Are these boreholes or ...

Are these boreholes or encases wells or springs? It is necessary to locate the sources of contamination and fix them. But in the short term it is essential to disinfect the wells. It is the simplest quickest and least expensive way to respond.  The standard technique for disinfecting wells is to add the appropriate amount of chlorine (as hypochlorite) to flush the system, and monitor regularly to determine whether the contamination has returned. See the American Water Works Association standards for new wells and well rehabilitation.