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Minnesota Stormwater Manual

Response to comments
Revision as of 17:00, 3 September 2014 by Mtrojan (talk | contribs)

In an attempt to provide feedback to comments we receive and to encourage greater use of the Comment box found at the bottom of each page, we provide responses to many of the comments we receive. This page will be updated about once a week or as we receive comments.

Comment: The construction sequencing schedule does not indicate when the infiltration basin is installed. Should it not be installed after Site Stabilization?

Response: The following language has been added to the scheduling sequence for infiltration systems:

The Construction Stormwater General Permit requires that infiltration systems not be excavated to final grade until the contributing drainage area has been constructed and fully stabilized unless rigorous erosion prevention and sediment controls are provided (Part III.D.1.c). The permit also requires when an infiltration system is excavated to final grade (or within 3 feet of final grade), the Permittee(s) must employ rigorous erosion prevention and sediment controls (e.g. diversion berms) to keep sediment and runoff completely away from the infiltration area. The area must be staked off and marked so that heavy construction vehicles or equipment will not compact the soil in the proposed infiltration area. It is Recommended that infiltration systems be installed or put online after final stabilization of the site.


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Comment: there are two slightly different infiltration rate tables that could be combined into one.

Response: We created two separate tables, one focused on Hydrologic Soil Groups and the other on soil texture. This is intended to meets the needs of the soil scientist and engineer. We may revert back to a single table if this causes confusion.

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Comment: References to the required water quality volume on this page reference the 0.5" requirement from the previous permit cycle. This should be updated to reference the current 1" requirement.

Response: We attempted to "fix" the Water Quality Volume (Vwq) "issue" on the Water quality criteria page. We realize the section on Unified Sizing Criteria is dated and needs to be updated. We hope to update this page in the next few months.

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Comment: Would be more useful if the links to calculate stormwater volume reductions/credits actually brought you to a page with that information, rather than a page to another link that might have what you're looking for....


Comment: Are Credits for Better Site Design the only way to calculate volume reduction credits?


Response: The Minnesota Pollution Control Agency is currently working with a Contractor to develop information for volume and pollutant credits for most of the BMPs discussed in this manual. We anticipate this information will incorporated into the Manual by early summer, 2014. Draft versions of this information can be found for the following BMPs.


The Minnesota Pollution Control Agency is also working with a Contractor to develop information on using the Minimal Impact Design Standards calculator to calculate credits for volume, phosphorus and total suspended solids. Drafts of that information can be found for the following BMPs.


The Manual also contains information on models that can be used to calculate credits for volume and pollutants. Information on models is found on the following pages.

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  • Comment: The equation for Rtp in the example calculation is written incorrectly or it contradicts what is written above. Please revise the page to have consistent formulas.
  • Response: The equation in the example was incorrect and has been corrected.

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  • Comment: It would be helpful if this page said WHAT the setback requirement refers to. What must be "set back" from the property line, building foundation, private well, etc.

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  • Response: The original manual combined information on swales and sand filters into a single chapter. We eventually intend to create separate sections for these BMPs but have not done so yet. To address this comment we added links to to Swales and Sand filters in the Table of Contents. Clicking on these results in a redirect to the Filtration page. On the filtration page we added links to the drawings referenced in the comment. We realize this is a temporary solution.

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  • Comment: Table of Contents item: infiltration basin and infiltration trench - does not contain any information on infiltration basins. These are one of the most common volume control practices in Minnesota and there is no guidance in the stormwater manual how to design and build these? Seems like a major disconnect.
  • Response: The manual does contain information on infiltration basins but the titles were misleading. We anticipate eventually having separate sections for trenches and basins but have not gotten around to creating those separate pages. in the interim we combined the two BMPs but mislabeled the pages. We have resolved the labeling.

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  • Comment: You need to expand this section (Design infiltration rates) to include the procedure for measuring infiltration rates. A search for "measured rates" yield the correction factor, but not the testing procedure.
  • Response: This information is undergoing final review and will be incorporated into the Manual in the next month or two. We would be happy to provide this information now, as draft material, upon request (contact mike.trojan@state.mn.us).

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  • Comment: This page should include additional types of porous pavements like durable versions of grass/gravel reinforced paving (BodPave85, Geoblock5150, Grasscrete) in addition to the unit pavers. These low-cost solutions have been utilized in low-med traffic sites very successfully and have incredible infiltration rates due to the high void space at surface for improved LID performance. However, I would not recommend the roll-out versions as these have not proved effective in trafficked areas, especially those with 4 seasons.
Response: We agree and are looking into incorporating this information into the Manual.

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  • Comment: I would like to be able to click on a main heading and see the contents of the whole chapter at once instead of having to click on each topic area under the heading
Response: If we understand the comment correctly, this option exits for every topic that has multiple articles (pages). Look for a sentence on the main page of each major topic that states all the individual articles may be viewed as a single article. See green roofs as an example.

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  • Comment: It is extremely hard to get back to where you were at. It would be nice to have a log in of some type or be able to flag currently visited locations.
  • Comment: I am periodically reminded of the wiki, but have not made use of it (but should). Not sure how to popularize it as a resource. I wonder if there could be a button made that could stay in my web browser? or an icon that could be installed on a desktop?
Response: If using Internet Explorer, the simplest solution is to place the website onto the Favorites bar. This can be done by clicking on the Add to Favorites bar icon found on the Favorites bar toolbar (look for the yellow star with a green arrow pointing to the right). Clicking on this icon places the current webpage onto the toolbar, where it remains until you choose to remove it. Similar bookmarking features can be utilized in other browsers.

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  • Comment: I am used to online manuals having navigation structure that allows the user to easily navigate to the next page or previous page easily. The current design seems to require the user to return to the TOC to both locate where you were and then choose the next page. Navigating through the entire manual page by page seems difficult. it would be helpful to have where one is in the TOC to be indicated by an html outline format on the left side and to have page navigation (back and next) on each page unless this could not be accomplished w/o programming at each page level which would be too laborious.
Response: There are some options for addressing this issue. First, at the top of each page is a breadcrumbs list of the three most recent pages that have been viewed within the wiki. second, a page can be opened in a new tab by right clicking on a link and selecting open in a new tab. This allos the user to have multiple pages open at the same time. We have also added a feature called Related pages. This is a section within all articles found within a specific topic. For example, green roofs is a topic that has 15 separate articles or pages associated with it. On each of those 15 pages is a section called Related pages that link to each of the 15 pages within the green roofs topic. This allows a user to stay within a specific topic without having to return to the Table of Contents. This feature has not been fully implemented yet, but visit one of the pages within green roofs to see an example.

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  • Comment: "I often find it quicker and easier to search Google with the MPCA's site focused than to try to find what I need using the internal search, generally there are too many non-relevant results. For instance, your site returns 10,000+ results for ""no"" another 2000+ results for exposure and 199 results for the ""no exposure"" I searched for. 200 results is manageable,but 200 to manage mingled in over 12,000 results that were not necessary is not."
Response: To search for a specific text string, the text string should be placed in quotation marks. For the example above, type in "no exposure" to see only instances where the full term appears in an article. For more information on searching for topics, see Finding a topic.

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  • Comment: The categories are confusing. I selected tables and the context that came up was not individual tables but pages that had tables. If one is already very familiar with the manual I can see how one could navigate easily to what one wanted, but I wonder if this design works as well for those just getting familiar with the manual. In that case, a highly linked and bookmarked pdf could serve equally well.
Response: We have resolved this issue (there is a noinclude command that allows us to categorize a page without the category being carried to another page). We also found, through the survey, that Categories are widely used for searching the Manual. we therefore intend on utilizing this feature to a greater extent.

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  • Comment: How to use it - there is no information on how to do searches or if there is it wasn't very obvious
Response: Next to the Search box near the upper right part of each page we added Seacrh Help, which is a link to our help page on finding topics within the wiki. We also edited the on finding topics help page.

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  • Comment: I had an incredibly difficult time finding figures and tables that were in the original manual. I would be surprised that any of them were simply deleted from the content. This should be improved. It was difficult to cross-reference between information locations in the old manual versus the wiki manual.
Response: We created a cross-reference between the old Manual and the wiki. There is an image at the top and right on the Main page and Table of Contents that takes you to the cross-reference.

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  • Comment: Please define where to start measuring three feet from (bottom of basin that you can see, bottom soil media used...) A minimum of 3 feet of separation between the bottom of the bioretention practice and seasonally saturated soils.
Response: There must be 3 feet of undisturbed soil beneath the infiltration practice and the seasonal high water table (saturated soil) or top of the bedrock. We have clarified that in the Manual.

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  • Comment: I did not have time read in depth about the BMPs, but I cannot stress enough that the best available information be included in here about protecting ground water, infiltration requirements in DWSMA's, vulnerable areas etc.
Response: This information will be updated in the coming year. See http://stormwater.pca.state.mn.us/index.php/Future_updates#Updates_to_information_on_infiltration_and_infiltration_constraints

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Response: Other webpages can be opened in a new tab by right clicking on the link and selecting "Open in a new tab". The Ag BMP handbook link has been added.

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  • Comment: Shouldn't ATLAS 14 be referenced here, rather than TP-40?
Response: This is part of on-going contract work and the Manual will be updated with respect to this issue.

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  • Comment: Although the data is lacking, it would be nice to have a 'What we Know' summary of that data and where it came from. (Note: this comment pertains to the page on Stormwater research and education.)
Response:The information on the Stormwater research and education page is from the original Manual. We agree it is in need of updating and will attempt to update this when resources allow.

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Response: For now, we've added an alert box informing people that the ban is in effect January 1, 2014. We anticipate additional information being added in August.

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  • Comment: Do US EPA WaterSense smart irrigation controllers fall into storm water quantity or quality BMPs for landscape management, and could it be used as a mitigation technique that qualifies for storm water credit in the City of Minneapolis? The controllers monitor plant, soil, and weather data to carefully control calculated daily irrigation schedules, eliminating saturated soils before rain events and minimizing the potential for overland flow generated on vegetated surfaces.
Response: We consulted with Lois Eberhart, City of Minneapolis Water Resources Adminstrator. Her response was:
"No, we would not consider any sort of irrigation management to be eligible for stormwater quality or stormwater quantity credits against the city’s Stormwater Utility Fee. Strictly speaking, irrigation water is non-stormwater and therefore is not intended to enter the MS4 stormwater system, under the city’s MS4 permit (although Minneapolis does not typically seek out, for purposes of enforcement, property owners/managers that are over-irrigating). (The irrigation control would of course save the user money on the water bill due to purchasing less potable water.)"
This is consistent with MPCA's view that irrigation water is non-stormwater and therefore credits should not be given. However, we believe the technology has value and would encourage its use in cases where irrigation is being used.

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  • Comment:It is really frustrating when you have to open each section separately. For example, I should have the option to be able to click on the main heading of Stormwater Modeling, etc. and view all six sections at the same time instead of having to click on each of the six sections separately.
Response: We have created an option to view all the articles as a single document. We will likely do the same where appropriate in other places in the Table of Contents. Another option for the Manual user is to create a book (see left toolbar), which allows customization of an article.

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  • Comment: Atlas 14 Volume 8 has been completed by NOAA. It is available on the web at http://hdsc.nws.noaa.gov/hdsc/pfds/ This information supercedes TP-40. There are references about using TP-40 throughout this document that should be updated.
Response: We understand the need to update the Manual on this topic and will be doing so in the near future.

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  • Comment: If all discharge is sheet flow, it would not be a regulated discharge correct? (My understanding is that it would need to form a channel at the point it left the property or entered waters of the state to be regulated).
Response: As long as the Permittee has chosen their Benchmark Monitoring Location in accordance with the definition of the Industrial Stormwater Permit, how they collect the sample doesn't change that it's a regulated industrial stormwater discharge.

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  • Comment: How about replacing these TP 40 maps with Atlas 14 which was has now been adopted by NOAA.
Response We have added a link to Atlas 14. The Stormwater Manual will be updated in the future.

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  • Comment: The heading notes that there are two different rates for group B soils, but only one is displayed. The old manual used to have a 0.6 inches per hour rate for group B soils.
Response: As part of the MIDS project, a technical team evaluated the infiltration table and determined there should be one value for B soils (0.3 in/hr). The heading is corrected. This is an important change and we are discussing how to inform Manual users about these types of changes.

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  • Comment: This (Stormwater pond/wetland O & M checklist) is a very comprehensive list; most of the criteria would be helpful. It should be reformatted so that it prints more clearly and in a smaller number of pages. A 4 page check list when you are inspecting a pond is too much.
Response: In the header for select checklists we have added an option to access an Excel version of the checklist

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  • Comment:The requirement for two year monitoring seems extremely hard on these systems. Monitoring requirements are not stipulated, pre-installation monitoring is required to characterize the runoff etc. No one in their right mind will do this on every site installation. Take into account that field monitoring devices themselves have been shown to be extremely inaccurate. With the move to MID design standards all tools are valid and for urban redevelopment underground systems may be the best option for the site. I strongly recommend replacing the monitoring requirement with a more stringent design process, say sizing on 50 um lab test using a treatment flow rate developed from the design storm event. Then require washout verification to say below 50 mg/l so that retention of sediment is also considered. A lot of work has been done at SAFL on this.
Response:This will not be required under the new CSW permit and it has therefore been removed.

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  • Comment: How about replacing these TP 40 maps with Atlas 14 which was has now been adopted by NOAA.
Response We have added a link to Atlas 14. The Stormwater Manual will be updated in the future.

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  • Comment: The heading notes that there are two different rates for group B soils, but only one is displayed. The old manual used to have a 0.6 inches per hour rate for group B soils.
Response: As part of the MIDS project, a technical team evaluated the infiltration table and determined there should be one value for B soils (0.3 in/hr). The heading is corrected. This is an important change and we are discussing how to inform Manual users about these types of changes.

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  • Comment: This (Stormwater pond/wetland O & M checklist) is a very comprehensive list; most of the criteria would be helpful. It should be reformatted so that it prints more clearly and in a smaller number of pages. A 4 page check list when you are inspecting a pond is too much.
Response: In the header for select checklists we have added an option to access an Excel version of the checklist

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  • Comment:The requirement for two year monitoring seems extremely hard on these systems. Monitoring requirements are not stipulated, pre-installation monitoring is required to characterize the runoff etc. No one in their right mind will do this on every site installation. Take into account that field monitoring devices themselves have been shown to be extremely inaccurate. With the move to MID design standards all tools are valid and for urban redevelopment underground systems may be the best option for the site. I strongly recommend replacing the monitoring requirement with a more stringent design process, say sizing on 50 um lab test using a treatment flow rate developed from the design storm event. Then require washout verification to say below 50 mg/l so that retention of sediment is also considered. A lot of work has been done at SAFL on this.
Response:This will not be required under the new CSW permit and it has therefore been removed.

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  • Comment: Do US EPA WaterSense smart irrigation controllers fall into storm water quantity or quality BMPs for landscape management, and could it be used as a mitigation technique that qualifies for storm water credit in the City of Minneapolis? The controllers monitor plant, soil, and weather data to carefully control calculated daily irrigation schedules, eliminating saturated soils before rain events and minimizing the potential for overland flow generated on vegetated surfaces.
Response: We consulted with Lois Eberhart, City of Minneapolis Water Resources Adminstrator. Her response was:
"No, we would not consider any sort of irrigation management to be eligible for stormwater quality or stormwater quantity credits against the city’s Stormwater Utility Fee. Strictly speaking, irrigation water is non-stormwater and therefore is not intended to enter the MS4 stormwater system, under the city’s MS4 permit (although Minneapolis does not typically seek out, for purposes of enforcement, property owners/managers that are over-irrigating). (The irrigation control would of course save the user money on the water bill due to purchasing less potable water.)"
This is consistent with MPCA's view that irrigation water is non-stormwater and therefore credits should not be given. However, we believe the technology has value and would encourage its use in cases where irrigation is being used.

—————————————————————————————————————————————————————————————————————

  • Comment:It is really frustrating when you have to open each section separately. For example, I should have the option to be able to click on the main heading of Stormwater Modeling, etc. and view all six sections at the same time instead of having to click on each of the six sections separately.
Response: We have created an option to view all the articles as a single document. We will likely do the same where appropriate in other places in the Table of Contents. Another option for the Manual user is to create a book (see left toolbar), which allows customization of an article.

—————————————————————————————————————————————————————————————————————

  • Comment: Atlas 14 Volume 8 has been completed by NOAA. It is available on the web at http://hdsc.nws.noaa.gov/hdsc/pfds/ This information supercedes TP-40. There are references about using TP-40 throughout this document that should be updated.
Response: We understand the need to update the Manual on this topic and will be doing so in the near future.

—————————————————————————————————————————————————————————————————————

  • Comment: If all discharge is sheet flow, it would not be a regulated discharge correct? (My understanding is that it would need to form a channel at the point it left the property or entered waters of the state to be regulated).
Response: As long as the Permittee has chosen their Benchmark Monitoring Location in accordance with the definition of the Industrial Stormwater Permit, how they collect the sample doesn't change that it's a regulated industrial stormwater discharge.

—————————————————————————————————————————————————————————————————————

  • Comment: How about replacing these TP 40 maps with Atlas 14 which was has now been adopted by NOAA.
Response We have added a link to Atlas 14. The Stormwater Manual will be updated in the future.

—————————————————————————————————————————————————————————————————————

  • Comment: The heading notes that there are two different rates for group B soils, but only one is displayed. The old manual used to have a 0.6 inches per hour rate for group B soils.
Response: As part of the MIDS project, a technical team evaluated the infiltration table and determined there should be one value for B soils (0.3 in/hr). The heading is corrected. This is an important change and we are discussing how to inform Manual users about these types of changes.

—————————————————————————————————————————————————————————————————————

  • Comment: This (Stormwater pond/wetland O & M checklist) is a very comprehensive list; most of the criteria would be helpful. It should be reformatted so that it prints more clearly and in a smaller number of pages. A 4 page check list when you are inspecting a pond is too much.
Response: In the header for select checklists we have added an option to access an Excel version of the checklist

—————————————————————————————————————————————————————————————————————

  • Comment:The requirement for two year monitoring seems extremely hard on these systems. Monitoring requirements are not stipulated, pre-installation monitoring is required to characterize the runoff etc. No one in their right mind will do this on every site installation. Take into account that field monitoring devices themselves have been shown to be extremely inaccurate. With the move to MID design standards all tools are valid and for urban redevelopment underground systems may be the best option for the site. I strongly recommend replacing the monitoring requirement with a more stringent design process, say sizing on 50 um lab test using a treatment flow rate developed from the design storm event. Then require washout verification to say below 50 mg/l so that retention of sediment is also considered. A lot of work has been done at SAFL on this.
Response:This will not be required under the new CSW permit and it has therefore been removed.

—————————————————————————————————————————————————————————————————————

  • Comment: How about replacing these TP 40 maps with Atlas 14 which was has now been adopted by NOAA.
Response We have added a link to Atlas 14. The Stormwater Manual will be updated in the future.

—————————————————————————————————————————————————————————————————————

  • Comment: The heading notes that there are two different rates for group B soils, but only one is displayed. The old manual used to have a 0.6 inches per hour rate for group B soils.
Response: As part of the MIDS project, a technical team evaluated the infiltration table and determined there should be one value for B soils (0.3 in/hr). The heading is corrected. This is an important change and we are discussing how to inform Manual users about these types of changes.

—————————————————————————————————————————————————————————————————————

  • Comment: This (Stormwater pond/wetland O & M checklist) is a very comprehensive list; most of the criteria would be helpful. It should be reformatted so that it prints more clearly and in a smaller number of pages. A 4 page check list when you are inspecting a pond is too much.
Response: In the header for select checklists we have added an option to access an Excel version of the checklist

—————————————————————————————————————————————————————————————————————

  • Comment:The requirement for two year monitoring seems extremely hard on these systems. Monitoring requirements are not stipulated, pre-installation monitoring is required to characterize the runoff etc. No one in their right mind will do this on every site installation. Take into account that field monitoring devices themselves have been shown to be extremely inaccurate. With the move to MID design standards all tools are valid and for urban redevelopment underground systems may be the best option for the site. I strongly recommend replacing the monitoring requirement with a more stringent design process, say sizing on 50 um lab test using a treatment flow rate developed from the design storm event. Then require washout verification to say below 50 mg/l so that retention of sediment is also considered. A lot of work has been done at SAFL on this.
Response:This will not be required under the new CSW permit and it has therefore been removed.
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