Arsenic (and other Heavy Metal) Testing and Assessment
Elevated levels of arsenic and other metals and metalloids are a common natural occurrence in some parts of the UK, including the southwest of England.
Where the levels exceed generic assessment criteria (GAC), bioaccessibility testing can be undertaken to assess whether or not the elevated levels are harmful to human health.
The GAC assume that 100% of the contaminant (e.g. arsenic) is taken up by systemic circulation (i.e. 100% bioaccessibility). However, naturally occurring arsenic and other metals and metalloids are commonly not 100% bioaccessible and therefore often less harmful to human health.
In order to provide data for a site-specific risk assessment, bioaccessibility testing using the unified BARGE method (UBM) or physiologically based extraction test (PBET) is undertaken on soil from the site. The UBM and PBET bioaccessibility tests are laboratory tests that simulates conditions in the gastrointestinal tract to assess the human bioaccessibility of potentially harmful elements by ingestion.
The CLEA model software is then used to produce a site-specific assessment criterion (SSAC) for the contaminant (e.g. arsenic) for the proposed land use.
Iron and Manganese Testing undertaken Instead of Remediation
An effervescent (oily) and rusty sheen was noted on water within initial foundation excavations and concern was raised about possible contamination from a nearby former railway siding.
A walkover survey and geological knowledge identified the effervescent and rusty sheen as being of natural origin. Some bacteria (leptothrix discophora) that live in waterlogged places get their energy from iron and manganese, and, as these harmless bacteria grow and decompose, the iron may appear oily or form red or orange films, fluffs and coatings. It was also noted that a mining report stated that mines in the area were mainly mined for manganese, i.e. the underlying geology is rich in manganese. Therefore, no remedial measures were required.
This was confirmed by UKAS accredited contamination laboratory testing.