Methods in the Exploratory Risk Assessment of Trace Elements in the Soil-Groundwater Pathway

Groundwater protection starts with soil protection. When soils are contaminated there is always a chance that the groundwater is or will be affected by this contamination as well. Analytical risk assessment is often very time-consuming and expensive. The goal of exploratory investigations is to investigate the risk of groundwater contamination with the minimum possible effort. Exploratory investigations concerning trace elements can be carried out by analyzing soil material, percolation water or groundwater (LABO 2003). While percolation water and groundwater analysis can only confirm a contamination, information gathered by soil analysis permits the current and future contamination risk for the groundwater to be estimated and additionally allows precautionary measures to be planned in order to protect the groundwater. The risk of contamination can only be judged when standards are available for a good quality of soil or percolation water. Local or regional background values of trace elements in the soil or percolation water can serve as adequate standards. This chapter will present and compare the analytical methods applied in exploratory investigations for assessing risks to the soil-groundwater pathway. We start with a little material science regarding trace element analysis in soil science and continue by listing some common methods used to analyze the total content of trace elements in the soil, presenting the conversion functions which allow results from different digestion agents to be translated. Subsequently an aqueous batch extraction method is presented which is routinely used to estimate the soluble fraction of trace elements in the soil for exploratory purposes, and its results are compared with results gained from direct percolation water sampling and a method which adjusts one parameter to in situ conditions.