For an Oregon example, witness the close correlation between rural development in the Bear Creek Valley of Jackson County and the location of the sewer lines of the Bear Creek Valley Sanitary Authority. The sewer lines explain, in large part, why the boundary was drawn to include so much Washington County farmland. Development will surely follow. They are expensive to build and maintain. Clackamas County understands the lesson.
None lies within an urban growth boundary.
The systems experience operational and maintenance problems and failure. Many private systems do fail. The Donald interchange on Interstate 5, midway between Portland and Salem, lies outside any urban growth boundary. Three of the four quadrants of the interchange are developed in highway commercial uses. Each has been served by a small, private wastewater system.