Stormwater re-use and rainwater harvesting

Rain water harvesting is the practice of collecting rain water from impermeable surfaces, such as rooftops, and storing for future use. There are a number of systems used for the collection, storage and distribution of rain water including rain barrels, cisterns, evaporative control systems, and irrigation.

Example of a residential rain barrel - Stillwater, MN

Design Criteria

• The system should be watertight, have a smooth interior surface, be located on level and stable ground, have a tight-fitting lid, good screens on the inlet and outlet and have an emergency overflow device.
• To prevent the breeding of mosquitoes, empty the water in less than 5 days or place a fine screen over all openings.
• Material can withstand the pressure of water over long periods of time.
• Disconnect and drain rain barrels and cisterns in the winter to prevent freezing and deformation of the rain water harvesting system.

Management suitability

• Water Quality (V_wq) - High¹
• Channel Protection (_Vcp) - Med.
• Overbank Flood Protection (_Vp10) - Low
• Extreme Flood Protection (Vp₁₀₀) - Low
• (Recharge Volume (V_re) - High¹

¹Assumes water is drained to a vegetated pervious area. does not apply to volume of runoff that bypasses the system.

Mechanisms

• Infiltration¹
• Screening/ Filtration¹
• Temperature Control
• Settling
• Evaporation
• Transpiration¹
• Soil Adsorption¹
• Biological/ Micro. Uptake¹

¹Assumes water is drained to a vegetated pervious area. does not apply to volume of runoff that bypasses the system.

Pollution Removal

• Total Suspended Solids - 100%¹
• Nutrients - Total Phosphorus/Total Nitrogen- 100%¹
• Metals - Cadmium, Copper, Lead, and Zinc- 100%¹
• Pathogens - Coliform, Streptococci, E. Coli- 100%¹
• Toxins - Hydrocarbons, Pesticides- 100%¹

¹Assumes water is drained to a vegetated pervious area. does not apply to volume of runoff that bypasses the system.

Site factors

• Drainage Area - Rooftop
• Max. Slope - NA
• Min. Depth to Bedrock - NA
• Min. Depth to Water Table - NA
• SCS Soil Type - can be used in C&D soil types with modifications (e.g. underdrains) - NA
• Poor Freeze/ Thaw Suitability - NA
• Potential Hotspot Runoff - Suitable

¹Assuming water is drained to a vegetated pervious area. Does not apply to volume of runoff that bypasses the system

Benefits

• Protects water supplies by reducing use during peak summer months.
• Mimics the natural hydrology of the area by infiltrating a portion of the rain water falling on the site.
• Reduces volume of storm water being delivered to downstream waterbodies.
• Results in cost savings by reducing municipal water bill.

Limitations

• Not suitable for the following roof types: tar and gravel, asbestos shingle and treated cedar shakes.
• Depending on the design, requires a certain amount of operation and maintenance.
• Proprietary systems can be expensive.

Description

Rain water harvesting can be accomplished using rain barrels and/or cisterns. Rain barrels are typically located at the downspout of a gutter system and are used to collect and store rainwater for watering landscapes and gardens.

The simplest method of delivering water is by the force of gravity. However, more complex systems can be designed to deliver the water from multiple barrels connected in a series with pumps and flow control devices.

Cisterns have a greater storage capacity than rain barrels and may be located above or below ground. Due to their size and storage capacity, these systems are typically used to irrigate landscapes and gardens on a regular basis reducing the strain on municipal water supplies during peak summer months. Again, cisterns may be used in series and water is typically delivered using a pump system.

The storage capacity of a rain barrel or cistern is a function of the catchment area, the depth of rainfall required to fill the system and the water losses. A general rule of thumb in sizing rain barrels or cisterns is that one inch of rainfall on a 1,000 square foot roof will yield approximately 600 gallons of runoff.

Executive summary

Recently, stormwater reuse is being looked to as more than a water conservation practice but also as a viable alternative to help meet stormwater management requirements. This Minimal Impact Design Standards (MIDS) workplan was focused specifically on stormwater reuse for irrigation of non-food crops, such as turf and ornamental landscaping, based on a request from the MIDS technical team.

The goal of the work completed as part of this MIDS workplan was to:

• Perform a literature review of select documents related to water reuse and summarizing the available information in the context of stormwater reuse for irrigation including:
  • general discussion about stormwater reuse,
  • concerns related to stormwater reuse systems,
  • existing guidelines, standards, treatment requirements, and (draft) code related to stormwater reuse,
  • typical contaminants and concentrations in stormwater, and
  • components of a typical reuse system for irrigation.
• Conduct preliminary modeling considering growing season/irrigation season use rates to estimate the relationship between stormwater volume reduction credits versus storage capacity including and estimated range of annual volume, phosphorus, and suspended solids removals for these systems.
• Conduct a total of three meetings with state agency staff and the MIDS technical team to begin discussing the guidelines and standards currently available, regulatory jurisdiction and concerns related to reuse systems and how these concerns may impact future guidelines, and the potential impact of these reuse system on stormwater management.

Based on the work completed, the following is a summary of the major conclusions related to stormwater harvesting and reuse for irrigation and the suggestions for the next steps:

Summary of conclusions:

• One of the major concerns related to stormwater reuse for irrigation (and other uses) is the public health risk due to exposure to pathogens, such as E. coli, and potential for crosscontamination of the potable water supply.
• The lack of national guidance for stormwater reuse has resulted in differing use and treatment guidelines/standards among state and local governments, and in many areas, rainwater and stormwater harvesting is largely unaddressed by regulations and codes. Additionally, many of the existing standards were originally developed for the reuse of reclaimed water (treated wastewater) rather than stormwater.
• Often, the treatment requirements ultimately come down to the risk of exposure to pathogens determining the most stringent levels of treatment. Many jurisdictions evaluate stormwater reuse projects based on whether the application area has restricted or unrestricted public access. However, the level of treatment required by each municipality can influence the number of harvesting and reuse systems that are actually implemented.
• Currently, the State of Minnesota does not have a state-specific code or guidance applicable to stormwater harvesting and reuse and generally relies on the State of California Water Recycling Criteria (2000) as guidance for water reuse projects. At present, there is limited regulatory jurisdiction by the various state agencies over stormwater reuse systems for irrigation.
• From the stormwater management perspective, there is a large range in the expected impact of a stormwater reuse system for irrigation on average annual volume and pollutant load reductions, ranging anywhere from 1 percent to upwards of 90 percent average annual removal. There are several variables that can impact the expected removal efficiency of the reuse system, including the reuse storage volume, the expected area for application, the irrigation rate and season, and any potential pretreatment prior to reuse (e.g., reuse from a wet pond meeting National Urban Runoff Program, NURP, criteria). Assuming that the reuse storage volume is optimized to the contributing watershed and there is sufficient application area to utilize the stormwater, typical volume reduction and pollutant removals from reuse alone would be expected to range from approximately 20 to 50 percent on an average annual basis.

Summary of suggestions for future work:

• Development of a workgroup with representatives of each state agency, including the Department of Labor and Industry (DLI), the Minnesota Department of Health (MDH), the Minnesota Pollution Control Agency (MPCA), the Minnesota Department of Natural Resources (MDNR), and Minnesota Department of Agriculture (MDA), focusing on stormwater reuse (for irrigation) to begin clarifying the roles and jurisdiction for each agency and any associated guidance. The intent of the work group would be to facilitate discussions surrounding stormwater reuse systems, jurisdiction of the various agencies, and potential guidance (appropriate water quality and treatment standards) for these systems.
• Completion of health risk assessments of non-potable water sources (including stormwater) and the potential uses for these sources, including investigation into cases of human illness related to stormwater reuse systems. These assessments will help begin quantifying the actual health risks associated with stormwater reuse (for irrigation) and to begin understanding if the current water quality guidelines (from the various programs in other states) are too stringent, appropriate, or not stringent enough and to help better define levels of required treatment. These assessments would eventually lead to the development of statewide water quality guidelines (or standards) and treatment requirements that would help guide the design of stormwater reuse systems (for irrigation and potentially other uses).
• Because one of the major demands for stormwater reuse systems in Minnesota is irrigation of golf courses and athletic fields from existing stormwater ponds, it is important to understand the actual water quality in stormwater ponds (after settling), in the context of the public health concerns, irrigation equipment function, and impact of stormwater pollutants on plant health. A comparison of the levels observed in actual stormwater ponds to current stormwater reuse water quality standards/guidelines would help regulators begin understanding if additional treatment, such as filtration or disinfection, is needed for reuse systems utilizing water from stormwater ponds.
• The purpose of the preliminary modeling analysis performed as part of this MIDS work was to begin understanding the potential impact of stormwater reuse for irrigation with regards to stormwater management standards. Performance curves were developed based on specific assumptions related to the various parameters. Therefore, these curves only apply to sites that would meet the specific assumptions that were included in the modeling analysis. However, it is expected that there would be significant variability in the model parameters related to the stormwater reuse. Therefore, additional modeling would be necessary to develop a full range of performance curves related to cover the potential site conditions and variability in watershed area, stormwater storage volume, application area for irrigation, irrigation rates, and irrigation periods to be incorporated into the MIDS Calculator.

Overview of stormwater harvesting and reuse for irrigation

Stormwater harvesting and reuse is a practice of collecting and reusing stormwater for a potable (for consumption) or non-potable applications. Outdoor irrigation is considered a non-potable water use. For this work plan, we have assumed irrigation of non-food crops, such as turf and landscaping. For the purposes of this document, stormwater is defined as runoff collected from roof and ground surfaces, including roadways, driveways, parking lots and other impervious areas. Rainwater is defined as runoff from roof surfaces only. Some of the literature sources reviewed as part of the development of this memorandum place emphasis on rainwater only, while others focus on stormwater for harvesting and reuse. Additionally, some of the documents and standards reviewed were originally developed for the reuse of reclaimed (treated wastewater).

The following documents were reviewed as part of the development of this memorandum:

• Stormwater Harvesting and Reuse: Literature Review (EOR, 2011 (draft))
• Guidelines for Water Reuse (EPA, 2012)
• Managing Wet Weather with Green Infrastructure Municipal Handbook Rainwater Harvesting Policies (EPA, 2008)
• Metropolitan Council Stormwater Reuse Guide (Metropolitan Council, 2011)
• Metropolitan Area Master Water Supply Plan (Metropolitan Council, 2010)
• Minnesota Stormwater Manual, Version 2 (MPCA, 2008)
• Municipal Wastewater Reuse. (MPCA, 2010)
• Water Use in Minnesota. (University of Minnesota Water Resources Center, 2010 (draft)).
• Chapter 16 Alternative Water Sources for Nonpotable Applications (Uniform Plumbing Code, 2012 (draft))
• Chapter 17 Nonpotable Rainwater Catchment Systems (Uniform Plumbing Code, 2012 (draft))
• Contech Webinar – Rainwater Harvesting as a Runoff Reduction Tool for Areas with Moderate to High Intensity of Rainfall (Contech, 2012)
• Managing Mosquitoes in Stormwater Treatment Devices (California Department of Health Services, 2004)
• Australian Guidelines for Water Recycling: Managing Health and Environmental Risks (Phase 2) Stormwater Harvesting and Reuse (Natural Resource Management Ministerial Council, the Environment Protection and Heritage Council, and the National Health and Medical Research Council (Australia), 2009)
• Watering Lawns and Other Turf (University of Minnesota Extension, 2009)

There are several overarching goals for the implementation of stormwater harvesting and reuse systems. These goals include (EOR, 2011 (draft)):

• reduction of stormwater pollutant loads and flows to surface waters, helping achieve local stormwater management requirements,
• reduction in the size of other stormwater Best Management Practices (BMPs) needed to achieve local stormwater management requirements,
• reduction of the demand on potable water sources, and
• reduction of stress on the existing water supply infrastructure.

Additionally, stormwater harvesting and reuse systems can be used to help achieve Leadership in Energy and Environmental Design (LEED) and other sustainable design credits related to stormwater quantity and quality as well as water efficiency.

The scale of stormwater harvesting and reuse systems can range from small residential systems to very large commercial systems. According to the EPA, when harvested rainwater is re-used, it generally is best for irrigation and non-potable uses of water closets, urinals, and HVAC, as these uses require a lesser amount of on-site treatment than potable uses (EPA, 2008). Because of this, one of the most common reuse applications of stormwater and rainwater is urban irrigation (EOR, 2011 (draft)), which can include irrigation of athletic fields, golf courses, parks, landscaping, community gardens, and creation of water features (Metropolitan Council, 2011).

Nationally, outdoor water uses represent 58% of the domestic daily water uses while for hotels and office buildings, outdoor uses represent 10 to 38% of the daily water uses, respectively (EPA, 2008). In Minnesota during the summer, as much as 50% of potable water supply is used for outdoor, non-potable uses. During hot weather and extended periods of drought, Twin Cities’ property owners will use 45 to 120 gallons of treated drinking water per person per day for outdoor uses with peak usage on large lots and new turf reaching as much as 200 gallons per person per day (Metropolitan Council, 2011).

Concerns related to stormwater harvesting and reuse

Although stormwater harvesting and reuse systems appear to be a viable alternative to help achieve the required stormwater management standards as well as reducing the demand on the potable water supply, it is not without its associated concerns.

One of the main concerns of regulatory agencies related to the harvesting and reuse of stormwater is public health and the risk of potential exposure to pathogenic bacteria (EOR, 2011 (draft)). These concerns includes human exposure to pathogens, cross-contamination of the potable water supply (EPA, 2008), and in the case of stormwater being reused for irrigation exposure during or after application and for crops and gardens, exposure due to ingestion of crops potentially contaminated with pathogens.

In addition to the public health concern, there are other documented environmental concerns related to stormwater reuse is the risk of toxic spills (within the stormwater reuse catchment area and potential for reuse of toxic/contaminated water), along with mosquito breeding and contaminated pond sediments (EOR, 2011 (draft)).

Additionally, there are often not well-defined operation and maintenance procedures for rainwater and stormwater harvesting and reuse programs (EOR, 2011 (draft)). These operation and maintenance programs help ensure that the stormwater reuse systems are functioning as designed and that they are meeting the required water quality to protect the public health.

Stormwater reuse treatment guidance

Background

In many areas, rainwater and stormwater harvesting is largely unaddressed by regulations and codes (EPA, 2008), although some cities and states have established stormwater harvesting and reuse requirements. Many of these standards were originally developed for the reuse of reclaimed water (treated wastewater) rather than stormwater. However, the confusion about the different types of water to be reused (reclaimed, rainwater, stormwater, etc.) and the lack of national guidance for this topic has resulted in differing use and treatment guidelines/standards among state and local governments. And because of the lack of guidance for rainwater and stormwater reuse, these sources of reuse water are often regulated the same level as reclaimed water, which typically has more clearly defined guidance and standards. Although the general guidance for the reuse of rainwater and stormwater would be similar to reclaimed and graywater, it may also differ because of lower levels of initial contamination and the potential ed uses (EPA, 2008). Often, the treatment requirements ultimately come down to the risk of exposure to pathogens determining the most stringent levels of treatment (EPA, 2008).

The level of treatment required by each municipality can influence the number of harvesting and reuse systems that are actually implemented. Simplifying the treatment requirements when public health is not at risk can lower the project cost for those entities intending to install stormwater harvesting and reuse systems and encourages broader adoption of the practices (EPA, 2008).

Because the main concern of stormwater reuse to human health is exposure to pathogenic bacteria, many jurisdictions evaluate stormwater reuse projects based on whether the application area has restricted or unrestricted public access. Restricted reuse applications are defined by areas where public access can be controlled such as irrigation of gated/private golf courses, cemeteries, and highway medians. Unrestricted use applications include areas where public access is not controlled which often includes irrigation in parks, playgrounds, school yards, and residences, and use in ornamental fountains and aesthetic impoundments. In order to limit the public health risk and exposure to pollutants in stormwater during reuse, reuse projects in unrestricted areas have more stringent water quality regulations than restricted areas (EOR, 2011 (draft)).

Australia has implemented numerous water reuse projects throughout the country and the guidelines for managing the human health risk associated with stormwater reuse includes recommendations about signage and fencing around the irrigated areas to limit public exposure. However, if access cannot be controlled, then the guidelines recommended secondary treatment (which includes disinfection) (EOR, 2011 (draft)).

In addition, the scale of the stormwater reuse system may impact whether the system is regulated. For example, in Portland, Oregon, residential rainwater that is only used for outdoor irrigation is not covered by code and needs no treatment prior to use (EPA, 2008). Often, larger scale applications of reuse require treatment, but the extent of treatment is determined by the end use and is up to the jurisdiction to determine what treatment is required. However, most systems are required to include some level of screening/filtration and most jurisdictions will require disinfection (UV or chlorination) (EPA, 2008). Some stormwater reuse systems primarily rely on the pollutant removal abilities of stormwater best management practices to treat stormwater (EOR, 2011 (draft)).

Cross-contamination of the potable water supply is another concern of water reuse systems and is often addressed in building codes. Cross-contamination concerns are usually most applicable when reuse water is brought inside for use within a building or if a potable water supply line is needed to make-up water in the reuse system if the harvested stormwater cannot meet the water demand, which is often the case for irrigation systems utilizing harvested stormwater. Codes will often require a backflow prevention device on the potable water supply lines, an air gap, or both along with a dual pipe system (purple pipes that indicate water reuse lines) and appropriate stenciling and signage (EPA, 2008).

Operation and maintenance of stormwater reuse systems are the responsibility of the property owner. However, there are often not well-defined operation and maintenance procedures for rainwater and stormwater harvesting and reuse programs (EOR, 2011 (draft)). Operation and maintenance should require regular maintenance to ensure the system is functioning as designed because of greater corrosion and clogging of pipes resulting from higher sediment and microbial loads in stormwater (EOR, 2011 (draft)). Maintenance of these systems can include backwashing or replacement of filters (depending on the system design), periodic flushing of pipes to remove sediment build-up and chlorination of pump heads or emitters to clear microbial scum.

Water testing to verify water quality is recommended as well as regular interval maintenance of the treatment system (replacement of filters, UV lights, etc.) (EPA, 2008). In Australia, officials have a major concern with lack of ongoing monitoring after construction which could lead to the potential risk of exceeding water quality guidelines. As a result, they recommends the biannual/quarterly monitoring of nutrients, sediments, pathogens to assess stormwater quality for irrigation (EOR, 2011 (draft)).

Many water reuse programs recommend municipal inspections occur during installation and annual inspections of backflow prevention systems. For example, the State of Florida requires filing of annual inspection reports and maintenance logs every two years. In North Carolina, the state requires inspection of the system (by owner/operator) within 24 hours of each rain event and on a monthly basis, keeping record of the operations and maintenance (EOR, 2011(draft)).

Because one of the environmental concerns related to stormwater reuse is the risk of toxic spills within the catchment area, guidelines in Australia require the incorporation of a 72-hour residence time into a stormwater pond prior to reuse. This provides a time buffer to stop the reuse of potentially contaminated stormwater (EOR, 2011 (draft)). However, this requirement of a 72-hour holding time is in conflict with suggestions for the control of mosquito breeding in stormwater management devices, which suggest that unless a storage system is completely sealed to prevent the entry of adult mosquitos, the water residence time should be less than 72 hours (CDHS, 2004).

Draft Uniform Plumbing Code and International Plumbing Code for reuse systems

In 2012, the Uniform Plumbing Code (UPC) and International Plumbing Code (IPC) released draft code related to rainwater harvesting for review and comments. However, the draft code only includes code for rainwater reuse (i.e., runoff from roof surfaces) and does not include any code regarding the collection and reuse of stormwater from surfaces other than roofs. The focus of the draft code is on treatment requirements, measures necessary to prevent cross-contamination with potable water, and appropriate signage and system labeling.

However, various stakeholders reviewed the UPC draft code and raised concerns related to its current form. Several comments were submitted to the Minnesota Pollution Control Agency (MPCA) MIDS Harvest and Reuse Technical Team, including:

• The draft code would require a permit for all systems greater than 360 gallons.
  • Because of the threshold volume (360 gallons), nearly all systems (with the exception of some residential systems) will required a permit, and depending on the permitting process established there is concern that the permitting will discourage harvesting and reuse.
  • What is the significance of the 360 gallon threshold?
• The draft code requires water treatment for all above ground irrigation systems.
  • The draft code does not provide any specific water quality treatment standards and leaves it up to each jurisdiction to decide what the guidance should be.
  • What are the appropriate water quality standards?
  • Concern that requirements that are “too stringent” could severely limit stormwater harvesting and reuse.
  • We account for potential reuse from stormwater ponds which can significantly improve water quality due to sedimentation of particles and degradation of pollutants by microorganisms in the pond.
• Restricting water sources for non-potable uses to roof surfaces only
  • Excludes the majority of stormwater sources that would greatly benefit from the volume and nutrient reduction benefits of stormwater harvesting and reuse.

As of December 2012, the recommended revisions to Chapters 16 & 17 of the (draft) plumbing code is to removal all mention of reuse for irrigation and that code only addresses water being used within a building.

Requirements for Stormwater Reuse Systems in Minnesota

Currently, the State of Minnesota does not have a state-specific code applicable to stormwater harvesting and reuse. The MPCA has developed guidelines for the use of reclaimed wastewater. In 2011, the Metropolitan Council developed the Stormwater Reuse Guide, which was developed based on review of water reuse programs and guidance from other states.

Current jurisdiction of existing state agencies on stormwater reuse systems for irrigation

Based on a meeting with staff from the MPCA, the Minnesota Department of Health (MDH), and the Minnesota Department of Labor and Industry (DLI) along with later follow-up with Minnesota Department of Natural Resource (MDNR) staff, Table 1 summarizes the current jurisdiction of the Minnesota state agencies in the context of stormwater reuse systems solely for irrigation.

Summary of Minnesota state agency jurisdiction as it relates to stormwater harvesting and reuse systems for irrigation

Minnesota Department of Labor and Industry (DLI)/p>

• The focus of the DLI is on protecting the public health and welfare. The DLI is responsible for administering the plumbing code. The state Plumbing Board has the rule making authority.
• The DLI primarily deals with the requirements related to stormwater conveyance systems (materials, fittings, etc.), which can include both interior as well as exterior storm piping. Typically, the DLI jurisdiction is over any conveyance to an approved “point of disposal,” which is either at grade or into a subsurface infiltration system. Beyond the point of disposal, the MPCA often is the regulating authority. The definition of “point of disposal” can vary depending on the site. For example, the conveyance system that outlets to a stormwater BMP (such as a pond, infiltration system, or subsurface infiltration system) or a water of the state, if within the property boundary, would be the point of disposal. If there is not a stormwater BMP or a water of the state within the property boundary, then the property boundary would serve as the point of disposal.
• In the case of reusing water for irrigation from a stormwater pond, the DLI would have jurisdiction over the conveyance system to the point where it discharges into the stormwater pond; however, the DLI would not have jurisdiction over the stormwater pond or the irrigation system taking water from the pond and would typically not review those components. In the DLI’s experience with stormwater reuse projects, it cannot dictate water quality standards (no rule), but highly recommends water treatment and the DLI has provided water quality guidance (fecal coliform limits and Total Suspended Solids—TSS limits).
• In terms of stormwater collection systems on/within buildings, the plumbing code does not regulate scuppers, gutters, or downspouts on the outside of buildings. (This is covered by building code.) However, the plumbing code does outline the requirements of interior roof drain systems. Additionally, plumbers can perform both interior and exterior pipe/conveyance work. Certified pipe layers can only install exterior piping.

Minnesota Department of Health (MDH)

• The MDH currently has limited jurisdiction over systems related to stormwater collection and reuse for irrigation. The MDH has no regulatory authority over most routine handling of stormwater, but does administer the Wellhead Protection Program and other drinking water protection programs. Staff in the Source Water Protection Unit assists public water suppliers with preparing and implementing wellhead protection plans, and offer some guidance on implementing stormwater management within wellhead protection areas (especially related to infiltration strategies).
• In addition, the MDH is concerned with the potential exposure to pathogens in the environment and the effects on public health. Currently there are no federal regulations regarding nonpotable reuse applications. State regulations or guidance for nonpotable reuse are not uniform across the country, and no state water reuse regulations or guidelines are based on rigorous risk assessment methodology. The MDH Health Risk Assessment unit is currently reviewing the EPA/USDA Microbial Risk Assessment (MRA) Guideline in order to assist with a strategy for nonpotable reuse applications. Nonconsumptive exposures such as inhalation through mists and aerosols are of particular concern and have not been the focus of current guidelines.

Minnesota Pollution Control Agency (MPCA)

• MPCA’s jurisdiction is typically over the water quality reaching the waters of the state and to ultimately protect the water quality in the lakes, streams, and groundwater. In terms of stormwater management, this typically applies to construction sites disturbing more than one acre of soil, industrial sites that currently have an industrial stormwater permit, or MS4s (Municipal Separate Storm Sewer System operators) trying to meet the requirements of their permits (which can include TMDL—Total Maximum Daily Load—wasteload allocations). Unless the stormwater harvesting and reuse systems for irrigation system is intended to demonstrate compliance with any of the above permits and stormwater management requirements, the MPCA would not be involved in the review of these systems.

Minnesota Department of Natuural Resources (MDNR)¹

• Appropriations permits are required for withdrawals from any waters of the state. Appropriate is defined as the withdrawal, removal, or transfer of water from its source, regardless of how the water is used. “Waters of the state” means all surface and underground waters, except surface waters that are spread and diffused over the land. By this definition, stormwater ponds (even if not a DNR public water lake or wetland or stream – but a pond constructed in an upland area) are waters of the state.
• A water appropriations permit is required from the MDNR for all users withdrawing more than 10,000 gallons per day or 1 million gallons per year from waters of the state. Exemptions to the appropriations permit include: domestic uses serving less than 25 person for general residential purposes, test pumping of a groundwater source, reuse of water already authorized by a permit (e.g., water purchased from a municipal water system), or certain agricultural drainage systems.
• In general, if water is pumped out of a stormwater basin, an appropriation permit is required. If the water is temporarily drained out of the basin via an operable outlet structure, an appropriation permit is not required.
• Additionally, in the Twin Cities seven-county metro area, there is a general permit (2000-6117) that has been issued that allows for temporary appropriations from public waters basins and ponded areas to facilitate flood protection, aquatic plant control, water quality improvement, and stormwater basin maintenance with minimal paperwork. However, this general permit does not apply to stormwater irrigation projects intended to operate consecutive years as all appropriations must be completed within one year of the start of pumping.

¹ – Per 12/3/2012 email conversation with Molly Shodeen, Area Hydrologist for the MDNR, 1/10/2013 personal communication with Jeff Berg, Area Hydrologist for the MDNR, and 2/28/2013 email conversation with Dale Homuth, MDNR.

Table titled "Summary of sate of Minnesota water quality guidelines for stormwater harvesting and reuse systems for Irrigation" summarizes the draft water quality guidelines for irrigation in areas with public access as were determined based on discussion during a meeting with staff from state agencies and a review of standards/guidelines available from other states. These draft guidelines are still considered preliminary to be used for discussion of these standards internally within each agency for additional comment and feedback. Additionally, the MDH would prefer to include treatment requirements along with the water quality outlined in these guidelines (similar to what is outlined in Tables R.3c.1 and R.3c.2 from the Metropolitan Council Stormwater Reuse Guide).

Summary of State of Minnesota water quality guidelines for stormwater harvesting and reuse systems for Irrigation
Link to this table

Water Quality Parameter	Impact of Parameter 10	Water Quality Guideline – Public Access Areas	Water Quality Guideline – Restricted Access Areas	Water Quality Guideline – Irrigation of Food Crops	Comments
E. coli	Public Health	126 E. coli/100mL	Guidance to be determined at a future date	Guidance to be determined at a future date	2,3
Turbidity	Irrigation System Function	2-3 NTU	Guidance to be determined at a future date	Guidance to be determined at a future date	4,5
TSS	Irrigation System Function	5 mg/L	Guidance to be determined at a future date	Guidance to be determined at a future date	4,5,6
pH	Plant Health	6-9	Guidance to be determined at a future date	Guidance to be determined at a future date	4
Chloride	Plant Health; Corrosion of Metals	500 mg/L	Guidance to be determined at a future date	Guidance to be determined at a future date	7
Zinc	Plant Health	2 mg/L (longterm use); 10 mg/L (shortterm use)	Guidance to be determined at a future date	Guidance to be determined at a future date	8
Copper	Plant Health	0.2 mg/L (longterm use); 5 mg/L (shortterm use)	Guidance to be determined at a future date	Guidance to be determined at a future date	8
Temperature	Public Health	Guidance to be determined at a future date	Guidance to be determined at a future date	Guidance to be determined at a future date	9

² – MPCA Bacterial Impairment Standard: 126 E. coli/100mL (geometric mean of 5 samples in 30 day period); no individual samples greater than 1260 E. coli/100mL
³ – EPA 2012 Recreational Water Quality Criteria – Recommendation 1 (Estimated illness rate = 36/1000)
⁴ – Based on typical range/value for water reuse programs in other states
⁵ –Useful for distribution system design, but often used a general indicator parameter, too.
⁶ – TSS guidance provided by Cathy Tran, DLI
⁷ – Per Table R.3b.6 in Metropolitan Council Stormwater Reuse Guide
⁸ – Suggested by Bruce Wilson. Per Table R.3b.5 in Metropolitan Council Stormwater Reuse Guide
⁹ - Recommendation from Anita Anderson on 12/6/2012 email as temperature impacts bacterial growth
¹⁰ –Per Tables R.1a.1 and R.3b.5 in Metropolitan Council Stormwater Reuse Guide

MPCA Municipal Wastewater Reuse Guidelines

In general, the State of Minnesota relies on the State of California Water Recycling Criteria (2000) as guidance for permitting of wastewater reuse and the MPCA has developed the Municipal Wastewater Reuse guidelines based on those requirements. In addition to the water quality limits established (see Table 3), this guidance requires the following to ensure protection of the public health and the environment:

• All use areas must be posted with signs stating that the water being used is recycled, nonpotable, and not fit for consumption.
• Setback distances from wells must be in accordance with the State Well Code.
• No spray irrigation can occur, other than disinfected tertiary water, within 100 feet of a residence, park, playground, school, or other area with similar public exposure.
• Irrigation must be done in such a manner as to prohibit runoff of recycled wastewater from the site.
• No physical connection shall be allowed between any recycled wastewater source and a potable water sources.
• No hose bibs can be installed in areas subject to access by the general public and only quick connect couplers that differ from those used on the potable water system can be used on recycled wastewater.