Solution for Sealing Stoplogs

To seal leaking stoplogs at its six hydro stations on the Winnipeg River, Manitoba Hydro uses Hydro-Lite blast furnace slag. This product seals the stoplogs, minimizing the leakage, and is more environmentally friendly than the cinders from steam locomotives previously used for this purpose. In addition, Hydro-Lite usually can be applied by plant staff, without the need to hire divers.

The need to seal the stoplogs

Manitoba Hydro operates six hydroelectric generating stations on the Winnipeg River with a total capacity of 586 MW. These facilities, which began operating between 1911 and 1952, have a total of 50 generators and 190 spillway openings. Much of the maintenance work performed for the generators and spillways requires the use of stoplogs to dewater the area.

Because of the ages of the stations and the variety of designs, there are many types of stoplogs in use. These include wood or steel logs, with steel, brass, wood, or rubber seals. The ages of these stoplogs and the lack of consistency in the design tolerances for the structures have caused numerous problems with sealing and maintaining a seal around the stoplogs. A common problem plant personnel faced was reducing the leakage around and through the stoplogs to a manageable amount, to allow for work to be performed in a dewatered area.

Methods used to seal stoplogs

Some materials Manitoba Hydro has used in the past to seal gaps or holes in stoplogs include straw, horse manure, oakum, granite dust, and sawdust mixed with oil. These were materials that were handy at the time. Often, this material was placed by divers, who manually chinked the openings.

From the 1940s to about 2000, it was common practice at Manitoba Hydro’s hydraulic stations to use cinders (unburnt coal residue or ash) to seal stoplogs and gates. On the Winnipeg River, Manitoba Hydro used cinders cleaned from the boilers of steam locomotives. Using this source, cinders were available in large quantities and had the right gradation for the application. Cinders worked well and could be applied by plant staff, without requiring a diver in most situations. The cinders were simply dropped into the water in the area of a leak, and they would sink and be drawn into the leak by the current. In addition to being relatively easy to use, these cinders were a relatively environmentally friendly material, Manitoba Hydro thought.

This blast furnace slag, known as Hydro-Lite, is used to seal leaking stoplogs. Manitoba Hydro uses the product as an alternative to cinders because it is more environmentally friendly.
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In 2001, Manitoba Hydro was performing reviews of all work practices, tools, and products in order to be certified as compliant to International Organization for Standardization (ISO) 14000 standards. During these reviews, personnel discovered that the utility may have risked violation of Canada’s Fisheries Act as a result of using cinders to seal the stoplogs. The act, passed in 1985, prohibits dumping of coal ash, stones, and other deleterious substances in waters where fish live. Because of this fact, as well as the efforts of an environmental management commitment formed in 2000 to minimize the company’s environmental effects, Manitoba Hydro began looking for alternatives to the use of cinders.

Researching an alternative

To find a suitable alternative, environmental specialist Alison Zacharias supervised the research efforts of a summer student in the utility’s Environmental Support section. In 2001, this student began canvassing other utilities across North America to assess materials they were using that could replace cinders.

One product the student uncovered was Hydro-Lite. Manitoba Hydro decided to assess this product’s environmental effects, as well as its suitability for replacing cinders for sealing stoplogs. Hydro-Lite is a blast furnace slag produced by Lafarge Canada Inc. Slag is a nonmetallic byproduct from the production of iron. Lafarge worked with Ontario Power Generation to develop this product.

After laboratory assessment was complete, Manitoba Hydro determined that Hydro-Lite should not be considered a material that is hazardous to health and safety. As part of this assessment, leachate extraction testing was performed to determine what types of materials and quantities would dissolve and leach into the water. Data from this testing was compared to the Manitoba Surface Water Quality Objectives for Drinking Water and Aquatic Life. This product fell well within the parameters of the regulation. The utility shared the data from the testing with Environment Canada, which approved of further field trials of Hydro-Lite on the Winnipeg River.

Using Hydro-Lite

Manitoba Hydro purchased a quantity of Hydro-Lite for testing during scheduled maintenance at its 133-MW Great Falls generating station. In November 2001, stoplogs were installed to dewater Unit 6. The Hydro-Lite was applied in the same way the cinders were applied previously. This trial showed that one application of Hydro-Lite performed very well in sealing any leakage and was comparable to cinders in this application. Further observations of the stoplogs over the following two-week maintenance period showed that the amount of leakage did not change. Additional testing was performed over a two-year period at other Manitoba Hydro stations, with favorable results. Thus, in about 2003 the utility decided to stop using cinders and change to Hydro-Lite.

To guide and track use of Hydro-Lite at its facilities, Manitoba Hydro developed an internal Environmental Best Practice document. This document is used to track quantities of Hydro-Lite used annually at each station. The document also includes the requirement that each load of Hydro-Lite purchased for a station must have leachate extraction tests completed in Manitoba Hydro’s lab. Before using the Hydro-Lite, results of these tests are compared to Manitoba’s water quality standards to determine if the material will leach hazardous products into the drinking water.


Since 2001, all stoplog and gate sealing on the Winnipeg River has been accomplished using Hydro-Lite. Over several years of using Hydro-Lite, Manitoba Hydro has determined that gradation of the material in Hydro-Lite is a key factor in the success of the application. A variety of granular sizes is important to allow the product to properly seal any leaks. In all respects, this material has matched or exceeded the utility’s expectations in replacing cinders. It has performed well and has the added bonus of being more environmentally friendly than cinders.

– By Paul Softley, utility supervisor, Great Falls operations, Manitoba Hydro, P.O. Box 70, Great Falls, Manitoba R0E 0V0 Canada; (1) 204-367-5123; E-mail:


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