How to submit a sample
The Tweed Laboratory Centre (Lab) recommends:
- keeping samples cool (all samples should be kept at approximately 4°C)
- labelling samples correctly - record time of sampling, date, sample description and your name
- providing samples within 24 hours of collection.
You can collect free sample containers from the Lab, see address and opening hours.
Samples must be received at the Lab by 4:30 pm or extra charges may apply.
Collecting samples
Chemistry samples (except for testing pesticides and other organic compounds)
- Call into the Lab to pick up your free container(s).
- Fill container halfway.
- Shake container and discard water.
- Refill to top, leaving no air space in the container.
- Drop the sample into the team at the Lab with a completed chain of custody record(PDF, 255KB).
Microbiology samples
Call into the Lab to pick up your free container(s). For chlorinated samples, you will need to use a sterile jar containing sodium thiosulphate – we can provide this.
- Do not rinse the container before taking the sample.
- Disinfect the tap. The Lab will be able to provide details on this.
- Let water flow to avoid splashing and collect the sample.
- Drop the sample into the team at the Lab with a completed chain of custody record(PDF, 255KB).
Pesticides, organic contaminants or acid sulfate soil samples
Please contact the Lab for details of sample collection and correct containers required – call 07 5569 3103.
Testing and tracking
You will receive a sample receipt and your results via email. Your unique LIMS number can be used to tracking the sample through the whole testing and reporting process.
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, contact us.
From samples to reports – an overview
Bringing in a sample
All samples brought in should be accompanied by a chain of custody record(PDF, 255KB).
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 on 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 how long the method dictates (for example, 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 previous 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.
- Duplicates are done on one in 10 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.
- 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 (for example, EPA wastewater effluent licenses). For this purpose, relevant MU are presented in the table below 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 measure and units of the test (for example, 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 |
Measurement Uncertainty |
| E. coli by Colilert B12 |
54% |
| E. coli by MI Agar B19 |
28% |
| Thermotolerant coliforms B1 |
38% |
| pH P1 |
1% |
| BOD C1 |
31% |
| Total suspended solids P4 |
11% |
| Chlorophyll 'a' C9 |
10% |
| Oil and grease C8 |
32% |
| Ammonia C3 |
13% |
| Total nitrogen C55 |
6% |
| Total phosphorus C17 |
4% |