ICI has been undertaking a limited dewatering programme at its Penrice Quarry since mid-1978 to allow quarrying of the 4th level (EL 327 m). Monitoring carried out for the programme has included recording of the groundwater levels in wells drilled within and around the quarry, and measuring the accumulated discharge from beneath the quarry. So far, the dewatering operations have had no measurable effect on regional groundwater levels. Results of the monitoring have been used to calculate an approximate transmissivity value for the marble aquifer of 40 m3/day/m. Calculations show that dewatering by a further 15 m, to allow for quarry deepening, is practical. However, to achieve effective dewatering with minimum groundwater pumpage, alternative pumping arrangements will have to be investigated. The regional effects of any dewatering will continue to be monitored by this Department.