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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. | 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== | + | ===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. | 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=== | ||
==WinSLAMM quick guide== | ==WinSLAMM quick guide== |
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). |
P8 is a continuous water quality model capable of summarizing runoff and associated total suspended solids (TSS) and 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.
P8 is capable of accurately predicting pollutant removal through BMPs in series as well as predicting runoff and pollutant bypass from undersized BMPs. 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 wasteload allocations (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.
Below are recommendations for P8 model inputs.