SECTION 3.0 – PROCESS DESIGN

As mentioned previously, the new WWTP will be set on Lot 1059 at the intersection of the  Klondike Highway and the Dome Road.  This location positions the plant between the primary townsite  and the more southern Klondike Valley areas – Bonanza, Guggieville, and C-4 Subdivisions.  Currently,  wastewater produced from these three areas is conveyed via a 150 mm forcemain up to the  Hydraulic Tower on Craig Street, where it then flows by gravity to the existing Screening Plant on  5 th Avenue for screening and final discharge to the Yukon River.

The No. 3 Dome Lift Station, situated on Lot 1059, collects the seasonal flow generated by the ball field  with provision to service future areas.  This flow is then lifted into the adjacent 150 mm forcemain  (originating from the Guggieville and Bonanza Lift Stations), running within a meandering right-of-way  corridor along the east side of the Klondike Highway.

With the construction of the new WWTP the Hydraulic Tower will be abandoned as the wastewater from  the Klondike Valley areas will be intercepted at the new plant.  The existing Screening Plant will,  therefore, not be required as a screening facility and with be adopted as the new Townsite Pump Station.   This adoption will require modifications to the existing facility.

3.1.1  Wet Well Modification

The existing wet well is partitioned down the centerline to provide an influent wet well for the pumps to  lift sewage to the existing screens, and an effluent wet well for the outfall pumps.  The existing screenings  facilities will be abandoned as will the pumps that supply the screens.  With the existing centerline  partition removed (modified as shown in the attached drawings) by means of opening an existing 300 mm  penetration and adding one additional 300mm cross over connection, this will allow the entire wet well  volume to be used for the Townsite Pump Station to pump the wastewater generated at the townsite to the wastewater treatment plant (WWTP) on Lot 1059.

The existing 5.5 meter diameter wet well provides an approximate 0.8 meter active depth and a resulting  active volume of 17 m 3.  Assuming the peak hour in town constitutes some portion (80%) of the  4,000 m 3/day peak generated by Dawson City as a whole; this would leave some 0.037 m3/s that must be  accommodated by the wet well and constituent pumps during the peak hour event.  The new WWTP  influent pumps that will be put into the existing Screening Plant will therefore need to be able to handle  this peak flow of 0.037 m 3/s, as there is limited storage available in the wet well.

3.1.2  Raw Wastewater Pump Criteria

All existing pumps in the Screening Plant will be replaced by 2 + 1 new submersible pumps.  One pump  for the average flow, one to accommodate the peak flows estimated at 80% of the WWTP peak flow, and  a final pump for standby.  Figure 4-1 below illustrates the required system pumping capacity and the  available pumping capacity of one of the pump model options (Flygt CP3152.181 25 hp).