Onderzoek van vier boor- en monsternemingsmethoden voorgrondwater tot vijf meter beneden de grondwaterspiegel in het zandgebied

摘要

The so-called Multi-Channel Well (MCW), installed using theSonicSampDrill, has proven to be the best method for analysinggroundwater on farms up to five metres below groundwater level. This isbecause this method - using just one sonic drilling allows placement ofmultiple sampling filters up to five metres below this level, so fewerboreholes are needed.At the moment, groundwater quality on farms in the Netherlands ismeasured in the uppermost one metre of the groundwater. Thesemeasurements, carried out in the framework of the Netherlands NationalMonitoring Programme for Effectiveness of the Minerals Policy (LLM inDutch) are used to determine effects of the fertiliser policy on thegroundwater quality; effects are reflected in the topmost metre.Besides this, measurements are also used to test the groundwater qualityagainst the nitrate standard. At the moment it is being investigated ifthe test depth can be lowered to five metres. First of all, because thisseems to be in line with the European regulations. And secondly, becauseconcentrations of nitrate deeper in the soil can decrease. This involvesthe possibility of too stringent testing at the moment. However, the LMMmethod does not allow such deep drilling, so a lower test depth willrequire another drilling and sampling method.RIVM has investigated four methods at four dairy farms. These dairyfarms are spread across the four large sandy areas in the Netherlands(north, east, centre and south). Every farm contains four drillingsites, totalling 16. The methods investigated are characterised, forexample, by hand or machine drilling and by the installation of temporaryor permanent filters. Methods are assessed on practical application andthe quality of the sampling. With the manual Van der Staay method, inwhich temporary filters are installed, the desired depth is achieved atonly 50 per cent of the sites. With the use of the mechanised ExtendablePoint Method, in which temporary filters are placed too, drilling andwater sampling forms a poor combination in practice. The MCW and theDirect Well (DW) methods allow placement of permanent filters aftermachine drilling. Contrary to the MCW method, the DW method requires aseparate borehole for each filter.