Graham Lake, a few minutes walk from the end of Mallard Way on the East side of Denman Island, is the water source for sixty-seven (67) properties within the Graham Lake Improvement District (GLID).
This beautiful body of water, surrounded by low, forested slopes is approximately 1.3 kilometers long and an average of 120 meters wide, an area of some 15.4 hectares or 38 acres. The volume of the lake has been estimated as 613 acre feet or just under 200 million gallons with a drop in level from April to September of between 0.26 and 0.4 meters due to evaporation and the draw-down of licensed water users.
Of the twelve licenses totaling 40,000 gallons per day, Graham Lake Improvement District’s two licenses account for 33,000 gallons per day. In practice however demand is far less, averaging approximately 18,000 gallons per day through the year, with a peak daily demand of some 29,000 gallons in the month of August.
The limitation on off-take is the processing and pumping of the water through the system. The original system was constructed about 1970 and consists of a small dam on Graham Lake, a submerged intake of six PVC pipes enclosed in wire mesh and approximately 750 metres of 150mm AC pipe leading to a water treatment and pumphouse building.
Between 2004 and 2006 the water treatment and pumping systems were significantly upgraded. Designed and built by Mike Comeau, then Chairman, and Rob Manering, former technician and operator, the new system ensures that, with regular monitoring and care, water quality complies with Canadian Drinking Water Quality Guidelines.
First, filtration occurs at the lake with 0.04” slots in the PVC pipes preventing salamanders and other aquatic creatures entering the system. At the pumphouse a pre-filter eliminates basic debris before water is passed through two parallel sand-filters for the removal of smaller particulates.
Following the filtration of the source water, a three-step disinfection process is applied. The first primary disinfection of the water is achieved via UV radiation with two parallel UV reactors (12 bulbs per unit). Each reactor has a capacity of up to 117 gallons per minute, though total flow in rarely exceeds 100 usg/min.
Chlorination is the second primary disinfection. After chlorine is added, the water enters a stainless-steel contact tank. Once the water has absorbed the chemical, it is released towards a concrete reservoir. Before the chlorinated water enters the reservoir, Ammonia is added. The Ammonia reacts with the chlorine to form Monochloramine, a disinfectant that is more stable than chlorine. Chloramination (the name of the process during which Monochloramines are formed) is a secondary disinfection process; the goal is to create a disinfectant with a lifespan longer than the lifespan of chlorine). From the reservoir, water is pumped into the distribution system by one or two 3hp pumps, depending on demand. In 2008 a propane-powered emergency generator was installed to ensure continuous treatment and pumping operations during BC Hydro power failures.
Two EOCP-certified Small Water System Operators, who collaborate closely with the Vancouver Island Health Authority (VIHA) and the Comox Valley Regional District (CVRD), ensure the safety of our drinking water and the integrity of our water system.
The Graham Lake Improvement District is administered and overseen by volunteers – an elected three-person Board of Trustees, plus a Manager, Secretary and Treasurer.