As part of a survey of pesticides in the UK Major Aquifers, which WRc are undertaking on behalf of the National Rivers Authority, a site at Assarts Farm near Mansfield on the Sherwood Sandstone aquifer has been selected for the study of pesticide movement in the unsaturated zone of the sandstone aquifer.
A difficulty in studying pesticide movement in the unsaturated zone is the need to obtain large volumes of water for analysis. WRc, in co-operation with the Soil Survey and Land Research Centre (SSLRC) has tackled this problem by using a modification of the SSLRC standard soil moisture suction sampler. The modified design (Fig. 1), manufactured by SSLRC, is intended to render the installation as chemically inert as possible, so the sampler shell is of stainless steel, tubes and caps of Teflon and the filter element ceramic. No adhesives or resins were used.
At the design stage it was anticipated that each sampler would yield between about 100 ml and 500 ml depending on the soil moisture at the time of sampling. In order to be able to obtain the necessary volume of water (1.71 for three groups of pesticides) needed to analyse pesticides to the required detection limit, a total of twelve samplers in four clusters (Table 1) of three have been installed. It was intended that under optimum conditions each cluster of three samplers, when bulked, would provide sufficient water for one analysis. Under progressively drier conditions, the samples from the clusters may need to be bulked