Guidance Manua pdf

 

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Figure 4-7.  Trend of within-canal MIB production and temperature at the Deer Valley WTP. 

 

Most of the MIB production in the Arizona Canal occurs in “hot spots.”  These include:

 

the upper Arizona Canal between Highway 87 and Mesa Drive and the Arizona Canal 

between the Squaw Peak and Deer Valley WTPs (Figure 4-8).  The latter is the single 

most significant hot spot for MIB production on the Arizona Canal.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4-8 

Two “hot spots” of MIB production in the Arizona Canal observed in 2001. 

 

 

An intensive monitoring program, beginning around June, should be initiated each year 

to detect MIB production within the Arizona Canal.  This monitoring program should 

collect samples once every one to two weeks at about 10 sites along the length of the 

Canal. 

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SECTION 5 

SPECIFIC MANAGEMENT PRACTICES 

5.1  BACKGROUND 

 

Decisions to alter management of water supplies, treatment of canals, or changes in 

water treatment plant operations require high-quality and up-to-date monitoring data (i.e., 

process control monitoring  – Section 4).  Without such information decision-making is 

usually too slow to have a significant benefit, and could actually be detrimental.  This 

section identifies details of specific management barriers.  Section 6 addresses methods 

for effective communication of data to allow rapid decision-making. 

 

5.2  WATER SUPPLY OPERATIONS  

5.2.1  Rationale 

 

Management of water supply operations can be used to minimize MIB inflows to the 

Arizona Canal.  Managing source waters to keep MIB as low as possible is important for 

three reasons: 

 

1. 

It significantly lowers the cost of in-plant PAC treatment. 

 

2. 

The Deer Valley and Squaw Peak WTPs currently cannot treat water with very high 

MIB (> 20 ng/L) levels because the current PAC-feed facilities are inadequate. 

 

3. 

It benefits many cities. 

 

Two major modifications that have been used with some success are (1) modified 

operation of Lake Pleasant, and (2) blending of SRP and CAP waters. 

 

5.2.2  Modification of Lake Pleasant Operation 

 

Lake Pleasant has two outlets located at 1506’ and 1610’ above mean sea level, and is a 

pumped storage reservoir.  The flexibility of Lake Pleasant’s plumbing system allows 

considerable flexibility in water operations.  The CAWCD has used this flexibility to alter 

the operation of Lake Pleasant and improve the quality of water delivered to the CAP 

Canal.    

 

Prior to 1999, normal operation was to pump water from the Colorado River from 

November through May.  Starting in May, water was released from Lake Pleasant to the 

CAP Canal downstream throughout the summer.  Water was released from the upper 

penstock.  During the summer, this meant that water was being released from the 

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epilimnion.  Because MIB was produced in the epilimnion, water released had high levels 

of MIB, creating a T&O problem downstream. 

 

In the fall of 1999, CAWCD responded to consumer complaints by switching to 

hypolimnetic release (Figure 5-1).  This kept MIB levels < 10 ng/L until turnover.  After 

turnover, the average concentration of MIB increased to 20 ng/L (Figure 5-1, October).  

At that time, CAWCD stopped releasing water from the reservoir and routed water from 

the Colorado River directly to the Phoenix metropolitan area (by-pass pumping).  This 

operational strategy succeeded in keeping MIB concentrations in water delivered to the 

Phoenix area < 10 ng/L throughout the season.  If CAWCD had not modified its 

operation, MIB levels in water delivered to customers would have approached 50 ng/L. 

Figure 5-1.  MIB in Lake Pleasant and the CAP Canal in summer-fall 1999. 

 

From 1999 to 2001, MIB concentrations in the CAP Canal at 7

th

 Street have consistently 

remained below 10 ng/L, even when MIB concentrations in the epilimnion were elevated 

(Figure 5-2). 

 

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Figure 5-2.  MIB in Lake Pleasant and the CAP Canal from 1999 to 2002. 

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