Transforming Urban Water Initiative

From Gray to Green Shorelines

Oro Loma Horizontal Treatment Levee


The Oro Loma Living Laboratory is designed to study the concept of a horizontal levee. Instead of a traditional levee to protect against storm surges, a horizontal levee uses vegetation on a gentle slope to break waves. The ecosystems that live on horizontal levees can thrive while helping to further process wastewater from treatment plants.

The Oro Loma Living Laboratory consists of a 1.4 acres experimental habitat slope. Wastewater that has already undergone secondary treatment is injected at the top and dispersed through 12 vertical cells, each one with a different combination of soil and plant habitat. The wastewater passes through the sub-layers of the cells, each one equipped with sampling wells at the top, bottom, and two thirds of the slope. The research team studies the idea that the sub-surface filtering processes will support native plants and purify the water enough so that one day this kind of system can be directly connected to the edge of the Bay.


Water quality monitoring findings reveal several key components. First, the Oro Loma Horizontal Levee significantly removes wastewater-derived contaminants while providing valuable habitat. Some contaminants that were found to be removed were nitrogen, phosphate and pharmaceuticals. Second, contaminant removal was influenced by hydrology more than other design and operational parameters. Subsurface flow is the key! Finally, that nitrogen was removed by microbial processing within the horizontal levee design.

Photos and Videos