Brother -
I have been slowly improving our small ranch over the last few years...doing some work as we save up the cash....and have buried 1500 feet of primary power line 5 feet deep and then the same length 2" water main at 4 feet...
The Short Story is: Go Big or Go Home....
Don't succumb to the lure of the lower rental cost of a tool designed to bury irrigation tubing in a suburban lawn or a home-brew or even a purpose-built commercial attachment for your tractor....and for GOODNESS SAKES don't even THINK about a walk-behind unit...that is madness...
You need to bury your water mains deep...don't scrimp...
18" is not a lot of overburden on a 2" water line...the pipe motion / deflection during pressure cycles or ground temperature changes may be enough to dislodge or flex your pipe, allowing enough motion to stress and break the glue joints...pin it down with enough weight...smaller lines of say 3/4" or so might be fine at a shallower depth, but consider that a 2" line at 40psi will exert 250 pounds against a closed valve, elbow or cap. 36" would not be too deep...48" would be better...
I went with a gasketed water pipe for my 2" mains to avoid the issue of glued joints almost entirely....but I had to account for a lot more motion of the pipe in exchange...a little enginerering work...
If you must do this work yourself...it won't easy, but you will save a bundle...
Have your right-of-way well marked with flags, paint, breadcrumbs or whatever...then call "ONE-CALL" or whoever surveys for buried utilities in your area....and let them certify it free of underground utilities....fail to do that and snag somebodies unmarked fiber-optic data line and you will regret it for the rest of your life...
Once you have the "One-Call" certification in hand -
RUN....do not walk....to the nearest sizable town....stop at a decent donut shop along the way and buy the BIG box of assorted sweets...
Find the local equipment rental dealer and schedule delivery of the BIGGEST ride-on trencher they have on the lot for early on the morning you want to do the job....then give the donuts to the crew in the shop and ask them to give you a good lesson on operating the beast....find a machine in the yard you like....one that you can operate confidently and smoothly....specify THAT machine....don't forget to buy a damage waiver....
Well before delivery day, have your pipe glued, pressure tested and laying to one side of the right-of-way...ready to bury...
Make sure you have a good spot to back the delivery truck into...check out EVERY switch and control on the machine....take pictures with your cell phone to show and settle who damaged what....
Get it on....
You will cut more trench faster than you will believe possible....the big machines will chew through hard-pan and roots, dislodge stones and buried trash that will choke a smaller machine....the heavy machine will give you almost perfect control of the depth and allow you to accurately pitch the line if you wish...and leave a level trench bottom covered with fines that will make a perfect bed for your pipe.
If you break the machine....a nice man in a service truck will come and fix it for you...or bring you a new machine....remember and rejoice in the money spent on that damage waiver...
Once the trench is the way you like it, lower your line into the trench and then use the blade on the front of the machine or a box-blade on your tractor to back-fill...
Knock the mud and crud off the machine...park it for the pick-up...have a cold bottle of water handy for the delivery driver...
After you wave goodby to the delivery guy, step back, pull the pin on a cold adult beverage and then admire your work and the roughly $5K - $10K you just saved...
...and next time you are going thru town, drop of a few more donuts off at the rental yard....you may need those folks again...
Be Safe and Good Luck....:thumbsup:
Terry