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{{alert|Page is in development|alert-under-construction}}
  
If a permittee is claiming to meet one or more <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> (WLA), they must submit documentation to the Minnesota Pollution Control Agency, using an approved method, that they are meeting the WLA. If a permittee uses the MPCA Simple Estimator, it is recommended they submit either of the following:
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MPCA anticipates several permittees will use the MPCA Simple Estimator to demonstrate compliance with or progress toward meeting <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> (TMDL) <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). If a permittee uses the MPCA Simple Estimator , it is recommended they submit either of the following:
*the entire Excel spreadsheet, or
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*an electronic copy of the entire Excel spreadsheet, or
*the worksheet called ''Summary sheet''
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*an electronic copy of the worksheet called ''Summary sheet'', or
 
*a printout or legible image of the worksheet called ''Summary sheet''.
 
*a printout or legible image of the worksheet called ''Summary sheet''.
  
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==Comparing the reduction (lbs or %) or final loading rate (lb/ac/yr) with the WLA, depending on how the WLA is expressed in the TMDL==
 
==Comparing the reduction (lbs or %) or final loading rate (lb/ac/yr) with the WLA, depending on how the WLA is expressed in the TMDL==
Wasteload allocations are typically expressed as a total load, a mass load reduction (e.g. pounds), a percent mass reduction, or a loading rate (lb/ac/yr). The value reported in the Estimator will be compared to the WLA as reported in the TMDL or as interpreted by the MPCA.
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[[File:Summary.png|400px|thumb|alt=screen shot of Summary tab from Estimator|<font size=3>Screen shot of the Summary worksheet from this Estimator example.</font size>]]
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Wasteload allocations are typically expressed as a total load, a mass load reduction (e.g. pounds), a percent mass reduction, or a loading rate (lb/ac/yr). The value reported in the Estimator will be compared to the WLA as reported in the TMDL or as interpreted by the MPCA. The Summary sheet from the Estimator is the source of this information.
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An example is shown in the adjacent image. This shows a Summary sheet from the Estimator, illustrating pounds of phosphorus reduced for a site having three subwatersheds. The pollutant of concern is phosphorus. The Summary sheet shows initial loading for each of the subwatersheds and for the entire site (2699.54 lbs), pounds reduced after BMP implementation (819.29 lbs), percent reduction from the initial load (30.35%), and final loading rate (0.57 lb/ac/yr). Each of these results is also displayed by subwatershed.
  
 
==Changes in default values for event mean concentration, runoff coefficients, bmp removal efficiencies, or the fraction of runoff that is treated and infiltrated by bmps==
 
==Changes in default values for event mean concentration, runoff coefficients, bmp removal efficiencies, or the fraction of runoff that is treated and infiltrated by bmps==
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[[File:Alert check.png|400px|thumb|alt=screenshot alert check for the Estimator|<font size=3>Screen shot showing the alert checks on the Summary sheet of the MPCA Simple Estimator</font size>]]
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Default values for these inputs are based on information from the literature and are therefore considered defensible. However, local information may exist to support changing these values. This includes water quality monitoring data, site-specific land use information, bmp performance monitoring, or some similar information. The Estimator spreadsheet contains cells for describing the rationale for changes to these inputs. The Stormwater Manual provides guidance for adjusting emcs and runoff coefficients. The adjacent image provides an example of some changes that MPCA staff would examine in determining compliance with a wla. Examples of changes that may merit further investigation by MPCA staff include the following.
 
Default values for these inputs are based on information from the literature and are therefore considered defensible. However, local information may exist to support changing these values. This includes water quality monitoring data, site-specific land use information, bmp performance monitoring, or some similar information. The Estimator spreadsheet contains cells for describing the rationale for changes to these inputs. The Stormwater Manual provides guidance for adjusting emcs and runoff coefficients. The adjacent image provides an example of some changes that MPCA staff would examine in determining compliance with a wla. Examples of changes that may merit further investigation by MPCA staff include the following.
 
*Improved bmp removal efficiency
 
*Improved bmp removal efficiency
 
*increased fraction of water infiltrating for a specific bmp
 
*increased fraction of water infiltrating for a specific bmp
 
*changes in emc or runoff coefficient greater than 10 percent compared to the default value
 
*changes in emc or runoff coefficient greater than 10 percent compared to the default value
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In the adjacent image, the user changed the default <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 the residential and agricultural areas. In these cases, MPCA staff would examine the changes. The permittee should provide a brief explanation of the reason for the change, either on the worklsheet where the change was made or in the Notes worksheet of the Estimator. The Notes worksheet is preferable because it allows the permittee to provide a detailed explanation of the change. For example, in the case of the image on the right, the emc was changed from the default of 0.325 mg/ L to 0.350 mg/L to account for high tree canopy, then modified again to 0.30 mg/L to account for enhanced street sweeping that targeted leaf removal during fall. The agricultural emc was changed as the land was developed and changed to mixed (multi-use) land use. The screen shot of the alert section of the spreadsheet also indicates the pollutant removal fraction for a sand filter was changed. In this case, it was due to incorporation of iron into the sand filter (<span title="Iron-enhanced sand filters are filtration Best Management Practices (BMPs) that incorporate filtration media mixed with iron. The iron removes several dissolved constituents, including phosphate, from stormwater. Iron-enhanced sand filters may be particularly useful for achieving low phosphorus levels needed to improve nutrient impaired waters. "> [https://stormwater.pca.state.mn.us/index.php?title=Iron_enhanced_sand_filter_(Minnesota_Filter) '''iron-enhanced sand filter''']</span>), resulting in a change from the default pollutant removal of 0.47 to 0.80.
  
 
==Changes in adjusted loads compared to unadjusted total loads==
 
==Changes in adjusted loads compared to unadjusted total loads==
 
The bmps included in the Simple Estimator have approved pollutant removal efficiencies. There are other actions that may reduce pollutant loading, or in some cases increase loading. Examples include changes in land use and street sweeping. Because there are not documented reductions for these activities, permittees can adjust emcs and/or runoff coefficients based on local data or information. MPCA encourages these adjustments when they are well supported and provide more realistic pollutant loading estimates. These activities should be documented in the spreadsheet. The spreadsheet is designed so that these adjustments will be noted and MPCA staff may request additional information about the basis for these adjustments.
 
The bmps included in the Simple Estimator have approved pollutant removal efficiencies. There are other actions that may reduce pollutant loading, or in some cases increase loading. Examples include changes in land use and street sweeping. Because there are not documented reductions for these activities, permittees can adjust emcs and/or runoff coefficients based on local data or information. MPCA encourages these adjustments when they are well supported and provide more realistic pollutant loading estimates. These activities should be documented in the spreadsheet. The spreadsheet is designed so that these adjustments will be noted and MPCA staff may request additional information about the basis for these adjustments.
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The Summary sheet in the worksheet does not display changes in loading associated with adjusted loads. MPCA staff will examine individual worksheets to identify these changes. The permittee should document the reason for these changes, preferably in the Notes worksheet where more detailed explanation can be provided.
  
 
==Land use distributions==
 
==Land use distributions==
 
MPCA staff will not conduct a comprehensive analysis of land use detailed in the Estimator spreadsheet. However, staff may request additional information under certain circumstances such as the entire area being in commercial land use.
 
MPCA staff will not conduct a comprehensive analysis of land use detailed in the Estimator spreadsheet. However, staff may request additional information under certain circumstances such as the entire area being in commercial land use.

Revision as of 15:20, 30 March 2020

This site is currently undergoing revision. For more information, open this link.
Page is in development

MPCA anticipates several permittees will use the MPCA Simple Estimator to demonstrate compliance with or progress toward meeting total maximum daily load (TMDL) wasteload allocations (WLAs). If a permittee uses the MPCA Simple Estimator , it is recommended they submit either of the following:

  • an electronic copy of the entire Excel spreadsheet, or
  • an electronic copy of the worksheet called Summary sheet, or
  • a printout or legible image of the worksheet called Summary sheet.

In reviewing the information in the Estimator, MPCA staff will focus on the following.

  • Comparing the reduction (lbs or %) or final loading rate (lb/ac/yr) with the WLA, depending on how the WLA is expressed in the TMDL
  • Changes in default values for event mean concentration (emc), runoff coefficients, bmp removal efficiencies, or the fraction of runoff that is treated and infiltrated by bmps
  • Changes in adjusted loads compared to unadjusted total loads
  • Land use distributions
  • BMPs implemenated

These are discussed briefly below.

Comparing the reduction (lbs or %) or final loading rate (lb/ac/yr) with the WLA, depending on how the WLA is expressed in the TMDL

screen shot of Summary tab from Estimator
Screen shot of the Summary worksheet from this Estimator example.

Wasteload allocations are typically expressed as a total load, a mass load reduction (e.g. pounds), a percent mass reduction, or a loading rate (lb/ac/yr). The value reported in the Estimator will be compared to the WLA as reported in the TMDL or as interpreted by the MPCA. The Summary sheet from the Estimator is the source of this information.

An example is shown in the adjacent image. This shows a Summary sheet from the Estimator, illustrating pounds of phosphorus reduced for a site having three subwatersheds. The pollutant of concern is phosphorus. The Summary sheet shows initial loading for each of the subwatersheds and for the entire site (2699.54 lbs), pounds reduced after BMP implementation (819.29 lbs), percent reduction from the initial load (30.35%), and final loading rate (0.57 lb/ac/yr). Each of these results is also displayed by subwatershed.

Changes in default values for event mean concentration, runoff coefficients, bmp removal efficiencies, or the fraction of runoff that is treated and infiltrated by bmps

screenshot alert check for the Estimator
Screen shot showing the alert checks on the Summary sheet of the MPCA Simple Estimator

Default values for these inputs are based on information from the literature and are therefore considered defensible. However, local information may exist to support changing these values. This includes water quality monitoring data, site-specific land use information, bmp performance monitoring, or some similar information. The Estimator spreadsheet contains cells for describing the rationale for changes to these inputs. The Stormwater Manual provides guidance for adjusting emcs and runoff coefficients. The adjacent image provides an example of some changes that MPCA staff would examine in determining compliance with a wla. Examples of changes that may merit further investigation by MPCA staff include the following.

  • Improved bmp removal efficiency
  • increased fraction of water infiltrating for a specific bmp
  • changes in emc or runoff coefficient greater than 10 percent compared to the default value

In the adjacent image, the user changed the default event mean concentration (emc) for the residential and agricultural areas. In these cases, MPCA staff would examine the changes. The permittee should provide a brief explanation of the reason for the change, either on the worklsheet where the change was made or in the Notes worksheet of the Estimator. The Notes worksheet is preferable because it allows the permittee to provide a detailed explanation of the change. For example, in the case of the image on the right, the emc was changed from the default of 0.325 mg/ L to 0.350 mg/L to account for high tree canopy, then modified again to 0.30 mg/L to account for enhanced street sweeping that targeted leaf removal during fall. The agricultural emc was changed as the land was developed and changed to mixed (multi-use) land use. The screen shot of the alert section of the spreadsheet also indicates the pollutant removal fraction for a sand filter was changed. In this case, it was due to incorporation of iron into the sand filter ( iron-enhanced sand filter), resulting in a change from the default pollutant removal of 0.47 to 0.80.

Changes in adjusted loads compared to unadjusted total loads

The bmps included in the Simple Estimator have approved pollutant removal efficiencies. There are other actions that may reduce pollutant loading, or in some cases increase loading. Examples include changes in land use and street sweeping. Because there are not documented reductions for these activities, permittees can adjust emcs and/or runoff coefficients based on local data or information. MPCA encourages these adjustments when they are well supported and provide more realistic pollutant loading estimates. These activities should be documented in the spreadsheet. The spreadsheet is designed so that these adjustments will be noted and MPCA staff may request additional information about the basis for these adjustments.

The Summary sheet in the worksheet does not display changes in loading associated with adjusted loads. MPCA staff will examine individual worksheets to identify these changes. The permittee should document the reason for these changes, preferably in the Notes worksheet where more detailed explanation can be provided.

Land use distributions

MPCA staff will not conduct a comprehensive analysis of land use detailed in the Estimator spreadsheet. However, staff may request additional information under certain circumstances such as the entire area being in commercial land use.