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Science Panel urges delay in filling reservoir                                               Fecal Coliform in Shawinigan Lake

Watching Victoria's water

Published in Monday Magazine (Victoria, BC weekly periodical)

September 23 - 29, 2004 Edition

 

Staff reports presented at this week's Regional Water Supply Commission meeting gave the public its first look at the safety of water in the capital region since June. As in other years the commission didn't meet in July or August, a time of year when warm weather typically leads to heavy growth of algae, some types of which are toxic.

According to the report on water quality trends in the main source of the region's drinking water, signed by the manager of the water quality division, Stewart Irwin, and the general manager of the water supply, Jack Hull, the turbidity of Sooke Lake Reservoir was double the long-term average and phosphorus was between 50 and 100 percent higher than before the dam was raised in 2002. Says the report, "Increased concentrations of total phosphorus can foster higher levels of algae."

Chlorophyll levels, which are a general measure of algal population, were also found to be higher overall in 2004 than in 2003 and "substantively higher than the long term pre-inundation average."

Much depends on what type of algae is dominant in the reservoir. Currently, the main species are asterionella and dinobryon, the latter of which gives water a fishy smell and taste, but poses no health risk. Blue-green algae pose a greater risk to human health, and the report states: "In June, a minor peak of blue-green algae occurred in the south basin but more recent months had declined. Samples collected for algal toxins did not produce detectable concentrations."

Hull and Irwin's report on their communication with the chief medical health officer for Vancouver Island Health Authority, Richard Stanwick, shows they were concerned enough that on June 29 they had a discussion with him "about emergency procedures for algal toxins." On July 5 they received abstracts of algae toxin research papers form Stanwick's office, and on July 6 had a "meeting at Royal Jubilee to discuss emergency preparedness related to water."

We seem to have avoided disaster again this year, but with another metre of new land to be flooded before the water level reaches the height on the new dam, we have at least one more year where nutrient levels, algae growth and health risks are likely to be higher than normal.

Science Panel urges delay in filling reservoir

Scientists advising the Regional Water Supply Commission recommended in October that the agency delay filling the expanded Sooke reservoir, the source of Victoria’s drinking water, “to see how the system responds as we get nearer to the full level.”

Since a new dam was built in 2002, water has flooded newly cleared land, four kilometres of an old rail bed and seven kilometres or road, picking up higher than usual levels of nutrients, which encourages the growth of algae.

In a report to the commission’s November 17 meeting, the manger of the water quality division, Stewart Irwin, and the general manager of the water supply, Jack Hull, write, “The concentration of total phosphorus continued to drive higher levels of algal growth. Chlorophyll concentrations (a measure of overall algal numbers) remained above normal.”

During September and October the chlorophyll concentration was up to double what had been normal before the new dam was built.

As has been pointed out here before, much depends on what kind of algae is present. In June there was a peak of blue-green algae, which can be toxic to people. In Brazil in 1988, a bloom of blue-green alga that grew after a dam was built killed 88 people, and sickened 2000. The conditions in our drinking water source are moving in a direction, says Hull and Irwin’s November report, that favours blue-green algae growth, “which is undesirable in the Sooke Reservoir.”

In early 2004 the water level in the Sooke Reservoir peaked at 78 centimetres below the top of the new dam. According to the report, the Inundation Scientific Advisory Working Group says the water supply managers should delay filling the reservoir.

Hull says, however, “There isn’t a final decision at this point on a strategy.” The managers may choose instead to “fill and spill” to flush out some of the nutrients. The changes in the reservoir’s nutrient levels and algal growth were expected, he adds, and “over the next few years that will decline.”                                                                                                            -A.G.

Written by Andrew MacLeod and Alisa Gordaneer. E-mail tips and comments to editorial@mondaymag.com .

Do you know someone who drinks water from  Shawinigan Lake?

Fecal Coliforms in Shawinigan Lake, Vancouver Island, B.C.

During August, 1995  

This report assesses the fecal coliform data collected at Shawinigan Lake on Vancouver Island in august, 1995.  A one month sampling program was undertaken in cooperation with the Cowichan Valley Regional District (C.V.R.D.) in response to their continued concerns with fecal coliforms in Shawinigan Lake.  It is anticipated that the C.V.R.D. will use this report in conjunction with other studies to assist in the determination of the best plan to inform local property owners about the need for disinfection and possibly other treatment of drinking water drawn from Shawinigan Lake.

6.2    Remediation

• All drinking water withdrawals from Shawinigan Lake should be disinfected.

• There is a need to identify and remediate the sources of fecal coliform contamination

    as 3 of 22 sampling sites failed to meet the raw drinking water criterion for water receiving only disinfection.

• There may be a need to increase the water treatment (i.e., filtration plus disinfection)

  or relocate some water intakes into deeper or more distant locations (i.e., away from the lake shore).

The website for this information is:

  http://wlapwww.gov.bc.ca/wat/wq/reference/shawnigancoliforms.pdf

Canadian Cataloguing in Publication Data

Webber, T. N.

            Fecal coliforms in Shawinigan Lake, Vancouver Island, B.C. during August, 1995

            Author: T. N. Webber. Cf. p.

            Includes bibliographical references: p.

            ISBN 0-7726-2878-5

  1.       Water Quality – British Columbia – Shawinigan Lake

         (Lake)  2. Sewage – Environmental aspects – British

         Columbia – Shawinigan Lake (Lake)  I. BC Environment.

          Water Quality Branch II. Title.