I'd dig test holes in as many areas as you can. Take a look at Mike Otto's article in the latest issue of Pond Boss magazine. That will give you a good reason why to dig as many test holes as you can.

www.hoosierpondpros.com

[Linked Image from lh6.ggpht.com]
http://www.pondboss.com/subscribe.asp?c=4
3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).