Additional casing diameter selection criteria include: 1) drilling or well installation method

used, 2) anticipated depth of the well and associated strength requirements, 3) anticipated

method of well development, 4) volume of water required to be purged prior to sampling, 5)

rate of recovery of the well after purging, and 6) anticipated aquifer testing.

6.2.5

Casing Cleaning Requirements

Well casing and screen materials should be cleaned prior to installation to remove any

coatings or manufacturing residues. Prior to use, all casing and screen materials should be

washed with a mild non phosphate detergent/potable water solution and rinsed with potable

water. Hot pressurized water, such as in steam cleaning, should be used to remove organic

solvents, oils, or lubricants from casing and screens composed of materials other than plastic.

At sites where volatile organic contaminants may be monitored, the cleaning of well casing

and screen materials should include a final rinse with deionized water or potable water that

has not been chlorinated. Once cleaned, casings and screens should be stored in an area that

is free of potential contaminants. Plastic sheeting can generally be used to cover the ground

in the decontamination area to provide protection from contamination. Aller et al. (1989)

describe the procedures that should be used to clean casing and screen materials.

6.3

Well Intake Design

The owner/operator should design and construct the intakes of monitoring wells to (1)

accurately sample the aquifer zone that the well is intended to sample, (2) minimize the

passage of formation materials (turbidity) into the well, and (3) ensure sufficient structural

integrity to prevent the collapse of the intake structure.

6.3.1

Well Screen

The goal of a properly completed monitoring well is to provide low turbidity water

that is representative of ground water quality in the vicinity of the well. Although wells

completed in rock often do not require screens, the majority of monitoring wells installed for

RCRA purposes are completed in unconsolidated sediments.

6.3.1.1

Screen Length

The selection of screen length usually depends on the objective of the well.

Piezometers and wells where only a discrete flow path is monitored (such as thin gravel

interbedded with clays) are generally completed using short screens (2 feet or less). To avoid

dilution, the Agency prefers that well screens be kept to the minimum length appropriate for

intercepting a contaminant plume, especially in a high yielding aquifer. The screen length

should generally not exceed 10 feet. If construction of a water table well is the objective,

either for defining gradient or detecting floating phases, then a longer screen is acceptable

because the owner/operator will need to provide a margin of safety that will guarantee that at

November 1992

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