Stinson Beach
County Water District

TITLE IV ONSITE WASTEWATER
MANAGEMENT CODE

CHAPTER 4.19 DESIGN STANDARDS: ALTERNATIVE WASTEWATER SYSTEMS

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Sections:

4.19.010  Use of Alternative Wastewater System Designs
4.19.020  Use of Alternative System Design - Repair or Replacement of Failed System - Granting of Variance
4.19.030  Use of Alternative System Design - Replacement of Failed System in Cases of Fire or Disaster - Granting of Variance
4.19.040  Use of Blowers
4.19.045  Grease Traps
4.19.050  Residential Systems - High Volume
4.19.100  Site Evaluation
4.19.110  Use of Drip Dispersal Fields
4.19.120  Site Criteria for Drip Dispersal
4.19.140  Septic and Sump Tank Design Standards
4.19.150  Drip Irrigation/Drip Dispersal Field Design Standards
4.19.160  Drip Irrigation - Installation and Cover
4.19.170  Material-Dripline
4.19.180  Filters
4.19.190  Ultra Violet Disinfection Systems
4.19.200  Pretreatment
4.19.210  Telemetry Control Panel
4.19.220  Drip System Maintenance

4.19.010  Use of Alternative Wastewater System Designs
Alternative wastewater system designs may not be used, unless approved through Variance by the Board of Directors of the Stinson Beach County Water District and the San Francisco Regional Water Quality Control Board.

4.19.020  Use of an Alternative System Design - Repair or Replacement of Failed System - Granting of variance
The District has determined that alternative treatment system technological improvements have increased performance in monitoring, operation, and process, and that a variance may be granted for installation of an alternative system which is approved by the National Sanitation Foundation in place of a standard onsite septic system for repair or replacement of failed systems.

4.19.030  Use of Alternative System Design - Replacement of Failed System in Cases of Fire or Disaster - Granting of Variance
Except as otherwise provided within this code, where a residence has been totally or partially destroyed by fire, flood, or other natural disaster, and it has been shown to the satisfaction of the District Manager and the District Engineer that a septic system which complies with this code cannot be constructed upon the property, a variance may be granted for installation of an alternative system as defined in Section 4.03.202, under the following conditions:

  1. The application for variance is made within five years of the destruction of the residence; and
  2. The replacement structure is within the same footprint as the destroyed residence; and/or
  3. The replacement structure does not contain greater square footage than the destroyed structure (if replacement structure exceeds original square footage a variance is required).

4.19.040  Use of Blowers
Setback requirements for blowers shall be 10 feet to adjoining property line.

4.19.045  Grease Traps
Grease Traps (UPC Listed) are required for commercial facilities that have the potential to produce grease-laden wastewater as determined by the District. Small Bed and Breakfast facilities may be exempt from commercial requirements at the discretion of the District. The following is required when it is determined that grease traps are required:

  1. Plans and specifications for the plumbing system including the grease trap shall be submitted to the District.
  2. Wastewater from dishwasher sinks and other plumbing fixtures shall be plumbed separately from other plumbing fixtures into the grease trap and then to the septic tank.
  3. Grease traps shall be located, installed, and constructed so that temperature of the waste shall be reduced to permit separation of grease and allow easy access for cleaning.
  4. Commercial facilities generating 200 gallons or more per day of waste shall install a grease trap sized in accordance with the following formula:
    Size of grease trap (in gallons) = (S) x (WW) x (ST) x (H) x (LF) where:
    S = Number of seats in dinning area
    WW = Wastewater per meal in gallons (5 gallons is normal)
    ST = Storage Capacity factor (2.5 is used for on site wastewater systems)
    H = Number of hours in operation of the facility
    LF = Loading Factor (a standard of 1.25 is used)
  5. Garbage Disposals shall be prohibited
  6. Grease traps shall be maintained in efficient operating condition by periodic removal of the accumulated grease. No such collected grease shall be introduced into any drainage piping or septic system.

4.19.050  Residential Systems - High Volume
Any onsite wastewater system design intended to serve wastewater design flows in excess of 600 gallons per day or average daily flows in excess of 400 gallons per day shall be considered a high volume residential system. A high volume residential system shall be considered an alternative system and may be approved only through the granting of a variance.

4.19.130  Site Evaluation
Site evaluation requirements shall be the same as for standard systems.

4.19.110  Use of Drip Dispersal Fields
Drip dispersal fields may be used when the site meets all standard wastewater system design requirements or as a repair/replacement option where standard repair options can be met.

4.19.120  Site Criteria
In order to utilize a drip dispersal system for new construction, a preliminary plan with calculations demonstrating that the site could meet the regulations for a standard type system shall be provided. The preliminary plan shall include a site plan showing all the major system items, property boundaries, setbacks, and site topography. Site setbacks, slope requirements and soil requirements shall be the same as other types of dispersal fields.

4.19.140  Septic and Sump Tank Design Standards
Septic and sump tank standards shall be the same as for standard systems.

4.19.150  Drip Irrigation/Drip Dispersal Field Design Standards
The following design loading rates assume a treated effluent with Biological Oxygen Demand (BOD) and Total Suspended Solids (TSS) per the drip tubing manufacture's requirements.

Soil Class Soil Type Est per rate
(min/in)
Hydraulic conductivity
(in/hr)
Design loading rate
(gal/ft2)
I Coarse sand <5 >2 1.400
I Fine sand 5-10 1.5-2 1.200
II Sandy loam 10-20 1.0-1.5 1.000
II Loam 20-30 0.75-1.0 0.700
III Clay loam 30-45 0.5-0.75 0.600
III Silt-clay loam 45-60 0.3-0.5 0.400
IV Clay no swell 60-90 0.2-0.3 0.200
IV Clay swell 90-120 0.1-0.2 0.100
IV Poor clay <120 <0.1 0.075

The required dispersal area shall be based on daily design flow and application rate. The design shall identify an area capable of 300% of the design daily flow.

The design shall utilize two dispersal areas sized for 100% of the design flow and further identify an area capable of 100% of the design flow reserved for future use, for a total of 300% of the design requirement.

4.19.160  Drip Irrigation - Installation and Cover
Drip irrigation shall be installed through the use of a plough type installation tool or by hand excavation. The dripline shall have a minimum cover of six inches and shall be installed in native material. Open trench excavation is permitted for the solid pipe connections and for valve installation.

4.19.170  Material-Dripline
Dripline Material shall be flexible 1/2" polyethylene dripline with in-line emitters. The emitters shall be part of the dripline and have flow rates to meet the application rate required. The drip line shall have a bactericide protection impregnated as part of the manufacturing process to prevent bacteria forming; additionally the dripline shall inhibit roots from clogging the emitters with herbicide and bactericide emitters. The dripline shall have fittings on the ends to allow connection to standard schedule 40 pipe, or alternatively non- emitting pipe to match the dripline.

4.19.180  Filters
A filter shall be placed between the pump and drip lines to keep debris out of the drip fields. The filter shall attach to a dripline between dispersal field and pump and shall be manufactured from a corrosion resistant material and shall be watertight. The filter be manufactured from stainless steel and shall be 100 micron, 150-mesh filter. The filter shall be self-cleaning during the flush cycles. Filter types shall be subject to approval by the District Engineer.

4.19.190  Ultra Violet Disinfection Systems
All drip dispersal fields shall require an ultra-violet light source mounted on a subassembly, which can be removed and reinstalled through the top of the riser for easy service. The UV light will operate continuously whether or not water is flowing in the disinfection chamber. The alarm relay circuit shall be connected to an external audible alarm and to a control panel telemetry module relayed to the District to warn of possible failure.

4.26.200  Pretreatment
All drip systems shall require treated effluent from a pretreatment device prior to dispersal. The National Sanitation Foundation (NSF) shall approve all treatment system options.

4.26.210  Telemetry Control Panel
All drip systems shall have a telemetry control panel with proper modules or remote readings as approved by the District. The panel shall have a phone line connection. Panel system parameters shall have remote operation access and the ability to be adjusted on site. The panel location shall be approved by District staff at an easily accessed outside location. The panel shall control the pump cycles based on programmed dosing, activate the solenoid valves to discharge each field, record pump(s) counts, record pump(s) elapsed time, and automatically flush the drip field and filter. The panel shall provide alarms for high water in the various pump chambers and failure of the pretreatment system. Alarms shall be located at the panel utilizing the system. The alarm shall be a minimum of 80 dB and shall be recorded in the digital memory of the control panel.

4.26.220  Drip System Maintenance Required
Required maintenance of a drip system shall include periodic monitoring and review of the system condition and parameters via remote telemetry.