# How much TCE is allowed by law in drinking water

```TCE Contamination and Cleanup Curriculum
How Much TCE is Allowed by Law in Drinking
Water?
Author: S. Stewart
Editor: Stephanie Nardei
Time:
30 min
Preparation
15 min
Time:
Materials:
Per student group:
Solution of green food coloring in water, 5 mL
Small beakers or cups, 6
Pipette to measure 1 mL, 1
Test tube brush
Abstract
This Explain lesson introduces students to Environmental Protection
Agency (EPA) limits on concentrations of contaminants in drinking
water. Students perform a serial dilution to produce a 5 ppb solution of
food dye, a simulation of the allowed concentration of TCE. Students
discover at this low concentration, detection of the contaminant is
difficult. This means cleaning up all of a contaminant is not possible
since detection methods cannot tell when the contaminant is
completely gone.
Purpose
This Explain lesson has students visualize the EPA limit on
concentration of TCE allowed in drinking water by creating an equivalent dye concentration
through serial dilution.
Objectives
Students will be able to:
1. Perform a serial dilution.
2. Calculate concentrations of dilutions.
3. Explain why EPA standards are above 0 ppb (why we can’t get rid of all the toxins).
National Science Education Standard:
Content
Teacher Background
The unit ppb is measured in micrograms solute per liter total solution (solute plus solvent).
Parts per billion = ppb = mass in ug of solute
volume in L of total solution
Example: 8 ppb TCE = 8 ug TCE
1 L solution of
TCE Contamination and Cleanup Curriculum
water and TCE
Prepare initial green dye solution ahead of time by adding green food dye to tap water. Color
should be deep green. Use at least five drops dye per 100 mL water.
Related and Resource Websites
Council on water quality: http://www.councilonwaterquality.org/
ATSDR Toxicological Profile for Trichloroethylene (TCE)
http://www.atsdr.cdc.gov/toxprofiles/tp19.html
Activity
1. Teacher explains that EPA sets limits for concentrations of contaminants allowed in drinking
water. Usually these limits are measured in parts per billion (ppb), because the amounts of
contaminants that can affect living things are often very tiny.
a. Teacher explains to students that the green dye represents the contaminant TCE.
They will be diluting it to the concentration allowed in drinking water by the EPA, in
order to visualize 5 ppb, the EPA standard for TCE.
2. Teacher explains how to make a serial dilution.
3. Students start with 5 mL green dye in 95 mL water, and then continue by transferring 1 mL of
the first solution into 99 mL water, and so on. See student lab sheet.
4. Students complete student lab sheet.
Closure
Teacher prompts discussion of questions on lab sheet.
Embedded Assessment
Assess the student responses on student lab sheet.
Homework
N/A
```