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FAQs (frequently asked questions)


Why do different laboratories get different EPH results on the same soil sample?

This is because there is no current standard method for TPH in soil, and laboratories use different solvents for extraction. A very polar solvent such as hexane/acetone will provide a higher result, but it may contain indigenous organic material normally found in soil.   DCM based solvents are more middle of the road in terms of polarity and may avoid the problem of indigenous material.


Why is it necessary to filter water samples on site?

This is now recommended best practice in the MCERTS for waters standard, as if samples are not filtered prior to adding to preserved bottles, then any sediment present can dissolve in the sample and cause falsely high results.  In addition, microbes present in the sample will continue to affect the composition if they are not removed by filtration through a 0.45 micron filter.


Will my samples lose accreditation if they exceed temperature?

The MCERTS standard for waters states that ‘the sample storage environment shall maintain a temperature of 1-8°C and although samples exceeding these limits will be reported as non-conforming, they will not lose their accreditation.


Which holding times will be used?

For many years, the USEPA holding times were used, but there are now two ISO standards covering soils (BS ISO 18512) and waters (BS ISO 5667), and some parameters have more stringent requirements in these standards.  In addition, the laboratory has performed stability trials on some parameters, and holding times derived from these trials may be used as an alternative – this particularly applies to holding times of 24 hours, which are not usually possible. 


When does the holding time start from?

In the two ISO standards, the holding time should commence from the date sampled.


If my volatile samples are not taken in separate vials/jars will the data lose accreditation?

They will be reported as non-conforming, but should not lose accreditation.

DETS – dependable data, dependable delivery