South Carolina Code of Regulations
Chapter 61 - DEPARTMENT OF HEALTH AND ENVIRONMENTAL CONTROL
Subchapter 61-67 - STANDARDS FOR WASTEWATER FACILITY CONSTRUCTION
Section 61-67.67.400 - Reliability Classifications

1. The Department has authority to establish reliability classification requirements for wastewater treatment facilities, for the primary purpose of protecting surface waters and their usage, such as shellfish harvesting areas, and designated recreational waters, as determined by the Department, as well as water supply intake areas.

2. The secondary purpose of this requirement is to provide standards for reasonable reliability of treatment performance.

1. These requirements shall not apply to pretreatment facilities or to existing facilities which are not subject to a construction permit.

2. The Department shall determine which reliability classification applies to individual wastewater treatment facilities.

3. The requirements of this regulation shall apply to:

4. For modifications which do not increase the capacity of a facility, the requirements of this regulation shall apply to the component(s) being added, modified or upgraded at the wastewater treatment facility.

5. Specific requirements of various classifications may be applied to treatment systems not specifically described in the classification requirements.

6. Facilities such as industrial operations that can reasonably shut down their operations to provide equivalent protection to the receiving waterbody may be exempt from specific requirements of this section if justified by the permittee and approved by the Department.

7. These reliability classification requirements may be waived for wastewater treatment facilities less than five hundred thousand (500,000) GPD, or for non-process industrial wastewater, if determined by the Department that they need not apply, based on site conditions and the absence of shellfish harvesting areas, designated recreational waters, water supply intake areas, and other areas that could be impacted by the subject wastewater treatment facility.

8. Influent and effluent pumping systems are considered part of the wastewater treatment facilities for the purposes of applying reliability classification criteria.

1. Holding tanks or other storage components are permissible as an alternative to component or system backup capability, where justified.

2. A backup pump shall be provided for each set of pumps which performs the same function. The capacity of the pumps shall be such that with any one (1) pump out of service, the remaining pumps shall have capacity to handle peak flow. It is permissible for one (1) pump to serve as a backup to more than one (1) set of pumps in a typical pump station. Backup pump requirements for wastewater treatment facilities shall be determined on an individual project basis. It is also permissible for the backup pump to be un-installed, provided that the installed pump can be easily removed and replaced.

3. When anaerobic digestion is utilized, at least two (2) anaerobic digestion tanks shall be provided, for all domestic wastewater treatment facilities and industrial wastewater treatment facilities as determined by the Department.

4. For aerobic digestion, at least two (2) blowers and/or mechanical aerators shall be provided. If only one (1) blower and/or aerator is installed, the backup shall be of equal size and the installed blower and/or aerator shall be easily removed and replaced.

5. When vacuum filters are used there shall be a sufficient number of vacuum filters provided to enable the design sludge flow to be dewatered with the largest capacity vacuum filter out of service. Each vacuum filter shall be serviced by two (2) vacuum pumps and two (2) filtrate pumps. It is permissible for the backup to the normal vacuum or filtrate pump to be an un-installed unit, provided that the installed unit can be easily removed and replaced with the un-installed unit.

6. When centrifuges or belt presses are used there shall be a sufficient number of centrifuges and belt presses provided to enable the design sludge flow to be dewatered with the largest unit out of service. An alternative sludge management plan (e.g., use of existing sand drying beds as a backup) may be proposed for the purpose of justifying the need for only one (1) unit, subject to the Department's approval. It is permissible for the backup unit to be an un-installed unit, provided that the installed unit can be easily removed and replaced with the un-installed unit.

1. Reliability Classification I requirements provide maximum protection for the waters of the State, by requiring backup components and auxiliary power for those wastewater treatment facilities discharging into waters of the State that may be in environmentally sensitive areas due to the close proximity to, but not limited to, shellfish harvesting areas, and designated recreational waters. Reliability Classification I requirements would apply to those facilities discharging within water supply intake areas. When a discharge is within such an area, the Department may consider the effect downstream lakes may have in providing additional protection within the water supply intake areas and the Department may consider the reduced risk associated with a discharge located downstream of a water supply intake point where the discharge would only affect the intake in certain limited tidal situations.

2. Wastewater treatment facilities shall have a holding basin or equivalent design feature to augment the storage capacity of the collection and interceptor system (i.e., at the influent of the plant, with consideration given to untreated wastewater storage basins located at other locations). Capacity shall accommodate the twenty four (24) hour average design flow of the wastewater treatment facility. The system shall be designed such that the wastewater retained by the holding basin shall be fully treated prior to discharge. A holding basin that can accommodate the twelve (12) hour average design flow may be considered (in lieu of twenty four (24) hour capacity) by the Department in cases where flow equalization at the head of a treatment facility is incorporated.

3. Excluding lagoon systems, when an aeration basin is utilized, at least two (2) aeration basins shall be provided.

4. When mechanically cleaned bar screens (or equivalent devices) are utilized, provisions for a backup bar screen, which may be designed for manual cleaning, shall be provided.

5. Backup pumps shall be provided for each set of pumps which performs the same function. The capacity of the pumps shall be such that with any one (1) pump out of service, the remaining pumps shall have capacity to handle the peak flow. It is permissible for one (1) pump to serve as a backup to more than one (1) set of pumps in a typical pump station.

6. When clarifiers are utilized, all domestic wastewater treatment facilities and industrial wastewater treatment facilities as determined by the Department, shall have at least two (2) clarifiers provided when the design flow of the wastewater treatment facility exceeds one hundred thousand (100,000) gallons per day.

7. Primary, intermediate and final sedimentation basins, trickling filters, and tertiary filters shall be designed with a sufficient number of units such that with the largest flow capacity unit out of service, the remaining units shall have a design capacity such that the appropriate design criteria are not exceeded, based on seventy five (75) percent of design flow.

8. Aeration blowers and/or mechanical aerators shall be provided in sufficient number to enable the design oxygen transfer to be maintained with the largest capacity unit out of service. It is permissible for the backup unit to be an un-installed unit, provided that the installed unit can be easily removed and replaced. However, at least two (2) units shall be installed.

9. Air diffusion systems shall be designed such that the largest section of diffusers can be isolated without measurably impairing the oxygen transfer capability of the system.

10. Where proposed or required, all domestic wastewater treatment facilities and industrial wastewater treatment facilities as determined by the Department, shall have at least two (2) chemical flash mixer basins provided, or a backup means of adding and mixing chemicals, separate from the basin, shall be provided. If only one (1) basin is provided, at least two (2) mixing devices and a bypass around the basin shall be provided. It is permissible for one of the mixing devices to be un-installed, provided that the installed unit can be easily removed and replaced.

11. Disinfection components, including basins shall have sufficient number of units such that with the largest flow capacity unit out of service, the remaining units shall have a design flow capacity of seventy five (75) percent of the total design average flow to the unit operation.

12. The backup power source shall be sufficient to operate all vital components required to meet effluent disposal permit limitations during peak wastewater flow conditions, together with critical lighting and ventilation.

1. Reliability Classification II requirements provide protection for the waters of the State by requiring backup components and auxiliary power for those wastewater treatment facilities discharging into waters of the State that may be near, but not limited to, shellfish harvesting areas, designated recreational waters, and water supply intake areas, but based on circumstances, may not require as much system reliability as Reliability Classification I.

2. Backup components may not be required to provide treatment in excess of typical biological or equivalent physical/chemical treatment and disinfection. This may include not providing backup for such components as: chemical flash mixers, chemical sedimentation basins, and filters.

3. Primary and final sedimentation basins and trickling filters shall be designed with sufficient number of units such that with the largest flow capacity unit out of service, the remaining units shall have a design flow capacity of at least fifty (50) percent of the design basis flow to that unit operation.

4. The backup power source shall be the same as Reliability Classification I, except that vital components used to support the secondary processes (e.g., mechanical aerators or aeration basin air compressors) need not be included as long as treatment equivalent to sedimentation and disinfection is provided.

5. Disinfection components, including basins shall have sufficient number of units such that with the largest flow capacity unit out of service, the remaining units shall have a design flow capacity of fifty (50) percent of the total design average flow to the unit operation.

6. Holding basins or equivalent design features may not be required.

7. Backup pump requirements for wastewater treatment facilities shall be determined on an individual project basis.

1. Reliability Classification III requirements provide protection for the waters of the State, by requiring backup components and auxiliary power for those wastewater treatment facilities discharging in areas not identified by the Department as being more appropriately covered under Reliability Classification I or II.

2. Backup components shall not be required for trickling filters.

3. When blowers or mechanical aerators are utilized, all domestic wastewater treatment facilities and industrial wastewater treatment facilities as determined by the Department, shall have at least two (2) aeration blowers and/or mechanical aerators available for service. One (1) of the units can be un-installed, if the installed unit can be easily removed and replaced.

4. For all domestic wastewater treatment facilities and industrial wastewater treatment facilities as determined by the Department, a single aeration basin is permissible.

5. When sedimentation basins are utilized, all domestic wastewater treatment facilities and industrial wastewater treatment facilities as determined by the Department, shall have at least two (2) primary, intermediate, and final sedimentation basins provided.

6. For all domestic wastewater treatment facilities and industrial wastewater treatment facilities as determined by the Department, the backup power source shall be sufficient to operate the screening facilities, the main wastewater pumps, the primary sedimentation basins, and the disinfection facility during peak wastewater flow condition, together with critical lighting and ventilation.