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<p>Additionally, many irrigation systems propose using stormwater directly out of wet retention ponds on the landscape. Although appropriately designed ponds can provide significant particle settling and removal, there is some uncertainty as to the expected level of pathogens within a stormwater pond. There was not specific data within the sources reviewed as part of the development of this memo outlining typical bacteria concentrations within stormwater ponds and information related to this would be useful. However, the Minnesota Stormwater Manual does summarize the expected removal efficiencies of wet ponds and stormwater wetlands for some of the more common contaminants in stormwater. These removal efficiencies are summarized in the table below</p> | <p>Additionally, many irrigation systems propose using stormwater directly out of wet retention ponds on the landscape. Although appropriately designed ponds can provide significant particle settling and removal, there is some uncertainty as to the expected level of pathogens within a stormwater pond. There was not specific data within the sources reviewed as part of the development of this memo outlining typical bacteria concentrations within stormwater ponds and information related to this would be useful. However, the Minnesota Stormwater Manual does summarize the expected removal efficiencies of wet ponds and stormwater wetlands for some of the more common contaminants in stormwater. These removal efficiencies are summarized in the table below</p> | ||
− | + | {{:Summary of pollutant removal efficiencies in wet stormwater ponds/stormwater wetlands}} |
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.
1Assumes water is drained to a vegetated pervious area. does not apply to volume of runoff that bypasses the system.
1Assumes water is drained to a vegetated pervious area. does not apply to volume of runoff that bypasses the system.
1Assumes water is drained to a vegetated pervious area. does not apply to volume of runoff that bypasses the system.
1Assuming water is drained to a vegetated pervious area. Does not apply to volume of runoff that bypasses the system
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.
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:
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:
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:
There are several overarching goals for the implementation of stormwater harvesting and reuse systems. These goals include (EOR, 2011 (draft)):
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).
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.
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).
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:
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.
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.
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.
Minnesota Department of Labor and Industry (DLI)/p>
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
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 below), this guidance requires the following to ensure protection of the public health and the environment:
MPCA municipal wastewater reuse water quality treatment limits (modified to only include irrigation-related uses)
Link to this table
Types of Reuse | Reuse permit limits | Minimum Level of Treatment |
---|---|---|
|
|
Disinfected Tertiary – secondary, filtration, disinfection |
Cemeteries
|
23 total coliform/100mL | Disinfected Secondary 23 – secondary, disinfection |
Fodder, Fiber, and Seed Crops
|
200 total coliform/100mL | Disinfected Secondary 200 – secondary, disinfection (stabilized pond systems with 210 days of storage do not need a separate disinfection process) |
The Metropolitan Council Stormwater Reuse Guide summarizes water reuse and water quality standards from a variety of states, with the focus on the California water reuse regulations as these are currently the regulations that the State of Minnesota refers to for guidance (for reclaimed water). The following tables summarize some of the key tables included in the Stormwater Reuse Guide. These tables have been modified from the tables in the Stormwater Reuse Guide to focus primarily on stormwater reuse for irrigation purposes only. The tables in this memo include:
Additionally, there are select tables from the Stormwater Reuse Guide attached to the end of this memorandum for reference and include the following tables:
Summary of California water recycling criteria (summarized from Table R.3b.1 of the Metropolitan Council Stormwater Reuse Manual)
Link to this table
Type of Use | Total Coliform Limits (daily sampling is required) | Treatment Required | Comment (in relation to MIDS) |
---|---|---|---|
Irrigation of fodder, fiber, and seed crops; orchards/vineyardsa; processed food cropsb, non-food bearing trees; ornamental nursery stock/sod farmsc | No Limits Established | Oxidation | Most likely applies to non-food bearing trees; ornamental nursery stock/sod farms with restricted access |
Irrigation of pasture for miling animals, landscape areas (controlled access); ornamental nursery stock and sod farms where public access not restricted); landscape impoundments |
|
Oxidation Disinfection | This includes Cemeteries, freeway landscaping, restricted access golf courses, and other controlled access areas |
Irrigation of food cropsa |
|
Oxidation Disinfection | |
Irrigation of food cropsd; Open access landscape areas; Decorative fountains |
|
Oxidation Coagulatione Filtratione Disinfection | This includes parks, playgrounds, schoolyards, residential landscaping, unrestricted access golf courses, and other uncontrolled access areas; This may also apply to scenarios such as community gardens, etc. |
a No contact between reclaimed water and edible portion of crop
b Food crops that undergo commercial pathogen destruction
c No irrigation 14 days prior to harvesting, sale, or allowing public access
d Contact between water and edible portion of crop including edible roots
e Related to turbidity – See Metropolitan Council Reuse Manual for specific details
Summary of water reuse criteria for irrigation of parks, playgrounds, schoolyards, and similar areas from reuse programs from several statesa
Link to this table
Water Quality Parameter | Water Quality Limits (Range based on information for all states included in table) | State of California Requirements | State of Minnesota – Limits Used by DLIb |
---|---|---|---|
Total Coliform | 2.2 total coliform/100mL | 2.2 total coliform/100mL | N/A |
Fecal Coliform | No Detect/100mL – 100 fecal coliform/100mL (2.2 fecal coliform/100mL most common) | N/A | 100 fecal coliform/100mL |
E. coli | 126 E. coli/100mL (only CO uses E. coli as a standard) | N/A | N/A |
Turbidity | 2 NTU – 3 NTU | 2 NTU | N/A |
TSS | 5 mg/L – 30 mg/L (5 mg/L most common) | N/A | 5 mg/L |
BOD | 5 mg/L – 30 mg/L (10 mg/L most common) | N/A | N/A |
pH | 6-9 | N/A | N/A |
NH3 | 4 mg/L (only NC has NH3 as a standard) | N/A | N/A |
Cl2 residual | 0.5-1.0 mg/L | N/A | N/A |
a – Includes review of water reuse programs in AZ, CA, CO, FL, GA, HI, NV, NM, NC, OR, TX, UT, WA, and US EPA guidelines
b – Per 11/28/2012 conversation with Cathy Tran, DLI; General guidance
Summary of water reuse criteria for select nonpotable applications from reuse programs from several statesa
Link to this table
Water Quality Parameter | Water Quality Limit – Food Crop Irrigation | Water Quality Limit – Restricted Access Irrigation | Water Quality Limit – Unrestricted Access Irrigation |
---|---|---|---|
Total Coliform | 2.2 total coliform | 23 total coliform/100mL | 2.2 total coliform/100mL |
Fecal Coliform | No Detect/100mL (some states prohibit usea) | 200 fecal coliform/100mL | No Detect/100mL – 20 fecal coliform/100mL |
E. coli | N/A | 126 E. coli/100mL (only CO uses E. coli as a standard) | 126 E. coli/100mL (only CO uses E. coli as a standard) |
Turbidity | 2 NTU | N/A | 2 NTU – 3 NTU |
TSS | N/A | 20-30 mg/L | 5 mg/L |
BOD | 10 mg/L BOD | 20-30 mg/L | 5-10 mg/L |
CBOD | N/A | 15-20 mg/L | 5-20 mg/L |
pH | N/A | N/A | N/A |
Note: Many of these standards are based on water quality limits established for reclaimed water (treated wastewater), not stormwater specifically
a – Includes review of water reuse programs in AZ, CA, CO, FL, GA, HI, NV, NM, NC, OR, TX, UT, WA, and US EPA guidelines
Because exposure to pathogens, including bacteria, is one of the main concerns related to stormwater harvesting and reuse for irrigation, we have also summarized the fecal coliform standards used by the Minnesota Department of Health (MDH) for swimming beach closures as well as the Minnesota Pollution Control Agency (MPCA) E. coli standards for listing water bodies for bacterial impairments for reference (See Table 7).
The MDH tests public beaches for elevated levels of fecal coliform and/or E. coli and when high levels are found, beaches are closed to reduce the likelihood of disease. The MDH has established recommendations related to coliform levels to maintain healthy swimming beaches. The MDH will be changing the beach closing standard to reflect the new EPA guidelines (126 E. coli/100mL) and additional changes to that standard are likely based on improved testing methodologies and may included additional indicators.
Additionally, the MPCA has established numeric water quality standards for water bodies throughout the state to determine if the water quality in a water body would attain its intended use. Water bodies not attaining those standards are placed on the MPCA 303(d) list of impaired water bodies. The MPCA has established standards for E. coli within a water body, with those exceeding the standards being classified as having a bacterial impairment.
Summary of MDH “swimmable” standards for public beaches & MPCA standards for bacterial impairments
Link to this table
Water Quality Parameter | Water Quality Limit | Source |
---|---|---|
Fecal Coliform | 200 fecal coliform/100mL (average of 5 samples in a 30- day period should not exceed) | MN Dept of Health |
1000 fecal coliform/100mL (no one sample should exceed) | ||
E. coli | 126 E. coli/100mL (Geometric mean based on 5 samples in a month) | MPCA Impaired Waters Criteria |
1260 E. coli/100mL (maximum standard for one sample) |
Common pollutants in stormwater runoff include nutrients, sediments, heavy metals, salinity, pathogens, and hydrocarbons (EOR, 2011 (draft)). The Metropolitan Council Stormwater Reuse Guide includes several tables that summarize typical stormwater runoff quality information that are attached to the end of this memo and include the following:
However, the fact that the water quality in stormwater runoff is highly variable due to differences in land use and from event to event is extremely important to emphasize and this variability should be considered when evaluating a stormwater harvesting and reuse system and determining what treatment might be necessary.
Additionally, many irrigation systems propose using stormwater directly out of wet retention ponds on the landscape. Although appropriately designed ponds can provide significant particle settling and removal, there is some uncertainty as to the expected level of pathogens within a stormwater pond. There was not specific data within the sources reviewed as part of the development of this memo outlining typical bacteria concentrations within stormwater ponds and information related to this would be useful. However, the Minnesota Stormwater Manual does summarize the expected removal efficiencies of wet ponds and stormwater wetlands for some of the more common contaminants in stormwater. These removal efficiencies are summarized in the table below
Summary of pollutant removal efficiencies in wet stormwater ponds/stormwater wetlands
Link to this table
Parameter | Wet Pond Removal Efficiency (%) | Stormwater Wetland Removal Efficiency (%) |
---|---|---|
TSS | 60-90 | 39-81 |
TP | 34-73 | 20-54 |
TN | 30 | 30 |
NO3 | N/A | N/A |
Metals | 60 | 60 |
Bacteria | 70 | 70 |
Hydrocarbons | 80 | 80 |