Executive Summary. Purpose and Need for Project. Background Work

Transcription

1 Executive Summary Purpose and Need for Project The City of St. John s, and 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 projected ultimate population for the area is 157,100 people. Municipal wastewater from these communities is currently being discharged untreated into St. John s Harbour. The Harbour is contaminated with this raw sewage, which is having detrimental effects on all aspects of the Harbour (social, environmental and economic). The purpose of the proposed project is to provide Phase 2 of a multi-phase Harbour Clean-Up Project. Background Work Numerous studies have been conducted addressing the clean-up of St. John s Harbour dating back to The St. John s Atlantic Coastal Action Plan Program (St. John s ACAP) was initiated in 1993 under an Environment Canada sponsored Green Plan program. As part of St. John s ACAP program, a study was conducted in 1995 to evaluate sewage treatment options and to develop a phased strategy approach for sewage treatment. The result of the work by the ACAP committee is the Comprehensive Environmental Management Plan (CEMP) for St John s Harbour completed March of The CEMP is the core document that established the plan for the St. John's Harbour Clean-up Project. The CEMP report evaluated three alternatives including upstream treatment, end-of-pipe treatment, and centralized treatment. These alternatives were evaluated based on cost, effectiveness, land requirements and acquisition problems, construction and operation complexity, impacts on local communities, and potential to phase the projects. The CEMP report recommended one centralized treatment facility within the Harbour at Southside Road or at Gunner s Cove outside the Harbour. Subsequently the Southside Road site was confirmed as the preferred site for the proposed new treatment facility. The CEMP also recommended a multi-phased approach to implementing the Harbour Clean-Up Project to ultimately provide secondary treatment of wastewater before discharging to the Harbour or directly to the ocean. Phase 1 of this project is completed and provides immediate relief to the western end of the Harbour, which received discharges from the Waterford Valley drainage basin, as well as raw sanitary sewage from local combined sewer areas. Phase 1 focused on collecting, redirecting and screening these sewage flows, and included a diffused outfall located on the south side of the Harbour. ES-1

2 Financial Setting Funding of $93 million has been established for the capital costs of Phase 2 of the multiphase St. John s Clean-Up Project. The federal and provincial governments are each contributing $31 million, while the remaining $31 million is being provided in a proportionate share by the City of St. John s, the City of Mount Pearl, and the Town of Paradise. The CEMP recognized that there are financial constraints in implementing the St. John s Clean-Up Project and therefore recommended the phased approach to meeting regulatory requirements and water quality objectives. The $93 million budget limitation for Phase 2 will provide a step toward meeting the ultimate requirements and objectives while providing for immediate improvements to the Harbour. Ongoing operating costs, in addition to their share of the capital costs, will be borne by the municipalities. Therefore, life-cycle costing is a key factor in the evaluation and selection of alternatives. Overall Plan The goal of the multi-phased St. John's Harbour Clean-Up Project is to ultimately provide secondary treatment of wastewater before discharging to the Harbour. The City of St. John's is in the process of implementing this phased approach to providing infrastructure to intercept and convey sewage to the Southside Road site, and providing treatment before discharging to the Harbour. The current project is Phase 2, which includes a conventional primary treatment facility. As part of the program the City is committed to several complementary initiatives to reduce flow and pollutant loadings to the treatment facilities. In addition, the overall project plan includes ongoing monitoring of the wastewater characteristics, the performance of treatment facilities and complementary initiatives, and the water quality of the Harbour. The phased approach allows for ongoing monitoring which will provide up-to-date information for better decision making for subsequent phases, to match the funding available, and for time to allow source control and flow reduction initiatives (i.e. Best Management Practices) to take effect. As a result there is opportunity to utilize the most suitable treatment alternatives available at the time of each phase. The City of St. John's is committed to implementing at least enhanced primary treatment, five years after commissioning the phase 2 works. Phase 2 Location and Scope The current project involves Phase 2 of the recommended multi-phase Harbour Clean-Up Program. The Phase 2 project generally includes the construction of the new primary treatment plant and expansion of the existing pumping station, construction of the Harbour Interceptor sewer from Temperance Street to the Southside Road treatment plant site, and additions to the existing diffused outfall. Figure 5-1 shows the Phase 1 work that has been completed and proposed Phase 2 components of the project. ES-2

3 New Primary Treatment Plant The major components of the new primary treatment plant will include the following: Expansion of the existing Main Pumping Station including screening; Grit removal; Primary treatment; Effluent disinfection; Sludge stabilization followed by dewatering; and Administration and service buildings. The new primary treatment plant (PTP) will be located on the south side of Southside Road, at the west end of the Harbour. Residential houses are located to the west of the site, and the Department of Fisheries and Oceans buildings are to the east. The site is backed to the south by a rock face, and substantial rock excavation will be required. It is proposed that two rock excavation and removal contracts will be issued to prepare the site before proceeding with the issuing construction contract(s) for the pumping station and treatment plant. Rock will first be excavated from the west part of the site where the digesters are to be located, and then the east part of the site for the primary clarifiers. Along with rock excavation, a warehouse currently being utilized by the federal government until later in 2003 will be removed for site preparation. Along with construction of the new PTP, the project will include expansion of the existing Southside Road Main Sewage Pumping Station that is currently located at the PTP site. Harbour Interceptor Sewer (HIS) The interceptor sewer will run from Temperance Street west along Water Street to Prescott Street, south to Harbour Drive, west on Harbour Drive to the intersection of Water and Waldegrave Streets and then west along Water Street to Jobs Bridge Crossing. The HIS will be constructed within existing road right-of-way using open cut excavation techniques. Numerous commercial establishments are along the routing. As well, the HIS will be located adjacent to the Harbour along Harbour Drive. Outfall The outfall will be expanded into the Harbour to increase its hydraulic capacity. It is anticipated that the expansion will be constructed by trench excavation with material excavated, side cast, and then reused to backfill the trench after the pipe is installed. Alternative Methods of Carrying Out Phase 2 Project Components A number of primary treatment alternatives were evaluated including variations of chemically enhanced primary treatment (CEPT) and conventional primary treatment. Conventional primary treatment is selected as the preferred alternative because; Harbour water quality improvements will be significant; the additional improvement in effluent quality from CEPT are not significant considering the high operating cost; conventional ES-3

4 primary treatment provides the lowest life-cycle cost; it is simplest to operate and maintain. The conventional primary treatment will be designed to be readily upgraded to enhanced primary treatment or secondary treatment in subsequent phases as required. Disinfection alternatives were also evaluated. The detailed review compared chlorination and UV disinfection. Chlorine disinfection followed by dechlorination was recommended as the preferred alternative. Due to the financial restraints for this project, UV with its significantly higher cost is not considered to be practical. Chlorination followed by dechlorination is an accepted method of disinfection by regulatory authorities. The potential negative effects of chlorination will be mitigated by dechlorination. The management of biosolids is an important part of the wastewater treatment process. Alternate solids handling and disposal systems were evaluated for this phase of the project. The Biosolids Management Report is provided in the appendix. 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 then dewatered to 25% solids concentration prior to landfill. Considering the volume of biosolids compared to the amount of municipal waste at the City's Robin Hood Bay landfill impact of the disposal of biosolids at the landfill is minimal. It is noted that if some beneficial uses become available, the proposed biosolids management approach will still be appropriate. A state of the art three-dimensional hydrodynamic model was set up and applied to St. John s Harbour. Existing data for physical conditions and water quality were used to calibrate the model. The existing condition was modeled and the results indicate that there are areas in the Harbour with degraded water quality as a result of discharges of untreated sewage and stormwater into the Harbour. The model was then run with disinfected effluent from the proposed conventional primary treatment facility discharged at the existing outfall diffuser location. A significant improvement in the harbour water quality will be achieved in terms of bacteria and solids. The model was also run with expected CEPT effluent. The model results show little improvement to the overall harbour water quality considering the high chemical costs and sludge handling requirements. Related Projects - Complementary Initiatives Elimination of pollutants at their source, water conservation, infiltration and inflow reduction are necessary complements to treatment facilities in the wastewater management. These source control and the City of St. John s to complement the Phase 2 works is implementing water reduction initiatives. Regulatory Requirements This Environmental Impact Statement report has been completed in accordance with the requirements of the Canadian Environmental Assessment Act. The report provides a description of the project, alternatives for carrying out the project, environmental impacts of the project and proposed mitigation measures and monitoring techniques. Consultation with government agencies and the public is also part of the environmental screening process. ES-4

5 This project is subject to numerous federal, provincial, and municipal laws, regulations and guidelines. For example, approvals and/or permits may be required by the following agencies: Infrastructure Canada to receive approval under CEAA; Department of Fisheries and Oceans to receive approval under the Fisheries Act; Department of National Defense; Port Authority; Canadian Coast Guard to receive approval under the Navigable Waters Protection Act; Provincial Authorities, such as the Department of Environment. Description of the Proposed Phase 2 Project Design Criteria Based on planning information the population projections for St. John's indicate a population of 147,100 people by The projected ultimate population based on build out of the service area is 157,100. This ultimate population will be used for the Phase 2 project 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 based on per capita flow rates and on past and recent flow measurement studies and assume that the rates of generation will be similar in the future. The design average daily flow, which includes wet weather flows, is 134,800 m 3 /day. The treatment process components of the plant will be sized for a peak flow of 2.5 times the total average flow or 337,000 m 3 /day. However the plant will have a hydraulic capacity for approximately 3 times the average flow of 409,300 m 3 /day, which is to be the design capacity of the two plant pumping stations. When the flow exceeds 409,300 m 3 /day, wastewater in excess of this will begin to overflow and discharge to the Harbour at the existing Temperance and Prescott Street/Beck s Cove outfalls. Screening options will be considered during predesign for these two overflows to direct screenings to the treatment plant. These overflows will operate only during major storm events. Initially it is anticipated that these overflows may occur only about two percent of the time. The frequency will decrease as flow reduction programs take effect. A flow diagram for the sewerage collection system is shown in Figure 5-2. Sewerage System Phase 2 includes the construction of the Harbour Interceptor Sewer (HIS) from Temperance Street to the Pumping Station at Southside Road. The interceptor sewer will run from Temperance Street west along Water Street to Prescott Street, south to Harbour Drive, west on Harbour Drive to the intersection of Water and Waldegrave Streets, and then west along Water Street to Jobs Bridge Crossing. It will be connected to an existing section of the interceptor between Water Street and Southside Road, which was installed as part of Phase ES-5

6 1. A short section of the interceptor sewer will also be constructed on Southside Road to complete the connection to the Phase 2 pumping station at the treatment plant site. Wastewater Treatment Components The pumping station and wastewater treatment plant site are located at Southside Road. The Table ES-1 summarizes the major processes and systems selected for the Phase 2 program. Table ES-1: Major Processes and Systems Process/Facility Process Selected and Details Screening Screening equipment including washing/compacting/grinding Screenings conveyance by screw conveyors to storage bin Raw Sewage Pumping Stations Shallow pumping station (existing) with 3 submersible pumps Deep pumping station with 3 submersible pumps Standby generator Grit Removal Four aerated grit tanks Grit collection by submerged grit augers Grit pumping by recessed impeller centrifugal pumps Grit dewatering by screw classifiers Conveyance by screw conveyors to storage Primary Clarification Four rectangular clarifiers with chain and flight mechanisms Scum collection by manual u-troughs and holding in scum tank, scum pumping by centrifugal pumps Raw sludge pumping by positive displacement pumps Disinfection Chlorination/dechlorination facility for chemical storage and feed equipment Concrete chlorine contact tank Sludge Stabilization Two mesophilic anaerobic digesters 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 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 ES-6

7 Process/Facility Process Selected and Details Service Buildings Workshop Boiler facility Administration and laboratory facility Staff facilities for approximately 14 people Outfall After disinfection, the treated effluent will be discharged into the Harbour through the existing plant diffused outfall. Additional diffusers will be provided to upgrade the capacity of existing outfall from present flows to the design peak wet weather flow capacity of 409,300 m 3 /day. It is proposed to lengthen the diffuser section as needed for the expected 18 additional diffusers. The diffuser section will be designed to provide a 20:1 dilution. Project Cost The estimated project capital costs are summarized as follows: Harbour Interceptor Sewer and Overflow facilities: $22,500,000 Primary Treatment Plant: $70,200,000 Outfall Modifications $1,000,000 Total Project Costs: $93,700,000 Phase 2 Project Scheduling The Phase 2 project schedule is based on having Phase 2 commissioned in Key milestones are as follows: Start first excavation contract Start Harbour Interceptor Sewer Start Phase 2 Pumping Station - Spring 2004 Start remaining excavation - Spring 2004 Start Primary Treatment Plant - Fall 2004 Commissioning Primary Treatment 2007 Public Comments Public consultation has been an important part of this project. The ACAP program provided opportunity for public and agency stakeholder input. A draft environmental scoping ES-7

8 document was prepared for this project and made available for public comment. Comments were received and addressed in this report. Mitigation Measures This Environmental Impact Statement report outlines the potential impacts of the proposed project and provides mitigation measures required to limit these impacts. The primary impact of the Phase 2 project is that it will greatly improve the water quality and the visual appearance of the Harbour. There will be some short-term impacts from construction; which will be mitigated during construction. On-going operation of the treatment plant will also have potential impacts (e.g. noise, odour, and truck traffic) on the area surrounding plant. Design features and operation procedures have been identified to mitigate these. Mitigation techniques will be implemented during and following construction to limit any impacts to the environment from this project. Monitoring for compliance with the mitigation plan will also be carried out during and after construction. The monitoring will help in continuing to control impacts to the environment, and will also serve to define future treatment requirements. An overview of the components of the environment affected, the mitigation techniques proposed, and the follow-up monitoring measures are provided in Table ES-2. Table ES-2 Summary of Mitigation, Monitoring and Follow-up Requirements Environmental Component Mitigation Monitoring and Follow-up Natural Environment Harbour Water Quality - The PTP will reduce contaminant loading to the Harbour - Harbour water quality will be re-assessed using modeling techniques after the plant has been in operation for at least 5 years - Information gained through the modeling exercise will be used to help define future treatment needs Effluent Quality - Effluent will meet PTP quality and quantity objectives as defined by the Provincial Department of the Environment in their Certificate of Approval for the PTP - Effluent quality will be monitored with parameters such as BOD, TSS, DO, TP, Ammonia, Fecal Coliform, temperature, ph, chlorine residual - Effluent flow and loading data may be used in the future to model impacts on Harbour water quality, which will help define future treatment needs Fish health Construction Post-Construction ES-8

9 Environmental Component Mitigation Monitoring and Follow-up Avoidance of fishing seasons for any marine construction. Compliance with DFO Guidelines Operation - The implementation of dechlorination is proposed as a mitigation measure to effectively eliminate free chlorine residual and chloramines, therefore alleviating concerns regarding the associated toxicity to fish. Chlorine residual will be monitored as a measure of toxicity. Regulatory agencies will continue to be consulted with respect to any other compliance monitoring Harbour Marine Sediment - Sediment discharges to the Harbour will be reduced - Quantity and quality of Harbour sediments and benthics will be sampled and assessed before and after implementation (i.e. after at least 5-years of PTP operation) Terrestrial Habitats vegetation, birds, mammals - Mitigation measures as described in Section 6 - This information will also help to define future treatment requirements Post-Construction None anticipated Watercourses and groundwater - Mitigation measures as described in Section 6 Post-Construction None anticipated Socio-Economic Environment Air Quality - The PTP will be designed such that air emissions from various processes will be controlled so they are below emission guideline levels. Post-Construction - Air emissions will be measured on a regular basis as per Certificate of Approval requirements Odour Construction None required Operation Raw sewage wet wells will be mechanically ventilated to dispersion stack Plant headworks will be enclosed and ducted to a stack Grit handling facilities will be equipped with a grit washing system to remove organic Post-construction - The public will be provided with a contact name and telephone number (e.g. Manager of Sewage Treatment Plant) - City will document and monitor complaints and modify procedures as needed ES-9

10 Environmental Component Mitigation Monitoring and Follow-up material from the grit and return it to the process stream. The tanks will be covered and the off gases ducted to stack Plant design will make adequate provision for the draining, cleaning and flushing of channels, scum pits, holding tanks, screens, grit conveyors, and other unit processes. Southside Road Sewage Pumping Stations will be capable of drawing the interceptor sewers down if needed to promote higher cleansing velocities. Hose bibs for pressurized process water will be located throughout the plant to allow for tank and equipment cleaning. Solids handling area will be provided with exhaust hoods over the dewatering equipment to contain and exhaust odours. Freeboard on tanks will be kept to over 500mm and tanks will be screened. Process tankage will be designed so that they can be covered if odours are found to be a problem. Noise Truck Traffic Construction Hours of work for construction will be specified Blasting at specific periods of the day will be specified Appropriate pre-blasting warnings alarm procedures will be implemented Operation Noise attenuation devices (barriers) will be placed around pumps, compressors, and other stationary sources of loud noise Construction All vehicles and construction equipment equipped with muffling devices Trucks will use designated haulage routes The City s noise by-law will be enforced Hours of work for construction Post-construction - The public will be provided with a contact name and telephone number (e.g. Manager of Sewage Treatment Plant) - City will document and monitor complaints and modify procedures as needed Post Construction - The public will be provided with a contact name and telephone number (e.g. Traffic Division) - City will monitor complaints and modify procedures as needed ES-10

11 Environmental Component Mitigation Monitoring and Follow-up Sludge Management and blasting will be specified Construction contracts for the H.I.S. will be sized and phased to minimize the impact on vehicular and pedestrian movement Construction activity will be scheduled to accommodate shipping activity Dust control measures will be implemented Regular cleaning of public roadways Watering of all stock-piled soil Placement of gravel at all heavily used areas Fuel Spills: In refueling construction equipment, spills could occur Proposed mitigation measures include: The preparation of a contingency plan Only designated areas will be allowed for refueling construction equipment. Operation Vehicles will be used during normal working hours Trucks will be required to use designated haulage routes Vehicles will be equipped with effective muffling devices Emissions and odours from sludge processes at the PTP will be controlled. Post Construction - Emissions will be monitored as required Increased truck traffic associated with landfill disposal of the biosolids from the new plant will be mitigated as described in Section Sludge will meet requirements with respect to treatment such that pathogens will be reduced. Disposal of sludge will meet all landfill disposal regulations. - Complaints regarding truck traffic will be recorded and addressed where necessary - Sludge quality will be monitored on a regular basis as required in the Certificate Approval Human Health Recreation and Tourism This project will greatly improve the water quality in the Harbour, which will have a positive impact on human health. The appearance of the Harbour will be improved which will have a positive impact for recreation and tourism in the Harbour. ES-11

12 Environmental Component Mitigation Monitoring and Follow-up Heritage Resources Construction - Contingency plans will be implemented should any resources be discovered during construction - Archaeological assessments will be completed before commencing construction of the HIS. Post-Construction None required Marine Transportation Construction Approval from the Canadian Coast Guard under the Navigable Waters Act must be received prior to construction and operation Meetings with the Harbour Master and Coast Guard will take place. Both agencies will be given advance notice of the construction period. All construction equipment and material, temporary structures and parts thereof will be removed from the navigable waters. Operation The diffuser area will be appropriately marked on the marine charts and noted in the Aids to Navigation bulletins. Post-Construction Monitoring of effectiveness by Canadian Coast Guard Malfunctions Malfunctions Accidents Accidents Standby generator and redundancy (i.e. extra capacity) will be build into the processes at the plant to reduce and control potential impacts of malfunctions. - Facilities and processes will be designed and operated to appropriate standards. - All health and safety requirements will be adhered to. Malfunctions will be reported and contingency procedures implemented - Accident reports will be filed and follow-up procedures implemented ES-12