When the mine was at its peak, the surrounding environment paid a stiff price. Local groundwater, creeks and the waters of nearby Howe Sound all suffered losses that hung on for many decades. The source of the problem was known as Acid Rock Drainage (ARD). To explain, ARD forms when water and oxygen react with metal sulphides such as pyrite. The result is sulphuric acid and dissolved metals. ARD occurs naturally, anywhere that metal sulphides are exposed to air and water. Digging in the mine's tunnels made for vast quantities of ARD. Once it formed, it inevitably flowed into creeks and Howe Sound.
Thankfully, Britannia's ARD issue is now ancient history. Working with the province, land owners and community, an intensive remediation campaign was launched. Since 2002, Golder Associates have spearheaded a cleanup of local contaminated soils. A further step was taken with EPCOR's water treatment plant in 2005. It collects all water coming from the mine. The end-result has been a successful turnaround. Life has returned to the waters surrounding the mine, including Howe Sound.
For a more in-depth look at Britannia's environmental story, see "The Facts About Britannia's Environment".
ARD is a natural process where oxygen and water react with metal sulphides. Usually, this happens when air meets rain. Bacteria (Thiobacillus ferrooxidans) also plays a role in the process. The biggest ARD producer is pyrite (iron sulphide), although at Britannia, chalcopyrite (copper ore), galena (lead ore) and sphalerite (zinc ore) were involved. The sulphuric acid and dissolved metals that were produced by ARD wound up polluting the local environment once they found their way into groundwater and local water sources.
When two pennies worth of copper are dissolved in a swimming pool, it becomes toxic to marine life. That said, the mine was pumping out the equivalent of 69 pennies worth of copper plus 20,800 pop cans worth of vinegar every minute. Obviously, this was a problem that called for a complex and thorough resolution. Fortunately, it came to pass.
The overwhelming size of the mine meant larger amounts of ARD were generated. Environmental regulations of the day were minimal, so little was done to attack the problem. To make matters worse, the digging of 210 km of tunnels in the mountains, plus the fractured nature of the rock, created a much larger surface for the damaging chemical reaction. To add to that, with high snow and heavy rainfall winding up in the mine's open pit, more water was becoming polluted.
Back in the 1930's, the issue was already a concern, but little was understood about the impact on the environment. Copper launders existed at the mine which helped slightly, but it was done for economic, not environmental, reasons. These launders were long troughs containing iron scraps. Mine water was fed through the troughs before being discharged. An iron-copper exchange meant the iron pieces became coated in copper, while relatively non-toxic iron dissolved and flowed with the water out of the troughs. The copper was then collected and sold. So it did help reduce the amount of copper entering Howe Sound, but only until the mine was closed in 1974.
On closure, mine owners Anaconda installed an outflow pipe that discharged the water 50 metres below sea level. The water was not treated, but was taken away from the intertidal zone, the most vulnerable area for aquatic life. Anaconda also installed a mud/earth dam near the 2200 portal (reinstated in 2001). As a result, water was stopped from entering Britannia Creek, until the dam failed sometime in the 1980's/90's.
These days, the mine water is captured and treated at the EPCOR Britannia Mine Water Treatment Plant. Now, it's clean. With the acidity neutralized and the metals removed, the water is discharged into Howe Sound. A mammoth challenge has been finally overcome with safety in mind. The mine's portals are sealed. All water flows down to a single portal near the top of the Mill building. Here, a concrete plug and outlet pipes control the water's exit to Howe Sound. Area residents now rest comfortably. For that matter, so does the surrounding aquatic life.
To neutralize the acidity, lime slurry (lime/water mixture) is added to a tank containing the ARD. This raises the pH from 3.8 to 9.3. In other words, it goes from being acidic to being alkaline. When this happens, the metals, which were dissolved in the ARD, naturally precipitate then become metal particles. Those particles go into another tank where a man-made customized polymer is added. This electrostatically attracts the metal particles. They sink to the bottom allowing the clean water to be removed at the top. Below, the metal sludge is removed and dewatered. Twice a year, it's taken up to the original Jane Basin mining pit. Here it helps cap the pit, preventing some of the water from entering the mine. Because the metal sludge is not in the form of metal sulphides, it cannot form ARD in the future. Every day, 600 to 700 kg of metal sludge is removed, all metal that is no longer discharged into Howe Sound.