15A NCAC 02T .0305 DESIGN CRITERIA
(a) Construction of sewers and sewer extensions are prohibited in the following areas unless the specified determinations are made:
(1) in a natural area designated on the State Registry of Natural Heritage Areas by a protection agreement between the owner and the Secretary, unless the Commission agrees that no prudent, feasible or technologically possible alternative exists; or,
(2) in a natural area dedicated as a North Carolina Nature Preserve by mutual agreement between the owner and State of North Carolina (Governor and Council of State), unless the Commission recommends and the Governor and Council of State agree that no prudent, feasible or technologically possible alternative exists;
(b) Engineering design documents. The following documents shall be prepared prior to submitting a permit application to the Division. If submittal of such documents is not requested in the permitting process (i.e., fast-track), they shall be available upon request by the Division. If required by G.S. 89C, a professional engineer shall prepare these documents:
[Note: The North Carolina Board of Examiners for Engineers and Surveyors has determined, via letter dated December 1, 2005, that preparation of engineering design documents pursuant to this Paragraph constitutes practicing engineering under G.S. 89C.]
(1) A plan and profile of sewers, showing their proximity to other utilities and natural features, such as water supply lines, water lines, wells, storm drains, surface waters, roads and other trafficked areas.
(2) Design calculations including pipe and pump sizing, velocity, pump cycle times and level control settings, pump station buoyancy, wet well storage, surge protection, detention time in the wet well and force main, ability to flush low points in force mains with a pump cycle, and downstream sewer capacity analysis.
(3) Specifications relative to the sewer system describing all materials to be used, methods of construction and means for assuring the quality and integrity of the finished project.
(c) All deeds, easements and encroachment agreements necessary for installation and operation and maintenance of the system shall be obtained prior to operation of the system.
(d) There shall be no by-pass or overflow lines designed in any new sewer system except for valved piping and appurtenances intended for emergency pumping operation(s).
(e) A minimum of two feet protection from a 100-year flood shall be provided unless there is a water-tight seal on all station hatches and manholes with control panels and vents extending two feet above the 100-year flood elevation.
(f) The following minimum separations shall be provided for the sewer system except as allowed by Paragraph (g) of this Rule:
Storm sewers and other utilities not listed below (vertical) 24 inches
Water mains (vertical-water over sewer including in benched trenches) 18 inches
or (horizontal) 10 feet
Reclaimed water lines (vertical – reclaimed over sewer) 18 inches
or (horizontal) 2 feet
Any private or public water supply source, including any wells, WS-I waters or Class I
or Class II impounded reservoirs used as a source of drinking water 100 feet
Waters classified WS (except WS-I or WS-V), B, SA, ORW, HQW, or SB from normal
high water (or tide elevation) and wetlands 50 feet
Any other stream, lake, impoundment, or ground water lowering and surface drainage ditches 10 feet
Any building foundation 5 feet
Any basement 10 feet
Top slope of embankment or cuts of 2 feet or more vertical height 10 feet
Drainage systems and interceptor drains 5 feet
Any swimming pool 10 feet
Final earth grade (vertical) 36 inches
(g) Alternatives where separations in Paragraph (f) of this Rule cannot be achieved. Nothing in this Paragraph shall supersede the allowable alternatives provided in the Commission for Public Health Public Water Supply Rules (15A NCAC 18C), Commission for Public Health Sanitation Rules (15A NCAC 18A) or the Groundwater Protection Rules (15A NCAC 02L and 15A NCAC 02C) that pertain to the separation of sewer systems to water mains or public or private wells:
(1) For storm sewers, engineering solutions such as ductile iron pipe or structural bridging to prevent crushing the underlying pipe.
(2) For public or private wells, piping materials, testing methods and acceptability standards meeting water main standards shall be used where these minimum separations cannot be maintained. All appurtenances shall be outside the 100 foot radius. The minimum separation shall however not be less than 25 feet from a private well or 50 ft from a public well.
(3) For public water main horizontal or vertical separations, alternatives as described in 15A NCAC 18C .0906(b) and (c).
(4) For less than 36-inches cover from final earth grade, ductile iron pipe shall be specified. Ductile iron pipe or other pipe with proper bedding to develop design supporting strength shall be provided where sewers are subject to traffic bearing loads.
(5) For all other separations, materials, testing methods and acceptability standards meeting water main standards (15A NCAC 18C) shall be specified.
(h) The following criteria shall be met for all pumping stations and force mains:
(1) Pump Station Reliability:
(A) Pump stations, except when exempted by Subparagraph (j)(2) of this Rule, shall be designed with multiple pumps such that peak flow can be pumped with the largest pump out of service.
(B) A standby power source or pump is required at all pump stations except for those pump stations subject to Subparagraph (j)(2) of this Rule. Controls shall be provided to automatically activate the standby source and signal an alarm condition.
(C) As an alternative to Part (B) for pump stations with an average daily design flow less than 15,000 gallons per day as calculated using Rule .0114 of this Subchapter, a portable power source or pumping capability may be utilized. It shall be demonstrated to the Division that the portable source is owned or contracted by the permittee and is compatible with the station. If the portable power source or pump is dedicated to multiple pump stations, an evaluation of all the pump stations' storage capacities and the rotation schedule of the portable power source or pump, including travel timeframes, shall be provided in the case of a multiple station power outage.
(D) As an alternative to Part (B) for pump or vacuum stations connecting a single building to an alternative sewer system, wet well storage requirements shall be documented to provide 24-hours worth of wastewater storage or, exceed the greatest power outage over the last three years or the documented response time to replace a failed pump, whichever is greater. Documentation shall be required pursuant to the permit application.
(E) All pump stations designed for two pumps or more shall have a telemetry system to provide remote notification of a problem condition to include power failure and high water alarm.
(F) high water audio and visual alarm.
(2) Pump stations shall have a permanent weatherproof sign stating the pump station identifier, 24-hour emergency number and instructions to call in case of emergency. Simplex pump or vacuum stations serving a single-family residence shall have a placard or sticker placed inside the control panel with a 24-hour emergency contact number.
(3) Screened vents for all wet wells.
(4) The public shall be restricted access to the site and equipment.
(5) Air relief valves shall be provided at all high points along force mains where the vertical distance exceeds ten feet.
(i) The following criteria shall be met for gravity sewers:
(1) for public gravity sewers, a minimum eight inch diameter pipe and for private gravity sewers, a minimum six inch diameter pipe;
(2) the maximum separation between manholes shall be 425 feet unless written documentation is submitted with the application that the owner/authority has the capability to perform routine cleaning and maintenance on the sewer at the specified manhole separation; and
(3) drop manholes shall be provided where invert separations exceed 2.5 feet.
(j) The following criteria shall be met for low pressure sewers, vacuum sewers, STEP and other alternative sewers discharging into another sewer system:
(1) Hydraulic modeling of the system shall be submitted using the statistical (projected) number of pumps running at one time. If computer modeling is provided by a pump manufacturer, it shall be indicated and shall be considered part of the design calculations pursuant to Subparagraph (b)(2) of this Rule.
(2) Simplex pump stations shall only be allowable for single-family residences. All other buildings connected to the system shall at a minimum have duplex pumps.
(3) Septic tanks shall adhere to the standards established in 15A NCAC 18A .1900.
History Note: Authority G.S. 143-215.1; 143-215.3(a);
Eff. September 1, 2006.