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

MONITORING NETWORKS AND METHODS
containing the fixing agent potassium dichromate. VOC samples for analyses by the ECD
method were collected in 137 ml amber glass bottles with teflon septa. VOC samples for
broad scan analyses were collected in 40 ml clear glass vials with teflon septa. VOC samples
were collected with no head space and stored upside down to minimise loss through the septa
. The VOC samples were analysed within two weeks of collection. All samples were kept in
an insulated cool box in the field prior to transfer to a fridge on return to the laboratory at the
end of each day.
4.10.4 Precision and Accuracy of Inorganic Analyses
The accuracy of the inorganic analyses was checked by comparing the milliequivalents of the
major cations and anions to derive the electroneutrality as the percentage ionic error of the
solution (100*(Cations-Anions)/(Cations+Anions)). Upon examination of the data a series of
negative ionic errors were identified associated with a malfunction in the ICP equipment
during March 2001. The cation results from the surface water sampling undertaken in
February have been discarded as a result of this. The error in the data was sporadic and only
detected as result of sudden changes observed in the Ca content that should show only gradual
variation along the surface water profile. The malfunction was not detected in subsequent
analyses.
Average errors (((ionic error) 2 ) 0.5 ) for each sample type were determined as abstraction wells
+/-3.5%, shallow groundwater +/-6.9%, the riverbed piezometers +/-6.4%, and the surface
water +/-5%. A link was found between sites of high contamination and increased error.
Negative errors were found to be reduced when the effects of additional contaminants were
included in the cation balance. A comparison of results for repeat sampling of a location at
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