A report has now been received, outlining the results of the second season of excavation on the medieval drain at Paisley Abbey. A limited archaeological excavation was carried out by Glasgow University ArchaeologicalResearch Division (GUARD) in September 2010 in collaboration with Renfrewshire Local History Forum, Renfrewshire Council and Paisley Museum. Earlier work had concentrated on the archaeological deposits and artefacts recovered from inside the drain. This excavation followed on from a similar small-scale excavation in 2009 to investigate the construction of the drain and the deposits surrounding it.
The 2010 trench was located over the point in the drain where a medieval manhole had been identified by the Royal Commission on the Ancient and Historical Monuments of Scotland (RCAHMS) during a survey of its interior. The manhole is located between two of the roofing arches of the drain and is approximately 0.7 m by 0.5 m in size. In addition, a possible feeder drain also entered the main drain at roof height at this point. The intention was therefore to investigate these two features from the outside, as well as to assess the survival and condition of the drain and any other associated deposits.
The excavation confirmed the presence of deep deposits of demolition material including an early 20th century tarmac surface and landscaping as was expected. More importantly, however, the excavation revealed masonry structures that might represent the feeder drain identified from the interior survey of the drain. These stones covered approximately half of the trench and included several large angular stones 0.4 m by 0.4 m by 0.25 m in size, which formed a line or edge that ran NW to SE. To the south of this line was another concentration of smaller stones and white mortar 0.7 m wide that lay parallel to the larger stones. The stones did not extend over the SW corner of the trench where grey silt overlay a mixed light-brown layer of clay, silt and mortar. After the whole trench was cleaned, photographed and recorded a small slot 0.2 m by 1 m was excavated into the mixed layer of clay, silt and mortar, which was found to be 0.2 m deep and covered a layer of light-brown mortar-rich silt. In the north of the trench one of the large square stones was removed to reveal more stones beneath. This stone was replaced prior to backfilling.
As the extensive layer of stones lay at a depth of 1.3m, which raised health and safety concerns about further excavation, and the present Scheduled Monument Consent did not allow for the removal of archaeologically sensitive material, the excavation stopped at this level. A protective layer of geotextile was placed over the base of the trench and the site backfilled. While these stones may represent the cap of the feeder drain, the size of the stones and their position suggest that these could also represent a wall foundation that may be contemporary with the drain and relate to the monastic precinct. As the stone structures were not excavated it was not possible to determine their exact nature and to confirm that they marked the location of the side drain or form the outer structure to the manhole.