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Warning: This page is an edit and testing page use by the wiki authors. It is not a content page for the Manual. Information on this page may not be accurate and should not be used as guidance in managing stormwater.

February 2022

It's been several months since our last update, as we were wrapping up a number of projects.

Updates to the Manual (February 2022)

• Street sweeping: We continue to update information on street sweeping. Below is a summary of the latest updates.
  • Recommended street sweeping practices for water quality purposes: This page includes a summary of recommended practices at the top of the page.
  • Case studies for street sweeping: In December we conducted interviews with staff from seven cities that were implementing street sweeping for water quality purposes. The interviews illustrate how cities are modifying their sweeping efforts to enhance water quality objectives. Information from these interviews were used to develop the recommended practices mentioned in the previous bullet.
  • Street Sweeping Phosphorus Credit Calculator How-to-Guide: This handy quick guide summarizes how to use the street sweeping calculator.
  • What's next: We plan on meeting with several stakeholders to identify additional tools and resources they would like to help continue enhancing street sweeping for water quality. Following this meeting, we will determine what tools and resources we can produce. These will be incorporated into the Stormwater Manual as appropriate and further communicated through other means such as newsletters.
• We have developed total suspended solid (TSS) and total phosphorus (TP) credits for manufactured treatment devices. These credits represent the reduction in TSS or TP loading expressed as a percent for water treated by the device. There are additional needs for crediting mtds, including the following.
  • Calculation of annual load reductions. The credits established for mtds only represent the percent reduction for water treated by a device. The volume of water treated by a device, typically expressed on an annual average basis, must be determined before calculating an annual pollutant reduction for the device.
  • Credits for dissolved phosphorus (DP). TP credits are currently limited based on the assumption the devices are not removing dissolved phosphorus. The credit scheme includes three tiers. Tier 3 will include credits for removing DP. Before Tier 3 credits can be determined, however, we must develop methods for calculating the performance of a device with respect to DP. Ultimately, DP credits may be given for devices that have a mechanism for removing DP (e.g. an amendment) or that retain runoff water (e.g. through infiltration).
  • Time frame: We anticipate completing guidance for calculating annual loads and for assigning Tier 3 credits by this summer.

What are we working on (February 2022)

• Iron enhanced sand filters. In 2019 we compiled a spreadsheet containing information on 164 iron-enhanced sand filters (IESFs) in Minnesota. At the time there was limited performance information for these bmps. We have executed a work order to revisit a subset of these bmps and analyze their performance. The resulting information will be used to update guidance on design, construction, operation, and maintenance of IESFs. Projected timeline - late summer 2022.
• Vegetation:
• Street sweeping: We are developing guidance on street sweeping (e.g. when and where to sweep, costs, managing sweeping wastes, etc.) and that should be available in early summer. We also expect to provide information on how to incorporate sweeping into the MIDS Calculator.
• Green infrastructure: A long-term project to improve information on Green Stormwater Infrastructure in the Manual started earlier this year. We recently added some case studies and anticipate having information on O&M this summer.
• Vegetation: Another long-term project to improve information in the Manual, this work has only recently started and is in a scoping phase to identify information needs on the topic of vegetation in stormwater practices.

Featured article - Chloride in runoff (February 2022)

It is widely acknowledged the most effective strategy for protecting receiving waters from chloride pollution is by reducing use of chloride-deicers. But elimination of deicers is not practical in the foreseeable future. Are there ways to manage urban runoff having elevated chloride concentrations?

A workgroup of stormwater and groundwater professionals recently produced a white paper, published by the Minnesota Groundwater Association, that addresses this topic. the paper, titled Impacts of Stormwater Infiltration on Chloride in Minnesota Groundwater, provides a discussion of chloride in stormwater runoff and potential groundwater impacts associated with infiltration of stormwater runoff.

Chloride concentrations in stormwater runoff are highly variable and seasonally dependent. Concentrations in winter range from several hundred mg/L to as high as 40,000 mg/L, with typical concentrations being closer 1000 mg/L. Concentrations outside the deicing season are typically less than 50 mg/L, with concentrations decreasing from spring into fall.

Chloride is toxic to aquatic life, with the aquatic life standard being 230 mg/L. The drinking water standard is based on taste and is 250 mg/L. Chloride is also toxic to vegetation, can corrode materials, and can inhibit lake mixing, which may in turn result in changes in phosphorus cycling.

Though chloride is not retained in soil, studies indicate it is attenuated in soil. As a result, there is a lag time between chloride entering soil, including a media-based stormwater best management practice, and its eventual movement to a receiving water. Understanding this process and the eventual receiving water can help manage runoff containing chloride.

Some other stuff of interest (June 2021)

• Stormwater is a major pathway for microplastics to receiving waters. Bioretention is an effective practice for retaining microplastics. ES&T Water, May, 2021.
• Stormwater Receives a ‘D’ in First-Ever ASCE Report Card Appearance - ASCE’s D+ for stormwater infrastructure results from decades of chronic underinvestment. Stormwater Report, March 2021.
• Nevada becomes the first state to formally ban “non-essential” grass. Digital Journal
• Stormwater newsletters
• On-going webinar series
• Stormwater research