Difference between revisions of "Potential stormwater hotspots"
Potential stormwater hotspots

Latest revision as of 20:49, 2 February 2023

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 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 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.

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 sheet^a	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	Varies, depending on the unique hotspot operation

^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 Urban Subwatershed Restoration Manual Series Manual 8: Pollution Source Control Practices. 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

Links

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. U.S. EPA

Related pages

@@ Line 1: / Line 1: @@
-[[File:Types of stormwater hotspots.png|thumb|500px|alt=types of stormwater hotspots|<font size=3>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>]]
+[[File:Technical information page image.png|right|100px|alt=image]]
+[[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.
+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 NPDES Multi-Sector General Permit for Industrial Activity, and/or local ordinances.
-==Overview and designation of PSHs==
+==Pollutant generating operations and activities==
-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 operations. 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 [http://www.pca.state.mn.us/index.php/water/water-types-and-programs/stormwater/industrial-stormwater/index.html industrial stormwater permits].
+[[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>]]
-===Commercial PSHs===
+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.
-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
-*animal care services;
-*building material;
-*commercial car washes;
-*convenience stores;
-*laundries and dry cleaners;
-*lawn care companies;
-*gas stations;
-*nurseries and garden centers;
-*petroleum wholesalers;
-*fast food restaurants
-*shopping centers;
-*vehicle maintenance and repair; and
-*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===
+{{:Pollutants of concern from operations}}
-Industrial PSHs are a major focus for [[Pollution prevention|pollution prevention]] if they use, generate, handle or store pollutants that can potentially be washed away in stormwater [[Glossary#R|runoff]], spilled, or inadvertently discharged to the storm drain system. Examples of industrial land use activities include
-*auto recyclers;
-*boat building and repair facilities;
-*recycling centers and scrap yards; and
-*warehouses
-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 compared to other land uses. Many industrial operations are regulated under the NPDES [http://www.pca.state.mn.us/index.php/water/water-types-and-programs/stormwater/industrial-stormwater/index.html industrial stormwater permit program], although individual owners or operators may be unaware of their permit status.
-===Institutional PSHs===
+===Vehicle operations ===
-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
+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.
-*cemeteries;
+*Improper disposal of fluids down shop and storm drains
-*churches;
+*Spilled fuel, leaks and drips from wrecked vehicles
-*colleges;
+*Hosing of outdoor work areas
-*corporate office parks;
+*Wash water from cleaning
-*hospitals;
+*Uncovered outdoor storage of liquids/oils/batteries/spills
-*private schools; and
+*Pollutant wash-off from parking lots
-*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===
+===Outdoor materials===
-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
+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.
-*composting facilities;
+*Spills at loading areas
-*fleet storage and school bus depots;
+*Hosing/washing of loading areas into shop or storm drains
-*landfills/solid waste facilities;
+*Wash-off of uncovered bulk materials and liquids stored outside, of particular concern in MN are road salt storage areas
-*local streets and storm drains;
+*Leaks and spills
-*pesticide use in rights-of-way;
-*public golf courses;
-*public schools;
-*public works yards;
-*maintenance depots;
-*solid waste facilities; and
-*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===
+===Waste management===
-Examples of transportation-related uses include
+[[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>]]
-*airports;
-*bus depots;
-*rental car lots;
-*railroad stations and associated maintenance facilities;
-*ports;
-*highway maintenance facilities; and
-*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.
-{{:Examples of potential pollutant generating land uses}}
+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
-==Contaminated soils and groundwater==
+===Physical plant maintenance ===
-Typically, stormwater infiltration practices are not recommended in areas with contaminated soils or groundwater. Water infiltrating through the soil may transport contaminants to groundwater. Stormwater infiltration may also mobilize contaminants in groundwater or alter groundwater flow. On some sites there may be opportunities for stormwater infiltration if the infiltration practice can be isolated from the contaminants or if the site can be remediated.
+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
-There are several useful sources of information related to stormwater infiltration in areas with contaminated soils or contaminated groundwater. Some of these studies are summarized below.
+===Turf and landscaping===
-*[http://www.epa.gov/brownfields/tools/swdp0408.pdf Design Principles for Stormwater Management on Compacted,Contaminated Soils in Dense Urban Areas.]. This EPA document provides an overview of basic design principles for Brownfield sites, including a 4 step process for incorporating green infrastructure into a Brownfield 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. Examples of pollutant-generating activities associated with turf and landscaping include the following.
-*[http://www.epa.gov/brownfields/tools/swcs0408.pdf Case Studies for Stormwater Management on Compacted,Contaminated Soils in Dense Urban Areas] is a companion to the EPA document discussed above. Three case studies are presented that demonstrate incorporation of green infrastructure into Brownfield sites. Numerous references and links are included in this document.
+*Non-target irrigation
-*[http://library.semcog.org/InmagicGenie/DocumentFolder/LIDManualWeb.pdf Low Impact Development Manual for Michigan] provides an extensive discussion of LID. Chapter 8 of this manual specifically addresses specific LID practices that can be implemented in special areas, including Brownfield sites.
+*Runoff of nutrients and pesticides
-*[http://texaslid.org/pdfs/San%20Antonio%20LID%20Guidance%20Manual.pdf San Antonio LID Guidance Manual] also provides an overview of LID and includes a discussion on implementing LID practices at Brownfield sites.
+*Deposition and subsequent washoff of soil and organic matter on impervious surfaces
-*[http://www.palocalgovtraining.org/pdfs/browfields08/Day1/0145-0245PM/John_Kennedy_and_Dominic_Rocco.pdf Successfully Navigating Brownfield Redevelopment and Stormwater Management] provides useful information on regulatory considerations, BMP options, role of public involvement, general guidance, and a case study for incorporating stormwater infiltration into brownfield sites. Several references are included.
-*[http://swimmablenyc.info/wp-content/uploads/2012/05/Sara-Margolis-Final-Thesis-Presentation.pdf Sustainable Stormwater Management on Redeveloped Brownfield Sites in New York City] provides information on BMP selection at Brownfield sites and includes a detailed case study.
-==Pollutant Generating Operations/Activities==
-[[File:Common operations for assessing pshs.png|thumb|300px|alt=common operations to assess pshs|<font size=3>Six common operations for assessing PSHs include management of turf, waste, loading docks, downspouts, vehicle fueling, and parking lots.</font size>]]
-Perhaps of more significant consideration is an understanding of the types of pollutant generating activities that commonly occur in association with various PSH operations. The following six common operations and a subset of related activities can contribute to stormwater quality problems at a site.
-#Vehicle operations
-##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 lot
-#Outdoor materials
-##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
-##Spills and leaks of fluids
-##Dumping into storm drains
-##Leaking dumpsters
-##Wash-off of dumpster spillage
-##Accumulation of particulate deposits
-#Physical plant maintenance
-##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
-##Non-target irrigation
-##Runoff of nutrients and pesticides
-##Deposition and subsequent washoff of soil and organic matter on impervious surfaces
-##Improper rinsing of fertilizer/pesticide applicators
-#Unique PSH operations (pools, golf courses, marinas, construction, restaurants, hobby farms)
-##Discharge of chlorinated water from pools
-##Improper disposal of sewage and grease
-##Wash off of livestock manure
-##Soil erosion
-##Runoff of pesticides
-##Salt storage
-Many pollutans are associated with PSHs, including nutrients, metals, oil and hydrocarbons, toxics, and other chemicals. Different operations at PSHs have different potential pollutants associated with the activity.
-{{:Stormwater pollutants associated With common operations at potential stormwater hotspots}}
+==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.
-===Vehicle operations===
+:'''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.
-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===
+:'''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.
-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===
+:'''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.
-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 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>]]
+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.
-===Physical plant practices===
+==General guidelines for managing stormwater at a PSH==
-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.
+{{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}}
-===Turf and landscaping===
+{{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}}
-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.
-===Unique hotspot operations===
+[[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>]]
-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>
-==Stormwater management design at PSHs==
+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>]]
+{{:Pollutants of concern from operations}}
-The most cost effective approach to managing stormwater at potential hotspot sites is to employ a variety of non-structural [[Pollution prevention|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.
+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.
+*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.
+**prevent or confine drips and spills, and
-*Prevent or confine drips and spills.
+**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 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.
+*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.
-<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 the following table (Schueler et al., 2004).</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.
+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.
 {{:Pollution prevention practices for PSH operations}}
-<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.
+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.
-Details on BMP design and performance can be found within web pages for individual BMPs.</p>
+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.
-{{alert|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. See data on BMP removal for the following pollutants:
+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.
-*[[BMP pollutant removal for phosphorus| phosphorus]]
-*[[BMP pollutant removal for total suspended solids|total suspended solids]]
-*[[BMP pollutant removal for total nitrogen|total nitrogen]]
-*[[BMP pollutant removal for hydrocarbons|hydrocarbons]]
-*[[BMP pollutant removal for bacteria|bacteria]]
-*[[BMP pollutant removal for metals|metals]]
-|alert-warning}}
-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.
+*[[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.
-*Convey and treat the mostly clean runoff separately from the dirty runoff.
+*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.
-*Infiltrate only the mostly clean water.
+*Consider use of liners, [[Glossary#U|underdrains]], or comparable safeguards against infiltration when runoff exceeds target concentrations.
-*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.
-*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 to 25 percent the allowable storage volume for sediment accumulation over time if sediment is a problem.
-<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 [[Gloassry#P|pre-treatment]], 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 [[Stormwater ponds|ponds]] and [[Stormwater wetlands|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 the NPDES/SDS Industrial Stormwater Multi-Sector General Permit must prepare a Stormwater Pollution Prevention Plan (SWPPP), and implement stormwater control measures at the facility. These plans must include sampling requirements, 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. Many communities and watershed districts are conducting their own site visits as part of its local stormwater program to verify compliance of regulated and un-regulated facilities. Storm drain systems should also be evaluated to determine if non stormwater discharges (illicit discharges) are leaving the facility. 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;
+*there is an immediate public health threat associated with ground water contamination in areas where ground water is the primary drinking water source, and
-Industrial Stormwater Permits are an important regulatory tool at many PSH operations. Significant penalties can be imposed for non-compliance. Communities can address compliance concerns through other programs, such as zoning, stormwater utility or conditional use permits, and can address potential problems whenever new construction at the facility occurs. A community should work with industry and state regulatory agencies to share hotspot inspection and enforcement responsibilities as part of industrial permitting or MS4 programs.
+*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.
-==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.
-This section focuses on these issues and presents a potential approach for establishing design guidelines for infiltration based on the [[potential stormwater hotspots#Pollutant Generating Operations/Activities|six common operational areas]] plus a seventh area that addresses major transportation routes (e.g., highways).
+{{:Infiltration guidelines for potential stormwater hotspots}}
-===Potential for PSH impact on ground water===
+==Links==
-[[File:source water protection areas.jpg|thumb|300px|alt=source water protection areas|<font size=3>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>]]
+*[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]
-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 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.
+==Related pages==
+*[[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]]
-===Infiltration guidance at PSHs===
+<noinclude>
-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.
+[[Category:Level 2 - Technical and specific topic information/infiltration]]
+</noinclude>

Difference between revisions of "Potential stormwater hotspots" Potential stormwater hotspots