Recharge through drift. Progress Report

The overall objective of this study is to quantify amounts of recharge to aquifers overlain by a covering of drift and to understand the flow mechanisms by which this occurs. This requires an identification of the key Chalk and Sherwood Sandstone Drift hydrogeological environments, the understanding of recharge processes and a quantification of recharge for each of these domains. The approach adopted by this project is to investigate three aspects: 1. Identify the various Drift domains, develop conceptual models for each domain and with the help of simple spreadsheet type calculations, perform sensitivity analysis to test recharge rates for a range of parameters and boundary conditions within their range of uncertainty. 2. Determine recharge mechanisms and likely rate at field sites in East Anglia and the Tern catchment. In the Tern catchment the study is based on recharge of the Sherwood Sandstone through a thin drift cover. The East Anglia field site has been established at a site where the Chalk is overlain by thick till. The study here will be largely based on water quality data including geochemical residence time indicators and will include the following objectives: • to ascertain whether recharge occurs through the till and to quantify rates. • to establish the degree of importance of (a) fissure-related bypass flow, and (b) flow through higher permeability sand lenses. • to determine the residence times of the various groundwater components in the till and underlying Chalk. • to determine the extent of denitrification within the till. Calculate catchment scale recharge rates using regional Environment Agency data (groundwater levels, hydrological and water quality) and working closely with the Environment Agency. Review recharge models associated with regional groundwater studies in the Environment Agency