Guidance Manua pdf

 

53

• 

continuous communications and analysis, and 

• 

annual evaluation. 

6.2.2.4 

Annual Workshops 

 

Annual workshops among COP staff are needed to plan strategy for each T&O season.  

The T&O situation is different each year, so the T&O strategy must be adaptive. 

 

Some key topics that need to be addressed in these workshops include: 

 

1.  Hydrologic forecast.  The hydrologic forecast is important for planning blending and 

source switching options.  SRP and CAWCD plan by March based on the 

hydrologic situation for the upcoming year. 

 

2.  Water delivery situation.  This issue depends upon both the hydrologic forecast and 

various institutional and infrastructure issues.  For example, the potential for source 

switching depends not only upon the hydrologic situation, but also upon the 

availability of excess treatment capacity.  The amount of excess treatment capacity 

will vary from year-to-year.  Legal and institutional issues also constrain the extent 

of blending that will be possible in a given year. 

 

3.  Other infrastructure issues.  The status of PAC delivery systems, the status of plant 

maintenance, canal shutdowns, and other issues affect the development of the 

season’s T&O management strategy. 

 

4.  Program evaluation.  It is critical that the T&O program be evaluated at the end of 

each season.  The program evaluation should result in a concise list of ideas to 

improve T&O management for the following year. 

---

 

54

SECTION 7 

CASE STUDIES 

 

7.1  INTRODUCTION 

 

The principles developed in this Manual are illustrated using three case studies.  These 

are actual events that were encountered during the T&O study.  They were selected to 

illustrate possible management practices that might be employed in response to T&O 

problems at the upper end of the water supply system, in the canal system, and at the 

water treatment plants.  Specifically, the case studies are: 

• 

high MIB in Saguaro Lake during late summer, 2001 

• 

high MIB in a "hot spot" along Arizona Canal during July, 2001 

• 

high MIB in the influent to the Squaw Peak WTP  

  

7.2  CASE STUDY #1 - HIGH MIB IN SAGUARO LAKE 

  

7.2.1  Process Control Monitoring 

MIB concentrations had been higher than geosmin levels during the summer of 2001 in 

Saguaro Lake.  By the end of August 2001 MIB concentrations in  the epilimnion of 

Saguaro Lake had reached 47 ng/L.  The following data were collected during sampling 

in Saguaro Lake (August 30, 2001): 

 

Depth from 

surface (m) 

MIB 

(ng/L) 

Geosmin 

(ng/L) 

Temperature 

(

o

C) 

Dissolved Oxygen 

(mg/L) 

0 

47 

7 

28.0 

7 

5 

36 

7 

25.8 

4 

10 

19 

5 

24.3 

2 

15 

16 

6 

23.8 

2 

20 

12 

4 

23.5 

2 

25 

12 

4 

23.4 

2 

30 

5 

4 

22.9 

2 

 

7.2.2  Diagnosis 

Water leaving Saguaro Lake via the hypolimnion withdraw was at approximately 30 m 

depth.  Therefore MIB concentrations were low, but significant MIB accumulated in the 

lake and would soon reach the withdrawal depth.  The reservoir had weak thermal 

stratification (

∆

Temp

max

 = 28.0  – 22.9 = 5.1 

o

C) but still exhibited a strong dissolved 

oxygen stratification.  Water above 5 m had oxygen concentrations > 4 mg/L and water 

---

 

55

at and below 10 m had oxygen concentrations of ~ 2 mg/L.  It was concluded that the 

reservoir would probably destratify within 30-45 days, resulting in higher MIB 

concentrations throughout the water column as the water became completely mixed.  

The result would be a significant increase in MIB concentration in the water leaving the 

reservoir from approximately 5 ng/L to > 15 ng/L. 

 

7.2.3  Treatment Selection 

Logistical, economic and political considerations prevented chemical or biological 

treatment for MIB in Saguaro Lake.  Therefore, it was decided that three implementation 

strategies should be undertaken to minimize MIB concentrations at downstream 

locations.   

 

First, SRP was contacted to determine the feasibility of switching from the Salt River to 

the Verde River as the dominant water source earlier than usual.  This switch in water 

supplies generally occurs in mid-October to mid-November.  Bartlett lake on the Verde 

River had much lower MIB concentrations (< 15 ng/L in the epilimnion and < 5 ng/L in 

the hypolimnion).  SRP determined that the Verde River did not have sufficient water 

volume to make the switch in water supplies earlier than scheduled.  This option was 

therefore not implemented. 

 

Second, CAP and SRP were contacted to determine if more CAP water could be 

delivered into the Arizona Canal and less SRP water (i.e., Salt River water).  The CAP 

canal had low MIB levels (< 5 ng/L) as did Lake Pleasant (< 15 ng/L).  It was 

determined that for approximately two weeks in late September or early October a 

larger delivery of low-MIB CAP water could be delivered into the Arizona Canal.  This 

would dilute MIB concentrations originating from Saguaro Lake via the Salt River.  This 

option was implemented. 

 

Third, City of Phoenix water production staff were contacted to evaluate the potential to 

increase finished water production at the Union Hills WTP rather than WTPs on the 

Arizona Canal.  MIB levels in the CAP canal would be significantly lower than MIB levels 

in the Salt River that supplies the major flow in the Arizona Canal.  It was decided to 

keep Deer Valley WTP off-line, minimize production at Squaw Peak WTP and increase 

production at Union Hills WTP.  This option was implemented. 

 

7.2.4  Treatment Application 

Increased CAP flows into the head of the Arizona Canal were implemented and 

production shifted from WTPs on the Arizona Canal to the CAP canal. 

 

7.2.5  Follow-up Monitoring 

Continued monitoring of Saguaro Lake proved that the MIB concentrations in the 

epilimnion continued to increase after August 30, 2001 as “predicted” (see Figure 7-1).  

MIB concentrations leaving Bartlett Lake on the Verde River never exceeded 10 ng/L 

---