When it rains excessively, a combined sewer system may not be able handle the volume of water, and some of the combined runoff and raw sewage will overflow from the system, discharging directly into the nearest waterbody without being treated. This combined sewer overflow (CSO) is considered point source pollution, and can cause severe damage to human health and the environment.
These images show the difference between a combined sewer overflow system found in many older cities, and a sewer system where sanitary and stormwater are completely separated. During heavy rains combined sewer overflow systems mix raw sewage with rainwater runoff and discharge it directly into the nearest waterbody without treatment. Photo: Washington DC Water and Sewer Authority.
Unregulated discharges from point sources can result in water pollution and unsafe drinking water, and can restrict activities like fishing and swimming. Some of the chemicals discharged by point sources are harmless, but others are toxic to people and wildlife. Whether a discharged chemical is harmful to the aquatic environment depends on a number of factors, including the type of chemical, its concentration, the timing of its release, weather conditions, and the organisms living in the area.
Large farms that raise livestock, such as cows, pigs and chickens, are other sources of point source pollution. These types of farms are known as concentrated animal feeding operations (CAFOs). If they do not treat their animals' waste materials, these substances can then enter nearby waterbodies as raw sewage, radically adding to the level and rate of pollution.
Large farms that raise livestock are often referred to as concentrated feeding operations (CFOs). These farms are considered potential point sources of pollution because untreated animal waste may enter nearby waterbodies as untreated sewage.
In addition to the highly variable locations of water pollutants, the impact of these pollutants can differ considerably depending on the characteristics of the area in which they occur. Locations with high populations of people, endangered species, important wildlife habitat, or popular recreation opportunities will generally have higher social costs from a given level of pollution than less densely populated or less sensitive environments.
Generating a comprehensive estimate of the social cost of water pollution, even for a single pollutant for a single region or watershed, will require identifying the sources of pollution, how those pollutants move through the environment, the impact on ecosystem services, and how the services are valued by people. In short, it is not very meaningful to talk about a single social cost of water pollution except on a conceptual level.
A Conceptual Diagram of the Social Cost of Water Pollution: When a pollutant is released into the environment, the resulting social costs will depend on how far that pollutant travels and what the impact of the pollution is on downstream water quality (changes in physical, chemical, and biological indicators). In turn, the change in social costs from the new levels of pollution depends on how the reduced water quality affects ecosystem services in the downstream locations (i.e., changes to services that people care about such as clear water for swimming, safe drinking water, or clean water that supports a variety of native flora and fauna) and the loss in value from the services among those affected by the reduction. A simple conceptual diagram is depicted on the opposite page. This figure sketches the pathways through which pollutants ultimately affect humans and contribute to the social cost of water pollution.
At the top of the schematic is the initial discharge of pollution into the environment. The social costs of this will depend on the location of the discharge, as well as the quantity and type of pollutant. A few examples include chemicals, suspended solids, and toxins. Depending on the pollutant and current state of the environment, changes will occur in physical, chemical, and/or biological indicators. These changes can occur in local waterways or far downstream, depending on the water system into which the pollutants are discharged.
How Important is Water Quality?: Although researchers and government agencies have made great strides in understanding the economic value of water quality, we still lack defensible estimates of the social costs of water pollution and how they vary across space. Recent research has highlighted the fact that many water pollution regulations in the United States fail a cost-benefit analysis. This may be due to several reasons, including, as highlighted above, an inadequate accounting of the costs of water pollution. A number of basic facts about how people use water and how closely water is intertwined in our daily lives suggests that these costs may be extensive. Although some facts are available, more research is needed to translate these facts into actual estimates of damages.
Most academic and government studies of the benefits of water quality improvements have focused on the recreation component of the social cost of water pollution. Among a number of likely reasons for this, the sheer magnitude of households participating is likely to generate significant benefits. In addition, the primary federal legislation governing water quality in the United States, the Clean Water Act, has as one of its primary goals to make all rivers fishable and swimmable.
Final Thoughts: Policy discussions related to water quality would benefit from estimates of the social cost of water pollution that are comprehensive but still consider the location of affected water sources. To develop such metrics at the national or subnational scales, it is necessary to highlight the concept of the social cost of water pollution and identify some of the information already available from prior research. Major efforts by academics, governments, and others have pushed forward our understanding of the social costs of carbon and local air pollutants, but we lack similar comprehensive estimates at a national scale for water. Obtaining such estimates would help guide policy recommendations for where resources could be targeted best, in order to achieve the highest rate of return on efforts to control water pollution. As we spend tens of billions of dollars each year on these endeavors, understanding the benefits, not the least of which is human health, is as important as ever.
Constant waterborne commerce at the Port of Houston, among the busiest in the United States, means accidents like this tallow spill in the Houston Shipping Channel are inevitable. The world's shipping lanes and ports are epicenters of manmade pollution, where accidental spills and deliberate dumping are commonplace.
One of the most visible and obvious signs of water pollution is an oil sheen. Seeing a shiny, translucent reflection on a pond or lake just looks wrong - but did you know that not all sheens are the result of pollution? Here is what you should know about sheens, how to tell the difference between naturally occurring sheens and those that are the result of pollution, and what you should do if you discover a sheen caused by pollution.
A sheen is "an iridescent appearance on the surface of the water." The iridescent, lustrous appearance could be caused by a petroleum spill finding its way into the water - or the sheen could be a naturally occurring result of iron bacteria. Iron bacteria are small living organisms which naturally occur in soil, shallow groundwater, and surface waters and are harmless to the environment. Petroleum sheens on the other hand are harmful to the environment and should be reported to the Pennsylvania Department of Environmental Protection (DEP). But how can you tell the difference between the two and what should you do if you discover a sheen caused by pollution?
The most important thing we all can do to help protect our environment is to not be a source of pollution. Preventing sheens caused by pollution requires safe transportation and disposal of petroleum materials. Oils (and other non-water soluble liquids) should not be dumped into sanitary drains, storm drains or streams. In the workplace, items requiring proper disposal range from lubricants and chemicals used in manufacturing to cooking oil used in restaurants. At home, care must be taken to properly dispose of used motor oil, oil-based paint and so on. DEP's website offers helpful information on how to properly dispose of items such as these.
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