NGWA Event and Education Recordings Archive

The City of Malibu, California has been ordered by the State Water Resources Control Board (SWRCB) to eliminate the use of Onsite Wastewater Disposal Systems (septic systems) in the Civic Center Area of the City as these systems have been determined to be one of the primary sources of bacteria and nutrients impacting the adjacent Malibu Creek and Lagoon. To meet the deadlines set by the SWRCB, the City has contracted with RMC Water and Environment to design a centralized wastewater collection system (sewer), a 0.5 mgd wastewater treatment plant and a recycled water distribution system.  The City’s goal is to reuse as much of the treated effluent as possible for landscape irrigation and other non-potable uses; however, only about 35% of the effluent can be reused - the remainder must be disposed of using alternative methods.  Given its location relative to Santa Monica Bay, premier surfing beaches, and sensitive riparian, bay and estuarine habitats, the City cannot construct an ocean outfall for disposal of unused recycled water; instead, injection into the underlying Malibu Valley Groundwater Basin has been selected as the preferred disposal method.  In order to design the injection system, the City spent several years conducting hydrogeological investigations, including a paleogeomorphologic investigation, to assess whether the relatively-shallow groundwater basin can accept the capacity of the proposed injection system; and to identify the best locations for injection. The results of these investigations identified and confirmed the location of an ancient buried Malibu Creek streambed that extends offshore and rises and thins in Santa Monica Bay. The results of the investigations were then used in detailed groundwater flow modelling to confirm the ability of the groundwater basin to accept and transmit the anticipated volume of injected recycled water to the ocean, without treated effluent reaching Malibu Creek and Lagoon.