Proceedings - Teaching and Learning Centre - Simon Fraser ...

Fraser River Action Plan 3rd Research Workshop
Summary
Effluent Dispersion from the Landsdowne Road
Wastewater Treatment Centre, Prince George
D. Hodgins
Seaconsult Marine Research Ltd.
On October 13, 1993, an effluent plume delineation study was carried out at the Prince George Landsdowne
Road Wastewater Treatment Centre to evaluate performance of the outfall in terms of dilution rate and
distribution of the effluent down-river.
A fluorescent red dye was added to the effluent stream to act as a measurable tracer of the effluent which
allowed mapping of the plume from the diffuser to 12 km downstream. During the survey, the Fraser River
discharge at Prince George was approximately 400 m 3 /s which was roughly 1,000 times the Lansdowne outfall
discharge. Surveying with an in situ fluorometer successfully traced the dye effluent to concentrations of less
than 0.05% with positional accuracy of +/-5 m in the horizontal.
Initial dilution was rapid from 100% effluent concentration in the diffuser to 0.65% or less within 250 m of the
outfall and vertical mixing was complete at 1 km. Beyond about 8 km no concentrations were observed
anywhere in the river that exceeded 0.1% effluent. North of the 8-km section, there was no observed contact
with the eastern shore.
Lateral mixing appeared to be inhibited by current shear zones separating the central, fast-moving core of the
river (which contained most of the freshly discharged effluent) and relatively quiescent areas along some
sections of the shorelines. Because mixing across the shear zones is slow, effluent in the quiescent waters will
tend to be of older origin (i.e., discharged earlier) than effluent in the main river core.
The diffuser discharged effluent in two persistent jets that were separated by roughly 10 m. This characteristic
appears to be indicative of the diffuser performance. No leaks were detected.
Page 59