Drain WWTP Improvements

The City of Drain plans to construct a new wastewater treatment plant immediately south of the existing facility on Division Avenue.  The proposed WWTP improvements will include:

  • A new headworks structure with ±18‑foot high walls.
  • A new SBR (sequencing batch reactor) treatment facility with two concrete tanks.  The tanks will extend ±5 feet below the ground surface.
  • A new UV facility with ±6-foot tall sidewalls.
  • A new operations building.  It is assumed the building will have conventional (shallow) footings and a slab‑on‑grade concrete floor.

To mitigate potential flood hazards the overall grade will be raised ±4 to 5 feet by filling.  However, the new site fill will induce unacceptably large settlements.  Project challenges included the presence of undocumented fill, shallow ground water, and soft or loose native soils.  Options for mitigating the settlement (and potential liquefaction during an earthquake) were provided in the investigation.  Foundation Engineering’s geotechnical investigation and site-specific seismic hazard study were completed ahead of schedule and within budget.