Hi catchup, if its not in any of your manuals and someone wants a reference you can direct them to JAR-OPS 1.480
(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
(0·125 in) deep, or by slush, or loose snow,
equivalent to more than 3 mm (0·125 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.
Here's the link, go to page 61
http://www.jaa.nl/section1/jars/494174.pdf
Scally