Waste management areas located above aquifers in which ground water flow
directions change seasonally;
Waste management areas located close to a property boundary in the
Waste management areas containing immiscible contaminants with densities
greater than or less than water;
Waste management areas located in areas where nearby surface water can
influence ground water elevations (e.g., river floodplains);
Waste management areas located near intermittently or continuously used
production wells; and
Waste management areas located in structurally complex areas where folded
strata or fault zones may modify flow.
In these situations, a monitoring well network in which the wells are located in a
circular pattern or on all sides of the waste management unit may be necessary.
Background wells should be located far enough from waste management units to avoid
contamination by the units. In the event that background wells become contaminated by a
release from the waste management unit(s), new background wells that will not be affected by
the release should be installed.
Ground Water Monitoring in Aquifers Dominated by Conduit Flow
As described in Section 4.3.1, conventional ground water hydrology considers aquifers
to be porous media having a well defined water table or potentiometric surface. The
following sections provide a strategy for conducting ground water monitoring in
hydrogeologic settings where conduit flow predominates.
Ground water monitoring regulations of Subpart F require a ground water monitoring
system consisting in part of monitoring wells installed at the hydraulically downgradient limit
of the waste management area(s) that are capable of detecting contamination that has migrated
to the uppermost aquifer. For a facility to receive an operating permit, the ground water
monitoring system at the facility must meet the requirements of 264.97 (unless the owner or
operator is exempted from the requirements under 264.90). While meeting these criteria is
typically not problematic in aquifers dominated by flow through porous media, it can be
difficult in aquifers dominated by conduit flow. In aquifers dominated by conduit flow,