Recommendations for revision of Auckland Regional Council long term baseline groundwater quality monitoring programme

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van der Raaij, R.W.; Moreau-Fournier, M. 2010 Recommendations for revision of Auckland Regional Council long term baseline groundwater quality monitoring programme Lower Hutt, N.Z.: GNS Science. GNS Science report 2010/56 68 p. + 1 CD

 Abstract: Auckland Regional Council (ARC) has recently reviewed the region’s state of the environment (SoE) groundwater quality monitoring network to ensure the comprehensiveness and validity of the programme’s objectives, and to ensure the programme is properly set up to meet these objectives (ARC, 2010). This report goes some way towards fulfilling four of the recommendations outlined in the review. The report consists of four parts: first an itemised process of all steps needed for a scientifically robust change over to use the NGMP data, including any further analysis required to complete this process, in order to be able to fully integrate the ARC groundwater (GW) monitoring with the NGMP. The second part of this report presents an evaluation of the existing ARC QA/QC procedure compared to the National Groundwater Monitoring Programme (NGMP) QA/QC procedure. The current ARC QA/QC procedure is performed through laboratory duplicate comparison. Comparison of a 3-year long paired water sample dataset indicated that the ARC QA/QC procedure was effective in detecting erroneous analysis. However, the procedure is presently undertaken manually and although differences that lead to re-analysis were detected the threshold for significance is yet to be defined. Moreover, while systematically comparing sample pairs, several transcription errors were identified, the database updates after re-analyses were not systematic, and discrepancies were found between data extracted from the database and QA/QC reports. Adoption of standard quantitative QA/QC procedures used in the NGMP is recommended to avoid such issues in the future. The third part of this report is a statistical assessment of total and dissolved phosphorus data to ascertain if these data sets are similar enough for only one analysis of phosphorous to be performed. Generally, total and dissolved phosphorus concentrations are not similar (P>0.0?) and discontinuing measurement of one parameter for the dataset as a whole is not justified on this basis. However, at seven sites there was no difference between total and dissolved phosphorus. These sites are BP Bombay, Ford Motor Co, Mt Richmond, OFR#1, RRR Shallow and Seagrove Road. Discontinuing measurement of dissolved phosphorus may be appropriate at these sites. For the remaining sites it may still be appropriate to discontinue measurement of dissolved phosphorus. As total phosphorus is always greater than or equal to dissolved phosphorus, monitoring of total phosphorus alone should be sufficient unless concentrations are near to the limit set by the particular standard of concern. When this is the case, and the standard requires the measurement of dissolved phosphorus, then sampling for dissolved phosphorus should resume. The fourth section of this report contains a proposed groundwater dating schedule for all groundwater sampling sites, initially targeting higher risk aquifers. The schedule reflects the need for long-term time series measur ements of the age-tracers, which are necessary for accurate estimation of groundwater age. (auth)