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

upgradient direction;

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.

5.2

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.

5.2.1

Introduction

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,

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