St. John s Harbour Clean-Up Phase 2. Project Description

Transcription

1 St. John s Harbour Clean-Up Phase 2 Project Description February 2003 NEWFOUNDLAND DESIGN ASSOCIATES LIMITED

2 1 Introduction The City of St. John s, the adjoining City of Mount Pearl and the Town of Paradise now encompass a development of approximately 12,000 hectares, with a population in the order of 130,000 people. The area is expected to increase by some 15% over the next 20 years to approximately 150,000 inhabitants. The ultimate projected population for the area is 157,100. Figure 1 provides a general area plan of the City and adjoining municipalities. While St. John s Harbour is the commercial, social and cultural heart of the region, it is also the receiving water body for sewage and stormwater. It is estimated that approximately 120 million litres (26.6 million gallons) of raw sewage and stormwater enters the Harbour daily through the City s sewer infrastructure. During wet weather storm events, the Harbour can receive 4 to 5 times the daily amount from its sanitary sewerage system. Presently, there is a system of combined and separated sanitary sewers that discharge wastewater into the Harbour as shown in Figure 2. Because the wastewater is not treated or disinfected, the Harbour is contaminated with potentially pathogenic bacteria. Bacteria levels are high enough that ear and gastrointestinal infection should be expected from bodily contact with Ha rbour water. There is visual pollution in terms of floating material on the water surface. Ammonia levels in certain areas are generally higher than desirable for aquatic life, and phosphorus is above recommended levels to control undesirable phytoplankton (algal) growth. While Harbour dissolved oxygen levels are generally satisfactory, there is localized dissolved oxygen depletion in the immediate vicinity of the existing overflows and outfalls. Considerable work has been carried out since 1974 to develop a viable wastewater treatment program. This earlier work, that included on-going consultation, culminated in a Comprehensive Environmental Management Plan (CEMP) that establish the preferred approach addressing the St. John's Harbour Cleanup. The following section provides a detailed description of the background work carried out and resulted in the preferred treatment strategy. The recommended program is a phased approach as follows; Convey wastewater to the south side of the Harbour Provide primary treatment and disinfection of the wastewater Provide a diffused outfall Convert existing wastewater outfalls at Temperance Street and Prescott Street to wet weather overflows Ultimately provide secondary treatment Phase 1 of the program, which has already been completed, focused on providing immediate relief to the western end of the Harbour. This end of the Harbour receives drainage from the Waterford Valley and raw sanitary wastewater from the local combined sewer areas. Phase 1 projects completed to date include: ES-1-1W TOR

3 FEBRU ARY, ATLANTIC OCEAN FIGURE -1 SCALE 1: GENERAL SERVICE AREA DRA INAGE AREA ST.JOHN'S AIRPORT < CONCEPTION BAY WINDSOR LAKE < CITY OF ST.JOHN'S < QUIDI VIDI LAKE ST.JOHN'S HARBOUR TOWN OF PARADISE < < CITY OF MOUNT PEARL Drainage Boundary < <

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5 INTRODUCTION Phase 1 Construction of the Southside Road Pumping Station (Shallow Pumping Station) ; Extension of the Waterford Valley Relief Sewer to the Shallow Pumping Station along Southside Road; Construction of the Outfall from the Shallow Pumping Station into St. John s Harbour; - Construction of Outfall Diffuser in the Harbour ; - Construction of the section of the Harbour Interceptor Sewer from Water Street to Southside Road, and; Diversion of a portion of sewage flow from the Waterford Valley Sewer to the Waterford Valley Relief Sewer at Syme s Bridge. The current project is Phase 2 of the Program and includes a Wastewater Treatment Plant located at Southside Road; refer to Figure 2. The general scope is as follows: Phase 2 Completion of the Harbour Interceptor Sewer; Temperance St to Job's Bridge crossing at Water St. Construction of Phase 2 of the Southside Road Pumping Station (deep pumping station) along with the short section of the Harbour Interceptor Sewer along Southside Road; A new Primary Treatment Plant, and; Modifications to the outfall diffusers In the longer term, when Harbour water quality dictates, secondary treatment will be implemented. The following sections of this document outlines the background work for the project and the project description for Phase 2 of the St. John's Harbour Cleanup Project. ES-1-2

6 BACKGROUND 2 Background Earlier Studies and Consultation Newfoundland Design Associates Limited in association with James F. MacLaren Limited carried out the first major study on the Harbour (involving the three levels of governments) in It recommended the eventual elimination of untreated sewage being discharged to St John s Harbour, and the conveyance of raw sewage to a wastewater treatment site out side the Harbour to the south on Freshwater Bay near Gunner s Cove. In the report, the discharge of treated wastewater to Freshwater Bay was of concern because of the lack of scientific knowledge related to the physical environment in the Bay. This lack of scientific knowledge included information on water quality, bottom sediments and current patterns. As a result, further study was recommended to determine the impact of wastewater discharges on this pristine marine environment. While the report was endorsed by both the Federal and Provincial governments, the capital cost of this program, estimated in 1974 at $50 million dollars, was considerably in excess of what the municipality could afford. Funding was received for design and construction of a number of trunk sewer projects within the City, however the funding program was terminated before any work commenced on the treatment plant and outfall works proposed in this study. In 1982 a second major study entitled St John s Sewage Disposal Study was carried out by Newfoundland Design Associates Ltd. in association with Gore & Storrie Limited and Newfoundland Oceans Research and Development Corporation. This report reviewed and updated the 1974 report and carried out further work on the physical environment of St John s Bay including Freshwater Bay and St John s Harbour. This study provided a better understanding of the impact of wastewater discharges to the receiving waters. Significant was the condition of the Harbour and the areas in the Harbour that were seriously degraded. Specifically they were where the discharge of raw sewage was in confined shallow areas of the Harbour such as Job s Bridge, the Basin (now eliminated) and Steers Cove. The model predicted, that by intercepting the present sewage discharges into the Harbour and conveying them to the south side of the Harbour and providing screening, primary treatment and disinfection, a marked improvement in water quality was possible without the need to go to secondary treatment or ocean discharge. This finding allowed consideration of a staged, more affordable approach to the Harbour Clean-up program that would not require secondary treatment initially and/or discharge to Freshwater Bay off Gunner s Cove. As part of this study, a proposed interceptor sewer alignment study was carried to locate existing discharges and establish routes to convey sewage to a new pumping station on Southside Road. Comprehensive Environmental Management Plan In February of 1993 under a program sponsored by Environment Canada s Green plan, St John s Atlantic Coastal Action Plan Program Inc. (St John s ACAP) was established. The group was formed by a number of concerned citizens and representatives from the Municipal, Provincial and Federal governments. Its mandate was to develop a community directed consensus-based comprehensive management plan for the Harbour. The group worked with many groups in the St. John s area to inform the public on the issues around wastewater in the region. The group provided background information to citizens of the ES-2-3

7 BACKGROUND area and carried out surveys to determine the public interest and knowledge of the issues. The group was successful in engaging the public and gaining wide public acceptance for this project. One of the successes of ACAP was the Cities of St. John s, Mount Pearl and Paradise proclaiming that they would adopt and support the ACAP plan for the Harbour. This proclamation was passed on November 28, 1996 and the report released in March of As part of the ACAP program Newfoundland Design Associates Limited, in association with CH2M Gore & Storrie Limited were engaged in 1995 to evaluate sewage treatment options and to develop a phased strategy for sewage treatment for the Region. It was anticipated that this approach would ease the financial burden on the municipalities. This study recommended collection and conveyance of wastewater to a central facility located either underground in Southside Hills or at Gunner s Cove on Freshwater Bay. Initially primary treatment and disinfection were to be provided. In the longer term secondary treatment was seen to be required and this would be dictated by Harbour water quality. ACAP Inc in reviewing the study recommended in the final site selection process that locating a facility at Gunner s Cove reconsider the difficult site access and the pristine nature of the area, versus the reputed higher cost of locating the facility underground in Southside Hills. Subsequent to ACAP s request no major objection was voiced to locating the proposed treatment plant on federal industrial land owned by Transport Canada and directly abutting the Stage 1 Southside pumping station. In this study the need to construct an underground treatment facility at Southside Hills was found to be unnecessary as the cost of rock removal for an above grade facility was cheaper. As well, from an occupational health and safety point of view an above grade facility is much preferred to an underground facility. With the support of the Cities, ACAP introduced the Comprehensive Environmental Management Plan (CEMP) for St John s Harbour in March of The CEMP serves as the core environmental planning document for the proposed Harbour Clean-up. This document outlines the several treatment options considered in arriving at the preferred alternative. An evaluation of these options was based on several different criteria including: cost, effectiveness, land requirements and acquisition problems, complexity (construction and operation), impacts on local communities and the potential to phase the projects (for a detailed description of this evaluation refer to the CEMP document itself). Recent Studies The City completed in 2002 an Archeological Study of the proposed Southside treatment plant site. The archeological assessment provides further information on the archeological issues on the site and recommends mitigation measures that will be dealt with during detailed design. Also in 2002 and early 2003 a Harbour Water Quality Assessment was carried using a threedimensional model. The modeling compared existing harbour conditions with the impacts of the proposed phase 2 improvements. The modeling predicted considerable improvements in harbour water quality. ES-2-4

8 PHASE 2 PROJECT DESCRIPTION 3 Phase 2 Project Description 3.1 Design Population, Wastewater Flows and Strength The wastewater flow contributions used are based on the population growth projections shown in Table 1 following. The ultimate population of 157,100 will be the basis for design of the Phase 2 components. Table 1 Population Growth for St. John's, Sewer Service Area - Current and Future Projections Service Area Population Ultimate St. John's (Total Sewerage System) 127, , ,100 1 From Newfoundland Design Associated Limited and CH2M Gore & Storrie Limited (1996) Wastewater flows Wastewater in the service area is generated from residential, commercial and light industrial areas and base infiltration flows collected in the service area. Wastewater quantity projections are calculated based on per capita flow rates and upon past and recent flow measurement studies and assume that the rates of generation will be similar in the future. The design flow distribution diagram for the sewerage collection system is shown in Figure 3. The design flows are summarized in Table 2 following. Table 2 Design Flows for Phase 1 & 2 Pumping and Treatment Facilities Flow Condition Sewerage System Phase 1 Pumping Phase 2 Pumping Primary Treatment Plant Phase 1 & 2 Pumping & Outfall Average Dry Day (L/s) ,560 1,560 Average Dry Day (m 3 /day) 134,800 50,700 84, , ,800 Peak Design (L/s) 4,737 2,304 2,433 3,900 4,737 Peak Design (m 3 /day) 409, , , , ,300 The treatment plant will be sized for a peak flow of 2.5 times the average dry weather flow (3,900 L/s). However the plant will have a hydraulic capacity for approximately 3 times dry weather flow (4,737 L/s), which is the capacity of the two plant pumping stations. When the flow exceeds 4,737 L/s, untreated wastewater in excess of this will begin to discharge to the Harbour at the existing sewer overflows. The capacity of the collection system is estimated at 6,385 L/s and overflows will occur at the existing Temperance and Prescott Street outfalls. These overflows will operate during major storm events and are anticipated to discharge approximately two percent of the time. Screens will be provided to reduce the ES-3-5

9 Waterford Valley Sewer DESIGN DESIGN DESIGN DESIGN Avg Dry Day 420 Avg Dry Day 228 Avg Dry Day 745 Avg Dry Day 745 Peak Dry Day 998 Peak Dry Day Peak Dry Day 1636 Peak Dry Day 1636 Peak Inst Peak Inst Design Peak 1864 Peak Inst Temperance St. Overflow WVS WVRS H.I.S Harbour Interceptor Sewer Prescott St. Overflow DESIGN DESIGN Avg Dry Day 193 Avg Dry Day 1560 Design Peak 963 WVRS (Jobs Bridge) DESIGN Design Peak 4737 Overflow Peak mm Diameter 1350mm Harbour Diffused Outfall-1800mm diameter DESIGN DESIGN DESIGN Avg Dry Day 395 Avg Dry Day 587 Avg Dry Day 587 Peak Inst Design Peak 2304 Phase 1 PS Design Peak 2304 Phase 2 PS DESIGN PTP DESIGN Avg Dry Day 973 Avg Dry Day 1560 Design Peak 2433 Design Peak 3900 Entire St John's Sewershed Pumpting Station Total Capacity PTP Capacity Harbour Outfall Capacity DESIGN DESIGN DESIGN DESIGN Avg Dry Day 1560 Avg Dry Day 1560 Avg Dry Day 1560 Avg Dry Day 1560 Peak Dry Day 3120 Peak Dry Day Peak Dry Day Peak Dry Day Peak Inst Design Peak 4737 Design Peak 3900 Design Peak 4737 Notes/Legend: 1. Flow distribution based on - "Comprehensive Environmental Management Plan", March 1997 of the St. John's Harbour Sewershed for Atlantic Coastal Action Program Inc. - Additional in-system flow monitoring in year existing sewer Phase 1 Sewer and Facilities Phase 2 Sewer and Facilities 3. All flows in units of Liters/second Figure 3 Sewage Flow Distribution Diagram St. John's

10 PHASE 2 PROJECT DESCRIPTION visual pollution at these two overflows. A flow diagram for the sewerage collection system is shown in Figure 3. Wastewater Concentrations The design of a wastewater treatment plant typically requires the knowledge of the following raw wastewater parameters: Total suspended solids (TSS) Total biological oxygen demand (BOD-T) Total kjeldahl nitrogen (TKN) Total phosphorus (TP) The wastewater flow to the proposed St. John s PTP is primarily from domestic sources, but it also includes wastewater from commercial and light industrial sources within the entire St John s sewer-shed. During wet weather events, the wastewater contains a certain amount of storm water from the combined sewer system. The present and ultimate design concentrations are shown in Table 3 below. Table 3 Summary of Design Wastewater Concentrations and Loadings Ultimate Design a Population 157,100 Flows Average Dry Day (m 3 /day) 134,800 Average Dry Day (L/s) 1,560 Peak Design (m 3 /day) 337,000 Peak Design (L/s) 3,900 Concentrations & Loadings BOD TSS TP mg/l 106 kg/d 14,310 mg/l 119 kg/d 16,065 mg/l 5.4 kg/d 729 Note: a: Newfoundland Design Associates Limited and CH2M HILL (1996) and St. John s Harbour ACAP Comprehensive Environmental Management Plan (1997) adjusted from in-sewer flow monitoring conducted by NDAL When compared to a typical municipal sewage, the above wastewater concentrations are lower than normal domestic wastewater. They reflect the combined and separate sewer systems and the influence of infiltration and inflow into the sewer system during both dry and wet weather events. Flow variations, while significant, are typical of this type of sewer systems. ES-3-6

11 PHASE 2 PROJECT DESCRIPTION Summary of Design Peaking Factors The design of the unit processes will be based on peaking factors shown in Table 4 below. Table 4 Flow Peaking Factors for the St. John s PTP Peaking Factor Factor Design Use for Sizing Peak Design Flow 2.5 Screens/grit removal Primary clarifier SOR Disinfection HRT Peak Month 1.2 Digestion and solids handling system sizing SOR = Surface overflow rate HRT = Hydraulic retention time 3.2 Biosolids Treatment Alternate solids handling and disposal systems were evaluated. These systems were: Agricultural application Reforestation application Composting Incineration Landfill In the St John s area there are insufficient agricultural and reforestation areas available for a sustainable biosolids application program. The more advanced solids handling processes such as incineration or composting are significantly more expensive to own and operate in terms of life cycle costs and are not recommended. Also, in the case of composting, there does not appear to be a local market because of the availability of high quality local material such as natural peat. Based on the review of biosolids disposal options it is proposed that the biosolids removed in the process be anaerobically digested to stabilize them and dewatered to 25% solids concentration prior to landfill. 3.3 Sewerage System Phase 2 includes the construction of the Harbour Interceptor sewer from Temperance Street to the phase 2 pumping Station at Southside Road. Refer to Figure 2 for the routing of Harbour Interceptor Sewer. The interceptor sewer will run from Temperance Street west along Water Street to Prescott Street, south to Harbour Drive and then west to Water Street at the west end of the Harbour. It will be connected to an existing section of the interceptor between Water street and Southside Road, that was installed as part of Phase1. A short Section of the Interceptor will also be constructed on Southside Road to complete the connection to the Phase 2 pumping Station at the Treatment Plant site. ES-3-7

12 PHASE 2 PROJECT DESCRIPTION 3.4 Wastewater Treatment Plant Proposed Wastewater Treatment Processes The Wastewater Treatment Plant is to be located at Southside Road. Refer to Figure 2. The following table summarizes the major processes and systems selected for the St John Phase 2 program. Process Process Selected and Details Screening Screenings washing/compacting/grinding Conveyance by shaftless screw conveyors to storage Raw Sewage Pumping Stations Shallow pumping station (existing) with 3 submersible pumps Deep pumping station with 3 submersible pumps Standby generator Grit Removal Aerated grit tanks Grit collection by submerged grit augers Grit pumping by recessed impeller centrifugal pumps Grit dewatering by screw classifiers Conveyance by shaftless screw conveyors to storage Primary Clarification Rectangular clarifiers with chain and flight mechanisms Scum collection by manual u-troughs and holding in heated scum tank, scum pumping by centrifugal pumps Raw sludge pumping by progressive cavity pumps Disinfection Chlorination/dechlorination Concrete chlorine contact tank Sludge Stabilization Mesophilic anaerobic digestion Sludge dewatering Mechanical dewatering Digester mixing by hydraulic system with chopper-type centrifugal pumps and discharge through specialized nozzles Digester gas utilization in firetube boilers, excess gas flared Sludge heating by concentric tube, counter-flow heat exchangers Sludge transfer to biosolids storage by chopper-type centrifugal pumps Polymer addition using chemical feeders Biosolids conveying using enclosed screw conveyors Sludge loading system using 20 m 3 containers Haulage and disposal to St John s municipal landfill A process block flow diagram of the proposed treatment plant is shown in Figure 4. ES-3-8

13 Pumping Screening Landfill Grit Removal Primary Treatment Sludge Digestion Dewatering Disinfection Treated Effluent to Diffuser Landfill Figure 4 Process Flow Diagram (PFD) St. John's Primary Treatment Plant

14 PHASE 2 PROJECT DESCRIPTION Outfall After disinfection, the treated effluent will be discharged into the Harbour through the existing plant diffused outfall, The diffusers will be modified to upgrade the capacity from present flows to the peak wet weather flow capacity of 4,737 L/s. ES-3-9

15 4 Project Schedule and Construction Packages The project schedule is based on having Phase 2 commissioned in The project has a number of distinctive components, some of which involve specialized contractors. Key milestones are as follows: Approvals to proceed Start site excavation - November 2003 Start Harbour Interceptor Sewer Start Phase 2 Pumping Station Start Primary treatment Plant Commissioning Primary Treatment Plant ES-4-10W TOR

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