Christchurch groundwater quality monitoring

Transcription

1 Christchurch groundwater quality monitoring Environment Canterbury

2 Report prepared for Christchurch City Council by Groundwater Quality Team Environment Canterbury ISBN: Report No. R14/ (print) (web) PO Box 345, Christchurch 8140 Phone (03) Fax (03) Church Street PO Box 550, Timaru 7940 Phone (03) Fax (03) Website: Customer Services Phone

3 1 Introduction What groundwater quality monitoring do we do around Christchurch? Each year in the springtime, Environment Canterbury collects groundwater samples from wells in the Christchurch-West Melton area as part of its regional monitoring programme. The samples are analysed for a range of water quality parameters including conductivity, ph, major ions, nitrate nitrogen, ammonia nitrogen, silica, iron, manganese and indicator bacteria. We also sample a few wells quarterly to look for seasonal variations, and we sample wells near the coast twice per year to monitor for seawater intrusion problems. Why springtime? What do we do with the data? The composition of the groundwater can vary over the year. Springtime is when we generally see contaminant concentrations at their highest. We use our sampling data for evaluating long-term, large-scale changes in groundwater quality. Keeping track of changes in the aquifer system is important for safeguarding the city s drinking water supplies. The data also provide an annual snapshot of groundwater quality in the Christchurch area. We send our data to the Ministry for the Environment when it compiles national statistics on the state of the environment in New Zealand. All the data we collect are stored in our water quality database and are publicly available. What terms do we use in this report? Christchurch-West Melton zone is one of ten water management zones in the Canterbury region, which has been designated under the Canterbury Water Management Strategy. Christchurch Groundwater Protection Zone is an area shown on the planning maps of the Canterbury Land and Water Regional Plan where groundwater is considered most vulnerable to contamination. Groundwater Management Zones refers to two areas in the Woolston-Heathcote area of Christchurch shown on the planning maps of the Canterbury Land and Water Regional Plan where groundwater abstraction is controlled by planning rules to manage the ingress of brackish water from the Avon-Heathcote Estuary/Ihutai into groundwater. NGMP (National Groundwater Monitoring Programme) is a nationwide programme of quarterly sampling of groundwater run by GNS Science. We contribute to this programme by collecting samples from six wells in Canterbury. Two of these wells are in Christchurch. MAV (Maximum Acceptable Value) of a chemical parameter in drinking-water is the highest concentration of a parameter in the water that, on the basis of present knowledge, is considered not to cause any significant risk to the health of the consumer over 70 years of consumption of that water (MoH, 2008). Environment Canterbury 3

4 GV (Guideline Value) of a chemical parameter sets a threshold above which objectionable aesthetic effects may be observed, such as odour, taste, corrosion or staining problems. The GV is not a health-based limit. Median, in statistics, is the numerical value separating the higher half of the sample set from the lower half. The median of a finite list of numbers is found by arranging all the observations from lowest value to highest value and picking the middle one. We use the median value to represent average water quality, because the arithmetic mean may be biased by samples with very high or very low concentrations. Mann-Kendall test is a non-parametric statistical test for determining whether there are trends in a set of data. Being non-parametric, it does not depend on the data being from a normally-distributed population. The Mann-Kendall test does not calculate the magnitude of a trend (i.e. the rate of change). It simply determines whether or not a trend is present, based on the frequency with which values observed in later samples are greater or less than those observed in earlier samples. 4 Environment Canterbury

5 2 Monitoring network & sample collection Each year we aim to sample about 35 wells in the Christchurch area for signs of changing groundwater quality. Sampling locations Most of the wells we sample are in the Christchurch Groundwater Protection Zone, which covers the gravel deposits to the west of the city. Here groundwater is most vulnerable to contamination from the surface. We have a high concentration of monitoring wells along the western edge of the city. To the east the surface sediments become finer-grained and the hydraulic gradient in the groundwater system changes from downward to upward flow (Weeber, 2008). Our quarterly monitoring wells are mostly to the west of this transition. We also monitor a number of wells across the industrial areas of southern Christchurch. Two wells near the coast and the Avon-Heathcote Estuary/Ihutai are sampled biannually as part of our seawater intrusion monitoring network. After a review of our monitoring network (Scott, 2013), we have separated out a set of wells that we sample to keep track of some known sources of contamination. We refer to these as targeted wells. Figure 1 shows a map of the wells in the Christchurch network. Well depths and aquifers sampled We are interested in detecting early signs of contamination, so most of our monitoring wells are shallow and have been selected because they are screened close to the water table. Christchurch City Council (CCC) is making increasing use of deeper wells in their public supply network. We also monitor a few wells that sample the deeper groundwater. These include one well around 140 metres deep at Southshore and our Russley NGMP well that is 200 metres deep. We have recently found two more deep wells (over 100 m deep) at Belfast to fill gaps in our coverage of the deeper aquifers as recommended in the network review. CCC samples additional wells in the central city and the deeper groundwater as part of their drinking water monitoring. This report does not include the data from the city council samples. Methods When collecting groundwater samples, we follow Environment Canterbury s standard procedure for the collection of groundwater quality samples, which is in line with national groundwater sampling protocols (MfE 2006). The procedure includes purging at least three well volumes before sampling, filtering samples for metal cations in the field and keeping the samples chilled during transport to the laboratory. We measure the depth to water before purging the well and the field parameters (groundwater temperature, dissolved oxygen concentration, ph and conductivity) after purging, immediately before taking each sample. Our groundwater samples are analysed by Hill Laboratories in Christchurch for major ion chemistry (sodium, potassium, calcium, magnesium, alkalinity, chloride and sulphate), ammonia and nitrate nitrogen, iron, manganese, silica, ph, conductivity and faecal indicator bacteria (E. coli and total coliforms). Environment Canterbury 5

6 Figure 1: Network changes and sampling frequencies for Christchurch monitoring wells 6 Environment Canterbury

7 Changes to the network The period between 2011 and 2014 has been a time of significant change for our groundwater quality monitoring network in the Christchurch-West Melton zone. The 2011 earthquakes damaged a number of the wells we sampled, which led to them being decommissioned. There were also changes in ownership and access problems that affected several other wells. In 2012/13 we conducted a review of our monitoring network (Scott, 2013) and identified wells that could be removed from the network as a result of poor reliability or redundancy and also some gaps in the network to be filled (Table 1). We also identified wells that show signs of being affected by some or other source of contamination (e.g. past saltwater intrusion, wood processing discharges, historic landfills). We want to keep monitoring these wells, but they do not represent the general state of groundwater quality in the Christchurch-West Melton zone. That is why we moved six wells to a separate list of targeted monitoring wells. Data from targeted wells will no longer included in the summary statistics we compile for the zone. We have recently completed the process of identifying and obtaining permission for sampling of six new wells to add to our network, but only one of these was ready for sampling in the 2013 survey. The others will be sampled this year (2014). There are also wells we have identified to be repaired or replaced and the work on these is in progress (Table 1). The location of new wells and wells that were damaged or removed from the network are shown on Figure 1. As a result of all the network changes, we only sampled 20 regular wells and four targeted wells in our springtime survey in Our active network now contains 33 wells, which are due to be sampled in Other than damage to wells, the Canterbury earthquakes seem to have had very little effect on the quality of the groundwater we sample. We discussed this in our Update #2 on earthquake impacts on groundwater (Groundwater Resources Section 2011). Environment Canterbury 7

8 Table 1: Changes to the Christchurch-West Melton groundwater quality network Well number Location Change made Reason for change Repair or replace M35/2379 Fendalton Removed Well out of use after earthquakes. M35/7281 Fendalton Replacement Replacement for M35/2379 M36/1057 Opawa Removed Changed ownership. No access after well filled in. M36/1016 Waltham Removed Was replacement for M36/1057, but this well is also now decommissioned. Owner has drilled new well. BX24/0347 Waltham Replacement New well. Owner needs to install sample point. M36/0974 Sydenham Removed Well decommissioned. Still looking for new well. M36/1059 Hillmorton Needs repair Not in use. Fault under investigation. Remove from network M35/1717 Coutts Island Removed Redundant/poor wellhead security M35/4189 Addington Removed Redundant Aquifer 2 well/poor wellhead security M35/1883 Sockburn Removed Well decommissioned by owner M35/2242 S. Brighton Removed Damaged well decommissioned M35/2557 Burnside Removed Well decommissioned by owner. M35/5086 Marshland Removed Damaged well decommissioned M36/3085 Wigram Removed Well decommissioned. Southern motorway route M36/1159 Heathcote Removed Damaged well decommissioned M36/4906 Woolston Removed Targeted well no longer accessible. Factory closed. New wells M35/1653 Harewood Added Fill spatial gap shallow groundwater M35/2325 City centre Added Fill spatial gap shallow groundwater M35/5139 McLeans Island Added Fill spatial gap shallow groundwater M35/9064 Yaldhurst Added Fill spatial gap shallow groundwater M35/10632 Belfast Added Fill spatial gap deep groundwater M35/11975 Belfast Added Fill spatial gap deep groundwater Targeted monitoring wells M35/5353 Harewood Targeted well Affected by wood treatment plant discharges M36/1059 Hillmorton Targeted well Affected by past hydrocarbon contamination M36/1045 Woolston Targeted well Groundwater management zone - saltwater M36/1160 Heathcote Targeted well Groundwater management zone - saltwater M36/2961 Hornby Targeted well Near historic landfill 8 Environment Canterbury

9 3 Snapshot of 2013 results Table 2 presents a summary of our results for the springtime 2013 sampling. Table 2: Groundwater quality indicators measured, summary of 2013 annual survey results and median values by aquifer for Christchurch groundwater monitoring 2013 Annual Survey Water Quality Units (20 wells sampled) Parameters Median Range Microbiological indicators E. coli MPN/100mL <1 <1 Total Coliforms MPN/100mL <1 <1 Major anions Nitrate nitrogen mg/l 0.42 <0.05 to 7.2 Alkalinity mg/l HCO to 151 Chloride mg/l to 45 Sulphate mg/l 4.5 <0.5 to 13.3 Major cations Calcium mg/l to 52 Magnesium mg/l to 42 Sodium mg/l to 30 Potassium mg/l to 3.2 Ammonia nitrogen mg/l <0.01 <0.01 to 3.2 Other parameters Conductivity (Lab) ms/m to 36 Dissolved Oxygen mg/l to 9.1 Total Hardness mg/l CaCO to 159 ph (field) to 8.1 Silica mg/l SiO to 46 Temperature o C to 16 Minor elements Iron mg/l <0.02 <0.02 to 2.7 Manganese mg/l < < to 0.64 Arsenic (2012)* mg/l <0.001 to Boron (2012)* mg/l to Cadmium (2012)* mg/l < < * Arsenic was previously tested for a small selection of wells where we had detected arsenic in the past, including four regular wells in 2012, but was excluded from the 2013 parameter list. Additional minor elements, cadmium and boron, were tested only in the 2012 annual survey (see Section 4). We have included their results in this summary. Groundwater quality is generally very good in the Christchurch area with low concentrations of dissolved species. No faecal indicator bacteria were detected in the 2013 samples. Environment Canterbury 9

10 What do the targeted wells show? We see quite different results for our targeted monitoring wells, which are summarised in Table 3. These wells can have high concentrations of cations and anions influenced by brackish water or leachate. They also typically have low concentrations of dissolved oxygen and higher ammonia, iron and manganese. Table 3: Summary of groundwater quality indicators measured in targeted wells known to be affected by contamination in the Christchurch-West Melton zone 2013 Targeted Survey Water Quality Parameters Units (4 wells sampled) Median Range Microbiological indicators E. coli MPN/100mL <1 <1 Total Coliforms MPN/100mL <1 <1 to 10 Major anions Nitrate nitrogen mg/l to 7.9 Alkalinity mg /L HCO to 200 Chloride mg/l to 180 Sulphate mg/l to 66 Major cations Calcium mg/l to 37 Magnesium mg/l to 36 Sodium mg/l to 113 Potassium mg/l to 13 Ammonia nitrogen mg/l <0.01 to 4.8 Other Conductivity (Lab) ms/m to 103 Dissolved Oxygen mg/l to 3.5 Total Hardness mg/l CaCO to 215 ph (field) to 8.1 Silica mg/l SiO to 32 Temperature o C to 16.4 Minor elements Iron mg/l 0.14 <0.02 to 3 Manganese mg/l to Arsenic (2012) mg/l 0.06 <0.001 to Boron (2012) mg/l to Cadmium (2012) mg/l < < to Environment Canterbury

11 What spatial patterns do we see in Christchurch groundwater? Figures 2 to 4 map the distribution of just three of the water quality parameters we measured in The circular symbols are located at the positions of the wells that we sampled and are scaled by the concentrations we measured. Most of the parameters we measure show similar patterns to the conductivity map. Our targeted wells are highlighted to show where individual contamination sources may be disturbing the larger scale pattern. Conductivity is a bulk measurement that describes the quantity of dissolved inorganic salts in the water. We see a pattern of very low values across the northern part of Christchurch and slightly higher values to the south. With a few exceptions (in areas of known discharges or saltwater influence), even the higher conductivity values are all still mostly in the range of very good quality fresh water. Dissolved oxygen at higher concentrations is usually a sign that a water body is less prone to water quality problems than one with very low dissolved oxygen (anoxic water). Dissolved oxygen concentrations in groundwater show the opposite pattern to conductivity. Higher concentrations occur in the north and lower concentrations in the south. Nitrate nitrogen is a highly soluble contaminant that is receiving much attention in Canterbury because of its increasing concentrations in our aquifers and waterways. Nitrate comes from sources such as soil cultivation, fertilisers and discharges of human and animal wastes. Christchurch has lower nitrate concentrations than many other parts of the region, but there are some higher concentrations and increasing trends to the south west of the city. What do these patterns mean? The same broad patterns in groundwater quality are seen year after year in the Christchurch area. We think they are controlled by the way the aquifer system functions. Large volumes of very clean water seep from the Waimakariri River into the northern parts of the Christchurch aquifer system. This gives the very good quality, low salinity, oxygenated groundwater we see across the northern areas. Farther away from the Waimakariri River, along the base of the Port Hills, most of the groundwater is replenished by rainfall percolating through the soil. The rainfall recharge picks up a small amount of dissolved salts as it infiltrates. Some of the recharge through the soils also carries contaminants from human activities on the land surface. Dissolved oxygen is used up by micro-organisms as they degrade organic matter. This leads to anoxic groundwater. The organic matter usually comes from waste discharges or from old swamp and estuary deposits, although a small amount may also be present in the gravel aquifers. Iron, manganese, ammonia and arsenic concentrations are higher in anoxic groundwaters because their solubilities increase under anoxic conditions. The best water quality occurs across the northern area thanks to seepage of clean water from the Waimakariri River into the aquifer. Groundwater quality in the south is still good, but the water contains more dissolved substances picked up during infiltration through the land surface. Environment Canterbury 11

12 Christchurch groundwater quality monitoring 2013 Figure 2: Distribution of conductivity values from spring 2013 groundwater sampling in the Christchurch area Figure 3: Distribution of dissolved oxygen concentrations from spring 2013 groundwater sampling in the Christchurch area 12 Environment Canterbury

13 Figure 4: Distribution of nitrate nitrogen concentrations from spring 2013 groundwater sampling in the Christchurch area 4 Cadmium and boron Why did we test for cadmium and boron in 2012? In 2012 we conducted some additional analyses of minor elements in our annual groundwater quality survey across Canterbury. Cadmium and boron were included because they can be present as impurities (cadmium) or additives (boron) in fertiliser products and we wanted to check if they could be leaching into groundwater. Figures 5 and 6 show maps of cadmium and boron concentrations in groundwater. Only one well had detectable cadmium and this was below the MAV. The well is on our targeted list for past saltwater contamination. Another targeted well near an old landfill had high boron concentrations above the MAV. Elevated boron concentrations were almost always associated with known contaminant discharges around the city including wood treatment discharges in the north west, old landfills in the south west and past areas of saltwater contamination in the south east of the city (shown by the highlighted squares around targeted monitoring wells in Figure 6). The concentrations of boron and cadmium we measured in Christchurch groundwater are generally very low. Environment Canterbury 13

14 Christchurch groundwater quality monitoring 2013 Figure 5: Distribution of dissolved cadmium concentrations from spring 2012 groundwater sampling in the Christchurch area Figure 6: Distribution of dissolved boron concentrations from spring 2012 groundwater sampling in the Christchurch area 14 Environment Canterbury

15 5 Drinking water quality Christchurch groundwater is widely used as a source of untreated drinking water for both private and public supply. We used the New Zealand Drinking-Water Standards (MoH 2008) to assess the groundwater quality. Table 4 summarises the number of samples from our 2013 survey that did not meet the standards. We have also included arsenic, cadmium and boron results that were only tested in Table 4: Number of samples not meeting drinking-water standards for the 2013 annual survey (out of 24 samples) Water quality parameter Drinking- water standard Number of samples that meet the standards Number of samples that exceeded the standards Health-based Maximum Acceptable Value (MAV) E. coli <1 MPN/100 ml 24 0 Nitrate nitrogen 11.3 mg/l 24 0 Manganese 0.4 mg/l 20 4 Arsenic (2012) 0.01 mg/l 5 2 Cadmium (2012) mg/l 26 0 Boron (2012) 1.4 mg/l 25 1 Aesthetic-based Guideline Value (GV) Ammonia nitrogen 1.2 mg/l 22 2 Chloride 250 mg/l 24 0 Hardness (as CaCO 3 ) 200 mg /L 23 1 Iron Manganese ph 7.0 to Sodium 200 mg/l 24 0 Sulphate 250 mg/l 24 0 Groundwater quality is generally very good and the vast majority of samples meet New Zealand drinking water standards without treatment. None of the wells that fail to meet drinking water standards are used for public water supply. The five wells that exceeded drinking-water criteria (Figure 7) are affected either by known point sources of contamination or by natural anoxic (low dissolved oxygen) conditions caused by old swamp deposits near the coast and estuary. These wells have all either been moved to our targeted monitoring list or are part of our seawater intrusion monitoring programme along the coast. They include: a stock water and garden irrigation well affected by leachate from a closed landfill at Wigram (arsenic and boron in 2012). This well has since been filled in and could not be tested in an industrial well affected by timber treatment discharges at Harewood (ph, manganese, iron, ammonia nitrogen). two naturally anoxic wells used for irrigation at New Brighton (manganese) and water level monitoring at Southshore (manganese, iron, ammonia nitrogen and arsenic). They are also in our seawater intrusion monitoring programme. a well with anoxic groundwater affected by saltwater drawn in from the estuary at Heathcote (manganese and hardness). Environment Canterbury 15

16 Figure 7: Comparison of spring 2012 and 2013 groundwater sampling results with New Zealand Drinking-Water Standards (NZDWS) criteria for manganese, arsenic and boron, which exceeded health-based limits in some wells. 16 Environment Canterbury

17 6 Long-term trends How do we analyse trends? We use a statistical method (Mann-Kendall test) to see if there is a significant increase or decrease in the concentrations of a particular parameter over time. For this report, we looked at the data for the last ten years of annual samples (2004 to 2013). For most wells, we tested 14 different water quality parameters to see if the values had increased or decreased overall, or if there was no consistent pattern of changes in the data. Some wells were tested for slightly different time periods or different numbers of parameters, depending on data availability. The wells shown with lighter symbols in Figure 8 have been lost from our programme since 2011, but we have still included them to give a better picture of the spatial patterns of groundwater quality trends. We assigned a status of degrading quality if the ph or dissolved oxygen concentrations were decreasing or if any of the other parameters were increasing. Decreasing concentrations of all parameters except ph and dissolved oxygen were assigned the status improving. We tallied up the number of parameters that were degrading, improving or showing no change for each well. We required five or more parameters to show the same trend (degrade or improve) for us to consider the groundwater quality at a well significantly changed. What do they show? There has been very little change in the overall quality of groundwater in Christchurch over the past decade of monitoring (Figure 8). Although some shallow wells have relatively large fluctuations in concentrations from year to year, most parameters we measured showed no significant long-term increases or decreases (shown by black circles on the map). Figure 8: Summary of groundwater quality trends over the past ten years for monitoring wells in and around Christchurch. Lighter symbols indicate wells that do not have data for 2012 or 2013 Environment Canterbury 17

18 Degrading quality Four wells had five or more parameters showing weak degrading trends since the early 2000s. They are all screened near the water table in the gravels to the west of the city where the groundwater hydraulic gradient is downward. Two of the wells to the south (Wigram and Hillmorton) are on our targeted list because we know they have been affected by old landfill leachate or industrial discharges. The other two wells (Sockburn and Burnside) have shown slow increases in the concentrations of some dissolved salts and nitrate nitrogen draining through the soil, with concentrations peaking after wet winters such as 2006 and especially Improving quality Five wells showed long-term improvements in groundwater quality. The wells with improved water quality are located across southern Christchurch in areas of historic water quality problems. We see the biggest improvements around Woolston-Heathcote (M36/1160 and to a lesser extent M36/4906). Previous overpumping in this area drew down brackish water from the estuary into the aquifer, leading to high salt concentrations in groundwater. These have decreased under the pumping controls of the groundwater management zones. Salt concentrations and nitrate nitrogen have also shown slow but steadily decreasing trends in our monitoring wells in the industrial area of Sydenham-Waltham. We have attributed this improvement in groundwater quality to a general improvement in industry practices, such as the discontinuation of contaminating discharges to land (Hayward 2002). Loss of monitoring wells Unfortunately, three of the four wells with degrading quality have been decommissioned and the fourth currently has problems with the pump, so we will have difficulty continuing to monitor these trends. Also three of the five wells with improving trends have been sealed up and are no longer accessible for sampling. A replacement well has been drilled for one of these, but we will need to collect a few years of data from it before we can see if it shows a similar trend. We found very little evidence of changing groundwater quality in Christchurch over the last ten years. 18 Environment Canterbury

19 7 Summary and conclusions Each year we sample about 35 wells in the Christchurch area for signs of changing groundwater quality. Over the last two years we have lost several of our wells to earthquake damage and owner changes, so we were only able to sample 24 wells in We have selected additional wells as replacement wells and gap-fillers and we are hoping to sample 33 wells in It will take some time to build up our long term records for trend analysis for the new wells. Groundwater quality is generally very good and the majority of samples meet New Zealand drinking water standards without treatment. o The best water quality occurs across the northern area thanks to seepage of clean water from the Waimakariri River into the aquifer. o Groundwater quality in the south is still good, but the water contains more dissolved substances picked up during infiltration through the land surface. o Some areas near the estuary and old coastal swamps have low dissolved oxygen, which causes naturally poorer groundwater quality. o One-off sampling for cadmium and boron found only one well near an old landfill where boron concentrations were above the drinking-water MAV. Cadmium concentrations were below detection levels in all but one well, which still had very low concentrations. We found very little evidence of changing groundwater quality in Christchurch over the last ten years. o Four wells show a possible long-term decline in quality near the groundwater table to the west and south west of the city. Two of these wells target known contamination sources and the other two show a slow general change in quality. o Another five wells show improved groundwater quality in previously affected areas of southern Christchurch after better management of abstraction and discharges. References Groundwater Resources Section, 2011: Earthquake impacts on groundwater. Environment Canterbury web publication, Hayward, SA, 2002: Christchurch-West Melton Groundwater Quality: A review of groundwater quality monitoring data from January 1986 to March Environment Canterbury technical report U02/47. MfE, 2006: A national protocol for State of the Environment groundwater sampling in New Zealand. Published by the New Zealand Ministry for the Environment, Wellington. 52 pages. MoH, 2008: Drinking-Water Standards for New Zealand 2005 (revised 2008). Published by the New Zealand Ministry of Health, Wellington. 163 pages. Scott, L 2013: Christchurch-West Melton groundwater quality monitoring review. Environment Canterbury technical report R13/3. Weeber, J 2008: Christchurch groundwater protection: A hydrogeological basis for zone boundaries, Variation 6 to the Proposed Natural Resources Regional Plan. Environment Canterbury technical report U08/21. Environment Canterbury 19

20 20 Environment Canterbury Appendix: Trend analysis summary Well number Location REGULAR MONITORING WELLS Count (years) Last record No. of parameters No. of unchanged Improved Degraded M35/0925 HALKETT none Cond, Si, Na, no change M35/1051 YALDHURST DO none no change M35/11059 WEST MELTON none Alk, Na no change M35/1382 HAREWOOD none DO no change M35/1860 SOCKBURN none K, SO 4 no change M35/1864 HORNBY none Cl, K, NO 3 no change M35/2249 AVONHEAD NH4 Mg no change M35/2960 NEW BRIGHTON DO, NH 4 Mg, K, SO 4 no change M35/2961 NEW BRIGHTON none K, NH 4 no change M35/3755 BELFAST none Mg no change M35/5119 YALDHURST none Alk, Si no change M35/5251 REDWOOD NH 4 Alk, Mg, SO 4 no change M35/6656 HAREWOOD ph, NH 4 Cl no change M35/6791 RUSSLEY none none no change M35/6935 WEST MELTON none Alk, K, Na no change M35/6946 MCLEANS ISLAND none Alk, ph no change M36/1225 SPREYDON none none no change M36/5893 SOUTHSHORE Cl, K, Fe ph, As no change M36/5894 SOUTHSHORE NH 4, Fe Mg, K, SO 4, ph no change M36/5895 SOUTHSHORE Cl, DO none no change TARGETED MONITORING WELLS M35/5353 HAREWOOD SO 4 NO 3, DO no change M36/1045 WOOLSTON SO 4 none no change Overall Status

21 Environment Canterbury 21 Well number Location Count (years) Last record No. of parameters M36/1160 HEATHCOTE M36/4906 WOOLSTON No. of unchanged Improved Degraded Ca, Cl, Mg, Na, SO 4, Cond, NO 3, Mn Ca, Cl, Mg, Na, SO 4, Cond, ph, DO Overall Status none improve none improve M36/2961 HORNBY Si none no change DISCONTINUED WELLS M35/1737 COUTTS ISLAND none Ca, Mg, NO 3, SO 4 no change M35/1883 SOCKBURN none Cl, Mg, K, NO 3, SO 4 degrade M35/2242 SOUTH BRIGHTON none NH4 no change M35/2379 FENDALTON NORTH none Ca, Cl, K, SO 4 no change M35/2557 BURNSIDE none Cl, Mg, NO 3, K, Na, SO 4 degrade M35/4189 ADDINGTON none none no change M35/5086 MARSHLAND none SO 4 no change M36/0974 SYDENHAM Cl, Mg, NO 3, Na, SO 4 NH 4 improve M36/1016 WALTHAM Cl, NO 3, SO 4, Cond, DO none improve M36/1057 OPAWA Cl, NO 3, SO 4 Alk, Ca, Na no change M36/1059 HILLMORTON none M36/1159 HEATHCOTE Ca, Cl, Cond, Mg, Mn, K, Na, SO 4 M36/3085 WIGRAM none NH 4, NO 3, K, Na, DO, ph degrade Alk improve Ca, Cl, K, Cond, NH 4, Mn degrade