The final interim surface mining regulations were published by the Office of Surface Mining on 12 December. Among the requirements are that the operation should minimize disturbances to the prevailing hydrological balance in order to prevent long-term adverse changes in water quality and quantity, in the depth of ground water and in the location of surface water drainage channels. Regulations for sedimentation ponds are retained but exemption may be granted to allow the pH to rise above 9 if manganese levels (4 mg/l) cannot be met. The 24-hour frequency event for which effluent limitations must be applied has been reduced from 25 years to 10 years. Large sedimentation ponds must be constructed to withstand, at a minimum, a 100-year frequency, 6-hour duration storm. The regulations are to take effect on the 3rd of May 1978.