Lisheen Mine Document to support the application to EPA for a new consent limit for sulphate

Transcription

1 TECHNICAL MEMORANDUM To: Steve McComb / Stephen Weston Company: Lisheen Mine SMcComb@lisheenmine.ie WMC Ref: 151 From: Geoff Beale Date: 11 April 27 Pages: 11 including this page 23 SWAN HILL, SHREWSBURY SHROPSHIRE, SY1 1NN, UK TEL: +44 () FAX: +44 () gbeale@watermc.com Lisheen Mine Document to support the application to EPA for a new consent limit for sulphate 1 Introduction The Lisheen Mine operates a groundwater dewatering system. In order to maintain safe working conditions, groundwater from the mine is continuously pumped to the surface. More than 65% of the water is collected directly from natural fracture systems occurring underground and does not have any significant contact with the mine workings. A relatively small portion of the water is collected from the workings themselves and is pumped to the water treatment plant. Excess water from the tailings management facility is also pumped to the water treatment plants. The natural groundwater and treated water are mixed in the conditioning pond system. The mixed water is discharged via pipelines into the Drish and Rossestown Rivers. The discharge points are located some 15 and 12 km, respectively, upstream of the River Suir. With the current discharge consent limit of 25 mg/l, it is not possible to efficiently manage water on site on a day-to-day basis. It will also impact on the ability to manage the water such to achieve an optimised final closure and reclamation programme for the site. The European/Irish drinking water standard for sulphate is 25 mg/l (SI 439 2). This standard is based on taste considerations of the drinking water source, rather than any toxicological criterion. The drinking water guideline value issued by the World Heath Organisation (WHO) in 24 was 4 mg/l. Sulphate is non-toxic to humans, and exerts no significant impact on aquatic wildlife at concentrations of below at least 1, mg/l. This document examines the uses of the Drish and Rossestown Rivers, the potential implications of an increased sulphate limit in terms of the downstream impacts in the rivers, and the potential effects on downstream receptors. It is noted that other local industrial operations have operated successfully with higher discharge limits for sulphate than 25 mg/l. 2 Uses of the Drish and Rossestown Rivers The main uses of the Drish and Rossestown Rivers are cattle watering and fishing. Although neither are listed in SI as salmonid rivers, the Drish would be considered to have better fishing with a population of trout. Both rivers are lowland streams whose headwaters are peat bogs. The EPA compiled National Abstraction Register has been reviewed to confirm the locations of potable water supplies on the Drish, Rossestown and Suir Rivers. There are no sources of public water supply on any of these rivers. Checks for abstractions from the Suir were carried out down to Waterford. The only potable water supplies obtained from surface waters are those at Clonmel. It has been confirmed through discussions with Clonmel Borough Council that these abstractions are taken from two tributaries of the Suir River, not the Suir River itself. Ltd Registered office: 1 Brassey Road, Old Potts Way, Shrewsbury SY3 7FA Registered Number: EPA Export :22:26:14

2 11 April 27 Page 2 The standards that are relevant to the Drish and Rossestown Rivers are those for waters capable of supporting freshwater fish and for salmonid waters, and those for cattle watering and irrigation. The guidelines related to salmonid rivers are listed in Table 1. Of these guideline sources, only the proposed UK Environmental Quality Standards specify limits for sulphate for freshwater fish or salmonid rivers and this is discussed further in section 3 The Canadian Environmental Quality Guidelines (ECG s) specify a value of 5 mg/l for sulphate with the basis for this guideline being aesthetic objective. This guideline is set for the general water community and there is no limit set specifically for aquatic life. The 5 mg/l limit is based on the potential for diarrhea in children and has no ecotoxicological basis. Table 1 Guidelines for salmonid rivers Source Date Author / reference Waters capable of supporting freshwater fish 1978 EC 78/659* Annex 1 EC (Quality of Salmonid Waters) Regulations 1988 SI 293 Surface Water (fishlife) (classification) 1997 N.Ireland rule 488 US EPA Water quality criteria summary Appendix A.2 Proposed environmental quality standards for sodium, chloride and sulphate in freshwater (UK) 22 Fittall et al R&D Technical Report P2-115/TR1. Water Framework Directive 2 2/6 EC Canadian Environmental Quality Guidelines 22 Summary Table Livestock watering is an important use of water in the Drish and Rossestown catchments. The WHO 24 background paper 1 reports that cattle can tolerate sodium sulphate (a sulphate compound with an essentially non-toxic metal couple) in their drinking water up to 2,61 mg/l (equivalent to 1,765 mg/l as SO 4 ) with no sign of toxicity except changes in the levels of methaemoglobin and sulfhaemoglobin. Weanling pigs drinking 3, mg/l of sulphate suffered no adverse effects other than diarrhoea (WHO, 24). Ohio State University 2 advice on livestock and water recommends an upper limit of 1, mg/l for cattle, swine, sheep, poultry and horses. The same level has been set by Agriculture and Agri-food Canada 3 for cattle, and the PigSite 4, a UK based web site devoted to providing advice on the welfare of pigs. It has not been possible to confirm whether the Drish, Rossestown and Suir are used for irrigation although any such use will be limited, if indeed it happens at all. Sulphate in irrigation water actually has fertility benefits and will not have any detrimental effect on plant growth unless concentrations are very high 5. No water guidelines for sulphate in irrigation water have been identified by this study. The FAO 6 do however state that the normal range for sulphate in irrigation water is 192 mg/l. 3 Ecotoxicological studies A search for toxicological studies on sulphate has been carried out by the Lisheen Mine. The US EPA database, ECOTOX, has no entries for the effect of the sulphate ion on aquatic systems. Consultation with conservation and pollution officers from the Environment Agency in England, the EPA in Scotland, and the Centre for Environment Fisheries & Aquaculture Science (CEFAS) did not uncover any instances where sulphate was a potential problem in a freshwater environment. The Irish Government s memorandum on water quality objectives (c 1978) suggests a sulphate level of 25 mg/l for salmonid 1 WHO (24) Sulphate in drinking water Background document for development of WHO Guidelines for Drinking-Water Quality. Document WHO/SDE/WSH/3.4/114. World Health Organisation, Geneva FAO 29 (1985): Water quality for agriculture ( 151 Lisheen Mine EPA Export :22:26:14

3 11 April 27 Page 3 waters, without discussion of the underlying reasons for, or significance of, this threshold. A poster from West Virginia University 7 suggests that up to 85 mg/l of active sulphate is acceptable to rainbow trout. In 22, the Environment Agency in the UK commissioned the Water Research Centre (WRc) 8 to update a previous technical report (NR2525, Gardiner and Smith ) proposing EQS values for sodium, chloride and sulphate. After a thorough review of the literature, they concluded that an EQS for the protection of freshwater life would be an annual average value of 4 mg/l. The most sensitive organisms found in the literature were a species of water flea (Ceriodaphnia dubia) and a freshwater shrimp (Hyalella armarta), both from North America. This EQS is repeated in CEFAS s Toxicity Database 1. The inference from the lack of toxicological studies and the omission of sulphate from legislation is that this is not a parameter of concern, and that a discharge limit higher than 25 mg/l would not have a significant impact on aquatic life in receiving waters or on livestock drinking the water. The principal justification for analysing sulphate as an integral component of surface and groundwater monitoring programmes is that it forms one of the major anions (along with chloride and bicarbonate) which control the ionic balance of the total solute load (in conjunction with all dissolved cations). It is thus an important Qa/Qc parameter, required to calculate the ionic balance and thus check the accuracy of the analysis. 4 Discharge concentrations and calculations The water from the conditioning pond discharges into the Drish River at point PWE-1 and into the Rossestown River at point PWE-2. The Drish is the larger of the two discharges. For each river, Lisheen analyses both the discharge and the river water at locations upstream and downstream of the discharge point on a daily basis for a range of determinands. Additional components and sites are analysed at a weekly or monthly frequency. A summary of the relevant water quality data is given in Tables 2 and 3 for the two rivers and the discharge. Table 2 Summary of measured concentrations in the Drish River and discharge PWE1 Upstream PWE1 discharge Downstream mean St. dev. 95 %ile mean st. dev. 95 %ile mean Flows Ml/d PH E. conductivity µs/cm TDS (calculated) mg/l Temperature ºC Alkalinity (estimated) Mg/L Calcium Mg/L Sulphate Mg/L Calculated from 25/26 daily data where data available, otherwise weekly or monthly data 95%ile is the upper or lower 95 percentile concentration. 95% of samples analysed have concentrations less than the value given in the table. The 95%ile is calculated as the mean ± (1.65 x st. dev.) Environment Agency (22) Proposed environmental quality standards for sodium, chloride and sulphate in water, by Fittall J, Hedgecott S and Young W. R&D Technical Report P2-115/TR1, Environment Agency, Bristol. 9 Gardiner J and Smith INH (199) Proposed environmental quality standards for sodium, chloride and sulphate in freshwater. R&D Note 131, National Rivers Authority, Bristol Lisheen Mine EPA Export :22:26:14

4 11 April 27 Page 4 Table 3 Summary of measured concentrations in the Rossestown River and discharge PWE2 Upstream PWE2 discharge Downstream mean st. dev. 95 %ile mean st. dev. 95 %ile mean Flows Ml/d PH E.conductivity µs/cm TDS (calculated) mg/l Temperature ºC Alkalinity (estimated) mg/l Calcium mg/l Sulphate mg/l Calculated from 25/26 daily data where data available, otherwise weekly or monthly data 95%ile is the upper or lower 95 percentile concentration. 95% of samples analysed have concentrations less than the value given in the table. The 95%ile is calculated as the mean ± (1.65 x st. dev.). The concentration of sulphate at PWE-1 and PWE-2 and the sum of the two discharges is shown in Figures 1 and 2 for 25 and 26, respectively. Figure 3 shows weekly-measured sulphate concentrations at the upstream sampling point on the Drish and Rossestown during 25. Figure 4 shows weekly-measured sulphate concentrations at the downstream sampling point on the Drish and Rossestown during 25. The downstream sampling point on the Drish is 3 m downstream of the discharge point PWE-1. The data for the downstream sampling point in Table 1 are likely to be representative of mixed conditions. However, the downstream sampling point on the Rossestown is only 2 m downstream of the discharge point PWE-2. This is too close to expect complete mixing. As a result, some of the perceived instability shown in Figure 4 may be due to lack of mixing of the discharge with the river water at the sampling point. 5 Increased consent limit for sulphate River gauging stations operated by the Office of Public Works are located on the lower Drish River (161 Athlummon) and Rossestown River (1651 Clobanna) towards the confluences with the Suir River. Flow duration curves have been calculated for the pre-mine discharge years of and standardised by dividing the flows by the catchment area of each river gauging station (Figure 5). The flow duration curves have provided flow statistics that have been used to estimate the concentration of sulphate at various points downstream of the discharge points for a future discharge consent limit of 5 mg/l. Figure 6 shows the probability distribution of sulphate concentrations at the downstream sampling points on the two rivers for a constant discharge concentration of 5 mg/l. The estimated concentrations at selected points on the probability distribution are presented in Table 5. The UK EQS value for sulphate is an annual average of 4 mg/l. A discharge of 5 mg/l would result in annual average sulphate concentrations considerably below the EQS value, with 5 percentiles of 264 mg/l and 289 mg/l in the Drish and the Rossestown, respectively. Table 5 Estimated concentrations of sulphate at the downstream sampling points Probability of nonexceedance Drish Mine discharge concentration of 25 mg/l Drish Mine discharge concentration of 5 mg/l Rossestown Mine discharge concentration of 25 mg/l Rossestown Mine discharge concentration of 5 mg/l 95 % % % Lisheen Mine EPA Export :22:26:14

5 11 April 27 Page 5 The concentrations calculated in Table 5 become further reduced downstream as the size of the catchment area increases. In Figures 7 and 8, the estimated profile of sulphate concentrations down the two rivers is shown under typical river conditions (Q 5 ) and under low flow conditions (Q 95 ). The background concentration of sulphate in the Suir at Thurles is assumed to be 3 mg/l, based on mass and ionic balance calculations from the other parameter concentrations that have been measured. The natural background concentration of sulphate at various points in the Drish and Rossestown rivers has been taken to be the same as the measured concentration above the discharge. The figures show that a sulphate concentration of 5 mg/l in the discharge would result in maximum sulphate concentrations in the stream at the downstream sampling points in the Drish and the Rossestown of about 467 mg/l or less for approximately 95% of the time, and 289 mg/l or less for approximately 5% of the time. At all points in the receiving waters, the resulting in-stream values are considerably less than the UK EQS value, which is an average annual value of 4 mg/l (i.e. would occur approximately 5% of the time). 6 Stream biology The biological status of river waters in Ireland is assessed using the Q-system. This is based on the species and abundance of aquatic invertebrates collected in a kick-sample. The pollution tolerance of the organisms has been assigned to a five point scale from which is computed a Q-value ranging from 1 to 5. This scoring system is based on the sensitivity of the organisms to organic pollution and dissolved oxygen, and may not correlate well with other pollutants. Values of 4 and 5 indicate good to excellent water quality and are expected to represent waters of good ecological status as defined by the Water Framework Directive (WFD). Biological surveys and assessments have been carried out at six sites on the Drish River in 24, 25 and Sites 1 m upstream of the discharge and at Longfordpass (5 km u/s) have values of Q2-3; essentially the same as the 1 m downstream values. Further downstream, at bridges NE and NW of Castletown and at Boolabeha Bridge, the values only reach Q3. Although further examination of the invertebrates revealed some effects relating to sedimentation and possibly metal toxicity, no impacts were attributed to elevated sulphate levels. Biological data are not available for the Rossestown. There is no thorough macrophyte survey of the rivers in the region of the discharge points. The brief description and photographs in the referenced biological survey report indicate healthy river margins, typical of freshwaters. Filamentous algae growth occurs upstream and downstream of the discharge points probably because of increased plant nutrients such as phosphates and nitrates. There is little experience in the UK of field observations on the effect of sulphate on invertebrates. In the River Line (Southern Region), which had a mean sulphate concentration of 43 mg/l in 1988, there was no reduction in species diversity attributable to sulphate Biological Assessment of the Water Quality of the Drish River in the Vicinity of the Groundwater Discharge from Lisheen Mines, P.Sweeney, May Environment Agency (22) Proposed Environmental Quality Standards for sodium, chloride and sulphate in freshwater, by Fittall J, Hedgecott S and Young W. R&D Technical Report P2-115/TR1, Environment Agency, Bristol. 151 Lisheen Mine EPA Export :22:26:14

6 11 April 27 Page 6 7 Conclusions The impact of an increased sulphate discharge limit of 5 mg/l on downstream water quality has been assessed. The sensitivity of the various receptors to increased sulphate levels has been evaluated through review of relevant standards and published research. A summary of the findings of this impact assessment is presented in Table 6. Receptor Table 6 Summary impact assessment for increased sulphate discharge limit of 5 mg/l Potable water supplies Impact assessment There are no potable water supplies on any of the rivers downstream of the discharges so further consideration of this receptor is not warranted. The most stringent water quality standard for livestock water supplies is 1 Livestock water supplies mg/l. A discharge of 5 mg/l will not therefore have any detrimental impact on livestock water supplies. The limited research on sulphate toxicity suggests that salmonid species can tolerate sulphate concentrations considerably higher than 5 mg/l. The UK EQS of 4 mg/l as an annual average has been set based on the toxicity of the most sensitive species, which include a type of water flea and a freshwater shrimp (see section 3). Below this level, there are no known effects to any form of aquatic life. Aquatic Life An increased discharge of 5 mg/l will result in downstream concentrations considerably lower than the UK EQS value, which suggest that any impact on aquatic life will be negligible. It should also be noted that studies of aquatic invertebrates in the Drish River have not detected any influence that can be ascribed to elevated sulphate levels from the current discharge of 25 mg/l No standards for sulphate in irrigation water supplies have been identified although.. Sulphate has also been shown to have fertility benefits for crops and Irrigation water supplies the normal range of sulphate concentrations in irrigation water supplies is from to 192 mg/l. A discharge of 5 mg/l is therefore extremely unlikely to have any impact on irrigation water supplies, if indeed they exist at all. The available data for the rivers have been used to generate sulphate duration curves. For a continuous discharge of 5 mg/l sulphate, the resulting in-stream values are consistently below the UK EQS value. For the Q 5 plot (upon which the EQS is based), the maximum in-stream sulphate value is estimated at 289 mg/l for the Rossestown and 264 mg/l for the Drish.. It is therefore argued that changing the discharge consent limit to 5 mg/l will have no future impact on invertebrates or fish in the Drish, Rossestown or Suir Rivers. 151 Lisheen Mine EPA Export :22:26:14

7 11 April 27 Page 7 Figure 1 Sulphate concentration (mg/l) in the mine discharge 25 Sulphate Concentration (mg/l) Mine Discharge (Ml/d) Sulphate Concentration (mg/l) Dec-4 Jan-5 Mar-5 Mar-5 Apr-5 May-5 Jun-5 Jul-5 Aug-5 Sep-5 Oct-5 Nov-5 Dec-5 PWE1 - Drish R. outfall PWE2 - Rossestown R. outfall total discharge Mld Figure 2 Sulphate concentration (mg/l) in the mine discharge Mine discharge (Ml/d) 5 1 Dec-5 Jan-6 Mar-6 Mar-6 Apr-6 May-6 Jun-6 Jul-6 Aug-6 Sep-6 Oct-6 Nov-6 Dec-6 PWE1 - Drish R. outfall PWE2 - Rossestown R. outfall total discharge Mld 151 Lisheen Mine EPA Export :22:26:14

8 11 April 27 Page 8 Figure 3 Drish River and Rossestown River sulphate upstream of the discharge point Jun-5 8-May-5 8-Apr-5 9-Mar-5 7-Feb-5 8-Jan-5 9-Dec-4 7-Jul-5 6-Aug-5 4-Dec-5 4-Nov-5 5-Oct-5 5-Sep-5 Drish-upstream Weekly Rossestow n-upstream Weekly Figure 4 Drish River and Rossestown River sulphate downstream of the discharge point 3 3-Jan mg/l Dec-5 29-Nov-5 3-Oct-5 3-Sep-5 31-Aug-5 1-Aug-5 2-Jul-5 2-Jun-5 3-May-5 3-Apr-5 4-Mar-5 2-Feb-5 3-Jan-5 Drish -downstream Daily Rossestown-downstream Daily 151 Lisheen Mine EPA Export :22:26:14

9 11 April 27 Page 9 Figure 5 Flow duration curves (1 day duration) for the Drish River and Rossestown River, River flow (litres/second/sq km) 1. Lisheen Mine Drish River at Athlummon Daily Mean Flow 1651 Rossestown River at Clobanna Daily Mean Flow Figure 6 Estimated percentile concentration of sulphate with an Increased discharge concentration of 65 mg/l sulphate 1-Jan-1994 to 31-Dec Concentration (mg/l) percentile Rossestown Drish 151 Lisheen Mine EPA Export :22:26:14

10 11 April 27 Page 1 Figure 7 Estimated Drish River sulphate profile at normal and low flow conditions for an increased discharge of 5 mg/l sulphate (the last point is in the Suir River, downstream of the confluence) 4 Drish R. sulphate concentration at Q5 flows mg/l distance from outfall Drish R. sulphate concentration at Q95 flows 3 mg/l distance from outfall 151 Lisheen Mine EPA Export :22:26:14

11 11 April 27 Page 11 Figure 8 Estimated Rossestown River sulphate profile at normal and low flow conditions for an increased discharge of 5 mg/l sulphate (the last point is in the Suir River, downstream of the confluence) 35 Rossestown R. sulphate concentration at Q5 flows 3 25 m g/l distance from outfall Rossestown R. sulphate concentration at Q95 flows m g/l distance from outfall 151 Lisheen Mine EPA Export :22:26:14