The pump track is a little hard to find the first time you go there. The street address is 242 Little York-Mount Pleasant Road, Milford, NJ 08848. The track is not visible as soon as you enter the park. Just drive straight back and you will see it on your right. I've heard that it will close for the winter in a week or two. Check out their web site for more info.
http://www2.jorba.org/index.php?title=Alexandria_Pump_Track
http://www2.jorba.org/index.php?title=Alexandria_Pump_Track