Ranney Collector 1 &1A Lateral Replacement Project

 Ranney Collector 1 &1A Lateral Replacement-Partially financed by Prop 84 funding

Humboldt Bay Municipal Water District (HBMWD or District) has Ranney Collector Wells located along the Mad River in the Essex reach below the City of Blue Lake.  These collectors are the source for HBMWD’s potable water system that delivers drinking water to the Cities of Arcata, Blue Lake and Eureka, as well as the Fieldbrook-Glendale, Humboldt Community, Manila and McKinleyville Community Services Districts and portions of the Samoa Peninsula.  The collector wells consist of concrete caissons that extend downward approximately 80 feet underground.  Near the bottom of the caissons, there are 12-inch screened laterals that extend horizontally outward from the caisson. Water flows through these laterals into the caisson and is then pumped from the caisson into the water system for treatment and distribution.  See the following presentation for maps and more information:  

 

HBMWD Coll 1&1A Board Pres 10_16.pptx

Due to the aging of these collectors, and the rusting of the original mild steel lateral material, the District has conducted a systematic approach to the assessment and planning for their refurbishment.  New stainless steel screened laterals were installed in the District’s Collector 3 in 2012.  This project will include the installation of two new laterals at Collector 1 and three new laterals at Collector 1A that will effectively replace the existing laterals in these collectors.  The construction process consists of the placement of a large hydraulic ram into the concrete caisson, which projects the new laterals out horizontally into the surrounding gravel matrix.  The valves on the existing laterals are closed and the caisson is dewatered. Holes are then cored through the walls of the caisson at the location of the proposed laterals, which will be located just above the existing laterals at a depth of approximately 70-feet below ground surface.  The hydraulic ram is then lowered into the caisson and a steel carrier pipe with a “cutting head” is pushed out into the gravels. 

The cutting head consists of a bullet shaped steel cutter with holes in it.  As the cutting head is pushed out into the gravels, flushed gravels are washed back through the head and the carrier pipe, back into the caisson, where they are pumped out to the surface. Occasionally, water is pumped through the cutting head to facilitate this flushing. When the carrier pipe reaches the length desired, in this case approximately 160-feet, the projection of the carrier pipe is halted, and stainless steel wire wrapped screen is inserted through the carrier pipe to the end. The carrier pipe is then withdrawn and removed, leaving the well screen behind. The well screen is then developed like a typical groundwater well, by pumping and surging the screen to settle the gravels around the well screen and remove the fines.  A valve is then placed on the end of the screen, and the core is sealed and the collector placed back into service.

Any groundwater that is extracted as part of the lateral construction and development process is pumped either to the percolation pond (from which the water percolates back into the groundwater) or to the District’s surface collector forebay, where it enters the river.  Only water that is free of sediment will be pumped to the forebay.

Collector 1-1A Monthly Status Report 7-16.docx