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Cook Inlet Water Quality

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Cook Inlet is a semi-enclosed tidal estuary that experiences some of the greatest tidal fluctuations in the world (Mulherin et al. 2001). Beneath the inlet’s 20,000 km2 surface area, a varied bathymetry exists, marked by shoals, canyons and mudflats, though Cook Inlet is generally shallow, with most water less than 73 m (240 ft.) deep. During low tides, mudflats constitute large areas of shoreline, which are submerged again during high tide. The presence of this bathymetry combined with tidal differentials of as much as 12 m (39 ft.), results in intense currents of up to 6.2 m/s (20.3 ft/s), and thus intense mixing conditions within the inlet. Such intense mixing means the sediment inputs from the inflowing riverine and glacial meltwaters of the contributing watershed are continually resuspended, and Cook Inlet is characterized by highly turbid water of low visibility.

The inlet is also marked by large temperature extremes between winter and summer, and the tidal turbulence vertically mixes the colder, denser water with warmer flows, both saline ocean water and riverine and glacial inputs.

Thus, Cook Inlet conditions are very effective in diluting and assimilating the treated wastewater effluent from the John M. Asplund Water Pollution Control Facility (Asplund WPCF), which has operated since its completion in 1973 as a conventional primary treatment facility. The year prior to Asplund’s completion, the Clean Water Act was established as a result of amending the Federal Water Pollution Control Act of 1948. Since its initial operation then, the Asplund WPCF has adhered to the strict requirements regulating pollutant discharges into the waters of the United States. These include meeting all water quality standards, permitted limits and all testing, monitoring and reporting requirements under the Clean Water Act. In 1985, AWWU received a modified permit from Secondary Treatment requirements of the federal Clean Water Act. Fourteen years of continual monitoring and reporting preceded the renewal of this modified permit in 2000. This modified permit was administratively extended by the EPA in 2005, and AWWU has since conducted a number of additional special studies, including the evaluation of effects on endangered species in support of further permit renewal as a result of the Cook Inlet Beluga Whale (Delphinapterus leucas) being listed as an endangered species (CH2M Hill, 2011). Many of the findings and associated plans for the Cook Inlet Beluga Whale can be found on NOAA Fisheries page for species research and recovery planning.

AWWU is committed to the environment, and our goal is simple:
To protect the quality of our Cook Inlet water, its aquatic life and the people who rely on Cook Inlet for recreation and livelihood.

Cook Inlet Annual Monitoring Program

The Asplund WPCF operates under the requirements of a permit authorized under the National Pollutant Discharge Elimination System (NPDES). The NPDES program mandates annual monitoring associated with the Asplund WPCF outfall. The main objectives of this monitoring are:

  • To ensure Cook Inlet aquatic environment is protected
  • To differentiate between natural changes and those that may be caused by the sewage discharge
  • To measure compliance with state and federal regulations
  • To help monitor facility performance

What gets monitored?

  • Influent, Effluent and Sludge
  • Receiving Water Quality
  • Sediment and Bioaccumulation

Where do I find monitoring results?