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[[File:Types of stormwater hotspots.png|thumb|500px|alt=types of stormwater hotspots|Figure 1:<p><font size=2>Five types of potential stormwater hotspots include commercial, industrial, institutional, municipal and transportation related land use.  Source: [http://www1.umn.edu/news/news-releases/2004/UR_RELEASE_MIG_1170.html University of Minnesota Design Center]</font size></p>]]
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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:Potential_stormwater_hotspots_-_Minnesota_Stormwater_Manual.pdf Download pdf]</font size>]]
  
Potential Stormwater Hotspots (PSHs) are defined as commercial, industrial, institutional, municipal, or transportation-related operations that produce or can produce relatively high levels of stormwater pollutants. PSHs include locations where there is a potential risk for spills, leaks or illicit discharges. It is important to note that designation as a PSH does not imply that a site is a hotspot, but rather that the land use and associated on-site activities have the potential to generate higher pollutant runoff loads compared to other land uses. Designation as a PSH serves as a useful reminder to designers and reviewers that more careful consideration of the site is warranted. Ultimately, a PSH site designation may dictate that certain practices and/or design criteria are promoted or discouraged.
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Potential Stormwater Hotspots (PSHs) are activities or practices that have the potential to produce relatively high levels of stormwater pollutants. Designation as a PSH does not imply that a site is a hotspot, but rather that the potential to generate high pollutant runoff loads or concentrations exists. PSHs include locations where there is a potential risk for spills, leaks, or illicit discharges. Stormwater hotspots may also be areas which produce higher concentrations of pollutants than normally found in urban runoff.  Because stormwater hotspots are found in a variety of land uses, there is no common pollutant for any type of hotspot. Instead the pollutants tend to be a unique mixture of pollutants [[References_for_stormwater_infiltration#C|(CWP, 2005)]]. Hotspots can be classified as Regulated, subject to state or federal permits, or Unregulated.  In Minnesota Regulated hotspots are subject to the [http://stormwater.pca.state.mn.us/index.php/Stormwater_program_for_industrial_activity NPDES Multi-Sector General Permit for Industrial Activity], and/or local ordinances.
  
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==Pollutant generating operations and activities==
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[[File:Common operations for assessing pshs.png|thumb|300px|alt=common operations to assess pshs|<font size=3>Common operations and areas for assessing PSHs include management of turf, waste, loading docks, downspouts, vehicle fueling, and parking lots.</font size>]]
  
==Overview and designation of PSHs==
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The potential for hotspots is related to the activities on the site more than the land use or category of operation.  The table below summarizes the most common pollutants generated at stormwater hotspots based on common operations at a site. These operations are discussed in greater detail below.
  
PSHs can be categorized by different land uses.  Five land use categories that may be classified as PSHs include commercial, industrial, institutional, municipal, or transportation-related operationser.  A description of the major land use category is provided below. Note that some of these land uses fall under the requirements for Phase II NPDES industrial stormwater permits.
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{{:Pollutants of concern from operations}}
  
===Commercial PSHs===
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===Vehicle operations ===
Commercial PSHs consist of a small group of businesses associated with a specific activity or operation that generates higher pollutant loads in a subwatershed. Examples include:
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Vehicle operations include maintenance, repair, recycling, fueling, washing, and long-term parking. Vehicle operations can be a significant source of trace metals, oil, grease, and hydrocarbons, and are the first operations inspected during a hotspot source investigation. Vehicle maintenance and repair operations often produce waste oil, fluids and other hazardous products, particularly if work areas are connected to the storm drain system. Routing protective rooftop runoff through a fueling area has become a common practice in Minnesota; simple re-routing of runoff away from a potential fuel wash-off location could eliminate this from the hotspot list. Examples of pollutant-generating activities associated with vehicle operations include the following.
*animal care services
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*Improper disposal of fluids down shop and storm drains
*building material
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*Spilled fuel, leaks and drips from wrecked vehicles
*commercial car washes
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*Hosing of outdoor work areas
*convenience stores
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*Wash water from cleaning
*laundries and dry cleaners
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*Uncovered outdoor storage of liquids/oils/batteries/spills
*lawn care companies
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*Pollutant wash-off from parking lots
*gas stations
 
*nurseries and garden centers
 
*petroleum wholesalers
 
*fast food restaurants
 
*shopping centers
 
*vehicle maintenance and repair
 
*wholesale food and beverage
 
Each kind of commercial hotspot generates its own blend of stormwater pollutants, which can include nutrients, hydrocarbons, metals, trash and pesticides. Commercial PSHs typically have a great deal of vehicle traffic, generate waste or wash water, handle fuel or repair vehicles, or store products outside. While commercial PSHs are quite diverse, they are often clustered together. Most commercial PSHs are unregulated, although a few are regulated under the NPDES industrial stormwater permit program by local ordinance or by federal/state law if they handle even small quantities of hazardous material.
 
  
===Industrial PSHs===
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===Outdoor materials===
Industrial PSHs are a major focus for pollution prevention if they use, generate, handle or store pollutants that can potentially be washed away in stormwater runoff, spilled, or inadvertently discharged to the storm drain system. Examples of industrial land use activities include:
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Improper handling or storage of materials outdoors can create stormwater problems. Techniques for properly handling materials outdoors include inventorying the type and hazard level of materials at the site, examining loading and unloading areas to see if materials are exposed to rainfall and/or are connected to the storm drain system, and investigating any materials stored outdoors that could potentially be exposed to rainfall or runoff. Public and private road salt and sand storage areas are of particular concern. Examples of pollutant-generating activities associated with outdoor materials include the following.
*auto recyclers
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*Spills at loading areas
*boat building and repair facilities
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*Hosing/washing of loading areas into shop or storm drains
*recycling centers and scrap yards
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*Wash-off of uncovered bulk materials and liquids stored outside, of particular concern in MN are road salt storage areas
*warehouses
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*Leaks and spills
Each type of industrial PSH generates its own blend of stormwater pollutants, but as a group, they generally produce higher levels of metals, hydrocarbons and sediment. Many industrial operations are regulated under the NPDES industrial stormwater permit program, although individual owners or operators may be unaware of their permit status.
 
  
===Institutional PSHs===
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===Waste management===
Institutional PSHs include larger, privately-owned facilities that have extensive parking, landscaping, or turf cover. In addition, institutions may contain fleet vehicles and large maintenance operations.  Examples include:
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[[File:Example of dumspter management at psh.png|thumb|300 px|alt=dumpster management at psh|<font size=3>Dumpster leaking directly into a storm sewer.</font size>]]
*cemeteries
 
*churches
 
*colleges
 
*corporate office parks
 
*hospitals
 
*private schools
 
*private golf courses
 
By and large, institutional PSHs are not regulated. The most common pollutants generated by institutional PSHs are nutrients and pesticides applied to maintain grounds and landscaping. In addition, large parking lots can produce stormwater runoff and associated pollutants, and are natural targets for stormwater retrofitting. Institutional landowners can be important partners in subwatershed restoration, given the importance of their stewardship practices on the open lands they maintain.  
 
  
===Municipal PSHs===
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Every business generates waste as part of its daily operations, most of which is temporarily stored at the site pending disposal. The manner in which waste products are stored and disposed of at a site, particularly in relation to the storm drain system, determine the likelihood of becoming a hotspot. In some sites, simple practices such as dumpster management can reduce pollutants, whereas other sites may require more sophisticated spill prevention and response plans. Examples of pollutant-generating activities associated with waste management include the following.
Municipal PSHs include many local government operations that handle solid waste, wastewater, road and vehicle maintenance, bulk storage areas for road salt and sand, and yard waste. Examples include:
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*Spills and leaks of fluids
composting facilities
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*Dumping into storm drains
*fleet storage and school bus depots
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*Leaking dumpsters
*landfills/solid waste facilities
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*Wash-off of dumpster spillage
*local streets and storm drains
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*Accumulation of particulate deposits
*pesticide use in rights-of-way
 
*public golf courses
 
*public schools
 
*public works yards
 
*maintenance depots
 
*solid waste facilities
 
*wastewater treatment plants
 
Many of these municipal operations are regulated PSHs in MS4 communities. Municipal PSHs must prepare the same pollution prevention plans and implement source control practices as any other regulated PSHs. Municipal PSHs can generate the full range of stormwater pollutants, including nutrients, hydrocarbons, metals, chloride, pesticides, bacteria, and trash. It is common in Minnesota for each municipality and many commercial centers to store a stockpile of road salt. Although these piles are generally not subject to regulation unless they cause a documented water quality problem, MS4 municipal programs should take responsibility for managing these piles in a pollution free manner.
 
  
===Transport-related PSHs===
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===Physical plant maintenance ===
Examples of transportation-related uses include:
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Plant maintenance relates to practices used to clean, maintain or repair the physical plant, which includes the building, outdoor work areas and parking lots. Routine cleaning and maintenance practices can cause runoff of sediment, nutrients, paints, and solvents from the site. Sanding, painting, power-washing, and resealing or resurfacing roofs or parking lots are activities that can result in increased pollutant loading or concentrations, especially when performed near storm drains. Examples of pollutant-generating activities associated with plant maintenance include the following.
*airports
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*Discharges from power washing and steam cleaning
*bus depots
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*Wash-off of fine particles from painting/sandblasting operations
*rental car lots
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*Rinse water and wash water discharges during cleanup
*railroad stations and associated maintenance facilities
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*Temporary outdoor storage
*ports
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*Runoff from degreasing and re-surfacing
*highway maintenance facilities
 
*trucking companies and distribution centers
 
Many, but not all, transportation-related uses are regulated PSHs. They tend to generate higher loads of hydrocarbons, metals, and sediment in stormwater runoff, can be associated with large areas of impervious cover, and have extensive private storm drain systems. Fluid leakage from these sites can be a major source of contamination, as can the addition of sand and salt during the cold weather season. Road surfaces are not automatically considered as PSHs unless they have been shown locally to be such sources.
 
  
[[File:examples of land use activities for stormwater hotspots.png|thumb|600px|alt=land use activities for stormwater hotspots|Figure 2:<p><font size=2>Examples of potential pollutant generating land uses and land use activities.  Note the list is not all-inclusive.  Each of these examples is included in the bulleted list within the discussion for the five land use categories (commercial, industrial, institutional, municipal, and transport related.</font size></p>]]
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===Turf and landscaping===
 
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Many commercial, institutional and municipal sites hire contractors to maintain turf and landscaping, apply fertilizers or pesticides, and provide irrigation. Current landscaping practices should be thoroughly evaluated at each site to determine whether they are generating runoff of nutrients, pesticides, organic carbon, or are producing non-target irrigation flows. Examples of pollutant-generating activities associated with turf and landscaping include the following.
 
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*Non-target irrigation
==Pollutant Generating Operations/Activities==
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*Runoff of nutrients and pesticides
[[File:Common operations for assessing pshs.png|thumb|500px|alt=common operations to assess pshs|Figure 3:<p><font size=2>Six common operations for assessing PSHs include management of turf, waste, loading docks, downspouts, vehicle fueling, and parking lots.</font size></p>]]
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*Deposition and subsequent washoff of soil and organic matter on impervious surfaces
 
 
Perhaps of more significant consideration is an understanding of the types of pollutant generating activities that commonly occur in association with various PSH operations. Six common operations and a subset of related activities that can contribute to stormwater quality problems at a site are discussed below.
 
  
[[File:pollutants associated with pshs.png|thumb|500px|alt=types of pollutants associated with pshs|Figure 4:<p><font size=2>Stormwater pollutants associated with common operations at potential stormwater hotspots. Source: Scheuler et al., 2004</font size></p>]]
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==Determining if a PSH is a hotspot==
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As stated previously, the designation of PSH does not mean a site is a hotspot, only that activities have the potential to generate higher pollution runoff loads or concentrations compared to the land uses in which they occur. When designing a stormwater management system at these sites, it is important to determine if the PSH is an actual hotspot. If it is a hotspot, additional stormwater management controls may be needed. A recommended process for determining whether a PSH is a hotspot is as follows.
  
===Vehicle operations===
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:'''Step 1''': Consider where the activities take place. If all activities using hazardous materials occur inside a building and no materials can be tracked outside, then the site is not a hotspot. The various activities involving hazardous materials should be monitored at regularly scheduled intervals to ensure that nothing changes that would cause the hazardous materials to come in contact with stormwater runoff.
Nearly all PSHs devote some portion of the site to vehicle operations such as maintenance, repair, recycling, fueling, washing or long-term parking. Vehicle operations can be a significant source of trace metals, oil, grease, and hydrocarbons, and are the first operations inspected during a hotspot source investigation. Vehicle maintenance and repair operations often produce waste oil, fluids and other hazardous products, particularly if work areas are connected to the storm drain system. Routing protective rooftop runoff through a fueling area has become a common practice in Minnesota; simple re-routing of runoff away from a potential fuel wash-off location could eliminate this from the hotspot list.
 
  
===Outdoor materials===
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:'''Step 2''': Review the Stormwater Pollution Prevention Plan/Program (SWPPP), if present. Sites subject to NPDES requirements through the Industrial Multi-Sector Permit or the MS4 Municipal General Permit may have created SWPPPs that guide the operations and housekeeping at sites where the potential exists for increased concentrations of certain pollutants in the runoff.
Most PSH sites handle some kind of material that can create stormwater problems if not properly handled or stored. The first step is to inventory the type and hazard level of materials at the site. Next, it is important to examine loading and unloading areas to see if materials are exposed to rainfall and/or are connected to the storm drain system. Third, any materials stored outdoors that could potentially be exposed to rainfall or runoff should be investigated. Public and private road salt and sand storage areas are of particular concern for this category.
 
  
===Waste management===
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:'''Step 3''': Conduct a site inspection. The Center for Watershed Protection (CWP) has developed inspection forms that can be used to record physical operations and observations at a site to assess whether the site should be designated as a hotspot. For sites with a SWPPP, the inspection should include whether the site is operated in compliance with the requirements in the SWPPP.  The CWP form includes an overall assessment of whether to designate the site as a hotspot. To access the CWP information go to [https://owl.cwp.org/mdocs-posts/urban-subwatershed-restoration-manual-series-manual-8/ this link] and find ''Urban Subwatershed Restoration Manual Series Manual 8: Pollution Source Control Practices'' to open the document as a pdf. Hotspot prevention profile sheets are found on pages 109-158. A discussion of stormwater hotspots is found on pages 13-24.
Every business generates waste as part of its daily operations, most of which is temporarily stored at the site pending disposal. The third common hotspot operation involves the way waste products are stored and disposed of at the site in relation to the storm drain system. In some sites, simple practices such as dumpster management can reduce pollutants, whereas other sites may require more sophisticated spill prevention and response plans.
 
  
[[File:Example of dumpster management at psh.png|thumb|500 px|alt=dumpster management at psh|Figure 5:<p><font size=2>Dumpster leaking directly into a storm sewer.</font size></p>]]
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:'''Step 4''': Sample collection and analysis. Further analysis may be required to determine if the PSH is a hotspot. Samples of the stormwater runoff at the site should be collected and analyzed for the pollutants of concern. Samples need to be collected from the runoff that is in contact with the waste to ensure that there is accurate site characterization. There is no specific criteria for concluding a location is a stormwater hotspot, although concentrations in runoff may be compared to water quality criteria to make this determination. See [https://www.revisor.mn.gov/rules/?id=7050 surface water quality standards] or [http://www.health.state.mn.us/divs/eh/water/factsheet/com/ioc.html drinking water standards].  Recommendations for design adjustments are included in the following section.
  
===Physical plant practices===
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The U.S. EPA developed a [https://www3.epa.gov/npdes/pubs/sw_idde_hotspot.pdf hotspot inspection checklist] that can be used to score a site to determine the likelihood that it is a stormwater hotspot.
The fourth hotspot operation relates to practices used to clean, maintain or repair the physical plant, which includes the building, outdoor work areas and parking lots. Routine cleaning and maintenance practices can cause runoff of sediment, nutrients, paints, and solvents from the site. Sanding, painting, power-washing, resealing or resurfacing roofs or parking lots always deserves particular scrutiny, especially when performed near storm drains.
 
  
===Turf and landscaping===
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==General guidelines for managing stormwater at a PSH==
The fifth common hotspot operation involves practices used to maintain turf or landscaping at the site. Many commercial, institutional and municipal sites hire contractors to maintain turf and landscaping, apply fertilizers or pesticides, and provide irrigation. Current landscaping practices should be thoroughly evaluated at each site to determine whether they are generating runoff of nutrients, pesticides, organic carbon, or are producing non-target irrigation flows.
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{{Alert|This discussion focuses on activities that may generate pollutants and areas associated with those activities. If a site is known or suspected to be contaminated, see the section on [http://stormwater.pca.state.mn.us/index.php/Stormwater_infiltration_and_contaminated_soils_and_groundwater Stormwater infiltration and contaminated soils and groundwater].|alert-warning}}
  
===Unique hotspot operations===
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{{alert| The [[MN CSW Permit Section 16 Infiltration Systems|Construction Stormwater General permit]] prohibits the use of infiltration BMPs in areas where the infiltrating stormwater will mobilize contaminants.|alert-danger}}
Some operations simply resist neat classification, and this last category includes unique sites known to generate specific pollutants. Examples include swimming pools, construction operations, golf courses, fairgrounds/racetracks, marinas, hobby farms, and restaurants.
 
<p>A particular PSH of concern is associated with salt storage and the environmental threats that result from our need as a state for safe winter roads. Water quality problems from very soluble Na, Cl and cyanide have been documented as resulting from stored salt piles. MPCA does not regulate the storage of salt unless the storage becomes a documented contamination problem. Instead, the state encourages all public and private entities storing salt to follow the [http://www.saltinstitute.org Salt institute's] recommended BMPs, which include such things as covering, impervious pads and drainage routing. MS4 communities are asked by MPCA to include a salt management component in their municipal pollution prevention programs.</p>
 
  
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[[File:examples of common pollution prevention practices.png|thumb|500px|alt=example of pollution prevention practices|<font size=3>Examples of three common pollution prevention practices include wash water containment, secondary containment of outdoor storage and covered loading areas.</font size>]]
  
==Stormwater management design at PSHs==
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Even if a PSH is determined to not be a hotspot, some additional considerations are needed for stormwater management. Runoff management at PSHs and hotspots should be linked to the pollutant(s) of greatest concern. Understanding the pollutants potentially generated by a site operation provides designers with important information on proper selection, siting, design, and maintenance of nonstructural (e.g., source control or pollution prevention) and structural practices that will be most effective at the site. Active inspection and monitoring of the site activities is required to ensure that a PSH does not become a hotspot. The table below provides a general summary of pollutants of concern from different operations. For a more detailed list of operations and associated pollutants, see Table 7 on page 18 of the CWP report ''Pollution Source Control Practices, Version 2.0''. To access the CWP information go to [https://owl.cwp.org/mdocs-posts/urban-subwatershed-restoration-manual-series-manual-8/ this link] and find ''Urban Subwatershed Restoration Manual Series Manual 8: Pollution Source Control Practices'' to open the document as a pdf.
Understanding the types of future operations expected to occur on a site helps designers develop a more thoughtful stormwater management and pollution prevention plan for a given site. This approach provides more flexibility in terms of what stormwater treatment approaches are appropriate for different portions of a site. Runoff management at PSHs should also be linked to the pollutant(s) of greatest concern in the subwatershed. Similarly, understanding the pollutants potentially generated by a site operation provides designers with important information on proper selection, siting, design, and maintenance of the nonstructural (e.g., source control or pollution prevention) and structural practices that will be most effective at the PSH site.
 
  
[[File:examples of common pollution prevention practices.png|thumb|500px|alt=example of pollution prevention practices|Figure 6:<p><font size=2>Examples of three common pollution prevention practices include wash water containment, secondary containment of outdoor storage and covered loading areas.</font size></p>]]
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{{:Pollutants of concern from operations}}
  
<p>The most cost effective approach to managing stormwater at potential hotspot sites is to employ a variety of non-structural pollution prevention, and source control measures. To do this effectively, it is necessary to have a thorough understanding of a site and the respective areas of the site where specific operations will occur. Hogland, et al. (2003) suggest most of the following principles for design:
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Non-structural approaches such as sweeping, indoor storage, employee training, and frequent trash collection should be employed as much as possible. Not only will they prevent stormwater generation, they are also the most cost effective approach. To implement these effectively, it is necessary to have a thorough understanding of a site and the respective areas of the site where specific operations will occur. Hogland, et al. (2003) suggest the following principles for design at PSHs and hotspots.
*Develop detailed mapping of the different areas of the site along with associated planned activities and the preliminary drainage design.
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*Develop detailed mapping of the different areas of the site along with associated planned activities and the preliminary drainage design. Identify PSHs on the site (i.e. areas where pollutants may potentially be released) and attempt to eliminate or minimize the likelihood there will be a release. Within PSHs,
*Separate hotspot activity areas from non-hotspot activity areas, if possible.
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**prevent or confine drips and spills, and
*Prevent or confine drips and spills.
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**enclose or cover pollutant generating activity areas and regularly provide cleanup of these areas.
*Enclose or cover pollutant generating activity areas and regularly provide cleanup of these areas.
 
 
*Provide spill prevention and clean-up equipment at strategic locations on site.
 
*Provide spill prevention and clean-up equipment at strategic locations on site.
 
*Provide pre-treatment and spill containment measures such as catch basins and inserts, oil-water separators, etc.
 
*Provide pre-treatment and spill containment measures such as catch basins and inserts, oil-water separators, etc.
*Strategically locate slopes and separation berms to prevent co-mingling of dirty and clean runoff.
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*Strategically locate slopes and separation berms to prevent co-mingling of the runoff that does and does not come in contact with the pollutant of concern.
 
*Retain and reuse stormwater for irrigation, wash down water, or other onsite uses.
 
*Retain and reuse stormwater for irrigation, wash down water, or other onsite uses.
 
*Maintain equipment to minimize leaks.
 
*Maintain equipment to minimize leaks.
*Train and educate employees, management and customers.</p>
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*Train and educate employees, management and customers.
<p>Meeting the design intent of the non-structural practices above typically involves simple and low-cost measures to address routine operations at a site. For example, the non-structural design components for a vehicle maintenance operation might involve the use of drip pans under vehicles, tarps covering disabled vehicles, dry cleanup methods for spills, proper disposal of used fluids, and covering and secondary containment for any outdoor storage areas.</p>
 
<p>Each of these practices also requires employee training and strong management commitment. In most cases, these practices save time and money, reduce liability and do not greatly interfere with normal operations.  A more complete summary of 15 basic pollution prevention practices applied at PSH operations is provided in Table 1 (Schueler et al., 2004).</p>
 
  
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Meeting the design intent of the non-structural practices above typically involves simple and low-cost measures to address routine operations at a site. For example, the non-structural design components for a vehicle maintenance operation might involve the use of drip pans under vehicles, tarps covering disabled vehicles, dry cleanup methods for spills, proper disposal of used fluids, and covering and secondary containment for any outdoor storage areas.
  
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Each of these practices also requires employee training and strong management commitment. In most cases, these practices save time and money, reduce liability and do not greatly interfere with normal operations. A more complete summary of 15 basic pollution prevention practices applied at PSH operations is provided in the table below.
  
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{{:Pollution prevention practices for PSH operations}}
  
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After considering the non-structural elements to incorporate into a site, designers need to assess what structural practices will provide the greatest pollutant loading reductions for targeted pollutants, if the pollutant is present in the runoff, given site constraints. Details on [http://stormwater.pca.state.mn.us/index.php/Category:Design_criteria BMP design] and performance can be found within web pages for individual BMPs. 
  
Table 1
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Caution, the literature contains a large amount of information concerning BMP removal capability for a range of common pollutants. When using this information, be aware of the assumptions and limitations of the data. Some of this data has been [http://stormwater.pca.state.mn.us/index.php/Stormwater_pollutant_removal,_stormwater_credits compiled for this Manual]. Targeted pollutants are phosphorus, total suspended solids, total nitrogen, hydrocarbons, bacteria, and metals.
<p><font size=2>Pollution prevention practices for PSH operations (Source: Scheuler et a., 2004).</font size></p>
 
<table border="1" cellpadding=10 align='left' frame="void" rules="all">
 
<tr>
 
<td width="20%">'''PSH operation'''</td>
 
<td width="5%">'''Profile sheet*'''</td>
 
<td width="75%">'''Pollution prevention practices'''</td>
 
</tr>
 
<tr>
 
  <td>Vehicle maintenance and repair</td>
 
  <td>H-1</td>
 
  <th rowspan="4">Drip pans, tarps, dry clean-up methods for spills, cover outdoor storage areas, secondary containment, discharge washwater to sanitary system,proper disposal of used fluids, disconnect storm drains, automatic shutoff nozzles, signs, employee training, spill response plans</th>
 
</tr>
 
<tr>
 
  <td>Vehicle fueling</td>
 
  <td>H-2</td>
 
</tr>
 
<tr>
 
  <td>Vehicle washing</td>
 
  <td>H-3</td>
 
<tr>
 
  <td>Vehicle storage</td>
 
  <td>H-4</td>
 
<tr>
 
  <td>Loading and unloading</td>
 
  <td>H-5</td>
 
  <th rowspan="2">Cover loading areas, secondary containment, storm drain disconnection or treatment, inventory control, dry cleaning methods, employee training</th>
 
</tr>
 
<tr>
 
  <td>Outdoor storage</td>
 
  <td>H-6</td>
 
</tr>
 
<tr>
 
  <td>Spill prevention and response</td>
 
  <td>H-7</td>
 
  <th rowspan="2">Inventory materials, employee training, spill planning, spill clean up materials, dumpster management, disconnect from storm drain or treat. Liquid separation/containment</th>
 
</tr>
 
<tr>
 
  <td>Dumpster management</td>
 
  <td>H-8</td>
 
</tr>
 
<tr>
 
  <td>Building repair and remodeling</td>
 
  <td>H-9</td>
 
  <th rowspan="3">Temporary covers/tarps, contractor training, proper cleanup and disposal procedures, keep wash and rinse-water from storm drain, dry cleaning methods</th>
 
</tr>
 
<tr>
 
  <td>Building maintenance</td>
 
  <td>H-10</td>
 
</tr>
 
<tr>
 
  <td>parking lot maintenance</td>
 
  <td>H-11</td>
 
</tr>
 
<tr>
 
  <td>Turf management</td>
 
  <td>H-12</td>
 
  <th rowspan="2">Integrated pest management, reduce non-target irrigation, careful applications, proper disposal of landscaping waste, avoid leaf blowing and hosing to storm drain</th>
 
</tr>
 
<tr>
 
  <td>Landscaping/grounds care</td>
 
  <td>H-13</td>
 
</tr>
 
<tr>
 
  <td>Swimming pool discharges</td>
 
  <td>H-14</td>
 
  <th rowspan="2">Varies, depending on the unique hotspot operation</th>
 
</tr>
 
<tr>
 
  <td>Other unique hotspots</td>
 
  <td>H-15</td>
 
</tr></table>
 
<font size = 0.7>* Due to the volume of material, the reader is referred to Scheuler ''et al.'' (2004) to see the profile sheets. Each profile sheet explains how the practice influences water quality and lists the type of PSH operation where it is normally applied.  The sheets also identify the primary people at the hotspot operation that need to be trained in pollution prevention.  Next, each sheet reviews important feasibility and implementation considerations and summarizes available cost data. Each profile sheet concludes with a directory of the best available internet resources and training materials for the pollution prevention practice.
 
<p>It should be noted that the profile sheets developed by Scheuler ''et al.'' (2004) are written primarily from the perspective that the site(s) in question is an existing site and pollution prevention measures are recommended as a retrofit approach. Designers of new sites, however, can still use the guidance effectively.</p>
 
<p>Wright ''et al.'' (2004) provide a detailed description of the rapid field assessment protocol for identifying PSHs and the appropriate pollution prevention practices for the activities causing pollution. The protocol is known as the Unified Subwatershed and Site reconnaissance (USSR) and the PSH assessment is called a Hotspot Site Investigation.  These methods are not directly applicable to greenfield development or redevelopment situations; however, they have significant application for NPDES Phase II communities that are working towards compliance with Minimum Control Measures 1, 2, 3, and 6 (public education and outreach, public participation/involvement, illicit discharge detection and elimination, and pollution prevention/good housekeeping, respectively),</p></font size>
 
  
<br>
+
The receiving water designation or watershed classification often drives the criteria and associated practices that are acceptable for use. However, at PSHs there is a set of general guidelines to consider when designing structural stormwater management systems. The following should be carefully considered by designers when specifying and siting practices at PSHs, specifically when it is determined that the site is an actual hotspot.
  
<p>After considering the non-structural elements to incorporate into a site based on its layout and proposed operations, designers need to assess what structural practices will be most appropriate given site constraints while providing the greatest pollutant loading reductions for targeted pollutants. Table 2 presents representative pollutant removal data for common PSH pollutants of concern as a function of practice group. Details on BMP design and performance occur in design and fact sheets in Chapter 12.</p>
+
*[[Pre-treatment|Pretreatment]]. This includes properly sizing sediment trapping features such as forebays and sedimentation chambers; incorporating appropriate proprietary and nonproprietary practices for spill control purposes and treatment redundancy; oversizing pretreatment features for infiltration facilities such as [https://stormwater.pca.state.mn.us/index.php?title=Dry_swale_(Grass_swale) swales], filter strips, and level spreaders; and ensuring full site stabilization before bringing practices online. If [[Stormwater infiltration|infiltration]] is to be utilized, appropriate site and conveyance designs are needed and the pretreatment BMP size should be increased or design redundancies included.
<p>It is often receiving water designation or watershed classification that will drive the criteria and associated practices that are acceptable for use. However, by virtue of being a PSH there are a set of general guidelines to always consider when designing structural stormwater management systems. The following should be carefully considered by designers when specifying and siting practices at PSHs.
+
*If pollutant generating activities exist on a site, runoff from these areas should be treated separately from other runoff at the site. BMPs such as [[Bioretention|bioretention]], [[Stormwater ponds|constructed ponds]], and [[Stormwater wetlands|constructed wetlands]] that receive runoff from pollutant generating activities should be designed with the necessary features to minimize the chance of groundwater contamination. This includes using impermeable liners. The use of ponds and wetlands without liners should also be avoided where water tables are shallow and the practice would likely intercept the water table. Bioretention BMPs can be designed and constructed with adjusted media content and media depth according to the [http://stormwater.pca.state.mn.us/index.php/Design_criteria_for_bioretention Bioretention Design Guidelines] to accommodate the pollutants of concern. 
*Convey and treat the mostly clean runoff separately from the dirty runoff.
+
*Consider use of liners, [[Glossary#U|underdrains]], or comparable safeguards against infiltration when runoff exceeds target concentrations.
*Infiltrate only the mostly clean water.
 
*Pre-treatment, pre-treatment, pre-treatment. This includes oversizing sediment trapping features such as forebays and sedimentation chambers; incorporating appropriate proprietary and nonproprietary practices for spill control purposes and treatment redundancy; oversizing pre-treatment features for infiltration facilities such as swales, filter strips, and level spreaders; and ensuring full site stabilization before bringing practices online.
 
*Consider closed systems with liners, under-drains, or comparable safeguards against infiltration for practices that manage dirty waters.
 
 
*Locate practices offline and minimize offsite run-on with appropriate diversions.
 
*Locate practices offline and minimize offsite run-on with appropriate diversions.
*Establish rigorous maintenance and inspection schedules for practices receiving the dirty waters.
+
*Establish rigorous maintenance and inspection schedules for practices receiving the runoff from the hotspot areas of concern.
*For ponds and wetlands, over-design by between 10-25% the allowable storage volume for sediment accumulation over time if sediment is a problem.</p>
 
 
 
<br>
 
 
 
Table 2
 
<p><font size=2>Percent removal of key pollutants by practice group.</font size></p>
 
<table border="1" cellpadding=10 align='left' frame="void" rules="all">
 
<tr>
 
<td width="40%">'''Practice'''</td>
 
<td width="15%">'''Total nitrogen''' (%)</td>
 
<td width="15%">'''Metals (%)<sup>1</sup>'''</td>
 
<td width="15%">'''Bacteria (%)'''</td>
 
<td width="15%">'''Hydrocarbons (%)'''</td>
 
</tr>
 
<tr>
 
<td>Detention ponds</td>
 
<td>25</td>
 
<td>60</td>
 
<td>70<sup>2</sup></td>
 
<td>80<sup>2</sup></td>
 
</tr>
 
<tr>
 
<td>Wet ponds</td>
 
<td>30</td>
 
<td>60</td>
 
<td>70</td>
 
<td>80<sup>2</sup></td>
 
</tr>
 
<tr>
 
<td>Stormwater wetlands</td>
 
<td>30</td>
 
<td>40</td>
 
<td>75<sup>2</sup></td>
 
<td>85<sup>2</sup></td>
 
</tr>
 
<tr>
 
<td>Filtering practices and bioretention</td>
 
<td>35</td>
 
<td>65</td>
 
<td>45<sup>2</sup></td>
 
<td>80<sup>2</sup></td>
 
</tr>
 
<tr>
 
<td>Infiltration practices<sup>3</sup></td>
 
<td>50</td>
 
<td>80<sup>2</sup></td>
 
<td>NA</td>
 
<td>NA</td>
 
</tr>
 
<tr>
 
<td>Vegetated swales and grass channels<sup>4</sup></td>
 
<td>80<sup>2</sup></td>
 
<td>60</td>
 
<td>NA</td>
 
<td>NA</td>
 
</tr></table>
 
<sup>1</sup> Average of zinc and copper.  Only zinc for infiltration.
 
<sup>2</sup> Based on fewer than five data points (e.g. independent monitoring studies)
 
<sup>3</sup> Includes porous pavement as primarily a volume reduction BMP
 
<sup>4</sup> Higher removal rates for dry swales
 
NA: data not available
 
Removals represent median values from Winer (2000)
 
 
 
<br>
 
  
<p>Infiltration practices are the practice group that requires the most scrutiny prior to implementation at a PSH. A conservative approach would avoid the use of infiltration practices at a PSH; however, with appropriate site and conveyance design it is possible for the designer to incorporate infiltration into many sites to treat areas sufficiently separated from pollutant generating activities. Most other practice groups should be acceptable for use in treating PSH runoff, so long as appropriate design modifications are incorporated. Most design modifications are simple and in the form of enhanced pre-treatment, over-design, or design redundancies. Others are added features that limit the likelihood of ground water recharge. For example, practice groups such as bioretention, ponds and wetlands that receive runoff from pollutant generating activities should be designed with the necessary features to minimize the chance of ground water contamination. This includes using impermeable liners. The use of ponds and wetlands without liners should also be avoided where water tables are shallow and the practice would likely intercept the water table.</p>
+
==Infiltration guidance==
 +
{{Alert|This discussion focuses on activities that may generate pollutants and areas associated with those activities. If a site is known or suspected to be contaminated, see the section on [http://stormwater.pca.state.mn.us/index.php/Stormwater_infiltration_and_contaminated_soils_and_groundwater Stormwater infiltration and contaminated soils and groundwater].|alert-warning}}
  
==Importance of plan review at proposed PSHs==
+
{{alert| The [[MN CSW Permit Section 16 Infiltration Systems|Construction Stormwater General permit]] prohibits the use of infiltration BMPs in areas where the infiltrating stormwater will mobilize contaminants.|alert-danger}}
Ultimately, the level of safeguards that are in place when providing stormwater management at PSHs should be related to the expected review process. Communities that can allocate adequate and qualified staff to effectively review all stormwater management plans for proposed PSHs can arguably provide designers with great flexibility as to how to meet the management criteria required at a site. In these cases, designers should have most of the accepted stormwater treatment practices at their disposal for implementation. However, for communities that don’t have the resources to provide the necessary level of site and stormwater management plan review, a more conservative approach to allowable treatment practices should be taken.
 
<p>In many cases, industrial PSHs will be covered by the NPDES industrial stormwater permit or by some other federal/state permitting program related to the materials they store or handle on site. Communities are encouraged to focus their attention on the unregulated PSH sites.</p>
 
  
==NPDES industrial stormwater requirements ==
+
Infiltration practices require scrutiny prior to implementation at a PSH. Preventing the introduction of contaminated runoff to groundwater is an essential consideration in developing effective stormwater management plans at PSHs. This is because
Industrial PSHs that are regulated under NPDES stormwater permits must prepare stormwater pollution prevention plans or SWPPPs, and implement source control practices at the facility. These plans must include spill response and prevention, employee training, and implementation of pollution prevention practices to reduce exposure of products to rainfall or runoff. In some cases, stormwater treatment practices may need to be installed at the site to remove pollutants from runoff. Permitted industrial PSHs should be regularly inspected to determine if they are complying with the SWPPP, or even possess a permit. However, the MPCA does not inspect any facilities because of the staffing cut-backs it has experienced. In lieu of this, communities could conduct their own site visits as part of its local stormwater program. The storm drain system should also be investigated to determine if an industrial PSH is generating illicit discharges of sewage or other pollutants. Methods to detect and correct illicit discharges are described in Brown et al. (2004).
+
*ground water contamination is hard to detect immediately and therefore can persist over long periods of time prior to any mitigation;
<p>Industrial NPDES stormwater permits are an important regulatory tool at many PSH operations. Significant penalties can be imposed for non-compliance. State and federal regulators are still grappling with the administration of industrial stormwater permits, and they remain an imperfect tool for several reasons. First, the permit system allows potential hotspot operators to prepare and implement their own pollution prevention plans and to keep them on site rather than sending them to MPCA. If a particular plan is weak or is only a paper exercise, the Agency might never know until it is too late. Second, very few trained state or federal-level inspectors are available to inspect and enforce the thousands of industrial sites covered by the permit program. Third, although communities usually have the best understanding of how the local stormwater network works, they lack direct authority to inspect or enforce regulated PSHs, although they can refer them to state agencies for enforcement. Communities can also address these sites through other programs, such as zoning, stormwater utility or conditional use permits, and can address potential problems whenever new construction at the facility occurs. All three problems can be overcome if the locality works with industry and state regulatory agencies to share hotspot inspection and enforcement responsibilities as part of industrial permitting or MS4 programs. Portland (OR) recently negotiated such an agreement to expand the reach of its hotspot inspection program (Pronold, 2000).</p>
+
*there is an immediate public health threat associated with ground water contamination in areas where ground water is the primary drinking water source, and
<p>From the regulated community standpoint, the lack of a viable, well funded state industrial stormwater permit program has resulted in uncertainty over regulatory status and frustration over paying an annual fee with no return. An industrial stormwater permit holder could conceivably have several different programs that address stormwater management, including local MS4 authority with its set of stormwater controls. Also, most industry handling polluting materials likely comes under the authority of related regulations, such as hazardous waste spill prevention or chemical storage laws, each of which could have a stormwater component.</p>
+
*mitigation, when needed, is often difficult and is usually very expensive.
<p>Most industrial stormwater permit issues will not be solved until a viable state and federal regulatory program exists. Until this happens, communities and industrial permit holders are urged to work together to define problems and solutions within the SWPPP framework.</p>
+
With appropriate site and conveyance design it is possible to incorporate infiltration into many sites to treat areas sufficiently separated from pollutant generating activities. Most design modifications are simple and in the form of enhanced pretreatment, over-design, or design redundancies. Others are added features that limit the likelihood of groundwater recharge. For example, practice groups such as bioretention, ponds and wetlands that receive runoff from pollutant generating activities should be designed with the necessary features to minimize the chance of groundwater contamination. This includes using impermeable liners. The use of ponds and wetlands without liners should also be avoided where water tables are shallow and the practice would likely intercept the water table. Where uncertainty is present, designers should avoid infiltration practices.
  
==Guidance on infiltration of runoff from PSHs==
+
The table below provides general infiltration guidelines associated with operational areas of concern.
Preventing or minimizing the likelihood of contaminated runoff from leaving a PSH site is the core objective of stormwater management at these sites. Introduction of contaminated runoff to the ground water is probably the greatest concern in developing effective stormwater management plans at PSHs. This is for three primary reasons:
 
*Ground water contamination is hard to detect immediately and therefore can persist over long periods of time prior to any mitigation;
 
*There is an immediate public health threat associated with ground water contamination in areas where ground water is the primary drinking water source, which is most of Minnesota; and
 
*Mitigation, when needed, is often difficult and is usually very expensive.
 
<p>This section focuses on these issues and presents a potential approach for establishing design guidelines for infiltration based on the six common operational areas presented in Table 13.6 plus a seventh area that addresses major transportation routes (e.g., highways). Figure 13.12 serves as a frame of reference for revisiting these areas.</p>
 
  
===Potential for PSH impact on ground water===
+
{{:Infiltration guidelines for potential stormwater hotspots}}
[[File:source water protection areas.jpg|thumb|500px|alt=source water protection areas|Figure 7:<p><font size=2>January 2004 location of Source Water Protection Areas in Minnesota.  The map includes vulnerability designations for Drinking Water Source Management Areas, ranging from very low to very high vulnerability, and designation of Source Water Assessment areas as vulnerable or not vulnerable.</font size></p>]]
 
  
Caution should be exercised when dealing with the introduction of stormwater runoff into the ground via infiltration systems or even low impact development-type techniques that encourage infiltration naturally. This issue gets particularly important when the infiltration occurs within a defined [[Wellhead protection areas|drinking water source area]][https://http://www.health.state.mn.us/divs/eh/water/swp/whp/index.htm]. It is important to note that the map illustrating Source Water Protection areas shows only the public systems covered under the Minnesota Department of Health program. There are thousands of additional private and domestic wells that could be impacted by PSHs and not subject to any special protections against stormwater runoff.
+
==Links==
 +
*[https://mde.maryland.gov/programs/Permits/WaterManagementPermits/Documents/GDP%20Stormwater/MD%20Stormwater%20Hotspots.pdf Stormwater Pollution Prevention Guidance - Vehicle Maintenance and Repair, Fueling, Washing or Storage Loading and Unloading, Outdoor Storage]. Maryland Department of the Environment Stormwater Pollution Prevention Guidance. 2013.
 +
*Hotspot inspection form. [https://www3.epa.gov/npdes/pubs/sw_idde_hotspot.pdf U.S. EPA]
  
===Infiltration guidance at PSHs===
+
==Related pages==
Table 13.10 provides potential infiltration guidelines associated with each of the seven operational areas. Infiltration at PSHs relies on overall site design and facility operations management. Good design and committed, well-trained facility staff should make infiltration possible for certain areas of the site. Where uncertainty is present, designers should avoid infiltration practices. The Minnesota Department of Health recommends that infiltration should not be used within the one-year wellhead protection area and limited in vulnerable wells for the 10-year wellhead protection area.
+
*[[Overview of stormwater infiltration]]
 +
*[[Pre-treatment considerations for stormwater infiltration]]
 +
*[[BMPs for stormwater infiltration]]
 +
*[[Pollutant fate and transport in stormwater infiltration systems]]
 +
*[[Surface water and groundwater quality impacts from stormwater infiltration]]
 +
*[[Stormwater infiltration and groundwater mounding]]
 +
*[[Stormwater infiltration and setback (separation) distances]]
 +
*[[Karst]]
 +
*[[Shallow soils and shallow depth to bedrock]]
 +
*[[Shallow groundwater]]
 +
*[[Soils with low infiltration capacity]]
 +
*[[Potential stormwater hotspots]]
 +
*[[Stormwater and wellhead protection]]
 +
*[[Stormwater infiltrations and contaminated soils and groundwater]]
 +
*[[Decision tools for stormwater infiltration]]
 +
*[[Stormwater infiltration research needs]]
 +
*[[References for stormwater infiltration]]
  
[[category:Stormwater articles 2]]
+
<noinclude>
 +
[[Category:Infiltration]]
 +
</noinclude>

Latest revision as of 21:47, 23 June 2021

image

Potential Stormwater Hotspots (PSHs) are activities or practices that have the potential to produce relatively high levels of stormwater pollutants. Designation as a PSH does not imply that a site is a hotspot, but rather that the potential to generate high pollutant runoff loads or concentrations exists. PSHs include locations where there is a potential risk for spills, leaks, or illicit discharges. Stormwater hotspots may also be areas which produce higher concentrations of pollutants than normally found in urban runoff. Because stormwater hotspots are found in a variety of land uses, there is no common pollutant for any type of hotspot. Instead the pollutants tend to be a unique mixture of pollutants (CWP, 2005). Hotspots can be classified as Regulated, subject to state or federal permits, or Unregulated. In Minnesota Regulated hotspots are subject to the NPDES Multi-Sector General Permit for Industrial Activity, and/or local ordinances.

Pollutant generating operations and activities

common operations to assess pshs
Common operations and areas for assessing PSHs include management of turf, waste, loading docks, downspouts, vehicle fueling, and parking lots.

The potential for hotspots is related to the activities on the site more than the land use or category of operation. The table below summarizes the most common pollutants generated at stormwater hotspots based on common operations at a site. These operations are discussed in greater detail below.

Pollutants of Concern from Operations (adapted from CWP, 2005).
Link to this table.

Pollutant of concern Vehicle operations Waste management Site maintenance practices Outdoor materials Landscaping
Nutrients X X X
Pesticides X X
Solvents X X
Fuels X
Oil and grease X X
Toxic chemicals X X
Sediment X X X X
Road salt X X
Bacteria X X
Trace metals X X
Hydrocarbons X X


Vehicle operations

Vehicle operations include maintenance, repair, recycling, fueling, washing, and long-term parking. Vehicle operations can be a significant source of trace metals, oil, grease, and hydrocarbons, and are the first operations inspected during a hotspot source investigation. Vehicle maintenance and repair operations often produce waste oil, fluids and other hazardous products, particularly if work areas are connected to the storm drain system. Routing protective rooftop runoff through a fueling area has become a common practice in Minnesota; simple re-routing of runoff away from a potential fuel wash-off location could eliminate this from the hotspot list. Examples of pollutant-generating activities associated with vehicle operations include the following.

  • Improper disposal of fluids down shop and storm drains
  • Spilled fuel, leaks and drips from wrecked vehicles
  • Hosing of outdoor work areas
  • Wash water from cleaning
  • Uncovered outdoor storage of liquids/oils/batteries/spills
  • Pollutant wash-off from parking lots

Outdoor materials

Improper handling or storage of materials outdoors can create stormwater problems. Techniques for properly handling materials outdoors include inventorying the type and hazard level of materials at the site, examining loading and unloading areas to see if materials are exposed to rainfall and/or are connected to the storm drain system, and investigating any materials stored outdoors that could potentially be exposed to rainfall or runoff. Public and private road salt and sand storage areas are of particular concern. Examples of pollutant-generating activities associated with outdoor materials include the following.

  • Spills at loading areas
  • Hosing/washing of loading areas into shop or storm drains
  • Wash-off of uncovered bulk materials and liquids stored outside, of particular concern in MN are road salt storage areas
  • Leaks and spills

Waste management

dumpster management at psh
Dumpster leaking directly into a storm sewer.

Every business generates waste as part of its daily operations, most of which is temporarily stored at the site pending disposal. The manner in which waste products are stored and disposed of at a site, particularly in relation to the storm drain system, determine the likelihood of becoming a hotspot. In some sites, simple practices such as dumpster management can reduce pollutants, whereas other sites may require more sophisticated spill prevention and response plans. Examples of pollutant-generating activities associated with waste management include the following.

  • Spills and leaks of fluids
  • Dumping into storm drains
  • Leaking dumpsters
  • Wash-off of dumpster spillage
  • Accumulation of particulate deposits

Physical plant maintenance

Plant maintenance relates to practices used to clean, maintain or repair the physical plant, which includes the building, outdoor work areas and parking lots. Routine cleaning and maintenance practices can cause runoff of sediment, nutrients, paints, and solvents from the site. Sanding, painting, power-washing, and resealing or resurfacing roofs or parking lots are activities that can result in increased pollutant loading or concentrations, especially when performed near storm drains. Examples of pollutant-generating activities associated with plant maintenance include the following.

  • Discharges from power washing and steam cleaning
  • Wash-off of fine particles from painting/sandblasting operations
  • Rinse water and wash water discharges during cleanup
  • Temporary outdoor storage
  • Runoff from degreasing and re-surfacing

Turf and landscaping

Many commercial, institutional and municipal sites hire contractors to maintain turf and landscaping, apply fertilizers or pesticides, and provide irrigation. Current landscaping practices should be thoroughly evaluated at each site to determine whether they are generating runoff of nutrients, pesticides, organic carbon, or are producing non-target irrigation flows. Examples of pollutant-generating activities associated with turf and landscaping include the following.

  • Non-target irrigation
  • Runoff of nutrients and pesticides
  • Deposition and subsequent washoff of soil and organic matter on impervious surfaces

Determining if a PSH is a hotspot

As stated previously, the designation of PSH does not mean a site is a hotspot, only that activities have the potential to generate higher pollution runoff loads or concentrations compared to the land uses in which they occur. When designing a stormwater management system at these sites, it is important to determine if the PSH is an actual hotspot. If it is a hotspot, additional stormwater management controls may be needed. A recommended process for determining whether a PSH is a hotspot is as follows.

Step 1: Consider where the activities take place. If all activities using hazardous materials occur inside a building and no materials can be tracked outside, then the site is not a hotspot. The various activities involving hazardous materials should be monitored at regularly scheduled intervals to ensure that nothing changes that would cause the hazardous materials to come in contact with stormwater runoff.
Step 2: Review the Stormwater Pollution Prevention Plan/Program (SWPPP), if present. Sites subject to NPDES requirements through the Industrial Multi-Sector Permit or the MS4 Municipal General Permit may have created SWPPPs that guide the operations and housekeeping at sites where the potential exists for increased concentrations of certain pollutants in the runoff.
Step 3: Conduct a site inspection. The Center for Watershed Protection (CWP) has developed inspection forms that can be used to record physical operations and observations at a site to assess whether the site should be designated as a hotspot. For sites with a SWPPP, the inspection should include whether the site is operated in compliance with the requirements in the SWPPP. The CWP form includes an overall assessment of whether to designate the site as a hotspot. To access the CWP information go to this link and find Urban Subwatershed Restoration Manual Series Manual 8: Pollution Source Control Practices to open the document as a pdf. Hotspot prevention profile sheets are found on pages 109-158. A discussion of stormwater hotspots is found on pages 13-24.
Step 4: Sample collection and analysis. Further analysis may be required to determine if the PSH is a hotspot. Samples of the stormwater runoff at the site should be collected and analyzed for the pollutants of concern. Samples need to be collected from the runoff that is in contact with the waste to ensure that there is accurate site characterization. There is no specific criteria for concluding a location is a stormwater hotspot, although concentrations in runoff may be compared to water quality criteria to make this determination. See surface water quality standards or drinking water standards. Recommendations for design adjustments are included in the following section.

The U.S. EPA developed a hotspot inspection checklist that can be used to score a site to determine the likelihood that it is a stormwater hotspot.

General guidelines for managing stormwater at a PSH

Caution: This discussion focuses on activities that may generate pollutants and areas associated with those activities. If a site is known or suspected to be contaminated, see the section on Stormwater infiltration and contaminated soils and groundwater.
Warning: The Construction Stormwater General permit prohibits the use of infiltration BMPs in areas where the infiltrating stormwater will mobilize contaminants.
example of pollution prevention practices
Examples of three common pollution prevention practices include wash water containment, secondary containment of outdoor storage and covered loading areas.

Even if a PSH is determined to not be a hotspot, some additional considerations are needed for stormwater management. Runoff management at PSHs and hotspots should be linked to the pollutant(s) of greatest concern. Understanding the pollutants potentially generated by a site operation provides designers with important information on proper selection, siting, design, and maintenance of nonstructural (e.g., source control or pollution prevention) and structural practices that will be most effective at the site. Active inspection and monitoring of the site activities is required to ensure that a PSH does not become a hotspot. The table below provides a general summary of pollutants of concern from different operations. For a more detailed list of operations and associated pollutants, see Table 7 on page 18 of the CWP report Pollution Source Control Practices, Version 2.0. To access the CWP information go to this link and find Urban Subwatershed Restoration Manual Series Manual 8: Pollution Source Control Practices to open the document as a pdf.

Pollutants of Concern from Operations (adapted from CWP, 2005).
Link to this table.

Pollutant of concern Vehicle operations Waste management Site maintenance practices Outdoor materials Landscaping
Nutrients X X X
Pesticides X X
Solvents X X
Fuels X
Oil and grease X X
Toxic chemicals X X
Sediment X X X X
Road salt X X
Bacteria X X
Trace metals X X
Hydrocarbons X X


Non-structural approaches such as sweeping, indoor storage, employee training, and frequent trash collection should be employed as much as possible. Not only will they prevent stormwater generation, they are also the most cost effective approach. To implement these effectively, it is necessary to have a thorough understanding of a site and the respective areas of the site where specific operations will occur. Hogland, et al. (2003) suggest the following principles for design at PSHs and hotspots.

  • Develop detailed mapping of the different areas of the site along with associated planned activities and the preliminary drainage design. Identify PSHs on the site (i.e. areas where pollutants may potentially be released) and attempt to eliminate or minimize the likelihood there will be a release. Within PSHs,
    • prevent or confine drips and spills, and
    • enclose or cover pollutant generating activity areas and regularly provide cleanup of these areas.
  • Provide spill prevention and clean-up equipment at strategic locations on site.
  • Provide pre-treatment and spill containment measures such as catch basins and inserts, oil-water separators, etc.
  • Strategically locate slopes and separation berms to prevent co-mingling of the runoff that does and does not come in contact with the pollutant of concern.
  • Retain and reuse stormwater for irrigation, wash down water, or other onsite uses.
  • Maintain equipment to minimize leaks.
  • Train and educate employees, management and customers.

Meeting the design intent of the non-structural practices above typically involves simple and low-cost measures to address routine operations at a site. For example, the non-structural design components for a vehicle maintenance operation might involve the use of drip pans under vehicles, tarps covering disabled vehicles, dry cleanup methods for spills, proper disposal of used fluids, and covering and secondary containment for any outdoor storage areas.

Each of these practices also requires employee training and strong management commitment. In most cases, these practices save time and money, reduce liability and do not greatly interfere with normal operations. A more complete summary of 15 basic pollution prevention practices applied at PSH operations is provided in the table below.

Summary of common pollution prevention practices for PSH operations (Source: Scheuler et al., 2004).
Link to this table

PSH operation Profile sheeta Pollution prevention practices
Vehicle maintenance and repair H-1 Drip pans, tarps, dry clean-up methods for spills, cover outdoor storage areas, secondary containment, discharge washwater to sanitary system,proper disposal of used fluids, disconnect storm drains, automatic shutoff nozzles, signs, employee training, spill response plans
Vehicle fueling H-2
Vehicle washing H-3
Vehicle storage H-4
Loading and unloading H-5 Cover loading areas, secondary containment, storm drain disconnection or treatment, inventory control, dry cleaning methods, employee training
Outdoor storage H-6
Spill prevention and response H-7 Inventory materials, employee training, spill planning, spill clean up materials, dumpster management, disconnect from storm drain or treat. Liquid separation/containment
Dumpster management H-8
Building repair and remodeling H-9 Temporary covers/tarps, contractor training, proper cleanup and disposal procedures, keep wash and rinse-water from storm drain, dry cleaning methods
Building maintenance H-10
parking lot maintenance H-11
Turf management H-12 Integrated pest management, reduce non-target irrigation, careful applications, proper disposal of landscaping waste, avoid leaf blowing and hosing to storm drain
Landscaping/grounds care H-13
Swimming pool discharges H-14 Varies, depending on the unique hotspot operation
Other unique hotspots H-15

aDue to the volume of material, the reader is referred to Scheuler et al. (2004) to see the profile sheets. Each profile sheet explains how the practice influences water quality and lists the type of PSH operation where it is normally applied. The sheets also identify the primary people at the hotspot operation that need to be trained in pollution prevention. Next, each sheet reviews important feasibility and implementation considerations and summarizes available cost data. Each profile sheet concludes with a directory of the best available internet resources and training materials for the pollution prevention practice. To access this information go to this link and find Urban Subwatershed Restoration Manual Series Manual 8: Pollution Source Control Practices to open the document as a pdf. Hotspot prevention profile sheets are found on pages 109-158. A discussion of stormwater hotspots is found on pages 13-24.

It should be noted that the profile sheets developed by Scheuler et al. (2004) are written primarily from the perspective that the site(s) in question is an existing site and pollution prevention measures are recommended as a retrofit approach. Designers of new sites, however, can still use the guidance effectively.

Wright et al. (2004) provide a detailed description of the rapid field assessment protocol for identifying PSHs and the appropriate pollution prevention practices for the activities causing pollution. The protocol is known as the Unified Subwatershed and Site reconnaissance (USSR) and the PSH assessment is called a Hotspot Site Investigation. These methods are not directly applicable to greenfield development or redevelopment situations; however, they have significant application for NPDES Phase II communities that are working towards compliance with Minimum Control Measures 1, 2, 3, and 6 (public education and outreach, public participation/involvement, illicit discharge detection and elimination, and pollution prevention/good housekeeping, respectively).


After considering the non-structural elements to incorporate into a site, designers need to assess what structural practices will provide the greatest pollutant loading reductions for targeted pollutants, if the pollutant is present in the runoff, given site constraints. Details on BMP design and performance can be found within web pages for individual BMPs.

Caution, the literature contains a large amount of information concerning BMP removal capability for a range of common pollutants. When using this information, be aware of the assumptions and limitations of the data. Some of this data has been compiled for this Manual. Targeted pollutants are phosphorus, total suspended solids, total nitrogen, hydrocarbons, bacteria, and metals.

The receiving water designation or watershed classification often drives the criteria and associated practices that are acceptable for use. However, at PSHs there is a set of general guidelines to consider when designing structural stormwater management systems. The following should be carefully considered by designers when specifying and siting practices at PSHs, specifically when it is determined that the site is an actual hotspot.

  • Pretreatment. This includes properly sizing sediment trapping features such as forebays and sedimentation chambers; incorporating appropriate proprietary and nonproprietary practices for spill control purposes and treatment redundancy; oversizing pretreatment features for infiltration facilities such as swales, filter strips, and level spreaders; and ensuring full site stabilization before bringing practices online. If infiltration is to be utilized, appropriate site and conveyance designs are needed and the pretreatment BMP size should be increased or design redundancies included.
  • If pollutant generating activities exist on a site, runoff from these areas should be treated separately from other runoff at the site. BMPs such as bioretention, constructed ponds, and constructed wetlands that receive runoff from pollutant generating activities should be designed with the necessary features to minimize the chance of groundwater contamination. This includes using impermeable liners. The use of ponds and wetlands without liners should also be avoided where water tables are shallow and the practice would likely intercept the water table. Bioretention BMPs can be designed and constructed with adjusted media content and media depth according to the Bioretention Design Guidelines to accommodate the pollutants of concern.
  • Consider use of liners, underdrains, or comparable safeguards against infiltration when runoff exceeds target concentrations.
  • Locate practices offline and minimize offsite run-on with appropriate diversions.
  • Establish rigorous maintenance and inspection schedules for practices receiving the runoff from the hotspot areas of concern.

Infiltration guidance

Caution: This discussion focuses on activities that may generate pollutants and areas associated with those activities. If a site is known or suspected to be contaminated, see the section on Stormwater infiltration and contaminated soils and groundwater.
Warning: The Construction Stormwater General permit prohibits the use of infiltration BMPs in areas where the infiltrating stormwater will mobilize contaminants.

Infiltration practices require scrutiny prior to implementation at a PSH. Preventing the introduction of contaminated runoff to groundwater is an essential consideration in developing effective stormwater management plans at PSHs. This is because

  • ground water contamination is hard to detect immediately and therefore can persist over long periods of time prior to any mitigation;
  • there is an immediate public health threat associated with ground water contamination in areas where ground water is the primary drinking water source, and
  • mitigation, when needed, is often difficult and is usually very expensive.

With appropriate site and conveyance design it is possible to incorporate infiltration into many sites to treat areas sufficiently separated from pollutant generating activities. Most design modifications are simple and in the form of enhanced pretreatment, over-design, or design redundancies. Others are added features that limit the likelihood of groundwater recharge. For example, practice groups such as bioretention, ponds and wetlands that receive runoff from pollutant generating activities should be designed with the necessary features to minimize the chance of groundwater contamination. This includes using impermeable liners. The use of ponds and wetlands without liners should also be avoided where water tables are shallow and the practice would likely intercept the water table. Where uncertainty is present, designers should avoid infiltration practices.

The table below provides general infiltration guidelines associated with operational areas of concern.

Infiltration guidelines for potential stormwater hotspots.
Link to this table.

Operational area Potential infiltration guidelines
Landscaping Infiltration is acceptable provided there is no run-on or co-mingling from higher pollutant loading areas and appropriate pretreatment is provided for the specified practice. Chemical management is needed to limit the amount of fertilizer and pesticides.
Downspouts Infiltration is acceptable provided there is no run-on or co-mingling from higher pollutant loading areas, there is no polluting exhaust from a vent or stack deposits on the rooftop, and there is appropriate pretreatment provided for the specific practice.
Vehicle operations Infiltration is acceptable with the following provisions:
  • No run-on from higher pollutant loading areas
  • Limited salt application or use of alternative deicers
  • Enhanced pretreatment requirements such as (suggested unless better local information is available) minimum vegetative filter lengths of 20 feet, maximum velocity in conveyance channels to infiltration practice of one foot per second, plunge pools and sediment basins/chambers with volumes of at least 25% of the water quality volume
  • Only daily “commuter” parking areas and no long-term car/truck storage sites.
Waste management and outdoor material storage1 Infiltration is typically not recommended but may be utilized if spill prevention and containment measures are in place, such as catch basin inserts and oil and grit separators; or if redundant treatment is provided, such as filtering prior to infiltration. Infiltration should be prohibited in areas of exposed salt and mixed sand/salt storage and processing.
Loading docks1 Infiltration is typically not recommended but may be utilized if spill prevention and containment measures are in place, such as catch basin inserts and oil and grit separators; or if redundant treatment is provided, such as filtering prior to infiltration.
Vehicle fueling1 Infiltration is not allowed under the CGP.
Highways1 Infiltration is possible where enhanced pretreatment is provided. Where highways are within source water protection areas and other sensitive watersheds, additional measures should be in place such as spill prevention and containment measures (e.g., non-clogging catch basin inserts and oil and grit separators.

1indicates operational area with likelihood of having higher pollutant loadings


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This page was last edited on 23 June 2021, at 21:47.