G-BASE sample collection and analytical techniques are described in a methods manual. Which is available from the downloads page.
The G-BASE sampling campaign involves the collection of stream sediment, water and soil samples. The samples are collected by Earth and Geo- science undergraduates, during the summer vacation.
Stream sediments and waters are collected at an optimum density of 1 per 1.5 to 2 km2 , and, are ideally taken from 1st or 2nd order streams avoiding any contamination that may lie upstream. Stream sediment collection involves removing the oxidised layer from the stream bed and removing the sediment using a trowel. This is then sieved through a coarse sieve (2 mm) and a fine sieve (150 µm).
The -150 µm fraction is left to settle in a fibreglass pan and is decanted into a sample collection bag. The excess sediment from the -2mm fraction is then panned to collect the heavy mineral concentrate.
Water samples are taken before the stream bed has been disturbed. In all four water samples are collected. Two filtered waters are collected (for major and trace elements) and two unfiltered waters (for bicarbonate, conductivity and pH).
Soil samples are collected at an optimum density of 1 every 2 km2. These are collected using a hand held dutch soil auger and are taken from the surface (5 – 20 cm) and from a depth of 35 – 50 cm. Each sample is made up of a composite of material from auger flights taken from five holes distributed within an area of approximately 20 m x 20 m.
The same sampling procedure is applied during urban soil sampling campaigns. The sampling density however is higher at 4 samples per 1 km2.
Stream water pH, Eh, conductivity and alkalinity are determined at the field base camp. All other samples are returned to the BGS laboratories in Keyworth for sample preparation and analysis. The less than 150 micron fraction of the stream sediments and deep soil sample fraction are ground to less than 53 micron using an agate ball mill.
Soils and sediments are analysed by X-ray fluorescence (XRF) for Mg, P, K, Ca, Ti, Mn, Fe, V, Cr, Co, Ba, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Pb, Bi, Th, U, Ag, Cd, Sn, Sb, Cs, La, Ce, Ge, Sc, Se, Br, Hf, Ta, W, Tl, Te and I. Loss on Ignition (LOI) is determined on soils and pH on all subsoil samples in a slurry of 0.01 M CaCl2. Water samples are determined by ICP-AES for 27 elements - Sr, Cd, Ba, Si, Mn, Fe, P, S (as SO42-), B, Mg, V, Na, Mo, Al, Be, Ca, Zn, Cu, Pb, Li, Zr, Co, Ni, Y, La, K and Cr; and by quadrupole ICP-MS for 24 trace elements - Li, Be, Al, V, Cr, Co, Ni, Cu, As, Rb, Y, Zr, Mo, Ag, Cd, Sn, Sb, Ba, La, Ce, Tl, Pb, Th and U. Automated colorimetric methods are used to determine Cl and NO3– and ion selective electrode is used to determine F. Waters are also analysed for non-purgeable organic carbon (NPOC) to determine dissolved organic carbon content.
After preparation and analyses all soil, stream sediment and panned concentrate samples and excess material are stored and archived at BGS's National Geoscience Data Centre (NGDC). The archive holds more than 40 years worth of material collected across the UK from the Shetland Isles in the north to Kent in the south. Archived samples can be made available for further tests and analyses.