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Sunday, April 30, 2017

Advanced Wastewater Treatment Systems (AWWTS)

 

Advanced Wastewater Treatment Systems (AWWTS)

There are a number of locations in the Anchorage and Eagle River area where site conditions are unsuitable to support a conventional onsite septic system. In the past, many of these areas were developed, only to find out later that the septic systems would not function properly. Many of these homes have since been put on holding tanks, and others are utilizing some alternative technology systems which are now available. Before determining what systems are viable for any particular lot, there must be a thorough engineering evaluation of the site conditions. Conditions which may prevent the installation of a conventional septic system are summarized as follows

 

  • The topography is too steep (slopes greater than 25%): Under current regulations, the drainfield must be at least 50 feet away from a downhill slope greater than 25%. The MOA will waive this on a case-by-case basis.
  • Shallow groundwater:  Typically, the bottom of a drainfield must be at least 4 feet above groundwater.  With the use of an AWWTS it is possible to get this separation distance reduced on a case-by-case basis.
  • Soils which percolate too slowly: If the percolation rate is between 60 and 120 minutes per inch, then an AWWTS will be required. If it takes greater than 120 minutes for the water level in the perk hole to drop 1 inch, the soil is unsuitable for any type of septic system.
  • The protective well radius' encompass all of, or a major portion of, the land area necessary to install a conventional septic system:
    1. Private wells (single family residence and duplexes) have a 100 foot protective radius
    2. Class "C" wells (serving less than 25 people) have a 150 foot protective radius
    3. Class "A" or "B" wells (generally these are wells serving greater than 25 people per day for more than 60 days per year) have a 200 foot protective radius
  • There are nearby surface waters, such as creeks, ponds, lakes, etcetera: The septic system must be at least 100 feet away from any surface water, unless mitigation is provided.
  • The area groundwater supply has high concentrations of nitrates (by-product of sewage decomposition), causing the MOA to mandate the installation of nitrogen removing AWWTS
  • Very shallow bedrock: Typically, the site must have at least 2 feet of naturally occurring, permeable soil over the bedrock.

    If site conditions prevent the installation of a conventional septic system, then it may be possible to install one of the alternative technology systems, referred to in Anchorage as "Advanced Wastewater Treatment Systems (AWWTS)". The systems currently being used in the Anchorage and Eagle River area are as follows:

     

    We would be happy to do a full engineering evaluation of your property and recommend the septic system which best meets your needs.

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