National Monitoring Network on Groundwater Quality ; Comparison of in situ pH measurement with the pH measurement in the laboratory
Landelijk Meetnet Grondwaterkwaliteit ; Vergelijking "in situ"-pH-meting met pH-meting in het laboratorium
Reijnders HFR, Boumans LJM, Gast LFL
RIVM Report 714801002
The pH was measured in samples from the National Monitoring Network on Groundwater Quality at the laboratory up to 1989. The pH has been measured in situ and in the laboratory from 1989. To quantify differences results of the in situ pH measurements and the pH measurements in the laboratory are compared. Results of the comparison are presented for the period from 1989 up to 1992. For the accuracy of the pH-measurements in the Monitoring Network on Groundwater Quality a limit of +-0.2 pH units is specified. In situ pH measurements and the pH measurements at the laboratory do not compare well since 35 to 40% of the differences between them are larger than the specification. It is recommended to use the results of the in situ pH measurements from 1992 as primary item in studies in which the chemical composition of groundwater is of interest.