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Ecological risks include any impact on the environment from the result of exposure to one or more environmental stressors such as chemicals, land change, disease, invasive species and climate change. Potential ecological risks from stormwater harvest and use systems include impacts to: | Ecological risks include any impact on the environment from the result of exposure to one or more environmental stressors such as chemicals, land change, disease, invasive species and climate change. Potential ecological risks from stormwater harvest and use systems include impacts to: | ||
*'''Plants''' – Pollutants found in stormwater runoff (e.g., heavy metals, salts, and hydrocarbons) may decrease the productivity of or even kill certain plant species under high irrigation rates or long-term exposure from irrigation ([https://nepis.epa.gov/Adobe/PDF/P100FS7K.pdf EPA, 2012]; [https://www.nap.edu/read/21866/chapter/7#131 National Academy of Sciences] (NAS), 2016). The Minnesota Stormwater Manual lists [http://stormwater.pca.state.mn.us/index.php/Minnesota_plant_lists plant species with known tolerance to salt]. These species may also have some tolerance to sediments and petroleum which are commonly associated with salt in road runoff. Salt tolerance has also been shown in some of the aggressive and invasive species found in the Midwest. One concern with using stormwater for irrigation is that the higher pollutant loads will increase susceptibility to exotic and invasive species, such as common buckthorn, box elder, and reed-canary grass. ([http://stormwater.pca.state.mn.us/index.php/Minnesota_plant_lists MPCA]). See Table 8 in Water Quality Considerations for chloride and metal water quality criteria. | *'''Plants''' – Pollutants found in stormwater runoff (e.g., heavy metals, salts, and hydrocarbons) may decrease the productivity of or even kill certain plant species under high irrigation rates or long-term exposure from irrigation ([https://nepis.epa.gov/Adobe/PDF/P100FS7K.pdf EPA, 2012]; [https://www.nap.edu/read/21866/chapter/7#131 National Academy of Sciences] (NAS), 2016). The Minnesota Stormwater Manual lists [http://stormwater.pca.state.mn.us/index.php/Minnesota_plant_lists plant species with known tolerance to salt]. These species may also have some tolerance to sediments and petroleum which are commonly associated with salt in road runoff. Salt tolerance has also been shown in some of the aggressive and invasive species found in the Midwest. One concern with using stormwater for irrigation is that the higher pollutant loads will increase susceptibility to exotic and invasive species, such as common buckthorn, box elder, and reed-canary grass. ([http://stormwater.pca.state.mn.us/index.php/Minnesota_plant_lists MPCA]). See Table 8 in Water Quality Considerations for chloride and metal water quality criteria. | ||
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*'''Soil''' - Salinity in stormwater is a key concern for soil health. Sodium in harvested stormwater that is applied for irrigation can replace calcium and magnesium in soils. Over time, this process can negatively impact soil structure, making the soil less permeable and more erodible, particularly soils with high clay content ([https://www.nap.edu/read/21866/chapter/7#131 NAS, 2016]). See Table 8 in Water Quality Considerations for chloride water quality criteria. | *'''Soil''' - Salinity in stormwater is a key concern for soil health. Sodium in harvested stormwater that is applied for irrigation can replace calcium and magnesium in soils. Over time, this process can negatively impact soil structure, making the soil less permeable and more erodible, particularly soils with high clay content ([https://www.nap.edu/read/21866/chapter/7#131 NAS, 2016]). See Table 8 in Water Quality Considerations for chloride water quality criteria. | ||
− | *Local hydrology – Stormwater harvest and use systems can impact local hydrology via (US EPA, 2012): | + | *'''Local hydrology''' – Stormwater harvest and use systems can impact local hydrology via (US EPA, 2012): |
**increased baseflow to surface waters if extensive land application of water increases groundwater elevations, | **increased baseflow to surface waters if extensive land application of water increases groundwater elevations, | ||
**increased runoff volumes or peak rates during wet periods if extensive land application of water shifts soil conditions from ‘dry’ to ‘wet’ preceding rainfall events, and | **increased runoff volumes or peak rates during wet periods if extensive land application of water shifts soil conditions from ‘dry’ to ‘wet’ preceding rainfall events, and | ||
**decreased local flow due to harvested stormwater for indoor uses being routed to the sanitary sewer system instead of discharging to surface waters. | **decreased local flow due to harvested stormwater for indoor uses being routed to the sanitary sewer system instead of discharging to surface waters. | ||
− | *Equipment degradation - Some [stormwater quality constituents] can negatively affect the performance of the harvest and use system increasing maintenance needs and potentially reducing the useful life of components. [Stormwater quality] should be characterized in the [pre-design phase] so that design choices optimize performance of the system. Ultimately, a system that does not perform as intended may pose risks to health or to the environment. The stormwater quality constituents that could affect the operation of the harvest and use system equipment and structures include (from Toolbox R.1a in the [https://metrocouncil.org/Wastewater-Water/Planning/Water-Supply-Planning/Studies-Projects-Workgroups-(1)/Completed-Studies-Projects/Stormwater-Reuse-Guide.aspx 2011 Met Council Reuse Guide]): | + | |
+ | *'''Equipment degradation''' - Some [stormwater quality constituents] can negatively affect the performance of the harvest and use system increasing maintenance needs and potentially reducing the useful life of components. [Stormwater quality] should be characterized in the [pre-design phase] so that design choices optimize performance of the system. Ultimately, a system that does not perform as intended may pose risks to health or to the environment. The stormwater quality constituents that could affect the operation of the harvest and use system equipment and structures include (from Toolbox R.1a in the [https://metrocouncil.org/Wastewater-Water/Planning/Water-Supply-Planning/Studies-Projects-Workgroups-(1)/Completed-Studies-Projects/Stormwater-Reuse-Guide.aspx 2011 Met Council Reuse Guide]): | ||
**Debris and particulates associated with sediment and leaves could potentially block or clog pipes, irrigation nozzles or drip irrigation systems, or damage pumps. See Table 8 in Water Quality Considerations for turbidity and TSS water quality criteria. | **Debris and particulates associated with sediment and leaves could potentially block or clog pipes, irrigation nozzles or drip irrigation systems, or damage pumps. See Table 8 in Water Quality Considerations for turbidity and TSS water quality criteria. | ||
**Organic matter (measured by BOD, COD, or TOC), for example from glass clippings, that causes reduced dissolved oxygen levels through decomposition could result in odors and release of pollutants from sediments. | **Organic matter (measured by BOD, COD, or TOC), for example from glass clippings, that causes reduced dissolved oxygen levels through decomposition could result in odors and release of pollutants from sediments. |
The construction and operation of stormwater harvest and use systems can pose potential risks from the pollutants and toxins found in stormwater and harvest and use system materials. These risks are largely addressed via water quality standards, plumbing and building codes, stormwater rules and regulations, required signage, and the engineering review process. Stormwater harvesting is, however, an emerging practice in water resource management and existing regulations may not fully address the risks associated with harvest and use practices.
Therefore, a risk assessment should be completed during the [pre-design phase] to ensure that potential risks are properly managed through system design, operation and maintenance. According to U.S. EPA, there are two types of risk assessments:
The following factors should be considered when assessing human health and ecological risks of stormwater harvesting and use systems (NAS, 2016):
Potential human health and environmental risks of stormwater harvest and use systems, and ways to manage those risks through design, operation and maintenance are summarized briefly below. For further guidance, refer to Chapter 5 of Using Graywater and Stormwater to Enhance Local Water Supplies: An Assessment of Risks, Costs, and Benefits (NAS, 2016) and the US EPA Risk Assessment webpage.
Specific guidelines for addressing health and environmental risks associated with stormwater harvest and use systems have been developed in Australia. See Figure 1.1 on page 6 of the Australian Guidelines for Water Recycling: Managing Health and Environmental Risks (Phase 2), Stormwater Harvesting and Reuse for a flow-diagram guide to their risk assessment approach.
Human health risks include any adverse health effects in humans who may be exposed to chemicals in contaminated environmental media, now or in the future. Potential hazards to human health from stormwater harvest and use systems include:
The main health concern with harvest and use of stormwater is exposure to pathogenic microorganisms. Studies have consistently reported high concentrations of fecal indicator microorganisms across different source areas of stormwater; however, the occurrence and fate of human pathogens in stormwater is not well characterized (NAS, 2016). The nature and severity of human health effects depend on the type of exposure (skin contact, ingestion, inhalation, etc.) as well as the duration and magnitude of exposure (Table 1). [Water quality health criteria] Treatment requirements will be stricter for beneficial use applications which have a high chance of exposure compared to those which have a low risk of exposure. Additional information on exposure and dose-response assessments can be found on the EPA Human Health Risk Assessment webpage. This webpage also provides detailed guidance on how to complete the following steps of a human health risk assessment:
Examples of potential exposure types and pathways
Link to this table
Exposure Types | Exposure Pathways |
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Skin contact |
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Direct ingestion |
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Indirect ingestion |
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Inhalation |
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Ecological risks include any impact on the environment from the result of exposure to one or more environmental stressors such as chemicals, land change, disease, invasive species and climate change. Potential ecological risks from stormwater harvest and use systems include impacts to:
Potential risks must be managed through proper design, operation, and maintenance of stormwater harvesting systems (Table 2). If potential risks cannot be addressed through cost-effective [design] or [operation and maintenance], the goals and objectives of the stormwater harvest and use system should be reconsidered in the [pre-design phase].
Elements of design, operation, and maintenance that address potential risks associated with stormwater harvesting and use
Link to this table
Risk Type | Design Considerations | O & M Considerations |
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Human Health Risks | ||
Source area pollutants |
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Hazardous spills in the source area, including sudden air releases of hazardous substances that could deposit in the collection and storage systems |
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Metals and other chemicals from roofing materials (link to table 4 in WQ considerations) |
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Bacteria, viruses |
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Mosquito and other vector-borne illnesses |
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Ecological Risks | ||
Plant communities |
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Soils |
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Aquatic ecosystems |
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Local hydrology |
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Equipment degradation |
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