The Collaborative International Dictionary of English v.0.48:

Surmountable \Sur*mount"a*ble\, a. [Cf. F. surmontable.]
   Capable of being surmounted or overcome; superable. --
   Sur*mount"a*ble*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

surmountable
    adj 1: capable of being surmounted or overcome; "situations of
           measurable and surmountable danger" [ant:
           insurmountable, unsurmountable]
    2: capable of being surmounted [syn: surmountable,
       climbable]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "surmountable":
   achievable, actable, assailable, attackable, attainable, beatable,
   compassable, conquerable, doable, expugnable, feasible, negotiable,
   operable, overcomable, penetrable, performable, practicable,
   practical, pregnable, realizable, superable, viable, vincible,
   vulnerable, weak, workable