A member agency of the Metropolitan Water District of Southern California (Metropolitan), Calleguas is located at Metropolitan’s northern boundary and is precariously dependent on State water deliveries provided by Metropolitan through a single pipeline. As such, the district’s entire water supply is subject to a host of external forces, natural and manufactured, ranging from drought and earthquakes to regulatory actions and water right determinations. The inherent vulnerability of Calleguas’ water supply provides the rationale for a large portion of the district’s capital improvement program that when completed will greatly enhance the reliability of the District’s water supply.

The Las Posas Basin Aquifer Storage and Recovery (ASR) project is undoubtedly the most noteworthy and ambitious element of Calleguas’ capital improvement program. The project is designed to alleviate a severe storage deficiency that currently exists in the District’s service area. This shortage was documented in the West Valley Area Study jointly prepared by Calleguas and Metropolitan in 1993. The study analyzed population and water supply and demand trends to estimate current and projected total storage requirements for the region.

Under the project, Calleguas, through utilization of ASR (Aquifer Storage and Recovery) technology, will develop up to 300,000 acre feet of storage in the Lower Aquifer System of the Las Posas Groundwater Basin. The use of surplus aquifer capacity has been endorsed by water industry officials and environmental organizations alike as an effective and environmentally-superior alternative to the development of surface water reservoirs. Surface reservoir facilities require large-scale capital and operation and maintenance costs and also hinder or preclude the beneficial and environmental uses of the land on which they are sited. In contrast, groundwater storage programs have relatively low capital costs, allow for the continued use of overlying lands, and do not result in water losses or reduced water quality due to evaporation.

ASR technology refers to the use of dual-purpose, injection/extraction groundwater wells for the purpose of storing water and subsequently producing the stored water as needed. The project will enable pre-delivery and storage of large volumes of State water in the Calleguas service area during periods of availability. The stored water will later be "recovered" (extracted) by Calleguas to meet seasonal, drought, and emergency demands.

Project Profile

The Lower Aquifer System (LAS) of the Las Posas Basin provides an optimal environment for ASR operations. A hydrogeologic study of the 18 mile-long and 4.5 mile-wide basin conducted in 1989 by Calleguas and Metropolitan suggests that available storage capacity within the basin is on the order of 300,000 acre feet. This surplus capacity is primarily due to chronic overdraft (estimated to be in excess of 10,000 acre feet per year) that has depleted groundwater reserves in the basin.

In addition to adequate capacity, the aquifers of the LAS, the Fox Canyon and Grimes Canyon, are confined except at outcrop areas in the hills along the northern and southern boundaries of the basin. This condition has insulated these deep aquifers from degradation by overlying, poor quality groundwaters and potential sources of surface contamination (i.e., agricultural operations, underground storage tanks, etc.). Likewise, the confined nature of this aquifer system will similarly prevent contamination of District stored water.

The project includes the installation of thirty ASR wells within an approximate nine-square mile area in the Las Posas Basin, nearly thirty miles of large diameter pipeline to connect the wells with existing District infrastructure in the cities of Simi Valley and Thousand Oaks, and a combined pump/hydroelectric generation station in the City of Moorpark to facilitate the flow of water to and from the wells. Funded by Metropolitan and Calleguas, the $50 million project will be constructed in phases over a ten year period. To date, one well, the Fairview ASR Well, is operational and has injected several hundred acre feet of imported water into the LAS for storage. Four other ASR wells are currently under development and should be operational in 1997. Negotiations with area property owners are underway for an additional 25 well sites.

Project facilities will enable the conveyance of water between the well field and distribution system at a rate of 100 cubic feet per second (cfs). This rate is based on an extraction capacity of 3.33 cfs (1,500 gallons per minute) per ASR well. Injection rates are estimated to be slightly lower at 2.66 cfs (1,200 gallons per minute). Given the projected extraction capacity, and assuming twelve months of around-the-clock production, the maximum annual extraction capacity of the project would be on the order 72,000 acre feet..

Local and Regional Benefits

In addition to providing essential water storage capacity for the Calleguas service area, the Las Posas Basin ASR project will produce numerous local and regional benefits. From a local perspective, existing well operators in the basin (a vast majority of which are agricultural entities) will greatly benefit from project operations due to increased groundwater levels. A three-dimensional groundwater flow simulation model of the basin indicates that groundwater levels will rise on the order of one to three hundred feet in response to injection operations (see adjacent figure). The increase in average groundwater levels will result in reduced pumping lifts for existing well operators, and consequently, reduced energy costs. As such, the principal adverse economic effect of basin overdraft -- increased pumping costs for well operators -- will be alleviated.

Furthermore, during injection periods, the project will cleanly and efficiently generate electrical power for use at other District facilities or sale to Southern California Edison and other users of electricity. Not only will the combined pump/hydroelectric generation station produce electricity, but also each ASR well will be capable of generating electricity while operating in reverse mode during injection periods. Electrical power produced by the project will reduce electrical demands on sources that contribute to the degradation of the region’s air quality.

On a regional level, the project offers increased operational flexibility in the event of a severe drought or emergency. The project will afford Metropolitan the option to divert elsewhere a portion of its State Water entitlement historically provided to Calleguas, as Calleguas meets service area demands with water previously stored in the basin. While unable to receive project water, other Metropolitan member agencies will derive an indirect benefit in that additional State water would be available to their service areas.

Moreover, the project will result in a beneficial impact to biological resources in the Sacramento/San Joaquin Delta region due to reduced demands for State water during low flow conditions. To the degree that stored water would be utilized to either supplement or supplant imported deliveries, an equivalent amount of water could remain in the Delta to aid in sustaining sensitive species and habitat during critical periods. South-of-the-Delta storage projects, such as the Las Posas Basin ASR project, have long been recognized by State and regional water officials as fundamental to both ensure adequate water supplies for southern California and to abate further deterioration of the Delta’s fragile ecosystem.

Project Rationale

As clearly stated in the California Department of Water Resources' Water Plan Update (Bulletin-160-93), the State acknowledges that:

". . . those areas of California relying on the Delta for all or a portion of their supplies face uncertain water supply reliability due to the unpredictable outcome of actions being taken to protect aquatic species and water quality. Until solutions to complex Delta problems are identified and put in place, and demand management and supply augmentation options are implemented, many Californians will experience more frequent and severe water supply shortages."

Calleguas considers such shortages unacceptable and, in response to the State’s troubling water supply "forecast", is striving to implement water supply management measures that maximize use of local resources. This strategy will reduce the region’s immoderate dependence on imported water deliveries thereby insulating the District from circumstances beyond its control that adversely impact these sources.

Among other factors, the social and economic vitality of southern California is contingent upon a reliable supply of high quality water. Serving as a hedge against future water shortages, the Las Posas Basin ASR project will ensure the reliability of Calleguas’ drinking water supply for generations to come.

Project Design Engineers