HYDROGEOLOGY AND HYDROGEOCHEMISTRY OF A SMALL, HARD-ROCK ISLAND - THEHEAVILY STRESSED AQUIFER OF JERSEY

The fractured basement aquifer of Jersey provides 30% of the total wat er needs of the island plus baseflow to surface catchment storage. A 3 -year field study has attempted to describe the groundwater resources in terms of quantity and quality. Borehole yields are typically less t han 11 s(-1) the island-wide estimate of transmissivity is 3 m(3) day( -1) and effective aquifer thickness is 30-40 m although deeper circula tion occurs in selected fracture systems. It is estimated that much of the renewable resource is exploited. Groundwaters are predominantly d erived from recent recharge, most being oxidising with measurable trit ium contents. There is widespread pollution from agricultural nutrient s but natural denitrification is apparent in some areas.