Washington Administrative Code › Title 246 - Health, Department of › SEWER SYSTEMS › Chapter 246-272A - On-site sewage systems › SPECIFIC REQUIREMENTS › Section 246-272A-0320 - Developments, subdivisions, and minimum land area requirements

Current through Register Vol. 24-14, July 15, 2024
(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.