Information for Subdividers Using On-site Systems
The On-Site Water and Wastewater Section reviews all proposed subdivisions within the Municipality of Anchorage with regard to on-site water systems and wastewater disposal systems. The following criteria serve as the basis for the review:
To determine the suitability of the proposed lots for on-site wastewater disposal, a number of factors must be considered. The requirements for development utilizing on-site wastewater disposal are defined in the Anchorage Municipal Code (AMC) Chapter 15.65 Wastewater Disposal Code.
The subdivider shall submit plans, data, tests and engineering reports required to substantiate the capability of the proposed subdivision to adequately dispose of wastewater. The subdivision wastewater disposal plan shall contain, but need to be limited to, all of the following information, prepared under the direction of an engineer:
- Soil testing and groundwater monitoring results– Each lot must have adequate soil testing and groundwater monitoring. At least one test-hole and frequently additional test-holes must be dug to show each lot’s capability to adequately dispose of wastewater from a residence. Test-holes must be sited in areas that could potentially be used for wastewater disposal. Each test-hole must have a perforated tube installed to the bottom of the hole and groundwater monitoring shall be done during seasonally high months of May and/or October.
- A site plan and report addressing the following:
a. Lot Size – The minimum required lot size is 40,000 square feet within lot lines. Other considerations such as topography, surface waters, or other limitations may dictate a size greater than 40,000 square feet.
b. Items requiring separations - The location of existing private and public water systems, groundwater wells, on-site wastewater disposal systems, replacement subsurface disposal field sites, public sewage systems, storm sewers, bodies of water, drainage features, curtain drains, and wetlands both in the proposed subdivision and outside the proposed subdivision if within 250 feet of the proposed wells and wastewater disposal system reserve areas.
c. Wells– The location of possible well locations on each proposed lot.
d. Reserved areas – Each lot in a proposed subdivision must have areas where original and replacement disposal systems may be placed. The applicant has a choice of showing:(a) reserved area set aside for wastewater disposal based on appropriate soils testing and sizing requirements shown in AMC 15.65.410C.1.(b) the areas which will support the original and replacement systems designed in accordance with this chapter. The plat shall designate the maximum number of bedrooms allowed on each lot. The area to be used for the wastewater disposal fields shall be designated on the plat for each lot as being unavailable for use as driveways, parking areas or structures. Reserved areas are not required if the proposed lot has an existing approved on-site wastewater disposal system. An area for a replacement wastewater disposal system shall be demonstrated.
e. Slope and setbacks – Topographic contours to demonstrate that the reserved areas meet code requirements regarding construction on slopes and slope setbacks. Additional information may be required to show compliance.
f. Nitrate Levels – Known groundwater nitrate levels in the general vicinity (within 250 feet) of the subdivision. The department may require a nitrate impact analysis if nitrate levels are found to exceed five mg/l in adjacent wells, or to exceed ten mg/l for short plat applications.
- Water Availability – All development that will be served by private wells must be supported by information which shows that adequate water supplies will be available. This information is typically obtained from area well logs, hydro-geologic evaluations, exploratory drilling or a combination of these. Since 1999, all proposed subdivisions with more than 5 lots to be served with on-site wells must have an aquifer test performed. If adequate water is not shown to be available, On-site may require the extension of public water to the subdivision. If public water is available, existing or proposed water mains should be shown.
- Community water supply documents – At the time of preliminary plat application, the applicant must submit a Certificate to Construct from the State of Alaska Department of Environmental Conservation (ADEC). Prior to the final plat, the applicant must provide an ADEC Certificate to Operate the water system and an approval from the Department of Natural Resources to appropriate water.