NAEP Science Grade 12

Category - Earth Science

A scientist is investigating the source of a petroleum contaminant in a high-yield drinking-water well. The well is deep and draws from a confined aquifer. Test wells drilled immediately to the north and to the east of the well are found to be contaminated. Test wells drilled to the south and west are not. The scientist concludes that the contaminant must be coming from the north and east. Which of the following factors would most reduce the validity of the scientist's conclusion?
  1. The contaminated test wells are on the up-gradient side of the drinking-water well where groundwater in the confined aquifer flows toward the well.
  2. The uncontaminated samples were collected when the pump for the drinking-water well was on, while the other samples were collected when it was off.
  3. The contaminated samples were collected on the same day by different people.
  4. The uncontaminated test wells were drilled to a depth that is above the confined aquifer supplying water to the drinking-water well.
Explanation
Correct Response: D. The scientist's conclusion would be undermined if the uncontaminated test wells were found to be drawing water from a different aquifer than the contaminated confined aquifer that supplies the drinking-water well. The test wells that are up-gradient from the drinking water well (A) would flow down-gradient to the drinking water well so that does not affect the validity of the scientist's conclusion. The fact that the pump at the contaminated test well was off when samples were collected (B) does not undermine the scientist's conclusion as contaminant levels would be higher if anything in a pumping well. There are strict protocols for collecting water samples that professional scientists are required to follow and the samples are processed in a laboratory, so having more than one person collect the samples (C) does not reduce the validity of the scientist's conclusion either.
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