Water

The design for Interstate Highway 94, east of St. Paul, Minnesota included a dead-end storm water retention pond constructed by the Minnesota Department of Transportation (Mn/DOT), for the purpose of collecting highway runoff. Flow into the pond will discharge primarily through the pond bottom into the groundwater system. Concern for potential impacts to both local and regional groundwater levels prompted Mn/DOT to conduct a groundwater study using an analytical element computer model. Presented in this report is a summary of the analytical aquifer modeling method, including basic theory, fundamental equations, and a brief description of how to access the computer program. As part of the study, an analytical element was developed to permit modeling of inhomogeneities in the aquifer hydraulic conductivity, thickness, and/or base elevation. Basic theory and equations for this element are discussed in the report. Use of the model for the storm retention pond is described including hydrogeology, site description, and simplifying assumptions used in the model. Results of the model are presented, including contour plots of groundwater levels prior to construction of the retention pond, as well as predicted levels when the pond reaches a steady state.

This Technical Summary pertains to Report 2023-25, “Stormwater Pond Maintenance and Wetland Management for Phosphorus Retention,” published June 2023.

Reduction in phosphorus is critical because phosphate, a dissolved form of phosphorus, sustains algal and cyanobacteria growth and causes a wide range of water-quality impairments in the ponds and downstream waters including algal blooms, excess floating plants, taste, and odor problems. Many stormwater ponds and wetlands that treat stormwater appear to be less effective than expected or originally intended in phosphorus retention, a key function of these ponds in urban environments. There is evidence that many old ponds are releasing phosphorus from bottom sediments at high rates and likely exporting phosphorus to downstream surface water bodies. A major outcome of this project is a pond Assessment Tool to assess the risk of high phosphorus concentrations in ponds and sediment release of phosphorus. The tool is based on 20 ponds with detailed water quality and phosphorus release measurements and a meta-analysis of 230 ponds in the Twin Cities metro area. Other outcomes included a working definition of a constructed stormwater pond and a wetland treating stormwater in the framework of water-body regulations, the development of recommendations for stormwater pond maintenance and wetland management, and an update to the sections on the constructed stormwater ponds section of the 2009 Stormwater Maintenance BMP Guide.

In 1973, a planned extension to Interstate 94 between I-694/494 and the St. Croix River was cancelled due to concerns raised by residents. This study is part of a restudy that was ordered by the Commissioner of Highways to find the best route for the freeway, taking in to account the resident's concerns. This report shows the effects of the proposed highway on the the local water system.

Five roadway sections in northeastern Ramsey County, Minnesota were monitored during 1993-95, to evaluate water quality and loading of constituents from roadway runoff. Two snowmelt-runoff and five rainfall-runoff events were monitored per year at each site. Additional samples of rainfall were analyzed to determine if rainfall was a direct source of constituent loading to roadway runoff. Roadway-runoff samples were analyzed for selected physical properties, dissolved solids, nutrients, dissolved ions, selected metals, and semi-volatile compounds. Concentrations of dissolved ions such as sodium, chloride, and metals such as aluminum, chromium, lead, and zinc were detected at much greater levels for snowmelt-runoff samples than rainfall-runoff samples. Analysis of chemical samples from rainfall indicate that rainfall was not a direct source for most constituents. Dissolved nitrate and dissolved ammonia in rainfall, however, can contribute up to one-half the amounts detected in roadway runoff. Concentrations of total phosphorus and fecal Streptococcus bacteria were greater at unguttered sites than at guttered sites. Concentrations of dissolved solids, and some metals were greater at guttered sites than at unguttered sites. This suggests that the vegetated road ditches associated with unguttered sites may filter out heavier particles such as metals and solids, while contributing additional organic matter. Concentrations of aliiminum, copper, lead, and zinc exceeded chronic condition standard limits established by the Minnesota Pollution Control Agency for metropolitan storm water from 96 percent, 52 percent, 9 percent, and 20 percent of the samples collected, respectively. Chemical loadings of specific constituents, such as suspended solids, from an individual rainfall-runoff event accounted for greater than 90 percent of the cumulative loadings of that constituent for all monitored events at site 4, for the entire study period. Length of latent period was statistically compared to constituent concentration levels of total phosphorus, dissolved sulfate, and total zinc and there was a correlation. Constituent loads were not associated with latent period. No correlation was found between traffic volumes which ranged from 1,888 to 7,172 vehicles per day and constituent concentrations or loads for this study.

This Technical Summary pertains to the LRRB-produced Report 2015-41, “Determination of Effective Impervious Area in Urban Watersheds,” published July 2015.

This Technical Summary pertains to Report 2019-22, Investigating Wastewater Reuse at MnDOT Truck Stations.

This Technical Summary pertains to Report 2014-25, “Flocculation Treatment BMPs for Construction Water Discharges,” published August 2014.

This Technical Summary pertains to the LRRB-produced Report 2010-38, “Improved Automatic Sampling for Suspended Solids,” published November 2010.

This Technical Summary pertains to Report 2006-43, “Water Quality Performance of Dry Detention Ponds with Under-Drains,” published December 2006.