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This page provides guidance and recommendations for determining the appropriateness of infiltrating stormwater in a Drinking Water Supply Management Area (DWSMA). For more information on source water protection see [http://www.health.state.mn.us/divs/eh/water/swp/ Minnesota Department of Health].
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[[File:Technical information page image.png|right|100px|alt=image]]
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[[File:Pdf image.png|100px|thumb|left|alt=pdf image|<font size=3>[https://stormwater.pca.state.mn.us/index.php?title=File:Stormwater_and_wellhead_protection_-_Minnesota_Stormwater_Manual.pdf Download pdf]</font size>]]
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This page provides guidance and recommendations for determining the appropriateness of infiltrating stormwater in a Drinking Water Supply Management Area (DWSMA). For more information on source water protection see [https://www.health.state.mn.us/communities/environment/water/swp/index.htm Minnesota Department of Health].
  
 
==Definitions==
 
==Definitions==
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The figure at the right illustrates protection designations used to manage public water supply wells that have wellhead protection plans.
 
The figure at the right illustrates protection designations used to manage public water supply wells that have wellhead protection plans.
 
*Drinking Water Supply Management Area (DWSMA) - the surface and subsurface area surrounding a public water supply well, including the wellhead protection area, that must be managed by the entity identified in a wellhead protection plan. This area is delineated using identifiable landmarks that reflect the scientifically calculated wellhead protection area boundaries as closely as possible.
 
*Drinking Water Supply Management Area (DWSMA) - the surface and subsurface area surrounding a public water supply well, including the wellhead protection area, that must be managed by the entity identified in a wellhead protection plan. This area is delineated using identifiable landmarks that reflect the scientifically calculated wellhead protection area boundaries as closely as possible.
*Drinking Water Supply Management Area Vulnerability. An assessment of the likelihood that the aquifer within the DWSMA is subject to impact from overlying land and water uses. It is based upon criteria that are specified under Minnesota Rules, part 4720.5210, subpart 3.
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*Drinking Water Supply Management Area Vulnerability. An assessment of the likelihood that the aquifer within the DWSMA is subject to impact from overlying land and water uses. It is based upon criteria that are specified under [https://www.revisor.mn.gov/rules/?id=4720.5210 Minnesota Rules, part 4720.5210], subpart 3.
*Emergency Response Area (ERA). The part of the wellhead protection area that is defined by a one-year time of travel within the aquifer that is used by the public water supply well (Minnesota Rules, part 4720.5250, subpart 3). It is used to set priorities for managing potential contamination sources within the DWSMA. This area is particularly relevant for assessing impacts from potential sources of pathogen contamination because this time of travel is believed to closely correspond with the survival period of many pathogens.
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*Emergency Response Area (ERA). The part of the wellhead protection area that is defined by a one-year time of travel within the aquifer that is used by the public water supply well ([https://www.revisor.mn.gov/rules/?id=4720.5250 Minnesota Rules, part 4720.5250], subpart 3). It is used to set priorities for managing potential contamination sources within the DWSMA. This area is particularly relevant for assessing impacts from potential sources of pathogen contamination because this time of travel is believed to closely correspond with the survival period of many pathogens.
 
*Public water supply well – a drinking water well as defined in Minnesota Statutes, section [https://www.revisor.mn.gov/statutes/?id=103I.005 103I.005], subdivision 21, that serves a public water supply.
 
*Public water supply well – a drinking water well as defined in Minnesota Statutes, section [https://www.revisor.mn.gov/statutes/?id=103I.005 103I.005], subdivision 21, that serves a public water supply.
 
*Time of travel - means the amount of time over which groundwater will move through a portion of an aquifer to recharge a well in use. Note this definition does not consider travel time within the unsaturated (vadose) zone.
 
*Time of travel - means the amount of time over which groundwater will move through a portion of an aquifer to recharge a well in use. Note this definition does not consider travel time within the unsaturated (vadose) zone.
 
*Vulnerable public supply well – a public water supply well is vulnerable if:
 
*Vulnerable public supply well – a public water supply well is vulnerable if:
 
# the well water contains ten (10) milligrams per liter or more nitrate plus nitrite nitrogen;
 
# the well water contains ten (10) milligrams per liter or more nitrate plus nitrite nitrogen;
# the well water contains quantifiable levels of pathogens as defined in part [https://www.revisor.mn.gov/rules/?id=7040.0100 7040.0100], subpart 26, or chemical compounds that indicate groundwater degradation as defined in Minnesota Statutes, section [https://www.revisor.mn.gov/statutes/?id=103H.005 103H.005], subdivision 6;
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# the well water contains quantifiable levels of pathogens as defined in part 7040.0100, subpart 26, or chemical compounds that indicate groundwater degradation as defined in Minnesota Statutes, section 103H.005, subdivision 6;
 
# the well water contains one tritium unit or more when measured with an enriched tritium detection method; or
 
# the well water contains one tritium unit or more when measured with an enriched tritium detection method; or
 
# an enriched tritium analysis of the well water has not been performed within the past ten years; and
 
# an enriched tritium analysis of the well water has not been performed within the past ten years; and
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### unconsolidated material 0.062 millimeters (fine sand) or larger; or
 
### unconsolidated material 0.062 millimeters (fine sand) or larger; or
 
### a combination of the materials specified in units (a) to (d).
 
### a combination of the materials specified in units (a) to (d).
* Wellhead Protection Area (WHPA) – the surface and subsurface area surrounding a well or well field that supplies a public water system, through which contaminants are likely to move toward and reach the well or well field (Minnesota Statutes, section 103I.005, subdivision 24).
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* Wellhead Protection Area (WHPA) – the surface and subsurface area surrounding a well or well field that supplies a public water system, through which contaminants are likely to move toward and reach the well or well field ([https://www.revisor.mn.gov/statutes/?id=103I.005 Minnesota Statutes, section 103I.005], subdivision 24).
 
* Wellhead Protection Plan - a document that provides for the protection of a public water supply, is submitted to the department, is implemented by the public water supplier, and complies with:
 
* Wellhead Protection Plan - a document that provides for the protection of a public water supply, is submitted to the department, is implemented by the public water supplier, and complies with:
#the wellhead protection elements specified in the 1986 amendments to the federal Safe Drinking Water Act, United States Code, title 42, chapter 6A, subchapter XII, part C, section 300h-7 (1986 and as subsequently amended); and
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#the wellhead protection elements specified in the 1986 amendments to the federal Safe Drinking Water Act, [https://www.law.cornell.edu/uscode/text/42/chapter-6A/subchapter-XII United States Code, title 42, chapter 6A, subchapter XII], part C, section 300h-7 (1986 and as subsequently amended); and
 
#parts [https://www.revisor.mn.gov/rules/?id=4720.5200 4720.5200] to [https://www.revisor.mn.gov/rules/?id=4720.5290 4720.5290].
 
#parts [https://www.revisor.mn.gov/rules/?id=4720.5200 4720.5200] to [https://www.revisor.mn.gov/rules/?id=4720.5290 4720.5290].
  
 
==Step-by-step process for determining applicability of infiltration==
 
==Step-by-step process for determining applicability of infiltration==
Step 1: Must the practice comply with requirements of the [http://stormwater.pca.state.mn.us/index.php/III._STORMWATER_DISCHARGE_DESIGN_REQUIREMENTS#III.D._PERMANENT_STORMWATER_MANAGEMENT_SYSTEM Construction Stormwater General Permit]?
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[[File:Wellhead flowchart 2018 permit.png|400px|thumb|alt=flowchart for infiltration in DWSMAs|<font size=3>Flowchart for determining if stormwater infiltration is appropriate in DWSMAs. To see an enlarged image click on the image and then click again on the new image.</font size><!-- Guidance and additional information to support the flowchart is found at the following links.<br>
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*Word document: [[file:Evaluating Proposed Stormwater Infiltration Projects in Vulnerable Wellhead Protection Areas.docx]]<br>
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*pdf document: [[file:Evaluating Proposed Stormwater Infiltration Projects in Vulnerable Wellhead Protection Areas.pdf]].</font size>-->]]
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<!--[[file:Flow Chart - MDH Stormwater Guidance for Sites in Drinking Water Supply Management Areas 1.png|400px|thumb|alt=flowchart for infiltration in DWSMAs|<font size=3>Flowchart for determining if stormwater infiltration is appropriate in DWSMAs. To see an enlarged image click on the image and then click again on the new image. Guidance and additional information to support the flowchart is found at the following links.<br>
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*Word document: [[file:Evaluating Proposed Stormwater Infiltration Projects in Vulnerable Wellhead Protection Areas.docx]]<br>
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*pdf document: [[file:Evaluating Proposed Stormwater Infiltration Projects in Vulnerable Wellhead Protection Areas.pdf]].</font size>]]-->
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The Minnesota Department of Health and Minnesota Pollution Control Agency developed joint guidance for determining the applicability of infiltration in a Drinking Water Supply Management Area (DWSMA). A step-by-step process for determining if infiltration is allowed and appropriate in a DWSMA is shown on the right.<!-- You can also access this flowchart at [[file:Flow Chart - MDH Stormwater Guidance for Sites in Drinking Water Supply Management Areas.pdf]].
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 +
Guidance and additional information to support the flowchart is found at the following links.
 +
*Word document: [[file:Evaluating Proposed Stormwater Infiltration Projects in Vulnerable Wellhead Protection Areas.docx]]
 +
*pdf document: [[file:Evaluating Proposed Stormwater Infiltration Projects in Vulnerable Wellhead Protection Areas.pdf]]
 +
These documents provide a summary of general requirements, discuss assembling information needed to apply the flowchart, include an expanded discussion for each step in the flowchart, and provide contact information.-->
 +
 
 +
===Step 1===
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Is the site located in a DWSMA?
 +
*If No, proceed with infiltration observing state and local stormwater requirements. See [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_and_wellhead_protection#Additional_requirements_and_guidance additional requirements and guidance below].
 +
*If Yes, proceed to Step 2
 +
 
 +
===Step 2===
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Is the site in a portion of the DWSMA that exhibits very high, high, or moderate vulnerability as defined by Minnesota Rules (4720.5100-5590)?
 +
*If No, proceed observing state and local stormwater requirements. See [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_and_wellhead_protection#Additional_requirements_and_guidance additional requirements and guidance below].
 +
*If Yes, proceed to Step 3
 +
 
 +
===Step 3===
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Is the site in the Wellhead Protection Area (WHPA) of an aquifer exhibiting fracture flow or [http://stormwater.pca.state.mn.us/index.php/Karst karst] conditions and that has less than 50 feet of unfractured geologic cover?
 +
*If Yes, infiltration is generally not appropriate due to the potential for adverse effects to the aquifer used for drinking water supply.
 +
*If No, proceed to Step 4a
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 +
===Step 4a===
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Is the site within the Emergency Response Area (ERA) and is vulnerability of the DWSMA very high or high?
 +
*If Yes, proceed to Step 4b
 +
*If No, proceed to Step 5a
 +
 
 +
===Step 4b===
 +
Is a [https://stormwater.pca.state.mn.us/index.php?title=2018_Minnesota_Construction_Stormwater_Permit Construction Stormwater General Permit] required?
 +
*If Yes, [https://stormwater.pca.state.mn.us/index.php?title=MN_CSW_Permit_Section_16_Infiltration_Systems#16.19 infiltration is prohibited]
 +
*If No, infiltration is generally not appropriate due to the potential for adverse effects to the aquifer used for drinking water supply. Consider other stormwater handling procedures such as stormwater retention and conveyance outside of the WHPA or moving the infiltration area to a non-vulnerable part of the DWSMA. For more information, discuss with MDH subject matter experts or the hydrologist or planner for the DWSMA or with stormwater staff at the MPCA.
 +
 
 +
===Step 5a===
 +
Is the proposed infiltration site within the ERA and the vulnerability is moderate?
 +
*If Yes, proceed to Step 5b
 +
*If No, proceed to Step 6
 +
 
 +
===Step 5b===
 +
Is a [https://stormwater.pca.state.mn.us/index.php?title=2018_Minnesota_Construction_Stormwater_Permit Construction Stormwater General Permit] required?
 +
*If Yes, proceed to Step 5c
 +
*If No, infiltration is generally not appropriate due to the potential for adverse effects to the aquifer used for drinking water supply. Consider other stormwater handling procedures such as stormwater retention and conveyance outside of the WHPA or moving the infiltration area to a non-vulnerable part of the DWSMA. For more information, discuss with MDH subject matter experts or the hydrologist or planner for the DWSMA or with stormwater staff at the MPCA.
 +
 
 +
===Step 5c===
 +
Has a [https://stormwater.pca.state.mn.us/index.php?title=Guidance_and_recommendations_for_conducting_a_higher_level_of_engineering_review_for_stormwater_infiltration_in_DWSMAs_and_Wellhead_Protection_Areas higher level of engineering review been performed] and if yes, does the review indicate that infiltration is acceptable?
 +
*If No, [https://stormwater.pca.state.mn.us/index.php?title=MN_CSW_Permit_Section_16_Infiltration_Systems#16.19 infiltration is prohibited]
 +
*If Yes, proceed to Step 7
 +
 
 +
===Step 6===
 +
Is the proposed site outside the ERA and the vulnerability is high or very high?
 +
*If Yes, proceed to Step 5b
 +
*If No, proceed to Step 7
 +
 
 +
===Step 7===
 +
Will runoff from [http://stormwater.pca.state.mn.us/index.php/Potential_stormwater_hotspots Potential Stormwater Hotspots] (PSHs), as defined in the Minnesota Stormwater Manual, or runoff from highways enter the infiltration practice?
 +
*If No, proceed observing state and local stormwater requirements. See [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_and_wellhead_protection#Additional_requirements_and_guidance additional requirements and guidance below].
 +
*If Yes, proceed to Step 8
  
*If Yes, go to Step 2
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===Step 8===
*If No, go to Step 5
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Are [http://stormwater.pca.state.mn.us/index.php/Potential_stormwater_hotspots#Infiltration_guidance infiltration guidelines for stormwater hotspots] as defined in the Minnesota Stormwater Manual followed?
 +
*If Yes, proceed observing state and local stormwater requirements. See [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_and_wellhead_protection#Additional_requirements_and_guidance additional requirements and guidance below].
 +
*If No, infiltration is generally not appropriate due to the potential for adverse effects to the aquifer used for drinking water supply. Consider other stormwater handling procedures such as stormwater retention and conveyance outside of the WHPA or moving the infiltration area to a non-vulnerable part of the DWSMA. For more information, discuss with MDH subject matter experts or the hydrologist or planner for the DWSMA or with stormwater staff at the MPCA.
  
Step 2: [http://stormwater.pca.state.mn.us/index.php/Stormwater_and_wellhead_protection#Prohibitions_to_infiltration Determine if infiltration is prohibited].  
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<!--Guidance and additional information to support the flowchart is found at the following links.
 +
*Word document: [[file:Evaluating Proposed Stormwater Infiltration Projects in Vulnerable Wellhead Protection Areas.docx]]
 +
*pdf document: [[file:Evaluating Proposed Stormwater Infiltration Projects in Vulnerable Wellhead Protection Areas.pdf]]
 +
These documents provide a summary of general requirements, discuss assembling information needed to apply the flowchart, include an expanded discussion for each step in the flowchart, and provide contact information.
  
* If prohibited, STOP - infiltration is not allowed
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===Step 1a===
* If it is not prohibited, proceed to Step 3
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Is the site located in a DWSMA?
 +
*If No, proceed with infiltration observing state and local stormwater requirements. See [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_and_wellhead_protection#Additional_requirements_and_guidance additional requirements and guidance below].
 +
*If Yes, proceed to Step 1b
  
Step 3: Is the proposed infiltration site in a Drinking Water Supply Management Area (DWSMA) as defined in Minn. R. 4720.5100, subp. 13.?
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===Step 1b===
 +
Is a [http://stormwater.pca.state.mn.us/index.php/III._STORMWATER_DISCHARGE_DESIGN_REQUIREMENTS#III.D._PERMANENT_STORMWATER_MANAGEMENT_SYSTEM Construction Stormwater General Permit] required?
 +
*If Yes, proceed to Step 2
 +
*If No, proceed to Step 3
  
* No: Meet state and local requirements
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===Step 2===
* Yes: Go to Step 4
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Is there a Local Government Unit with a current Municipal Separate Storm Sewer System permit that allows infiltration?
 +
*If No, infiltration is prohibited by [http://stormwater.pca.state.mn.us/index.php/III._STORMWATER_DISCHARGE_DESIGN_REQUIREMENTS#III.D._PERMANENT_STORMWATER_MANAGEMENT_SYSTEM Part III.D.1.j.vii of the CSW permit].
 +
*If Yes, proceed to Step 3
  
Step 4: does a local unit of government with a current MS4 permit allow infiltration?
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===Step 3===
 +
Is the site in a portion of the DWSMA that exhibits very high, high, or moderate vulnerability as defined by Minnesota Rules (4720.5100-5590)?
 +
*If No, proceed observing state and local stormwater requirements. See [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_and_wellhead_protection#Additional_requirements_and_guidance additional requirements and guidance below].
 +
*If Yes, proceed to Step 4
  
* No – infiltration is not allowed
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===Step 4===
* Yes – infiltration is allowed in accordance with local requirements. [http://stormwater.pca.state.mn.us/index.php/Stormwater_and_wellhead_protection#Guidance_for_practices_required_to_meet_requirements_of_the_Construction_Stormwater_General_Permit Follow recommendations for infiltrating stormwater in DWSMAs]
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Is the site in the Wellhead Protection Area (WHPA) of an aquifer exhibiting fracture flow or [http://stormwater.pca.state.mn.us/index.php/Karst karst] conditions and that has less than 50 feet of unfractured geologic cover?
 +
*If Yes, infiltration is generally not appropriate due to the potential for adverse effects to the aquifer used for drinking water supply. Consider other stormwater handling procedures such as stormwater retention and conveyance outside of the WHPA or moving the infiltration area to a non-vulnerable part of the DWSMA. For more information, discuss with MDH subject matter experts or the hydrologist or planner for the DWSMA or with stormwater staff at the MPCA.
 +
*If No, proceed to Step 5
  
STOP
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===Step 5===
 +
Is the site within the Emergency Response Area (ERA) and is vulnerability very high or high?
 +
*If Yes, infiltration is generally not appropriate due to the potential for adverse effects to the aquifer used for drinking water supply. Consider other stormwater handling procedures such as stormwater retention and conveyance outside of the WHPA or moving the infiltration area to a non-vulnerable part of the DWSMA. For more information, discuss with MDH subject matter experts or the hydrologist or planner for the DWSMA or with stormwater staff at the MPCA.
 +
*If No, proceed to Step 6
  
Step 5: Follow [http://stormwater.pca.state.mn.us/index.php/Stormwater_and_wellhead_protection#Guidance_for_practices_not_required_to_meet_requirements_of_the_Construction_Stormwater_General_Permit recommendations for practices that do not have to meet requirements] of the Construction Stormwater General Permit.
+
===Step 6===
 +
Is the proposed infiltration site within the ERA and the vulnerability is moderate, or outside the ERA (but still inside the WHPA) and the vulnerability is high or very high?
 +
*If No, proceed observing state and local stormwater requirements. See [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_and_wellhead_protection#Additional_requirements_and_guidance additional requirements and guidance below].
 +
*If Yes, proceed to step 7
  
==Guidance for practices required to meet requirements of the Construction Stormwater General Permit==
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===Step 7===
The following guidance applies to practices required to meet requirements of the Construction Stormwater General Permit.
+
Will runoff from [http://stormwater.pca.state.mn.us/index.php/Potential_stormwater_hotspots Potential Stormwater Hotspots] (PSHs), as defined in the Minnesota Stormwater Manual, or runoff from highways enter the infiltration practice?
 +
*If No, proceed observing state and local stormwater requirements. See [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_and_wellhead_protection#Additional_requirements_and_guidance additional requirements and guidance below].
 +
*If Yes, proceed to Step 8
  
===Prohibitions to infiltration===
+
===Step 8===
Under the [http://stormwater.pca.state.mn.us/index.php/III._STORMWATER_DISCHARGE_DESIGN_REQUIREMENTS#III.D._PERMANENT_STORMWATER_MANAGEMENT_SYSTEM Construction Stormwater General Permit], stormwater infiltration is prohibited in the following areas regardless of whether the site is located in a DWSMA.
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Are [http://stormwater.pca.state.mn.us/index.php/Potential_stormwater_hotspots#Infiltration_guidance infiltration guidelines for stormwater hotspots] as defined in the Minnesota Stormwater Manual followed?
#Areas that receive discharges from vehicle fueling and maintenance.
+
*If Yes, proceed observing state and local stormwater requirements. See [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_and_wellhead_protection#Additional_requirements_and_guidance additional requirements and guidance below].
#Areas with less than three (3) feet of separation distance from the bottom of the infiltration system to the elevation of the seasonally saturated soils or the top of bedrock.
+
*If No, infiltration is generally not appropriate due to the potential for adverse effects to the aquifer used for drinking water supply. Consider other stormwater handling procedures such as stormwater retention and conveyance outside of the WHPA or moving the infiltration area to a non-vulnerable part of the DWSMA. For more information, discuss with MDH subject matter experts or the hydrologist or planner for the DWSMA or with stormwater staff at the MPCA.-->
#Areas that receive discharges from industrial facilities that are not authorized to infiltrate industrial stormwater under an NPDES/SDS Industrial Stormwater Permit issued by the MPCA.
 
#Areas where high levels of contaminants in soil or groundwater will be mobilized by the infiltrating stormwater.
 
#Areas of predominately Hydrologic Soil Group D (clay) soils unless allowed by a local unit of government with a current MS4 permit.
 
#Areas within 1,000 feet up‐gradient, or 100 feet down‐gradient of active karst features unless allowed by a local unit of government with a current MS4 permit.
 
#Areas where soil infiltration rates are more than 8.3 inches per hour unless soils are amended to slow the infiltration rate below 8.3 inches per hour or as allowed by a local unit of government with a current MS4 permit.
 
For those conditions above in which a local unit of government with a Municipal Separate Storm Sewer System (MS4) permit allows infiltration, follow the [http://stormwater.pca.state.mn.us/index.php/Stormwater_and_wellhead_protection#Recommendations_for_infiltrating_stormwater_in_DWSMAs recommendations for infiltration practices in a DWSMA].
 
  
===Recommendations for infiltrating stormwater in DWSMAs===
+
==Additional requirements and guidance==
The following are recommendations for infiltration practices in a DWSMA.
+
The following requirements and guidance apply to infiltration practices regardless of whether the site is located in a DWSMA.
  
#Infiltration is not recommended for the following conditions.
+
===Prohibitions to infiltration under the Construction Stormwater permit===
##If the proposed infiltration site is within the Emergency Response Area (1-year time-of-travel area) as designated by the Minnesota Department of Health and the vulnerability of the aquifer is very high or high
+
If the site requires a [https://stormwater.pca.state.mn.us/index.php?title=2018_Minnesota_Construction_Stormwater_Permit Construction Stormwater General Permit], stormwater infiltration is prohibited in the following areas regardless of whether the site is located in a DWSMA.
##If the aquifer receiving water from the infiltration practice exhibits fracture- or solution-enhanced flow conditions and less than 50 feet of unfractured geologic cover unless the [http://stormwater.pca.state.mn.us/index.php/Karst guidelines for karst areas] in the Minnesota Stormwater Manual are followed, including conducting site investigations, managing infiltration, remediating a site if necessary and feasible, and monitoring after BMPs are installed.
+
#Areas that receive discharges from vehicle fueling and maintenance
#Ensure that [http://stormwater.pca.state.mn.us/index.php/Stormwater_infiltration_and_setback_%28separation%29_distances separation distances] are met and that existing or proposed structures or infrastructure (e.g. rate control BMPs, utilities, buildings, roadway, easements) do not prevent infiltration.
+
#Areas with less than three (3) feet of separation distance from the bottom of the infiltration system to the elevation of the seasonally saturated soils or the top of bedrock
#A Local Government Unit (LGU) should be available to provide engineering review to ensure a functioning system that prevents adverse impacts to groundwater.
+
#Areas that receive discharges from industrial facilities that are not authorized to infiltrate industrial stormwater under an NPDES/SDS Industrial Stormwater Permit issued by the MPCA
#If there is a potential for the [http://stormwater.pca.state.mn.us/index.php/Shallow_groundwater seasonal high water table] or [http://stormwater.pca.state.mn.us/index.php/Shallow_soils_and_shallow_depth_to_bedrock bedrock to be within 6 feet of the bottom] of proposed infiltration practices, follow guidelines in the Minnesota Stormwater Manual for conducting site investigations and managing infiltration in these areas.
+
#Areas where high levels of contaminants in soil or groundwater will be mobilized by the infiltrating stormwater
#If there is the potential for presence of contaminated soils, contaminated groundwater, and/or hotspot runoff, follow [http://stormwater.pca.state.mn.us/index.php/Stormwater_infiltrations_and_contaminated_soils_and_groundwater guidelines in the Minnesota Stormwater Manual] for conducting site investigations and managing infiltration in these areas.
+
#Areas of predominately Hydrologic Soil Group D (clay) soils
#If there is a potential for presence of soils with steady-state infiltration rates less than 0.2 inches per hour, follow [http://stormwater.pca.state.mn.us/index.php/Soils_with_low_infiltration_capacity guidelines in the Minnesota Stormwater Manual] for conducting site investigations and managing infiltration in these areas.
+
#Areas within 1,000 feet up‐gradient, or 100 feet down‐gradient of active karst features
#If infiltration could result in adverse surface water hydrologic impacts, such as impacting a perched wetland, minimize infiltration to a point where adverse surface water hydrologic impacts are avoided.
+
#Areas where soil infiltration rates are more than 8.3 inches per hour unless soils are amended to slow the infiltration rate below 8.3 inches per hour
#If the infiltration practice is constructed in industrial, commercial, or transportation land uses, ensure that emergency procedures for containment of spills are established and acceptable.
 
  
==Guidance for practices not required to meet requirements of the Construction Stormwater General Permit==
+
===Recommendations for infiltrating stormwater in DWSMAs===
Infiltration is not recommended for the following conditions.
+
The following are recommendations for infiltration practices in a DWSMA regardless of whether the above step-by-step process indicates infiltration is appropriate or a Construction Stormwater permit is required.
#Areas that receive discharges from [http://stormwater.pca.state.mn.us/index.php/Potential_stormwater_hotspots#Vehicle_operations vehicle fueling and maintenance].
 
#Areas with less than three (3) feet of separation distance from the bottom of the infiltration system to the elevation of the [http://stormwater.pca.state.mn.us/index.php/Shallow_groundwater seasonally saturated soils] or the [http://stormwater.pca.state.mn.us/index.php/Shallow_soils_and_shallow_depth_to_bedrock top of bedrock].
 
#Areas that receive discharges from industrial facilities that are not authorized to infiltrate industrial stormwater under an [http://stormwater.pca.state.mn.us/index.php/Stormwater_program_for_industrial_activity NPDES/SDS Industrial Stormwater Permit] issued by the MPCA.
 
#Areas where high levels of contaminants in soil or groundwater will be mobilized by the infiltrating stormwater.
 
#Areas of predominately [http://stormwater.pca.state.mn.us/index.php/Soils_with_low_infiltration_capacity Hydrologic Soil Group D (clay) soils] unless allowed by a local unit of government with a current MS4 permit.
 
#Areas within 1,000 feet up‐gradient, or 100 feet down‐gradient of active [http://stormwater.pca.state.mn.us/index.php/Karst karst] features unless allowed by a local unit of government with a current MS4 permit.
 
#Areas where soil infiltration rates are more than 8.3 inches per hour unless soils are amended to slow the infiltration rate below 8.3 inches per hour or as allowed by a local unit of government with a current MS4 permit.
 
#If the proposed infiltration site is within the Emergency Response Area (1-year time-of-travel) as designated by the Minnesota Department of Health and the vulnerability of the aquifer is very high or high.
 
#If the aquifer receiving water from the infiltration practice exhibits fracture- or solution-enhanced flow conditions and has less than 50-feet of unfractured geologic cover unless the [http://stormwater.pca.state.mn.us/index.php/Karst guidelines for karst areas in the Minnesota Stormwater Manual] are followed, including conducting site investigations, managing infiltration, remediating a site if necessary and feasible, and monitoring after BMPs are installed.
 
  
The following are recommendations for infiltration practices in those portions of a DWSMA that are considered to have a vulnerability of very high or high by the Minnesota Department of Health but that are outside the Emergency Response Area (1-year time-of-travel) as designated by the Minnesota Department of Health (see section above on recommendations for infiltration stormwater in DWSMAs).
+
*Ensure that [http://stormwater.pca.state.mn.us/index.php/Stormwater_infiltration_and_setback_%28separation%29_distances separation distances] are met and that existing or proposed structures or infrastructure (e.g. rate control BMPs, utilities, buildings, roadway, easements) do not prevent infiltration.
#Ensure that [http://stormwater.pca.state.mn.us/index.php/Stormwater_infiltration_and_setback_%28separation%29_distances setback distances] are met and that existing or proposed structures or infrastructure (e.g. rate control BMPs, utilities, buildings, roadway, easements) do not prevent infiltration.
+
*If there is a potential for the [http://stormwater.pca.state.mn.us/index.php/Shallow_groundwater#What_are_general_stormwater_management_guidelines_for_areas_with_shallow_groundwater.3F high water table] or [http://stormwater.pca.state.mn.us/index.php/Shallow_soils_and_shallow_depth_to_bedrock#What_are_general_stormwater_management_guidelines_for_areas_with_shallow_bedrock.3F bedrock to be within 6 feet of the bottom] of proposed infiltration practices, follow guidelines in the Minnesota Stormwater Manual for conducting site investigations and managing infiltration in these areas.
#A Local Government Unit (LGU) should be available to provide engineering review to ensure a functioning system that prevents adverse impacts to groundwater.
+
*If there is the potential for presence of contaminated soils, contaminated groundwater, and/or hotspot runoff, follow [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_infiltration_and_contaminated_soils_and_groundwater guidelines in the Minnesota Stormwater Manual] for conducting site investigations and managing infiltration in these areas.
#If there is a potential for the seasonal high water table or bedrock to be within 6 feet of the bottom of proposed infiltration practices, follow [http://stormwater.pca.state.mn.us/index.php/Shallow_groundwater guidelines in the Minnesota Stormwater Manual] for conducting site investigations and managing infiltration in these areas.
+
*If there is a potential for presence of soils with steady-state infiltration rates less than 0.2 inches per hour, follow [http://stormwater.pca.state.mn.us/index.php/Soils_with_low_infiltration_capacity#What_are_general_stormwater_management_guidelines_for_sites_with_low_infiltration_capacity_soils.3F guidelines in the Minnesota Stormwater Manual] for conducting site investigations and managing infiltration in these areas.
#If there is the potential for presence of contaminated soils, contaminated groundwater, and/or hotspot runoff, follow [http://stormwater.pca.state.mn.us/index.php/Stormwater_infiltrations_and_contaminated_soils_and_groundwater guidelines in the Minnesota Stormwater Manual] for conducting site investigations and managing infiltration in these areas.
+
*If infiltration could result in adverse surface water hydrologic impacts, such as impacting a perched wetland, minimize infiltration to a point where adverse surface water hydrologic impacts are avoided.
#If there is a potential for presence of soils with steady-state infiltration rates less than 0.2 inches per hour, follow [http://stormwater.pca.state.mn.us/index.php/Soils_with_low_infiltration_capacity guidelines in the Minnesota Stormwater Manual] for conducting site investigations and managing infiltration in these areas.
+
*If the infiltration practice is constructed in industrial, commercial, or transportation land uses, ensure that emergency procedures for containment of spills are established and acceptable.
#If infiltration could result in adverse surface water hydrologic impacts, such as impacting a perched wetland, minimize infiltration to a point where adverse surface water hydrologic impacts are avoided.
+
*Infiltration is not allowed in areas that receive discharges from [http://stormwater.pca.state.mn.us/index.php/Potential_stormwater_hotspots#Vehicle_operations vehicle fueling and maintenance].
#If the infiltration practice is constructed in industrial, commercial, or transportation land uses, ensure that emergency procedures for containment of spills are established and acceptable.
+
*Infiltration is not recommended in areas that receive discharges from industrial facilities that are not authorized to infiltrate industrial stormwater under an [https://www.pca.state.mn.us/business-with-us/industrial-stormwater NPDES/SDS Industrial Stormwater Permit] issued by the MPCA.
 +
*Infiltration is not recommended in areas within 1,000 feet up‐gradient, or 100 feet down‐gradient of active [http://stormwater.pca.state.mn.us/index.php/Karst karst] features. If infiltration is being considered, follow [http://stormwater.pca.state.mn.us/index.php/Karst#General_stormwater_management_guidelines_for_karst_areas stormwater management guidelines for karst areas].
 +
*Infiltration is not recommended in areas where soil infiltration rates are more than 8.3 inches per hour unless soils are amended to slow the infiltration rate below 8.3 inches per hour.
  
 
==Maps==
 
==Maps==
Maps showing DWSMAs, DWSMA vulnerability, Emergency Response Areas, and Wellhead protection Areas can be found on an [http://www.health.state.mn.us/divs/eh/water/swp/maps/index.htm MDH website]. Shapefiles and .pdf files are available.
+
[[File:Dwsma 5.png|300px|thumb|alt=DWSMA image|<font size=3>Using the [https://www.pca.state.mn.us/water/stormwater-special-and-impaired-waters-search MPCA mapping tool], go to the site of interest by magnifying the image or entering an address. In this example, six sites are shown. Make sure the Legend (lower left) displays the proper legend. Infiltration is acceptable at site 1 because, even though it overlies an Emergency Response Area (ERA), the site is located in an area with low vulnerability. Infiltration is prohibited at site 2, unless a higher engineering review indicates infiltration is acceptable, because it is a DWSMA with high vulnerability. Infiltration is acceptable at site 3 because it is not in an ERA and is in a low vulnerability DWSMA. Infiltration is acceptable at site 4 because it is outside an ERA and DWSMA. Infiltration is prohibited at site 5 because the area overlies an ERA and vulnerability is high. Infiltration is prohibited at site 6, unless a higher engineering review indicates infiltration is acceptable, because the site overlies an ERA in a moderate vulnerability session.</font size>]]
 +
*The [https://mpca.maps.arcgis.com/apps/webappviewer/index.html?id=8d310e604baa43699b25395834d0c69a MS4 mapping tool] includes a coverage illustrating DWSMAs and their vulnerability. For more information, see [[Guidance for using the Stormwater Special and impaired waters search tool]].
 +
*Shapefiles and maps showing DWSMAs, DWSMA vulnerability, Emergency Response Areas, and Wellhead protection Areas can be found at the following.
 +
**[https://www.health.state.mn.us/communities/environment/water/swp/maps/index.htm Shapefile downloads]
 +
**[https://www.health.state.mn.us/communities/environment/water/swp/mapviewer.html New interactive SWP map viewer (this link goes to intro page)]
 +
**[https://mdh.maps.arcgis.com/apps/View/index.html?appid=5051b7d910234421b0728c40a1433baa Direct link to the interactive map]
 +
 
 +
==Guidance and recommendations for conducting a higher level of engineering review for stormwater infiltration in DWSMAs and Wellhead Protection Areas==
 +
The Construction Stormwater Permit requires a higher level of engineering review for proposed infiltration projects in areas overlying an Emergency Response Area (ERA) where the vulnerability of the DWSMA (Drinking Water Supply Management Area) is classified as moderate, or in areas outside the ERA where the vulnerability of the DWSMA (Drinking Water Supply Management Area) is classified as high or very high. To see guidance and recommendations for conducting a higher level of engineering review see [[Guidance and recommendations for conducting a higher level of engineering review for stormwater infiltration in DWSMAs and Wellhead Protection Areas]]
  
 
==Related pages==
 
==Related pages==
 +
*[[Guidance and recommendations for conducting a higher level of engineering review for stormwater infiltration in DWSMAs and Wellhead Protection Areas]]
 
*[[Overview of stormwater infiltration]]
 
*[[Overview of stormwater infiltration]]
*[[Pre-treatment considerations for stormwater infiltration]]
+
*[[Pre-treatment considerations for stormwater infiltration|Pretreatment considerations for stormwater infiltration]]
 
*[[BMPs for stormwater infiltration]]
 
*[[BMPs for stormwater infiltration]]
 
*[[Pollutant fate and transport in stormwater infiltration systems]]
 
*[[Pollutant fate and transport in stormwater infiltration systems]]
Line 117: Line 202:
 
*[[Potential stormwater hotspots]]
 
*[[Potential stormwater hotspots]]
 
*[[Stormwater and wellhead protection]]
 
*[[Stormwater and wellhead protection]]
*[[Stormwater infiltrations and contaminated soils and groundwater]]
+
*[[Stormwater infiltration and contaminated soils and groundwater]]
 
*[[Decision tools for stormwater infiltration]]
 
*[[Decision tools for stormwater infiltration]]
*[[Stormwater infiltration research needs]]
+
*[https://stormwater.pca.state.mn.us/index.php?title=Determining_soil_infiltration_rates Determining soil infiltration rates]
 +
*[[Design infiltration rates]]
 +
*[[Understanding and interpreting soils and soil boring reports for infiltration BMPs]]
 +
*[[Supporting material for infiltration]]
 
*[[References for stormwater infiltration]]
 
*[[References for stormwater infiltration]]
  
 
<noinclude>
 
<noinclude>
[[Category:Infiltration]]
+
[[Category:Level 2 - Technical and specific topic information/infiltration]]
 
</noinclude>
 
</noinclude>

Latest revision as of 13:56, 12 February 2023

image

This page provides guidance and recommendations for determining the appropriateness of infiltrating stormwater in a Drinking Water Supply Management Area (DWSMA). For more information on source water protection see Minnesota Department of Health.

Definitions

image illustrating designations for public supply protection
Example map illustrating different protection designations for public supply wells with wellhead protection plans.

The figure at the right illustrates protection designations used to manage public water supply wells that have wellhead protection plans.

  • Drinking Water Supply Management Area (DWSMA) - the surface and subsurface area surrounding a public water supply well, including the wellhead protection area, that must be managed by the entity identified in a wellhead protection plan. This area is delineated using identifiable landmarks that reflect the scientifically calculated wellhead protection area boundaries as closely as possible.
  • Drinking Water Supply Management Area Vulnerability. An assessment of the likelihood that the aquifer within the DWSMA is subject to impact from overlying land and water uses. It is based upon criteria that are specified under Minnesota Rules, part 4720.5210, subpart 3.
  • Emergency Response Area (ERA). The part of the wellhead protection area that is defined by a one-year time of travel within the aquifer that is used by the public water supply well (Minnesota Rules, part 4720.5250, subpart 3). It is used to set priorities for managing potential contamination sources within the DWSMA. This area is particularly relevant for assessing impacts from potential sources of pathogen contamination because this time of travel is believed to closely correspond with the survival period of many pathogens.
  • Public water supply well – a drinking water well as defined in Minnesota Statutes, section 103I.005, subdivision 21, that serves a public water supply.
  • Time of travel - means the amount of time over which groundwater will move through a portion of an aquifer to recharge a well in use. Note this definition does not consider travel time within the unsaturated (vadose) zone.
  • Vulnerable public supply well – a public water supply well is vulnerable if:
  1. the well water contains ten (10) milligrams per liter or more nitrate plus nitrite nitrogen;
  2. the well water contains quantifiable levels of pathogens as defined in part 7040.0100, subpart 26, or chemical compounds that indicate groundwater degradation as defined in Minnesota Statutes, section 103H.005, subdivision 6;
  3. the well water contains one tritium unit or more when measured with an enriched tritium detection method; or
  4. an enriched tritium analysis of the well water has not been performed within the past ten years; and
    1. information on the well construction is not available; or
    2. the geological material from the land surface to where the groundwater enters the public water supply well is:
      1. fractured bedrock;
      2. solution weathered bedrock;
      3. sandstone bedrock;
      4. unconsolidated material 0.062 millimeters (fine sand) or larger; or
      5. a combination of the materials specified in units (a) to (d).
  • Wellhead Protection Area (WHPA) – the surface and subsurface area surrounding a well or well field that supplies a public water system, through which contaminants are likely to move toward and reach the well or well field (Minnesota Statutes, section 103I.005, subdivision 24).
  • Wellhead Protection Plan - a document that provides for the protection of a public water supply, is submitted to the department, is implemented by the public water supplier, and complies with:
  1. the wellhead protection elements specified in the 1986 amendments to the federal Safe Drinking Water Act, United States Code, title 42, chapter 6A, subchapter XII, part C, section 300h-7 (1986 and as subsequently amended); and
  2. parts 4720.5200 to 4720.5290.

Step-by-step process for determining applicability of infiltration

flowchart for infiltration in DWSMAs
Flowchart for determining if stormwater infiltration is appropriate in DWSMAs. To see an enlarged image click on the image and then click again on the new image.

The Minnesota Department of Health and Minnesota Pollution Control Agency developed joint guidance for determining the applicability of infiltration in a Drinking Water Supply Management Area (DWSMA). A step-by-step process for determining if infiltration is allowed and appropriate in a DWSMA is shown on the right.

Step 1

Is the site located in a DWSMA?

Step 2

Is the site in a portion of the DWSMA that exhibits very high, high, or moderate vulnerability as defined by Minnesota Rules (4720.5100-5590)?

Step 3

Is the site in the Wellhead Protection Area (WHPA) of an aquifer exhibiting fracture flow or karst conditions and that has less than 50 feet of unfractured geologic cover?

  • If Yes, infiltration is generally not appropriate due to the potential for adverse effects to the aquifer used for drinking water supply.
  • If No, proceed to Step 4a

Step 4a

Is the site within the Emergency Response Area (ERA) and is vulnerability of the DWSMA very high or high?

  • If Yes, proceed to Step 4b
  • If No, proceed to Step 5a

Step 4b

Is a Construction Stormwater General Permit required?

  • If Yes, infiltration is prohibited
  • If No, infiltration is generally not appropriate due to the potential for adverse effects to the aquifer used for drinking water supply. Consider other stormwater handling procedures such as stormwater retention and conveyance outside of the WHPA or moving the infiltration area to a non-vulnerable part of the DWSMA. For more information, discuss with MDH subject matter experts or the hydrologist or planner for the DWSMA or with stormwater staff at the MPCA.

Step 5a

Is the proposed infiltration site within the ERA and the vulnerability is moderate?

  • If Yes, proceed to Step 5b
  • If No, proceed to Step 6

Step 5b

Is a Construction Stormwater General Permit required?

  • If Yes, proceed to Step 5c
  • If No, infiltration is generally not appropriate due to the potential for adverse effects to the aquifer used for drinking water supply. Consider other stormwater handling procedures such as stormwater retention and conveyance outside of the WHPA or moving the infiltration area to a non-vulnerable part of the DWSMA. For more information, discuss with MDH subject matter experts or the hydrologist or planner for the DWSMA or with stormwater staff at the MPCA.

Step 5c

Has a higher level of engineering review been performed and if yes, does the review indicate that infiltration is acceptable?

Step 6

Is the proposed site outside the ERA and the vulnerability is high or very high?

  • If Yes, proceed to Step 5b
  • If No, proceed to Step 7

Step 7

Will runoff from Potential Stormwater Hotspots (PSHs), as defined in the Minnesota Stormwater Manual, or runoff from highways enter the infiltration practice?

Step 8

Are infiltration guidelines for stormwater hotspots as defined in the Minnesota Stormwater Manual followed?

  • If Yes, proceed observing state and local stormwater requirements. See additional requirements and guidance below.
  • If No, infiltration is generally not appropriate due to the potential for adverse effects to the aquifer used for drinking water supply. Consider other stormwater handling procedures such as stormwater retention and conveyance outside of the WHPA or moving the infiltration area to a non-vulnerable part of the DWSMA. For more information, discuss with MDH subject matter experts or the hydrologist or planner for the DWSMA or with stormwater staff at the MPCA.


Additional requirements and guidance

The following requirements and guidance apply to infiltration practices regardless of whether the site is located in a DWSMA.

Prohibitions to infiltration under the Construction Stormwater permit

If the site requires a Construction Stormwater General Permit, stormwater infiltration is prohibited in the following areas regardless of whether the site is located in a DWSMA.

  1. Areas that receive discharges from vehicle fueling and maintenance
  2. Areas with less than three (3) feet of separation distance from the bottom of the infiltration system to the elevation of the seasonally saturated soils or the top of bedrock
  3. Areas that receive discharges from industrial facilities that are not authorized to infiltrate industrial stormwater under an NPDES/SDS Industrial Stormwater Permit issued by the MPCA
  4. Areas where high levels of contaminants in soil or groundwater will be mobilized by the infiltrating stormwater
  5. Areas of predominately Hydrologic Soil Group D (clay) soils
  6. Areas within 1,000 feet up‐gradient, or 100 feet down‐gradient of active karst features
  7. Areas where soil infiltration rates are more than 8.3 inches per hour unless soils are amended to slow the infiltration rate below 8.3 inches per hour

Recommendations for infiltrating stormwater in DWSMAs

The following are recommendations for infiltration practices in a DWSMA regardless of whether the above step-by-step process indicates infiltration is appropriate or a Construction Stormwater permit is required.

  • Ensure that separation distances are met and that existing or proposed structures or infrastructure (e.g. rate control BMPs, utilities, buildings, roadway, easements) do not prevent infiltration.
  • If there is a potential for the high water table or bedrock to be within 6 feet of the bottom of proposed infiltration practices, follow guidelines in the Minnesota Stormwater Manual for conducting site investigations and managing infiltration in these areas.
  • If there is the potential for presence of contaminated soils, contaminated groundwater, and/or hotspot runoff, follow guidelines in the Minnesota Stormwater Manual for conducting site investigations and managing infiltration in these areas.
  • If there is a potential for presence of soils with steady-state infiltration rates less than 0.2 inches per hour, follow guidelines in the Minnesota Stormwater Manual for conducting site investigations and managing infiltration in these areas.
  • If infiltration could result in adverse surface water hydrologic impacts, such as impacting a perched wetland, minimize infiltration to a point where adverse surface water hydrologic impacts are avoided.
  • If the infiltration practice is constructed in industrial, commercial, or transportation land uses, ensure that emergency procedures for containment of spills are established and acceptable.
  • Infiltration is not allowed in areas that receive discharges from vehicle fueling and maintenance.
  • Infiltration is not recommended in areas that receive discharges from industrial facilities that are not authorized to infiltrate industrial stormwater under an NPDES/SDS Industrial Stormwater Permit issued by the MPCA.
  • Infiltration is not recommended in areas within 1,000 feet up‐gradient, or 100 feet down‐gradient of active karst features. If infiltration is being considered, follow stormwater management guidelines for karst areas.
  • Infiltration is not recommended in areas where soil infiltration rates are more than 8.3 inches per hour unless soils are amended to slow the infiltration rate below 8.3 inches per hour.

Maps

DWSMA image
Using the MPCA mapping tool, go to the site of interest by magnifying the image or entering an address. In this example, six sites are shown. Make sure the Legend (lower left) displays the proper legend. Infiltration is acceptable at site 1 because, even though it overlies an Emergency Response Area (ERA), the site is located in an area with low vulnerability. Infiltration is prohibited at site 2, unless a higher engineering review indicates infiltration is acceptable, because it is a DWSMA with high vulnerability. Infiltration is acceptable at site 3 because it is not in an ERA and is in a low vulnerability DWSMA. Infiltration is acceptable at site 4 because it is outside an ERA and DWSMA. Infiltration is prohibited at site 5 because the area overlies an ERA and vulnerability is high. Infiltration is prohibited at site 6, unless a higher engineering review indicates infiltration is acceptable, because the site overlies an ERA in a moderate vulnerability session.

Guidance and recommendations for conducting a higher level of engineering review for stormwater infiltration in DWSMAs and Wellhead Protection Areas

The Construction Stormwater Permit requires a higher level of engineering review for proposed infiltration projects in areas overlying an Emergency Response Area (ERA) where the vulnerability of the DWSMA (Drinking Water Supply Management Area) is classified as moderate, or in areas outside the ERA where the vulnerability of the DWSMA (Drinking Water Supply Management Area) is classified as high or very high. To see guidance and recommendations for conducting a higher level of engineering review see Guidance and recommendations for conducting a higher level of engineering review for stormwater infiltration in DWSMAs and Wellhead Protection Areas

Related pages

This page was last edited on 12 February 2023, at 13:56.