Reunification must take place?

If a bio parent is skimming by doing their service plan,does CPS have no other choice but to place the child back with the bio parent? I'm in a situation where CPS is telling me that they don't see that the parent has made any changes, including stating that they think parent could very easily be manipulating the drug test in order to get a negative reading (I've been told this is very common, esp when bio parent is given 24 hours drug testing notice). CPS has even gone so far to say in no waiving terms to me (foster parent) that they do not want the child to go back to the parent. However, the way I understand it CPS's hands are tied because parent is squeaking by doing the service plan and getting negative drug testing results. Anyone have experience with this? Seems to me if CPS has an uneasy feeling, they hold a lot of power in not returning the child until they get a good feeling about the reunification. Shouldn't they feel 100% that the child will be returned to a healthy and safe environment? I understand that the court has the final say, but I haven't seen too many cases where the courts do not side with CPS recommendations or, at the very least, ask for more information and delay placement with parent. I do feel CPS is doing what they can to delay, but I wasn't sure if there is anything in CPS's policy that helps them in this situtation. Anyone else have experience with this scenario who can lend advice?