I have an interview with ASRC in Washington DC on Monday. Has anyone ever worked there before? My bigest concerns are the work environment, the benefits (I have a family) and the fact that my employment is based on this company keeping its federal contract, which they assure me is very secure.

Yes, they are a contractor, so you are working for them in name but your actual place of employment and work environment will likely not be with them, but at a library they are hiring for. For example, if they contract with EPA libraries, you'd be working at an EPA library, not at their offices. They have a solid reputation as far as I've heard. Yes, they do occasionally get in bidding wars for contracts, so that could happen while you work for them. Ask them when their contract is up for renewal. Usually the benefits are OK for contractors. Not as good as for federal employees, but not bad either. Norm is 10 days vacation, decent health and 5 days sick in the beginning, per year. 401K as well. Ask them about this in the interview.