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Minnesota Stormwater Manual

Response to comments
Revision as of 14:30, 24 April 2017 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: I think the page would be better served by starting it this way, with language from farther down on the page: "Welcome to the Minnesota Stormwater Manual website. The Manual was created to be serve as a single source to guide stormwater managers through the maze of regulations, Best Management Practices (BMPs) designs, models/techniques and terminology that constitute good stormwater management. It is designed to be user-friendly..." etc. I think to get to the point about the purpose of the manual right away, and then talk about its features and design process, would improve the clarity of the page.

Response: Thanks. Please see our adjusted language. ________________________________________________________________________________

Comment: How about being able to click to the next page

Response: Resolved. Scroll down to a section called Links to other sections in CSW permit.

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Comment: Would be helpful to include link to download all in combined .pdf (link)

Response: Done. Look for links to pdf documents

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Comment: Couldn't find what I was looking for. PDF download link does not work.

Response: Regarding the pdf link issue, we are aware the pdf function does not always work in Mediawiki. We've found it to work about half the time. There are other options for saving or creating a document. First, you can save the page as a web page. Second, you can download (save) the page as a pdf from your browser. Go to this link or this link or other similar pages to determine how to do this. It is a relatively simple process. A final option is to copy and paste the page into Microsoft Word.

Regarding finding information in the website, the Search tool at the top of the page is effective if you know exactly what you are looking for. This page may be helpful.

Finally, if you have questions, concerns, or suggestions, please contact us. You may contact Mike Trojan at the MPCA or include your contact information in a comment that you submit. A comment box is found at the bottom of most pages.

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Comment: It would be nice to know how to reference the manual in a literature cited section. How should the manual be cited when information is being referenced in other reports?

Response: On the left toolbar, under Tools, you'll see a link (highlighted in blue) to Cite this page. Click on the link and you are taken to a page that provides a description of how to cite the page you want to reference.

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Comment: How about being able to click to the next page (referencing I. PERMIT COVERAGE AND LIMITATIONS)

Response: At the end of each section of the Construction Stormwater Permit, we added a section called Links to other sections in CSW permit. This should enhance moving between sections within the permit.

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Comment: when is an EAW required? (from page Construction Program FAQ).

Response: Minn. R 4410.4300 list what the Mandatory EAW Categories are. There is not one specific to CSW. Citizens may also petition for an EAW per Minn. R 4410.1100.

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Comment: (Regarding the MIDS calculator and permeable pavements), To meet the drawdown requirement, wouldn't a more applicable measure be the EFFECTIVE depth below the underdrain? This would take into account the media porosity.

Response: While it is correct that media affects the volume of water that infiltrates, it does not affect the calculation of drawdown time.

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Comment: The baffle sizing doesn't let you input data

Response: This table was not linked to other information in the manual. The link has now been established. We have also added information to the table header that allows users to access the sizing tool and other information on SHSAM.

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Comment: Why is there a potential for malicious code to be present in your documents (see example)?? trying to rewrite a city stormwater ordinance and I'm including links to each BMP, but when I clicked on the technical document link for "green roofs" I saw that message. The reason I am concerned more than I normally would be (as this can be considered a safe site) is because the contributor for the edits has the word "trojan" in the username, implying a virus.

Response: Mediawiki, by default, provides the following warning when it does not recognize certain standard formats - Warning: This file type may contain malicious code. By executing it, your system may be compromised. This appears to be the case for all Word and Excel documents. It may be true for other documents, such as .pdf, .jpg, etc. The author of this page has the Username MTrojan. The MPCA has control of access to the wiki and any files that have been uploaded into the wiki. We will add the following alert to appropriate places in the manual.

Caution: Mediawiki, by default, provides the following warning when someone downloads certain file formats - Warning: This file type may contain malicious code. By executing it, your system may be compromised. This appears to be the case for all Word and Excel documents. It may be true for other documents, such as .pdf, .jpg, etc. The MPCA has control of access to the wiki and any files that have been uploaded into the wiki. However, if you have concerns for downloading material from the wiki, email Mike Trojan at the MPCA.

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Comment: have the "following pollutants" on this page been added somewhere if not on this page?

Response: We had the idea of creating these pages because we felt they would be useful to people dealing with a specific pollutant. Unfortunately we got sidetracked with other work and never got back to completing these pages. It is still our intention to complete them, but it will be a while before we can get to them.

Note, however, that the one page that was created, Total Suspended Solids, was largely built using information that is already in the manual, albeit scattered among different pages. Some of the information on this page is applicable to all pollutants, such as the sections on antidegradation, pretreatment, and TMDLs. Until we are able to get back to completing these other pages, we recommend the following pages for sources of information.

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Comment: This page states that dry ponds do not receive credit for volume or credit removal, however these often behave like wet swales, which do receive credit in the MIDS calculator.

Response: Wet swales do not receive a volume credit in the MIDS calculator. Dry swales do receive volume credit.

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Comment: Dead link at BMP sediment quality, testing and disposal guidelines

Response: This page has been redirected to Managing stormwater sediments

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Comment: Why was the period of inundation definition changed from 3-6 inches above bottom of the facility to 1-2 inches above bottom of the facility. The SW manual had 3-6 inches in 2008, but now it is 1-2 inches. Why?

Response: The original manual had conflicting information on this point. The bioretention section used a value of 1 to 2 inches, while the infiltration section stated a value of 3 to 6 inches. It is unclear why there were two values. The manual has been updated and consistently discusses a value of 1 to 2 inches. Specifically, the manual states: "experience has demonstrated that, although the drawdown period is 48 hours, there is often some residual water pooled in the infiltration practice after 48 hours. This residual water may be associated with reduced head, water gathered in depressions within the practice, water trapped by vegetation, and so on. The drawdown period is therefore defined as the time from the high water level in the practice to 1 to 2 inches above the bottom of the facility. This criterion was established to provide the following: wet-dry cycling between rainfall events; unsuitable mosquito breeding habitat; suitable habitat for vegetation; aerobic conditions; and storage for back-to-back precipitation events. This time period has also been called the period of inundation." We believe that the value of 3 to 6 inches may indicate a system that is not properly draining.

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Comment: in centimeters (Design infiltration rates)

Response: Units of cm/hr have been added to this table

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Comment: I would like to know where this table came from. Can you please provide a reference? I am writing a paper and would like to be able to cite. Thanks.

Response: See page 57 at this link.

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Comment: I'm hoping this program [MIDS calculator] can be made more stable with the updates, as LGUs/agencies are beginning to require its use, regardless of it's significant limitations. I understand the calculator is nothing more than a spreadsheet "model" performing simple calculations; however, if it's going to feature a GUI, it would be nice if it weren't crashing and/or binding up excel regularly. Please don't put out another beta product.

Response: We understand the MIDS calculator is widely used. It is important that specific instances where the calculator is not performing properly be brought to our attention so they can be addressed. If you have questions or concerns about the calculator, please contact Mike Trojan at the MPCA.

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NOTE: We recently received a comment asking us to contact someone. Because of computer security issues it is imperative that if you want us to contact you, you must clearly define the purpose as well as your full contact information. You may also contact Mike Trojan at the MPCA.

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Comment: For filtration and biofiltration practices the storm water manual requires a 3 foot separation from the seasonal groundwater table and the bottom of the practice. The MPCA General NPDES Permit under section III.D.1.h. says an impermeable liner is allowed where it is less than a 3' separation. These two items don't jive. can you help clarify and provide direction. Thank you!

Response: When constructing an infiltration or filtration system to meet the requirements of the construction stormwater permit – the infiltration or filtration system must have a minimum of 3 feet of separation to the seasonally saturated soils or from bedrock. If you are proposing to construct an infiltration system and have less than three feet of separation to the seasonally saturated soils or bedrock – infiltration is prohibited in that location. If you are proposing to construct a filtration (or biofiltration) system and have less than three feet of separation to the seasonally saturated soils or bedrock -the filtration (or biofiltration) system must have an impermeable liner.

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Comment: We received several comments on the Annual report. below are the comments with responses.

1) It would be nice if we could move forward and backward through the pages while leaving questions blank.

Response: This is a limitation of the Annual Report on Snap Surveys—required fields cannot be bypassed before moving to the next page. A fillable word document was released with the Annual Report so that users may see all the questions contained in the Annual Report. It is available here: https://www.pca.state.mn.us/sites/default/files/wq-strm4-06a.doc.

2) Add an index page to move up and down on the annual report. You have to click through each page to get the the beginning of the report. Then you have to go through each page again to get to the end of the report.

Response: Doubtful that this option exists in Snap Surveys, but we will look into it for next year’s Annual Report.

3) It would be helpful to be able to “Save” and stay on the page.

Response: Doubtful that this option exists in Snap Surveys, but we will look into it for next year’s Annual Report. Please note, clicking the ‘Back’ or ‘Next’ buttons also saves the Annual Report. Clicking the ‘Next’ button will save even if you cannot advance to the next page because you have not filled out all of the required fields.

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Comment: The title says infiltration trench, but the sources are about basins.

Response: The original manual combined infiltration trench and infiltration basin into a single chapter. we are in the process of redoing this section of the manual and anticipate calling these "infiltration practices". This would include infiltration basins, trenches, dry wells, and underground infiltration practices. The work order to produce updates for this expires July 31 and we expect to have the changes incorporated into the manual by late summer.

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Comment: I had a question about the impact of using a bioinfiltration basin with an elevated underdrain. While using the MIDS calculator for a given basin with and without elevating the underdrain, I consistently see higher TP, TSS, and volume removals when NOT elevating the underdrain. Why is this? Since using an elevated underdrain "allows for more infiltration and evaporation compared to bioretention with underdrain at the bottom (2)" and "elevating underdrain (1) allows for more infiltration and evaporation compared to bioretention with underdrain at the bottom" I would expect higher removals when elevating the underdrain. Especially since TP and TSS from infiltrated water is considered to have 100% removal rates. Can anyone explain these results? Thanks! - Sorry for a duplicate comment, but I forgot to leave an email. If someone could please get back to me at dmoberly@srfconsulting.com that would be most appreciated. Thanks!

Response: This will be corrected in the next version of the MIDS calculator, which we hope to release in late summer (2016).

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Comment: There are no units listed in the notes #3 under the table.

Response: Resolved - units are Number per 100 milliliters.

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Comment: This comment pertains to this page. This is more of a reflection of the wording of the construction stormwater permit. Am I correct in my assumption that SWPPPs for construction sites under permit are only required to consider impairments for phosphorus, turbidity, dissolved oxygen, and biotic impairment for water bodies to which a site discharges within 1 aerial mile? I have a site that discharges to a water body which has a mercury in fish tissue impairment, for example, which does have TMDL. However, because it is not one of the four impairments listed in the permit, I assume the additional requirements identified for special or impaired waters in Appendix A of the permit do not apply to this site. More clarity here, on the construction stormwater page, or in a separate fact sheet would be a nice alternative to re-writing the permit.

Response: That is correct, there are no additional requirements for a mercury impairment. We will modify the language on this page to make this clearer.

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Comment: It would be nice if the TMDL pages that we upload would be viewable when we are printing the document to ensure that the right thing is being uploaded and submitted. Now we just have to trust that what we thought was being uploaded is being uploaded.

Response: There is no way for a respondent to view the attached uploads. It is a limitation of Snap Surveys. If you upload the wrong attachment and it is a required component, such as the TMDL Annual Report, the MPCA will contact you.

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Comment: more design information on non vegetated filters for pre treatment would be helpful. Hydro dynamic systems, fore bays etc. Thank you

Response: We currently have a Work Order to provide information on pretreatment. Another Work Order will start June 1 to provide design information for vegetated filter strips. See here.

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Comment: What can we do, as homeowners, to environmentally and responsibly reduce the mosquito population in our back yards of Minnesota? It seems that mosquitoes are on the rise again, after several years of limiting their proliferation in Minnesota lake areas, even in the Mpls./St. Paul area.

Response: With the Zika virus making the news recently, this issue has become more important to many people. The section in the manual addressing residential control of mosquitoes offers useful information. If implemented collectively throughout an entire neighborhood, the actions described in this section can suppress mosquito populations. Unfortunately, these actions cannot eliminate mosquitoes, since we not only live in the land of 10,000 lakes but in the land of hundreds of thousands of wetlands. As the comment points out, it is important to employ environmentally-safe methods. The use of chemicals to control mosquitoes in residential settings can be problematic since they may kill non-target organisms, such as bees. We have added some links to additional information in the section on residential control of mosquitoes. For more information, visit the Metropolitan Mosquito Control District website. _________________________________________________________________________________

Comment: Consider moving up the "other surface waters" requirement, it appears that buffers/redundant BMPs are required only for special waters, as 'other surface waters' are buried at the bottom.

Response: The page referred to in this comment is newly created and was migrated from our main construction stormwater page on MPCA's website. In the process of migrating information into this wiki we have noticed several needed updates. This is part of a process of building a construction stormwater section in the Manual, including migrating parts of the old Blue Book into this wiki. Once we have everything migrated we will go back and begin editing pages. thanks for the comment and we will consider it when we begin the review process.

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Comment: is it possible to download a pdf version of the document? I understand that this approach makes it easy to update, and it may even be easy to find a particular topic, but it is not easy to navigate and digest if one seeks to gather a broad understanding of the overall MN stormwater program. The "download a pdf" link on the bottom left only provides a pdf of the first three pages.

Response: The full manual is not available as a pdf document. The Create a Book function can be used to create a pdf document that includes multiple pages (we acknowledge this feature is a bit frustrating as the download doesn't always work smoothly, but it is functional). We are also considering developing a much more detailed Table of Contents as an alternative to the existing highly abbreviated TOC. We will also gladly create pages or pdf documents upon request provided the requests are manageable. We understand that some people prefer pdf documents and we went through an extensive process before deciding that the wiki platform offers tremendous advantages.

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Comment: Hi there, I was looking at your model comparisons found here [1] and was wondering how would you classify HEC-FIA model? Please kindly advise. Thank you.

Response: The User's Manual states: "The HEC-FIA program enables users to calculate flood damage and benefit accomplishment attributed to flood control projects. The analysis period can be the duration of a single flood event or a longer period of record. The program calculates agricultural damage, urban damage, and benefits for use after an event or annually and summarizes the results in reports. HEC-FIA can also look at dam failure events and evaluate the consequences to support risk assessments for dams." An article by Lehman and Needham indicate that further hydraulic modeling using other modeling tools is needed to enhance interpretation of the HEC-FIA model results. It therefore appears the HEC-FIA does not fit into the categories we use for classifying models.

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Comment: Bioretention soil "Mix D" appears to be the best option for a biofilter with underdrain to meet treatment goals, though the recommended mix ratios shown in the description and table are not in agreement. The "suggested mix ratio" in the description includes more compost, and topsoil, than shown in the table, and is very similar to "Mix A".

Response: The discussion of mix ratios includes a quantity of compost to add, while the table shows a quantity of organic matter desirable in the mix. This can lead to confusion, since compost will be about 50 percent solids and the solids will be about 50 percent organic carbon. Thus the values given for compost and organic matter are consistent. We have added some language to clarify this.

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Comment: Have more ideas (links to Temporary Erosion and Sediment Control page)

Response: We are in the process of migrating and updating information from Chapter 6 of the "Blue Book" into the Stormwater Manual. This process is on-going but should gradually improve the content on this topic.

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Comment: constructed pond (links to page on constructed ponds)

Response: We assume this comment is asking about performance curves for constructed ponds for the MIDS calculator. Performance curves were not developed for constructed ponds. The information built into the MIDS calculator for constructed ponds is found here.

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Comment: The performance of stormwater ponds does not differentiate between dry ponds and wet ponds. I believe that they have a different performance.

Response: This is correct - dry ponds do not receive credit for volume or pollutant removal. Several alert boxes have been included in appropriate places to convey this information.

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Comment: This is a pretty good story http://www.shoreviewmn.gov/departments/public-works/our-story/pervious-roadway#ad-image-1.

Response: This story has been noted in In the News and Case studies for permeable pavement

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Comment: The hyperlinks aren't working for me. One in the survey on MCM5 didn't work and the Click here on this page to visit the MPCA MS4 page didn't work.

Response: We occasionally get error messages in the wiki. Try reloading the link. If problems persist or if you have any questions, contact Mike Trojan (mike.trojan@state.mn.us, 651-757-2790) regarding the manual wiki or Cole Landgraf (cole.landgraf@state.mn.us, 651-757-2880) or Rachel Stangl (rachel.stangl@state.mn.us, 651-757-2879) regarding the survey.

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Comment: Re Rainfall Distribution The NRCS Type II Storm distribution was developed from TP-40 data and you should consider updating Stormwater Manual to use storm distributions based on Atlas 14 data. NRCS has updated rainfall distributions using Atlas 14 data. Minnesota NRCS has issued guidance that Type II storms no longer be used, and instead NRCS projects should use the MSE 3 storm that is based on Atlas 14 data. See their document at address below: http://www.nrcs.usda.gov/wps/PA_NRCSConsumption/download?cid=stelprdb1270686&ext=pdf MnDOT Drainage Manual is not current for design storm recommendation and should not be included as a reference until it has been updated. It has been superseded by Technical Memorandum 15-10-B-02. For urban areas, the recommendation is to use a rainfall distribution derived from Atlas 14 data, or use the NRCS MSE 3 distribution. See Tech Memo at: http://dotapp7.dot.state.mn.us/edms/download?docId=1651055

Response: The page containing this information (Introduction to stormwater modeling) has been updated and should address the above comments. Note this page is under review through January, 2016.

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Comment: The rainfall frequency/rainfall volume graphs for Cloquet, Fargo, Grand Forks...on this page were not developed from TP-40 and it may be confusing to put them here with the Statewide TP-40 figures. Issue Paper B states that the MSP graph is based on data from 1971 - 2000, and I assume the others were as well. These were developed by doing analysis of all rainfall events greater than 0.1 in. By contrast, TP-40 and Atlas 14 just analyze the extreme events. They use the highest precipitation amount for a particular duration for each calendar year.

Response: We removed the frequency-volume from the indicated page and created a new page summarizing frequency-volume relationships. We refer the reader to Issue Paper B, which includes a detailed discussion of the methodology and results, but provide some interpretation of volume estimates from the graphs since the graphs can be misleading.

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Comment: Could you please provide dimensions of #3 or #5 AAHSTO STONE.

Response: We added a footnote that includes links to the requested information. See the table referenced in the comment.

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Note: CADD images and .dwg files for CADD use are located on separate pages. The images are .pdf diagrams. We have created links on each of these pages to allow users to toggle back and forth between the two pages.

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Comment: Contact numbers would be helpful. Wouldn't they?

Response: Done

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Comment: It would be helpful to have the name of the BMP type along with a photo of it for this page.

Response: The photo in the table is intended as one example for the type of BMP being discussed. In the third column of the table, labeled BMP examples, we have indicated which specific BMP the photo refers to.

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Comment: The formula given for sizing bioretention practices not under the Stormwater General Permit (the A=VwqDm/(Ir(Hf+Dm)DDT) formula) seems to be incorrect. According to this formula, as you decrease the media/filter depth you also decrease the area needed for the practice which seems counterintuitive. Either the formula has an error of some kind or there needs to be more background included on the proper use of this formula (or maybe its derivation?).

Response: This equation, from the original Stormwater Manual, is inaccurate and has been modified

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Comment: Please provide a suggested citation/reference for the Minnesota Stormwater Manual. Thank you!

Response: In the toolbar on the left of each page, under Tools, look for a link called Cite this page. Click on that link and you will see citation styles for that page. Styles include APA, MLA, MHRA, Chicago, CBE/CSE, Bluebook, and BibTex. For example, if you were on the page Design criteria for permeable pavement and clicked on Cite this page, you would be directed to this page.

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Comment: This page [2] says that MIDS is an excel calculator, and that there is a folder called MIDSCalculatorGUIInstallerJuly8.zip. However at the link above there is only a folder called MIDSCalculatorGUIInstaller1.2.zip and it seems to be in ArcGIS? Anyway I can't find anything in excel, and I can't find a manual that is available without actually installing the set.exe. Is there documentation somewhere so I can figure out whether to install?

Response: Download just the Excel version of the calculator: File:MIDS calculator Excel only.xls. A link to this file has also been placed on the Calculator page.

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Comment: Give me some soil types (referring to [3]).

Response: We added a table showing infiltration rates for different soil textural classes and provided links to other sites where information for specific soil series can be found. See [4].

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Comment: Create a page for definitions. Try searching for the definition of impervious. One should be able to find definitions for regulatory terms ASAP. If you cannot find what is defined as impervious, your site needs a lot of work.

Response: Definitions can be found in the Glossary in the Stormwater Manual Table of Contents. We welcome suggestions about new terms that should be included in the Glossary, changes to existing definitions, or places in the Manual where we should create links to the Glossary.

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Comment: Is there any information on manipulating fish communities in stormwater ponds to optimize sw pond performance - for example using rotenone or other methods to reduce goldfish or black bullhead populations?

Comment:we are unaware of any information on this topic. We welcome information on this topic from any of our readers.

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Comment: make a PDF copy of the entire permit available for easy fownloadiong. Currently you have to copy and paste the entire thing into a document to save as PDF. Formatting gets all messed up doing that.

Response: There is an option to view the entire industrial permit as a single article. Click on this option at the top of the Industrial permit page. We have added an alert box to highlight this option.

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Comment: Please provide EMC for other constituents, especially TSS.

Response: We are in the process of gathering this information for a wide range of pollutants through an on-going contract. We anticipate having this information within the next couple months. The information will be updated on the current page, which currently only contains EMCs for phosphorus. The updated information will include a range of concentrations found in the literature in addition to median concentrations. In the interim, feel free to contact us as we have draft data, or consult this report (see Table 4.1).

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Comment: One someone has earned credit for tree trenches and tree boxes, what is their value? How can the credits be used?

Response: There is a section in the Manual that discusses stormwater credits. An excerpt from that page states

"Stormwater credit is a tool for local stormwater authorities who are interested in

  • providing incentives to site developers to encourage the preservation of natural areas and the reduction of the volume of stormwater runoff being conveyed to a best management practice (BMP);
  • complying with antidegradation requirements, including meeting the MIDS performance goal; or
  • meeting or complying with water quality objectives, including Total Maximum Daily load (TMDL) Wasteload Allocations (WLAs)."

We are currently gathering additional information on stormwater credits for individual BMPs and hope to have this information in the Manual in the next few months.

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Comment:Underway: In failed tree nursery deceased trees in polyethylene grow bags are being removed. Need to know proper means of disposal of grow bags with contained tree root balls. Incineration or other?

Response: We forwarded this message to some tree experts and received the following response from Chad Giblin, a Research Fellow at the University of Minnesota.

"I spoke with Doug Lauer at UMN Landcare with regard to disposing or processing the dead nursery stock in poly grow bags. Doug works with Rumpca Co. who processes the wood waste and organic material at the UMN facility in Saint Paul. Doug thought that the polyethylene would probably not be an issue if the trees could be finely processed using a tub grinder, his bigger concern was field soil attached to the root balls. He suggested that if 90% or more of the soil was removed from the dead trees they could be probably processed using the tub grinder. He did advise me that Rumpca and other wood processing facilities and/or operators may have different policies depending on how things processed and that a final decision would require a more in-depth examination of the dead trees and the resulting product. In general, it sounds like there's options available but it would take working with a contractor who's willing to accept and process the dead nursery stock."

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Comment: I think the minimum drainage area for stormwater ponds should be revisited. A 25-acre minimum drainage area seems too small. Many ponds that treat runoff from highways have much smaller drainage areas.

Response: MPCA staff agree. Language has been changed to indicate a recommended drainage area of 10 to 25 acres, although smaller drainage areas, down to 5 acres, may be acceptable. See [5]

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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.

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

  • 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: 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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