Date:August 28, 1998

To:Works and Utilities Committee

From:Michael A. Price, General Manager, Water & Wastewater Services

Subject:Drinking Water Taste and Odour

Purpose:

To provide information on the recent occurrence of an unpleasant taste and odour in drinking water and our strategy to address the issue.

Funding Sources, Financial Implications and Impact Statement:

There are no funding implications resulting from this report.

Recommendations:

It is recommended that this report be received for information.

Council Reference/Background/History:

During the past decade, there have been a few occurrences of unpleasant taste and odour formation in the water treated at Toronto's water treatment plants. These events were caused by seasonal changes in the lake water resulting in higher than normal temperatures and blooms of naturally occurring algae.

The noticeable earthy, musty taste and odour was an aesthetic condition which did not pose a health risk to consumers. The duration of these episodes have ranged from a few days to ten days. The most recent events occurred in 1996 on a limited basis and in 1994 on a City-wide basis.

Comments and/or Discussion and/or Justification:

Every year during late summer and early fall, the temperature of the raw water being drawn into our water treatment plants, through intake lines one to three kilometres from shore, increases to maximum levels and the growth of algae in the lake water heightens.

These naturally occurring phenomena do not in themselves bring about taste and odour episodes. The cause of these episodes, which have been sporadic, is the formation of trace amounts of compounds produced during the life cycle of only certain species of algae.

Subsequent to the 1994 episode, expertise was developed in our Quality Control laboratories to enable detection of compounds well known in the water industry for producing taste and odour which is noticeable at extremely low levels (parts per trillion). This has enabled us to determine the type and level of compounds responsible for a particular taste and odour event.

During the early morning hours on Monday, August 10, 1998, an earthy, musty odour was detected by Operations staff at our F.J. Horgan Filtration Plant, the most easterly of Toronto's four water treatment plants.. The temperature of the raw water at our plants had increased from about 10 degrees Celsius on July 31 to 22 degrees Celsius.

In communications with Region of Durham staff, it was confirmed that they had noticed taste and odour in the water treated at their plants a few days earlier. Inquiries and complaints started to be received from Toronto consumers, mainly in Scarborough District.

Given the likelihood of a major taste and odour event, a communications action plan was initiated immediately. This involved:

(a)faxing a letter of notification to City of Toronto and Region of York Works and Health offices with copies to the Mayor's office, all City Councillors, neighbouring Regional Municipalities and the Ministry of the Environment;

(b)issuing a media release (attached);

(c)establishing telephone hot lines at our Communications and Quality Control units; and

(d)having the Director of Water Supply available for media interviews.

A sampling strategy was also activated to enable identification of the compounds causing the taste and odour and confirmation that the quality of water being produced and distributed was not affected.

During the first three days of the episode, the taste and odour also became noticeable at our R.C. Harris and R.L. Clark Plants and over 800 inquiries and complaints from the public were handled. Most callers were reassured when they were advised of the cause of the taste and smell and that the water was safe to consume. They were also advised of methods to reduce the intensity of taste and smell in their drinking water through cooling. Our laboratory staff determined that addition of small amounts of lemon juice was quite effective in reducing the taste and odour.

There was extensive media coverage by TV networks, radio stations and the major daily newspapers, which was very effective in communicating the key information to our consumers during the initial days of the occurrence.

Subsequently, the inquiries and complaints dropped off dramatically. The taste and odour in the water treated at our plants continued to be noticed, albeit at differing levels of intensity, for eleven consecutive days since the start of the event, and the water temperatures remained between 20 to 23 degrees Celsius.

The Regions of Durham, Peel and Halton and the City of Hamilton were similarly affected during this interval.

On Friday, August 21, there was a significant decrease in the raw water temperatures at our three operational plants and taste and odour was no longer detectable at any of the plants by Monday, August 24.

Analytical results of samples taken on a daily basis confirmed that the bacteriological quality continued to be excellent throughout the event and that the water remained safe to consume.

There have been several requests submitted to us for rebates on the water bills or reimbursement of bottled water costs. We have taken the approach that the water is safe to drink and we are continuing to deny all such requests.

Given that significant temperature spikes may be experienced again at any time up until the beginning of October, recurrence of an episode is possible should taste and odour compounds be present in the high temperature currents.

Analyses of samples from our plants and the distribution system determined that the cause of the taste and odour was a compound called geosmin which is produced by certain species of algae and can cause taste and smell noticeable to some people at a level as low as 10 parts per trillion (ppt). This is equivalent to a $10 share of a million $1 million jackpots. The geosmin levels in the treated water samples analyzed ranged from 10 to 56 ppt, a level which will produce taste and smell noticeable to most people, but is not harmful to health.

Geosmin is one of various taste and odour compounds which can only be removed through special water treatment processes.

Our four water treatment plants employ conventional water treatment processes. Although operational process changes can be made to reduce the taste and odour to some extent, special processes utilizing activated carbon are required for taste and odour control. Because of the relatively short duration and infrequent occurrences of past taste and odour episodes, expenditures required for modifications to our water treatment plants to incorporate a taste and odour control process have not been justified.

Given our experience this year with increases in lake water temperature occurring earlier than normal and ecological changes resulting in blooms of algae at lower depths, it is likely that the frequency, duration and intensity of taste and odour episodes will increase in the future.

Accordingly, we are investigating the feasibility of alternative processes for taste and odour control at our plants.

The process which will be most effective in removal of compounds causing taste and odour is Granular Activated Carbon (GAC) contactors following the conventional filtration process. This process will also enable further reduction in the levels of trace organic compounds such as trihalomethanes.

The estimated Capital costs of installing this process at our four water treatment plants is in excess of $100 million.

There are lower cost, but less effective, alternatives to GAC contactors for taste and odour control which may be feasible to implement on an interim basis pending the longer term solution. These alternatives include powdered activated carbon and capping of existing filters with GAC. The impacts of these modifications to our existing treatment process need to be carefully evaluated to ensure that the excellent bacteriological quality of our treated water is maintained.

The processes to be recommended will be the subject of a future report.

The deeper intake proposed for the Island Plant as part of the Deep Lake Water Cooling project will result in raw water temperatures below 4 degrees Celsius year round and will likely preclude any taste and odour. The feasibility of extending intakes at our Harris, Horgan and Clark Plants to draw water from deeper levels will be reviewed as an alternative approach to process changes.

Conclusion:

The unpleasant taste and odour in the drinking water in August of this year was caused by minuscule levels of a compound produced by algae and higher than normal water temperatures. Water quality was otherwise not affected and the water remained safe to consume.

Given the likelihood of increased frequency and duration of taste and odour occurrences in future, the feasibility of alternative processes for taste and odour control at our water treatment plants is being investigated.

Contact Name and Telephone Number:

Mr. H.A. Taniguchi, P. Eng.

Director of Water Supply Division

Phone: (416) 392-8220

Fax: (416) 392-3639

E-mail: htaniguchi@metrodesk.metrotor.on.ca

Michael A. Price

General Manager, Water and Wastewater Services

Barry H. Gutteridge

Commissioner, Works and Emergency Services

HAT/rah

Attachment