High PSV sandstone test results from the Cribarth area, Garth, Builth Wells, Powys

Due to the failure of the draft Powys Unitary Development Plan (UDP) to identify high Polished Stone Value (PSV) resource areas, the British Geological Survey has undertaken a study jointly funded by Powys County Council and the Welsh Assembly Government to collect and test samples from the Cribarth and Crychan formations within the County. The Cribarth and Crychan formations are broadly homogenous muddy sandstones, and whilst of different ages, were deposited in similar geological settings. A quarry in the Cribarth Formation currently extracts rock for use as a skid-resistant top dressing for major roads and motorways. A total of ten rock samples from both formations were collected from surface outcrops and shallow cuttings and were sent for testing at an external, independent laboratory. None of the samples collected were totally unweathered, and as a consequence, the results obtained could be expected to be lower than those for unweathered rock currently being extracted from the quarry. The specifications for High Skid Resistant Aggregate sets a PSV of 60 as the lower limit for materials classed as High Skid Resistant Aggregate. The results obtained for both the Cribarth and Crychan formations, even in the slightly weathered state, were above this lower limit value, the Cribarth Formation consistently showing the higher PSV values. As a consequence, both formations can be considered to be a high PSV aggregate resource and therefore should be considered for safeguarding within the Powys County Council UDP.