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

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Table 7—Loading Rates

Loading Rates
Percolation Absorption Loading

Rate Area Rate*

(sq. ft./

(min. in.) 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; and

D. 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 groundwater 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; and

G. 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
Loading Rate

Percolation 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; and

C. 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.); and

E. 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.


3. The following shall apply to pressure dosed sand filter systems:

A. Conventional pressure dosed sand filters use an intermittent filter with two feet (2') or more of medium sand designed to filter and biologically treat sewage tank effluent from a pressure distribution system at an application rate not to exceed one and twenty-five hundredths gallons per square foot (1.25 gals./sq. ft.) sand surface area per day, applied at a dose not to exceed one-half gallon (1/2 gal.) per orifice per dose. These sand filters may be buried or open.

B. Recirculating pressure dosed sand filters use a recirculating filter with two feet (2') or more of medium filter media designed to filter and biologically treat sewage tank effluent from a pressure distribution system at an application rate not to exceed five gallons per square foot (5 gals./sq. ft.) filter surface per day, applied at a dose not to exceed two gallons (2 gals.) per orifice per dose. These sand filters shall be uncovered and open to the surface.

C. Minimum filter area for these filters shall be as follows:

(I) Conventional pressure dosed sand filters for single family residences shall be a minimum of three hundred and sixty square feet (360 sq. ft.) in surface area with a design sewage flow not to exceed six hundred gallons (600 gals.). If sand filter design flows exceed an average of four hundred and fifty gallons per day (450 gpd), the minimum sand surface will be based on one and twenty-five hundredths gallons per day per square foot (1.25 gpd/sq. ft.); and

(II) Pressure dosed sand filters for commercial facilities shall be sized on the basis of projected daily sewage flow. If the waste strength is proposed to be greater than residential strength waste, pretreatment shall be required which will reduce the biological oxygen demand to levels not to exceed three hundred (300), total suspended solids to levels not to exceed one hundred-fifty (150), and oil and grease to levels not to exceed twenty-five (25). The minimum sand surface will be based on two to five gallons per day per square foot (2–5 gpd/sq. ft.).

D. Design criteria shall include the following:

(I) Sewage tanks shall be in accordance with section (4) of this rule. Set-back distances as shown in Table 1 of subsection (1)(D) and as specified in subsection (1)(E) of this rule shall apply, unless a variance has been allowed by the administrative authority. Tanks shall be watertight and tested in the field. The test shall be performed by filling the tank two inches (2") above the riser inlet. At the end of the first twenty-four (24)-hour period, the tank water level should be refilled. After another twenty-four (24)-hour period, no more than one inch (1”) of water should have dropped from the original reading. All sewage and pump tanks will be supplied with vandal-proof access risers to grade over the pump units. Risers should have a waterproof epoxy seal between the tank and riser;

(II) Pumping systems for a pressure dosed sand filter system should provide pumping apparatus that is capable of filtering gross solids larger than one-eighth inch (1/8") and draw from the clear zone near the outlet side of the sewage tank. This zone is described as the layer of effluent between the sludge and scum layers of the sewage tank. Pumps should be able to deliver adequate head pressure to control orifice plugging. Pumps should be made of a corrosive resistant material such as Type 316 stainless steel, suitable plastic, or 85-5-5-5 bronze. Screens should have at least ten square feet (10 sq. ft.) of surface area, with one-eighth inch (1/8") openings;

(III) Operation controls should be on a timer dose that distributes the average daily flow over an eighteen (18)-hour period. Recirculating filters will be set to recirculate five (5) times the average daily flow over a twenty-four (24)-hour period. Systems should be designed with a high water alarm and light signal. Control panels should be located on an exterior location. Control operations should be located in an area available for maintenance;

(IV) Intermittent filter media shall be a mixture of sand or durable inert particles with one hundred percent (100%) passing the three-eighths inch (3/8") sieve; ninety to one hundred percent (90–100%) passing the No. 4 sieve; sixty-two to one hundred percent (62–100%) passing the No. 10 sieve; forty-five to eighty-two percent (45–82%) passing the No. 16 sieve; twenty-five to fifty-five percent (25–55%) passing the No. 30 sieve; ten percent (10%) or less passing the No. 60 sieve; four percent (4%) or less passing the No. 100 sieve; or sand meeting the ASTM-C 33 concrete sand specification minus four percent (4%) or less passing the No. 100 sieve. All drainage rock should be a river washed, hardened and weathered rock. The treatment media will be two inches (2") deep and of a coarse media with an effective size of one and one-half to three millimeters (1 1/2–3 mm) and a uniformity coefficient of less than two (2). Limestone or dolomite is not acceptable for drainage rock;

(V) Recirculating filter media shall be a mixture of sand or durable inert particles with one hundred percent (100%) passing the three-eighths inch (3/8") sieve; seventy-nine to one hundred percent (79–100%) passing the No. 4 sieve; eight to ninety-two percent (8–92%) passing the No. 8 sieve; zero to fifteen percent (0–15%) passing the No. 30 sieve; zero to one percent (0–1%) passing the No. 50 sieve. All drainage rock should be a river washed, hardened and weathered rock. The treatment media will be two inches (2") deep and of a coarse media with an effective size of one and one-half to three millimeters (1–1/2 3 mm) and a uniformity coefficient of less than two (2). Limestone or dolomite is not acceptable for drainage rock; and

(VI) Container designs may be concrete containers consisting of watertight walls and floors to prevent groundwater from infiltrating or effluent from exfiltrating from the filter. All penetrations through the walls shall be watertight. Containers may also consist of a thirty (30) mil polyvinyl chloride liner covering the sand filter bottom and side wall areas. Polyvinyl chloride liners should be supplied with repair kits and boots for passage through the liner wall. The bottom area of the liner should be bedded in two inches (2") of leveling sand. The liner should be constructed to form a waterproof membrane between the trench bottom and trench walls. The polyvinyl liner should incorporate all seams to be a chemically or heat bonded waterproof seam.

E. The filter design criteria shall include the following:

(I) The interior base of the filter container shall be level or constructed at a grade of one percent (1%) or less to the underdrain pipe elevation;

(II) The underdrain piping shall consist of a pipe with one-fourth inch (1/4") grooves cut every four inches (4") along the pipe length to a depth of one-half (1/2) of the pipe diameter. The bottom of the filter container shall be covered with a minimum of six inches (6") of drain media. The underdrain pipe shall be enveloped in an amount and depth of drainage rock to prevent migration of the underdrain media into the pipe perforations;

(III) A minimum of twenty-four inches (24") of approved filter media shall be installed over the underdrain media. The media shall be damp at the time of installation to insure compaction of the media. The top surface of the media shall be level;

(IV) There shall be a minimum of three inches (3") of clean drain media below the distribution laterals, and sufficient media above the laterals equal to or covering the orifice shields and/or pipe;

(V) Distribution laterals shall be evenly spaced on minimum, thirty-inch (30") centers. Orifices shall be placed such that there is one (1) orifice or more on average per six square feet (6 sq. ft.) of sand surface. Orifice holes shall be one-eighth inch (1/8") in diameter. The diameter of the piping manifold and lateral shall be no less than one-half inch (1/2"). The ends of the distribution laterals should be constructed with a means to perform flushing of the piping, collectively or individually, through the operation of a flushing valve. The flushed effluent may be discharged to the sand filter;

(VI) The top of the intermittent media in which the pressure distribution system is installed shall be covered with a breathable nylon or polypropylene spun filter fabric rated at eighty-five hundredths ounce per square yard (0.85 oz./sq. yd.) to eliminate soil intrusion into the filter media. Recirculating filters shall be open-topped;

(VII) The top of the intermittent sand filter area shall be backfilled with a soil cover, free of rocks, vegetation, wood waste, etc. The soil cover shall have a textural class of loamy sand. The soil cover shall have a minimum depth of six inches (6") and a maximum depth of twelve inches (12"). Intermittent sand filters designs may delete soil cover and incorporate three to six inches (3–6") of a quality cypress or cedar mulch over the entire filter area;

(VIII) Where the effluent from a sand filter is to be discharged via a pump, the pump and related apparatus shall be housed in a vandal resistant vault designed to withstand the stresses placed upon it and not allow the migration of drain media, sand or underdrain media to its interior. The vault shall have a durable, affixed floor. The vault shall provide watertight access to the finished grade with a diameter equal to that of a gravity discharge sand filter. The depth of the underdrain and the operational level of the pump cycle and alarm shall not allow effluent to come within two inches (2”) of the bottom of the sand filter media. The pump off level shall be no lower than the invert of the perforations of the underdrain piping. The internal sand filter pump shall be electrically linked to the sand filter dosing apparatus in such a manner as to prevent effluent from entering the sand filter in event the internal sand filter pump fails; and

(IX) Other sand filters which vary in design from those described in this rule may be authorized by the administrative authority if they can be demonstrated to produce a comparable effluent quality.

F. Effluent from these sand filters may discharge to the ground surface, provided the effluent is maintained on the owner’s property and the following separation distances are maintained:

(I) The discharge shall be a minimum of one hundred feet (100') from private water supply wells; one hundred-fifty feet (150') from unplugged abandoned wells or wells with less than eighty feet (80') of casing; and three hundred feet (300') from public water supply wells;

(II) The discharge shall be a minimum of one hundred feet (100') from springs; five hundred feet (500') from the edge of surficial sink holes; fifty feet (50') from a classified stream; and twenty-five feet (25') from a stream or open ditch; and

(III) The discharge shall be a minimum of seventy-five feet (75') from property lines.

G. If effluent can not meet the minimum separation distances as described in subparagraph (6)(G)2.F., then the effluent must be disposed of into a soil absorption system. The required footage of the soil absorption system may be reduced by up to one-third (1/3) of that required for a conventional soil absorption system. Shallow bury designs should be utilized whenever possible to achieve the best absorption rates.

(H) Drip Soil Absorption. Drip soil absorption also known as trickle irrigation may be approved by the administrative authority in accordance with section (6) of this rule. Due to the various pretreatment methods and appurtenances and lack of extensive experience, drip soil absorption systems must be viewed as experimental, and back-up design for another system shall be approved in case of failure of the drip soil absorption system.

1. Drip lines shall be placed two feet (2') apart in a parallel arrangement. Emitters shall be placed in the drip lines every two feet (2') so there will be a two-foot by two-foot (2'×2') grid pattern. Other configurations and spacings of the drip line and emitters may be used; however, each emitter will be considered to cover four square feet (4 sq. ft.) of absorption area.

2. The application rate shall not exceed the values as shown in Table 7 for low pressure pipe systems in subparagraph (6)(C)3.A. of this rule.

3. Drip soil absorption systems may be allowed at sites where the soil is classified as being in group IVb. A minimum separation distance of twelve inches (12") shall be maintained between the drip lines and emitters and a high ground water table or other limiting condition. The maximum application rate for IVb soils shall be from five-hundredths to one-tenth gallons per day per square foot (0.05 0.10 gpd/sq. ft.) of absorption field

(I) Wetlands. Constructed wetlands provide secondary levels of treatment, which means that some form of pretreatment (septic tank, aeration tank, lagoon, etc.) must be used prior to the wetland, as wetlands cannot withstand large influxes of suspended solids. The pretreatment used must be capable of removing a large portion of these solids. Effluent from wetlands must be contained on the owner’s property with the same set-back distances as required for lagoons in Table 1, located in subsection (1)(D) of this rule.

1. Free water surface wetlands are shallow beds or channels with a depth less than twenty-four inches (24") and filled with emergent aquatic plants. This type of wetland shall not be allowed.

2. Submerged flow wetlands are similar to free water surface wetlands except that the channels are filled with shallow depths of rock, gravel or sand. The depth of the porous media is usually less than eighteen inches (18”). The porous media supports the root systems of the emergent aquatic vegetation. The water level is to be maintained below the top of the porous media so that there is no open water surface.

3. The surface area of wetlands shall be determined by using the following equation:

As = [Q(inCo — InCe)]/(kT × f × d)

where: As = wetland surface area, sq. ft.

Q = daily flow rate to wetland,

cu.ft./day([gallons/day]÷7.5);

Co = influent BOD5 concentration,

mg/L;


Ce = effluent BOD5 concentration,

mg/L;


kT = temperature dependent rate

constant, per day;

d = water depth in wetland, ft; and

f = void fraction of rock media,

decimal.
4. After a surface area has been determined, a cross-sectional area shall be calculated against hydraulic loading by using the following equation:
Ah = Q/(Kh × S)

where: Ah = cross-sectional area (hydraulic

loading), sq. ft.;

Kh = hydraulic conductivity of rock

media, ft./day*; and

S = slope of wetland bottom, deci-

mal
 * A value of eight hundred feet per day (800 ft./day) may be used for the hydraulic conductivity for rock of one inch (1") diameter.
** Values for slope should range between twenty-five hundredths and one percent (0.25 –1%).
5. After the hydraulic loading has been determined, an organic loading shall be calculated using the following equation:
Ao = OGL/0.05

where: Ao = cross-sectional area (organic

loading), sq. ft.; and

OGL = organic loading, lbs BOD5/day.

6. The larger of the two (2) calculations, the hydraulic loading or the organic loading, shall be used to determine the wetland dimensions. Wetlands should not be long and narrow.

7. The width of the wetland shall be calculated by dividing the larger cross-sectional area by the water depth. The calculated width should not be less than one-third (1/3) of the length (a length: width ratio of three to one (3:1)). Should it be necessary to construct a wetland with a ratio greater than three to one (3:1), step-loading along the length of the wetland shall be considered.

8. The configuration of a wetland for an individual home can be a one (1) cell or two (2) cells in series, depending upon the soil properties at the site. Larger systems may consist of multiple cells in parallel or series in order to provide more management options.

A. Single cells may be used where there will be no percolation of water through the bottom of the wetland. Water movement properties of the soil at the wetland construction site must be determined either by use of properly performed percolation tests or a thorough soil profile analysis performed by a qualified person meeting the criteria of 19 CSR 20-3.080.

B. For soils with percolation rates of sixty minutes per inch (60 min./in.) or less and where geological limitations are not severe, a two (2)-cell wetland may be used. The first cell shall be lined, allowing no percolation. The second cell may be unlined and filled with sand (not rock) to promote some percolation from the bottom of the wetland. The second cell shall not be larger than the first cell.

9. Crushed limestone or other rock with sharp edges shall not be used for a porous media as this type of rock will compact with time. Rock with rounded edges, such as creek gravel, shall be used. Rock must be thoroughly washed to remove fines which may cause plugging. Rock substrate size should be one inch (1") diameter, while rock to be used around inlet and outlet pipes may be two to four inches (2–4") diameter to reduce potential clogging. A three to four inch (3–4") layer of washed pea gravel may be used on top of the one inch (1") substrate for decorative purposes.

10. All piping shall be SDR 35 sewer pipe, Schedule 40 polyvinyl chloride (PVC) DWV pipe, or material of equivalent or stronger construction. Piping shall be a four inch (4”) diameter.

11. Influent shall be distributed and effluent collected by header pipes running the width of the wetland. Perforated sewer pipe can be used for the headers. For unperforated pipe, a one and one-half inch (1 1/2”) hole shall be drilled every twelve inches (12”) along the header. Headers shall be placed at the bottom of the wetland on a bed of rock and covered with two to four inch (2–4”) rock. A cleanout shall be placed before the influent header.

A. If effluent from the septic tank flows to the wetland by gravity and there are parallel cells in the wetland, a distribution box shall be placed ahead of the wetland so that flow can be controlled to individual cells.

B. If effluent is pumped, the pumping rate shall not exceed twenty-five gallons per minute (25 gpm) and no more than one-third (1/3) of the daily design flow shall be pumped at one (1) time.

12. Water level in a wetland shall be controllable. The range of control shall be from two inches (2") above the surface of the rock to complete draining of the wetland. Maximum water level in the wetland shall be a minimum of twelve inches (12") below the outlet of the septic tank so that water does not back up into the septic tank.

A. To conveniently check the water level relative to the gravel surface, a four inch (4") diameter perforated pipe may be placed in the bottom of the wetland, through the channel embankment, and then elbowed up to the elevation of the top of the channel.

B. Water level control may be obtained by use of swivel standpipes or collapsible tubing.

13. Surface water shall be kept out of the wetland. This may be accomplished by diverting runoff away from the wetland or constructing an earthen berm around the wetland. Berms shall be a minimum of six inches (6") above the surface of the porous media.

14. Emergent plants shall be selected by the ability of the plants to: root and grow in the wastewater-rock environment, treat wastewater to acceptable levels, produce biomass in amounts that can be controlled and aesthetics. Reference may be made to Tables 11 and 12 in selecting desired plants.

(J) Privy. A privy will be allowed only under limited conditions and will not be recognized as a method of sewage disposal for a continuously occupied dwelling, business or other structure. A privy will only be considered for remote area not served by a piped water source. Example of these areas may be rural cemetery, a rural church with a small congregation and where hand-washing facilities are available, or a river access point provided by the Department of Conservation. Plans and construction of a privy will need to meet the approval of the administrative authority.

1. The privy shall be use to receive only human excreta and toilet paper. The privy shall not be used as a depository for other wastes.

2. A pit shall be provided for the privy. The sides of the pit shall be curbed to prevent cave-in. If the pit has an earth bottom, the bottom shall be at least three feet (3') above saturated soil conditions. If this separation distance cannot be achieved in the location of the privy, then the pit shall be liquid tight.

3. The pit shall be periodically pumped out by someone who services septic tank systems. At no time shall the pit contents be allowed to accumulate to within one foot (1') of the pit top. The pit contents shall then be transported and disposed into a community sewer system that is in compliance with Chapter 644, RSMo.

4. Both the pit and the privy shall be vented, Inspect-proof openings shall be placed in the walls, below the seat. A vent shall extend from the underside of the seat board through the roof or up to a horizontal vent open to the sides of the toilet. This vent must be flush with the underside of the seat board and shall not extend down into the pit. All vent openings to the outside shall be properly screened to keep out insects. The top of the privy shall have a screened opening on each side. It is preferable the opening be all the way around the top of the privy in order to allow to allow air to pass through and to carry away any odors which may seep into the upper part of the structure. If a crescent-shaped opening is cut into the door or wall of the privy, it shall also be screened.

5. The inside of the privy shall be of durable, smooth, nonabsorbent material. If wood is used, the inside of the structure shall be coated with a polyurethane-type coating so as to minimize the penetration of liquids and odors into the wood.

6. A tight-fitting door, preferably with a self-closing feature, such as a door spring, shall be used.

7. A privy shall be set back from surface waters, buildings, property lines and water supply wells the same distance as required for soil treatment areas. This information may be found in subsection (1)(D), Table 1 of this rule.

8. The privy shall be of sufficient capacity for the facility it serves, but shall have at least fifty cubic feet (50 cu. ft.) of capacity.

9. Abandoned pits shall have the contents removed, transported and disposed into a community sewer system that is in compliance with Chapter 644, RSMo. This activity shall be performed by someone who services septic tank systems. The pit shall then be filled with clean earth and slightly mounded to allow for settling.

(K) Other Systems. Where unusual conditions exist, special systems of treatment and disposal, other than those specifically mentioned in this rule, may be employed provided—

1. Reasonable assurance of performance of the system is presented to the administrative authority;

2. The engineering design of the system is first approved by the administrative authority;

3. Adequate substantiating data indicate that the effluent will not contaminate any drinking water supply, groundwater used for drinking water or any surface water;

4. Treatment and disposal of the wastes will not deteriorate the public health and general welfare;

5. Discharge of effluent, if any, shall be within set-back distances as described in Table 1, located in subsection (1)(D) of this rule; and

6. These systems comply with all applicable requirements of this rule, with all local codes and ordinances, and all applicable requirements of sections 701.025–701.055 and Chapter 644, RSMo.

(L) Variances. Variances may be considered and granted by the administrative authority concerning repair to on-site sewage disposal systems existing prior to January 1, 1996 with site limitations or for property platted prior to January 1, 1996 with site limitations. Where variances have been allowed from the standards, the administrative authority may require that a higher level of pretreatment than that of a septic tank be provided. At the discretion of the administrative authority and with relative assurance for protection of the public health and preservation of the quality of surface and ground waters, variances may be allowed for the following:

1. Setbacks as specified in Table 1, located in subsection (1)(D) of this rule.

2. Minimum distance between the infiltrative surface and restrictive feature or bedrock.

3. Minimum areas for infiltrative surfaces as shown in Table 5 (see (5)(A)4.), Table 6 (see (5)(A)16.C.), Table 7 (see (6)(C)3.A.), Table 8 (see (6)(E)3.), Table 9 (see (6)(E)7.) and Tables 13 and 14 (see (7)(M)) of this rule.

4. A written application for a variance shall be provided to the administrative authority and shall provide the following:

A. An explicit description explaining why the requirements of this rule cannot be complied with, including a description of specific sections of this rule for which a variance is being requested;

B. A design of the proposed system. The design shall show that as much soil absorption as is practically possible will be installed;

C. The existing and maximum occupancy pattern and the existing water usage records, if any;

D. Potential impact, if any, on neighboring property owners and the names and mailing addresses of these property owners; and

E. Adequate substantiating data to indicate that the effluent will not contaminate any drinking water supply, groundwater used for drinking water or any surface water.

5. These systems shall comply with all applicable requirements of these standards except where variances have been granted.

6. No variance will be granted for any system that would result in noncompliance with Chapter 644, RSMo Missouri Clean Water law and subsequent rules. On-site sewage disposal systems with a discharge, other than a system serving a single family residence lot, must be referred to the Department of Natural Resources and comply with Chapter 644, RSMo, Missouri Clean Water Law and subsequent rules.

7. If effluent can not meet the minimum separation distances as described in Table 1 of subsection (1)(D), then the effluent must be disposed of into a soil absorption system. Set-back distances for lagoons will be considered applicable to alternative systems. The required footage of the soil absorption system following alternative systems may be reduced by up to one-third (1/3) of that required for a conventional soil absorption system. Shallow bury designs should be utilized whenever possible to achieve the best absorption rates.

8. All adjacent and/or affected property owners shall be notified in writing by the administrative authority whenever consideration for granting a variance is likely to result in effluent crossing property lines. The party requesting the variance shall be responsible for supplying the names and addresses of all adjacent and/or affected property owners to the administrative authority. Adjacent and/or affected property owners shall be allowed thirty (30) days from the date of the written notification to contact the administrative authority to express comments concerning the consideration of granting a variance.

9. In cases of complaint abatement, where effluent cannot be maintained on the owner’s property, within the required set-back distances and presents a nuisance or threat to public health or surface or ground water quality, the administrative authority may require a holding tank be placed at the optimum location within the sewage system, in order to abate the complaint. The owner shall be responsible for assuring the holding tank is pumped as needed, with the contents being disposed of in a Department of Natural Resources permitted facility.

(7) Detailed Soils Evaluation.

(A) General. The intent of this section is to provide minimum standards for site evaluations based upon evaluation of the soil characteristics, namely texture, color, structure, drainage and depth. Criteria are also given for sizing standard systems and some alternative systems.

(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. Nothing in this rule or section shall require any administrative authority to allow an installation based upon the criteria contained in this section. The administrative authority may require percolation tests in addition to evaluation of soil characteristics. Whenever percolation tests and these criteria are used, the size of the proposed system or suitability of a site should be based upon which criteria produce the most conservative system. This type evaluation should be conducted by a professional soil scientist, engineer, sanitarian or registered geologist with special training in determining soil morphological characteristics in the field.

(C) Site Evaluation. An investigation of a proposed soil absorption site shall consider the following factors:

1. Topography and landscape position;

2. Soil characteristics (morphology) which includes texture, structure, porosity, consistence, color and other physical, mineral and biological properties of various horizons, and the thickness and arrangement of the horizons in the soil profile;

3. Soil drainage, which includes both external (surface) and internal (soil);

4. Soil depth;

5. Restrictive horizons; and

6. Available space.

(D) Site evaluations shall be made in accordance with subsections (7)(E)–(M) of this rule. Based on this evaluation, each of the factors listed in subsection (7)(C) of this rule shall be classified as suitable, provisionally suitable or unsuitable.

(E) Topography and Landscape Position. Uniform slopes under fifteen percent (15%) shall be considered suitable with respect to topography. 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 lines shall follow the contour of the ground.

1. Uniform slopes between fifteen percent (15%) and thirty percent (30%) shall be considered provisionally suitable with respect to topography, if the soils are thirty-six inches (36") or more thick. 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 period. Usable areas larger than minimum are ordinarily required in this slope range.

2. Slopes greater than thirty percent (30%) shall be considered unsuitable except when a thorough study of the soil characteristics indicates that a soil absorption system will function satisfactorily and sufficient ground area is available to properly install such a system. Slopes greater than thirty percent (30%) may be classified as provisionally suitable when all of the following conditions are met:

A. The slope can be terraced or otherwise graded or the absorption lines located in naturally occurring soil to maintain a minimum ten-foot (10') horizontal distance from the absorption trench and the top edge of the fill embankment;

B. The soil characteristics can be classified as suitable or provisionally suitable to a depth of at least one foot (1') below the bottom of the absorption trench;

C. Surface water runoff is diverted around the absorption field so that there will be no scouring or erosion of the soil over the field;

D. If necessary, groundwater flow is intercepted and diverted to prevent the water from running into or saturating the soil absorption system; and

E. There is sufficient ground area available to install the septic tank system with these modifications.

3. Complex slope patterns and slopes dissected by gullies and ravines shall be considered unsuitable to topography.

4. Areas subject to frequent flooding shall be considered unsuitable to landscape positions.

5. Depressions shall be considered unsuitable with respect to landscape positions except when the site complies essentially with the requirements of this section and is specifically approved by the administrative authority.

6. If directed by the administrative authority, the surface area on or around a ground absorption system sewage treatment and disposal system shall be landscaped to provide adequate drainage. The interception of perched or lateral groundwater movement shall be provided where necessary to prevent soil saturation on or around the ground absorption sewage treatment and disposal system.

(F) Soil Characteristics (Morphology). Soil borings or pits shall be taken at the site to be used for soil absorption systems. These borings shall be taken to a depth of forty-eight inches (48") or as required to determine the soil characteristics. Soil borings or pits and core samples shall be evaluated and a determination made on the suitability of the soil to treat and absorb septic tank effluent. The important soil characteristics which shall be reviewed by the administrative authority are as follows:

1. The relative amounts of the different sizes of mineral particles in a soil are referred to as soil texture. All mineral soils are composed of sand, two to five hundredths millimeters (2–.05 mm) in size; silt, which includes intermediate-sized particles that cannot be seen with the naked eye but feel like flour when pressed between the fingers, five hundredths to two thousandths millimeter (0.05–0.002 mm) in size; or clay, which is extremely small in size and is the mineral particle that gives cohesion to a soil, less than two thousandths millimeters (0.002 mm) in size or a combination of these. The texture of the different horizons of soils may be classified into five (5) general groups and shall be used for determining the application rates shown in Tables 6 and 7 of this rule.

A. Soil Group I. Sandy texture soils contain more than seventy percent (70%) sand-sized particles in the soil mass. These soils do not have enough clay to be cohesive. Sandy soils have favorable sewage application rates, but may have a low filtering capacity leading to malfunction due to contamination of groundwater. The sandy group includes the sand and loamy sand soil textural classes and shall generally be considered suitable in texture.

(I) Sand. Sand has a gritty feel, does not stain the fingers and does not form a ribbon or ball when wet or moist.

(II) Loamy sand. Loamy sand has a gritty feel, stains the fingers (silt and clay), forms a weak ball and cannot be handled without breaking.

B. Soil group II. Coarse loamy texture soils contain more than thirty percent (30%) sand-sized particles and fewer than twenty percent (20%) clay-sized particles in the soil mass. They exhibit slight or no stickiness. The coarse loamy group includes sandy loam and loam soil textural classes and shall generally be considered suitable in texture.

(I) Sandy loam. Sandy loam feels gritty and forms a ball that can be picked up with the fingers and handled with care without breaking.

(II) Loam. Loam may feel slightly gritty but does not show a fingerprint and forms only short ribbons ranging from twenty-five hundredths to fifty hundredths inch (.25–.50") in length. Loam will form a ball that can be handled without breaking.

C. Soil group III. These fine loamy texture soils contain fewer than forty percent (40%) clay-sized particles and not more than thirty percent (30%) sand-sized particles in a soil mass. Also this group is limited to less than thirty-five percent (35%) clay when the clay minerals exhibit high shrink/swell characteristic and exhibit slight to moderate stickiness. The fine loamy group includes sandy clay loam, silt loam, clay loam and silty clay loam textural classes and shall generally be considered provisionally suitable in texture.

(I) Silt loam. Silt loam feels floury when moist and will show a fingerprint but will not ribbon and forms only a weak ball.

(II) Silt. Silt has a floury feel when moist and sticky when wet but will not ribbon and forms a ball that will tolerate some handling.

(III) Sandy clay loam. Sandy clay loam feels gritty but contains enough clay to form a firm ball and may ribbon to form seventy-five hundredths to one-inch (.75–1") pieces.

(IV) Silty clay loam. Silty clay loam is sticky when moist and will ribbon from one to two inches (1–2"). Rubbing silty clay loam with the thumbnail produces a moderate sheen. Silty clay loam produces a distinct fingerprint.

(V) Clay loam. Clay loam is sticky when moist. Clay loam forms a thin ribbon of one to two inches (1– 2") in length and produces a slight sheen when rubbed with the thumbnail. Clay loam produces a non-distinct fingerprint.

D. Soil group IV. These clayey texture soils contain forty percent (40%) or more clay-sized particles and include sandy clay, silty clay and clay. This group may also include clay loam and silty clay loam when the clay fraction is greater than thirty-five percent (35%) and of a high shrink/swell nature. There are two (2) major types of clays nonexpandable and expandable. The nonexpandable clays, when wet, are slightly sticky to sticky; when moist, are friable to firm; and when dry, they are slightly hard to hard. The nonexpandable clays (Group IVa) shall generally be considered provisionally suitable in texture. The expandable clays, when wet, are very sticky and very plastic and when moist, these clays are very firm to extremely firm and when dry, are very hard to extremely hard. The expandable clays (Group IVb) shall be considered unsuitable in texture.

(I) Sandy clay. Sandy clay is plastic, gritty and sticky when moist and forms a firm ball and produces a thin ribbon to over two inches (2") in length.

(II) Silty clay. Silty clay is both plastic and sticky when moist and lacks any gritty feeling. Silty clay forms a firm ball and readily ribbons to over two inches (2") in length.

(III) Clay. Clay is both sticky and plastic when moist, produces a thin ribbon over two inches (2") in length, produces a high sheen when rubbed with the thumbnail and forms a strong ball resistant to breaking.

E. Soil group V. This soil group may be of any texture, however, the most predominant are cherty and very cherty clays, silt loams and silty clay loams. The amount of rock fragments in these soils is of a concern in areas of residual soils overlying highly permeable bedrock where groundwater could become contaminated. In general, soils with less than fifty percent (50%) rock fragments will be considered suitable. In general, soils with greater than fifty percent (50%) rock fragments over highly permeable bedrock will be considered unsuitable. Soils with greater than fifty percent (50%) rock fragments will be considered provisionally suitable if geological limitations are not severe.

F. The soil texture shall be estimated by field testing; and

2. Soil consistency. Soil consistency is comprised of the attributes of soil material, typically clay, that are expressed by the degree and kind of cohesion and adhesion or by the resistance to deformation or rupture.

A. Soil consistency when wet shall be considered as follows:

(I) Stickiness. Stickiness is the quality of adhesion to other objects. For field evaluation of stickiness, wet soil material is pressed between thumb and finger and its adherence noted. Degrees of stickiness are described as follows:

(a) Slightly sticky. After pressure, soil material adheres to both thumb and finger but comes off one or the other cleanly. It is not appreciably stretched when the digits are separated;

(b) Sticky. After pressure, soil material adheres to both thumb and finger and tends to stretch somewhat and pull apart rather than pulling free from either digit; and

(c) Very sticky. After pressure, soil material adheres to both thumb and finger and is decidedly stretched when they are separated; and

(II) Plasticity. Plasticity is the ability to change shape continuously under the influence of an applied stress and to retain the impressed shape on removal of the stress. For field determination of plasticity, the soil material shall be rolled between the thumb and finger to observe whether or not a wire or thin rod of soil can be formed. Degree of resistance to deformation at or slightly above field capacity is as follows:

(a) Slightly plastic. Wire formable but soil mass easily deformable;

(b) Plastic. Wire formable and moderate pressure required for deformation of the soil mass; and

(c) Very plastic. Wire formable and much pressure required for deformation of the soil mass.

B. Soil consistency when moist. Consistence when moist is determined at a moisture content approximately midway between air dry and field capacity. At this moisture content, most soil materials exhibit a form of consistency—characterized by tendency to break into smaller masses rather than into powder; some deformation prior to rupture; absence of brittleness; and ability of the material after disturbance to cohere again when pressed together. To evaluate this consistency, a mass that appears slightly moist shall be selected and attempt made to crush in the hand.

(I) Friable. Soil material crushes easily under gentle to moderate pressure between thumb and finger, and coheres when pressed together.

(II) Firm. Soil material crushes under moderate pressure between thumb and finger but resistance is distinctly noticeable.

(III) Very firm. Soil material crushes under strong pressure; barely crushable between thumb and finger.

(IV) Extremely firm. Soil material crushes only under very strong pressure; cannot be crushed between thumb and finger and must be broken apart bit by bit.

C. Soil consistency when dry. The consistency of soil materials when dry is characterized by rigidity, brittleness, maximum resistance to pressure, more or less tendency to crush to a powder or to fragments with rather sharp edges, and inability of crushed material to cohere again when pressed together. For evaluation, the air-dry mass shall be selected and broken in the hand.

(I) Slightly hard. Weakly resistant to pressure, easily broken between thumb and finger.

(II) Hard. Moderately resistant to pressure; can be broken in the hands without difficulty but is barely breakable between thumb and finger.

(III) Very hard. Very resistant to pressure; can be broken in the hands only with difficulty; not breakable between thumb and finger.

(IV) Extremely hard. Extremely resistant to pressure; cannot be broken in the hands.

3. Soil structure. In many soils, the sand, silt and clay particles tend to cling or stick to one another to form a ped or a clump of soil. This is known as soil structure. Soil structure may have a significant effect on the movement of effluent through a soil. Structure is usually not important in soil groups I and II, and these types of soils shall generally be considered suitable as to structure. The three (3) kinds of soil structure that are most significant in movement of sewage effluent through groups III and IV soils are block-like, platy and the absence of soil structure or massive conditions. These kinds of soil structure are described as follows:

A. Block-like soil structure. In groups III and IV soils, if the soil exhibits many peds of angular and subangular peds, then the soils have block-like structure. The sewage effluent may move between the cracks of these types of peds. Block-like structure in groups III and IV soils is frequently destroyed by mechanical excavating equipment manipulating the soil when it is too wet. Trenches for absorption lines being placed in groups III and IV soils with block-like structure should only be dug when the soils are moist or dry. Block-like soil structure in groups III and IV soils shall be considered provisionally suitable;

B. Platy soil structure. If groups III and IV soils fall out into plate-like sheets, then the soil would have platy structure. Water or effluent movement through these soils would be extremely slow, and the structure shall be considered unsuitable; and

C. Absence of soil structure. Some groups II, III and IV soils are massive and exhibit no structural aggregates. In these kinds of soils, water or effluent movement would be negligible. This structure shall be considered unsuitable.

(G) Soil Drainage. Soils with seasonally high water tables are of major concern in evaluating sites for sewage effluent disposal. These are the soil areas that give good sewage absorption rates during dry seasons of the year but force sewage effluent to the surface during the wetter seasons.

1. The depth of the seasonal high water table can commonly be recognized by those examining soil profiles. The criterion for recognition of high water tables is that of soil color. Subsurface horizons that are in colors of reds, yellows and browns generally indicate good soil aeration and drainage throughout the year. Subsurface horizons that are in colors of gray, olive or bluish colors indicate poor aeration and poor soil drainage. These dull or grayish colors may occur as a solid mass of soil or may be in mottles of localized spots. The volume of grayish color is indicative of the length of time that free water stands in that soil profile. There are soils that have light-colored mottles which are relic from the light-colored rock from which the soils have weathered. These soils would not have high water tables, so one must distinguish between a true soil composed of sand, silts and clays, or the rock material that may still exist in the soil profile. Similarly, there are also some soils with surface or subsurface eluvial horizons with light colors which can be unrelated to drainage conditions.

2. Any soil profile that has the grayish colors of chroma 2 or less (Munsell color chart) indicative of high water tables, or is either subject to periodic high water, within twenty-four inches (24") of the surface, or is less than twelve inches (12") between the proposed trench bottom and the high water table, shall be considered unsuitable as to drainage. Soils where the seasonally high water table is less than forty-eight inches (48") and more than twenty-four inches (24") below the naturally occurring surface shall be considered provisionally suitable for soil drainage, provided there remains at least twelve inches (12") of soil between the proposed trench bottom and the seasonally high water table. Soils where the seasonally high water table is greater than forty-eight inches (48") below the naturally occurring surface shall be considered suitable for soil drainage. Drainage systems installed for groundwater lowering shall be maintained so that a minimum separation of one foot (1') occurs between the absorption trench bottom and the seasonally high water table. For extensive drainage systems, such as groundwater lowering in subdivisions, easements shall be recorded and shall have adequate width for reasonable egress and ingress for maintenance.

(H) Soil Thickness. The thickness of soils to rock which are classified as suitable or provisionally suitable in texture and structure shall be at least forty-eight inches (48") when conventional soil absorption systems at conventional depths are to be utilized. Soil thickness greater than forty-eight inches (48") shall be considered as suitable as to soil thickness. Soil thickness less than forty-eight inches (48") and greater than thirty-six inches (36") shall be considered provisionally suitable. Where special design and installation modifications can be made to provide at least two feet (2') of naturally occurring soil below the bottom of the absorption trench, these soils may be reclassified as provisionally suitable in thickness.

(I) Restrictive Horizons. Restrictive horizons in soils are recognized by their apparent resistance in excavation or in the use of a soil auger. Restrictive horizons may occur as fragipans or claypans. The fragipan is a layer that owes its hardness mainly to extreme density or compactness as opposed to high clay content or cementation. The layer is typically dense and brittle. Although fragments are friable when removed, when in place the material is so dense that water moves through it very slowly. Unlike fragipans, the claypan is a compact, slowly permeable layer in the subsoil having a much higher clay content than the overlying material. A sharply defined boundary exists between the claypan and the overlying material. Claypans are typically hard when dry and plastic and sticky when wet.

1. Restrictive horizons that are greater than six inches (6") thick severely restrict the movement of water and sewage effluent and do not adequately respond to groundwater lowering drainage systems. Where these horizons are less than six inches (6") thick, they do not severely restrict the movement of water and sewage effluent, but rather indicate the presence of a seasonally high water table and may be modified after special investigation.

2. Soils in which restrictive horizons are six inches (6") or more in thickness and at depths greater than forty-eight inches (48") below the ground surface shall be considered suitable as to depth to restrictive horizons. Restrictive horizons six inches (6") or more in thickness and at depths between forty-eight inches and twenty-four inches (48–24") shall be considered provisionally suitable as to depth to restrictive horizons. Restrictive horizons six inches (6") or more in thickness encountered at depths less than twenty-four inches (24") below the ground surface shall be considered unsuitable as to depth to restrictive horizons.

(J) Other Applicable Factors. The site evaluation should include consideration of any other applicable factors involving environmental principles including:

1. The potential environmental hazard of possible failures of soil absorption systems involving large quantities of sewage, which would dictate larger separation distances than the minimums specified in subsection (1)(D) of this rule; and

2. The potential environmental and health hazard of possible massive failures of soil absorption systems proposed to serve large numbers of residences, as in residential subdivisions or mobile home parks.

(K) Determination of Overall Site Suitability. All of the criteria in subsections (7)(E)–(J) of this rule shall be determined to be suitable, provisionally suitable or unsuitable as indicated. If all criteria are classified the same, that classification shall prevail. Where there is a variation in classification of the several criteria, the following shall be used in making the overall site classification. The lowest of the uncorrectable characteristics will determine the overall site classification. The administrative authority shall make this determination—

1. If the topography is classified as unsuitable, it may be reclassified provisionally suitable under the conditions outlined in subsection (7)(E) of this rule;

2. If the soil texture is classified as unsuitable, the overall classification will be unsuitable regardless of the other criteria unless the provisions of subsection (6)(K) of this rule are met;

3. If the soil structure is classified as unsuitable, the overall classification will be unsuitable regardless of the other criteria unless the provisions of subsection (6)(K) of this rule are met;

4. When soil thickness is classified as unsuitable, it may be reclassified as provisionally suitable under the conditions outlined in subsection (7)(H) of this rule;

5. When the restrictive horizon is classified unsuitable, it may be reclassified as provisionally suitable under the conditions outlined in subsection (6)(K) of this rule; and

6. When drainage (groundwater level) is unsuitable, it may be reclassified as provisionally suitable under the conditions outlined in subsection (7)(G) of this rule.

(L) Site Classification. Sites classified as suitable may be utilized for a ground absorption sewage treatment and disposal system consistent with this rule. A suitable classification generally indicates soil and site conditions favorable for the operation of a ground absorption sewage treatment and disposal system or have slight limitations that are readily overcome by proper design and installation.

1. Sites classified as provisionally suitable may be utilized for a ground absorption sewage treatment and disposal system consistent with this rule but with moderate limitations. Sites classified provisionally suitable require some modifications and careful planning, design and installation for a ground absorption sewage treatment and disposal system to function satisfactorily.

2. Sites originally classified as unsuitable may be used for soil absorption disposal systems, provided engineering, hydrogeologic and soil studies indicate to the administrative authority that a suitable septic tank system or a suitable alternate system can reasonably be expected to function satisfactorily. These sites may be reclassified as provisionally suitable upon submission to the administrative authority and meeting the department's requirements in subsection (6)(K) of this rule.

(M) Design Criteria. Tables 13 and 14 shall be used when determining application rates for the appropriate sewage disposal system design.

1. Table 13 shall be used when determining the application rate for septic tank systems of conventional design when using the site evaluation criteria in this rule.

2. The construction of any conventional or LPP system must meet the other applicable requirements as set forth in section (6) of this rule. Soils for LPP systems must be classified as suitable or provisionally suitable to a depth of two feet (2') from the original ground surface. Table 14 shall be used when determining the application rate when using the site evaluation criteria in this rule.

AUTHORITY: sections 701.040(1) and 701.043.1., RSMo 1994.* Emergency rule filed April 17, 1995, terminated April 26, 1995. Original rule filed April 17, 1995, effective Dec. 30, 1995.
*Original authority: 701.040 and 701.043, RSMo 1994.




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