And every one of them should be tested:
Duke Energy officials have identified 830 private and public drinking water supply wells near the company’s 32 coal ash storage ponds in North Carolina, according to an initial survey the N.C. Department of Environment and Natural Resources released on Friday. Duke Energy conducted the survey to meet a requirement of the Coal Ash Management Act, which recently became state law.
DENR staff members are reviewing the surveys to determine which wells should be sampled first, and how frequently and how long sampling should continue. The determination will be completed based on the hydrologic potential for impacts to the drinking water wells. The sampling plan can be amended as additional information is gathered about the flow of groundwater and the extent of any detected contamination.
One of the best (only?) ways to determine the flow of groundwater is to test for the migration of specific elements, and the easiest way to do that is to, you know, test all the fricking wells. You can speculate about the flow by examining (what we believe) is the nature of the sub-strata, but computer models won't be much consolation to a family exposed to contamination.