2002:1565 - CLONMACNOISE, Offaly

Dúchas applied to Offaly County Council for permission to install a new wastewater treatment system for the Visitor Centre at Clonmacnoise. Permission was granted for large septic tanks to the west of the existing system, with a direct outflow pipe to the Shannon. The work was to be monitored.

Three test-trenches were opened on the proposed location of the tanks on the crest of the esker to the north of the Visitor Centre, where limited archaeological deposits are known to exist. Trench 1 was opened in an area that had been previously disturbed by the existing sewerage system; evidence was uncovered that some archaeological features survived intact, so the location of the tanks was moved farther west (see below). During the monitoring of the excavation of the trench three pits were discovered. Further test-trenches were opened on the line of the outflow pipe, and archaeological deposits were revealed at a depth of c. 0.3m on the raised ground between the existing percolation area and the Shannon flood-plain.

Excavation of the pit for the tanks, 15m by 4m, revealed that the stratigraphy comprised 0.4–0.6m of redeposited material from the demolition of the schoolmaster’s house that was situated to the west of the monastic site in the 1980s. This material lay above the original sod layer and an agricultural horizon under which was a black layer that produced cut antler, iron objects, charcoal, animal bone and some slag. A fragment of a rotary quern was also recovered from this feature. A section of a small hearth containing slag was noted in the north section face. Three pits were uncovered: two on the north (downhill side) of the cutting and one on the south. One pit (F4) on the north side contained yellow brick, piping and plastic refuse from the demolition work of the 1980s, and the other two (F2 and F5) were medieval. F2 had no stratified layers and produced animal bone, an iron knife and nails, a bronze pin fragment and a bronze, collared, stud-headed pin (11th–13th century). F5 had a number of deposits, with evidence of having been open for a considerable time, and produced iron objects, cut bone and antler, lignite, a bone bead fragment, a fragment of a hone and some slag.

Further excavation was necessary on the high ground to the east in the area already tested, as an extra tank was required. The only stratified feature in this area was a platform of large stones measuring c. 1m by c. 3m. It consisted of a single layer of large stones, 0.2–0.5m, with small cobbles laid between. It had been curtailed to the north and south by the existing pipes and percolation area. The layer into which these stones were laid produced a bone pin tip and a piece of cut antler.

Excavation in the trench for the outflow pipe has been discontinued but to date has produced evidence of extensive ironworking, stone settings, pits and hearths, as well as a number of early medieval finds. This will be reported on after completion of the excavation in 2003.

Work has currently halted owing to adverse weather conditions and the rise of the Shannon in late October/November.

Skidoo, Ballyboughal, Co. Dublin