PVC Pipe Facilitates Water Distribution System

California’s San Bernardino County, the nation’s largest with an area of some 20,105 sq miles, has been growing rapidly for more than four decades. Located in the southeast part of the state, its geography extends eastward from the outskirts of the Los Angeles metropolitan area to the Nevada border and is a mix of desert and mountains.

Comprising residential communities, manufacturing industries, retail trades, recreational facilities, and assorted government and military establishments, its population growth rate has exceeded 35% per decade since 1960, and an additional 65% increase is expected by the year 2020.

Water networking

Perhaps like no other area in the U.S., the availability of water is the most critical issue facing growing municipalities in southern California. The history of this state is replete with concerns over water supplies, and many of the state’s undertakings are related to conveying water to its drier, populous regions. The California Aqueduct, a 450-mile-long north-to-south concrete-lined aqueduct with capacities up to 650 mgd, is but one example of what’s involved in meeting the water needs of the drier parts of the state. The aqueduct and its subsidiary components are frequently upgraded to provide greater capacity, storage and additional branches to accommodate growth in southern California, where the potential for water shortages is almost always a major concern.

The Mojave Water Agency (MWA) is one of 29 California Public Water Agencies and one of several such agencies within San Bernardino County. Under the auspices of the California Department of Water Resources (DWR), MWA’s primary task is to manage water resources within an area encompassing about 4,900 sq miles of the High Desert Country near the Nevada border.

It operates under California’s State Water Project, an extensive 40-year-old state water management system with authority to construct and manage whatever facilities are needed to protect, restore and enhance water resources. It has grown into the nation’s largest state-built water and power development and conveyance system, and includes—among othe structures—various aqueducts, pipelines, canals, tunnels and siphons that facilitate water distribution.

Distribution programs

The 29 State Water Contractors in California operate as water wholesalers by selling and delivering water obtained from the DWR to local retailers in their respective service areas and, in some cases, directly to end-use customers. While these agencies can draw upon water from the DWR—MWA is allotted a maximum of 75,800 acre-ft (one acre-ft equals about 326,000 gal) of water from the State Water Project via the California Aqueduct—they also strive to optimize the use of indigenous water supplies.

For the MWA, such naturally occurring groundwater is in subterranean aquifers that are normally fed by irrigation return flow, natural stream flow and snowmelt in the San Bernardino Mountains. Because the desert region typically receives less than 6 in. of yearly rainfall, natural replenishment is slow.

Although MWA has an ample annual allotment of available water via the State Water Project, funding restrictions and inadequate delivery facilities for recharging groundwater have hindered its capacity to use imported water. Consequently, its annual usage has averaged less than 10% of that available and has forced an over-reliance on dwindling groundwater supplies.

Had MWA been able to use its full allotment, it may have prevented the risky groundwater overdrafts. To sustain the existing population and manage expected growth, MWA estimated its future annual groundwater recharge requirements at about 75,000 acre-ft by 2020 (roughly equal to its DWR water allotment).

Conflict resolution

The growing conflict arising from continued population growth and steady groundwater overdraft urged MWA to undertake an ambitious program to ensure its water supply for the foreseeable future. Completely funded by local taxes and user fees, MWA’s first major water delivery system project—the Morongo Basin Pipeline & Hi-Desert Extension—was a 78-mile pipeline consisting of 54-, 30- and 24-in. diameter pipe from the California Aqueduct in Hesperia to recharge facilities at Yucca Valley in the southern section of MWA’s service area. Completed in the mid-1990s, this pipeline provides much-needed water for recharging groundwater levels in parched underground storage basins.

Almost immediately after completing the Morongo Basin Pipeline, MWA began construction of the Mojave River Pipeline (so named because it parallels the Mojave River) within the central section of their service area. As part of its broader “Water Supply Reliability and Groundwater Replenishment Program” plan for upgrading existing facilities and building new ones to recharge and extract sufficient quantities of groundwater, the new water transmission line begins at the California Aqueduct and curves northeastward toward its terminus at Newberry Springs. Along the way, it disperses water to four large storage/infiltration basins for recharging aquifers.

The $53-million Mojave River Pipeline was initially designed in the early 1990s using cement mortar lined and coated steel pipe in sizes ranging 20 to 48 in. in diameter. Cement mortar lined and coated steel water pipe is manufactured at several facilities in southern California. With actual construction beginning in 1995, the Mojave River Pipeline was bid in sections (reaches) corresponding to distinct points along the pipeline route.

Reaches 1 through 3 of the pipeline brought water from the California Aqueduct to recharge sites some 60 miles to the northeast. Adhering to initial plans, the first sections were built using welded steel pipe. As the project evolved, however, MWA decided to evaluate alternative materials—one being AWWA C905 PVC pressure pipe.

The PVC alternative

According to Gary Martin, MWA’s director of engineering, “The project design occurred on a reach-by-reach basis, and the agency began considering PVC as an alternative to steel when pipe sizes dropped to 36 in. and smaller. This being their first potential application of PVC pressure pipe, MWA thoroughly examined every aspect of the product before committing. MWA’s evaluation process involved meeting industry representatives and touring a PVC manufacturing facility; their major concerns were PVC’s strength, durability, installation requirements, and compatibility with native materials being used for bedding and backfill.”

Once convinced of the capabilities of PVC pressure pipe, MWA specified it as the alternative to 34,000 ft of steel pipe beginning with Reaches 3D and 3E (separate bids were taken for materials and installation). Material bids for 40,450 ft of 24-in. pipe for Reach 4A resulted in PVC pressure pipe being the low bid alternate and, in December 2003, the MWA Board of Directors approved a $1.575 million contract with Utah Pacific Construction for constructing Reach 4A using 24-in. SDR 32.5 PVC pipe (pressure rated 125 psi).

MWA indicated that the use of PVC pipe in this section resulted in a savings of approximately $800,000 compared to steel pipe. Although MWA anticipated slower installation rates for PVC pipe than for steel (about 1,000 ft per day), the contractor’s actual average daily installation rate was about 1,500 ft of PVC pipe.

The completion of Reach 4A, including hydrostatic testing to 140 psi for 24 hours in 2-mile segments, required only 40 work days. All PVC pipeline segments passed the necessary acceptance tests, which also included examining for visible and measurable installation damage, and the pipeline was officially accepted for service in mid-August 2004.

Performance

After a year in service, the PVC pressure pipe in Reach 4A had experienced no operational problems. The entire Mojave River Pipeline was completed in January 2006, distributing water as far north as Newberry Springs.

Beverly J. Lowry, president of the MWA Board of Directors, described the pipeline project as “an essential step toward a physical solution to the overdraft [problem].” Satisfied with the performance of PVC pressure pipe on this project, the MWA staff indicated that PVC will be considered as a specified alternative pipe material for future projects.

Up to the challenge

Southern California has been growing continuously since World War II, and its current growth rate easily surpasses most other areas. While the various parts of California provide almost every conceivable climatic condition, its southern areas are some of the most arid in the U.S., and providing its residents with a continuous supply of water can be a challenging assignment.

The MWA, whose responsibility is to “do any and every act necessary to be done so that sufficient water may be available for any present or future beneficial use of the lands and inhabitants,” has completed a commendable 10-year construction and rehabilitation program that will help sustain its water resources. PVC pressure pipe helped MWA control costs on a large portion of the Mojave River Pipeline with a hefty savings on materials and installation and, with PVC’s remarkable history of durability, MWA can expect further benefits through lower operation and maintenance costs.

David E. Beck, P.E., is an independent consultant and technical author. He can be reached at 513/423-7836 or by e-mail at debeck422@sbcglobal.net.

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