Executive Summary: Tritium Study


What did we conclude from this study ?

A study of the effect of tritium release from Bruce Power on Lake Huron shoreline was conducted during the summer of 1996. Based on the current Ontario Drinking Water Objectives, the municipal water supplies at Kincardine, Southampton and Port Elgin are safe to drink. Drilled wells are relatively unaffected by the releases of tritium. Shallow wells north of Bruce Power exhibit the highest levels of tritium. Recreational use of the Lake Huron beach waters in the study areas and during the study period did not pose a health risk to the public. Typically, the tritium concentrations in drinking water are highest north of Bruce Power and decrease exponentially with distance. Concentrations of tritium are commonly 14 times lower by the time they reach Port Elgin, two to four days after their release at Bruce Power.

Why did we do this study?

The availability of safe, clean drinking water has been a public health interest around the world for over a century. In Bruce County there was a growing public concern regarding radioactive tritium released into Lake Huron during nuclear power production at Bruce Power. Although the area’s municipal water treatment plants are monitored for tritium, nothing was known about the private water supplies in the area.

The study was designed to obtain specific, local information on the average or background tritium levels in drinking and recreational waters along the Lake Huron shoreline. Furthermore, fluctuations in the release of tritium at Bruce Power would be observed and tracked to evaluate their effect on the local water supply.

What are the current standards?

The maximum acceptable level of tritium in drinking water, set by the Ontario Drinking Water Objectives, has been lowered from 400,000 to 40,000 and now stands at 7,000 Bq/L as an annual average. This standard ensures that the annual effective dose from drinking water sources does not exceed 0.1 mSv per year. In other words, no more than 10% of the recommended maximum public dose of radiation (1 mSv/year) may come from drinking water. Within these guidelines, individual releases of more than 7,000 Bq/L are not considered to pose a health risk unless they result in an annual average dose over 7,000 Bq/L.

Who participated?

On April 4, 1996, a meeting was held to discuss acquiring better information on tritium levels in private water supplies. The meeting was hosted by the Bruce Township and attended by the Regional Emergency Planning Co-ordinator, representatives from Kincardine Township Council, Bruce Township Council, Ontario Hydro, Ministry of Labour, Ministry of Natural Resources and the Health Unit. The group decided the study was needed along the lakefront area from Kincardine to Southampton. The neighbouring township of Saugeen was, at that time, invited to participate. An Ontario Environmental Youth Corps Grant, Bruce Township and Ontario Hydro provided financial support for the study.

What did we do?

The Health Unit managed a pilot study involving three major steps:

• Step1: Establish baseline data on land use, drinking and recreational water use along the Lake Huron shoreline, north and south of Bruce Power in June 1996.
   

• Step 2: Monitor the level of tritium in a representative drinking water sample and recreational water sample along the shoreline from July 8 to August 23, 1996.
   

• Step 3: Describe the movement of tritium through the water supply by relating the level of tritium in the local water supplies with the discharge of tritium from the two nuclear power plants, Bruce A and Bruce B.
   

Lake Huron Shoreline Study Area Map

 
What information did we get?

The majority of land use was seasonal residential (76%), with the remaining (24%) being permanent residential. The reported water sources were drilled wells (27%), communal water supplies (26%), dug wells (22%), sandpoints (16%), bottled water (6%) and pumped water (3%). All the communal water supplies, with one exception, were served by drilled wells. Drilled wells had a mean depth of 39 meters and dug wells had a mean depth of 5 meters. There were three water treatment plants within the study area.

Water movement in the vicinity of Bruce Power is predominately along the shore in a northeasterly direction. Tritium discharges from Bruce Power generally have the greatest effect on the shoreline area north of the site, excluding drilled wells.
The closest recreational site directly north of Bruce Power was Baie du Dore, which recorded an average reading of 141 Bq/L and a peak reading of 240 Bq/L. Drilled wells, regardless of location, measured at or near the level of detection. Drilled wells do not appear to be affected by tritium discharges into Lake Huron. Surface wells south of Bruce Power recorded tritium levels higher than the nearby recreational water supplies. This may be caused by the additional burden of airborne tritium.

The closest water treatment plant to Bruce Power is the Port Elgin Water Treatment Plant on the north side. The mean tritium concentration at the plant during the study period was 25.9 Bq/L with a peak reading below 180 Bq/L. Readings were lower further north in Southampton at 22.9 Bq/L. South of Bruce Power, in Kincardine, the average level was below the level of detection. Overall, the tritium concentration decreases exponentially with distance north of Bruce Power.

Accurately determining the amount of tritium released into Lake Huron from Bruce Power is not a straightforward exercise. Two measurements of the tritium released at each of the two outfalls at Bruce Power were available: weekly composite tritium levels and calculated tritium levels. No data is available for the combined effects of tritium releases from Bruce A. However, a strong relationship was found between the calculated tritium levels and the nearby sampling points; for example, 81% of the variation in the tritium levels at Scott Point may be accounted for by knowing the calculated tritium levels at Bruce A.

Ontario Hydro uses a dilution ratio of 1:14 to calculate probable tritium concentration at Port Elgin Water Treatment Plant as compared to Bruce Power. For example, a weekly average tritium concentration discharge of 1400 Bq/L from Bruce Power would result in 100 Bq/L at Port Elgin Water Treatment Plant using the ratio. For the time period from April 1 to August 31, 1996, the dilution factor at the Port Elgin Water Treatment Plant approximated 1:14.5. The limitation of using this dilution factor is that it only applies to the Port Elgin Water Treatment Plant and does not give us any information for sites closer to Bruce Power.
 

What future recommendations came from this study?

• Ontario Hydro should extend its environmental monitoring program north of the Bruce A outfall channel to at least include Baie du Dore, Scott Point and Brucedale Conservation Area. Shoreline lake samples and shallow wells in the area should be routinely monitored for tritium concentrations. Samples should be taken during each of the four seasons.
   

• Following an abnormally high tritium release to the lake, samples should be taken at least daily at multiply sites north of Bruce Power. This information would enable the Health Unit to better inform the public of any risk from the release.
   

• Following an abnormally high tritium release to the lake, samples taken at the Port Elgin Water Treatment Plant should be analysed daily.
   

• Shallow wells surrounding Bruce Power should be monitored for tritium to establish airborne contamination. Wells should be chosen at varying distances from Bruce Power to the north, east and south of the plant.
   

• The composite sampler system at the Bruce A outfall needs repair or replacement. The tritium concentrations recorded by this system do not accurately reflect tritium concentrations in the outfall stream.
   

• A model should be developed to show tritium concentrations that result from liquid tritium emissions from Bruce Power. The model should include depth, distance and dilution offshore and along the Lake Huron shoreline, north and south of the Bruce A and the Bruce B outfall channels.
   

What did we not find out?

The study was limited in scope and of a relatively short duration. The return rate of the survey of shoreline property owners was 51%. Therefore, many of the water supplies in the area may still need to be identified.

During the study period, consistently low and even releases of tritium were observed from Bruce Power. A controlled, elevated release would have better simulated an emergency and provided the study with some peak data, which would have been more easily tracked through the water supply.

The data reported from each of the two plants was presented in a different manner and detail, making it difficult to compare or combine the tritium levels entering the lake from the two plants.

This study reflects only the summer of 1996. It may be possible that, within different time periods and seasons, the movement of tritium through the water supply would be substantially different.


For a copy of the report contact the Grey Bruce Health Unit.