.1957 DESIGN CRITERIA FOR DESIGN OF ALTERNATIVE SEWAGE SYSTEMS

(a) LOW-PRESSURE PIPE SYSTEMS: Low-pressure pipe (LPP) systems with a two to five-foot pressure head may be utilized on sites which are SUITABLE or PROVISIONALLY SUITABLE for conventional or modified systems and on sites where soil and site conditions prohibit the installation of a conventional or modified septic tank system if the requirements of this Paragraph are met.

(1)The LPP system shall consist of the following basic components:

(A) a network of small-diameter (one to two inches) perforated PVC 160 psi pipe or equivalent placed in
naturally occurring soil at shallow depths (generally 12 to 18 inches) in narrow trenches not less than eight inches in width and spaced not less than five feet on center. Trenches shall include at least five inches of washed stone or washed gravel below the pipe and two inches above the pipe; and four inches of soil cover.
(B) a properly designed, two-compartment septic tank or other approved pretreatment system, and a pumping or dosing tank;
(C) a watertight supply manifold pipe, of Schedule 40 PVC or equivalent, for conveying effluent from the dosing chamber to the low-pressure network.

(2) The soil and site criteria for LPP systems shall meet the following minimum requirements:

(A) LPP nitrification fields shall not be installed on slopes in excess of ten percent unless special design
procedures to assure proper distribution of effluent over the nitrification field are approved. Landscaping of the LPP distribution field shall be constructed to shed rainwater or runoff. All other requirements of Rule .1940 of this Section shall be met.
(B) Site suitability for an LPP system shall be based on the first 24 inches of soil beneath the naturally occurring soil surface. This 24 inches shall consist of SUITABLE or PROVISIONALLY SUITABLE soil as determined in accordance with Rules .1941 through .1944 and .1956 of this Section.
(C) Location of the septic tank, other approved pretreatment unit, pumping or dosing chamber, and nitrification field shall be in accordance with Rule .1950 of this Section. Horizontal distances from the nitrification field shall be measured from a margin two and one-half feet beyond the lateral and manifold pipes.
(D) There shall be no soil disturbance of the site or repair area for an LPP system except the minimum required for installation.
(E) The available space requirements of Rule .1945 of this Section shall apply.

(3) Table IV shall be used in determining the long-term acceptance rate for LPP systems. The long-term acceptance rate shall be based on the most hydraulically limiting, naturally occurring soil horizon within two feet of the ground surface or to a depth of one foot below the trench bottom, whichever is deeper.

The long-term acceptance rate shall not exceed the mean rate for the applicable soil group for food service facilities, meat markets, and other places of business where accumulation of grease can cause premature failure of a soil absorption system. Long-term acceptance rates up to the maximum for the applicable soil group may be permitted for facilities where data from comparable facilities indicates that the grease and oil content of the effluent will be less than 30 mg/l and the chemical oxygen demand (COD) will be less than 500 mg/l.
(4) In calculating the number of square feet for the nitrification field, the design sewage flow shall be divided by the long-term acceptance rate from Table IV. In calculating the minimum length of trenches in the LPP system, the total square footage of the nitrification field shall be divided by five feet.
(5) Low-pressure systems shall be designed for uniform distribution of effluent. The trenches shall be level and parallel to the ground elevation contours.
(A) The maximum lateral length shall yield no more than a ten-percent difference in discharge rate between
the first and last hole along the lateral.
(B) Minimum hole size shall be 5/32-inch for at least two-thirds of the field lateral lines. Smaller holes (no
less than 1/8-inch) may be used in no more than one-third of the lateral lines where necessary to balance flow distribution on sloping sites. However, for systems serving restaurants, foodstands, meat markets and other establishments where effluent is expected to have a high clogging potential, the minimum hole size shall be 5/32-inch.
(C) Maximum hole spacing shall be as follows: Soil Group I, five feet; Soil Group II, six feet; Soil Group III, eight feet; and Soil Group IV, ten feet.
(D) The following design provisions are required for sloping sites:
(i) Separately valved manifolds are required for all subfield segments where the elevation
difference between the highest and lowest laterals exceeds three feet.
(ii) The hole spacing, hole size or both shall be adjusted to compensate for relative head differences
between laterals branching off a common supply manifold and to compensate for the bottom lines receiving more effluent at the beginning and end of a dosing cycle. The lateral network shall be designed to achieve a ten to 30 percent higher steady state (pipe full) flow rate into the upper lines, relative to the lower lines, depending on the amount of elevation difference.
(iii) Maximum elevation difference between the highest and lowest laterals in a field shall not exceed
(6)
Septic tanks, pump tanks, pump dosing systems, siphons, and siphon dosing tanks shall be provided in accordance with Rule .1952 of this Section.
(A) Design flow rate shall be based upon delivering two feet to five feet of static pressure head at the distal
end of all lateral lines.
(B) Dose volume shall be between five and ten times the liquid capacity of the lateral pipe dosed, plus the
(E)
(F)
(G)
ten feet unless the flow is hydraulically split between subfield segments without requiring
simultaneous adjustment of multiple valves.
Turn-ups shall be provided at the ends of each lateral, constructed of Schedule 40 PVC pipe or equivalent, and protected with sleeves of larger diameter pipe (six inches or greater). Turn-ups and sleeves shall be cut off and capped at or above the ground surface, designed to be protected from damage, and easily accessible.
The supply manifold shall be sized large enough relative to the size and number of laterals served so that friction losses and differential entry losses along the manifold do not result in more than a 15 percent variation in discharge rate between the first and last laterals.
(i) The ratio of the supply manifold inside cross sectional area to the sum of the inside cross sectional areas of the laterals served shall exceed 0.7:1.
(ii) The reduction between the manifold and connecting laterals shall be made directly off the manifold using reducing tees.
(iii) Cleanouts to the ground surface shall be installed at the ends of the supply manifold.
Gate valves shall be provided for pressure adjustment at the fields whenever the supply line exceeds 100 feet in length. Valves shall be readily accessible from the ground surface and adequately protected in valve boxes.
liquid capacity of the portions of manifold and supply lines which drain between doses.
(b) FILL SYSTEM: A fill system (including new and existing fill) is a system in which all or part of the nitrification
trench(es) is installed in fill material. A fill system, including an existing fill site, may be approved where soil and site conditions prohibit the installation of a conventional or modified septic tank system if the requirements of this Paragraph are met.
(1) Fill systems may be installed on sites where at least the first 18 inches below the naturally occurring soil surface consists of soil that is suitable or provisionally suitable with respect to soil structure and clay mineralogy, and where organic soils, restrictive horizons, saprolite or rock are not encountered. Further, no soil wetness condition shall exist within the first 12 inches below the naturally occurring soil surface and a groundwater lowering system shall not be used to meet this requirement. Fill systems shall not be utilized on designated wetlands unless the proposed use is specifically approved in writing by the designating agency. The following requirements shall also be met:
(A) Nitrification trenches shall be installed with at least 24 inches separating the trench bottom and any soil horizon unsuitable as to soil structure, clay mineralogy, organic soil, rock or saprolite. However, if a low pressure pipe system is used, the minimum separation distance shall be 18 inches.
(B) Nitrification trenches shall be installed with at least 18 inches separating the trench bottom and any soil wetness condition. This separation requirement for soil wetness conditions may be met with the use of a groundwater lowering system only in Soil Groups I and II, with suitable structure and clay mineralogy. However, if a low pressure pipe system is used, the minimum separation distance shall be 12 inches.
(C) Systems shall be installed only on sites with uniform slopes less than 15 percent. Storm water diversions and subsurface interceptor drains or swales may be required upslope of the system.
(D) The long-term acceptance rate shall be based on the most hydraulically limiting soil horizon within 18 inches of the naturally occurring soil surface or to a depth one foot below the trench bottom, whichever is deeper. The lowest long-term acceptance rate for the applicable soil group shall be used for systems installed pursuant to this Rule. However, the long-term acceptance rate shall not exceed 1.0 gallons per day per square foot for gravity distribution or 0.5 gallons per day per square foot for low-pressure pipe systems installed on sites with at least 18 inches of Group I soils below the naturally occurring soil surface or to a depth of one foot below the trench bottom, whichever is deeper.
(E) If the fill system uses low-pressure pipe distribution, all the requirements of Paragraph (a) of this Rule, except Paragraph (a)(2)(B), shall apply. Systems with a design daily flow greater than 480 gallons per day shall use low-pressure pipe distribution.
(F) Fill material shall have such soil texture to be classified as sand or loamy sand (Soil Group I) up to the top of the nitrification trenches. The final six inches of fill used to cover the system shall have a finer texture (such as Group II, III) for the establishment of a vegetative cover. Existing fill material shall have no more than ten percent by volume of fibrous organics, building rubble, or other debris and shall

not have discreet layers containing greater than 35 percent of shell fragments.
(G) Where fill material is added, the fill material and the existing soil shall be mixed to a depth of six
inches below the interface. Heavy vegetative cover or organic litter shall be removed before the
additional fill material is incorporated.
(H) The fill system shall be constructed as an elongated berm with the long axis parallel to the ground
elevation contours of the slope.
(I) The side slope of the fill shall not exceed a rise to run ratio of 1:4. However, if the first 18 inches
below the naturally occurring soil surface is Group I soil, the side slope of the fill shall not exceed a
rise to run ratio of 1:3.
(J) The outside edge of the nitrification trench shall be located at least five feet horizontally from the top of
the side slope.
(K) The fill system shall be shaped to shed surface water and shall be stabilized with a vegetative cover
against erosion.
An existing fill site that does not meet the requirements of Paragraph (b)(1) of this Rule may be utilized for a sanitary sewage system if the following requirements are met:
(A) Substantiating data are provided by the lot owner (if not readily available to the local health
department) indicating that the fill material was placed on the site prior to July 1, 1977.
(B) The fill material placed on the site prior to July 1, 1977 shall have such soil texture to be classified as
sand or loamy sand (Group I) for a depth of at least 24 inches below the existing ground surface. This fill material shall have no more than ten percent by volume of fibrous organics, building rubble, or other debris. This fill shall not have discreet layers containing greater than 35 percent of shell fragments. However, if at least 24 inches of Group I fill material was in place prior to July 1, 1977, additional fill with soil texture classified as Group I may be added to meet the separation requirements of Paragraph (b)(2)(D) of this Rule.
(C) Soil wetness conditions, as determined by Rule .1942(a) in this Section, are 18 inches or greater below the ground surface of the fill placed on the lot prior to July 1, 1977. This requirement shall be met without the use of a groundwater lowering system.
(D) Low-pressure pipe distribution shall be used and shall meet all the requirements of Paragraph (a) of this Rule, except (a)(2)(B). The long-term acceptance rate shall not exceed 0.5 gallons per day per square foot. However, for existing fill sites with 48 inches of Group I soils, conventional nitrification trenches utilizing a maximum long-term acceptance rate of 1.0 gallons per day per square foot may be installed in lieu of low-pressure pipe systems. The minimum separation distance between the trench bottom and any soil wetness condition or any soil horizon unsuitable as to soil structure, clay mineralogy, organic soil, rock, or saprolite shall be 24 inches for low pressure pipe systems and 48 inches for conventional systems. This separation requirement may be met by adding additional Group I soil, but shall not be met with the use of a groundwater lowering system. Where fill is to be added, the requirements of Paragraphs (b)(1)(C), (F), (G), (H), (J), (K), of this Rule and the following requirements shall be met:
(i) (ii)
The side slope of the fill shall not exceed a side slope ratio of 1:3, and;
The setback requirements shall be measured from the projected toe of the slope. However, if this setback cannot be met, the setback requirements shall be measured from a point five feet from the nearest edge of the nitrification trench if the following conditions are met:
(I) Slope of the site shall not exceed two percent;
(II) The lot or tract of land was recorded on or before December 31, 1989; and
(III) A condition is placed upon the Improvement Permit to require connection to a public or community sewage system within 90 days after such system is available for connection and after it is determined that 300 feet or less of sewer line is required for connection.
(L) The setback requirements shall be measured from the projected toe of the slope. However, if this
setback cannot be met, the setback requirements shall be measured from a point five feet from the nearest edge of the nitrification trench if the following conditions are met:
- (i) Slope of the site shall not exceed two percent;
- (ii) The first 18 inches of soil beneath the naturally occurring soil surface shall consist of Group I
  soils;
- (iii) The lot or tract of land was recorded on or before December 31, 1989; and
- (iv) A condition is placed upon the Improvement Permit to require connection to a public or
  community sewage system within 90 days after such system is available for connection and after
  it is determined that 300 feet or less of sewer line is required for connection.
(M) The available space requirements of Rule .1945 of this Section shall apply.
(E) The available space requirements of Rule .1945 of this Section shall apply.
(F) The design flow shall not exceed 480 gallons per day.
accordance with this Rule to serve a design unit with a design flow rate of up to 1500 gallons per day, as determined in Rule .1949(a) or .1949(b) of this Section. ATUs shall not be used, however, where wastes contain high amounts of grease and oil, including restaurants and food service facilities. The strength of the influent wastewater shall be similar to domestic sewage with Biological Oxygen Demand (BOD) and suspended solids not to exceed 300 parts per million. ATUs shall comply with the requirements of the National Sanitation Foundation (NSF) Standard 40 for Individual Aerobic Wastewater Treatment Plants and shall be classified as meeting Class I effluent quality. NSF Standard 40 for Individual Aerobic Wastewater Treatment Plants is hereby incorporated by reference including any subsequent amendments and editions. Copies of the standards may be inspected in and copies obtained from the Division of Environmental Health, P.O. Box 27687, Raleigh, N.C. 27611-7687 at no cost. ATUs shall bear the NSF mark and the NSF listed model number or shall bear the certification mark and listed model number of a third party certification program accredited by the American National Standards Institute (ANSI), pursuant to ANSI Policy and Procedures for Accreditation of Certification Programs to certify ATUs in accordance with NSF Standard Number 40. The ANSI Policy and Procedures for Accreditation of Certification Programs is hereby incorporated by reference including any subsequent amendments and editions. Copies of the standard may be inspected in and copies obtained from the Division of Environmental Health, P.O. Box 27687, Raleigh, N.C. 27611-7687 at no cost. ATUs shall only be permitted where the unit is to be operated and maintained by a certified wastewater treatment facility operator employed by or under contract to the county in which the unit is located, and in accordance with this Rule.
(1) ATUs shall be constructed and installed in accordance with the plans which have been approved by the Division of Environmental Health and shall comply with all requirements of this Rule. Procedures for plan review and approval shall be in accordance with Rule .1953 of this Section.
(2) The rated capacity of ATUs listed as complying with NSF Standard 40 shall not be less than the design daily flow as determined by Rule .1949(a) or .1949(b) of this Section.
(3) The following are minimum standards of design and construction of ATUs:
- (A) Blockouts in concrete ATU inlet openings shall leave a concrete thickness not less than one inch in the
  plant wall. Inlet and outlet blockouts shall be made for a minimum of four inch pipe and a maximum of
  six inch pipe. No blockouts or openings shall be permitted below the liquid level of the ATU.
- (B) The inlet into the ATU shall be a straight pipe.
- (C) The invert of the outlet shall be at least two inches lower in elevation than the invert of the inlet.
- (D) Interior baffle walls in concrete units shall be reinforced by the placing of six-inch by six-inch No. 10
  gauge welded reinforcing wire. The reinforcing wire shall be bent to form an angle of 90 degrees on the ends in order to form a leg not less than four inches long. When the wire is placed in the mold, the four inch legs shall lay parallel with the side wall wire and adjacent to it.
- (E) Access openings shall be provided in the ATU top. Access shall be provided for cleaning or rodding out the inlet pipe, for cleaning or clearing air or gas passage spaces, as an entrance for inserting the suction hose in compartments that are required to be pumped out, to allow for sampling the effluent, and for access to repair or maintain any system components requiring repair and maintenance. All access openings shall have risers sealed to the top of the ATU and extended at least to six inches above finished grade and designed and maintained to prevent surface water inflow. Rule .1950(i) of this Section shall also be met.
- (F) Concrete ATUs shall be constructed in accordance with Rule .1954(a)(9), (10), (11) and (12) and .1954(b)(4) of this Section.
- (G) Fiberglass reinforced plastic ATUs shall be constructed with materials capable of resisting corrosion from sewage and sewage gases, and the active and passive loads on the unit walls.
  - (i) ATUs shall have the following minimum physical properties:
(3) Other fill systems may be approved by the local health department on a site-specific basis in accordance with
Rule .1948(d) of this Section.
(c) Individual aerobic sewage treatment units (ATUs) shall be sited, designed, constructed and operated in
accordance with this Rule to serve a design unit with a design flow rate of up to 1500 gallons per day, as determined in Rule .1949(a) or .1949(b) of this Section. ATUs shall not be used, however, where wastes contain high amounts of grease and oil, including restaurants and food service facilities. The strength of the influent wastewater shall be similar to domestic sewage with Biological Oxygen Demand (BOD) and suspended solids not to exceed 300 parts per million. ATUs shall comply with the requirements of the National Sanitation Foundation (NSF) Standard 40 for Individual Aerobic Wastewater Treatment Plants and shall be classified as meeting Class I effluent quality. NSF Standard 40 for Individual Aerobic Wastewater Treatment Plants is hereby incorporated by reference including any subsequent amendments and editions. Copies of the standards may be inspected in and copies obtained from the Division of Environmental Health, P.O. Box 27687, Raleigh, N.C. 27611-7687 at no cost. ATUs shall bear the NSF mark and the NSF listed model number or shall bear the certification mark and listed model number of a third party certification program accredited by the American National Standards Institute (ANSI), pursuant to ANSI Policy and Procedures for Accreditation of Certification Programs to certify ATUs in accordance with NSF Standard Number 40. The ANSI Policy and Procedures for Accreditation of Certification Programs is hereby incorporated by reference including any subsequent amendments and editions. Copies of the standard may be inspected in and copies obtained from the Division of Environmental Health, P.O. Box 27687, Raleigh, N.C. 27611-7687 at no cost. ATUs shall only be permitted where the unit is to be operated and maintained by a certified wastewater treatment facility operator employed by or under contract to the county in which the unit is located, and in accordance with this Rule.
(1) ATUs shall be constructed and installed in accordance with the plans which have been approved by the Division of Environmental Health and shall comply with all requirements of this Rule. Procedures for plan review and approval shall be in accordance with Rule .1953 of this Section.
(2) The rated capacity of ATUs listed as complying with NSF Standard 40 shall not be less than the design daily flow as determined by Rule .1949(a) or .1949(b) of this Section.
(3) The following are minimum standards of design and construction of ATUs:
1. (A) Blockouts in concrete ATU inlet openings shall leave a concrete thickness not less than one inch in the
  plant wall. Inlet and outlet blockouts shall be made for a minimum of four inch pipe and a maximum of
  six inch pipe. No blockouts or openings shall be permitted below the liquid level of the ATU.
2. (B) The inlet into the ATU shall be a straight pipe.
3. (C) The invert of the outlet shall be at least two inches lower in elevation than the invert of the inlet.
4. (D) Interior baffle walls in concrete units shall be reinforced by the placing of six-inch by six-inch No. 10
  gauge welded reinforcing wire. The reinforcing wire shall be bent to form an angle of 90 degrees on the ends in order to form a leg not less than four inches long. When the wire is placed in the mold, the four inch legs shall lay parallel with the side wall wire and adjacent to it.
5. (E) Access openings shall be provided in the ATU top. Access shall be provided for cleaning or rodding out the inlet pipe, for cleaning or clearing air or gas passage spaces, as an entrance for inserting the suction hose in compartments that are required to be pumped out, to allow for sampling the effluent, and for access to repair or maintain any system components requiring repair and maintenance. All access openings shall have risers sealed to the top of the ATU and extended at least to six inches above finished grade and designed and maintained to prevent surface water inflow. Rule .1950(i) of this Section shall also be met.
6. (F) Concrete ATUs shall be constructed in accordance with Rule .1954(a)(9), (10), (11) and (12) and .1954(b)(4) of this Section.
7. (G) Fiberglass reinforced plastic ATUs shall be constructed with materials capable of resisting corrosion from sewage and sewage gases, and the active and passive loads on the unit walls.
  1. (i) ATUs shall have the following minimum physical properties:

(ii) A vacuum test shall be performed on at least one ATU of each model number by an independent testing laboratory, in accordance with ASTM D-4021, Standard Specification for Glass-Fiber Reinforced Polyester Underground Petroleum Storage Tanks, which is hereby incorporated by reference including any subsequent amendments and editions. Copies of the standards may be inspected in and copies obtained from the Division of Environmental Health, P.O. Box 27687, Raleigh, N.C. 27611-7687 at no cost. Unit must withstand negative pressure of 2.5 pounds per square inch (69.3 inches of water) without leakage or failure. Test results shall be included with the specifications that are provided to the state for approval.

(iii) Composition of the finished unit shall be at least 30 percent fiberglass reinforcement by weight. Minimum wall thickness shall be one-fourth inch. However, a wall thickness of not less than three-sixteenth inch may be allowed in small, isolated areas of the ATU.

(iv) Interior and exterior surfaces shall have no exposed fibers or projections, no blisters larger than one-fourth inch in diameter, and no pores or indentations deeper than one-sixteenth inch. The tank shall be watertight.

(H) Prefabricated ATUs other than precast reinforced concrete or fiberglass reinforced plastic units shall be approved on an individual basis based on information furnished by the designer which indicates the unit will provide effectiveness equivalent to reinforced concrete or fiberglass reinforced plastic units.

(I) ATUs shall bear an imprint identifying the manufacturer, serial number assigned to the manufacturer's plans and specifications approved by the Division of Environmental Health, and the liquid or working capacity of the unit. The imprint shall be located to the right of the blockout or opening made for the outlet pipe on the outside of the unit. ATUs shall also be permanently marked with the date of manufacture adjacent to the unit imprint or on the top of the unit directly above the imprint.

(J) The design, construction, and operation of ATUs shall prevent bypass of wastewater.

(K) Electrical circuits to the ATU shall be provided with manual circuit disconnects within a watertight, corrosion-resistant, outside enclosure (NEMA 4X or equivalent) adjacent to the ATU securely mounted at least 12 inches above the finished grade. Control panels provided by the manufacturer shall be installed in a watertight, corrosion-resistant enclosure (NEMA 4X or equivalent) adjacent to the unit or on the side of the facility readily visible from the unit and accessible by maintenance personnel. Conductors shall be conveyed to the disconnect enclosure and control panel through waterproof, gasproof, and corrosion-resistant conduits. Splices and wire junctions, if needed, shall be made outside the ATU in a watertight, corrosion-resistant enclosure (NEMA 4X or equivalent) securely mounted adjacent to the unit at least 12 inches above the finished grade. Wire grips, duct seal, or other suitable material shall be used to seal around wire and wire conduit openings inside the ATU and disconnect enclosure. The ATU shall have an alarm device or devices to warn the user or operator of a unit malfunction or a high water condition. The alarm shall be audible and visible by system users and securely mounted adjacent to the ATU, on the side of the facility in clear view of the unit, or inside the finished occupied space of the facility. If mounted outside, the alarm shall meet NEMA 4X standards or equivalent. The alarm circuit or circuits shall be supplied ahead of any ATU electrical control circuit overload and short circuit protective devices.

(4) A settling tank shall be required prior to an ATU serving a design unit with a design daily flow greater than 500 gallons, as determined in Rule .1949(a) or .1949(b) of this Section. The liquid capacity of the settling tank shall be at least equal to the design daily flow as determined in Rule .1949(a) or (b) of this Section. The settling tank may either be an approved prefabricated septic tank or another tank specially designed for a specific individual aerobic sewage treatment plant and approved by the Division of Environmental Health as a part of the plans for the plant.

(5) Ground absorption systems receiving effluent from approved ATUs may be used on sites classified as suitable or provisionally suitable for conventional, modified, or alternative systems in accordance with this Section. The following modifications to siting and design criteria shall be acceptable:

(A)The minimum horizontal setback requirements of Rule .1950(a) of this Section shall be met, except as follows:

(i) Any private water supply source, except any uncased well or spring . . . . . . 50 feet.

(ii) StreamsclassifiedasWS-I ....................................... 70feet.

(iii) WatersclassifiedasSA ......................................... 70feet.

(iv OthercoastalwatersnotclassifiedasSA ........................... 35feet.

(v) Anyotherstream,canal,marsh,orothersurfacewaters ................ 35feet.

(vi) AnyClassIorClassIIreservoir .................................. 70feet, from normal pool elevation.

(vii) Anypermanentstormwaterretentionpond .......................... 35feet, from flood pool elevation.

(B)

(viii) Anyotherlakeorpond .......................................... 35feet, from normal pool elevation.

The requirements of Rules .1955(m), .1956(1), .1956(2), .1956(6), .1957(b)(1), and .1957(b)(2) of this Section shall be met, except as follows:

(i) A low-pressure pipe system shall not be required where the separation between the bottom of the nitrification trench and any soil wetness condition is at least 12 inches, but less than 18 inches, and more than six inches of this separation consists of Group I soils.

(ii) The restriction in Rule .1956(6)(a)(v) of this Section that saprolite be overlain by at least one foot of suitable or provisionally suitable naturally occurring soil shall not apply.

(iii) For new fill systems, a low pressure pipe system shall not be required in order for the minimum separation distance between the trench bottom and any unsuitable soil horizon, rock, or saprolite to be reduced to 18 inches.

(iv) For existing fill systems, the minimum separation requirements of Rule .1957(b)(2)(D) of this Section shall be reduced from 48 to 36 inches for conventional systems and from 24 to 18 inches for low-pressure pipe system.

The maximum long-term acceptance rate shall be increased by 25 percent for any ground absorption system in soils which are Groups I or II with suitable structure and clay mineralogy. No other reductions in linear footage of nitrification trench or system area shall be applied, except where based on an adjusted design daily sewage flow rate granted in accordance with Rule .1949(c) of this Section.

(C)

(6) Prior to issuance of an Operation Permit for an ATU, the manufacturer or his licensed representative shall certify that the unit has been properly installed and a contract for operation and maintenance shall have been executed between the unit owner and the county in accordance with Rule .1961(b) of this Section. It shall be a condition of the Operation Permit that subsequent owners of an ATU execute such a contract.

The contract shall include the specific requirements for maintenance and operation, responsibilities for maintenance and operation, responsibilities of the owner and system operator, provisions that the contract shall be in effect for as long as the system is in use, and other requirements for the continued proper performance of the ATU.
A condition of the Operation Permit shall be that the unit continue to perform in accordance with Class I effluent quality requirements of the National Sanitation Foundation (NSF) Standard Number 40 effective on the date the improvement permit was issued.

(A)

(B)

During each inspection, the operator shall confirm proper mechanical performance, conduct a visual check for unusual color, clogging, oily film, odors, foam, measure settleable aeration chamber solids, and ascertain the need for removing solids, backwash and cleaning of filters, and other maintenance activities. The ground absorption system shall also be inspected and an evaluation of performance shall be made. The operator shall take the necessary steps to assure that needed maintenance is carried out.

Semi-annually, samples shall be collected by the system operator and analyzed by a state-approved wastewater testing laboratory of the effluent for Five-Day Biological Oxygen Demand, Suspended Solids, and pH. The aeration tank shall be sampled for mixed liquor suspended solids.
Performance monitoring results shall be reported to the local health department and the state quarterly. Remedial action and additional sampling shall be required if monitoring results or inspection indicate that Class I effluent standards are not met.

Authority G.S. 130A-335(e),(f); 130A-342;
Eff. July 1, 1982;
Amended Eff. April 1, 1993; May 1, 1991; December 1, 1990; January 1, 1990.