A new 24" pipeline is installed with a depth to invert of 5 feet. The 7,500 foot long trench will be excavated 18 " wider than the pipe on each side. The trench will be overexcavated by 6 " for a layer of sand bedding. What is the total volume of excavated material in cubic yards?

Step 1 ：Convert all measurements to the same unit, feet. The diameter of the pipe is 24 inches, which is 2 feet. The trench is 18 inches wider than the pipe on each side, which is 1.5 feet on each side. So the total width of the trench is 2 feet (pipe width) + 1.5 feet (extra width on one side) + 1.5 feet (extra width on the other side) = 5 feet.

Step 2 ：The depth of the trench is 5 feet (to the invert of the pipe) + 0.5 feet (for the sand bedding) = 5.5 feet.

Step 3 ：The length of the trench is 7500 feet.

Step 4 ：Calculate the volume of the trench by multiplying the length, width, and depth. This gives a volume in cubic feet.

Step 5 ：Convert the volume from cubic feet to cubic yards, since 1 cubic yard is 27 cubic feet.

Step 6 ：The total volume of excavated material is \(\boxed{7638.89}\) cubic yards.