Glennamaddy Sewerage Scheme Proposed Waste Water Treatment Design Standards and Disposal of Treated Effluent

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1 Consulting Engineers Fairgreen House, Block 10-4, Market Square, ul. Cystersów, CAB International, Fairgreen Road, Blanchardstown Corporate Park, Castlebar, Kraków, Nosworthy Way, Wallingford Galway, Ireland. Dublin 15, Ireland Co. Mayo, Ireland Poland Oxfordshire OX10 8DE, United Kingdom Tel: (0) Tel: (0) /6 Tel: +353 (0) Tel: Tel: Fax: (0) Fax: (0) /10 Fax: +353 (0) Fax: Fax: Our Ref: MMcD 4458/02/01 24 th October 2014 Irish Water, Colvill House, Talbot Street, Dublin 1. Att: Fiona Lane Sludge Strategy Specialist Re: Glennamaddy Sewerage Scheme Proposed Waste Water Treatment Design Standards and Disposal of Treated Effluent Dear Ms. Lane, I refer to our recent discussions with regard to the Glennamaddy Sewerage Scheme and in particular the application by Irish Water for a discharge licence for the existing wastewater treatment plant and options available with regard to the proposed waste water treatment infrastructure and disposal of the treated effluent. As you are aware the scheme is currently at design review stage where the following main details are being reviewed or undertaken: a. Location of proposed wastewater treatment facilities. b. Location of the proposed discharge point/receiving waters. c. Site Investigations which are now underway and include tests such hydraulic conductivity of the subsoil and physical characterisation of the soils encountered. d. Provision of Outline Designs, and e. Provision of Planning Permission for the proposed Works. While the site investigation commenced on site on Tuesday 21 st October 2014, work associated with the provision of outline designs and provision of planning permission are under review. As part of the current stage of the project we have been requested by Irish Water to provide an indication as to the most appropriate level of treatment and discharge location for the proposed treated effluent discharge. Directors: L.E. Waldron (Chairman) R.F. Tobin (Managing Director) M.F. Garrick B.J. Downes D. Grehan J.P. Kelly E. Connaughton (Company Secretary) M. McDonnell C. McGovern B. Mulligan Associate Directors : T. Cannon P. Cloonan D. Conneran B. Gallagher B. Heaney E. McPartlin A. O Brien S. Tinnelly Co. Reg. No Registered Office: Fairgreen House, Fairgreen Road, Galway. Ireland.

2 The updated design review of the Glenamaddy Sewerage Scheme is being undertaken on the following basis: a. The estimated load entering the existing waste water treatment plant is equivalent to 563persons (or 563p.e.) with a future design capacity of 583p.e. by the year 2020AD.This yields a Dry Weather Flow (DWF or Hydraulic Loading rate of approximately 105m 3 /day at 180l/hd/day and a Flow for Full Treatment of 3DWF or 315m 3 /day at 180l/hd/day. b. The discharge of the existing effluent to the Glenamaddy Turlough (csac) is no longer permitted under the Ground Water Regulations (S.I. 9 of 2010). c. The discharge of a proposed highly treated effluent to the Glenamaddy Turlough (csac) will not be permitted under the Ground Water Regulations (S.I. 9 of 2010). With specific reference to point c above, and in light of the draft document issued by the EPA in January 2014, titled Guidance on the Authorisation of Direct Discharges to Groundwater Draft for Consultation January 2014, the publication states that discharge of domestic type waste water to ground water: can only be considered if, in order of priority : a. Discharge options to surface water are precluded, b. Indirect discharges to ground water (via percolation) are precluded. The current review of the scheme is now considering the following two main scenarios for the treatment and disposal of waste water generated within the agglomeration of Glenamaddy. Treatment Scenario 1 a surface water discharge. This scenario assumes that the proposed treatment plant is to be located on a greenfield site outside the csac and outside the Glenamaddy village environs, pump the raw wastewater to the new location and discharge the treated effluent to a new surface water. The surface waters in the area include the Springfield River, the Shiven River and the Sinking River all located within a 4.75km to 10.5km range of Glenamaddy. These three options have been considered in light of the draft publication issued by the EPA in January 2014 ( Guidance on the Authorisation of Direct Discharges to Groundwater Draft for Consultation January 2014) where the discharge of domestic type waste water to ground water should only be considered where a surface water option or an indirect discharge option are precluded due to economic factors or are not technically feasible. The estimated capital cost (excluding operational costs) for the provision of the sewer upgrades, waste water treatment and discharge to surface water options range from approximately 2.56 to 3.40m. When this cost estimate is compared with the lower estimated capital cost of 1.64m for the use of an indirect discharge to ground, via a new percolation area, this surface water option is not considered to be economically viable. Treatment Scenario 2 an indirect discharge to ground water. On the basis that the discharge of treated effluent to a surface water, in the general geographical area of Glenamaddy, is not considered to be economically viable, the option of indirect ground water disposal has been considered. This scenario assumes that the proposed treatment plant is to be located on a greenfield site outside the csac, but within the Glenamaddy village environs, and pump the raw wastewater to the new location, treat to a high standard and discharge the treated effluent into a percolation area. The percolation area may be located on a site adjacent to the proposed new wastewater

3 treatment plant. The use of a percolation area, designed in accordance with the EPA s Code of Practice for Waste Water Treatment and Disposal Systems serving Single Houses may prove suitable if there is sufficient depth of suitable unsaturated subsoil. This option, provided the ground conditions are suitable, can be considered to be an indirect discharge to ground water and when subject to exemptions and defined inputs under Regulation 14 of S.I. 9 of 2010 may be the most feasible option available. The estimated capital cost (excluding operational costs) for the provision of the sewer upgrades, waste water treatment and percolation area is approximately 1.64m. The following Figure 1 illustrates the location of the proposed main pumping station, waste water treatment plant and the extent of lands for the percolation area (area highlighted = approx 5.0ha) which are being considered for the treatment and disposal of the effluent generated within the agglomeration of Glenamaddy. Figure 1 Proposed Location of Main Pumping Station, Waste Water Treatment Plant and Percolation Area The document Guidance on the Authorisation of Direct Discharges to Groundwater Draft for Consultation January 2014, noted at Section 4.2, that some of the minimum criteria that must be met before a verdict on potential exemption cases for the discharge of domestic type waste water effluents to ground water can be reviewed, are as follows: A Tier 3 technical assessment is required and based on the findings of this review this technical assessment has commenced and intrusive Site Investigations (Boreholes/Rotary Cores and Hydraulic Conductivity Assessments) are currently underway. The treated effluent has to meet high quality standards.

4 A full technical assessment must be prepared in a hydrogeological report and submitted to the relevant body for review. The technical assessment must examine cumulative impacts on ground water bodies. With reference to Treatment Scenario 2 and to the EPA s publication (dated 2011), Guidance on the Authorisation of Discharges to Groundwater, the discharge of domestic type waste water with a volume in excess of 20m 3 /day will require a Tier 3 Assessment and such assessments require infiltration capacity testing, subsoil characterisation and ground water characterisation. Such assessment are now underway and very early indications from the site investigation (4 No. boreholes undertaken on 21 st October 2014) is that the depth of subsoil in the lands highlighted in yellow in Figure 1 is of the order of 2.8 to 3.0m (shell and auger boreholes taken to 3.0m only) and that each of the boreholes undertaken have not encountered ground water indicating that there is available unsaturated subsoils. Further geotechnical investigations are underway over the course of the next seven to eight weeks to confirm the suitability of the proposed site and to also determine, at detailed design stage, the extent of imported material required to supplement the depth of existing subsoils. Turning to the disposal of a proposed treated effluent, via an indirect discharge to ground, the Ground Water Regulations (S.I. 9 of 2010), particularly Regulation 14 (b) states that: The Agency may, where it considers it appropriate or necessary, establish technical rules under which the following categories of pollutant inputs may be exempted from the provisions of this Act (b) inputs considered to be of a quantity and concentration so small as to obviate any present or future danger of deterioration in the quality of the receiving water. In order to ensure that the quantity and concentration of the treated effluent arising from the Glenamaddy Waste Water Treatment Plant is so small, that it obviates the present deterioration in the quality of the receiving water, a high standard of treatment will be required. Table 1 summarises the proposed final effluent standards for the new waste water treatment plant in Glenamaddy. These final effluent standards will be below the emission limit values specified in the Urban Wastewater Treatment Regulations. Table 1 Proposed Final Effluent Standards for Glenamaddy Wastewater Treatment Plant (Note these standards are to be applied upstream of the proposed percolation area) Parameter BOD Suspended Solids Ortho-phosphate (as P) Total Ammonia (as N) Total Nitrogen Pathogenic Reduction Discharge Standards 10 mg/l 10 mg/l 0.5 mg/l 1.0 mg/l 15 mg/l 3 Log Reduction

5 With regard to the planned disposal route, via an indirect discharge to ground water, we would propose to follow the Relevant Calculations contained in Appendix E of the EPA s publications Guidance on the Authorisation of Discharges to Groundwater and the Waste Water Treatment Systems Manual for Single Houses. The percolation area will be the subject of detailed design in accordance with these design guidelines and will be subject to the outputs from the current Site Investigations. The detailed design of the waste water treatment plant and percolation area will consider: a. Hydraulic Loading to the Ground Water from the treated effluent and natural recharge from rainfall, b. Infiltration capacity of the subsoils, c. Chemical Loading to Ground Water, and d. The Ground Water Protection Response Matrices. For the purposes of the requirements of the current discharge licence application, and on the assumption that a percolation area will not be required for treatment but used solely for disposal of a highly treated effluent and to act as a barrier between the source (treated effluent) and receptors (springs), it would be proposed that a Design Loading Rate of 40l/m 2 /day be applied in developing the detailed design of the system. The impact of utilising an indirect discharge to the ground water in the area has also been considered by way of a desktop review of the hydrogeology in the area. This desktop review shows that the area in general comprises a Regionally Important Karstified Aquifer dominated by conduit flow. The bed rock consists of karstified limestones overlain mainly by tills of varying thickness and permeability and there are a number of large springs, turloughs and swallow holes in the area. The national vulnerability ratings for the area of lands highlighted in Figure 1 ranges from Moderate to Low with the northerly most area of the lands listed as been of Low Vulnerability. Two source protection zones are located in the area namely; the Gortgarrow Spring and the Kilkerrin Public Water Supply Scheme. The proposed percolation area is not located within these source protection zones. The karstified features together with the zones of contribution of both the Lettera and Gortgarrow Springs are shown in Figure 2.

6 Bushtown Spring Lettera Spring Gortgarrow Spring Glenamaddy Turlough Figure 2 Main hydrogeological features: Glenamaddy turlough, Lettera, Gortgarrow and Bushtown springs, Tracer Data, ZOC for Gortgarrow, estimated ZOC for Lettera Glenamaddy Turlough into which the existing discharge directly flows has been traced to Lettera Spring, some 3.5km west (Drew, 1983) and tracers, used to define the underground flow paths, indicate that the flow patterns are predominantly east to west. The subsoils in the area consist of a complex arrangement of tills (blue and red), gravels (green) and peat (brown) shown in Figure 3. In the vicinity of Glenamaddy and the turlough the subsoil permeability patterns are variable predominantly low permeability around the turlough, and east and northeast of the town, but moderate permeability tills to the west of the turlough and north of Glenamaddy.

7 Figure 3 Mapped subsoils with tracer lines and karst features (Teagasc, GSI) The Groundwater body status in the area is poor whereby the contribution of nutrients, to a less than good status river, via groundwater causes the surface water to fail its water quality objectives. The particular nutrient that places many of the WRBD Karst groundwater bodies into the poor status is phosphate. Glenamaddy Chemistry data is available from both Galway County Council and EPA for two karst springs in the area namely, Gortgarrow and Bushtown, and there is no data currently available for the Lettera Spring. A review of available chemistry data at the Gortgarrow spring shows that the average concentration of molybdate reactive Phosphorus (MRP) at this location is 0.035mg/l (based solely on the Galway Co Co dataset) and 0.027mg/l (based solely on the EPA dataset). It is not clear to why there is a variance between these data sets and further sampling is currently underway as part of the site investigation contract to verify the background concentrations of nutrients in the local surface waters and ground water springs. Recent monitoring put in place in 2007 by the EPA indicates that the average value of MRP in the period 2007 to 2011, when the earlier 2002 to 2004 EPA data is not considered, is of the order of mg/l and this data is presented in Figure 4.

8 Figure 4 Graph for Gortgarrow (MRP, mg/l P) A review of available chemistry data at the Bushtown spring shows that the average MRP at this location is 0.038mg/l (Galway Co Co dataset). There is no EPA monitoring data available. The available data for the Bushtown spring would indicate that there is no available assimilative capacity for phosphorus, in the ground water, when compared with the threshold value of 0.035mg/l detailed in Schedule 5 of S.I. No. 9 of A review of available chemistry data at the Gortgarrow and Bushtown springs shows that Nitrates concentration of 10mg/l at the Gortgarrow spring are not of concern when compared with the threshold value of 37.5mg/l detailed in Schedule 5 of S.I. No. 9 of Further examination of the chemical characteristics of the ground water will be required to determine if assimilative capacity exists in the ground water. Further sampling is currently underway as part of the site investigation contract to verify the background concentrations of nutrients in the local surface waters and ground water springs. Pathogens, are present in samples taken at both the Gortgarrow and Bushtown springs and there are persistent exceedances of faecal and total coliforms, and occasionally faecal coliform counts exceed 100/100ml. This data indicates that there is faecal contamination of the groundwater. Further sampling is currently underway as part of the site investigation contract to verify the background concentrations of pathogens in the local surface waters and ground water springs.

9 As discussed earlier in this report the next stages in the development of the Glennamaddy Sewerage Scheme include: 1. Site Investigations, which are now underway and include tests such hydraulic conductivity of the subsoil and physical characterisation of the soils encountered, will be used to inform the ground water risk assessment as to the potential effectiveness of the percolation area as a barrier between the source (effluent) and the receptors (springs). 2. Provision of Outline Designs, and 3. Provision of Planning Permission for the proposed Works. However, at the current design review stage of the project and assuming that the site conditions are suitable, it can be concluded on a preliminary basis that by: a. treating the waste water from the Glenamaddy Agglomeration to the proposed high standards, and b. discharging the treated effluent to ground via a percolation area with suitable depths of unsaturated subsoils, the development of the proposed WWTW upgrade works can meet the requirements set out in the EPA s Guidelines Guidance on the Authorisation of Discharges to Groundwater and achieve compliance with the Ground Water Regulations (S.I. No. 9 of 2010) and ultimately decommission the existing direct discharge to the Glenammaddy Turlough and local ground water bodies. Yours faithfully, Michael McDonnell Operations Director Water Services Tobin Consulting Engineers