I have a buried water line with a leak in it and I want to locate approximately where it is. The line runs uphill to a storage tank. I've isolated the leak to one section of the pipe. The diameter of the pipe is 1.5" and the isolated section is about 300 feet long. If I measure the water pressure at the bottom of the pipe it is at 42 psi. This is after letting the pipe sit overnight with no water pressure coming into it from above so I assume that all the water in the pipe above the leak has drained out. Is it possible to tell roughly how many feet in elevation the leak is above the bottom?
IF all of the water above the leak point has indeed completely drained away, and the water is completely stationary throughout the pipe's entire length (those are important "if"s), then your problem is quite straightforward!
With the density of water, we can easily come up with a direct relation between water height (regardless of the horizontal path taken to get there) and the corresponding pressure at the bottom.
Check out this table for a quick reference: http://www.engineeringtoolbox.com/hydrostatic-pressure-water-d_1632.html
Looks like the leak should be just under 98 feet up (vertically). Of course, you'll still have to work out how that number maps to a position on the hill!