In 2011; the Minnesota Department of Transportation (MnDOT) installed an iron-enhanced sand filter (IESF) at Trunk Highway (TH) 610 and County Road 81 in Maple Grove; Minnesota. This feature is a two-cell filtration system into which part of Trunk Highway 610 and County Road 81 drain. From 2012 through 2018; MnDOT monitored the influents and effluents into the IESF to determine its effectiveness in removing particulate and dissolved phosphorus from stormwater runoff from the nearby highways. MnDOT also retained Barr Engineering Co. (Barr) to analyze the data collected during this period. As part of the data analysis; Barr developed a hydrologic model to account for all inflows and outflows from the system. The model was calibrated to the data collected in 2018 and applied to the prior years. The results of data analysis and watershed modeling showed that all influents and effluents have not been accounted for and the collected data were inconclusive in assessing the effectiveness of this IESF. This report summarized the analyses performed on the data collected; determined the potential effectiveness of the IESF; and provided some guidelines for design and future monitoring of other IESFs.
The first MnModel hydrographic modeling procedures were developed in 2008 (Stark et al. 2008) utilizing modern hydrographic data, digital soils data, and geomorphic data to model locations of historic and prehistoric surface water. MnDOT updated the hydrographic model in 2018 to take advantage of the newly digitized data from the Public Land Survey maps, more comprehensive digital soils data (gSSURGO), statewide geomorphic data from the MnModel Phase 4 Landscape Model, and wetland distributions as modeled by the MnModel Phase 4 Historic Vegetation Model. The updated procedures produce two models, one for historic hydrography and one for prehistoric hydrography. The historic hydrographic model approximates surface water features (lakes, rivers, varied types of wetlands, and floodplains) at the time of the Public Land Survey. The prehistoric hydrographic model approximates surface water features over a time period exceeding thirteen thousand years, using historic hydrographic data, soils data, geomorphic data, and modern hydrographic data to identify areas that provide evidence of having been lakes, wetlands, shores, and floodplains at some time in the more distant past.
