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Part One: Introduction

Purpose of the Protocol

This document describes a standardised protocol for the collection of groundwater samples in New Zealand for the purpose of State of the Environment (SOE) monitoring. SOE monitoring aims to:

  • characterise the ambient groundwater quality on a regional scale
  • identify significant groundwater quality issues, such as spatial or temporal trends in quality, which may result from pressure on the resource such as land use, point source discharges and non-point source discharges
  • assess compliance with groundwater quality management objectives
  • provide data to assess the effectiveness of groundwater management policies.

It is well established that analytical results can be heavily influenced by the way a groundwater sample is collected, preserved and transported prior to analysis. While there are numerous existing guidelines to assist samplers, they typically present a number of options for sampling without providing a recognised best-practice procedure that is appropriate for New Zealand conditions. As a result, several different methods for SOE groundwater sampling are currently in use in New Zealand. Thus SOE monitoring data may not be readily comparable between different regions, and even within a single region, older groundwater quality data may not be directly comparable to newer data.

The aim of this sampling protocol is to facilitate robust assessments of groundwater quality, particularly at an inter-regional and national scale. Use of this protocol will:

  • ensure groundwater samples are representative of groundwater in the aquifer
  • ensure results from samples which are taken in different regions, at different times, and/or by different samplers can be compared with more confidence.

It is important to note that this protocol is not a mandatory requirement or official national standard. Any sampler may choose to collect a non-compliant sample at any time based on professional judgement. It is acknowledged that there may be practical constraints to following this protocol in certain cases. However, it is hoped that, as a minimum, labelling and recording samples as 'compliant' or 'non-compliant' with the protocol will become a standard practice for all SOE groundwater samples. This will lead to improved awareness of the status of results from around the country.

Development of the protocol

The need for a standardised groundwater sampling protocol was identified as a priority by the Regional Groundwater Forum (RGF) in 2004. The RGF comprises groundwater scientists from all regional and unitary councils in New Zealand. The protocol has been developed by a working group of groundwater scientists from GNS Science, Greater Wellington Regional Council, Environment Canterbury and Marlborough District Council, under contract to the Ministry for the Environment.

A draft version of the sampling protocol was produced in August 2005 (see Daughney et al 2006). It was developed by collating and condensing existing guidelines into a single best-practice procedure. The draft protocol described step-by-step instructions for well purging, sample collection and treatment, and other critical steps in groundwater sampling. Justification for each step in the protocol was provided through reference to existing national and international groundwater sampling guidelines.

In September 2005, the draft protocol was reviewed by members of the RGF and by representatives from United States Geological Survey, the British Geological Survey, and the Australian CSIRO. The reviewers made several recommendations for modification to the sampling procedures specified in the draft protocol. Many of the recommended changes seemed to be based on adherence to common industry practice without reference to published scientific literature. A search of the scientific literature did not shed light on the magnitude of the possible biases that might be caused by particular sampling methods, or indeed whether or not these potential biases would be significant for typical SOE groundwater sampling conditions in New Zealand.

In March and April 2006, a field trial was undertaken to assess the possible effects of different sampling procedures on the chemistry of groundwater samples collected from typical SOE monitoring sites in New Zealand. The field trial involved 49 SOE monitoring sites in the Wellington (including Wairarapa), Marlborough and Canterbury regions, and set out to address specific questions raised by the reviewers. The results of the field trial justified several modifications to the procedures specified in the draft groundwater sampling protocol (Daughney et al 2006).

This current version of the protocol (October 2006) is updated in accordance with the recommendations of the national and international reviewers and the results of the field trial. This version of the protocol may be updated in the future, following its release for general use in New Zealand in late 2006.

What the protocol covers

The protocol is a prescriptive field procedure for the collection, preservation and transport of groundwater samples. This protocol includes detailed instructions for:

  • off-site preparation for sampling
  • on-site preparation for sampling
  • purging of standing water from the well and field measurement of pH, conductivity and temperature
  • collection and preservation of samples
  • site clean up
  • sample storage, transport and delivery to the laboratory.

In accordance with standard analyses conducted for the purpose of SOE monitoring in New Zealand, this protocol includes instructions for collection of:

  • unfiltered, unpreserved samples collected in isolation from the atmosphere, which are suitable for the analysis of chlorofluorocarbons (CFCs), sulphur hexafluoride (SF6) and some other dissolved gases
  • filtered, acid-preserved samples, which are suitable for analysis of major cations and some metals
  • filtered, unpreserved samples, which are suitable for analysis of major anions and nutrients
  • unfiltered, unpreserved (raw) samples, which are suitable for analysis of pH, conductivity, alkalinity and isotopes of oxygen and hydrogen (including tritium)
  • sterile unfiltered, unpreserved samples, which are suitable for analysis of microbiological indicators.

This protocol does not apply to collection of groundwater samples for the analysis of parameters which are not usually monitored for SOE purposes in New Zealand. Many "non-SOE" parameters have unique sampling requirements and therefore have been excluded from the protocol. However, aspects of this protocol may still be applicable to sampling for these parameters, for example the purging criteria. Sampling for these parameters should be discussed with the laboratory that will ultimately perform the analysis. Otherwise, assume that this protocol is not suitable for:

  • organic carbon compounds, including volatiles and non-aqueous phase liquids (see Rosen et al 1999)
  • pesticides
  • metals at concentrations less than 0.01 g m-3 (see Rosen et al 1999)
  • geothermal samples (gassy or hot) (see Rosen et al 1999; Stansfield et al 2001)
  • sulphide (a specific preservative is required; see Rosen et al 1999)
  • cyanide (a specific preservative is required; see Rosen et al 1999)
  • isotopes of nitrogen, sulphur or carbon (large sample volumes or special reagents may be required; see Rosen et al 1999).

This protocol does not include instructions for monitoring network design or site selection. The protocol is strictly a field procedure, and it is therefore assumed that the wells being sampled form part of a well-designed groundwater monitoring network. In accordance with most SOE monitoring sites in New Zealand, this protocol is intended for sampling of bores and wells. The suitability of any site for SOE monitoring is addressed only to the extent of confirming the ability of the site to be purged and sampled in compliance with the protocol. Hughes (2000) provides advice on selection of wells for SOE monitoring. Rosen et al (1999) and Hughes (2000) provide recommendations on the timing and frequency of sampling suitable for New Zealand. See Sinton (1986) and Hughes (2000) for information on sampling springs and seeps.

This protocol does not provide guidance on quality assurance (QA) or quality control (QC) of data. Although QA/QC measures are an essential component of a monitoring programme, these measures are not discussed here because this protocol is limited to field actions required for the collection of samples. Hughes (2000), Crowcroft and Scoble (1997) and Standards New Zealand (1998) discuss the use of these QA/QC methods. Commonly used QA/QC methods include duplicate samples, blanks, spiked samples, control standards and inter-laboratory comparisons.

This protocol does not provide specific guidance on sampling safety or etiquette. Although sampling safety and etiquette are crucial in any sampling programme, they are not discussed here because, as stated above, the protocol is limited to the field actions required for sample collection. Measures that should be taken to ensure the safety of sampling staff are discussed by Rosen et al (1997), Crowcroft and Scoble (1997), Standards New Zealand (1998a), Hughes (2000) and Stansfield (2001). Rosen et al (1997) and Hughes (2000) discuss appropriate sampling etiquette that minimises any inconvenience to well owners.

Organisation and use of this document

The protocol comprises four parts:

  • this guideline document, describing the sampling procedures in detail and providing the rationale behind them
  • a flow diagram for use in the field, providing a simplified step-by-step two-page guide that is cross-referenced to the more detailed guideline (Appendix 1 of this document)
  • an example field sheet that can be used for recording information in the field (Appendix 2 of this document)
  • a separate report that describes and interprets results from the field trials (Daughney et al 2006).

This protocol separates the actions which are required for compliance with this protocol from the actions which are recommended for collection of samples. For all procedural steps, essential actions are indicated by the words "must" and "required", whereas non-essential optional actions are indicated by the words "should" and "recommended". For example, Step 2.2 states that all samples must be collected from a sample point that is in good condition, and that all samples should be collected upstream of any pressure tank or similar device. These instructions indicate that any sample which is collected from a corroded sample point will be non-compliant with this protocol, whereas a sample collected downstream from a pressure tank will be compliant with this protocol (although the sampler should observe the recommendation to collect the sample from upstream of the pressure tank if possible).

In the organisation of this document, an effort has been made to list all essential actions at the beginning of the description of each sampling step, followed by a list of actions which are recommended as best-practice but not required for compliance with this protocol. The description of recommended actions is kept to a minimum for the sake of brevity.

This protocol is intended to provide a stand-alone reference for groundwater sampling. For all required actions, reference to other existing guidelines is provided only for justification, and is not intended to imply that other guidelines should be consulted prior to sampling. For some recommended actions, the reader is directed to other existing guidelines simply in order to keep this protocol document as brief as possible. The protocol does not include a glossary, but certain terms that might be unfamiliar to some readers are defined in the text at their first occurrence. For definitions of any other terms used in this document, readers are directed to Standards New Zealand (1998a).