In the past, Deschutes County denied proposals to replace or remodel previously existing residences in high groundwater areas (groundwater less than 24 inches from ground surface). Current information and experience shows:
- The onsite systems on these lots discharge incompletely treated wastewater into an unconfined aquifer that is the sole source of drinking water in the region.
- Groundwater monitoring and modeling in the region have shown that existing onsite systems must be replaced to solve the nitrate pollution problem.
- Wastewater treatment systems designed for residential use can reduce nitrogen loading to the groundwater. (Note: Deschutes County does not guarantee that repairing or replacing the onsite systems on properties with high groundwater will alleviate any other site conditions associated with development in these areas. Current siting criteria (a minimum of 24 inches of separation from ground surface to groundwater) still apply to all new site evaluations.)
Therefore, in order to protect public health and the environment, existing residences may be replaced or remodeled if all the following criteria are met:
- An existing onsite wastewater treatment system currently serves an existing residence on the property.
- The site does not meet minimum siting requirements for any type of system. For example, the site is located in a high groundwater area.
- The applicant is willing to abandon the existing system and complete the repair using the best available nitrate reducing technology. It is likely that the new system will consist of an Alternative Treatment Technology (ATT) that includes a denitrifying process and is followed by a surface mounted bottomless sand filter for the disinfection and soil absorption portion of the system.
- The proposal for the replacement residence meets the following restrictions:
- If the existing house is less than 1,000 square feet, the new house can be a maximum of 1,300 square feet and include three bedrooms and two bathrooms.
- If the existing house is greater than 1,000 square feet then the new house can be no more than 30% larger than the existing house square footage and a maximum of 3 bedrooms and 2 bathrooms. If the existing house has more than three bedrooms, no additional bedrooms are permitted.
- Detached structures are excluded from the calculation of the square footage of the existing house if they have no plumbing.
- The sizing requirements are based on research that correlates the square footage of the house with flow (Sizing Onsite Systems).
- Any lots with high water table must have a wetland determination and/or delineation and the report or fill and removal permit submitted to the County. Property owners must contact the Division of State Lands at (541) 388-6112 for information on this process. A conditional use permit for fill and removal in wetlands may also be required from the Deschutes County Planning Division.
- The repair must be installed and a Certificate of Satisfactory Completion issued before an Authorization Notice can be approved and building permits for the replacement residence or remodel issued. Building permits could be released if existing system was properly abandoned (via permit) and another Authorization Notice (No Field Visit) was applied for and approved.
- Future additions will not be approved.