Wet Weather Flow Management

The management of wet weather flows is a critical part of our wastewater strategy. The majority of the CRD’s current wastewater collection system is composed of separated sanitary and storm water systems. Columbia Boulevard Wastewater Treatment Plant

However, rainwater inflow and groundwater infiltration often enters the sanitary sewer system through unauthorized connections or cracks in pipes or manholes. During extreme weather events, this water overwhelms the wastewater collection system, resulting in sanitary sewer overflows (SSOs). Overflows can cause environmental damage through flooding and contamination.

The policy of the Provincial Government is to ultimately eliminate SSOs. This is a significant undertaking, and will take decades to achieve, but the CRD is working toward this goal.

What is the CRD doing to manage overflows?

Albert Head

The CRD is planning for the management of overflows as part of the new wastewater treatment process. Proposed programs will focus on managing the surplus wet weather flows on a more local basis, as overflow rates vary significantly between municipality. See table below:

Municipality Average Sewer Age

1996 Peak Rate

2004-5 Peak Rate 2005-6 Peak Rate 2006-8 Peak Rate

Colwood
Including DND
Excluding DND


20
9		 not sewered
40-45,000
18-22,000
40-45,000
18-22,000
40-45,000
18-22,000
Esquimalt 82 80-90,000 95-100,000 95-100,000

100-115,000
Langford 8 not sewered 15-20,000 17-22,000 17-22,000
Oak Bay
Uplands		 69
74		 80-110,000
>120,000		 110-115,000
>400,000		 110-120,000
>400,000		 110-120,000
>400,000
Saanich 33 18-22,000 18-22,000 18-22,000 18-22,000
Victoria 89 130-140,000 160-165,000 150-160,000 145-150,000
View Royal 21 15-20,000 18-22,000 18-22,000 20-25,000

Numbers provided are the estimated five year peak rate (L/ha/day)

CRD Commitments

  • Develop plans for Inflow and Infiltration (I&I) reduction
  • Commit funds for I&I reduction
  • Measure flows before and after work
  • Establish ongoing sewer system evaluation
  • Submit Biennial progress reports to the Ministry (next report due March 2009)

Wet weather flows from the upper reaches of the wastewater collection system may be treated and reused or discharged at a smaller plant. This would both decrease the overall wet weather flow and free up capacity to handle additional flow downstream.

When looking at possible solutions to sanitary sewer overflows, the CRD is researching the following:

  • Overflow events precipitation amounts
  • Flows that will be received at each wastewater plant both at start-up and in the future
  • Flows amounts contributed from each political jurisdiction, in order to provide a basis for the development of user rate strategies
  • The frequency, duration and volume of overflows in all locations of the CRD
  • Strategies and improvements needed to eliminate overflows over time