Guidance Manua pdf

 

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The difference in MIB production between the Arizona Canal at  Deer Valley and MIB 

production at Squaw Peak represents MIB production between Deer Valley and Squaw 

Peak.  During the late summer and fall, MIB production in the canal stretch between the 

two water treatment plants can exceed 20 ng/L.  The very high MIB production in this 

stretch of the canal is probably exacerbated by well pumping into the canal, which 

increases the nitrate concentration in the canal.  This increase is not large relative to 

drinking water standards, but it is sufficient to promote algae growth. 

 

2.3.3  Water Treatment Plants 

 

Algae grow in the WTPs and should be controlled (see Section 4).  Analysis of temporal 

and spatial patterns in several water treatment plants has shown some in-plant 

MIB/geosmin production. Antidotal evidence suggests  that periodic prechlorination may 

prevent colonization of T&O “culprit” algae. 

 

 

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SECTION 3 

MULTIPLE BARRIER T&O CONTROL 

3.1  MULTIPLE BARRIER STRATEGY 

 

The central theme of the proposed T&O management strategy is the concept of multiple 

barriers.  The multiple barrier concept in water treatment is widely used for pathogen 

control.  “Barriers” in pathogen control include watershed management (for example, 

eliminating animal and human waste inputs into streams), sedimentation and filtration 

within water treatment plants to remove pathogens, initial chlorination to kill pathogens, 

and maintenance of chlorine residual to kill any pathogens that might enter the 

distribution system by regrowth, plumbing malfunctions, etc. 

 

The concept is similar for T&O control. During the T&O study, more than 20 specific 

control measures were evaluated.  Several measures emerged as the key elements of 

an overall T&O management strategy.

  

These are discussed briefly below and in more 

detail in Section 5:  

• 

Reservoir management.  Blending of waters from the Colorado River and the 

two outlet structures (upper and lower) in Lake Pleasant was an effective 

reservoir management practice.  Through managing waters from these three 

sources, CAWCD has been able to keep MIB and geosmin in the CAP Canal 

below Lake Pleasant < 10 ng/L.  

• 

Canal treatments.  Canal treatments were effective in removing T&O-producing 

algae growing on the sides of the Arizona Canal, thereby reducing the 

production of MIB.  Because algae growing on the canal walls can be a major 

source of MIB, sometimes contributing > 50 ng/L MIB to water flowing through 

the canal, canal treatments to remove algae are an important part of the overall 

T&O management program.  

• 

SRP-CAP Blending.  During the late summer and fall, CAP water generally has 

lower concentrations of MIB than SRP water.  This provides an opportunity for 

blending the two source waters to reduce MIB concentrations in water delivered 

to the treatment plants.  For most years, using more SRP water early in the 

season, and  more CAP water later in the season, would improve the quality of 

water delivered to Phoenix’s municipal customers.  The opportunity for 

blending, however, depends upon the hydrologic status of the system.  

Revisions in the legislation controlling the SRP-CAP Water Exchange 

Agreement in 2002 enhance the opportunity for blending as an effective T&O 

control measure. 

• 

Source switching.  The concept behind source switching is that poor quality 

water can sometimes be avoided by switching production from a plant that is 

receiving poor-quality water to one or more plants that are receiving better 

tasting water.  For example, taking the Deer Valley WTP off-line during 2001 

and shifting production to the Union Hills and Squaw Peak WTPs avoided the 

problem of high MIB in the lower end of the Arizona Canal and resulted in 

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better quality water delivered to consumers.  Phoenix now has five water 

treatment plants and will have a sixth within about five years.   

• 

In-plant treatment.  PAC treatment in the WTPs, thereby enhancing this 

capability, has been an effective method of removing MIB from source waters.  

Although PAC treatment could theoretically keep MIB levels below 10 ng/L 

throughout the year with no upstream management, practical limitations 

constrain the effectiveness of PAC treatment.  These limitations include limited 

PAC storage capacity, problems with pumping systems, and hydraulic short-

circuiting.  Furthermore, even if these limitations could be overcome, a multi-

barrier strategy would be more cost-effective than reliance on PAC treatment 

alone.

 

 

3.2  RAPID RESPONSE SYSTEM  

 

A key concept of the T&O Management Strategy is the use of a rapid response system 

that allows COP and other water supply agencies to respond quickly to emerging T&O 

problems.  This idea was adapted from the MWD, which established the general 

concept in the mid-1980s.  The concept was revised and implemented to meet the 

specific needs of Phoenix’s water supply system (Figure 3-1). 

Figure 3-1.  Flow chart of the rapid response system.  Dashed lines indicate feedback and validation of 

correction actions. 

 

 

Central to the rapid response system are intensive monitoring and a communication 

strategy.  The monitoring program is described in Section 4.  The core of the 

communication system is an e-mail-based  Taste and Odor Newsletter that has four 

functions: 

 

C a n a l s   a n d   w a t e r   t r e a t m e n t  

p l a n t s   s a m p l e d   ( 1 0   t o   2 0  

l o c a t i o n s )

D a y   1

G C / M S   a n a l y s i s

D a y   2

D a t a   a n d  

r e c o m m e n d a t i o n s   t o  

W S D   o p e r a t o r s   a n d   s t a f f  

v i a   T & O   N e w s l e t t e r

( e - m a i l )

O p e r a t i o n s   m o d i f i e d

D a y   4

I n t e r p r e t a t i o n   o f  

r e s u l t s   a n d  

r e c o m m e n d a t i o n s

D a y   3

Q u e s t i o n s   a n d   f e e d b a c k  

f r o m   W S D   s t a f f

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