Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p31
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 31/117)
Character Range: 433211–436342

at the United States Geological Survey website: http://ny.water.usgs.gov/projects/bgag/intro.text.html.

    8.2.3          Well construction
Monitoring wells should be constructed to an appropriate standard and from suitable materials to ensure that high quality samples can be collected over the projected lifetime of the well. The assessor should ensure that the drilling technique, depth and diameter of the borehole, screen length, well construction materials (screen, casing, filter pack, seals and grout) and headworks design selected are compatible with the monitoring objectives.

For general guidance on monitoring well installation procedures see ASTM D5092-04.
A decision on the appropriate means of constructing monitoring wells involves consideration of a number of factors including the hydrology, geology and geochemistry of the formation, the nature of the contamination, the chemical resistance and leaching properties of the construction materials, the cost and the necessity to maintain the integrity of samples. Further information may be found in EPA Victoria (2006), SA EPA (2007), EA (2006) and ASTM D 5092-04.

There are several standard drilling methods available including hollow-stem auger, air and mud rotary, cable tool, sonic and direct push. The general suitability of these techniques for a range of ground conditions is discussed in EA (2006). The assessor should consider drilling methods that minimise the introduction of drilling additives wherever possible.

Certain drilling techniques can cause smearing (for example, rotary auger) or compaction (cable tool) of borehole walls and may also promote transport of geological formation materials and drilling fluids into different aquifer zones. In a worst-case scenario, this can result in almost complete blockage of the well screen resulting in non-representative groundwater samples when the boreholes are monitored.

Drilling fluids are used to clean and lubricate the drill bit, to remove rock cuttings from the borehole and to keep the borehole open during drilling. These may include air, water and specific drilling mud formulations or native clay slurries. Drilling fluids can have a range of effects on groundwater quality such as the following:
    * air may severely disturb hydrochemical profiles through oxidation processes, e.g.  oxidation of ferrous Fe2+ to ferric Fe3+
    * water may dilute or flush groundwater near the borehole and cause precipitation of minerals, thereby blocking or obstructing groundwater pathways
    * mud may invade the permeable formations and block pathways to the well screen.
Care should be taken to avoid contamination of the borehole and surrounding geology during drilling and construction of the well through the inappropriate use of lubricants, oils, grease, solvents, or materials with incompatible coatings. If the groundwater quality is altered, the samples obtained may not be representative, leading to uncertainties and potential errors in the assessment. Some considerations for material selection (EA 2006) include:
    * the chemical environment in which the installation is placed –