Results of the Orange County Water District Induced Riverbed Filtration Pilot Project

In an effort to reduce suspended solids and organic carbon loading and to increase long-term groundwater recharge rates at Orange County Water District’s spreading basins, a 4500 gallon per minute pilot project was conducted to evaluate riverbed filtration as a technology to treat river water prior to groundwater recharge.  A shallow under-channel lateral drain system was constructed within a channel adjacent to the Santa Ana River to induce and capture infiltration.  Water pumped from the drain system was analyzed for a variety of water quality parameters and then recharged into percolation columns to evaluate recharge rates compared to Santa Ana River water without treatment.  At the pilot project drain system, phreatic surface and temperature were continuously monitored at thirteen points.  River water inflow and outflow and drain system pumping rates were also monitored. 

The pilot test was divided into two periods: Period 1 had shallow overflow (3- to 8-cm) within the river channel; Period 2 achieved deeper surface water depths (8- to 30-cm).  Lateral drain system pumping during both test periods were incrementally increased to establish the maximum pumping capacity of the drain system for each test period.  Monitoring data indicate that riverbed filtration effectively removed essentially all suspended solids and reduced turbidity with the bulk of water captured by the under-channel drain system from induced infiltration.  The phreatic surface and subsurface water movement within the drain system area was shown to be very sensitive to changes in surface water flow rates and depth, and drain system pumping rates.  In addition, surface clogging was observed.  The pilot project results indicate that riverbed filtration is a viable technology for treating surface water prior to recharge operations, however, additional testing and optimization is needed.