I'd dig the pipe out 20' back on the pond side, pack the dug out area with clay and call it good.

Filling the pipe allows the metal outside of the concrete to rust away, and how do you know water won't seep thru that area?

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).