(a) Surface water protection. Discharges to surface waters shall meet or exceed quality limitations in the National Pollution Discharge Elimination System permit. Plant configurations and piping shall be arranged to avoid the bypassing of process units that could result in inadequately treated sewage reaching the receiving surface water.
(b) Groundwater protection. Seepage and/or discharge to groundwater shall comply with Chapter 8 of the Water Quality Regulations. Plan configurations and piping shall be arranged to avoid the bypassing of process units that could result in inadequately treated sewage reaching the groundwater.
(c) Siting requirements. - (i) Isolation. Treatment facilities shall be located to minimize public and private nuisances and health hazards on inhabited areas or residential areas. Where treatment plant siting does potentially affect inhabited areas, appropriate measures to minimize nuisances or hazards shall be incorporated in the design.
- (ii) Flood protection. All treatment process structures, mechanical equipment, and electrical equipment shall be protected from the 100-year flood. The treatment facilities shall remain fully operational and accessible during the 25-year flood.
(d) Hydraulic and treatment reliability. - (i) Alternative power source. All treatment plants shall have an alternative source of power to provide reliable pumping and disinfection of sewage if required. The alternative source of power shall be sized to provide the capability to pump design maximum day flow rates through the treatment process and to disinfect the sewage if necessary. Acceptable alternative power sources include:
- (A) A diesel, natural gas, or propane fueled engine generator.
- (B) A second independent electrical supply.
- (C) Storage of sewage and subsequent treatment
- (ii) Bypass treatment units. Complete by-passing of treatment units is prohibited. Provide means to bypass any duplicate process unit or single unit where adequate downstream process capability is provided. Sewage shall be treated in parallel singular units and/or subsequent processes.
- (iv) Multiple equipment. Mechanical process equipment shall be provided in multiple units. All pumping functions shall include sufficient pumping capacity that the peak flow can be pumped with the largest single unit not in service. Blowers and mechanical aerators for process aeration shall include sufficient capacity that the maximum day design capacity can be delivered with the largest single unit not in service. Other equipment shall have standby units where their function is critical to the treatment process.
(e) Electrical. - (i) Equipment location. Service transformers and other critical electrical equipment shall be located above the 100-year flood and above grade. Transformers shall be located in a manner that they are remote from or protected by substantial barriers from traffic. Motor controls shall be located in superstructures and in rooms that do not contain sewage, chemical processes, or corrosive atmospheres.
- (ii) Code requirements. All electrical work shall comply with the National Electrical Code as enacted and amended by the Wyoming Department of Fire Prevention and Electrical Safety. Areas in which the occurrence of explosive concentrations of hazardous gases or flammable fluids can occur Class 1, groups C and D, Division 1 locations shall be designed for hazardous locations in accordance with the National Electrical Code.
(f) Structural. - (i) Construction materials. Construction materials shall be selected, apportioned, and/or protected to provide water tightness, corrosion protection, and resistance to weather variations.
- (ii) Coatings. Coatings used to protect structures, equipment and piping shall be suitable for atmospheres containing hydrogen sulfide and volatile organics. Surfaces exposed in chemical areas shall be protected from chemical attack. Concrete surfaces in confined spaces containing sewage shall be protected. Paints containing lead or mercury shall not be used.
- (iii) Geological conditions. Structural design shall consider the seismic zone, groundwater and soil support. Soils investigations shall be made, or adequate previous soils investigations shall be available to develop structural design.
(g) Safety. The Wyoming Occupational Health and Safety Rules and Regulations shall be complied with. The following items shall also be provided: - (i) Instruction manuals. Instruction manuals shall be provided for all mechanical and electrical equipment describing operation, maintenance, and safety.
- (ii) Handrails. In addition to all Wyoming OSHA requirements, barriers around treatment basins shall be provided.
- (iii) Warning Signs. Provide warning signs for nonpotable water, electrical hazards, chemical hazards, or other unsafe features. Warning signs shall be permanently attached to the structure or appropriate equipment.
- (iv) Equipment guards. Provide shields to protect from rotating or moving machinery.
- (v) Lighting. Provisions shall be made to light walkways, paths, and other accessways around basins, in buildings and on the site. All areas shall be lit in a manner that the failure of one lighting fixture will not cause an area to be dark, or the loss of power will not cause a room or enclosed area to be dark.
- (vi) Climate conditions. Design of facilities such as exposed stairs, walkways, and sidewalks shall include nonskid surfaces.
(h) Instrumentation. - (i) Location. A flow measuring device shall be provided for the plant effluent unless it is a mechanical plant where an influent flow measuring device will be acceptable.
- (ii) Type. For plants having an average design flow of 50,000 gpd (189 m 3 /d) or more, the flow measuring device shall provide recording of instantaneous flow rate, enable calculation of average daily flow rate and have provisions for calibration and correction.
- (iii) Controls. Automatic controls shall be designed to permit manual override.
- (iv) Alarms. Conditions that may affect discharge quality or personnel or public safety shall be alarmed at an attended location.
(i) Sampling. Access shall be provided to sample untreated wastewater ahead of the treatment facilities prior to adding any process return flows, and sampling of the effluent after all treatment process units, but before discharge to the receiving stream. An automatic sampler that composites samples in proportion to the flow rate on the effluent shall be provided if required by the NPDES permit.
(j) Ventilation. All enclosed spaces shall be provided with forced ventilation, excepting pumping station wetwells, scum pits, anaerobic process units, and man-holes. In areas where there are open sewage channels, wet pits exposed to the room or process units without gas tight enclosures, ventilation shall be provided to maintain a higher pressure in the room than atmospheric and shall provide twelve (12) air changes per hour. In equipment rooms, ventilation shall be provided to limit the temperature rise in the room to less than 15° F (8° C) above ambient, but not less than six air changes per hour. Rooms housing chlorine storage and/or feeders shall have provisions for exhausting the room contents in two (2) minutes and continuous ventilation to provide twelve (12) air changes per hour.
(k) Dewatering of treatment units. All treatment units, channels, housing screens, or other embedded equipment, and wetwells shall be provided with drains or sumps that facilitate draining the unit for access and maintenance. Drainage shall be to upstream process units. Basin slabs shall be designed to successfully resist the hydrostatic uplift pressure or relief valves shall be provided.
(l) Cold weather protection. All equipment including pumps, bar screens, grit washers, electrical equipment and other equipment not required to be in or on open basins (such as clarifier drives and surface aerators) shall be housed in heated, lighted, and ventilated structures. Structure entrances shall be above grade. Piping shall be buried below frost level, placed in heated structures, or provided with heat and insulated. Walkways shall be located away from areas of spray and/or ice buildup.
(m) Chemical storage. All chemical storage shall be housed or buried. Areas designated for storage of specific chemicals shall be separated from areas designated for other reactive chemicals. Liquid storage containers shall be isolated from other portions of the structure by a curb that will contain and/or drain ruptured tank contents. Concrete floors, walls and curbs in chemical storage and feed areas shall be coated to protect the concrete from aggressive chemicals. Floors in polymer feed and storage areas shall be provided with nonslip surfaces. Rooms for chlorine storage and feed equipment shall be gas tight and be provided with entry from outdoors. All toxic chemical storage areas shall be provided with lighting and ventilation that are switched from outside the room, and windows to permit viewing the room from outside.
(n) Design capacities. - (i) Flow. In the absence of flow measurement information, the design average daily flow shall be based on a per capita daily flow rate of 100 gallons (378 liters). Allowances shall be made for return flows from digesters, sludge thickeners and the like, and the infiltration and wet weather inflow into older sewer systems. Significant industrial waste flows shall be added to the per capita flow rate.
- (ii) Organic loads. In the absence of wastewater strength data, domestic waste treatment design shall be based on a per capita daily BOD and suspended solids contribution of 0.22 lb (0.10 kg) and 0.25 lb (0.11 kg), respectively. The influence of sidestream return flows and significantly strong industrial wastes shall be considered and included in the design where applicable.
020-11 Wyo. Code R. § 11-11