GNS Science Consultancy Report water/update-of... · any use of or reliance on any contents of this report by any person ... MfE commissioned GNS Science to report on New Zealand

Project Number 630W0112-00

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: June 2015

BIBLIOGRAPHIC REFERENCE

Moreau, M.; Riedi, M.A.; Aurisch, K. 2016. Update of National Groundwater Quality Indicators: State and Trends 20052014, GNS Science Consultancy Report 2015/107. 42 p.

GNS Science Consultancy Report 2015/107 i

CONTENTS

EXECUTIVE SUMMARY ....................................................................................................... III

1.0 INTRODUCTION ........................................................................................................ 1

1.1 Scope of work ................................................................................................................ 1 1.2 Data source ................................................................................................................... 2

1.2.1 Inorganic chemistry and microbiology (NGMP and SOE) ................................ 2 1.2.2 Pesticides ......................................................................................................... 4

1.3 Previous investigations .................................................................................................. 5 1.3.1 Inorganic chemistry and microbiology .............................................................. 5 1.3.2 Pesticides ......................................................................................................... 6

2.0 METHODS .................................................................................................................. 7

2.1 Key indicators of groundwater quality and guidelines used .......................................... 7 2.2 Reported statistics ......................................................................................................... 8 2.3 Trend analysis settings .................................................................................................. 9 2.4 Minimum data requirements .......................................................................................... 9 2.5 Data processing ........................................................................................................... 10 2.6 Limitations ................................................................................................................... 11

3.0 RESULTS ................................................................................................................. 12

3.1 Site-specific assessment of state and trends .............................................................. 12 3.2 National overview ........................................................................................................ 12 3.3 Key indicators .............................................................................................................. 14

3.3.1 NO3-N ............................................................................................................. 14 3.3.2 NH4-N ............................................................................................................. 15 3.3.3 DRP ................................................................................................................ 15 3.3.4 Fe and Mn ...................................................................................................... 16 3.3.5 Conductivity .................................................................................................... 16 3.3.6 E.coli ............................................................................................................... 17

3.4 Factors controlling groundwater quality ...................................................................... 17 3.4.1 Well depth and aquifer confinement ............................................................... 17 3.4.2 Aquifer lithology .............................................................................................. 17

4.0 CONCLUSION .......................................................................................................... 19

5.0 RECOMMENDATIONS ............................................................................................. 20

6.0 ACKNOWLEDGEMENTS ......................................................................................... 20

7.0 REFERENCES ......................................................................................................... 21

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TABLES

Table 1: Number of sites monitored for inorganic chemistry, microbiology and pesticides, per region. .......................................................................................................................................... 4

Table 2: Calculated national percentiles and maximum values for groundwater quality indicators, based on site-specific median values for the period 20052014. ............................................... 13

Table 3: Percentage of New Zealand monitoring sites at which median concentrations calculated for the period 20052014 are in excess of water quality standards or guidelines. ..................... 13

Table 4: Number of monitoring sites (n) across New Zealand at which trend tests could be performed for the period 20052014. ......................................................................................... 14

Table 5: National (absolute and relative) rates of change in groundwater quality parameters for sites with statistically significant trends. ..................................................................................... 14

Table 6: National medians for median concentrations values per aquifer lithology. ................................. 18

FIGURES

Figure 1: Monitoring of nitrogen species throughout the SOE network, collected for this study. ............... 24 Figure 2: Monitoring of phosphorus species throughout the SOE network, collected for this study. ......... 24 Figure 3: Monitoring of iron and manganese species throughout the SOE network, collected for

this study. ................................................................................................................................... 25 Figure 4: Location of SOE and NGMP sites and main aquifers in New Zealand. ...................................... 26 Figure 5: Location of sites included in the 4-yearly pesticides surveys from 1998 to 2010 and main

aquifers in New Zealand. ............................................................................................................ 27 Figure 6: National and regional summary statistics for state and trends in NO3-N indicators of

groundwater quality, based on all data collected from 2005 to 2014. ......................................... 28 Figure 7: National and regional summary statistics for state and trends in NH4-N concentrations

based on all data collected from 2005 to 2014. .......................................................................... 29 Figure 8: National and regional summary statistics for state and trends in dissolved phosphorous

concentrations based on all data collected from 2005 to 2014. .................................................. 30 Figure 9: Scatterplot comparing median concentrations of DRP with nitrogen species (left), and

with Fe and Mn concentrations (right) at NGMP and SOE sites for the 20052014 period. ....... 31 Figure 10: National and regional summary statistics for state and trends in Fe based on all data

collected from 2005 to 2014. ...................................................................................................... 32 Figure 11: National and regional summary statistics for state and trends in Mn based on all data

collected from 2005 to 2014. ...................................................................................................... 33 Figure 12: National and regional summary statistics for state and trends of conductivity based on all

data collected from 2005 to 2014. .............................................................................................. 34 Figure 13: National and regional summary statistics for state of E. coli based on all data collected

from 2005 to 2014. ..................................................................................................................... 35 Figure 14: Scatterplot of NO3-N median concentrations versus depth. ....................................................... 36

GNS Science Consultancy Report 2015/107 iii

EXECUTIVE SUMMARY

The Ministry for the Environment (MfE) commissioned GNS Science to summarise groundwater quality state and trends for the 20052014 period. This report updates the previous assessment of groundwater state and trends for the 19952008 period by GNS Science for MfE that used data from the National Groundwater Monitoring Programme (NGMP) and the State of the Environment (SOE) monitoring programmes (Daughney and Randall, 2009). Similarly, this report summarises groundwater quality data from an amalgamated NGMP and SOE dataset (20052014). It also includes a summary of New Zealands pesticides surveys (1990 to 2010, 4-yearly) conducted by the Institute of Environmental Science and Research. This report follows the report focusing on state and trends on NGMP data for the 20042013 period (Moreau and Daughney, 2015).

Trend analysis was conducted for key groundwater quality indicators, selected by MfE: nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-H), dissolved reactive phosphorous (DRP), dissolved iron (Fe), dissolved manganese (Mn), electrical conductivity (conductivity), E.coli and pesticides. The data collected comprised other forms of nitrogen and phosphorous, which are inconsistently monitored across New Zealand. To maximise data coverage, other monitored forms of nitrogen and phosphorous data were aggregated to nitrate-nitrogen (NO3-N) or ammonium-nitrogen (NH4-H), which is the dataset presented in this report. Reported values are medians for characterising state and trend magnitudes and trends, which is consistent with previous reporting (Daughney and Randall, 2009). Due to the frequency of monitoring, trends are not reported for E.coli and pesticides.

At the national level, groundwater state and trends for the 20052014 period were found to be in general agreement with the medians reported for the 19982008 period. At a minority of sites (up to 22%, depending on the parameter of interest), exceedance of guidelines set in the drinking-water standards for New Zealand (DWSNZ) were observed for all the parameters, either for aesthetic, ecosystem or human health. Statistically significant trends were detected in a portion of the sites (with conductivity measurements having the maximum of 16% of the sites), and both increases and decreases were observed. The most common trend magnitudes were 0.01 or 0.001 mg/L per year (increases and decreases, respectively). 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 NO3-N concentration was 1.5 mg/L, concentrations of up to three times the DWSNZ maximum acceptable values (MAVs) were encountered. Higher NO3-N concentrations affected the Canterbury and Southland regions. Elevated NO3-N concentrations were found mostly in samples from unconfined, shallow wells. Increases were more frequent than decreases, and upwards and downwards trends within the same region were not uncommon.

Nationally, DRP concentrations were generally low, although regional variations were observed. All regions 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 (3%). Trend magnitudes were of the order of 0.001 mg/L per year.

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Fe and Mn were mostly found in low concentrations for the 20052014 period. However, when detectable, concentrations for these ions could be quite high, indicating reducing conditions. The DWSNZ MAV was exceeded at 9% of the sites for Mn. Where trends were detected, their magnitudes were low.

There were large regional variations in conductivity; with some regions (Bay of Plenty, Canterbury, Marlborough, Southland, Waikato, West Coast and Wellington) characterised by dilute groundwater and other regions with higher conductivities (Gisborne, Northland, Auckland and Wanganui-Manawatu). Gisborne conductivities were significantly higher than anywhere else in New Zealand. Decreases in conductivity were more common than increases.

E.coli levels exceeded the DWSNZ in all but two regions. However, median E.coli levels were below detection at the majority of the sites (61%).

Pesticides were detected at 24% of the wells in the 2010 survey; most detections were herbicides. Typically, analyses included a large number (66) of pesticide species and detections were below the NZDWS. Wells where pesticide were detected showed statistically significantly higher NO3-N concentrations than wells without detection (t-test p-value=0.03).

The characterisation of New Zealand ground water quality state and trends could be improved by the collection of additional variables (e.g., age tracer, major elements). It is recommended to develop a national consensus on the species to be monitored for robust comparison of groundwater quality data between regions. This consensus should extend to sampling collection and data quality assurance procedures. The use of international data exchange format will also improve efficiency in reporting.

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1.0 INTRODUCTION

The Ministry for the Environment (MfE) has recently committed to issuing regular reporting and providing a fair representation of the state of New Zealands 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 and Domain reports, which will focus on the overall picture of the New Zealand environment, MfE commissioned GNS Science to report on New Zealand 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 (ESR).

Produce a brief technical report and summary statistics that can be used as the primary basis for national reporting.

This report is the second report produced by GNS Science that addresses these tasks, and focuses on the analysis of the amalgamated dataset from both the NGMP and the SOE networks for the 20052014 period. It also includes E.coli and pesticide monitoring, which were not covered in the first report. State and trends obtained from the NGMP data for the 20042013 period were summarised in the first report (Moreau and Daughney, 2015).

1.1 SCOPE OF WORK

The New Zealand 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, phosphorous species, E. coli, dissolved iron, dissolved manganese, salinity, 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 parameters, by region and nationally.


Deliverables:

1. Quality assured raw data used for trend analysis, accompanied with a quality assurance summary (Spreadsheet 1);

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 (Spreadsheet 2). 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 trends 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 include 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 amalgamated NGMP and SOE datasets 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. Spreadsheet 1 and 2 are freely available as electronic files from the MfE website.

1.2 DATA SOURCE

1.2.1 Inorganic chemistry and microbiology (NGMP and SOE)

The NGMP programme is a long-term monitoring programme operated by GNS Science in collaboration with fifteen regional authorities, and is funded by the Ministry for Business, Innovation and Employment. The NGMP aims 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). A more detailed description of the NGMP site selection, programme is given in the first report (Moreau and Daughney, 2015). Except for a few sites where purging is impractical, samples are collected according to standard New Zealand protocols (Daughney et al., 2006; Rosen et al., 1999). Exceptions to the sampling protocol are recorded.


The dataset consists of quarterly collected groundwater samples from about 106 sites nationwide. Each sample is analysed for the following parameters: calcium (Ca), magnesium (Mg), potassium (K), sodium (Na), bicarbonate (HCO3), carbonate (CO3), chloride (Cl), sulphate (SO4), fluoride (F), bromide (Br), ammonium-nitrogen (NH4-H), nitrate-nitrogen (NO3-N), iron (Fe), manganese (Mn) and silica (SiO2). For cost effectiveness, dissolved reactive phosphorous (DRP) and laboratory conductivity are only analysed in March. Quality assurance is performed through charge balance error (CBE) calculations and comparison of new analyses to historical records (Moreau-Fournier and Daughney, 2010).

The national SOE network consists of a subset of regional scale networks, operated by each regional authority. The number of sites sampled, sampling frequency (from monthly to annually), sampling methods, and groundwater quality parameters measured, vary between regions. Monitoring objectives are set individually. Regional authorities report regularly on the results of SOE monitoring within their own regions, with the exception of occasional national surveys of nitrate contamination (Daughney and Wall, 2007). Nation-wide, the total number of monitored SOE sites exceeds 1,000. Regional and unitary councils, in partnership with the electricity generation industry and the National Institute for Water and Atmospheric Research, are currently working on developing National Environmental Monitoring Standards. This initiative involves an external review and working group, which includes MfE and other Crown Research Institutes, and aims to promote a nationally consistent use of sampling protocols and quality coding for groundwater quality databases (Land Air Water Aotearoa, 2015). As a result, some data collected for this report were provided after some quality control procedure. In some regions, routine collection and analyses of duplicate samples is used as a measure of quality assurance.

With regards to the analytical parameter selection relevant to this report, the following conclusions were based on the data collated for the purpose of this study. Six nitrogen species are inconsistently monitored: total nitrogen, total oxidised nitrogen (TON), NO3- N, nitrite-nitrogen (NO2-N), NH4-N, total Kjeldhal nitrogen (Figure 1). Of these parameters, only NH4-N and NO3-N are monitored in all regions, which is likely due to the NGMP programme. Each nitrogen form may be measured in its total or dissolved form (in this report, dissolved refers to species found in groundwater after a 0.45m filtration). It is also noted that the SOE data may be recorded with various units, for instance the reduced form of nitrogen may be expressed as NH4-N, NH3-N or ammonia (NH3). Phosphorous is monitored in one, or a combination of the following forms: total; acid-hydrolysable and reactive; and, reactive phosphorus (Figure 2). Total and dissolved forms exist for each phosphorus species. DRP is the most frequent form monitored across all regions. In some regions, such as Canterbury, DRP is monitored alongside total phosphorus (TP). E.coli is monitored consistently across the country. Iron and manganese are monitored either in their total or dissolved forms (Figure 3). Total dissolved content is monitored either as total dissolved solids (TDS) (in four regions) or conductivity. Filtration may occur upon sampling collection or in the laboratory, as part of the analytical procedure. For the purpose of SOE monitoring, the NZ protocol for groundwater sampling recommends field-filtering (Daughney et al., 2006).

The aggregated NGMP and SOE dataset assembled for this study consist of 969 sites, of which 116 sites are monitored as part of both the NGMP and SOE programmes (Table 1, Figure 4). The number of sites varies by region in accordance with the different monitoring objectives and network designs devised by the individual regional authorities. There are between four and 15 NGMP sites per region, such that the proportion of sites shared by NGMP and the 15 different regional SOE programmes ranges from 2% (Canterbury) to 100% (West Coast). Of the 969 sites, six are springs and 280 do not hold depth information. For


the remaining sites, median well depth is 23 m below the ground level (BGL), and the minimum, lower quartile, upper quartile and maximum well depths were 1, 10, 55 and 500 m BGL, respectively.

Site-specific details pertaining to surrounding land use, aquifer confinement and aquifer lithology are listed in Spreadsheet 1. The current NGMP data is freely accessible from the Geothermal Groundwater (GGW) Database, which is operated and maintained by GNS Science (http://ggw.gns.cri.nz/ggwdata/).

Table 1: Number of sites monitored for inorganic chemistry, microbiology and pesticides, per region. Grey cells indicate regions where pesticides were detected.

Abbreviation Data Source Shared NGMP and SOE

SOE 2010 Pesticides Survey

AC Auckland Council 6 20 12

BOPRC Bay of Plenty Regional Council 4 23 6

ECAN Environment Canterbury 7 323 5

ES Environment Southland 7 30 11

GDC Gisborne District Council 7 49 6

GWRC Greater Wellington

Regional Council 15 56 10

HBRC Hawke's Bay Regional Council 8 35 11

HZ Horizons

Regional Council 4 33 35

MDC Marlborough District Council 8 18 17

NRC Northland Regional Council 9 33 12

ORC Otago Regional Council 7 40 8

TDC Tasman District Council 11 7 15

TRC Taranaki Regional Council 5 74 8

WCRC West Coast Regional Council 10 10 0

WRC Waikato Regional Council 9 111 6

1.2.2 Pesticides

National pesticides surveys have been undertaken and reported on by ESR at four-yearly intervals since 1990 (Close and Skinner, 2011). Some regions also undertake their own more intensive programme (Close and Skinner, 2011). The initial network comprised 82 wells (6 regions) and gained national coverage in 1998 (95 wells, Figure 5). At the time of writing of this report, results from the 2014 survey were still under review and are therefore not included in this report. During the 2010 survey, the network counted 162 wells spread across 14 out of the 15 regions (Table 1). Wells are selected considering regional aquifer use, application and storage of pesticides, and aquifer vulnerability to surface contamination

http://ggw.gns.cri.nz/ggwdata/


(Close and Skinner, 2011). Most of the selected wells were screened in unconfined aquifers. The minimum, lower quartile, median, upper quartile and maximum well depths in the 2010 surveys were 1.7, 8.6, 15.3, 28.2 and 200 m BGL, respectively. Twenty-six wells did not hold depth information.

The full list of tested pesticides includes 66 parameters: 26 pesticides (22 organochlorine and 4 organophosphorus); 40 herbicides (23 organonitrogen and 17 acid herbicides). Some herbicides were only detected in the 1998 surveys (2, 4-D, cyanazine, MCPA, MCPB, triclopyr, trifluralin). The detection limits from 1998 onwards were significantly lower than the 1990 and 1994 surveys (between 5 and 10 times lower), thus hindering direct comparison and qualitative assessment of trends for these early periods. Samples are collected after three purged volumes are extracted, where possible. Duplicate samples are taken at 5% of the wells for quality assurance (Close and Skinner, 2011).

The frequency of sampling and the step-change in detection limit prevent the use of quantitative trend analysis. Collated pesticides data for the 1998, 2002, 2006 and 2010 are presented in this report, and listed in Spreadsheet 1. These were provided by Close (2015). Conclusions of the 2010 survey report are summarised in Section 1.3.2. No additional data manipulation was performed on the dataset as part of this study.

1.3 PREVIOUS INVESTIGATIONS

1.3.1 Inorganic chemistry and microbiology

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 New Zealand based on data collected from 973 monitoring sites over the period 1995 to 2008. 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 NO3-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 NH4-H, Fe and Mn concentrations were found in many regions, especially in Manawatu-Wanganui, Hawkes 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;

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 and including age tracers, linked land use impact to groundwater quality through a reconstruction of the two-stage land use intensification (Morgenstern and Daughney, 2012).

1.3.2 Pesticides

The main conclusions for the 2010 national pesticide survey were (Close and Skinner, 2011):

Pesticides were detected at 24% of the monitored wells. There were a total of 68 individual pesticide detections, with a maximum of five detected pesticides per well (15 wells, less than a half, exhibited more than one pesticide). Detection affected nine out of the 14 regions that were tested (Table 1).

Herbicides were the most detected type of pesticides (91%), followed by insecticides and fungicides. This is consistent with the fact that herbicides account for the majority of pesticides annual sales in New Zealand. Only three wells (


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 2 L 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 eight key indicators of groundwater quality:

Nitrogen-species: nitrogen is present in the form of NO3-N in oxygen-rich groundwaters, whereas in oxygen-poor groundwaters nitrogen exists as NH4-N. The conversion from one form to another occurs under natural processes. NO3-N is monitored for health and environmental reasons. High NO3-N concentrations in drinking-water are associated with blood disease (blue baby syndrome), particularly in infants (DWSNZ MAV of 11.3 mg/L). High NO3-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


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 New Zealand groundwaters. The threshold of 2.5 mg/L NO3-N was proposed for indication of land use intensity by Morgenstern and Daughney (2012). NH4-N 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 drinking-water MAV is 1.2 mg/L).

Phosphorous species: phosphorous is essential for the development of life forms. It can be present in groundwater 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 is detected in drinking-water (MAV corresponds to 1 colony forming unit (cfu) per 100 mL of water). The ANZECC guidelines have a TV of 100 cfu per 100 mL of water for livestock consumption.

Fe: Fe is only soluble in oxygen-poor groundwater. It is, therefore, often used in conjunction with NH4-H to investigate low NO3-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 NH4-H to investigate low NO3-N concentrations. High manganese concentrations in water results in the 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.

Conductivity: conductivity is a measure of TDS content. It is used in this report in conjunction with salinity. The measured ratio between salinity and 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.

2.2 REPORTED STATISTICS

The following statistics are reported for the 20052014 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)

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Percentiles (5th, 25th, 50th, 75th, 95th): these also inform the data spread around the median. The median is the 50th percentile (Helsel and Hirsch, 2002).

Trend magnitudes: the rate of change in each parameter. In this report, the trend magnitudes are based on Sens 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 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 0.05 for all tests as this value is standardly used in statistical reporting of environmental data (Helsel and Hirsch, 2002). 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 ANALYSIS SETTINGS

Trend analysis was performed using the non-parametric Mann-Kendall over a ten-year period. The Kruskal-Wallis test was used to investigate seasonality. This is consistent with the first report (Moreau and Daughney, 2015) that analysed state and trends at NGMP wells (discussions on the selection of the trend tests and time period are included in the report).

Trend analysis was obtained using the NGMP Calculator (Daughney, 2007; 2010). The trend analysis was performed for the period starting on 1/01/2005 and ending on 31/12/2014, 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.

2.4 MINIMUM DATA REQUIREMENTS

Published values for the minimum data point requirements for robust trend detection range between eight and 10 (US Environment Protection Agency, 2006; Daughney, 2007; State of Idaho Department of Environmental Quality, 2014). In the first report, it was possible to ensure even temporal data coverage by splitting the entire time period into 5-year windows and setting a minimum data point threshold for each time window, per parameter (Moreau and Daughney, 2015). Setting data point thresholds per parameter and time window resulted in the exclusion of sites (about 30% of the NGMP sites). The minimum data were: sixteen data points for NH4-H, NO3-N, Fe, Mn, aggregated TDS, and; three data points for DRP and laboratory measured conductivity (Moreau and Daughney, 2015).

Although this option was investigated, it was found that applying this criterion to the cleaned, amalgamated NGMP and SOE dataset would result in the exclusion of 50% to 84% of the sites, depending on the parameter. It was, therefore, decided to use a minimum requirement of 10 data points for the 10-year period, for all parameters.


2.5 DATA PROCESSING

SOE data were collected for the period 20092014 from individual regions. NGMP data and pre-2009 SOE data were collected from the GGW database (GNS Science, 2015). This was done because data collected from the previous state and trend reports (Daughney and Randall, 2009) were subsequently stored in the GGW database in a uniform format. In one region, data was provided for the 19992014 period, following internal quality assurance procedure (Gordon, 2015). The corresponding records in the GGW database were therefore updated. Although reference tables between individual council and the GGW databases were reported previously (Moreau-Fournier et al., 2010), it was found that the new data had to mostly be remapped due to the provision of either additional information, additional wells, or provision of a new format differing from that provided during the last update (118 analytical parameters were created to enable upload to the database).

A common difficulty was to separate parameters into dissolved or total forms. The New Zealand protocol for SOE monitoring recommends the monitoring of dissolved species, preferably field-filtered (Daughney et al., 2006). Sampling protocol or information was provided for six regions. This ranged from reported references to notes included in the data files (Hanson, 2012; Horizons Regional Council, 2012; Tidswell, 2015; Gordon, 2015; Hadfield, 2015; Hapu, 2015; Kalbus, 2015; Rissmann, 2015). There were instances where newly collected data included clear parameter descriptions with regard to its dissolved or total forms. However, the dissolved form might refer to either field or laboratory filtration. Unless either the analytical method was provided alongside the data or the sampling protocol was clearly specified, parameters were defaulted to the total form. Analytical results obtained by calculation were not captured as part of this study.

In addition to the selected species, the original data request included 15 additional parameters to enable the calculation of either total dissolved content or CBE, following the procedure described in the NGMP report (Moreau and Daughney, 2015). However, once amalgamated, it was not possible to conduct these checks because some parameters were missing for more than four regions. The data presented in this report is, therefore, mostly used as it was received. Exceptions were:

Readings of zero concentration of Fe, Mn, DRP, TP, NH4-N were removed.

zero E.coli were replaced by the usual notation which is


reported units (as NO3 and N). The lowest detection limit was 0.001 mg/L and the highest 0.01 mg/L (for Fe, Mn and DRP).

NH4-N: aggregation of dissolved and total forms, and in some cases conversions were performed between the reported units (as NH3 and NH3-N). The lowest detection limit was 0.001 mg/L and the highest 0.01 mg/L.

Conductivity is a combination of field and laboratory measurements. Where possible, the field measurement was selected first.

Fe, Mn, DRP, E.coli: no aggregation, the values presented in this report correspond to the dissolved form. The lowest detection limit was 0.0005 mg/L (Mn) and the highest 0.01 mg/L.

Pesticide data are presented as provided.

The final dataset consists of 19,995 unique inorganic chemistry and microbiology analyses for 969 wells (individual results). The full pesticides dataset comprises 553 analyses, for 258 wells (all surveys included). Cleaned, raw data have been made freely available as electronic files from the MfE website in Spreadsheet 1, which includes SOE parameter conversion tables for each region.

2.6 LIMITATIONS

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.

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 for all of 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).

It is unclear whether the monitored sites (NGMP, SOE, pesticides) are representative of New Zealand 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.


3.0 RESULTS

3.1 SITE-SPECIFIC ASSESSMENT OF STATE AND TRENDS

Site-specific statistics for the 20052015 period and national summary tables have been made freely available as electronic files from the MfE website (Spreadsheet 2). Note that the following paragraphs do not include pesticides, as the minimum data requirements were not met. Wells included in the amalgamated dataset at which pesticides were detected are highlighted in Spreadsheet 2. Trend analysis was performed on E. coli data, although it is likely that assumption of monotony is violated, due to the nature of this parameter.

3.2 NATIONAL OVERVIEW

National level statistics are compiled in Spreadsheet 2 and summarised in Tables 2 to 5 (analogous to Tables 3, 4, 5, and 6 from Daughney and Randall, 2009). The national level statistics show:

National medians for all indicators were similar to previously reported values. This differs slightly from the conclusion of the NGMP report, where NO3-N and Mn medians were found to differ from previously reported value (the NGMP report NO3-N median was 0.55 mg/L compared to 1.5 mg/L in this report). The difference may be due to the sample size and the site selection criteria difference between the programmes. The difference in Mn medians may also be explained by the occurrence of multiple detection limits in the dataset. Some of the detection limits were higher than that of the NGMP analytical suites, which correspond to the median (


Table 2: Calculated national percentiles and maximum values for groundwater quality indicators, based on site-specific median values for the period 20052014. Global average concentration from river water and groundwater are given for comparison. All values are in mg/L except conductivity, which is expressed in S/cm.

Parameter NO3-N NH4-N DRP Fe Mn Conductivity E.coli

Units mg/L mg/L mg/L mg/L mg/L S/cm cfu per 100 mL

New Zealand Groundwater (this report)

n 911 850 825 843 837 955 717

Perc

entil

es

5th 0.002


Table 4: Number of monitoring sites (n) across New Zealand at which trend tests could be performed for the period 20052014. 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 S/cm. ND means non-determined.

Parameter n %INCR %DECR %N %ND

NO3-N 969 13.2 6.6 64.7 15.5

NH4-N 969 2.2 2.7 48.7 46.4

DRP 969 1.4 1.2 38.1 59.2

Fe 969 2.1 4.0 38.4 55.5

Mn 969 3.0 4.4 50.9 41.7

Conductivity 969 16.0 6.5 68.7 8.8

E.coli 969 0.0 0.1 10.6 89.3

Table 5: 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 2.

Parameter n Min. Median Max. Relative Median

(% per year)

NO3-N 192 -1.10 0.07 1.39 4.9%

NH4-N 47 -0.14 -0.001 0.04 -11.9%

DRP 26 -0.05 0.001 0.06 9.3%

Fe 59 -1.16 -0.005 0.11 -25.5%

Mn 72 -0.08 -0.0003 0.04 -6.3%

Conductivity 218 -45.4 2.1 63.3 1.0%

E.coli 1 - - - -

3.3 KEY INDICATORS

National and regional percentiles, exceedances, trends and significant trend statistics for the seven selected groundwater quality indicators for the 20052014 period are presented in Figures 6 to 8, and Spreadsheet 2.

3.3.1 NO3-N

The national median NO3-N concentration was 1.5 mg/L for the 20052015 period (n=912). This concentration is consistent with previously reported medians (Table 2). NO3-N concentrations below the detection level occurred at 9% of the sites and in all regions but Hawkes Bay and Otago. Low NO3-N concentrations were most commonly found in Canterbury (23 wells) and Waikato (22 wells). The lowest regional median was Auckland


(0.003 mg/L), and the highest was Southland (4.9 mg/L). Four regional medians were above the national median (Canterbury, Southland, Taranaki and Waikato; Figure 6).

The DWSNZ MAV was exceeded at 4% of the sites, across nine regions (up to 36.7 mg/L, which is three times the MAV). Most sites (72%) exceeded the ANZECC guidelines value for ecosystem health, whereas 15% exceeded the toxicity value (Table 3).

The majority (64.7%) of sites did not show statistically significant trends for NO3-N (Table 4). Where trends were detected, statistically significant decreases of down to -1.1 mg/L per year (Feature 3144, Canterbury) and increases up to 1.39 mg/L per year (Feature 348, Waikato) were observed. The national median trend was +0.07 mg/L per year. Increases were more frequent than decreases (13.2% and 6.6%, respectively; Table 5); Concurrent trends were observed in all regions, at different sites (Figure 6). There were 142 sites at which it was not possible to conduct trend analysis due to insufficient data.

3.3.2 NH4-N

The national median NH4-N concentration was 0.01 mg/L for the 20052015 period (n=850). Censoring affected about 30% of the sites (most common limit of 0.01 mg/L). This observation is consistent with previous reporting and the global average reported for river water (Table 2). The ANZECC TV for ecosystem health was exceeded at 36% of the sites, and the DWSNZ MAV was exceeded at 5% of the sites Table 3).

The NH4-N medians exhibited variability at both the national and the regional level (Figure 7). NH4-N concentrations below the national medians were observed in 10 regions. High NH4-N concentrations (above 0.03 mg/L, 75th percentiles) occurred in all but the Southland region. The highest median was found in Gisborne (0.79 mg/L), followed by Wanganui-Manawatu (0.10 mg/L) (Figure 7). Some of the high Gisborne medians were associated with detected iron concentrations (up to 17.5 mg/L), suggesting reducing conditions in the aquifer. However there were no concurrent measurements for iron or manganese for the majority of NH4-N measurements (lowest median for the region was 0.01 mg/L (n=55).

Due to high censoring, trend analysis could not be undertaken at almost half of the sites (46%, Table 4). No statistically significant trends were observed at 49% of sites. For the remaining sites (5%, spread across ten regions), an almost equal share between increases and decreases, with occurrences of gain (up to 0.04 mg/L per year) and loss (-0.14 mg/L per year). The national trend magnitude was a loss of 0.001 mg/L per year (Table 5; Figure 7).

3.3.3 DRP

The national median DRP concentration was 0.02 mg/L for the 20052014 period (n=825). This observation is consistent with previous reporting and the global average reported for river water (Table 2). Only a limited number of sites (3%) exhibited median DRP concentration below the detection limit. Medians ranged from 0.001 to 5.0 mg/L (Table 2), with 9 sites above 0.1 mg/L. Most sites (58.5%) exhibited DRP concentrations above the ANZECC TV for ecosystem health, nationwide (Table 3).

The DRP medians exhibited variability at both the national and the regional level (Figure 8). Highest concentrations of DRP (>0.7 mg/L) were found in Hawkes Bay, Manawatu-Wanganui and Wellington (Figure 8). The highest DRP concentrations were found where nitrogen was mostly present in the NH4-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 and Johnson, 2011). The elevated iron concentrations suggest that iron oxides may not be stable, and therefore, may release phosphorous (Domagalski and Johnson, 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. This observation is consistent with the NGMP report (Moreau and Daughney, 2015).

Only 2.6% of the sites exhibited statistically significant trends (Table 4), with decreases observed in Gisborne, Wellington, Hawkes Bay, Wanganui-Manawatu and Northland (as low as -0.05 mg/L per year, Figure 8; Table 5). Increases were observed in Canterbury, Gisborne, Hawkes Bay and Southland (up to 0.06 mg/L per year). The isolated high DRP increase shown on Figure 8 was based on a single site and was not found statistically significant.

3.3.4 Fe and Mn

The national medians for Fe and Mn were 0.02 and 0.01 mg/L, respectively, for the 20052014 period (n=843 for Fe and n=837 for Mn). These values are consistent with previously reported medians (Table 2). Censoring affected a third of the sites (30% for both parameters). The range of medians however was wide, with maximums up to 25.2 mg/L Fe (Feature 2596, Otago) and 16.4 mg/L Mn (Feature 2485, Wanganui-Manawatu). Elevated concentrations were consistent in magnitudes and locations with previously reported state values (Daughney and Randall, 2009). Most sites (84% and 78%, respectively for Fe and Mn) did not exceed the lowest DWSNZ guidelines value (aesthetic criteria, Table 3). Mn exceeded the ANZECC TV toxicity threshold at 1% of the sites (11 regions). The DWSNZ MAV was exceeded at 95 of the sites in all but Bay of Plenty, Northland, Southland and the West Coast (Table 3).

Although there were overlaps, regional distributions of Fe and Mn concentrations showed differences. Fe concentrations were significantly higher in Gisborne and Wanganui-Manawatu, whereas for these regions, Mn concentrations were similar to those observed elsewhere. It is noted that despite having the larger sample size (n=326), the distribution of Fe medians in Canterbury was the narrowest (between 0.02 and 0.03 mg/L; Figure 10). Manganese concentrations were highest in the Bay of Plenty and Wanganui-Manawatu regions (Figure 11).

Where trend analysis was possible (45% to 59% of the sites), for both Fe and Mn, the absence of a statistically significant trend was frequent (38% and 51%, respectively, Table 4). Waikato was the only region where only an increase in Fe was detected. No Fe trend was found in Taranaki. A limited number of sites with solely increasing Mn were detected in Tasman, Taranaki and the West Coast. National median trends were decreases of -0.005 and -0.0003 mg/L per year for Fe and Mn, respectively (Table 5). These values are consistent with previous reporting.

3.3.5 Conductivity

There were large regional variations in conductivities (Figure 12) with regional medians ranging from 105 S/cm (West Coast) to 968 S/cm (Gisborne). Bay of Plenty, Canterbury, Marlborough, Southland, Waikato, West Coast and Wellington sites exhibited conductivities below 215 S/cm (national median). Aside from Gisborne, the highest conductivities were


found in Northland, Auckland and Wanganui-Manawatu (307 to 455 S/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 conductivity, however, high TDS content is often linked with high individual ion concentrations, which in turn may have specific guidelines.

The majority of sites (69%) did not exhibit any statistically significant trend (Table 5). Where detected, increases were more common (16%) than decreases (6.5%) and were encountered nationwide, save for the Wanganui-Manawatu region. The West Coast was the only region where only increases were observed. The fastest increases occurred at a rate of 63.3 S/cm at Feature 2590 (Otago) and the fastest loss occurred at Feature 10207 (Hawkes Bay) at a rate of -45.4 S/cm.

3.3.6 E.coli

The large majority (61% of the sites) of E.coli measurements were below detection (1 cfu per 100 mL, n=685). E. coli was detected in all but two regions: Hawkes Bay and Tasman. The maximum count of E.coli was 460 (Figure 13). Only a limited number of sites contained sufficient information to undertake trend analysis, and, in all but one case, censoring prevented trend detection. The DWSNZ MAV, which corresponds to the detection limit, was exceeded at 9.6% of the sites (Table 3).

3.4 FACTORS CONTROLLING GROUNDWATER QUALITY

3.4.1 Well depth and aquifer confinement

Well depth and aquifer confinement should be considered jointly because they are correlated (Daughney and Randall, 2009). NGMP and SOE sites presented in this report consist mostly of shallow wells (262 sites of less than 10 m; 455 sites with depths ranging from 10 to 50 m out of a total of 916 wells of known depth). Unconfined, semi-confined and confined status are encountered respectively at 221, 80 and 133 sites. Note that there are 482 sites at which confinement status is unknown.

Relationships with depth were investigated through depth scatterplots (Figure 14). No statistical relationships were found for any of the selected parameters. However, the following patterns were observed: NO3-N concentrations were higher in shallow wells than in deep and confined wells (Figure 14). This is consistent with previous reporting and independent studies (Daughney and Randall, 2009; Morgenstern and Daughney, 2012).

3.4.2 Aquifer lithology

Most sites did not hold lithological information. Of the sites that did, most were screened in sand (120) and gravels (262), the other lithological categories do not hold sample sizes greater than 50 (Table 6). Two lithological categories included a single site (rhyolite and breccia) and, therefore, will not be discussed further. High NO3-N medians are encountered in volcanics, basalt, gravel, pumice, sand, and sand and gravel aquifers. High Fe, Mn, NH4-N and EC medians are encountered in greywacke. Sand, sandstone and ignimbrite aquifers


exhibited higher DRP medians. Trends were not included in the table below since most sites did not exhibit trends (Table 6).

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).

Table 6: National medians for median concentrations values per aquifer lithology.

Lithology n NO3-N NH4-N DRP Fe Mn Conductivity E.coli

Basalt 35 2.27 0.010 0.012 0.020 0.003 225


4.0 CONCLUSION

Groundwater state and trends for the 20052015 period are in general agreement with state and trends found for the 19952008 period (Daughney and Randall, 2009).

Although the national median NO3-N concentration was 1.5 mg/L, concentrations of up to 36.7 mg/L (which is about three times the New Zealand MAV for DWSNZ) were found at some sites. The Higher NO3-N concentrations affected the Southland and Canterbury regions. Elevated NO3-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 NO3-N.

The national median DRP concentration was 0.01 mg/L for the 20052015 period (n=825), although there were regional variations. All regions 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 (3%). Trend magnitudes were of the order of 0.001 mg/L per year.

Iron and Mn were mostly found in low concentrations for the 20052014 period. However, concentrations of these parameters could be quite high (up to 25 mg/L), which indicates reducing conditions. The DWSNZ MAV for Mn was exceeded at 9% of the sites. 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 (Bay of Plenty, Canterbury, Marlborough, Southland, Waikato, West Coast and Wellington) 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).

E.coli levels exceeded the DWSNZ in all but two regions. However, median E.coli levels were below detection at the majority of the sites (61%).

Pesticides were detected at 24% of the wells in the 2010 survey; most detections were herbicides. Typically, analyses included a large number (66) of pesticide species and detections were below the DWSNZ. Single pesticide species detections were common. However, there were wells in which up to five species were detected. Results for the 2014 pesticides survey are currently being processed.

Wells where pesticide were detected showed statistically significantly higher NO3-N concentrations than wells without detection (t-test p-value=0.03).


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 that state of the environment monitoring is continued at the national scale, and at regular intervals. In addition, the following should be considered:

Develop a national consensus on the species of nitrogen and phosphorus that should be monitored for robust comparison of groundwater quality between regions. Currently, twelve nitrogen species and eight phosphorus species are recorded in the NGMP and SOE dataset. Future monitoring could aim to analyse less species and this would be best addressed with a national consensus.

Documentation of data quality assurance procedure for each region. The NGMP monitoring suite could be extended to the SOE network, to enable routine checks such as CBE calculations. Sample collection procedure, particularly regarding well purge and filtering, should also be recorded.

Alignment of reporting units between regional databases and national-level reporting (e.g., reporting nitrate as nitrogen). In this report, and the previous ones, nitrogen was reported as NH4-N and NO3-N. However, New Zealand guidelines values for nitrogen species are expressed as NO3 and NH3, respectively.

Use of a template, or international data exchange format, to improve the efficiency of reporting for future updates.

Bi-or tri-ennial surveys should be undertaken to assess the occurrence of emerging contaminants, such as pharmaceuticals, cadmium, etc. (Daughney and Randall, 2009).

Residence time information should be included in future analysis and reporting, as it has been shown to effectively link land use with impacts on groundwater quality (Morgenstern and Daughney, 2012).

Monitoring network reviews 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. With the recent release of the National Policy Statement on Freshwater Management (Ministry for the Environment, 2014), regional SOE monitoring network may be reviewed based on values defined by communities. However, a concern with this approach is that subsequent modification to the current networks or analytical suites may disconnect the regional monitoring programmes from the national one.

6.0 ACKNOWLEDGEMENTS

The regional and district councils are thanked for sharing their data. Zara Rawlinson and Conny Tschritter (GNS Science) are thanked for providing a review of a draft version of this report.


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Moreau-Fournier, M.; Reeves, R.R.; Reshitnyk, L.; Daughney, C.J. 2010. Incorporation of New Zealand regional authority state of the environment groundwater quality data into the GNS Science Geothermal-Groundwater Database. GNS Science Report 2010/44. 113p.

Morgenstern, U.; Daughney, C.J. 2012. 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: 79-93.

Parliament of New Zealand. 2014. Environment Reporting Bill (explanatory note). 16p. Rissmann, C. 2015. Personal communication. Science Manager/Principal Scientist,

Environment Southland. Rosen, M.R. 2001. Hydrochemistry of New Zealands aquifers. In: Rosen, M.R.; White, P.A.

(eds.) Groundwaters of New Zealand, New Zealand Hydrological Society, Wellington, New Zealand: 77-110.

Rosen, M.R.; Cameron, S.G.; Taylor, C.B.; Reeves, R.R. 1999. 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. 2014. Statistical guidance for determining background groundwater quality and degradation. 103p.

Tidswell, S. 2015. Personal communication. Environmental Scientist, Greater Wellington Regional Council.

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http://www.lawa.org.nz/http://www.health.govt.nz/publication/annual-report-drinking-water-quality-2013-14.%20Accessed%20April%202015http://www.health.govt.nz/publication/annual-report-drinking-water-quality-2013-14.%20Accessed%20April%202015


FIGURES


Figure 1: Monitoring of nitrogen species throughout the SOE network, collected for this study. Note that the

split between total or dissolved species is described in Section 2.5. The numbers in brackets indicate the number of wells for which there was chemistry information over the 2005 to 2014 period.

Figure 2: Monitoring of phosphorus species throughout the SOE network, collected for this study. Note that

the split between total or dissolved species is described in Section 2.5. The numbers in brackets indicate the number of wells for which there was chemistry information over the 2005 to 2014 period.

0%10%20%30%40%50%60%70%80%90%

100%N

umbe

r of s

ites

Region

Kjeldahl nitrogen

Ammonium-nitrogen (dissolved)

Ammonium-nitrogen

Nitrite-nitrogen (dissolved)

Nitrite-nitrogen

Nitrate-nitrogen (dissolved)

Nitrate-nitrogen

Total oxidised nitrogen (dissolved)

Total oxidised nitrogen

Total nitrogen (dissolved)

Total nitrogen

0%10%20%30%40%50%60%70%80%90%

100%

Num

ber o

f site

s

Region

Total acid-hydrolysablephosphorusTotal phosphorus

Total phosphorus (dissolved)

Dissolved reactive phosphorus

Dissolved reactive phosphorus(dissolved)Dissolved acid-hydrolysablereactive phosphorusDissolved acid-hydrolysable,reactive phosphorus (dissolved)


Figure 3: Monitoring of iron and manganese species throughout the SOE network, collected for this study.

Note that the split between total or dissolved species is described in Section 2.5. The numbers in brackets indicate the number of wells for which there was chemistry information over the 2005 to 2014 period.

0%10%20%30%40%50%60%70%80%90%

100%

Num

ber o

f site

s

Region

Manganese

Manganese (dissolved)

Iron

Iron (dissolved)


Figure 4: Location of SOE and NGMP sites and main aquifers in New Zealand. Aquifer shapefiles were

sourced from Moreau and Bekele (2015).


Figure 5: Location of sites included in the 4-yearly pesticides surveys from 1998 to 2010 and main aquifers in

New Zealand. Aquifer shapefiles were sourced from Moreau and Bekele (2015).


Figure 6: National and regional summary statistics for state and trends in NO3-N indicators of groundwater quality, based on all data collected from 2005 to 2014. 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 75th and 25th percentiles, respectively. The vertical lines extend from the 95th to the 5th percentiles.


Figure 7: National and regional summary statistics for state and trends in NH4-N concentrations based on all data collected from 2005 to 2014. 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 75th and 25th percentiles, respectively. The vertical lines extend from the 95th to the 5th percentiles.


Figure 8: National and regional summary statistics for state and trends in dissolved phosphorous concentrations based on all data collected from 2005 to 2014. 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 75th and 25th percentiles, respectively. The vertical lines extend from the 95th to the 5th percentiles.


Figure 9: Scatterplot comparing median concentrations of DRP with nitrogen species (left), and with Fe and Mn concentrations (right) at NGMP and SOE sites for the

20052014 period.

0.0001

0.001

0.01

0.1

1

10

0.001 0.01 0.1 1 10Initr

ogen

spe

cies

med

ian

conc

entra

tion

(mg/

L)

DRP median concentration (mg/L)

NH4-N

NO3-N

0.0001

0.001

0.01

0.1

1

10

0.001 0.01 0.1 1 10

Iron

and

man

gane

se m

edia

n co

ncen

tratio

n (m

g/L)

DRP median concentration (mg/L)

Fe

Mn


Figure 10: National and regional summary statistics for state and trends in Fe based on all data collected from 2005 to 2014. 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 75th and 25th percentiles, respectively. The vertical lines extend from the 95th to the 5th percentiles.


Figure 11: National and regional summary statistics for state and trends in Mn based on all data collected from 2005 to 2014. 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 75th and 25th percentiles, respectively. The vertical lines extend from the 95th to the 5th percentiles.


Figure 12: National and regional summary statistics for state and trends of conductivity based on all data collected from 2005 to 2014. 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 75th and 25th percentiles, respectively. The vertical lines extend from the 95th to the 5th percentiles.


Figure 13: National and regional summary statistics for state of E. coli based on all data collected from 2005 to

2014. Numbers above X axes show the number of sites at which state 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 75th and 25th percentiles, respectively. The vertical lines extend from the 95th to the 5th percentiles.


Figure 14: Scatterplot of NO3-N median concentrations versus depth. The colour-code reflects the aquifer

confinement status.

0

5

10

15

20

25

30

35

40

0 50 100 150 200 250 300 350

Nitr

ate-

nitro

gen

med

ian

conc

entra

tion

(mg/

L)

Depth (m)

Confined

Unconfined

Semi-confined

Unknown

Aquifer confinement

1 Fairway Drive

Avalon

PO Box 30368

Lower Hutt

New Zealand

T +64-4-570 1444

F +64-4-570 4600

Dunedin Research Centre

764 Cumberland Street

Private Bag 1930

Dunedin

New Zealand

T +64-3-477 4050

F +64-3-477 5232

Wairakei Research Centre

114 Karetoto Road

Wairakei

Private Bag 2000, Taupo

New Zealand

T +64-7-374 8211

F +64-7-374 8199

National Isotope Centre

30 Gracefield Road

PO Box 31312

Lower Hutt

New Zealand

T +64-4-570 1444

F +64-4-570 4657

Principal Location

www.gns.cri.nz

Other Locations

EXECUTIVE SUMMARY1.0 INTRODUCTION 1.1 Scope of work1.2 Data source1.2.1 Inorganic chemistry and microbiology (NGMP and SOE) 1.2.2 Pesticides

1.3 Previous investigations1.3.1 Inorganic chemistry and microbiology1.3.2 Pesticides

2.0 METHODS2.1 Key indicators of groundwater quality and guidelines used2.2 Reported statistics2.3 Trend analysis settings2.4 Minimum data requirements2.5 Data processing2.6 Limitations

3.0 RESULTS3.1 Site-specific assessment of state and trends 3.2 National overview3.3 Key indicators3.3.1 NO3-N3.3.2 NH4-N3.3.3 DRP3.3.4 Fe and Mn3.3.5 Conductivity3.3.6 E.coli

3.4 Factors controlling groundwater quality3.4.1 Well depth and aquifer confinement3.4.2 Aquifer lithology

4.0 CONCLUSION5.0 RECOMMENDATIONS6.0 ACKNOWLEDGEMENTS7.0 REFERENCESFIGURES

Report Type: GNS Science Consultancy Report 2015/107Month Year: August 2016 Revised Report Title: Update of National Groundwater QualityIndicators: State and Trends 20052014Author Names: M. Moreau K. AurischAuthor-box 2: M.A. Riedi

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