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.
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.
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
6 15






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