Runoff

Storm-water runoff from the Woodbridge neighborhood of the City of Shoreview had previously been managed through culverts and other hydraulic structures. In adherence to the Clean Water Act, many watersheds instituted limits to the percentage of storm water that may be allowed into certain lakes and rivers. To minimize this run-off and the associated impacts and in accordance with the City’s sustainable design policy, the City of Shoreview built the Woodbridge neighborhood local roads using pervious concrete pavements in 2008. Pervious concrete pavements exhibit high hydraulic conductivity and high sound absorption coefficient in local or low volume roads. They also provide cost savings through the minimization of hydraulic structures.

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 2023-21, “Climate Change Adaptation of Urban Stormwater Infrastructure,” published August 2023.

The final analysis of historical (TP-40), current (Atlas 14), and future predicted storm events for three watersheds in Minnesota (Duluth, Minneapolis, Rochester) has shown that current design philosophy is not sufficient to prevent flooding from 10-year and larger design storm events and that flood depth and duration will increase given current climate projections. Several stormwater infrastructure adaptation strategies were assessed for reducing flood depth and duration: Baseline (existing conditions), adding rain gardens (aka, Infiltration Basins), adding new wet ponds, retrofitting existing stormwater ponds to be “Smart Ponds, adding new Smart Ponds while also converting existing ponds into Smart Ponds, or upsizing of stormwater pipes to convey more water. In watersheds that are mixed urban, suburban, and rural like Rochester’s Kings Run or Duluth’s Miller Creek sub-watersheds, the most cost-effective climate change adaptation strategy was to build new stormwater wet ponds (Extra Ponds strategy) to treat the impervious surfaces not currently treated by existing wet ponds and other stormwater BMPs. In the fully developed urban 1NE watershed in Minneapolis, the most cost-effective (excluding land costs) climate change adaptation strategy was building wet ponds (Extra Ponds). Securing property for building new stormwater infrastructure in fully developed urban watersheds like 1NE may be a substantial cost compared to other watersheds. Smart Ponds do not require additional land for implementation and thus represent a relatively low-cost alternative that will be more beneficial in watersheds with numerous existing wet ponds.

This report provides a summary of the current Storm Water rules and proposed rules as they may effect the construction and operation of the streets and highways of Minnesota Cities and Counties. This report also summarizes The Quantity and Quality of Runoff from Selected Guttered and Unguttered Roadways in Northeast Ramsey County, Minnesota; a study and resulting report that was conducted for the Minnesota Local Road Research Board (LRRB) by the United States Geological Survey. The rules summarized include the Federal Phase II Storm Water Rules, the Minnesota Pollution Control Agency's response to the proposed rules, and the process of obtaining Industrial and Municipal Storm Water Permits and Construction Storm Water Permits.

The Stockpile Runoff Project addressed environmental concerns regarding the quality of runoff water from salvaged pavement stockpiles. Three experimental stockpiles were studied, one pile consisted of coarse concrete, a second consisted of fine concrete material, and the third consisted of salvaged bituminous material (recycled asphalt product) obtained from a pavement milling project. The leachate water from the piles flowed through a sampling and flow monitoring system with data loggers and automated sequence samplers. Composite water samples were analyzed using EPA approved methods and quality control protocols. Comparing the observed median values for the stockpile runoff with Minnesota standards for surface waters, the pH exceeded and chromium may have exceeded the standards. Although there are sediment and leachates emanating from stockpiles, the long-term concern reduces to suspended and dissolved solids, and pH. Polynuclear aromatic hydrocarbons (PAH) concentrations from the bituminous millings pile were near or below detectable limits. Planning for stockpile storage sites should include management practices of controlling runoff similar to those that are used for construction sites. Berms, straw bales, grass or other filter channels, and locating stockpile sites some distance from surface waters may be appropriate practices. Possible impacts on the ground water system should be considered.

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.

Accelerated soil erosion and the sedimentation caused by it pose serious problems for the construction industry and state and local agencies. Runoff from construction sites has high sediment loads which may contain various pollutants, including oil, chemicals, and soil wastes. Natural erosion in ditches and along roadways may result in sedimentation that may result in costly damage to water and land. Drainage channels, culverts, and storm sewers may be filled and plugged by sediment, resulting in frequent and costly maintenance. This report addresses those problems and outlines methods for controlling erosion both during and after construction. Structural and vegetative practices for reducing sedimentation are given, and turf establishment techniques for native grasses and wildflowers are discussed. Information regarding the National Pollution Discharge Elimination System (NPDES) Storm Water Permit Requirements is also given.

This Technical Summary pertains to report 2017-46, Comparing Properties of Water Absorbing/Filtering Media for Bioslope/Bioswale Design, published November 2017.

This Technical Summary pertains to the LRRB-produced report 2017-50, Study of De-icing Salt Accumulation and Transport Through a Watershed, published December 2017.