I have recently had an aco drain fitted to the drive. It was bedded on concreate and the drive re-instated round the drain with tarmac. When it rains some of the rain is soaking into the tarmac and away. It has been a week since the tarmac was laid. The rest of the water does not and stays on top and eventually goes into the drain and away. I thought tarmac would not let water through?. It was Patchmac pre-bagged tarmac that was fitted. Does this matter as the water will soak through into the water table anyway?