What's New

This page provides a summary of significant recent changes to this website. We anticipate this page will be updated infrequently. You may also access our responses to comments that have been submitted via the comment box found on each page of the website.

Information: IMPORTANT CHANGES

• June, 2015. Several pages addressing the topic of stormwater credits for runoff volume and pollutants have been added. These are under review through the month of June. These pages are specific to credits for individual BMPs. Each page is formatted similarly and contains information on the basis of credits for the BMP, methods for determining credits, recommended values, and references. Links to these pages can be found here.
• We have added a new page called In the News. You can find it in the left toolbar. If you are aware of a newsworthy event in the stormwater world, send us an email. We don't guarantee including it on the page, but we'll give it a look.
• February 24, 2015. We have created two pdf documents containing sections of the Manual. One is for iron enhanced sand filters and the other is for green roofs. These were created using the Create a Book function in the left toolbar. NOTE that these documents have not been formatted in the manner typical for pdf documents and instead compile different articles from the wiki. There may therefore be unusual formatting. Using the Create a Book function you can build a customized document containing multiple pages from the Manual. See [1] for help on creating a book. If you have an interest in other pdf documents being created, submit a comment using the Help Improve this Page box at the bottom of this page or submit an email to us.
• February 24, 2015. Several pages have been created related to the TMDL Reporting Form, which is a form that must be submitted by MS4 permittees that have TMDL Wasteload Allocation requirements approved by the U.S. EPA prior to August 1, 2013. The following pages have been added.
  • An upload page containing individual TMDL Reporting Forms for those permittees required to submit a form by June 30, 2015.
  • Guidance for completing the TMDL Reporting Form. Quick guides are also available for different sections of the Reporting Form (Activities completed tab and Cumulative reductions tab).
  • Examples for completing the Reporting Form
• January 29, 2015
  • The original Manual recommended using the lowest infiltration rate within 5 feet of the bottom of the BMP when designing an infiltration BMP. In 2013 this was changed to 3 feet based on data presented for other states. Based on our experience over the past year, we are recommending returning to the 5 foot depth. This builds in a factor of safety for situations where you may have a low permeability unit right at the minimum 3 foot separation distance. We have revised the Manual to reflect this 5 foot recommended distance. Therefore, when designing an infiltration practice, use the lowest permeability unit within 5 feet of the bottom of the practice, or, if the separation distance is less than 5 feet, the lowest permeability unit within that separation distance.
  • If using permeameter tests to determine the soil infiltration rate at a site, the recommended number of measurements is 5 per each additional 5000 square feet of area. For large sites, this can result in a large number of samples. We have included a recommendation that the number of permeameter tests may be reduced under certain conditions. One method to determine the number of samples is to plot standard deviation versus sample number. At a point where the curve flattens, infiltration testing may be halted. A minimum of 5 samples is recommended. For more information, see the NOTE in [2].
• January 26, 2015. We continue to make minor changes to the Manual. Some of these changes may be noteworthy and are summarized below.
  • A new page on BMP terminology has been added. This page summarizes the various math terms used throughout the Manual. We initially noticed several inconsistencies in terminology as the Minimal Impact Design Standards work progressed. We believe most of those inconsistencies have been addressed. However, some terminology from the original manual still needs to be addressed and we will trying to update that information over the next couple months.
  • The Construction Stormwater permit requires the water quality volume of one (1) inch of runoff from the new impervious surfaces created by a permitted project to be retained on site (i.e. infiltration or other volume reduction practices) and not discharged to a surface water. The 1 inch represents an instantaneous volume of water captured by the BMP. We are therefore in the process of updating sizing calculations to be consistent with the permit. For an example, see [3].
  • A literature review of bacteria removal in filtration practices shows the removal percentages in the original manual were too high, particularly for vegetated practices. Removal percentages in the original manual were 70 percent for both media and vegetated filters. The values have been updated to 50 percent for media filters and 0 percent for vegetated practices. We anticipate conducting a more thorough literature review in the future to clarify these values.
  • We have expanded the discussion of suspended pavements for tree practices to include Strata cells in addition to Silva cells. See [4]. We have also updated information on soil volume requirements for rock-based systems for tree practices. See [5].
• November 19, 2014. We created a new page called Alleviating compaction from construction activities. This page does not present new information on this topic, but instead brings existing information on alleviating compaction, currently scattered in different places in the manual, onto a single page.
• November 4, 2014. The Tree section of the Manual has been undergoing updates over the past several months. The section is now fully updated

The most recent information on this topic includes the following:

• Design guidelines for tree quality and planting - tree trenches and tree boxes;
• Construction guidelines for tree trenches and tree boxes;
• Protection of existing trees on construction sites;
• Operation and maintenance of tree trenches and tree boxes; and
• Assessing the performance of tree trenches and tree boxes.

NOTE: A street sweeping spreadsheet calculator tool, developed by Kalinosky et al.(2013) and referenced on the street sweeping section of the Manual is now available.

• August 29, 2014: New pages have been added discussing and illustrating the following:
  • Requirements, recommendations and information for using bioretention with an underdrain BMPs in the MIDS calculator
  • Requirements, recommendations and information for using infiltration basin/underground infiltration BMPs in the MIDS calculator
  • Requirements, recommendations and information for using stormwater pond as a BMP in the MIDS calculator
• August 26, 2014
  • A new page has been added discussing and illustrating Requirements, recommendations and information for using green roofs as a BMP in the MIDS calculator
  • A new page has been added discussing and illustrating Requirements, recommendations and information for using permeable pavement BMPs in the MIDS calculator
• August 19, 2014: A new page has been added discussing and illustrating the use of performance curves for the MIDS calculator.
• August 19, 2014: A new page has been added to provide guidance on using the Minimal Impact Design Standards (MIDS) calculator. The page addresses bioretention systems without an underdrain (bioinfiltration).
• August 18, 2014: Four pages have been added to provide guidance on using the Minimal Impact Design Standards (MIDS) calculator. These pages provide guidance and examples for using the MIDS calculator for the following BMPs.
  • Swale with an underdrain
  • Wet swale
  • Swale side slope
  • Sand filter
• August 13, 2014: A page has been added to provide guidance on using the Minimal Impacts Design Standards (MIDS) calculator. This page provides a description of how the calculator treats swales with no underdrain, how credits for volume, phosphorus and TSS are calculated, guidance on using the calculator for swales with no underdrain, and provides an example application of the calculator for this BMP. See Requirements, recommendations and information for using swale without an underdrain as a BMP in the MIDS calculator.
• July 22, 2014: An updated version of the Minimal Impact Design Standards calculator has been released. The newest version of the calculator includes the following updates from the previous version.
  • Tree trench/box credits for canopy interception and evapotranspiration
  • Bioretention with underdrain updated to apply the equation for phosphorus credit reduction based on media depth.
  • Summary table of total phosphorus and total suspended solids percent removal by BMP on the summary tab of the calculator
  • Annual runoff volumes to BMP summary tab was added
  • Bioretention media phosphurus credits to tree box/infiltration trench with underdrain
  • Bioretention medial phosphorus credits to swale with underdrain was added
  • Sizing inputs for stormwater ponds
  • Swale annual TSS, dissolved phosphorus and particulate phosphorus removals were adjusted
  • A stormwater reuse function!
• July 22, 2014: Two pages have been added to provide guidance on using the Minimal Impacts Design Standards (MIDS) calculator. These pages provide a description of how the calculator treats tree trenches/tree boxes, how credits for volume, phosphorus and TSS are calculated, guidance on using the calculator for tree trench/tree box BMPs, and provides example applications of the calculator for these BMPs.
  • Requirements, recommendations and information for using trees as a BMP in the MIDS calculator
  • Requirements, recommendations and information for using trees with an underdrain as a BMP in the MIDS calculator
• May 19, 2014: The Minimal Impact Design Standards (MIDS) Community Assistance Package (CAP) is available.
• April 23: A page addressing stormwater management for lake protection and restoration has been added. The page primarily brings information and links relevant to lake management from other places in the manual together in a single location.
• March 25: A section on Operation and maintenance of tree trenches and tree boxes has been added.
• February 27: The section on design criteria for bioretention has been updated. New and updated information is summarized in a table.
• February 27: The section on construction specifications for bioretention has been updated. This includes new information on soil compaction and alleviating soil compaction, bioretention mixes and planting.
• February 12: A section on road salt has been added. For now, the section is very general and primarily contains links to other sites. We are working with a contractor to enhance this site and it should be updated in late summer, 2014.
• February 3: The Minimal Impact Design Standards calculator is now available.
• January 30: New information on pollutant removal by BMPs has been added. This page includes information on TSS and TP outflow concentrations and removal percentages for ponds, wetlands, grass filters, and sand filters, as well as additional discussion on pollutant removal for bioretention and infiltration BMPs.
• January 30: A table summarizing phosphorus reduction credits has been added.
• January 30: A section on soil amendments to enhance phosphorus sorption has been added.
• January 29: A section on funding has been added in the left column of the navigation page. We added a description of funding opportunities for stormwater projects. You will find information on projects that were recently funded with Clean Water Land and Legacy funds. We also started adding projects that are currently and previously funded. We will continue to add projects to the list.
• January 15: We updated existing information on bioretention mixes A and B and added information for two new mixes (C and D). These mixes are summarized in a table. NOTE that there are recommended changes for Mixes A and B. Mixes C and D were included because they are considered to retain phosphorus, while mixes A and B are considered to leach phosphorus.
• January 15: We added a section on design guidelines for soil characteristics for tree trenches and tree boxes. The site is under review through February.
• January 3: We continue to add material to the section on Trees. The material on the site is currently under either construction or review. Additional material on design guidelines, construction, maintenance, and monitoring of tree trenches and tree boxes will eventually be added. We hope to have the site fully populated within the next month, although it will remain under review for some time after that.
• January 3: We have added some items to the Events page. If you are aware of events that are appropriate for posting, please let us know via the comment box. NOTE: the MPCA cannot promote or endorse specific products, companies, etc. and we must therefore be selective about what events are posted at this site.
• December 20: The phosphorus removal efficiency for bioretention BMPs has been changed. Previously, a single value of 60 percent was given for this BMP. The new values are 100 percent for water that is infiltrated, 25 percent for water that passes through an underdrain, and 0 percent for water that bypasses the bioretention BMP. See Pollutant removal percentages for bioretention BMPs. This change is likely temporary as a technical workgroup is evaluating phosphorus removal rates for bioretention BMPs. Factors such as initial soil/media phosphorus content, depth above an underdrain, and presence of P-sorbing amendments in the soil/media will affect the removal efficiency of the BMP. It is anticipated the recommendations of the workgroup will be incorporated into the Manual in mid- to late January.
• December 16: Following a meeting of technical experts, an infiltration rate of 0.45 inches per hour was established for SM soils. The rate for these soils was previously 0.3 inches per hour. In the original Manual the rate for these soils was 0.6 inches per hour. See Design infiltration rates.
• December 4: We added information to the section on trees. This includes an overview, several tables listing properties for several tree species, and supporting material. We have additional information on trees that will be added in the next couple months, including design guidelines, construction specifications, and more.
• October 9: The section on Vegetated filter strips has been updated.
• September 26: We added two links in the left toolbar. The first is Categories, which provides a shortcut to the list of categories. Categories are basically an index of similar webpages. For example, one of the categories is Photos, which shows all the photos in the wiki. Results of our recent survey suggest people frequently use the Categories feature. The second link in the left toolbar is Response to comments. Unfortunately there is no easy way to display our responses to comments submitted via the Comment box on each page. Clicking on the comment link in the left toolbar shows most comments we receive along with our reply. We encourage people to submit comments using the Comment box on the bottom of each page. Comments can be on content of a page, suggested edits, errata, comments on wiki functionality, etc.
• August 2: A section on filter strips (as pre-treatment) has been added.
• July 16: A section on green roofs has been added. The section includes several pages (articles) discussing different aspects of green roofs, including general terminology, information on design, construction and maintenance, plant lists, references, case studies, and more.
• July 16: A separate page has been created called Information on pollutant removal by BMPs. The page contains links to tables showing data on pollutant removal, sections that contain information on pollutant removal, and external links to information on pollutant removal. The page was created to provide easy access to this data.
• May 21: Information on infiltration practices at contaminated (Brownfield) sites was added.
• May 7: A new section on iron enhanced sand filters was added. It will be open for review through June, 2013.
• April 15: Table with design infiltration rates
  • The table now contains one value for B soils (0.3 inches/hour). The previous version of the manual included rates of 0.3 and 0.6 inches/hour based on texture. The value of 0.6 was not supported by literature and a technical group determined there should be one value for B soils.
  • The design rate for D soils is 0.06 inches/hour. This replaces the previous value of <0.2 inches/hour and is in line with the Minimal Impact Design Standards calculator.
  • A/D, B/D, and C/D soils are assigned infiltration rates of 0.06 inches/hour, corresponding with a D soil. These soils are subject to seasonal high water tables, at which time they behave like a D soil.
• April 15: Safety factors - safety factors, previously called correction factors, are applied to field measured infiltration rates. They are intended to account for natural variability in infiltration rates of soils and in decreased infiltration performance of a BMP over time. A safety factor of 2 shall be applied to infiltration BMPs other than permeable pavement. A safety factor of 2.5 shall be applied to permeable pavement. For example, a measured infiltration rate for a bioretention system of 1.0 inches per hour shall be divided by the safety factor of 2, resulting in an infiltration rate of 0.5 inches per hour. In Version 2.X of the Manual, safety factors were calculated using information in a table.

We completed migration of content from the 2008 Manual to this website during the last week of March, 2013. We do not anticipate further significant changes in Manual content during the wiki website rollout in April. Following that, we hope to incorporate the following changes into the Manual:

• new information on green roofs in May and June;
• updates to the bioretention section in early to mid summer
• incorporation of information on trees in late summer and early fall;
• new sections on stormwater Minimal Impact Design Standards; and
• new information on iron-enhanced filters this summer.

Information: Mediawiki automatically saves all edits made to any page in this website. Viewers can therefore see all edits made to the website by visiting the Recent changes page, which can be accessed via a link in the left toolbar.