Chapter III. Sewage Disposal by Individual Onsite Wastewater Treatment Systems
Sec. 603-1 Consideration should be given to the construction of a community sewerage system and treatment plant if connection to a public sewer is not possible. Where sewage disposal by individual onsite wastewater treatment systems (OWTS) such as septic tanks with disposal fields or seepage pits is proposed, the following standards shall apply:
1. A soils report regarding the feasibility of using individual OWTS in accordance with the standards of good public health and engineering practice is required. Three copies of the report must be submitted. The report must be prepared by a registered civil engineer, qualified in the field of soils engineering, or by some other specialist acceptable to the EHD. The report is subject to the review and approval of the Division.
2. The report must include the results of soil percolation tests. Percolation tests shall be made in accordance with the U.S. Public Health Service test procedure (Manual of Septic Tank Practice, Part I). Any departure from that procedure must first be approved by the EHD. The submittal of soil test hole logs is also required, with soils classified in accordance with the Kern County Onsite Systems Manual and by either the U.S.D.A. Soil Classification System or Unified Soil Classification System.
Where soil and bedrock conditions permit, the test pits or borings shall extend to minimum depths of seven (7) feet below the bottoms of proposed disposal trenches or twelve (12) feet below the bottoms of pits. The Engineer must specify whether disposal trenches and/or pits are to be used. The number of test holes and percolation tests is ordinarily at the discretion of the engineer, but they are required to state whether or not the soil in each lot in a development is capable of satisfactorily absorbing sewage effluent.
Soil and percolation test hole locations must be accurately plotted on the map which accompanies the report. If the soil types vary within the development, the map shall indicate limits of the different types, and a lot-by-lot list of soil types shall be submitted.
3. For purposes of standardization, Appendix Tables 1 and 2 shall be used to correlate percolation rates with soil types.
Sec. 603-2 Individual OWTS may be used only where sufficient area for them is provided and where the density of such systems and of the resulting sewage effluent will not have an adverse effect upon water quality or public health.
- The minimum allowable lot size where individual OWTS are used is considered to be a function of soil properties, climate, geology, and topography. The required minimum lot size where individual OWTS are used is 10,000 square feet net, except as follows:
- In desert, valley, or foothill areas, lots may be less than 10,000 square feet net but no less than 7,200 square feet net, where individual systems are used, provided that the following criteria, over and above those contained elsewhere in these Standards, are satisfied:
- A functioning public entity providing potable water exists or is provided.
- The site is shown on the Geologic Map of California as “Recent Alluvium”, as published by the California Division of Mines and Geology.
- The soils for septic tank purposes are Type 2 (Fine sand) per Appendix Table 2.
- The natural slope of the surface of the ground throughout the site does not exceed ten (10%) percent.
- Other pertinent environmental quality control factors, in the discretion of the Director of the Public Health Services Department, allow the smaller lot size.
2. In all areas, each lot shall be provided with an adequate site for subsurface disposal of sewage effluent within the boundaries of the lot. The site must have a natural slope of thirty (30%) percent or less; it must be located to allow disposal by gravity flow, and its size for single family residential use, whether leaching trenches or disposal pits are used, shall be in accordance with Appendix Table 3.
3. The required minimum size of the effluent disposal field area for multiple dwelling lots, in which leaching trenches or seepage pits are used, shall be determined by the following information:
- The required area in square feet and the required septic tank capacity in gallons, in accordance with requirements in the Kern County Onsite Systems Manual (Part 1).
- The proposed number of dwelling units, the number of bedrooms in each unit, and the soil type in the future effluent disposal area must be known in order to derive the required area.
- Also, the use of dual disposal systems, which entails alternate, periodic use and resting of trenches or pits, is required on multiple dwelling lots.
Sec. 603-2.02 In designing lots and sewage disposal sites prior to the filing of a tentative map, the following factors shall be considered:
- Space shall be allowed on the lot for expansion of the original disposal field. The square footages given in Appendix Table 3 are intended to satisfy initial expansion area requirements for disposal fields. The use of dual disposal systems, which entails alternate, periodic use and resting of trenches and pits, may be required at the reasonable discretion of the Director of the Public Health Services Department. Where dual disposal systems are to be used, each one-half of the system shall have an absorption area equal to at least two-thirds of that required by the current Kern County OWTS design standards, per Onsite Systems Manual, Part 1, an expansion area capable of accommodating at least 50% of the original installation is required in Types 1, 2, and 3 soils; at least 87% in Type 4 soil; and 125% in Type 5 soil.
- The design of the lot should be easily accessible for future maintenance, repair, reconstruction, or connection to future public sewers.
- The installation of sewage disposal systems within easements is not permitted without prior approval of the easement holder. Slope easements are included in this prohibition.
- The disposal system must be located so that sewage effluent will not percolate out through the surface of the embankment. As a guideline, disposal systems should be set back at a ratio of 4 to 1 from embankments; for example, for each vertical foot of embankment height, the disposal system should be located four feet horizontally from the top of the embankment. Setbacks should be adjusted to suit local geologic conditions. The following minimum setbacks from water wells are required:
| System |
All Water Wells |
Public water supply wells |
| Sewer or water-tight septic tank |
100 feet |
150 feet |
| Leaching Field |
100 feet |
150 feet |
| Seepage Pit |
150 feet |
150 feet |
*200 feet for any trench or seepage pit >10’ deep; 2-yr microbial travel study required for seepage >20’ deep within 600 feet of public water supply well.
- These setback distances may be increased where deemed necessary by the Director of the Public Health Services Department.
- Disposal systems should not have to be installed underneath pavement or other impervious ground surface coverings. If it is necessary to install disposal fields beneath impervious surface coverings, the disposal system and required areas shall: (1) be increased by 25%; and (2) be installed using traffic-rated chambers in place of standard pipe and drain rock, with no reduction credit for chambers.
- The use of aerobic or other supplemental treatment equipment in place of or in addition to conventional septic tanks is not acceptable as a basis for reduction of the subsurface disposal area. The installation of electro-mechanical sewage disposal devices must have a provision for periodic professional maintenance, and is subject to approval by the EHD as an “alternative OWTS” in accordance with provisions of Kern County OWTS Ordinance Article 3.
- A lot is not suitable for residential use if the sewage disposal system cannot be installed within its boundaries.
- Bedrock, other impervious formations, and the maximum seasonal elevation of the ground water level shall be at least seven (7) feet below the bottoms of disposal trenches or twelve (12) feet below the bottoms of seepage pits. In very pervious soils, for example, Types 1 and 2, the required separation between ground water level and the bottoms of disposal trenches or pits may be increased at the discretion of the Director of the Public Health Services Department.
- The installation of sewage disposal systems in areas underlain by carbonate rocks or by fractured bedrock is not permitted unless evidence indicates that solution cavities or open fractures will not serve as conduits for the passage of improperly filtered sewage effluent into ground waters, springs, or surface streams. Professional findings or opinions in this regard shall be submitted where applicable.
- No sewage or sewage effluent may be discharged within 100 feet (horizontally) of any water source or the high water mark of a river, stream, canal, lake, or other surface body of water. Sewage disposal systems shall be located as far as possible from a non-classified stream or its established easement and in no case closer than 25 feet thereto unless certified by a qualified engineer that is safe to do so without creating a nuisance or endangering the watershed.
Sec. 603-3 The engineer is required to submit a statement that all lots have been designed in compliance with these standards. For “alternative OWTS” and other specially engineered systems, the engineer shall certify that the system(s) have been installed according to the approved plans when required by the EHD.
Sec. 603-4 One copy of a topographical analysis map on the tentative map base (or on a larger scale map) may be required at the Director of the Public Health Services Department discretion. Slope percentage categories shall be depicted in accordance with the following color code:
Slope Range Color
0 to 30% Uncolored
Greater than 30% Colored
Additionally, the map shall show all easements and locations of rock out-crops, high ground water, and spring discharge. The portions of lots allocated for the subsurface disposal of sewage effluent shall be delineated, and their approximate areas in square feet indicated. The approximate size of irregularly shaped lots must also be shown.
Sec. 603-5 Where watercourses, significant drainage channels, or bodies of water traverse or adjoin a lot, a predevelopment plan, showing how OWTS can be installed and still remain at least the necessary distance from the high-water mark, may be required. Lines depicting the required setbacks from such watercourses, drainage channels, or bodies of water shall be indicated on a copy of the tentative map.
Sec. 603-6 The use of disposal fields, wherever conditions permit, is preferred to that of pits. Seepage pits are prohibited where percolation rates for them exceed 25 minutes per inch (U.S. Public Health Service test procedure). In lieu of seepage pits, the engineer may consider the use of “alternative OWTS” or “specially designed”, deeper disposal trenches in accordance with applicable provisions and requirements of Kern County OWTS Ordinance, Article 3 and Onsite Systems Manual.
Sec. 603-7 If the engineer determines that the building of fill pads for the installation of disposal fields is necessary, he/she must submit design criteria for such pads and fields. Where any fill pad is to be built in sloping terrain, EHD shall require the subdivider to furnish findings of an engineer or engineering geologist qualified in such matters regarding the possibility of soil slippage or landslide of the pad area, along with recommended design measures to mitigate such hazards. The Engineer shall certify that the fills are constructed in accordance with the design.
Sec. 603-8 If lot-grading adversely changes the engineer's initial report on percolation characteristics of the soil in a proposed sewage disposal area, the system installed therein shall be designed in accordance with specific recommendations of a soils engineer or other specialist acceptable to EHD .
Sec. 603-9 If underground irrigation lines or other pipelines, either abandoned or proposed for abandonment, exist within a proposed land development, their locations must be shown on the tentative map, and they must be removed or destroyed as part of the subdivision improvements.
Sec. 603-10 When a geologic hazards report for land development is prepared (either at the developer's will or as a requirement of any governmental agency), it shall include findings and recommendations concerning probable adverse effects of such hazards on the integrity of water supply and sewage disposal facilities. A copy of the report shall be furnished to EHD.
Sec. 603-11 When a flood hazard is found to exist, the engineer shall define it and shall submit their recommendations for protecting the integrity of water wells, water quality, and OWTS. Where applicable, the limits of the 100-year flood line shall be indicated on the tentative map.
The installation of public or private sewage disposal systems in a primary floodplain is prohibited. In a secondary floodplain, individual sewage disposal systems are not permitted unless protected by flood control devices approved by the Kern County Public Works Department and constructed in accordance with the requirements of the EHD so as to minimize infiltration of floodwaters into the systems and discharges from the systems into the floodwater.
Sec. 603-12 EHD acceptance of proposed water supply and sewage disposal methods is contingent upon clearance of those proposals through the State Regional Water Quality Control Board or State Water Resources Control Board.
Sec. 603-13 If a private domestic water well and individual OWTS are to be constructed on a lot, the minimum lot size shall be 2 ½ acres gross. In order to preclude interference with neighboring installations, water wells shall be located with consideration of required setback distances from existing or future neighboring OWTS. Where demonstrated by a qualified civil engineer or geologist to be practical from the public health and engineering viewpoints, an exception may be granted to allow lot design of one (1) acre net minimum size where the construction of a private water well and individual OWTS is proposed. This will normally entail completion of a cumulative impact assessment per Kern County OWTS Ordinance, Article 3 and applicable guidelines contained in the Onsite Systems Manual, Part 1.
Sec. 603-14 In accordance with the California Plumbing Code and County ordinance, all individual OWTS must be installed under permit with the Building Inspection Division of the Kern County Public Works Department.
Sec. 603-15 In areas which are determined by EHD to be unsafe for installation of individual sewage disposal systems, and where it is considered likely that a nuisance or health hazard might be created, said areas shall be served by an approved public or community sanitary sewer system.
Sec. 603-16 If a "package treatment plant" is proposed as a means of community sewage disposal, the engineer must submit design criteria for the plant to EHD and receive approval from the appropriate Regional Water Quality Control Board.
Sec. 603-17 In larger land developments, consideration should be given to setting aside easements and areas for possible future use for sewage collector lines and treatment plant sites. In some cases, EHD may require such provisions.
Sec. 603-18 If a proposed land development is to be served by a public or community sewerage system, a letter from the appropriate agency or company signifying its capability and its intention to furnish its sewerage facilities to the property must be submitted to EHD. If construction has not begun within one year of the date the "will serve" letter is issued, an updated letter will be required.
Sec. 603-19 The sewerage statement on the tentative map for a land development for which individual sewage disposal systems are proposed should be worded: "Sewerage: Individual septic tank systems to be furnished by each subsequent lot owner", or similar.
Sec. 603-20 The findings and comments of EHD regarding a proposed land development are ordinarily based upon the most recent of available tentative maps. If the design is later changed significantly, a reappraisal of the development by the Division may be necessary.
