he first step in the septic system design process is to identify locations on the property that have suitable site conditions to support an onsite septic system. For more information on septic systems in general, please see our Description of a Typical Septic System page. Consideration of potential sites must take into account the following regulatory constraints: The drainfield must be at least 50 feet away from any downhill slope greater than 25%; however, the MOA can waive this requirement, on a case-by-case basis. There must be 2 feet of unsaturated, naturally occurring soil below the organic layer (topsoil/roots) on which to place the septic system. Percolation test: If the percolation test results yield an absorption rate of less than 60 minutes per inch, a conventional system can be installed. Percolation rates between 60 and 120 minutes per inch necessitate using an alternative technology septic system. If it takes greater than 120 minutes for the water level in the percolation hole to drop 1 inch, the soil is unsuitable for an onsite septic system. There must be adequate room to install 2 drainfields (primary and reserve) on the lot and not encroach upon the protective radii of the neighboring wells and proposed well for the lot. The protective radii are summarized as follows: Private wells (single family residence and duplexes) have a 100 foot protective radius. Class "C" wells have a 150 foot protective radius. Class "A" or "B" wells have a 200 foot protective radius. The septic system must be at least 100 feet away from any surface water. The MOA can waive this on a case-by-case basis. If the lot is covered with snow it may be difficult to assess whether there are surface waters present. Clearly, there are some areas where surface waters are not a concern, and there are others where it is always questionable. Typically, it is not possible for an engineer to make absolute statements regarding surface waters during winter conditions, unless he/she has done work in the immediate vicinity during summer months. The only other options are to talk to the neighbors owning adjacent developed lots, or to rely on statements from the sellers. If the area groundwater supply has high concentrations of nitrates (by-product of sewage decomposition), the MOA may prohibit the installation of a conventional onsite septic system and require a more expensive alternative technology septic system that is designed to remove nitrates (like the RTF system).

rior to making the initial site visit and identifying potential septic sites, records research is done on the subject and adjacent properties to identify the locations of all wells, septic systems, structures, surface waters, easements, and pertinent topographical information within 200 feet of the subject property. This information is usually compiled from records on file at the MOA, ADEC, and as-built surveys obtained from title companies. The location of all pertinent items are then drawn to scale on a site plan by a CAD technician. As you can see, there can be a considerable amount of preparatory work before the initial site visit!

ith this drawing in hand, the engineer can make some preliminary determinations as to what areas on the lot may be potential septic sites. If the property lines are not clearly identified in these areas, they should be flagged by a registered land surveyor prior to the initial site visit.

uring the site visit, the engineer will make a visual assessment of the potential septic sites previously identified and selects the site/s which are best suited. Typically, the following objectives are considered: If possible, the septic system should be downhill from the existing or proposed house so as to insure that there is gravity flow from the house to the septic tank and drainfield. There are cases where this cannot be achieved and the installation of a lift station is necessary. The septic system cannot be under an existing or proposed driveway/ parking area. The MOA will not allow this. The proposed septic site should be as accessible as possible for purposes of construction and maintenance. The septic tank must be in a location where it can be reached by a pump truck. Avoid putting the septic system in a drainage swale or depression that may seasonally carry or have standing water in it. The drainfield must be at least 10 feet, or 2 times the drainrock depth (whichever is greater), from any existing septic systems.

ith the septic site(s) selected, the field engineer then narrows the site selection down to the most suitable areas and establishes the location for the test holes. If the property is undeveloped, and this is the first septic system to be installed on it, the MOA will require that the engineer establish the location for a reserve (future) drainfield site also. In short, we will need to have the room to install two septic systems, however only one will have to be installed at this time. If the property is currently developed and the existing septic system is being upgraded (because it has failed) then identification of a reserve drainfield site is not required, unless the number of bedrooms in the house has increased since the original septic system was installed. If so, then a reserve drainfield site will need to be identified. Both the upgrade and reserve drainfield will need to be adequate to serve the current or proposed number of bedrooms in the residence.

nce the test holes are excavated, the soils are classified and percolation tests are performed. Per MOA requirements the groundwater levels are monitored in the test hole for a period of at least 7 days. The information and data gathered in this investigation are used to establish what type of septic system can be installed and how large the drainfield will be. The size of the septic tank is not dependent upon the site conditions, but rather the number of bedrooms in the residence.

ypically, the most cost effective system to install is a conventional septic system, however, the soil and site conditions may be such that it is not feasible. For marginal sites, the utilization of an alternative technology system (RTF, BioCycle, and Intermittent Sand Filters) may be necessary in order to install a septic system. On some properties the site conditions are so poor that the only viable alternative is to install a holding tank.

tilizing the information gathered to this point, the engineer will prepare the design drawings and specifications. This package is them submitted to the applicable regulatory body for issuance of a permit. For single family residences inside the MOA (Girdwood to the Knik River), the permit is issued by the MOA, Development Services Department. For multi-family dwellings the permit (called a certificate to construct) is issued by the State of Alaska, ADEC. Both regulators charge a fee for review of the design package and issuance of the permit.

he construction costs to install the septic system can vary widely. The property owner then selects the contractor of his/her choice. During the installation of the system, the engineer must perform mandatory inspections at various stages of the construction. The final step of the installation process is for the engineer to prepare as-built drawings of the new system and submit them to the regulator for their review and final approval.

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