History

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).

Wetland Restoration Goals

The primary goal of the Calera Creek wetland restoration is to improve its riverine waters and wetland ecosystem functions, including hydrology, water quality, plant community maintenance and habitat/faunal support. A secondary goal of the project is to create habitat for the threatened California Red-Legged Frog and the endangered San Francisco Garter Snake (thamnophis sirtalis tetrataenia) including optimal conditions for colonization by the prey species of the endangered snake.

Wetland Restoration Objectives

The project objectives for the restoration of wetlands associated with the lower reach of Calera Creek are: to restore the lower reach of Calera Creek by removing the stream from its currently ditched channel and placing it in a restored stream channel; to restore the adjacent riparian and depressional wetlands associated with the lower reach of Calera Creek; to increase the level of ecosystem function of the wetlands associated with lower Calera Creek; and to provide habitat for the threatened California Red-Legged Frog and the endangered San Francisco Garter Snake.

The setting of the Calera Creek Wetland Restoration and Wastewater Treatment Plant is a large (60 acres) and complex site bounded by Mori Point Ridge on the northwest and north, an old railroad fill bank on the northeast, Pacific Coast Highway (Route 1) on the east and southeast, the Rockaway Beach district on the south, and the Pacific Ocean on the west.

The lower Calera Creek valley was primarily floodplain and low terrace before filling and stream channelization occurred. The southwestern end of the site near the beach was probably a marine terrace. Alluvial toe-slopes along the northern ridge can be seen as subtle foot-slopes from the alluvial valley. The main upland areas surrounding the lower Calera Creek valley are a large artificial railroad bed fill, an undisturbed hillslope and a highly perturbed hillslope/quarry to the northwest.

Projected Benefits

The wetland restoration and wastewater treatment plant will provide significant benefits. Specifically, the restored creek channel, riparian and depressional wetlands will result in placement of the previously ditched flow into a naturally configured channel positioned within a relatively wide floodplain, with depression and berm topography that simulates soil pockets created as a result of wind throw. The city has achieved an increase in channel length on the site by approximately 1400 feet (ca. 44 percent), as well as a riparian corridor vegetated with a mosaic of native forest, scrub/shrub and emergent wetland plant species habitat for protected species in the form of two ponds providing approximately 3260 square feet of water on a terrace above the floodplain. The project will result in no net loss of wetland area or function, but instead a net gain of approximately 0.91 acres and an increase in wetland ecosystem functions.