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Email Link   Your Testing Process

To maintain the integrity of sampling and testing, the Tweed Laboratory Centre recommends that our customers:
  • Keep samples cool - all samples should be kept at approximately 4°C
  • Collect their free sample containers from the Tweed Laboratory Centre (46 Enterprise Ave, South Tweed or council chambers in Murwillumbah)
  • Label their samples correctly - Record the time of sampling, date, sample description and client name.
  • Samples should be received by the laboratory within 24 hrs of sampling.
The Tweed Laboratory Centre are on hand to help with any technical enquiries that you may have and, if required are able to provide further clarification on the best way to submit your samples.

Sampling Techniques

Collecting a Chemistry Sample (except for testing pesticides and other organic compounds)

  1. Call into the Tweed Laboratory Centre to pick up your free container(s)
  2. Fill bottle halfway
  3. Shake container and discard water
  4. Refill to top, leaving no air space in the container.
  5. Drop the sample into the team at the Tweed Laboratory Centre

Collecting a microbiology sample

  1. Call into the Tweed Laboratory Centre to pick up your free container(s). For chlorinated samples, you will need to use a sterile jar containing Sodium Thiosulphate. The Tweed Laboratory Centre can provide this
  2. Do not rinse the container before taking the sample
  3. Disinfect the tap. The Tweed Laboratory Centre will be able to provide details on this
  4. Let water flow to avoid splashing
  5. Collect the sample

Collecting a pesticides, organic contaminants or acid sulfate soil sample

Please contact the Tweed Laboratory Centre for details of sample collection and correct containers required.

Next steps

You will receive a sample receipt and your results via email providing a unique LIMS number for tracking the sample through the whole testing and reporting system.

The results will also be sent to you by email and hard copy in the mail. We send out separate reports for biological and chemical testing signed by authorised staff with associated NATA accreditation endorsements.

If you have any questions about your results, please contact the helpful team at the Tweed Laboratory Centre.

An Overview from Samples to Reports

Bringing in a sample

All samples brought in should be accompanied by a Chain of Custody form available from the lab upon arrival or download here: COC Blank (66kB DOC). A completed form provides information regarding who submitted the sample(s), who needs the results, description of the samples/project, date samples taken, the testing required and for non-routine council work, a job number.

Processing a sample

Once the samples are received, the job is registered into the lab’s database (LIMS) so each job has a unique number and each sample in that job has a unique trailing number.

The time it takes to process a sample depends on the type of analysis and total number of samples. Depending upon the range of testing required for the sample, there might be a multitude of different analysts and pieces of equipment/instrumentation used to test the water/soil. Some tests take a few days, because that is what the method dictates (e.g. BOD takes 5 days) while others can be completed within an hour or so from sample receipt (e.g. pH, Alkalinity). Metals, nutrients and many other tests are usually batched so a large run is performed on a weekly basis to do all those received during the last few days.

Quality Control

As part of the requirements for accreditation with NATA, a number of quality control checks are performed which need to be within prescribed criteria before a batch of sample results can be validated: The control checks are:

  • Duplicates are done on one in ten samples
  • Blanks are included with sample runs to ensure there is no carry over or contamination between samples
  • Certified Reference Materials are standards provided by external suppliers with known values These are plotted over time from each run of tests so that any trends away from the certified value can be assessed
  • Proficiency testing is completed regularly using samples with unknown values. These are tested by a group of laboratories and evaluated for outliers
  • Measurement Uncertainty is a calculated variance from the stated value based on repeating the test on the sample a number of times.
  • Standard Calibrations are used for instrument based testing where a number of different concentrations of a standard are graphed. The regression of the points along the calibrated line also has acceptance criterion

Measurement Uncertainty – What Is It?

For any laboratory, each test result is subject to some level of error. An estimate of this error is known as Measurement Uncertainty (MU) and is normally expressed with a 95% confidence range. If the test was repeated 20 times, 19 of those results would fall into that range extrapolated by the MU%.

The International Standard ISO/IEC 17025, which our NATA accreditation is assessed against, requires laboratories not only to be able to estimate MU, but have these values available to clients; particularly where the Uncertainty affects compliance to a specification limit (e.g. EPA Waste water effluent licenses). For this purpose relevant MU are presented in the table below for this purpose and available to all clients

MU for a particular lab/test may also vary over time, so this is periodically reassessed and updated. MU can't be used to compare the performance of different laboratories because the way labs calculate MU and the samples used to determine MU may differ and do not necessarily reflect the actual accuracy of a result.

When specifically requested by a client, MU will be provided with the report in the measurand units of the test (e.g. BOD of 52 mg/L, MU range of 38.5 - 65.5 mg/L).

Current Measurement Uncertainty Percentage for Tests that may affect Compliance to a Specification Limit.

Method and Lab Code

MU %

E.coli by Colilert B12


E.coli by MI Agar B19


E.coli in Oysters B7


Thermotolerant Coliforms B1


pH P1




Total Suspended Solids P4


Chlorophyll 'a' C9


Oil and Grease C8


Ammonia C3


Total Nitrogen C55


Total Phosphorus C17


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