Non-PRO English to Chinese Tech/Engineering Mining & Minerals / Gems

(viii) Ore pass: Excavation and construction of two ore passes: (1) From 13 1/2L to 19L with opening at 13 1/2L, 15L, 16 1/2L and 18L. (2) From 18 1/2L to 22L with opening at 18 1/2L and 21L.
(ix) Waste rock pass: Excavation and construction of a waste rock pass from 13 1/2L to 22L with opening at 13 1/2L, 15L, 161/2L, 18L 19 1/2L and 21L.
(x) Second outlet: A second outlet having finished size of 3.5m X 3.5m is to be constructed from 15L to 221/2L with openings at 16 1/2L, 18L, 191/2L, 21L and 22 1/2L. The second outlet shall be completed and furnished with sinking bucket hoisting arrangement with rigid guide.

This is a shaft design document. Does"L" stand for" Liter" here? I am totally confused with it. How to translate the above like " at 13 1/2L, 15L, 161/2L, 18L 19 1/2L and 21L" into Chinese?

Many thanks! ( 13 1/2L is 13+1/2L , and 18 1/2L is 18+1/2L )