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Title: 14 - Buildings and Constructions

Chapter: 12 - On-Site Sewage Disposal Systems

Section: 80 - Design criteria

A.  Septic Tank. Septic tank size requirement and design shall be based on the current edition, adopted by the county, of the International Association of Plumbing and Mechanical Officials (IAPMO) Uniform Plumbing Code, except that the minimum size tank for residential use shall be one thousand two hundred gallons, the tank shall have more than one compartment and shall have inlet and outlet "T\'s" or baffles.

B.  Leachfield System. For on-site systems of less than one thousand five hundred gallons per day (gpd), leachfield design and disposal area requirements shall be based upon the United States Public Health Services (USPHS) Manual of Septic Tank Practice (MSP). Those sections of the EPA Design Manual for on-site wastewater treatment and disposal systems that are equal to or more stringent than the basin plan and the MSP can be used for design and evaluation purposes. For on-site systems with greater than one thousand five hundred gallons per day (gpd), sizing shall be approved by the regional board.

C.  Construction. Construction of disposal field and septic tanks shall be in conformance with the current edition, adopted by the county, of the IAPMO Uniform Plumbing Code. The county may require and/or approve more detailed or modified specifications when conditions warrant. Data supporting the suitability of an alternative means of construction shall be submitted by the applicant.

D.  Sewage Flows. When quantities of sewage flow are not known or cannot be accurately determined, Table B in Section 14.12.130 shall be used to estimate sewage flow. Table B shall take precedence unless the applicant\'s engineer provides specific justification for different flows.

E.  Setback Requirements. Minimum setback distances for individual waste treatment and disposal systems shall be as provided in Table A of Section 14.12.130.

F.  Standard Systems. Standard on-site waste treatment and disposal systems may be developed for use in soil zones which have been demonstrated to comply with the provisions of this chapter and are effective designs of on-site sewage treatment and disposal.

G.   Intercept Drains. The use of intercept drains to lower the level of perched groundwater in the immediate leachfield area shall be acceptable under the following conditions:

1.     Natural ground slope is greater than five percent

2.     Site investigations show groundwater to be perched on bedrock, hardpan, or an impermeable soil layer,

3.     The intercept drain extends from ground surface into bedrock, hardpan, or the impermeable soil layer.

In no case shall the pervious section of an intercept drain be located less than fifteen feet upgradient or fifty feet laterally from any septic tank or leachfield, or twenty-five feet from any property line. Where all of the above conditions cannot be met, detailed engineering plans must be supplied or actual performance of the intercept drain demonstrated prior to approval.

H. Fills. The use of fills to create a leachfield cover shall be acceptable under the following conditions:

1.      Where the natural soils and the fill material meet the evaluation criteria as described in Section III of the North Coast Regional Water Quality Control Board water quality control plan

2.      Where the quantity and method of fill application is described

3.      Where the natural slope does not exceed twelve percent

4.      Where site investigations by a registered geologist, registered sanitarian or registered civil engineer demon­strate that placement of fill will not aggravate slope stability or significantly alter drainage patterns or natural watercourses. The investigations are to be included in a report which contains engineered plans as well as a specific evaluation of the suitability of the system to accept wastewater and protect water quality:

5.      Leachfield sizing shall be based on the most limiting soil type within the filled area-,

6.      Leachlines for wastewater disposal shall be placed entirely within natural soils. Except that fill material which has been in place for a sufficient period of time and otherwise has been demonstrated to meet site suitability criteria may be allowed. Fill material shall not be used to create a basal area for alternative systems or mounds.

I. Alternative Systems. Systems which have been demonstrated to the regional board to function in such a manner as to protect water quality and preclude health hazards and nuisance conditions may be approved by the county.  Alternative systems are subject to a program of maintenance and inspections.

1.  Mounds. Where site conditions are determined to be suitable, use of mounds for wastewater disposal may be considered.  The mound design shall be based on current edition of the Design Construction Manual for Wisconsin Mounds, Small Scale Wastewater Management Project, University of Wisconsin.

2.  Pit Privies.  Pit privies may be utilized for sewage disposal on sites in rural areas which are designated by the board of supervisors for such use.

3.  Other alternative systems included in the current edition of the Basin Plan including but not limited to pressure distribution systems, at-grade systems, sand filters, and alternative systems that have been evaluated by the Regional Water Board staff and the County on a case by case basis.

J. Compliance Certificate. Each submittal for a new installation shall contain a statement by the preparer stating that the submitted design complies or fails to comply with the provisions of this chapter and such statement shall contain a "wet signature" across the registration of the preparer issued by the state.

K. Qualifications Necessary of Person Preparing On-Site Waste Treatment and Disposal System Designs. One of the following registrations with the state is required of the person(s) preparing an on-site waste treatment and disposal system design, who may perform such design services to the extent permitted by state law:

1.  California Registered Civil Engineer.

2.  California Registered Environmental Health Specialist

3.  California Registered Geologist or Soil Scientist. 


(Ord. 2005-25B §§ 11,12, and 13, 2005 Ord. 88-34 § 2 (part), 1988.)