Dissolved Organic Carbon as an Indicator Parameter for Groundwater Flow and Transport

The bulk parameter dissolved organic carbon (DOC) is often successfully exploited in the context of investigations into the collective behavior of dissolved organics contained in water. Though being an unspecific parameter, increased DOC concentrations can indicate anthropogenic influences (such as bank filtration or artificial recharge) on groundwater quality. To this end, DOC as an organic surrogate parameter was investigated for its potential to indicate and characterize such influences. The advantages of using DOC as an indicator parameter are the low time and cost investments required for analysis of DOC concentrations but also the fact that DOC reflects the collective behavior of the dissolved organics contained in water. Existing models for DOC characterization are limited to the identification of one or two compound groups with different degradability. Based on first order degradation kinetics, a multi-component approach is mathematically derived. The approach is demonstrated for the example of four compound groups that are (i) easily, (ii) moderately, (iii) poorly and (iv) under the given conditions not degradable as a function of time scale and flow path length. By means of the conceptual model, a decision tool is given for finding the necessary contact time as a function of hydraulic conditions and flow path length, such as in the case of bank filtration or groundwater recharge site design, as well as in finding the required distance between infiltration areas and points of interest. The discussion of contact time and time scales is a step towards a comparable interpretation of laboratory and field conditions in terms of biodegradation rate constants for DOC as well as for single organic compounds.