N. Somaratne, H. Zulfic, B. Swaffer and G. Ashman 25 November 29
Contents Executive Summary 6 1. INTRODUCTION 7 1.1 Background 7 1.2 Objectives 7 2. GEOLOGY AND HYDROGEOLOGY 7 2.1 Geology 7 2.2 Hydrogeology 1 2.3 Groundwater Quality - Hydrochemistry 14 2.4 Extent and thickness of the fresh water lens and link to Uley South basin 2 3. ASSESSMENT OF RECHARGE 24 3.1 Bore hydrograph response to rainfall method 24 3.2 Limiting winter rainfall method 27 3.3 Chloride mass balance method 28 3.4 Chloroflurocarbon (CFC) Method 29 3.5 Summary of recharge estimates and sustainable resource 3 4. GROUNDWATER USE AND AVAILABLE RESOURCE 31 5. CONCEPTUAL MODEL AND WATER BALANCE 33 6. CONCLUSION 35 7. REFERENCES 36 APPENDIX A: Geological Cross Sections 37 APPENDIX B: Monitoring Bore Hydrographs and Major Ion Chemistry 44 APPENDIX C: Salinity Profiles 54 APPENDIX D: Recharge Calculations 6 Report No: SA Water 29/1 Page 2 of 63
LIST OF TABLES Page Table 1 Coffin Bay current monitoring wells and production well details 11 Table 2 Thickness of the fresh water lens at different locations 21 Table 3 Uley South well details- East from the Gap 22 Table 4 Recharge values from chloride mass balance method 28 Table 5 Summary of recharge estimates 3 Table B1 Major ion chemistry and water types 52 Table D1 Recharge calculations-water level fluctuation method 61 Table D2 Recharge calculations Limiting winter rainfall method 62 Table D3 Recharge calculations- CFC method 63 LIST OF FIGURES Page Figure 1 Figure 2 Basement elevation contour map with the locations of monitoring bores, other stratigraphic bores, production. Manual measurements and water level monitoring from data loggers in LKW 38 and LKW 39 with daily rainfall data for Big Swamp station. 9 12 Figure 3 Potentiometric surface contours- July 29. 13 Figure 4 Piper diagram displaying major ion composition of Coffin Bay Lens A. 14 Figure 5a Major ion concentrations vs Chloride for shallow wells 16 Figure 5 b Major ion concentrations vs Chloride for deep wells 17 Figure 5c TDS and Br ion concentrations Vs Chloride for shallow wells 18 Figure 5d TDS and Br ion concentrations Vs Chloride for deep wells 18 Figure 6 Deuterium vs Oxygen-18 for Coffin Bay groundwaters. 2 Figure 7 Chloride against Deuterium excess plot. 2 Figure 8 Saline water boundary at -53 m AHD in Coffin Bay. 23 Report No: SA Water 29/1 Page 3 of 63
Figure 9 Cumulative deviation from mean rainfall Big Swamp 24 Figure 1a Figure 1 b Data logger records for ULE 22 with pumping data for TWS 1 in Uley South basin for 3 May 22 to 3 December 24. Data logger records for ULE 22 with pumping data for TWS 1 in Uley South basin. For 3 March to 3 July 23 26 26 Figure 11 Drawdown / recovery response Kaltjiti pumping bore. 27 Figure 12 LWRF Method-Winter rainfall (mm) vs water level rise (m). 27 Figure 13a CFC11 ages against groundwater depth. 29 Figure 13b CFC12 ages against groundwater depth 3 Figure 14 Coffin Bay wellfield Annual pumping volume. 31 Figure 15 Coffin Bay wellfield Monthly pumping pattern. 32 Figure 16 Available resource and current allocation Lens area discharging to northern coast 32 Figure 17 Available resource and current allocation Total Lens A area 33 Figure 18 Schematic representation of conceptual model. 34 Figure A1 Locations of cross sections 38 Figure A2 North-south trending cross section across the wellfield, Line A2-A2 39 Figure A3 North south trending cross section from Uley South to the Coffin Bay coast, Line A3-A3. 4 Figure A4 East west trending cross section from LKW 3 to LKW 55, Line A4-A4. 41 Figure A5 Cross section along basement high ride between Coffin Bay Lens A and Lens B, Line A5-A5. 42 Figure A6 3-D view of cross sections. 43 Figure B1 Water level variations in LKW 27. 45 Figure B2 Water level variations in LKW 37. 46 Figure B3 Water level variations in LKW 38. 47 Figure B4 Water level variations in LKW 39. 48 Figure B5 Water level variations in LKW 4. 49 Report No: SA Water 29/1 Page 4 of 63
Figure B6 Water level variations in LKW 41. 5 Figure B7 Water level variations in LKW 43. 51 Figure C1 Composite well log LKW 56 (Smith et al, 27) 55 Figure C2 LKW 37 Salinity profiles 56 Figure C3 LKW 38 Salinity profiles 57 Figure C4 LKW 39 Salinity profiles 58 Figure C5 LKW 4 Salinity profiles 59 Report No: SA Water 29/1 Page 5 of 63
Executive Summary The South Australian Water Corporation (SA Water) is committed to the sustainable management of water resources that it utilises for the public water supply system. As part of this commitment, SA Water has invested significant resources towards improving the level of understanding of the groundwater system in Coffin Bay A lens. The considerable activities in the recent past include; completion of the Aerial Electromagnetics Survey project, construction of two nested piezometers within Coffin Bay National Park, acquiring salinity profiles to identify the presence of salinity stratification, hydrochemical and isotope studies, continuous water level monitoring using data loggers on two observation bores and routine monthly groundwater monitoring. The Aerial Electromagnetic Survey (AEM) provides a more comprehensive understanding of the boundary extent between Coffin Bay and Uley South aquifers. The results of the survey revealed a boundary between the fresh water lens that was compatible with bore hole based elevations. This information was used to identify the location of the basement high marking the separation of the Coffin Bay A lens from the western boundary of Uley South. The AEM also confirms the presence of a freshwater lens under the Coffin Bay National Park, approximately 4 metres thick and situated above a layer of naturally occurring saline water. This new knowledge significantly expands the previously known extent of the Coffin Bay A lens, about 134 Ha derived in the 1992-93 period from the available data. According to the new information, the lens now covers an area of around 76 Ha. It is now estimated that close to half (35 Ha) of the lens discharges groundwater along the northern coastline, and the remainder (41 Ha) towards the south-western coastline. The Quaternary aquifer (Bridgewater Formation) is locally recharged with salinity in the 3-48 mg/l range and a residence time in most parts of less than 42 years. The hydraulic conductivity varies between 3-1 m/day and therefore does not hold recharge mounds. This is supported by the gentle hydraulic gradient found in the lens. The hydrochemical characteristics of the underlying Tertiary Sands aquifer suggests the saline water is entrapped sea water, which has been enriched with Calcium, Magnesium and Bicarbonate ions over geological time through recharge by the Quaternary lens. In this aquifer, at sixty metres depth, salinity is in the range of 44, mg/l; greater than that of sea water. Recharge to the groundwater system was assessed using four different methods. The limiting winter rainfall method provided the largest recharge value of 265 mm/year; followed by chloride mass balance method of 76 mm/year; the bore hydrograph method of 6 mm/year; and the CFC method of around 49-6 mm/year. Whilst spatial and temporal recharge may vary between 6-265 mm/year, the long-term (1987-29) recharge to the lens is considered to be 6 mm/year, with recent recharge (averaged over the last ten years) of about 64 mm/year. This value is consistent with three of the four methods used. Accordingly, average annual recharge to the total lens area is estimated to be 456 ML/year and recharge to the area discharging to the northern coastline is estimated to be 21 ML/year. This recharge to the aquifer will discharge around 172 ML/year along the northern coastline. In line with current allocation principles in the Southern Basin Prescribed Wells Area Water Allocation Plan, 31% of annual recharge is considered a sustainable allocation for public water supply purposes. On this basis, the total available allocation is estimated to be 14 ML/year, with 65 ML/year available from the area discharging to the north. This compares to the current SA Water allocation of 112 ML/year which is 8% of the estimated total available allocation. The remainder of the water would primarily discharge to the sea. Report No: SA Water 29/1 Page 6 of 63
1. INTRODUCTION 1.1 Background In the recent past, Coffin Bay A lens has assumed particular significance as a source of reticulated public water supply. Consequently an understanding of the extent of the lens and available resource has become an important issue. Whilst it is generally known that the Coffin Bay lens A extends under the Coffin Bay National Park, land access for drilling to confirm this has been limited. Therefore, in 26, South Australian Water Corporation (SA Water) in association with the Department of Water, Land and Biodiversity Conservation (DWLBC) and the Eyre Peninsula Natural Resources Management Board (EPNRMB) initiated the Coffin Bay Aerial Electromagnetic (AEM) Survey Project as a non intrusive method of assessing aquifer extent. Subsequently, two monitoring wells were also drilled in the National Park in order to verify the AEM results. The AEM results show that a large fresh water lens, exceeding 4 m in thickness exists under Coffin Bay National Park. This was also confirmed by two new boreholes drilled in 27. With this new information, it is considered timely to undertake an allocation review and develop a portion of this resource for town water supply. 1.2 Objectives Contrary to previous belief, Coffin Bay Lens A is spread over a wider area, including into the National Park. The previous water resources assessment in Coffin Bay Lens A was limited to investigation work carried out by the former Department of Mines and Energy in 1985-1986 for Coffin Bay town water supply wellfield development. Since then, a variety of groundwater and salinity monitoring have been undertaken, without a major review until the AEM survey in 26 and associated drilling program. In 29, EPNRMB extended the monitoring network by installing two additional monitoring wells. With this new information, it is considered timely to re-define the extent and available resource. The objectives of this study are: I. A compilation of existing knowledge/data II. A compilation and summary of the relevant results from recent drilling program(s) and analysis of AEM data III. A description of the improved understanding of the hydro-stratigraphy, groundwater levels, groundwater flow, recharge and extent and thickness of fresh water lens. IV. Sample, analyse and interpret additional hydrochemical and isotope data. V. Combine the above into a conceptual model for the Coffin Bay Lens A 2. GEOLOGY AND HYDROGEOLOGY 2.1 Geology Borehole Data Borehole data in the adjacent Uley South Basin occurs predominantly within three different Geological Formations, namely the Quaternary Limestone (Bridgewater Formation), the Tertiary Clay aquitard (Uley Formation) and the Tertiary Sand aquifer (Wanilla Formation). The occurrence of these Formations is typical across the Southern Eyre Peninsula, including Coffin Bay. Report No: SA Water 29/1 Page 7 of 63
The study area is overlain by an unconsolidated calcareous sand which is capped by calcrete in the wellfield area. Available lithological data for monitoring bores (Figure 1) was used to plot four geological cross sections across the Lens A, which are shown in Appendix A. Figure A2 is the north south trending cross section across the wellfield. The sand overlies a soft sticky plastic brown clay which thins towards production bore 2. Beneath this clay is a moderately to well indurated fossiliferous calcarenite (Bridgewater Formation) thinning towards LKW 37 with white grey clays occurring at depth. Immediately underlying the Bridgewater Formation are brown green stiff plastic clays, possibly the Tertiary clay aquitard with weakly cemented sands and soft clays of Wanilla Formation (Denis, 1989) In Figure A3, the east to north-west trending geological cross section is presented, starting from Uley South Basin to the sea at Coffin Bay. This cross section intersects LKW 32 bore (a dry bore) which is located in the basement high ridge, that separate Coffin Bay Lens A from Lens B (Figure 1). It is noted here that the Tertiary Clay layer found in production wellfield area is absent in the upper part of the catchment as shown in LKW 27 well and that both the Limestone and Tertiary Sand contains fresh water of salinity about 42-44 mg/l. Towards the coast, Tertiary Clay is found in LKW 4 onwards to LKW 37 and possibly beyond. In this part of the lens the Tertiary Sand contains saline water. Figure A4 shows a cross section running west to east of the lens from LKW 57 to LKW 3. Once again, it is clear that Tertiary clay presence is limited to the depression area of the lens where the production wellfield is located. It is also noted that despite LKW 57 in the National Park being drilled to 6 m depth, neither the Tertiary Sand layer nor the basement rock has been intersected. Saline water was found at a depth of 55 m indicating the availability of fresh water to about 5 m depth in this area. The cross section L5 in Figure A5 shows the basement high area between Lens A and B. AEM Survey Data One of the main aims of the use of airborne electromagnetic is to map elements of the Quaternary and Tertiary aquifer system in the study area and the basement elevations. In addition, the AEM survey identifies high conductivity areas, which are either clay rich areas or areas containing saline groundwater. A complete description of AEM survey methodology, data and analysis is described by Fitzpatrick et al (29). For brevity, data pertinent to this study is presented in this report. An important element of the AEM is to define base elevations of the Tertiary Sand aquifer. It was found difficult to distinguish the base of the sand layer from the weathered basement. Both exhibit similar properties, and hence base elevation data is combined with the weathered regolith layer. On close examination of the base elevation data, it was found that in the study area, there is a coordinate shift required of approximately 7 m east. This was corrected and the contoured aquifer basement is presented in Figure 1. It is noted here that basement high areas of the AEM survey are reasonably well matched to the basement high areas mapped using the borehole data. An example is the northsouth running basement high ridge between Coffin Bay Lens A and B. A similar match was found in the adjacent Uley South Basin where the AEM survey basement high area agreed with borehole data described by Evans (1997). Elsewhere in Coffin Bay, deep boreholes such as LKW 38, LKW 4, LKW 55 and LKW 57 confirm that basement is below -4 to-5 m AHD as indicated by AEM data. As these aquifer bounds compare well with borehole data, it provides confidence in extrapolating basement elevations into areas where bore data is absent. Therefore, the eastern boundary of Coffin Bay Lens A is now extended to the basement high ridge running in a north-south direction, and is conservatively marked as lying between -1 & -2 m AHD as shown in Figure 1. Accordingly, the western boundary of Uley South Basin is also adjusted to a new position indicated by the line A-B-C in Figure 1. Report No: SA Water 29/1 Page 8 of 63
Wellfield Area C The Gap B A Figure 1. Basement elevation contour map with locations of monitoring bores, other stratigraphic bores (unit number) with Coffin Bay production bores TWS 1-6. Report No: SA Water 29/1 Page 9 of 63
2.2 Hydrogeology Aquifer Characteristics In 1985-86, a water resources survey/investigation was carried out in the depression area of the lens, where the production wellfield is located. In this investigation, four of the wells were deep investigation bores in order to define the formation and salinity stratification. These wells were completed as monitoring wells LKW 37 to LKW4. In addition three production wells (TWS 1-3) were also drilled. In 29, SA Water drilled an additional three productions wells (TWS 4-6) in order to replace TWS 1 and to reduce the pumping rate of each production bore to a low value (5 L/s) and spread pumping load across a larger area. These production bores were pump tested by DWLBC and analysed by Water Search Pty Ltd. Each bore was subjected to a 3x1 minutes step drawdown tests at 3, 6, 9 L/s with resultant drawdowns of.77 m, 1.36 m and 9.17 m respectively. The well number TWS 6 was also subjected to a constant flow rate test at 9 L/s for 6 hours and was found to have drawdowns of 8.74 m. During pump tests, water levels were monitored in LKW 38 & 39 as well as two new production wells and no response was found to the pumping. In each test well it was found that water level recovered to pre-pumping levels in less than three minutes. Transmissivity values calculated by Denis (1989) indicate that the aquifer is moderate to highly transmissive (Table 1). Aquifer hydraulic characteristics may be variable throughout the basin depending on the nature of the limestone, degree of cementation etc, as found in the wellfield area. Highest hydraulic conductivity (K) was found in the production well no 1 (TWS 1). Fast recovery of water levels following pump tests also indicate relatively high transmissivity of the aquifer, similar to that found in the Uley South wellfield area. The storage coefficient of in the order of.17 is typical of this kind of aquifer. Water Level Monitoring Observation bores were first established in the lens by the former Department of Mines and Energy with the construction of LKW 27 in 1959. Significant groundwater monitoring commenced after Oct 1986 by establishing four additional wells (LKW 37, LKW 38, LKW 39 and LKW 4) as part of the investigation work for establishing the town water supply wellfield. A reliable data set is currently available for the above wells from 1986 (Figures B1-B7 in Appendix B). In 22, SA Water and DWLBC installed two data loggers in LKW 38 and LKW 39 wells located in the wellfield area for the purpose of assessing recharge. Water level data from the loggers and Big Swamp rainfall are shown in Figure 2. It is noted that Big Swamp rainfall is the closest weather station but does not necessarily reflect actual Coffin Bay rainfall. It is also noted that there is an apparent survey error of the elevation of LKW 38 which is currently about.3 m lower than actual value. LKW 38 and LKW 39 are monitoring the same aquifer at two different depth intervals and when the elevation is correct the data from both overlaps. Both of these sites were completed as dual completion wells. As a part of the AEM study, SA Water drilled two additional deep bores (LKW 55 and LKW 57) and two shallow bores (LKW 56 & LKW 59) in the National Park in 27. The EPNRMB further expanded the monitoring network by adding two more bores LKW 58 & LKW 6, in 29. Report No: SA Water 29/1 Page 1 of 63
Table 1. Coffin Bay current monitoring wells and production well details. Well Name Unit Number Drilled Depth(m ) Complete d Depth (m) Cased to (m) Production Zone (m) Yield L/s T (m 2 /day) S y Aquifer LKW 27 628-143 82.3 6 43 43-6 QLS/S LKW 37 5928-31 41 36.5 35.5 35.5-36.5.5 - - T Clay LKW 38 5928-33 49 27 15.5 15.5-21.5 QLS LKW 39 5928-34 36 36 27 27-36 17 72 QLS LKW 4 5928-36 6 54 48 48-54 T Sand LKW 43 5928-38 NA NA NA NA NA NA NA QLS LKW 55 5928-418 61 61 47 47-59 QLS LKW 56 5928-421 6 6 3 3-6 QLS LKW 57 5928-419 63.5 63.5 43 43-61 QLS LKW 58 5928-435 18 18 14 14-17 QLS LKW 59 5928-422 6 6 3 3-6 QLS LKW 6 5928-436 22 22 9.5 9.5-22 QLS TWS 1 5928-35 39 34 26 26-34 12 QLS TWS 2 5928-37 36 36 24 24-36 79.17 2 QLS TWS 3 5928-32 31 31 22 22-31 27-35 QLS TWS 4 5928-437 28.6 19.3 16 16-19.3 2 QLS TWS 5 5928-438 34 33.6 26 26-33.6 15 QLS TWS 6 5928-439 29 27.8 25 25-29 9 QLS QLS: Quaternary Limestone; S: Sand; T Clay: Tertiary Clay; T Sand: Tertiary Sand; NA=Not Available Report No: SA Water 29/1 Page 11 of 63
RSWL (mahd) Daily RF mm Coffin Bay Groundwater Lens A 1.4 1.2 LKW38 LKW39 LKW 38 BR LKW 39 BR 7 6 1 5.8.6 4 3 2.4 1.2 13-Jul-9 4-Apr-9 25-Dec-8 16-Sep-8 8-Jun-8 29-Feb-8 21-Nov-7 13-Aug-7 5-May-7 25-Jan-7 17-Oct-6 9-Jul-6 31-Mar-6 21-Dec-5 12-Sep-5 4-Jun-5 24-Feb-5 16-Nov-4 8-Aug-4 3-Apr-4 21-Jan-4 13-Oct-3 5-Jul-3 27-Mar-3 17-Dec-2 8-Sep-2 31-May-2 Figure 2. Manual measurements and water level monitoring from data loggers in LKW 38 and LKW 39 wells with daily rainfall data from Big Swamp station (Note: LKW 38 and LKW 39 monitor the same aquifer at two different depths. There is an apparent survey error of measuring point elevation of LKW 38) Water level data for the Quaternary Limestone aquifer was used to construct a water level elevation map for the lens (Figure 3). Along the coast, zero heads were assigned as control points, although it is known that several springs emerge at the coast, suggesting head values are higher than zero. In addition to this, an extrapolated water level for LKW 9 (5.3 mahd) on the western boundary of Uley South Basin was used as the eastern most control point. Water level contours show a relatively flat hydraulic gradient of about.5 towards the sea. Flow vectors were used to identify a streamline that divides groundwater flow in the Coffin Bay Lens A to the northern or southern coastlines. This streamline divides the lens into two distinct parts assuming groundwater discharge occurs in opposite directions. Report No: SA Water 29/1 Page 12 of 63
Groundwater divide Figure 3. Potenziometric surface contours for Quaternary aquifer - Sep 29 Report No: SA Water 29/1 Page 13 of 63
2.3 Groundwater Quality - Hydrochemistry Major ion chemistry An important task of this groundwater investigation, which has not been undertaken prior to this study, is the compilation and presentation of chemical data of the Coffin Bay Lens A. For this purpose, groundwater sampling was undertaken in Sep 29, using the low flow groundwater sampling technique. Piper Diagrams as shown in Figure 4 are a common method used to present chemical data. Data used for this study is contained in Table B1 in Appendix B. According to Figure 4, the fresh groundwater in the lens has no dominant cation, instead containing a mixture of either Ca- Mg, with Na ions present, suggesting dolomitic limestone may be the dominant rock type in Bridgewater Formation, and hence the origin of groundwater. In contrast, the presence of HCO 3 ions indicate a dominance of anions in fresh water bores. High salinity water in LKW 4 and LKW 57 are plotted with seawater since these waters are dominant with Na + and Cl ions. Groundwaters in LKW 58, LKW 37 and LKW 39 are moving towards the NaCl end. Piper Plot 2 4 8 6 4 2 Mg 8 V SR U T E EA NM O H L P 6 4 Cl + SO4=> 8 6 P KI BC FG IQ 2 N H VLO ME SR UA E T I 8 6 K BC 2 <=Ca + Mg 4 FG IQ 2 SV RI NO LE MU AE T 4 SO4 8 6 HP 6 4 K BC 8 2 FQ GI Legend Legend E LKW 38_18.5 m E LKW27_48.5 m B LKW 39_27 m I LKW 37_35.5 m C LKW 39_31.2 m F LKW 4_48 m A LKW 38_15 m H LKW 57_43 m U CB_TWS 4 Q Sea Water at Coffin Bay R CB_TWS 1 S CB_TWS 2 G LKW 4_53 m V CB_TWS 6 T CB_TWS 3 L LKW 59_3 m I LKW 57_6.5 m P Rain Gauge at LKW 38 M LKW 6_14 m N LKW 6_19.5 m O LKW 27_43 m K LKW 58_14 m Ca Na+K HCO3 Cl Figure 4.. Piper diagram displaying major ion compositions of Coffin Bay Lens A. The composition of fresh groundwater in coastal aquifers such as Coffin Bay is often dominated by Ca +2 (or Ca +2 and Mg +2 ) and HCO3 ions which results from calcite (or dolomite) dissolution. The cation exchanger is then also dominated by adsorbed Ca +2 (or Ca +2 and Mg +2 ). In seawater, Na + and Report No: SA Water 29/1 Page 14 of 63
Cl - are the dominant ions, and sediments in contact with seawater will have mostly Na + on the exchanger. When seawater intrudes into the coastal fresh water aquifer, an exchange of cations takes place according to: Na+ + ½ Ca-X 2 Na X + ½ Ca 2+ where X indicates the soil exchanger. In the reaction, Na + is taken up by the exchanger while Ca 2+ is released. Since the dominant anion Cl - remains the same, the water quality changes from a NaCl to a CaCl 2 type of water. This water was not observed in either coastal bores LKW 37 or LKW 58. The reverse process takes place during freshnening, i.e when fresh recharge groundwater with Ca 2+ and HCO 3 ions, flushes a salt water aquifer, Na X + ½ Ca 2+ Na+ + ½ Ca-X 2 The sediments now adsorb Ca 2+ while Na + is released and a Na HCO 3 type water results. In this way, the water composition can indicate whether up-coning of seawater occurs, or conversely whether fresh water is flushing salt water from the aquifer (Appelo and Postma, 27). Such is the case of LKW 37 and LKW 58 waters, where Na-Mg-HCO 3 -Cl waters occur. This freshening of the saline wedge (diffuse zone) is seen in low ion ratios of; Ca/Cl and Mg/Cl, with about.2 in LKW 37 and about.9 in LKW 58 respectively. Similarly, high Na/Cl ratios of 1.1 particularly in LKW 37 and average (.47) in LKW 58 were also observed. Three high salinity water samples, LKW 4 at 48 m, LKW 4 at 53 m, and LKW 57 at 6.5 m are presented in Figure 5b and 5d. These plots show that Na, K, Br and Mg are on the seawater dilution line, with the exception of Na, TDS and Mg in LKW 57 at 6.5 m depth. Elevated Na, and hence TDS in LKW 57 at 6.5 m may be due to ancient sea water being enriched with these elements over the geological period. Similarly with increasing depth, depletion of SO 4 is observed, and this may be due to precipitation of gypsum. High salinity water of about 44, mg/l found in LKW 57 at 6.5 m depth is due to enrichment of entrapped sea water, primarily by Na, Ca, Mg and HCO 3 ions. The occurrence of Br - along the seawater dilution line in both shallow (freshwater) and deep (brackish/saline water) wells is due to Br - ions not undergoing any changes throughout the hydrological cycle (from evaporation of sea water to discharge of groundwater). Report No: SA Water 29/1 Page 15 of 63
SO4 2- (mmol/l) HCO3 - (mmol/l) Na+ (mmol/l) K+ (mmol/l) Ca2+ (mmol/l) Mg2+ (mmol/l) Coffin Bay Groundwater Lens A 2 L59_4 2.4 L58_14 1.6 2 1.2.8 L27_48.5 L27_43 L6_14 T4_ 16 L6_19.5 L38_18.5 L38_15 T6_25 L57_43 L39_27 L39_3.2 L58_14 1.6 1.2.8 T4_ 16 L38_18.5 L38_15 L27_48.5 L27_43 L59_4 T6_25 L6_19.5 L37_35.5 L57_43 L39_3.2 L39_27 L6_14.4 L37_35.5.4 2 4 6 8 1 12 14 16 18 2 Cl- (mmol/l) 2 4 6 8 1 12 14 16 18 2 Cl- (mmol/l) 1 2.8 L39_27 15.6 L39_3.2 1 L39_27 L39_3.2 L58_14.4 L37_35.5 5 4 3.6 3.2 2.8 2.4 2 1.6 1.2.8.4 L37_35.5 T4_ 16 L59_4 L27_48.5 T6_25 L6_19.5 L27_43 L6_14 L38_18.5 L38_15 2 4 6 8 1 12 14 16 18 2 Cl- (mmol/l) L59_4 L38_18.5 L37_35.5 L38_15 L6_19.5 T4_ 16 T6_25 L27_48.5 L6_14 L27_43 L57_43 L57_43 L39_27 L39_3.2 L58_14 2 4 6 8 1 12 14 16 18 2 Cl- (mmol/l).2 1 9 8 7 6 5 4 3 2 1 L38_15 T6_25 L59_4 L6_14 L6_19.5 2 4 6 8 1 12 14 16 18 2 Cl- (mmol/l) L37_35.5 L59_4 T4_ 16 L27_48.5 L27_43 L38_15 L38_18.5 T6_25 T4_ 16 L27_48.5 L6_14 L6_19.5 L38_18.5 L27_43 L57_43 L57_43 L39_27 L39_3.2 L58_14 L58_14 2 4 6 8 1 12 14 16 18 2 Cl- (mmol/l) Figure 5a. Major ion concentrations versus chloride (Cl) concentrations for shallow wells. Report No: SA Water 29/1 Page 16 of 63
SO4 2- (mmol/l) HCO3 - (mmol/l) Na+ (mmol/l) K+ (mmol/l) Ca2+ (mmol/l) Mg2+ (mmol/l) Coffin Bay Groundwater Lens A 4 72 64 L57_6.5 3 56 48 2 L57_6.5 4 32 L4_53 1 L4_48 L4_53 24 16 8 L4_48 6 1 2 3 4 5 6 Cl- (mmol/l) L57_6.5 3 1 2 3 4 5 6 Cl- (mmol/l) 5 24 4 18 3 2 L4_53 12 L57_6.5 1 L4_48 6 L4_48 L4_53 12 1 2 3 4 5 6 Cl- (mmol/l) 1 1 2 3 4 5 6 Cl- (mmol/l) 9 1 8 8 6 7 6 5 L4_48 L4_53 L57_6.5 4 4 3 2 L4_48 L4_53 L57_6.5 2 1 1 2 3 4 5 6 Cl- (mmol/l) 1 2 3 4 5 6 Cl- (mmol/l) Figure 5b. Major ion concentrations versus chloride (Cl) concentrations for deep wells. Report No: SA Water 29/1 Page 17 of 63
Figure 5c. TDS and Br ion concentrations versus chloride (Cl) concentrations for shallow wells. Figure 5d. TDS and Br ion concentrations versus chloride (Cl) concentrations for deep wells. Report No: SA Water 29/1 Page 18 of 63
Stable Isotopes The empirical relationship of δ 2 H =8δ 18 O+1 (Craig, 1961) for meteoric water on a global scale is a common reference for local studies. Water samples were taken in Sep 29 for stable isotopes 18 O and 2 H analysis as part of this study. Low flow sampling technique was employed for sample collection at targeted depths. All samples were stored in 5ml McCartney glass bottles and analysed by CSIRO Land and water laboratory by Isotope Ratio Mass Spectrometry (IRMS). The world meteoric water line (WMWL) relationship varies depending on location and it is necessary to define a local meteoric water line relationship derived from the annual weighted mean of δ 2 H and δ 18 O in local rainfall. Because of lack of sufficient data for either Port Lincoln or more specifically for Uley South, the Adelaide MWL is taken as the reference in this study. Stable isotope data were plotted with the World & Local Meteoric Water Line (LMWL) Adelaide and presented in Figure 6. Groundwater samples from the Coffin Bay are plotted with the Adelaide winter and summer average isotope (Evans, 1997). In Coffin Bay groundwaters, isotopic values are clustering around Adelaide winter rainfall average isotopes indicates that recharge is taking place predominantly during winter months. The groundwaters are significantly depleted in the heavy isotopes relative to sea water (δ 2 H and δ 18 O =%) which indicates a meteoric origin for Coffin Bay groundwaters. The predominantly tight cluster of points suggests that the recharge process is similar across the lens (after Evans, 1997). When water is subject to evaporation the lighter isotopic species are preferentially removed thus remaining water becomes relatively enriched in the heavier isotopic species. Relative to MWL this enriched water will plot below and on a line of slope less than eight (and 6.84 for Adelaide MWL). Lack of evaporation effect on shallow wells indicate that recharge process relatively fast and hence no opportunity to undergo evaporation during recharge. Stable isotope compositions of groundwater samples exhibit an approximate linear trend on a conventional δ 2 H - δ 18 O plot, reflecting the strong control that evaporation has on these groundwaters. The degree of evaporative enrichment of the groundwater compositions is correlated well with chloride (Figure 7). This suggests that the recharge mechanism for the fresh samples may be distinct from that of the more saline sample of LKW57 at 6.5 m depth. The stable isotope signatures of the most saline groundwater sample (LKW57 at 6.5 m) is not significantly negative than sea water, therefore demonstrate that these waters were derived originally from sea water, and enriched to salinities even higher than that of sea water. Report No: SA Water 29/1 Page 19 of 63
Figure 6. Deuterium vs Oxygen-18 for Coffin Bay groundwaters Figure 7. Deuterium Vs Chloride plot Report No: SA Water 29/1 Page 2 of 63
2.4 Extent and thickness of fresh water lens and link to Uley South basin Extent As mentioned in Section 1, the extent of the Coffin Bay Lens A is controlled hydrogeologically by the basement and water level elevations of the aquifer, with the eastern boundary of the lens formed by the north-south trending basement high ridge. The coastal boundary of the lens is taken as the.2 mahd contour line, which is at least 5-75 m from the coast. The total Lens A area within these boundaries is about 76 Ha. When the lens is divided into two portions according to groundwater discharge direction, an area of about 35 Ha of the lens discharges to the northern coastline and 41 Ha discharges to the southern coastline. For comparison, the 1992/93 estimate of the Coffin Bay Lens A is about 134 Ha, of which all the groundwater discharges to the northern coast line (Figure 3). Thickness Assessment of the thickness of the lens was approached in different ways in different parts of the lens since the number of controls needed to be considered was varied. For example, to the eastern boundary of the lens, fresh water thickness is the elevation difference between water levels and the basement. Within the wellfield area, fresh water thickness is the elevation difference between water levels and top of the Tertiary Clay layer, since this clay layer is the control. Elsewhere in the National Park area, where saline water is present (Figure C1 in Appendix C) but the Tertiary Clay layer is absence, the control is the salinity level in the profile, which is considered as 1 mg/l. Using this approach the estimated thickness of the fresh water lens at different locations is given in Table 2 below. Table 2. Thickness of the fresh water lens at different location. Location Fresh Water Thickness (m) Criteria Eastern boundary of the lens 12-22 Extrapolated water level and AEM survey basement elevation LKW 27 33 Measured water level and basement elevation (from bore log) Wellfield area (LKW 38 LKW 39 and LKW 4) 28-35 Measured water level and elevation of Tertiary Clay (from bore log) Towards the coast: LKW 37 25 Measured water level and elevation of Tertiary Clay (from bore log) National Park : LKW 55 & LKW 57 47 Measured water level and elevation of 1 mg/l salinity Report No: SA Water 29/1 Page 21 of 63
The AEM survey produced maps of the salinity distribution in the Lens A. As indicated in Figure 8, the AEM results agree sufficiently with findings from borehole data and hence are considered reliable. Note, for example, the salinity profiles (as shown in Appendix C) for LKW 56 in the National Park and LKW 4 in the wellfield, which penetrates into the saline Tertiary sands. As previously discussed in Section 2.3, hyper-saline water found in the lens below -53mAHD is entrapped seawater that has been enriched over its geological history. Link to Uley South Basin The linking of Coffin Bay Lens A to the adjacent Uley South Basin in the east occurs at the small basement low area at coordinate points 545,941 E, 6161, 716 N (indicated as The Gap in Figure 1). The Limestone in most parts of the Uley South Basin east from the Gap to the Uley Wanilla Basin is dry. It is therefore considered that, if any hydrogeological link does exist, it would be via the thin Tertiary Sand aquifer and not via the Limestone. Details from wells drilled in the Uley South side of the gap indicate that depth to water is over 23 m (Table 3). The well yields are low, and hence it is not expected that any significant groundwater flow occurs from Uley South through the Gap to Coffin Bay. Table 3. Uley South well details- East from the Gap. Parameter Bore Name LKW 9 LKW 11 LKW 12 LKW 13 LKW 14 Bore Depth (m) 5.3 45.7 61 62.4 85 Cased to (m) 38-36 - 5.6 Depth to Limestone Base (m) 34.14 29.8 27.4 3.4 51 Depth to Tertiary Clay Base (m) No Clay 45.7 No Clay 44.2 No Clay Depth to Tertiary Sand Base (m) 47.8 NA 61 56.6 58.6 Standing Water level (m) 27 23.3 25 39.5 43.5 Year SWL 1989 199 29 1996 1981 Yield (L/s) 2.5.63 - - 2.5 Water Cut (m) 29.8 NA NA 48.7 49.3 Comments 4.3 m water in Limestone NA 62 m west of LKW 13 Dry Limestone 1.7 m of water in Limestone Report No: SA Water 29/1 Page 22 of 63
LKW 4 Saline water at this depth LKW 27 No saline water,tds 44 mg/l in Sand Saline Water at this Depth (LKW 55 & 57) Saline/brackish water/clay Figure 8. Saline water boundary at -53 m AHD in Coffin Bay (Red colour area) from AEM Survey (after, Fitzpatrick et al, 29). Report No: SA Water 29/1 Page 23 of 63
Rainfall deviation mean % Annual Rainfall mm Coffin Bay Groundwater Lens A 3. ASSESSMENT OF RECHARGE 3.1 Bore Hydrograph Response to Rainfall Long-term rainfall patterns will influence the amount of water available for recharge and surface runoff. In general, the trend in rainfall pattern can be evaluated by comparing the cumulative deviation from the mean (monthly or yearly) rainfall over time. Annual rainfall data with deviation from the annual mean (546 mm) and the percentage of cumulative deviation is presented in Figure 9. The positive trend of the cumulative deviation graph indicates a period of above average rainfall and the negative trend indicates below average rainfall years. The horizontal trend, parallel to the time axis, is the period of average rainfall. According to Figure 9, in 1992 (874 mm) and in 2 (654 mm) above average rainfall was recorded. Similarly, in 1994 (413 mm) and 1998 (433 mm), below average rainfall occurred. 1.5 1.5 -.5-1 -1.5 Deviation Annual Rainfall Cum Dev % Average 1 8 6 4 2-2 -4-6 -8-1 Figure 9. Cumulative deviation from mean rainfall 195 to 28 Big Swamp Report No: SA Water 29/1 Page 24 of 63
Changing water levels across the basin reflects the recharge characteristics of aquifers and hence is widely used for recharge estimation. In Coffin Bay Lens A, there are four monitoring bores available; LKW 27, LKW 37, LKW 38, LKW 39 and LKW 4 that provide reasonably continuous data since 1986. A decision was made to exclude data from LKW 4 as this bore is completed in Tertiary Sand. Similarly, because LKW 41, LKW 26 and LKW 43 have been subjected to pumping, this data was also excluded. Despite LKW 37 being completed in the Tertiary Clay underlying the Quaternary Limestone aquifer, data from this well was used. This is because LKW 37 was completed just below the Limestone with a short screen interval and is likely to be influenced by fresh recharge. The water levels of this bore may reflect the behaviour of the limestone aquifer. The monitoring bores LKW 38 and LKW 39 were completed adjacent each other in the Quaternary Limestone aquifer at two different depths. The bores are located within the wellfield and at approximately 5 m, 14 m and 24 m away from production bores TWS 1, TWS 2 and TWS 3 respectively. The influence of pumping from the production bores on adjacent monitoring bores such as LKW 38 and LKW 39 was closely examined. Inspections of the data logger records (two hour intervals) of both LKW 38 & LKW 39 do not show any drawdown-recovery signatures (Figure 2), despite the production bores being pumped for 1 hours continuously. This is further illustrated by comparing hourly pumping data obtained from the SCADA system for TWS 1 in Uley South with water level records from the data logger installed in ULE 22. The TWS 1 bore pumps at 34 L/s continuously for approximately 1 hours per day on most days, (except during periods of pump failure/repair etc). If there had been any influence of pumping on water level at ULE 22, which is about 6 m from the pumping bore, a drawdown/recovery response would be recorded in the data logger corresponding to pump on/off cycles (Figures 1 a & b). By way of comparison, an example is given in Figure 11 to illustrate the influence of pumping on data logger records. The data is for the Kaltjiti pumping bore in the far north of South Australia (AGT Report No: 28/31) which is also used as a monitoring bore. A data logger has been installed and full drawdown and recovery is recorded corresponding to pump operating cycles. If there had been any significant drawdown/recovery influence on water levels in LKW 38, LKW 39 and ULE 22 corresponding to pumping, that should have been recorded in data loggers in a similar manner to the Kaltjiti bore, albeit at low amplitude. It was therefore concluded that, due to the high transmissivity of the Coffin Bay and Uley South aquifers, the influence of pumping on water levels in monitoring bores appears insignificant. An important factor that this method relies upon to estimate recharge is the specific yield of the aquifer. Pump test data at the wellfield provides a single value of specific yield of.17 (Table 1). This value is assumed to be fairly constant throughout the sandstone/sand aquifer system. The recharge values obtained by this method are given in Table D1 in Appendix D. Report No: SA Water 29/1 Page 25 of 63
RSWL (m AHD) RSWL (m AHD) Coffin Bay Groundwater Lens A 1.4 1.2 1.8.6.4.2 Pumping ULE 22 Logger ULE 22 Bore Run 3-May-2 3-Nov-2 3-May-3 3-Nov-3 3-May-4 3-Nov-4 8 75 7 65 6 55 5 45 4 35 3 25 2 15 1 5 Figure 1 a. Data logger records for ULE 22 with pumping data for TWS 1 in Uley South basin for 3 May 22 to 3 December 24.(Note: Recharge pulses recorded in April, May June 23 are corresponding to rainfall at Big Swamp records 7.7 mm, 88 mm and 19 mm respectively). 1.4 1.2 1.8.6.4.2 Pumping ULE 22 Logger 3-Mar-3 3-Apr-3 3-May-3 3-Jun-3 3-Jul-3 8 75 7 65 6 55 5 45 4 35 3 25 2 15 1 5 Figure 1 b. Data logger records for ULE 22 with pumping data for TWS 1 in Uley South basin for 3 March to 3 July 23. Report No: SA Water 29/1 Page 26 of 63
Figure 11. Drawdown / recovery response from the Kaltjiti pumping bore in the far north of South Australia (AGT Report No. 28/31). 3.2 Limiting Winter Rainfall Method Barnett (1978) used and described the Limiting Winter Rainfall Method (LWRF) as an appropriate method for assessing recharge in the Uley South basin. This method was subsequently used for developing the conceptual model for Uley South by Harington et al (26). The LWRF assumes a threshold of winter rainfall, below which no recharge occurs, and above which all winter rainfall contributes to recharge. Hydrograph analysis was conducted in order to obtain water level rise during the winter months (April-September) plotted against total winter rainfall (see Figure 12). This resulted in an estimation of the threshold value of 13 mm winter rainfall, which was used for subsequent calculation of recharge values for 1987-29 period, (see Table D2 in Appendix D). Threshold value = 13 mm Figure 12. LWRF Method Winter Rainfall (mm) vs Water Level Rise (m) Report No: SA Water 29/1 Page 27 of 63
3.3 Chloride Mass Balance Average recharge over the Coffin Bay lens can be estimated from a knowledge of the concentration of the chloride ion in the rain water and the groundwater from the simplified form : R= P C p / C g where; P: Average annual rainfall (mm/year), C p : Chloride ion concentration in rain water (mg/l), C g : Chloride ion concentration in groundwater (mg/l); and R is the recharge (mm/year). This assumes no surface runoff takes place and no chloride ion is added to the recharging water by dissolution of halite or due to saline water intrusion. In the absence of direct measurement, the chloride concentrations in the rainfall can be estimated from Hutton and Leslie (1958) using: Chloride[mg/L]=35.45 x {.99/d.25 -.23}, where d is distance in km from the ocean. In this study, considering prevailing wind direction, distance is taken from the southern coast line rather than the closer northern coast line of Coffin Bay. Chloride concentrations in groundwater were determined by employing the low flow sampling technique on targeted bores in Sep 29. The mean annual rainfall was taken as 546 mm, and the calculated recharge values are tabulated in Table 4. Table 4. Recharge values-chloride mass balance Bore Name Distance from prevailing wind direction South west coast (km) Cp (mg/l) TDS (mg/l) Cg (mg/l) Recharge (mm/year) LKW 27 1.2 11.4 42 85 73 LKW 38 1.2 11.4 44 11 62 LKW 59 6.4 11.3 49 15 72 LKW 6 9.8 13.9 3 65 98 TWS 4 1.2 11.4 46 14 6 TWS 6 1.2 11.4 35 65 96 Average recharge of the lens 76.8 mm/year Note: LKW 58 was ignored since this bore may contain saline water from the diffuse zone of the saline wedge. Report No: SA Water 29/1 Page 28 of 63
Depth below watertable (m) Coffin Bay Groundwater Lens A When distance from the northern coastal line is considered, average recharge is about 137 mm/year. 3.4 Chlorofluorocarbon (CFC) Method Recharge estimates based on CFC concentrations in groundwater assumes recharge takes place through diffuse, piston flow of water. Hence with increasing depth, decreasing CFC concentrations are expected. In order to determine the recharge date, i.e. CFC has been isolated from the atmosphere and introduced in to groundwater; CFC concentrations (pg/kg) were converted to an equivalent air concentration (pptv). The likely recharge is primarily in the winter season, and so the winter temperature of 13.2 C was used. Recharge calculations assumed 2% of aquifer porosity. Groundwater concentrations of CFCs, and estimated groundwater ages with recharge are contained in Table D3 in Appendix D. According to groundwater samples that detected CFC11 and CFC12, the maximum groundwater residence time is about 42 years. Typically, in a groundwater system receiving recharge as a diffuse, piston flow, an increasing age with depth would be expected. However, in Figures 13a and b below, no distinct residence time-depth correlation was found. This may be due to a number of reasons including; highly spatial variability of recharge rates, the heterogeneous nature of the aquifer, the Karstic nature, loss of CFC through biodegradation or adsorption to aquifer matrix/soil/pvc casing or slotted screen, non-uniform atmospheric distribution of CFC in the area etc. For example, in LKW 59 at a shallow depth to water of 4 m (sample point 1.18 m below groundwater) the year of CFC11 and CFC 12 were estimated to be 1969 and 1973 respectively. This is despite the theory suggesting that the youngest water (say 29) should be found in this upper layer. This aspect is further discussed in Section 3.5 below. Age of groundwater (years) 1 2 3 4 5 5 1 y =.5448x - 1.545 R² =.1838 15 2 25 Figure 13a. CFC 11 ages against groundwater depth Report No: SA Water 29/1 Page 29 of 63
Depth below watertable (m) Coffin Bay Groundwater Lens A Age of groundwater (years) 1 2 3 4 5 5 1 y =.5125x - 8.5227 R² =.1914 15 2 25 3.5 Summary of recharge estimates Figure 13b. CFC 12 ages against groundwater depth There are a variety of methods available for quantifying groundwater recharge as there are different processes of recharge. Determination of groundwater recharge is neither straightforward nor easy. Each of the methods has its own limitations in terms of applicability. The selection of appropriate methods is an important factor for quantifying groundwater recharge as this may dictate the required space and time scale of the recharge estimate. This is also a necessary step in order to reduce uncertainty. Table 5. Summary of recharge estimates Method Long-term Average Recharge (mm/year) Recent Recharge (mm/year) (3) Comments Bore hydrographs response to rainfall Limiting winter rainfall (1) 6 64 Direct method-reliable long-term data 265 245 Poor correlation; R2=.4 No site specific rainfall data Chloride mass balance 76 NA Good reliable data. Insignificant surface flows out from the system CFC Method 49-6 (2) NA Modern recharge, less than 4 years old groundwater, since looking for extremely small concentrations, Errors could easily be introduced at all stages Report No: SA Water 29/1 Page 3 of 63
1986 1987 1988 1989 199 1991 1992 1993 1994 1995 1996 1997 1998 1999 2 21 22 23 24 25 26 27 28 Annual Pumping (ML/Year) Coffin Bay Groundwater Lens A Note 1: average water level rise in the National park bores about.33 m in 29 (April-Sep). This is equivalent to recharge of 15 mm. Note 2: Average recharge including CFC data for LKW 58 and LKW 59 = 49 mm/year; Excluding LKW 58 and LKW 59, average Recharge = 6 mm/year Note 3: Recent recharge means average of last ten years. The estimated groundwater recharge using four different methods is summarised in Table 5. There are inherent difficulties in applying the CFC method for recharge estimation and hence any interpretation of this data should be undertaken with caution. Ideally the CFC method should be used as a guide only to confirm the existence of modern water and the results of other methods. For example, the 29 winter (April-September) water level rise in LKW 55 and LKW 57 are.36 m and.31 m respectively, averaging.33 m. This level of hydrograph rise equates to a recharge of 112 mm/year and compares well with results of the chloride mass balance method for LKW 59 with an estimated recharge of 72 mm/year. In contrast the CFC method estimates 5-6 mm/year at LKW 59. For groundwater resource assessment purposes, recharge assessment based on direct hydrological methods such as bore hydrographs response to rainfall and/or limiting winter rainfall are preferred since they provide a good spatial and temporal average. The chloride mass balance method (chemical and hydrological method) also provides good spatial distribution of long-term average recharge. Therefore, the average annual recharge to Coffin Bay Lens A is estimated to be in the range 6-265 mm/year with 6 mm/year being taken as the conservative long-term average. Similarly, recent recharge (last 1 years) is estimated at 64 mm/year. 4. GROUNDWATER USE AND AVAILABLE RESOURCE Groundwater Use Well abstraction is one of the most important components of this study, since its aim is to assess the sustainable resource. At present, groundwater extraction from the Lens A is largely limited to SA Water groundwater pumping for municipal water supply, with 112 ML/year allocation. Historical extraction since the inception of the wellfield is given in Figure 14 with average monthly extraction in Figure 15. 2 18 16 14 12 1 8 6 4 2 Report No: SA Water 29/1 Page 31 of 63
Average Monthly Pumping (ML) Coffin Bay Groundwater Lens A Figure 14. Coffin Bay Wellfield Annual pumping volumes 16 14 12 1 8 6 4 2 Figure 15. Coffin Bay Wellfield - Monthly pumping pattern Although there are other groundwater users, it is considered these abstractions are too small to cause any impact on water levels. The total amount of these other groundwater extractions is not known. Available Resource for Development Groundwater is a replenishable but finite resource. Rainfall is the principal source of recharge of the lens and it is this recharge that essentially provides the exploitable quantity of groundwater. Although recharge estimates are made with different methods to improve accuracy of the renewable resource, this is not taken as equating to the environmentally sustainable allocation. Lens Area Discharging to Northern Coast Available resource (31% of recharge) (ML) Current Allocation (ML) 17% 83% Figure 16. Available resource and current allocation- lens area discharging to northern coastline. Report No: SA Water 29/1 Page 32 of 63
Total Lens A Area Available resource (31% of recharge)(ml) Current Allocation (ML) 8% 92% Figure 17. Available resource and current allocation from the total lens The environmentally sustainable allocation takes into account the water needs of the environment as well as those of existing users. The average annual recharge to the total lens area is estimated to be 456 ML/year and recharge to the area that discharges to the northern coastline is estimated to be 21 ML/year. According to current allocation principles in the Southern Basins Prescribed Wells Area Water Allocation Plan, the environmentally sustainable allocation for Public Water Supply purposes is considered to be 31% of the annual recharge. Accordingly, the available resource from the total lens area is estimated to be 14 ML/year and from that portion of the lens discharging to the northern coastline is estimated to be 65 ML/year. For comparison, the current SA Water allocation of 112 ML/year is about 8% and 17% respectively of the available resource (Figures 16 & 17). The remainder of the water would primarily discharge to the sea. 5. CONCEPTUAL MODEL A conceptual groundwater model is a basic graphical presentation of a complex natural aquifer system that can be more easily adjusted prior to dedicating the effort in developing the numerical model. The elements of a conceptual model include; defining the extent and characteristics of the aquifer system and developing an understanding of groundwater flow directions, sources and sinks, physical and hydraulic boundaries, hydraulic properties and the water fluxes in and out of the system. Proper knowledge of these driving forces/processes and interactions are a prerequisite for the development of a conceptual model. This approach has not previously been applied in assessing the sustainable resource in the study basins, but is considered central to this study. A graphical presentation of the water balance of that portion of Lens A discharging to the north coast is presented in Figure 18. Report No: SA Water 29/1 Page 33 of 63
Figure 18. Schematic representation of the conceptual model for the area of Coffin Bay Lens A discharging to northern coastline. According to the above description of accepted conceptualization practice, the Coffin Bay Lens A is conceptualized as follows. The primary aquifer system is formed by the limestone/aeolianite/calcarenite Bridgewater Formation. The underlying Tertiary clay layer is absent elsewhere except in the wellfield area and acts as a minor aquitard. The basement of the aquifer is deeper than 6 m in the wellfield area and there is no exchange between the aquifer and layers that underlie the basement. Recharge to the aquifer is by direct rainfall infiltration and estimated to be between 6-265 mm/year. For the water balance calculation, a long-term average of 6 mm/year was adopted. Although it is known that areas of high hydraulic conductivity (of 1 m/day) exist, the lowest value found in the wellfield area, about 3 m/day, was adopted for calculating discharge to the sea. The water loss from the aquifer is primarily by extraction and discharges to the sea along the 12 km of northern coastline (estimated to be 172 ML/year), and 14 km of southern coastline. Groundwater flow is generally from the basement high zone in the east towards the coast. Rates of flow are primarily controlled by the rate of distribution of recharge and discharge and by the distribution of hydraulic conductivity. A flat hydraulic gradient of.5 indicates the highly transmissive nature of the aquifer which does not hold groundwater mounds. The link to the adjacent Uley South Basin in the east occurs at a small basement low area. Since limestone in the eastern part of Uley South is dry, the link is considered to be via the low permeability Tertiary Sand aquifer. Hence groundwater through flow from the Uley South basin is considered insignificant. Report No: SA Water 29/1 Page 34 of 63
6. CONCLUSION A great deal of information, both existing and new, on hydrogeology and hydrochemistry of the Coffin Bay Lens A has been used in this report in the development of the final product, the conceptual model for groundwater flow in the basin. Some of the major conclusions drawn from this study are: Quaternary aquifer (Bridgewater Formation) groundwaters have residence times less than 42 years. Even though a link exists between Coffin Bay Lens A and Uley South basin in the east, groundwater inflows receive to Coffin Bay A lens through the limestone aquifer are insignificant. Rainfall recharge is the only input to the groundwater system. The analysis of the long-term bore hydrograph response to rainfall provides an average annual recharge of 6 mm/year, with recent recharge (last 1 years) of 64 mm/year. The limiting winter rainfall method provides an average annual recharge of 265 mm/year. Poor correlation of.46 is partly due to correlating with winter rainfall measured outside the basin. The Big Swamp Station is about 2 km east from the basin. The chloride mass balance method provides a good spatial average of recharge, 76 mm/year. Whilst inherent difficulties exist in the application of the CFC method, it provides point estimates of average recharge of 49-6 mm/year. The total lens area, 76 Ha is much larger than the 1992/93 estimate (134 Ha). Of the total area of 76 Ha, groundwater from 35 Ha of the lens discharges to the northern coastline and the balance of 41 Ha discharges to south-west coastline. Average annual recharge to the total lens area is estimated to be 456 ML/year and recharge to the area discharging to the northern coastline is estimated to be 21 ML/year. The sustainable resource of the total lens is estimated to be 14 ML/year and the area discharging to the northern coastline is estimated to be 65 ML/year. The Tertiary clay aquitard is limited to the depression area of the basin where the SA Water wellfield is located. High salinity groundwater is found in lower reach of the Tertiary Sand aquifer. These waters are originally derived from sea water and enriched with Ca, Mg, Na and HCO 3 ions. In the upper reach of the basin, the Tertiary sand contains fresh water. Salinity of this water is similar to that of upper aquifer, the Bridgewater Formation. Report No: SA Water 29/1 Page 35 of 63
7. REFERENCES AGT Report No. 28/31. Sustainable water resources in Anangu Pitjantatjara Yankunytjatjara lands, Malinga Tjarutja lands & Aboriginal Land Trust Lands, South Australia. Report prepared for Department of land & Biodiversity Conservation and South Australian Water Corporation. Australian Groundwater Technologies, 28. Appelo, C.A.J and D. Postma (27) Geochemistry, Groundwater and Pollution, 2 nd Edition. A.A. Balkema Publishers. Barnett, S.R (1978). Eyre Penninsula Groundwater Survey Uley South Basin, Progress Report No. 5- Water Balance and Safe Yield. South Australian Department of Mines and Energy, Rept Bk 78/22 Coffin Bay Production Wells testing ( 29). Water search private Ltd. Groundwater and Geological Consultants. Craig (1961) Isotopic variations in Meteoric Waters. Science Vol. 133, pp 172-173. Denis, K, 1989. REPT. BK. NO 89/9: EW&S Coffin Bay Town Water Supply. Mines and Energy, South Australia. Department of Evans, S (1997) Estimating long-term recharge to thin, unconfined carbonate aquifers using conventional and environmental isotope techniques: Eyre Penninsula, South Australia. Fitzpatrick, A, K. Cahill, T. Munday and V. Berens (29) Informing the hydrogeology of Coffin Bay, South Australia, through the constrained inversion of TEMPEST AEM data. CSIRO Report No. P29/3. Smith, A, B. Howe, S. Evans, A. Costar and P. Magarey (227) Well completion report: Coffin Bay National Park Investigatory Drilling. Technical Note, Department of Water, Land and Biodiversity Conservation. Report No: SA Water 29/1 Page 36 of 63
APPENDIX A Geological Cross Sections Report No: SA Water 29/1 Page 37 of 63
Wellfield Figure A1. Locations of cross sections. Report No: SA Water 29/1 Page 38 of 63
Bridgewater Formation Sandy Clay Tertiary Clay Tertiary Sand Basement rock Figure A2. North south trending section across the wellfield, A2-A2. Report No: SA Water 29/1 Page 39 of 63
Bridgewater Formation Sandy Clay Tertiary Sand Basement rock Tertiary Clay Tertiary Sand Figure A3. North South trending cross section from Uley South to the coast in Coffin Bay, Line A3-A3 Report No: SA Water 29/1 Page 4 of 63
Bridgewater Formation Sandy Clay Tertiary Clay Tertiary Sand Basement rock Figure A4. East-West trending cross section from LKW 3 to LKW 55, Line A4-A4 Report No: SA Water 29/1 Page 41 of 63
Bridgewater Formation Sandy Clay Basement Rock Tertiary Sand Figure A5. Cross section along basement high ridge between Coffin Bay Lens A and Lens B, Line A5-A5 Report No: SA Water 29/1 Page 42 of 63
Figure A6. 3-D view of cross sections Report No: SA Water 29/1 Page 43 of 63
APPENDIX B Monitoring Bore Hydrographs and Major Ion Chemistry Data Report No: SA Water 29/1 Page 44 of 63
rswl mahd Annual Rainfall mm Coffin Bay Groundwater Lens A 2 Bridgewater Formation Quaternary limestone aquifer 1 9 1.5 8 7 1 6 5.5 Annual Rainfall 2 per. Mov. Avg. (LKW27) 2 per. Mov. Avg. (Cum Dev RF %) 4 3 2 1 -.5 Figure B1. Water level variation in LKW 27 Report No: SA Water 29/1 Page 45 of 63
rswl mahd Annual Rainfall mm Coffin Bay Groundwater Lens A 2 1.5 Tertiary Clay Aquitard Annual Rainfall 2 per. Mov. Avg. (LKW37) 1 9 8 2 per. Mov. Avg. (Cum Dev RF %) 7 1 6 5.5 4 3 2 1 -.5 Figure B2. Water level variation in LKW 37 Report No: SA Water 29/1 Page 46 of 63
rswl mahd Annual Rainfall mm Coffin Bay Groundwater Lens A 2 1.5 Bridgewater Formation Quaternary limestone aquifer Annual Rainfall 2 per. Mov. Avg. (LKW38) 2 per. Mov. Avg. (Cum Dev RF %) 1 9 8 7 1 6 5.5 4 3 2 1 -.5 Figure B3. Water level variation in LKW 38 Report No: SA Water 29/1 Page 47 of 63
rswl mahd Annual Rainfall mm Coffin Bay Groundwater Lens A 2 Bridgewater Formation Quaternary limestone aquifer Annual Rainfall 1 9 1.5 2 per. Mov. Avg. (LKW39) 8 2 per. Mov. Avg. (Cum Dev RF %) 7 1 6 5.5 4 3 2 1 -.5 Figure B4. Water level variation in LKW 39 Report No: SA Water 29/1 Page 48 of 63
rswl mahd Annual Rainfall mm Coffin Bay Groundwater Lens A 2 Wanilla Formation Tertiary sand aquifer Annual Rainfall 1 9 1.5 2 per. Mov. Avg. (LKW4) 8 2 per. Mov. Avg. (Cum Dev RF %) 7 1 6 5.5 4 3 2 1 -.5 Figure B5. Water level variation in LKW 4 Report No: SA Water 29/1 Page 49 of 63
rswl mahd Annual Rainfall mm Coffin Bay Groundwater Lens A 2 1.5 Bridgewater Formation Quaternary limestone aquifer Annual Rainfall 2 per. Mov. Avg. (LKW41) 2 per. Mov. Avg. (Cum Dev RF %) 1 9 8 7 1 6 5.5 4 3 2 1 -.5 Figure B6. Water level variation in LKW 41 Report No: SA Water 29/1 Page 5 of 63
rswl mahd Annual Rainfall mm Coffin Bay Groundwater Lens A 2 Bridgewater Formation Quaternary limestone aquifer Annual Rainfall 1 9 1.5 2 per. Mov. Avg. (LKW43) 8 2 per. Mov. Avg. (Cum Dev RF %) 7 1 6 5.5 4 3 2 1 -.5 Figure B7. Water level variation in LKW 43 Report No: SA Water 29/1 Page 51 of 63
Table B1. Major ion chemistry and water types Station ID Sample Depth (m) Water Type Alkalinity (mg/l) CaCO 3 TDS (mg/l) Cond. (us/cm) ph K (mg/l) Na (mg/l) Ca (mg/l) Mg (mg/l) Br (mg/l) Cl (mg/l) F (mg/l) SO 4 (mg/l) HCO 3 (mg/l) LKW 27 48.5 Mg-Na-Ca-HCO 3 -Cl 222 41 755 7.6 2.26 5.4 43.8 28.3.37 87.75 23.7 271 LKW 37 35.5 Na-Mg-Cl-HCO 3 25 41 75 8 16.9 91 16.8 18.7.22 82 1.6 24 35 LKW 38 15 Mg-Na-Ca-HCO 3 -Cl 23 44 792 8.1 6.29 5.7 32 28.27 11 1.2 26.1 28 LKW 38 18.5 Mg-Na-Ca-HCO 3 -Cl 229 44 82 8.1 6.59 53.6 34.3 28.4.3 15 27.3 279 LKW 39 27 Na-Cl-HCO 3 21 1 19 8 26.5 228 33.6 37.5 1.6 456 1.1 44.1 245 LKW 39 31.2 Na-Cl-HCO 3 22 11 197 8.1 21.1 214 3.7 33.9 1.7 477 1.1 47.7 247 LKW 4 48 Na-Mg-Cl 227 98 168 7.5 93.4 283 214 347 13.6 376 1 468 277 LKW 4 53 Na-Cl 264 18 294 7.3 16 54 382 681 36.7 991 438 322 LKW 57 43 Na-Mg-Cl-HCO 3 235 73 133 7.8 5.8 112 37.1 37.9 262.77 31.8 286 LKW 57 6.5 Na-Mg-Cl 247 44 645 7.2 461 132 74 156 66 178.69 12 31 LKW 58 14 Na-Mg-HCO 3 -Cl 23 13 239 8.1 11.6 261 53.3 53.8 555 1.1 93.9 281 LKW 59 3 Ca-Na-Mg-HCO 3 -Cl 27 49 887 7.8 1.69 56.6 76.7 22.1 15 1.1 26.7 329 Report No: SA Water 29/1 Page 52 of 63
Table 1 (cntd) Station ID Sample Depth (m) Water Type Alkalinity (mg/l) CaCO 3 TDS (mg/l) Cond. (us/cm) ph K (mg/l) Na (mg/l) Ca (mg/l) Mg (mg/l) Br (mg/l) Cl (mg/l) F (mg/l) SO 4 (mg/l) HCO 3 (mg/l) LKW 6 14 Ca-Na-Mg-HCO 3 -Cl 168 3 549 7.8 1.52 33.6 36.4 18.4 65.81 15.9 25 LKW 6 19.5 Ca-Na-Mg-HCO 3 -Cl 174 3 54 7.9 1.47 25.8 35.3 17.6 6.85 15.9 212 LKW 27 43 Ca-Na-Mg-HCO 3 -Cl 222 41 751 7.7 2.12 42.8 42.4 25.3.38 85.75 23.7 271 TWS 1 TWS 2 TWS 3 TWS 1_28 TWS 2_28 TWS 3_28 Mg-Na-Ca-HCO 3 -Cl 35 7.9 5.4 48.9 35 37.4 69 22 264 Mg-Na-Ca-HCO 3 -Cl 35 7.9 5.2 48.3 35 37.6 66 21.9 262 Na-Mg-HCO 3 -Cl 45 7.9 11.8 79.4 3.3 41.8 113 25.7 285 TWS 4 TWS 4_16m Mg-Na-Ca-HCO 3 -Cl 257 46 832 7.9 4.13 59.6 35.2 38.9 14 1.1 3.6 313 TWS 6 TWS 6_25m Mg-Na-Ca-HCO 3 -Cl 25 35 631 7.9 3.96 31.1 3 25.6 65 1.1 19.5 25 Report No: SA Water 29/1 Page 53 of 63
APPENDIX C Salinity Profiles Report No: SA Water 29/1 Page 54 of 63
Figure C1. Composite well log LKW 56 (Smith et al, 27) Report No: SA Water 29/1 Page 55 of 63