§ 19.07.022. Private sewage disposal systems.

The use of a private, on-site sewage disposal system is allowed only within the rural areas of the county and within urban and village areas where no community sewage collection, treatment and disposal system exists. Private sewage disposal systems shall be designed and constructed as provided by this section, in addition to satisfying all applicable requirements of the California Plumbing Code. In the event of any conflict between the provisions of this section and the California Plumbing Code, the most restrictive shall govern.

(1)

Legislative Findings. These regulations are enacted in part to implement the requirements of the "Water Quality Control Plan, Central Coastal Basin", adopted by the California Regional Water Quality Control Board. To the extent that these regulations change applicable provisions of the California Health and Safety Code and California Code of Regulations as they would otherwise apply to local construction, the board of supervisors finds that the changes herein are necessary because of local geological and topographic conditions which change applicable provisions of the California Health and Safety Code and California Code of Regulations as they would otherwise apply to local construction, the board of supervisors finds that the changes herein are necessary because of local geological and topographic conditions which involve limitations on the capability of soils in the unincorporated areas of San Luis Obispo County to effectively handle sewage effluent disposal from private sewage disposal systems. Such limitations include high groundwater, soils with poor percolation capability and steep slopes.

(2)

General Requirements.

a.

Percolation Tests. Percolation tests may be required by the chief building official pursuant to Appendix B of this section.

b.

Minimum Site Area with Well. As required by the Land Use Ordinance, Title 22 of this code, or the Coastal Zone Land Use Ordinance, Title 23 of this code. An existing parcel that contains a water well may be approved for a private sewage disposal system only if the parcel is one acre or larger. A parcel smaller than one acre may use a private sewage disposal system only where the well serving the parcel is a public water supply or is located on another parcel that is one acre or larger. The minimum site area for a new parcel where a well and septic system are both proposed is determined by the Land Use Ordinance, Title 22 of this code, and the Coastal Zone Land Use Ordinance, Title 23 of this code.

c.

Minimum Site Area in Reservoir Watershed. Within any domestic reservoir watershed, all private sewage disposal systems shall be located on individual parcels of at least 2-1/2 acres or within subdivisions with a maximum density of 2-1/2 acres or more per dwelling unit. No land within a horizontal distance of 200 feet from a reservoir, as determined by the spillway elevation, shall qualify for computing parcel size or density, or for septic system sitting.

(3)

Septic Tank and Leach Area Systems. On-site sewage disposal systems that utilize a buried tank for the processing of solids, and leaching areas, trenches or seepage pits for the disposal of liquid waste through soil infiltration shall be located, designed and constructed in accordance with all of the following standards:

a.

Minimum Site Characteristics. Septic tank and leach area systems shall be used only where the proposed site can maintain subsurface disposal, and satisfy the following standards on a continuous basis, unless an exception is approved as set forth in subsection (4) of this section.

1.

Subsurface Geology. The proposed site for a soil absorption disposal area shall be free from soils or formations containing continuous channels, cracks or fractures, unless a setback distance of at least 250 feet to any domestic water supply well or surface water is assured.

2.

Site Flooding. No sewage disposal system shall be allowed within an area subject to inundation by a 10-year flood.

3.

Minimum Percolation Required. A percolation rate from 0 to 30 minutes per inch of fall is sufficient to permit the use of leaching systems. Such systems shall not be used where percolation rates are slower than 120 minutes/inch unless the parcel is at least 2 acres. Such systems shall not be used where soil percolation rates are slower than 60 minutes/inch unless the effluent application rate is 0.1 gallon per day/square foot or less, using a minimum flow rate of 375 gpd/dwelling unit, or as provided by Appendix K of the California Plumbing Code for commercial uses. Percolation rates of more than 30 minutes per inch of fall may be approved only where the system is designed and certified to have been installed as designed by the design engineer.

4.

Site Slope. Septic tanks or leaching systems installed on slopes of 20 percent or more shall be designed and installation certified by a registered engineer. Design shall minimize grading disruption associated with access for installation and maintenance. No soil absorption sewage disposal area shall be located where the natural slope is 30 percent or greater.

5.

Separation from Impermeable Strata. A minimum distance of 10 feet shall be maintained from the bottom of leaching systems to impermeable strata. This distance shall be verified by test borings pursuant to the California Plumbing Code where required by the building official.

6.

Groundwater Separation. Depth from the bottom of the leach area to usable groundwater (including usable perched groundwater) shall be as follows, based upon the percolation rate found at the site:

Percolation rate, minutes per inch	Minimum distance to groundwater in feet
Less than 1 min./in.	50 feet*
-4	20 feet*
5-29	8 feet
30+	5 feet

 

**Unless a minimum horizontal separation of 250 feet between the disposal area and any domestic water supply well or surface water is assured, in which case minimum groundwater separation shall be 20 feet when the percolation rate is less than one minute/inch, and eight feet when the percolation rate is one to four minutes/inch.

The chief building official may require a piezometer test or other appropriate documentation to verify the groundwater separation required by this section.

b.

System Location. A private sewage disposal system shall be located on the parcel it serves. Soil absorption disposal systems, including but not limited to leach areas and seepage pits, shall be located in accordance with the setbacks in the following table, except that where disposal system location is proposed with less groundwater separation than required by subsections b(1)(vi) or b(3)(ii) of this section, the increased setbacks required by those subsections shall be provided.

Setback from	Distance in feet
Domestic water supply wells in unconfined aquifer.	100
Watercourse where geologic conditions permit water migration.	100
Natural spring or any part of man-made spring.	100
Reservoir, spillway elevation.	200
Public water supply wells.	100

 

c.

Seepage Pit Standards. The following standards apply only to seepage pit disposal facilities, in addition to all other applicable standards of this section.

1.

Soil Particle Size. Seepage pits shall be used only where soils or formations at the pit location contain less than 60 percent clay (a soil particle less than 2 microns in size) in the percolation zone used for seepage calculation, unless the parcel is at least two acres.

2.

Groundwater separation. Seepage pits shall be used only where distances between pit bottom and useable groundwater (including perched groundwater) is equal to or greater than the following minimum separations, based upon the soil type found at the site as follows:

Soil type	Minimum distance to groundwater in feet
Gravels	50 feet*
Gravels with few fines	20 feet*
Other	10 feet

 

**Unless a minimum horizontal separation of 250 feet between the disposal area and any domestic water supply well or surface water is assured, in which case minimum groundwater separation shall be 20 feet when the soil type is gravels and 10 feet when the soil type is gravels with few fines.

The chief building official may require a piezometer test or other appropriate documentation to verify the groundwater separation required by this section.

d.

System Design and Sizing.

1.

Replacement Area Required. Individual systems on new land divisions, and commercial, institutional, and sanitary industrial systems shall be designed and constructed to either reserve sufficient site area for dual leach fields (100 percent replacement area), or construct the dual leach fields with a diverter valve at the time of initial septic system installation. Installation of dual leachfields will be required if site access for installation of the expansion area could be limited after initial site development.

2.

Non-Residential Systems. Commercial, institutional, or sanitary industrial systems shall be designed based upon the daily peak flow estimate for the proposed use.

3.

Residential Systems. A minimum leaching area of 125 square feet per bedroom shall be provided for sewage disposal systems serving residential uses.

4.

Replacement of failed private sewage disposal systems. Where an existing private sewage disposal system has failed and a replaced system cannot be installed to meet the criteria of this section, the building official may approve a replacement system that meets all of the following minimum standards and is designed to satisfy as many of the other requirements of this section as possible:

(i)

The system is designed by a registered engineer.

(ii)

The proposed system is approved by the county health department.

(iii)

The installation of the approved system is inspected and certified to be installed as designed by the design engineer.

(3)

Use of Non-Standard Engineered Systems. Systems proposed under Section K1(J), Appendix K of the California Plumbing Code, including mound and evapotranspiration systems shall be designed as provided by the "Water Quality Control Plan, Central Coastal Basin", adopted and as amended by the California Regional Water Quality Control Board, by an engineer or sanitarian registered by the State of California competent in sanitary engineering, and shall be approved by the building official and the regional water quality control board.

(4)

Relief from Standards. Any applicant for a permit to install, repair or replace a private sewage disposal system who is aggrieved by the administration of the requirements of this section by the building official may appeal the matter to the board of appeals as provided in Section 19.02.020. In cases where an exception is requested to any provision of this section that prohibits use of a private sewage disposal system under specified conditions, no exception granted by the board of appeals shall be effective unless the California Regional Water Quality Control Board has also approved an "Exemption to Basin Plan Prohibitions" for the proposed exception.

(Ord. No. 3343, § 1, 12-6-16)