Md. Code Regs. 26.04.02.05

Current through Register Vol. 51, No. 24, December 2, 2024

Section 26.04.02.05 - Design and Construction of Conventional On-Site Sewage Disposal Systems

A. Sewage from bathrooms, kitchens, laundry fixtures, and other household plumbing, exclusive of the backwash from potable water treatment devices, shall receive adequate treatment from a sewage treatment unit before the effluent is discharged to an approved on-site sewage disposal area.

B. On-site sewage disposal systems and replacement areas location requirements:

(1) The sewage disposal system is at least 100 feet removed from any water well system in unconfined aquifers and 50 feet from any water well system in confined aquifers.

(2) The on-site sewage disposal system is located downgrade from a private water supply. A variance to this requirement may be granted by the Department of the Environment after consideration of hydrogeologic conditions and recommendations of the Approving Authority.

C. The owner of a restaurant or an establishment discharging grease shall install a grease interceptor on each separate kitchen waste drain.

D. Residential Septic Tank Size Criteria. Septic tanks serving a residential use, not requiring a BAT system, shall meet the following criteria and tables. This table provides for use of garbage disposal units, automatic clothes washers, and other household appliances.

Septic Tank Criteria
Number of Bedrooms	Minimum Septic Tank Capacity Below Outlet
3 or less	1,000 gallon
4	1,250 gallons
For each additional bedroom, add 250 gallons

E. Criteria of a Residential Septic Tank.

(1) A residential septic tank shall have a minimum of two compartments or two tanks in series.

(2) A residential septic tank shall be made of materials and constructed in a manner acceptable to the Approving Authority.

(3) A residential septic tank shall be watertight. Manufacturers shall certify that septic tanks are watertight. The Approving Authority may require one of the following tests to determine watertightness.

(a) Vacuum Testing. Seal the empty tank and apply a vacuum to two inches of mercury. The tank is acceptable if 90 percent of the vacuum is held for 2 minutes.

(b) Water-Pressure Testing. Seal the tank with all the inlet and outlet pipes installed. Fill with water and let stand for 24 hours. Refill the tank. The tank is acceptable if the water as level measured in the tank remains the same for one hour.

F. Institutional Septic Tank Criteria. The applicant for an institutional or commercial installation, not requiring a BAT system, shall calculate the minimum septic tank capacity according to the following criteria:

(1) Flows of 1,500 gallons per day (gpd) or greater: V = 1,125 gallons + 0.75Q where V = minimum septic tank volume, Q = estimated daily peak sewage flow;

(2) Flows of less than 1,500 gallons per day (gpd): V = 1.5 Q; and

(3) 1,000 gallons is the minimum septic tank capacity.

G. Septic Tank Criteria where a BAT system is required under Regulation .07 of this chapter. If an approved BAT system includes a septic tank, the permitee shall size the septic tank in accordance with the requirements of the manufacturer or designer of the BAT.

H. Pump Chambers and Equipment Criteria.

(1) Pressure distribution systems, including sand mound and at-grade systems, have a pump that provides adequate capacity for handling peak flow at the design head. The design head shall include static head, friction head, and an additional 2 feet of discharge head.

(2) The pump is installed to allow the sewage to drain back to the pumping chamber from the distribution system to prevent freezing. Use of check valves is not recommended.

(3) A pump is used that can resist the corrosive effects of septic tank effluent.

(4) A minimum of 6 inches is provided between the pump intake and the floor of the pumping chamber.

(5) The pump is constructed and located to prevent the entrance of surface water or ground water.

(6) The dosing frequency is approximately 6 times a day.

(7) A minimum of 1-day storage capacity is provided above the high water alarm.

(8) A high water alarm is installed within the pumping chamber and wired on a circuit separate from that of the pump.

(9) The pumping chamber provides adequate volume to store the sewage between doses.

(10) The pump control sensor is located so that it is not affected by flow entering the pump chamber.

I. For residential property the minimum design flow is based on 150 gpd per bedroom. The Approving Authority may establish design flows based on equivalent square footage; however, the minimum design flow may not be less than 300 gpd per residence and 150 gpd per bedroom.

J. The Department shall provide guidance on estimating design flows for commercial and institutional establishments. Design flow is based on the maximum daily flow. Applications for commercial and institutional establishments shall include a proposed design flow for the system. The Approving Authority may approve design flows based upon actual flow measurements, estimated flows for square footage or estimated flow for similar establishments. The design flow may not be less than 400 gpd for a commercial or institutional establishment. Any facility discharging waste other than domestic sewage may be required to obtain an individual groundwater discharge permit.

K. Loading Rates for Onsite Sewage Disposal Systems.

(1) A domestic, commercial, or institutional establishment with effluent quality stronger than 300 mg/l biological oxygen demand or 300 mg/l suspended solids shall employ a pretreatment unit to pretreat the effluent to a maximum of 300 mg/l biological oxygen demand and 300 mg/l suspended solids.

(2) Maximum loading rates are based on wastewater with the equivalent strength of typical domestic sewage.

(3) The maximum loading rates for on-site disposal of sewage by sewage disposal systems are as follows:

Maximum Loading Rates for Systems with Design Flow Less than 5,000 Gallons per Day
Percolation Rate in Minutes for 1-Inch Drop After Prewetting	Maximum Loading Rate (Gallons per Day per Square Foot)
2 - 5	1.2
6 - 15	0.8
16 - 30	0.6

Maximum Loading Rates for On-Site Disposal by Sewage Disposal Systems with Design Flow Greater Than or Equal to 5,000 Gallons Per Day
Percolation Rate in Minutes for 1-Inch Drop After Prewetting	Maximum Loading Rate (Gallons / Day/ft2)	Maximum Loading Rate for effluent with BODs and TSS 30 mg/l or less * (Gallons / Day/ ft2)	Maximum Loading Rate for MBR effluent** (Gallons / Day/ ft2)
2-5	0.8	1.6	2.0
6-15	0.6	1.2	1.6
16-30	0.4	0.8	1.2
* An individual groundwater discharge permit is required and advanced pretreatment employed. ** MBR effluent is defined as BOD5 <3 mg/L, TSS <1 mg/L, and TN <3 mg/L. An individual groundwater discharge permit is required and advanced pretreatment employed.

L. The absorptive area required is calculated by dividing the appropriate design flow by the appropriate loading rate.

M. Standard trench length is calculated by dividing the required absorptive area by the proposed trench width.

N. Standard Trench System.

(1) Approval of Standard Trench System. A standard trench system may be approved by the Approving Authority if an adequate treatment zone and absorptive area are available. The system size is based on bottom absorptive area only.

(2) Standard trench length = a amp;Atilde;amp;middot; w

Where:

a = The absorptive area required for the desired use by reference to regulation .05M.

w = Width of trench in feet;

(3) Minimum distance, sidewall to sidewall, between standard trenches is at least 6 feet of undisturbed soil between 2-foot wide trenches and 9 feet between 3-foot wide trenches.

O. Deep Trench System.

(1) Approval of Deep Trench Systems. A deep trench system may be approved by the Approving Authority when sufficient soils are available to allow the use of side walls in determining minimum absorption area requirements and an adequate treatment zone is available.

(2) Deep trench length = x a amp;Atilde;amp;middot; w

Where:

w = Width of trench in feet;

d = Depth of usable sidewall area on the basis of percolation tests, observation of the soil profile at various soil depths, and other hydrogeologic data as may be required by the Approving Authority; and

a = The absorptive area required for the desired use by reference to regulation .05M.

(3) Minimum distance, sidewall to sidewall, between deep trenches shall be two times the effective absorptive depth of gravel in the deepest trench or 18 feet, whichever is the lesser distance. The distance between trenches may not be less than 10 feet.

P. The minimum distance between seepage pits is equal to three times the diameter of the largest pit.

Q. Criteria for Large Onsite Sewage Disposal Systems

(1) Property with an accumulative maximum daily flow of 5,000 gpd or greater, served by onsite sewage disposal, is a large onsite sewage disposal system.

(2) An applicant for a large onsite sewage disposal system with a maximum daily flow of 10,000 gpd, or more, shall obtain an Individual Groundwater Discharge Permit from MDE. The Department may require an applicant for a system with a maximum daily flow of less than 10,000 gpd to obtain an Individual Groundwater Discharge Permit if specific project characteristics warrant additional monitoring or control or special permit requirements.

(3) An application for a large on-site sewage disposal system is submitted by the property owner, or property owner's agent, to the Approving Authority and MDE. Evaluation and review of an application is performed jointly by the Approving Authority and MDE.

(4) A large system incorporates uniform low-pressure distribution with dosing and resting features in its design and construction.

(5) Suitable sewage disposal area is set aside for the installation of an initial and two replacement systems at 100 percent of the peak daily flow.

(6) The initial installation is designed and constructed for 150 percent of the peak daily flow.

(7) A nitrogen balance analysis for the groundwater system is performed by a qualified professional and submitted to the Approving Authority and MDE. The nitrogen concentration at the property line or at any point adjacent to a water course does not exceed 10 mg per liter.

(8) A mounding analysis is performed by a qualified professional and submitted to the Approving Authority and MDE. The 20-year mound height is estimated and does not rise to a point where the minimum required separation distance between the bottom of the system and the water table is not maintained.

R. Maximum daily flow is used as the basis of disposal area design regardless of the type of treatment unit or disposal method proposed.

S. Greater absorption area than provided for in this regulation may be required by the Approving Authority based on local conditions and experience.

T. Fill material may not be used in conventional subsurface sewage disposal systems except as placed over open chambers or perforated pipe.

U. Sand Mound Systems.

(1) The criteria for a sand mound system are:

(a) Ground water is located at least 2 feet below the ground surface as measured during the period of the highest water table;

(b) Excessively permeable material or fractured bedrock is located at least 2 feet below the ground surface;

(c) Percolation rates measured after prewetting utilizing a method that measures vertical permeability are not faster than 1 inch per 2 minutes and not slower than 1 inch per 60 minutes; and

(d) The sewage disposal area has a slope of less than 12 percent.

(2) The Approving Authority may require the depth to groundwater or fractured rock to be greater than 2 feet below the ground surface to ensure proper operation of a sand mound system if the Approving Authority determines that local conditions make greater depths necessary.

(3) The criteria and conditions for performing site evaluation and testing for a sand mound system area:

(a) Tests are performed in the least permeable soil horizon which is located in the upper 24 inches of soil; and

(b) Tests are conducted with an apparatus which minimizes horizontal movement of water.

(4) The criteria for construction of a sand mound are:

(a) The long axis of the sand mound and the trench or bed is perpendicular to the slope.

(b) All parts of a sand mound shall meet the horizontal separation distance in Regulation .04J of this chapter.

(c) The linear loading rate, determined by dividing the design flow by the length of the gravel bed does not exceed 10 gallons per day per foot.

(d) A two compartment septic tank or two tanks in series, with an effluent filter installed in the outlet baffle of the second tank or compartment, is used for pretreatment for all sand mounds that do not require BAT.

(e) Sand mounds shall use a pressure distribution system which is designed to have a minimum pressure of 2 feet of head at the distal end.

(f) The distribution system is installed level on a bed or in a series of trenches with at least 6 inches of gravel below the pipe.

(g) The gravel is between 3/4 inch and 2 inches in size and free of fines.

(h) A minimum of 2 inches of gravel is placed above the distribution pipe.

(i) The gravel is covered with a geotextile filter fabric to prevent sand and fines from entering the gravel.

(j) The trench or bed is constructed so that the bottom of the trench or bed is level.

(k) The sand beneath the trench or bed is:

(i) Of an effective size between 0.25 and 0.5 mm and have a uniformity coefficient of 3.5 or less; or

(ii) Of an effective size between 0.15 and 0.3 mm and have a uniformity coefficient between 4 and 6 and contain less than 20 percent of material larger than 2.0 mm and less than 5 percent of material less than 0.053 mm.

(l) Holes in the distribution lines are free of burrs and other protrusions.

(m) The sand mound is covered with approximately a 6 inch layer of top soil and seeded.

(n) The sand mound side slopes may not exceed a 3 to 1 grade regardless of the natural slope of the ground.

(o) The top of the sand mound is crowned to allow rain water to run off.

(p) Settling problems are corrected when they are detected.

(q) Observation ports to measure effluent levels in the mound are installed:

(i) At the gravel and sand interface in the gravel bed or trench; and

(ii) At the soil and sand interface beneath the gravel bed.

(5) The criteria for sizing sand mounds are:

(a) The bed or trenches in the mound are sized to absorb not more than:

(i) 1.2 gallons per square foot per day based on the bottom area of the beds or trenches for sand meeting the specification set forth in §V(4)(k)(i) of this regulation; and

(ii) 1.0 gallons per square foot per day based on the bottom area of the beds or trenches for sand meeting the specification set forth in §V(4)(k)(ii) of this regulation.

(b) The sand mound has a basal area sized to absorb effluent in accordance with the following:

(i) For a vertical percolation rate between 2 minutes per inch and 30 minutes per inch, not more than 1.2 gallons per square foot per day;

(ii) For a vertical percolation rate between 31 minutes per inch and 45 minutes per inch, not more than 0.75 gallons per square foot per day; and

(iii) For a vertical percolation rate between 46 minutes per inch and 60 minutes per inch, not more than 0.5 gallons per square foot per day.

(c) The basal area includes only that area that is directly below the trenches or bed and that area downslope from the trenches or bed.

(d) The amount of sand fill below the trench or bed may not be less than 1 foot.

(e) The total distance from the bottom of the trench or bed to the high water table may not be less than 4 feet except when a lesser separation is approved pursuant to Regulation .04C(3)(a) of this chapter.

(f) A minimum 25 foot wide area downslope of the sand mound is designated on a plan as an area protected from compaction and grading and free of structures such as buildings and driveways. If a limiting horizon that may restrict the vertical flow of effluent through the soil beneath the sand mound is present, this 25 foot wide area may be increased.

(6) Site preparation requirements are:

(a) The site is not compacted by earthmoving or other equipment;

(b) The grass or other vegetation is cut and removed as much as possible;

(c) The soil is plowed to a depth of 6 inches perpendicular to the slope;

(d) Work may not be done during wet weather, during wet soil conditions, or during freezing and thawing conditions;

(e) Trees on the site are cut at ground level and the stumps left in place; and

(f) A certified sand mound installer is present during construction of all sand mounds.

(7) Certification of Installers.

(a) A sand mound system may only be installed by a certified installer.

(b) The Maryland Department of the Environment may award a sand mound installer certification if the applicant has successfully completed a course of study and examination in the practice of construction of mound systems. The course and examination shall be approved by the Department of the Environment.

(c) The course of study and examination shall be given at least once each year by the Department of the Environment or the Department's designee.

(d) The certification is valid for a period of 3 years and may be renewed if the installer has complied with all the applicable laws and regulations.

(e) The Maryland Department of the Environment may withdraw certification at any time for violation of these regulations.

V. At-Grade Systems.

(1) The criteria for the use of an at-grade system are:

(a) Ground water is located at least 4 feet below the ground surface as measured during the period of the highest water table;

(b) Excessively permeable material or fractured bedrock is located at least 4 feet below the ground surface;

(c) Percolation rates measured after prewetting utilizing a method that measures vertical permeability are not faster than 1 inch per 2 minutes and not slower than 1 inch per 60 minutes; and

(d) The sewage disposal area has a slope of less than 12 percent.

(2) The criteria and conditions for performing a site evaluation and testing for an at-grade system are:

(a) Tests are performed in the least permeable soil horizon which is located in the upper 30 inches of soil; and

(b) Tests are conducted with an apparatus which minimizes horizontal movement of water.

(3) The criteria for construction of an at-grade system are:

(a) The long axis of the trench or bed is perpendicular to the slope;

(b) All parts of an at-grade system shall meet the horizontal separation distance in Regulation .04J of this chapter;

(c) The linear loading rate, determined by dividing the design flow by the length of the gravel bed may not exceed 9 gallons per day per foot;

(d) A two compartment septic tank or two tanks in series is used for pretreatment for all at-grade systems that do not require BAT;

(e) An at-grade system uses a pressure distribution system designed to have a minimum pressure of 2 feet of head at the distal end;

(f) The distribution system is installed level on a bed or in a series of trenches with at least 6 inches of gravel below the pipe;

(g) The gravel is free of fines and is between 3/4 inch and 2 inches in size;

(h) A minimum of 2 inches of gravel is placed above the distribution pipe;

(i) The gravel is covered with a geotextile filter fabric to prevent fines from entering the gravel;

(j) Holes in the distribution lines are free of burrs and other protrusions;

(k) An at-grade system is covered with approximately a 12 inch layer of top soil and seeded;

(l) An at-grade system's side slopes may not exceed a 3 to 1 grade and shall extend a minimum distance of 5 feet from the gravel bed regardless of the natural slope of the ground;

(m) The top of the at-grade system is crowned to allow rain water to run off; and

(n) Settling problems are corrected when they are detected.

(4) Criteria for Sizing an At-Grade System.

(a) The at-grade system has an effective gravel absorption area sized to absorb effluent in accordance with the following:

(i) 2 to 15 minutes per inch - 0.8 gallons per day per square foot;

(ii) 16 to 30 minutes per inch - 0.6 gallons per day per square foot; and

(iii) 31 to 60 minutes per inch - 0.4 gallons per day per square foot.

(b) The total distance from the bottom of the trench or bed to the high water table may not be less than 4 feet except when a lesser separation is approved pursuant to Regulation .04C(3)(a) and.04D of this chapter.

(c) A minimum 25 foot wide area downslope of the at-grade system is designated on a plan as an area protected from compaction and grading and shall remain free of structures such as buildings and driveways. If a limiting horizon is present beneath the at-grade system, this 25 foot wide area may be increased.

(6) The criteria for preparing a site for an at-grade system area:

(a) The site may not be compacted by earthmoving or other equipment;

(b) The grass or other vegetation is cut and removed as much as possible;

(c) The soil beneath the entire at-grade is plowed to a depth of 6 inches perpendicular to the slope;

(d) Work may not be done during wet weather, during wet soil conditions, or during freezing and thawing conditions; and

(e) Trees on the site are cut at ground level and the stumps left in place.

(7) Certification of Installers.

(a) At-grade systems may only be installed by a certified installer.

(b) The Maryland Department of the Environment may award an at-grade installer certification, if the applicant has successfully completed a course of study and examination in the practice of construction of at-grade systems. The course and examination shall be approved by the Department of the Environment.

(c) The course of study and examination shall be given at least once each year by the Department of the Environment or the Department's designee.

(d) An at-grade system may be installed if a certified at-grade installer is present during the construction of the at-grade system.

(e) The certification is valid for a period of 3 years and may be renewed prior to its expiration if the installer has complied with all the applicable laws and regulations.

Md. Code Regs. 26.04.02.05

Regulations .05 effective November 16, 1953; amended effective July 1, 1957, November 15, 1957, June 8, 1965, October 15, 1966, April 1, 1967, December 1, 1970
Regulations .05 adopted effective November 18, 1985 (12:23 Md. R. 2218)
Regulation .05 amended effective November 3, 1986 (13:22 Md. R. 2398)
Regulation .05O and Q amended effective April 27, 1992 (19:8 Md. R. 806)
Regulations .05 adopted effective 41:9 Md. R. 522, eff.5/12/2014 ; amended effective 46:7 Md. R. 371, eff. 4/8/2019