SECTION F – EXISTING ENVIRONMENT & IMPACT OFTHE DISCHARGE(S)

Attachment F1: Assessment of Impact on Receiving Surface or Ground Water

Attachment F.1(ii): Tier 3 Groundwater Risk Assessment

10001648 Glenamaddy Sewerage

Glenamaddy Sewerage Scheme

Tier 3 Groundwater Risk Assessment

10001648 Glenamaddy Sewerage

DOCUMENT AMENDMENT RECORD

Client: Irish Water

Project: Glenamaddy Sewerage Scheme

Title: Glenamaddy Sewerage Scheme – Tier 3 Groundwater Risk Assessment

PROJECT NUMBER: 4458 DOCUMENT REF: 4458-TR11-Glenammaddy

Sewerage Scheme Tier 3 Assessment

B For Issue

Coran Kelly PGeo IGI

Registration Number 177

MSc Groundwater

Engineering

08/0

1/2

016

Malcolm Doak PGeo

IGI Registration

Number 074 MSc

Hydrogeology

08/01/

2016

MMcD

04/0

2/1

6

Revision Description Originated Date Checked Date Authorised Date

TOBIN Consulting Engineers

4458 Glenamaddy Groundwater Tier 3 Risk Assessment

Table of Contents

1 INTRODUCTION ................................................................................... 1

2 METHODOLOGY .................................................................................. 4

3 TOPOGRAPHY, SURFACE HYDROLOGY AND LANDUSE ............... 7

4 HYDROMETEOROLOGY ................................................................... 14

5 GEOLOGY .......................................................................................... 15

5.1 INTRODUCTION .............................................................................................. 15

5.2 BEDROCK GEOLOGY ..................................................................................... 15

5.3 SOILS AND SUBSOILS .................................................................................... 17

5.4 DEPTH TO BEDROCK ..................................................................................... 20

6 GROUNDWATER VULNERABILITY .................................................. 23

HYDROGEOLOGY ................................................................................... 25

6.1 INTRODUCTION .............................................................................................. 25

6.2 GROUNDWATER BODY AND STATUS .......................................................... 25

6.3 REGIONAL GROUNDWATER FLOW DIRECTIONS AND GRADIENTS AND

AQUIFER CHARACTERISTICS ................................................................................ 25

6.4 LOCAL GROUNDWATER FLOW DIRECTIONS .............................................. 27

6.5 HYDROCHEMISTRY AND WATER QUALITY ................................................. 31

6.6 GROUNDWATER MOUNDING ........................................................................ 35

6.7 HYDROGEOLOGICAL CONCEPTUAL MODEL .............................................. 35

6.8 LETTERA SPRING CATCHMENT ................................................................... 37

6.9 WATER BALANCE ESTIMATIONS .................................................................. 38

7 RISK ASSESSMENT .......................................................................... 39

7.1 POLLUTANT (CHEMICAL AND HYDRAULIC LOAD) ...................................... 39

7.2 CONSIDERATION OF DISCHARGE OPTIONS ............................................... 40

7.3 ASSIMILATIVE CAPACITY .............................................................................. 41

8 SUMMARY AND CONCLUSIONS ...................................................... 45

9 REFERENCES .................................................................................... 46

APPENDIX A – MAIN SITE INVESTIGATION REPORT .......................... 47

APPENDIX B –DR. MEEHANS INVESTIGATIONS ................................. 48

List of Tables

Table 1 Proposed Design Requirements for Glenamaddy Waste Water Treatment Plant .......................... 1

Table 2 Average Final Effluent Quality at Glenamaddy Waste Water Treatment Plant ............................... 3

Table 3 Summary information of the bedrock encountered (full details in Appendix A) ............................. 16

Table 4 Summary profile of soil and subsoil investigated site .................................................................... 18

Table 5 Water level data for site investigated ............................................................................................. 28

Table 6 Bacteria counts per 100 ml for sampling sites ............................................................................... 31

Table 7 Ammonium concentrations for sampling sites ............................................................................... 32

Table 8 Effluent Quality ............................................................................................................................... 39

Table 9 Design Effluent Standard ............................................................................................................... 39

Table 10 Design Loading ............................................................................................................................ 40

Table 11 Assimilative capacity phosphate (mg/l as P) in the Turlough ...................................................... 43

Table 12 Assimilative capacity phosphate (mg/l as P) in the groundwater body when the turlough is dry 43

Table 13 Assimilative capacity Ammonia (mg/l as N) in the turlough ......................................................... 44

Table 14 Assimilative capacity ammonium (mg/l as N) in the groundwater body when the turlough is dry44

List of Figures

Figure 1 Location of waste water treatment plant, main swallow holes (St. Josephs, Pollanargid and

Pollnadeirce), location of main site investigation, Glenamaddy, Glenamaddy Turlough, on aerial

photography .................................................................................................................................................. 2

Figure 2 Proposed Location of the main site investigated ....................................................................... 6

Figure 3 Main hydrogeological features including Lettera spring (headwaters for the Sinking River),

Gortgarrow Spring and proven trace connections ........................................................................................ 7

Figure 4 OSI mapping showing the locations of Pollanargid and Pollnadeirce Swallow holes in

Glenamaddy Turlough and St Joseph’s Swallow Hole located adjacent to St. Josephs school .................. 8

Figure 5 Extract from floodmaps.ie ............................................................................................................... 9

Figure 6 Preliminary Flood Risk Assessment Maps for Glenamaddy Area ........................................... 10

Figure 7 Sinking stream at St. Josephs and where it is known to back up ............................................ 11

Figure 8 Mapped Geology and Aquifer classification ............................................................................. 16

Figure 9 Mapped soils with proven tracer lines and karst features (Teagasc, GSI) .............................. 17

Figure 10 Mapped subsoils with tracer lines and karst features (Teagasc, GSI) ................................. 18

Figure 11 Clay percentages for samples taken across the site ........................................................... 20

Figure 12 Bulk Texture for the subsoils (BS5930) ................................................................................ 20

Figure 13 Depth to bedrock and location of cross section profile ........................................................ 21

Figure 14 Cross Section A-B ................................................................................................................ 22

Figure 15 Mapped groundwater vulnerability; karst features; proven underground connections ........ 24

Figure 16 Groundwater wells and springs (GSI database) .................................................................. 26

Figure 17 Bedrock Aquifer and Groundwater Bodies ........................................................................... 27

Figure 18 Chart of water levels on the site ........................................................................................... 28

Figure 19 Water levels (mOD) (January 2014) plotted to indicate northerly groundwater flow

component toward the main stream at the northern margin of the site ...................................................... 29

Figure 20 Water levels (mOD) (Dec 2016) plotted to indicate northerly groundwater flow component

toward the main stream at the northern margin of the site just using piezometers intersecting the bedrock

30

Figure 21 Water sample locations ........................................................................................................ 33

Figure 22 Chart of bacteria counts from field data collected for this study (Appendix A) .................... 34

Figure 23 Chart of mean ammonium concentrations from field data collected for this study (Appendix

A) 34

Figure 24 Chart of mean phosphate concentrations from field data collected for this study (Appendix

A) 35

Figure 25 Zone of contribution to Lettera ............................................................................................. 38

1

1 INTRODUCTION

This report outlines the principal hydrogeological characteristics of the area and describes the results of site

investigations and suitability assessments that were undertaken as part of this study which all form the basis

of this hydrogeological risk assessment. The report concludes on the suitability of the region for

groundwater discharges and investigates in some detail whether the subsoils in the area are suitable for an

indirect discharge and also assesses what impacts a direct discharge may have on groundwater in the

region.

This Tier 3 assessment considers the options associated with both direct and indirect discharges to

groundwater in the Glenamaddy region.

This hydrogeological “Tier 3” technical risk assessment has been prepared in accordance with the “Source-

Pathway Receptor” model for environmental management and follows the EPA’s prescribed guidance

documents:

Guidance on the Authorisation of Discharges to Groundwater (EPA, 2011); and,

Proposed Guidance on the Authorisation of Direct Discharges to Groundwater (EPA, 2014).

Irish Water are proposing to upgrade the existing sewerage scheme and replace the existing plant with new

infrastructure that will treat the waste water to a much higher standard. The proposed design requirements

and standards that will be applied are detailed in Table 1.

Table 1 Proposed Design Requirements for Glenamaddy Waste Water Treatment Plant

Design Parameter Value

Design Population 700p.e.

Design Load 42kg/d

Hydraulic Load

(Dry Weather Flow) 126m

3/day

Hydraulic Load

(3 DWF Peak Flow) 378m

3/day

Peak Storm Water Flow to Pumping Station

95.4m3/hr recorded during flow monitoring of

the existing sewerage scheme

4 hours storage to be provided at new WWTW 380m

3

Design Parameter Discharge Standards

BOD 10 mg/l

Suspended Solids 10 mg/l

Ortho-phosphate (as P) 0.5 mg/l

Total Ammonia (as N) 1.0 mg/l

Pathogen Reduction 3 Log Reduction

A number of options for the disposal of treated effluent have been assessed as part of the planning stages of

the proposed scheme. The options considered include a number of surface water discharges and both

direct and indirect groundwater discharges.

2

The objective of the report is to outline the risk to groundwater from an improved treated waste water

discharged directly into groundwater. A conceptual site model has been prepared using the investigations

and data from groundwater and surface water sampling.

The existing waste water treatment plant, serving Glenamaddy Town, is currently operating above its design

capacity and elements of the existing sewer network require upgrading to cater for the future needs of the

town. The existing sewerage infrastructure, which has been in place since circa 1950, consists of combined

sewers which discharge, by gravity, to a waste water treatment plant with two distinct processes, namely;

a) An inlet screening chamber where coarse bar screens remove gross solids and floating debris.

b) An Imhoff Settlement tank which was designed to cater for a population equivalent less than 300.

This tank when working within its design parameters should retain the influent for a certain period of

time allowing gross solids to settle and form a sludge which can be periodically removed for

dewatering and disposal.

Partially treated effluent from the existing waste water treatment plant discharges to the Pollnadeirce swallow

hole which forms part of the Glennamaddy Turlough (Figure 1), a Special Area of Conservation (SAC).

Figure 1 Location of waste water treatment plant, main swallow holes (St. Josephs, Pollanargid

and Pollnadeirce), location of main site investigation, Glenamaddy, Glenamaddy Turlough, on aerial

photography

3

The average quality of effluent (September 2004 to March 2015) from the existing Glenamaddy Waste Water

Treatment Plant is detailed in Table 2.

Table 2 Average Final Effluent Quality at Glenamaddy Waste Water Treatment Plant

BOD

mg/l

Suspended Solids

mg/l

Ortho Phosphate

as P (mg/l)

136 138 6.4

Surface and groundwater quality monitoring in the area shows that the existing discharge is having an

impact on the groundwater in the region. This discharge does not currently meet the requirements of the

European Communities Environmental Objectives (Groundwater) Regulations (S.I. No. 9 of 2010).

The surface water options, considered for the disposal of treated effluent, assumed that the proposed waste

water treatment plant would be located on a greenfield site outside the SAC and that all waste water would

be pumped to this new location for treatment and that the treated effluent would then be pumped to the

surface water. The surface water courses in the area include the Springfield River, the Shiven River and the

Sinking River, located approximately 5 km to 10 km of Glenamaddy. These three options were considered in

light of the publication issued by the EPA “Guidance on the Authorisation of Direct Discharges to

Groundwater” where the discharge of domestic type waste water to groundwater should only be considered

if […] discharge options to surface water are precluded due to economic factors or are not

technically feasible, or are disproportionately expensive.

The surface water options, considered for the disposal of treated effluent, were not considered to be viable

on the basis that each of the three rivers in question does not have an assimilative capacity for nutrients

such as phosphorus and on the basis that excessive pumping (of up to 10.5 km) would be required for the

relatively small agglomeration of 700 population equivalent.

The option of indirect groundwater disposal was also considered during the planning stages of the project.

This scenario also assumed that the proposed waste water treatment plant would be located on a greenfield

site outside the SAC and following treatment to a high standard the treated effluent would be discharged

indirectly to ground via a new percolation area (gravity based, pressurised pumped system or integrated

constructed wetland) (Figure 1). This option, provided the ground conditions are suitable, is an indirect

discharge to groundwater and when subject to exemptions and defined inputs would comply with Regulation

14 of S.I. No. 9 of 2010.

The option of direct groundwater disposal was also considered during the planning stages of the project.

This scenario also assumed that the proposed waste water treatment plant would be located on a greenfield

site outside the SAC but following treatment to a high standard the treated effluent would be discharged

directly to ground via the existing outfall at Pollnadeirce swallow hole within Glenamaddy Turlough or at “St

Joseph’s” swallow hole to the north of the town. This option, if progressed, will require prior authorisation

“provided such discharges, and the conditions imposed, do not compromise the achievement of the

environmental objectives for the body of groundwater into which the discharge is made” Regulation 8 (b) of

S.I. No. 9 of 2010.

The Guidance on the Authorisation of Discharges to Groundwater (EPA, 2011) specifies that Tier 3

assessments must be carried out by a suitably qualified person. This hydrogeological “Tier 3” technical risk

assessment has been prepared by Coran Kelly, a professional hydrogeologist, and is registered as such with

the Institute of Geologists of Ireland. The site investigated as part of this study included investigations both

by Coran Kelly and Dr. Robert Meehan, a professional geologist and an expert specifically in subsoils and

waste water discharge to soils.

4

2 METHODOLOGY

The methodology comprised an iterative approach by advancing the historical, current and new knowledge

and information through desk studies, site visits, site investigation and field mapping. Analysis of the

information collected during the studies was used to inform the risk assessment.

A relatively large greenfield site, hereafter referred to as ‘the site’, was investigated in the environs of

Glenamaddy village to determine if a better, suitable and more sustainable solution could be found for the

disposal of the treated waste water, in lieu of the existing direct discharge (Figure 1, Figure 2).

Following a desktop review of the geological conditions it was initially determined that the best possible sites,

for an indirect discharge, would be located to the north of the town.

Figure 2 illustrates the location of the proposed main pumping station, waste water treatment plant and the

extent of lands considered for the proposed percolation area (area outlined in red = approximately 5.0 ha)

which was considered for the treatment and disposal of the effluent generated within the agglomeration of

Glenamaddy.

Site investigation works were conducted between October 2014 and December 2015. The site investigation

works can be summarised as follows:

Intrusive site works which included excavated trial pits and boreholes.

Soil and subsoil and bedrock in-situ and laboratory tests.

Particle size analyses.

In-situ hydraulic testing (in-situ permeability tests, percolation tests).

Water sampling of surface waters and springs in the area.

Water level monitoring within the proposed site.

Field walkovers, hand augering and hydrogeological mapping.

The site investigation was iterative and comprised three main phases:

Phase 1. A comprehensive site investigation carried out by Priority Geotechnical Limited to

investigate the characteristics of the soils, subsoils, depth to bedrock and bedrock and water quality

and water levels in the area around Glenamaddy with a particular focus in a proposed site. The full

geographical extent of the investigation is shown in Appendix A (Drawing number P14100-SI-A)

whilst Figure 2 shows the main site investigated. The geological and hydrogeological details are

reported in Sections 5, 6 and 7. The works included:

o 17 No. trial pits (depth range generally 1.5 m - 2 m).

o 41 Cable percussion boreholes (depth range of 1 m – 3 m).

o 17 Rotary core boreholes (depth range of 4 m – 16 m).

o Installation of 9 No. piezometers on the main site investigated.

o 15 Slit trenches (depth range of 1.2 m – 1.5 m).

o Water sampling (level in piezometers, quality from surface water and springs across

the region (Figure 21).

o In-situ permeability tests.

o Particle size analyses (including hydrometer tests for clay percentage) and standard

geotechnical laboratory tests.

Phase 2. Consideration of the data from phase 1 required investigation of the percolation capacity of

the soils and subsoils.

5

o Percolation tests in the proposed site by a FETAC approved site assessor (Figure 2

and Appendix A). Sites chosen and depths for testing specified by Coran Kelly.

o Hand augering and walkovers by Coran Kelly and Dr. Robert Meehan.

Phase 3. Investigation of the characteristics of the deeper subsoil in the proposed site and the

potential for permeability differences within these layers which was completed by Priority

Geotechnical and supervised by Dr. Robert Meehan (a subsoils geologist) and Coran Kelly from

TOBIN Consulting Engineers. Full details are reported in Appendix B.

o 12 No. 3 m deep strategically located trial pits (Figure 2).

o Particle size analyses.

The results of these site investigations are contained in Appendix A (Priority Geotechnical Report), and

Appendix B which comprises the report and detailed logs by Dr. Robert Meehan and staff from TOBIN

Consulting Engineers.

Site walkovers and site visits were also carried out to record the water levels in the piezometers and to

record stream levels and swallow holes and surface water ponding during December 2015 to examine the

effect of the early winters storms on the area and on the site investigated.

The bulk lump sum costs of the site investigation amount to over €105,000.

6

Figure 2 Proposed Location of the main site investigated

7

3 TOPOGRAPHY, SURFACE HYDROLOGY AND LANDUSE

Glenamaddy village is located 0.5 km west of the turlough and extends along the two main roads that pass

the turlough to the north and west (Figure 1). The villages waste water and surface water runoff is collected

and conveyed to the waste water treatment site adjacent to the turlough (Figure 1). The partially treated

waste water is channelled by pipe into the main swallow hole. The fields around the village comprise both

grassland and some tillage. East and south of the turlough the land consists mainly of raised bog and

cutover bog, and there are also a few forestry stands.

The Glenamaddy area is located in Hydrometric area 30 of the Western River Basin District, in the

catchment of the Sinking River which is a tributary of the Clare River that flows into Lough Corrib.

Glenamaddy is located in a relatively subdued low-lying landscape that generally slopes westwards; from

approximately 100 mOD to 70 mOD as shown in Figure 3. At a localised scale there are small ridges, hills

and rises.

Figure 3 Main hydrogeological features including Lettera spring (headwaters for the Sinking

River), Gortgarrow Spring and proven trace connections

8

Figure 4 OSI mapping showing the locations of Pollanargid and Pollnadeirce Swallow holes in

Glenamaddy Turlough and St Joseph’s Swallow Hole located adjacent to St. Josephs school

Glenamaddy Turlough is located to the east of the village, where ground levels are of the order of 75 to

78 mOD (Malin Head) (Figure 1, Figure 3, Figure 4). Lands to the south of the groundwater body slope in a

northerly direction towards the turlough. The lands to the south of the turlough are drained by three streams

that feed into the turlough from the southeast and east. The land in the southern parts of the town slopes

inwards toward the turlough in a southerly direction and are bounded on the north side by a low amplitude

ridge which is oriented northeast to southwest and rises to approximately 80 to 90 mOD. North of this ridge

there is a small unnamed stream that sinks on the northern side of the village adjacent to the R364 (Figure

1, Figure 3, Figure 4).

Glenamaddy Turlough itself is a large deep turlough that according to Goodwillie (1992) has a short season

where it is uncovered. It occupies over 175 hectares and has a topographic catchment of over 1300

hectares. The three streams that feed the turlough originate in raised bog to the east and southeast, with

one of the streams flowing from Lurgeen Lough (Figure 3). In the northwestern part of the turlough there are

distinct swallow holes known as Pollandeirce and Pollanargid (Figure 3). There is no surface drainage from

the turlough and it is known that the turlough is linked to Lettera spring located 3.5 km west ((Drew, 1973;

Drew and Daly, 1993). The sinking stream on the northeastern part of the village is also linked to Lettera.

Killtullagh Lough is another prominent surface water body, located approximately 1.5 km southwest of

Glenamaddy Turlough (Figure 3). Kiltullagh Lough also drains underground and has been linked to

Gortgarrow Spring that is located approximately 3 km west of Kiltullagh Lough and which forms the

Dunmore–Glenamaddy Public Water Supply Scheme (Meehan, et al, 2010).

9

Known turloughs, swallow holes, sinking streams, enclosed depressions and springs are recorded karst

features (Figure 3). Generally, there are relatively few enclosed depressions mapped. Only one possible

enclosed depression was observed during the field mapping, located just east of Trial Pit 11 (Photograph 1).

The site investigation indicates that the depth to bedrock at this location is approximately 10 m.

Photograph 1. Enclosed depression (December 2015)

Glenamaddy has experienced a number of flooding events which have been recorded over the course of the

last twenty to thirty years. A review of mapping contained on the website, www.floods.ie, has identified three

flood occurrences in the area including pluvial flooding which results from high water levels in the

Glenamaddy Turlough (Figure 5).

Figure 5 Extract from floodmaps.ie

Glenamaddy

Turlough

10

A review of the draft Preliminary Flood Risk Assessment (PFRA) map of the area, as published by the OPW,

highlights an area of land which is at risk from pluvial flooding (Figure 6).

Figure 6 Preliminary Flood Risk Assessment Maps for Glenamaddy Area

The small stream channel sinking to the northeast of the village at St. Joseph’s has undergone arterial

drainage and the historical OSI topographic maps indicate portions of the area have flooded in the past

(Figure 7). Site visits during December 2015 indicate the degree to which the stream backs up from the

swallow hole (Photograph 2 and 3). The area of flooding corresponds to historical flooding on OSI

topographic maps, known as Mill Lough. Deep drains bound fields that make up ‘the site’, conveying water

to the sinking stream.

Surface water ponding was evident across the fields of the investigated during site walkovers in December

2015 (Photographs 5 and 6).

Glenamaddy Turlough

11

Figure 7 Sinking stream at St. Josephs and where it is known to back up

12

Photograph 2. St Josephs swallow hole, backing up under flood conditions (December 2015)

Photograph 3. The stream sinking at St Josephs swallow hole, under flood conditions (December

2015). Taken at the northeast corner of the investigated site. The area of flooding corresponds to

historical flooding on OSI topographic maps, known as Mill Lough

13

Photograph 4. The sinking stream at the northern margin of the site (December 2015)

Photograph 5. Surface ponding on the site (December 2015)

14

Photograph 6. Surface ponding on the site (December 2015)

4 HYDROMETEOROLOGY

Establishing groundwater source protection zones requires an understanding of general hydrometeorological

patterns across the area of interest. The information presented below was obtained from Met Éireann.

Annual Average Rainfall: 1200 mm. The contoured map of rainfall data in Ireland (Met Éireann

website, data averaged from 1981-2010) shows that the source is located between the 1200 mm

and the 1600 mm average annual rainfall isohyets. The closest meteorological (rainfall) station is at

Glenamaddy (Gortnagier), with a 30-year (1961-1990) average annual rainfall of 1,057 mm.

Annual evapotranspiration losses: 475 mm. Potential evapotranspiration (P.E.) is estimated to be

475 mm/yr (based on data from Met Éireann).

Actual evapotranspiration (A.E.): 450 mm, estimated as 95% of P.E., to allow for seasonal soil

moisture deficits.

Annual Average Effective Rainfall: 750 mm. The annual average effective rainfall is calculated by

subtracting actual evapotranspiration (450 mm) from rainfall (1200 mm).

15

5 GEOLOGY

5.1 Introduction

This section briefly describes the relevant characteristics of the geological materials that underlie the

Glenamaddy area. It provides a framework for the assessment of groundwater flow and the risk

assessment. The geological information is based on a desk based study of the available information, which

comprised the following:

Geology of South Mayo. Bedrock Geology 1:100,000 Map series, Sheet 11, Geological Survey of

Ireland (McConnell et al, 2002);

Geology of Longford-Roscommon. Bedrock Geology 1:100,000 Map series, Sheet 12, Geological

Survey of Ireland (Morris et al, 2003);

The Groundwater Vulnerability Map of County Galway (Geological Survey of Ireland webmapping);

Dunmore – Gortgarrow Groundwater Source Protection Zones, Geological Survey of Ireland

(Meehan, et al, 2010).

Daly, 1985. A Report on the Flooding in the Glenamaddy Area (GSI, 1995)

As well as this, geological information was obtained from the site investigation works conducted in the

Glenamaddy area for this project. The details of the site investigation are provided in Appendix A and B.

5.2 Bedrock Geology

Undifferentiated Visean limestones (Dinantian Pure Bedded Limestones) dominate the bedrock in the region

(McConnell, et al., 2002; Morris, et al., 2003) and is generally described as pale grey, clean, medium to

coarse grained, and bedded. Immediately north of Glenamaddy village there is a relatively small isolated

block of Lower Impure Limestones (Ballysteen Limestone) mapped, which is generally considered to be a

dark impure limestone with varying amounts of shale (Figure 8).

Bedrock drilling was conducted by the Geological Survey of Ireland as part of the investigation into the

flooding in the area (Daly, 1995) and fossiliferous, slightly clayey limestones are recorded with a varying

degree of weathering and fracturing present.

There are very few bedrock exposures in the area due to extensive thick subsoil. At a regional scale there

are faults mapped which tend to be orientated northeast-southwest. There are no faults mapped in the

bedrock in vicinity of Glenamaddy.

The current site investigation included investigation of the bedrock in the vicinity of Glenamaddy (Figure 1,

Figure 2). Appendix A includes the logs of the rotary core boreholes. In summary, the bedrock is recorded

as fractured and weathered dark grey limestone with fossils, and styolites also recorded in some of the logs.

The bedrock portion of the logs are summarised in Table 3.

16

Figure 8 Mapped Geology and Aquifer classification

Table 3 Summary information of the bedrock encountered (full details in Appendix A)

Number Summary Description

RC01 2.6-4m

Lithology: Moderately strong, dark grey LIMESTONE. Weathering: Slightly weathered with minor clay infill. Fractures: Sub horizontal with undulating smooth fracture surfaces and close spacing.

RC09 6-8m

Lithology: Moderately strong, dark grey argillaceous LIMESTONE. Weathering: Slightly weathered with minor clay infill. Fractures: 2 sets. horizontal and vertical with undulating smooth fracture surfaces.

RC10 4-8m

Lithology: Moderately strong, dark grey LIMESTONE. Weathering: Slightly weathered with minor clay infill. Fractures: 2 sets. Horizontal with undulating smooth fracture surfaces and sub-vertical with undulating rough fracture surfaces.

RC14 3.7-5m

(from 3m to 3.7, it is possible that it is transition zone – broken rock zone) Lithology: Moderately strong, dark grey, LIMESTONE with minor styolite veins. Weathering: Slightly weathered with brown staining and minor clay infill. Fractures: Sub horizontal with planar smooth fracture surfaces.

RC15 2.3-5m

(from 1.3m to 2.3, it is possible that it is transition zone – broken rock zone) Lithology: Moderately strong, dark grey fossiliferous LIMESTONE with minor calcite veining. Weathering: Slightly weathered with minor brown staining and minor clay infill. Fractures: Sub horizontal with undulating smooth fracture surfaces.

RC16 3.8-9.8m

(possible broken rock zone 3.4-3.8m) Lithology: Moderately strong, dark grey LIMESTONE. Weathering: Slightly weathered with minor brown staining and minor clay infill. Fractures: Sub horizontal with undulating rough fracture surfaces.

RC01A 14-16m

Lithology: Moderately strong, dark grey, fossiliferous LIMESTONE. Weathering: slightly weathered with rare brown staining. Fracture sets: 1) dipping 45 degrees with undulated, smooth surfaces; 2) dipping horizontally with undulated, smooth surfaces.

17

5.3 Soils and subsoils

The soils have been mapped by the EPA and Teagasc and comprise a complex arrangement of ‘wet’ and

‘dry’ soils and cutover peat (Figure 9).

Figure 9 Mapped soils with proven tracer lines and karst features (Teagasc, GSI)

Cutover peat and deep poorly drained mineralised peaty soils bound Glenamaddy turlough. West of the

turlough and in the immediate vicinity of the village, the soils are predominantly deep well drained mineral

soils. East of the village and north of the turlough the soils are predominantly poorly drained mineral soils

and peaty soils. A small strip of alluvium is mapped along the stream that sinks to the north of the village,

which further east sees cutover peat where the stream originates. The strip of alluvium is shown to cross the

road but there is no actual extension of the stream or drainage across the road (Figure 9).

The subsoils consist of a complex arrangement of tills, gravels and peat as shown in Figure 10. In the

immediate vicinity of the village the subsoils are dominated by till derived from limestone with cutover peat

around the turlough itself and peat to the north of the ridge east of the village.

Lake clays, thin shelly marls and silts make up the sediments flooring the turlough, and sand and gravel is

also reportedly present intermixed with the tills beneath the peat east of the turlough at Lurgeen Lough (Daly,

1985).

Till is sediment deposited by or from glacier ice. The former term ‘glacial drift’ referred to the coarsely

graded and extremely heterogeneous sediment of a glacier; till is the part of glacial drift deposited directly by

the glacier, and the terms has now superseded ‘drift’ as the descriptive term for glacial deposits. Its content

may vary from clays to mixtures of clay, sand, gravel, and boulders. This material is mostly derived from the

subglacial erosion and entrainment by the moving ice of the glaciers of previously available unconsolidated

18

sediments. Bedrock can also be eroded through the action of glacial plucking and abrasion and the resulting

clasts of various sizes will be incorporated to the glacier's bed.

Figure 10 Mapped subsoils with tracer lines and karst features (Teagasc, GSI)

In the vicinity of Glenamaddy and the turlough the regional subsoil permeability patterns are variable;

predominantly ‘low’ around the turlough, and east and northeast of the town, whilst there is also ‘moderate’

permeability till mapped west of the turlough and north of the Glenamaddy (www.gsi.ie). There are also

glaciofluvial sands and gravels and an esker mapped further west of the turlough and Glenamaddy Village.

During the current site investigation the soils and subsoils were examined through intrusive site works and

laboratory tests. The locations of the site investigations are shown in Figure 1 and Figure 2. Full details of

the site investigation are included in Appendices A and B.

The main site investigated is on the northern slope of the ridge located around Mountkelly north of the

turlough. A representative vertical profile is provided in Table 4 and seen in Photograph 7.

Table 4 Summary profile of soil and subsoil investigated site

Layer Depth m Texture BS5930 Density/Colour

Soil 0.2-0.65 (mean depth 0.4) Sandy to sandy clay

loam Soft, crumb, dark brown

Subsoil Unit 1 0.2/0.5-1.4/2.4 SILT/CLAY

Soft to firm, massive, extensively

mottled dark yellowish brown to

greenish grey

Subsoil Unit 2 1.4/2.4-+3.1 SILT/CLAY Stiff to hard, massive, fissile. Mottled

along fissile partings.

19

The soil is consistent across the site and is recorded as a very dark brown to black, sandy loam to sandy

clay loam texturally, with a mean depth of 0.4 m (Appendix B). The soils are classed in terms of soil types as

generally either an acid brown earth or a brown podzolic; both of which are well drained soils (Photograph 3).

Photograph 7 Typical profile, free draining soil over low permeabilty subsoil (typically a mottled yellowish brown to grey over a very dark grey unit)

The following extract from Appendix B describes the subsoils units: “Within the trial pits, several subsoil units

were encountered in each pit. The major subsoil layer extends from approx. 0.2m/0.5m to approx.

1.4m/2.4m depth, and is a soft to stiff, massive (yet fissile), sandy SILT/CLAY with occasional to abundant

gravels (as per BS5930, 1999), and with occasional cobbles and boulders. The layer is a mottled dark

yellowish brown to grey to greenish grey in colour. From this, the unit seems to be saturated through the

winter months.

This unit is underlain throughout the site by a gravelly sandy SILT/CLAY layer, between approx. 1.4m/2.4m

and 3.1m+ depth. This is very stiff to hard and massive, yet fissile. The unit has mottling throughout its

profile along the fissile parting structures within the unit; therefore, within individual subsoil localities portions

of unmottled material occurs. This unit therefore retards infiltration somewhat across the site, and much of

the mottling in the upper subsoil unit (and associated saturation therein) may be owing to the texture,

structure and bulk density of this lower subsoil material. ” (Meehan, 2015, Appendix B).

Samples were taken from the subsoil units for testing in the laboratory to include particle size analyses. The

particle size analyses and the BS5930 textures recorded by Tobin Engineers and Dr. Meehan are

summarised in the charts presented in Figure 11 and Figure 12, and demonstrate that the subsoil

permeability is ‘Low’. This corroborates the field-mapped data, as the fields are bounded by deep drainage

ditches and there are rushes evident in many of the adjacent pasture fields around the investigated site.

20

The site investigation (Appendix A) conducted in-situ falling head tests at depths of 1 m and/or 2 m bgl. The

permeability ranged from 10-4

to less than (slower) 10-7

m/s, including two of the tests at 2 m where there

was no water level movement.

Percolation tests as per EPA Code of Practice (2009) were carried out on the soils and subsoils to determine

an appropriate loading rate should percolation be viable (Appendix A). The results were wide ranging and a

pattern is not obvious; in some cases both ‘T’ and ‘P’ values passed and in others not. Classification of the

texture by Tobin Engineers for the subsoils mainly indicated ‘low’ permeability subsoil.

Figure 11 Clay percentages for samples taken across the site

Figure 12 Bulk Texture for the subsoils (BS5930)

5.4 Depth to bedrock

The depth to bedrock is variable across the region though markedly deeper in general in east Galway (Daly

1985; GSI web mapping). In the Glenamaddy area, the depth to bedrock ranges from rock at the surface to

greater than 10 m, and in general greater than 10 m east, northeast and south of the village and the

turlough. To the west of the village, the depth to bedrock is generally 3 m to 10 m. Drilling by the GSI into

the sediments flooring the turlough indicates depths ranging from 3 m to 10 m in the immediate vicinity of

21

Pollanargid (Daly, 1995). Anecdotal information indicates that there was a borehole drilled east of

Pollnadeirce with a reported depth to bedrock of 18 m (Daly, 1995). Pollnadeirce itself reportedly became

infilled with 6 m of sediment over a 30 year period (Daly, 1985).

The site investigation data, which focussed on a site east of the village and north of turlough (Figure 1,

Figure 13, Appendix A and B) indicates that the subsoils range from 2.5 m – 9 m in the village; and across

the main ridge investigated, the depths to rock range from 2 m – 4 m on the highest part of the ridge (RC14,

RC15) to greater than 8 m to 14 m (RC06 (01A), RC07, RC08) in the central portion of the ridge to 4 m to

6 m on the lowermost part of the site (RC09, RC10). The majority of the northern part of the ridge generally

has relatively deep depths to rock. A north–south cross section is provided in Figure 14, which illustrates

the interpreted rock head between the sinking stream to the north of the ridge and the turlough, south of the

ridge. The relatively steep incline toward the top of the ridge followed by a relatively shallow incline into the

turlough suggests a ‘Crag and Tail’ feature (pers comm. Dr. Meehan, 2015).

Figure 13 Depth to bedrock and location of cross section profile

22

Figure 14 Cross Section A-B

RC09

RC08

RC06 (01A) RC15RC14

GSI94/32GSI94/30

Pollnadeirce

Sinking Stream St. Josephs

Rock Head

Ground surfaceRC05

>8m

>8m

14m

2.3m

5.8m

3.7m

8m

3m

?

?

23

6 GROUNDWATER VULNERABILITY

Groundwater vulnerability is dictated by the nature and thickness of the material overlying the uppermost

groundwater ‘target’. This means that vulnerability relates to the thickness of the unsaturated zone in sand

and gravel aquifers, and the permeability and thickness of the subsoil in areas where the sand/gravel aquifer

is absent. A detailed description of the vulnerability categories can be found in the Groundwater Protection

Schemes document (DELG/EPA/GSI, 1999) and in the draft GSI Guidelines for Assessment and Mapping of

Groundwater Vulnerability to Contamination (Fitzsimons et al, 2003).

The Groundwater Vulnerability map (2008) for the region, as mapped by Dr. Meehan on behalf of the GSI

and Galway County Council as part of the Galway Groundwater Protection Scheme (GSI, 2008) ranges from

‘extreme – X’ to ‘low’ vulnerability across the region as shown in Figure 15.

‘Low’ vulnerability is mapped across the majority of the area south, east and north east of Glenamaddy

Turlough. West of the turlough, the groundwater vulnerability is predominantly mapped as ‘moderate’ to

‘high’ with point features (swallow holes and dolines) mapped as ‘extreme – X’ groundwater vulnerability.

The stream that sinks to the swallow hole north of the village is mapped as ‘extreme – X’ groundwater

vulnerability. Similarly, Glenamaddy turlough and the streams it collects are mapped as ‘extreme – X’

groundwater vulnerability as it drains to the groundwater via swallow holes.

To the east of the village and north of the northwestern portion of the turlough, there is a mapped boundary

between ‘low’ and ‘moderate’ groundwater vulnerability. This is the locality of the current site investigation.

The subsoils have been classified as ‘low’ permeability. The cross section in Figure 14 indicates the depth

to bedrock across the site; ranging from approximately 5 m on the northernmost part of the site to greater

than 10 m across much of the northern slopes of the ridge to 3 m to 4 m to 8 m on the southern part of the

site toward the turlough. A slight revision is suggested to the groundwater vulnerability map taking account

of the information from the drilling conducted as part of the site investigation (Appendix A). The main

footprint of the ‘site’ on the northern slopes is considered to be ‘low’ vulnerability rather than ‘moderate’

vulnerability. From the summit of the ridge southwards it is ‘extreme’ to ‘high’.

24

Figure 15 Mapped groundwater vulnerability; karst features; proven underground connections

25

HYDROGEOLOGY

6.1 Introduction

This section describes the current understanding of the hydrogeology in the vicinity of the source.

Hydrogeological and hydrochemical information was obtained from the following sources:

GSI website.

Daly, 1985. A Report on the Flooding in the Glenamaddy Area (GSI, 1995).

Drew, D. 1973, Hydrogeology of the North Co. Galway – South Co. Mayo Lowland Karst Area,

Western Ireland. International Speleology, Proceedings of the 6th International Congress of

Speleology. Prague.

Drew, D., and Daly, 1993. Groundwater and Karstification in Mid-Galway, South Mayo and North

Clare.

Moe, et al, 2011. Establishment of Groundwater Source Protection Zones for Kilkerrin Public Water

Supply. Report on behalf of the Environmental Protection Agency.

Dunmore–Glenamaddy (Gortgarrow) Groundwater Source Protection Zones (Meehan, et al, 2010).

Report on behalf of Galway County Council and the Geological Survey of Ireland.

Galway Groundwater Protection Scheme (Meehan, 2007). Report for Galway County Council and

the Geological Survey of Ireland.

County Council Staff.

EPA website and Groundwater Monitoring database.

Local Authority water quality data.

Site investigation, water sampling level monitoring (Appendix A and B).

Hydrogeological mapping by TOBIN Consulting Engineers.

6.2 Groundwater body and status

The environs of Glenamaddy are located in the Clare–Corrib Groundwater body, out of which a subset is

delineated for Glenamaddy Turlough, named the Glenamaddy Turlough Groundwater Dependent Terrestrial

Ecosystem (GWDTE) Groundwater Body (Figure 17). Both the Clare–Corrib and the Glenamaddy Turlough

GWDTE Groundwater bodies are currently classified as being of ‘Good Status’, though were previously

classed at ‘Poor Status’ due to failing the WFD Surface Water Quality test, i.e., impact of groundwater quality

on surface water ecology with groundwater contributing greater than 50% load to cause a breach of the river

phosphate environmental quality standard. However, Glenamaddy Turlough GWDTE Groundwater Body is

‘At Risk’ of not achieving ‘Good Status’ due to the risk of the Glenamaddy urban waste water treatment not

being upgraded. The groundwater body descriptions are available from the GSI website: www.gsi.ie and the

‘status’ is obtained from the EPA Envision website.

6.3 Regional groundwater flow directions and gradients and aquifer characteristics

The region comprises a highly karstified limestone bedrock system, classed as a Regionally Important Karst

Aquifer (Rkc) and there are a number of large springs, turloughs and swallow holes mapped (Figure 17).

The location of known wells and springs from the GSI well database is shown in Figure 16. There are few

known boreholes in the region.

26

Figure 16 Groundwater wells and springs (GSI database)

The publically available hydrogeological work to date and in particular the tracer data provide information on

the groundwater geometry and indicates the broad groundwater divides, which indicates the regional

groundwater flow patterns are predominantly east to west. In the Glenamaddy area the groundwater flow

directions converge on Lettera Spring which is located approximately 3.5 km west of Glenamaddy Turlough.

Lettera spring been directly traced from four distinct swallow holes: two in Glenamaddy Turlough; one on the

northeastern side of the village (St. Josephs sink, Photographs 1 and 2); and one from a swallow hole in

Boyounagh 2 km north of Lettera spring (Drew, 1973; Drew and Daly, 1993; Moe, et al, 2010). The flow

rates are rapid, as evidenced by the traced conducted by Moe, et al., (2011), from the ‘roadside sink’ at

Glenamaddy Turlough which has a recorded groundwater flow rate of 72 m/hour.

Lettera Spring is considered to consist of a deep and shallow groundwater component (Drew, 1973; Drew

and Daly, 1993). During drier weather, hardness and electrical conductivity increase and the flow stabilises.

There is no long term record of flow from Lettera (Drew, 1973; Drew and Daly, 1993) suggests a mean flow

of 100 l/s and data presented in Daly (1995) indicates a mean flow of approximately 50 l/s and a median of

approximately 45 l/s.

A considerable amount of tracing has been conducted for Gortgarrow Spring and Kilkerrin Spring, which are

located approximately 7 km southwest and 7 km south of Glenamaddy Turlough. The proven groundwater

connections (traces) illustrate the regional flow patterns, and allow for inferences to be made on the broad

groundwater catchments (Figure 17). It is considered that the catchment to Lettera is distinct from the other

catchments and includes within it the catchment to Glenamaddy Turlough.

27

Figure 17 Bedrock Aquifer and Groundwater Bodies

Whilst the tracer work indicates high permeability/transmissive zones within the bedrock, there are likely to

be zones of lower permeability bedrock present as suggested by drilling by the GSI in assessing the flooding

around Glenamaddy (Daly, 1995). The site investigation work carried out for this study indicates that the

bedrock under the site is a fractured and weathered dark grey limestone.

6.4 Local groundwater flow directions

Nine piezometers were installed in the area that was investigated on the site as part of this study (Figure 2

Figure 14, Figure 19 and Appendix A). Three are finished in the bedrock (RC09, RC10, and RC01A) and

the remainder bottom into the subsoil. They are all open for most of their depth and provide information

across the site as a whole. Groundwater levels were measured in the piezometers on five occasions from

January 2015 to December 2015. The water level data is presented in Table 5 and graphed in Figure 18;

the details, locations of the piezometers are in Appendix A. Aerial photographs in Figure 19 and Figure 20

illustrate the northerly groundwater flow component and a cross section shown in Figure 14 illustrates the

water table for December 2015.

The water levels declined from January to July and then rose over the two subsequent monitoring events.

The levels in RC09 and RC10 are relatively shallow for the whole year and less than a metre below ground

in the latest event in December 2015. RC08 and RC11 are located on the lower slopes of significant break

in slope down to the stream and the water levels reflect this: approximately 3–4 m bgl during the summer

and rising to within 2 m of ground surface during the winter. Piezometers RC05, RC01A, RC07, RC12, and

RC13 are located on the uppermost parts of the site (southern extremities of the site as shown in Figure 1).

28

The water levels range from 4–7 m bgl in RC07, RC12, and RC13 during the summer to 1–3 m bgl during

the winter. The water levels in RC05, located on the highest point of the site drop below the base of

piezometer during the summer and rise to within 2 m of the ground surface during the winter. RC13 is

located close to where a ‘rising’ or spring is mapped and close to where one of the major drains runs

northwards; the winter water levels in the piezometer are very close to ground surface during the winter and

in the summer drop to 4 or 5 m bgl.

The data suggest that the groundwater flow direction is toward the stream on the northern margin of the site.

It is assumed that this represents a localised groundwater flow direction and is not reflective of the overall

regional groundwater flow direction which is westward.

Table 5 Water level data for site investigated

Figure 18 Chart of water levels on the site

Location x y mOD 21/01/2015 22/06/2015 07/07/2015 06/10/2015 11/12/2015

RC05 163462 262008 89.304 5.3 8.0 8.0 6.71 1.68

RC06 (01A) 163295 262075 88.46 3.46

RC07 163333 262166 87.453 4.1 6.6 7.1 5.90 2.75

RC08 163417 262268 82.877 2.33 4.2 4.5 4.08 1.41

RC09 163444 262325 80.477 1.95 2.5 2.7 1.49 0.60

RC10 163556 262307 80.391 0.84 1.5 1.6 1.46 0.52

RC11 163566 262225 83.255 1.82 3.3 3.5 2.87 1.09

RC12 163573 262143 88.535 7.1 5.4 6.1 4.92 2.79

RC13 163482 262152 86.115 0.65 4.3 5.0 2.96 0.57

RC16 162791 261360 82.19 3.1

0

1

2

3

4

5

6

7

8

9

mb

gl

RC05

RC06

(01A)RC07

RC08

RC09

RC10

RC11

29

Figure 19 Water levels (mOD) (January 2014) plotted to indicate northerly groundwater flow

component toward the main stream at the northern margin of the site

30

Figure 20 Water levels (mOD) (Dec 2016) plotted to indicate northerly groundwater flow

component toward the main stream at the northern margin of the site just using piezometers

intersecting the bedrock

31

6.5 Hydrochemistry and water quality

Hydrochemical analyses are available from both Galway County Council and the EPA for two karst public

water supply springs in the area, namely; Gortgarrow (Dunmore/Glenamaddy Public Water Supply) and

Bushtown (Glenamaddy Public Water Supply). The data include untreated water analyses.

There are limited data available for Lettera Spring (WS6) that has been supplemented by data collected

specifically for this study. The water sampling for this study also included Gortgarrow (WS5), Bushtown

(WS7), the Yellow River (WS9) a tributary of the Sinking River, Kingstown Stream (WS8), Springfield river

(WS10 Blackers Bridge), two tributaries of the Shiven River (WS2, and WS3), one of the streams leading into

Glenamaddy Turlough (WS4), and the waste water at the existing plant (WS11) (Figure 21) (Appendix A).

The sampling events consisted of 9 samples taken for bacteriological analysis and 8 samples for

hydrochemical analysis between October 2014 and February 2015.

Key points:

It is known that Lettera spring responds quickly to rainfall events and that the water is more turbid,

with increased suspended solids and lower electrical conductivity (Drew, 1973; Drew and Daly,

1993).

Persistent microbial contamination is evident in the majority of the water samples taken for this study

(Figure 22, Table 6). However, at Lettera the faecal coliform counts are greater than 100 per 100 ml

in 8 out of 9 samples, and are generally greater than Bushtown and Gortgarrow Springs, and the

surface water sampling points, with the exception of WS9 (Yellow River), and WS4 – one of the

streams feeding Glenamaddy Turlough. Historical untreated water quality data for Bushtown (2007

to 2015, 37 samples) and Gortgarrow springs (1995 to 2015, over 40 samples from Galway County

Council and nearly 40 from EPA) indicate persistent and occasionally ‘gross’ contamination1.

Generally, in Ireland the highest coliform counts in groundwater are in karst springs (EPA, 2015).

Table 6 Bacteria counts per 100 ml for sampling sites

Nitrate concentrations are generally less than 10 mg/l. The data collected for Lettera Spring

indicates an average of 5 mg/l as NO3 which is below the groundwater threshold value for the

drinking water test (37.5 mg/l as NO3) (Groundwater regulations, S.I. No. 9 of 2010).

Figure 23 charts the mean ammonium concentrations for the water samples collected for this study

and Table 7 provides the data collected. An assessment of the data indicates that elevated

ammonium concentrations occur in the springs and that there is an increase in the autumn/winter

months. From the data collected for this study (8 samples from October 2014 to March 2015), the

ammonium concentrations at Lettera Spring range from 0.013 to 0.32 mg/l, with a mean of

0.12 mg/l, which is below the groundwater threshold value for the drinking water test (0.175 mg/l as

1 Faecal counts in untreated water greater than 100 counts per 100 ml may indicate ‘gross’ contamination. It is used as a criterion

in technical assessments (EPA 2011, 2015). The drinking water standard is 0 counts per 100 ml.

32

N) and above the groundwater threshold value for the surface water test (0.065 mg/l as N)

(Groundwater regulations, S.I. No. 9 of 2010). Daly (1985) records ammonia concentrations at

Lettera at 0.63 mg/l as N (22nd

February 1984). The mean concentrations in the surface water

samples range from 0.14 mg/l to 0.4 mg/l as N (Table 7). The surface water samples (WS4) for one

of the streams feeding Glenamaddy Turlough have an elevated mean ammonium concentration of

0.4 mg/l. Similarly, though not as elevated, the samples at WS2 and WS3 have means of 0.28 mg/l

and 0.15 mg/l respectively. These data suggest that ammonia concentrations in the turlough may be

elevated prior to contributions from the waste water plant. Ammonium concentrations in the existing

effluent discharge range from 13 mg/l to 100 mg/l (number of samples is 8) and have a mean of

60 mg/l as N. The mean concentrations at Gortgarrow and Bushtown using the data collected for

this study are slightly higher than Lettera, both at 0.14 mg/l. However, the mean concentration from

the EPA dataset over the period of 2007 to 2013 for Gortgarrow is 0.06 mg/l with a range of 0.01 to

0.29 mg/l. The EPA water quality report (2015) indicates that the mean ammonium concentration for

Gortgarrow is in the range 0.04 to 0.065 mg/l. Elevated ammonium concentrations can occur in

peatland areas as well as from human activities.

Table 7 Ammonium concentrations for sampling sites

The mean phosphate (filtered molybdate reactive phosphate) concentrations for the samples

collected for this study are shown in Figure 24. The phosphate concentrations at Lettera Spring

range from less than the limit of detection (0.05 mg/l as PO43-

) to 0.083 mg/l as PO43-

, with a mean

of 0.05 mg/l as PO43-

(8 samples) (0.0082 to 0.027 mg/l as P with a mean of 0.016 mg/l as P) over

the period of October 2014 to March 2015 which is below the groundwater threshold value for the

surface water test (0.035 mg/l as P) (Groundwater regulations, S.I. No. 9 of 2010). The EPA data for

Gortgarrow record that the phosphate concentrations as filtered molybdate reactive phosphate are

generally below the limits of detection (0.015 mg/l as P) over the period of 2009 to 2013. Using

untreated water quality data for Bushtown from Galway County Council, phosphate concentrations

range from below the limits of detection to 0.206 mg/l, with an average of 0.026 mg/l as P. The

surface water samples for the streams have mean phosphate concentrations ranging from 0.013 to

0.02 mg/l as P. The mean concentration at WS4, one of the streams feeding into Glenamaddy

Turlough is 0.0198 mg/l as P which is higher than the concentration at Lettera. Samples at WS2 and

WS3 by contrast are somewhat lower, with mean concentrations of 0.013 and 0.014 mg/l as P. At

Lettera and Gortgarrow total phosphorous concentrations are 0.018 and 0.013 mg/l as P

respectively. The mean phosphorous concentration at WS4 is 0.0198 mg/l as P, and at WS2 and

WS3 the mean concentrations are 0.013 and 0.014 mg/l as P respectively. These concentrations fall

into the range of 0.01–0.02 mg/l as P for oligotrophic and mesotrophic turloughs (NPWS, 2013).

One potassium:sodium ratio is available for Lettera and records a ratio of 0.22 (Potassium 2.9 mg/l;

Sodium 13.3 mg/l) (Daly, 1985).

In summary, microbial contamination is present in all the sampling points; however, Lettera is nearly always

‘grossly’ contaminated. Ammonium and phosphate concentrations are occasionally elevated at Lettera,

though the mean concentrations are low. The mean ammonium concentration at Lettera is 0.12 mg/l as N

which is double that at Gortgarrow (0.06 mg/l as N) from the EPA dataset and greater than the groundwater

threshold value for the surface water test (0.065 mg/l as N) (Groundwater regulations, S.I. No. 9 of 2010).

33

The phosphate concentrations at Lettera are generally higher than the other springs and generally lower

than those taken from the larger streams, and lower than the small stream tributaries (WS2 and WS3). The

phosphate concentrations appear to be rapidly attenuated. Concentrations of ammonium and phosphate

and coliform counts are notably higher in the northerly surface stream (WS4) feeding Glenamaddy Turlough

than the two streams (WS2 and WS3) that flow east away to the Shiven River, which indicates that this

influent stream to the turlough appears to be polluted.

Figure 21 Water sample locations

34

Figure 22 Chart of bacteria counts from field data collected for this study (Appendix A)

Figure 23 Chart of mean ammonium concentrations from field data collected for this study

(Appendix A)

0

50

100

150

200

250

300

350

400

18-Sep-14 08-Oct-14 28-Oct-14 17-Nov-14 07-Dec-14 27-Dec-14 16-Jan-15 05-Feb-15 25-Feb-15 17-Mar-15

Bac

teri

a C

ou

nt

(per

100

ml)

Lettera Spring Gortgarrow Spring Bushtown Spring

WS4 into G. Turlough WS9 Yellow River WS2 trib of Shiven

WS3 trib of Shiven WS10 Springfield river WS8 Kingstown river

Gross contamination (100 counts/100ml)

35

Figure 24 Chart of mean phosphate concentrations from field data collected for this study

(Appendix A)

6.6 Groundwater Mounding

Allied to the site investigation a limited modelling assessment was conducted to predict the response of the

water table to the hydraulic load. This exercise was based on Hantush (1967) and used available software

(USGS, 2010). One of main assumptions is that the geological materials are saturated. This assumption is

considered appropriate for the site investigated given the highest water levels, the subsoil textures, evidence

of flooding and the recent winter conditions and therefore appropriate to use this simple model to predict the

effects of rainfall and an additional treated waste water load onto the site. The predictions using rainfall and

very low loading rates (3 and 10 l/m2/d) indicate that the water level would rise above ground surface is

discharge to ground took place at the site. This indicates the site could not take the hydraulic load. The wet

weather conditions in December 2015 caused surface water ponding on the site as shown in Photographs 5,

6 in Section 3. This makes sense when the drainage ditches cut around each of the fields is taken into

consideration. Such deep drainage ditches are there to take away excess water.

6.7 Hydrogeological Conceptual Model

The study area primarily focuses on Lettera Spring and Glenamaddy Turlough due to the urban

waste water discharge into the turlough and the definitive links to the spring from both the turlough

and other swallow holes outside the turlough.

The bedrock in the region consists of Regionally Important Karstified limestones and there a number

of distinctive karstic landforms mapped, including turloughs, sinking streams, swallow holes and

springs.

Glenamaddy Turlough collects drainage from several influent streams east and southeast, which rise

in raised bog. The turlough rarely dries and is associated with occasional flooding.

0.0000

0.0100

0.0200

0.0300

0.0400

0.0500

0.0600

18-Sep-14 08-Oct-14 28-Oct-14 17-Nov-14 07-Dec-14 27-Dec-14 16-Jan-15 05-Feb-15 25-Feb-15 17-Mar-15

ph

osp

hat

e fi

lter

ed (

mg/

l) a

s P

WS6 Lettera WS5 Gortgarrow WS7 Bushtown WS9 Sinking River WS2

WS3 WS4 WS10 WS8 Kingstown stream River EQS

36

Several swallow holes on the western and northwestern side drain the turlough and tracing has

proved a connection to Lettera Spring. Consequently, it is considered that the catchment to Lettera

Spring includes the catchment to the turlough and a topographic area to the north and all the area

between the spring and the turlough.

Additionally, two other swallow holes outside the turlough definitively link to Lettera Spring. These

are St. Joseph’s swallow hole in Glenamaddy village and Boyounagh Sink north of Lettera Spring.

The traces undertaken historically in the region around Glenamaddy indicate rapid groundwater flow

velocities in the bedrock.

The regional groundwater flow directions converge on Lettera Spring. Lettera Spring is considered

to be the main discharge point and forms part of the headwaters of the Sinking River. The Sinking

River itself loses along stretches of the river bed in dry conditions.

Over much of the area to the east of Glenamaddy Turlough there are deep ‘low’ permeability

subsoils and there is pronounced natural and artificial drainage. Much of the rainfall therefore flows

overland to sinking streams or into the streams that feed the turlough. The turlough and the swallow

holes are sites of concentrated recharge.

The site investigated, located between the sinking stream to the north of the turlough and the

turlough itself, is comprised of deep well drained soils overlying ‘low’ permeability subsoil. The fields

are bounded by deep (up to 2.5 m deep) extensive drains that convey water to the sinking stream.

The mapped regional groundwater vulnerability is generally ‘low’. In the vicinity of Glenamaddy

village and the area northwest of the turlough the subsoils are generally shallower and the

groundwater vulnerability is ‘moderate’ to ‘high’ with the karst features classed as ‘extreme – X’

vulnerability. The site investigated is mainly ‘low’ vulnerability becoming ‘moderate’ to ‘high’ proximal

to the sinking stream (St. Josephs) on the northern side of the ridge; ‘low’ to ‘extreme’ approaching

the summit of the ridge and then ‘extreme’ to ‘high’ on the southern side of the slope toward the

turlough.

Lettera spring as well as the other karst springs in the area react quickly to rainfall and is susceptible

to contamination as evidenced by high turbidity, bacterial exceedances, occasionally elevated

ammonia and phosphate. Despite the hydraulic connection from the swallow hole into which the

existing outfall discharges the phosphate concentrations appear to be rapidly attenuated by the time

the water gets to Lettera Spring. This may be related to sediments in / around the swallow hole and

in the fissures and conduits and/or to hydrological conditions of the turlough itself, i.e., mixing/dilution

of the waste water in the water body of the turlough prior to going underground.

The hydrochemical behaviour of the turlough is unknown; however, the surface water samples

provide an indication of the influent hydrochemistry. The ammonium data suggest that

concentrations in the turlough in the order of 0.2 mg/l to 0.4 mg/l; thus, elevated prior to contributions

from the waste water plant. The phosphate data indicate mean concentrations in the order of

0.013 mg/l to 0.02 mg/l.

Limitations in the conceptual model mainly lie with uncertainties associated with general

groundwater flow in the northernmost area of the Lettera catchment and the detailed

hydrological/hydrochemical behaviour of the turlough. The discharge flow data for Lettera are

limited.

37

6.8 Lettera Spring catchment

Based on the conceptual model and the tracer connections, a zone of contribution to Lettera Spring can be

delineated. The boundaries of the area contributing to Lettera Spring (Zone of Contribution (ZOC)) are

based on the considerations and limitations described above.

The size of the ZOC is a function of:

the total outflow from the spring;

the permeabilities of the subsoils in the region, and;

the rainfall and evapotranspiration across the region, and;

the consequent recharge in the area.

The location of the ZOC is a function of:

the groundwater and surface water flow directions and gradient;

the subsoil and bedrock permeability.

The shape and boundaries of the ZOC (Figure 25) were determined using hydrogeological mapping, dye-

tracing, water balance estimations, and conceptual understanding of groundwater flow.

The boundaries are broadly based on topography, with the regional groundwater flow directions defined by

the tracing results and the stream catchments that feed into Glenamaddy Turlough. As such, the

topographic catchment to Glenamaddy Turlough, and topographic divides to the north, and northwest are

used to define the groundwater catchment to Lettera Spring.

To the west and south of Lettera, the boundary is difficult to define and are simply based on topography and

assumed groundwater flow lines. There are uncertainties with the northwestern boundary. It is extended to

take account of elevated topography and a swallow hole northwest of Boyounagh that has not been traced.

There is some uncertainty with the northern boundary; no work has been done on the likely divide between

the catchments to Lettera and Bushtown to date. There is also uncertainty with the conditions during very

high flow stages and there may be cross boundary flow.

38

Figure 25 Zone of contribution to Lettera

6.9 Water balance estimations

The term ‘recharge’ refers to the amount of water replenishing the groundwater flow system. The recharge

rate is generally estimated on an annual basis, and assumed to consist of input (i.e., annual rainfall) less

water loss prior to entry into the groundwater system (i.e., annual evapotranspiration and runoff).

The main parameters involved in the estimation of recharge are: annual rainfall; annual evapotranspiration;

and a recharge coefficient (Groundwater Working Group 2005; Hunter Williams et al., 2011, & in press).

These calculations are summarised as follows:

Average annual rainfall (R) 1200 mm

Estimated P.E. 475 mm

Estimated A.E. (95% of P.E.) 450 mm

Effective rainfall (Potential recharge) 700 mm

Bulk recharge coefficient 4 – 60%

Recharge 28 – 600 mm

Water balance: The water balance calculation states that the recharge over the area contributing to the

spring should equal the discharge. The estimations of recharge are for diffuse recharge and do not take

account of the concentrated recharge at the swallow holes. An upper limit of 600 mm is allowed for to take

account of direct recharge. The area described above and shown in Figure 25 is 34 km2 and corresponds to

an approximate mean discharge in the order of 35 to 50 l/s.

39

7 RISK ASSESSMENT

7.1 Pollutant (chemical and hydraulic load)

Table 8 presents data for BOD, suspended solids and orthophosphate over the period of 1998 to 2008 of the

discharge entering Glenamaddy Turlough, and it indicates that approximately 229 kg P/ year is entering the

groundwater system based on an estimated dry weather flow of 100 m3/day (though peaks at over

300 m3/day).

Table 8 Effluent Quality

Date of Sampling BOD

mg/l

Suspended Solids

mg/l

Ortho

Phosphate

as P (mg/l)

17th Sept 2004 316 210 2.9

19th Sept 2004 204 105 3.7

25th Sept 2004 129 133 3.8

13th Feb 2007 122 369 10.3

8th Aug 2007 240 129 21.8

12th Aug 2007 150 87 3.3

28th Mar 2008 152 121 21

7th Aug 2008 92 59 3.1

12th Dec 2008 144 84 6.3

22nd Oct 2014 88 150 6

5th November 2014 37 76 4

10th November 2014 16 98 1

17th November 2014 190 160 6

27th January 2015 55 230 3

3rd February 2015 290 130 5

10th February 2015 58 94 6

3rd

March 2015 26 81 2

Average 136 138 6.4

The proposed design standards are summarised in Table 9.

Table 9 Design Effluent Standard

Parameter Final Effluent Design Standards

BOD 10 mg/l

Suspended Solids 10 mg/l

Total Phosphorus 0.5 mg/l

Total Ammonia 1.0 mg/l

Pathogen reduction 3 log reduction

The hydraulic load is presented in Table 10.

40

Table 10 Design Loading

Design Parameter Value

Design Population 700p.e.

Design Load 42kg/d

Hydraulic Load

(Dry Weather Flow) 126m

3/day

Hydraulic Load

(Peak Flow) 378m

3/day

Peak Storm Water Flow to Pumping

Station 4 hours storage to be provided 380m3

7.2 Consideration of discharge options

7.2.1 Direct to surface water

Discharging directly to the various rivers is not viable principally due to the absence of an available

assimilative capacity for phosphate and that the WFD Risk Score has highlighted that the rivers in the area

are “At risk of not achieving good status”.

7.2.2 Indirect via percolation to ground

The subsoil permeability is mapped as ‘low’ across the area and whilst there may be pockets or portions of

higher permeability it is unlikely that they are present in a significant mappable area big enough for

percolating the hydraulic load. A drive through and walkover was done at the outset to select a site that

appeared that it might have reasonable drainage characteristics. The site investigated comprises ‘low’

permeability subsoils and is considered representative of the land in the area around Glenamaddy. The

topsoil on the site is relatively well drained but overlies ‘low’ permeability subsoil and all the field boundaries

of the site comprise deep drains. Wet weather conditions as recorded in December 2015 indicate that the

site ponds. The recorded water levels indicate the water levels are at or close to ground surface during wet

weather conditions. A simple basic groundwater mounding exercise suggests that the site could not take the

proposed hydraulic load. Based on the conceptual model, discharge via percolation is not technically feasible

on the site investigated principally due to the ‘low’ permeability of the subsoils.

7.2.3 Indirect via Integrated Constructed Wetland

The groundwater vulnerability assessment of the site indicates that the Groundwater Protection Response is

R22, therefore the requirements as per DECLG Guidelines (2010) for a Constructed Wetland are considered

to be as follows:

• A minimum, unsaturated subsoil depth of 1 m

• A textural classification of CLAY, SILT/CLAY (as per BS5930)

• In situ permeability of 1E-8m/s

• CLAY % >13%.

The overall site characteristics meet the technical requirements for an Integrated Constructed Wetland.

However, the outlet of the ICW would be to a sinking stream, which sinks several hundred metres west to St.

Josephs swallow hole, which is proven to connect underground to Lettera Spring. It is known from OSI six-

inch topographic mapping that there is an area of flooding along the stream to the northeast of the site.

Despite the arterial drainage, in times of heavy rainfall the stream backs up such as evidenced in December

2015 (Photograph 2, 3, 5 Section 3) and encroaches onto the lowermost margins of the site and floods an

41

area upgradient as seen in Photograph 3 and depicted on Figure 7. The addition of a further hydraulic load

from the WWTW and ICW would present an additional flood risk in this area.

In addition both swallow holes (Pollnadeirce and St Joseph’s) definitively link to Lettera Spring and thus

there is no clear advantage of using one swallow hole over the other.

7.2.4 Direct to swallow hole at Glenamaddy Turlough

The physical setting is challenging with respect to discharge of effluent. It is technically unfeasible to

indirectly discharge via percolation. Discharge of highly treated effluent using the current outfall appears to

be the best choice, which is inside the SAC and an exemption under Regulation 14 (Groundwater

Regulations, S.I. No. 9 of 2010) is required. The catchment to Lettera Spring is reasonably well known and

Lettera Spring would be the main monitoring point.

It also allows for an assessment of assimilative capacity in the groundwater body. Consideration is also

given to the turlough water body itself and three hydrological conditions are calculated: 1) when the turlough

is ‘full’; 2) when the turlough is nearly empty; and, 3) when the turlough is dry.

7.3 Assimilative capacity

A dilution calculation is used to calculate the assimilative capacity for phosphate and ammonia of the design

discharge to groundwater body using flow at Lettera as the monitoring point to represent the groundwater

body volume and using a representative background concentration from the field data; and, to calculate the

assimilative capacity of the turlough itself when the turlough is ‘wet’.

There are limitations and assumptions made regarding ammonia and phosphate. The adopted approach for

the groundwater body calculation is taken is as per “Example 13” in EPA guidance document on the

Authorisation of Discharges to Groundwater (EPA, 2011) and the approach to the turlough calculation is

based on EPA guidance on ambient and discharge monitoring in relation to surface water regulations.

Limitations and Assumptions

1. With respect to pathogens, the design standard will be to achieve a 3 log reduction in the bacterial

concentrations in the incoming waste water. Considering that all the springs are known to be

susceptible to contamination and the treated water is expected to have a positive impact on the

bacteria counts in the groundwater. However, with elevated bacterial counts naturally present in the

groundwater, it will be difficult to quantify the exact reduction in such counts that may occur at

Lettera Spring.

2. The design standard of 0.5 mg/l Total Phosphorous that is entering the groundwater via the turlough

or St Joseph’s swallow hole is directly and wholly made up of MRP.

3. That there is no attenuation of phosphorous which the water quality data does not support.

4. The zone of contribution to Lettera spring is the ‘groundwater body’ on which to perform the

assimilative capacity, and that Lettera is the relevant monitoring point. It is the discharge point that

is clearly being polluted. There is some information on the mean flow at Lettera which allows for

dilution calculations.

5. The mean flow at Lettera is in the order of 35 l/s to 50 l/s based on a water balance and a set of

measurements by GSI (GSI, 1995).

6. The background groundwater phosphate concentration is based on the concentrations at Lettera,

Gortgarrow and the streams that feed the turlough and is approximately 0.015 mg/l as P.

42

7. The phosphate threshold concentration used for the purposes of a Groundwater Body capacity

calculation is 0.035 mg/l as P (surface water environmental quality standard).

8. The design standard for Total Ammonia is 1.0 mg/l and the groundwater threshold value used is

0.065 mg/l as ammonium as N. The background groundwater concentration is based on the mean

ammonium concentration at Gortgarrow 0.06 mg/l as N.

9. The depth of the turlough for two scenarios is based on an average depth of 3 m and 0.3 m. This

data is inferred from ordnance survey data.

10. The turlough water body is assumed to be static in the two ‘wet’ scenarios.

11. The range of background phosphorous concentrations for the turlough water body calculations are

based on the background groundwater concentrations, influent stream field data and recently

published data for turloughs studied for hydrochemistry (da Cunha Pereira, 2011).

Calculations and results

The calculations are presented in Table 11, 12 13 and 14 for phosphate and ammonium for ranges of flow,

background and discharge concentrations.

Phosphate

The calculations for the turlough indicate that for the design discharge of 0.5 mg/l as P of phosphate,

then, for a background concentration of 0.015 mg/l as P, and a depth of 3 m to 0.3 m in the turlough,

the concentration would increase slightly; occurring in the range of 0.015 to 0.016 mg/l as P. The

main critical driver is the background concentration. This calculation assumes that all the ‘plume’ is

going into the turlough water body.

The calculations for the groundwater body are done for when the turlough is dry. They demonstrate

that for a background groundwater body concentration of 0.008 to 0.015 mg/l as P that the

concentration would not exceed 0.035 mg/l as P. The ‘groundwater body’ would be at ‘Good Status’

and the theoretical capacity used up would range from 60% to 97% for a background concentration

of 0.015 mg/l as P (45% to 73% for a background concentration of 0.008 mg/l as P).

Ammonia

The ammonium data suggest elevated concentrations may be present in the turlough; thus, elevated

prior to contributions from the waste water plant. The assimilative capacity calculations are done on

both the groundwater body and the turlough but those for the turlough are limited. Only when the

background concentrations are in the order of 0.06 mg/l as N do the calculations demonstrate

compliance of the design standard against the nutrient conditions expected for ‘Good Status’ in the

lake water body.

The calculations for the groundwater body are done for when the turlough is dry. The calculations

for the groundwater body indicate that the for the design discharge of 1 mg/l of ammonium as N,

then, assuming a range of background concentrations of 0.04 mg/l to 0.06 mg/l as N then the

predicted concentration would range from 0.069 mg/l to 0.098 mg/l, which is below the groundwater

threshold concentration for drinking water though above the groundwater threshold value for the

surface water test (Groundwater regulations, S.I. No. 9 of 2010). This does not take account of

attenuation or that the turlough is generally ‘wet’. They indicate an improvement on the current

mean value at Lettera (0.12 mg/l).

43

Table 11 Assimilative capacity phosphate (mg/l as P) in the Turlough

Table 12 Assimilative capacity phosphate (mg/l as P) in the groundwater body when the turlough is

dry

Discharge

flow

(m3/d)

Concentration

exiting dry

turlough

(mg/l as P)

35 l/s 50 l/s 126 MRP as P 35 l/s 50 l/s

3024 4320 126 4 0.05 0.208 0.167

3024 4320 126 0.5 0.05 0.068 0.065

3024 4320 126 4 0.015 0.174 0.132

3024 4320 126 0.5 0.015 0.034 0.030

3024 4320 126 4 0.008 0.168 0.125

3024 4320 126 0.5 0.008 0.028 0.023

Lettera

(m3/d)

Background concentration

(mg/l)

Total Concentration

(mg/l as P)

44

Table 13 Assimilative capacity Ammonia (mg/l as N) in the turlough

Table 14 Assimilative capacity ammonium (mg/l as N) in the groundwater body when the turlough is

dry

Factor b

(depth) m

Factor F

flow rate

(m3/hr)

Dilution

8930 b/F

Discharge

flow

(m3/d)

Concentration

in discharge

(mg/l)

3 5.25 5102.857 126 Ammonia 0.065

60 0.3 0.312

1 0.3 0.300

60 0.15 0.162

1 0.15 0.150

60 0.06 0.072

1 0.06 0.060

0.3 5.25 510.2857 126 0.065

60 0.3 0.417

1 0.3 0.301

60 0.15 0.267

1 0.15 0.152

60 0.06 0.177

1 0.06 0.062

Turlough (Full, ~3m

Background concentration

(mg/l)

Total Concentration

(mg/l as N)

Turlough (0.3m deep)

Discharge

flow

(m3/d)

Concentration

exiting dry

turlough

(mg/l as N)

35 l/s 50 l/s 126 NH4 35 l/s 50 l/s

3024 4320 126 60 0.06 2.458 1.785

3024 4320 126 1 0.06 0.098 0.089

3024 4320 126 60 0.04 2.438 1.765

3024 4320 126 1 0.04 0.078 0.069

Lettera

(m3/d)

Background concentration

(mg/l)

Total Concentration

(mg/l as N)

45

8 SUMMARY AND CONCLUSIONS

Hydrogeology

The physical setting comprises a karstified aquifer with turloughs, karst springs, sinking streams

and other karst features present in the area. Surface water and groundwater are inextricably linked.

For example, tracing indicates the connections from Glenamaddy Turlough and a number of other

swallow holes to Lettera Spring, which forms the headwaters of the Sinking River, which in turn is

known to sink underground under certain conditions.

The subsoils comprise relatively thick ‘low’ permeability till in the vicinity of Glenamaddy and the

investigated site, and also large areas of peat further afield. There are swallow holes and areas of

shallow subsoils which allow for rapid point and diffuse recharge.

The springs in the region are inherently susceptible to contamination and the water quality does

demonstrate that. Lettera is directly connected to Glenamaddy Turlough into which the waste water

from the village is discharged. Consequently, microbial contamination and phosphate

concentrations are generally higher than other springs. Ammonia is elevated generally in all the

sampling points and natural influences are a factor due to the extensive presence of peat. There

does appear to be attenuation of ammonia and particularly phosphate at Lettera. Glenamaddy

Turlough is fed by three streams; one of these was sampled and appears to be contaminated.

Suitability of site investigated

An indirect discharge by infiltration is technically not feasible due to the presence of ‘low’

permeability subsoils.

The most feasible technical approach appears to be discharge high quality treated effluent into the

current outfall.

Predicted Water Quality

The phosphate calculations for the groundwater body are done for when the turlough is dry and

indicate that the design standard will comply with the Groundwater regulations.

The calculations for the turlough indicate that for the design standard that the resultant phosphorous

concentrations will be within the range of 0.01–0.02 mg/l.

Ammonia

The ammonium data suggest elevated concentrations may be present in the turlough prior to

contributions from the waste water plant. Only when the background concentrations are in the

order of 0.06 mg/l as N do the calculations demonstrate compliance of the design standard against

the nutrient conditions expected for ‘Good Status’ in the lake water body.

The calculations for the groundwater body are done for when the turlough is dry and indicate that

the design standard will improve resultant concentrations. However, background concentrations in

the regional sampling point indicate elevated ammonium concentrations. There is a significant

reduction in the design standard (1 mg/l as N) from the current input that averages approximately

60 mg/l as N.

46

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