Tythegston quarry lies near Bridgend in South Wales Fig. 1

The quarry covers an area of about 9 hectares and has been used as a waste disposal site since 1968. The maximum depth of the quarry was 38 m, with rock benches along the northwest and south sides about 20 m below ground level. Solid wastes, 50% being crude domestic refuse, have been tipped at the rate of about 86 000 tonnes per annum since December 1968. Initial disposals were into the central, seasonally flooded, depression located just to the right of the area photographed (fig.) In 1971, drums of chemical wastes and motor tyres were codeposited but since 1972 only untreated domestic and paper mill wastes have been tipped.

The quarry is excavated into the Main Limestone Series of the Carboniferous Limestone Table 1, at the C1 and C2/S1 zonal boundary. The limestone is massively bedded (Fig.2) with a northerly dip of 5° (B) but with some cross folding and associated small faults, for example, the zone of intense fissuring visible on the rock face (F), locally increasing dips to between 35° and 55°N. The photograph is of part of the northern wall of the quarry defined by conjugate joints trending 010–190° (J1) and 115–295° (J2). The northerly joints (J2) show evidence of solution widening (karstification) but with Triassic sediment infilling to depths of over 40 m. The widened joints in zone F have been infilled with more recent, possibly Pleistocene, material. The

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