"The engineer may need elevations referenced to mean sea level (MSL) because it is required by local government or he/she needs to compare the existing elevations to local flood maps and so on.
Below is a link to NGS's data maps with horizontal…"
Safety should be your priority
Canada should have some type of safety requirements for excavation, such as shoring and/or trench slopes, which would permit someone to enter the work area safely.
If not, my suggestion is to have the pipe…"
"It may be the position of the satellites at the time of observation. If the satellites orientation are near the horizon you will get higher error for elevations. Check your PDOP (position dilution of precision)"