Points and Plumes. What are the similarities and differences between point and non-point source contamination?

Transcription

1 GROUNDWATER CONTAMINATION: INVESTIGATION 5 Points and Plumes CHALLENGE What are the similarities and differences between point and non-point source contamination? MATERIALS For each group of four students 1 30-mL dropper bottle of groundwater contaminant access to sink or tub for wastewater For each team of two students 1 Chemplate 1 plastic cup of water 1 syringe 1 contaminant plume tray 2 moistened paper layers The geologic cross section of Fruitvale showed that a contaminant in water or another liquid could easily percolate down and spread out into an aquifer. The part of the aquifer that becomes contaminated is called a plume. Knowing this, you decide to find out more about how contaminants move once they have been released onto the earth s surface. You discover that substances released into the environment, whether they are harmful or not, can be classified into two categories, depending on their source. If there is a single source of the chemical, such as a leaky fuel storage tank or an overturned tractor-trailer, the contamination is called a point source. If there are a number of sources, such as millions of automobile exhaust pipes, or acres of fertilized farmland, the contamination is called a non-point source. Point source and non-point sources can produce very different plumes. Safety Note: Food coloring can stain clothes, and work surfaces. Immediately rinse any spills with water. 65

2 66 GROUNDWATER CONTAMINATION PROCEDURE Part A: Point and non-point source plumes in horizontal layers Before modeling a contaminant plume, draw a prediction in your science notebook. After modeling a contaminant plume, draw the actual shape that appears on both the top paper layer and the bottom paper layer. 1. Fill the syringe with 5 ml of water. 5 drops here 2. Place the contaminant plume tray on the tabletop and place the two paper layers, stacked on top of one another, inside the tray. 3. Squeeze 5 drops of groundwater contaminant, one on top of the other, onto the center of the filter papers as shown to the left. Sketch what you observe. 4. Gently drop 5 ml of the water in the syringe over the entire area of the filter papers as evenly as possible. 5. Wait 30 seconds, and while waiting, describe any changes you observe in the food coloring. 6. Carefully peel both layers off the plastic tray and separate them. Describe, sketch, and compare the appearance of the top paper layer and the bottom one. 7. Empty the water out of the tray into a sink or washtub. 8. Carefully and thoroughly rinse the color out of the paper layers Note: Do not squeeze the paper layers. Repeat Steps 1 8, except this time place each of the 5 drops of groundwater contaminant adjacent to, not on top of each other, in the center of the paper, as shown below.

3 GROUNDWATER CONTAMINATION: ACTIVITY 5 / MODELING GROUNDWATER CONTAMINATION 67 Part B: Point and non-point source plumes in tilted layers 13. Repeat Part A, except this time prop one end of the contaminant plume tray on your Chemplate as shown below. ANALYSIS Individual 1. Compare and contrast point source and non-point source groundwater contamination. Which type of contaminant plume do you think might be easier to clean up?

4 GROUNDWATER CONTAMINATION: ACTIVITY 5 / MODELING GROUNDWATER CONTAMINATION 69 Thinking More About Investigation 5 Predicting the Spread of Groundwater Contaminants CHALLENGE How might a contaminant spread under different circumstances in Fruitvale? MATERIALS For each group of four students 4 colored pencils The colored areas that you observed on the paper layers represented a groundwater contaminant plume. The shape and size of a contaminant plume is affected by a number of factors related to the contaminant and to the local environment. These factors include the amount of contaminant released, whether it was a point or non-point source, the For each student 1 Student Sheet 5.1, Predicting Plumes Using Geologic Cross Sections type of earth material through which the contaminant is spreading, the amount of time the contaminant has been spreading, the amount of precipitation or irrigation that has occurred during that time, and the amount and direction of groundwater flow. PROCEDURE Draw your plumes for the following scenarios on the geologic cross sections. 1. Choose a colored pencil and draw the contaminant plume you predict would occur if a 200-liter barrel of pesticide spilled at the Eat Em Up Berry Farm. 2. Choose a different colored pencil and draw the contaminant plume you predict would occur if 200 liters of pesticide had been evenly spread over the Eat Em Up Berry Farm. 3. Choose a different colored pencil and draw the contaminant plume you predict would occur if a 200-liter barrel of pesticide spilled at the orchard. 4. Choose a different colored pencil and draw the contaminant plume you predict would occur if 200 liters of pesticide had been evenly spread over the orchard.

5 70 GROUNDWATER CONTAMINATION ANALYSIS Group 1. Which of the scenarios described in Procedure Steps 1 4 are point sources and which are non-point sources? Explain. Individual 2. For each of the scenarios, explain why it is likely or unlikely to produce a contaminant plume that would include a. the water well marked X on the map. b. the Fruitvale Municipal Water Well. Note: If you like, you may provide your response in the form of a data table.