Chapter 13, Problem 139DIA

Data Interpretation and Analysis

Read CHEMISTRY IN THE ENVIRONMENT: Water Pollution and the Flint River Water Crisis at the end of Section 12.8. The table shown here features a set of data on lead levels in drinking water in Flint, Michigan, collected by the Virginia Tech team described in the box. The lead levels in water are expressed in units of parts per billion (ppb), which is a way of reporting solution concentration that is similar to mass percent. Mass percent is the number of grams of solute per 100 grams solution, while ppb is the number of grams of solute per ${10}^9$ grams solution. In other words, $\text{1}\text{ppb}\text{Pb=1}\text{g}{\text{Pb/10}}^{\text{9}}\text{g}$ solution- Examine the tabulated data and answer the questions that follow-

Sample #	Lead level first draw (ppb)	Lead level 45-sec flush (ppb)	Lead level 2-min flush (ppb)
1	0.344	0.266	0.145
2	8.133	10.77	2.761
3	1.111	0.11	0.123
4	8.007	7.446	3.384
5	1.951	0.048	0.035
6	7.2	1.4	0.2
7	40.63	9.726	6.132
8	1.1	2.5	0.1
9	10.6	1.038	1.294
10	6.2	4.2	2.3
11	4.358	0.822	0.147
12	24.37	8.796	4.347
13	6.609	5.72	1.433
14	4.062	1.099	1.085
15	29.59	3.258	1.843

Lead Levels in Flint Tap Water

Source: FlintWaterStuo‘y org (2015) JLead Results from Tap Water Sampling in Flint, MI during the Flint Water Crisis"

(a) Determine the average value of lead for first draw, 45-second flush, and 2-minute flush (round to three significant figures). (b) Do the data support the idea that running the tap water before taking a sample made the lead levels in the water appear lower? Why might this be the case?

(c) The EPA requires water providers to monitor drinking water at customer taps. If lead concentrations exceed 15 ppb in 10% or more of the taps sampled, the water provider must notify the customer and take steps to control the corrosiveness of the water. If the water provider in Flint had used first-draw samples to monitor lead levels, would it have been required to take action by EPA requirements? If the Flint water provider used 2-minute flush samples, would it have had to take action? Which drawing technique do you think more closely mimics the way residents actually use their water? (d) Using the highest value of lead from the first-draw data set, and assuming a resident drinks 2 L of water per day, calculate the mass of lead that the resident would consume over the course of 1 year. (Assume the water has a density of 1-0 g/mL.)