Chaparral Water Treatment Plant: Good taste will prevail in Scottsdale
Dan Meyer, Project Manager, Black & Veatch, Phoenix, Arizona
Nader Kavakeb, AIA, Design Architect, Swaback Partners, Scottsdale, Arizona
Bill Peifer, Project Manager, City of Scottsdale, Arizona
A water treatment plant now under construction in Scottsdale, Arizona, will tastefully address the City's water supply and treatment concerns. The Chaparral Water Treatment Plant (WTP) was designed not only to quench area residents' thirst for safe, good-tasting, and odor-free drinking water but also to receive a warm reception as a new neighbor. The architectural and landscaping treatments chosen for the public facility and park are just as special as the advanced treatment technologies selected to produce high quality potable water from the City's new source of supply.
Treatment to ensure exceptional water
In the process of replacing the purchase of treated Salt River Project (SRP) water from Phoenix with treatment of their own allotment of SRP water, Scottsdale public works leaders realized that any treatment facility would need to include taste and odor control. Other communities that use a similar SRP blend of waters from the Verde and Salt Rivers and the Central Arizona Project (CAP) Canal have experienced periodic taste and odor problems attributable to methylisoborneol (MIB) and geosmin. These compounds, which tend to form with excessive growths of blue-green algae, are periodically responsible for earthy or musty tastes and smells. The question was how best to proactively incorporate taste and odor control in addition to arsenic removal and control of disinfection byproduct precursors in the design and construction of the proposed water treatment plant.
Scottsdale retained Black & Veatch, a global engineering, consulting and construction company with a local Phoenix office, to evaluate treatment processes and develop design criteria for the 30-million-gallon-per-day Chaparral WTP. Treatment plants that currently treat SRP water face a significant challenge not only in controlling taste and odor but also in complying with the proposed Stage 2 Disinfectants/Disinfection Byproducts Rule (D/DBPR). The rule will establish limits for trihalomethanes (THMs) and haloacetic acids (HACs) at individual locations rather than limits for the system average as is now the case. Removal of naturally occurring organic matter was determined to be the most cost-effective and least problematic way to meet the proposed requirements of the Stage 2 D/DBPR.
Site constraints also played a part in the selection and design of appropriate treatment processes for the Chaparral WTP. Membrane filtration was selected due to its small footprint, high water product quality, and proven performance at the award-winning Scottsdale Water Campus. Two processes were selected for evaluation: (1) microfiltration/ultrafiltration (MF/UF) membranes followed by ozonation and/or granular carbon (GAC) adsorption, and (2) MF/UF followed by reverse osmosis membranes. When financial and feasibility analysis indicated that the first process would be more cost effective, the second option was eliminated from further consideration.
A six-month membrane and GAC pilot study was conducted to establish design parameters and to prequalify acceptable membrane manufacturers for bidding. Pilot and bench studies included evaluation of GAC with and without ozone and demonstrated that GAC columns alone could effectively control taste, odor, and disinfection byproducts. Two of the four low-pressure membrane systems proved successful through pilot study and were carried forward to the procurement phase of the project. The application of ferric sulfate coagulation directly to MF/UF membrane filtration will also help Scottsdale meet its arsenic treatment goals. Associated plant facilities include onsite sodium hypochlorite generation and disinfection facilities, solids dewatering facilities, a buried finished water reservoir, and a finished water pump station.
"We needed to address other water quality issues in addition to regulatory compliance because the local surface water supply can have significant taste and odor problems if not treated properly," says Scottsdale Water Quality and Treatment Director Jim Clune. "The citizens of Scottsdale deserve the best water quality we can provide."
All that and looks, too
The site designated for the new treatment plant is highly visible due to its location at a busy intersection and in a well-developed area. It is also near an upscale neighborhood within a city that promotes art and culture and which requires detailed architectural review of all new facilities. A treatment plant is rarely welcomed with open arms into an existing neighborhood, even in the best of circumstances. Tasteful architectural and landscaping design was essential.
As a subconsultant to Black & Veatch, Swaback Partners provided conceptual architectural design consultation to redefine and help transform a functional treatment plant "mega box"—a windowless mass—into an architectural statement to enhance the overall context. To avoid controversy and encourage community acceptance of the new water treatment plant, the firm incorporated several systematic concepts into the architectural design of the new facility. All of the following elements of design were developed as metaphors to promote an appreciation of desert art and culture.
Architectural sculptures—gigantic weathered metal panels—were incorporated into the design as an expression of material in its natural state, taken from and given to the desert. With a weathered look and a monumental scale, these panels combined with woven metal mesh represent the water filtration process behind a 30-foot-high, 320-foot-long wall that stages the drama of light and abstraction of forms to enhance the streetscape.
The Chaparral WTP architectural design also features what is believed to be the largest installation of tensile structures of its kind in the area. Approximately 16,000 square feet of delicately engineered and boldly stated shading systems represent the nomadic desert dwellings of the past and art within technology of the present.
Gabion walls—a system of rocks in metal baskets—will effectively produce unity and beauty between the park and the building. Serving as garden walls in primitive times, gabion walls in modern times serve to capture the beauty and rustication of the desert.
Scottsdale's Chaparral Water Treatment Plant, now under construction, was designed to satisfy many needs.
A second phase of the Chaparral project, scheduled to begin in 2005, will focus on the development of the adjacent public park area and will feature a xeriscape garden (one that employs drought-resistant plants to conserve water), a relocated and expanded dog park, and multi-use ball fields.
Plants in a terraced xeriscape demonstration garden will act as living "bio-sponges" to soak up and harvest rainwater and to create habitat for native wildlife.
The dog park will include three gated off-leash zones that vary in size from 3/4 acre to over an acre. Each zone includes an extensive lawn running area and a play area for digging, climbing on large boulders and going through tunnels. Park personnel will be able to rotate zone closings to maintain turf conditions throughout.
Also included in the park renovation are two new 325-foot multi-use ball fields with dedicated parking for 104 cars and new restroom and maintenance buildings that repeat architectural elements of the water treatment facility.
"The park visitor will leave with an appreciation of our most precious resource—water," says Christine Ten Eyck of subconsultant Ten Eyck Landscape Architects. "It will demonstrate that saving water in our daily lives affords us the luxury of the green public park atmosphere."
When it begins operation in the spring of 2006, the Chaparral WTP will eliminate Scottsdale's dependence on purchased water, ensure compliance with current and anticipated drinking water regulations, and provide residents with drinking water of exceptional quality. It will also exemplify the successful blending of beauty and function, art and technology, and architecture and engineering. It will be a welcome addition and a good neighbor.
Dan Meyer can be reached at (602) 381-4417 or at firstname.lastname@example.org; Nader Kavakeb can be reached at (480) 367-2100 or at email@example.com; and Bill Peifer can be reached at (480) 312-7869 or at BPeifer@scottsdaleaz.gov.