Monitoring Data from a Pilot-Scale Horizontal Levee System
Data was collected from a pilot-scale treatment wetland at the Oro Loma Sanitary District wastewater treatment facility in San Lorenzo, CA. This experimental system was completed in 2017 and was constructed to test a new type of treatment wetland known as the horizontal levee. Horizontal levees are constructed treatment wetlands that were first proposed for use in San Francisco Bay and were intended to be situated between coastal storm control levees and tidal mud flats. These systems provide simultaneous removal of contaminants from wastewater effluent in subsurface treatment layers while providing flood control benefits by protecting coastal levees against wave action and storm surges. Additional benefits, such as the establishment of valuable habitat and recreational opportunities, may also be afforded by these systems. The experimental constructed wetland consisted of a set of twelve separate wetland cells that were designed with various "treatments" based on differences in their plant community, soil type and topography. Data were collected to: (1) assess the relative influence of design parameters on water quality improvements observed in these systems; (2) evaluate the importance of various mechanisms to the observed contaminant transformation and removal; and, (3) develop new methods for monitoring nature-based treatment systems. Measurements of water quality parameters and contaminant concentrations, flow measurements, characterizations of soils and plant biomass, and satellite imagery are provided within this dataset. The results of various models used to interpret these data are provided as well. Metadata are provided within the spreadsheets for each dataset or in separate text files for each subfolder to facilitate interpretation of these data. References are provided if data are related to other spreadsheets, datasets or specific publications wherever possible. We expected design parameters to have a significant impact on contaminant removal, but this was not the case with respect to fractional removal of a range of contaminants (i.e., nutrients, trace organic contaminants and pathogen indicators). Rather, hydrological conditions controlled contaminant removal, although these conditions were influenced by design parameters. For example, the inclusion of willows led to relatively higher subsurface flow rates, which increased the mass of contaminants removed in those cells. We also hypothesized that denitrification would be the primary removal mechanism for nitrate in these systems. As expected, nitrate removal occurred primarily through microbial processes in the saturated subsurface, with plant uptake contributing only 8% of the observed removal of total nitrogen. Seasonality was observed with respect to the electron donors used to fuel denitrification. Additional information on the key findings of studies associated with these data, as well as guidance on how to interpret those data, are provided for each folder in this dataset.