Written by E. Philip Small on July 25, 2009
The site photo below was taken in 1997 It depicts one of the last sprayfields to go into anaerobic failure in Washington State. Before this time, sprayfield designs tended to ignore application uniformity and soil moisture effects on BOD treatment capacity. In most sprayfields, loading of oxygen demanding constituents is not a design limiting parameter, and warrants abbreviated consideration. That is not the case with high strength wastewater, and professional judgement is required to distinguish when further consideration is warranted. When in doubt, have a qualified soil scientist evaluate soil-based BOD treatment capacity.
Startup design for this wastewater sprayfield near Lacey, WA was intended to closely match expanded cheese processing operations to sprayfield capacity. However the design team failed to mitigate for the risk of anaerobic failure, resulting in the hydraulic "blinding" depicted in the site photo. Curtailed plant operations resulted due to no reserve treatment capacity, impaired post-failure sprayfield treatment capacity, and no economical alternative treatment option.
Originally posted to http://www.nscss.org/content/bod-overload-cheese-processor-sprayfield