The Jetset boys were absolutely right with their figure of 25%. There is definitely nothing in OUR company ops or Jarops manuals.....BUT, here is the reference from the JAR site. Must tell our tech people.
http://www.jaa.nl/jar/jar/jar/jar.ops.1.480.htm
(2) Contaminated runway. A runway is considered to be contaminated when more than 25% of the runway surface area (whether in isolated areas or not) within the required length and width being used is covered by the following:
(i) Surface water more than 3 mm (0Š125 in) deep, or by slush, or lose snow, equivalent to more than 3 mm (0Š125 in) of water;
(ii) Snow which has been compressed into a solid mass which resists further compression and will hold together or break into lumps if picked up (compacted snow); or
(iii) Ice, including wet ice.