Once upon a time in these parts, the ground would freeze in the winter to a depth of about five feet. Accordingly, people buried their septic lines and drain-fields six feet deep. Then global warming began and annoyingly made it drier in the winter here, meaning less snow cover. Without the insulating blanket of snow the ground began to freeze seven feet deep causing untold misery of drains frozen for weeks on end. It became evident that septic lines should be buried eight feet deep however, in the meantime, concern had also arisen about the danger of groundwater contamination from deeply buried drain-fields, and recommended or regulated practice had changed to shallow or mound-system drain-fields. The combination of a deep line and a mounded drain-field requires a lift pump. Said pump is obviously, you know, mission-critical.
Nobody likes these things due to the expense and reliability issue, but the idea particularly irked the designers of this cottage - to put such a high-tech, energy-sucking thing into what was supposed to be a low-energy mostly-natural building. So they ended up putting both the line and the drain-field shallow so that it would gravity drain. There have been freezing problems in both winters since it was installed. Insulating it by placing large straw bales on top of the line was successful the first time but not the second time, and they had to be removed in the spring in order to allow the ground to warm. This is a lot of wasted motion.
This past spring, the installation of an electric heating tape (gutter de-icing cable) saved the day. These things however also suck a lot of power, six watts per foot or so and the line is 170 feet long. In order to detect when de-icing is needed, today we installed several temperature sensors alongside the septic line.