DISCLAIMER BIBLIOGRAPHIC REFERENCE

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2 DISCLAIMER This report has been prepared by the Institute of Geological and Nuclear Sciences Limited (GNS Science) exclusively for and under contract to Ministry for the Environment. Unless otherwise agreed in writing by GNS Science, GNS Science accepts no responsibility for any use of or reliance on any contents of this report by any person other than Ministry for the Environment and shall not be liable to any person other than Ministry for the Environment, on any ground, for any loss, damage or expense arising from such use or reliance. Use of Data: Date that GNS Science can use associated data: May 2015 BIBLIOGRAPHIC REFERENCE Moreau, M.; Daughney C Update of National Groundwater Quality Indicators: State and Trends December , GNS Science Consultancy Report 2015/ p. Project Number 630W

3 CONTENTS EXECUTIVE SUMMARY... III 1.0 INTRODUCTION Scope of work Data source: the NGMP dataset Previous investigations METHODS Key indicators of groundwater quality and guidelines used Reported statistics Trend test, and settings Minimum data requirements Time period selection Effect of time period selection Data processing Limitations RESULTS Site-specific assessment of state and trends National overview Key indicators NO 3 -N NH 4 -N DRP Fe and Mn Salinity and electrical conductivity Factors controlling groundwater quality Well depth and aquifer confinement Aquifer lithology CONCLUSION RECOMMENDATIONS ACKNOWLEDGEMENTS REFERENCES FIGURES Figure 1: Location of NGMP sites and main aquifers in New Zealand Figure 2: National and regional summary statistics for state and trends in NO 3-N indicators of groundwater quality, based on all data collected from 2004 to Figure 3: National and regional summary statistics for state and trends in NH 4-N concentrations based on all data collected from 2004 to Figure 4: National and regional summary statistics for state and trends in dissolved phosphorous concentrations based on all data collected from 2004 to GNS Science Consultancy Report 2015/16 i

4 Figure 5: National and regional summary statistics for state and trends in Fe based on all data collected from 2004 to Figure 6: National and regional summary statistics for state and trends in Mn based on all data collected from 2004 to Figure 7: National and regional summary statistics for state and trends in calculated TDS based on all data collected from 2004 to Figure 8: National and regional summary statistics for state and trends of electrical conductivity based on all data collected from 2004 to Figure 9: Scatterplot comparing median concentrations of DRP (DRP) with nitrogen species (left), and with Fe and Mn concentrations (right) at NGMP sites for the period Figure 10: Scatterplot of NO 3-N median concentrations versus depth TABLES Table 3.1 Table 3.2 Table 3.3 Table 3.4 Table 3.5 Calculated national percentiles and maximum values for groundwater quality indicators, based on site-specific median values for the period Percentage of New Zealand monitoring sites at which median concentrations calculated for the period are in excess of water quality standards or guidelines Number of monitoring sites (n) across New Zealand at which trend tests could be performed for the period National (absolute and relative) rates of change in groundwater quality parameters for sites with statistically significant trends National medians for median concentrations values and trend magnitudes per aquifer lithology GNS Science Consultancy Report 2015/16 ii

5 EXECUTIVE SUMMARY The Ministry for the Environment (MfE) commissioned GNS Science (GNS) to summarise groundwater quality state and trends for the period. This report updates the previous assessment of groundwater state and trends for the period by GNS for MfE which used data from the National Groundwater Monitoring Programme (NGMP) and the State of the Environment (SOE) monitoring programmes (Daughney and Randall 2009). This report focuses on NGMP data and will be followed by another, late in 2015, summarising NGMP and SOE data for the period. Trend analyses was conducted for key groundwater quality indicators, selected by MfE: nitrate-nitrogen (NO 3 -N), ammonium-nitrogen (NH 4 -H), dissolved reactive phosphorous (DRP), dissolved iron (Fe), dissolved manganese (Mn), total dissolved solids content (TDS) and electrical conductivity (conductivity). The second report will also include other forms of nitrogen and phosphorous, E.coli and pesticides. Reported values are medians for characterising state and trend magnitudes and trends, which is consistent with previous reporting (Daughney and Randall 2009). At the national level, groundwater state and trends for the period were found to be in general agreement with the previous report, although medians for NO 3 -N and Mn were consistently lower than corresponding medians for the period. Exceedance of guidelines set in the drinking-water standards for New Zealand (DWSNZ) for NO 3 -N, NH 4 -H, Fe, and Mn concentrations were observed, either for aesthetic, ecosystem or human health at a minority of sites (up to 32%, depending on the parameter of interest). Statistically, significant trends were detected in a portion of the sites (max. 35.7% of the sites, NO 3 -N concentrations), and both increases and decreases were observed. The most common trend magnitudes were of the order of 0.01 or mg/l per year (increases and decreases). These rates are considered slow and consistent with previous reporting (Daughney and Reeves 2006; Daughney and Randall 2009). No relationships were found between median concentrations and absolute trend magnitudes. Although the national median NO 3 -N concentration was low, high concentrations were observed in several regions, some of which exceeded the DWSNZ maximum acceptable values (MAVs). Higher NO 3 -N concentrations affected the Southland and Waikato regions. Elevated NO 3 -N concentrations were found mostly in samples from unconfined, shallow wells. Increases were more frequent than decreases, and it was not uncommon to observe both upwards and downwards trends within the same region. Nationally, DRP concentrations were generally low, although regional variations were observed. All but one region (Otago), exhibited DRP concentrations above international guidelines for ecosystem health. Elevated DRP concentrations were associated with elevated Fe and Mn concentrations. It is likely that reducing conditions in the aquifers facilitate the transport of phosphorous species. Only a very limited number of sites exhibited trends (4%). Trend magnitudes were of the order of mg/l per year. Fe and Mn were mostly found in low concentration for the period. However, when detectable, concentrations for these ions could be quite high, indicating reducing conditions. Two sites exceeded the DWSNZ MAV for Mn. Where trends were detected, their magnitudes were low, typical of the natural evolution of groundwater. GNS Science Consultancy Report 2015/16 iii

6 There were large regional variations in conductivity with regions characterised by dilute groundwaters (West Coast, Marlborough, Bay of Plenty, Otago, and Waikato) and regions with higher conductivities. Gisborne conductivities were significantly higher than anywhere else in New Zealand. Decreases in conductivity were more common than increases, with increases only occurring in Canterbury, Marlborough, and Northland. It is recommended that regular updates on national groundwater quality should continue to be conducted to identify important changes in groundwater quality in New Zealand. Age tracer data should also be considered, as this information is key to establishing the linkage between change in land use practice and groundwater quality. GNS Science Consultancy Report 2015/16 iv

7 1.0 INTRODUCTION The Ministry for the Environment (MfE) has recently committed to issue regular reporting and provide a fair representation of the state of New Zealand (NZ) freshwater resources and pressures that may cause, or have the potential to cause changes to the state of groundwater (Parliament of New Zealand, 2014). In order to inform the 2015 Environmental Synthesis Report, which will focus on the overall picture of the NZ environment, MfE commissioned GNS to report on NZ groundwater quality state and trend. This involved the following tasks: collect, groom, analyse (state and trends), and report groundwater quality data collected as part of the National Groundwater Monitoring Programme (NGMP) and the regional State of the Environment (SOE) programmes. collect, analyse and report pesticide data collected as part of the National Survey of Pesticides operated by the Institute of Environmental Science and Research Limited (ESR). produce a brief technical report and summary statistics that can be used as the primary basis for national reporting. This report focuses on the analysis of NGMP data for the period. A second report, amalgamating data from both the NGMP and the SOE networks for a slightly different time period ( ) will also be produced. At the time of writing this report, datasets for the second ( ) report were being collected from NZ regional authorities. 1.1 SCOPE OF WORK The NZ groundwater quality state and trend update involved both data analysis and the provision of set deliverables detailed below: Data analysis: - Recommendations for: two reporting time periods, trend tests, descriptive statistics and minimum data requirements for state and trend in groundwater quality reporting; - State: determine median and other percentile statistics for key indicators of groundwater quality by region and nationally, with analyses conducted for two time periods. Key parameters identified by MfE were: nitrogen species (in this report this consists of nitrate-nitrogen and ammonium-nitrogen), phosphorous species (in this report this consists of dissolved reactive phosphorous), E. coli, dissolved iron, dissolved manganese, salinity, electrical conductivity, and pesticides. Selection of these parameters is consistent with recommendations from Daughney and Randall (2009); - Trends: identify and quantify time-trends for key indicators of groundwater quality for the two periods, by region and nationally; and - Land use and aquifer confinement relationships: evaluate relationships between land use, aquifer confinement and state and trends of key indicators of groundwater quality, by region and nationally. GNS Science Consultancy Report 2015/16 1

8 Deliverables: 1. Quality assured raw data used for trend analysis, accompanied with a quality assurance summary; 2. Summary tables: presented using the convention of Tables 1 and 4 in Daughney and Randall (2009); 3. Summary spreadsheets (for mapping): tabulation of location details (easting, northing), land use, aquifer confinement and site-specific median and trend magnitudes for key indicators for two time periods. This table is consistent with Spreadsheet 1 in Daughney and Randall (2009); 4. Figures: box and whisker plots of state statistics and proportional bar graphs, following the convention of Figure 1 in Daughney and Randall (2009), and scatter plots of key parameters following the convention of Figure 10 in Daughney and Randall (2009); and, 5. Reports: two reports were requested, one summarising state and trend at NGMP sites, and another using the amalgamated NGMP and SOE datasets. Each report includes a brief explanation of methods, results and conclusions, and a discussion of necessary caveats. The results includes background information (NGMP/SOE site selection criteria; description of the land use characterisation at monitoring sites; general groundwater chemistry discussion; previous regional, national and international groundwater quality surveys), as detailed in Daughney and Wall (2007). The reports were staged at different times to enable amalgamation of the SOE data, while ensuring delivery of a national overview in time for the 2015 Synthesis Report. In this report, a summary of the state and trends from the NGMP dataset is presented. The data analysis and deliverables are consistent with the methods of Daughney and Wall (2007) and are in accordance with the scope of work detailed by MfE in the proposal. 1.2 DATA SOURCE: THE NGMP DATASET The NGMP programme is a long-term monitoring programme operated by GNS in collaboration with fifteen regional authorities, and is funded by the Ministry for Business, Innovation and Employment (MBIE). The NGMP was originally envisioned primarily as a network for the detection of temporal trends in groundwater quality (Rosen 1997; Rosen et al.,1999). More recently, the applications of the NGMP have been widened, specifically to: 1) provide a national perspective on groundwater quality in New Zealand, including determination of natural baseline groundwater quality; 2) associate observed state and trends in groundwater quality with specific causes such as land use, pollution or natural processes; and 3) provide data to develop and convey best-practice methods for groundwater sampling, chemical analysis and interpretation (Rosen 2001; Daughney and Reeves 2005, 2006). The NGMP monitoring network was established in 1990 and attained national coverage by late The structure of the NGMP network has remained relatively constant since, and at the time of writing of this report the network included 106 sites (Figure 1). Selection criteria for NGMP bores include data availability, such as: confinement status; bore logs; surrounding land use; and, if possible, a suitable location to give early warning of trends, but not in the immediate recharge area (Daughney et al., 2012; Rosen et al., 1999). There are GNS Science Consultancy Report 2015/16 2

9 very few cases where a single aquifer is monitored by more than one NGMP site. Rather, sites are located in discrete aquifers (or on discrete flow lines in larger aquifer systems) and are selected to encompass a range of surrounding land use, aquifer confinement and aquifer lithology variables. The NGMP network has recently been shown to be representative of the fifteen State of the Environment (SOE) networks (Daughney et al., 2012), comprising a considerably larger number of sites (in excess of 1,000). Median well depth is 26 m below ground level (b.g.l.), and the minimum, lower quartile, upper quartile and maximum well depths across all NGMP sites are 3, 10, 55 and 337 m b.g.l., respectively. Site-specific details pertaining to well location, construction and hydrogeology are described by Daughney and Reeves (2005) and Daughney et al. (2012). Most NGMP sites are sampled quarterly according to a standard national protocol (Rosen et al., 1999; New Zealand Ministry for the Environment, 2006). There are a limited number of sites where the sampling protocol has been adapted by the samplers for practical reasons (e.g. deep well purging time exceeding a day, Spreadsheet 1). The sampling schedule for NGMP sites is: March, June, September and December, with about one month variation in the exact date of sampling amongst regions. Field parameters of ph, temperature, conductivity, dissolved oxygen and groundwater level are measured on site at the time of sampling. All samples are consistently analysed for calcium (Ca), magnesium (Mg), potassium (K), sodium (Na), bicarbonate (HCO 3 ), carbonate (CO 3 ), chloride (Cl), sulphate (SO 4 ), fluoride (F), bromide (Br), ammonium-nitrogen (NH 4 -H), nitrate-nitrogen (NO 3 -N), iron (Fe), manganese (Mn) and silica (SiO 2 ). For cost effectiveness, dissolved reactive phosphorous (DRP) and laboratory electrical conductivity are only analysed in March. Details of the analytical procedures are provided by Daughney and Reeves (2005) and Daughney et al. (2012). Note that Spreadsheet 1 only includes data used within the scope of this report (raw analytical results, calculated total dissolved solids (TDS), quality assurance quantities such as ion differences and charge balance errors). The full and up-to-date NGMP dataset is freely accessible from the Geothermal Groundwater (GGW) Database, which is operated and maintained by GNS ( 1.3 PREVIOUS INVESTIGATIONS Information presented in this report updates information presented in previous reports; including Daughney and Wall (2007) and Daughney and Randall (2009). These reports summarised state and trends in groundwater quality in NZ based on data collected from 973 monitoring sites over the period 1995 to The main conclusions from previous reports were: Nitrate and/or microbial pathogen contamination occurs in all regions, but were especially common in Waikato, Southland, and Canterbury. Shallow wells sited in unconfined aquifers in oxygen-rich groundwater conditions were particularly affected. Median NO 3 -N concentrations exceeded drinking-water standards at 4.8% of the sites, and ecosystems-related standards at 13.2% of the sites (Daughney and Randall 2009). Elevated NH 4 -H, Fe and Mn concentrations were found in many regions, especially in Manawatu-Wanganui, Hawke s Bay, and the Bay of Plenty. Deeper wells, extracting groundwater under confined and oxygen-poor conditions were particularly affected (Daughney and Randall 2009). Three types of groundwater were identified (Daughney and Randall 2009): 1) sites showing little or no human influence (30%), where any introduced nitrate or sulphate would persist; GNS Science Consultancy Report 2015/16 3

10 2) sites with oxygen-poor groundwaters (31%), where high nitrate levels are unlikely but elevated ammonium, iron, manganese, and arsenic may occur under natural processes; and, 3) sites showing some level of human influence (39%), with nitrate and sulphate concentrations above background levels. Most sites (66%) displayed a slow change or constant groundwater quality (change of less than 2 to 5% per year). Higher trends in parameters such as nitrate and sulphate suggested human influence (Daughney and Randall 2009). Although there were observable relationships between groundwater quality, well depth, and aquifer confinement, no relationships were detected between groundwater state, trends, land use or land cover. A separate study, based on NGMP data, linked land use impact to groundwater quality through a reconstruction of the two-stage land use intensification (Morgenstern and Daughney, 2012). This study included age tracer data. GNS Science Consultancy Report 2015/16 4

11 2.0 METHODS 2.1 KEY INDICATORS OF GROUNDWATER QUALITY AND GUIDELINES USED Both the Drinking Water Standards for New Zealand (DWSNZ) (Ministry of Health, 2008) and the Australia and New Zealand Environment Conservation Council (ANZECC) guidelines for fresh and marine water quality (Australia and New Zealand Environment Conservation Council, 2000) were used in this report to compare national groundwater quality data. This is consistent with previous reporting by Daughney and Wall (2007) and Daughney and Randall (2009). The following description of the guidelines is reproduced verbatim from Daughney and Randall (2009): The DWSNZ defines health-related maximum acceptable values (MAVs) and aesthetic guideline values (GVs) related to taste, odour, or colour. The ANZECC guidelines define trigger values (TVs) based on specified protection levels for aquatic ecosystems. This report used TVs that correspond to the 95% protection level for freshwater ecosystems. Some ANZECC TVs (e.g. for heavy metals, ammonia) are directly related to toxicity to biota, whereas other TVs (e.g. for nutrients) are not directly related to toxicity, but if exceeded may lead to adverse ecological changes. The ANZECC guidelines also define TVs for stock drinking water, which are referred to in some sections of this report. Comparisons to both water quality standards are performed on a per-parameter basis, to determine the number and percentage of monitoring sites at which calculated medians exceed the relevant MAVs, GVs, or TVs. It is important to note that exceedance of a DWSNZ threshold does not always indicate a threat to human health, because some DWSNZ guidelines are purely aesthetic, and in the case of health-related standards, water treatment methods can often be employed to remove or reduce the concentration of the parameter of concern. Similarly, exceedance of an ANZECC TV in groundwater will not necessarily lead to adverse ecological consequences in adjacent surface waters on all occasions, because groundwater discharging to a surface water body may mix with the surface water, leading to dilution and reduction of the concentration of the parameter of concern. A given pesticide may have MAVs or a provisional MAV (PMAV). PMAVs were developed because the World Health Organisation has no guidelines, and therefore, the DWSNZ has developed their own thresholds. Early pesticides (pre-1990s) were toxic and affected plants and animals that were not considered as pests (Ministry of Health, 2008). Most early pesticides and their degradation products were persistent and therefore have PMAVs assigned to them. Newer pesticides have less broad toxicity and target biochemical pathways. These pesticides do not have MAVs because their use is seasonal while MAVs are based on 2L water consumption for a lifetime (Ministry of Health, 2008). In accordance with the scope of work detailed by MfE, analytical results for selected parameters were compiled to conduct quality assurance checks and calculate TDS content. However, this report focuses on six key indicators of groundwater quality: Nitrogen-species: nitrogen is present in the form of NO 3 -N in oxygen-rich groundwaters, whereas in oxygen-poor groundwaters, nitrogen exists as NH 4 -H. The conversion from one form to another occurs under natural processes. NO 3 -N is monitored for health and environmental reasons. High NO 3 -N concentrations in drinking-water are associated with blood disease ( blue baby syndrome ), particularly in infants (DWSNZ MAV of 11.3 mg/l). High NO 3 -N concentration may also affect biota by causing overgrowth (ANZECC guidelines of 7.5 mg/l for direct toxicity to biota and 0.17 mg/l for aquatic system protection). Nitrogen species may occur naturally from GNS Science Consultancy Report 2015/16 5

12 nitrogen-rich bedrock and natural soil leaching; however, elevated concentration of nitrogen is a potential indicator of land use impact on groundwater quality through sewage and fertilisers. Based on multivariate statistics, Daughney and Reeves (2005) established threshold values of 1.6 and 3.5 mg/l, respectively, for probable and almost certain land use impact on NZ groundwaters. The threshold of 2.5 mg/l NO 3 -N was proposed for indication of land use intensity by Morgenstern and Daughney (2012). NH 4 -H levels also have toxicity thresholds (ANZECC guidelines of 0.01 mg/l for direct toxicity to biota and 0.74 mg/l for aquatic system protection; the drinkingwater MAV is 1.2 mg/l). Phosphorous species: phosphorous is essential for the development of life forms. It can be present in groundwaters as orthophosphate ion, but also in cellular material. Phosphorous is naturally derived from rock interaction or decomposition of plant and animal tissue, or waste. It is also a land use impact indicator, as fertilisers, manure and composted material contain phosphorous. DRP is the only form of phosphorous monitored in the NGMP. E.coli: E. coli is a species of bacteria, which if detected, indicates occurrence of faecal matter in groundwater. The DWSNZ requires that no E.coli (MAV corresponds to 1 colony forming unit or cfu per 100 ml of water) is detected in drinking-water. The ANZECC guidelines have a TV of 100 cfu per 100 ml of water for livestock consumption. E.coli is not included in this report, as it is not part of the routine monitoring suite for the NGMP programme. However, it will be reported in the second report, using the amalgamated NGMP and SOE data. Fe: Fe is only soluble in oxygen-poor groundwater. It is therefore often used in conjunction with NH 4 -H to investigate low NO 3 -N concentrations. High concentrations of iron may impart an unpleasant taste to drinking water (aesthetic GV of 0.2 mg/l). Mn: like Fe, Mn is only soluble in oxygen-poor groundwater. It is therefore often used in conjunction with NH 4 -H to investigate low NO 3 -N concentrations. High manganese concentrations in waters result in staining of laundry and whiteware (aesthetic GV of 0.04 mg/l). Mn may also present toxicity to human health and ecosystems (MAV 0.4 mg/l and TV 1.9 mg/l). Salinity: salinity pertains to the TDS content. In most cases, salinity values were calculated from individual parameter concentrations. TDS content is affected by spatial and/or temporal changes in abstraction, saltwater intrusion, and recharge mechanisms. MAVs for salinity have not been defined, but aesthetic GVs for TDS content are 1,000 mg/l. Electrical conductivity: electrical conductivity is a measure of TDS content. It is used in this report in conjunction with salinity. The measured ratio between salinity and electrical conductivity ranges from 0.55 to 0.7 (American Public Health Association; American Water Works Association; Water Environment Federation 2005). Pesticides: pesticides are manufactured chemical substances intended to prevent, destroy, repel or mitigate any pest. The term pesticides applies to herbicides, fungicides, and other substances. Pesticides are not included in this report, as it is not part of the routine monitoring suite for the NGMP programme. However, pesticides will be reported on the second report, using the amalgamated NGMP and SOE data. GNS Science Consultancy Report 2015/16 6

13 2.2 REPORTED STATISTICS The following statistics are reported for the dataset, in accordance with the MfE brief and previous reports: median and median absolute deviation: the median is a measure of central tendency. It is a more resistant measure than mean values because it is not affected by outliers. The median absolute deviation gives an indication of the data spread around the median; it is likewise more robust than the standard deviation (Helsel and Hirsch 2002) percentiles (5 th, 25 th, 50 th, 75 th, 95 th ): these also inform the data spread around the median. The median is the 50 th percentile (Helsel and Hirsch 2002). trend magnitudes: the rate of change in each parameter. In this report, the trend magnitudes are based on Sen s slope estimator, which is commonly used for environmental reporting (Helsel and Hirsch 2002). However, there are other methods of deriving trend magnitudes. For example: the excel-based NGMP Calculator developed by Daughney (2007), used in this study, also provides linear regression magnitudes. statistical test p-values: in this report several statistical tests were conducted to assess either the statistical significance of a trend (Mann-Kendall trend test), seasonality (Kruskal-Wallis) or distribution difference (sign-test, and Wilcoxon rank-sum test). For each test, a hypothesis is formulated and test statistics are calculated. An acceptable error rate is arbitrarily set to reject or accept the hypothesis, based on a data-calculated probability value (p-value). For this report, the significance level was set as α=0.05 for all tests. Detailed information about the use of hypothesis tests in general and the tests used in this report can be found in Helsel and Hirsch (2002). 2.3 TREND TEST, AND SETTINGS The Mann-Kendall test was recommended by GNS, in consultation with MfE, for trend detection of temporal trends in groundwater quality. This test has a long history of use in water quality studies in general (Helsel and Hirsch 1992) and has been applied in previous investigations of groundwater quality in New Zealand (Daughney and Reeves 2006; Daughney and Wall 2007; Daughney and Randall 2009). To investigate the necessity of adjusting the Mann-Kendall test for seasonality, a preliminary analysis on NGMP NO 3 -N concentrations was undertaken. The Kruskal-Wallis test results on these concentrations showed that statistically significant seasonal (i.e. quarterly) variations occurred at about 25% of the NGMP sites (Daughney 2014). Furthermore, a Chi square hypothesis test showed that the percentage of NGMP sites displaying seasonal differences was not statistically significantly related to the length of the data record (5,10 and 15 years were used for comparison). It was therefore recommended that seasonal trend tests should be used for the characterisation of state and trend of NZ groundwater quality (Daughney, 2014). The NGMP Calculator (Daughney 2007) uses the non-parametric Mann-Kendall and Kruskal- Wallis tests to assess trend and seasonality (Daughney 2010). If the appropriate settings are used, the Calculator effectively de-trends time series data prior to conducting the Kruskal- Wallis test for seasonality (Daughney 2010). The trend analysis was performed for the period starting on 1/01/2004 and ending on 31/12/2013, using four seasons, starting on Julian day 60. Outliers, defined as values falling outside of four times the median absolute deviation, were excluded for the analysis. GNS Science Consultancy Report 2015/16 7

14 2.4 MINIMUM DATA REQUIREMENTS Published values for the minimum data point requirements for robust trend detection ranges between 8 and 10 (US EPA 2006; Daughney 2007; State of Idaho Department of Environmental Quality 2014). However, in this study, the minimum data requirement was adjusted to ensure even temporal data coverage throughout the time period. This was completed by splitting the entire time period into equally-sized, small time windows and examining each time windows data density. Because some parameters are monitored annually, the smallest time window possible is five years. Typically, ensuring a minimum requirement of 10 data points for a 10-year period requires a minimum of five data points per time window. Setting data point thresholds per parameter and time window resulted in the exclusion of sites (between 64 and 99 sites from a total of 146). The parameter-specific thresholds were selected in conjunction with MfE as a compromise between: even temporal data coverage; minimum data requirements for robust trend detection; and, inclusion of a sufficient number of NGMP sites to represent NZ groundwater quality. The threshold for number of data points per 5-year time window used in this study were: sixteen data points for NH 4 -H, NO 3 -N, Fe, Mn, aggregated TDS, and; three data points for DRP and laboratory measured conductivity. 2.5 TIME PERIOD SELECTION The minimum time period recommended to report on groundwater quality state varies between two and six years (European Commission 2009). The longer period applies to time series with seasonal variations (European Commission 2009). Analysis of the processed NGMP dataset showed that seasonality affects up to 25% of parameter-specific data. Furthermore, NO 3 -N concentration trend magnitudes and seasonal Mann-Kendall p-values (at the 95% confidence level) obtained for the 5-, 10-, and 15-year time periods were calculated using the NGMP dataset. It was not possible to generate a 20-year dataset, since national coverage of the NGMP network was achieved in The number of sites showing statistically significant trends was significantly smaller in the 5-year dataset, whereas these numbers were comparable between 10 and 15 years. An analysis of variance (ANOVA) test was performed on non-statistically significant trend magnitudes to test whether the lowest detection was due to the lack of statistical power, or a difference in the number of sites exhibiting trends depending on record length (Daughney, 2014). It was found that using just five years of data introduces the risk that real increasing or decreasing trends in groundwater quality will not be detected due to a lack of statistical power. As a result, and in accordance to the MfE s scope of work, it was proposed to conduct trend analysis on two time periods: 10 years and 15 years. However, applying the minimum data requirements per time window described in the previous section, no time series was deemed acceptable for the 15 year time period. Therefore, only the medians and trends are presented in the main body of this report. 2.6 EFFECT OF TIME PERIOD SELECTION To investigate the influence of the time window selection on trend and median values, a paired dataset was prepared using the cleaned raw dataset (details on quality assurance procedures are outlined in the following section). However, the minimum data point requirements per time widow was lowered to ten for NO 3 -N, NH 4 -H, Fe, Mn and aggregated GNS Science Consultancy Report 2015/16 8

15 TDS, because the original setting resulted in the exclusion of all sites. The adapted minimum data requirements still fulfills the international standard for trend detection (US EPA 2006; State of Idaho Department of Environmental Quality 2014). The resulting dataset consists of parameter-specific pairs with size ranging from 30 sites (TDS) to 89 sites (DRP and conductivity). This dataset is included in Spreadsheet 2. The differences in trend analysis results between the 10- and 15-year time periods were investigated in terms of systematic over/under estimation (sign-test) and distribution of paired medians and statistically significant trend magnitudes (Wilcoxon signed rank-test) for each parameter. There was evidence that medians obtained for the period were smaller than for the period (sign test p-value<0.005) for DRP, iron, manganese and NH 4 -H. However, medians for both time periods exhibited similar distributions (Wilcoxon test p-value <0.05), save for DRP and NH 4 -H. Trends for manganese concentrations for the period were found smaller than for the period. Trends exhibited a similar distribution for both time periods (p-value<0.05), except for DRP and TDS. 2.7 DATA PROCESSING NGMP data was collected for the period (GNS Science 2015). Data was first aggregated to account for historical changes in analytical methods and reporting units (e.g. NH 4 -H vs NH 3 ). Results with either a high charge balance error (>5% threshold for acceptance), or in the case of dilute samples (<3 meq/l), a high cation-anion difference (>0.2 meq/l) were excluded (American Public Health Association, American Water Works Association and Water Environment Federation 2005). This resulted in the rejection of less than 2% of the original dataset (6,316 analyses kept). TDS content (TDS) was calculated for samples at which bicarbonate, sodium, potassium, calcium, magnesium, chloride, sulphate, silica and nitrate were analysed simultaneously, using the following equation (American Public Health Association, American Water Works Association and Water Environment Federation, 2005): TDS=0.6*alkalinity (as CaCO 3 )+(Na + )+(K + )+(Ca 2+ )+(Mg 2+ )+(Cl - )+(SO 4 2- )+(SiO 3- )+(NO 3 - )+(F - ) Calculated TDS were then compared to field conductivity, with an acceptable range for the ratio between calculated TDS and laboratory-measured TDS of (American Public Health Association, American Water Works Association and Water Environment Federation 2005). About 30% of the calculated TDS were found out of range from a total of 6,308 calculated values. The last selection was based on the minimum data requirements per 5- year time window (Section 2.3). Applying the threshold resulted in the exclusion of 30 to 45% of results across all parameters (30% of the sites) for the period. Cleaned, raw data have been made freely available as electronic files from the MfE website (Spreadsheet 1). GNS Science Consultancy Report 2015/16 9

16 2.8 LIMITATIONS As mentioned in previous reports, it is important to note that data from the SOE and the NGMP is not representative of drinking-water quality in New Zealand (Daughney and Wall 2007; Daughney and Randall 2009). Further information on the subject can be obtained from the Annual Review of Drinking Water Quality reports produced by the Ministry of Health (Ministry of Health, 2015). This report focussed on key indicators, however parameters that are not routinely monitored as part of the NGMP, SOE program, or the pesticides monitoring program (e.g. organic volatile compounds, endocrine disruptors) are not included in this report. Sampling and analytical methods were provided where this information was available (Spreadsheet 1). Where unrecorded, these can influence the data obtained, particularly for parameters such as Fe and Mn. It is unclear whether the monitored sites (NGMP, SOE, pesticides) are representative of NZ groundwater quality. This is because the selection of a monitoring site is based on monitoring objectives, available information on the groundwater sources, and site access. Groundwater quality may be influenced by the land use at the time of recharge, within the groundwater source capture zone. Groundwater age dating has been undertaken at each active NGMP well to assess groundwater mean residence time (Moreau and Cameron, 2014). However, for most monitoring sites (NGMP, SOE, pesticides), groundwater capture zones for the wells have not yet been delineated. GNS Science Consultancy Report 2015/16 10

17 3.0 RESULTS 3.1 SITE-SPECIFIC ASSESSMENT OF STATE AND TRENDS Site-specific statistics and national summary tables have been made freely available as electronic files from the MfE website (Spreadsheet 2). Medians and trend changes between the and the periods were investigated using the non-parametric, paired observation sign-test. NH 4 -H, DRP, and Fe recent medians were found to be statistically higher (p-values <0.005). Recent TDS content was found to be lower than for the period. A limited number of paired sites have statistically significant trends during both time periods. The sign-test could only be performed on NO 3 -N trends, and showed that the difference in the trend magnitudes was not statistically different between the two time periods (p-value = 0.332). 3.2 NATIONAL OVERVIEW National level statistics are compiled in Spreadsheet 2 and summarised in Tables 1 to 4 (analogous to Tables 3, 4, 5, and 6 from Daughney and Randall 2009). The national level statistics show: National medians for NO 3 -N and Mn differed from previously reported values. The NO 3 -N median was found to be about half the previously reported value, possibly owing to the inclusion of the Gisborne sites in this report. Most Mn concentrations were below the detection limit compared to above in the previous report, although within the same order of magnitude. A minority of sites exceeded the NZDWS guidelines (up to 32%), for NO 3 -N, NH 4 -H, Fe, and Mn concentrations. There were isolated occurrences of exceedance of the MAVs. Statistically significant trends were only detected in a portion of the sites (mostly around 15% of the sites), and the percentage of sites varied, depending on the parameters. Omitting TDS (as it contained calculated values), most trends were observed in NO 3 -N concentrations (35.7% of the sites). In contrast, only 4% of the sites exhibited statistically significant DRP trends. Individual parameter increases and losses over the period were observed, most commonly in the order of 0.01 or mg/l per year. These rates are considered slow and consistent with previous reporting (Daughney and Reeves 2006; Daughney and Randall 2009). No relationship was found between median concentrations and absolute trend magnitudes. GNS Science Consultancy Report 2015/16 11

18 Table 3.1 Calculated national percentiles and maximum values for groundwater quality indicators, based on site-specific median values for the period Global average concentration from river water and groundwater are given for comparison. All values are in mg/l except conductivity, which is expressed in µs/cm. Parameter NO3-N NH4-N DRP Fe Mn Conductivity TDS Units mg/l mg/l mg/l mg/l mg/l µs/cm mg/l n New Zealand Groundwater (this report) Percentiles 5 th 0.00 <0.01 <0.004 <0.02 < th 0.00 < <0.02 < th 0.55 < <0.02 < th th Max ,550 1, th th 1.3 Global Averages River water Groundwater < Table 3.2 Percentage of New Zealand monitoring sites at which median concentrations calculated for the period are in excess of water quality standards or guidelines. All values are in mg/l except conductivity, which is expressed in µs/cm. DWSNZ ANZECC Parameter Reason MAV or GV %Sites exceeding Reason TV %Sites exceeding NO 3 -N Health NH 4 -N Aesthetic Ecosystem Toxicity Ecosystem Toxicity DRP - Ecosystem Fe Aesthetic Mn Aesthetic Health Toxicity Conductivity - - TDS - - GNS Science Consultancy Report 2015/16 12

19 Table 3.3 Number of monitoring sites (n) across New Zealand at which trend tests could be performed for the period Percentages without significant trends (%N) or with significant increasing (%INCR) or significant decreasing (%DECR) trends at the 95% confidence level are indicated.all values are in mg/l except conductivity, which is expressed in µs/cm. ND means non-determined. Parameter n %INCR %DECR %N %ND NO 3-N NH 4-N DRP Fe Mn Conductivity TDS Table 3.4 National (absolute and relative) rates of change in groundwater quality parameters for sites with statistically significant trends. Relative median rates of change were calculated by dividing the median absolute trend by the relevant median concentration from Table 3.1. Parameter n Min. Median Max. Relative median (% per year) NO 3-N % NH 4-N % DRP % Fe % Mn % Conductivity % TDS % 3.3 KEY INDICATORS National and regional percentiles, exceedances, trends and significant trend statistics for the seven selected groundwater quality indicators for the period are presented in Figure 2 to 8, and Spreadsheet NO 3 -N The national median NO 3 -N concentration was 0.55 mg/l for the period (n=86). This concentration is less than half of the previously reported medians (Table 3.1). It was noted previously that the median was slightly higher than expected due to the exclusion of sites from the Gisborne region (Daughney and Randall 2009). Median concentrations for the period for Gisborne were below 0.3 mg/l (lowest regional distribution, Figure 2). Mild to high (12 to 84%) censoring (values below the detection limit) was encountered at all the Gisborne sites (detection limit of 0.02 mg/l). The lowest median NO 3 -N concentrations (below of at the detection limit) were found in Auckland (5 out of 6 sites), Gisborne (all 6 sites) and Taranaki (4 sites) regions (Figure 2). Median concentrations of mg/l were also encountered at about half of the Hawke s Bay sites. Southland and Waikato sites exhibited the highest medians, with values ranging from 0.3 to 10.9 mg/l (Figure 2). Most sites (62%) exceeded the ANZECC guidelines value GNS Science Consultancy Report 2015/16 13

20 for ecosystem health, whereas only 9% exceeded the toxicity value. The NZDWS MAV was exceeded at two sites located in the Tasman region: 14.1 mg/l at Feature 9 and 14.1 mg/l at Feature 10 (Table 3.2). The majority (59.3%) of NGMP sites did not show statistically significant trends for NO 3 -N (Table 3.3). Where statistically significant trends were detected, losses (minimum of mg/l per year at Feature 347, West Coast) and increases (maximum of 2.0 mg/l per year at Feature 348, West Coast) were observed. Most trends were less than 0.01 mg/l per year. Increases were more frequent than decreases (25.6% and 15.1%, respectively; Table 3.4); however, concurrent trends were observed in eight regions, at different sites (Figure 2). There were no sites at which it was not possible to conduct trend analysis NH 4 -N Nationally, NH 4 -H concentration was commonly (64%) reported as undetected (limit 0.01 mg/l) for the period (n=86). This observation is consistent with previous reporting and the global average reported for river water (Table 3.1). The NH 4 -H medians exhibited variability at both the national and the regional level (Figure 3). The ANZECC TV for ecosystem health was exceeded at 32.6% of the NGMP sites. Only a small number of regions (Auckland, Gisborne, Hawke s Bay, Wanganui-Manawatu and Taranaki) exhibited medians above 0.1 mg/l. The highest concentrations were found in Gisborne (up to 5.6 mg/l) and Hawke s Bay (up to 3.8 mg/l; Figure 3). At these wells (4.7% of sites), medians exceeded both the toxicity and the guidelines value for human health (Figure 3; Table 3.2). These values were associated with detected iron concentrations (up to 8.6 mg/l), suggesting reducing conditions in the aquifer. Confined conditions were identified at three of the four sites where high NH 4 -H concentrations were found at depths of 29.5 to 83 m bgs. Censoring affected the detection of trends at the majority of sites (58.1% not determined, Table 3.3). Statistically significant increases were found for NH 4 -H (at 12.8% of NGMP sites), although a large proportion of detected trends were not statistically significant (29.1%). Increasing rates ranged between <0.001 mg/l per year to 0.03 mg/l per year. The median increase was mg/l per year, which at most sites would be difficult to detect if the median was below the detection limit (Table 3.4). Increases above the national range occurred in Marlborough (0.002 and 0.03 mg/l per year at two sites) and Hawke s Bay (0.002 to 0.07 mg/l per year at two sites; Figure 3). No decreasing trends were observed (Table 3.4) DRP The national median DRP concentration was 0.02 mg/l for the period (n=99). This observation is consistent with previous reporting and the global average reported for river water (Table 3.1). The DRP medians exhibited variability at both the national and the regional level (Figure 4). The median was at the detection limit at a limited number of sites (5.1%). Detected medians ranged from to 1 mg/l (Table 3.1), with 17 sites above 0.1 mg/l. Most sites (57.6%) exhibited DRP concentrations above the ANZECC TV for ecosystem health (Table 3.2). These sites were generally distributed throughout the country, with the only exception being Otago. Highest concentrations of DRP were found in Hawke s Bay (1 mg/l at Feature 364) and Manawatu-Wanganui (0.9 mg/l at Feature 14; Figure 4). The highest concentrations were GNS Science Consultancy Report 2015/16 14

21 found where nitrogen was mostly present in the NH 4 -N form, although no statistical relationship was found between DRP and nitrogen-species concentrations (Figure 9). High DRP medians were associated with high Fe and Mn, and therefore reducing conditions. Although phosphorous is soluble in water, it can bind to mineral surfaces along the flowpath. The most common binding minerals are clays and iron oxides (Domagalski, 2011). The elevated iron concentrations suggest that iron oxides may not be stable, and therefore, may release phosphorous (Domagalski, 2011). A more detailed analysis using major chemical element concentrations along the flow path, and review of the aquifer material, would be required at the affected sites for it to be conclusive. Only five sites exhibited statistically significant trends (4% of the sites, Table 3.3), with decreases at a rate of less than mg/l per year observed in Canterbury and increases of about mg/l per year observed in the Tasman and West Coast regions (Figure 4; Table 3.4). These trends were not correlated with systematic trends in the other selected parameters Fe and Mn The national medians for Fe and Mn were found below their detection limits (0.02 and mg/l respectively) for the period (n=86 for both species). These are slightly lower, but of similar magnitude, than the previously reported medians (Table 3.1). Censoring affected just over half of the sites (57% for both parameters). The range of medians however was quite wide, with maximums up to 17.1 mg/l Fe (Feature 81, Gisborne) and 2.6 mg/l Mn (Feature 11, Tasman). Elevated concentrations were consistent in magnitudes and locations with previously reported state values (Daughney and Randall 2009). Although there were overlaps, regional distributions of Fe and Mn concentrations showed differences. Fe concentrations were significantly higher in Gisborne, whereas large variations in concentrations were observed in Auckland, Hawke s Bay and Wanganui-Manawatu (Figure 5). Manganese concentrations were highest in the Gisborne and Hawke s Bay regions (Figure 6). Most sites (77% and 59%, respectively for Fe and Mn) did not exceed the lowest DWSNZ guidelines value (aesthetic criteria, Table 3.2). There was one instance where Mn exceeded the ANZECC TV toxicity threshold (Feature 11, Tasman). The NZDWS MAV was exceeded at two sites located in the Tasman region (14.1 mg/l at Feature 9 and 14.1 mg/l at Feature 10; Table 3.2). Where trend analysis was possible (about 40% of the sites), for both Fe and Mn, the absence of a statistically significant trend was frequent (about 30%, Table 3.3). A limited number of sites with increasing Fe (8.1%) were detected in Auckland, Bay of Plenty, Canterbury, Gisborne, and Wellington. A similar proportion (11.6%) of sites, with a Mn increase, were detected in Auckland, Canterbury, Southland, Gisborne, and Marlborough. Median trends were 0.02 and mg/l per year for Fe and Mn, respectively (Table 3.4). Previously reported trends for Fe were mostly decreases Salinity and electrical conductivity The national median for TDS content was 156 mg/l for the period (n=64), which is consistent with the previously reported median of 135 mg/l (Table 3.1). The corresponding national conductivity median was 235 µs/cm (n=99), which is also consistent with the previously report. Available data suggests a national ratio of about 0.59 (R 2 =0.9836) for conductivity versus TDS (excluding the isolated, maximum values from Feature 81). This GNS Science Consultancy Report 2015/16 15

22 ratio falls in the natural range of 0.55 to 0.7 (American Public Health Association, American Water Works Association and Water Environment Federation, 2005). Box and whisker plots for median concentrations and trends were unsurprisingly very similar, as both parameters are linked (Figure 7, Figure 8). There were large regional variations in conductivities (Figure 7) with regional medians ranging from 104 µs/cm (West coast) to 912 µs/cm (Gisborne). Marlborough, Bay of Plenty, Otago and Waikato sites exhibited conductivities below 200 µs/cm. Apart from Gisborne, the highest conductivities were found in Northland, Taranaki and Hawke s Bay (329 to 345 µs/cm). High conductivities encountered in the Gisborne region are due to natural evolution, where groundwater becomes more saline owing to prolonged water-rock interaction (Daughney and Reeves 2005). Groundwater at these sites often exhibits moderately to highly reduced conditions, due to a longer residence time. There are no DWSNZ or ANZECC guidelines for electrical conductivity, however high TDS content is often linked with high individual ion concentrations, which in turn may have specific guidelines. The majority of sites (84.8%) did not exhibit any statistically significant trend (Table 3.4). Where detected, decreases were more common (11%) than increases (4%) and were encountered in Auckland, Southland, Gisborne, Wellington, Northland, Tasman and Waikato. Increases were only observed in Canterbury Marlborough and Northland. The fastest increases occurred at a rate of 20 µs/cm at Feature 2013 (Northland) and the fastest loss occurred at Feature 79 (Gisborne) at a rate of -33 µs/cm. 3.4 FACTORS CONTROLLING GROUNDWATER QUALITY Well depth and aquifer confinement Well depth and aquifer confinement should be considered jointly because they are correlated (Daughney and Randall 2009). NGMP sites presented in this report consist mostly of shallow wells (27 sites of less than 10 m; 54 sites with depths ranging from 10 to 50 m). Unconfined, semi-confined and confined status are encountered respectively at 30, 14 and 36 sites. Note that there are 22 sites at which confinement status is unknown. Relationships with depth were investigated through depth scatterplots. No statistical relationships were found for any of the selected parameters. However, the following patterns were observed: NO 3 -N concentrations were higher in shallow wells than in deep and confined wells (Figure 10). This is consistent with previous reporting and independent studies (Daughney and Randall 2009; Morgenstern and Daughney, 2012); Higher conductivity, Mn, DRP and NH 4 -H were associated with deep wells, mostly under confined conditions. GNS Science Consultancy Report 2015/16 16

23 3.4.2 Aquifer lithology Most sites are sourced from sand (18) and gravels (57), the other lithological categories do not hold sample sizes greater than 5. It was, therefore, not possible to investigate relationships between lithology and medians or trends for other lithologies. Both sand and gravels exhibited similar medians and trends for Fe, Mn and NH 4 -N. Sand aquifers exhibited higher medians for DRP and lower NO 3 -N and conductivities. Sand aquifers also exhibited decreasing Fe trends, unmatched by gravel aquifers (Table 3.5). Table 3.5 National medians for median concentrations values and trend magnitudes per aquifer lithology. Parameter NO 3 -N NH 4 -N DRP Fe Mn Conductivity TDS Median Gravel Sand n Gravel n Sand Trend Gravel 0 < < Sand n Gravel n Sand Previous studies have reported a lack of relationships between aquifer lithology and medians or trends and noted that lithology has an impact on oxygen persistence, which in turn will control concentrations of nitrogen species and redox indicators (Daughney and Wall, 2007). GNS Science Consultancy Report 2015/16 17

24 4.0 CONCLUSION Groundwater state and trends for the period are in general agreement with state and trends found for the period (Daughney and Randall 2009). Although the national median NO 3 -N concentration was 0.55 mg/l, concentrations of up to 14.1 mg/l (which is above the NZ MAV for NZDWS) were found at some sites. Higher NO 3 -N concentrations affected the Southland and Waikato regions. Elevated NO 3 -N concentrations were found mostly in unconfined, shallow wells. Increases were more frequent than decreases and it was not uncommon to observe both upwards and downwards trends within the same region. Most sites did not exhibit any statistically significant trends for NO 3 -N. The national median DRP concentration was 0.02 mg/l for the period (n=99), although there were regional variations. All but one region exhibited DRP concentrations above the ANZECC TV for ecosystem health. High phosphorous medians were associated with high Fe and Mn. It is likely that reducing conditions in each aquifer facilitate the transport of phosphorous species. Only a very limited number of sites exhibited trends (4%). Trend magnitudes were of the order of mg/l per year. Iron and Mn were mostly found in low concentrations for the period. However, when detectable, Fe and Mn concentrations could be quite high, indicating reducing conditions. Two sites exceeded the NZDWS MAV for Mn. Where trends were detected, their magnitudes were low, typical of the natural evolution of groundwater. There were large regional variations in conductivity with regions characterised by dilute groundwaters (West Coast, Marlborough, Bay of Plenty, Otago and Waikato) and regions with higher conductivities elsewhere. Gisborne conductivities were significantly higher than anywhere else in New Zealand. Decreases in conductivity were more common than increases (Canterbury, Marlborough and Northland). GNS Science Consultancy Report 2015/16 18

25 5.0 RECOMMENDATIONS This report supports previous recommendations from Daughney and Randall (2009), that indicated regular updates should be conducted to identify and monitor changes in the status of groundwater quality in New Zealand. It is recommended to continue to monitor the state of the environment at the national scale, and at regular intervals. In addition, the following should be considered: It is expected that this report will be followed by a second report that includes the amalgamated SOE dataset. This will provide further spatial coverage as the SOE dataset comprises more than 1,000 sites nationwide. As indicated previously (Daughney and Randall 2009), bi-or tri-ennial surveys should be undertaken to assess the occurrence of emerging contaminants, such as pharmaceuticals, cadmium, etc. It is expected that pesticides will be included in the second 2015 report. Residence time information should be included in future analysis and reporting, as it has been shown to effectively link land use to impact on groundwater quality (Morgenstern and Daughney 2012). With the recent release of the National Policy Statement on Freshwater Management (Ministry for the Environment 2014), regions may revise their SOE monitoring network in order to monitor freshwater management, based on values defined by communities. This may have an impact on SOE monitoring site distribution and may induce decoupling of the monitoring network and analytical suites to accommodate regional freshwater management. It is recommended that monitoring network review should consider maintaining long-term baseline monitoring sites to ensure that data will be available for future updates of state and trend reporting at the national level. It is recommended that SOE monitoring suites for national reporting should be extended beyond the NGMP network. 6.0 ACKNOWLEDGEMENTS Abigail Lovett, Zara Rawlinson and Constanze Tschritter (GNS Science) are thanked for providing a review of a draft version of this report. GNS Science Consultancy Report 2015/16 19

26 7.0 REFERENCES American Public Health Association; American Water Works Association; Water Environment Federation, Standard Methods for the Examination of Water and Wastewater (21st ed.), Washington, DC. 1368p. Australia and New Zealand Environment Conservation Council Australian and New Zealand Guidelines for Fresh and Marine Water Quality. Volume 1: The Guidelines. Australian Water Association, Artarmon. 314p. Daughney, C. J Personal communication. Environment & Material Division Director, GNS Science. Daughney, C. J Spreadsheet for automatic processing of water quality data: 2010 update Calculation of percentiles and tests for seasonality. GNS Science Report 2010/42. 19p. Daughney, C. J Spreadsheet for automatic processing of water quality data: 2007 update. GNS Science Report 2007/17. 15p. Daughney, C. J.; Raiber, M.; Moreau-Fournier, M.; Morgenstern, U.; van der Raaij, R Use of hierarchical cluster analysis to assess the representativeness of a baseline groundwater quality monitoring network: comparison of New Zealand's national and regional groundwater monitoring programs. Hydrogeology Journal, 20(1): DOI: /s Daughney, C.; Randall, M National Groundwater Quality Indicators Update: State and Trends , GNS Science Consultancy Report 2009/145. Prepared for Ministry for the Environment, Wellington, New Zealand. 60p. Daughney, C. J. and Reeves, R. R Definition of Hydrochemical Facies in the New Zealand National Groundwater Monitoring Programme. J. Hydrol. (NZ) 44: Daughney, C. J.; Reeves, R. R Analysis of Long-Term Trends in New Zealand s Groundwater Quality based on data from the National Groundwater monitoring Programme. J Hydrol. (NZ) 45:41-62 Daughney, C. J.; Wall, M Groundwater quality in New Zealand: State and trends GNS Science Consultancy Report 2007/23. 65p. Domagalski, J.L.; Johnson, H Subsurface transport of orthophosphate in five agricultural watersheds, USA. Journal of Hydrology. 409: European Commission Common implementation strategy for the water framework directive (2000/60/EC). Guidance Document No. 18. Technical Report p. GNS Science GNS Science Geothermal and Groundwater Database. Zealand/ggwdata/, last accessed: 28/01/2015. Helsel D., R.; Hirsch R., M Statistical methods in water resources. USGS publication, book 4, hydrologic analysis and interpretation. 510p. Ministry for the Environment National Policy Statement for Freshwater Management Online publication. 34p. GNS Science Consultancy Report 2015/16 20

27 Ministry of Health Drinking-Water Standards for New Zealand 2005 (Revised 2008), Wellington. 175p. ISBN Ministry of Health Annual Report on Drinking-Water Quality Wellington: Ministry of Health.129p. Accessed April Moreau, M.; Bekele, M Groundwater component of the Water Physical Stock Account (WPSA), GNS Science Consultancy Report 2014/ p. Moreau, M.F.; Cameron, S.G Outputs from GNS Science hydrogeology research programmes. GNS Science consultancy report 2014/254LR. 10 p. + 1 CD. Morgenstern, U.; Daughney, C.J Groundwater age for identification of baseline groundwater quality and impacts of land-use intensification : The National Groundwater Monitoring Programme of New Zealand. Journal of hydrology, 456/457: New Zealand Ministry for the Environment A national protocol for state of the environment groundwater sampling in New Zealand. Report ME781, Ministry for the Environment, Wellington, New Zealand. Accessed September Parliament of New Zealand Environment Reporting Bill (explanatory note). 16p. Rosen, M.R The national groundwater monitoring network (NGMP): structure, implementation and preliminary results. Institute of Geological and Nuclear Sciences Science Report 97/26. 47p. Rosen, M.R Hydrochemistry of New Zealand s aquifers. In: Rosen, M.R.; White, P.A. (eds.) Groundwaters of New Zealand, New Zealand Hydrological Society, Wellington, New Zealand: Rosen, M.R.; Cameron, S.G.; Taylor, C.B.; Reeves, R.R New Zealand guidelines for the collection of groundwater samples for chemical and isotopic analyses. Institute of Geological and Nuclear Sciences Science Report 99/9. State of Idaho Department of Environmental Quality Statistical guidance for determining background groundwater quality and degradation. 103p. US EPA Data quality assessment: statistical methods for practitioners. EPA QA/G-9S. 190p. GNS Science Consultancy Report 2015/16 21

28 FIGURES GNS Science Consultancy Report 2015/16 22

29 Figure 1: Location of NGMP sites and main aquifers in New Zealand. Aquifer shapefiles were sourced from Moreau and Bekele (2015). GNS Science Consultancy Report 2015/16 23

30 Figure 2: National and regional summary statistics for state and trends in NO 3-N indicators of groundwater quality, based on all data collected from 2004 to Numbers above X axes show the number of sites at which state and trend statistics were calculated for the parameter in question for the region of interest. Colour coding for box-whisker plots shows national-level statistics (vivid blue) and regional-level statistics (blue). Most of the figures in this section show the distribution of data as box and whisker plots. The horizontal lines in the middle of each box are median values and the upper and lower limit of the box are the 75 th and 25 th percentiles, respectively. The vertical lines extend from the 95 th to the 5 th percentiles. GNS Science Consultancy Report 2015/16 24

31 Figure 3: National and regional summary statistics for state and trends in NH 4-N concentrations based on all data collected from 2004 to Numbers above X axes show the number of sites at which state and trend statistics were calculated. Most of the figures in this section show the distribution of data as box and whisker plots. The horizontal lines in the middle of each box are median values and the upper and lower limit of the box are the 75 th and 25 th percentiles, respectively. The vertical lines extend from the 95 th to the 5 th percentiles. GNS Science Consultancy Report 2015/16 25

32 Figure 4: National and regional summary statistics for state and trends in dissolved phosphorous concentrations based on all data collected from 2004 to Numbers above X axes show the number of sites at which state and trend statistics could be calculated. Most of the figures in this section show the distribution of data as box and whisker plots. The horizontal lines in the middle of each box are median values and the upper and lower limit of the box are the 75 th and 25 th percentiles, respectively. The vertical lines extend from the 95 th to the 5 th percentiles. GNS Science Consultancy Report 2015/16 26

33 Figure 5: National and regional summary statistics for state and trends in Fe based on all data collected from 2004 to Numbers above X axes show the number of sites at which state and trend statistics were calculated. Most of the figures in this section show the distribution of data as box and whisker plots. The horizontal lines in the middle of each box are median values and the upper and lower limit of the box are the 75 th and 25 th percentiles, respectively. The vertical lines extend from the 95 th to the 5 th percentiles. GNS Science Consultancy Report 2015/16 27

34 Figure 6: National and regional summary statistics for state and trends in Mn based on all data collected from 2004 to Numbers above X axes show the number of sites at which state and trend statistics were calculated. Most of the figures in this section show the distribution of data as box and whisker plots. The horizontal lines in the middle of each box are median values and the upper and lower limit of the box are the 75 th and 25 th percentiles, respectively. The vertical lines extend from the 95 th to the 5 th percentiles. GNS Science Consultancy Report 2015/16 28