Did the study results indicate a correlation between arsenic concentrations in bedrock wells and bedrock geology?
Yes. The 478 bedrock well water samples collected for the study were distributed amongst the many different types of bedrock geologic units that are mapped in the study area. The results indicated a correlation between the probability of exceeding the public drinking water standard for arsenic and the type of bedrock. The study also indicated a strong correlation between arsenic concentrations and the well’s proximity to the Clinton-Newbury fault zone. The Clinton-Newbury fault zone extends from near the eastern end of the Massachusetts and Connecticut border in the south to the Merrimack River Valley in the northeast. The USGS predicted the estimated number of wells within the study area expected to exceed the arsenic standard by multiplying the probabilities obtained from the sample results by the estimated number of wells in the area. This method resulted in a prediction that approximately 5,700 residential bedrock wells out of 90,000 in the study area may have arsenic concentration
