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===Applicability=== | ===Applicability=== | ||
− | *The Simple Estimator is capable of predicting annual total suspended solid (TSS) and 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 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 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 WLA compliance for non-annualized WLAs. | + | **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 empirical model 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 and bypass from undersized BMPs in considered minimal. | + | **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. | **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. | ||
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*Within each sub-watershed, determine land uses and acreages within each land use. | *Within each sub-watershed, determine land uses and acreages within each land use. | ||
*Within each land use, determine acreages treated by each BMP type. | *Within each land use, determine acreages treated by each BMP type. | ||
− | *Evaluate the default values for event mean concentration and runoff coefficient for each land use and adjust if necessary. | + | *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=== | ===Model output=== |
This page provides a list of considerations when using models to meet MS4 (Municipal Separate Storm Sewer System) total maximum daily load permit requirements. For detailed guidance or additional information, see the links section for each model.
The Minimal Impact Design Standards calculator is a moderately simple tool for estimating pollutant load reductions associated with best management practices (BMPs).
The MIDS calculator has a Site informationtab for site information and a Schematics'' tab for inputting information for individual BMPs.
The Results tab displays summary information for the site and for each BMP.
The following table summarizes a QAQC list for interpreting results.
General MIDS Calculator result QAQC list
Link to this table
QAQC / Review Item | Related MIDS Calculator Output |
---|---|
Review device routing | Review routing in "Schematic" window |
Confirm area routed to individual BMPs is correct | BMP Properties --> Watershed |
Confirm total watershed area is correct | Review "Site Information" window |
Confirm annual precipitation total is correct | Review zip code in "Site Information" window |
Review watershed pollutant concentrations | Compare watershed areal loading to literature values |
Review TSS/TP removal rates | Compare pollutant removal values to literature values |
Confirm no routing between non-volume reduction BMPs | Removal estimates for non-volume reduction BMPs in series are incorrect. For this reason, routing between non-volume reduction BMPs should be disconnected |
Review BMP sizing recommendations and review contributing watershed area | Bypass from undersized BMPs is not calculated for non-volume reduction BMPs. For this reason, only the area for which the BMP is correctly-sized should be modeled to the BMP (the remainder should be modeled as untreated) |
The 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).
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
Link to this table
QAQC / Review item | Related MIDS Calculator Output |
---|---|
Confirm total watershed area is correct | Review land use-based area assigned in the "total load" table |
Confirm annual precipitation totals are correct | Review annual rainfall values in column G and confirm all are the same value |
Review watershed pollutant concentrations | Compare watershed areal loading values in the "total load" table to literature values in Table 9 |
Review watershed routing to BMPs | Review land use-based area assigned to each BMP type |
Confirm only the directly-contributing watershed area is applied for each BMP | The area assigned to a given BMP should be only the directly-contributing watershed area and should NOT include area tributary to other BMPs upstream |
Review TSS/TP removal rates | Compare pollutant removal values to literature values. Note: percent load reduction shown for each BMP type is calculated based on the total watershed loading |
Review BMP sizing recommendations and review contributing watershed area | Bypass from undersized BMPs is not calculated. For this reason, only the area for which the BMP is correctly-sized should be modeled to the BMP (the remainder should be modeled as untreated). |