Evaluating Expansions Needs for the Alamitos Seawater Intrusion Barrier

The Alamitos Barrier was initially constructed in 1965 in the Long Beach/Seal Beach area to protect the Central Basin of Los Angeles County and the Orange County Groundwater Basin from seawater intrusion through the Alamitos Gap.  Barrier facilities have been expanded over the years and currently include 43 injection wells.  However, based on monitoring well data, pulses of groundwater with elevated salinity appear to have migrated through and/or around the barrier into the Orange County Groundwater Basin and to a lesser extent into the Central Basin.  During 2009 and 2010, four additional monitoring wells were installed, a pipe network hydraulic model of the barrier injection system was developed, and a detailed numerical groundwater flow and transport model of the Alamitos Gap area was developed and used for simulating barrier expansion alternatives.  The presentation will include the technical setting of the seawater intrusion, the practical operations and options for enhancing the barrier, and the results of three groundwater model scenarios pertaining to barrier expansion.