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246-272B-06200  <<  246-272B-06250 >>   246-272B-06350

PDFWAC 246-272B-06250


(1) Treatment to produce effluent of a higher quality than STE is required when:
(a) LOSS conditions match those in Table 6 of this section that require minimum Treatment Levels E, C, B, HQE, N10, N20, or P;
(b) Sewage characteristics exceed typical values expected from residential strength sewage; or
(c) The department determines it is needed based on results of the site and environmental review process.
(2) Treatment level parameters are shown in Table 5 of this section. The values represent maximum annual average effluent requirements.
(3) Treatment technology requirements are in WAC 246-272B-06550.
(4) Table 6 shows minimum required treatment levels for various conditions.
(5) To determine the minimum treatment level for a proposed LOSS, the design engineer shall:
(a) Identify the coarsest textured soil within the vertical separation shown in the soil logs;
(b) Use Table 6 in this section with the coarsest textured soil type, and proposed design flow and sewage characteristics to identify a minimum treatment level; and
(c) Increase the treatment level, if the drainfield is near areas where pathogens or other effluent parameters are a public health or environmental concern including, but not limited to:
(i) Shellfish growing areas;
(ii) Designated swimming areas; and
(iii) Well head protection areas.
(6) The design engineer shall propose, at a minimum, specific values for Treatment Level HQE parameters and performance levels based on project-specific site and soil conditions. The department shall review and, if appropriate, confirm parameter values and performance levels.
(7) For LOSS with design flow of 14,500 gpd or less, the design engineer shall not use disinfection treatment to meet the fecal coliform standard in:
(a) Treatment Level B for drainfields in Type 1 soils; or
(b) Treatment Level C.
(8) For LOSS with design flow above 14,500 gpd, the department may allow disinfection treatment to meet the fecal coliform standard if all of the following conditions are met:
(a) The owner shall employ a qualified operator for the lifetime of the LOSS;
(b) The monitoring and reporting plan described in WAC 246-272B-04300 must demonstrate performance standards are consistently met; and
(c) The management plan described in WAC 246-272B-04100 must verify that the ownership, management, and financial resources are adequate to meet subsection (7)(a) and (b) of this section for the lifetime of the LOSS.
(9) The department may:
(a) Impose more stringent treatment and design requirements if necessary to protect public health or the environment;
(b) Require, as a condition of the operating permit, ongoing influent, effluent, and groundwater monitoring, to assure performance requirements are met;
(c) Require the owner to have a service contract with the proprietary treatment manufacturer or a qualified operator according to WAC 246-272B-07200(3) when the department determines the proposed treatment requires frequent operator attention to meet performance requirements; or
(d) Deny approval for LOSS designs that propose using specific technologies or treatment processes that have monitoring and sampling histories indicating inadequate or unreliable performance.
Table 5: Treatment Levels
Effluent Parameters *
Treatment Level
(#/100 ml)
The values represent effluent maximum annual averages.
Site specific; see WAC 246-272B-06250(7).
Table 6: Requirement Minimum Treatment Levels for Various Conditions
Minimum Required Treatment Level
Project Specific1
Vertical Separation of 2 to < 3 feet, design flow higher than 14,500 gpd
Soil Type 1
Vertical Separation of 2 to < 3 feet, design flow 14,500 gpd or less
Sewage that is not residential strength
All sites not requiring B, C, E or HQE
Sites where nitrogen or phosphorus is identified as a contaminant of concern
N10, N20, or P3
Table 6 notes:
As identified during the site review process.
HQE: High quality effluent; project specific standards are set case-by-case. Treatment Level HQE is required where Treatment Level B is inadequate, or may be chosen by the LOSS owner.
As required by the department, based on the environmental review. Nitrogen treatment higher than N10 may be required for some sites. Phosphorus or other treatment value will be project specific, determined in the environmental review or by local or state regulation.
[Statutory Authority: RCW 70.118B.020. WSR 11-12-035, § 246-272B-06250, filed 5/25/11, effective 7/1/11.]
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