Process of Science: Discovering Flint’s Water Crisis 3 of 3 We now know that the

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Process of Science: Discovering Flint’s Water Crisis

3 of 3

We now know that the water coming out of many Flint residents’ taps also contained the metal lead, which can act as a neurotoxin and negatively affect fetuses’ and children’s brain development. Many locations in Flint had lead pipes, and corrosive pollutants in the Flint River water flowing through those pipes caused lead to leach from the pipes into the water.

The Michigan Department of Environmental Quality (DEQ) tested the water in Flint during 2015. Their results did not indicate a significant problem with the water, and therefore, the public was not warned against drinking the water.

Part A - Scientific method: The importance of sample size

The Lead and Copper Rule of the Safe Drinking Water Act states that if more than 10% of homes test above 15 ppb (parts per billion) for lead, a city is legally required to take corrective action and warn residents about lead in their water. The DEQ reported that less than 10% of homes in Flint had high lead levels, and therefore no action was taken.

Many people in Flint didn't trust the DEQ results given other problems with the water and the symptoms they were experiencing. One resident contacted an expert on lead in municipal water, and the expert questioned if the sample size in the DEQ study was large enough. Sample size refers to the number of samples collected and tested in a particular study.

With the expert’s help, the community initiated a lead testing project they called the Flint Water Study (FWS). They sampled many more locations than the DEQ did, and they arrived at a far different conclusion.

This table shows the FWS results compared to the DEQ results. (Flint is divided into 9 areas called wards, and water samples were taken from each ward.)

Drag the numbers and terms on the left to answer the questions on the right. Not all terms will be used.

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2

4

9

19

69

270

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1. The DEQ study had a sample size of ___ and the FWS had a sample size of ____ .

2. The FWS had a sample size that was about ___ times larger than the DEQ study.

3. While the FWS found all 9 wards to have 10% or more of the homes with high lead levels, the DEQ found only ___ wards to have 10% or more of the homes with high lead levels.

4. Overall, the DEQ study found about ____ % of the houses sampled had high lead levels; the FWS found about % had high lead levels.

5. Based on the difference in their samples sizes, the results from the FWS are ____ reliable than the results from the DEQ.

Ward # Number of samples taken by DEQ Number of DEQ samples above the 15 ppb high lead standard Percentage of DEQ samples above the 15 ppb high lead standard Number of samples taken by FWS Number of FWS samples above the 15 ppb high lead standard Percentage of FWS samples above the 15 ppb high lead standard 1 6 0 0% 30 3 10% 2 3 0 0% 24 6 25% 3 4 0 0% 22 4 18% 4 4 0 0% 35 4 11% 5 7 2 29% 18 5 28% 6 13 1 8% 32 9 28% 7 15 1 7% 39 11 28% 8 9 0 0% 29 6 21% 9 8 2 25% 41 8 20% Total 69 6 ? 270 52 ? ATER Photo credit: artzenter. Shutterstock

Explanation / Answer

1. The DEQ study had a sample size of 69 and the FWS had a sample size of 270.

2. The FWS had a sample size that was about (270/69) = 3.91 times larger than the DEQ study.

3. While the FWS found all 9 wards to have 10% or more of the homes with high lead levels, the DEQ found only 2 wards to have 10% or more of the homes with high lead levels.

4. Overall, the DEQ study found about (6/69) x 100 = 8.69% of the houses sampled had high lead levels; the FWS found about (52/270) x 100 = 19.25 % had high lead levels.

5. Based on the difference in their samples sizes, the results from the FWS are 270/69= 3.91 times reliable than the results from the DEQ.

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