Volquez could have 4 or 5 starts left depending on how strictly the Reds stick to a 5-man rotation. So, he's got an outside chance at 20 wins, but it's doubtful. I don't know how important 20 wins would be given that it would simply be a cherry on the crap sundae that is this season.
Then again, Volquez and Arroyo have a chance to do something that hasn't been accomplished in the NL since 1986. That is, they can combine for more than 32 wins while playing for a team that finished at least 10 games under .500. The last pair of pitchers to accomplish that in the NL were Fernando Valenzuela (21 wins) and Orel Hershiser (14 wins) for the Dodgers in 1986 while playing for a team that finished 73-89. Yeah, pitcher wins are a lousy stat to follow, but c'mon, I'm grasping at straws this late in the season.
In other news, if the Reds win the rest of their games and the Brewers lose the rest of theirs, the Reds will finish one game in front of the Brewers at the end of the season. I think that makes the goal pretty clear.