Civil Engineering - Wastewater
As development works to keep pace with Washington’s growing population, communities often find their existing wastewater infrastructure inadequate. BHC Consultants have helped a number of municipalities react to and prepare for this growth. Wastewater services provided include:
- Sewer System Analysis and Design
- Comprehensive Sewer Planning
- Wastewater and Water Reuse System Design
- Wastewater Treatment Plant Design
- Engineering Feasibility Study/Report
- Construction Services
- Hydraulic Modeling
- Capital Improvement Plans and Funding Analysis
- LID and ULID Formation
- Grant and Loan Application Assistance
- Permitting Assistance
- Easement Preparation and Acquisition
- Biosolids Handling Design
- Pump Station Design
- Industrial Wastewater Treatment
Wastewater Project Briefs
2012 Wastewater Comprehensive Plan Update, City of Lynnwood, WA
Lynnwood retained BHC to update planning for the City sewer system including the 7.7 MGD treatment facility. After an initial review of the sewer system, BHC interpolated City forecasts of population and employment to produce 6 and 20-year projections. Existing wastewater treatment plant flow records were interpreted to identify existing unit flows. City GIS data of sewer piping and lift stations were input to MIKE URBAN software to create a dynamic hydraulic model of the existing system including pump operations. Existing population and employment was distributed among 18 sub-basins. The unit flows were applied to the model and adjusted to calibrate the model output flows to within 5 percent of the recorded flows. Projected 2032 population and employment were input to the model and peak day flow simulated in the existing system. The Pipeflow module was used to plot hydraulic profiles of peak hour flows and identify needed capacity improvements. Alternatives considered included flow diversions to other sewerage agencies, reclamation and reuse, additional lift stations, and added pipe capacity.
Comprehensive Sewer Plans, Cities of Everson and Nooksack, WA
BHC completed two distinct, but coordinated General Sewer Plans for the Cities of Everson and Nooksack. The City of Everson Wastewater Treatment Plant treats raw sewage from both cities. The combined population of the cities is approximately 3,800 people.
The plans included determining system flow characteristics and flow projections, evaluation of wastewater treatment alternatives, hydraulic modeling, capital improvement planning, analyzing wastewater reuse, and analyzing financial information to determine funding requirements. Coordination between the two cities was key to the success of the two projects.
Beach Sewer Line Rehabilitation, Southwest Suburban Sewer District, Burien, WA
BHC was selected by Southwest Suburban Sewer District to design improvements for the failing sewer beach line in Seahurst Pak. In the 1950’s, installing buried sewer mains in the tidal zones of Puget Sound was commonly done because it offered unobstructed corridors. However, these pipes, which are subjected to brackish water and shifting foundation support, have approached, and in some cases, exceeded their useful life. Dislocated joints, differential settlement, and thinning pipe wall thicknesses have resulted in increasing maintenance issues and the need for routine flushing.
Alternatives evaluated included: abandonment of the beach line and re-directing flow from the beach into a different drainage basin; installation of a new beach line; repair of the gravity line in place; and sliplining the existing pipe with a new force main.
The selected option involved sliplining the main with a 4-inch force main, constructing a new waterfront pump station, and serving the parcels along this 6,000 foot segment with grinder pumps.
Permits obtained included a Corps Nationwide Permit (wetlands), Shoreline Permit, Biological Evaluation (endangered species), JARPA, SEPA Checklist, and WSDOT agreements.
Wastewater Pump Stations Nos. 2, 10, 12, and 15 Rehabilitation, City of Redmond, WA
Wastewater Pump Stations Nos. 2, 10, 12, and 15 are submersible pump stations located within Redmond city limits. All four stations have reached the end of their useful life and the City desires to replace all of the mechanical, electrical, and instrumentation components of these pump stations. Pump Station No. 2 is located along the shoreline of Lake Sammamish adjacent to several residences. Both Pump Station No. 10 and Pump Station No. 15 are located within several feet of an adjacent residence, and Pump Station No. 12 is located within a business park. Design challenges include environmental and aesthetic sensitivity, spatial limitations, maintaining service during construction, construction sequence, and the low flow/high head conditions of the existing stations. The predesign phase of the project, completed in June 2013, included an alternatives analysis of upgrade options, including performing an analysis of pump options so that the City could make an informed decision on the optimal pump for each station, identification and assistance in obtaining permanent easements, and an evaluation of existing facilities for reuse. Due to the proximity of the stations to adjacent residences and businesses, coordination with the property owners and the consideration of aesthetics in the design alternatives was required. The results of the evaluation of the existing facilities gave the City confidence that they could optimize use of, and extend the life of, the existing concrete infrastructure by coating the existing facilities. This will require bypass pumping during construction. BHC develops the design criteria for bypass operations so that the Contractor can design and operate the bypass facilities. The design phase is at the 100% level for Pump Stations Nos. 10 and 12, and the project is expected to advertise for construction in 2014. Pump Stations Nos. 2 and 15 designs are on hold pending easement and entitlement negotiations that BHC is assisting the City with. BHC is also under contract to provide engineering services during construction.
Sludge Dewatering & Biogas Utilization Project, Washington Beef, Toppenish, WA
Following completion of the liquid stream expansion in 2010, BHC was retained for preliminary and final design, major equipment procurement, and construction assistance for a project to provide for sludge dewatering of secondary sludge from the liquid stream SBR treatment process. The project also includes biogas capture from an existing anaerobic lagoon, gas scrubbing, storage, and beneficial utilization at the processing plant’s existing 800 HP boilers.
Sludge dewatering includes a new mixed sludge blend tank and a new FKC screw press housed in a new building, along with sludge feed pumps, a polymer feed system, and pressate discharge pumps. The system also includes a dewatered sludge screw conveyor for loading haul trucks.
The biogas utilization system includes installation of a new floating, gas-hold membrane cover over an existing anaerobic lagoon. The captured biogas is then scrubbed and had moisture removed, prior to storage in a 100,000 cubic foot membrane storage dome. The stored gas is then pressurized and conveyed about 1,800 feet to the existing boilers. The boiler fuel system is being retrofitted to burn either natural gas or biogas. Biogas production has averaged over 300,000 cubic feet per day.
Central Kitsap Wastewater Facilities 2011-2016 Collection and Conveyance System Upgrades, Kitsap County, WA
BHC was selected to prepare a preliminary design report and final construction documents that addressed necessary upgrades to Pump Stations 1, 6, 8, 18 and their associated conveyance piping systems. Design flow rates are 2,100, 3,000, 1,200, and 300 gpm respectively. These pump stations have aging equipment that is no longer operating efficiently or reliably. In addition, the pumping capacities at the three stations are either exceeded by current peak incoming flows or projected to be exceeded in the near future. BHC used MIKE URBAN, a sanitary sewer model, to review the improvements recommended in the Kitsap County Wastewater Facility Plan and then assessed whether alternative improvements would be more cost effective. Opinions of probable project costs were prepared to compare the alternatives and to assist the County in updating its Capital Improvement Plan (CIP). The result was a plan that addressed the capacity issues at Pump Stations 1, 6, 8, and 18 and their associated conveyance pipelines for less money than was originally included in the County’s CIP. Design challenges include minimizing impacts to neighborhoods and sensitive areas such as wetlands and streams, addressing traffic impacts, and constructing the upgrades without interrupting the existing sewer service.
Meridian Ave. Sewer LID No. 1, City of Edgewood, WA
This project consisted of the design and construction of three pump stations, approximately 22,300 linear feet of sanitary sewer force main and 25,200 feet of gravity sewer main. The scope of work included preliminary design, design, permitting, and construction management services as well as assistance with the formation of a Local Improvement District (LID). The preliminary design services consisted of evaluating potential service areas, reviewing probable construction costs, and defining the LID boundary. Design efforts included preparing the construction documents for the gravity sewer, force mains, and sewage pump stations, developing detailed construction cost estimates, applying for the required permits, assisting in the acquisition of easements, and assisting the City with the formulation of the LID. The design team also prepared environmental reports, provided survey, and geotechnical support. Design challenges included highly saturated ground conditions, two Jack and Bore operations to maintain traffic in SR 161 and multiple utility crossings. The construction management services involved observing the contractor’s work for compliance with the contract, interfacing with the public to determine the location for the side sewers, administering the construction contract, and coordinating with the numerous regulatory agencies.
Membrane Filtration Feasibility Study, City of Marysville, WA
BHC Consultants has prepared a feasibility study for the City of Marysville to assess the addition of membranes at the wastewater treatment plant for the purpose of producing reclaimed water. As part of this study, BHC also assessed the feasibility of adding further biological treatment for removal of nitrogen to potentially allow year-round discharge to Steamboat Slough, rather than seasonally pumping effluent to the City of Everett’s wastewater treatment plant. Facilities that would need to be added to accomplish these objectives were identified to include an aeration basin for nitrogen removal, membrane bioreactor, disinfection for reclaimed water, equalization and pumping for reclaimed water, and a new transmission main for conveyance of reclaimed water. With the development of a conceptual design for these facilities, BHC is now working with the City on planning, executing and evaluating a pilot system to test the efficacy of the membrane bioreactors with the existing sand filters and lagoons to produce reclaimed water and remove nitrogen.
Water Reclamation Facility Improvements, SunLand Water District, Sequim, WA
SunLand Water District, located near Sequim, WA, owns and operates a 150,000 gallon per day Class A Water Reclamation Facility (WRF) that uses the Sequencing Batch Reactor (SBR) treatment process. The WRF produces a Class A effluent that is sprayed on nearby fields. In 2013 SunLand contracted with BHC to perform preliminary engineering, design and construction support of improvements at the WRF. Those improvements include:
- Removing biosolids from an existing facultative lagoon and repurposing the lagoon to be used as an aerobic digester and equalization basin to comply with State regulations and provide plant redundancy.
- Removing the chlorine gas disinfection system and installing a new, safer disinfection system.
- Installing a new disk filter in parallel with the existing disk filter to increase capacity and provide redundancy.
BHC prepared an Engineering Report for the WRF improvements in accordance with Department of Ecology requirements. During this preliminary engineering phase, it was determined that the most cost efficient method of disinfection on a life-cycle basis was bulk sodium hypochlorite injection. This disinfection method resulted in nearly $200,000 savings to the District over the life of the system than other alternatives, including UV disinfection.
BHC also evaluated several options for disposal of the facultative lagoon materials, and performed a cost analysis of those options. The lowest cost option resulted in savings of over $100,000 compared to the other disposal options.
The District has secured a Public Works Trust Fund (PWTF) loan for the WRF Improvements. BHC is performing the preliminary design, design and construction on a fast-track basis so that the improvements are implemented as quickly as possible and the best possible interest rate is secured on the loan. BHC conducted meetings with the Department of Ecology before starting the Engineering Report and coordinated with Ecology throughout the preliminary design to facilitate compliance and prompt approvals.
Combined Sewer Overflow (CSO) Phase I Project, City of Snohomish, WA
BHC provided preliminary engineering, final design, and services during construction for facilities to intercept and control existing combined sewer overflows (CSO) in the City of Snohomish. The new facilities include a new 6,500 gpm combined CSO and stormwater pump station, nearly 6,200 feet of 18-inch and 24-inch force main and gravity sewer pipe, 3,000 feet of 18- to 30-inch stormwater pipe, and 1,200 feet of 12-inch water main. Special design considerations included stabilization of the pump station site using a stone column system, architectural pump station features to conform to the historic neighboring community, and location of separate sanitary sewer, stormwater, and potable water pipelines within a relatively narrow existing City street. The pump station consists of two suction lift pump sets, one at 6,500 gpm (sewer), and one at 5,400 gpm (storm).
BHC also provided services during construction including field observation, office engineering, construction documentation processing (RFIs, submittals, pay requests), coordination and cooperation with local and State agencies, and the preparation of an operations/maintenance manual.
BHC’s work on the City of Snohomish CSO Project won the 2012 American Council of Engineering Companies (ACEC) Silver Award for Social, Economic, and Sustainable Design Considerations and the 2012 Infrastructure Assistance Coordinating Council (IACC) Best Wastewater Infrastructure project for the Combined Sewer Reduction and Raingarden category.
CSO Retrofits for Henderson and Magnolia Basins, Seattle Public Utilities, Seattle, WA
BHC is performing options analysis to identify alternatives for reducing combined sewer overflows (CSOs) in the Magnolia and Henderson basins in the City of Seattle. By consent decree, the City of Seattle is limited to an average of one overflow per outfall per year, and these basins have historically experienced more overflows than this limit. The initial phase of this project included reviewing existing basin data and performing hydraulic modeling to determine the control volume required to reduce CSOs to the consent decree limit. With the control volume known, options for reducing CSOs included pump station upgrades, construction of in-line and off-line storage, and upsizing of existing conveyance systems. These options were evaluated for engineering and construction risks, permitting requirements, and construction cost. For the Magnolia basin, the preferred option is to upgrade the existing pump station capacity from 1.2 mgd to 3.3 mgd and construct a new 12” diameter force main to the Fort Lawton combined sewer. The total project cost for this option is approximately $6M. For the Henderson basin, the retained options that are undergoing further evaluation include in-line and off-line storage and constructing a new pipeline to increase capacity. The storage options include approximately 600,000 gallons of below-ground storage with pumped discharge and real time controls. The new pipeline to increase capacity consists of approximately 4,000 feet of 18 inch diameter sewer pipe. Total project costs for these options range from approximately $10M to $15M. After Asset Management Committee review and approval, the projects will proceed into design and construction.
Municipal Wastewater and Water Treatment Facilities Energy Performance Contracts, Trane US, Inc., Various Western Washington Cities
Trane US, Inc. (Trane), a Washington Department of Enterprise Services (DES) certified energy services company (ESCO) is providing Energy Performance Contracts for Cities throughout Western Washington. Recently Trane expanded these services from the traditional municipal building and school lighting and HVAC retrofits, to include municipal water and wastewater treatment facilities. Trane has subsequently retained BHC Consultants to help identify and quantify energy savings opportunities, and to subsequently provide preliminary and final design for these accepted finance/design/ build retrofits. The following plants and energy saving opportunities being evaluated and/or constructed include:
- City of Bremerton – project under construction includes replacing the primary effluent pumping system. The 5 existing x 150 HP eddy-current drive pumps are being replaced with new more energy efficient variable frequency drive (VFD) submersible pumps.
- Lakehaven Sewer District – the energy saving features being constructed include replacing the existing disc type fine bubble diffusers in the four aeration basins with higher efficiency strip diffusers complete with accessories and appurtenances.
- City of Lynnwood – the energy saving features being designed include replacing the City’s existing 110 HP centrifuges with 15 HP screw or fan presses. Other alternatives being analyzed include utilization of the waste heat from the City’s existing sludge incinerator and providing a micro-turbine on the existing outfall.
- City of Monroe – the energy saving features being analyzed include replacing the aeration system with turbine blowers and fine bubble diffusers. The City is also considering replacing the existing belt press with a screw or fan press, in order to save energy with the reduced odor fan and wash water booster system.
- City of Port Angeles – the energy saving features being analyzed include replacing the existing digester mix system with a draft tube mix system and splitting the wash water system into high and low pressure zones for the different uses (low pressure surface sprays/ high pressure wash). This project also includes replacing the existing belt press with a screw press. An energy savings of about 30 HP can be achieved through the elimination of odor fans and wash water booster pumps.
- Midway Sewer District – Potential energy saving projects include replacing one of the constant speed rotary lobe blowers on the aeration basin with a VFD turbine blower, providing VFDs on the trickling filter ventilation fans, and separating the non-potable wash water system into low and high pressure zones. These projects are pending consideration by Trane and the District.
Unalaska Wastewater Treatment Plant Facility Final Design, City of Unalaska, AK
The existing City of Unalaska wastewater treatment plant (WWTP) has been designed to provide primary treatment for 1 MGD in accordance with primary treatment standards specified in an NPDES discharge permit. The new chemically enhanced primary treatment (CEPT) facility will include an upgraded influent pump station, hypochlorite chlorination-dechlorination disinfection facilities and new solids processing equipment consisting of a rotary fan press and lime stabilization facilities. The press will be housed in an existing building on an elevated fabricated metal stand. A rotary fan press was chosen based on the small footprint required, slow speed of rotation, easy expansion capability and redundancy of the equipment.