Mo. Code Regs. tit. 19 § 20-3.060
Current through Register Vol. 49, No. 23, December 2, 2024
Section 19 CSR 20-3.060 - Minimum Construction Standards for On-Site Sewage Disposal SystemsPURPOSE: This rule establishes minimum construction standards for on-site sewage disposal systems. In accordance with the authority granted in section 701.040, RSMo, this rule establishes the minimum standards and criteria for the design, location, installation and repair of individual on-site sewage disposal systems to promote the public health and general welfare and to protect the surface and ground waters of the state.
PUBLISHER'S NOTE: The secretary of state has determined that the publication of the entire text of the material which is incorporated by reference as a portion of this rule would be unduly cumbersome or expensive. Therefore, the material which is so incorporated is on file with the agency who filed this rule, and with the Office of the Secretary of State. Any interested person may view this material at either agency's headquarters or the same will be made available at the Office of the Secretary of State at a cost not to exceed actual cost of copy reproduction. The entire text of the rule is printed here. This note refers only to the incorporated by reference material.
(1) General. (A) Definitions. Definitions as set forth in Chapter 701, RSMo, On-Site Sewage Disposal Law shall apply to those terms when used in this rule unless the context clearly requires otherwise or as noted in this subsection. For the purposes of these standards, certain terms or words used here shall be interpreted as follows. The word shall is mandatory and the words should and may are permissive. All distances, unless otherwise specified, shall be measured horizontally: 1. Administrative authority-The governing body which may include, but is not limited to, county health departments, planning and zoning commissions, county building departments, county public works department, sewer districts, municipalities and the Missouri Department of Health which has, as authorized by statute, charter or other form of enabling authority, adopted these standards for individual on-site sewage disposal systems;2. Aeration unit-Any sewage tank which utilizes the principle of oxidation in the decomposition of sewage by the introduction of air into the sewage;3. Alluvium-Soil parent material which was transported and deposited in a running water setting;4. Alternative-An individual sewage disposal system employing methods and devices as presented in section (6) of this rule;5. Approved-Considered acceptable by the administrative authority;6. Baffle-A device installed in a septic tank for proper operation of the tank and to provide maximum retention of solids. This includes vented sanitary tees and submerged pipes in addition to those devices normally called baffles;7. Bedrock-That layer of geologic material which is consolidated;8. Bedroom-Any room within a dwelling that might reasonably be used as a sleeping room. The number of bedrooms in a residence as given by an appraiser will be used in determining volumes in the sizing of on-site sewage disposal systems;9. Black water-Liquid-carried waste from a dwelling or other establishment, which contains organic wastes, including excreta or other body wastes, blood or other body fluids, and garbage;10. Building sewer-That part of the drainage system which extends from the end of the building drain and conveys its discharge to an on-site sewage disposal system;11. Capacity-The liquid volume of a sewage tank using inside dimensions below the outlet;12. Color-The moist color of the soil based on the Munsell soil color system;13. Distribution pipes-Perforated rigid pipes that are used to distribute sewage tank effluent in a soil treatment system;14. Dosing chamber (or pump pit or wet well)-A tank or separate compartment following the sewage tank which serves as a reservoir for the dosing device;15. Dosing device-A pump, siphon or other device that discharges sewage tank effluent from the dosing chamber to the soil treatment system;16. Dwelling-Any building or place used or intended to be used by human occupants as a residential unit(s);17. Effluent-The liquid discharge of a septic tank or other sewage treatment device;18. Gravelless system-An absorption system recognized by the administrative authority as an acceptable method of subsurface disposal of sewage without the required use of gravel. The following are examples: A. Large diameter, eight inch (8") and ten inch (10") corrugated, perforated plastic pipe, wrapped in a sheath of spun-bonded filter wrap;19. Gray water-Liquid waste, specifically excluding toilet, hazardous, culinary and oily wastes, from a dwelling or other establishment which is produced by bathing, laundry or discharges from floor drains;20. Grease trap-A device designed and installed so as to separate and retain oils and fats from normal wastes while permitting normal sewage or wastes to discharge into the drainage system by gravity;21. Ground absorption sewage treatment and disposal system-A system that utilizes the soil for the subsurface disposal of partially treated or treated sewage effluent. The following are examples:A. Chamber system-A system that uses an open bottom structure which forms an underground chamber over the soil's infil-trative surface. The wastewater is discharged into the chamber through a central weir, trough or splash plate and is allowed to flow over the infiltrative surface in any direction;B. Conventional soil absorption sys-tem-A system that distributes effluent by gravity flow from the septic or other treatment tank and applies effluent to the soil through the use of a seepage trench or bed;C. Dosing soil absorption system-A system that distributes effluent by a pump or automatic siphon to elevate or distribute effluent to the soil through the use of a seepage trench or bed;D. Drip soil absorption system-An experimental system that distributes effluent through drip lines in a grid pattern (also known as trickle irrigation); andE. Pressure distribution system-A soil absorption system that distributes effluent by a pump and smaller diameter distribution piping with small diameter perforations to distribute effluent;22. Hazardous waste-Any waste or combination of wastes, as determined by the Hazardous Waste Commission by rules, which, because of its quantity, concentration, or physical, chemical or infectious characteristics, may cause or significantly contribute to an increase in mortality or an increase in serious irreversible, or incapacitating reversible, illness, or pose a present or potential threat to the health of humans or the environment;23. High ground water-Zones of soil saturation which include: perched water tables, shallow regional groundwater tables or aquifers, or zones that are seasonally, periodically or permanently saturated;24. High-water level-The highest known flood water elevation of any lake, stream, pond or flowage or the regional flood elevation established by a state or federal agency;25. Holding tank-A watertight tank for temporary storage of sewage until it can be transported to a point of approved treatment and disposal;26. Horizon-A layer of soil, approximately parallel to the surface, that has distinct characteristics relative to adjacent layers;27. Individual sewage disposal system- A sewage disposal system, or part of a system, serving a dwelling(s) or other establish-ment(s), which utilizes subsurface soil treatment and disposal;28. Intermittent sand filters-Intermittent sand filters are beds of granular materials twenty-four to thirty-six inches (24-36") thick underlain by graded gravel and collecting pipe. Waste water is applied intermittently to the surface of the bed through distribution pipes or troughs and the bed is under-drained to collect and discharge the final effluent. Uniform distribution is normally obtained by dosing so as to flood the entire surface of the bed. Filters may be designed to provide free access (open filters) or may be buried in the ground (buried filters or subsurface sand filters);29. Matrix color-The dominant color of a soil material;30. Mottling-Spots or splotches of color interspersed in the dominant (or matrix color) of a soil material. Mottles may be of a wide variety of colors;31. Mound system-A system where the soil treatment area is built above the ground to overcome limits imposed by proximity to water table or bedrock or by rapidly or slowly permeable soils;32. Non-ground absorption sewage disposal system-A facility for waste treatment designed not to discharge to the soil, land surface, or surface waters, including, but not limited to, incinerating toilets, mechanical toilets, composting toilets and recycling systems;33. Other establishment-Any public or private structure other than a dwelling which generates sewage;34. Pan-A soil horizon compacted, hard or very high in clay content. These horizons are usually very slowly permeable. Common pans in Missouri are claypans and fragipans;35. Perched water table-A saturated zone above and separated from the water table by a horizon which is unsaturated;36. Percolation rate-The time rate of drop of a water surface in a test hole as specified in subsection (2)(C) of this rule and expressed in minutes per inch;37. Permeability-The ease with which liquids and gases move within the soil or rock;38. Plastic limit-A soil moisture content below which the soil may be manipulated for purposes of installing a soil treatment system and above which manipulation will cause compaction, puddling and smearing, as determined by the administrative authority. This is not to be confused with plastic limit as used or defined in the Unified Soil Classification System;39. Privy-An outhouse or structure used for receiving human excrement in a container or vault beneath the structure;40. Registered geologist-A person who meets the requirements of Chapter 256, RSMo;41. Restrictive horizon-A soil horizon that is capable of perching groundwater or sewage effluent and that is brittle and strongly compacted or strongly cemented with iron, aluminum, silica, organic matter or other compounds. Restrictive horizons may occur as fragipans, iron pans or organic pans and are recognized by their resistance in excavation or in use of a soil auger;42. Rock fragments-The percentage by volume of rock fragments in a soil that are greater than two millimeters (2 mm) in diameter or retained on a No. 10 sieve which may include, but is not restricted to, chert, sandstone, shale, limestone or dolomite;43. Sanitarian-A person registered either as a sanitarian or environmental health professional by the National Environmental Health Association or the Missouri Board of Certification for Environmental Health Professionals or employed as a sanitarian or environmental health professional by the administrative authority;44. Seepage bed-An excavated area larger than three feet (3') in width which contains a bedding of aggregate and has more than one (1) distribution line;45. Seepage trench-An area excavated one to three feet (1-3') in width which contains a bedding of aggregate and a single distribution line;46. Septage-Those solids and liquids removed during periodic maintenance of a septic or aeration unit tank or those solids and liquids removed from a holding tank;47. Septic tank-Any watertight, covered receptacle designed and constructed to receive the discharge of sewage from a building sewer, separate solids from liquid, digest organic matter, store liquids through a period of detention and allow the clarified liquids to discharge to a soil treatment system;48. Setback-A separation distance measured horizontally;49. Severe geological limitations-Site-specific geologic conditions which are indicative of rapid recharge of an aquifer and likely groundwater contamination. Locations with significant groundwater contamination potential should be investigated by a registered geologist to determine if the site has severe geological limitations. Standardized criteria for determination of severe geological limitations are available in the form Assessment of Individual On-Site Waste Disposal Geological Limitations from the Department of Natural Resources, Division of Geology and Land Survey;50. Sewage-Any water-carried domestic waste, exclusive of footings and roof drainage. Domestic waste includes, but is not limited to, liquid waste produced by bathing, laundry, culinary operations, liquid wastes from toilets and floor drains and specifically excludes animal waste and commercial process water. Also known as wastewater;51. Sewage flow-Flow as determined by measurement of actual water use or, if actual measurements are unavailable, as estimated by the best available data provided by Table 2A in subsection (1)(E) of this rule;52. Sewage tank-A watertight tank used in the treatment of sewage which includes, but is not limited to, septic tanks and aeration units;53. Sewage tank effluent-That liquid which flows from a septic tank or aeration unit under normal operation;54. Significant groundwater contamination potential-Any condition which would cause or indicate rapid recharge of an aquifer. This includes, but is not limited to, the following conditions or parameters: a water sample from an on-site well which exceeds drinking water standards with respect to fecal coliform; a hydrologic connection is established between the on-site waste disposal system and any well; a disposal field to be placed in Class V soils or soils with a percolation rate less than ten minutes per inch (10 min./in.); a disposal field within one hundred feet (100') of the topographic drainage of a sinkhole; or a sewage tank with fifty feet (50') of the topographic drainage of a sinkhole;55. Sinkhole-A land surface depression that is hydraulically connected with a subterranean passage developed by a solution or collapse into the underlying bedrock, or both;56. Site-The area bounded by the dimensions required for the proper location of the soil treatment system;57. Slope-The ratio of vertical rise or fall to horizontal distance;58. Soil-The naturally occurring, unconsolidated mineral or organic material of the land surface developed from rock or other parent material and consisting of sand, silt and clay-sized particles and variable amount of organic materials;59. Soil characteristics, limiting-Those soil characteristics which preclude the installation of a standard system, including, but not limited to, evidence of water table or bedrock closer than three feet (3') to the ground surface and percolation rates slower than one hundred twenty minutes per inch (120 min./in.);60. Soil saturation-The condition that occurs when all the pores in a soil are filled with water;61. Soil scientist-An individual who has a minimum of fifteen (15) semester credit hours of soils course work including a minimum of three (3) hours in the area of soil morphology and interpretations, and has a minimum of two (2) years of field experience;62. Soil textural classification-Soil particle sizes or textures specified in this rule refer to the soil textural classification in the Soil Survey Manual Handbook No. 18, United States Department of Agriculture, 1993;63. Soil treatment area-That area of trench or bed bottom which is in direct contact with the trench rock of the soil treatment system;64. Soil treatment system-A system where sewage tank effluent is treated and disposed of below ground surface by filtration and percolation through the soil. It includes those systems commonly known as seepage bed, trench, drainfield, disposal field and includes mound and low pressure pipe systems;65. Standard system-An individual sewage disposal system employing a building sewer, sewage tank and the soil treatment system commonly known as seepage bed or trenches, drainfield or leachfield;66. Toilet waste-Fecal matter, urine, toilet paper and any water used for flushing;67. Trench rock-Clean rock, washed creek gravel or similar insoluble, durable and decay-resistant material free from dust, sand, silt or clay. The size shall range from one inch to two and one-half inches (1"-2 1/2"). If limestone, dolomite or other crushed white rock is used, it shall be washed and be a minimum size of one and one-half inches (1 1/2");68. Valve box-Any device which can stop sewage tank effluent from flowing to a portion of the soil treatment area. This includes, but is not limited to, caps or plugs on distribution or drop box outlets, divider boards, butterfly valves, gate valves or other mechanisms;69. Very slowly permeable-Soils, bedrock and soil horizon or layer having a vertical permeability less than one inch (1") in twenty-four (24) hours;70. Wastewater-same as sewage as defined in paragraph (1)(A)50. of this rule;71. Wastewater stabilization pond-A sealed earthen basin which uses the natural unaided biological processes to stabilize wastewater (also known as a sewage lagoon);72. Water table-The highest elevation in the soil or rock where all voids are filled with water, as evidenced by presence of water or soil mottling or other information. This includes perched water tables or perched zones of saturation; and73. Watertight-Constructed so that no water can get in or out below the level of the outlet.(B) Applicability. For this rule, on-site wastewater treatment and disposal system means all equipment and devices necessary for proper conduction, collection, storage, treatment and disposal of wastewater from a dwelling or other facility producing sewage of three thousand gallons (3000 gals.) or less per day. Included within the scope of this rule are building sewers, septic tanks, subsurface absorption systems, mound systems, intermittent sand filters, gravelless systems, aeration unit wastewater treatment systems and single family wastewater stabilization ponds. Commercial or industrial facilities and developers of subdivisions must first contact the Department of Natural Resources concerning compliance with the Missouri Clean Water Law and Regulations before applying for any approvals or permits under this rule.(C) Responsibilities. 1. The design, construction, operation and maintenance of sewage treatment and disposal systems, whether septic tank systems, privies or alternative systems, shall be the responsibility of the designer, owner, developer, installer or user of the system.2. Actions of representatives of the administrative authority engaged in the evaluation and determination of measures required to effect compliance with the provisions of this rule shall in no way be taken as a guarantee or warranty that sewage treatment and disposal systems approved and permitted will function in a satisfactory manner for any given period of time. Due to the development of clogging mats, which adversely impact the life expectancy of normally functioning ground absorption sewage treatment and disposal systems and variables influencing system function which are beyond the scope of this rule, no guarantee or warranty is implied or given that a sewage treatment and disposal system will function in a satisfactory manner for any specific period of time.3. Prior to the issuance of a permit to install or effect major repair of an on-site sewage disposal system as regulated by Chapter 701, RSMo, plans and specifications shall be required for review. Approval by the administrative authority shall be required for- A. Plans for absorption field showing the following:(I) Field locations with slope(s) indicated or with contour lines based on field measurement. If field areas are essentially flat or of uniform grade, spot elevations will be required for alternate systems;(II) Field layout, length, spacing, connection, pipe sizes and cleanout details, invert elevations of flow distribution devices and laterals, valves and appurtenances;(III) Trench plan and profile drawings and flow distribution device details;(IV) Location and design of associated surface and ground water drainage systems;(V) Name, address and telephone number of the person(s) drafting the plans; and(VI) Any other information required by the administrative authority; andB. Alternative systems whether or not specifically described in this rule.4. The entire sanitary sewage system shall be on property owned or controlled by the person owning or controlling the system. Necessary easements shall be obtained permitting the use and unlimited access for inspection and maintenance of all portions of the system to which the owner and operator do not hold undisputed title. Easements shall remain valid as long as the system is required and shall be recorded with the county recorder of deeds.(D) Minimum Set-Back Distances. All on-site wastewater treatment and disposal systems shall be located in accordance with the distances shown in Table 1. Click to view image
(E) Sewage Flow Rates. Table 2A or 2B shall be used to determine the minimum design daily flow of sewage required in calculating the design volume of sanitary sewage systems to serve selected types of establishments. The minimum design volume of sewage from any establishment shall be one hundred gallons (100 gals.) per day. Design of sewage treatment and disposal systems for establishments not identified in this rule shall be determined using available flow data, water-using fixtures, occupancy or operation patterns and other measured data. 1. Volume determination. In determining the volume of sewage from single family dwellings, the minimum flow rate shall be one hundred twenty gallons (120 gals.) per day per bedroom. The minimum volume of sewage from each single family dwelling shall be two hundred forty gallons (240 gals.) per day. When the occupancy of a single family dwelling exceeds two (2) persons per bedroom, the volume of sewage shall be determined by the maximum occupancy at a rate of sixty gallons (60 gals.) per person per day.2. Other establishments. For establishments or housing developments other than a single family residence, either Table 2A shall be used to estimate the sewage flow rate or actual measured flow rate for existing systems may be used. Values for estimated sewage flow for establishments having food service operations shall be increased by a factor of one and one-half (1.5) to compensate for the high organic strength. Grease traps shall be required at food service facilities, meat markets and other places of business where the accumulation of grease or oils can cause premature failure of a soil absorption system. The following design criteria shall be met: A. The grease trap shall conform to Plumbing & Drainage Institute Standard PDI-G101 or equivalent;B. The grease trap shall be plumbed to receive all wastes associated with food handling and no toilet wastes;C. The grease trap liquid capacity shall be sufficient to provide for at least five gallons (5 gals.) of storage per meal served per day, at least two-thirds (2/3) of the required septic tank liquid capacity, or a capacity as determined in accordance with the following: LC = D x GL x ST x HR/2 x LF where LC = grease trap liquid capacity
(gallons)
D = number of seats in dining area
GL = gallons of wastewater per meal
(1.5 single-service; 2.5 full-service)
ST = storage capacity factor = 2.5
HR = number of hours open
LF = loading factor (1.25 interstate highway
= 1.0 other highways and recreational areas =
0.8 secondary roads);
D. Two (2) or more chambers must be provided, with total length-to-width ratio at least two to one (2:1). Chamber opening and outlet sanitary tee must extend down at least fifty percent (50%) of the liquid depth;E. Access manholes, with a minimum diameter of twenty-four inches (24"), shall be provided over each chamber and sanitary tee. The access manholes shall extend at least to finished grade and be designed and maintained to prevent surface water infiltration. The manholes shall also have readily removable covers to facilitate inspection and grease removal; andF. Where it has been demonstrated that specially designed grease interceptors will provide improved performance, the grease trap liquid capacity may be reduced by up to fifty percent (50%). Click to view image
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3. Population to be served. Unless satisfactory justification can be given for using lower per-unit occupancies, the figures in Table 2B shall be used in determining the population for which to design the sewage works.4. Reduction in sewage flow. Reductions in design sewage flow rates may be allowed by the administrative authority on a case-by-case basis depending upon water conservation plans. Sewage flow rates may be reduced up to forty percent (40%) for gray water systems where the toilet wastes are discharged to a holding tank and disposed of off-site or where waterless toilets are utilized.(2) Site Evaluation. (A) All proposed sites for on-site sewage treatment and disposal systems shall be evaluated for the following: 1. Either percolation tests or soil conditions, properties and permeability as determined by a soil morphology examination; a profile pit shall be required for all new installations in order to conduct soil morphology examination;3. The existence of lowlands, local surface depressions, rock outcrops and sinkholes;4. All required setback distances as required in subsection (1)(D) of this rule;5. Surface water flooding probability and depth to water table;6. Location of easements and underground utilities;7. Amount of available area for the installation of the system and an area for replacement;8. Location of homesite or dwelling as well as management of surface runoff water from those buildings;9. Any other cultural feature, such as roads, streets and the like in the surrounding areas which influences surface and subter-rainal flow of water on or near the proposed site; and10. Any significant groundwater contamination potential.(B) Preliminary Soils Information. During a site evaluation reference may be made of county soil survey reports which are available from the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) for a majority of the counties in Missouri. NRCS soil survey reports should not be used as sole final determination for a specific site, but only as a guide to which soils are expected in a given area.(C) Soil Permeability and Soil Percolation. Soil permeability and soil percolation are two (2) different soil features with no direct correlation. 1. Soil permeability is that quality that enables soil to transmit water or air. It can be measured quantitatively in terms of rate of flow of water through a unit cross section of saturated soil in unit time under specified temperature and hydraulic conditions.2. Soil percolation rate is based on a standard method which includes a twenty-four (24)-hour presoak in a six to eight inch (6-8") diameter hole to the depth of the proposed absorption field. After the presoak, water is poured into the hole to a level of eight inches (8") above the bottom. The drop in water level is then measured at thirty (30)-minute intervals until a stabilized rate is obtained. Results are recorded as minutes per inch (min./in.) for the water level to drop. (D) Procedures for Percolation Tests and Profile Holes. Two (2) types of site evaluations are acceptable. Each type depends upon the technical expertise of the individual conducting the evaluations. When percolation tests are slower than sixty minutes per inch (60 min./in.), the design must be drafted and signed by a registered engineer unless site suitability and system sizing has been determined by soil evaluation in accordance with section (7) of this rule. This would apply to all systems except for lagoons or other systems that do not use the soil for treatment. When percolation tests are slower than one hundred and twenty minutes per inch (120 min./in.), on-site sewage disposal systems shall not be permitted, except for lagoons or other systems designed in accordance with sections (6) and (7) of this rule. The administrative authority will determine which method(s) is to be used. The types of site evaluations are described as follows: 1. Percolation tests only. This type of site evaluation is where site suitability and sizing of the soil absorption system is made by percolation tests and there is no other evaluation of soil characteristics. This type of site evaluation can be used only for siting and sizing standard systems in areas which are not classified as having significant groundwater contamination potential. When using this type of evaluation, only percolation rates between ten minutes and sixty minutes per inch (10-60 min./in.) will be acceptable. Percolation tests shall be conducted by an engineer, sanitarian, registered geologist, soil scientist or a person who has been trained and certified by the Department of Health in accordance with section 701.040(2), RSMo. These tests shall be performed in accordance with the following procedure: A. A minimum of four (4) percolation test holes are required with three (3) of the holes around the periphery within the proposed soil absorption site and one (1) in the middle of the proposed soil absorption site;B. Each test hole shall be six to eight inches (6-8") in diameter, have vertical side walls and be bored or dug to a depth of the bottom of the proposed soil absorption system;C. The bottom and sides of the hole shall be carefully scratched to remove any smearing and to provide a natural soil surface into which water may penetrate. All loose material shall be removed from the bottom of the test hole and two inches (2") of one-fourth to three-fourths inch (1/4-3/4") washed gravel shall be added to protect the bottom from scouring;D. The hole shall be carefully filled with clear water to a minimum of twelve inches (12") over the soil bottom of the test hole and maintained for no less than four (4) hours. The hole shall then be allowed to swell for at least twenty-four (24) hours. In sandy soils, the saturation and swelling procedure shall not be required and the test may proceed if one (1) filling of the hole has seeped away in less than ten (10) minutes;E. In sandy soils, the water depth shall be adjusted to eight inches (8") over the soil bottom of the test hole. From a fixed reference point, the drop in water level shall be measured in inches to the nearest one-eighth inch (1/8") at approximately ten (10)-minute intervals. A measurement can also be made by determining the time it takes for the water level to drop one inch (1") from an eight-inch (8") reference point. If eight inches (8") of water seeps away in less than ten (10) minutes, a shorter interval between measurements shall be used but in no case shall the water depth exceed eight inches (8"). The test shall continue until three (3) consecutive percolation rate measurements vary by a range of no more than ten percent (10%);F. In other soils, the water depth shall be adjusted to eight inches (8") over the soil at the bottom of the test hole. From a fixed reference point, the drop in water level shall be measured in inches to the nearest one-eighth inch (1/8") at approximately thirty (30)-minute intervals, refilling between measurements to maintain an eight-inch (8") starting head. The test shall continue until three (3) consecutive percolation rate measurements vary by a range of no more than ten percent (10%). The percolation rate can also be made by observing the time it takes the water level to drop one inch (1") from an eight-inch (8") reference point if a constant water depth of at least eight inches (8") has been maintained for at least four (4) hours prior to the measurement;G. Percolation rate shall be calculated as follows:(I) The time interval shall be divided by the drop in water level to obtain the percolation rate in minutes per inch;(II) The slowest percolation rate of the four (4) tests shall be used to determine the final soil treatment system design. Where the slowest percolation rate varies by more than twenty minutes per inch (20 min./in.) from the other tests, a detailed soils morphology evaluation must be conducted to justify a design based upon the average percolation rate; and(III) For reporting the percolation rate, worksheets showing all calculations and measurements shall be submitted; andH. Depth to bedrock or other restrictive layer shall be determined in areas where it is known that bedrock may exist at depths less than ten feet (10'); and2. Soil morphology. This evaluation shall be conducted by a soil scientist unless an engineer, registered geologist or sanitarian has had special training and field experience to determine the required soil characteristics. This type of evaluation is recommended for sites that are classified as having significant groundwater contamination potential, severe geological limitations or severe limitations relating to restrictive layers. Section (7) of this rule contains criteria for this type of site evaluation. Since this type of soil analysis pertains to the factors that relate directly to permeability, no percolation test is required, however the administrative authority may retain the option of requiring percolation tests for additional information in determining site suitability.(3) Building Sewers. Building sewers used to conduct wastewater from a building to an on-site wastewater treatment and disposal system shall be constructed of material meeting the minimum requirements of American Society for Testing and Materials (ASTM) Standards and listed by that agency for such use. Suitable materials meeting ASTM standards include: Acrylonitrile, butadiene styrene (ABS), cast iron pipe, concrete pipe, copper or copper-alloy tubing, polyvinyl chloride (PVC) or vitrified clay pipe. Although listed by ASTM, asbestos cement pipe will not be accepted due to potential health hazards to installers. Building sewer specifications are as follows: (A) Size. Building sewers shall not be less than four inches (4") in diameter;(B) Slope. Building sewers shall be laid to the following minimum slope: 1. Four-inch (4") sewer-twelve inches (12") per one hundred feet (100'); and2. Six-inch (6") sewer-eight inches (8") per one hundred feet (100');(C) Cleanouts. A cleanout shall be provided at least every one hundred feet (100') and at every change in direction or slope if the change exceeds forty-five degrees (45o). A cleanout should be provided between house and tank; and(D) Connection to Sewage Tank. The pipe going into and out of the sewage tank shall be schedule 40 PVC or cast iron and shall extend a minimum of two feet (2') beyond the hole of excavation for the sewage tank.(4) Sewage Tanks. (A) General. All liquid waste and washwater with the following exceptions shall discharge into the sewage tank. Roof, garage, footing, surface water, drainage, cooling water discharges and hazardous wastes shall be excluded from the sewage tank. Backwash from water softeners and swimming pool filtration systems may be excluded from the sewage tank. In such event of excluding swimming pool filter backwash, the Department of Natural Resources shall be contacted for applicability of a discharge permit. All sewage tank effluent shall be discharged to a soil absorption system that is designed to retain the effluent upon the property from which it originated. All tanks regardless of material or method of construction shall- 1. Be watertight and designed and constructed to withstand all lateral earth pressures under saturated soil conditions with the tank empty;2. Be designed and constructed to withstand a minimum of two feet (2') of saturated earth cover above the tank top; and3. Not be subject to excessive corrosion or decay. Metal sewage tanks shall not be used unless specifically allowed by the administrative authority on a case-by-case basis. The tank shall be thoroughly coated inside and out with a bituminous or other suitable coating. Any damage to the bituminous coating shall be repaired by recoating. Additionally, plastic sanitary tees shall be used for the inlet and outlet for the sewage tank. The administrative authority shall use Table 3 regarding minimum gauge thickness for metal sewage tanks. Click to view image
(B) Septic Tanks. Septic tanks, regardless of material or method of construction, shall conform to the following criteria: 1. The liquid depth of any septic tank or its compartment shall be not less than thirty-six inches (36"). A liquid depth greater than six and one-half feet (6 1/2') shall not be considered in determining tank capacity;2. No tank or compartment shall have an inside horizontal dimension less than twenty-four inches (24");3. Inlet and outlet connections of the tank shall be protected by baffles or sanitary tees as defined in paragraph (4)(B)6. of this rule;4. The space in the tank between the liquid surface and the top of the inlet and outlet baffles shall not be less than twenty percent (20%) of the total required capacity, except that in horizontal cylindrical tanks, this space shall be not less than fifteen percent (15%) of the total required liquid capacity;5. Inlet and outlet baffles shall be constructed of acid-resistant concrete, acid-resistant fiberglass or plastic;6. Sanitary tees shall be affixed to the inlet or outlet pipes with a permanent waterproof adhesive. Baffles shall be integrally cast with the tank, affixed with a permanent waterproof adhesive or with stainless steel connectors top and bottom;7. The inlet baffle shall extend at least six inches (6") but no more than twenty percent (20%) of the total liquid depth below the liquid surface and at least one inch (1") above the crown of the inlet sewer;8. The outlet baffle and the baffles between compartments shall extend below the liquid surface a distance equal to forty percent (40%) of the liquid depth, except that the penetration of the indicated baffles or sanitary tees for horizontal cylindrical tanks shall be thirty-five percent (35%) of the total liquid depth. They also shall extend above the liquid surface as required in paragraph (4)(B)4. of this rule. In no case shall they extend less than six inches (6") above the liquid surface;9. There shall be at least one inch (1") between the underside of the top of the tank and the highest point of the inlet and outlet devices;10. The inlet shall be not less than three inches (3") above the outlet;11. The inlet and outlet shall be located opposite each other along the axis of maximum dimension. The horizontal distance between the nearest points of the inlet and outlet devices shall be at least four feet (4');12. Sanitary tees shall be at least four inches (4") in diameter. Inlet baffles shall be no less than six inches (6") or no more than twelve inches (12") measured from the end of the inlet pipe to the nearest point on the baffle. Outlet baffles shall be six inches (6") measured from beginning of the outlet pipe to the nearest point on the baffle;13. Access to the septic tank shall be as follows:A. Manholes. Access shall be provided over both the inlet and outlet devices and to each tank compartment by means of either a removable cover or a manhole. Where the top of the tank is located more than eighteen inches (18") below the finished grade, manholes and inspection holes shall extend to approximately eight inches (8") below the finished grade. The extension can be made using riser of approved material and fitted with tight covers of heavy metal or concrete. Proper attention must be given to the accident hazard involved when manholes are extended close to the ground surface. Manhole risers are not required when the top of the tank is within eighteen inches (18") of final grade. All manhole openings must be provided with a substantial, fitted, water-tight cover of concrete, cast iron or other approved material. All manhole covers which terminate below grade shall be covered with at least six inches (6") of earth. Manhole covers which terminate above grade shall have either an effective locking device or otherwise be adequately sealed in a manner to prevent accidental access; andB. A six-inch (6") inspection port shall be provided over the inlet and outlet baffles of each tank and terminate at or above grade. An inspection port shall not be used as a pumpout access. A manhole cover at or above grade may also serve in place of inspection ports;14. Compartmentation of single tanks shall be in accordance with the following: A. Septic tanks larger than fifteen hundred gallons (1500 gals.) and fabricated as a single unit shall be divided into two (2) or more compartments;B. When a septic tank is divided into two (2) compartments, not less than one- half (1/2), nor more than two-thirds (2/3), of the total volume shall be in the first compartment;C. When a septic tank is divided into three (3) or more compartments, one-half (1/2) of the total volume shall be in the first compartment and the other half equally divided in the other compartments;D. Connections between compartments shall be baffled so as to obtain effective retention of scum and sludge. The submergence of the inlet and outlet baffles of each compartment shall be as specified in paragraphs (4)(B)7. and 8. of this rule;E. Adequate venting shall be provided between compartments by baffles or by an opening of at least fifty (50) square inches near the top of the compartment wall; andF. Adequate access to each compartment shall be provided by one (1) or more manholes with a minimum opening twenty inches (20") square or in diameter and located within six feet (6') of all walls of the tank;15. The use of multiple tanks shall conform with the following: A. Where more than one (1) tank is used to obtain the required liquid volume, the tanks shall be connected in series;B. Each tank shall comply with all other provisions of this section;C. No more than three (3) tanks in series can be used to obtain the required liquid volume; andD. The first tank shall be no smaller than any subsequent tanks in series;16. The liquid capacity of a septic tank serving a dwelling shall be based upon the number of bedrooms contemplated in the dwelling served and shall be at least as large as the capacities given in Table 4. Table 4-Dwelling Septic Tank Capacity*
| Numberof Bedrooms | Minimum Liquid Capacity |
| (gallons) |
| 1-3 | 1000 |
| 4 | 1250 |
| 5 | 1500 |
*These figures provide for use of garbage grinders, automatic clothes washers and other household appliances. Garbage grinders are not recommended due to the introduction of fats and other high organic loads.
A. For six (6) or more bedrooms, the septic tank shall be sized on the basis similar to an establishment. See paragraph (4)(B)17. of this rule.B. No tank shall be designed to retain less than two (2) days', forty-eight (48) hours' flow; and17. Individual residences with more than five (5) bedrooms, multiple-family residences, individual septic tank systems serving two (2) or more residences or any place of business or public assembly where the design sewage flow is greater than one thousand gallons per day (1000 gpd), the liquid capacity of the septic tank shall be designed in accordance with the following: V = 1.5Q + 500 where V = the liquid capacity of the sep tic tank and
Q = the design daily sewage flow.
The minimum liquid capacity of a septic tank serving two (2) or more residences shall be fifteen hundred gallons (1500 gals.).
(C) Location. Location of the sewage tank shall include the following: 1. The sewage tank shall be placed so that it is accessible for the removal of liquids and accumulated solids;2. The sewage tank shall be placed on firm and settled soil capable of bearing the weight of the tank and its contents; and3. The sewage tanks shall be set back as specified in subsection (1)(D) of this rule.(D) Solids Removal. The owner of any septic tank or his/her agent shall regularly inspect and arrange for the removal and sanitary disposal of septage from the tank whenever the top of the sludge layer is less than twelve inches (12") below the bottom of the outlet baffle or whenever the bottom of the scum layer is less than three inches (3") above the bottom of the outlet baffle. Yearly inspections of septic tanks are recommended and tanks shall be pumped whenever the bottom of the scum layer is within three inches (3") of the bottom of the outlet device or the sludge level is within eight inches (8") of the bottom of the outlet device.(E) Aeration Units. An aeration unit wastewater treatment plant utilizes the principle of oxidation in the decomposition of sewage by the introduction of air into the sewage. An aeration unit may be used as the primary treatment unit instead of a septic tank except where special local conditions may limit their use. All aeration unit type treatment systems shall comply with the general requirements for sewage tanks set forth in subsection (4)(A) of this rule and with the following: 1. Limitations. Special conditions where aeration units should not be used may include, but not be limited to, the following: A. Where intermittent use (interruptions allowing more than five (5) days without continuous flow) will adversely affect the functioning of the plant; andB. Where local ordinances restrict their use;2. General. The aeration unit shall be located where it is readily accessible for inspection and maintenance. Set-back distances for aeration units shall be in accordance with subsection (1)(D) of this rule;3. Design. All aeration units shall comply with National Sanitation Foundation Standard No. 40 or as required by the administrative authority. In addition, all aeration unit treatment plants shall comply with the requirements stipulated in this section. The aeration unit shall have a minimum treatment capacity of one hundred twenty gallons per bedroom per day (120 gals./pbd) or five hundred gallons (500 gals.), whichever is greater;4. Effluent disposal. Effluent from an aeration unit shall be discharged into a soil absorption system or other final treatment system in accordance with section (6) of this rule. No reductions in the area of soil absorption systems or other final treatment systems shall be permitted because of the use of an aeration unit instead of a septic tank; and5. Operation and maintenance. Where aeration units are used in institutional or administrative arrangements to control their use, operation and maintenance are recommended. Aeration units should be inspected at least one (1) time each year and pumped when mixed liquor solids concentrations result in excessive clarifier loading.(5) Absorption Systems. The common design of absorption systems is the use of absorption trenches, each separate from the other and each containing a distribution pipe. This type system should be used whenever practical. Other types of absorption systems may be used as alternatives where the site conditions meet the specific design requirements of the alternative systems. Installation shall not be made while the soil is wet or moist. This is to prevent smearing and destroying the structure of the soil. All absorption systems should have curtain drains, terraces or use of other flow diversion methods to minimize surface or ground water from loading the absorption field. (A) Absorption Trenches. The absorption trench gives additional treatment to the sewage from the treatment tank. Regardless of its appearance of clarity or transparency, the outflow or effluent from a sewage tank is a dangerous source of contamination. The satisfactory operation of the sewage disposal system is largely dependent upon the proper site selection, design and construction of the absorption trench. 1. Absorption trenches should not be constructed in soils having a percolation rate slower than sixty minutes per inch (60 min./in.) and in no case shall absorption trenches be constructed in soils with percolation rates slower than one hundred twenty minutes per inch (120 min./in.) or where rapid percolation may result in contamination of water-bearing formations or surface waters.2. The absorption trench shall be located on the property to maximize the vertical separation distance from the bottom of the absorption trench to the seasonal high groundwater level, as determined by the presence of mottling, bedrock or other limiting layer. The vertical separation between the bottom of the absorption trench and limiting layer or seasonal high water table shall be no less than one foot (1') for standard systems. Greater vertical separation may be required where water-bearing formations are in danger of contamination.3. Absorption trenches shall not be constructed in unstabilized fill or ground which has become severely compacted due to construction equipment.4. The minimum area in any absorption trench system shall be in accordance with Table 5. Absorption trenches in these highly permeable soils shall have a minimum vertical separation of four feet (4') between the absorption trench bottom and seasonal high groundwater table or bedrock. Cherty clays may have percolation rates between zero (0) and sixty (60) minutes per inch. Cherty clay soils located in areas of severe geological limitations shall have less than fifty percent (50%) rock fragments and a vertical separation distance of four feet (4') or more between the absorption trench bottom and bedrock. Unlined absorption trenches shall not be installed in cherty clays when the field evaluation indicated the presence of large voids. Regardless of the percolation rate, absorption trenches installed in areas of severe geological limitations with cherty clays should be designed for a maximum loading rate of forty-five hundredths gallons per square foot (0.45 gals/sq. ft.) or a minimum of two hundred sixty-five square feet per bedroom (265 sq. ft./bedroom). Table 5 Minimum Absorption Area
| Percolation Rate | AbsorptionLoadingArea | Loading Rate |
| (min./in.) | (sq. Ft./ bedroom) | (gal./sq. ft.)* |
| <=10** | 150 | 1.0 |
| 11-30 | 200 | 0.8 |
| 31-45 | 265 | 0.45 |
| 46-60*** | 300 | 0.4 |
| 61-120 æ*** | 600 | 0.2 |
* Gallons of sewage tank effluent per day per square foot of trench bottom.
** Soils with percolation rates of one to ten minutes per inch (1 10 min./in.) or less shall either be evaluated for severe geological limitations by a registered geologist or a soil morphology examination shall be required.
*** Note: When percolation rate is greater than forty-five minutes per inch (45 min./in.), backfill above infiltration barrier shall be sand, loamy sand or sandy loam when available. Two to four inches (2 4") of loamy soil shall be used to cap the sandy backfill. This is to keep rainwater from entering the system.
æ Must be designed and approved by a Missouri registered engineer.
5. Each absorption trench system shall have a minimum of two (2) trenches with no one (1) trench longer than one hundred feet (100') unless approved by the administrative authority on a case-by-case basis. The absorption trenches shall be located not less than three (3) times the trench width on centers with a minimum spacing of five feet (5') on centers.6. Absorption trenches shall be at least eighteen inches (18") wide and no more than thirty-six inches (36") wide. Thirty-six inch (36") wide trenches should not be utilized in soils with percolation rates slower than forty-five minutes per inch (45 min./in.). The bottom of standard absorption trenches shall be at least eighteen inches (18") and no more than thirty inches (30") below the finished grade except as approved by the administrative authority.7. The pipe used between the sewage tank and the absorption system shall be a minimum of four-inch (4") inside diameter equivalent to the pipe used for the building sewer as set forth in section (3) of this rule. The pipe shall have a minimum fall of not less than one-eighth inch (1/8") per foot. All joints shall be of watertight construction.8. Gravity-fed absorption field distribution lines should be at least four inches (4") in diameter. Perforated distribution line shall have holes at least one-half inch (1/2") and no more than three-fourths inch (3/4") in diameter. A. Pipe used for distribution lines shall meet the appropriate ASTM standard or those of an equivalent testing laboratory. Fittings used in the absorption field shall be compatible with the materials used in the distribution lines.B. When four-inch (4") or six-inch (6") diameter corrugated plastic tubing is used for distribution lines, it shall be certified as complying with applicable ASTM standards. The corrugated tubing shall have either two (2) or three (3) rows of holes, each hole between one-half inch (1/2") and three-fourths inch (3/4") in diameter and spaced longitudinally approximately four inches (4") on centers. Coiled tubing shall not be used.9. The absorption trenches shall be constructed as level as possible, but in no case shall the fall in a single trench bottom exceed one-fourth inch (1/4") in ten feet (10'). The ends of distribution lines should be capped or plugged, or when they are at equal elevations, they shall be connected.10. Rock used in soil absorption systems shall be clean gravel or crushed stone, and graded or sized between one and one-half and three inches (1 1/2 3") with no more than ten percent (10%) material to pass through a one-half inch (1/2") screen. The rock shall be placed a minimum of twelve inches (12") deep with at least six inches (6") below the pipe and two inches (2") over the pipe and distributed uniformly across the trench bottom and over the pipe. Limestone and dolomite shall be avoided when possible. Before placing soil backfill over the trenches, the gravel shall be covered with one (1) of the following: A. Unfaced, rolled, three and one-half inch (3 1/2") thick fiberglass insulation;B. Untreated building paper;C. Synthetic drainage fabric; orD. Other material approved by the administrative authority laid as to separate the gravel from the backfill.11. Complex slope patterns and slopes dissected by gullies shall not be considered for installation of absorption trenches. Uniform slopes under fifteen percent (15%) shall be considered suitable slope for installation of absorption trenches. When slopes are less than two percent (2%), provisions shall be made to insure adequate surface drainage. When slopes are greater than four percent (4%), the absorption trenches shall follow the contour of the ground. Uniform slopes between fifteen percent (15%) and thirty percent (30%) should not be used for installation of absorption trenches unless the soils are three feet (3') or more below the trench bottom. Slopes within this range may require installation of interceptor drains upslope from the soil absorption system to remove all excess water that might be moving laterally through the soil during wet periods. Usable areas larger than minimum are ordinarily required in this slope range. Slopes greater than thirty percent (30%) shall not be utilized for installation of absorption trenches unless the following requirements can be met and approval is obtained from the administrative authority: A. The slope can be terraced or otherwise graded or the absorption trenches can be located in naturally occurring soil so as to maintain a minimum ten foot (10') horizontal distance from the absorption trench and the top edge of the fill embankment;B. The soil is permeable and no restrictive layers or water tables occur at a depth within two feet (2') of the trench bottom;C. Surface water runoff is diverted around the absorption trench field so that there will be no scouring or erosion of the soil over the field or to allow surface runoff onto the field;D. If necessary, groundwater flow from heavy rainfall is intercepted and diverted to prevent that water from running into or saturating the soil absorption system; andE. There is sufficient ground area available to install the absorption trench system with these modifications.12. Effluent distribution devices, including distribution boxes, flow dividers and flow diversion devices, shall be of sound construction, watertight, not subject to excessive corrosion and of adequate design as approved by the administrative authority. Effluent distribution devices shall be separated from the sewage tank by a minimum of two feet (2') of undisturbed or compacted soil and shall be placed level on a solid foundation of soil, gravel or concrete to prevent differential settlement of the device. Distribution boxes provided with flow equalizers are recommended. A. Each distribution line shall connect individually to the distribution box and shall be watertight.B. The pipe connecting the distribution box to the distribution line shall be of a watertight construction laid on undisturbed earth.C. No more than four (4) distribution lines should be connected to a distribution box receiving gravity flow unless the ground surface elevation of the lowest trench is above the flow line elevation of the distribution box.13. Stepdowns or drop boxes may be used where topography prohibits the placement of absorption trenches on level grade. Serial distribution systems should be limited to a separation of at least three feet (3') between the bottom of the absorption trenches and the limiting condition such as slow permeability or zone of seasonal saturation as evidenced by mottling. Whenever the design sewage flow rate requires more than seven hundred and fifty lineal feet (750 lin. ft.) of distribution line in a stepdown or drop-box type system, the absorption field shall be divided into two (2) or more equal portions. Stepdowns shall be constructed of two feet (2') of undisturbed soil and constructed to a height level with the top of the upper distribution line. The inlet to a trench should be placed either in the center or as far as practical from the outlet (overflow) from the same trench. Drop boxes shall be constructed so that the inlet supply pipe is one inch (1") above the invert of the outlet supply pipe which is connected to the next lower drop box. The top of the trench outlet laterals, which allow effluent to move to the distribution lines, shall be two inches (2") below the invert of the outlet supply line. It is recommended that drop boxes be designed to close off the trench outlets to provide for periods of resting when the absorption trench becomes saturated.14. Dosing is recommended for all systems except serial distribution systems and shall be provided when the design sewage flow requires more than five hundred lineal feet (500 lin. ft.) of distribution line. When the design sewage flow requires more than one thousand lineal feet (1000 lin. ft.) of distribution line, the absorption field shall be divided into two (2) equal portions and each half dosed alternatively, not more than four (4) times per day. Dosing may be accomplished by the use of a pump. Each side of the system shall be dosed not more than four (4) times per day. The volume of each dose shall be the greater of the daily sewage volume divided by the daily dosing frequency, or an amount equal to approximately three-fourths (3/4) of the internal volume of the distribution lines being dosed (approximately one-half gallon per lineal foot (1/2 gal./lin. ft.) of four-inch (4") pipe). Whenever dosed distribution box systems are utilized, the separation distance between the absorption trench bottom and limiting condition should be at least two feet (2').15. Gravelless subsurface absorption systems may be used as an alternative to conventional four-inch (4") pipe placed in gravel filled trenches, however they cannot be used in areas where conventional systems would not be allowed due to poor permeability, high groundwater or insufficient depth to bedrock. Design approval for these systems may be required from the administrative authority prior to installation and all manufacturing specifications and installation procedures shall be closely adhered to. Gravelless trench systems using fabric wrapped tubing shall not be used, however, where wastes contain high amounts of grease and oil, such as in restaurants. A. The eight (8)-, ten (10)-, and twelve (12)-inch (inner diameter) corrugated polyethylene tubing used in gravelless systems shall meet the requirements of ASTM F667, Standard Specification for Large Diameter Corrugated Polyethylene Tubing. For purpose of calculation, the eight-inch (8") pipe may be considered equal to eighteen inches (18") in width of a standard absorption trench. The ten-inch (10") pipe may be considered equal to twenty-five inches (25") in width of a standard absorption trench.B. Two (2) rows of perforations shall be provided located one hundred twenty degrees (120o) apart along the bottom half of the tubing, each sixty degrees (60o) from the bottom centerline. The tubing shall be marked with a visible top location indicator one hundred twenty degrees (120o) away from each row of holes. Perforations shall be cleanly cut and uniformly spaced along the length of the tubing and should be staggered so that there is only one (1) hole in each corrugation. The tubing shall be marked with a visible top location indicator. All gravelless drainfield pipe shall be encased at the point of manufacture with a filter wrap of spun-bonded nylon, spun-bonded polypropylene or other substantially equivalent material approved by the administrative authority.C. Rigid corrugated tubing shall be covered with filter wrap at the factory and each joint shall be immediately encased in a protective wrap that will prevent ultraviolet light penetration which shall continue to encase the large diameter pipe and wrap until just prior to installation in the trench. Filter wrap encasing the tubing shall not be exposed to sunlight (ultraviolet radiation) for extended periods. Rocks and large soil clumps shall be removed from backfill material prior to being used. Clayey soils (soil group IV) shall not be used for backfill. The near end of the large diameter pipe shall have an offset adapter (small end opening at top) suitable for receiving the pipe from the septic tank or distribution device and making a mechanical joint in the trench.D. The trench for the gravelless system shall be dug with a level bottom. On sloping ground, the trench should follow the contour of the ground to maintain a level trench bottom and to ensure a minimum backfill of six inches (6"). It is recommended that the minimum trench width for the gravelless system be eighteen inches (18") in friable soils to ensure proper backfill around the bottom half of the pipe. In cohesive soils, the minimum width of excavation should be twenty-four inches (24"). In clay soils, it is recommended that the trench be backfilled with sandy material, sandy loam, loam, clay loam, silt loam or silty clay loam. The grav-elless system may be installed at a trench bottom depth of eighteen inches (18") minimum to thirty inches (30") maximum, but a more shallow trench bottom depth of eighteen to twenty-four inches (18-24") is recommended. To promote equal effluent and suspended solids distribution, the slope of the drain pipe should be from zero to one-half inch per one hundred feet (0-1/2 in./100 ft.).E. A gravelless chamber may be installed based on bottom absorption area utilizing a reduction of up to twenty-five percent (25%) in the size of a standard gravel absorption area based upon a soil morphology evaluation indicating the feasibility of a reduction. However, as described in Table 6, the maximum loading rate provided for any particular soil group must not be exceeded when sizing for the thirty-four inch (34") chamber. For this purpose, the fifteen inch (15") chamber may be considered equal to twenty-four inches (24") in width of a standard absorption trench. The twenty-two inch (22") chamber may be considered equal to twenty-eight inches (28") in width of a standard absorption trench. The thirty-four inch (34") chamber may be considered equal to forty-two inches (42") in width of a standard absorption trench.F. Installation of the chamber system shall be in accordance with this rule except: (I) The installation shall be made in accordance with the manufacturer's specifications;(II) The side walls of trenches placed in Group I Va soils shall be raked to open pores which were damaged or sealed during excavation; and(III) Chambers utilizing maximum sidewall absorption features shall be installed per the manufacturer's recommendations to maximize the use of upper soil horizons; andG. A reduction of up to twenty-five percent (25%) in the size of the absorption field may be allowed based upon a soil morphology evaluation indicating the feasibility of a reduction. However, as described in Table 6, the maximum loading rate provided for any particular soil group must not be exceeded. Table-6 Loading Rate for Chamber Systems*
| Soil Group | Range for Chambers |
| (gpd/sq. ft) |
| I | 1.0-1.2 |
| II | 0.7-0.8 |
| III | 0.5-0.6 |
| IVa | 0.3-0.4 |
| IVb | Unsuitable |
| V** | 0.4-0.6 |
* Note: All application rates are for area of trench bottoms only.
** Note: No reduction is allowed for chamber systems in Group V soils.
16. Dosing/alternating systems are encouraged, especially in slowly permeable soil conditions.17. The administrative authority may permit the use of a bed system on sites where the minimum soil permeability is a percolation rate of forty-five minutes per inch (45 min./in.) and essentially meeting the other requirements of this section, and only on lots which are limited by topography, space or other site planning considerations. In such cases the number of square feet of bottom area needed shall be increased by fifty percent (50%) over what would be required for a trench system. Distribution lines shall be at least eighteen inches (18") from the side of the bed and shall have lines on three-foot (3') centers and care must be taken to divert surface water away from the bed. When the design volume of sewage exceeds six hundred gallons (600 gals.) per day, adequate space shall be provided to accommodate a trench system for the absorption field. There shall be no less than a two-foot (2') separation between the bed bottom and the limiting layer or seasonal high water table.(B) Possible modifications to standard absorption systems which may be utilized to overcome selected soil and site limitations and must be approved by the administrative authority include the following: 1. Shallow placement of absorption trenches shall be utilized where insufficient depth to seasonally high or perched water table or where insufficient soil thickness prevents the placement of conventional distribution lines in accordance with this section. Shallow trenches shall be designed and constructed to provide a minimum of two feet (2') of natural soil separation between the trench bottom and the uppermost elevation of the seasonally high or perched water table and rock. Shallow trenches may be constructed by placing the top of the gravel at original ground level and covering the absorption field with loamy soil, (sandy loam, loam, clay loam, silt loam or silty clay loam) to a depth of eight to twelve inches (8-12") at the center. The cover over the absorption field shall extend at least five feet (5') beyond the edge of any trench and have a turf grass cover established immediately after construction. If an area is to be filled and the trenches constructed in the fill with the bottom of the trenches in at least six inches (6") of natural soil, the following procedures must be followed: A. The fill material should be of a sandy texture with a maximum clay content of twenty percent (20%). The fill material should not be hauled or worked wet. The area to be filled must be protected from traffic and small brush and trees removed prior to placement;B. The soil surface must be loosened with a cultivator or garden plow. This work must be done when the soil is dry;C. The fill is moved onto the site without driving on the loosened soil. The fill material is then tilled into the natural soil to create a gradual boundary between the two (2). The remaining fill is then added in layers until the desired height is obtained with each layer being tilled into the preceding layer; andD. The site is then shaped to shed water and fill all low spots before the absorption system is installed. After installation of the absorption system, the site must have a turf grass cover established as soon as possible;2. Alternating dual field absorption systems may be utilized where soils are limited by high clogging potentials, percolation rates slower than sixty minutes per inch (60 min./in.) or high shrink/swell potential soils and where the potential for malfunction and need for immediate repair is required. Alternating dual field absorption systems shall be designed with two (2) complete absorption fields, each sized a minimum of seventy-five percent (75%) of the total area required for a single field and separated by an effluent flow diversion valve. The diversion valve shall be constructed to resist five hundred pounds (500 lbs.) crushing strength, structurally sound and shall be resistant to corrosion. A valve placed below ground level shall be constructed so that it may be operated from the ground surface; and3. Sand-lined trenches may be used in areas where the soil has greater than fifty percent (50%) rock fragments and there are severe geological limitations. For a maximum loading rate of forty-five hundredths gallons per day per square foot (.45 gpd/sq. ft.) or a minimum of two hundred sixty-five square feet per bedroom (265 sq. ft./bedroom), the sand is not required to meet the requirements for intermittent sand filters. The material must be natural or manufactured sand and have no more than fifteen percent (15%) clay content. Manufactured sand shall be chat, fines manufactured from igneous rocks or chert gravel or manufactured from crushed glass. Crushed limestone is not acceptable. For higher loading rates, the sand must meet the requirements for an intermittent sand filter. A. In standard four-inch (4") pipe and gravel trenches, the depth of liner material must be twelve inches (12") below the gravel and at least six inches (6") on the sides of the gravel up to the top of the gravel. To place sand on the sides of the trenches, the trench walls must be excavated on a slope instead of vertically. The side slopes should be two horizontal to one vertical (2:1) and in no case steeper than one horizontal to one vertical (1:1).B. In gravelless pipe systems the minimum thickness of liner material is six inches (6") around the pipe.C. The effluent to sand-lined systems in areas of potential groundwater contamination should be equally distributed as much as practically possible. Serial and drop-box systems shall not be used. As a minimum, a distribution box shall be used to evenly distribute the effluent to the trenches. Dosing is recommended in order to more positively assure even distribution.D. The sand-lined trenches may be used, with the approval of the administrative authority, where the percentage of rock fragments is less than seventy percent (70%) for at least four feet (4') below the trench bottom. For sand-lined trenches to function properly, the permeability of the natural material should be similar to the permeability of the liner material. Sand-lined trenches must not be used over fragipans or other restrictive layers which have potential to perch water tables and could cause saturation of the liner material.(6) Alternative Systems. (A) General. The intent of this section is to provide minimum standards for the design, location, installation, use and maintenance of alternative sewage disposal systems in areas of limiting soil characteristics, where a standard system cannot be installed or a standard system is not the most suitable treatment. Where these systems are employed, they shall comply with all local codes and ordinances and should be subject to timely inspections to assure adherence to specifications. These systems, except for wastewater stabilization ponds, shall be designed and stamped by a licensed engineer. All absorption systems should have curtain drains, terraces or use of other flow diversion methods to minimize surface or ground water from loading the absorption field.(B) Adoption and Use. Where this rule is administered by an administrative authority, those administrative authorities may adopt this section in whole or in part as part of a local code or ordinance. Further, nothing in this rule or section shall require any administrative authority to allow the installation of any system in this section.(C) Low Pressure Pipe (LPP) System. A low pressure, two- to four-foot (2-4') pressure head, pipe system may be utilized where soil and site conditions prohibit the installation of a conventional or modified septic tank system due to the presence of shallow soil conditions, seasonally high water table conditions and slow soil permeability. The administrative authority may permit the use of a LPP system where there are cherty clay soils, severe geological limitations or both. The separation distance in these areas of concern for groundwater between the trench bottoms and bedrock shall be at least four feet (4') or more. The administrative authority may require that the hydraulic design of LPP systems be designed by an engineer. The administrative authority may also require the LPP trenches to be sand-lined if the soils have severely diminished treatment capability due to excessive rock content. The amount of rock fragments shall be less than fifty percent (50%) and in no case more than seventy percent (70%), unless the trenches are lined with sand.1. The LPP shall consist of the following basic components: A. A network of one- to two-inch (1- 2") diameter perforated PVC, one hundred sixty pounds per square inch (160 lbs./sq. in.) pipe or equivalent placed in natural soil at shallow depths, generally no more than twelve inches (12"), in narrow trenches not less than eight inches (8") in width and spaced not less than five feet (5') on center. Trenches shall include at least five inches (5") of pea gravel, if available; or if necessary, no less than three-quarter inch (3/4") crushed stone below the pipe and two inches (2") above the pipe; and four inches (4") of soil cover. The holes in the perforated pipe should be spaced from two feet (2') to no more than eight feet (8'). The minimum hole size is five thirty-seconds inch (5/32");B. A properly designed, two (2)-com-partment septic tank or other approved pre-treatment system and a pumping or dosing tank. The pumping or dosing tank shall be a minimum of five hundred gallons (500 gals.) or have the capacity to store one (1) day's flow above the pump on level, whichever is greater. The tank shall be provided with a filter or screen capable of preventing the passage of suspended solids to the soil absorption system;C. A submersible sewage effluent pump (not a sump pump) with appropriate on/off controls for controlled dosing and a high water alarm or other approved pressure dosing and distribution system; andD. A watertight supply manifold pipe for conveying effluent from the pump to the low pressure network.2. The soil and site criteria for low pressure pipe systems shall meet the following minimum requirements: A. LPP absorption fields shall not be installed on slopes in excess of ten percent (10%). LPP absorption fields may be installed on slopes greater than ten percent (10%), but require special design procedures to assure proper distribution of effluent over the absorption field;B. There shall be at least twenty-four inches (24") of separation between the naturally occurring soil surface and bedrock, water-impeding formation, seasonally high water table or evidence of chroma 2 mottles. This twenty-four-inch (24") depth shall consist of permeable soils with percolation rates less than or equal to sixty minutes per inch (60 min./in.) or be classified as SUITABLE or PROVISIONALLY SUITABLE in accordance with section (7) of this rule. The bottom of percolation test holes must be dug or bored to the bottom of the proposed trenches. The bottom of the proposed trenches must be located a minimum of one foot (1') above rock, water-impeding formation, seasonally high water table or where there is evidence of chroma 2 mottles. In areas where there are severe geological limitations and the soils have a high chert content, the bottom of the proposed trenches shall be at least four feet (4') above bedrock unless an evaluation by a registered geologist determines that the separation distance may be reduced;C. Components of the LPP shall not be located in depressions or areas subject to frequent flooding. Surface water, perched ground water and other subsurface lateral water movement shall be intercepted or diverted away from all components of the LPP. Final shape of the LPP distribution field shall be such that rainwater or runoff is shed;D. Location of the septic tank, pumping or dosing chamber and LPP absorption field is subject to the same horizontal setbacks specified in subsection (1)(D) of this rule. Horizontal setback distances in Table 1 shall be measured in the LPP absorption field from a margin of two and one-half feet (2 1/2') beyond the lateral and manifold pipes;E. An area that is at least equal in size to the LPP distribution field area plus a two and one-half foot (2 1/2') margin beyond the lateral and manifold pipes and which meets all other site and soil criteria shall be set aside for a replacement field; andF. There shall be no soil disturbance to an approved site for an LPP system except the minimum required for installation.3. The following application rates shall be used in determining the maximum application rate for low pressure pipe systems: A. In calculating the number of square feet for the absorption field (not square footage of trench bottom), the design sewage flow shall be divided by the application rate from Table 7. The lateral lines shall have a minimum spacing of five feet (5') on centers within the areas calculated for the absorption field area; and Table 7-Loading Rates Loading Rates
| Percolation Rate | Absorption Area | Loading Rate* |
| (min. in.) | (sq. ft./ bedroom) | (gal./sq. ft.) |
| <=10** | 200 | 0.6 |
| 11-30 | 300 | 0.4 |
| 31-45 | 400 | 0.3 |
| 46-60 | 600 | 0.2 |
* Gallons of sewage tank effluent per day per square foot of total area.
** In areas where there are severe geological limitations and the soils consist of very gravelly soils of thirty-five or greater percent (>=35%) gravels by volume, the loading rate of two-tenths gallons per day per square foot (0.2 gpd/sq. ft.) should be used even when the percolation rate would indicate a higher loading.
B. The systems shall be designed so that the discharge from any one (1) lateral line does not vary more than ten percent (10%) from the other laterals. All laterals shall have an envelope of trench rock surrounding the pipe. The trench rock shall be placed to a minimum depth of four inches (4") below the pipe and two inches (2") above the pipe.4. Design of the LPP shall comply with accepted practices and be specifically approved by the administrative authority. The system shall be designed and bear the seal of a Missouri registered engineer.(D) Wastewater Stabilization Ponds (Lagoon). A waste stabilization pond can provide satisfactory sewage disposal in rural areas where soils are not suited for absorption systems. Single residence wastewater stabilization ponds are not generally suitable in subdivisions with lots less than three (3) acres in size. No more than one (1) single family residence will be allowed on one (1) stabilization pond. 1. The following minimum separation distances may be modified as necessary to accommodate site requirements or local codes: A. The pond shall be located a minimum of seventy-five feet (75') from property lines as measured from the adjoining pond shoreline. However, this distance must be increased where necessary to be sure that all effluent is disposed upon the property from which it originated;B. The pond shall be located a minimum of two hundred feet (200') from the nearest existing residence and a minimum of one hundred feet (100') from the residence that it serves;C. The pond shall be located at least one hundred feet (100') from a potable water supply or pump suction line; andD. The pond shall be located at least fifty feet (50') from a stream, water course, lake or impoundment.2. Ponds may be utilized when there are no significant limitations related to ground-water from their use and the soils have been demonstrated to be very slowly permeable such as percolation rates slower than one hundred twenty minutes per inch (120 min./in.). There shall be either a minimum separation distance between the pond bottom and creviced bedrock of three feet (3') or installation of a clay liner with a minimum thickness of one foot (1') or a synthetic liner, either of which must be acceptable to the administrative authority. Percolation losses from the pond shall not exceed one-eighth inch (1/8") per day to prevent groundwater contamination or nuisance conditions. Site modifications may be accomplished to provide these soil requirements. In areas of severe geological limitations, restrictive layers such as fragipans shall be a minimum of twelve inches (12") thick and shall not be breached during construction.3. Steeply sloping areas should be avoided.4. Selection of the pond site should consider a clear sweep of the surrounding area by prevailing winds. Heavy timber should be removed for a distance of fifty feet (50') from the water's edge to enhance wind action and prevent shading.5. The administrative authority may require that a properly sized and constructed septic tank or aeration unit precede the pond. If irrigation of the effluent is required to maintain the wastewater on the property from which it originated, a septic tank or aeration unit should precede the pond. The use of a septic tank or aeration unit should not be used as a basis for reduction of the set-back distances as set forth in subparagraphs (6)(D)1.A.-D. of this rule.6. The pond shall be designed on the basis of four hundred forty square feet (440 sq. ft.) of water surface area per bedroom at the three-foot (3') operating level. This square footage may be reduced by a maximum of twenty percent (20%) if a septic tank, aeration unit or other pretreatment device precedes the pond. The minimum water surface area at the three-foot (3') level shall be nine hundred square feet (900 sq. ft.).7. A single cell is generally acceptable for single residence pond systems. If multiple cells are used for further polishing or storing of the effluent, the secondary cell should be one-half (1/2) the size of the primary cell.8. The minimum embankment top width shall be four feet (4'). The embankment slopes shall not be steeper than three to one (3:1) on the inner and outer slopes. Inner embankment slopes shall not be flatter than four to one (4:1). Outer embankment slopes shall be sufficient to prevent the entrance of surface water into the pond. Freeboard shall be at least eighteen inches (18") and preferably twenty-four inches (24"). Additional freeboard may be provided.9. To minimize erosion and facilitate weed control, embankments shall be seeded with a locally hardy grass from the outside toe to one foot (1') above the water line. Alfalfa or similar long-rooted crops which might interfere with the structure of the embankment shall not be used. Rip rap may be necessary under unusual conditions to provide protection of embankments from erosion.10. The influent line shall be of a sound, durable material of watertight construction of SDR 35 or greater. The line shall have a minimum diameter of four inches (4") and be laid on a firm foundation at a minimum grade of one-eighth inch (1/8") per foot from the point of entry into the pond. The influent line shall discharge as far as practical from the possible outlet side of the pond. A cleanout or manhole should be provided in the influent line near the pond embankment. From this point the line shall either be laid to the inner toe of the embankment and then on the bottom of the pond to the terminus point or the line shall be supported and secured every five feet (5'). A concrete splash pad three feet (3') square should be placed under the terminus of the pipe. The elevation of the cleanout or manhole bottom should be a minimum of six inches (6") above the high water level in the pond.11. The pond shall be shaped so there are no narrow or elongated portions. Round, square or rectangular cells are considered most desirable. Rectangular cells shall have a length not exceeding three (3) times the width. No islands, peninsulas or coves shall be permitted. Embankments should be rounded at corners to minimize accumulation of floating materials.12. The floor of the pond shall be stripped of vegetation and leveled to the proper elevation. Organic material removed from the pond area shall not be used in embankment construction. The wetted area of the pond must be sealed to prevent excessive exfiltration. Seals consisting of soils must be adequately compacted by the construction equipment.13. Embankments shall be constructed of impervious materials and compacted sufficiently to form a stable structure with very little settlement.14. Any effluent should be withdrawn from six inches (6") below the water surface. This can be accomplished by placing a tee on the inlet end of the pipe or by placing the outlet pipe eight to ten inches (8-10") lower on the inlet end than the outlet end of the pipe.15. The pond area shall be enclosed with a fence conforming to the following conditions: A. The fence shall be at least four feet (4') in height;B. The fence shall be welded, woven or chain link material with no smaller than fourteen gauge (14 ga.) wire. Cattle or hog panels can be substituted with a tee post being used for a line post;C. Fence posts shall be pressure-treated wood, galvanized and/or painted steel. Fence posts shall be driven, tamped or set in concrete. Line posts should be at least eighteen inches (18") deep and shall be spaced no more than ten feet (10') apart. Corner posts should be at least twenty-four inches (24") deep and shall be properly braced;D. The fence shall be of sound construction with no gaps or openings along the bottom;E. The fence shall be no closer than the center of the berm to the water's edge at the three-foot (3') deep operating level. Fence set-backs should not exceed thirty feet (30') from the water's edge;F. A properly hinged four foot (4') high gate or comparable materials shall be installed and provided with an effective latching device. The gate should be thirty-six to forty-eight inches (36-48") in width to accommodate maintenance and mowing equipment; andG. The fence must be completed prior to occupancy of the dwelling.16. Effluent from a pond must be disposed of on the property from which it originated. This may be accomplished by locating the outlet as far as practical from the property line and out of any natural drainage ditches or swales. The minimum distance from the outlet to a property line shall be one hundred feet (100'). Another method is to construct a terraced swale with a minimum length of one hundred fifty feet (150'). If these methods are unsuccessful, or whenever there is less than twelve inches (12") of permeable soil over a restrictive layer, controlled surface irrigation must be used. To utilize controlled surface irrigation, the pond must be capable of operating up to five feet (5') deep with one foot (1') of freeboard or have a second cell for storage. The administrative authority shall approve the method of effluent disposal.17. It may be necessary to introduce water into the pond to facilitate start-up of the biological processes, however, there shall be no permanent connection of any roof drain, footing drain or any source of rainwater to the wastewater stabilization pond.18. Odor problems caused by spring turnover of water, temporary overloading, ice cover, atmospheric conditions or anaerobic conditions may be controlled by broadcasting sodium or ammonium nitrate over the surface of the pond. In general, the amount of sodium or ammonium nitrate should not exceed two pounds (2 lbs.) per day until the odor dissipates.(E) Elevated Sand Mounds. Elevated sand mounds may be considered whenever site conditions preclude the use of absorption trenches. The construction of a mound shall be initiated only after a site evaluation has been made and landscaping, dwelling placement, effect on surface drainage and general topography have been considered. Due to the nature of this alternative system, actual selection of mound location, size of mound and construction techniques must be carefully considered and the criteria established in this rule implicitly followed. A set-back distance of fifty feet (50') from the downslope property line is recommended. 1. Elevated sand mounds shall not be utilized on soils where the high groundwater level as evidenced by mottling, bedrock or other strata having a percolation rate slower than one hundred twenty minutes per inch (120 min./in.) occurs within twenty-four inches (24") of natural grade. Up to four feet (4') of soil thickness over bedrock may be required in areas where there is a significant potential for groundwater contamination. Mounds shall be constructed only upon undisturbed naturally occurring soils.2. Elevated sand mounds are subject to the setback distances required in subsection (1)(D) of this rule.3. The fill material from the natural soil plowed surface to the top of the rock-filled bed shall be sand, loamy sand or sandy loam. Loading rates on the sand fill shall not exceed the values in Table 8. Table 8-Recommended Loading Rates
for Soil Textures Suited to Use as Fill in a Mound System
| Texture | Loading Rate |
| (gal./sq. ft./day) |
| Medium to |
| coarse sand | 1.2 |
| Fine sand | 1.0 |
| Loamy sand | 0.8 |
| Sandy loam | 0.6 |
Note: Rock fragments larger than one-sixteenth inch (1/16") shall not exceed fifteen percent (15%) by volume of the material used for sandy fill.
4. There shall be a minimum of one foot (1') of fill material and two feet (2') of naturally occurring soils between the bottom of the trench rock and the highest elevation of the limiting conditions as defined in paragraph (6)(E)1. of this rule.5. Whenever possible, mounds should be located on flat areas or crests of slopes. Mounds should not be located on natural slopes of more than six percent (6%) if the percolation rate is slower than sixty minutes per inch (60 min./in.) to a depth of at least twenty-four inches (24") below the sand layer. Mounds may be located on slopes up to a maximum of twelve percent (12%) if the soil percolation rate is faster than sixty minutes per inch (60 min./in.) to a depth of twenty-four inches (24") below the sand layer.6. In no case shall the width of the trench rock in a single bed exceed ten feet (10').7. The required bottom area of the trenches or bed and the effective basal area of the mound shall be based on one hundred twenty gallons per bedroom per day (120 gals./pbd). The basal area of the mound shall have the minimum area as shown in Table 9. Table 9-Loading Rate
| Percolation Rate | Loading Rate of Basal Area |
| (min./in.) | (gpd/sq. ft.) |
| 1-30 | 1.2 |
| 31-45 | 0.75 |
| 46-60 | 0.5 |
| 61-120 | 0.25 |
8. The area of sand fill shall extend beyond the basal area and the sides shaped to a three to one (3:1) or four to one (4:1) slope. The sand fill shall be covered with six inches (6") of fine textured soil and a final cap of six inches (6") of good topsoil applied. Also the mound shall be seeded with a hardy grass to establish a turf grass cover as soon as possible. No shrubs shall be planted on the top of the mound. Shrubs may be placed at the foot and side slopes of the mound.9. The land area fifty feet (50') down slope of the elevated sand mound is the effluent dispersal area and the soil in this area may not be removed or disturbed.10. Dosing shall be required for all elevated sand mounds. The mound shall be dosed not more than two (2) times per day. The size of the dosing pump shall be selected to maintain a minimum pressure of one pound per square inch (1 psi), two and three-tenths feet (2.3') of head, at the end of each distribution line. A. Perforation holes and hole spacing shall be determined to insure equal distribution of the effluent throughout the bed or trenches.B. The perforated pipe laterals shall be connected to a two-inch (2") diameter manifold pipe with the ends capped. The laterals shall be spaced no farther than forty inches (40") on center and no farther than twenty inches (20") from the edge of the trench rock. The perforated pipe laterals shall be installed level with the perforations downward. There shall be a minimum of nine inches (9") of trench rock below the laterals and two inches (2") above the laterals. The material used to cover the trench rock shall be untreated building paper, six inches (6") of compacted straw and three and one-half inch (3 1/2") unbacked fiberglass insulation or a geotextile.C. The manifold pipe shall be connected to the supply pipe from the pump. The manifold shall be sloped toward the supply pipe from the pump. Antibackflow valves are prohibited in the pump discharge line. The pump discharge line shall be graded to permit gravity flow to the absorption area or back to the dosing tank. Proper air relief and anti-siphon devices shall be installed in the piping to prevent siphoning of effluent from the dosing tank or from the mound.11. Prior to preparing the area selected for the mound, aboveground vegetation must be closely cut and removed from the ground surface. Prior to plowing, the dosing pump discharge line shall be installed from the pump chamber to the point of connection with the distribution manifold. The area shall then be plowed to a depth of seven to eight inches (7-8") parallel to the land contour with the plow throwing the soil upslope to provide a proper interface between the fill and natural soils. A rubber-tired tractor may be used for plowing but in no case shall a rubber-tired tractor be used after the surface preparation is completed. Tree stumps should be cut flush with the surface and the roots should not be pulled. The soil shall be plowed only when the moisture content of a fragment eight inches (8") below the surface is below the plastic limit.12. Mound construction shall proceed immediately after surface preparation is completed. A. A minimum of twelve inches (12") of sand fill shall be placed where the trench rock is to be located. A crawler tractor with a blade shall be used to move the sand into place. At least six inches (6") of sand shall be kept beneath equipment to minimize compaction of the plowed layer. The sand layer upon which the trench rock is to be placed shall be level.B. After hand leveling of the trench rock, the distribution system shall be placed and the pipes covered with two inches (2") of rock. After installation of the distribution system, the entire mound is to be covered with topsoil native to the area. The entire mound shall be crowned by providing twelve inches (12") of topsoil on the side slopes with a minimum of eighteen inches (18") over the center of the mound. The entire mound shall then have a turf grass cover established to assure stability of the installation.C. The area surrounding the elevated sand mound shall be graded to provide diversion of surface runoff waters.(F) Holding Tanks. The use of holding tanks is generally discouraged and their interim use should be limited to situations where construction of satisfactory sewage treatment and disposal systems will occur within one (1) year. Use of a holding tank must be specifically approved by the administrative authority on a case-by-case basis which may require stipulations in a signed agreement regarding the use and the length of time for use of the holding tank. 1. A holding tank shall be constructed of the materials and by the same procedures as those specified for watertight septic tanks.2. A cleanout pipe of at least six inches (6") diameter shall extend to the ground surface and be provided with seals to prevent odor and exclude insects and vermin. A manhole of at least twenty inches (20") least dimension shall extend through the cover to a point within twelve inches (12") but no closer than six inches (6") below finished grade. The manhole cover shall be covered with at least six inches (6") of earth.3. The tank shall be protected against flotation under high water table conditions. This shall be achieved by weight of the tank, earth anchors or shallow bury depths.4. For a residence, the size shall be one thousand gallons (1000 gals.) or four hundred gallons (400 gals.) times the number of bedrooms, whichever is greater. For permanent structures, other than residences, the capacity shall be based on measured flow rates or estimated flow rates. The tank capacity shall be at least five (5) times the daily flow rate.5. Holding tanks shall be located as follows:A. In an area readily accessible to the pump truck under all weather conditions;B. As specified for septic tanks in Table 1 set forth in subsection (1)(D) of this rule; andC. Where accidental spillage during pumpage will not create a nuisance.6. A contract for disposal and treatment of the sewage wastes shall be maintained by the owner with a pumper, municipality, agency or firm which possesses a current and valid permit issued by the Department of Natural Resources for such activity.7. Holding tanks shall be monitored to minimize the chance of accidental sewage overflows. Techniques such as visual observation, warning lights or bells, or regularly scheduled pumping shall be used. For commercial establishments, a positive warning system shall be installed which allows twenty-five percent (25%) reserve capacity after actuation.8. Holding tanks used in conjunction with permanent black water/gray water systems must conform to the requirements of this section except that the minimum size tank is one thousand gallons (1000 gals.). In these situations, the holding tank is to receive toilet wastes only.(G) Sand Filters. Septic tanks or aeration units and sand filters may be used along with soil absorption systems in soils with percolation rates between sixty and one hundred twenty minutes per inch (60-120 min./in.). These systems must be specifically approved by the administrative authority. 1. The septic tank and aeration units must be in accordance with section (4) of this rule. Setback distances as shown in Table 1 and as specified in subsection (1)(D) of this rule shall apply except that the minimum distance to the downslope property line should be fifty feet (50').2. The following shall apply to gravity flow sand filter systems: A. All piping in a sand filter shall be four inch (4") polyvinyl chloride (PVC). Perforated pipe should be used for distribution and collection lines;B. All sand filters shall be dosed at two (2) times per day. Dosing shall provide uniform distribution of wastewater throughout the filter cross-section and allow time for reaeration of the pore spaces to occur. Dosing may be accomplished by either pumps or siphons;C. Effluent from filter underdrains must be collected and disposed of properly. Effluent shall not discharge off the owner's property;D. Buried sand filters shall be in conformance with Table 10 of this rule. One (1) collector line shall be provided for every six feet (6') of bed width, with a minimum of two (2) collector lines per bed. The collector lines shall have a minimum grade of one percent (1%). (I) Distribution lines shall be level and spaced a maximum of three feet (3') apart. Each distribution line must be vented (downstream end) or connected to a common vent. Vents should extend at least twelve inches (12") above the ground surface with the outlet screened or capped (perforated).(II) Septic tank effluent shall be applied to the filter through a distribution box. Buried filters shall be dosed with a pump or siphon. The dosing volume shall be sufficient to fill the pore spaces in the gravel to a depth of four inches (4"). For single bed filters receiving septic tank effluent, the hydraulic loading rate shall not exceed one gallon per day per square foot (1 gpd/sq. ft.) with a maximum organic loading of one and three-fourths pounds (1 3/4 lbs.) of biological oxygen demand (BOD) per day per one thousand square feet (1000 sq. ft.) of surface area. Total surface area shall not be less than two hundred square feet (200 sq. ft.); andE. Open sand filters are similar to buried filters with the exception that no soil backfill or gravel is used on the top of the sand and the filter must be enclosed within concrete walls or other substantially equivalent material. Open sand filters shall be in conformance with Table 10. (I) Distribution of wastewater shall be applied by pipes directly over the sand surface at the center of the bed or at the four corners. Splash plates beneath points of discharge must be used to prevent erosion of the sand. Curbs around the splash plates or large stones placed around the periphery of the plate will help prevent scouring. All exposed pipes shall slope to drain.(II) Filter walls shall be concrete, masonry, compacted clay, high density polyethylene plastic with a minimum thickness of thirty (30) mil, or other material acceptable to the administrative authority; and extend six inches (6") above the sand and six inches (6") above the adjacent ground level.(III) Dosing shall flood the bed to a depth of two inches (2") with a hydraulic loading of two to five gallons per day per square foot (2-5 gpd/sq. ft.) (septic tank effluent). Maximum organic loading is five and thirteen-hundredths pounds (5.13 lbs.) of BOD per day per one thousand square feet (1000 sq. ft.) of surface area.(IV) The filter may be covered to provide protection against severe weather, prevent growth of weeds and to keep children and animals out of the filter. Such cover may include six inches (6") of clean one to two inch (1-2") gravel, if so designed by an engineer as part of the system. In such event, a vent for the system would not be required if so determined by the engineer.