Case study - Westbay System reduces construction costs by 65%


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Multilevel monitoring network delivers unprecedented definition of groundwater flow and water quality at a reduced cost


OCWD had determined that information  on the piezometric level and water quality  of each aquifer layer was required to  optimize management of the recharge,  storage, and recovery of groundwater.


A cost analysis indicated that for 10 zones  through a depth of 1,500 ft, the Westbay  System instrumentation would result in a  total cost 55% to 65% lower than that for  clustered wells or two five-well nests


The increased data density from the  Westbay System multilevel wells provides  OCWD with an unprecedented definition  of groundwater flow and variations in  water quality.

California residents depend on groundwater for drinking water supply

The Orange County Water District (OCWD) in Southern California, USA, is responsible for  supplying clean water to more than 2 million residents in a 380-mi2 [970-km2] service area.  The facilities have the capacity to recharge approximately 250,000 ac-ft [3.1x103m] of water  per year by percolation along the channel of the Santa Ana River and off-channel basins.

Groundwater supplies more than 60% of the total water demand in the area and managing this  groundwater resource is the OCWD’s number one priority.

Water level and quality data required to optimize groundwater management

Management of groundwater over a large area is an involved process. Each year, OCWD  monitors groundwater levels, production, and recharge quantities to evaluate groundwater  storage changes in the basin, replenishes the basin, and conducts an assessment program to  pay for operating expenses and the cost of the imported replenishment water. The district has  an ongoing effort to increase available local water supplies through innovative programs such  as expanding the capacity of existing percolation facilities, treating poor-quality water to make  it useable, and reclaiming water.

The geology of the groundwater basin consists of alternating layers of uncemented fine- and  coarse-grained sediments in a synclinal trough that plunges toward the northwest. Wellbores  typically penetrate 10 to 15 different water-bearing layers over a depth of up to 1,500 ft [460 m] .  By the mid-1980s, OCWD had determined that information on the piezometric level and water quality of each aquifer layer was required to optimize management of  the recharge, storage, and recovery of groundwater.

Three methods of accessing the aquifer layers were considered:

  • Cluster of separate wells, with each well completed in a separate zone
  • Nest of wells with up to five well casings, each completed in a separate zone, in a single borehole
  • ƒMultilevel well using the Westbay System  for groundwater monitoring

Westbay System reduces construction costs by up to 65%

A cost analysis indicated that for 10 zones through a depth of 1,500  ft the Westbay System instrumentation would result in a total cost  (including drilling, construction, and instrumentation)  55% to 65%  lower than that for clustered wells or two five-well nests. OCWD  selected Westbay System technology on the basis of performance  and cost and in the late 1980s began a multiyear program of drilling  and constructing multilevel monitoring wells throughout the basin.

Including pre-existing and new traditional single-point wells,  approximately 200 monitoring wells have been established in the  OCWD groundwater basin to provide the data integral to management  of the resource. The focus of the monitoring network is 57 Westbay  System multilevel monitoring wells, installed to depths of up to 2,000  ft [600 m] . Because each Westbay System enables measuring the  water pressure, sampling for water quality, and testing hydraulic  characteristics from multiple discrete zones, these 57 wells  provide data equivalent to approximately 550 traditional monitoring  wells. When first installed, the wells are used for characterizing  the groundwater basin. Later, the same wells provide long-term  monitoring data.

OCWD gains critical insight from extensive, high-resolution monitoring data

The increased data density from the Westbay System multilevel wells  provides OCWD with an unprecedented definition of groundwater  flow and variations in water quality. The water-level data is key to the  development of three-dimensional, transient groundwater models,  and the water quality data provides information on the movement of  recharge water and identifies areas with poor-quality water to avoid  and mark for future remediation. This insight into water quality is used  in designing new production wells to avoid the undesirable water.  Without the aid of this detailed monitoring network, the district could  not model the groundwater basin with the degree of confidence it  currently has.

The groundwater models are the basis for a long-term management  plan that encompasses maximizing the sustainable pumping capacity  of the basin. Under consideration is the development of inland well  fields and additional recharge facilities to support a higher operable  yield. Total groundwater production is currently approximately  320,000 acre-ft [3.95 × 108 m3] per year. The extensive, detailed data  collected with Westbay System instrumentation makes it evident that  the implementation of new programs and projects can increase the  annual groundwater production to more than 450,000 acre-ft [5.55 ×  108 m3] per year.

OCWD recognizes that there are distinct major phases to optimizing  groundwater management: detailed characterization and monitoring,  interpretation and evaluation of the data collected, and planning  future management of the resource. The phases must be followed  sequentially. There are no shortcuts—detailed characterization  and monitoring are the foundation for effective basin management  decisions. Westbay System multilevel monitoring systems provide the  key data for a sound foundation.

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