Percolation Ponds at STP8

Percolation Ponds at STP8

The STP8 ponds were originally built into a hillside, as shown in figure 103. A levee encloses the three down-slope sides. Dense riparian vegetation exists below the western levee and out into the shallow swale below. There are also several patches of wet meadow vegetation in the swale. There is evidence to suggest that the existing riparian and wet meadow vegetation is being supported in large part by water leaking from the ponds. As noted, use of the riparian habitat by least Bell's vireo has been documented, and waterfowl utilize the ponds.

The design, seen in figure 104, recommends removing the levees and regrading the site. The pond basin would be graded toward the hillside at a 1% slope with steeper transition slopes to meet the 30% grade of the existing hillside. All material from the levees and additional off-site fill would be required to achieve the designated grades. To protect existing riparian vegetation, no grading beyond the outer edge of the former west levee would be permitted.

The regraded site would be revegetated to a native grass/forb community on the flatter slopes and CSS on steeper slopes, following revegetation plant mixes and specifications currently used on MCB Camp Pendleton.

For all three projects, site grading and planting should be completed during the winter months to avoid disturbing birds during their breeding season. In all cases, an intense weed control program for at least three years after planting at all three sites would be mandatory. In addition, removal of giant reed, Arundo donax, and salt cedar, Tamarix spp., from the meander corridor could significantly reduce ground water loss from evapotranspiration. This action could also reduce stress to existing riparian plant communities. The restoration of each of the three sites has been conceptually developed as as integral part of the adjacent plant communities, expanding patch size, increasing edge, and maintaining riparian biodiversity.