Test page 6

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 (June 2021)

• 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 (June 2021)

• 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.
• Engineered media: We continue to populate the Manual with information on engineered media, including amendments and materials in engineered media. This is a significant project and will continue through the summer. We continue to work closely with University of Minnesota researchers working on bioretention media. Most recently we have added information on wood chips and calcium-based water treatment residuals. Click on this link for more information.
• 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.
• Managing stormwater media waste: By this summer we expect to have information on disposal and management of engineered media used in stormwater applications, focused primarily on bioretention media.

Featured article - Pretreatment (June 2021)

The Minnesota Construction Stormwater Permit requires pretreatment for filtration and infiltration practices. Forebays or other pretreatment practices are highly recommended for constructed stormwater ponds. The permit, however, does not specify the type of or sizing for pretreatment practices. We are discovering that many stormwater best management practices (bmps, also often called stormwater control measures or scms) are not performing as designed, often due to heavy sediment loads to the bmp and to poor design.

Proper pretreatment can extend the life and improve performance of downstream bmps. But we frequently hear stories about inadequate or improperly designed pretreatment. This is unfortunate, since the Manual contains a wealth of information on pretreatment. For example, did you know the Manual contains the following?

• A pretreatment selection tool
• Tables with information and links to information on design, sizing, pollutant removal, installation, and maintenance
• Sizing guidelines
• Guidance for managing wastes from pretreatment practices
• Case studies

Below are examples of some design issues that have been brought to our attention.

• Pre-treatment baffles with shallow sumps showing up on plans (2 or 3 foot deep sumps regardless of inlet/outlet pipe size diameters and/or manhole housing diameter). Questions have been raised whether shallow sumps would function the same for large (24 inch +) inlet pipes as they would for smaller inlet pipes. Same issue goes for diameter of the structure. Much deeper sumps would seem to be required for larger inlet pipes.
• Hoods or skimmer devices are being placed over the outlet pipe with baffles, which results in a change to the flow path and likely performance of the baffle. Stormwater should flow “unimpeded” from inlet to outlet as tested in past studies. In addition to effecting the hydraulic flow, trash and floatables will build up and can negatively impact the baffle function.
• Questions specific to the use baffles with the following designs have been raised.
  • Multiple inlet pipes entering a manhole with a baffle. Observations have been made where the design shows the flows short-circuit the baffle, undermining expected treatment and promoting premature bypass.
  • Grated inlets which does not direct flows to one side of baffle, resulting in flows and pollutants prematurely bypassing the pretreatment device

The information in the manual could be better organized and made more accessible. So, we hope to execute a work order this summer to better organize the information on pretreatment. You can help by providing the following (NOTE: We cannot endorse or promote specific commercial products, processes, or services).

• Examples (case studies) of good and bad pretreatment practices you are finding
• Photos
• Comments and suggestions for improving information on pretreatment

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