ARALUEN GROUNDWATER STUDY WATER QUALITY SAMPLING REPORT Department ofLand & WaterConservation Resource Assessment andPlanning Sydney-South CoastRegion March, 2000 Cover Photograph: Araluen Creek downstream of Neringla Road Bridge PDF Version Araluen Groundwater Study Water Quality Sampling Report S. Pritchard G N Russell NSW Department of Land & Water Conservation Resource Assessment & Planning Sydney-South Coast Region March, 2000 Araluen Groundwater Investigation Water Quality Sampling Report i CONTENTS Executive Summary Acknowledgements 1 Introduction 1 1.1 Location 1 1.2 Background 1 1.3 Previous Work 3 1.4 Objectives of the Field Program 3 2 Physical Setting 5 1.1 Topography 5 1.2 Climate 5 1.3 Geology 5 1.4 Hydrogeology 5 3 Water Quality Sampling Program 7 3.1 Introduction 7 3.2 Sample Collection Methodology 9 3.3 Field and Laboratory Testing 10 3.3.1 Field Measurements 10 3.3.2 Laboratory Analyses 10 3.4 Sampling Procedures 11 3.4.1 Purging 11 3.4.2 Sample Collection, Storage and Transport 11 3.4.2.1 Water Quality 11 3.4.2.2 Isotopes 12 3.4.3 Equipment Decontamination 14 3.5 Quality Control 14 4 Groundwater Sampling Results 15 4.1 Field Test Results 15 4.2 Laboratory Analysis Results 16 4.2.1 Privately Owned Installations 16 4.2.2 DLWC Monitoring Bores 19 4.2.3 Surface Watercourses 22 4.3 Sample Quality Control 24 4.3.1 Sample Storage and Transport Checks 24 4.3.2 Duplicate Samples and Laboratory Precision 24 4.4 Isotope Samples and Hydrograph Separation 26 5 Discussion 29 5.1 Water Quality Variations 29 5.2 Pesticide Residues 31 5.3 Mercury Contamination 31 5.4 Suitability of DLWC Monitoring Bores for Selective Monitoring 32 5.5 Impacts on Health 33 5.6 Streamflow Contributions 33 5.6.1 Groundwater Types 33 5.6.2 Hydrograph Separation 34 5.7 Mitigative Measures and Alternatives 38 6 Conclusions 40 Araluen Groundwater Investigation Water Quality Sampling Report ii CONTENTS (continued) 7 Recommendations 42 8 References 43 Appendix A – Araluen Water Quality Sampling Protocol Appendix B – Chain-of-Custody Documentation Appendix C – Sampling Field Logs Appendix D – Laboratory Analytical Results List of Tables 1 Groundwater Installation Distribution 2 Sample Locations 3 Summary Sample Point Distribution 4 Summary Water Quality Sample Collection Details 5 Summary Isotope Sample Collection Details 6 Results of Field Measurements 7 Water Types from Private Installations 8 Water Types from DLWC Monitoring Bores 9 Water Types from Surface Watercourses 10 Duplicate Sample Comparison 11 Results of Deuterium and Oxygen-18 Analysis 12 Comparison with Previous Results 13 DLWC Monitoring Bore Comparison List of Figures 1 General Location Plan 2 Location of Groundwater Works and Sampling Points 3 Comparative Plots of All Results and Private Bore/Well Results 4 Comparative Plots of All Results and DLWC Monitoring Bore Results 5 Comparative Plots of All Results and Surface Water Results 6 Plot of Deuterium vs Oxygen-18 7 Deuterium and Oxygen-18 Hydrograph Separation Plot 8 Cumulative Hydrograph Separation Plot 9 Relative Contributions to Streamflow in Araluen Creek Araluen Groundwater Investigation Water Quality Sampling Report i Executive Summary The rural community of Araluen, located 56 km northwest of Moruya, is almost totally dependent on groundwater for their domestic, stock and agricultural needs. The Araluen Valley groundwater resource, is deemed of highest beneficial use, as it provides drinking water, water for large scale crop irrigation, plus stock and domestic supplies. This aquifer system is also ranked as the third most “at risk” aquifer in the Sydney South Coast Region, based on both the quantity and quality pressures on the groundwater resource. In response to concern over declining water levels in local wells and bores, the Department of Land and Water Conservation (DLWC), undertook a preliminary groundwater study in the Araluen valley in September 1997. The study aimed at gaining an insight into the groundwater resource and addressing issues raised by local groundwater stakeholders. The groundwater sampling component of the 1997 study (Sanders, 1997), discovered water quality issues within the Araluen valley. The results indicated that 14 of the 15 bores/wells sampled showed signs of faecal pollution. The Health Department was subsequently alerted to the study findings, and Araluen residents were advised to boil their drinking water. In response to the 1997 study further work was undertaken by DLWC. A DLWC drilling program was undertaken in 1998 to install nine monitoring bores throughout the valley. Subesquently, all of the nine DLWC monitoring bores have had automatic groundwater level recording devices installed, with ongoing maintenance and data retrieval. In response to concerns regarding pesticide use and heavy metal contamination, a water quality study covering a broad range of analyses was undertaken in October, 1999. The water quality study is the subject of this current report. Additional to the fifteen bores sampled in the 1997 study were five more private bores, the nine DLWC monitoring bores, and four surface water samples. Sampling procedures and methods used in this program were carried out in accordance with a documented protocol written to address site specific issues in the study area. All sample collection was recorded and transport occurred according to DLWC protocols. The results of laboratory analysis suggest groundwater quality in the Araluen valley is generally good, with low total dissolved solids (TDS) and few instances of iron or manganese concentration reported. Most parameters tested were found to occur in low concentrations, with the exception of several microbiological analytes that have health problems associated. This study, therefore confirms the findings of the previous study by Sanders (1997), in reiterating that there are ongoing water quality problems in the Araluen area. Key indicators of faecal pollution were detected in fourteen of the twenty private installations, five of the nine DLWC monitoring bores and the four surface water samples taken from Araluen Creek and Long Flat Creek. This pollution is thought to have originated from the leakage of septic tanks and from the contributions of stock grazing on the valley floor. In most cases, the groundwater pollution appears to be reasonably localised, however, the high levels of E. coli in Araluen Creek and one of its tributaries is of concern. The pesticide sampling, apart from one isolated result, indicated that no significant levels of the nominated pesticides were to be found in either the groundwater or surface water tested, but the suitability of the sampling methods and equipment may be questionable. Similarly, the testing for mercury contamination revealed only three sites with detectable concentrations, albeit below the guideline values. Again, the sampling methods used mean that these results are only preliminary and not entirely definitive. In conjunction with the water quality sampling, the source of baseflow in Araluen Creek was also investigated. By means of sampling the creek water, groundwater and rainfall, then quantifying the naturally occurring isotopes deuterium and oxygen-18, a greater understanding of the baseflow components of the creek has been achieved. Isotope analysis Araluen Groundwater Investigation Water Quality Sampling Report ii has revealed that in one minor rainfall event less than 40% of the flow in Araluen Creek was from rainfall, with the larger component coming from either shallow or deep groundwater or from a source outside the valley. The isotope study also identified several different sources of recharge in the Araluen valley. The bores and wells sampled can be distributed into 4 recharge groups: the shallow alluvial aquifer, a deeper aquifer possibly associated with a major fault zone, a shallow recharge zone of highly permeable material that responds rapidly to rainfall events, and another yet to be identified source. The options for the mitigation of the faecal pollution include: requests for Shire survey of septic tanks in and around Araluen; the construction of a community bore somewhere central within the township and reticulation infrastructure; the use of rainwater for drinking water supply; and the replacement of existing septics with new environmental systems. All of these options have problems associated with the costing and implementation of alternatives, thereby requiring ongoing discussion with various stakeholders and Government agencies. The water quality sampling undertaken in this study was by no means extensive, with less than one third of Araluen’s wells and bores sampled. A more rigorous and detailed investigation of water quality within the valley may be required and could form a major part of any future studies. A holistic approach to the water quality issues in the valley is required to successfully manage the resource. The information gained from this study, along with that of preceding investigations and any future ongoing resource monitoring, will lead to the formulation of a Groundwater Management Plan for the Araluen valley. A meeting between the relevant Government agencies is recommended as the first step in addressing and mitigating the contamination of the groundwater resource. Araluen Groundwater Investigation Water Quality Sampling Report iii Acknowledgements This sampling program was successfully undertaken with the assistance of many individuals. From the Department of Land and Water Conservation, John Bradd, Sarah Bish, Col Maes, Andrew Philippa, Andrew Rose, and Lyn Waldock. From the Araluen Community; Margaret and Stan Wisbey, John Marlton, Noel Wisbey, John Mullins and Charlie Harrison. Also, thanks to Neville Marsden and the other officers at the Braidwood Ambulance Service, who provided a secure base for drop-off and pickup of samples and to Buckleys Transport for the safe transportation of these samples. Barry Horsburgh, from ECOWISE Environmental, provided a prompt and obliging service for the analysis of samples. Sue Wang, from the University of Wollongong, for her assistance in the isotope analysis. Finally, many thanks to all the Araluen landholders for their co-operation and participation in this important study.