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Malakal Natural Wastewater Treatment Park Design/Build Malakal, Koror State, Republic of Palau

ftrd-wastewaterMalakal Natural Wastewater Treatment Park
This was a two part design/build project consisting of the design, environmental permitting and construction of a 2.0MGD average daily flow and 5.3MGD peak flow secondary wastewater treatment facility to serve Koror, the capitol of the Republic of Palau.  The work involved modification and renovation of portions of the old 1.0 MGD Malakal wastewater treatment plant and the addition of a new 0.5 acre, 331,000CF, HDPE lined primary fermentation pond with two 10HP surface aerators and 3.13 acres of new man-made settling and polishing wetlands.Modifications and renovations to the existing plant included a new 2,880SF administration-operations building, conversion of the existing clarigester into a new 45’ diameter x 10’ deep trickling filter with 10’ deep wetwell, refurbishing the existing 60’ x 4’ deep trickling filter with a new rotary distributor and filter media, installing two new 800 GPM 20HP recirculation pumps, two new 1,940GPM 25HP effluent pumps and magnetic flow meter, new grinder pump station, new yard piping and valving, concrete flow splitter box and transfer structures, new 225KVA pad mounted transformer, MCC, panelboards, and buried equipment power ducts and cabling, new fencing, Malakal Natural Wastewater Treatment Parkdriveways, parking, drainage, landscaping, and painting works.

Additionally, the former headworks and secondary clarifier were emptied, backfilled and capped in place and the existing chlorine contact tank was cleaned and secured for potential future use.Malakal Natural Wastewater Treatment ParkStartup assistance and basic operation and maintenance training were provided to ROP Sewer Branch operators at the conclusion of the project.CHALLENGES

During the course of the project the ROP Government added 86 days to the contract period for rain days due to the extremely wet tropical climate of Palau which has an average rainfall of 150 inches per year. To help minimize rain delays during the project, Black routinely graded the site to maintain positive drainage, sealed soil areas with smooth drum rollers, and covered up soil stockpiles and embankment fills with tarps and plastic sheeting before leaving the job each evening. Where necessary, sump pits, trash pumps and Malakal Natural Wastewater Treatment Parktemporary sedimentation basins were used to dewater low areas. As standard practice, Black maximized earthwork production during periods of dry and sunny weather whenever they occurred, including Sundays and holidays.Malakal Natural Wastewater Treatment Park

During construction intermittent upland surface flows and underground seeps above the primary pond excavation and wetlands cell A were discovered which were not picked up by the subsurface soil investigation. These had to be addressed to prevent unnecessary flow into the treatment facilities. Black, with its design engineer’s concurrence, used a combination of concrete rubble masonry check dams, lean concrete swales and underlying French drains on the uphill sides of the primary ponds and wetlands cell A to intercept this stormwater and direct it to natural drainage courses.Malakal Natural Wastewater Treatment Park