Section 246-272A-0320 - Developments, subdivisions, and minimum land area requirements(1) Prior to approving any development, the local health officer shall: (a) Require site evaluations under WAC 246-272A-0220;(b) Require information consisting of field data, plans, and reports supporting a conclusion that the proposed land area is sufficient to: (i) Install conforming OSS;(ii) Preserve reserve areas for proposed and existing OSS; and(iii) Properly treat and dispose of the sewage;(c) Require information demonstrating that the proposed development will minimize adverse public health effects from the accumulation of contaminants in groundwater and surface water;(d) Determine the minimum land area required for the development using Table XI of this section, or the alternative methodology in Table XII of this section. The local health officer may require larger lot sizes than the minimum standards established in Table XI or Table XII of this section; Table XI
Minimum Land Area Requirement For Each Single-Family Residence or Unit Volume of Sewage and Minimum Usable Land Area
| Soil Type (defined by WAC 246-272A-0220) |
1 | 2 | 3 | 4 | 5 | 6 |
Minimum Land Area | Public Water Supply | 21,780 sq. ft. (0.5 acre) | 13,000 sq. ft. | 16,000 sq. ft. | 19,000 sq. ft. | 21,000 sq. ft. | 23,000 sq. ft. |
2.5 acres1 |
Nonpublic Water Supply | 1.0 acre | 1.0 acre | 1.0 acre | 1.0 acre | 2.0 acres | 2.0 acres |
2.5 acres 1 |
Minimum Usable Land Area | 2,000 sq. ft. | 2,000 sq. ft. | 2,500 sq. ft. | 3,333 sq. ft. | 5,000 sq. ft. | 10,000 sq. ft. |
1 OSS consisting of only sewage tanks and gravity SSAS must have a minimum land area of 2.5 acres per WAC 246-272A-0234(7).
Table XII
Maximum Allowable Total Nitrogen (TN) Load Per Day by Type of Water Supply, Soil Type, and Land Area1
Water Supply Type | Maximum Daily TN Load | Soil Type2 |
1 | 2 | 3 | 4 | 5 | 6 |
Public | mg per sq. ft. | 3.8 | 6.3 | 5.1 | 4.3 | 3.9 | 3.6 |
lb per acre | 0.36 | 0.60 | 0.49 | 0.41 | 0.37 | 0.34 |
Nonpublic | mg per sq. ft. | 1.9 | 1.9 | 1.9 | 1.9 | 0.9 | 0.9 |
lb per acre | 0.18 | 0.18 | 0.18 | 0.18 | 0.09 | 0.09 |
1 Based on 60 mg/L TN and 360 gal/day OSS effluent.
2 As defined in Table V in WAC 246-272A-0220.
(e) Require all proposals not meeting the minimum land area requirements in Table XI of this section to demonstrate the proposed development: (i) Minimizes adverse impacts to public health, surface water, or groundwater quality;(ii) Considers: (A) Topography, geology, and ground cover;(B) Climactic conditions;(C) Availability of public sewers; and(D) Present and anticipated land use and growth patterns;(iii) Complies with current planning and zoning requirements;(iv) Does not exceed the nitrogen limit per land area as identified in Table XII of this section; and(v) Does not allow new lots smaller than 13,000 square feet if served by nonpublic water supplies;(f) Require minimum land area of 13,000 square feet or larger, except when a proposal includes:(i) OSS within the boundaries of a recognized sewer utility having a finalized assessment roll; or(ii) A planned unit development with a signed, notarized, and recorded deed covenant restricting any development of lots or parcels above the approved density with the overall density meeting the minimum land area requirements of (d) or (e) of this subsection in perpetuity or until the OSS is no longer needed as identified in WAC 246-272A-0200(6);(g) Require that developments other than single-family residences: (i) Meet the minimum land areas required for each unit's volume of sewage;(ii) Do not exceed 3.35 unit volumes of sewage per day per acre if served by public water supplies; and(iii) Do not exceed 1.0 unit volume of sewage per day per acre for nonpublic water supplies; and(h) Require that the use of a reduced-sized dispersal component does not result in a reduction of the minimum land area requirements established in this section.(2) The local health officer shall require the following prior to approving any subdivision: (a) A recommendation for approval as required by RCW 58.17.150;(b) Where a subdivision with nonpublic wells are proposed: (i) Configuration of each lot line to allow a supply protection zone to fit within the lot lines; or(ii) Water supply protection zones on more than one lot when the person proposing the subdivision or development provides a copy of a recorded restrictive covenant to each property that is sited partially or completely within the water supply protection zone;(iii) Water supply protection zone of at least 100 foot radius for each existing or proposed well site.(3) The local health officer may:(a) Require detailed site plans and OSS designs prior to final approval of subdivision proposals;(b) Require larger land areas or lot sizes to achieve public health protection;(c) Prohibit development on individual lots within the boundaries of an approved subdivision if the proposed OSS design does not meet the requirements of this chapter; and(d) Permit the installation of an OSS, where the minimum land area requirements or lot sizes in Table XI of this section or maximum total nitrogen in Table XII of this section cannot be met, only when the following criteria are met:(i) The lot is registered as a legal lot of record created prior to the effective date of the rule;(ii) The lot is not within an area identified in the local management plan developed under WAC 246-272A-0015 where minimum land area is listed as a design parameter necessary for public health protection; and(iii) The proposed OSS meets all requirements of this chapter without the use of a waiver under WAC 246-272A-0420.Wash. Admin. Code § 246-272A-0320
Amended by WSR 24-06-046, Filed 3/1/2024, effective 4/1/2024Statutory Authority: RCW 43.20.050. 05-15-119, § 246-272A-0320, filed 7/18/05, effective 7/1/07.