Inspectors Report
Total Page:16
File Type:pdf, Size:1020Kb
An Bord Pleanála Inspector’s Report PL 11.JA0026 Development Description: Upgrading and extension of Mountmellick Wastewater Treatment Plant. Address: Mountmellick, County Laois. Planning Application Planning Authority: Laois County Council. Applicant: Laois County Council. Type of Application: Application under Section 175 Planning Authority Decision: Not Applicable (Application made to the Board Under S.175) Planning Appeal Observers: 1. An Taisce. 2. Michael Hoey. 3. EPA 4. Inland Fisheries Ireland 5. Offaly County Council 6. Mountmellick Angling and Conservation Association Date of Site Inspection: 15/12/11. Inspector: Paul Caprani PL 11.JA0026 An Bord Pleanála Page 1 of 47 1.0 INTRODUCTION Case reference 11.JA0026 relates to an application by Laois County Council under the provisions of Section 175 of the Planning and Development Act 2000 for approval to An Bord Pleanála for the upgrading of the wastewater treatment works at Mountmellick, County Laois. An Environmental Impact Statement, a Preliminary Design Report and an Appropriate Assessment on the potential impact of the proposed development on the River Owenass which forms part of the River Barrow and River Nore candidate Special Area of Conservation have all been submitted with the application. Two observations were also submitted on foot of the application by An Taisce and by Mr. Michael Hoey objecting to the proposed upgrade. Observations were also submitted by a number of prescribed bodies the contents of which are set out further in this report. An oral hearing was held in relation to the application on the 18 th of January 2012. It is summarised in an appendix to this report. A number of other appendices are attached to this report including an evaluation of the contents of the EIS in the context of whether it complies with the requirements of the Directive and a summary of the information contained in the Appropriate Assessment. 2.0 SITE LOCATION AND DESCRIPTION The existing wastewater treatment plant is located in the north-eastern edge of Mountmellick village on the eastern side of Bay Road which runs northwards from Emmet Street, one of the main thoroughfares in the village. The site is located approximately three-quarters of a kilometre from O’Connell Square in the centre of Mountmellick. The existing wastewater treatment works is setback from the Bay Road and is located adjacent to the Owenass River which runs along the eastern boundary of the existing treatment works. There are a number of single-storey dwellings facing onto the Bay Road to the west of the site. The separation distance between the dwellings and the existing wastewater treatment plant is between 150 and 200 metres. Two football pitches are located to the south of the site, one on either side of the Owenass River. A residential estate is located further south of the football pitch, again between 150 and 200 metres from the wastewater treatment works. The nearest residential dwellings to the west of the site are located in the Cullenwood Residential Estate, the closest dwellinghouse being approximately 100 metres to the west of the site, on the opposite side of the Owenass River (no. 40 Cullenwood). Lands to the north of the site are currently vacant and unused. It is proposed to expand the wastewater treatment works into this area. A County Council depot is located immediately adjoining the western boundary of the site between the wastewater treatment works and the existing dwellinghouses which front onto Bay Road. The site is surrounded by c.2 metre high palisade fencing and there is little landscaping along the site boundary. PL 11.JA0026 An Bord Pleanála Page 2 of 47 Access to the site is provided off Bay Road to the west of the site. This 200 metre long access road also serves the local football club to the south of the site. The Owenass River is a tributary of the River Barrow and its confluence point with the River Barrow is approximately 1.5 kilometres to the north east of the site. According to the information contained in the EIS (based on OPW data) the Owenass River has a 95%ile flow of 0.117m 3/s and an average flow is 1.85m 3/s. 3.0 EXISTING WASTEWATER TREATMENT WORKS ON SITE The existing wastewater treatment plant has been the subject of upgrading which was completed in 2009 and this upgrade formed Phase 1 of the intended expansion of the plant. The existing treatment plant has an organic treatment capacity of 7,000 p.e. which was recently upgraded from 5,000 p.e. The existing wastewater treatment works, including the recent expansion under phase 1 are set out below. Wastewater is received at an inlet works which comprises of preliminary treatment and also incorporates a newly constructed storm tank under Phase 1 which accommodates storm water flows. A considerable portion of the wastewater infrastructure serving Mountmellick relies on a combined sewer system network thus there was a need to incorporate a storm water tank. The preliminary treatment comprises of a 6 millimetre automatic screen based on an Archimedes screw principle. Flows from the preliminary works go directly into an oxidation ditch for secondary treatment. There is no form of primary treatment provided on site. The oxidation ditch permits microbial breakdown and nitrification of the effluent. The dissolved oxygen within the oxidation ditch is generated by eight ‘triton propeller type’ floating aerators and two brush type aerators which run continuously to introduce the dissolved oxygen content. The propeller type floating aerators move back and forth across the ditch. The oxidation ditch is approximately 80 metres long, 8 metres wide and has a capacity of just less than 1,500 cubic metres. The retention time of effluent within the oxidation ditch is approximately two days. The sludge removed from the oxidation ditch is divided into Waste Activation Sludge (WAS) and Return Activation Sludge (RAS). The effluent is then transported to two clarifiers (one circular and two rectangular side by side). The rectangular clarifiers were built as part of the original treatment works in the mid-70s before being replaced by the circular clarifier. As part of the Phase 1 improvement works the rectangular clarifiers were refitted and incorporated into the overall design to cater for the increase in p.e. After clarification the effluent is discharged into an open-ended outfall into the Owenass River immediately east of the site. The maximum flow concentration at the inlet works is 66 litres per second. PL 11.JA0026 An Bord Pleanála Page 3 of 47 Sludge is treated on site by way of a picket fence thickener and a centrifuge which results in a dry solid content with the sludge of about 14%. The sludge is then removed from site to the sludge treatment works in Portlaoise. Recently, a further temporary plant has been commissioned as part of phase 1 in the north-western corner of the site adjacent to the sludge treatment area. This comprises of two large tanks containing secondary treatment in the form of rotating bio discs and general aeration before being transferred onto a final clarification tank prior to discharge. 4.0 PROPOSED DEVELOPMENT The proposed development comprises of a capacity upgrade of the existing wastewater treatment works through the provision of an expansion of further wastewater treatment facilities and an improvement in the level of treatment to be provided at the plant. This expansion is to take place over three phases, the first of which has already been carried out on site and essentially comprised of the provision of new storm tanks adjacent to the inlet works and the provision of temporary secondary treatment and final clarification tanks adjacent to the sludge treatment building in the north-western portion of the site (see previous section above). The existing wastewater treatment works under Phase 1 upgraded the treatment capacity from 5,000 p.e. to 7,000 p.e. Under Phase 2 it is proposed to increase the capacity upgrade to 8,000 p.e. The Board will be aware that the proposed development involves a design build and operative scheme and therefore only the general design parameters are set out in the EIS. The detailed design has yet to be finalised. More detailed descriptions of the proposed development as envisaged are contained in Section 6 of the preliminary report. The details provided in Section 6 of the preliminary report together with the indicative layout scheme are indicated on Drawing 20421-56. It is recommended that the full flow of the wastewater treatment plant be limited to three times the dry weather flow for both Phase 2 and Phase 3 developments. 4.1 Phase 2 As already stated Phase 2 would see an increase in p.e. from 7,000 to 8,000 and will involve the following works on site. The demolition and rebuilding of the existing inlet works. The inlet works will incorporate a 6 millimetre screening with ancillary screenings processing facilities and a grit separation with an ancillary grit handling system. PL 11.JA0026 An Bord Pleanála Page 4 of 47 Under Phase 2 it is also proposed to incorporate a new primary settlement tank together with an odour control unit to the north of the existing storm storage tanks. It is proposed to incorporate covering tanks to ensure that acceptable odour limits are met. A primary clarifier (9 metres in diameter) should provide a 40% reduction in BOD passing forward to the secondary treatment process. This will reduce energy costs in the secondary treatment system. In terms of secondary treatment Phase 2 works will involve a new 4,000 p.e. aeration stream and refurbishment of the existing oxidation ditch.