Pascal & Ludwig Constructors (P&L) is no stranger to highly technical and complex jobs. So, when Irvine Ranch Water District (IRWD) put their North Conversion Zone C Plus Reservoir project out to bid it seemed a perfect match for P&L’s skill set.

Under the direction of Project Manager Scott Floyd, the $11 plus million contract called for the construction of a 2.4 million gallon reservoir and pair of high capacity separating strainers to filter the water originating from nearby Lake Irvine.

P&L mobilized for the job in October, 2016 and expects to wrap up by October, 2019, following operational testing that was being conducted as this article was being written.

Prestressed Concrete Tank

The concrete reservoir was constructed by P&L and prestressed by DN Tanks of El Cajon. The tank floor and walls were constructed of high strength concrete with minimal rebar used in the construction of the reservoir and seismic cables attached the wall to the floor.

Following the floor, wall and concrete deck construction, the tank wall was circumferentially prestressed with continuous high strength steel. Circumferential prestressing is critical to the tank structure, placing the tank wall in permanent compression and resulting in the most durable structure possible. Vertical tendons were cast in the walls every four feet and vertically stressed giving the reservoir added strength. Shotcrete was then applied over the exterior providing a permanent bond and corrosion protection.

Dual Strainers

The dual strainers are at the heart of this system and have the capacity to process 78 cubic feet of water per second. The units alternate in operation and can fill the 2.4 million gallon reservoir in just 120 minutes.

The strainers collect debris from the inflow via brushes inside the housing with the resultant material collected in settling basins which are periodically pumped out when their capacity is reached.

The system’s flow meters, control valves, and air gap structure work in unison to fill the 2.5 million gallon prestressed reservoir that is predominantly below grade, 29 feet deep and 139 feet in diameter.

The project also required extensive earthwork, a lengthy keystone segmental retaining wall, 48” and 42” cement mortar lined inlet and outlet piping, a 38 foot deep sub drain pump station, and complicated mechanical pipe interties at IRWD’s nearby Rattlesnake, Or- chard Hills, and Baker Pump Station facilities.

Assisting Project Manager Scott Floyd were field supervisors Sam Davis overseeing concrete work, and Britt Floyd for the mechanical installations. Additional ECA members participating in the project were Hardy and Harper, Old Castle Precast, Ferguson Waterworks, and Trench Shoring Company.

Top: The 2.4 million gallon prestressed concrete reservoir contains treated water from Lake Irvine.

Above: Dual strainers can separate debris from inflow at the rate of 78 cubic feet of water per second and fill the concrete reservoir in just 120 minutes.

Left: Collection pits with metal gates raised allow access for debris separated by dual strainers to be vacuumed out for removal.

By John Simpson, ECA Editor – [email protected]