Arcata Wastewater Treatment Plant and Wildlife Sanctuary - Conventional Pollutants or Wetland Detritus

Conventional Pollutants or Wetland Detritus

Wetland plants use the energy of sunlight to produce five to ten times as much carbohydrate biomass per acre as a wheat field. Detritus from decomposing wetlands vegetation forms the base of a food chain for aquatic organisms, birds and mammalian predators. Individuals who value wetland environments may not realize the effluent characteristics necessary for release of treated wastewater to Humboldt Bay. Although there is no evidence of harm to wildlife, some regulators suggest potential risk to wildlife using treatment wetlands because of an absence of significant research on wildlife exposure to partially treated effluent and to potential accumulation of chemicals being removed from effluent in wetland treatment processes. Ongoing research at Humboldt State University minimizes potential risk to Humboldt Bay wetlands and wildlife.

The City of Arcata generates an average volume of 2.3 million US gallons (8,700 m3) of sewage per day. Winter rainfall onto the large surface area of treatment ponds and marshes increases the volume of effluent discharged from the wetland treatment system to as much as 16.5 million US gallons (62,000 m3) per day. National Pollutant Discharge Elimination System regulations require average effluent concentrations of biochemical oxygen demand and of total suspended solids to be no greater than 30 mg/L, with an additional requirement for removal of 85 percent of the quantities measured in untreated sewage from the City of Arcata. Unfortunately, when measuring concentrations leaving treatment wetlands, neither of these analytical methods can distinguish between unremoved conventional pollutants originally arriving in sewage, or detritus of decomposing wetland vegetation; so the limitations may apply to the sum of both.

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