The requirements of this Division shall apply to both new individual sewage disposal systems and to replacement of or additions to existing systems.
No person shall install, construct, extend, alter or remodel any sewage disposal system unless he obtains a permit from the Health Officer.
A permit shall not be required in connection with the repair of a sewage disposal system. A field work order shall be issued by the Health Officer as an authorization to perform repairs.
Any person desiring to obtain a permit, a permit renewal, or to conduct a percolation test, or test for an Innovative/Alternative disposal system, pursuant to this Division shall apply to the Health Officer on forms provided for that purpose by the Health Officer. Application for a permit shall be made only by the owner of an individual lot or his authorized representative. It is the responsibility of the applicant to maintain a current address on the application.
The fee for each application filed shall be as designated in the Table of Fees, section 2-253.63, Attachment A and payable upon filing the application. No fee shall be assessed for filing an application for a privy.
Upon completion of satisfactory percolation tests, applicants for a permit under this Division shall furnish the following information:
A completed Sewage Disposal Permit Application.
Six (6) copies of completed site plans of a scale of 1":10' - 1":50' which will include:
Location of the proposed structure to be serviced by the disposal system.
A diagram including the house dimensions and number of floors of the proposed structure to be served by the disposal system.
Location of utilities entering and crossing the lot.
Original and final contours at one (1) or two (2) foot intervals, as may be appropriate, to show the topography and final grading of the lot. On a remodel of a system, the topography shall be furnished if requested by the Health Department.
Location of all satisfactory and unsatisfactory percolation tests and water table holes.
Location of wells on the property and wells within one hundred (100) feet of the property line.
Detailed plan of the proposed disposal system shall include:
Size of septic tank;
Dimensions of disposal trench, seepage pits or seepage bed;
Location of trench to be shown on contour;
Elevation profile of entire disposal system;
Location of all components of disposal system.
Storm water management proposal.
Any pertinent groundwater and geological data as the Health Officer may require.
Evidence to demonstrate to the satisfaction of the Health Officer that there is no part of a community sewerage system legally and economically available to the building to be served.
A fee designated in the Table of Fees, section 2-253.63, Attachment A shall be charged for a plat review of a private septic system or well.
A fee designated in the Table of Fees, section 2-253.63, Attachment A shall be charged for each time plans are required to be resubmitted for additional review because of errors or missing information, and the fee is payable when the plan is resubmitted.
Upon payment of the fee provided under Section 22-117, filing the proper application and compliance with this Subtitle and any applicable law or regulation of the State and County, a permit shall be issued.
All permits issued under this Division shall expire one (1) year from the date of issuance. The Health Officer may issue one renewal for a period not to exceed six (6) months.
Any permit that has been allowed to expire shall only be renewed upon submittal of a new application and payment of a fee as designated in the Table of Fees, section 2-253.63, Attachment A.
The Health Officer shall refuse to issue a permit:
Where a public sewer abuts the property in question, unless the public sewer is not legally and/or economically available to the building to be served;
Where the installation of such a system would be contrary to any County Water and Sewerage Plan adopted pursuant to Sections 9-503 through 9-515, Environment Article, Annotated Code of Maryland;
Where issuance of such permit is in conflict with this or other applicable laws, ordinances, or regulations.
Any person whose application for a permit under this Division has been denied shall be notified by the Health Officer by the sending of a notice of denial to the address of the applicant as listed on his application. The decision to deny an application may be appealed in Circuit Court. Any appeal shall be taken within thirty (30) days of the receipt of the notice of decision.
The minimum lot size shall depend upon the site plan, the percolation test conducted on the lot and be in accordance with COMAR 26.04.03 and the Prince George's County Ten Year Water and Sewerage Plan. Lot size shall not prohibit the remodeling of an existing system that has failed under normal use.
The recovery area of the building site must meet the requirements of the Ten Year Water and Sewerage Plan and COMAR 26.04.03. The recovery area must remain undisturbed and be free of permanent structures, easements, driveways, utility lines, or other physical structures that would prohibit the installation of future replacement drainfields.
The recovery area, as shown on the approved site plan, as well as the septic system, shall remain as part of the lot until such time as the building is connected to public sewer, except as provided for in the Prince George's County Ten Year Water and Sewerage Plan.
A completed application or form provided by the Health Department for percolation tests must be filed with the Health Department specifying the following information:
Owner's name, address, and telephone number;
Applicant's name, address, and telephone number;
Proposed use of the building;
Number of people to be served by this building;
Square footage of proposed building;
Residential use: number of bedrooms, basement plumbing anticipated;
Commercial use:
Fixture count by type and number;
Type of operation;
Number of employees;
Type of waste expected to be discharged;
Other pertinent information as may be necessary.
A proposed site plan must accompany any commercial application specifying the proposed building site, property lines, proposed parking lot, and two (2) foot contours.
A site plan may be required for subdivisions showing the house locations, proposed wells (if applicable), five (5) foot contours, and property lines for each lot.
On lots where the Prince George's County Soil Survey maps or soil borings indicate severe limitations based on seasonally perched, seasonally high water tables, or flood hazards, soil percolation tests and any other tests, as may be required, shall be performed from February 1 - April 30 when the highest water table can be expected at the on-site sewage disposal site. The time period can be expanded or restricted by the Health Officer depending on the static water levels observed in water table wells located throughout the County. If the Health Officer or a professional soil scientist certified by the American Registry of Certified Professionals in Agronomy, Crops, or Soils (ARCPACS) finds that the soil conditions found at the on-site sewage disposal site are contrary to the County Soil Survey and that seasonably high water tables, perched water tables or flood hazards do not exist, the percolation test may be conducted at any time.
Property Identification and Water Table Observation Hole.
The applicant shall locate the property lines and proposed building on the site.
A water table observation hole shall be required from which the static groundwater level shall be determined after a twenty-four (24) hour observation period. The hole shall be located within the proposed recovery area. Subsequent percolation tests shall be conducted in the absorptive layers a minimum distance (buffer) above the determined groundwater table as determined in Table 1 of Appendix B (Section 22-152).
The Health Department is responsible for approving the proposed location of all percolation tests and water table observation holes.
Shallow Test Procedures (less than five (5) feet).
Dig or bore a minimum of four (4) test holes with a diameter from four (4) inches to twenty-four (24) inches and vertical sides to the depth of the proposed absorption trench.
Preparation of test holes.
Remove any smeared soil surfaces and provide a natural soil interface into which water may percolate. Remove all loose material from the hole. Add two (2) inches of coarse sand or fine gravel to protect the bottom from scouring and sediment.
Prewetting and test measurement.
Fill the hole with clean water so that the water level is approximately six (6) inches over the gravel. Measure the drop every thirty (30) minutes, readjusting the water level to six (6) inches above the gravel for two (2) hours. The last measurement observed will determine the percolation rate and shall be recorded as the time in minutes for the water to drop one (1) inch. If the water level in the hole fails to drop the minimum amount in Table 2 (Section 22-153) within a thirty (30) minute period, the hole is unsatisfactory. A more extensive prewet may be required in clayey soils.
Minimum requirement.
A test shall be satisfactory when the percolation rate is demonstrated to be at least .2077 gallons per square foot which is equivalent to the required minimum Maryland State Standard percolation rate of one (1) inch in thirty (30) minutes, based on a one (1) foot square test hole. Percolation rates for round percolation test holes can be found in Table 2. (Section 22-153).
In soils in which the first six (6) inches of water seeps away in less than thirty (30) minutes, the time interval between measurements shall be ten (10) minutes for a maximum of forty (40) minutes. The drop that occurs during the final ten (10) minutes is used to calculate the percolation rate.
Deep Testing Procedures (five (5) feet or greater).
Number and location of tests.
Test holes eight (8) inches to twenty-four (24) inches in diameter shall be bored to a depth where absorptive soil conditions are observed. A minimum of two (2) satisfactory tests shall be conducted to establish adequate disposal area. If deemed necessary, additional tests, or soil borings may be called for.
Prewetting and Percolation Rate Measurement.
Procedures.
The test boring shall be filled with a minimum of four (4) feet of water at which time the water level is allowed to drop a prescribed amount of inches as specified in Table 3 (Section 22-154). After the water level has dropped the prescribed number of inches, the water level is adjusted back to its original level and the procedure is repeated. A more extensive prewet may be required at the discretion of the Health Officer. The last measurement observed will determine the percolation rate and shall be recorded as the time in minutes for the water to drop one (1) inch. If the water level within any of the holes fails to drop the prescribed amount of inches within a thirty (30) minute time period, the hole is considered unsatisfactory.
Minimum requirement.
A test shall be satisfactory when the percolation rate is demonstrated to be at least .2077 gallons per square foot which is equivalent to the required minimum Maryland State Standard percolation rate of one (1) inch in thirty (30) minutes, based on a one (1) foot square test hole. Percolation rates for round percolation test holes can be found in Table 3 (Section 22-154).
Supplementary percolation tests may be required by the Health Officer if needed.
Grading and filling of the sewage disposal area may negate the percolation test. Grading and filling of the proposed sewage disposal and recovery area will not be permitted.
Supplementary percolation tests may be required by the Health Officer after three (3) years from the date of testing, or if the percolation test requirements under which they were conducted are changed by new regulations.
Once a proposed sewage disposal area has proven to be unsatisfactory due to unsatisfactory soil percolation rates, that area may not be retested at the same depth. Unsatisfactory water tables and percolation tests may not be included in the proposed recovery area.
The design of the individual sewage disposal system shall take into consideration topography, water table, soil characteristics, available area, the quantity and type of sewage, the cost of constructing the system, projected sewage flow based on maximum occupancy of the structure, square footage of the structure, or other acceptable methods.
The type of system to be installed shall be determined on the basis of location, soil permeability, and groundwater conditions, including depth to the water table.
The system shall be designed to receive and treat all sewage, including wastes from garbage grinders and automatic washing machines, from the structures. Drainage from basement footings or from roofs shall not enter the system. In addition, wastes shall not be discharged into the system when their introduction would interfere with proper operation of the system.
The treated wastes from a septic tank shall be discharged into subsurface disposal systems approved by the Health Officer.
The minimum distances that shall be observed in locating the various components of the individual sewage system from other structures shall be as indicated in Table 4 (Section 22-155).
Under unusual circumstances, the Health Officer may approve variances to the design criteria, or may require the installation of special sewage disposal components such as alternating drainfields, low pressure distribution, diversion valves or dosing when appropriate.
Individual sewage disposal systems must be designed, constructed, altered, extended or enlarged, or remodeled in accordance with the requirements set forth in this Subdivision.
The building sewer shall be constructed in accordance with the Washington Suburban Sanitary Commission plumbing regulations.
Septic tanks shall meet the following specifications:
The septic tank shall have a capacity of not less than that shown in Table 5 (Section 22-156).
In tanks having two (2) compartments, the inlet compartment shall have a capacity between one-half (1/2) and two-thirds (2/3) of the total tank capacity. If an inverted fitting is used on the inlet compartment side of the baffle, its opening shall be located forty (40) percent of the liquid depth below the flow line. In each case, the total area of the opening provided by the pipe fitting shall be equal to, or greater than, the area of the inlet to the tank.
Septic tanks shall be constructed of reinforced concrete, or other material approved by the Health Officer, and be of permanent construction. Precast concrete tanks should have a minimum wall thickness of three (3) inches and should be adequately reinforced. The cover of the tank shall be designed for a dead load of not less than three hundred (300) pounds per square foot and, if of concrete, should be reinforced and not less than three (3) inches thick. Septic tanks which are subject to vehicular loadings shall be constructed of reinforced concrete adequate to withstand the loadings.
The inlet and outlet of the septic tank shall be provided with manholes. Each compartment in multiple compartment tanks shall be provided with a manhole. Manhole openings shall be at least twenty (20) inches in minimum dimension and provided with covers which can be sealed watertight. Manhole extensions shall be required where necessary to provide access for maintenance to the septic tank and be so constructed to be watertight.
Pipe inlets shall be installed consisting of a sanitary tee of cast iron, PVC, or other material as authorized by the Washington Suburban Sanitary Commission plumbing regulations. Outlets may be sanitary tees of cast iron, vitrified clay pipe, plastic or other acceptable material. Short sections of pipe shall be installed in the tees to the required outlet depths. Baffles may be installed when approved by the Health Officer.
The invert of the inlet pipe shall be located at least two (2) inches above the invert of the outlet.
Construction Standards for Absorption Trenches.
The minimum absorption trench length shall be calculated according to Appendix A (Section 22-150).
The trench shall be filled with filter material to a level two (2) inches above the distribution line. The filter material shall cover the tile and extend the full length, width and depth of the trench and be not less than six (6) inches below the tile and two (2) inches over the tile. The filter material shall be washed gravel or other material approved by the Health Officer ranging in size from one and one-half (1 1/2) to two and one-half (2 1/2) inches. The filter material shall be reasonably free of fines, dirt, clays and other associated material and shall be covered by untreated paper or similar material one (1) foot from the top of the ground.
Distribution lines in absorptive trenches shall be constructed of ridged perforated plastic pipe that shall meet National Sanitation Foundation (NSF) Standard 14 or other material approved by the Health Officer. Each pipe must sustain a minimum pressure of twenty-five (25) psi and must have a minimum of three (3) rows of perforations with each row having three (3) perforations of three-quarter (3/4) inch diameter per lineal foot. The invert of each distribution line shall be installed approximately eighteen (18) inches below ground grade.
Absorptive trenches with depths of three (3) feet or less shall not be constructed on ground having a slope greater than ten (10) percent. Absorptive trenches with depths of greater than three (3) feet, but less than five (5) feet shall not be constructed on slopes exceeding fifteen percent (15%). Absorptive trenches with depths of five feet or greater shall not be constructed on ground with slopes in excess of twenty-five percent (25%).
All absorptive trenches shall be constructed at the same depth as the percolation test.
Absorption drainfields depths of less than five (5) feet will be spaced according to Table 6 (Section 22-157). Absorption drainfields depths of five (5) feet or greater will maintain a spacing of twice the gravel depth between drainfields up to a maximum of twenty (20) foot separation.
The distribution lines within one (1) absorption trench shall not exceed one hundred (100) feet in length. A one percent (1%) slope shall be maintained on the first twenty (20) feet of pipe while the remainder of pipe should maintain zero percent (0%) slope.
Seepage Pits; specifications.
Absorptive area. Seepage pits may be installed where the absorptive strata is seventeen (17) feet or greater below grade.
Location. Seepage pits shall not be located in swales or ravines and shall not be installed on slopes exceeding twenty-five percent (25%).
Number of Pits. The number of pits shall be calculated based on the equivalent length of drainfield as determined by Appendix A (Section 22-150).
Depth of Excavation. The seepage pit excavation shall be constructed to the depth of the percolation tests.
Seepage pits shall be separated a minimum of twenty (20) feet from center to center.
The general construction of seepage pits shall be in accordance with Figure 1 (Section 22-158).
No person shall construct a privy for a structure served by a water supply under pressure. All privy pits shall be covered with a privy house, the floor and riser of which shall be constructed of concrete or tightly fitted wood. The riser shall be capped with a tight fitting, self- closing lid. The pit shall be vented through a screened stack extending from the top of the pit to above the roof of the house. Construction of the pit, floor, riser, seat and vent shall be such as to prevent flies and rodents from access to the pit contents. On request, a plan of a privy may be made available by the Health Officer. See Figure 2 (Section 22-159).
At the discretion of the Health Officer, privies shall only be used in areas of the County where no other means of sewage disposal is available or in parks owned or operated by a governmental agency.
Privies will not be approved for new construction except for campgrounds or at the discretion of the Health Officer. All privies, with the exception of vault privies, must be constructed so that the bottom of the privy pit shall meet minimum buffer requirements as established in Table 1 (Section 22-152).
A chemical toilet may only be used as a method of sewage disposal under the following conditions:
As a temporary alternative for an existing building where water under pressure is not available until such time that a permanent means of sewage disposal is provided for that building;
For a temporary event not to exceed fourteen (14) days;
Building construction sites during construction;
At the discretion of the Health Officer, in parks owned or operated by a governmental agency.
Chemical toilets must be maintained and emptied as necessary by a licensed scavenger to prevent a sewage disposal nuisance.
Holding tanks shall not be used as a means of sewage disposal for new construction.
The Health Officer may authorize the use of a holding tank as a method of sewage collection and disposal under the following conditions:
As a temporary means of sewage disposal during repair or remodel of an existing individual sewage disposal system.
As a interim means of sewage disposal where correction of a malfunctioning septic system is impractical until such time as a connection to public sewer can be made. The property must connect to the public sewerage system when it becomes available to the property.
Prior to issuance of a permit for a holding tank the applicant shall submit to the Health Officer a copy of a valid contract with a licensed septic tank scavenger. The contract shall indicate that the holding tank will be properly cleaned and maintained during its use.
The holding tank must be maintained and emptied as necessary by a licensed scavenger to prevent a sewage disposal nuisance.
In the interest of preserving the public health, the Health Officer may, if necessary, impose more stringent requirements than provided in this Subdivision.
Any method of sewage disposal, by which the sewage is accessible to humans, flies, animals, surface drainage, or is endangering a water supply or which is detrimental to health in any way, shall constitute a sewage disposal nuisance. The Health Officer shall condemn all sewage disposal nuisances, and any sewage disposal method condemned shall not be reapproved unless the nuisance is abated.
No person shall occupy for dwelling or business purpose any dwelling, apartment house, store, or other building where the sewage disposal system has been condemned or the method of sewage disposal is detrimental to health.
The Health Officer shall have the power to make inspections of all methods of sewage disposal. If a sewage disposal nuisance is found to exist, the Health Officer shall notify the owner or occupant of the property to reconstruct or replace the existing system under permit as prescribed in this Subtitle or to connect to public sewer if it is available. No owner or occupant shall maintain a sewage disposal nuisance after the time limit specified by the Health Officer.
If a sewage disposal nuisance is found to exist, the Health Officer may, in addition to notices served in other ways, post a notice on or about any building affected by or contributing to the nuisance.
Upon receipt of a written request from the current owner, contract purchaser, or an authorized agent and an inspection fee as designated by the Health Officer, the Health Officer may investigate both the sewage disposal and water supply systems serving the property and shall make comments appropriate to both systems. The written request shall include complete property description by street address or complete legal description by subdivision, lot, block, or tax map, grid, and parcel numbers.
Upon receipt of a written request from the current owner and an inspection fee as designated by the Health Officer, the Health Officer may investigate the use of an existing water supply system to be maintained for agricultural use. The written request shall include a complete property description by street address and the telephone number of the property owner. The inspection fee does not include any costs for water sample analysis.
Calculation of minimum absorption trench length.
Design Flow (gallons per day).
Residential flow must be designed in accordance to Table 5 (Section 22-156).
Nonresidential design sewage flow shall be equal to twice the daily average sewage flow.
Loading Rate (gallons per day per square foot).
The loading rate is determined by Figure 3 (Section 22-160) using the State equivalent percolation rate.
Available Absorptive Area (square feet per linear feet).
Deep trenches. The available absorptive areas shall be equal to the height of the absorptive layer found on the percolation test report.
Shallow trenches. The available absorptive area shall equal the bottom area per linear foot of drainfield.
Dry wells. The available absorptive area shall be equal to the height of the absorptive layer found on the percolation test report multiplied by the circumference.
Required Absorptive Area.
Design Flow (gpd)
Minimum Length of Trench
= Required Absorptive Area (ft 2 ) = feet of Trench
Available Absorptive Area (ft 2 ) / ft
| TABLES |
| Table 1 - |
Buffer requirements for various months of the year. |
| Table 2 - |
Minimum water level drop in thirty (30) minutes as a function of diameter of test hole (shallow tests). |
| Table 3 - |
Minimum water level drop in thirty (30) minutes as a function of diameter of test hole (deep tests). |
| Table 4 - |
Minimum distance requirement. |
| Table 5 - |
Septic tank capacity and design flow. |
| Table 6 - |
Shallow trench spacing. |
| FIGURES |
| Figure 1 - |
Dry Well Configuration. |
| Figure 2 - |
Privy Configuration. |
| Figure 3 - |
Loading Rate Graph. |
Buffer requirements for various months of the year.
| MONTHS |
BUFFER REQUIREMENTS |
| December 1 - January 31 |
5' |
| February 1 - May 15 |
4' |
| May 15 - June 15 |
5' |
| June 16 - October 16 |
8' |
| October 17 - November 30 |
6' |
Shallow Percolation Tests - Minimum drop as a function of hole diameter.*
| DIAMETER INCHES |
CORRECTION FACTOR |
DROP IN 30 MINUTES |
MINUTES PER INCH DROP |
| 4 |
2.33 |
2.33" |
13 |
| 6 |
1.67 |
1.67" |
18 |
| 8 |
1.33 |
1.33" |
23 |
| 10 |
1.13 |
1.13" |
27 |
| 12 |
1.00 |
1.00" |
30 |
| *Equivalent to State standard test of linear inches in 30 minutes. |
Deep percolation tests - minimum drop as a function of hole diameter with four feet of water in the hole.*
| DIAMETER INCHES |
DROP IN 30 MINUTES |
MINUTES PER INCH DROP |
| 8 |
8.0 |
3.6 |
| 10 |
6.0 |
5.0 |
| 12 |
5.0 |
6.0 |
| 14 |
4.5 |
6.6 |
| 16 |
4.0 |
7.5 |
| 18 |
3.5 |
8.5 |
| 20 |
3.0 |
10.0 |
| 22 |
3.0 |
10.0 |
| 24 |
2.5 |
12.0 |
| *Equivalent to State standard test. .2077 gallons/square foot in 30 minutes. |
For test holes with more than four feet of water, the minimum drop shall be determined by the following formula:
| Minimum Drop = 16H / D |
| H = Height of water column (feet) |
| D = Diameter of hole (inches) |
Minimum Distance Requirements.
| COMPONENT OF SYSTEM |
SHALLOW WELL |
DEEP WELL |
PRESSURE WATER LINE |
STREAM |
DWELLING |
PROPERTY LINE |
| Building Sewer |
50 |
50 |
7 |
- |
- |
- |
| Septic Tank |
100 |
50 |
10 |
- |
15** |
10** |
| Disposal Field |
100 |
50 |
10 |
25* |
20** |
10** |
| Dry Well |
100 |
50 |
10 |
50* |
20** |
10** |
| *Field or pit must not be in a floodplain. **These minimum distances may be reduced by the Health Officer. |
Septic Tank Capacity and Design Flow.
RESIDENTIAL SINGLE-COMPARTMENT TANK
| GROSS SQUARE FOOTAGE |
SEPTIC TANK CAPACITY |
DESIGN FLOW |
MINIMUM DRAINFIELD LENGTH |
| 0 - 1,750 sq. ft |
1,000 gals. |
720 gal/day |
70 |
| 1,751 - 2,250 sq. ft |
1,500 gals. |
900 gal/day |
100 |
| 2,251 - 3,000 sq. ft |
1,750 gals. |
1,000 gal/day |
120 |
| > 3,000 sq. ft |
2,000 gals. |
1,000 gal/day |
130 |
RESIDENTIAL DOUBLE-COMPARTMENT TANK
| GROSS SQUARE FOOTAGE |
SEPTIC TANK CAPACITY |
DESIGN FLOW |
MINIMUM DRAINFIELD LENGTH |
| 0 - 1,750 sq. ft |
1,000 gals. |
720 gal/day |
70 |
| 1,751 - 2,250 sq. ft |
1,250 gals. |
900 gal/day |
100 |
| 2,251 - 3,000 sq. ft |
1,500 gals. |
1,000 gal/day |
120 |
| > 3,000 sq. ft |
1,800 gals. |
1,000 gal/day |
130 |
Commercial Septic Tank Capacity.
Tank Capacity will be based on a forty-eight (48) hour retention capacity as calculated from the average sewage flow.
Two-compartment septic tanks shall be required for commercial establishments having a design flow in excess of 1,000 gallons/day.
Shallow trench spacing.
| WIDTH (FEET) |
DEPTH (FEET) |
SPACING (FEET) |
| 1 |
2-3.0 |
3 |
| 1 |
3.5 |
4 |
| 1 |
4.0 |
5 |
| 1 |
4.5 |
6 |
| 2 |
2-4.5 |
6 |
| 3 |
2-4.5 |
9 |
A privy pit may be constructed by boarding a square or rectangular pit to prevent earth caving or by providing a watertight structure in the pit.
The pit shall provide a minimum capacity of 50-cubic feet. The pit should be lined with boards and a privy building shall be placed over the pit. The floor of this building shall be of wood or concrete with the privy seat of wood. A vent located adjacent to the seat shall extend from the pit to a point above the roof of the building. The seat shall be provided with a cover which shall be self-closing.
All openings in the building shall be screened to prevent the entrance of flies. Earth shall be mounded on all sides of the building to prevent the entrance of rats to the pit.
State Standard Test.
Area for absorption.
Bottom = 1 ft 2
4 sides at 1/2 ft 2
TOTAL = 1 + 4 (.5) = 3 ft 2
Absorptive Rate in gallons / ft 2 / 30 minutes.
| .62333 gallons |
= |
.2077 gallons |
| 3 ft 2 / 30 mins. |
ft 2 / 30 mins. |
Conversion to State equivalent.
Theory. State standard passing percolation test is .2077 gallons/ft/30 minutes. Any diameter hole can be used for a test hole provided that the equivalent State percolation test rate is achieved in terms of gallons per square foot in 30 minutes, that being .2077 gallons for every square foot of absorptive area (i.e., a hole with ten (10) square feet of wetted area would have to absorb 2.077 gallons of water). This volume can be converted into an inch drop as a function of test hole diameter.
Shallow Test Conversion: (Test hole with six (6) inches of water)
Volume as a function of test hole diameter.
Formula H × Pi R 2 × 7.48 H = Height = 6 inches = .5 feet R = Radius = D/2 Pi = 3.14159 7.48 converts cubic feet to gallons
Volume = (.5) (Pi) (D/2) 2 (7.48)
D in inches = (.5) (Pi) (D/12) 2 (1/4) (7.48)
Volume absorbed = Pi (X/12) (D/12) 2 (1/4) (7.48) X = inches dropped
Available Absorptive Area (Based on six (6) inches of water).
Includes sidewall and bottom
Area = Pi D H + Pi (D/2)2
H = Height = 6 inches = .5 feet D = Diameter (inches)
Converting D into feet = D/12
Area = Pi(D/12)(.5) + Pi (D/12) 2 (1/4)
Volume/Area as a function of diameter and inch drop.
Pi (X/12) (D/12) 2 (1/4) (7.48) Pi (D/12) (.5) + Pi (D/12)2(1/4)
Simplifying:
(X/12) (D/12) (1/4) (7.48) (.5 + D/48)
Set equal to .2077 and solve for X.
.2077 = .0129861 (D) (X) (.5 + D/48)
Varying D from 4 to 12 inches gives minimum inch drop in 30 minutes being equal to State standard test in terms of gallons per square feet in 30 minutes. This was reported in Table 2.
To convert to equivalent State test rate, multiply the rate in minutes per inch by the correction factor found in Table 2.
Deep Test Conversion: (Bottom area not included, with four (4) feet of water)
Volume formula: V = Pi (H) (D/12) 2 (1/4) (7.48)
Volume absorbed = Pi (D/12) 2 (1/4) (7.48) (X/12)
Pi = 3.14159 D = Diameter (inches) X = Equivalent drop inches = H in general formula
Area formula: Pi (D/12)
Pi = 3.14159 D = Diameter (inches) H = Height = 4 feet
Simplifying: Pi (D/12) (4) = Area
Volume (gallons) / Area (ft 2 )
| Pi (X/12)(D/12)(D/12)(1/4)(7.48) |
= |
(X/12)(D/12)(7.48)(1/4) = |
| Pi (D/12)4) |
|
4 |
|
| .0129861 (D)(X) |
= |
.0032465 (D)(X) |
| 4 |
Set this formula equal to the minimum State standard rate.
.0032465 (D) (X) = .2077 gals/ ft 2 /30 minutes
Varying D and solving for X gives minimum rates found in Table 3.
To convert to State equivalent rate, 30 minutes/inch is divided by the ratio of percolation rate gallons/ft/minute to the State maximum rate of .2077 gallons/ ft 2 /30 minutes by the following formula:
Where D = Diameter (inches) X = Drop recorded (inches) T = Time to measure drop (minutes)
Simplifying equation.
| 30 minutes/inch .469 (D)(X) |
= |
____ minutes/inch |
| T |
| 64 = (D) (X) |
= |
____ minutes/inch |
| T |
i.e., 8 inch diameter hole drops 8 inches in 15 minutes. Find equivalent State standard rate.
|
64 |
| = Equivalent rate = |
(D) (X) |
= 15 minutes/inch |
|
T |