Carlow County Council

Transcription

1 Carlow County Council WASTEWATER DISCHARGE LICENCE APPLICATION FOR THE AGGLOMERATIO OF CARLOW TOWN AND ENVIRONS AND SECTIONS OF GRAIGUECULLEN IN COUNTY LAOIS WASTEWATER DISCHARGE LICENCE APPLICATION NON-TECHNICIAL SUMMARY Rev A May 2008

2 Introduction The purpose of a Waste Water Discharge licence is to make provision for the protection of the environment and the protection of human, animal and plant life from harm or nuisance caused by the discharge of Dangerous Substances to the aquatic environment as well as to ensure compliance with National Law. Waste Water Discharge Licensing encourages the use of advanced waste water treatment technologies, the regularisation of waste water discharges from primary and secondary discharge points and storm water overflows, improved efficiency and effectiveness of pollution control, and allows for a more streamlined regulatory system that is open and transparent. The licensing process is a quasi-judicial process, the detail of which is set out in the Waste Water Discharge (Authorisation) Regulations, The Regulations detail in the Second and Third Schedules the deadlines for the various sizes of wastewater treatment plants and the associated fees for the applications. This application refers to the Carlow Town Waste Water Works which serves an agglomeration including Carlow Town and Environs and an area under the administrative control of Laois County Council on the west side of the River Barrow at Graiguecullen. The Mortarstown WWTP in Carlow Town is the primary discharge point and discharges to the River Barrow just south of Carlow Town. There are also six Storm Overflows within the Waste Water Works discharging into the River Barrow and three Storm Overflows discharging into the River Burrin. The Carlow Surface Water Drainage Scheme will involve upgrades to these existing CSOs and will result in ten new outfall into the River Barrow and one new outfall into the River Burrin. The sewage flow generated in the agglomeration drains in a mainly southern direction towards the Mortarstown WWTP which is located on the southern side of Carlow Town via a series of pump stations culminating in the main pump station on the Kilkenny Road. From here it is pumped via a 600mm rising main to the WWTP. A smaller local pump station with a loading of 150 P.E. also discharges to the WWTP. The Mortarstown WWTP also receives leachate from the Powerstown Landfill. The current design capacity for the waste water plant is 36,000pe.The current loading is 33,500 pe. OVERVIEW The Dangerous Substances Directive (76/464/EEC) Council Directive of 4 May 1976 on pollution caused by certain dangerous substances discharged into the aquatic environment of the Community- has the objective of reducing pollution caused or induced by certain defined dangerous substances discharged into the aquatic environment. The Dangerous Substances Directive (DSD) requires Member States to take: appropriate steps to eliminate pollution (of the aquatic environment) by the dangerous substances in the families and groups of substances in List I of the

3 Annex and to reduce pollution of the said waters by the dangerous substances in the families and groups of substances in List II of the Annex to the DSD. Among the requirements of the DSD are provisions for reducing pollution from List II substances. Member States are required to establish programmes for implementation within defined deadlines. These programmes must contain provisions for: Prior authorisation of discharges to waters, and Emission Limit Values for discharges based on quality objectives for water in accordance with existing Directives. A Waste Water Discharge licence shall supersede licences/permits issued under the following legislation: Foreshore Act, Planning and Development Act, The waste water discharge licence regulates all discharges of waste water from a waste water works. It is important to note that the licence does not regulate the following: Waste water treatment plants Odours from waste water treatment plants Sludge disposal from waste water treatment plants Noise from waste water treatment plants Discharges are classed in three distinct types: Primary Discharge Point refers to the largest volumetric flow from the works. Secondary Discharge Point refers to discharges other than the primary discharge or storm water overflows Storm Water Overflows are overflows designed for the purpose of relieving stresses in the collection network usually caused by excessive flows that result from heavy rainfall in the catchment. Mortarstown Waste Water Treatment Plant

4 Mortarstown WWTP treats all effluent generated within the Carlow Town Agglomeration. The WWTP was commissioned in 1986 with a design capacity to treat 28,500 pe. The plant is of a conventional extended aeration design with a discharge to the River Barrow downstream of Carlow Town. The plant consisted of the following: Inlet works with a coarse screen and detritor Measurement flume Aeration Tanks Secondary Settlement Tanks RAS Pump Stormwater Tank Sludge Building with Belt Press Due to significant economic growth and population increase within Carlow Town and Environs and with the requirement for improved discharge standards to the River Barrow, in line with the Phosphorus Directive, The Urban Waste Water Treatment Directive and Carlow Co Co Water Quality Management Plan, in 1999 Nicholas O Dwyer Ltd were commissioned to prepare preliminary and detailed design documents for the upgrading and refurbishment of the Mortarstown WWTP, including : (1.) Improvement in overall plant performance (2.) Maximization of the plant treatment capacity using the existing tankage infrastructure The upgraded plant is designed to cater for a population equivalent of 36,000 meeting an effluent standard of BOD 15mg/l, suspended solids 25mg/l, total phosphorus 1 mg/l, ammonia 5mg/l and nitrate NO3-N 10mg/l. As the waste water plant was also a significant phosphorus point source in the River Barrow Catchment, the upgrade works were also designed to reduce phosphorus and nitrogen levels being discharged to the river. The resultant recommendations proposed the following works be carried out; Inlet Works: Provision of fine screening Grit Classifer Ultrasonic Flume

5 Activated Sludge Process: Create aerobic, anoxic and anaerobic zones in aeration tanks Replace surface aerators with a fine bubble diffused air system Installation of submersible mixers in the anoxic and anaerobic zones Provision of chemical dosing facilities to remove phosphorus New Air Blower Building Variable Speed Drives on Return Sludge Internal pumped mixed liquor recycle Flow Divider 1: Alterations to inflow arrangements to ensure that the returning mixed liquor is equally divided among the four effluent streams from the divider. The sewage flow into the plant is now made up of the following: The main town flows which are pumped unto the plant from the Kilkenny Road Pump Station The flow from a recently installed local pump station Controlled flow from the recently installed leachate storage tank. This would primarily deal with leachate from the Landfill at Powerstown. Facility for receiving Sludge and septic tank effluent from other plants and domestic sources Main Liquid Stream I n the recently upgraded works the sewage passes through a Screening System (consisting of a mechanical 6 mm screen and washpactor unit and a bypass through a 25mm screen) and then on through a grit trap and grit classifier The effluent then passes through the plant in the following sequence: 1. Measurement flume to 2. Flow dividing chamber to 3.Four aeration basins to 4.Two clarifiers From clarifiers treated effluent gravitates through an outfall pipeline to the River Barrow Sludge Treatment

6 The sludge waste and return activated sludge are taken by gravity from the clarifiers to the Sludge Pumping Station. The sludge waste is pumped to two Sludge Holding Tanks where it is thickened from 0.8% to 3% solids content and thence to the sludge dewatering building where two belt presses dewater the sludge to a dry solids content of 15% dry. The final sludge is then stabilised using lime and spread to land. The supernatant then goes to the Stormwater Recycling Station from where it is pumped to discharge into the inlet works downstream of the screening system. The Return Activated Sludge is pumped from the Sludge Pumping Station to discharge into the Flow Dividing Chamber. Stormwater When the flow into the Kilkenny Road Pump Station reaches a designated level the storm pumps pump the stormwater via a 400mmdia pipe to the wastewater treatment plant. Here it receives a primary treatment and is subsequently pumped back into the inlet works to be treated in the works. The proposed works were completed in The Carlow Surface Water Drainage Scheme There are 9 existing storm overflows/outfalls into the River Barrow and the River Burrin. The Carlow Surface Water Drainage Scheme proposes to upgrade these outfalls in line with the Urban Waste Water Treatment Directive, particularly in line with Formula A. Following the Carlow Surface Water Drainage Scheme there will be 11 CSOs, 2 No into the River Burrin at 1) Ballinacarrig Bridge on the N80 and at Hanover Bridge. The following Storm Overflows will discharge to the Barrow: Location 1 Year Return Flows (l/sec) Q in Q spill Q cont Ballinacarrig Bridge Oak Park Montgomery St Haymarket Hanover Bridge Carlow Weir Sleaty St Chapel St Bridge St Walls Forge Maryborough

7 Kilkenny Road Pembroke 1, Total 5,273 3,451 The upgrading of the Storm Overflows will improve the quality of the receiving waters through the following: Reduction in surface flooding Elimination of a number of unsatisfactory storm water overflows (e.g. Skinners Lane) which can cause sewage discharge to the Barrow in dry weather conditions Elimination of possibility of objectionable material being discharged to the Barrow or Burrin river from poorly designed existing storm water overflows by reconstructing them in accordance with the latest guidelines and recommendations Elimination of the bulk of infiltration water presently being pumped to the Mortarstown Treatment Works, thereby improving plant efficiency and final effluent quality Operation of the Works The Mortarstown Waste Water Treatment Plant is operated by the following staff: 1 No Plant Supervisor 1 No Caretaker 1 No General Operative The plant is manned between the hours of and Monday to Friday with the plant being also manned between the hours of and on Saturday and between the hours of and on Sunday. Call out systems are in place whereby staff are notified of malfunctions in the plant operation and are in a position to get to the plant and address the problems immediately. A contract is in place with a service provider to carry out maintenance to the plant on a regular basis. The contract is awarded through a tendering process. The contract includes rates for rapid response to emergency situations and call out rates for breakdowns. Sludge is drawn away from the plant on a daily basis to landspread. The above staff also maintain and manage the pump stations and storm overflows throughout the agglomeration.

8 The staff are supervised and managed by the Carlow Town Engineer and his management team consisting of a Town Foreman and an Executive Engineer. The post of Town Engineer is that of Senior Engineer. Environmental Impacts of Emissions from Waste Water Works.. All effluent from the Mortarstown WWTP discharges to the River Barrow through a single discharge point to the south of Carlow Town in the townsland of Mortarstown. The treatment plant collects sewage from a catchment area including Carlow Town and Environs and sections of Graiguecullen in Co Laois. The incoming effluent is treated in the wastewater plant through a series of primary and secondary processes. The treated effluent entering the River Barrow would be consistent with the type of effluent that would result from the extended aeration type process that is employed at Mortarstown. The incoming untreated effluent entering the works is consistent with a predominantly domestic source, i.e Carlow Town with some commercial and industrial loadings included. There is no loadings coming to the plant that would be considered radically different from what would be considered normal municipal sewage. The potential loadings to the receiving waters would be BOD, COD, Suspended Solids, Phosphorus, Nitrates and Ammonia. Chemicals injected as part of the treatment at the plant would be Ferric Sulphate for phosphorus removal and poly dosing for the sludge dewatering process. These potential loadings to the aquatic environment are greatly reduced by the process and levels leaving the works are well below levels indicated in the Urban Waste Water Directive and the parameters indicated for the plant. In the case of Mortarstown these values would be BOD 15mg/l, suspended solids25mg/l, total phosphorus 1 mg/l, ammonia 5mg/l and nitrate NO3-N 10mg/l. We attach below a table outling the emissions to the receiving waters from the Primary Discharge Point at Mortarstown WWTP. Number Substance As discharged Max. daily average 1 ph Temperature - 3 Electrical Conductivity(@25 o C) Max. daily average kg/day (mg/l) 4 Suspended Solids Ammonia (as N)

9 Biochemical Oxygen Demand Chemical Oxygen Demand Total Nitrogen (as N) 9 Nitrite (as N) Nitrate (as N) Total Phosphorus (as P) Orthophosphate (as P) Note 1 13 Sulphate (SO 4 ) Phenols (sum) Note 2 (ug/l) The treated effluent is currently meeting the required parameters. A concern with a waste water plant like Mortarstown would be the potential for point loading into the receiving waters with regard to phosphates and nitrates. These concerns have been addressed in recent improvement works to the plant. Upgrade works to the wastewater plant in recent years have focused on reducing phosphates and nitrates. To achieve this the aeration tanks were modified to include anaerobic, aerobic and anoxic zones. The aerobic zone is designed to achieve nitrification, the anoxic zone denitrification and the anaerobic zone to achieve enhanced biological phosphorus removal. The new works also allow for the dosing of Ferric Sulphate to assist in the reduction of phosphates. Emissions from the Storm Overflows will be improved by the proposed works included for in the Carlow Surface Water Drainage Scheme. Discharges will only occur during periods of very heavy rainfall. Flows in the rivers Burrin and Barrow will be in flood conditions during these spillages and dilution factors will be very high. The Catchment The catchment area for the Mortarstown Wastewater Plant extends from the Northern Environs of Carlow Town eastwards to Chapelstown and Walls Forge on the eastern extremities of the town and southwards to Mortarstown. It also includes an area west of the River Barrow and extending out to the Eastern Relief Road. As outlined above sections of this area are in Co Laois. A series of pump stations located throughout the catchment lift the effluent towards the WWTP at Mortarstown.. The Graiguecullen Pump Station located directly on the west side of Wellington Bridge lifts all the effluent

10 generated on the west side of the Barrow unto the east side of the river. All effluent eventually arrives at the main pump station which is called the Kilkenny Road Pump Station. It is located adjacent to the Regional College on the west side of the N9. All effluent is pumped from here to the waste water works via a 600mm rising main. Laid along side the foul main is a 400mm storm water rising main which pumps storm water unto a storm tank at the works. The network also includes a number of storm overflows which are outlined on attached drawings. The existing network of sewers is over stressed at several locations and a new drainage scheme entitled the Carlow Town Surface Water Drainage Scheme is currently going to tender and construction should commence in This will involve construction of new pump stations and new storm, foul and combined sewers. The new pump stations will include storm overflows designed in accordance with the Urban Waste Water Treatment Directives. The new overflows will also replace existing overflows that are currently operating outside the parameters of the Urban Waste Water Treatment Directives. Annex 1 (A) of the Directive stipulates that the design, construction and maintenance of collection systems shall be undertaken in accordance with the best technical knowledge not entailing excessive costs, notably regarding limitation of pollution of receiving waters due to storm water overflows. The new storm overflows are designed in accordance the Formula A which is recommended by the UK Technical Committee on Storm Overflows and Disposal of Storm Sewage Final Report in1970. Formula A is Q = DWF P + 2E Where Q is flow retained in sewage system (l/d) DWF is dry weather flow P is population served by upstream network E is average industrial effluent flow Design of SWOs in this country is currently based on advice given by the DOEHLG in the Circular Procedures and Criteria in relation to Storm Water Overflows and a paper presented by Gerry Galvin, Principal Advisor, titled Storm Water Flows. These proposed improvement measures in the form of new storm overflows into the River Barrow and its tributary the River Burrin will improve the levels of emissions into these receiving waters and ensure better control over the discharges into the aquatic environment. One of the key aims of the storm overflows will be to ensure spillages at times of high dilution levels in the rivers. This should in turn contribute to an increase in Q values in the River Barrow.

11 Receiving Waters The primary discharge and most of the storm water overflows discharge into the River Barrow. The Barrow is 220km in length and flows through the counties of Laois, Kildare, Carlow, Kilkenny and Wexford merging with the rivers Nore and Suir before discharging into Waterford Harbour. The 2006 EPA Water Quality Report indicates that there has been an improvement in water quality d/s of the Sugar Factory since 2004 and d/s of the Mortarstown Wastewater Plant since The Q value at Graiguecullen is noted as 4 as is the Q value at Cloghrennan Lock which is the next station d/s of the station at the wastewater plant. There is a value of 4 for the Q value indicated at the station directly downstream of the wastewater plant station in the 2007 River Water Quality Report. The 2007 Report notes a slight disimprovement in quality at this station. The EPA Biological Quality Ratings (Q-Values) are the parameters used to monitor river water quality. Q5, Q4-5, Q4 Unpolluted Q3-4 Slightly Polluted Q3, Q2-3 Moderately Polluted Q2, Q1-2, Q1 Seriously Polluted The River Barrow through Carlow Town at a Q4 is unpolluted. Recent improvements to the Mortarstown WWTP have been carried out with a view to reducing nitrogen and phosphorus levels and it appears that these improvement works have contributed to the improvement in water quality in the Barrow. Monitoring of Emissions into the Environment Monitoring of the inlet and outlet to the works takes place bimonthly for the following parameters: Ammonium, BOD, COD, o-p, total nitrogen, total phosphorous, and total suspended solids. In addition monitoring of the upstream and downstream of the outlet is undertaken bymonthly for the following parameters, BOD, COD and Total Suspended Solids. There are permanent composite samplers on the inlet and outlet. They are not in permanent use and are switched on when required. Grab samples are taken from the river to represent upstream and downstream monitoring points. Conclusion The Wastewater Treatment Plant at Mortarstown provides treatment for the sewerage effluent generated by the agglomeration of Carlow Town and Environs including a

12 section of Co Laois. The agglomeration also includes several overflows that discharge into the River Barrow and the River Burren. To comply with Phorsphorus Regulations (S.I. No 258 of 1998) and the Urban Waste Water Treatment Directives works were carried out at the plant in the early 2000s. These works included modifications to the aeration tanks to include anaerobic, aerobic and anoxic zones. These additional works serve to facilitate the removal of nitrates and phosphates from the effluent. In addition chemical dosing facilities have been installed to provide for the injection of Ferric Sulphate which will further improve the removal rate of phosphorus. Carlow Co Co have also progressed the Carlow Surface Water Drainage Scheme to the tender stage. This scheme includes the construction of new storm overflows. These new overflows will comply with the requirements of the Urban Waste Water Directive. New pipelines will also prevent unnecessary overflows. These proposed works will improve the standards of emissions to the aquatic environment and further enhance the Q-ratings for the Rivers Barrow and Burren. It will also work in tandem with the objectives of the Water Framework Directive and will further tie in with the South East River Basin District Management Plan.