Assimilative Capacity. Assessment of River Deele

Transcription

1 Assimilative Capacity Assessment of River Deele Text No Attachment No Description Date Check By COV/LA/F1(ii) Attachment F.1 Assimilative Capacity Assessment of River Deele 02/03/09 Donal Casey EPA Export :13:08:04

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15 EPA Export :13:08:05 se Co n f c Fo op r i yr ns ig pe ht ct ow ion ne pu r r rp eq os ui es re o d nl fo y. ra ny nt o se. ru he ot

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24 Addendum to Preliminary Report 2006 Text No Attachment No Description Date Check By COV/LA/G3 Attachment GN Addendum to Preliminary Report /03/09 Donal Casey EPA Export :13:08:05

25 Jennings O'Donovan & Partners Consulting Engineers Sligo DONEGAL COUNTY COUNCIL CONVOY SEWERAGE SCHEME ADDENDUM TO PRELIMINARY REPORT 3463/DT/TC SUMMARY OF FINDINGS CONTENTS Page No. 1.0 INTRODUCTION Terms of Reference Background 2003 Preliminary Report Funding Land Acquisition Overview of Information DESIGN POPULATION REVIEW Preliminary Report Population Equivalent Existing Population Review Proposed Development Possible Future Development Design Population Equivalent Recommended Design Loadings RECEIVING WATERS, DISCHARGE REQUIREMENTS & ENVIRONMENTAL CONSIDERATIONS Introduction Relevant Statutory and Policy Considerations Water Quality data for the River Deele Standard of Treatment Required EXISTING SEWER NETWORK Description of Existing Network Proposed/Recent Modifications to Sewer Network Problematic Sewers Network Survey Post Network Improvements Network Improvements Cost Estimate 20 Contents PR (i) May 2006 EPA Export :13:08:06

26 Jennings O'Donovan & Partners Consulting Engineers Sligo 5.0 SECONDARY TREATMENT PROCESS Design Loadings Preliminary Report Recommendations Secondary Treatment Process Evaluation of Options Discussion of Treatment Options DESCRIPTION OF PROPOSED EXTENSION TO WASTE WATER TREATMENT WORKS Secondary Treatment Sludge Draw Off and Pumping Chamber Sludge Holding Tank Phosphorous Removal Final Effluent Measurement and Sampling Control/ Compressor Buidling Existing Works Site Investigation PROCUREMENT OPTIONS Introduction Options Recommend Procurement Option SUMMARY OF COST ESTIMATES Capital Costs Operation & Maintenance Costs RECOMMENDATIONS 31. APPENDICES Appendix A - Breakdown of Non-Domestic p.e. Appendix B - Water Quality Data for Deele River Appendix C - Drawings Appendix D - Secondary Treatment Options Schematics Appendix E - Cost Estimates Appendix F - Design Calculations for Secondary Treatment Process Contents PR (ii) May 2006 EPA Export :13:08:06

27 Jennings O'Donovan & Partners Consulting Engineers Sligo DONEGAL COUNTY COUNCIL 3463/DT/TC CONVOY SEWERAGE SCHEME ADDENDUM TO PRELIMINARY REPORT 1.0 INTRODUCTION 1.1 Terms of Reference This report is an addendum to the Preliminary Report prepared for Convoy Sewerage Scheme dated June This report assesses suitable secondary treatment options for extending the existing works and recommends the most appropriate method and approach for extending the works. A review of existing and possible future population in Convoy is undertaken and the existing sewer network is examined and assessed with a view to upgrading and extending the network within the village. 1.2 Background 2003 Preliminary Report The Preliminary Report for Convoy Sewerage Scheme prepared by Jennings O'Donovan & Partners and dated June 2003 made recommendations for the upgrade of the wastewater treatment works. Upgrading and extending the sewer network was not considered at that stage. Tender documents for preliminary and storm water treatment were prepared in August 2004 and included for provision of the following elements at the Waste Water Treatment Works: - Storm Overflow Chamber - Inlet Flow Measurement & Sampling - Inlet Screening and Grit Removal - Measurement of Forward Flow to Full Treatment - Modifications to existing Imhoff Tank - Storm Water Holding Tank and Storm Water Return Pumping Chamber - Final Effluent Measurement and Sampling The Contract was tendered in February/March 2005 and was awarded to Waste Water Controls Ltd. Construction and is on-going at present with commissioning and testing scheduled for end- April. Preliminary Report May 2006 EPA Export :13:08:06

28 Jennings O'Donovan & Partners Consulting Engineers Sligo A review of the Preliminary Report is now required due to reflect rapid housing development in Convoy and the impact of the works on the Deele River. 1.3 Funding Under the National Development Plan Water Services Investment Programme , 1,120,000 of funding is available for Convoy Sewerage Scheme. Donegal County Council propose to use this funding to extend the Wastewater Treatment Works to Secondary treatment and to carry out necessary upgrading to the sewer network. 1.4 Land Acquisition Donegal County Council have purchased the field adjacent to the existing Waste Water Treatment Works. The field, 2.38 acres in area, is sufficient to accommodate the proposed extension to the works and any future extension. 1.5 Overview of Information (see attached sheet) Section 2 presents a review of the design population recent, proposed and possible future development in Convoy are discussed. Section 3 discusses the Deele River, legislation and effluent discharge requirements Section 4 discusses the existing sewer network, recent/ proposed modifications to the network, problematic sewers and recommendations for a network survey. Section 5 discusses the secondary treatment options and extends the evaluation carried out in the 2003 Preliminary Report. Section 6 describes the proposed extension to the works. Section 7 of this Report discusses procurement options for the project. Section 8 summaries cost estimates. Section 9 summaries the recommendations of this Addendum to Preliminary Report. Preliminary Report May 2006 EPA Export :13:08:06

29 Jennings O'Donovan & Partners Consulting Engineers Sligo 2.0 DESIGN POPULATION REVIEW Preliminary Report The design population calculated in the Preliminary Report, June 2003 was 2,335 p.e. At a meeting held with Donegal County Council on 15 th June 2004 it was agreed to increase the design p.e. from 2,335p.e. to 3,500p.e. due to a large number of planning applications for housing. At that time, approximately 340 dwellings were proposed. Preliminary and storm water treatment elements are designed and constructed for 3,500 p.e. based on a hydraulic load of 250 l/p.e./day or a Dry Weather Flow of l/s. 2.2 Population Equivalent A review of existing and possible future population was carried out to take into account changes over the last three years since the Preliminary Report was prepared. The review presented in this section reveals that a design p.e. of 3,500 will provide sufficient capacity for Convoy for the next 20 years. Population Equivalent (p.e.) is the value used to estimate the volume and quality of wastewater generated. The EPA wastewater treatment manual for Treatment Systems for small communities, Business, Leisure Centres, Hotels advises that the true per capita wastewater flow is 180 l/p.e./day. Based on this advice, a hydraulic loading of 180 l/p.e./day and an organic loading of 60 g/p.e./day will be used in the design of secondary treatment at Convoy. The dry weather flow loading at 3,500 p.e. at 180 l/p.e./day will be 7.29 l/s. Preliminary and storm water treatment elements will therefore have capacity to deal with flows associated with 4,862 p.e. at 180 l/p.e./day which may be adequate to deal with any further extension of the works. 2.3 Existing Population Review For the purpose of this report, existing population shall be those connected to the existing sewer network. This includes housing developments that are currently under construction that will be connecting to the public sewer. Preliminary Report May 2006 EPA Export :13:08:06

30 Jennings O'Donovan & Partners Consulting Engineers Sligo Domestic Population There are 621 existing houses (including those at construction) connected to public sewer, as follows: Convoy Townparks 114 Main Street (West of Milltown Turn-off) - Houses on Main Street 46 - Rising Main Serving 10 No. County Council Houses to MH Rising Main Serving New Housing Development at Construction 42 Main Street (East of Milltown Turn-off) Oak Park Development 24 Houses on Main Street 20 J. Dolan Housing Development 24 Letterkenny Road Houses Connected 23 Main Street - Milltown County Council Housing Development 19 McGinley 1 Housing Development 50 McGinley 2 Housing Development (at construction) 62 Whiterow Housing Development (at construction) 94 Single House 1 Milltown Road - WWTW Single Houses 35 McFeely Development 49 Ballyboe Single Houses 8 Total Number of Houses Connected 621 Preliminary Report May 2006 EPA Export :13:08:06

31 Jennings O'Donovan & Partners Consulting Engineers Sligo Table 1 of Census 2002 delineates the Number of private households and number of persons in each province, County and City, classified by type of household. The table shows that the average number of persons per private household in County Donegal is 3.0. The state average is 2.94 persons per household. Applying the County Donegal average to the number of dwellings recorded in Convoy equates to a domestic population of 621 x 3 = 1,863 p.e Non-Domestic Population Non-Domestic entities in Convoy include various commercial and retail premises, pubs, a petrol station, two nursing homes, national school and Natural Dairies. The non-domestic entities were identified on a survey of the village and the loading from each premises have been estimated using the Recommended Wastewater loading rates from Commercial Premises delineated in Table 3 of the Environmental Protection Agency s Wastewater Treatment Manuals Treatment Systems for Small Communities, Business, Leisure Centres and Hotels. The non-domestic population equivalent in Convoy has been calculated to be 466 based on (180 l/p/day). A breakdown of all non-domestic entities is presented in Appendix A and summarised in Table 2.1. Sector Population (p.e.) Commercial/Retail 20 Institutional 267 Pubs 12 Industry (Natural Dairies) 167 TOTAL 466 Table 2.1: Summary of Existing Non-Domestic Population Total Existing Population The existing population is calculated to be 2,329 p.e. (1, p.e.) Preliminary Report May 2006 EPA Export :13:08:06

32 Jennings O'Donovan & Partners Consulting Engineers Sligo 2.4 Proposed Development A search of recent planning applications revealed the following proposed development (Refer to Drawing 3463/PR2/001 for location/reference): Reference Developer Development Description p.e. P1 M. Pearson P2 M. Pearson P3 P4 P5 L.. O Neill D. McFeely G&P McCauley * 20 Restaurant Seats Assumed 15 No. Dwellings Restaurant (conversion of railway building) 20 No. Dwellings 26 No. Dwellings 66 No. Dwellings Table 2.2: Summary of Proposed Development * Total p.e Possible Future Development Within the development control points, there are approximately acres of potential development land, labelled F1 to F7 on Drawing 3463/PR2/001. The average housing density of existing developments in Convoy is 5 houses per acre. Applying this density to potential development land equates to 218 possible future houses or 654 p.e. within the development control points. 2.6 Design Population Equivalent The design population equivalent for Convoy is as follows: Existing Domestic Existing Non-Domestic Total Existing p.e. Proposed Development 1,863 p.e. 466 p.e. 2,329 p.e. 391 p.e. Total Existing and Proposed p.e. 2,720 p.e. Spare Capacity Design p.e. 780 p.e. 3,500 p.e. Provision of a wastewater treatment works with capacity to treat 3,500 p.e. would provide 780 p.e. of spare capacity for future domestic and non-domestic growth. This equates to a 28.7% increase on existing/proposed population or an annual growth rate of 1.27% over 20 years. Section 3 of the 2003 Preliminary Report demonstrates that the annual growth rate based on Census figures between 1971 and 2002 to be 0.89%. Based on the pre 2002 growth rate and assuming that the Preliminary Report May 2006 EPA Export :13:08:06

33 Jennings O'Donovan & Partners Consulting Engineers Sligo recent surge of development can not be sustained, the annual growth rate of 1.27% provided as spare capacity at the WWTW is reasonable. As demonstrated in Section 2.5, there is scope within Convoy for provision of a further 218 houses (654 p.e.) leaving spare capacity of 126 p.e. for non-domestic and other domestic. 2.7 Recommended Design Loadings Applying typical hydraulic and organic loadings of 180 l/p.e./day and 60g x BOD/p.e./day respectively, equates to the following loadings: Population Equivalent DWF (m 3 /d) 3 DWF (l/s) 6 DWF (l/s) BOD Load (kg/d) Existing 2, Design 3, Table 2.3: Existing and Design Loadings Preliminary Report May 2006 EPA Export :13:08:06

34 Jennings O'Donovan & Partners Consulting Engineers Sligo 3.0 RECEIVING WATERS, DISCHARGE REQUIREMENTS & ENVIRONMENTAL CONSIDERATIONS 3.1 Introduction Any proposed infrastructure should satisfy relevant legislation, planning policies and environmental designations. The relevant legislation pertaining to outfalls for treated effluent and the protection of surface water are reviewed below for their potential relevance to Convoy Wastewater Treatment Works. 3.2 Relevant Statutory and Policy Considerations Urban Waste Water Treatment Regulations 2001 (S.I. 254 of 2001) These regulations revoke and generally re-enact in consolidation form the Environmental Protection Agency Act, 1992 (Urban Waste Water Treatment) Regulations, 1994, as amended. The regulations concerning Urban Waste Water Treatment give effect to the provisions of directive 91/271/EEC, as amended, concerning urban wastewater treatment. They govern the planning and design of all sewage infrastructures. The Urban Waste Water Treatment Regulations, 2001 require under Article 4 (1) of the regulations that:...a sanitary authority shall provide treatment plants which provide for secondary treatment or an equivalent treatment (a) By 31 December 2005 in respect of all discharges to freshwaters and estuaries from agglomerations within population equivalent of between 2,000 and 10,000. This requirement thus applies to Convoy Waste Water Treatment Works, which has a proposed design population of 3,500p.e. In addition, Article 5 of the Urban Waste Water Treatment Regulations, 2001 states that: Not withstanding the provisions of article 4, more stringent requirements than those specified in Parts 1 and 2 of the Second Schedule shall be applied to discharges from a treatment plant where Preliminary Report May 2006 EPA Export :13:08:06

35 Jennings O'Donovan & Partners Consulting Engineers Sligo this is required to ensure that the receiving waters satisfy any other relevant Community Directives. Part 1Parameter Concentration Minimum % of Reduction Biochemical Oxygen Demand 25mg/l O Chemical Oxygen Demand 125 mg/l O 2 75 Total Suspended Solids 25 mg/l 90 Table 3.1: Concentration of discharge from wastewater treatment works as specified within the second schedule of S.I 254 of The fifth Schedule of S.I 254 of 2001 specifies the frequency of monitoring, which is required dependant upon the size of the treatment plant. Influent and Effluent Parameters Sample Type Frequency BOD (Biological Oxygen Demand) COD (Chemical Oxygen Demand) TSS (Total Suspended Solids) TP (Total Phosphorus) MRP (Molybdate Reactive Phosphate) TN (Total Nitrogen) TON (Total Oxidised Nitrogen) Flow Table 3.2: 24 hour Composite Sample 2,000 to 9,999 p.e. 12 samples during the first year. Four samples in subsequent years, if it can be shown that the water during the first year complies with the provisions of the regulations, if one sample of the four fails, 12 samples must be taken in the year that follows Automatic Continuous Monitoring Frequency of Monitoring required at Convoy Waste Water Treatment Works Water Framework Directive (2000/60/EC) The Water Framework Directive (2000/60/EC) requires, inter alia, a review of the impact of human activity on the status of surface waters and groundwater. The review requires an assessment of the likelihood that water bodies in river basin districts will fail to meet the Directive s environmental objectives. A four-category risk classification scheme has been adopted by the Risk Assessment Working group in Ireland as follows: Preliminary Report May 2006 EPA Export :13:08:06

36 Jennings O'Donovan & Partners Consulting Engineers Sligo EU Commissions reporting risk categories for water bodies Water bodies for which it is already clear without the need for further characterisation or additional monitoring data, that the objectives will be failed; Water bodies for which it is possible that the objectives of the Directive will be failed but, because of inadequate data, further characterisation and operational monitoring are considered necessary to be sufficiently confident that this is the case; Water bodies for which it is already clear, without the need for further characterisation or additional monitoring data, that the achievement of the objectives are not at risk. Table 3.3 Irish equivalent reporting categories for water bodies 1a - Water Body at significant risk on the basis of available information for which confidence in the available information being comprehensive and reliable is high 1b - Water Body probably at significant risk but for which further information will be needed to confirm that this view is correct 2a - Water Body probably not at significant risk on the basis of available information for which confidence in the available information being comprehensive and reliable is lower 2b - Water Body not at risk on the basis of available information for which confidence in the available information being comprehensive and reliable is high Water Framework Directive Category Risk Classification The Deele River is in the North Western International River Basin District and has an overall Risk Result of 1a Water Body at significant Risk. (NS Share, 2005). A copy of the water body report for the Deele River is contained in Appendix B Water Quality Phosphorus Regulations, 1998 (S.I 258/1998) The Local Government (Water Pollution) Act, 1977 (Water Quality Phosphorus) regulations, 1998 (S.I 258/1998) implements in part EU Directive 76/464/EEC on pollution caused by substances discharged into the aquatic environment. The regulations require that water quality has to be maintained or improved by reference to the Biological Quality (Q) Rating assigned by the EPA in Waters, which have specified unsatisfactory Biological Quality (Q) Ratings in 1997(or the first available data thereafter) must be improved to achieve specified minimum target Q or median annual molybdate-reactive phosphorus (MRP) values by There is a strong statistical relationship between biological Q-ratings and MRP concentrations in Irish rivers. The empirical relationship suggests that, once annual median MRP values exceed 30µg P/l, there is a strong statistical likelihood that the river reach in question will have a significant eutrophication problem. Therefore either Q or median MRP targets can be used as a measure of achievement of the Preliminary Report May 2006 EPA Export :13:08:06

37 Jennings O'Donovan & Partners Consulting Engineers Sligo standards set in the regulations (Cleneghan, C., 2003 Phosphorous regulations national Implementation report, 2003 EPA). EPA biological monitoring points on the River Deele are designated for monitoring under the phosphorous regulations. Target and current values at three monitoring stations upstream and downstream of Convoy WWTW are presented in Table 3.4. The location of these monitoring stations are shown in Figure 3.1. EPA monitoring Station No. Location of monitoring point w.r.t Convoy WWT discharge point Q value (1997) Q Value (1998)* Minimum Target Q to be achieved by 2007 Median MRP (µg P/l) to be achieved by 2007** km upstream km downstream km downstream * Most recent published data is 1998 ** There is currently no MRP data available for the EPA monitoring stations on the Deele River. Table 3.4 Current and Target Q and median MRP values for EPA monitoring points on the Deele River (EPA River Code; 01D01) In general, Q values equal to 4 or above 4 are considered as satisfactory, whereas values below 4 are considered unsatisfactory, therefore in general a Q4 or greater value is aspired to in terms of biological quality (Toner et al, 2005 Water Quality in Ireland ). Details of the Q values and their general characteristics are contained in Table 3.5. The EPA Monitoring Station, 0500, downstream of the WWTW has a value of 2-3 and is therefore below the minimum satisfactory standard of Q4 or above. Improvements to the standard of effluent being discharged from the works following secondary treatment will improve the quality of the river and associated Q value. Preliminary Report May 2006 EPA Export :13:08:06

38 Jennings O'Donovan & Partners Consulting Engineers Sligo Table 3.5 General characteristics of the various Biological Quality Classes (Toner et al, 2005 Water Quality in Ireland ) Quality Classes Class A Class B Class C Class D Quality Ratings (Q) Q5 Q4 Q3 4 Q3 Q2 Q1 Pollution Status Pristine, Unpolluted Unpolluted Slight Pollution Moderate Pollution Heavy Pollution Gross Pollution Organic Waste Load None None Light Considerable Heavy Excessive Maximum B.O.D. Low (<3 mg/l) Low (<3 mg/l) Occasionally elevated High at times Usually high Usually very high Dissolved Oxygen Close to 100% 80% - 120% Fluctuates from <80% Very unstable Low, sometimes Very low, often zero to >120% Potential fish-kills zero Annual Median ortho- Phosphate ~0.015 mg P/I ~0.030 mg P/I ~0.045 mg P/I ~0.070 mg P/I Usually > 0.1 P/I Usually >0.1 mg P/I Siltation None May be light May be light May be considerable Usually heavy Usually very heavy and anaerobic Sewage Fungus Never Never Never May be some Usually abundant May be abundant Filamentous Algae Limited Considerable growths Cladophora may be Cladaphora may be May be abundant Usually none development Diverse communities abundant excessive Macrophytes Diverse communities Limited growths Diverse communities Considerable growths Reduced diversity Luxuriant growths Limited diversity Excessive growths Tolerant species only. May be abundant. Usually none or tolerant species only. Macroinvertebrates (from shallow riffles) Diverse communities. High diversity Increased density. Very high diversity. Very high density. Sensitive forms absent. Tolerant Tolerant forms only. Very low diversity. Most tolerant forms. Minimal diversity. Normal density. Sensitive forms usually numerous. Sensitive forms scarce or common. Sensitive forms scarce. forms common. Low diversity. Water Quality Highest quality Fair quality Variable quality Doubtful quality Poor quality Bad quality Abstraction Potential Suitable for all Suitable for all Potential Problems Advance treatment Low grade abstractions Extremely limited Fishery Potential Game fisheries Good game fisheries Game fish at risk Coarse fisheries Fish usually absent Fish absent Amenity value Very high High Considerable Reduced Low Zero Condition Satisfactory Satisfactory Transitional Unsatisfactory Unsatisfactory Unsatisfactory Preliminary Report May 2006 EPA Export :13:08:06

39 Jennings O'Donovan & Partners Consulting Engineers Sligo The parameters, which have defined thresholds in the general characteristics for each Q class and which are measurable in terms of the wastewater treatment works discharge are: Maximum BOD, Dissolved Oxygen (DO) and (Annual Median) orthophosphate. Phosphate data is available and is considered broadly comparable to orthophosphate for the purposes of surface water biological quality. Therefore for the purpose of comparing water quality with standards to be achieved in the phosphorus regulations, Q values as represented by the parameters BOD, DO and orthophosphate/phosphate are used. Based on the requirement for two of three the monitoring stations examined on the Deele River to maintain Q4 by 2007, Q4 will be taken as the standard to be maintained in the receiving waters Salmonid Water Regulations The Deele River is not designated as a Salmonid river under the European Communities Quality of Salmonid Rivers Regulations, SI 293/1988. However, it does contain trout, dipper and probably otter (Ecological Assessment, April 2003) Standards Required in River Deele Table 3.6 summarises the environmental quality standards to be achieved in the receiving waters for parameters associated with discharge from the wastewater treatment plant. Following the precautionary principle, the most stringent of these standards should be adopted where more than one standard exists. Parameter Standard Standard Source Max. BOD <3 mg/l Q4 value: WFD (2000/60/EC) & Phosphorus Regulations (S.I 258/1998) Dissolved Oxygen % Q4 value: WFD (2000/60/EC) & Phosphorus Regulations (S.I 258/1998) Annual Median PO 4 /Orthophosphate Table mg P/l Q4 value: WFD (2000/60/EC) & Phosphorus Regulations (S.I 258/1998) Quality Standards to be achieved in the Deele River Preliminary Report May 2006 EPA Export :13:08:06

40 Jennings O'Donovan & Partners Consulting Engineers Sligo 3.3 Water quality data for the Deele River The most recent data of relevance to the environmental quality standards and the wastewater treatment plant discharge is available from Donegal County Council. This data is presented in Table 3.7. Date Location P.H. B.O.D. (Mg/l) S.S. (Mg/l) C.O.D. (Mg/l) NH3- N(Mg/l) ORTHO P(Mg/l) TOTAL P(Mg/l) 10/01/2005 Convoy - inlet /03/2005 Convoy - inlet /04/2005 Convoy - inlet /05/2005 Convoy - inlet /06/2005 Convoy - inlet /07/2005 Convoy - inlet /08/2005 Convoy - inlet /09/2005 Convoy - inlet /10/2005 Convoy - inlet /11/2005 Convoy - inlet /12/2005 Convoy - inlet /01/2005 Convoy - downstream /02/2005 Convoy - downstream /03/2005 Convoy - downstream /04/2005 Convoy - downstream /06/2005 Convoy - downstream /07/2005 Convoy - downstream /09/2005 Convoy - downstream /11/2005 Convoy - downstream /01/2005 Convoy - outlet /02/2005 Convoy - outlet /03/2005 Convoy - outlet /04/2005 Convoy - outlet /05/2005 Convoy - outlet /06/2005 Convoy - outlet /07/2005 Convoy - outlet /08/2005 Convoy - outlet /09/2005 Convoy - outlet /10/2005 Convoy - outlet /11/2005 Convoy - outlet /12/2005 Convoy - outlet /01/2005 Convoy - upstream /02/2005 Convoy - upstream /03/2005 Convoy - upstream /04/2005 Convoy - upstream /06/2005 Convoy - upstream /07/2005 Convoy - upstream /09/2005 Convoy - upstream /11/2005 Convoy - upstream Table Physio-Chemical Results for inlet & outlet to Convoy WWTW and the Deele River upstream & downstream of the WWTW (Source: Donegal County Council Laboratory, Magheranan, Letterkenny) Preliminary Report May 2006 EPA Export :13:08:06

41 Jennings O'Donovan & Partners Consulting Engineers Sligo The results presented in Table 3.7 indicate that the quality of water within the Deele River is presently meeting the standards specified within Table 3.6 upstream of the discharge point at Convoy WWTW for BOD and orthophosphate (Dissolved oxygen results are not available). Downstream of the works, water quality drops dramatically with the river failing to meet BOD and orthophosphate standards in This is a result of the poor quality of effluent being discharged from the works in The standard of effluent should improve marginally in 2006 following commissioning of the preliminary and storm water treatment elements of the works. Provision of secondary treatment in the next phase of the works will produce an effluent standard compliant with the Urban Waste Water Treatment Directive and water quality downstream of the WWTW will improve. The level of Orthophosphate upstream of Convoy WWTW ranged from mg/l (0.351mg/l recorded on 19/04/05 is assumed to be an isolated incident) indicating that the high levels of orthophosphate downstream of the works ( mg/l) are a consequence of the discharge from the works. In order to maintain the level of orthophosphate at 0.03 mg/l (Q4 Standard) it is recommended that phosphate removal facilities be incorporated within the proposed extension to the treatment plant. The level of ammonia discharged to the Deele River in 2005 as detailed within Table 3.7 was between 2.935mg/l and mg/l. The level of ammonia recorded in the Deele upstream of the discharge point for same period is mg/l N. In order to maintain this level within the Deele and to minimise the effects of the treatment plant discharge on the quality of the receiving waters it is recommended that nitrification and denitrificaiton processes be incorporated into the design of the proposed new treatment works. The construction of the new treatment plant will increase the level of treatment, which is currently being achieved within the treatment plant and will therefore reduce the biological and nutrient load being discharged to the Deele River. 3.4 Standard of Treatment Required According to the Urban Waste Water Treatment Regulations, 1994 appropriate treatment to meet the standards set out in these regulations is what is required at Convoy WWTW. The treated effluent from the proposed upgraded works will discharge through a new outfall to the Deele River. Preliminary Report May 2006 EPA Export :13:08:06

42 Jennings O'Donovan & Partners Consulting Engineers Sligo Table 3.7 below summaries the effluent standards which should be achieved in the discharge to the Deele River. Parameter Standard Required BOD 25 mg/l Suspended Solids 35 mg/l Orthophosphate 1 mg/l (Best Practice) Total Ammonia Best Practice Table 3.7: Standard of Effluent Required Preliminary Report May 2006 EPA Export :13:08:06

43 Jennings O'Donovan & Partners Consulting Engineers Sligo 4.0 EXISTING SEWER NETWORK 4.1 Description of Existing Network The extent of the existing sewer network in Convoy is shown on Drawing 3463/PR2/001. The total length of network is approximately 5.2km with sewers ranging in diameter from 100mm to 300mm. This length excludes networks within housing developments and sewers constructed privately (not taken over by Donegal County Council). 4.2 Proposed/Recent Modifications to Sewer Network The final sewer line to the wastewater treatment works is a 300mm diameter sewer from MH21 to MH30, flowing into a 150mm diameter sewer from MH30 to the works with a storm overflow manhole located at MH31. A 300mm diameter sewer laid in the field on the river side of the road was constructed in January This sewer replaces the 150mm line from MH30 to the wastewater treatment works. The total length of the upsized sewer is 193m A 225mm sewer was constructed from the Oak Park development to MH53. A surface water sewer also from Oak Park runs alongside this foul sewer and discharges to a tributary of the Deele River. A new 225mm sewer from Natural Dairies connects into the 225mm foul sewer at the fork in the road opposite the Catholic Church At present, the 225mm diameter sewer on Smylies Brae flows into a 150mm diameter sewer from MH 53 to MH29 where it connects to the 300mm diameter sewer line leading to the works. It is proposed to lay 360m of 300mm diameter sewer alongside the existing 150mm from MH53 to MH29. The 150mm sewer will then be made redundant. Tenders are currently being sought by Donegal County Council for construction of this sewer line. 4.3 Problematic Sewers A number of problematic sewer lines within the sewer network have been identified by Donegal County Council staff: Preliminary Report May 2006 EPA Export :13:08:06

44 Jennings O'Donovan & Partners Consulting Engineers Sligo (i) Milltown - MH20 to MH25 Surcharging of the sewer with localised flooding at MH 20 and MH21 is known to occur. Two sewer lines (a 150mm and a 225mm diameter) converge at MH20, one sewer serves the Townparks area and buildings on the Northside of the main street, while the second serves buildings on the south side of the Main Street. The 225mm diameter concrete sewer from MH20 to MH21 flows into a 300mm concrete sewer from MH21 to the works. A section of this 300mm sewer from MH21 to MH 25 is in excess of forty years old and it is possible that this section of sewer is subject to high levels of infiltration and associated silting thus causing blockages and surcharging upstream. It is recommended that this section of sewer from MH20 to MH25 be replaced with a new 300mm diameter concrete sewer. The total length is approximately 243m. (ii) Smylies Brae - MH52 to MH53 This section of sewer serves the houses on the south side of Smylies Brae. The sewer line form Natural Dairies used to connect to this sewer line at MH 52 but now connects to a recently constructed 225mm sewer within the road on Smylies Brae that connects to MH53. It is probable that the section of sewer from MH52 to MH53 is corroded by acidic wastewater discharged from Natural Dairies in the past. Natural Dairies have now installed an on-site treatment system and no further problems should be caused to the sewer network. Upgrade of the existing sewer from MH53 to MH28 is proposed and tenders are currently being sought for this section of sewer. The sewer line from Natural Dairies to MH53 has recently been replaced, therefore the sewer from MH52 MH53 will be the only remaining section of sewer affected by corrosion. It is recommended that this 69m of 150mm diameter concrete sewer be replaced. (iii) Main Street MH 43 to MH47 A section of this sewer line runs under the warehouse belonging to the Morris Bros. Wholesalers. It appears that the ground level in this area has been raised as the warehouse has been extended giving a resultant sewer depth of up to 3.5m. It is recommended that this sewer line be replaced with a new sewer taking a direct line from MH44 to MH47 Preliminary Report May 2006 EPA Export :13:08:07

45 Jennings O'Donovan & Partners Consulting Engineers Sligo through the concrete yard, approximately 70m. The existing sewer (82m long) under the building should then be blocked and made redundant. 4.4 Network Survey Section 4.3 outlines the main problems with the sewer network at present. There may be other sections of sewer that require repair or replacement given (1) the age of the sewer network and (2) the recent increase in flows that these sewers are carrying due to rapid housing development. It is therefore recommended that a Network Survey of the main sewer network be carried out to include: CCTV Survey Manhole Survey (e.g. SUS 25, SUS2000) Sewer Flow and Rainfall Survey Organic Load Survey Impermeable Area Survey Network Model CCTV Survey A CCTV Survey of the main sewer lines on Main Street, Townparks, Letterkenny Road and on Smylies Brae would confirm sewer gradients and identify and locate: - Connections to Sewer - Obstructions in Sewers - Collapsed or Dropped Inverts - Cracks, Fractures or breaks - Bad Pipe Joints - Infiltration of Ground Water Preliminary Report May 2006 EPA Export :13:08:07

46 Jennings O'Donovan & Partners Consulting Engineers Sligo The approximate length of sewer to be CCTV surveyed is broken down as follows: Location Diameter Length Comments Letterkenny 150mm 306m Excludes Private Sewer Townparks/Longlands 150mm 225mm 340m 575m Main Street to WWTW 150mm 140m Excludes section MH44 to MH47 to be replaced 225mm 434m 300mm 301m Excludes MH20 MH25 to be replaced and MH30 to WWTW recently replaced Oak Park to MH53 150mm 266m Excludes MH52 to MH53 to be replaced Church Car Park to 225mm 252m MH53 Natural Dairies to 150/225mm 135m Smylies Brae MH58 to MH54 150mm 115m MH61 to MH29 150mm 141m Total Length 3,005m Table CCTV Summary of Sewers to be surveyed Manhole Survey A manhole survey would determine the exact location and condition of manholes within the sewer network. It would also allow new and recent extensions to the network to be identified providing an up to date map of the network. The total number of manholes to be surveyed is estimated at 75 (excluding manholes within housing development) Flow & Load Survey at the Waste Water Treatment Works This survey would identify the quantity and quality of wastewater entering the WWTW and ascertain the amount of surface water that enters the sewer network by recording the response to rainfall events. The survey would normally be carried out over a period of five weeks in order to record at least three significant storm events. A raingauge would be installed to record rainfall during storm events Impermeable Area Survey This survey determines the surface run-off draining into individual pipe lengths and hence the total surface run-off entering the sewer network. Alternatively consultation with County Council staff who are familiar with the network could determine where surface water is entering the network and where it is most feasible to separate surface and foul flows. Preliminary Report May 2006 EPA Export :13:08:07

47 Jennings O'Donovan & Partners Consulting Engineers Sligo Network Survey Cost Estimate The estimated cost of a network survey as detailed above is 59, VAT, broken down as follows: Insurances, Safety, Traffic Management etc 6,000 CCTV Survey 9,400 Provisional Sum for Sewer Cleaning 5,000 Provisional Sum for Raising Manhole Covers 5,000 Manhole Survey 8,900 Sewer Flow & Rainfall Survey 8,500 Impermeable Area Survey 6,000 Organic Load Survey 6,000 Network Model 5,000 Total (excl. VAT) 4.5 Post Network Survey Improvements 59,800 + VAT The network survey will identify sections/areas of the network that require repair or replacement. A budget of 150,000 is provided for such sewer improvements and remedial works. 4.6 Network Improvements Cost Estimate Cost estimates have been prepared for the recommended improvements to the sewer network set out in Section 4.3. Table 4.2 sets out a cost estimate for sewer improvements and sewer network survey/ model. Sewer Improvement/ Upgrade Length Cost Estimate Milltown MH20 to MH25 243m 51, mm upgrade/ replacement Smylies Brae MH52 to MH53 63m 11, mm replacement Main Street MH5 205mm re route/ upgrade 70m 21, Total Improvements to problematic sewers outlined in Section , Network Survey Estimate 59, Post Network Survey Improvements/Remedial Works 150,00.00 Total (excluding VAT) 293, Table 4.2 Cost Estimate for Sewer Improvements and Network Survey Preliminary Report May 2006 EPA Export :13:08:07

48 Jennings O'Donovan & Partners Consulting Engineers Sligo 5.0 SECONDARY TREATMENT PROCESS 5.1 Design Loadings The secondary Waste Water Treatment Process at Convoy will be designed to treat the following loadings. Design Population equivalent (p.e.) = 3,500 p.e. p.e. loading = 180l/day and 60g BOD/day Dry weather flow = 630m 3 / day Peak flow for full treatment (3DWF) = 1,890m 3 / day = 21.87l/s BOD Load = 210kg/day Preliminary Report Recommendations Section 5 of the Preliminary Report prepared in 2003 considered four options for secondary treatment as follows: A Extended Aeration and Settlement in separate tanks B Modular Rotating Biological Contractor Units with Reed Beds C Extended Aeration and Settlement in Concentric Tanks D Membrane Bioreactor Treatment Units Analysis of the above options based on capital and operation costs, treatment efficiency, environmental impact and land area required was carried out and Option B emerged as the most favourable option. RBC units with reed beds was recommended with phased implementation. The analysis and decision making matrix was based on a phased design p.e. of 2,335 which has now increased to 3,500p.e. to be implemented in one phase as discussed in Section 2 of this report. In light of this significant change, the options outlined above are re-evaluated in this report for 3,500 p.e. New capital and operational costs have been prepared for each option. Schematic drawings of the existing works and each of the four options are presented in Appendix D. Preliminary Report May 2006 EPA Export :13:08:07

49 Jennings O'Donovan & Partners Consulting Engineers Sligo 5.3 Secondary Treatment Process The treatment processes were discussed in detail in the 2003 Preliminary Report. They are not reiterated in this report rather they are re-evaluated based on the same criteria used n the earlier evaluation. 5.4 Evaluation of Options Treatment Efficiency All of the process options proposed are expected to achieve a final effluent standard of 25/35 in terms of BOD/Suspended Solids and therefore meet the requirements outlined in Section 3. Options A and C, Extended Aeration and settlement are most able to cope with fluctuating inlet loads and would provide a stable treatment system due to the retention period within the treatment tanks being in excess of 24 hours. The RBC unit Option B will achieve a standard of 25/35 providing the inlet flow is continual and not in excess of the normal parameters for domestic sewage i.e mg/l BOD. With reed beds after the RBC units an effluent standard of 10/10 is anticipated. The membrane bioreactor system (Option D) has an effective solids removal separation system capable of achieving high and suspended solids removal Environmental Impact The extension to the works is proposed within the field adjoining the existing WWTW. The field used for agricultural purposes has good boundary vegetation which will assist in screening the extension. The process chosen may vary the visual impact to an extent as in some instances tanks will be raised out of the ground while in others they will be below ground level. Appropriate landscaping of the site where necessary should mitigate against any visual impacts. An effluent treated to a standard of 25/35 BOD/SS is required from each process. All processes are capable of achieving this standard and will therefore have equal environmental impact the receiving water. Preliminary Report May 2006 EPA Export :13:08:07

50 Jennings O'Donovan & Partners Consulting Engineers Sligo Land Area Required All four options require the existing site to be extended into the adjoining field, now purchased by Donegal County Council. Option B, RBC s and Reed Beds requires the largest area of land Capital Cost Table 5.1 sets out capital cost estimates for each treatment Option. Capital Costs are based on quotations received from various mechanical and electrical suppliers of treatment plants and estimates for civil works. A breakdown of each option is presented in Appendix E. All costs are exclusive of VAT. It can be seen from Table 5.1 Options A and C both extended aeration and secondary clarification have the lowest initial capital cost with Option A 10.3% lower than Option C. Option B and D rotating biological contactors and membrane bioreactors are 86% and 125% more expensive than Option C respectively. Treatment Treatment Total Costs Option Process Civil Costs M & E Costs A. B. C. D Extended Aeration of Secondary Clarifier (Separate tanks) Rotating Biological Contactors Extended Aeration & Secondary Clarifier (Concentric Tanks) Membrane Bioreactor 475, , , , , , ,100 1,160, ,150 1,224, ,600 1,480,100 Table 5.1 Summary of Capital Costs for Secondary Treatment Options Operational and Maintenance Costs All four options have varying degrees of operation and maintenance costs. These costs are outlined in Table 1.4 Appendix F and summarised below in Table 6.2. Preliminary Report May 2006 EPA Export :13:08:07

51 Jennings O'Donovan & Partners Consulting Engineers Sligo Option A Total Operational and Process Maintenance Costs Extended Aeration and Secondary Clarifier (separate tanks) 103,233 B Rotating Biological Contactors & Reed Beds 58,888 C Extended Aeration and Clarification (concentric tanks) 105,379 D Membrane Bioreactor treatment units 103,868 Table 5.2 Summary of Operation and Maintenance Costs for Each Treatment Option The estimated annual costs for secondary treatment range from approximately 59k to 105k. The RBC process which emerged as the most expensive capital cost has the lowest operation and maintenance costs. Essentially what distinguishes this process from the others is that it has significantly lower energy requirements than the other options considered. The Extended Aeration and process is energy intensive due to the blowers providing oxygen to the aeration tanks. 5.5 Discussion of Treatment Options Following on from the discussion above on various criteria and their applicability or relevance to each identified treatment option, a matrix giving a rating for each option under the specified headings is outlined below. In some instances the same rating for a specified criteria is given for each option, thus the specific treatment process is considered to have equal significance on the criteria in question. The scores are as follows. Option A Extended Aeration (Separate Tanks) Option B RBC Option C SBR (Extended Aeration Concentric Tanks) Option D Membrane Bioreactors Capital Cost Operational Costs Environmental Impact Land Area Treatment Efficiency Total Table 5.2 Scoring Matrix for Treatment Process Preliminary Report May 2006 EPA Export :13:08:07

52 Jennings O'Donovan & Partners Consulting Engineers Sligo From the above matrix it can be seen that Option A scores highest of the four options. However, there is very little between Option A and C. Both options are an extended aeration process and have emerged most favourable mainly due to lower initial capital costs. It should also be noted that costs included in this assessment are indicative budget costs and thus are used as guidelines to assess each option. Option A Extended Aeration and Secondary clarifier in separate tanks is recommended as the secondary treatment process at Convoy. This option also includes provision of an anoxic tank for denitrification and phosphate removal facilities as recommended in Section 3.3. Preliminary Report May 2006 EPA Export :13:08:07

53 Jennings O'Donovan & Partners Consulting Engineers Sligo 6.0 DESCRIPTION OF PROPOSED EXTENSION TO WASTE WATER TREATMENT WORKS 6.1 Secondary Treatment It is proposed to provide an anoxic tank, 2 No. aeration tanks, clarifier and a sludge draw-off and pumping chamber. Two precast concrete circular aeration tanks with separate circular pre-aeration/ anoxic tank are proposed. Two adjustable penstocks at the outlet of the anoxic tank to the aeration tanks shall be provided to control flow to one or both aeration tanks. A circular pre-cast clarifier is proposed with a tank scraper mechanism of the rotating half bridge type. Sludge will be drawn from the base of the clarifier to a new sludge draw-off and pumping chamber. Aeration will be carried out by a diffused aeration system using fine pore diffusers. These exhibit higher oxygen transfer efficiencies (OTE s) than surface aerators resulting in lower annual energy consumption. Typical oxygen transfer efficiencies for fine pore diffusers are kgo2/kw.hr compared to kgo2/kw.hr for surface aerators. The diffusers will be uniformly placed to distribute the air evenly at the base of the tank. Transfer efficiencies are also dependant on depth so a minimum tank depth of 4.0 meters is recommended. Design Calculations for the Secondary Treatment process are attached as Appendix F. 6.2 Sludge Draw Off and Pumping Chamber A new sludge draw-off and pumping chamber will be required to return the activated sludge to the anoxic zone or waste it to the existing sludge holding tank. The pumps from the existing sludge pumping station may be suitable for use in the new sludge pumping station. 6.3 Sludge Holding Tank The Donegal County Sludge Management Plan (Draft Revision 2) requires sludge storage at Convoy Waste Water Treatment Works. No thickening or dewatering facilities are required. Table 5.2, Appendix 5 (Transportation Plan Details) indicates that sludge will be collected at Convoy every four days and transported to Letterkenny for further treatment. Assuming 1.0kg sludge dry solids is produced per kg BOD removed for extended aeration sludge, 210 kg/d sludge Preliminary Report May 2006 EPA Export :13:08:07