The pipeline in the previous problem has been decommissioned. A Phase II environmental site

assessment $($ESA$)$ was completed to delineate the horizontal and vertical extents of petroleum

hydrocarbon $($PHC$)$ contamination in soil that exceeds the Alberta Tier $1$ Soil Remediation Guidelines

$($Alberta Environment and Parks, $2022)$ for natural land use and coarse$-$grained soil. The PHC

contamination in soil extends from ground surface to $4$ metres below ground surface $($mbgs$).$ The water

table is at $3$ mbgs and the associated aquifer has an average hydraulic conductivity of $104$ m$/$s$.$ The top

of a clayey soil underlying the sandy soil is at $8$ mbgs$.$ Since the site is remote, the environmental

engineer recommends on$-$site, ex situ remediation of the PHC$-$contaminated soil and proposes a $30-$m

long, $10-$m wide, and $4-$m deep soil excavation.

Should the walls of the excavation be cut vertically or sloped? Provide a rationale and brief

instructions on the slope angle.

Using the guidance in Section $13\mathrm{.}8$Estimation of Steady$-$State Discharge Flow Rate of the book

by Cashman and Preene $(2021),$ estimate the steady$-$state rate of groundwater infiltration to the

excavation in m$3$

$/$day$.$ Assume that an objective is not to have ponded groundwater at the base of the

excavation. State all references, assumptions, and rationale.