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Wastewater Facilities Planning

City of Point Arena.  Was asked by the City to recommend Infiltration/Inflow improvements to the sewer system since the City’s percolation ponds had nearly overflowed during the preceding winter.  Determined that improvements of the percolation ponds would increase the capacity of the system at only a fraction of the cost of improving the sewer system.

Pinecrest Permittees Association.  Conducted a “repair, replace, or abandon” evaluation on the rotating biological contactor (RBC) process at this small treatment plant in the Sierra Nevada mountains.  When the shaft of the existing RBC unit broke for the second time, the Association requested an evaluation of whether it should be repaired or whether some other treatment technology should be selected.  Careful attention was given to the limitations of the steeply sloping site, large differences between winter and summer flows, and severe icing problems in winter.

City of Mill Valley.  Evaluated the alternatives of improving the Enchanted Knolls Pump Station versus replacing the station with a gravity line connected to a force main leading to the wastewater treatment plant.  The feasibility of using a gravity line depended upon the actual height of the hydraulic gradeline in the force main during periods of peak flow.  A program to investigate the actual height of the hydraulic gradeline was developed as a part of the work.  The gravity sewer line proved to be technically feasible, if provided with several safeguards, and was designed and constructed, allowing the City to abandon the pump station.

Portola Valley Sewer Alternatives Evaluation Study.  Conducted a major study of how best to serve an unsewered area that was experiencing scattered failures of leach fields.  The report considered:  conventional gravity sewers;  on-site grinder pumps and pressure sewers; septic tank effluent pump (STEP) systems; and septic tank effluent gravity (STEG) systems.  A detailed estimate was made of the actual operation and maintenance cost of existing STEP systems and a survey was conducted of how other agencies handled such systems.  Alternative financing arrangements for sewer improvements were evaluated.

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