FRTR Field Sampling and Analysis Technologies Reference Guide

3 ACCESS TOOLS

3.1 DRILLING METHODS - UNCONSOLIDATED FORMATIONS

3.1.1 HOLLOW-STEM AUGER

Use:

Most commonly used method for well installation in unconsolidated materials. Rigs are capable of reaching most sites and a wide variety of sampling or measurement instruments can be utilized.

Description:

The hollow-stem auger column rotates as it drills into the ground and is designed to push soil up and out of the borehole along the outside of the auger. The auger itself is driven either mechanically or by a hydraulically-powered drill rig. A plug is placed through the auger to prevent soil from rising through the hollow portion of the stem. Samples are retrieved by retracting the plug and lowering the sample collection tube (see Tubes) through the auger. Casings and screens for access holes can be placed in the hollow stem to prevent the borehole wall from collapsing and to ensure discrete interval samples. Casings can also be used to isolate near-surface contamination while drilling continues using a smaller diameter auger.

Analytes:

1. Non-Halogenated VOCs	5. PAHs	9. Inorganics
2. Non-Halogenated SVOCs	6. Pesticides/Herbicides	10. Explosives
3. Halogenated VOCs	7. Metals	11. TPHs
4. Halogenated SVOCs	8. Radionuclides

Media:

Soil:	Ground Water:	Surface Water:	Gas/Air:
MINIMUM	MODERATE	Not Applicable	MAXIMUM

Hollow-stem augers allow for a variety of soil core sampling methods. This method does not require the use of drilling fluids or lubricants and allows for the installation of casings and screens prior to removal of the auger, ensuring minimum impact on soil samples. Formation waters can be sampled during drilling by using a screened lead auger or advancing a well point ahead of the auger. However, there is a potential for vertical mixing of formation water and geologic materials (see limitations).

Maximum Depth:

Up to 100 feet.

Production Rate:

Sample is available after a short amount of time. Setup time is relatively quick.

Investigation Derived Waste Volume:

Large volume of waste.

Technology Status:

Commercially available and routinely used field technology.

Certification/Verification:

Technology has not participated in CalEPA certification and/or CSCT verification program.

Relative Cost per Sample:

Mid-range expense. Usually less expensive than rotary or cable drilling (complete kits range from $2,500 to $3,000). The following cost guidance is provided for samples to a 100-foot depth:

2 inch spoon sample:	$10-$15/sample
3 inch spoon sample:	$25-$35/sample

Limitations:

Cannot be used in consolidated formations.
Potential loss of volatile compounds.
May be difficult to seal the annular space between the well casing and the formation to prevent contaminants from moving upward or downward to uncontaminated areas. Improper selection and placement of annular seal materials can result in chemistry alteration of ground water samples, plugging of the filter pack and/or well screen, and cross-contamination between water-bearing units that have not been adequately isolated.
Pressure equalization of water-bearing sands or silts and "flowing" or "heaving" of these fluid-like materials into the hollow-stem auger column can be a problem requiring use of fluid in the hollow auger to equalize the pressure head and keep the intrusive fluid-like materials from entering the hollow auger.
Soil samples collected from auger flight are "disturbed" making it difficult to determine the precise depth of sample.
Difficult drilling in extremely dry, fine materials.
Hollow-stem auger drilling is difficult in saturated soils and soils containing very coarse gravels, cobbles, or boulders.

ASTM Standards:

D 5784 - 95

Guide for Use of Hollow-Stem Augers for Geoenvironmental Exploration and the Installation of Subsurface Water-Quality Monitoring Devices

Sample Access/Collection Matrix

Sample Analysis Matrix

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