Microorganisms in Stormwater and Treatment Options in Developing Countries

In: Stormwater: Sources, Monitoring and Management 24 October 2019 Nova Publishers Inc, New York Chapter 7 MICROORGANISMS IN STORMWATER AND TREATMENT OPTIONS IN DEVELOPING COUNTRIES Ndubuisi C. Onwa, PhD1 and Ernest O. Nnadi, PhD2 1 Department of Applied Microbiology, Ebonyi State University, Abakaliki Nigeria 2 Centre for Water, Agriculture and Resilience (CAWR), Coventry University, UK 2 Ndubuisi Collins Onwa and Ernest O. Nnadi ABSTRACT Microorganisms are present in stormwater. Their numbers and diversity is influenced by the microbial flora of that environment and they can come from different sources namely the air, soil and through human activity. Stormwater runoffs carry pollutants including microorganisms. Stormwater runoffs that contain organic materials and some pathogenic microorganisms when discharged into bodies of water can lead to outbreaks of infections if such receiving bodies of water are not treated to remove the microbial contaminants. Another effect of microbial presence in a stormwater runoff discharged into a body of water without treatment is the possibility of creating anoxic condition in the receiving water body. This happens when the aerobic heterotrophic bacteria in the water body multiplies thereby utilizing the dissolved oxygen in the water. The end result is the death of fish and other aquatic organisms that require oxygen for survival. Stormwater runoffs can be treated biologically through activated sludge process, trickling filter or through the oxidation pond method to reduce the organic and microbial load. The effluents resulting from such treatment can then be disinfected to destroy the remaining microorganisms and organic matter in the water. Keywords: stormwater, microorganisms, runoff, pollution INTRODUCTION Stormwater is the water generated from the precipitation of atmospheric waters. Atmospheric waters precipitates mainly in the form of rain, snow and hail. In temperate countries, rain, hail and snow all serve as means by which atmospheric waters precipitate. In tropical countries however, snow is unknown except perhaps at the peak of high mountains and hail falls only occasionally, therefore atmospheric waters precipitates in the tropics mainly in the form of rainfall. Precipitation is one of the processes in the hydrologic cycle. The hydrological cycle is the continuous circulation of water from the earth to the atmosphere and from the atmosphere back to the earth. The cycle is powered by the energy of the sun. The heating of the ocean by the sun causes the evaporation of water as Microorganisms in Stormwater and Treatment Options … 3 water vapor into the atmosphere. Other processes involved in the hydrologic cycle are transpiration and condensation. The volume of stormwater at any time is related to the level of precipitation at that time as well as the nature of the surface. Hence, heavy rainfall will produce more stormwater than little/low rainfall and vegetative surfaces will increase the rate of percolations and infiltrations, and slow runoff while there is little or no percolations and infiltrations on impervious surfaces and there is more runoff of stormwater. The three major ways that stormwater may be removed from the surface after each precipitation events are: percolation/infiltration, evaporation and runoff. Percolation/Infiltration Percolation/infiltration of stormwater into the soil: Percolation involves the movement of water downwards through pores in the soil or cracks in rocks. Some of the precipitation percolates or infiltrates through cracks and pores in soils and rocks until it gets to the water table where it becomes groundwater; water held in cracks and pore spaces which may flow to support streams or may be tapped by wells. Evaporation Stormwater can also be held on the surface and may evaporate; storm water on the surface land is heated by the sun, causing its evaporation that is loss of the stormwater as vapour back to the atmosphere. Runoff Stormwater can also be lost as runoff and end up in nearby streams, rivers and other surface water bodies. Runoff is the visible flow of water into surface waters. The steeper the land, and the less porous the soil, the 4 Ndubuisi Collins Onwa and Ernest O. Nnadi greater the runoff. Storm water runoffs may be regarded as waste water especially when it carries waste. Stormwater runoff may mix with household waste water, debris, solids and pollutants and indiscriminately disposed solid wastes left in the path of the stormwater runoff. Pollutants in stormwater may be toxic metals like medicines, pesticides, herbicides and also excess solvents, paints and other household chemicals (Figure 1). Particles from motor exhausts and deposition of atmospheric pollutants can contaminate stormwater. These pollutants in stormwater runoffs will definitely affect the quality of the receiving water bodies. Also, disposal of human sewerage into stormwater conveyance systems are sources of pollution to receiving water and a major souce of disease outbreaks (Figure 2). Stormwater pollution could come from diverse sources (point and non-point sources) including contamination from agricultural areas located on high grounds as runoff carries fertilizers and farmwastes into stormwater. Figure 1. Indiscriminate Disposal of chemicals in Stormwater Drains (USEPA, 2017). Microorganisms in Stormwater and Treatment Options … 5 Figure 2. Disposal of sewerage into stormwater (SightLine Institute, 2018). Environmental impacts of stormwater can be tangible. Solids in stormwater runoffs settle at the bottom and form sediments that can clog drains, pipes, streams and rivers. Particles in stormwater runoffs can form scums that are aesthetically undesirable. Nutrients like nitrogen (N) and Phosphorus (P) in storm water runoffs causes eutrophication of water bodies when such stormwater runoff end up in slow moving water bodies like streams, lakes, etc. The presence of nutrients (N and P) stimulate algal growth, increase in the activity of aerobic heterotrophic bacteria in the water body. The resultant effect is the consumption of dissolved oxygen in the water body by activities of the aerobic heterotrophic bacteria producing anoxic condition in the water body. The absence of oxygen in such water bodies will lead to the death of fish and other aerobic aquatic organisms and may result in distortion of their ecosystem as some organisms flourish to the disadvantage of others. Microorganisms in stormwaters that percolates or infilterates the soil are normally trapped in soil particles as the stormwater moves downwards. The soil particles acts as a sieve, hence deep underground waters or groundwaters have few or no microorganisms. 6 Ndubuisi Collins Onwa and Ernest O. Nnadi Microorganisms are single celled organisms that cannot be seen with the naked eye. They include Bacteria, Algae, Fungi, Protozoa and Viruses. Microorganisms are ubiquitous in nature and can be found in almost every environment including environments where other forms of life are impossible to live. Microorganisms are independent beings that carry out their life processes independently of other cells, making them different from cells of plants and animals that are unable to live alone but exist as parts of multicellular structures. Microorganisms being ubiquitous in nature are found in storm water. Major microbial groups that can be found in storm water include: Bacteria, Viruses, Algae Fungi and Protozoa. Bacteria are prokaryotes; unicellular microorganisms that are very small in size usually on the order of 1µ m in diameter and the absence of a nuclear membrane. The DNA of almost all bacteria is circular and is basically the prokaryotic chromosome. Most prokaryotes have a single chromosome. The region of the cell containing the DNA is termed the nucleoid. Bacteria contain an enormous variety of species with a large variety of morphologies and physiologies. All known disease-causing (pathogenic) prokaryotes are bacteria, as are thousands of nonpathogenic species. Examples of bacteria genera that can be found in storm water include the Staphylococci, Micrococci, Streptococci, Escherichia, Pseudomonas, Flavobacterium, Achromobacter, Proteus, Bacillus, etc. Fungi are eukaryotic microorganisms which do not contain chlorophyll and hence do not carry out photosynthesis. They usually grow as a mass of branching, interlacing filaments (filamentous) known as mycelium like the molds but may also grow as single cells (unicellular) like the yeasts. Fungi reproduce asexually with spores and they contain chitin and/or cellulose in their cell wall. Examples include Phycomycetes, Hyphomycetes, Sapromyces, Allomyces, Fusarium, Yeasts like Saccharomyces cerevisae Candida albicans, etc. Protozoa are unicellular nonphotosynthetic microorganisms. Protozoa are regarded as the evolutionary ancestors of all multicellular organisms including fungi, animals and plants. This is so because Protozoa contain members which like plants carry out photosynthesis are phototrophic, and Microorganisms in Stormwater and Treatment Options … 7 some of its members which like animals and fungi feed on organic compounds and are heterotrophic. Protozoa also contain species with capability for autotrophic and heterotrophic existence. Examples include Giardia lamblia, Amoeba proteus, Entamoeba histolytica, and Pneumocystis carinii. Algae are photosynthetic eukaryotic microorganisms. They lack the structure of vascular plants and they contain chlorophyll in the photosynthetic membrane of their subcellular chloroplasts. The cyanobacteria or the blue-green bacteria once classified as algae are prokaryotic and no longer classified as algae. Many algae species are unicellular while some others may form extremely large multicellular structures like the brown algae. They are primarily aquatic organisms. The species encountered include Microcystis aeroginesa, Anaebena spp, Melosira spp, Tribonema bombycinum, etc. Viruses are particles that contain nucleic acid but are incapable of replication on its own. They only grow and reproduce in living cells. They lack many of the attributes of a cell and are much smaller than cells. Viruses contain either DNA (Deoxyribonucleic acid) or RNA (Ribonucleic acid) but never both unlike living organisms that contain both DNA and RNA. Viruses have a nucleic acid inner core and capsid, the outer protein cover. They have no metabolic capabilities of their own. They lack ribosomes. Viruses are known to attack and infect all living cells including microorganisms. Other properties of viruses are that they enter only susceptible cells; a virus attacking one type of cell will not attack another type of cell. Viruses that infect animal cells will not infect plant cells. Even among the animal or plant, some viruses will attack some members and not others. Some viruses infect one microbial species and not others. Most viruses are present in aquatic environments as phages; viruses that attack “eat” cells and eat them. Viruses that attack bacteria are called bacteriophages, and viruses that attack fungi are called mycophages, and viruses that attack algae are called phycophages. Examples of viral groups that can be found in storm water include: Enteroviruses, Adenoviruses, Papillomaviruses, Noroviruses, Mulluscipoxvirus, etc. 8 Ndubuisi Collins Onwa and Ernest O. Nnadi Normally atmospheric waters are sterile but as it precipitates to the earth it gets contaminated with microorganisms. As rain falls from clouds, rain water collects with it dissolved gases, dust particles and microorganisms. If rain falls for a sufficiently long period, rain water would have brought down microorganisms and dust particles circulating in the atmosphere. Sources of microorganisms in stormwater are mainly from the air, land/soil and impervious structures and human activity. Air Air is normally not a habitat for microorganisms because it lacks the requisite nutrients for their growth and survival. The atmosphere as a habitat is characterized by extreme temperature variations, high light intensities, and low content of organic matter and scarcity of available water making it a non hospitable environment for most microorganisms. The atmosphere has various layers but the layer nearest to the Earth is called the troposphere. Troposphere layer contains substantial loads of microorganisms. Microorganisms suspended in the air are called bioaerosols and these bioaerosols condense with storm water during precipitation events. The aerosols are significant because they can be associated with diseases in humans, animals and plants. Microorganisms suspended in the cloud are thought to perform processes that alter the chemical composition of the cloud and may induce precipitation along with water droplets, dust particles and other matter. Many different microorganisms can be in aerosol forms in the atmosphere. They include the bacteria, viruses, fungi, yeast and the protozoa. These microbial groups may be found in air as vegetative cells, spores or as cysts. Since air is exposed to the rays of the sun, its temperature is high with less moisture. The implication to microbial cells is that if they are not protected from dessication by for example attachment to surfaces, most of them will die in the air. Hence when compared to soil and water, there are less numbers and diversities of microorganisms in air. Some of these microbes have adapted to surviving Microorganisms in Stormwater and Treatment Options … 9 the harsh conditions of the atmosphere by producing structures like endospores that allow them to survive extreme conditions. Microorganisms rarely grow in the air. Microorganisms in the air can be carried by wind and deposited on the roof of buildings, leaves of trees, mountain tops and other structures that extend above the ground. In such cases, the microorganisms present in such structures are washed off the surfaces during rainfall and they are found in stormwater after precipitation events. Air does not have indigenous microflora though a number of microorganisms are present in it. Most microorganisms in the air originate from the soil. Soil microorganisms when disturbed, by wind blow liberate microorganisms from the soil into the air and they remain suspended there for a long period of time. Also the activities of man like digging or ploughing the soil may release microorganisms into the air. Apart from the soil, microorganisms found in water may also be released into the air in the form of aerosols or water droplets. Movements or splashings of water by tidal or wind action may produce aerosols. Wind may dislodge microorganisms from plant or animal surfaces into the air. The dispersal of microbes in air starts with the discharge of microbial cells, its spores or aerosols to the atmosphere. It is then followed by subsequent transport through diffusion and dispersion and finally their deposition on any surface. The organisms introduced into the air may be commensals or plant or animal pathogens. It is known that plant pathogens are spread over long distances through the air for example; spores of Puccnia graminis can tavel. Human beings are the main sources of airborne microorganisms. Through human activities like coughing, sneezing, talking and laughing the microbial flora of the mouth and the upper respiratory tract are constantly discharged into the air. Some bacteria groups in the atmosphere are: Proteobacteria, Planctomyces, Firmicutes, Bacteroids, Actinobacteria, Acidobacteria and others. These bacteria groups are also found in rain but at different numbers. For example Proteobacteria group make up about twenty five percent of the bacteria found in the atmosphere but they make up about fifty five percent of the bacteria found in rain. Some pathogenic microbial species transmitted through the air includes Bacteria; Bacillus 10 Ndubuisi Collins Onwa and Ernest O. Nnadi anthracis, Streptococcus pyogenes, Streptococcu pneumonia, Haemophilus influenza, Mycobacterium tuberculosis, etc. Fungi; Puccinia spp, Alternaria spp, Aspergillus spp, Coccidioides immitis, Aspergillus fumigatus. Viral groups found in the air include: Rhinovirus, Orthomyxoviruses, Morbillivirus, Adenovirus, Mumps virus, etc. These microorganisms found in the air can be found in stormwater after precipitation events like rainfall. Soil Soil refers to the loose outer material of the Earth’s surface. It is distinct from the bedrock that lies underneath it. Microorganisms and macro organisms comprise about five percent of the components of soil. Other components include inorganic mineral water about forty percent of the soil volume, organic matter usually five percent and air and water roughly fifty percent. The most extensive growth of microorganisms in soils occurs on the surfaces of soil particles. Hence soil surface harbors numerous numbers and diversities of microorganisms. This is so because oxygen (air) required by aerobic microorganisms, are available at the surface of the soil and also nutrients are readily available on soil surface, than the other soil horizons. The nutrients on the surface of the soil are mostly organic materials in the form of plant leaf litters, dead animals and plants and organic wastes left on the surface of the soil. The major factor affecting microbial activity in soil is the availability of water. Soil water content, depends on soil composition, rainfall, drainage and plant cover. Under favorable conditions microbial growth on soil surface is high, resulting in high microbial populations. During storm water runoff, these microbial populations are washed off the soil surface and are carried along to the receiving water body. Hence researches have shown that the microbial flora of a water body especially after rainfall is similar to the microbial flora of the soil near the water body. Microorganisms that can be found in soil include the Bacteria, Archae, Fungi, Algae, Viruses and the Protozoa. Bacteria species that live in the Microorganisms in Stormwater and Treatment Options … 11 soil include both pathogenic and pathogenic species of Bacillus, Clostridium, Flavobacteriun, Micrococcus, Staphylococus, Coliform group, Streptococcus, etc. Penicillium spp, Mucor spp, Aspergillus spp, Fusarium spp, are some of the Fungi species in soil. Human activity also contributes to the presence of microorganisms in storm water. They include but not limited to the generation and dumping of refuse on water ways, farm fields, roads, lawns. Human activity also leads to the release of microorganisms in the air and soil that contaminate the storm water. Human activity over the years have caused increased storm water runoff and reduced the rate of percolations/infiltrations of storm water into the ground. EFFECTS OF MICROORGANISMS IN STORMWATER Microorganisms in stormwater may be pathogenic, opportunistic pathogens or non pathogenic species. Pathogenic microbial species may be among the microorganism found in storm water. These species are able to cause disease in a healthy individual and include species like Salmonella typhi, Mycobacterium tuberculosis, Vibrio cholera, Escherichia coli, Shigella spp, Campylobacter spp, Yersinia spp, etc. These pathogens may be carried with storm water runoff from the soil or surfaces of the earth in sewage or human/bird feces especially in developing countries where the collection and treatment of storm water runoff is not carried out. When the storm water runoffs that carry the pathogens contaminate water bodies used for drinking or other purpose and are not treated to remove the pathogens, they can lead to infectious diseases. There are ways by which water may be associated with disease and they are waterborne diseases caused by the ingestion of water contaminated with human feces, animal feces or urine containing pathogenic bacteria or viruses. Such diseases include cholera, typhoid, amoebic dysentery and other diarrheal diseases (Gleick et al. 2004). Waterwashed diseases are caused by poor personal hygiene and eye or skin contact with contaminated water. These include scabies, trachoma, flea, 12 Ndubuisi Collins Onwa and Ernest O. Nnadi etc. water-related diseases are caused by insect vectors which breed in water. Examples include malaria, yellow fever, dengue, onchocerciasis, trypanosomiasis, etc. water-based diseases are caused by parasites found in intermediate organisms living in water. They include dracunculiasis, schistosomiasis, etc. Pathogens like Salmonella typhi and Salmonella paratyphi the causative agents of typhoid fever, Shigella boydii, Shigella flexneri, Shigella dysenteriae and Shigella sonnei, the causative agents of shigellosis, Vibrio cholera the causative agent of cholera, Cryptosporidium parvum the causative agent of cryptosporodiosis, Enteropathogenic Escherichia coli (EPEC) the causative agent of infantile diarrhea can all be transmitted through contaminated water to humans. Other microbial groups like Giardia lamblia the causative agent of giardiases, Drunculus medinensis the causative agent of dracunculiasis and Entamoeba histolytica the causative agent of Amoebiasis can also be transmitted to humans through contaminated water. Storm water carries large quantities of sediments, pollutants like, organic compounds and nutrients. Storm water runoff may contain much household wastewater depending on the pollutants and debris in the path of the stormwater runoff. Large numbers of microbial species in storm water runoffs that enters water bodies like lakes and rivers that contain organic nutrients will result in the microbial species in the stormwater runoffs utilizing the organic materials. As the microbial species, degrade the organic nutrients in the water bodies, dissolved oxygen are being utilized thereby depleting the water of its dissolved oxygen. The resultant effect is that such water bodies becomes anoxic leading to the death of aquatic organisms like fishes, crustaceans that require oxygen for survival. Presence of large quantities of nutrients like nitrogen and phosphorus in stormwater can cause eutrophication; a process whereby water bodies such as lakes receive excess nutrients that stimulate excessive growth of microorganisms including algae and cyanobacteria in the receiving water body especially in slow moving water bodies. A major source of stormwater pollution is hydrocarbon contamination mainly as a result of oil leakeages from vehicles, spillages that occurs Microorganisms in Stormwater and Treatment Options … 13 during transportation of oil and oil related products and garages as well as from indiscriminate disposal of oil Figure 3. Runoff carries pollution to natural water bodies (Chester County PA). BIOLOGICAL TREATMENT OF STORMWATER RUNOFFS Storm water runoffs when carried with organic materials, pollutants, and microorganisms should be treated before discharge into water bodies. There are many ways by which storm water runoffs may be treated such as chemically, physically and biologically. Biological aerobic treatment of storm water runoffs or waste water to reduce both the organic load and the microbial load involves three conventional methods namely: the activated sludge, the trickling filter and the oxidation ponds. Activated Sludge System The process is a biological method of treating water with concentration of organic material by a mixed population of microorganisms in an aerobic 14 Ndubuisi Collins Onwa and Ernest O. Nnadi acquatic environment. The conventional activated sludge system comprises of an aeration tank and a sedimentation tank. The raw storm water runoff to be treated first enters the aeration tank where it is mixed with a portion of the sludge from the sedimentation tank. The activated sludge uses different and complex microbial populations of especially bacteria and protozoa to reduce the organic matter in a storm water runoff or waste water. The microorganisms occur in flocs made up of bacterial cells, extracellular polymeric substances, adsorbed organic matter and also inorganic matter. The microorganisms derive nourishment from organic matter in the aerated waste water for the production of new cells. Some of the bacterial species convert ammonia nitrogen to nitrate nitrogen a process called nitrification. The most important bacteria in the activated sludge process is the bacterium Zooglea ramigera which produces extracellular matrix in large quantities. The extracellular matrix helps in formation of flocs. Other bacterial species involved in activated sludge process are Pseudomonas, Achromobacter, Flavobacterium, Microbacterium, Bacillus, Azotobacter, Staphylococcus, Micrococci, etc. Fungi associated with activated sludge process are Penicillium spp, Zoophagus spp, Geotrichum spp, Arthrobotrys Alternaria spp, etc. Trickling Filter This consists of round rocks arranged in a bed. The rocks are about 1 to 4 inches in diameter and the bed is arranged about 6 to 10 feet deep. Waste water is uniformly spread on the bed by a rotating distributor powered by an electric motor. The water percolates by gravity over the rocks and through the spaces between the rocks. The effluent is then collected in an under-drain which is then allowed to settle in a sedimentation tank. The microorganisms in the waste water breaks down the organic matter as it percolates over the stones. Although the process is aerobic, most of the bacterial species involved in the trickling filter are facultative organisms. Aerobic conditions operate mainly when the filter is fresh and also at the outer areas of the coating of microorganisms in the Microorganisms in Stormwater and Treatment Options … 15 rock. A trickling filter is a type of waste water treatment system. It consists of a fixed bed of rocks lava, coke, gravel, slag, ceramic, sphagnum, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime (biofilm) to grow, covering the bed of media. Aerobic conditions are maintained by splashing, diffusion, and either by forced-air flowing through the bed or natural convection of air if the filter medium is porous. Oxidation Pond Oxidation ponds also called stabilization ponds are shallow lagoons into which water to be treated is discharged at a particular point usually at the centre but may also be at the side. It is designed to treat waste water through the interaction of sunlight, bacteria and algae. Algae grow within the pond and utilize sunlight to produce oxygen during photosynthesis. The oxygen produced by algae is used by aerobic bacteria in the oxidation pond to degrade the organic matter in the waste. After suitable period of holding, the degraded solid organic matter settle at the bottom of the pond and the effluent is discharged at a single point. The effluent is usually low in BOD before discharge. Oxidation ponds are suited in warm and sunny climates. In large oxidation ponds, algal aeration by photosynthesis may not be adequate, hence floating turbine aerators may be installed to complement the process of aerating the oxidation pond. Also natural winds assist the diffusion of oxygen into the water. The carbon dioxide released by the aerobes is utilized by the algae. Bacteria genus predominant in oxidation ponds are Pseudomonas, Flavobacterium and Alcaligenes. The algae involved are Chlorella, Spirogyra, Ulothrix and Vaucheria. Oscillatoria are confined to the surface of the pond. Effluents Treatment 16 Ndubuisi Collins Onwa and Ernest O. Nnadi The effluents resulting from the different biological treatments methods of storm water or waste water are normally discharged into the receiving water bodies while the sludge which is the solid/semi-solid part of the waste water are digested anaerobically in the absence of oxygen. In order to drastically reduce the microbial load in the effluents before discharge, they are usually disinfected. Disinfection is usually done by the use of chlorine and its compounds e.g., calcium hypochlorite or chloride of lime. It is important to note that complete sterilization that is the removal of all microorganisms from the effluents is not the aim. Apart from chlorine, other halogens like iodine have been used to disinfect waste water. CONCLUSION Different microbial species are found in stormwaters and are carried in stormwater runoffs or trapped in the soil as the stormwater percolates or infiltrates the ground. Stormwater runoffs generated by the precipitation of atmospheric waters may be a source of pollution to the environment especially if there are presence of high numbers of aerobic heterorophic bacteria, presence of pathogenic microbial species and also presence of organic and inorganic contaminants. Hence it is required that stormwater runoffs be properly managed and treated before it is channeled to a receiving water body. REFERENCES Chester County (nd) Chester County’s Stormwater Pollution Prevention Program https://www.chesco.org/2891/Stormwater-Program. Gleick, P. H., Cain, N. L., Hassz, D., Henges-Jeck, C., Kipersky, M., Hunt, C., Moench, M., Palaniappan, M., Srinivasan, V. & Wolff, G. H. (2004). ‘The World’s Water 2004-2005: The Biennial Report on Freshwater Resources, Part 8, Island Press, London. Microorganisms in Stormwater and Treatment Options … 17 Geo, F. Brooks., Karen, C. Carrol., Janet, S. Butel., Stephen, A. Morse. & Timothy, A. Mietzner. (2013). Jawetz, Melnick & Adelberg’s Medical Microbiology 26th ed. McGraw-Hill Companies Inc. USA, pp. 1-7. Michael, Madigan., John, Martinko., David, Stahl. & David, Clark. (2012). Brock Biology of Microorganisms Global Thirteenth Edition. Pearson Education Inc. San Franscisco USA, pp. 1035-1037. Nduka, Okafor. (2011). Environmental Microbiology of Aquatic and Waste Systems. Springer Publishing New York,. pp. 8-10. SightLine Institute. (2018). ‘Are rain gardens mini toxic cleanup sites?’ http://www.sightline.org/2013/01/22/are-rain-gardens-mini-toxiccleanup-sites/. USEPA. (2017). ‘NPDES Permits & Stormwater’ https://www3. epa. gov/region9/water/npdes/stormwater-feature.html.