Title 19—department of health and senior services division 20—Division of Community and Public Health Chapter 3—General Sanitation


Table 4—Dwelling Septic Tank Capacity*



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Table 4—Dwelling Septic Tank Capacity*
Number

of Minimum Liquid

Bedrooms 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; and

17. 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; and

3. 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; and

B. 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; and

5. 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
Absorption

Percolation Loading Loading

Rate Area Rate

(sq. Ft./ (gal./sq.

(min./in.) bedroom) 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; or

D. 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; and

E. 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 (120°) apart along the bottom half of the tubing, each sixty degrees (60°) from the bottom centerline. The tubing shall be marked with a visible top location indicator one hundred twenty degrees (120°) 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 gravelless 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 IVa 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; and

G. 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; and

D. 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; and

3. 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)-compartment septic tank or other approved pretreatment 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; and

D. 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; and

F. 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




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