Guidance Manua pdf

 

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system, and the water treatment plants.  Initially more than 20 potential 

management alternatives were evaluated.  At the midpoint of the project, about 

half these were discarded on the basis of either technical evaluation, political 

feasibility, or cost.  The others were implemented and are discussed in this 

manual. 

 

2. 

Continuous monitoring would be needed to manage tastes and odors.  The 

monitoring system that evolved now has 20 baseline monitoring sites located 

throughout the water supply system that are sampled once a month (Figure 1.1) 

and another dozen “intensive monitoring” sites that are sampled as frequently as 

once a week during T&O episodes. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1-1.  Schematic of watershed and locations of baseline monitoring sites (R#) and location of 

Phoenix’s water treatment plants (R10  – Val Vista WTP; R4  – Union Hills WTP; R15 – Squaw 

Peak WTP; R16 – Deer Valley WTP). 

 

3. 

A rapid response system was needed to provide data to COP staff quickly. Tastes 

and odor problems are episodic, often arising quickly at various locations. To 

manage the problem effectively, COP Water Services Division (WSD) and water 

quality managers at SRP and the CAWCD need to be able to implement control 

measures quickly, often in the time span of one or two weeks.  An electronic “Taste 

and Odor  Newsletter” evolved that is now distributed during the T&O season, from 

approximately June through November.  The  Newsletter reports system-wide 

monitoring data and recommends treatment strategies. 

 

4. 

The effort would require  broad collaboration.  Everyone involved with water 

treatment and delivery would have to participate for the program to be successful.  

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Biannual T&O project meetings facilitated broader involvement, as did the 

Newsletter.  In the end, at least 50 individuals from WSD staff, SRP, CAWCD, and 

ASU contributed specific ideas or otherwise facilitated implementation of the 

program.  

 

5. 

The program was to be sustainable beyond the life of the project.  This  Guidance 

Manual and the accompanying research report represent part of that effort. 

 

6. 

Because algae are a source of dissolved organic carbon (DOC), which reacts with 

disinfectants to form regulated disinfection by-products, the study would also 

include an effort to identify sources of DOC within the watershed and to elucidate 

characteristics of this DOC.  The watershed design approach for studying sources 

of tastes and odor compounds was ideally suited for studying sources of DOC with 

little incremental cost.  This document focuses exclusively on T&O management.  

The DOC-DBP work is reported elsewhere (Nguyen, 2002; Nyguen, et al., 2002). 

 

1.4  LONG-TERM IMPLEMENTATION GOALS FOR T&O CONTROL PROGRAM 

Most metropolitan water utilities agree that a target concentration of < 10 ng/L for MIB or 

geosmin is appropriate for finished drinking water.  Achieving this goal requires a 

combination of upstream watershed management strategies followed by an 

economically-optimized series of controls within the distribution canals that transport 

water to water treatment plants.  The key to controlling episodes of high MIB or geosmin 

lies within careful and frequent monitoring, implementation of controls that effectively 

limit production and in-plant treatment.  Long-term strategies for minimizing tastes and 

odors may include: 

• 

System monitoring using in-situ probes within the reservoirs, remote sensors at 

key locations in  the canals, flavor profile analysis panels (FPAs) and/or rapid 

and sensitive genetic methods for detecting the presence of culprit algae known 

to produce MIB and geosmin.   

• 

Managing surface and ground water resources to minimize MIB or geosmin 

concentrations in raw water by using source water with the lowest MIB or 

geosmin concentration.  Care should be taken to limit input of nitrogen or 

phosphorous nutrients into the water supply. 

• 

Optimizing practices to remove attached algae (brushing and chemical 

addition) while reducing risks of turbidity plumes or potentially harmful 

chemicals.  Minimizing algae attached to concrete-lined canal walls through the 

use of state-of-the-art biocide coatings that are applied to concrete walls.   

• 

Optimizing water production at different WTPs within a city to minimize 

production at the facility with the highest historical MIB or geosmin levels.  Use 

historical MIB or geosmin levels to determine which in-plant WTP controls are 

most important at each facility, and upgrade the facilities appropriately. 

• 

Optimizing existing processes for MIB and geosmin removal, and design 

upgrades in treatment processes to meet multiple water quality objectives. 

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SECTION 2 

BACKGROUND ON TASTE AND ODOR EPISODES IN THE METRO-

PHOENIX AREA WATER SUPPLY SYSTEM

 

 

2.1  SOURCES OF TASTE AND ODOR PROBLEMS 

 

Dozens of chemicals may cause T&O problems in surface waters, but in most systems, 

only a few are important.  This is true for the Phoenix metropolitan area water supply.  

By far, the most prevalent T&O compounds are MIB and geosmin.  These two volatile 

compounds are usually present, but not necessarily at levels above human sensory 

thresholds throughout much of the year and at most locations in the water supply 

system.   

 

MIB and geosmin are produced by blue-green algae (cyanobacteria) found in the 

reservoirs and the canals  (Bruce, et al., 2000).  Although there are numerous species of 

blue-green algae in the water supply system, laboratory culture studies have revealed 

only ten (10) isolates  that are confirmed MIB or geosmin producers out of approximately 

1300 algal strains that have been isolated from the water system.   

 

These “T&O culprits” were collected and isolated from six baseline sampling sites and 

four intensive sampling sites in the system.  The 10 isolates belong to six distinct taxa. 

Nine of the isolates were periphytic (attached algae living on rocks or attached to larger 

plants) and one was  planktonic (algae suspended in the water column).  The types and 

locations of the T&O culprits were: 

• 

periphyton growing on the cement-lined walls of the Arizona Canal,  

• 

periphyton in the Verde River below Bartlett Lake,  

• 

periphyton in the Verde River between Horseshoe Lake and Bartlett Lake, and  

• 

periphyton and plankton in Saguaro Lake. 

 

2.2  FREQUENCY AND DISTRIBUTION OF T&O EPISODES 

2.2.1  Seasonal Pattern of the T&O Problem 

Concentrations of MIB at Phoenix’s water treatment plants vary depending on the 

individual plant and the time of year.  MIB concentrations at the Union Hills WTP have 

generally remained < 10 ng/L since the CAWCD modified its operation of Lake Pleasant 

in 1999.  MIB concentrations at the Val Vista WTP generally remain < 20 ng/L except 

during late summer/early fall (Figure 2-1). 

 

 

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