Leighton begins the geotechnical exploration and Initial Site Assessment for the Santa Ana River Interceptor (SARI) Line Relocation between Prado Dam and Weir Canyon Road.
The SARI Line is a regional sanitary sewer line that conveys raw sewage and brine (wastewater from agriculture, commercial and other sources) from the Inland Empire and Orange County to the Orange County Sanitation District (OCSD) treatment plant in Fountain Valley. Leighton’s field exploration will include more than 60 borings, and installation of groundwater monitoring wells. The use of electrical resistivity imaging (ERI) will be used to evaluate the location of the Whittier and Whittier-Elsinore faults. Four electrical resistivity lines will range in length between 550 and 1,100 feet. This process is a non-destructive geophysical technique for imaging subsurface structures from electrical measurements by means of injection of DC current in the ground, measuring the voltage drops produced at points on the surface and mapping the subsurface distribution of electrical resistivity. The electrical resistivity values are digitally recorded on the Sting meter and processed using specialized software to build a three-dimensional model of a site which can be used to evaluate existing void spaces, depth of conductive materials, and approximate volumes of conductive objects within the subsurface soils. This subsurface information along with the available geological data of the site will be used to interpret the potential of faults crossing the SARI Line alignment.
Constructed as a joint project of OCSD and the Santa Ana Watershed Project Authority in the early 1970s, the SARI Line was originally buried about 20 feet below the river bed. Over time, the soil cover over the SARI Line between Weir Canyon Road and Prado Dam has experienced heavy erosion and the pipeline is exposed at some locations. The probability of damage to the SARI Line is expected to be higher when Prado Dam’s planned maximum controlled release increases from 10,000 to 30,000 cubic feet per second as part of the Santa Ana River Mainstem Project (SARMP) improvements. The Orange County Flood Control District is the local sponsor of the SARMP and is responsible through its Local Cooperative Agreement with the U.S. Army Corps of Engineers to mitigate the impacts of Prado Dam improvements on existing utilities such as the SARI Line.
