As in effect on May 1, 2008
1.1 SCOPE: These regulations shall apply to large underground disposal systems for domestic wastewater discharges which exceed 5,000 gallons per day (gpd) and all other domestic wastewater discharges not covered under the definition of an "Onsite wastewater disposal system" in R317-1-1.13. Usually these systems should not be designed for over 15,000 gpd. In general, it is not acceptable to dispose of industrial wastewater in an underground disposal system.
1.2 ENGINEERING REPORT: An engineering report shall be submitted which shall contain design criteria along with all other information necessary to clearly describe the proposed project and demonstrate project feasibility.
1.3 SUBMISSION OF PLANS FOR REVIEW: Plans for new large underground wastewater disposal systems or extensions of existing systems shall be submitted to the Department for review as required by R317-1. All designs shall be prepared and submitted under the supervision of a registered professional engineer licensed to practice in the State of Utah. A construction permit must be issued by the Utah Water Pollution Control Committee prior to construction of the wastewater disposal system or the building(s) to be served by the wastewater system. After January 1, 2002, the design must be prepared by a person certified pursuant to R317-11, and the system designer must, following construction of the system, certify in writing that the system was installed in accordance with the approved plans and specifications.
1.4 OPERATION AND MAINTENANCE: Operation and maintenance shall be provided by the owner to insure the disposal system is functioning properly at all times. A written operation and maintenance document describing the treatment and disposal system and outlining routine maintenance procedures, including checklists and maintenance logs needed for proper operation of the system, shall be required. The document must be available at the time of final inspection.
1.5 LARGE UNDERGROUND WASTEWATER DISPOSAL SYSTEM REQUIRED:
The drainage system of any building or establishment covered herein shall receive all wastewater as required by R309-100, the Utah Plumbing Code and shall have a connection to a public sewer except when such sewer is not available for use, in which case connection shall be made as follows:
A. To an underground wastewater disposal system found to be adequate and constructed in accordance with requirements stated herein.
B. To any other type of disposal system acceptable under R317-3.
1.6 MULTIPLE UNITS UNDER SEPARATE OWNERSHIP: Multiple Units Under Separate Ownership shall not be served by a common large underground disposal system except when, based upon sound engineering judgment, other alternatives are determined infeasible. In such cases, a common subsurface system may be used provided the following requirements are met:
A. The common subsurface disposal system and conveyance sewers shall be under the sponsorship of a body politic.
B. The subsurface absorption system shall be designed and constructed to provide duplicate capacity (two independent systems). Each system shall be designed to accommodate the total anticipated maximum daily flow. The duplicate systems shall be designed with appropriate valving, etc., to allow for periodic alternation of the use of each system.
C. Sufficient land area with suitable characteristics shall be available to provide for a third absorption system capable of handling the total maximum daily wastewater flow. This area shall be kept free of permanent structures, traffic or soil modification (See Section R317-5-3.1(L)).
D. The subsurface absorption system should be used only until a more permanent system becomes available.
1.7 NEW PROCESSES AND METHODS OF DISPOSAL: Where unusual conditions exist, other methods of disposal not described herein may be employed if approved by the Utah Water Pollution Control Committee and by the local health authority having jurisdiction. The approval will be based on evidence of adequacy to meet water quality standards and other requirements of the Code.
1.8 UNITS REQUIRED IN A LARGE UNDERGROUND WASTEWATER DISPOSAL SYSTEM: The underground wastewater disposal system shall typically consist of the following:
A. A wastewater drainage line or building sewer.
B. A septic tank.
C. A subsurface absorption system. This may be an absorption field, seepage pits, seepage trenches or an absorption bed, depending on location, topography, soil conditions and maximum ground water level.
1.9 LOCATION AND INSTALLATION: Location and installation of the wastewater disposal system shall be such that with reasonable maintenance it will function properly and will not create a nuisance, health hazard or endanger the quality of any waters of the State. Due consideration shall be given to the size and shape of the area in which the system is installed, slope of natural and finished grade, soil characteristics, maximum ground water elevation, proximity of existing or future water supplies or water courses, possible flooding and expansion potential of the disposal system.
1.10 ISOLATION: The system shall be isolated as shown in Table 5-1.
TABLE 5-1
MINIMUM HORIZONTAL SEPARATION IN FEET
(Undisturbed Earth)
Building Septic Absorption Seepage Absorption
Sewer Tank Field Pit or Bed
Trench trench
Drinking Water
Supply Source
Deep Well (a)100 100 100 100 100
Shallow Well
or Spring (b) (b) (b) (b) (b)
Domestic Water
Supply Lines (c) 10 10 10 10
Ponds, Lakes,
Reservoirs and
Water Courses --- 25 (d) (d) (d)
Foundation Walls 3 5 25 25 25
Land Drain
Located upslope --- 10 20 20 20
Located
downslope --- 25 100 100 100
Property Line 5 5 5 15 10
Seepage Pits
(Trenches) --- 5 10 12(e) 10
Absorption beds --- 5 10 10 10
Absorption fields --- 5 (f) 10 10
Footnotes:
(a) Sewers may be constructed within the 100 foot protective zone, provided the sewer construction meets the
requirements of R309-106-2.3.4.
(b) It is recommended that the listed concentrated sources of pollution be located at least 1,500 feet from shallow
wells and springs. Any proposal to locate closer than 1,500 feet will be reviewed on a case-by-case basis, taking into
account geology, topography, existing land use agreements, designated use of water system (public or non-public) and
potential for pollution of water sources. It is the responsibility of the water supply owner to establish an adequate
protection zone in accordance with the applicable drinking water regulations. Even separation of 1500 feet or greater from
concentrated sources of pollution will not guarantee suitability of the water supply system.
(c) The requirements stated in R317-5-1.13(F) must be met
(d) A minimum of 100 feet is desirable, but may be modified to a lesser or greater distance, depending on soil
conditions or mitigating measures such as lining the water course with impervious material.
(e) Seepage pits or seepage trenches must be installed within an established absorption zone. The absorption zone
will be sized based on the ratio of ground surface area "GSA" to the required sidewall area "SWA". The GSA/SWA ratio must
be at least 2.5. The trenches and pits shall be installed within the absorption zone such that the spacing between trenches
will be equal. Spacing of 12 feet (sidewall to sidewall) shall be a minimum. Distance to the edge or boundary of the
established absorption zone shall be a minimum of 15 feet. The system must also conform to all other separation
requirements identified in Table 5-1.
The required sidewall area "SWA" shall be computed based on the design application rate with the associated soil type
depicted in Table 5-8. The ground surface area identified within the absorption zone will be a minimum of 2.5 times the
required sidewall area. An example of a typical seepage trench design with variation is available from the Bureau of Water
Pollution Control.
(f) See Table 5-4.
1.11 CONSTRUCTION INSPECTION: Approval to operate the constructed/installed facilities shall be issued following a final inspection by a representative of the Department of Health. The facilities must be inspected after installation but prior to backfilling.
1.12 CONSTRUCTION MATERIALS: Materials used in construction of the system shall be durable, sound, and not unduly subject to corrosion. Pipe, pipe fittings and similar materials shall comply with the requirements of R309- 100.
1.13 WASTEWATER DRAINAGE LINE OR BUILDING SEWER: Wastewater drainage lines (or building sewers) shall comply with R309-100, the Utah Plumbing Code, or meet the following requirements, whichever is more restrictive.
A. Any generally accepted material will be given consideration, but material selected shall be suitable for local conditions to include soil characteristics, external loadings, abrasions and similar problems.
B. The lines shall have a minimum inside diameter of 4 inches, in which case they shall be laid on a minimum slope of 1.25 percent. For sewer lines serving more than one dwelling unit, it is recommended that the line be sized greater than 4 inches in diameter. Lines of greater sizes should be designed for a minimum velocity of 2 feet per second based on the pipe flowing full. See R317-3 for calculation of flow velocities.
C. The lines shall have cleanouts every 50 feet and at all changes in direction or grade, except where manholes are installed every 400 feet and at every change in direction or grade.
D. On 4-inch and 6-inch lines, two 45 degree bends with cleanout will be acceptable in lieu of a manhole, and 90 degree ells are not recommended.
E. The design of wastewater pump stations shall comply with the requirements contained in R317-3.
F. Lines shall be separated from water service pipes in separate trenches and by at least 10 feet horizontally. If the local conditions prevent a 10 foot separation, or when sewer lines must cross water lines, the two lines may be placed within the 10 feet of each other, provided:
1. The bottom of the water service pipe, at all points, shall be at least 18 inches above the top of the wastewater drainage line at its highest point.
2. The water service pipe shall be placed in a separate trench or the line should be placed on a shelf of undisturbed soil to one side of the sewer line trench.
3. The number of joints in the service pipe shall be kept to a minimum and the materials and joints of both the sewer line and water service line shall be of a strength and durability to prevent leakage under known adverse conditions. The joints between the two lines shall be staggered to the extent possible.
4. When it is impossible to obtain the proper horizontal and vertical separation as stipulated above, both the water and sewer line shall be constructed in accordance with the requirements of R309-112.2.
1.14 ESTIMATES OF WASTEWATER QUANTITY: The maximum daily wastewater flow to be disposed of should be determined as accurately as possible, preferably by actual measurement. Where this is not possible, Table 5-2 may be used to estimate the flow.
TABLE 5-2
ESTIMATED QUANTITY OF DOMESTIC WASTEWATER
TYPE OF ESTABLISHMENT GALLONS PER DAY
Construction/work camps (semi-permanent) 60 per person
Resort camps with limited plumbing 60 per person
Country Clubs 25 per person
Dwellings
a. Boarding house 60 per person
Additional kitchen waste for
non-resident boarder 10 per person
b. Boarding schools 75-100 per person
c. Condominium 400 per unit
d. Mobile home 400 per unit
e. Single family dwelling 400 per day
f. Rooming House 40 per person
Highway Rest Areas (improved with
restroom facilities) 5 per vehicle
Hospitals 250 per bed
Nursing Homes 200 per Bed
Institutions other than Hospitals
and Nursing Homes 75-125 per person
Motels and Hotels 62 per person
Industrial Buildings (exclusive of
industrial waste) 15-35 per person
Launderette (self-service) 50 per load
Office Buildings
a. With cafeteria 25 per employee
b. Without cafeteria 15 per employee
Recreational Vehicle Parks/
Campgrounds
a. Sanitary stations for
self-contained Vehicles 50 per space
b. Independent spaces (temporary
or transient with sewer
connections) 125 per space
c. Dependent spaces (temporary
or transient with no sewer
connections) 125 per space
with service building
including showers 35 per person
(Campground)
(1) with service building
but no showers 85 per space
25 per person
(Campground)
d. Campground with no flush
toilets 5 per person
Restaurants 35 per seat
a. Additional for bars and
cocktail lounges 2 per person
Schools
a. Boarding 75 per person
b. Day, without cafeteria,
gymnasiums or showers 15 per person
c. Day, with cafeteria, but
no gymnasium or shower 20 per person
d. Day, with cafeteria, gymnasium
and shower 25 per person
Service Station (per vehicle served) 5 per vehicle
Ski Areas and Visitor Centers 5 per visitor
2.1 GENERAL REQUIREMENTS: Septic tanks shall be constructed of durable materials designed to withstand expected physical loads and corrosive forces. They shall be watertight and designed to provide settling of solids, accumulation of sludge and scum, and access for cleaning, as specified in the following paragraphs.
2.2 TANK CAPACITY: Septic tanks shall be sized on the following basis:
(1) V = 1.5Q for Q less than or equal to 1500
(2) V = 1125 + 0.75 Q for Q greater than 1500
V = liquid volume of tank in gallons
Q = (Maximum anticipated) wastewater discharge in gallons per day
2.3 TANK DIMENSIONS: In general, tank length should be at least 2 or 3 times the width. Liquid depth of tanks shall be at least 30 inches. A liquid depth greater than 6 feet shall not be considered in determining tank capacity.
2.4 TANK COMPARTMENTS: Septic tanks may be divided into compartments, or separate tanks may be installed in series, up to a maximum of 3, provided the following requirements are met:
A. The volume of the first compartment or tank must equal or exceed the volume of any other compartment.
B. No compartment or tank shall have an inside horizontal dimension less than 24 inches.
C. Inlets and outlets shall be designed as specified for tanks, except when a partition wall is used to form a multi-compartment tank. Under such conditions, an opening in the partition may be used to allow for flow between compartments, provided the minimum dimension of the opening is 4 inches, the cross-sectional area is not less than 30 square inches, and the mid-point is below the liquid surface a distance approximately equal to 40% of the liquid depth of the tank.
2.5 INLETS AND OUTLETS:
A. Inlets and outlets of tanks or compartments shall be submerged or baffled to divert incoming flow toward the tank bottom and minimize the discharge of sludge or scum in the effluent.
B. Sanitary Tees may be used in lieu of baffled inlet or outlet structures.
C. All outlet baffles shall extend below the liquid surface a distance equal to approximately 40% of the liquid depth. Space between the baffle top and the underside of the tank cover shall be at least 1 inch.
D. Scum storage volume shall consist of 15% or more of the required liquid capacity of the tank and shall be provided in the space between liquid surface and top of inlet devices, which shall be set at least 1 inch below the underside of the tank cover.
E. Inlets and outlets shall allow free venting of tank gases back through the drainage system.
F. The inlet invert shall be at least 1 inch above outlet invert.
2.6 ACCESS TO TANK:
A. Access to inlet and outlet devices shall be provided through properly placed openings not less than 18 inches in minimum horizontal dimension.
B. The top of the tank shall be at least 6 inches below finished grade.
C. If the top of the tank is located more than 18 inches below finished grade, all access openings required by sub-section (1) above, shall be extended to within 18 inches of the finished grade.
2.7 ABANDONED SEPTIC TANKS: Septic tanks, cesspools and seepage pits which are no longer in use shall be completely pumped and filled with sand or soil.
2.8 DISCHARGE TO ABSORPTION SYSTEM: Septic tank effluent shall be conducted to the absorption system through a watertight sewer line meeting the requirements for wastewater drainage lines as contained in R317-5-1.13(A), (B), and (F). Tees, wyes, or other distributing devices may be used as needed. If a distribution box is used, it shall be of sufficient size to accommodate the necessary distribution line connections. Outlet inverts shall be at the same elevation and at least 1 inch below the inlet invert. Conveyance to the absorption system must be adequately sized to handle peak hydraulic flow.
3.1 GENERAL REQUIREMENTS:
A. Suitable soil exploration, to a depth of about 10 feet, or at least 4 feet below the bottom of the proposed absorption systems and percolation tests, shall be made to provide information on subsoil conditions. Percolation tests and soil exploration reports shall be completed and submitted as part of the engineering report for the disposal facility. After January 1, 2002, the soil evaluation and percolation tests must be done in accordance with certification requirements in R317-11. A minimum of 5 percolation tests must be conducted at different sites for each disposal system. Additional tests may be required, where necessary to adequately evaluate the total absorption system or where there is significant variability in test results. In general, the system will be sized based on the slowest stabilized percolation test rate. Soil logs should be prepared in accordance with the Unified Soil Classification System by a qualified individual. Requirements outlined in R317-5-4.1 and Table 5-8 will be helpful in developing this information.
B. Absorption devices, including seepage pits or trenches, placed in sloping ground should be so constructed that the horizontal distance between the distribution line and the ground surface is at least 10 feet.
C. Soil having excessively high permeability, such as gravel with large voids, affords little filtering and is unsuitable for absorption systems. Percolation rates (R317-5-4.1) of approximately 5 minutes per inch or less usually will not be acceptable.
The extremely fine-grained "blow sand" found in some parts of Utah is generally unsuitable for absorption systems and should be avoided. If no choice is available, systems may be constructed in such material, provided it is within the required percolation range specified in this code, and the required area is calculated on the minimum percolation rate (60 minutes per inch for absorption fields and 30 minutes per inch for absorption beds).
D. Absorption system excavations may be made by machinery provided that the soil in the bottom and sides of the excavation is not compacted. Strict attention shall be given to the protection of the natural absorption properties of the soil. Absorption systems shall not be excavated when the soil is wet enough to smear or compact easily. All smeared or compacted surfaces should be raked to a depth of one inch, and loose material removed before the filter material is placed in the absorption system excavation.
E. Effluent distribution lines or pipe shall be perforated and should consist of 4-inch diameter pipe of appropriate material which has demonstrated satisfactory results for the given application. The distribution pipe shall be bedded true to line and grade, uniformly and continuously supported on firm, stable material.
F. The coarse material in the absorption system shall consist of crushed stone, gravel, or similar material of equivalent strength and durability. It shall be free from fines, dust, sand or clay. The top of the stone or gravel shall be covered with a pervious material such as an acceptable synthetic filter fabric, a 2-inch compacted layer of straw, or similar material before being covered with earth backfill to prevent infiltration of backfill into the stone or gravel.
G. Distribution pipes placed under driveways or other areas subjected to heavy loads shall receive special design considerations to insure against crushing or disruption of alignment. Absorption area under driveways or pavement shall not be considered in determining the minimum required absorption area.
H. Absorption systems shall be backfilled with earth that is free from debris and large rocks. The first 4 to 6 inches of soil backfill should be hand placed. Distribution pipes shall not be crushed or misaligned during backfilling. When backfilling, the earth should be mounded slightly above the surface of the ground to allow for settlement.
I. Heavy equipment shall not be driven in or over absorption systems during backfilling or after completion.
J. That portion of absorption system below the top of distribution pipes shall be in natural soil. Under unusual circumstances the Utah Water Pollution Control Committee may allow installation in acceptably stabilized earth fill. The earth fill and location will have to be evaluated on a case-by-case basis, taking into consideration the soil characteristics and degree of consolidation of the fill material.
K. Soil and Ground Water Requirements. In areas where absorption systems are to be constructed, soil cover must be adequate to insure at least 4 feet of soil between bedrock or any other impervious formation, and the bottom of absorption systems. Maximum ground water elevation must be at least 2 feet below the bottom of absorption systems and at least 4 feet below finished grade.
L. Replacement Area for Absorption System. Adequate and suitable land shall be reserved and kept free of permanent structures, traffic, or adverse soil modification for replacement of the absorption system. Suitability must be demonstrated through soil exploration and percolation tests results.
3.2 ABSORPTION FIELDS: Absorption fields are the preferred type of absorption system. They consist of a series of gravel-filled trenches provided with perforated pipes designed to distribute septic tank effluent into the gravel fill, from which it percolates through the trench walls and bottom into the surrounding sub-surface soil.
A. Design of absorption fields shall be as outlined in Tables 5-3 and 5-4.
TABLE 5-3
ABSORPTION FIELD CONSTRUCTION DETAILS
ITEMS UNITS MINIMUM MAXIMUM
Number of lateral trenches 2 -
Length of trenches Feet - 100
Width of trenches Inches 12 36
Slope of pipe (bottom) In./100 ft. Level Level
Depth of coarse material:
Under pipe Inches 6 -
Under pipe located within
10 ft. of trees Inches 12 -
Over pipe Inches 2 -
Size of coarse material Inches 3/4 2-1/2
Depth of backfill over
coarse material Inches 6 -
TABLE 5-4
SIZE AND MINIMUM SPACING FOR ABSORPTION FIELD TRENCHES
Minimum Spacing of wall to
Trenches Width of wall (ft.)
trench at bottom
(inches)
12 to 18 6.0
18 to 24 6.5
24 to 30 7.0
30 to 36 7.5
B. The minimum absorption area (total bottom area of trenches) of the absorption field shall be determined from the following equation but in no case the maximum allowable application rate shall exceed 2.2 gallons per square foot per day
Q = 5 / square root of t
Where Q = maximum rate of effluent application to the soil in gallons per square foot per day
t = stabilized percolation rate in minutes per inch
Percolation tests shall be performed as specified in R317-5-4.1. Rates in excess of 60 minutes per inch indicate a soil unsuitable for absorption field construction.
C. Wherever possible all trench bottoms should be constructed at the same elevation. Distribution pipes and trenches should be level and should be connected at both ends to provide a continuous system. If ground surface slope is too steep to permit a level installation, then a system of serial trenches following land contours should be used, with each trench and distribution pipe being constructed level but at a different elevation. A schematic diagram showing the recommended layout of trenches and distribution systems is available from the Bureau of Water Pollution Control.
1. The system should include drop boxes which should generally conform to the detail in Appendix 1 and should operate in such a manner that a trench will be filled with wastewater to the depth of the gravel fill before the wastewater flows to the next lower trench. The drop boxes shall be watertight and should be provided with a means of access at the top.
2. The lines between the drop boxes should be a minimum of 4 inches in diameter and should be watertight with direct connections to the distribution box. They should be laid in a trench excavated through undisturbed earth to the exact depth required. Backfill should be carefully tamped.
3.3 ABSORPTION BEDS: Absorption beds consist of large excavated areas provided with gravel fill in which effluent distribution lines are laid. They may be used in place of absorption fields when trenches are not considered desirable, and shall conform to requirements applying to absorption fields, except for the following:
A. They shall comply with construction details specified in Table 5-5.
TABLE 5-5
ABSORPTION BED CONSTRUCTION DETAILS
ITEM UNIT MINIMUM MAXIMUM
Distance between
distribution lines Feet - 6
Distance between
distribution lines
and wall Feet - 3
Depth to bottom of bed Feet 1-1/2 -
Size of coarse material Inches 3/4 2-1/2
Depth of coarse material
Under pipe Inches 6 -
In bed within 10 ft.
of trees Inches 12 -
Over pipe Inches 2 -
Depth of backfill over
coarse material Inches 6 -
B. Required absorption area (total bottom area of bed) shall be determined from the following equation, but in no case shall it exceed 1.1 gallons per square foot per day.
Q = 2.5/square root of t
Where Q = maximum rate of effluent application to the soil in gallons per square foot per day.
t = stabilized percolation rate in minutes per inch.
Percolation tests shall be performed as specified in R317-5-4.1. Rates in excess of 30 minutes per inch indicate a soil unsuitable for absorption bed construction.
3.3 SEEPAGE PITS: If absorption fields or beds are not feasible, seepage pits will be considered. These consist of deep pits which receive septic tank effluent and allow it to seep through sidewalls into the adjacent subsurface soil. Seepage pits may be either hollow lined or filled with clean coarse material. They shall conform to the following requirements:
A. Number and size of seepage pits required shall be determined by calculation of seepage rate into each stratum of soil encountered in pit sidewall by reference to Table 5-8. Only pervious side-wall area below the inlet shall be considered. In order to calculate a sidewall seepage rate a representative number of soil explorations shall be evaluated to adequately identify the type and depth of each soil stratum expected throughout the absorption area. In general, a minimum of 5 explorations will be evaluated. This information shall be provided in the engineering report.
B. For the purposes of confirming an appropriate sidewall seepage rate, the owner shall submit a statement describing the character and thickness of each stratum of soil encountered during pit construction. Soil classification and assumed seepage rates shall be as specified in Table 5-8 except when valid seepage measurements are available.
C. The lining may be brick, stone, block or similar materials, at least 4 inches thick, laid in cement mortar above the inlet and with tight butted joints below the inlet. The annular space between the lining and the earth wall shall be filled with crushed rock or gravel varying in diameter from 3/4 inch to 2-1/2 inches.
D. A structurally sound and otherwise suitable top shall be provided. Structural design and materials used throughout shall assure a durable safe structure.
E. If more than one seepage pit is provided, the installation may be operated in series or parallel with distribution of effluent as specified in R317-5-2.1(G).
F. For hollow lined pits, the inlet pipe should extend horizontally at least 1 foot into the pit with a tee to divert flow downward and prevent washing and eroding the sidewall.
G. For filled pits a thin layer of crushed rock or gravel ranging from 3/4 to 2-1/2 inches in diameter, free from fines, sand, clay or organic material shall cover the coarse material to permit leveling of the distribution pipe.
TABLE 5-6
SEEPAGE PITS CONSTRUCTION DETAILS
ITEM UNIT MINIMUM MAXIMUM
Generals
Distance between
seepage pits feet 12(a) -
Diameter of
distribution pipe inches 4 -
Size of coarse
material inches 3/4 12
Bottom of pit to
maximum ground
water feet 2 -
Bottom of Pit in
unsuitable soil
or bedrock
formations feet 4 -
Hollow-lined Pits:
Width of annular
space between
lining and sidewall
containing crushed
rock (3/4 to 2-1/2
inches in diameter) inches 6 -
Thickness of brick,
or block linings inches 4(b)
Filled Pits:
Depth of coarse material:
Under pipe feet 4 -
Over distribution pipe inches 2 -
Depth of backfill over
material inches 6 -
Footnotes:
(a) See Table 5-1
(b) Pre-manufactured linings may be approved with thicknesses less than 4 inches.
3.5 SEEPAGE TRENCHES (MODIFIED SEEPAGE PITS):
Seepage trenches are considered as modified seepage pits and consist of deep trenches filled with clean, coarse material. They shall conform to the requirements applying to seepage pits except for the following:
A. The effective sidewall absorption area shall be considered as the outside surface of the seepage trench (vertical sidewall area) calculated below the inlet or distribution pipe. Only pervious sidewall area below the inlet shall be considered.
TABLE 5-7
SEEPAGE TRENCH DETAIL
ITEM UNIT MINIMUM MAXIMUM
Seepage trench width feet 2 -
Seepage trench length feet - 100
Effluent Distribution pipe
Diameter inches 4 -
Slope percent level level
Distance between seepage trenches feet 12(a) -
Footnote:
(a) See Table 5-1.
TABLE 5-8
SEEPAGE TRENCHES AND PITS
ALLOWABLE SIDEWALL SEEPAGE RATES
SYMBOL AND CHARACTER OF SOIL GALLONS/
BY UNIFIED SOIL CLASSIFICATION DAY/
SYSTEM SQ. FT.
Hardpan or bedrock (including
fractured bedrock with little
or no fines). 0
GW Well graded gravels,
gravel-sand mixtures little
or no fines. 1.55
GP Poorly graded gravels or
gravel-sand mixtures, little
or no fines. 1.55
SW Well graded sands, gravelly
sand, little or no fines. 1.20
SP Poorly graded sands or gravelly
sands, little or no fines. 1.20
SM Silty sand, sand-silt mixtures. 0.8
GM Silty gravels, poorly graded
gravel-sand-silt mixtures. 1.0
GC Clayey gravels,
gravelly-sand-clay mixtures. 0.45(a)
SC Clayey sands, sand-clay
mixtures. 0.45(a)
ML Inorganic silts and very fine
sand, rock flour, silt or
clayey find sands or clayey
silts with slight plasticity. 0.45(a)
MH Inorganic silts, micaceous
or diatomaceous fine sandy
or silty soils, elastic silts. 0.45(a)(b)
CL Inorganic clays or low to
medium plasticity, gravelly
clays, sandy clays, silty
clays, lean clays. 0.45(a)(b)
CH Inorganic clays of high
plasticity, fat clays. 0
OL Organic silts and organic
silty clays of low plasticity. 0
OH Organic clays of medium to
high plasticity, organic silts. 0
PT Peat and other highly organic
silts. 0
Other Impervious formations. 0
Footnotes:
(a) For the purpose of this table, whenever there are reasonable doubts regarding the suitability and estimated
absorption capacities of soils, percolation tests shall be conducted in those soils in accordance with R317-4-1. Soils
within the same classification may exhibit extreme variability in permeability, depending on the amount and type of clay
and silt present. The following soils categories, SC,GC, and ML, MH and CL soils, may prove unsatisfactory for absorption
systems, depending upon the percentage and type of fines present.
(b) These soils are usually considered unsuitable for absorption systems, but may be suitable, depending upon the
percentage and type of fines in coarse-grained porous soils, and the percentage of sand and gravels in fine-grained soils.
A. General Requirements.
1. A percolation test measures the rate which subsurface soil absorbs water for the purpose of identifying porous soil strata and site suitability for absorption systems, and is also a basis for estimating the design criteria of such systems to insure a reasonably long lifespan.
2. While percolation tests constitute a valuable guide for successful operation of disposal systems, considerable judgment must be used in applying the results. Percolation test results shall not be presumptive, prima facie, or conclusive evidence as to the suitability for absorption systems. Such percolation tests may be considered and analyzed as one of many criteria in determining soil suitability for absorption systems. There is no need for conducting percolation tests when the soil or other site conditions are clearly unsuitable.
3. When percolation tests are made, such tests shall be made at points and elevations selected as typical of the area in which the absorption system will be located. Consideration should be given to the finished grades of building sites so that test results will represent the percolation rate of the soil in which absorption systems will be constructed. After the suitability of any area to be used for absorption systems has been evaluated and approved for construction, no grade changes shall be made to this area unless the health authority is notified and a reevaluation of the area's suitability is made prior to the initiation of construction.
B. Required Test Procedures.
1. Test results when required shall be considered an essential part of plans for absorption systems and shall be submitted on a signed "Percolation Test Certificate" or equivalent, certifying that the tests were conducted in accordance with these requirements, and indicating the depth and rate of each test in minutes per inch, the date of the tests, the logs of the soil exploration pits, a statement of the present and maximum ground water table, and all other factors affecting percolation test results. Percolation tests shall be conducted at the owner's expense by or under the supervision of a registered sanitarian, registered engineer, or other qualified person approved by the health authority in accordance with the following:
(a) Conditions Prohibited for Test Holes.
Percolation tests shall not be conducted in test holes which extend into ground water, bedrock, or frozen ground. Where a fissured soil formation is encountered, tests shall be made under the direction of the health authority.
(b) Number and Location of Percolation Tests.
One or more tests shall be made in separate test holes on the proposed absorption system site to assure that the results are representative of the soil conditions present.
Where questionable or poor soil conditions exist, the number of percolation tests and soil explorations necessary to yield accurate, representative information shall be determined by the health authority and may be accepted only if conducted with an authorized representative present.
(c) Type, Depth, and Dimensions of Test Holes.
Test holes shall be dug or bored, preferably with hand tools such as shovels or augers, etc., and shall have horizontal dimensions ranging from 4 to 18 inches (preferably 8 to 12 inches). The vertical sides shall be at least 12 inches deep, terminating in the soil at an elevation 6 inches below the bottom of the proposed absorption system.
2. Test Procedure for Sandy or Granular Soils
For tests in sandy or granular soils containing little or no clay, the hole shall be carefully filled with clear water to a minimum depth of 12 inches over the gravel and the time for this amount of water to seep away shall be determined. The procedure shall be repeated and if the water from the second filling of the hole at least 12 inches above the gravel seeps away in 10 minutes, or less, the test may proceed immediately as follows:
(a) Water shall be added to a point not more than 6 inches above the gravel.
(b) Thereupon, from the fixed reference point, water levels shall be measured at 10 minute intervals for a period of 1 hour.
(c) If 6 inches of water seeps away in less than 10 minutes a shorter time interval between measurements shall be used, but in no case shall the water depth exceed 6 inches.
(d) The final water level drop shall be used to calculate the percolation rate.
3. Test Procedure for Other Soils Not Meeting the Above Requirements.
The hole shall be carefully filled with clear water and a minimum depth of 12 inches shall be maintained above the gravel for at least a 4-hour period by refilling whenever necessary. Water remaining in the hole after 4 hours shall not be removed. Immediately following the saturation period, the soil shall be allowed to swell not less than 16 hours or more than 30 hours. Immediately following the soil swelling period, the percolation rate measurements shall be made as follows:
(a) Any soil which has sloughed into the hole shall be removed and water shall be adjusted to 6 inches over the gravel.
(b) Thereupon, from the fixed reference point, the water level shall be measured and recorded at approximately 30 minute intervals for a period of 4 hours unless 2 successive water level drops do not vary more than 1/16 of an inch and indicate that an approximate stabilized rate has been obtained.
(c) The hole shall be filled with clear water to a point not more than 6 inches above the gravel whenever it becomes nearly empty.
(d) Adjustments of the water level shall not be made during the last 3 measurement periods except to the limits of the last water level drop.
(e) When the first 6 inches of water seeps away in less than 30 minutes, the time interval between measurements shall be 10 minutes, and the test run for 1 hour.
(f) The water depth shall not exceed 6 inches at any time during the measurement period.
(g) The drop that occurs during the final measurement period shall be used in calculating the percolation rate.
4. Calculation of Percolation Rate.
The percolation rate is equal to the time elapsed in minutes for the water column to drop, divided by the distance the water dropped in inches or fractions thereof.
5. Using Percolation Rate to Determine Absorption Area.
The minimum or slowest percolation rate shall be used in calculating the required absorption area.
C. Recommendations to Enhance Test Procedures.
1. Soil Exploration Pit Prerequisite to Percolation Tests.
Since the appropriate percolation test depth depends on the soil conditions at a specific site, the percolation test should be conducted only after the soil exploration pit has been dug and examined for suitable and porous strata and ground water table information. Percolation test results should be related to the soil conditions found.
2. Test Holes to Commence in Specially Prepared Excavations.
All percolation test holes should commence in specially prepared larger excavations (preferably made with a backhoe) of sufficient size which extend to a depth approximately 6 inches above the strata to be tested.
3. Preparation of Percolation Test Hole. Carefully roughen or scratch the bottom and sides of the hole with a knife blade or other sharp pointed instrument in order to remove any smeared soil surfaces and to provide an open, natural soil interface into which water may percolate. Nails driven into a board will provide a good instrument to scarify the sides of the hole. Remove all loose soil from the bottom of the hole. Add up to 3 inches of clean coarse sand or pea-sized gravel to protect the bottom from scouring or sealing with sediment when water is added.
Caving or sloughing in some test holes can be prevented by placing in the test hole a wire cylinder or perforated pipe surrounded by clean coarse gravel.
4. Saturation and Swelling of the Soil. It is important to distinguish between saturation and swelling. Saturation means that the void spaces between soil particles are full of water. This can be accomplished in a relatively short period of time. Swelling is a soil volume increase caused by increase intrusion of water into the individual soil particles. This is a slow process, especially in clay-type soil, and is the reason for requiring a prolonged swelling period.
5. Placing Water in Test Holes.
Water should be placed carefully into the test holes by means of a small-diameter siphon hose or other suitable method to prevent washing down the side of the hole.
6. Percolation Rate Measurement, General.
Necessary equipment should consist of a tape measure (with at least 1/16-inch calibration) or float gauge and a time piece or other suitable equipment. All measurements shall be made from a fixed reference point near the top of the test hole to the surface of the water.
water pollution, sewerage
August 28, 2001
October 2, 2007
19-5
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