A. 
The subdivider shall submit plans, data, tests and engineering reports required to substantiate the capability of the proposed subdivision to adequately dispose of wastewater. Where individual on-site wastewater disposal is proposed, the subdivision wastewater disposal plan shall contain, but need not be limited to, all of the following information, prepared under the direction of an engineer:
1. 
Soil, percolation, and groundwater table observations and test results conducted in accordance with standards outlined in this chapter.
2. 
A site plan and report addressing the following:
a. 
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.
b. 
The location of a possible well and wastewater reserve area for each lot in the proposed subdivision and within 250 feet of the proposed subdivision. The plans shall show the required separation distances of each well.
c. 
Topographic contours. Areas exceeding a 25 percent slope shall be delineated.
d. 
Potable water source separation distances.
e. 
Known groundwater nitrate levels in the general vicinity (within 250 feet) of the subdivision.
3. 
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.
(AO No. 2017-129, § 3, 1-23-2018)
A. 
All lots in a proposed subdivision served by on-site wastewater disposal systems shall conform to this section.
B. 
The minimum area of any lot shall be 40,000 square feet. The department may require a larger lot area where necessary to meet the requirements of this section.
C. 
Each lot in a proposed subdivision shall contain minimum reserved area suitable for on-site wastewater disposal systems. A holding tank shall not be considered as either the original or replacement site. Reserved areas shall be based on test holes completed on each lot. The department may require additional tests to better assess the ability of the soils to accept wastewater. Groundwater monitoring shall be done during seasonally high months of May and/or October. Groundwater monitor tubes shall not be removed until construction of the on-site wastewater disposal system has commenced. The minimum reserved area may be determined by either of the following two methods:
1. 
Total reserved area requirements may be determined from Table 7 without consideration of subsurface disposal field designs or the number of bedrooms allowed on the lot. The reserved area shall meet all separation distances required in this chapter. Test holes shall be located within the designated reserved area.
Table 7. Reserved Area Requirements
Percolation Rate
(minutes/inch)
Reserved Area
(square feet)
1—5
10,000
6—12
12,000
1—24
14,000
25—60
16,000
2. 
The lot shall contain sufficient area to provide for structures, and a well or other water source, and sufficient area for an original on-site wastewater disposal system and one replacement subsurface disposal field 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.
Exception: Reserved areas are not required if the proposed lot has an existing approved on-site wastewater disposal system. Existing on-site disposal systems on proposed lots shall have been approved by the regulatory agency or shall be documented and approved in accordance with this chapter. An area for a replacement wastewater disposal system shall be demonstrated.
Exception to section 15.65.410 subdivision standards: Proposed subdivisions containing on-site wastewater disposal systems approved by the regulatory agency may be approved without conforming to this section if the number of lots in the subdivision is not increased, and for decreased lot sizes the subdivider demonstrates all of the following:
 
1.
Lot sizes must be decreased in order to resolve a surveying error or fix violations to municipal code, provided the decrease in lot size of any one lot does not exceed 15 percent of the lot size prior to the decrease.
2.
Strict application of this section would be impractical and unreasonable or not in the best interests of the public health, safety, or welfare.
3.
The proposal would not be detrimental to the public welfare or injurious to other property.
4.
The proposal will not nullify the intent and purpose of this chapter.
5.
A site for a replacement wastewater disposal system is available.
6.
Undue hardship would result from strict compliance with the requirements of this section.
(AO No. 2017-129, § 3, 1-23-2018)