Guidance Manua pdf

 

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The  Guidance Manual is supported by other products from this project.  The  Final 

Project Report is a detailed compilation of research conducted throughout the project 

and an assessment of the implemented T&O mitigation program.  A CD-based 

Interactive Taxonomic Guide is a tool developed to assist in the identification of T&O 

“culprit” algae.  Finally, the project has generated numerous scientific presentations and 

publications that add to the understanding of T&O problems. 

 

This document is a living document and should change over time to include new 

information and improved practices.  It should, however, continue to serve as a practical 

guide to detect and respond to taste and odor problems in municipal and other water 

supply and distribution systems. 

 

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SECTION 1

 

INTRODUCTION 

1.1  PREFACE 

Metropolitan Phoenix regional drinking water utilities have a long history of providing 

water that meets all health standards.  Unfortunately, water delivered to customers often 

has unpleasant tastes and odors which have no primary regulatory limits.  For the most 

part, these tastes and odors are caused by several soluble compounds released into 

the water by blue-green algae (cyanobacteria) growing in the canals and reservoirs of 

the water supply system.  The two compounds responsible for the bulk of the problem 

are 2-methylisoborneol (MIB) and geosmin.  These compounds are not harmful, but 

they depart to the water earthy, musty or moldy tastes at very low concentrations.  For 

most people, the sensory threshold for these compounds is about 10 ng/L (10 parts per 

trillion).  Usually these tastes and odors are mildly unpleasant, but on occasion the 

water can become undrinkable by a segment of the  population.  During these “T&O 

episodes,” MIB levels can frequently exceed 50 ng/L. 

 

1.2  HISTORICAL PERSPECTIVE 

 

In the mid-1980s analytical techniques emerged (e.g., closed-loop stripping with gas 

chromatography-mass spectroscopy) that enabled detection and identification of 

specific compounds in water that are responsible for earthy, musty, and moldy odors 

(Suffet et al., 1999).  The Metropolita                                                                                                                    

n Water District of Southern California (MWD; see www.mwdH2O.com) was one of the 

first utilities to address the T&O problem.  During the 1980s, MWD developed an 

integrated strategy to control tastes and odors  (Means  and McGuire, 1986; Taylor, et 

al., 1994).  Their strategy utilized both source water control and water treatment.  As a 

result, water utilities and customers in Southern California are provided with water 

containing less than 10 ng/L of MIB or geosmin throughout the year.  Like the Phoenix 

Metropolitan Area, MWD imports its water from the Colorado River, stores water in 

terminal reservoirs, and has multiple local water suppliers.   

 

Throughout the 1980s and 1990s cities in the metropolitan Phoenix region were coping 

with rapid population growth, and associated increasing water demand, and a series of 

USEPA regulations regarding disinfection and disinfection by-products.  During this 

period, water departments also noted seasonal customer complaints of unpleasant and 

earthy, musty, or moldy tastes and odors.  Some cities established trained panels 

(flavor profile analysis panels) of customers and city personnel to identify and track the 

odors, and guide changes to water treatment plant operations.  Other cities applied the 

standard water treatment process of powdered activated carbon (PAC) addition to treat 

seasonal taste and odor events.  At that time, it was unclear where taste and odor 

compounds were produced.  Possible sources included watershed reservoirs, rivers, 

concrete-lined and unlined canals, water treatment plant holding basins, or pressurized 

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finished water distribution systems.  Some local water utilities and contract laboratories 

had the analytical capability to detect MIB and geosmin, but turnaround times were slow 

(2 to 6 weeks), making the data of limited use.  Analytical costs were also high. 

 

From 1996 through 1998 separate studies by the University of Arizona and Arizona 

State University, funded by metropolitan Phoenix water providers and users, 

documented trends in MIB and geosmin occurrence throughout the upstream water 

supply reservoirs, canals, and water treatment plants.  The conclusion was that some of 

the water treatment plants in the region received water with MIB and geosmin 

concentrations ranging from 20 to more than 70 ng/L during the late summer and early 

fall of each year.  The concentrations in finished water were not well-documented.  In 

source waters, concentrations over 100 ng/L were occasionally reported.  While MIB 

concentrations were higher than geosmin concentrations in upstream reservoirs and at 

the head of the SRP canal, geosmin concentrations occasionally exceeded MIB 

concentrations at some locations in the SRP canal system (e.g., Consolidated Canal 

near wells pumping ground water containing elevated nitrate concentrations).  Frequent 

customer complaints and the high cost of PAC treatment prompted cities to develop a 

watershed approach to taste and odor control, rather than simply relying upon PAC 

treatment within water treatment plants.  Managing taste and odors in the water supply 

before it enters a specific WTP, offered the opportunity to control MIB and geosmin 

concentrations to a large number of downstream raw water WTP intakes. 

 

Since the mid-1990s a number of new water treatment plants have been designed to 

treat T&O problems, even though the USEPA has no regulated limit for these 

compounds.  Treating the compounds improves the aesthetic quality of the finished 

drinking water.  For example, ozonation and/or biofiltration have been designed into 

treatment plants in Chandler, Gilbert, and Peoria, Arizona.  These systems are 

optimized for taste and odor control and minimization of regulated by-products (e.g., 

bromate, trihalomethanes, haloacetic acids). 

 

1.3  HISTORY OF THE ASU/CITY OF PHOENIX TASTE AND ODOR PROJECT 

(1999-2002) 

 

Taste and odor episodes in 1997 resulted in hundreds of complaints from customers 

and spurred the development of a three-year collaborative project between the City of 

Phoenix and Arizona State University.  The Salt River Project (SRP) and Central 

Arizona Water Conservation District (CAWCD) were active participants in the project.  

The project’s primary goal was: to reduce the prevalence of T&O problems in the City’s 

water supply.  Achievement of the project’s goal was underpinned by the following 

principles: 

 

1. 

The T&O management program would be based on the  multiple barrier concept 

that has long been used by the water treatment industry as a model for controlling 

pathogens  (Baker, et al., 1999);  (Baker, et al., 2000).  The barriers (treatment 

measures) would be implemented in the watershed, the reservoirs, the canal 

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