Water Stewardship Information Sources
| ID | 1868 |
|---|---|
| Citation | Urban Systems Ltd. 2013. City of Vernon Environmental Impact Study: Effluent Discharge to Okanagan Lake, Final Report. City of Vernon. |
| Organization | City of Vernon |
| URL | http://www.vernon.ca/services/operations/documents/LWMP/APPENDIX%20F_EnvironmentalImpactStudy.pdf |
| Abstract/Description or Keywords | The City of Vernon last completed a Liquid Waste Management Plan (LWMP) in 1999 and from the BC Ministry of Environment recommendation, the City is currently undertaking a review of the LWMP. As part of the LWMP review, there is the need to assess the options for effluent release to the environment. Under the current practices, the City's effluent is used for irrigation on surrounding agricultural lands. Through the LWMP review, an environmental impact study is required to evaluate the potential to formalise the lake discharge, which would result in effluent being directed to Okanagan Lake on a more regular basis. The primary aim of the environmental impact study is to assess the discharge of effluent to Okanagan Lake while developing effluent criteria which will protect public health and the environment, with the primary focus being on nutrients and bacteriological indicators. Dilution analyses were performed to provide an indication of the dilution potential and the factors which will affect mixing between the effluent and lake water. The analyses were completed for combinations of lake conditions, effluent temperatures and discharge rates. The two discharge rates that were analysed were an effluent flow rate of 16,700 m3 /d, which is the 20 year design flow, and 10,160 m3 /d, which assumes the optimisation of irrigation. The dilution ratio at the end of the initial dilution zone (IDZ) was determined to be between 23:1 and 230:1 for an effluent flow rate of 16,700 m3 /d and between 29:1 and 314:1 for an effluent flow rate of 10,160 m3 /d. In all cases, the available dilution is higher than the minimum 10:1 dilution which is indicated in the BC Municipal Wastewater Regulation. Additional dilution is achieved before the plume reaches the closest shoreline, which is approximately 1,300 m away, if the plume moves in the direction of the closest shoreline. The dilution ratio at the shoreline was determined to be between 70:1 and 820:1 for an effluent flow rate of 16,700 m3 /d and between 88:1 and 1,118:1 for an effluent flow rate of 10,160 m3 /d. These dilution ratios are considered to be conservative, as winddriven mixing was ignored in the analysis. Wind and waves can easily generate more mixing and increased dilution, regardless of the season. The highest dilution ratios occur during the winter months, as the lake is not stratified which allows a greater potential for mixing to occur between the effluent and lake water. However, due to the lack of stratification, the effluent is likely to move to the surface of the lake. The lowest dilution ratios occur during the summer months, as the effluent is trapped below the thermocline. However, this means that the effluent will not rise to the surface of the lake in the summer months. water quality, effluent, pollution |
| Information Type | report |
| Regional Watershed | Okanagan |
| Sub-watershed if known | Okanagan Lake |
| Aquifer # | |
| Comments | |
| Project status | complete |
| Contact Name | Joanne Harkness |
| Contact Email | [email protected] |