techniques for monitoring well installation taking into consideration hydrogeologic settings

and the objectives of the monitoring program.

The Agency has developed basic guidance to assist in the selection of drilling

procedures for installing monitoring wells pursuant to 40 CFR Part 264, Subpart F, as

follows:

Drilling should be performed in a manner that preserves the natural properties

of the subsurface materials;

Contamination and/or cross contamination of ground water and aquifer

materials during drilling should be avoided;

The drilling method should allow for the collection of representative samples of

rock, unconsolidated materials, and soil;

The drilling method should allow the owner/operator to determine when the

appropriate location for the screened interval has been encountered;

The drilling method should allow for proper placement of the filter pack and

annular sealants. The borehole should be at least 4 inches larger in diameter

than the nominal diameter of the well casing and screen to allow adequate

space for placement of the filter pack and annular sealants;

The drilling method should allow for the collection of representative ground 

water samples. Drilling fluids (including air) should be used only when

minimal impact to the surrounding formation and ground water can be ensured.

The following guidance applies to the use of drilling fluids, drilling fluid additives,

and lubricants when drilling ground water monitoring wells:

Drilling fluids, drilling fluid additives, or lubricants that impact the analysis of

hazardous constituents in ground water samples should not be used;

The owner/operator should demonstrate the inertness of drilling fluids, drilling

fluid additives, and lubricants by performing analytical testing of drilling fluids,

drilling fluid additives, and lubricants and/or by providing information

regarding the composition of drilling fluids, drilling fluid additives, or

lubricants obtained from the manufacturer;

The owner/operator should provide the Regional Administrator with a

discussion of the potential impact of drilling fluids, drilling fluid additives, and

November 1992

6 2