CHAPTER VIII SEWAGE PUMPING STATIONS TOC-VIII-1 of 2 CHAPTER VIII SEWAGE PUMPING STATIONS CHAPTER CONTENTS Page No. I. GENERAL A. B. C. II. Introduction ..................................................................................................... VIII-1 Ordinances and Authority ............................................................................... VIII-2 Abbreviations .................................................................................................. VIII-2 DESIGN CRITERIA A. B. C. D. Applicable Regulations ................................................................................... VIII-2 Pre-Design Meeting......................................................................................... VIII-3 Schematic Design Report ................................................................................ VIII-3 1. Schematic Design Phase...................................................................... VIII-3 Flow................................................................................................................. VIII-4 1. Planning Period ................................................................................... VIII-4 2. Existing and Projected Flowrates ........................................................ VIII-4 3. Composition ........................................................................................ VIII-5 Hydraulics/Pumps ........................................................................................... VIII-5 1. Pump/System Curve............................................................................ VIII-5 2. Water Hammer .................................................................................... VIII-6 3. System Hydraulics/Pump Selection .................................................... VIII-6 Siting ............................................................................................................... VIII-7 1. Topography ......................................................................................... VIII-7 2. Access.................................................................................................. VIII-7 3. Floodplain............................................................................................ VIII-7 4. Wetlands.............................................................................................. VIII-7 5. Land Use.............................................................................................. VIII-8 6. Aesthetics ............................................................................................ VIII-8 7. Overflow.............................................................................................. VIII-8 8. Ownership ........................................................................................... VIII-8 Selection .......................................................................................................... VIII-9 1. Custom Built-In-Place Wet Well/Dry Well Sewage Pumping Station............................................................... VIII-9 2. Package Sewage Pumping Station ...................................................... VIII-9 3. Other Configurations......................................................................... VIII-10 Site Improvements......................................................................................... VIII-10 1. Access Road ...................................................................................... VIII-10 2. Sewage Pumping Stations ................................................................. VIII-11 3. Structures........................................................................................... VIII-12 Sewage Pumping Station Features ................................................................ VIII-13 Revised: E. F. G. H. I. Published: 01/01 TOC-VIII-2 of 2 Page No. 1. Wet well ............................................................................................ VIII-13 2. Dry Wells .......................................................................................... VIII-16 3. Pumping and Piping System.............................................................. VIII-18 4. Emergency Station Operation............................................................ VIII-21 5. Miscellaneous.................................................................................... VIII-22 Package Sewage Pumping Station Standards................................................ VIII-24 Vibration and Alignment Standards .............................................................. VIII-24 Corrosion Protection ..................................................................................... VIII-25 Energy Conservation ..................................................................................... VIII-25 Minimum HVAC Requirements ................................................................... VIII-25 Power Requirement ....................................................................................... VIII-25 Minimum Architectural Standards ................................................................ VIII-25 Security Systems ........................................................................................... VIII-25 Compatibility with Surrounding Planned Development ............................... VIII-25 Lightning and Surge Protection..................................................................... VIII-25 Confined Space Entry Warnings ................................................................... VIII-26 Remote Terminal Units ................................................................................. VIII-27 1. General .............................................................................................. VIII-27 2. RF Path Study.................................................................................... VIII-27 3. Telemetry........................................................................................... VIII-27 4. Screen Displays ................................................................................. VIII-27 5. Communications Protocols ............................................................... VIII-27 6. RTU Equipment ................................................................................ VIII-28 J. K. L. M. N. O. P. Q. R. S. T. U. III. CONTRACT DRAWINGS AND DOCUMENTS A. B. C. Reports .......................................................................................................... VIII-28 Design Computations .................................................................................... VIII-28 Specification.................................................................................................. VIII-28 1. Standard Specifications ..................................................................... VIII-28 2. Instruction of County's Personnel ..................................................... VIII-28 3. Operation and Maintenance (O&M) Manuals................................... VIII-29 4. Spare Parts......................................................................................... VIII-29 5. Start-Up Assistance ........................................................................... VIII-29 IV. APPENDIX ...................................................................................................................... 29 A. B. Odor Control Selection Decision Tree Design Checklist Published: 01/01 Revised: VIII-1 of 29 ANNE ARUNDEL COUNTY DESIGN MANUAL CHAPTER VIII SEWAGE PUMPING STATIONS I. GENERAL A. Introduction This Chapter of the Manual outlines the design of sewage pumping stations to meet the service needs of users and the operational responsibilities of the Department. The sewage pumping station design standards include: criteria, guidelines, drawings and technical specifications. The Reference Drawings for Wet/Dry Well and Submersible Pumping Stations as referred to herein are available from the County as a separate publication. This Chapter includes the criteria and guidelines for designing sewagepumping stations within the limits of applicability for these design standards. The design standards generally apply to sewage pumping stations up to 3.0 million gallons per day (MGD) capacity. Sewage pumping stations of 3.0 MGD pumping capacity and below shall be designed as a package pumping station of either the submersible or the wet well/dry well type as discussed in Section II. Paragraph G., later in this document. Design of larger sewage pumping stations with greater than 3.0 MGD capacity shall be considered on case-by-case basis, with special requirements as determined by the Department of Public Works. The design professional shall check with the Department to determine the applicability of these design standards to planned sewage pumping stations. It is the responsibility of the design professional to integrate all applicable criteria and guidelines for sewage pumping stations incorporated into the Anne Arundel County Sewerage System. The Anne Arundel County Sewerage System consists of House and Building Connections, Collecting Sewers, Intercepting Sewers, Sewage Pumping Stations, Force Mains and Wastewater Treatment Plants. This Chapter discusses the sewage pumping stations. To the extent practical, sewage pumping station designs shall conform to the guidelines given herein. The guidelines shall be applied to design conditions in a careful and thoughtful fashion. Significant deviations from the guidelines must be brought to the attention of the Department. All deviations should be justified to the Department, in writing, from an engineering evaluation standpoint and include consideration of life cycle costs and ease of maintenance. All standards and regulations shall conform to the latest publication. Published: 01/01 Revised: SEWAGE PUMPING STATIONS B. Ordinances and Authority VIII-2 of 29 The material presented in this Chapter is in accordance with the authority and responsibility delegated by ordinance, resolution, an executive or administrative order to the various County agencies named herein. C. Abbreviations Whenever in this chapter or other chapters, the following abbreviations are used, they will stand for: BOCA COMAR DHHS DPW EPACT GPM HIS HP HVAC IEEE KW LPI MCC MDE MGD NEC NFPA NIOSH OSHA PACE PVC SRC TVSS UL II. Building Officials Conference of America Code of Maryland Department of Health and Human Services Department of Public Works The Energy Policy Act of 1992 Gallons per Minute Hydraulic Institute Standards Horsepower Heating, Ventilation and Air Conditioning Institute of Electrical and Electronic Engineers Kilowatt Lightning Protection Institute Motor Control Center Maryland Department of the Environment Million Gallons per Day National Electric Code National Fire Protection Association National Institute for Occupational Safety and Health Occupational Safety and Health Administration Department of Planning and Code Enforcement Polyvinyl Chloride State Road Commission Transient Voltage Surge Suppressors Underwriters' Laboratory DESIGN CRITERIA A. Applicable Regulations Sewage pumping stations must satisfy the regulations of agencies having jurisdiction. Sewage pumping stations shall conform to the Design Guidelines for Sewerage Facilities, 1978 edition or latest addenda as published by the Maryland Department of Health and Mental Hygiene, now the Maryland Department of the Environment (MDE). The design professional shall also ensure that the sewage pumping station Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-3 of 29 conforms to Design Guidelines for Wastewater Pumping Stations for the Protection of Shellfish Waters and Swimming Waters, effective June 1, 1996, published by MDE Anne Arundel County Department of Planning and Code Enforcement (PACE) land use regulations shall be considered in the selection and development of sewage pumping station sites. Buildings shall comply with BOCA requirements and permitting requirements of the Anne Arundel County Department of Planning and Code Enforcement. Other regulations governing facilities and construction shall be adhered to, including regulations published by the Occupational Safety and Health Administration, the National Fire Protection Association, National Electric Code, Anne Arundel County Plumbing Code, and others as applicable. B. Pre-Design Meeting Prior to commencing any design work on a Capital Project, a pre-design meeting shall be held as provided in Chapter I, General Instructions. For Developer Projects, a presketch meeting may be held at the request of the developer. These meetings will discuss, at a minimum, the following design parameters pertinent to this Chapter, in addition to items, which pertain to any other Chapter, which will govern the design of the project: · · · · · · · · · · Odor Control Measures for Air Release Values near Populated Areas Blowoffs Type of Sewage Pumping Station Type of Bubbler System Flowmeters Pump Material Pressure Gauges Dual Feed Power Supply Security Systems Remote Terminal Unit C. Schematic Design Report For the Design Professionals guidance, below are listed major elements constituting the Schematic Design Phase of a Sewer Pumping Station Design Project: 1. Schematic Design Phase The Schematic Design Phase shall include the verification of the facility plan or any preliminary reports supplied by the County. It will also include the description of design criteria to be utilized, preliminary flow computations, design calculations, calculated system curves, surge protection analysis/recommendation, identification of right-of-way requirements, number of property owners involved, listing of permit requirements, and cost estimate based Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-4 of 29 on unit costs for major elements of work. In addition, the following design criteria shall be developed: · · · · · · · · · · Site Development Structural Design Architectural Design Hydraulic Analysis Mechanical Design Electrical Design Instrumentation and Process Control Corrosion Control (If necessary) Odor Control (If necessary) Noise Control (If necessary) All information and data developed during the Schematic Design Phase shall be presented to the DPW in the Schematic Design Report. D. Flow Sewage pumping stations must satisfy the design flowrate. The design flow for the sewage pumping stations shall consider existing and projected peak flowrates and sewage composition. 1. Planning Period Sewage pumping station discharge flowrates shall, at minimum, accommodate a 20-year planning horizon. In circumstances where the status of a planned pumping station is interim, the planning period for establishing flowrate may be shorter with the Department's approval. For all pumping stations, consideration shall be given to future upgrading flexibility necessary to accommodate flows beyond the normal planning horizon. This is especially important for larger (more than 400 GPM) sewage pumping stations. 2. Existing and Projected Flowrates Sewage pumping stations shall be designed to pump the flow for existing and future users. In developed areas, population shall be determined by house count and non-domestic user inventory with allowances made for remaining undeveloped tributary areas. Population densities and per capita flows shall be as established by Facility Plans or in their absence, in agreement with the Water & Sewer Master Plan or instruction of the Department. Institutional, commercial and industrial flows shall be determined by a study of the establishment. PACE shall be consulted for future domestic and non-domestic land use and population densities. A "SWAMP" analysis should be requested from PACE to establish flows in existing service areas. Flowrate computations shall follow guidance given in the Water and Sewer Master Plan, Appendix A, as well as Part A, Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-5 of 29 Appendix D of the Anne Arundel County Design Guidance for Wastewater and Waterworks Facilities. If applicable, Guidelines for Design and Operation of Recreational Vessel Wastewater Facilities by MDE - Water Management Administration shall be incorporated in the design flow rate. A tabulation of the design flow shall appear on the Drawings (See Reference Drawings for Wet/Dry Well and Submersible Pumping Stations, Dwg. PS-M1-4). 3. Composition Sewage composition can vary widely depending upon the proportion of design flow generated by non-domestic users. Non-domestic user sewage composition shall be investigated. In the absence of existing non-domestic user information for planning purposes, reference is made to the Pretreatment Ordinance. Adequate consideration and necessary provisions shall be taken to ensure that sewage pumping station equipment and materials are suitable for the anticipated composition of sewage. Consultation with the Department is required in the event that the sewage composition affects standard material and equipment requirements. E. Hydraulics/Pumps Sewage pumping stations must satisfy the hydraulic conditions of the system. A complete analysis of each sewage pumping station is required. An investigation and analysis of the sewage pumping station force main system to consider features of configuration, operation and potential impacts on existing force mains, gravity sewers and pumping stations when the new pumping station is added to the system shall be conducted. Sewage pumping stations shall be designed to operate at the appropriate discharge head and flowrate. 1. Pump/System Curve System curve characteristics shall be determined by the Hazen-Williams formula for piping head loss. The pump/system curve shall be shown on the drawings (See Reference Drawings for Wet/Dry Well and Submersible Pumping Stations, Dwg. PS-M1-1). Pump/system curves shall be shown for both new and aged force main conditions, as well as for multiple pump operation in stations having three or more pumps. Hazen-Williams "C" factors used in evaluating pump and system curves shall be selected using good engineering judgement and in accordance with the standards of the Hydraulic Institute. As a guideline, "C" factors for the following types of pipe are listed in Table VIII-1 below: Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-6 of 29 TABLE VIII-1 HAZEN-WILLIAMS "C" FACTORS Type of Pipe Ductile/Cast Iron:* New 5 years old 10 years old Size All All, up to 24" 24" and over 4" 12" 30" and over 4" 16" All "C" Factor 130 120 115 105 110 85 65 80 Same as for ductile/cast iron 5 years and older 140 40 years old Welded Steel Concrete* Large sizes, good workmanship, steel forms Centrifugally spun 135 All 150 PVC++ All 155 HDPE * Use of ductile/cast iron and concrete pipe is no longer permitted ++ Use of PVC pipe is subject to approval by the DPW 2. Water Hammer The potential impact of water hammer shall be evaluated. If the combined effects of static head and water hammer do not exceed the weakest piping system component working pressure, no special provisions need to be included to control water hammer. Where the maximum water hammer pressure exceeds the weakest piping system component working pressure, strengthen those elements affected, reevaluate pipe size and velocities, or select an appropriate device to control water hammer as prescribed by the Allievi method. Wherever possible, spring type, oilcushioned elbow hydraulic surge relief valves are the preferred choice by the Department. No pressure vessel/surge tank type devices will be acceptable. The decision to strengthen piping system components instead of utilizing a water hammer control device or different pipe size shall be based upon life cycle cost economic comparison. In the evaluation of water hammer conditions, it will be necessary to include the impacts of the appropriately provided air release and air vacuum valves along the force main as required in Chapter 7. 3. System Hydraulics/Pump Selection Provide proper wet pit design and suction line design per Hydraulic Institute Standards to avoid vortexing cavitation related vibration problems. The design Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-7 of 29 professional shall perform a net positive suction head available (NPSHA) analysis and include this information in the pump specification. The NPSHA shall be calculated for the expected design flows and shall exceed the pump manufacturer's requirements by an added margin of safety of not less than 2 feet. Avoid applications where pumps must operate in an adverse area of their performance curve. Examples would be pumps operating at very low flows and high heads, near shutoff heads, of "runout" conditions. These conditions can result in excessive hydraulic loading or cavitation damage to impellers, casings and shafts, rapid bearing and mechanical seal wear, and high vibration. F. Siting Sewage pumping stations must satisfy the site characteristics. Sewage pumping station site selection is dependent on a number of factors. Topography, access, availability of power supply, floodplain, wetlands, land use, aesthetic concerns, overflow potential and impact to the environment shall collectively be considered in the process of site selection. 1. Topography Sewers tributary to sewage pumping stations commonly dominate site selection. Adjacent drainage areas potentially served by the sewage pumping station must also be considered. Sewage pumping station site selection shall also be compatible with suitable site access, and soil capability with respect to land grading in conjunction with site development. 2. Access All sewage pumping stations shall be sited to permit access by all-weather surface roads capable of accommodating a large tanker truck. 3. Floodplain Sewage pumping stations shall be sited to remain operational and permit access during a 100-year return frequency flood. Pumping station top slab elevation shall be set a minimum of one foot above the 100-year floodplain elevation. 4. Wetlands Avoid direct impacts wherever possible and minimize impacts to wetland buffer areas. Buffer areas include the first 100 feet beyond tidal wetlands, or 25 feet beyond non-tidal wetlands. Published: 01/01 Revised: SEWAGE PUMPING STATIONS 5. Land Use VIII-8 of 29 Sewage pumping station sites should be selected to occupy vacant land. In new subdivisions the sewage pumping station site shall occupy an area at least equivalent in size to the minimum allowable lot size. In existing subdivisions site size shall meet the minimum allowable lot size if possible. Pumping station sites acquired "fee simple" is preferable to those where permanent easements are obtained. Pump station sites wherever possible must conform to land use regulations such as building restriction lines and setbacks in relation to neighboring properties. Variances may be required where restrictions cannot be met. Special exceptions may be required if the pumping station is not a conforming use under Anne Arundel County Zoning Regulations. Pump station siting shall consider the Critical Areas Requirements for those installations where bayfront or wetlands proximity necessitates, and shall consider requirements to meet MDE shellfish requirements for emergency holding capacity. 6. Aesthetics Natural screening and remoteness of the site should be a primary element of site selection wherever possible. Where pump stations are sited in proximity to developed areas, predominant wind direction for potential odor dispersion and building aspects such as generator exhaust and ventilation fan noises shall be considered. Similarly, building setbacks shall be considered to provide minimal impact to neighboring properties. 7. Overflow Sewage overflow at sewage pumping stations is not permitted. Sewage pumping station sites shall be selected to permit site development, which will preclude onsite overflows. 8. Ownership It is the County's intent to not allow pump stations to be designed and built for private ownership. In the rare and extenuating circumstances where private ownership must be considered, the pump station and all appurtenances shall be in strict compliance with the County Standards. Pump station site shall be separately subdivided lots to be deeded to the Department. Lot size shall be large enough to allow for minimal environmental impacts to wooded buffers, steep slopes, wetlands, etc., while maintaining sufficient land area for the following necessary features: · · Pumping station wetwell and drywell, if any Pump-around vault Published: 01/01 Revised: SEWAGE PUMPING STATIONS · · · · · Control/generator building Truck access with turnaround area Odor control systems Stormwater management facilities VIII-9 of 29 Emergency holding capacity per MDE shellfish protection requirements. G. Selection The type of sewage pumping station required by the Department will be governed by station capacity in terms of flowrate and horsepower. Sewage pumping stations will be either custom built-in-place wet well/dry well type or engineered package wet well / dry well type, or engineered package submersible type subject to the limitations set forth. Reference Drawings for Wet/Dry Well and Submersible Pumping Stations are available as separate documents from the County DPW. These reference drawings provide the design professional with the minimum notes, details and drawing layouts which the DPW requires on design drawings for sewage pumping stations. 1. Custom Built-In-Place Wet Well/Dry Well Sewage Pumping Station This type of sewage pumping station will be designed for installations with design flows above 3.0 MGD. Custom built-in-place stations shall be engineered to meet the requirements of these guidelines, as well as any supplemental guidelines imposed by the Department on a case-by-case basis. 2. Package Sewage Pumping Station This type of sewage pumping station will be utilized for design flows of 3.0 MGD and less. Depending upon flowrate and motor horsepower, the packaged pump stations will be wet well/dry well configuration or submersible configuration. Packaged sewage pumping stations shall be engineered to meet the requirements of these guidelines. a. Submersible: Submersible sewage pumps with guide rail and pump discharge elbow assemblies installed in the wet well shall be used for small sewage pumping stations. Submersible type sewage pumping stations shall be used at locations where design flow does not exceed 400 GPM and motor horsepower is 20 or less. If either motor horsepower or design flow limitations for submersible type sewage pumping stations are exceeded, a dry well/wet well configuration shall be used. Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-10 of 29 b. Dry Well/Wet Well: .Dry Well/Wet Well sewage pumping stations shall be used where flows are in excess of 400 GPM or where a submersible station would require a motor greater than 20 HP. Dry Well/Wet Well sewage pumping stations shall use dry pit submersible type pumps and motors. 3. Other Configurations In special circumstances due to extraordinary sewage composition, rehabilitation of an existing installation or other reasons, the Department shall be consulted to determine the acceptability of other configurations before sewage pumping station design commences. H. Site Improvements Sewage pump stations must be developed with the necessary improvements to ensure adequate and reasonable access, security, drainage and maintainability. 1. Access Road All sewage pumping stations must provide complete vehicular access. a. Duty and Section: Access roads should be designed to accommodate all types of vehicles at low speeds from passenger automobiles up to large tanker trucks. An all weather surface with cross section design adequate to support the vehicular loads anticipated should be designed for local soil conditions. Access roads shall be a minimum 12-foot wide single lane with 2 percent cross slope to provide surface drainage. Two foot wide shoulders on each side of the road surface shall be included with a cross slope of 6 percent (See Reference Drawings for Wet/Dry Well and Submersible Pumping Stations, Dwg PS-C1-3). Swales, pilot ditches and culverts as necessary shall be provided to ensure adequate storm drainage for a 10-year return frequency rainfall event. Grading and slope stabilization in conjunction with access road design shall be compatible with local soil conditions. b. Geometry: Horizontal access road geometry shall permit vehicular movement such that vehicle tires can remain on road and shoulders at all curves. Turning flares shall be provided at the intersection with traveled roads. Vertical access road geometry shall provide smooth grade transitions and adequate site angles at intersections with traveled roads. Access road grades should be limited to 8 percent, but in no case may exceed 12 percent. Access roads shall satisfy all horizontal and vertical geometry requirements for vehicles in size up to large unit trucks. c. Security: Access roads longer than 75 feet in length shall include a padlocked entrance chain between pipe bollards across the access road. The chain and pipe bollards shall be set back a minimum of 5 feet from the right-of-way line. Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-11 of 29 Consideration may be given to access road entrance chain and pipe bollards for access roads less than 75 feet in length. 2. Sewage Pumping Stations All sewage pumping station sites shall be improved with paved surfaces, security fences, site lighting and screening. Certain locations and attendant conditions may require other improvements, which may consist of storm drainage systems or more extensive security provisions. a. Perimeter Fence: All sewage pumping stations must have a minimum 7 foot high chain link fence surrounding the parking area, building, wet well, dry well and vaults. In areas particularly subject to vandalism higher fences and electronic security systems should be considered on a case by case basis. Full width sliding fence gates, up to fourteen feet wide, with padlocked astrigal shall be located to suit entry and exit of the pump station site. All exposed fencing materials shall be black vinyl coated. A two foot wide, 6 inches thick, reinforced concrete mowing strip shall be cast beneath the perimeter fence (except across gate openings) with expansion joints spaced a maximum of 10 feet apart, and 1 foot each side of all posts (See Reference Drawings for Wet/Dry Well and Submersible Pumping Stations, Dwg. PS-C1-5). b. Paving and Other Surfaces: Sufficient bituminous paved surfaces, within the sewage pumping station perimeter fence, shall be provided to enable the maneuvering and turning of vehicles in size up to unit trucks. The paving section composition shall consist of band SF surface course, an underlying band BF and a CR-6 crushed stone base course, all of a composite thickness necessary to support all anticipated wheel loads in consideration of local soil conditions (See Reference Drawings for Wet/Dry Well and Submersible Pumping Stations, Dwg. PS-C1-1). The remaining surfaces inside the perimeter fence not occupied by structures shall be covered with a compacted course of washed SRC-2A stone of thickness equal to bituminous concrete site paving and underlain by a CR-6 crushed stone base course of thickness equivalent to the paved surface base course placed on a geotextile fabric. A 1/4-inch x 6" epoxy or bituminous-coated steel edge strip shall be installed adjacent to paved areas to provide a protective edge for the paving.. c. Grading: Sewage pumping station grades for paved areas shall prevent local ponding, provide positive drainage away from structures and generally be limited to no greater than 4 percent slopes. Stone surfaces around paved areas shall provide proper site drainage at slopes 10 percent or less. Land grading outside of the sewage pump station perimeter fence shall not exceed 3 to 1 slopes; 4 to 1 slope maximums are desirable. Lesser slopes wherever possible are preferred. Site grading design shall be compatible with slope stability for soils encountered. Slope stabilization shall be appropriate for the degree of Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-12 of 29 slope and soil conditions. The use of retaining walls on or adjacent to the sewage pumping station site shall be avoided. d. Landscaping: All sewage station sites shall be screened as appropriate for surrounding development. Landscaping materials should be aesthetically pleasing and require minimal maintenance (watering, fertilizing, trimming, etc.). e. Lighting: Exterior lights shall be wall-mounted on the pump station building, high pressure sodium type controlled by an on-off switch. 3. Structures All structures shall be protected from 100-year return frequency floods. Structure foundation design shall be based upon geotechnical evaluation of underlying bearing stratum. The design professional shall include the geotechnical report and soil boring report in the project specifications. a. Building: Sewage pumping station electrical, control and standby power systems are to be housed in an at-grade brick and block building with wooden roof trusses and shingles. The building shall be sized to afford reasonable access to and removal of all components housed within. Details of construction shall follow the architectural, structural, mechanical and electrical standard design (See Reference Drawings for Wet/Dry Well and Submersible Pumping Stations). All buildings shall be designed to comply with the BOCA 1993 National Energy Conservation Code. The control room shall be heated with an electric unit heater to automatically maintain a minimum temperature of 55º F during the winter. The unit heater will be controlled by a thermostat rated for a maximum temperature setting of not greater than 75º F. The control room shall be ventilated to eliminate heat build up during the summer. An exhaust fan shall be provided and controlled by a thermostat. All motor operated dampers/louvers shall be of heavy-duty aluminum design and of airtight energy efficient construction. b. Pumping Station: Sewage pumping equipment will be located in a below grade concrete structure of the type indicated for the capacity planned. The pumping station concrete structure(s) shall extend at least 12 inches above finished grade (See Reference Drawings for Wet/Dry Well and Submersible Pumping Stations). Bituminous concrete paving shall surround the pumping station structure(s) and be continuous to the mowing strip. In areas where stone is used, a 1/4" X 6" epoxy or bituminous-coated steel edge strip will be used where the stone ends and paving begins to provide a crisp edge. c. Vaults: Precast concrete vaults for emergency station bypass pumping connections and valves shall have an interior epoxy paint finish and an Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-13 of 29 exterior elastomeric membrane waterproofing in accordance with the Reference Pumping Station Specifications. Valve vaults for submersible sewage pumping stations shall be segmented and contain emergency connection couplings and valves in one compartment and all pump discharge check valves, isolation valves, gauges and flushing connection control valve in a separate compartment (See Reference Drawings for Wet/Dry Well and Submersible Pumping Stations). Sewage pumping station vaults shall extend 12 inches above grade and shall have hatches and ladders with spring-loaded extension poles to access valves and emergency connection couplings. Vault dewatering will be accomplished with the use of a cast iron mud valve and drain line discharging into the wet well. The mud valve shall have extended operating stem for easy operation from above grade through the open hatch. Vaults normally will be surrounded with bituminous concrete paving. I. Sewage Pumping Station Features Sewage pumping station structures, equipment systems, piping, controls and accessory systems must be engineered according to these guidelines to form a cohesive design integrating the intended service and operational characteristics stipulated. To fulfill the intent of these guidelines, the design professional must exercise judgment to use the special knowledge relating to project site characteristics and conditions of service (head, flow, force main, etc.) particular to the sewage pumping station design under development. 1. Wet well Wet wells shall be considered a hazardous environment, classified as NEC Class I, Division I for explosive gases. Wet wells shall be designed and constructed to be as hazard free as possible, and corrosion-resistant materials shall be used throughout. All materials and equipment used in wet wells shall meet NEC Class I, Division I standards, with the exception of control floats. Conduit between the junction box and control building shall be sealed at the junction box with explosion-proof seal. Conduit carrying float cables between the junction box and wet well shall contain removable seal for ease in removal and replacement of control floats. a. Structure: Sewage pumping station wet wells shall be constructed of reinforced concrete. Package sewage pump station wet wells shall have precast base slabs and riser sections, and cast-in-place top slabs. Custom built-in-place sewage pump station wet wells shall be compartmented and constructed entirely of cast-in-place reinforced concrete. The structural design of cast-in-place concrete is the responsibility of the design professional. Wet wells shall have an interior epoxy paint finish and exterior elastomeric membrane waterproofing in accordance with the Technical Specifications. Wet wells shall be adequately designed to prevent flotation. Wet well size and depth shall be as required to accommodate the influent sewer, pump suction Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-14 of 29 submergence as recommended by Hydraulic Institute Standards or in the case of submersible pumps complete pump submergence. The required working volume and preferred intervals between sewer and control elevations shall be determined as follows: 1) Working Volume (in Gal.) =
TQ = 4 T = minimum time between motor starts or 7 minutes whichever is greater; for pumps 30 horsepower (HP) and larger, minimum cycle time shall be 12 minutes Q = ultimate design discharge rate of one pump in operation in GPM Working Volume = lead pump on - lead pump off 2) Minimum inside width - 8 feet (considerations shall include retention time & pipe/pump configuration & access) 3) Minimum elevation difference between influent sewer and high water alarm - 18 inches 4) Minimum elevation difference between control elevations - 6 inches 5) Emergency storage per Design Guidelines for Wastewater Pumping Stations for the Protection of Shellfish Waters and Swimming Waters, published by MDE. b. Access: Package pump station wet well access shall be through a top slab opening with aluminum hatch cover and frame. The top slab access hatch shall be 36 by 36 inches minimum size and as large as necessary to allow removal of equipment from the wet well. Permanent aluminum safety railings shall be provided around the access hatch in accordance with OSHA regulations. An aluminum ladder with extendable spring-loaded aluminum safety poles at the top shall be provided to permit safe entry. Rungs shall be square with serrated top surfaces. Structures 20 feet in height or more shall be equipped with removable intermediate landings as required to obtain less than 20-foot intervals. The ladder landing on the wet well floor shall be flat. Custom built-in-place wet well personnel access shall be stairs, minimum of 36 inches wide. Provisions should be made for wet well access openings large enough for equipment removal. c. Wet Well Work Platform: Package pump station wet wells shall have an intermediate platform completely covering the wet well. The work platform shall be constructed of aluminum grating sections and grating supports of structural aluminum shapes fastened to the wall. Custom built-in-place pump Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-15 of 29 station wet wells shall have an aluminum perimeter platform with handrail over the wet well and screening channel. Seven feet minimum of headroom over work platforms is desirable. Care shall be taken to locate removable grating sections consistent with equipment placement and removal requirements. All fixed grating shall be bolted down as detailed. All fasteners are to be stainless steel. d. Debris Removal: All sewage pumping stations will have bar racks for debris removal. Package sewage pumping stations will have manually cleaned static bar racks attached to the wet well wall and work platform (See Reference Drawings for Wet/Dry Well and Submersible Pumping Stations). Static bar racks shall be of welded aluminum and stainless steel construction. Custom built-in-place sewage pump stations shall have a special debris-screening channel and bypass channel upstream of the segmented wet well. Aluminum stop gate guides shall be cast into the channel walls for insertion of flow isolating aluminum stop gates. Maximum clear opening between bars shall be 1¼ inches for all bar racks. Bar rack headloss shall not cause any reduction in influent sewer flow velocity. Bottom of bar racks shall be located 12 inches below the invert of the influent sewer pipe. e. Invert Slope: Wet wells shall have sloping sides to form a hopper at the bottom of the wet well. Package sewage pumping stations shall have grout fill slopes of 1 horizontal to 1.75 vertical (See Reference Drawings for Wet/Dry Well and Submersible Pumping Stations, Dwg. PS-M1-6). Custom built-inplace sewage pumping station-wet wells shall have side slopes of 1 horizontal to 1 vertical if possible. The flat portion of the wet well floor shall be sufficient in area to accommodate equipment mounting, ladder landings and recommended pump suction hydraulic conditions as outlined by Hydraulic Institute standards. f. Bubbler and Floats: Wet well liquid levels are controlled by a bubbler system with back up float switches. These systems within the wet well shall be located to minimize the turbulent influences of flow into the wet well on the control of liquid level. Bubbler tube piping and float staffs shall be readily removable from the wet well work platform. Bubbler systems shall be manual purging. At the Department's discretion, a Gorman-Rupp differential pressure level control system may be used in lieu of the standard bubbler system. g. Odor Control: Odor control method selection for pumping stations is to be based upon the decision tree in Appendix A. It should be assumed that a pump station with a greater than two-hour upstream force main detention time will produce both H2S and NMOC levels greater than 5 ppm. See Reference Drawings for Wet/Dry Well and Submersible Pumping Stations and the Special Provisions Design Standards for Sewage Pumping Stations for design requirements. For grinder pump systems with more than 15 units discharging Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-16 of 29 to a collection system, the effects of H2S on the downstream infrastructure shall be addressed by the design professional. Analyses shall be submitted to the DPW for approval. h. Lighting: Wet wells shall be provided with wall-mounted explosion proof incandescent light fixtures with guard and globe. One fixture shall be installed near the top of the wet well and another three feet above the grating. An explosion-proof switch shall be installed to operate the lights. i. Ventilation: Wet wells shall be provided with a separate ventilating system and shall be sized to provide a minimum of 30 complete air changes per hour. In addition to manual control, time clock operation of fans shall be provided to allow a minimum of 2 complete air changes per hour. Ventilation shall be accomplished by the introduction of fresh air into the wet well under positive pressure. If the fan is installed outdoors, the fan assembly and housing shall be of corrosion-resistant and weatherproof construction. The entrance hatch to the wet well shall be provided with a limit switch to energize the fan whenever the hatch is open. The fan shall be direct drive. j. Dewatering: Package sewage pumping station shall be designed with pump around vaults and flushing valves. Custom built-in-place sewage pumping station wet wells shall have individual valved drains to a common station drain sump. Designer shall incorporate provisions for the periodic dewatering of the wet well for the abatement of grit accumulation in the wet well which will be determined by the individual pumping station's size and sewage composition. k. The design professional shall evaluate the likelihood of grease accumulation in the wet well based on the station size and sewage composition. Design should include measures for preventing grease accumulation, such as air infusion systems, if grease problems are anticipated. If grease accumulation is not anticipated, then typical maintenance measures, such as providing for easy washdown of the wet well, will be sufficient. 2. Dry Wells Below grade dry wells shall be designed to provide suitable environments for operating and maintaining pumping equipment and piping systems and shall incorporate the use of corrosion resistant materials throughout. Configuration of dry well components shall promote safe access and adequate space for equipment and valve maintenance. Proper design shall minimize hazards for maintenance personnel. a. Structure: Sewage pumping station dry wells shall be constructed of reinforced concrete. Package sewage pump station dry wells shall have segmented precast concrete base, riser, access tube and top slab sections as Published: 01/01 Revised: SEWAGE PUMPING STATIONS VIII-17 of 29 necessary on a cast-in-place structural concrete base slab foundation (See Reference Drawings for Wet/Dry Well and Submersible Pumping Stations). Custom built-in-place sewage pump station dry wells shall be constructed integral with the wet well and above grade building structures. The structural design of all cast-in-place concrete is the responsibility of the design professional. Dry wells shall be adequately designed to prevent flotation. Dry well exteriors shall be waterproofed with elastomeric membrane as specified in the Technical Specifications. Dry well interiors shall have a smooth, easy to clean special coating finish as specified in the Technical Specifications. Dry well depth and size shall be adequate to provide proper wet well suction and spaces for maintenance and removal of all equipment. b. Access: Package pump station dry well access shall be through a top slab opening with aluminum hatch cover and frame. The top slab access hatch and precast access tube riser shall be of sufficient size to permit the removal of an assembled sewage pump or any other station component, if larger. Minimum hatch size shall be 36 by 36 inches. Permanent aluminum safety railings shall be provided around the access hatch in accordance with OSHA regulations. An aluminum ladder with extendable spring-loaded safety poles at the top shall be provided to permit safe precast concrete dry well entry. Rungs shall be square with serrated surfaces. Structures 20 feet or more in height shall be equipped with removable intermediate landings as required to obtain less than 20-foot intervals. The ladder landing area shall be sufficiently clear to permit easy ladder use and equipment removal. Custom built-in-place dry well personnel access shall be ladders equipped with fall protection systems, minimum 16 inches wide. Additional grating, plate or concrete covered access openings shall be provided directly above each pump. c. Lighting: Precast concrete dry wells shall have wall-mounted vapor-proof incandescent lights. Cast-in-place concrete dry wells shall have lighting system specifically designed to provide illumination best suited for the dry well layout which may include suspended, wall, or ceiling mounted; energy efficient fluorescent, or other types of fixtures. Dry well lighting shall be at levels adequate for routine service inspections and maintenance activities. Portable supplemental lighting will be utilized for unusual or non-routine maintenance activities. d. Ventilation: Dry wells shall be provided with a separate ventilating system and shall be sized to provide 10 air changes per hour. In addition to manual control, time clock operation of the ventilating fans shall be provided. Ventilation shall be accomplished by the introduction of fresh air into the dry well under positive pressure. Precast dry well ventilating fans shall be continuously energized whenever the access hatch is open. Fans shall be direct drive. Published: