Y

Leakage from Sewer Lines Effluent that leaks from sewer lines is generally untreated raw sewage. It may contain industrial waste chemicals. When leaking sewer lines are located deep underground below the biologically active portion of the soil, the sewage can enter groundwater directly. This can result in the introduction of chlorides, microorganisms, organics, trace metals and other chemicals that may cause disease and foul tastes or odors in drinking water. –

http://extoxnet.orst.edu/faqs/safedrink/sewage.htm