I want to estimate a trenching job to do with my Kubota KX91-3 mini-excavator. The job is to dig trenches of up to 1,500 feet in length, about 12 inches deep, 12 inches wide for perforated drain pipe, and washed gravel. The depth should be as close as I can reasonably get with the machine, but I know that some manual adjustments will be necessary along the way to be very accurate. The area is actually a ball field at a school, so accessibility is very good, and the only obstacle might be an irrigation system. The ground in the area is clay, and usually hard packed. Since is not the primary work that I do, I need some advice about estimating it. How many hours should it take to dig the trenches with my machine? I will very much appreciate any feedback from anyone that has experience with such work. Thank you.