 One of our concerns in environmental science and in environmental engineering is dealing with runoff pollutants. Now what is a runoff pollutant? Basically a stormwater runoff is any water that kind of moves over the surface of the land and it's a natural part of the hydrologic cycle. Notice with hydrology we have precipitation, rain that comes down and some of that rain will filter into the ground, some of it will evaporate and some fraction of it will accumulate and run across the surface and end up in rivers and streams. But notice we can change the normal conditions that occur naturally by adding impervious surfaces, roofs and roads and things like that that prevent some fraction of the water from infiltrating and change perhaps how much evaporates or how much is absorbed into plants and transpires leading to a significant more amount of runoff, a significant larger amount of water that runs over the surface. And the thing that happens is as more water runs over the surface more of what is sitting on the surface is likely to end up in the water. So we have a number of different pollutants that can actually runoff in stormwater. Okay we can have erosion, we can have solids and sediments that are dirt that results from erosion. We can have different nutrients that result from the erosion of soils that have organic material in them. We can have metals which might result from little bits and pieces stuff that's accumulated from our various mechanical workings. We can have oil and grease. There are often living bacteria that result that that are sitting somewhere that can get mixed into the water as part of runoff. You can have pesticides and herbicides and even interestingly temperature can be considered a pollutant that if you have a very hot surface and the water falls upon it the water will absorb a significant amount of that temperature and heat and then flow away taking that heat with it and you'll have very warm water that can ultimately affect an aquatic ecosystem downstream. Most of these kind of pollutants cannot be traced back to one source or one location. They are often called what we call non-point source pollutants. That there are many different small sources of these things and particularly things like nutrients or suspended solids they're ubiquitous. They're pretty much anywhere that the rain will fall so that the rain can pick up little bits of those things at any location in its travels. We can measure these things. We've actually spent some time and sometimes studying and figuring out how much for example nutrients how many how many much nutrient might be picked up from non-point source depending on how different land with the different uses of land are. For example if you have cropland you have a certain amount of nutrient that will be dissolved that will actually get dissolved in the water and move with the water as it accumulates and flow and you'll have a different amount that will actually be attached to various sediments and if the sediment itself erodes and you have certain amount of sediments little particles of sand or clay that travel with the water a certain fraction of that sediment will be a nutrient and we're concerned about nutrients because while they have a definite purpose and they're being recycled as part of the biological cycle if those nutrients are transported away from the forest floor for example and into an aquatic environment they might create a major imbalance by providing more nutrient than the aquatic environment is of is used to having and you have things like algal blooms where the algae in a system will suddenly say hey I have a whole bunch of extra phosphorus and nitrogen and be able to create much more algae than the system is able to maintain and so we will often consider nutrients which are good in some contexts to be negative or a pollution in other contexts if they end up being in significantly larger amounts so just like we talked about non point source pollution we can also consider sources of pollution direct sources of places where we will contribute things that we don't necessarily want in the water a pretty standard location is landscaping and lawn care many people will take care of their plants but in order to keep the plants looking nice they will either add excessive amounts of nutrients that make the plant thrive in its environment but also the extra nutrients end up in the water system also pesticides to keep the bugs off of these plants it's pretty typical that they'll be added and it will kill bugs there but then those same poisons end up in the water system pest control again pesticides being applied at different locations and usually we don't apply pest control over larger locations we have usually applied directly to certain flowers or certain crops that we wish to keep the kill the bugs on occasionally we have problems where we have spills where there is some sort of accident and we have some something a paint or some sort of grease or some sort of oil that leaks from something that it was supposed to be contained in okay and again these are considered point source locations sometimes these locations are something that stays and sits in one place for example if we have leakage of some waste that was stored somewhere underground and it begins to leak and continues to pollute other times we'll have a very short term leakage but in a case of something like this it might you might be able to clean up the stuff that's on the surface but some of the stuff goes into the ground and then anytime any water flows through it it would actually take some of the pollution and move with it pet waste is a major source of pollutants any pet waste that's left behind is going to potentially end up in the water system along with the nutrients that are within it vehicle and equipment maintenance when you work on your car anything that actually happens it spills out of your car often there are rules and in ways that you can collect it safely but occasionally things will spill for example on the floor of the garage and then if the garage is cleaned out maybe by spraying water across it that water ends up flowing down into the larger system and these are again sources of undesirable pollutants street cleaning again a similar situation the things often the things that are being that are being cleaned will be collected but sometimes it's just being brushed up or moved so that it will flow away and that ends up in our water system a pretty big contributor in northern climates where there's a need for melting ice is the use of road salt there are actually certain regions in northern areas where you're not allowed to use road salt because it's directly affecting a source of drinking water for example and they have to minimize the use of road salt or eliminate it all together in certain areas when you wash your car often when you wash your car you'll have the flow of the various soaps that you use and everything that you wash off your car very rarely is any of this collected now in green and responsible car washes they will collect and process the water differently and not allow it to end up in storm water but that's rarely done in sort of normal locations most of you can probably think about a place in your home where you have things various fluids that are used for cleaning or for removing something or for gluing something and then the question that becomes what happens when you're done with those things where do they go how are they disposed of how what happens when they're spilled well if they're thrown into a dump somewhere eventually the can that they're in might erode might degrade and result in some of these things leaking into the system so dealing with waste materials and those hazardous materials and preventing them from getting into our water system is actually sort of a critical the critical idea and these are again another common point source of pollution the question is locating things when they are disposed of so how do we go about treating it well we can't capture all water unlike capturing the water that comes out of our homes and processing it with a variety of physical and chemical processes we can't necessarily do that with all storm water we have a number of strategies and most of the strategies deal with creating biological buffers vegetative buffers of different forms which will slow down the water first of all and sometimes catch or capture things that we do not want elsewhere often it'll catch and capture some of the nutrients sometimes it will simply slow it down and allow whatever the if it's a poison or if it's something like that to degrade to the point where it's no longer dangerous or to be sort of contained in that area and this is a pretty standard process and you'll notice that whenever new parking lots are built or new roadways are built they will almost always include a substantial amount of vegetation both within and around the periphery that allows some of the storm water to run off and or capture some of the storm water or some of the the runoff in a way that allows it to infiltrate and keep some of the nutrients and pollution in that general area people have begun to do this in residential areas where they actually create recognize that there are low lying areas on their property and they will often plant plants that thrive in those low lying areas and that allow the water to sit there accumulate and then eventually either evaporate or transpire and sort of prevent some of the nutrients and other pollutants from flowing away and polluting the rest of the watershed there are larger scale projects like this whenever there's a housing development for example that's created usually there are laws and many municipalities that require different types of areas for water to flow into in this case the one in the upper left is a bio retention basin which is there to sort of again keep the water there and allow the biology to deal with some of the water and there are other sort of things here designed wetlands okay areas that are meant to sort of contain the water for a while or sediment basins or underground collection you'll see a lot more projects like this and that's really a key thing for what environmental engineering is doing is to take advantage of some of the normal transport processes the normal biological processes to help us deal with and treat runoff and the pollutants associated with runoff