most cases, the Agency discourages the sole use of the driven well construction method for

the purpose of installing monitoring wells. This is primarily because of the inability to

collect representative samples of the materials that are penetrated during well installation, and

of the inability to seal the well properly unless an outer casing is driven first. However, if

samplers can be driven in advance of the casing to allow subsurface sample collection, the

driven well method may be a viable well installation option.

6.1.8

Jet Percussion

The jet percussion drilling method uses a wedge shaped drill bit attached to the end of

the drill pipe. Water is forced under pressure down the drill pipe and is discharged through

ports on the sides of the drill bit. The bit is lifted and dropped while rotating. The water is

forced up the annular space between the drill pipe and the borehole wall, carrying cuttings to

the surface. The method is limited to unconsolidated or soft consolidated formations. The

disadvantages of this method include the inability to collect representative samples of ground 

water, soil, or unconsolidated deposits during drilling and the potential for disturbing the

formation.

6.1.9

Decontamination of Drilling Equipment

All drilling equipment that will encounter formation materials (e.g., augers, samplers,

tremie pipes) should at a minimum be decontaminated between boreholes, and in the case of

samplers, between samples. When cross contamination between zones within a single

borehole is a concern, equipment should be decontaminated more frequently. Aller et al.

(1989) provide a comprehensive discussion of decontamination of drilling and formation 

sampling equipment.

The types of drilling and sampling equipment that should be decontaminated (Aller et

al., 1989) include:

Drill bits;

Auger sections;

Drill string tools;

Drill rods;

Sampling equipment (e.g., split spoons);

Bailers used for well development or for the removal of fluids from the well;

Tremie pipes;

November 1992

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