Garberville Sanitary District Water System Improvements Engineering and Environmental Compliance

The Town of Garberville is a rural community in Southern Humboldt County with approximately 395 residential and commercial service connections; with raw water obtained from the Eel River. Garberville Sanitary District (GSD) retained LACO to design water system improvements including a new surface water treatment plant, 750,000-gallon storage tank, and booster pump station. Our project goals included the following:

  • Amending a pre-existing Preliminary Engineering Report (PER)
  • Defining the preferred project alternative
  • Developing preliminary design and project cost estimate
  • Completing NEPA and CEQA-PLUS documents to qualify the project for State Revolving Fund/Proposition 50 funding

The initial phase of the project included review and amendment to the original PER to define the preferred project. Our team’s updates to the PER detailed the following needs:

  • Adequate treated water storage to mitigate periodic plant shut-downs during seasonal high raw water turbidity events
  • Selection of LT2 Surface Water Treatment direct filtration equipment consistent with the system operator’s understanding and capabilities
  • Design and supporting calculations of a below-ground chlorine contact chamber having a baffle factor of 0.8
  • Sizing and preliminary design of a metal treatment plant building matching the surrounding rural/woodland setting
  • Complete hydraulic analysis of the water system to ensure pressure management of a system having multiple pressure zones between the proposed storage tank, the town’s distribution system, and the proposed surface water treatment facility

Our project team utilized computerized hydraulic modeling to analyze water system pressure during average, maximum day, and fire flow conditions to establish adequate flow capacity and pressure management throughout the system. We evaluated existing facilities and equipment in the system to incorporate an existing pressure filter for flocculation and spare submersible pump which was accurately sized for relocation and reuse at the new treatment facility. Our team designed the system to produce up to 325 gpm.

Coordination with the GSD Manager, California Department of Public Health, and other local agencies and districts resulted in a concise project consisting of:

  • New submersible river intake pumps and emergency power supply
  • Over one mile of new water mains and distribution piping
  • New surface water treatment plant with new pressure filters, highly efficient chlorine contact chamber, and a backwash water recycling system
  • Retrofit of an existing booster pump station with new pumps, valving, and controls
  • A new 750,000 gallon finished water storage tank

These improvements resulted in a redundant, reliable system capable of meeting Title 22 drinking water standards and will allow the system to mitigate seasonal plant shut-down.

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