Las Posas Basin

General Information:
18 ASR wells (as of 2006) in operation within the East Las Posas Basin, accessing the Fox Canyon Aquifer.

  • 18 wells
  • Well Depth 800-1200 ft
  • Total Injection Capacity = 63 cfs
  • Total Extraction Capacity = 90 cfs
  • Well Extraction Capacity = 4cfs
  • Well Injection Capacity = 3 cfs
  • Operated by the Calleguas Municipal Water District

Additional Information:

The American Society of Civil Engineers published the following article:

Implementing an Aquifer Storage and Recovery Project

Pipelines 2010: Climbing New Peaks to Infrastructure Reliability—Renew, Rehab, and Reinvest
Proceedings of the Pipelines 2010 Conference
Robert E. Beamer, P.E., M. ASCE, Donald R. Kendall, Ph.D., P.E., and Susan B. Mulligan, P.E.


Calleguas Municipal Water District (Calleguas) is a member agency of the Metropolitan Water District of Southern California (MWD). One‐hundred percent of Calleguas' potable water supply comes from M

WD, through the California State Water Project; the water enters Calleguas' service area in Ventura County through a single pipeline at the eastern end of its service area. Until recently, there was no redundancy or alternate supply of water, other than a 10,000‐acre‐foot reservoir (Calleguas' annual demand is approximately 120,000 acre‐feet). Calleguas' entire water supply could be shut off in the event of an emergency such as an earthquake. In the late 1980s, Calleguas began planning a means of supplementing the supply from MWD. They executed a conjunctive use agreement with MWD, whereby Calleguas would construct aquifer storage and recovery facilities to allow Calleguas to take excess water from MWD during periods of low demand (i.e., the wet periods) to store in an underground aquifer, and then pump the stored water from the aquifer into the transmission system during periods of high demand (summer months or droughts) or in the event of an emergency or outage from MWD. Calleguas' service area encompasses an aquifer about 18 miles long and 4.5 miles wide, with about 300,000 acre feet of available storage space. Calleguas began a multi‐year effort to plan, design, and construct the aquifer storage and recovery (ASR) facilities necessary to implement a conjunctive use project using the Las Posas Basin Aquifer. The facilities included a wellfield with 18 ASR wells with a total capacity of 70 cfs, five miles of large‐diameter pipelines ranging in size from 60‐ to 72‐inches in diameter and located in a major thoroughfare, a five million gallon reservoir, chloramination facilities to disinfect the water when it is pumped from the aquifer, and a new pump

station and pressure regulating station. The wellfield and pipeline facilities were completed in 2006, and have operated to store about 70,000 acre‐feet of water in the aquifer to date. The pump station was completed in 2009, and was put into immediate use due to cutbacks in the supply from MWD; it has operated nearly continuously since it was completed. This paper discusses the need for the project, the agreement with MWD for conjunctive use, and the process of planning, designing, and constructing the ASR facilities. It presents some of the many challenges encountered during planning, design, and construction of the facilities, particularly during the construction of the large‐diameter pipelines and associated tunnels.

In addition:

Fox Canyon Aquifer Info: Hydrologic Region South Coast California’s Groundwater

Las Posas Valley Groundwater Basin (

Las Posas Aquifer Storage and Recovery Project document: (

Groundwater Basin Report: Chapter IV – Groundwater Basin Reports Northwest Metropolitan Service Area - Ventura County Basins :link