Information for Subdividers Using On-site Systems
The On-Site Water and Wastewater Program 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:
When public sewer will not be available to a subdivision, the developer must plan for each lot to be served by an individual wastewater disposal system. To determine the suitability of a particular lot 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 and AMC Title 21, Planning and Zoning.
- Lot Size – When on-site wastewater disposal is planned for a lot, the minimum required lot size is 40,000 square feet within lot lines. No portion of the adjacent right-of-way may be considered as part of this calculation. Other considerations such as topography, surface waters, or other limitations may dictate a size greater than 40,000 square feet.
- Soil testing and water monitoring – Each lot that will utilize on-site wastewater disposal must have adequate soil testing and water 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. Test-holes must be dug to a minimum depth of 14 feet unless bedrock or groundwater is encountered. In addition each test-hole must have a perforated tube installed to the bottom of the hole and water-monitoring results shall be obtained after a minimum period of seven days. In cases when shallow groundwater is found during the initial monitoring period or suspected during a high water period, long term monitoring may be required. This long term monitoring would include a period of high ground water in the spring or fall of the year. In cases of long term monitoring, filter fabric should be wrapped around the monitoring tubes to prevent silt from entering the tubes.
- Reserve area options – Each lot in a proposed subdivision must have areas where an original and two replacement disposal systems may be placed. The applicant has a choice of (a) showing a total reserve area set aside for wastewater disposal based on appropriate soils testing and sizing requirements shown in AMC 15.65; or (b) designating the measured areas which will support the original and two replacement systems on the lot. When designating three sites, the total number of bedrooms that may be supported by these systems shall be specified by a notation on the plat. Sites for the three systems per lot shall be shown on the final plat.
- Slope and setbacks – A topographic map is required with the submittal with areas exceeding 25% slope noted. On-site wastewater disposal systems may not be installed in areas that exceed 25% slope and such areas shall not be used for reserve areas or for designated areas for three platted systems. In addition, no wastewater disposal systems may be installed within 50 of a slope that exceeds 25%.
- Identification of existing systems – The developer is required to show on the preliminary plat the location of existing drinking water sources, on-site wastewater disposal systems, sewage systems, treatment works and bodies of water within 200 feet of the proposed subdivision. The areas of influence from such systems must also be shown on the plat.
- Documentation of existing disposal systems – When on-site wastewater disposal systems exist within the proposed plat area, they must be shown to be in compliance with municipal and state regulations. If no inspection report exists, an engineer must document the system. Contact the department for information on documentation requirements. If public sewer is available, show the location of existing or proposed sewer lines.
- Water Availability – All development that will be served by a community well system or by private wells must be supported by information which shows that adequate water supplies will be available. This information my 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, DSD 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.
- Designating surface water – Under state and municipal laws, all surface waters must be protected from wastewater discharges by protective separation. All streams, lakes, or other bodies of water must be shown on the preliminary plat with appropriated setbacks shown.