Attachment 9: Conceptual Servicing Brief (McElhanney)

CONCEPTUAL SERVICING BRIEF

To: Town of View Royal Engineering Department
From: Nathan Dunlop, P.Eng., Project Engineer, McElhanney Ltd. (Victoria office)
Re: 167/169/171 Island Highway Conceptual Servicing Brief
Date: June 18, 2021

1. INTRODUCTION

The proposed development is located along Island Highway at 167, 169 and 171 Island Highway, in View Royal, BC.

The properties require Rezoning.

This Conceptual Servicing Brief is submitted in support of the Rezoning Application. This brief will provide information on the existing and proposed storm, sanitary and water infrastructure for the proposed development.

2. EXISTING CONDITIONS

2.1. ISLAND HIGHWAY

• Storm:
  • 375 mm dia Polyvinyl Chloride (PVC) main along Island Highway, connects to a 600 mm dia Corflo main crossing the road south (near the north-east side of the development). This pipe connects to a 675 mm dia main running through Portage Park.
  • Storm connection (size unknown) to 167 Island Highway connects to the 675 mm dia main
  • A combined 200 mm dia storm connection to 169 and 171 Island Highway connects to the 375 mm PVC main in the road
• Sanitary:
  • 200 mm dia PVC sanitary main
  • 200 mm dia PVC road crossing near the north-east side of the development. This connection then splits to provide a service to each of to 167, 169 and 171 Island Highway
• Water:
  • 200 mm dia Ductile Iron (DI) distribution main
  • 813 mm dia Steel supply main
  • combined 50 mm dia Copper water service to 167, 169 and 171 Island Highway

3. DESIGN CRITERIA AND ASSUMPTIONS

3.1. STORM

• Design Criteria:
  • Provide post-development runoff equal to or less than pre-development runoff, up to a 1 in 10 year rainfall event.
  • Flows above the 1 in 10 year rainfall event will flow overland.
• Assumptions:
  • Victoria-Gonzales IDF curve used in the PCWMM model.

3.2. SANITARY

• Design Criteria:
  • Sewage flows will be calculated in accordance with the Master Municipal Construction Documents (MMCD) Design Guidelines 2014. As MMCD does not provide per capita rates for residential units, the Sewage Disposal Regulation of the Health Act (Appendix A) will also be utilized.
• Assumptions:
  • The occupancy load is based on the number of residential units (and unit mix) as proposed in the Rezoning Applications.

3.3. WATER

• Design Criteria:
  • Fire Flows in accordance with the Fire Underwriters Survey (FUS) with 140 kilo Pascals (kPa) or 20 pounds per square inch (psi) of residual pressure.
  • Domestic Flows: meter sizing will be based on the American Water Works Association (AWWA) M22 calculation.
• Assumptions:
  • The FUS calculation and the AWWA M22 calculations will be based on the building configuration and occupancy load as proposed in the Rezoning Applications.

4. PROPOSED FLOWS AND LOADS

Please refer to the attached Conceptual Servicing drawing dated June 18, 2021 in conjunction with the information below.

4.1. STORM

Storm water from within the development lot will be collected via roof and area drains and connected to the storm water management system. The SWM system will consist of onsite conveyance mains, storm water storage tanks and a flow control manhole. Storm water will be discharged from the site through an orifice controlled outlet into the existing 675 mm dia storm main in Portage Park (existing service size will be confirmed and upsized if required). Storm water discharges will be limited to pre-development runoff rates for the 2- and 10-year events.

All rainfall events greater than a 10-year event will follow the overland flood route to Portage Park.

4.1.1. Stormwater Calculations:

A PCSWMM model was used to calculate pre- and post-development runoff. The model also calculated required storage volumes to maintain post-development runoff at pre-development rates.

4.1.1.1. Model Input Parameters

• IDF Data = Victoria-Gonzales
  • Intensity (24 hr 1:2-year storm event) = 44.9 mm / day
  • Intensity (24 hr 1:10-year storm event) = 75.3 mm / day
• Rainfall Distribution = SCS Type 1A

See attached Appendix B for a detailed breakdown of the model input parameters.

4.1.1.2. Model Outputs

The following is a summary of the model outputs, detailing the pre-development and post-development flows as well as the required storage for both the 2- and 10-year rainfall events. Post-development storage volumes determined limited post-development flows to pre-development levels.

• 2-year rainfall event:
  • Pre-development runoff = 5.7 L/s
  • Post-development runoff (without flow control) = 10.4 L/s
  • Required storage = 20.5 m³
• 10-year rainfall event:
  • Pre-development runoff = 12.6 L/s
  • Post-development runoff (without flow control) = 18.3 L/s
  • Required storage = 25.1 m³

To limit the discharge during the 10-year event, the orifice size in the flow control manhole is to be 84mm diameter. This orifice size is a function of the stormwater storage facility used and will be confirmed during detailed design.

See attached Appendix C for a detailed breakdown of the model outputs.

4.2. SANITARY

The proposed flows including residential, peaking factor and infiltration is approximately 2.08 L/s. Please refer to Appendix D for detailed calculations.

There is an existing sanitary main along Island Highway that also has an existing 200 mm diameter sanitary service crossing Island Highway. This crossing (from SMH 128 to SMH 117) is located near the north-east corner of 167 Island Highway. It is proposed that flows from the development connect to this existing service.

The elevation of SMH 128 is approximately 8.7m so any onsite sanitary system that cannot flow by gravity to that location / elevation will require pumping.

View Royal is to review the sanitary calculation and confirm that the existing system has adequate capacity.

4.3. WATER

When reviewing fire flow coverage for a given development, both the available flow in the water system and maximum velocity through the water system during a fire is analysed:

• The available flow for the site, not accounting for velocity, has been provided by the CRD Water Services (see Appendix E). The hydrant data for Hydrant #VRFD079 indicates a maximum flow is over 450 Litres per second (L/s) at a pressure of 20 pounds per square inch (psi).
• The maximum available flow through a 200mm diameter main, with flows from two directions, is 240 L/s. This corresponds to a maximum velocity of 3.5 meters per second (m/s).

A Fire Underwriter’s Survey (FUS) demand is a function of the building construction materials, fire zone areas, separation distances and the use of sprinklers. An FUS calculation was completed, based on the parameters of the proposed building, which indicates a required fire flow of approximately 193 L/s (Appendix F). Final FUS calculation will be completed / confirmed during detailed design.

Since the FUS calculation (ie. the required fire flow) is less than the available flow provided by the CRD with a residual pressure of 20 psi and the velocity through the water main is less than 3.5 m/s during that fire flow, it appears the existing system can satisfy the demand.

The CRD is to review the FUS calculation and confirm that the existing system has adequate fire flow capacity.

The available flow for the domestic water demand can be satisfied if the demand for the fire flow is achieved.

5. CONCLUSION

Based on the current design and the available information, it appears the development can be serviced. The assumptions and flows should be reviewed by the CRD and View Royal to ensure adequate offsite capacities.

This report was completed by McElhanney Ltd.

Nathan Dunlop, P.Eng.
Project Manager

Ian McCall, P.Eng.
Senior Project Engineer

[Conceptual Servicing site plan drawing for 171 Island Highway]