Environmental study of the alternatives for the sewer system of a small coastal community in the Bay of Biscay

Zumaia is a small tourist community on the northern coast of Spain, situate d along the estuary of the Urola river. This ecosystem has been affected by urban discharges coming from the villages surrounding the estuary. Accordi ng to the 91/27T European Community Directive, regarding wastewater treatme nt, this situation should be addressed in order to achieve the quality obje ctives established for the restoration of the natural values of the area. T he local Water Authorities of the Basque Country (Spain) have adopted an in tegrated model for the design of the sewer system of this community. The mo del was developed specifically for the study of coastal sewerage under domi nant wet weather conditions and includes: 1) Establishment of the site spec ific statutory requirements and environmental objectives: 2) Design of sewe r system components with specific reference to influences on marine water q uality; 3) Development of monitoring programs. The construction of a sewer pipe alongside the river to collect the foul an d the stormwater flow will prevent a large proportion of the discharges of contaminants into the receiving waters. However, the presence of overflows in the system during storms leads to the release of a great deal of polluta nts into these waters. The main problems related to this type of discharge in the littoral zone arise from the bacteriological contamination of the ba thing waters and from the oxygen depletion over the estuary. These two topi cs have been the predominant issues conditioning the consideration of diffe rent schemes of management of the sewer system. The aim of this paper is to analyze, from an environmental point of view, the structural and functiona l scheme considered for the sewage management of this community. (C) 1999 P ublished by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved .