AN ASSESSMENT OF THE IMPACT OF INLAND SURFACE-WATER INPUT TO THE BACTERIOLOGICAL QUALITY OF COASTAL WATERS

The introduction of ultraviolet disinfection in Jersey has achieved si gnificant improvements in water quality. However, bathing waters in St Aubin's Bay and shellfish flesh have failed to comply with microbial standards. Streams and seepages from coastal. structures were investig ated as potential indicator organism sources (total and faecal colifor ms, faecal streptococci). Seepages were an unimportant bacterial sourc e as concentrations were low. Geometric mean concentrations in streams were up to four orders of magnitude higher than in final sewage-treat ment works effluent, and concentrations increased significantly at hig h stream discharge. Rainfall-induced pulses of poor water quality occu rred two to three times per week during the 1993 summer season. Natura l discharges from island catchments thus contribute significantly to t he bacterial load received at the coast, especially during high flow e vents. These observations have implications for other UK and European schemes using tertiary disinfection technology to attain water quality targets in coastal waters.