Clamps;

Hand tools;

Steel cable; and

Drill rigs and support vehicles.

The general cleaning procedure for drilling equipment should include washing the

equipment with potable water and/or hot pressurized potable water. For more contaminated

equipment, this procedure should be followed by a wash with non phosphate detergent and a

final rinse with potable water (Moberly, 1985; Aller et al., 1989). Moberly (1985) presents a

list of additional cleaning solutions that may be used to clean drilling and formation sampling

equipment, and provides their specific uses. If formation samples are being collected for

chemical analysis, then the cleaning procedure followed for the samplers should be analogous

to that provided for ground water sampling equipment in Section 7.3.8.

6.1.10

Well Diameter

To avoid the possibility of having to handle large amounts of purged contaminated

water, the Agency recommends the use of either 2 inch or 4 inch diameter wells. If an

owner/operator believes that wells with diameters larger than 4 inches would improve sample

integrity at some or all of the well locations, then he/she should submit substantive

justification before installation of the larger diameter well(s). The use of larger diameter

wells may be necessary where dedicated purging or sampling equipment is used or where the

well is screened in a deep formation. When considering whether to install larger diameter

wells, the investigator should recognize that the quantity of contaminated ground water that

will require proper disposal, and in some settings the time required for well recovery, will

increase with well diameter.

6.1.11

Stratigraphic Control

Adequate stratigraphic control is critical to the proper vertical placement of well

screens. Samples should be collected from boreholes at all suspected changes in lithology.

The deepest borehole drilled at the site should be continuously sampled. For boreholes that

will be completed as monitoring wells, at least one sample should be collected from the

interval that will be the monitoring well intake interval (i.e., screened interval or open

(uncased) interval). EPA recommends that all boreholes be continuously sampled to ensure

stratigraphic control. Borehole samples should be classified according to their lithology or

pedology by an experienced professional in geology. Care should be taken to ensure that

samples of every geologic formation, especially all confining layers, are collected, and that

the nature of stratigraphic contacts is determined.

November 1992

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