Mohseni, Omid

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.

A pilot study was conducted to characterize and map the areas susceptible to slope failure using state-wide available data. The objective was to determine whether it would be possible to provide slope-failure susceptibility mapping that could be used by local road and highway officials to understand better where slope failure may occur. This would allow the possibility of taking preventative measures where indicated; or developing contingency plans for areas of likely failure. As a first step; a review of pertinent slope-failure literature was conducted to determine which past studies could offer information or guidance useful for developing the mapping. The review helped identify which methods and factors could be most effectively used in assessing susceptibility to slope failure. Then; using physics-based concepts; and making use of publicly-available topographic; soils; and hydrologic information; an approach was developed for using the data to identify conditions under which slope failure would be likely. This approach was incorporated into a GIS-based model that produced mapping wherein slopes were identified and assigned one of five levels (very high to very low) of slopefailure susceptibility. The model was tested against a relatively small area in Carlton County to confirm that the indicated susceptibility to failure correlated well with locations in which there was observable or documented slope failure. The method was then validated by applying it to small areas in Sibley and Carver Counties where slope failures had occurred. Having validated the underlying physics-based approach; the mapping was then expanded to two Carlton and Sibley Counties.

The Minnesota Department of Transportation (MnDOT) in conjunction with the Saint Anthony Falls Laboratory (SAFL) has conducted a research study on the use of matrix riprap, or partially grouted riprap, as a spill-through abutment countermeasure. Spill-through abutments at river bridges require a countermeasure to protect the abutment from erosion and scour and often riprap is used. However obtaining large enough stone to protect the abutment can significantly increase construction costs. Matrix riprap, or partially grouted riprap, is an option that will allow for smaller stone, that when partially grouted, will provide equivalent protection to larger sized riprap. This study focused on matrix riprap applied to bridge abutments and included a review of published literature; site visits and observation of matrix riprap installation; laboratory experiments to evaluate matrix riprap application/installation (e.g., non-hydraulic experiments looking at rock and grout placement); experiments to test matrix riprap on a prototype abutment within a flume (hydraulic flume experiments), and finally hydraulic experiments focused on quantifying matrix riprap strength (steep flume experiments). Study results showed that the shear strength of matrix riprap was determined to be more than three times greater than conventional riprap in a laboratory setting. Additional investigation should be completed to better understand the application and performance of the matrix riprap, however this study can be used to support the use of matrix riprap in place of larger stone or other bridge countermeasures.

In order to improve the performance of standard sumps as a best management practice (BMP) in treating stormwater runoff, a baffle was designed to be installed as a retrofit in standard sumps. The retrofit is a porous baffle called "SAFL Baffle." The effect of the SAFL Baffle on the performance of standard sumps was assessed by conducting laboratory tests on small scale as well as full scale straight flow-through standard sumps equipped with the baffle. In addition, a number of tests were conducted to determine the performance of standard sumps with the SAFL Baffle when the baffle is clogged with debris like trash and vegetation. Furthermore, the performance of two other configurations of the baffle was studied: (1) the SAFL Baffle in a sump with an outlet pipe 90 degrees to the inlet pipe, and (2) the SAFL Baffle in a sump with some water entering the sump through an overhead inlet grate. Standard sumps equipped with the SAFL Baffle were evaluated using two metrics: (1) How well the system captures sediment during low flow conditions (Removal Efficiency Testing), and (2) how well the system retains the previously captured sediment during high flow conditions (Washout Testing). The results of the tests showed that the SAFL Baffle dissipates the energy of water entering the sump and as a result, at low flow rates, it captures sediment better than a standard sump with no baffle. More importantly, at high flow rates, the washout of the previously captured sediment reduces to near zero. Vol 1 is 2011-08.

Volume I: Standard sumps are installed in many urban and suburban storm sewer systems. They may qualify as a best management practice (BMP) to pre-treat stormwater runoff by removing suspended sediment from the water. However, no data exist on the effectiveness of sediment removal by and maintenance requirements for sumps. Such data could justify giving pollution prevention credits to transportation departments, municipalities, counties and other local governments for the use of standard sumps. To determine whether the standard sumps remove suspended sediments from stormwater runoff, two standard sumps with different sizes were tested in a laboratory setting to determine their removal efficiencies under lowflow conditions as well as the effluent concentrations under high-flow conditions. The removal efficiency tests included feeding a specific sediment size and concentration into the influent pipe and then collecting, drying and weighing the sediments removed by the sump at the test conclusion. The high-flow condition tests involved placing a commercial sediment mix inside the sump and assessing the amount of sediment remaining after the sump was subjected to high flows for a period of time. At the conclusion of testing, removal efficiency functions as well as washout functions were developed for the sumps, which can be used to predict the performance of all standard sumps. In addition, an uncertainty analysis was conducted to aid with data interpretation.

Hydrodynamic separators are widely used in urban areas for removal of suspended sediments and floatables from stormwater due to limited land availability for the installation of above ground stormwater best management practices (BMPs). Hydrodynamic separators are often sized based on 2-yr stormwater runoff from the drainage basins that they serve. However, during less frequent storm events, e.g. 10-yr storm events, device design treatment rates are exceeded and previously captured sediments can be scoured and washed out. At the St. Anthony Falls Laboratory, three devices have been studied and tested and, subsequently, a testing method has been developed to assess sediment retention in hydrodynamic separators under flow rates exceeding their maximum design treatment rates (MDTR). This new testing protocol has been used in controlled field and laboratory tests on full-scale commercial devices under high water flow conditions to determine sediment retention performance of hydrodynamic separators. In addition, velocity profiles have been taken to observe the complex flow patterns in these devices. Application of this work is primarily to establish the frequency of required cleaning for installed devices.

A study was conducted to generate knowledge on the environmental effects of de-icing salt, particularly sodium chloride (NaCl), on water quality in Minnesota, especially the Twin Cities Metropolitan Area (TCMA). The Mississippi River receives substantial sodium chloride inputs from the Minnesota River and waste water treatment plants as it passes through the TCMA. In addition, road salt applications in the TCMA use about 350,000 short tons of NaCl every year. A chloride budget at the scale of the TCMA and on individual sub-watersheds in the TCMA indicates that about 70% of the road salt applied in the TCMA is not carried away by the Mississippi River. Rates of seasonal road salt use are correlated with snowfall, road miles and population. Salinity in TCMA lakes increases in winter and decreases in summer. Ionic composition of dissolved substances in lakes of the TCMA suggests unnaturally high sodium and chloride concentrations compared to lakes and other water bodies in the Midwestern U.S. Data indicate a rising trend in urban lake water salinity over the last 30 years. Shallow groundwater in the TCMA, especially near major roadways, has started to show increasing chloride concentrations. Salinity trends in lakes and shallow aquifers of the TCMA are of concern.

The objectives of this research were threefold: to investigate the feasibility and practicality of field testing to assess the performance of underground devices used for stormwater treatment in urban areas; evaluate the effects of sediment size and stormwater flow rate on the performance of four different manufactured devices; and to develop a universal approach for predicting the performance of a device for any given application. Field testing that used a controlled and reproducible synthetic storm event that contained sediment of a fixed size distribution and concentration fed to pre-cleaned devices led to the development of uniform performance models. The results of this project show that controlled field tests are a practical, robust and accurate means of determining an underground device's performance, based on solid size distribution and density of the influent, in addition to water discharge and temperature. This premise was successfully verified in field tests on four devices and in laboratory tests on two devices. The resulting protocol and results of testing will be a useful tool for consultants, manufacturers, local governments, and state agencies for selecting, sizing, and evaluating stormwater treatment technologies to protect water resources.

It has been about fifteen years since soil bioengineering and bioengineering technology have been used in projects to protect slopes and river banks against erosion. Now many consulting firms as well as state and federal agencies promote and practice these techniques. Despite a widespread support of these techniques, many projects have failed. Therefore, it is deemed necessary to develop a set of design guidelines to ensure a higher rate of success. In order to develop design guidelines for soil bioengineering and bioengineering technology, a pilot study was conducted to determine the amount of work already done in these areas, and to define the existing research needs. This report comprises (a) a summary of literature review, (b) interviews with eleven practitioners in the field, (c) an evaluation of three projects done in Minnesota, (d) current research needs, (e) and a brief evaluation of three sites in the vicinity of the Twin Cities area as potential outdoor laboratories to conduct research in the needed areas. It also includes a summary of a site visit of the department of Soil Bioengineering and Landscape Construction at the University of Agricultural Sciences in Vienna, Austria. The study shows that a significant number of studies have been done on topics related to soil bioengineering techniques. However, these studies mainly address the problems at a micro scale, and hence, there is a gap between existing knowledge and practice. Therefore, there is an urgent need to not only study some of the fundamental processes and mechanisms involved in soil bioengineering techniques, but also to investigate these processes at a macro scale to evaluate their strengths and impacts when applied to streambanks and slopes.