Selling land to government for wastewater project

I live in rural Texas. Recently we received a letter saying that the city wanted to run a wastewater line through our land for a new subdivision. They want to buy only .33 acres out of our 10. The part they want is in a flood plain. It's at the far edge of our property; we'll never do anything with it. They're offering fair market value--better, considering the flood plain issue.

The mortgage company--Bank of America, rot them for many reasons--is holding up the business for 75 days while they think about it. They've tried to order new surveys (not sure if they'll be successful), and I understand that it's possible that they'll claim the money for themselves, or at least that it's up to them to decide if we should get any or just a part.

Does anyone have any experience with this kind of transaction? Any advice? I've held off accepting the purchase price, though I've granted the easement. I was thinking of hiring an attorney in case the presence of one might influence BoA's decision, which sounds totally wrong to me, but this is Texas after all.

Cross-posting to General because I've no idea where to post this.