Unlike Java's EnumSet, an Enumeration.ValueSet in Scala is not based on a bit set. Conversions between ValueSets and bit masks can currently be implemented like this:

  def toLong(vs: Enumeration#ValueSet): Long = vs.foldLeft(0L){ (z,n) => (2L << n.id) + z }
  def fromLong[T <: Enumeration](e: T, l: Long): T#ValueSet = e.ValueSet.empty ++ (new BitSet1(l)).map(i => e(i-1))

Such conversion method should be built in (not even BitSet itself currently provides a way of getting a bit mask out), and be based on a more efficient implementation like Java's EnumSet.