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Scottsdale, AZ
Background: Water Quality Characteristics
The Scottsdale Municipal Water System serves approximately 180,000 consumers with a
combination of surface and ground water. The
City has 31 wells, and transports surface water
from the Colorado River via an aqueduct, and
surface water from the Verde and Salt Rivers
through canals. In 1998, average annual water
demand was 63 million gallons per day (MGD).
28 MGD comes from the system's ground
water sources.
Scottsdale's ground water is generally only
treated with chlorination. The system treats the
water coming from the Colorado River, but the
surface water from the Verde and Salt Rivers is
treated by the City of Phoenix and then piped
to customers in Scottsdale.
To meet the revised 0.010 mg/L arsenic
maximum contaminant level (MCL), the system
will need to install new treatment technologies.
The City of Scottsdale recently pilot-tested
several new treatment technologies.
Typical Raw Water Quality - Scottsdale
Test Site1
PH
Arsenic (As(V))
Chloride
Fluoride
Iron
Nitrate (as N)
Silica (as SiOJ
Sulfate
Total Organic Carbon
9.0
0.039 mg/L
156 mg/L
1.3 mg/L
0.5 mg/L
2 mg/L
25.3 mg/L
23 mg/L
<0.2 mg/L
Norton, M; Chang, Y;& Kommineni, S. "Evaluation of
Micro-Sand-Based Technologies for Arsenic Removal -
Ballasted Sedimentation and Metclean Process.
AWWARF
Pilot Testing
Scottsdale tested multiple arsenic treatment technologies at various sites around its system. Most
recently, the system simultaneously tested a number of emerging arsenic removal technologies at its
City's Well No. 4 including:
• Activated alumina (conventional, iron-modified, and high porosity); and,
• Granular ferric hydroxide.
Sponsored by the American Water Works Association Research Foundation (AWWARF), the goal
of this pilot project was to test emerging technologies for arsenic removal. This project was one of
the first to simultaneously test multiple technologies on a large-scale, year-round basis and was run
in conjunction with the pilot testing at the Tucson, AZ water system.
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Figure 2: Scottsdale Pilot Testing Unit
A skid-mounted apparaais holding foul-
separate, identical fixed-bed columns, was
installed at the Scottsdale treatment site.
Each column, operated in parallel,
contained 25 gallons of adsorbent media.
The flow rate to the skid was 20 gpm.
Four different proprietary adsorption
media were tested:
• Conventional activated
alumina;
• Iron-modified activated
alumina;
• High porosity activated
alumina; and,
• Granular ferric hydroxide.
The goals of the tests were to: discover whether the adsorbents would allow Scottsdale to meet the
revised 0.010 mg/L arsenic MCL (taking operation and maintenance, labor, and personnel costs into
account); test whether there was any seasonal impact on the effectiveness of the technologies; and
establish optimum operation protocols for full-scale systems.
Scottsdale collected data from January, 2001 to November, 2001. After chlorination, the raw water
pH at Well No. 4 ranged from 8.7 to 9.2. This high average pH as well as high concentrations of
silica in the ground water rendered the activated alumina technologies less effective. Despite acid
additions to the feed water in February 2001, there was little improvement in the effectiveness of the
alumina-based media.
The granular ferric hydroxide proved to be the most effective technology of the four technologies
that were pilot-tested even though there were initial problems with the column due to inadequate
backwashing.
Ion Exchange Technology
Scottsdale Municipal Water also pilot-tested two emerging ion exchange treatment processes:
advanced ion exchange operations (AIXO), and indefinite brine recycling (IBR). Ultimately, it was
determined that AIXO was capable of maintaining an effluent arsenic concentration of less than
0.010 mg/L. Initial operational problems with the IBR technology made it difficult to conclude
whether the technology'was effective in lowering arsenic concentrations. After the operational
problems at Scottsdale were resolved, IBR proved to be a promising treatment technology.
Micro-Sand-B ased Technology
Through funding from the Arsenic Research Partnership (comprised of AWWARF, EPA, and the
Association of California Water Authorities), Scottsdale pilot-tested micro-sand ballasted
coagulation-sedimentation (MBCS) technology from June 21, 2001 to July 2, 2001. Here, ground
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water from two wells was pumped into and combined in a reservoir. This blended water was fed
into the MBCS unit.
Scottsdale added varying doses of ferric chloride upstream of their sedimentation process. Higher
ferric chloride doses were required for effective arsenic removal due to the high pH (8.5-8.9) of the
raw water. A dose of 15 parts per million (ppm) was determined to be the minimum required for
achieving the target arsenic level of 0.010 mg/L MBCS proved to be a promising arsenic removal
technology for the Scottsdale plant and the process generated non-hazardous residuals that can be
disposed of in a domestic landfill.
Conclusions
The Scottsdale system is conducting additional studies using granular ferric hydroxide. The first
round of tests indicated that granular ferric hydroxide is a promising treatment method, while
activated alumina (the cheapest option) is not, due to the high pH and silica levels in the raw water.
The City is considering simplifying the treatment process by treating water at numerous central
locations, rather than at each wellhead. The proposal calls for approximately six major clusters of
wells (ranging in size from 4-6 MGD) and numerous individual wells, all receiving treatment. In
some parts of the City, the water system will blend the ground water with treated surface water from
their other sources in order to meet the community's demands.
Cost of the treatment for arsenic has not yet been determined. The City is currently working with
two major GFH suppliers to pilot their media and competitively bid for media delivery. The City
anticipates that the cost of any new or improved treatment for arsenic will be primarily funded
through water rates.
Office of Water (4606M) EPA 816-F-03-013 May 2003 www.epa.gov/safewater
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