Calendar Year	1998	1999	2000	2001	2002	2003	2004
Sulphate (tonnes)	233	127	365	341	4	9.5	16.9
Sewage ('000's m 3)	122	130	127	124	104	109	97.5

Burrard Generating Station chlorinates its marine-sourced cooling water to reduce biofouling of the cooling system. Chlorination only occurs when mussel larva are likely to present, typically from late May through mid December. Before the water is discharged, it is treated with sulphur dioxide at the rate of 20 to 50 micrograms per litre to remove the residual chlorine that can be harmful to aquatic life. The treated discharge contains primarily sulphate and chloride as the products of the dechlorination reaction. Because the sulphate concentration in Burrard Inlet is approximately three per cent by weight, this discharge does not change the local concentration detectably.

Sewage is the estimated total volume of sanitary effluent generated from all BC Hydro buildings and offices, excluding generating stations and Surrey Oil Operations.