In 1995, Pacifica identified six wastewater treatment alternative projects for upgrading its wastewater treatment capacity. The city ultimately chose construction of a new plant and a "polishing" wetland for the treatment of tertiary effluent in the lower reach of Calera Creek within and adjacent to an abandoned rock quarry.
A primary goal in the development of project alternatives was to maximize the benefits of wastewater treatment and minimize the cost of these benefits. Specific benefit directives included production of reclaimed water, improvement of the ocean environment that now receives the effluent, wetlands restoration and expansion of recreational uses.
In its exploration of the six project alternatives, the city focused on identifying approaches that would: comply with water quality laws; have the potential for implementation; account for social and economic constraints; and would be accountable for future development of the City of Pacifica. The city then screened each of the alternatives with respect to each's capital and annual costs. The apparent best alternative was to construct a sequenced batch reactor (SBR) and tertiary units in the northeast end of the Calera Creek quarry (the sequenced batch reactor is the preferred treatment technology because it is mechanically simple and produces high quality effluent in a minimum number of steps).