans.

The lower extent of the two-state study area was sampled for groundwater quality from March through April 2011. Water samples were analyzed for a wide range of constituents, including but not limited to trace elements, inorganics, nutrients, dissolved gases, tritium, and a full spectrum of pesticide compounds. The well network will be re-visited annually to monitor water levels, and a subset of five wells will be sampled every other year. Future plans are to re-sample the entire network for water-quality trends on a 10-year rotation. Land-use surveys were conducted within a 500-meter radius of each well to determine the current land use, and to provide a baseline for future land-use changes.

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Technical Sessions

1 Best Management Practices #1
2 Delta Water Assessment
3 Flood Assessment & Mgmt.
4 Wetlands
5 Watershed Mgmt. #1
6 Non-Point Source Assessment
7 Modeling
8 Water Quality
9 Best Mgt. Practices #2
10 Delta Water Conservation
11 Sedimentation
12 Storm Water
13 Watershed Mgt. #2
14 Public Water Systems
15 Surface Water Assessment & Evaluation

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