Article 4 — OWTS SITING AND DESIGN

a.

Where an OWTS is required, it shall, at a minimum, consist of a conventional OWTS as defined in this chapter. The septic tank and subsurface effluent dispersal system must be designed by a qualified OWTS design professional, permitted, and so constructed as to meet the requirements of this chapter and the rules, regulations and guidelines prescribed in the Onsite Systems Manual.

b.

No Person may construct, add to, repair or alter any new or existing OWTS without first submitting plans to Environmental Health for approval and obtaining a Permit pursuant to the requirements of this chapter and the Onsite Systems Manual.

c.

A primary dispersal field must be installed, consisting of two sets of effluent dispersal trenches interconnected with an approved flow diversion device (dual dispersal system), intended to allow alternate use of the two fields as prescribed in the Onsite Systems Manual. Additional dispersal fields equivalent to and separate from the primary dual dispersal fields, must be identified and such area held in reserve for potential future replacement of the primary field(s).

d.

For all locations where an OWTS is proposed to be installed or expanded, including designated replacement fields, soil percolation testing and other exploratory tests, as necessary, shall be performed to verify adequate depth and permeability of soil and separation between trench bottom and groundwater. Testing shall be conducted in accordance with requirements and guidelines prescribed in the Onsite Systems Manual. Such procedures shall include provisions for completion of Groundwater observations during the wet season, as well as wet season soil percolation testing in cases where soils exhibit high shrink-swell characteristics related to clay content, plasticity and/or structure.

e.

Soil percolation testing, groundwater determinations, and designation of adequate dispersal system area to meet the requirements of this chapter for divisions of land will be required on each proposed parcel.

(Ord. No. 04754, § 1, 1-5-2016)

Approval of all OWTS shall require compliance with the following minimum siting criteria:

a.

The septic tank, drainfield, and other components of the OWTS shall be located within the boundaries of the parcel upon which the structure requiring the system is built.

b.

Minimum depth of soil beneath the bottom of the proposed dispersal field shall be three (3) feet.

c.

No dispersal of effluent shall be allowed within soil fill. All dispersal systems shall have at least twelve (12) inches of soil cover, except for shallow subsurface drip dispersal systems, which must have at least nine (9) inches of soil cover.

d.

The average soil percolation rate in the proposed dispersal field area shall not be faster than twelve (12) inches per hour (five (5) minutes per inch) nor slower than 0.75 inches per hour (eighty (80) minutes per inch), determined by soil percolation testing in accordance with procedures prescribed by this chapter and the Onsite Systems Manual. Dispersal system areas with percolation rates between 0.75 inches per hour and 0.99 inches per hour must utilize pressure-dosing distribution consistent with article 5 of this chapter.

e.

Underground utility lines, conduits or trenches, including irrigation lines, shall not be installed in or across drainfields, nor shall they be located near drainfields so as to pose a potential preferential pathway for effluent.

f.

Minimum required vertical groundwater separation distance between trench/distribution system bed bottom and groundwater shall be at least five (5) feet. Vertical groundwater separation distance between trench bottom and groundwater may be reduced to three (3) feet by utilizing supplemental treatment or pressure-dosing distribution systems OWTS in compliance with article 5 of this chapter and the Onsite Systems Manual.

g.

OWTS shall not be located in areas subject to flooding, consistent with criteria as prescribed in the Onsite Systems Manual.

h.

OWTS must be located to be easily accessible for maintenance and repairs.

i.

OWTS shall not be located in areas subject to vehicular traffic or other areas subject to significant compaction, including areas of concentrated livestock use. Maximum ground slope in the dispersal field area shall not equal or exceed fifty percent (50%). Where ground slope in the dispersal field area is thirty- five percent (35%) up to fifty percent (50%), pressure-dosing distribution is required. For any site where the ground slope exceeds twenty percent (20%), approval shall be dependent upon completion of a geotechnical report as prescribed in the Onsite Systems Manual.

j.

Minimum horizontal setback distances from various site features to OWTS components shall be as follows:

Site Feature Minimum Setback Distance (feet)

To Septic Tank To Dispersal Field

Building or foundation 5 10

Septic Tank N/A 10

Property line      From properties served by wells or springs 50 50 From properties served by approved public water 10 10 supply

Swimming pool or spa 25 25

Road easement, pavement or driveway 5 5

Watercourses      General (from top bank) 100 100 Between 1,200 to 2,500 feet from a public or state 100  200 1 small water system intake     Within 1,200 feet downstream from a public or 100 1  400 state small water system intake

All wells and domestic/irrigation springs 100 100

Public and state small water system supply wells or     springs 150 150

Reservoirs (from high water mark)      General 200 200 Within 1,200 feet from a public or state small water 200 400 system intake

Groundwater interceptor trench or drain 5 25

Stormwater infiltration trench, gallery or well 25 25

Drainage swale or ditch (from edge of flow path)      General, lined or unlined     Evidence of sustained wet conditions or ponding 25 25 25 50

Cuts or embankments (from top of cut) 10 4 x h 2, 3

Steep slopes (lower in elevation than OWTS) 4      Height of steep slope less than 12 feet 10  25 3 Height of steep slope greater than 12 feet 10 50

Unstable land mass 4 100 4 100 4

1 For areas tributary to and upstream of water supply intake, setback distance is measured from high water mark. Exceptions may be allowed per SWRCB OWTS policy, as follows:

(a)

For replacement OWTS, comply with the maximum extent practicable and incorporate supplemental treatment unless Environmental Health finds no impact or significant threat to water source; and

(b)

For new OWTS on pre-existing lot of record (pre-May 13, 2013), comply to maximum extent practicable and incorporate supplemental treatment for pathogens per article 5 of this chapter and the Onsite Systems Manual.

2 "h" equals the height of cut or embankment, in feet. The required setback distance shall not be less than twenty-five (25) feet nor more than fifty (50) feet.

3 Steep slope is considered to be land with a slope of greater than or equal to fifty percent (50%). Where there is clearly discernible embankment and/or break in slope, treat as cut or embankment. Setback of less than fifty (50) feet must be confirmed by appropriate geotechnical evaluation, including but not limited to investigation of slope stability, evidence of rock or impermeable soil layers intersecting slope, seeps, or springs.

4 Setback distance may be reduced in accordance with recommendations provided in a geotechnical report prepared by a California civil engineer or professional geologist consistent with guidelines prescribed in the Onsite Systems Manual.

k.

Additional OWTS-related setbacks may be included in other County policies or ordinances based on the specific land use, including but not limited to the County Confined Animal Policy and San Mateo County Ordinance Code, chapter 4.68, Wells.

(Ord. No. 04754, § 1, 1-5-2016)

a.

Review and approval by the applicable CRWQCB is required for OWTS in cases where:

The peak wastewater design flow handled by the OWTS is more than ten thousand (10,000) gallons per day;

The OWTS is categorized as a community system, which serves multiple discharges under separate ownership; or

The CRWQCB has otherwise determined that its review and approval is necessary and appropriate for water quality protection.

b.

OWTS that are subject to the requirements and approval of the CRWQCB are also required to obtain approval of Environmental Health as prescribed in the Onsite Systems Manual.

(Ord. No. 04754, § 1, 1-5-2016)

Repairs or alterations to an existing OWTS must comply with this chapter and the Onsite Systems Manual to the maximum extent practicable. Such repairs or alterations may require an exemption (variance) consistent with section 4.84.185 of this chapter.

(Ord. No. 04754, § 1, 1-5-2016)

Every OWTS that has been abandoned, has been discontinued from further use, or to which no waste or waste discharge pipe from a plumbing fixture is connected must be properly destroyed under Permit issued by Environmental Health as prescribed in the Onsite Systems Manual.

(Ord. No. 04754, § 1, 1-5-2016)

a.

The conventional dispersal method approved for use in San Mateo County shall be a gravity trench dispersal system designed and constructed as prescribed in the Onsite Systems Manual, with the total length determined based on soil percolation rates and the number of bedrooms, or in the case of non- residential design, projected wastewater flow rate of the building(s) being served. Trench system designs utilizing shallower trenches, chambers or other filter material in place of gravel may be approved by Environmental Health as prescribed in the Onsite Systems Manual.

b.

In addition to the provisions of subsection a., any OWTS proposed for construction on slopes exceeding thirty-five percent (35%) shall require the use of pressure-dosing distribution dispersal methods, which are classified as an alternative OWTS and shall be designed and permitted in accordance with applicable provisions contained in article 5 of this chapter and the Onsite Systems Manual.

c.

Alternative OWTS shall only be permitted as detailed in article 5 of this chapter.

(Ord. No. 04754, § 1, 1-5-2016)