The impact of urban groundwater upon surface water - eTheses ...

MONITORING NETWORKS AND METHODS
different times was undertaken and identified a sporadic under-estimation of alkalinity (>150
mgl -1 as CaCO3). The alkalinity tests were usually conducted in the field to reduce the
likelihood of carbonate precipitation and the error is likely to be associated with the titration
process. In some cases positive errors were seen in association with high levels of SO4 and
NO3 and it is suspected that some microbial reduction took place during sample storage,
which was over a period of several weeks in some cases. A decrease in nitrate levels was
observed when a set of analyses were repeated after a 5 day interval and smaller peaks on the
ion chromatograph were often observed which may indicate the presence of sulphite and
nitrite. Further investigation would be necessary to confirm this.
For the available 2000 and 2001 data set for which all cation and anion analyses were
available, the mean error (((ionic error) 2 ) 0.5 ) was +/- 5.5% (median error +/- 3.6). The error is
considered acceptable for results derived from three different methods of analyses (ion
chromatography, field alkalinity titration and ICP). The precision of each method of analyses
is as quoted by the laboratory and verified by a number of repeat and standard analyses. The
typical errors are given in Table 4.6.
Type of analyses Typical error
Alkalinity +/- 4%
Cations – ICP +/- 3%
Anions – Dionex +/- 10%
Chlorinated Solvents – ECD +/- 10%
Environment Agency Metals +/- 10%
Environment Agency VOCs +/- 10%
Table 4.6 Typical errors for the different methods of chemical analyses
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