While studying for the AP® Environmental Science exam, you have probably run across the subject of water pollution, but you might not have a through understanding of what water pollution is, why it is important for the APES exam, and how to answer questions about water pollution on the AP® Environmental Science exam. In this AP® Environmental Science crash course review, we will thoroughly explain water pollution, giving you everything you need to know for the AP® Environmental Science exam.

What is Water Pollution?

First, you may be wondering what water pollution is. Water pollution is defined as any chemical, biological, of physical change in water quality that causes a harmful impact on living organisms. There are two different categories of water pollution. The first is pollutants that cause health problems and the second is pollutants that disrupt ecosystems.

Water pollution can be natural or it can be caused by humans. Natural sources of water pollution include sediment caused by erosion and naturally occurring oil seeps. Water pollution caused by humans includes infectious agents, wastes that require oxygen, inorganic chemicals, organic chemicals, plant nutrients, and heat.

Identifying, Regulating, and Cleaning Up Water Pollution

In order to effectively clean up water pollution, the source of pollution first needs to be identified. There are two different types of pollution sources: point and non point. Point sources release pollution from a specific identifiable location. Examples of point sources include power plants, factories, coal mines, or other locations. Point sources are relatively easy to identify, regulate, and monitor.

Non point locations have no specific point of origin. This makes them significantly more difficult to regulate and monitor. Examples of non point sources of pollution include runoff from fields, lawns, parking lots, and other areas. Precipitation such as snow may spread pollutants through the environment when melts. The single biggest source of ocean pollution is runoff from terrestrial sources.

It is also important to note that non point sources of water pollution can also come from the air. Pollutants can be carried by air currents and then released through precipitation. Pollutants deposited in this manner can originate from thousands of kilometers away. This great distance obviously makes it impossible to regulate or monitor these pollutants.

Groundwater Pollution

Groundwater is a highly important source of drinking water in the US. Nearly 50% of people get their drinking water from an underground aquifer. It is commonly assumed that natural processes in aquifers clean any contaminated water, but overuse has stressed these reservoirs, which can result in groundwater pollution.

Fertilizers and pesticides are common pollutants of groundwater, particularly in farming communities. Nitrates from fertilizers commonly exceed safe levels in rural water supplies. The largest source of groundwater pollution is chemicals and wastes from agriculture. Residence time, the amount of time water stays in an aquifer, can be very long, meaning that some pollutants can be very stable underground. The high expense of pumping water out of an aquifer to clean it means that contaminated water does not always get cleaned.

Sewage

Sewage is a significant source of water pollution and can easily create health related problems as a result. Pathogenicity is the level of severity and virulence of illnesses that biological agents cause and varies by the biological agent. The EPA sets limits on the amount of common biological agents that can be present in water supplies. In the following sections we will discuss ways that water-borne diseases can be prevented.

Septic Systems

While human and animal wastes are used in some cultures as a fertilizer for crops, they can also introduce disease causing pathogens into the food supply. As a result, septic systems were developed as a way to improve public health, particularly in rural areas. In a septic system, water drains into a septic tank. Solids sink to the bottom while oils and other lighter density items rise to the top. Solids decompose in the bottom. Extra liquid is then channeled out through drain pipes which are surrounded by gravel. Excess water then evaporates. Septic systems must be pumped occasionally and the effluent must be taken to a treatment plant.

Municipal Sewage Treatment

In a municipal sewage system, there are typically three levels, the first being primary treatment. In the primary treatment stage, raw sewage enters the treatment plant and large solids are separated from general waste. Screens remove large debris and small objects. Sand and gravel settle in one tank and the waste stream continues into a different tank where about half of the organic solids settle to the bottom and become sludge.

Next is the secondary treatment phase where dissolved organic compounds are biologically degraded. This process starts when the primary treatment phase material flows through an aeration tank, this is sometimes referred to as activated sludge process. A bacteria-rich slurry is mixed with the material from primary treatment. Air is then pumped into this mixture which encourages the bacteria to grow. The amount of air required is determined by the biological oxygen demand, defined as the amount of oxygen required by anaerobic organisms to decompose the organic matter in water. The bacteria then break down the organic matter. This results in sludge and water. If the sludge is not contaminated with heavy metals, it can be used as fertilizer. If it has been contaminated, it has to be disposed of properly at a large expense.

The third step of treating municipal solid waste removes plant nutrients, including nitrates and phosphates that are still in the waste from the second step of treatment.

Once treated, waste water is free of pathogens and organic matter, but may contain high levels of inorganic nutrients. If it is released into surface waters, this can cause algal blooms or eutrophication, the natural nutrient enrichment of a lake. This nutrient overload can lead to high growth of algae and other microorganisms.

Clean Water Legislation

The Clean Water Act, passed in 1972, was passed to return all surface waters in the United States to “fishable and swimmable” conditions. Clean water thus became a national priority. Specific point sources of pollution are required to acquire permits and develop technology to control their output in order to be in compliance with the Act. The Act also requires the best available and economically achievable technology for limiting the discharge of toxic substances and allows no discharge of 126 toxic pollutants.

Through the efforts of the Clean Water Act, conditions in surface water in the United States have dramatically improved. All water is not yet swimmable and fishable, but there have been significant improvements and significant allocation of federal and state monies to build municipal sewage treatment facilities.

The Safe Drinking Water Act regulates drinking water in municipal and commercial systems. It is criticized as having too loose of regulations in rural areas and allowing the presence of herbicides and pesticides in rural drinking water.

The Great Lakes Water Quality Agreement was signed between the US and Canada in 1972. This agreement focuses on cleaning up the Great Lakes and has made great strides in improving the water quality in the Great Lakes.

Water Pollution on the AP® Environmental Science

On the AP® Environmental Science exam, you will encounter questions about water pollution both in the multiple choice and extended response sections of the exam. In the multiple choice section, you simply need to be able to recognize the correct answer from a list of options. Having a general understanding of water pollution is enough to correctly answer these questions.

In the free response section of the APES exam, you will need to apply your knowledge of water pollution to specific situations. This requires a greater understanding of water pollution and its effects. To prepare you for free response section, we will walk through a free response question about water pollution from the 2014 AP® Environmental Science exam. Let’s get started.

2. Like many communities, Fremont has a combined sewer system that collects both sewage and storm water. When storm water runs into storm drains that connect to the city’s sanitary sewer system, the storm water and sewage flow together to the Fremont Waste water Treatment Plant (FWTP). During a major storm event, however, the combined volume of storm water and sewage may exceed the plant’s capacity, and the overflow bypasses the FWTP. The untreated overflow is discharged into Fremont Creek along with the treated waste. Recently parts of Fremont received 5 cm of rain in 60 minutes. The storm caused widespread flooding in the northeast section of town. Especially hard hit was the Shoppes at Fremont shopping center. Use the data from the table below to answer the questions that follow. Show all calculations.

(a) Identify TWO specific pollutants in storm-water runoff that degrade the quality of surface water.

(b) Calculate the volume of water (in { m }^{ 3 }) that runs off the Shoppes at Fremont parking lot after a 5 cm rainfall event. Assume that all the water that falls on the parking lot runs off.

(c) Calculate the volume of storm-water runoff (in { m }^{ 3 }) generated in all of Fremont by the 5 cm rainfall event. Assume that only the impervious surfaces generate runoff.

(d) Assume that all the runoff that you calculated in part (c) is captured by the storm sewers in one day.

Calculate the volume of untreated water (in { m }^{ 3 }) that bypasses the plant as a result of the storm. (Note that the plant still receives 5,000 { m }^{ 3 } of domestic sewage per day.)

(e) Describe TWO ways that the volume of storm-water runoff can be reduced.

(f) Describe one environmental problem (other than pollution from runoff and from untreated sewage) that results from having extensive paved areas.

This free response question is worth ten points in total. In part (a), you can earn two points- one for each specific pollutant. Some correct answers to this part include nitrogen, phosphates, pesticides, herbicides, trash, and detergents.

In part (b) of this question, you can earn a total of two points. One is for setting up the math correctly and one is for arriving at the correct answer. In order to get credit for having the correct answer, you need to show your work. The image below shows a correct set up for this question as well as the correct answer.

200m \times 100m \times 0.05m = 1,000{ m }^{ 3 } or 1 \times { 10 }^{ 3 } { m }^{ 3 }

In part (c) of this question, you can also earn two points. It is important to note that you are to assume that only impervious surfaces generate runoff. Because of this, you need to ensure that you multiply the area of Freemont by 0.20 to account for the percentage of Freemont that is composed of impervious surfaces. Your math should look something like this.

5cm \times \dfrac { 1m }{ 100cm } \times 10 { km }^{ 2 } \times \dfrac { 1 \times { { 10 }^{ 6 } } { m }^{ 2 } }{ 1 { km }^{ 2 } } \times 0.20 = 100,000 { m }^{ 3 }

or 1 \times { 10 }^{ 5 } { m }^{ 3 }

In part (d) of this question, you can receive one point for showing your work and achieving the correct answer. In part (d), it is especially important to note that the plant still receives 5,000 { m }^{ 3 } of domestic sewage per day. If this amount is not accounted for in your math, your answer will be incorrect. Your work should look something like this, with the correct amount of water that bypasses the plant being 95,000 { m }^{ 3 }.

100,000 { m }^{ 3 } + 5,000 { m }^{ 3 } - 10,000 { m }^{ 3 } = 95,000 { m }^{ 3 }

In part (e) of this question, you can earn two points, one for each way to reduce the volume of storm water runoff. Some correct answers to this part include the installation of ponds or other basins to hold runoff water, installing rain barrels or other devices to store water, and decreasing the amount of impervious surfaces in Fremont.

In part (f) of this question, one point is available for correctly naming an environmental problem resulting from having extensive paved areas that is not related to untreated sewage or pollution from runoff. Some correct answers to this question include increased flooding, groundwater depletion, and habitat destruction.

In this AP® Environmental Science crash course review, we have reviewed everything you need to know about water pollution for the APES exam and walked through a sample free response question about water pollution from a previous AP® Environmental Science exam.

Looking for AP® Environmental Science practice?

Check out our other articles on AP Environmental Science.

You can also find thousands of practice questions on Albert.io. Albert.io lets you customize your learning experience to target practice where you need the most help. We’ll give you challenging practice questions to help you achieve mastery of AP® Environmental Science.

Start practicing here.

Are you a teacher or administrator interested in boosting AP® Environmental Science student outcomes?

Learn more about our school licenses here.