Stormwater Pump and Lift Station Cost Optimization using 1-D Modeling

We recently completed a project on a 25ha industrial greenfield site located in Western Canada where the scope included:

• Grading for Site Pads
• Design of Roads, Entrances and Parking Lots
• Sizing the storm water system

Due to extremely cold winter temperatures, storm pipes required a cover of 2.8m for frost protection. Also due to flat topography existing land surfaces ranged from 0.25% to 0.50%.

Using 2.8m cover, 0.05% pipe slopes and 0.05m drops at manholes; resulted in downstream inverts 5m below existing ground. This necessitated incorporating pumps, lift stations and storage chambers to allow for discharge into detention ponds and watercourses.

The following scenarios were investigated:

• One lift station with one pump
• One lift station with two pumps
• Two parallel lift stations each with a single pump
• Two parallel lift stations each with a single pump and a storage chamber

To ensure stability, continuity and routing errors less than 1.00%, lift stations consisted of:

• 1.5m depth below the inlet pipe to the bottom
• Fittings along the walls of the lift station
• A force main at the outlet
• Depth versus area curves quantifying storage volume

Submersible xylem pumps were evaluated based on the peak flows, static head and friction losses. Only curves for pumps with efficiencies greater than 80% were used.

In consultation with the manufacturer it was determined that pumps operate best when:

• They do not turn on and off for more than 30 times in a hour
• For each on and off cycle the curve should be trapezoidal instead of triangular
• The bottom of the pump shall be submerged at all times

Pump start up and shut off depths were set to ensure optimal pump operation requirements were achieved.

The most efficient and economical solution was two parallel lift stations each with a single pump and a storage chamber.