Environmental Protection (Water) Policy 2009 - Monitoring and Sampling Manual

Sampling design and preparation

Version: February 2018

Quality control for water and sediment sampling

1 Purpose and scope

This document outlines an approach for collecting control samples during a monitoring program—it does not

 Background to water quality sampling using automated sampling equipment

 Water quality sampling using automated sampling equipment

 Chlorophyll a sample collection methods

 Collection and preservation of sediment

 Guidance on the sampling of groundwaters

Biological assessment: Direct toxicity assessments

3 Introduction

The number and type of quality control samples collected will depend on the type of analysis being undertaken,

the number of samples being collected and the level of contamination expected. For example, blank samples

may be more important when assessing low levels of environmental contamination (e.g. ultra-trace metals in

closeness of the results of multiple analyses to each other. It gives no indication of a results relationship to

a true value.

The number of quality control samples should be defined during the sampling design process, and acceptance

criteria should be determined during this phase. Acceptance criteria are the agreed upon limits that ensure data

are of acceptable quality. If the quality control results are outside the acceptance criteria, investigations should

be undertaken, and in some cases data will have to be rejected.

Note: The analytical method used for the quality control samples should be exactly the same as used to

analyse other samples from the sampling program.

each sampling program will depend upon the programs objectives and size, and the types and concentrations

of analytes being measured. Blanks should analysed for the same analytes as all other samples. Blank water

should be ultra-pure MilliQ water provided by the analytical laboratory, or if from another source routinely tested

to show no contamination is present. Guidance on the number of blank samples is provided in Table 1.Some

types of blanks are outlined below:

 Container blank: used to quantify and trace contamination problems associated with the sample

containers and preservation. A bottle is filled with ultra-pure MilliQ supplied by the analytical laboratory,

preservative is added (if required), and the sample is stored for the same time as the samples for analysis.

 Trip or transport blanks: used to estimate contamination of a sample from shipping and laboratory

sources of contamination. A bottle is filled with ultra-pure MilliQ, preservative is added (if required), and the

water, preservative is added (if required), and for example, if a sample is field filtered, the field blank will

also be filtered. It is recommended that water is supplied by the testing laboratory, or if produced in house,

undergoes testing to ensure it is contaminant free.

 Rinsate/Equipment blank: used where an analyte free liquid is poured over or through decontaminated

field sampling equipment to assess potential contamination from the equipment. Generally, ultra-pure MilliQ

water is used, but other liquids may be more appropriate (e.g. analytical grade hexane if testing for

hydrocarbons or organics).

Note: Distilled water purchased from retailers is not adequate for use as a blank.

 Trip spikes. Particularly useful for volatile compounds. Prior to field trip, clean analyte free water spiked

with a known concentration of compound of interest and taken to field and returned unopened for analysis.

laboratory to confirm the primary laboratory’s results.

 Certified reference material (CRM): certified reference materials are available for some analytes in some

matrixes. Certified reference material can be used to assess laboratory accuracy and precision. Samples

should be sent in as a blind sample. The concentration of analytes in the CRM should be in the range of the

analytes expected in the environmental samples.

Note:

A blind sample is a sample named so that it is indistinguishable from the other samples. This means the

source and chemical composition of the samples are not known to the analyst. Blanks, duplicates and CRM are

often used as blind samples. Blind samples can determine variability within a laboratory or bias and variability

between two or more laboratories.

Replicates: replicate samples are obtained by collecting two or more samples across a site at the same time.

Replicate samples provide estimates of the sample variability, including experimental sampling error and

analytical error. The number of replicate samples collected depends upon the program objectives. See

Sampling design and preparation—sampling scope and design for further information.

Any reported concentrations of inorganic or organic contaminants in blanks should be investigated immediately.

Collection of adequate blank data should indicate if the source of contamination is the container, equipment,

field, transport or the laboratory.

5.2 Duplicates

The assessment of duplicates is commonly undertaken by expressing the duplicate results as the Relative

Percent Difference (RPD). As a rule of thumb, a RPD of ≤ 20% may indicate an acceptable result for duplicate

aqueous samples (Equation 1), provided the result is five to ten times the limit of reporting (LOR). In those

circumstances where the result is close to the LOR, RPD may exceed 20%. However, the acceptable RPD can

be strongly influenced by the analyte and matrix.

Therefore, specific acceptance criteria should be discussed with the laboratory prior to the sampling program

commencing. The Australian Standard for Soils (AS 4482.1-2005), which can be applied to sediments, gives an

acceptance criteria RPD of 30-50%, noting that the variation is higher for organic than inorganic analyses.

Equation 1

Where: RPD is relative percentage difference

C

C

as the total metals.