November 25, 2017

Division Six - Environmental Health Standards, Rules & Regulations - Chapter II. Sewage Disposal by Individual Absorption Systems

Chapter II. Sewage Disposal by Individual Absorption Systems

Sec. 602-1 Where connection to a public sewer is not possible, consideration should be given to the construction of a community sewerage system and treatment plant. Where sewage disposal by individual soil absorption systems (for example, septic tanks with disposal fields or pits) is proposed the following standards shall apply:

602-1.01 A soils report regarding the feasibility of using individual sewage disposal systems in accordance with the standards of good public health and engineering practice is required. Three copies of the report shall 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 Environmental Health Services Department. The report is subject to the review and approval of the Environmental Health Services Department.

602-1.02 Unless waived by the Environmental Health Services Department, the report shall include the results of soil percolation tests (the results of all such tests performed must be submitted). 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 Environmental Health Services Department. The submittal of soil test hole logs is also required, with soils classified in accordance with the California Plumbing Code soil-type system and by either the Unified Soil Classification System or other standard method. 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 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 he is required to state whether or not the soil in each lot in a land 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 CPC soil types (for disposal purposes) vary within the development, the map shall indicate the limits of the different types, and a lot-by-lot list of soil types shall be submitted. (Effective September 24, 1979; Resolution #79-716).

602-1.03 For purposes of standardization, the following table shall be used to correlate percolation rates with the California Plumbing Code soil types:

Percolation Rate Minutes/Inch CPC Soil Type
Less than one 1
1 to 3 2
3+ to 10 3
10+ to 25 4
25+ to 60* 5
Greater than 60 Unacceptable
*unacceptable for seepage pits

NOTE: Regional Board guidelines require that where percolation rates of less than five (5) minutes per inch are present, it must be shown that a sufficient distance of soil is available to ensure proper filtration.

Sec. 602-2 Individual sewage disposal systems may be used only where sufficient area for them is provided and where, in the opinion of the Director of the Environmental Health Services Department, the density of such systems and of the resulting sewage effluent will not have an adverse effect upon water quality or public health.

602-2.01 The minimum allowable lot size where individual sewage disposal systems are used is considered to be a function of soil properties, hydraulic properties, climate, geology, and topography. The required minimum lot size where individual sewage disposal systems are used is 10,000 square feet net, except as follows:

  1. In other than mountain and foothill areas, lots may be less than 10,000 square feet net but not less than 7,200 square feet net, where individual sewage disposal systems are used, provided that, in addition to other criteria contained in these Standards, a functioning public entity, as defined herein (See Sec. 602-22 following) exists or is provided.
  2. In mountain and foothill areas lots may be less than 10,000 square feet net but not less than 7,200 square feet net, where individual sewage disposal systems are used, provided that the following criteria, over and above those contained elsewhere in these Standards, are satisfied:
    1. A functioning public entity, as defined herein (See Sec. 602-22 following), exists or is provided.
    2. The site is shown on the Geologic Map of California (as published by the California Division of Mines and Geology) as "Recent Alluvium", that is symbol, "Qal".
    3. The soils, for septic tank system purposes, are Type 1 or Type 2 of the California Plumbing Code.
    4. The natural slope of the surface of the ground throughout the site does not exceed ten (10) percent.
    5. Other pertinent environmental quality control factors, at the discretion of the Director of the Environmental Health Services Department, allow the smaller lot size.

602-2.02 Notwithstanding the minimum lot size specification in Sec. 602-2.01 of this section, in all areas each lot shall be provided with an adequate site for subsurface disposal of sewage effluent within the boundaries of the lot. That site must have a natural slope of 30% 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 the following table:

CPC Soil Type in Disposal Area Required Minimum Size of Disposal Site (square feet)*
1 2,000
2 2,500
3 4,500
4 13,000
5 21,000

* exclusive of any areas occupied by structures, setbacks, and easements on the lot and in accordance with the requirements of the California Plumbing Code and these "Standards".

The minimum disposal area required by the table above (which includes expansion area) is for standard leaching trenches which provide three (3) square feet of leaching area per lineal foot, or special leaching trenches which provide seven (7) square feet of leaching area per lineal foot.

602-2.03 The required minimum size of the effluent disposal field area for multiple-dwelling lots (i.e., R-2 and R-3 zones), whether leaching trenches or seepage pits are used, shall be determined by the following formulae, where "A" equals the required area in square feet and "C" equals the required septic tank capacity in gallons in accordance with the California Plumbing Code. Two factors must be known in order to derive the required area, namely: (1) the proposed number of dwelling units and the number of bedrooms in each unit, and (2) the CPC soil type in the future effluent disposal area):

CPC Soil Type in Disposal Area Required Minimum Size of Disposal Site (square feet)*
1 A = 2.0C - 480
2 A = 2.5C - 640
3 A = 4.1C - 690
4 A = 11.0C - 940
5 A = 17.1C - 900259

* exclusive of any areas which are unsuited for disposal system installation in accordance with the requirements of the California Plumbing Code and these Standards. Minimum size septic tank provided shall be 1,500 gallons.

Also, the use of dual disposal systems (which entails alternate, periodic use and resting of trenches or pits) is required on multipledwelling lots. Each one-half of the dual system shall have an absorption area equal to at least two-thirds of that required by the California Plumbing Code (i.e., two-thirds of a conventional system).

602-2.04 In designing lots and sewage disposal sites prior to the filing of a tentative map, the following factors shall be considered:

  1. Space shall be allowed on the lot for expansion of the original absorption facility. The square footages given in the preceding tables are intended to satisfy initial and expansion area requirements for disposal fields. The use of dual disposal systems (which entails alternate, periodic use and resting of trenches or pits) may be required at the reasonable discretion of the Director of the Environmental 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 California Plumbing Code (i.e., two-thirds of a conventional system). For such dual systems an expansion area capable of accommodating at least 50% of the original installation is required in Types 1, 2, and 3 soils; at least 87-1/2% in Type 4 soil; and 125% in Type 5 soil.
  2. The design of the lot should allow the system to be easily accessible for future maintenance, repair, reconstruction, or connection to future public sewers. For example, on smaller lots the design should allow for installation of the system in the front portion of the lot; the back portion of a lot may be used where an alley is provided.
  3. 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. 
  4. Where cut or fill banks are, or will be, nearby, 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 four (4) to one (1) from embankments (i.e., for each vertical foot of embankment height, the disposal system should be located four (4) feet horizontally from the top of the embankment). Setbacks should be adjusted to suit local geologic conditions.
  5. The following minimum setbacks from water wells are required: 
    System All Water Wells
    Sewer or water-tight septic tank 50 feet
    Leaching field 100 feet
    Seepage pit 150 feet

    These setback distances may be increased where deemed necessary by the Director of the Environmental Health Services Department.
  6. 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 be increased by 25%.
  7. The use of aerobic-treatment equipment in place of conventional septic tanks is not acceptable as a basis for reduction of the required subsurface disposal area. The installation of electro-mechanical sewage disposal devices without provision for periodic professional maintenance is not encouraged, and is subject to disapproval by the Director of the Environmental Health Services Department.
  8. A lot is not subject to residential use if the sewage disposal system cannot be installed within its boundaries.
  9. 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 (e.g., CPC Types 1 and 2) the required separation between the ground water level and the bottoms of disposal trenches or pits may be increased at the discretion of the Director of the Environmental Health Services Department.
  10. The installation of sewage disposal systems in areas underlain by carbonate rocks (e.g., limestone) 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. Where applicable, professional findings or opinions in this regard shall be submitted.
  11. 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 practical 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 it is safe to do so without creating a nuisance or endangering the watershed.For purposes of interpreting this section, the following definitions apply:

Stream - a continual or seasonal flow of water in a definite channel having a bed or banks.

Non-classified stream - flow of water within a well-defined course only during period of storm.

Sec. 602-3 The engineer is required to submit a statement that all lots have been designed in compliance with these Standards. For specially engineered systems, the engineer shall certify that the system(s) have been installed according to the approved plans.

Sec. 602-4 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 Environmental Health Services Department's discretion. Slope percentage categories shall be depicted in accordance with the following color code:

Slope Range Color
0 to 30% Uncolored
Greater than 30% Red

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. 602-5 Where watercourses, significant drainage channels, or bodies of water traverse or adjoin a lot, a predevelopment plan, showing how sewage disposal systems 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. 602-6 Wherever conditions of soil, topography, etc. permit, the use of disposal fields 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 might consider the use of "specially designed", deeper disposal trenches as described in the California Plumbing Code.

Sec. 602-7 If the engineer determines that the building of fill pads for the installation of disposal fields is necessary, he must submit design criteria for such pads and fields. Where any fill pad is to be built in sloping terrain, the Environmental Health Services Department may 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. The Engineer shall certify that the fills are constructed in accordance with the design.

Sec. 602-8 If lot-grading adversely changes the engineer's initially-reported percolative 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 the Environmental Health Services Department.

Sec. 602-9 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. 602-10 When a geologic hazards report for land development is prepared (either at the developer's volition 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 the Environmental Health Services Department.

Sec. 602-11 When a flood hazard is found to exist, the engineer shall define it and shall submit his recommendations for protecting the integrity of water wells, water quality, and sewage disposal systems. Where applicable, the limits of the floodplain shall be indicated on the tentative map.

The installation of public or private sewage disposal systems in a floodway is prohibited. In an area subject to inundation (by the CSDD/See Division Four or areas identified on the Flood Insurance Rate Maps), individual sewage disposal systems are not permitted unless protected by flood control devices approved by the Department and constructed in accordance with the requirements of the Environmental Health Services Department so as to minimize infiltration of floodwaters into the systems and discharges from the systems into the floodwater.

Sec. 602-12 Environmental Health Services Department acceptance of proposed water supply and sewage disposal methods is contingent upon clearance of those proposals through the State Regional Water Quality Control Board and/or the State Department of Health Services.

Sec. 602-13 If a private domestic water well and individual sewage disposal system are to be constructed on a lot, the minimum lot size shall be 2-1/2 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 sewage disposal systems. 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.

Sec. 602-14 In accordance with the California Plumbing Code and County ordinance, all individual sewage disposal systems must be installed under permit with the Building Inspection Division of the Engineering, Surveying & Permit Services Department.

Sec. 602-15 In areas which are determined by the Environmental Health Services Department 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. 602-16 If a "package treatment plant" is proposed as a means of community sewage disposal, the engineer must submit design criteria for the plant to the Environmental Health Services Department for approval.

Sec. 602-17 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, the Environmental Health Services Department may require such provisions.

Sec. 602-18 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 the Environmental Health Services Department. If construction has not begun within one year of the date the "will serve" letter is issued, an updated letter will be required.

Sec. 602-19 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. Proposals to utilize "cesspools" are not acceptable.

Sec. 602-20 The findings and comments of the Environmental Health Services Department 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 this Department may be necessary.

Sec. 602-21 Whenever possible, all unbound maps for submittal to the Environmental Health Services Department should be folded to 8 ½" x 11" with the title showing.

Sec. 602-22 Definition:

Public Entity--a local agency which is empowered to plan, design, finance, construct, operate, maintain, and to abandon, if necessary, any sewerage system or the expansion of any sewerage system and sewage treatment facilities serving a land development. In addition, the entity shall be empowered to provide permits and to have supervision over the location, design, construction, operation, maintenance, abandonment of individual sewage disposal systems and to conduct any monitoring or surveillance programs required for water quality control purposes.


Public Services Building
2700 M Street, Suite 570
Bakersfield, CA 93301-2370

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