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Quick guides for using models to meet MS4 TMDL permit requirements

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[[File:General information page image.png|left|100px|alt=image]]

This page provides a list of considerations when using models to meet <span title="A municipal separate storm sewer system (MS4) is a means of transportation, individually or in a system, (e.g. roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, storm drains, etc.) that are: owned or operated by a public entity (e.g. cities, townships, counties, military bases, hospitals, prison complexes, highway departments, universities, etc.) with jurisdiction over disposal of sewage, industrial wastes, stormwater, or other wastes. This includes special districts under State law (sewer, flood control, or drainage districts, etc.), an authorized Indian tribal organization, or a designated and approved management agency under section 208 of the Clean Water Act; designed or used for collecting or transporting stormwater; not a combined sewer; and not part of a publicly owned treatment works."> '''MS4'''</span> (Municipal Separate Storm Sewer System) <span title="the amount of a pollutant from both point and nonpoint sources that a waterbody can receive and still meet water quality standards"> [https://stormwater.pca.state.mn.us/index.php?title=Total_Maximum_Daily_Loads_(TMDLs) '''total maximum daily load''']</span> permit requirements. For detailed guidance or additional information, see the links section for each model.

==MIDS calculator quick guide==
[[file:Screen shot of calculator.png|thumb|400px|alt=schematic showing routing of BMPs|<font size=3>{{pop|MIDS calculator screenshot| |This screenshot illustrates examples of BMPs available in the calculator and how they can be routed in a treatment train.}}</font size>]]
[[File:mids logo.jpg|300px|right|thumb|alt=image of Minimal Impact Design Standards logo]]

The [https://stormwater.pca.state.mn.us/index.php?title=MIDS_calculator Minimal Impact Design Standards calculator] is a moderately simple tool for estimating pollutant load reductions associated with best management practices (BMPs).

===Applicability===
*The MIDS Calculator is capable of predicting annual runoff, [https://stormwater.pca.state.mn.us/index.php?title=Total_Suspended_Solids_(TSS)_in_stormwater total suspended solid] (TSS) and [https://stormwater.pca.state.mn.us/index.php?title=Phosphorus total phosphorus] (TP) loading from three land cover categories (impervious area, forest/open space, and managed turf), and annual runoff and pollutant removal for a variety of BMP types.
*The MIDS Calculator reports on an annualized-basis, and is therefore not suitable for evaluating WLA compliance for non-annualized WLAs.
*The MIDS Calculator is an <span title="A model based on experimental data. Empirical models can be deterministic or probabilistic."> '''empirical model'''</span> which is limited in its ability to model pollutant removal through BMPs in series (e.g. <span title="multiple BMPs that work together to remove pollutants utilizing combinations of hydraulic, physical, biological, and chemical methods"> [https://stormwater.pca.state.mn.us/index.php?title=Using_the_treatment_train_approach_to_BMP_selection '''treatment train''']</span>) and <span title="Stormwater runoff in excess of the design flow, which is diverted around a stormwater structure"> '''bypass'''</span> from undersized BMPs. For this reason, the MIDS Calculator should only be used to demonstrate <span title="the portion of a receiving water's assimilative capacity that is allocated to one of its existing or future point sources of pollution"> '''wasteload allocation'''</span> WLA compliance for simplified study area where the impact of pollutant removal through BMPs in series and bypass from undersized, non-infiltration BMPs is considered minimal.

===Model inputs===
The MIDS calculator has a '''''Site information'''''tab for site information and a '''''Schematics''''''' tab for inputting information for individual BMPs.

====Site information tab====
*Ensure you have the correct zip code for the site
*Choose the most appropriate <span title="the average pollutant concentration for a given stormwater event, expressed in units of mass per volume (e.g., mg/L)"> '''event mean concentration'''</span> (emc) for your site or input a site-specific emc if data is available. If you have widely differing emcs across your site, run the model separately for areas with different emcs and compile results from different calculator simulations.
*Select "No" for the question regarding compliance with the [https://stormwater.pca.state.mn.us/index.php?title=Construction_stormwater_program Construction Stormwater General Permit].
*Ensure all pervious and impervious acreages are accounted for and pervious acres are assigned to the correct soil type (see [[Design infiltration rates]].

====Schematic tab====
*Ensure that BMPs are properly sized
*Ensure that BMPs are properly routed
*Ensure that all acreages are accounted for - check the site summary on the left side of the calculator

===Results tab===
The Results tab displays summary information for the site and for each BMP.
*Examine the BMP Summary table. Ensure that BMPs are not over- or under-sized and that inflow and outflow, including pollutant mass, makes sense.
*Examine the Summary Information. This will be the pounds of TSS or TP reduced for this site. If you have multiple sites, compile the results across all sites.

The following table summarizes a QAQC list for interpreting results.

{{:General MIDS Calculator result QAQC list}}

===Links===
*[[Recommendations and guidance for utilizing the MIDS calculator to meet TMDL permit requirements]]
*[[MIDS calculator]]
*[[Case study for using the MIDS calculator to meet TMDL permit requirements]]
*[[Links to Manual pages that address the MIDS calculator|Requirements, recommendations and information for using specific BMPs in the MIDS calculator]]
*[[MIDS calculator sample exercises]]


==MPCA Simple Estimator quick guide==
[[File:Estimator 2.png|500px|thumb|alt=screen shot of simple estimator|<font size=3>Screen shot of the Simple Estimator</font size>]]

The [https://stormwater.pca.state.mn.us/index.php?title=MPCA_Simple_Estimator MPCA Simple Estimator] is a spreadsheet-based tool used to predict watershed-based loading for total phosphorus (TP) and total suspended solids (TSS), and estimate pollutant removal at water quality best management practices (BMPs).

===Applicability===
*The Simple Estimator is capable of predicting annual [https://stormwater.pca.state.mn.us/index.php?title=Total_Suspended_Solids_(TSS)_in_stormwater total suspended solid] (TSS) and [https://stormwater.pca.state.mn.us/index.php?title=Phosphorus total phosphorus] (TP) loading from several land use categories (e.g. commercial, industrial, residential, etc.), several BMP types (e.g. biofiltration, infiltration, constructed ponds, etc.), and up to 10 sub-watersheds.
*The Simple Estimator is easy to use but has limitations, including the following.
**The MPCA Simple Estimator reports on an annualized-basis, and is therefore not suitable for evaluating <span title="the portion of a receiving water's assimilative capacity that is allocated to one of its existing or future point sources of pollution"> '''wasteload allocation'''</span> WLA compliance for non-annualized WLAs.
**The MPCA Simple Estimator is an <span title="A model based on experimental data. Empirical models can be deterministic or probabilistic."> '''empirical model'''</span> which has limited ability to model pollutant removal through BMPs in series and bypass from undersized BMPs. For this reason, the MPCA Simple Estimator should only be used to demonstrate WLA compliance for simplified study areas where the impact of pollutant removal through BMPs in series (i.e. <span title="multiple BMPs that work together to remove pollutants utilizing combinations of hydraulic, physical, biological, and chemical methods"> [https://stormwater.pca.state.mn.us/index.php?title=Using_the_treatment_train_approach_to_BMP_selection '''treatment train''']</span>) and <span title="Stormwater runoff in excess of the design flow, which is diverted around a stormwater structure"> '''bypass'''</span> from undersized BMPs in considered minimal.
**The MPCA Simple Estimator is not capable of identifying and/or distinguishing unique removal rates for individual BMPs that may be undersized or would not otherwise meet BMP design criteria.

===Model inputs===
[[File:Estimator summary 2.png|300px|thumb|alt=screen shot of summary sheet|<font size=3>Screen shot of the summary tab from the Estimator. The sheet shows total initial and adjusted loads, pounds and percent load reduced, and final loading rates. Click on image and then click on image again to enlarge.</font size>]]

*Identify the sub-watersheds you will model. Consider modeling undersized BMPs or BMPs in series as separate sub-watersheds.
*Within each sub-watershed, determine land uses and acreages within each land use.
*Within each land use, determine acreages treated by each BMP type.
*Evaluate the default values for <span title="the average pollutant concentration for a given stormwater event, expressed in units of mass per volume (e.g., mg/L)"> '''event mean concentration'''</span> and <span title="The runoff coefficient (C) is a dimensionless coefficient relating the amount of runoff to the amount of precipitation received. It is a larger value for areas with low infiltration and high runoff (pavement, steep gradient), and lower for permeable, well vegetated areas (forest, flat land)."> [https://stormwater.pca.state.mn.us/index.php?title=Runoff_coefficients_for_5_to_10_year_storms '''runoff coefficient''']</span> for each land use and adjust if necessary.

===Model output===
The spreadsheet consists of 10 worksheets, one for each sub-watershed. Data from these worksheets is compiled on an eleventh worksheet called "Summary sheet". This summary sheet shows results for each sub-watershed and cumulative for the project/study.

Quality assurance/quality control procedures are summarized in the following table.

{{:General MPCA Simple Estimator result QAQC list}}

===Links===
*[[MPCA Simple Estimator]]
*[[Case study for using the MPCA Simple Estimator to meet TMDL permit requirements]]
*[[Guidance and examples for using the MPCA Estimator]]
*[[Quick Guide: MPCA Estimator tab]]
*[[Forms, guidance, and resources for completing the TMDL annual report form]]

==P8 quick guide==
[[File:P8 icon.png|300px|thumb|alt=P8 icon|<font size=3></font size>]]

P8 is a <span title="a model of a physical system that continuously tracks system response according to a set of equations typically involving differential equations."> '''continuous water quality model'''</span> capable of summarizing runoff and associated [https://stormwater.pca.state.mn.us/index.php?title=Total_Suspended_Solids_(TSS)_in_stormwater total suspended solids] (TSS) and [https://stormwater.pca.state.mn.us/index.php?title=Phosphorus total phosphorus] (TP) generation, removal, and outflow loading from individual catchments, individual BMPs and pipes (referred to as “devices”), or as a model wide summary.

===Applicability===
P8 is capable of accurately predicting pollutant removal through BMPs <span title="multiple BMPs that work together to remove pollutants utilizing combinations of hydraulic, physical, biological, and chemical methods"> '''in series'''</span> as well as predicting runoff and pollutant <span title="Stormwater runoff in excess of the design flow, which is diverted around a stormwater structure"> '''bypass'''</span> from <span title="a BMP that does not treat the full water quality volume"> '''undersized BMPs'''</span>. Due to this flexibility, P8 is capable of providing accurate pollutant removal estimates regardless of BMP network and subwatershed configuration, and is capable of demonstrating compliance to mass-based <span title="the portion of a receiving water's assimilative capacity that is allocated to one of its existing or future point sources of pollution"> '''wasteload allocations'''</span> (WLAs) (e.g. pounds of TSS per year), concentration-based WLAs (e.g., mg/L of TSS), and areal-loading based WLAs (e.g., pounds of TSS per acre per year) for both TSS and TP.

Limitations of P8 include the following.
*The P8 model is a relatively complex tool and likely requires some training. 
*Phosphorus reductions are based on assumptions associated with particle size distributions and may not accurately reflect phosphorus fate in situations where dissolved phosphorus comprises a large percentage of total phosphorus.

===Model inputs===
Below are recommendations for P8 model inputs.
*Use local climatological data to develop required temperature and precipitation data inputs [https://www.ncdc.noaa.gov/cdo-web/search see the National Oceanic and Atmospheric Administration] (NOAA) website].
*''Air Temperature Offset'' (degrees): default value of zero should be applied unless there is a known shift in the temperature input file.
*''Passes Thru Storm File'': typically a value of “5” will be sufficient to initialize the model, but may need to be increased if there are BMPs with very large permanent pool volumes (e.g., large stormwater ponds and stormwater wetlands) relative to the tributary runoff volume. 
*''Precipitation Scale Factor'': default value of one should be applied unless there is a known shift in the precipitation input file (e.g., if precipitation values in the file were known to under-predict observed precipitation by 20%, a value of 1.2 should be used to correct for this recording error).
*''Start Date / Keep Date / Stop Date'': it is typically not necessary to specify a “Start Date” earlier than the “Keep Date”.
*''Rainfall Breakpoint'' (inches): the default value of “0.8” inches should be applied.
*''Time Steps Per Hour'': for models with simple P8 devices and routing, the default value of four (4) is recommended. If the specified value is too low, P8 will be unable to resolve inflow and outflow loading and will report a hydraulic continuity error. If this occurs, the user can increase the number of “Time Steps Per Hour” to increase calculation resolution and reduce model error.
*''Maximum Continuity Error'': apply the default value of 2 percent.
*''Particle size distribution'': use the NURP50 (“nurp50.p8p”) default value.
*Use values [https://stormwater.pca.state.mn.us/index.php?title=Recommend_filtration_efficiency_for_P8 in this table] for filtration efficiency values
*If using an aquifer device to model baseflow, update monthly ET coefficients based on information specific to the modeled region. If no such devices are modeled, the user can retain the default values in the ET table. 
*Retain default parameters for snowmelt for most areas in Minnesota.
*Use methodology outlined in the USDA TR-55 manual (USDA, 1986) to calculate the pervious curve number for each modeled watershed, which will be weighted with the indirectly connected impervious fraction by the model. It is recommended that directly and indirectly connected impervious area be estimated based on site-specific information when possible.
*Remove open water area from the total area and directly connected impervious area modeled.
*''Ponds'': reduce the particle removal scale factor (PRSF) for shallow permanent pool depths and/or other BMPs that do not meet flow-through criteria specifically designed to control scour or resuspension of settled sediment. Including the permanent pool volume in the flood pool volume will cause P8 to overestimate sediment and pollutant removal.
*''Infiltration basin'': If the infiltration/filtration BMP has a normal outlet (e.g., a pipe or orifice outlet), it is more accurate to model using a “Pond” device with infiltration rates applied to the permanent pool and/or flood pool. Filtration efficiency in the “Particle Parameters” dialog box should be adjusted based on the filtration media of the BMP (see [https://stormwater.pca.state.mn.us/index.php?title=Recommend_filtration_efficiency_for_P8 suggested filtration efficiencies for standard media and iron-enhanced media]).

===Model outputs===
*Output Explorer is a windowed pane within the P8 graphical user interface (GUI) that allows the user to use selectors and dropdown menus to review a variety of outputs in tabular form. The method allows for quick evaluation of model results, but typically only model-wide or BMP-specific model results.
*Output Tables (accessed through the “List” menu) allow the user to export a variety of model inputs and outputs into a text or spreadsheet document. Output tables provide the most flexibility reviewing output results, and allow the user to review results at all BMPs simultaneously. Additionally, if the model is run in “Traced” model (“Run” --> “Model Traced”) the user can export results on a daily or hourly basis.
*Output Charts (accessed through the “Charts” menu) allows to user to visualize model outputs summarized for the entire model run or by individual events. Additionally, the output charts spreadsheet provides a tabular summary of traced precipitation, inflow loading, and outflow loading results.

[https://stormwater.pca.state.mn.us/index.php?title=Recommendations_and_guidance_for_utilizing_P8_to_meet_TMDL_permit_requirements#Model_outputs Link here for guidance on how to interpret model results].

===QA/QC===
A general model result QAQC list and description of P8 outputs to review is provided [https://stormwater.pca.state.mn.us/index.php?title=General_P8_result_QAQC_list here] and provided below.

{{:General P8 result QAQC list}}

===Links===
*[[Recommendations and guidance for utilizing P8 to meet TMDL permit requirements]]
*[[Case study for using P8 to meet TMDL permit requirements]]

==WinSLAMM quick guide==