I did spread the dirt from the walkway excavation under several of the
Spruce trees

Consider the possibility that adding soil beneath the trees caused/contributed
to their problem:

http://www.msue.msu.edu/imp/modzz/00001629.html

"Raising or lowering the grade of the root zone during
construction injures plants. Lowering the grade removes
part of the root system. Raising the grade decreases the
movement of air and water into and out of the root zone.
Piling soil deeply around the aboveground portions of the
trunk can lead to rots."

...."Dieback can occur quickly or take several
years, depending on the severity of the root injury or
altered root environment...."

Another article from "Western Arborist" magazine, regarding the symbiosis of
mycorrhizae with many tree species, including spruce, states: "Do not allow
soil addition (grade change). Even as little as 2 or 3 inches of soil added on
top of original grade can weaken the roots/mycorrhizae enough to predispose the
tree to disease."

See: http://tinylink.com/?cc9EUm1KD6