Regulations for Design, Construction, Repair and Operation of Nonstandard Sewage Disposal Systems Pursuant to Sonoma County Code Chapters 7 and 24

Transcription

1 Regulations for Design, Construction, Repair and Operation of Nonstandard Sewage Disposal Systems Pursuant to Sonoma County Code Chapters 7 and 24 Table of Contents PURPOSE... 1 Monitoring of Nonstandard Systems... 2 Types of Systems... 2 Experimental Systems... 2 Alternative Systems... 4 Restrictions on the Use of Nonstandard Systems... 4 Site Criteria for Nonstandard Systems... 7 Soil Criteria for Nonstandard Systems... 8 Mound Systems... 9 Pressure Distribution Systems (STPD)... 9 Mound 2 Systems At-Grade Systems Shallow In-Ground Systems Design Criteria for Nonstandard Systems Plot Plan Requirements Sewage Flows Septic Tanks Design Criteria for Mound Systems Distribution Bed Sand Fill Area Soil Cover Distribution System i S:\OFCFORMS\POL_PROC\WELL_SEP\9-2-8 Non-std Sew Disp Syst.wpd Effective: 09/14/07

2 Monitoring Wells Design Criteria for Pressure Distribution Systems (STPD) STPD Trenches Absorption Area Soil Cover STPD Systems Monitoring Wells Design Criteria for Mound 2 Systems Design Criteria for Wisconsin At-Grade systems Design Criteria for Shallow In-Ground Systems Design Criteria for Sand Filters Sump Pump Chamber Concrete Tanks Lined Pit Wooden Containment Tanks Distribution Beds Filter Bed Sizing Daily Wastewater Flow Sand Filter Location Requirements Monitoring Wells Effluent Distribution Designer / Installer Qualifications Designer Installer Construction Requirements of Designing Engineer / Environmental Health Specialist.. 32 Requirements of Contractors in Constructing Mounds ii

3 Requirements of Contractors in Constructing STPD Systems Operation and Maintenance Operational Permits...36 Easement Agreements...36 Maintenance of Nonstandard Systems...37 Definitions...37 Tables...42 Percolation Rate Conversions...42 Illustrative Table for Percolation Rate Conversions...43 Estimated Quantities of Sewage Flow...44 Winery Waste Design Criteria...45 Mound Correction Factors for Sloping Sites...46 Mound Sand Selection Dosing Quantities...48 Appendix...49 Topographic Map Requirements Mound Cross-Section Mound Plan View STPD Trench Detail Balancing Valve Detail Purge Valve Detail Monitoring Well Detail Mound Sizing Formulas Mound Loading Rates Mound Topographic Instructional Detail Sump and Pump Requirements Sump Detail iii

4 Regulations for Design, Construction, Repair and Operation of Nonstandard Sewage Disposal Systems Pursuant to Sonoma County Code Chapters 7 and 24 PURPOSE These regulations are intended to provide regulatory oversight of the non-standard sewage disposal system program in Sonoma County GENERAL It is well known that Sonoma County has many types of problem soils and conditions not suitable for standard sewage disposal systems. The U.S.D.A. Soils Survey Book has demonstrated that over 90% of the land mass in Sonoma county is unsuitable for standard systems. In 1978 the Sonoma County Public Health Department (SCPHD) and the North Coast Regional Water Quality Control Board (NCRWQCB) entered into a policy known as the Joint Innovative Waste Treatment and Disposal System Evaluation Agreement. This agreement (amended in 1983 and 1984) became a procedure used by both agencies to evaluate specific proposal for the installation and use of innovative individual sewage treatment systems in Sonoma County. In 1994, a similar agreement was entered into with the San Francisco Bay Regional Water Quality Control Board (SFBRWQCB). In 1995, the SCPHD transferred the Land Use Section to the Sonoma County Permit and Resource Management Department (PRMD) taking over this function and all program responsibility. Each year PRMD now prepares the annual Monitoring Report (the Report) which gives the Regional Water Quality Control Boards detailed information on the non-standard sewage disposal systems currently in service in the Monitoring Program. For clarity of information in the balance of this document, the term non-standard will be used in lieu of innovative. The two types of non-standard systems are experimental and alternative. See definitions. Currently, Sonoma County has approved pressure distribution and mound systems as alternative systems. The mound², at-grade, shallow in-ground, aerobic treatment and filter pretreatment (pre-treatment and final disposal) are being used as experimental systems. The criteria outlined in the Joint Innovative Agreements called for design concepts of nonstandard systems to incorporate: (1) the prevention of transmission of disease (2) disposal of sewage and sewage effluent below the surface of the ground (3) the prevention of contamination of ground water and other beneficial water by discharge from sewage disposal systems. AUTHORITY The legal authority to issue non-standard septic system permits lies within: Page 1

5 A. A Memorandum of Understanding with the North Coast Regional Water Quality Control Board dated August 27, B. A Memorandum of Understanding with the San Francisco Bay Regional Water Quality Control Board dated May 11, C. Sonoma County Code Chapters 7 and 24. PROCEDURE 110 MONITORING OF NON-STANDARD SYSTEMS PRMD is required by the Regional Water Quality Control Boards to monitor the operation and maintenance of all non-standard systems. Inspection frequency may vary but is generally based upon a frequency of one inspection per year. See Section 126. A. PRMD shall submit results of the monitoring inspections to the Regional Water Quality Control Boards in the form of an annual report for each calendar year. B. PRMD shall notify each Regional Water Quality Control Board in writing whenever the monitoring program is inadequately staffed. 125 TYPES OF SYSTEMS There are two basic types of non-standard systems. 126 A. Experimental Systems. Proposals for experimental types of non-standard systems are reviewed by the liquid waste specialist of the PRMD. The Liquid waste specialist reviews all technical and research information regarding proposed experimental nonstandard systems. 1. Design Criteria a. General written description of the experimental system including absorption, filtration, biological treatment, black/grey water system, etc. b. Methods of treatment and disposal, including loading parameter, design raw waste strength and effluent characteristics of disposal as related to treatment and the site and soil characteristics. c. All proposals include a reference list to specifically substantiate design source and applicability to the experimental system. d. Proposals that include designs which cannot be substantiated by suitable reference materials and field monitoring results of experimentation will not be classified as an experimental research proposal, and as such, will not be considered. The liquid waste specialist will present any promising experimental non-standard system to the appropriate Regional Water Quality Control Board for technical review and approval. If both Page 2

6 PRMD and Regional Water Quality Control Board staff approve the experimental non-standard system, design parameters, site and soil characteristics, and a site specific monitoring program will be established. The liquid waste specialist reviews plans and issues permits to install and operate experimental non-standard systems. After installation, the system shall be intensely monitored. 2. Phase 1 a. Intensive monitoring (two or more inspections per year) performed for at least two normal winters. Up to a maximum of 10 systems per year for new construction (in each Regional Board jurisdiction) installed at locations with similar site and soil characteristics. b. The liquid waste specialist may request the Regional Water Quality Control Board for permission to proceed to Phase II if the intensive monitoring indicates satisfactory results. 3. Limitations to Phase 1 a. Repair of existing malfunctioning residential and commercial on-site sewage disposal systems. There are no limits on the number of repairs that may be done. b. The expansion of use for existing residential and commercial systems shall be limited to 33%. c. New construction of single family dwellings with discharges up to 450 gallons per day. d. Not acceptable as justification for land division. e. Not approved for use in a sewer hookup area, septic tank ban area, or Regional Water Quality Control Board Waiver Prohibition Area. 4. Phase II Less intensive monitoring (one or more inspections per year) for an additional two normal winters. Up to a maximum of 20 systems per year for new construction (in each Regional Board jurisdiction) installed at locations with similar site and soil characteristics. Note: PRMD may consider whether an additional period of monitoring or an additional number of systems shall be installed prior to Phase III consideration. 5. Limitations to Phase II a. Repair of existing malfunctioning residential and commercial on-site septic systems. There are no limits on the number of repairs that may be done. b. For expansion of existing residential and commercial systems, the maximum increase in peak discharge is 33%, up to a maximum total of 600 gallons. Page 3

7 c. Maximum peak loads are 600 gallons per day for new single family homes and 1000 gallons per day for new commercial establishments d. Not acceptable as justification for land division. e. Not approved for use in a sewer ban area, septic tank ban area, or RWQCB Waiver Prohibition Area. 127 B. Alternative Systems. Under Phase III, the experimental type of system is considered an acceptable alternative non-standard system in Sonoma County by both the Permit Resource Management Department and the Regional Water Quality Control Board. 1. Phase III a. Systems for residential and commercial uses may exceed 1500 gallons per day (waste discharge permits from the Regional Water Quality Control Board may be required for systems larger than 1500 gallons per day peak load). b. Standards shall be established for the installation and evaluation of each type of non-standard system developed by PRMD and Regional Water Quality Control Board staffs. c. A long term, on-going monitoring and inspection program shall be maintained by Sonoma County PRMD. d. Sonoma County PRMD shall maintain a homeowner education program. e. Sonoma County PRMD shall establish criteria for evaluation of potential cumulative impacts to groundwater and surface water sources per Regional Water Quality Control Board Basin Plan standards. 200 RESTRICTIONS ON USE OF NON-STANDARD SYSTEMS The technology of non-standard on-site sewage disposal systems is constantly evolving and changing. Commonly technical information is gathered about non-standard systems in use through the Sonoma County Permit and Resource Management Department s monitoring program. Because of evolving technology and problems discovered through the monitoring program, the regulations for non-standard systems may change. 201 A. Property owners are cautioned that regulations for non-standard systems may change by actions of the Regional Water Quality Control Boards or PRMD. Therefore, despite previously performed and accepted work by PRMD, any proposal for a nonstandard system must meet the regulations that are in effect at the time that PRMD approves the septic system permit application. 202 B. Non-standard systems are prohibited in areas that have been filled, excavated, ripped plowed, altered, modified, or in areas of flooding, drainage problems or geologic Page 4

8 instability. The only exception or variance to this is for repairing septic systems for existing legal residences or businesses that are malfunctioning. Exceptions or variances will not be granted to allow increases of existing sewage discharges. 203 C. Mounds are generally prohibited for winery wastewater disposal systems. 204 D. When a non-standard system is proposed in order to increase the sewage discharge of an existing use, the existing septic system must be brought into compliance with all current regulations. 205 E. Setbacks non-standard disposal systems Disposal Tanks/Sumps 1. Buildings or Structures System a. Up gradient & laterally 10 feet 5 feet b. Down gradient from system 25 feet 5 feet 2. Property lines and/or Underground Utility Easements* a. Uphill 10 feet 5 feet b. Laterally 10 feet 5 feet c. Downhill 25 feet 5 feet 3. Water Wells 100 feet 50 feet** 4. Perennially Flowing Stream 100 feet 50 feet 5. Ephemeral Watercourse 50 feet 25 feet 6. Ten-Year Flood Elevation 100 feet 50 feet 7. Ocean, Lake, Reservoir 100 feet 50 feet 8. Springs, Seepage Areas 100 feet 100 feet 9. Cut Banks or Bluffs a. A man-made excavation of the natural terrain in 50 feet 25 feet excess of 3 feet. b. Where soil depth or depth to ground water below 50 feet 25 feet leaching trench is less than five feet. Page 5

9 10. Areas of Geologic Instability 50 feet 50 feet 11. Public Water Main 10 feet 10 feet 12. Domestic water line 5 feet 5 feet 13. In ground pools and Excavations (Down gradient) 25 feet 5 feet 14. Well Destruction performed with PRMD permit 15 feet 5 feet ** Septic tanks and sumps shall be watertight * See increased requirements for experimental systems (Section 302) Note: Requests for setback reductions may be considered with the waiver procedure on a case by case basis. 206 F. Operational Permits. Operation of non-standard sewage disposal systems requires the issuance and possession of valid operational permits. 1. Applications to construct non-standard sewage disposal systems must be accompanied by applications and fees for operational permits. 2. Operational permits are transferable subject to notification of PRMD and within 2 months of permit issuance. 207 G. Easement Agreements (Recorded). The purpose of easement agreements is to allow the associates and employees of PRMD and/or the Regional Water Quality Control Board onto the properties to monitor and test the nonstandard sewage disposal systems. 1. Primary and reserve test areas for non-standard sewage disposal systems are required to have the standard easement agreement recorded against the parcel before issuance of the sewage disposal permit. 2. Easement agreements may not be removed from the title of the property unless authorized in writing by PRMD. 208 H. Self-Monitoring is Required. Monitoring forms will be provided by the Permit and Resource Management Department to the property owner two times per year for recording information regarding sewage disposal system operation. 1. Property owners shall complete the monitoring reports and submit them to PRMD within fifteen days of receipt. 2. Failure to perform the self-monitoring program is cause for revocation of the operational permit. 209 I. Performance Standards for Monitoring Wells. All non-standard systems must be designed with a series of monitoring wells to sample for potential subsurface groundwater degradation. Monitoring wells are strategically placed upgradient, Page 6

10 laterally, down gradient and within all non-standard systems. See Sections 515 and 526. PRMD may occasionally sample monitoring wells for total coliform bacteria, fecal coliform bacteria, and nitrates as indicators of the degree of sewage treatment and function of nonstandard sewage disposal system. The following are limits of maximum contaminant levels to analyze degree and function of nonstandard sewage disposal systems. 1. Sample results greater than 240,000 M.P.N. (most probable number) total coliform bacteria and/or a fecal coliform count greater than 2.2 M.P.N. exceeds the maximum contaminant levels and is deemed to have an adverse effect on subsurface water. a. Such level of contamination as sampled from any purged monitoring well located 25 feet or greater downgradient from the disposal field indicates a failing system. b. Failing systems shall be corrected or abated. 2. Sample results exceeding 3,000 M.P.N. but less than 240,000 M.P.N. total coliform and/or less than 2.2 M.P.N. fecal coliform, do not exceed the maximum contaminant levels. However, these results define a nonstandard system as operating marginally. a. The contaminant levels are results of samples that have been taken from any purged monitoring well located 25 feet Down gradient from the disposal field. b. For the purpose of the Annual Monitoring Report, systems that show ponding of effluent within 12 inches of trench bottom (but do not exceed M.C.L. s mentioned above) are defined as operating marginally. 3. Any non-standard system that causes sewage to surface or discharge at ground level is deemed to have an adverse effect on surface water and is considered a public health hazard. It is defined as a failing on-site sewage disposal system. Such a system shall be immediately corrected or abated. 300 SITE CRITERIA FOR NON-STANDARD SYSTEMS 301 A. Site and soil evaluations of each proposed site must be done per PRMD standards. See Sonoma County Site Evaluation and Percolation Test Methods. 1. Site evaluations typically include a. Soil profile evaluations b. Testing of soil parameters such as hydrometer, plasticity index, sieve size, shrink- Page 7

11 swell, etc. c. Topographic layout d. Evaluation of slope stability, etc. e. Groundwater determination tests f. Percolation tests % reserve area is required for all experimental systems (Phase 1 and Phase II) % reserve area is required for all septic systems including non-standard systems involved with a subdivision. Note: See Sonoma County Subdivision Ordinance. 4. Reserve area requirements for all alternative systems. a. Mounds % reserve area for residential systems (lots created before October 1971) % reserve area for residential systems (lots created after October 1971) % reserve area for all commercial systems. b. Shallow Trench Pressure Distribution Systems % reserve area for residential and commercial systems. 2. Exception: The 200% reserve requirement may be reduced to 100% if a dual primary system is designed and installed and the parcel was created prior to October B. Initially, new experimental systems shall have a minimum setback of 50 feet from property lines. See specific experimental system design criteria for current setbacks. 1. May be reduced, on a case by case basis, to a minimum of 25 feet from lateral or side slope property lines. 2. May be reduced, on a case by case basis, to a minimum of 15 feet from upslope property lines on slopes exceeding 6%. 303 C. Reduced setback requirements may be allowed for each type of alternative nonstandard system on a case by case basis if a formal waiver submitted for review to the Regional Board is approved. 304 D. Non-standard systems should be avoided on concave landscape formations to prevent convergence of flow. See Section Proposals to place non-standard systems in a concave landscape formation shall be considered on a case by case basis. 2. Such proposals shall be reviewed by the liquid waste specialist. 400 SOIL CRITERIA FOR NON-STANDARD SYSTEMS Page 8

12 401 A. Mound Systems. Mound type non-standard systems are based upon the Small Scale Waste Management Project, University of Wisconsin at Madison. The 2000 Mound standards of the California Conference of Environmental Health Directors may also be used. Mound systems are designed to overcome reduced criteria for soil permeability and depth to groundwater below the bottom of the system. Designers shall use the same methodology and nomenclature as the Wisconsin Small Scale Waste Management Project. 1. Minimum Criteria for percolation tests. a minutes per inch (mpi) for mound systems b. Percolation rate requirements apply to the first 24 inches of soil as measured from native grade. See percolation test requirements. c.. Rates faster than 1 mpi are not acceptable. 2. Minimum elevated groundwater level is 24 inches from native grade. 3. Minimum depth of suitable permeable soil is 24 inches from native grade. The rock content (as retained on the #10 Sieve) shall not exceed 50% by volume within the first 24 inches of soil from native grade. 4. The minimum depth to fractured rock, impermeable soils, such as hardpans and claypans, and consolidated bedrock is 24 inches. Note: the minimum depth of permeable soil (24 inches) shall extend a minimal horizontal distance of 25 feet downgradient from the edge of the sand perimeter. See Section 511 for design parameters for special site and soil conditions. 402 B. Shallow Trench Pressure Distribution Systems (STPD) Pressure distribution systems are designed for sites that typically have shallow top soils over slowly permeable or fractured subsoils on slopes up to 30%. 1. Percolation rate of mpi for STPD systems on slopes up to 30%. 2. Rates faster than 1 mpi are not acceptable. 3. Percolation depth measured from native grade a. 24 inches minimum on slopes up to 20%. b. 30 inches minimum on slopes from 20 to 25%. c. 36 inches minimum on slopes from 25 to 30%. d. 60 inches maximum on slopes up to 30%. 4. Systems shall have a minimum depth of 24 inches of suitable soil beneath proposed trench bottom as established by a. Visual field observations and soil texturing to identify a limiting condition. Page 9

13 b. The rock content (as retained on the #10 sieve) shall not exceed 50% by volume within the first 24 inches of soil below trench bottom. c. Soil hydro and bulk density tests (Zone 1 or Zone 2 soils). d. Plasticity Index tests as measured by ASTM D Atterburg Series, with results of <20 for Zone 3 or 4 soils. e. Soil percolation testing with rates of 120 mpi or better 5. Systems shall have a minimum depth of 24 inches to groundwater, fractured rock, consolidated rock, bed rock, or impermeable soils. (See Memo of Understanding with San Francisco Bay Regional Water Quality Control Board) Note: A minimum of 24 inches below trench bottom of permeable soil shall extend a horizontal distance of no less than 25 feet downgradient from the edge of the last proposed trench. See Section 511 for design parameters for special site and soil conditions. 6. To maximize evapotranspiration, pressure distribution systems may not be installed below non-permeable type soils such as high shrink well clays, highly compacted soils, highly cemented soils, and/or massive or platy soil structures. 410 C. Mound²Systems. See Section D. At-Grade Systems. See Section E. Shallow In-Ground Systems. See Section DESIGN CRITERIA FOR NON-STANDARD SYSTEMS 501 A. Plot Plan Requirements 1. Four copies of the plot plans are required. The scale to use shall be 1" = 20 feet. The following items must be included on sewage disposal plot plans submitted for permit approval. a. Lot dimensions with north point. b. Vicinity map, correct address and assessor parcel number. c. Accurate topographic contours shall be shown in the area of the leachfield and reserve area. See Appendix A: Topographic Map. d. Location of the proposed sewage disposal system to existing and proposed wells, springs, lakes, ponds, marsh areas, streams, and drainage ditches or channels within 150 feet of any portion of the sewage disposal system including the reserve area. e. Cross sections of the proposed leach lines, interceptor drain, drainage ditches, etc. f. Location of existing and/or proposed structures, driveways, swimming pools, Page 10

14 502 B. Sewage Flows patios, retaining walls, paved areas, large trees and cut banks. g. Location of existing sewage disposal systems and existing and/or proposed easements, water lines, and underground utilities. h. Location of all percolation test holes (including the holes that have failed) profile holes, and soil sampling locations. i. Designated reserve leachfield areas with potential system design. j. Complete schematic of the distribution system indicating spacing of the perforations, orifice size, lateral size, and spacing of the trench bed is required. k. Cross section and plan view of the mound systems must be shown. See Appendix B and C. l. Cross sections of the sump detail, including dose counter and alarm system. Specify dose volume and proper float setting. (See diagram, Appendix J) m. Plan view and design of the distribution network including hydraulic calculations for pump sizing. n. Cross sections and locations for monitoring wells. o. Cross sections for the manifold balancing valve assembly and the purge valve detail. p. For all nonstandard systems, cross sections of the transmission line detail including pipe size, orifice size and spacing. Orifice shields are required when the orifice is discharging upward. 1. Single and Multiple Family Dwellings. For design purposes, minimum sewage flows from residential buildings shall be calculated based on 120 gallons per day per bedroom, provided that the residence installs low flow toilets and shower heads. If large fixtures are used, the flow calculation will need to be increased.. All septic systems shall be sized for peak daily flows. 2. Other Uses. Sewage flows for commercial establishments and other nonresidential buildings shall be estimated in accordance with the quantities listed in Table III, the 2002 EPA Design Manual, or the California Plumbing Code (CPC), or other approved source. Other sewage flow estimates may be considered by PRMD if supported by technical documentation such as a comparitive study of at least three similar type establishments. 3. Water Saving Devices. Reduction in design flows may be granted by PRMD when certain water saving devices are permanently incorporated into the buildings being served. Page 11

15 a. Reductions of up to 20% may be granted for domestic water flow where 1.6 gallon low flush toilets are installed in all bathrooms. b. Installations where water saving devices will reduce more than 20% of design flows shall require designs and final inspections by Registered Civil Engineers or Registered Environmental Health Specialists and recordation of water use restrictions against the deed. 4.. Large Septic Systems Flows. In cases where the peak wastewater flow for a residential or commercial flow exceeds 1500 gallons per day; the designer shall evaluate the potential impact of hydraulic mounding below the septic system and nitrate plume or migration analysis of the impact of wastewater. The Assessment of Cumulative Impacts of Individual Waste Treatment and Disposal Systems, Ramlit 1982, or other comparable methodologies may be used as a guideline in the evaluation of large wastewater flows. 503 C. Septic Tanks. a. The estimated peak rise in groundwater levels for large wastewater systems shall not infringe upon the minimum separation required from the trench bottom. b. Large wastewater septic systems that could potentially reduce the minimum separation to groundwater are prohibited. c. Nitrate as N may not exceed 10 mg/l (drinking water standard) at the following gradient locations. 1. Any wells or spring. 2. The edge of the ten-year flood elevation. 3. Property lines (unless the nitrate plume travels into a restricted land mass) 4. Banks of any creeks, ponds, streams, or roadside cuts. 1. All septic tanks (reinforced concrete, fiberglass, or the other durable noncorrodible synthetic materials) installed for all the types of septic systems must be accepted by IAPMO as meeting standard PS-1. a. All septic tanks shall be watertight. b. Metal or wooden tanks are prohibited. c. All septic tanks shall be of two-compartment construction. The first shall be twice the capacity of the second and separated by a baffle. 2. Placement. a. Septic tanks shall be installed per manufacturers specifications. b. The tank shall be installed level on a solid bed. Page 12

16 c. Soil around the tank shall be compacted; sand must be jetted. 3. Structural Strength. a. Tank must be capable of withstanding anticipated structural loads. b. Septic tanks must meet the all standards of Sonoma County Ordinance # Access Risers. a. An approved riser shall extend from each manhole to a height of at least two inches above the ground surface to allow inspection access and maintenance of the tank and be of sufficient size for removal of the manhole cover. b. Concrete, PVC, or fiberglass watertight risers that are structurally capable of supporting the backfill soil loading. c. All risers shall be fitted with durable, airtight lids that have a locking mechanism to prevent unwanted entry and insect and rodent access. 5. Septic Tank Connections. a. All connections from buildings to septic tanks shall be made in accordance with the most recent edition of the Uniform Plumbing Code which is incorporated by reference into the county s building ordinance. b. PRMD is the inspecting authority for connection to the septic tank. c. All septic tanks shall be fitted with effluent filters capable of removing 1/8 inch solids. 6. Variances. a. Septic tanks which deviate from the above design criteria must be approved by PRMD. b. In such cases, a registered civil engineer shall submit plans and specifications to PRMD for approval and inspection. All tanks must, however, meet IAPMO standards of approval. 7. Size. a. According to the Uniform Plumbing Code, septic tank size is determined by the number of bedrooms for residential uses: 1-2 bedrooms requires a minimum 750 gallon precast tank; 3 bedrooms, a minimum 1000 gallon precast tank; 4 bedrooms, a minimum 1200 gallon precast tank; and 5-6 bedrooms, a minimum 1500 gallon precast tank b. The minimum size septic tank for commercial uses must be based on the formula V+1, Q where V = Net volume of tank (gal.) Q = daily water flow (gal.) A larger tank may be required if wastewater has high BOD Page 13

17 or high fat/oil content. c. Septic tank capacity for winery wastewater subsurface disposal systems shall be sized at 1500 gallons or based on a 5-day retention period whichever is greater. Septic tanks for winery wastewater systems may be placed in a series. Domestic wastewater may not be mixed in a septic tank that has winery water solids. D. Dose Quantity. See Table VI. 510 DESIGN CRITERIA FOR MOUNDS The design of a mound type nonstandard system is based on the Small Scale Waste Management Project, University of Wisconsin, Madison. The following criteria shall be used to design mounds in addition to the most current edition of the Wisconsin Mound Soil Absorption System Siting, Design and Construction Manual (Converse and Tyler) that has been adopted by PRMD. Designers shall use the same methodology and nomenclature as the Wisconsin Small Scale Waste Management Project. See Appendix B and C for typical mound plan view and cross section. Wastes with a high biological oxygen demand are not suitable for mound systems without approved pretreatment. 511 A. Distribution (Gravel) Bed 1. Loading Rate a. 1.2 gallons/square foot/day for residential type systems. b. 1.0 gallons/square foot/day for all commercial type systems. 2. Linear Loading Rate a. Designers shall estimate the linear loading rate for all proposed mound systems and shall design the width dimensions of the gravel bed accordingly, so that the distribution bed is long and narrow and on the contour. (See Section 510, CCDEH mound standards, and Appendix H-2) b. When the depth to a limiting condition, e.g., impermeable soil layer or fractured rock is only 24 inches, the linear loading rate shall not exceed 4 gallons/lineal foot/day. c. If it can be demonstrated that the wastewater flow will be vertical, as well as horizontal, a higher loading rate may be proposed. 3. Configuration. a. Only single distribution beds are acceptable. Dual beds are not allowed. b. The maximum width of any gravel bed is 10 feet. c. The depth of the gravel bed shall be 9 inches for residential systems and 12 inches for commercial systems. Page 14

18 4. Aggregate. a. 3/8 inch double washed pea gravel size to 2.0 inch double washed drain rock. b. The percentage of fines of washed gravel shall not exceed 1% by weight. 5. Natural Contour. 512 B. Sand Fill Area a. The distribution bed shall explicitly follow the natural contour of the ground. The bed must be installed within a tolerance of 0.25 feet (3 inches) vertically per 100 feet horizontally. b. Distribution beds shall be angled or curved to meet this requirement. c. The distribution bed shall not be placed in a concave landscape position. See Appendix I and Section 304D. 6. Reserve Expansion Area. a. On parcels created before October 1971, a 100% reserve area is required. b. For commercial systems and parcels created after October 1971, a 200% reserve area is required. c. See Section 301A. 1. Absorption Area. The sand-fill area, shall, at a minimum, provide adequate absorption area. The sand area size is based upon the average percolation rate and the sewage application rate chart. See Table I. a. On the ground slopes greater than 1%, the area uphill from the edge of the gravel distribution bed shall not be included in the calculations for the required absorption area. b. Areas beyond the longitudinal end of the gravel bed shall not be included in the calculations for the required absorption area for systems exceeding 1% slope. 2. Configuration. a. The toe of the sand fill shall follow contour, and shall not deviate more than 0.25 feet (3 inches) in elevation per 100 foot run. The sand fill material shall meet the sand specification to Wisconsin mound criteria. See Table V. b. The sand fill configuration shall extend a minimum of 24 inches level from the edge of the distribution bed on all sides, then uniformly slope as determined by the mound dimensions. On the slopes greater than 2%, the 24 inch dimension may be reduced to 12 inches (minimum) on the uphill side of the distribution bed only. Slope correction factors shall be applied as per the Page 15

19 513 C. Soil Cover. Wisconsin Manual. See Table IV. 1. Depth of the soil cover. a. A minimum of 12 inches in depth over the gravel bed portion of the mound and over the remainder of the sand portion. b. Mounded to a height of 18 inches at the midsection of the gravel bed. 2. Width. a. 4 feet - distal ends and uphill sides b. Width of the soil cover at the down hill toe of the mound shall be minimum of: 4 feet - 0-2% slope 6 feet - 2-4% slope 8 feet - 4-6% slope 10 feet % slope 3. Quality of Soil Cover. The quality of the soil structure and texture (USDA Classification) shall be at least equal to that of the topsoil existing on the site. 514 D. Distribution System. 1. Total Dynamic Head Loss. Designers shall calculate the total dynamic head loss of the entire distribution systems. a. Vertical differences. b. Length of entire piping system. c. Loss of all valves, tees, elbows, and appurtenances. d. Head Loss shall be referenced as feet of elevation. e. Hydraulic orifice discharge shall be a minimum of 24 inches to a maximum of 36 in height when designed for downward discharge. f. Hydraulic orifice discharge shall be a minimum of 60 inches for upward discharge. Orifices shall have a protective shield. g. Orifice spacing shall be a maximum of 36 inches on center 2. Balancing Valves and Purge Valves. System distribution manifolds shall have a balancing valve at the beginning of each perforated pressurized line and a purge valve at the end. a. All valves shall be protected and encased within plastic, concrete or other Page 16

20 approved type box to provide easy access and maintenance. Metallic valves are prohibited. b. Box size shall be 10 inches across or larger, round or square, and must allow enough room for maintenance and/or to install stand pipes onto the ends of the purge valves. c. Balancing valves shall be PVC Schedule 80 (or higher) gate valves. d. Purge valves shall be PVC Schedule 80 gate or ball type valves. 3. Perforated Pressurized Lines. Spacing of pressurized lines shall be based on gravel bed width. Width of Gravel Bed No. of Pressurized Lines 3-4 feet feet feet feet 4-5 a. Maximum length of pressurized lines shall be 75 feet. b. Maximum distance between perforations shall be 36 inches. c. If perforations are directed upward, they must be protected with a shield. E. Sump and Pump. Refer to Appendix J for required sump and pump features. Note: Automatic dosing siphons are NOT allowed in mound sewage disposal systems. 515 F. Monitoring Wells. A minimum of seven monitoring wells shall be installed within and around the mound system to a depth of 24 inches below original grade. Well screen is required for the perforated sections of the monitoring wells. See detail in Appendix G. 1. Two monitoring wells extending to the bottom of the gravel bed shall be installed within the distribution gravel bed in proportionate locations. 2. Two monitoring wells shall be installed at the downslope sand toe of the mound at proportionate locations from centerline. 3. Two monitoring wells shall be installed 25 feet downslope of the sand toe mound at proportionate locations from the centerline. 4. One monitoring well shall be installed 10 feet upslope of the sand toe at mound centerline for sloping sites and 25 feet upslope of for level terrain. 5. Monitoring wells shall be protected and encased within plastic, concrete or an approved equivalent to provide easy access. Page 17

21 6. All monitoring wells shall have concrete seals for the upper 12 inches 516 G. Sizing formulas for mound systems. See Appendix H-1 and H DESIGN CRITERIA FOR SHALLOW TRENCH PRESSURE DISTRIBUTION SYSTEMS (STPD) 521 A. STPD System Trenches. 1. The minimum trench spacing shall be 6 feet, center to center, on slopes less than 20%. Greater trench spacing is required on steeper slopes. 2. Distribution trenches shall follow the natural contour of the ground; trench bottoms shall be level. The maximum deviation along the downhill side of the trench shall not vary more than 0.25 feet (three inches) vertically per a 100 foot run. Distribution trenches shall be angled or curved to meet this requirement. The distribution field should not be placed on concave land forms. See Section 304D. 3. Approved distribution trench design. See Appendix D. a. Approved aggregate below the pipe 1. Perk rate of mpi-- 3/8 to 3/4 double washed gravel with less than 1% fines passing the 200 Sieve. 2. Perk rate faster than 5 mpi--pretreatment required before disposal field. b. Two inches of aggregate is required over the perforated sections of the pressurized line. c. Minimum requirement of backfill is 12 inches. d. Maximum trench depth shall be 60 inches. 522 B. Absorption Area. Shall be calculated as the sidewall beneath the location of the distribution pipe. The bottom area of the trench is not included as absorption area for sizing purposes. 1. The maximum sidewall area allowed for any system design is 3 square feet per lineal foot of trench. 2. Center trench spacing shall be increased by 1 foot for every 6 inch increase in gravel depth. 523 C. Soil Cover. The quality of the back fill shall be consistent in structure and texture as the topsoil already existing on the site. A minimum depth of 12 inches is required. 1. Soil structure and texture above the trench is extremely important to maximize evapotranspiration. 2. Trenches shall not be installed below non-permeable types of soils (high shrinkswell clays, soils with massive structure, or highly compacted soils). Page 18

22 524 D. STPD Systems. 1. Designers shall calculate the total dynamic head loss of the entire distribution system. a. Vertical differences. b. Length of entire piping system. c. Loss of all valves, tees, elbows, and appurtenances. d. Head loss shall be referenced as feet of elevation. e. Hydraulic orifice discharge shall be a minimum of 24 inches to a maximum of 36 inches in height when designed for downward discharge. f. Hydraulic orifice discharge shall be a minimum of 60 inches for upward discharge. Orifices shall have a protective shield. g. The recommended orifice spacing is 24 inches on center, however the maximum spacing is 36 inches. The first and last orifice shall be located one half orifice space from the ends of the distribution lines. 2. Balancing Valves and Purge Valves. System shall have a balancing valve at the beginning of each perforated pressurized line and a purge valve at the end. See Appendix E and F. a. All valves shall be encased in plastic or concrete boxes. Metallic valves are prohibited. 1. All balancing valves shall be PVC Schedule 80 (or better) gate valves. 2. All purge valves shall be ball or gate PVC Schedule 80. b. All boxes shall allow enough room for maintenance and adequate room to install stand pipes onto the end of the purge valves. 3. There shall be a minimum of 3 foot separation from the transmission line to the beginning of the aggregate portion of the trench or gravel bed. See Appendix D. 4. The cross section of the transmission line and the beginning of the gravel portion of the trench shall be stepped so as to prevent seepage of effluent from trench to trench. 5. Orifice spacing greater than 36 inches may be approved if distribution pipe is placed within a 3-inch diameter, perforated pipe or covered with a half section of 3-inch pipe with orifices pointed up. 6. Maximum length of run for a perforated pressurized line shall be 75 lineal feet. 7. In the distribution network, orifices may be placed in upward or downward position. See Section 514 D. l, e. and f. Page 19

23 8. The sump and pump installation shall be as specified in Appendix J. 9. Dosing siphons are prohibited in all pressure distribution type systems. 525 E. Monitoring Wells. A minimum of six monitoring wells shall be installed within and around the system to a depth of 24 inches below proposed trench bottom. 1. One or more monitoring wells shall be installed between trenches in the middle of the leach field. 2. One or more monitoring wells shall be installed 10 feet downslope of the lowest trench line. 3. Two monitoring wells shall be installed 25 feet downslope of the lowest trench line. 4. One or more monitoring well shall be installed at 10 feet upslope of the highest trench line. 5. Additional monitoring wells may be required for systems longer than 75 feet. 6. Permit & Resource Management Department may require that monitoring well locations be changed in special situations. 7. Monitoring wells shall be properly installed to provide easy access. See Appendix G: Monitoring Well Detail. 8. Monitoring wells shall be a minimum of 24 inches below trench bottom. Sections of this document (marked with an asterisk *) are current Permit & Resource Management Department guidelines for Phase I and Phase II experimental systems. These guidelines are site/soil, design, installation, and operational criteria mutually agreed upon between the Permit & Resource Management Department and Regional water Quality Control Board. For experimental systems, the guidelines may change at anytime. These types of systems are not subject to the regulation posting, review, and comment periods. If an experimental system meets the criteria under Phase I and Phase II, the Permit & Resource Management Department with the concurrence of the Regional Water Quality Control Board will adopt regulations for the system. As of this date, Mound 2, Wisconsin At-Grade, Shallow In-Ground, Sand Filters, NSF Class 40 Aerobic Treatment Units (ATU) and Textile Filters are experimental systems. Subsurface Drip Dispersal (SDD) is expected to be added to the experimental classification. Note: Sand filters, NSF Class 40 ATU s, and Textile Filters are generally methods of wastewater pretreatment prior to disposal into any type of subsurface sewage disposal system. Since sand filters are relatively new in Sonoma County, they will fall into the non-standard systems program until a successful track record has been established. Then regulations will be established. Page 20

24 530* DESIGN CRITERIA FOR MOUND 2 SYSTEMS Mound 2 systems may be suited on many sites with steeper terrain, reduced soil permeability, and/or shallow groundwater. Mound 2 systems are based upon the design parameters of the Small Scale Waste Management Project, School of Natural Resources, College of Agricultural and life Sciences, University of Wisconsin-Madison, * A. Site and Soil Parameters 1. Refer to Section 401 for general siting criteria. Mound 2 systems may be sited on slopes from 12 ½% to 16 ½%. An average percolation rate of mpi is required. Minimum setbacks of the Mound 2 systems to property lines: a. 25 feet laterally b. 50 feet downhill c. 15 feet uphill as measured from the edge of the soil cover d. See section 200 for restrictions on use and minimum setbacks for Mound 2 and other systems. 532* B. Design Parameters for Mound 2 Systems: See requirements for mounds. 1. Section 511 Distribution Beds. 2. Section 512 Sandfill Areas. 3. Section 513 Soil Cover. 4. Section 514 Distribution Systems. 5. Section 515 Monitoring Wells. Page 21

25 540* DESIGN CRITERIA FOR WISCONSIN AT-GRADE SYSTEMS The Wisconsin At-Grade soil absorption system accepts septic tank effluent and treats and disperses it in an environmentally acceptable manner. It serves the same function as inground soil absorption trenches and mound systems. The following figure is for illustration purposes only. 541* A. Soil and Site for At-Grade Systems. At-grade systems are designed to allow reduced criteria for soil permeability and depth to groundwater below the bottom of the system. 1. Minimum criteria for percolation test. Permeable soil is required to a depth of 36 inches. Percolation testing done at 12, 24, and 36 inches must meet the following criteria: a mpi for At-Grade systems on slopes up to 20%. Note: A sand filter or other approved pretreatment unit is required when percolation rates are faster than 5 mpi or slower than 90 mpi. b. Rates faster than 1(one) mpi are not acceptable. c. Separation from native grade to elevated groundwater is 36 inches, but may be reduced to 24 inches with the use of a sand filter or other acceptable pretreatment unit. 2. Minimum separation to elevated groundwater levels is 24 inches from native grade with the use of sand filter. 3. Minimum separation is 36 inches from fractured rock, rock exceeding 50% by volume, or bedrock as measured from native grade. Page 22

26 4. Minimum setbacks of At-Grade Systems to property lines as measured from the edge of soil cover a. 25 feet laterally b. 50 feet downhill c. 15 feet uphill Note: Additional guidelines can be found in the current edition of Wisconsin At- Grade Soil Absorption System Sites, Design, and Construction Manual. 542* B. Design Parameters for At-Grade Systems: See requirements for Mounds. 1. Section 511 Distribution Beds. Note that multiple gravel beds are permitted for At-Grades only if designed to the Wisconsin guidelines above. 2. Section 513 Soil Cover. 3. Section 514 Distribution Systems. 4. Section 515 Monitoring Wells. 5. Appendix J: Sump/Pump Requirements. 543* C. Construction Requirements for At-Grade Systems: See Section 701, 702. Note: The estimated wastewater design soil loading rates for the surface horizon shall be based on soil morphological conditions for Wisconsin At-Grade Systems. See article Estimating Wastewater Loading Rates Using Soil Morphological Descriptions by Tyler, Drozd & Peterson, Proceedings of the 1991 Conference of the American Society of Agricultural Engineers or Permit & Resource Management Department s Soil Percolation Testing Regulations and Related Sizing Chart, whichever results in the larger system. 550* DESIGN CRITERIA FOR SHALLOW IN-GROUND (SIG) SYSTEMS 551* A. Shallow In-Ground Systems (SIG) utilize shallow depth trenches and pressure distribution methods of disbursal of effluent. 1. SIG systems are designed with the acceptable fill material as soil cover. 2. The fill or soil cover is placed in a manner similar to the PRMD requirements for Filled Land systems. 3. SIG systems are designed for sites that typically have shallow top-soils over slowly permeable or fractured subsoils on slopes up to 20%. 552* B. Site and Soil Criteria for Shallow In Ground Systems. 1. Percolation rate of mpi for systems on slopes up to 20%. 2. Percolation rates faster than 1 mpi are unacceptable. Page 23

27 3. Percolation tests shall be at trench depth and and at two and three feet below the trench depth. 4. Visual field observations and soil texturing to identify any limiting conditions. a. Systems shall have a minimum depth of 36 inches of suitable soil beneath trench bottom and 36 inches from trench bottom to groundwater. These may be reduced to 24 inches if an approved pretreatment is used. b. The rock content (as retained in the #10 Sieve) shall not exceed 50% by volume within the first 24 inches of soil below trench bottom. c. Soils hydrometer and bulk density tests (Zone 1 or Zone 2 soils). d. Plasticity Index test results <20 for Zone 3 or 4 soils (ASTM D Attenburg Series). 5. System sizing shall be based on upon soil morphology and average percolation rate if that results in larger system. Refer to sizing recommended in the article Estimating Wastewater Loading Rates Using Soil Morphological Descriptions (Tyler et. al., ASAE Proceedings) or to Sonoma County Percolation Test and Sizing Chart for non-standard systems. 6. Systems shall have a minimum separation of 36 inches to groundwater, fractured or impermeable soils beneath trench bottom and 48 inches to bedrock as measured beneath proposed trench bottom. Note that minimum separation may be reduced to 24 inches below trench bottom if acceptable pretreatment is used. 7. To maximize evapotranspiration pressure distribution systems as the SIG may not be installed below non-permeable soils such as high shrink-swell clays, highly compacted soils, and/or soils with massive or platy structures. 8. Minimum setbacks of SIG systems from property lines as measured to the edge of the soil cover. a. 25 feet laterally b. 50 feet downhill c. 15 feet uphill d. See Section 200 for restrictions on use and other required setbacks. 9. Soil cover of 12 inches minimum is required. 553* C. Design Parameters for Shallow In-Ground Systems 1. See Section 520 Design Criteria for Pressure Distribution Systems. Refer also to the following standards. a. PRMD regulations for Filled Land Systems. b. PRMD Mound Construction Regulations. See Sections Page 24