SCIENCE LITERACY WORKING WITH DATA

Methane (CH4) can normally occur in upper levels of the soil because it is produced by bacteria and can accumulate to high levels over time in some areas. Ethane (C2H6), however, is only created under high temperature and pressure, such as might occur deep underground at the site of shale gas deposits. Robert Jackson and colleagues suspected that methane contamination in water from wells in northeastern Pennsylvania might be linked to nearby fracking gas wells. For their study, they asked the question “Does being close to fracking gas wells increase the likelihood that the water will contain methane or ethane contamination?” They measured the amounts of methane and ethane in 141 water wells close to and far away from fracking wells. Look at Graph A and Graph B and answer the following questions.

Interpretation

Question 19.17

What was the hypothesis that these researchers tested in this experiment?

The closer a gas fracking well is to a water well, the higher the methane and ethane contamination of the water will be.

Question 19.18

For each chemical (methane and ethane), identify the relationship between its level in well water and the water well’s proximity to fracking wells. Do these relationships represent causation or correlation? Explain.

Methane and ethane contamination of water is more likely to occur in wells that are close to fracking gas wells than those further away from the fracking wells. In general, the closer the water well to the fracking well, the higher the contamination. This represents a correlation. Since this is an observational study with no before and after data and no ability to control other variables, fracking wells cannot be identified as the cause of the contamination but this data does suggest they might be.

Question 19.19

How many water wells had levels of methane that fell within the range where mitigation should be considered? How many fell within the range where mitigation is strongly recommended?

Eleven water wells are in the range where mitigation should be considered; 12 fell in the range where mitigation is strongly recommended.

Advance Your Thinking

Question 19.20

Do all wells that are very close to a fracking well (within 0.5 kilometer) show evidence of methane or ethane contamination? (Are there any close-by wells with no contamination?) Does this negate the conclusion that methane and ethane contamination are due to fracking in the area?

The majority of wells actually had no methane or ethane contamination. (141 water wells were tested and only 44 showed methane levels above 0; 15 showed the presence of ethane.) This does not negate the conclusions of the study. Some of the fracking wells might be more likely to leak fluids into the ground or groundwater than others.

Question 19.21

Why might methane be high in water even in areas that are not close to fracking wells?

This could represent methane naturally present in the soil or water.

Question 19.22

Why did researchers need to measure ethane in water wells to strengthen their conclusion that the water contamination is linked to fracking activity?

Ethane is not naturally present at the level of groundwater but it is present at the depths where fracking occurs and will be present in the fracking fluid brought up in the fracking procedure. Its presence in well water suggests that there is leakage from well pipes or spillage of fracking fluid on the surface of the ground since this is the only known source of the chemical.