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Development of Groundwater Flow and Solute Transport Models to Simulate Contaminant Transport and Well Capture at the NIROP Facility, Fridley, Minnesota

Project Chief: Hal Davis
Cooperator: Department of Defense, U.S. Navy
Period of Project: January 2010 - October 2012

Problem Statement

Figure 1. Naval Industrial Reserve Ordnance Plant in Fridley, Minnesota.

The Naval Industrial Reserve Ordnance Plant (NIROP) is located on the southernmost tip of Anoka County, Minnesota, within the city of Fridley and approximately one-quarter mile east of the Mississippi River (fig. 1). Industrial production began at NIROP in 1941 with a manufacturing facility and it has been in continuous operation ever since, producing weapon systems of increasing complexity. Solvent spills and other disposal practices in the past led to significant groundwater contamination beneath the facility. A groundwater recovery (and containment) system began operation in 1992 in an effort to prevent contaminated groundwater from migrating off site. The U.S. Geological Survey evaluated the drawdown and recovery response of the monitoring wells in an effort to determine well capture zones and further delineate the geology in 2007.

Part of the difficulty in evaluating the recovery system is due to the complex geology which consists of river and glacial-drift deposits ranging in thickness up to 130 ft. These deposits consist of a combination of fine, medium, and coarse sand, gravel, and discontinuous very fine-grained (clay, silty clay, sandy clay, and silt) interbeds.

Objectives

1) Develop a groundwater flow and solute transport model that can simulate hydrologic conditions at the NIROP facility

2) Use the model to simulate capture zones of both actual and proposed wells

Approach

The groundwater and solute transport modeling included assembly of model datasets (boundary conditions, aquifer characteristics, water levels, etc.), calibration of models, and use of models to define well capture zones. The approach for the groundwater model development included seven separate tasks:

1) Review of the existing groundwater flow models and model documentation to develop an understanding of the approach used by others to simulate the aquifer conductivities, vertical conductance, river presence, and boundary conditions;

2) Completion of a literature review to determine pertinent research, locate potentiometric maps, and information on the area; and develop geologic understanding of NIROP hydrology and the area surrounding NIROP;

3) Development of a groundwater flow model using MODFLOW that incorporates the NIROP site and surrounding area geology. The model was calibrated using historical water levels, stream flows, and pumping rates from the site;

4) Development of a solute transport model using MT3D/RT3D. The model was calibrated to historical contaminant concentrations measured at the site;

5) Use of the calibrated groundwater flow and solute transport models to simulate capture zones for the existing and proposed pumping wells, and to determine the extent to which contaminants are being contained by the pumping wells;

6) Attend meetings with the Navy, state, and federal regulators to present modeling results;

7) Documentation of methods and results in a USGS report.

Results

The groundwater and solute transport modeling is in the development phase and results are not available yet.

Information Product

A USGS scientific investigations report (SIR) will describe the groundwater flow and solute transport models used to simulate contaminant transport and well capture at the NIROP facility in Fridley, Minnesota.