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Water pollution — All messed up
Grade Level: 6–12
Duration: 1–2 classes
Subject: Water pollution
- Students will map and calculate the area of the school parking lot.
- Students will calculate the volume of water falling on the school parking lot.
- Students will map the route surface runoff will take to the nearest water body.
- Students will describe the roles that human activity and runoff play in urban nonpoint source pollution.
- Meter or yardstick
- Tape measure
- Trundle or measuring wheel (optional)
- Long piece of twine or rope (marked in meter or foot increments)
- Magnetic compasses
- Writing materials
- Graph paper or computer graphing program
- Local rainfall data
Urban stormwater runoff may contain sediment, debris, and harmful chemicals such as herbicides, pesticides, gasoline, oil, road salts (in northern states), and heavy metals. Heavy metals from parking lot runoff, for example, might include lead, chromium, cadmium, iron, and manganese from grinding car parts.
Runoff from large paved areas is particularly likely to contain pollutants, because none of the water or pollutants can be absorbed through the pavement. When it rains, more water runs off at a higher speed because it is not absorbed into the ground.
Potential pollutants are quickly transported from the land to waterways. This sometimes causes a phenomenon to occur called “shock loading.” This can result in fish kills and algal blooms, depending on the types of pollutants in the runoff.
Suspended materials in runoff can also absorb and store heat, which increases the water temperature. Changes in water temperature can harm aquatic life. The increased turbidity also affects the amount of dissolved oxygen available in an aquatic system.
- Explain to students that they are going to examine the impacts of runoff from the school parking lot.
- Review reading a magnetic compass:
- Hold the compass level in front of you where no metal object (e.g., a belt buckle) will interfere. Point the direction-of-travel arrow (located on the base plate of the compass) facing away from you toward a landmark or reference point.
- Next, twist the compass housing (the circular dial) until the compass needle (the red moving arrow) lies in the orienting arrow (outline of arrow on circular dial). Note: Make sure the north part of the compass needle points toward the letter N (north) on top of the compass housing.
- Read the number on the compass housing where the direction of travel arrow touches the compass housing. This is the bearing expressed in compass degrees.
- Choose a central reference point such as a flagpole or other landmark that will not change over time. Their map will be drawn in relation to this point. Note: Use only one reference point.
- Begin sketch by locating the landmark selected in the center of the paper. Then use the compass to note N, S, E, and W.
- Locate all prominent features and other relevant information on the sketch.
- For example, determine the course of the runoff and the distance to an aquatic habitat, if appropriate. Where does the water go from the parking lot? What route does it take? What is the nature of the route? What is the groundcover? Is it below or above the ground? Have students put arrows on their maps to show the direction of stormwater flow.
- Instruct them to record any evidence of potential nonpoint sources of pollutants (type and approximate location.)
- Identify points around the edge of the parking lot that they can use later as reference points when they take their measurements. Permanent features like doors, windows, trees, or signs work well. Have them clearly mark these points on the sketch.
- Have the team member with the compass stand next to the central or reference point. The recorder should be standing next to him/her with a copy of the sketch.
- The magnetic compass is used to determine angles (in compass degrees) between measurements. To use the compass, point it at one of the permanent features you previously selected and placed on the sketch. Take a compass reading and have recorder write this on the sketch next to that point.
- Measure the distance from the central point to this feature and record on the sketch.
- Repeat this procedure by choosing another point and taking a new compass reading and measurement. Use this information to make a more accurate map on graph paper later.
Note: An alternative to using this method would be to use a survey instrument or GPS (global positioning system) unit to develop a topographic map with locations.
- Place the central reference point in the center of the graph paper. Note: Be sure this point is located where two lines bisect.
- Use a protractor to mark the compass degrees from the reference point. Use the measurements on the rough sketch and the map scale chosen to determine the number of squares away from the central point each measurement should be. Mark the point.
- Connect the appropriate dots.
- Determine what area each square on the graph paper will represent using the map scale selected. For example, if the vertical side were 2 ft or m and the horizontal scale 2 ft or m, the area would be 4 square feet (ft2) or square meters (m2).
- Count and record the number of squares completely within the boundaries of the parking lot on your map.
- Then count the squares only partially within the boundaries, divide this number by two, and add to the number of complete squares.
- Multiply the total number of squares by the conversion factor determined by the map scale used. Record this information on a piece of paper.
Conversion Formula: # of complete squares + (# of partial squares/2) = total # of squares. From map scale, 1 square = Y ft2 (or m2); let Y = your choice of map scale; thus, the total # of squares x Y ft2 = area of parking lot in ft2 or m2.
- 1 ft3 = 7.4805
- 1 m3 = 1,000 liters
- 5-minute shower = 25 gallons or 95 liters
- Density of water: 1 gallon = 8.34 lbs; 1 liter = 1 kilogram
- 1 standard ton = 2,000 lbs
Example Problem Using Standard Units:
- Average annual rainfall is 100 inches (in.), and the area of the parking lot is 12,000 ft2.
- Convert the rainfall from inches to feet (12 in. = 1 ft):
100 in. (annual rainfall)/12 in. = 8.33 ft
- Multiply the rainfall by the parking lot area to find the volume of runoff:
8.33 ft (annual rainfall) x 12,000 ft2 (area) = 99,960 ft3 (annual runoff)
- Now, convert the volume of gallons (1 ft3 = 7.4805 gallons):
53,978 ft3 x 7.4805 gallons/ft3 = 747,750.8 gallons runoff
- Next, determine how many 5-minute showers could be taken with this amount of water:
747,750.8 gallons (annual runoff)/25 gallons/5-minute showers = 29,910 showers
- If you took one shower every day, how long would it take to shower this many times?
29,119 showers x 1 shower/1 day x 1 year/365 days = 81.95 years worth of showers (divide by 4 for a family of 4; = 20 years worth of showers for the family of 4, assuming one shower per day per person)
- Determine the weight of runoff: 747,750.8 gallons x 8.34 lbs/gallons = 6,228,016.3 lbs
- Convert pounds to tons: 6,228,016.3 lbs divided by 2,000 lbs/ton = 3,114 tons
- Comparison of student estimates to the information calculated.
- How does runoff relate to nonpoint source pollution?
- Review the types of pollutants that may enter a water body from a parking lot.
- What kinds of pollutants did the students observe when they took their measurements?
- What could be done to reduce nonpoint source pollution from their school parking lot?
Updated on 2-14-2014