Quality control of regional geochemical stream water samples collected in 2005 in Northern Ireland for the Tellus project

Stream water samples were collected at a total of 3069 individual sites in the 2005 sampling campaign in Northern Ireland. These were submitted, with a full complement of control samples, for analysis for a suite of 57 analytes. Analysis was performed under contract by ALcontrol Laboratories NV, of the Netherlands. ALcontrol subcontracted some of the analyses to the Geological Survey of Finland (GTK). The data reported for these analytes have been considered by reference to their abundance in relation to the detection limit of the method, and in comparison with various control samples which were ‘blind’ to the analysts, submitted as part of the routine batches. These checks have produced information on the quality of the data, and any causes of increased uncertainty which should be recognised in the presentation and interpretation of results. Levelling was applied to the Ba and Sr data (described in section 7.2). It has been found that, with a few exceptions, the data is fit-for-purpose and checks using provisional geochemical images have confirmed this. A summary of this information, listed by analyte, is provided below: Analytes with no significant limitations identified in this report (n = 47): Al, As, B, Ba, Be, Br, Ca, Cd, Cl, Co, Conductivity, Cr, Cs, Cu, DOC, F, Fe, HCO3, Ho, K, La, Li, Mg, Mn, Mo, Na, Ni, NO2, NO3, P, Pb, pH, Rb, Sb, Si, SO4, Sr, Th, Ti, Tl, Total alkalinity, U, V, W, Y, Zn, Zr Analytes where most (>99%) sample site data is below the detection limit: Ag, Au, Bi, Pd, Pt, Rh, Se Analyte where blank water concentrations compromise sample site data: Sn Analyte with no measurable data by a semi-quantitative analytical method: Hg