Remediation of a Leaking Landfill Site Problem Set # 4 Remediation of a Leaking Landfill Site river 3 layers MODFLOW’s River Package transient flow remediation design municipal water supply well In layer 3

Objectives Determine the impacts of contamination from the leaking landfill (shown in light blue) at the river and the municipal well. Design a strategy to mitigate the effects of the contamination.

Head Dependent Boundaries Review from Geology 724 Head Dependent Boundaries in MODFLOW Q = C h  River Package Drain Package General Head Boundary (GHB) Package ET Package

River Package Q = C (hR – hijk) where C = (Kv/m) L w hR = head in the river hijk is the head at the node below the river Q = C (hR – hijk) where C = (Kv/m) L w

River Package Q = C (hR – hijk) where C = (Kv/m) L w hR = head in the river Typically the width of the river is smaller than the width of the grid cell. hijk is the head at the node below the river Q = C (hR – hijk) where C = (Kv/m) L w Length of the river within each cell also may vary. Areal view of the river

Q = C (hR – hijk) hijk m RBOT w Gaining River Cell

Q = C (hR – hijk) RBOT Losing River Cell

Q = C (hR – hijk) RBOT Losing River Cell

Percolating River Cell Q = C (hR – RBOT) RBOT Percolating River Cell

Definitions Riverbed Conductance = (Kv/m) wL Leakance = Kv/m Resistance = m/Kv Kv = vertical hydraulic conductivity of riverbed sediments m = thickness of riverbed sediments w = width of the river L = length of the river within the cell

Resistance River with sandy bottom = 1 day Small stream with silty bottom = 1- 10 days Stream/lake in till = 100 days

In PS4, we consider the alternative to “do nothing” as a remediation strategy. This is called “natural attenuation”. Recommended groundwater monitoring network for demonstrating natural attenuation. Source: EPA circular

Initial conditions In Part 3A of PS4, We will use I.C. of the type shown in Figure a. This is done in the initial concentrations window of GWV. Zheng & Bennett