Ground Water Resources of British Columbia
Chapter 13 — Case Histories
13.5 THE USE OF GROUND WATER IN AIR CONDITIONING
Woodward Stores Limited, one of Vancouver's three original department stores, opened the city's first suburban shopping centre at Oakridge in 1959. Oakridge lies at the heart of the main residential area of Vancouver. The centre was expanded in 1983-84 and now includes a completely covered and air conditioned shopping area with adjacent office, residential and parking spaces. The complete complex covers an area of 12 ha.
The shopping area is air conditioned continuously throughout the year using outside air and ground water. Ground water provides 40% of the peak cooling load capability.
The use of ground water provided capital cost savings in excess of 600,000 dollars Canadian and will provide operating cost savings of 25% per year based on 1984 energy costs.
Seven wells were constructed close to the perimeter of the site and put into production in 1959. These wells were drilled by a cable tool percussion rig using a 400 mm diameter working casing drilled to the bottom of the aquifer. Two hundred mm diameter well screens were set in the lower half to one-third of the aquifer with 300 mm diameter blank casing being set to surface. A select formation stabilizer of "pea" gravel was placed around the screens as the working casing was removed and the screen was developed by surging and bailing.
During the 1983-84 expansion, the wells were redeveloped and the pumps refurbished. The Johnson Everdur bronze screens were found to be in excellent condition after being in the ground for almost 25 years. Testing revealed that the wells had deteriorated by 11% to 30%. Redevelopment by surging and bailing in conjunction with dry acid pellets and chlorine returned all wells to close to their original 1959 specific capacities. Deterioration was found to be caused by iron slime bacteria even though the ground water contains only 0.21 mg/L of iron and is very low in total dissolved solids.
The sediments lying beneath the Oakridge complex consist of glacial till up to 10 m in thickness overlying the sand and gravel aquifer that ranges from 25 to 15 m in thickness. The aquifer in turn overlies 75 m of clays, silts and tills. Sandstone bedrock lies below this sequence at a depth of 110 m or an elevation of 25 m below sea level.
Pump tests run at various times during the past 25 years indicate that the transmissivity at the wells averages 8.1 x 10-3 m2/s, but that the transmissivity between wells across the well field is approximately one-half this figure at 4.1 x 10-3 m2/s. The difference is probably caused by variations in the aquifer caused by the "cut and fill" deposition of the sand and gravel from glacial meltwater streams. Storativity is approximately 5 x 10-3 indicating an artesian aquifer condition.
Analysis of pumping rates, water levels and precipitation data indicates that the well field can safely produce 4.75 x 105 m3 per year of ground water with a peak monthly production not to exceed 6.6 x 104 m3 during the summer months of July and August.
Ground water will be used throughout the year with monthly rates ranging from 1.25 x 104 m3 to 6 x 104 m3 totalling 4.09 x 105 m3 per year. The ground water is discharged to the sewer after use because recharge to the aquifer has been shown to heat the ground water to unacceptable levels of up to 18° C from a normal temperature of 10° C.
Back to Table of Contents
| 
