HDD Tech: Getting Fluids To Pass The Paint Test

By George M. Dugan, Regional Manager, CETCO Drilling Products | September 2008 Vol. 63 No. 9

As if horizontal directional drilling contractors do not have enough issues to contend with in performing the contracted tasks, cleanup of the drilling operation is becoming increasingly difficult because of issues associated with the disposal of drill spoils.

This author has actually received several phone calls from drilling contractors who were sitting in the back seat of police cars for illegally dumping/discharging used drilling fluid.

Disposal issues may not be a big problem for contractors installing residential waterwells in rural communities, but can be a nightmare for large horizontal directional drilling contractors. They often have multiple drill crews working in heavily populated areas and constantly struggle to find environmentally responsible yet cost effective methods to dispose of drill spoils.

Landfills are not allowed to receive material containing free liquids, determined by a Paint Filter Test. Material is placed in a paint filter and if there are no liquids dropping out of the filter after five minutes, the material is considered to have no free liquids. Drill spoils containing free liquids can wreak havoc on a landfills leachate collection and treatment system, and can bog down trucks and other machinery operating in the facility.


There are several options for getting drill spoils to pass a Paint Filter Test such as separating the solid phase from the liquid phase (dewatering), or solidifying the entire volume of material.

Centrifuge dewatering (separating the liquid phase from solids) is one method of processing leftover drilling fluid, and is currently used on some oilfield drilling operations as well as large HDD river crossings. Liquid/solids separation enhancement chemicals, such as those used for pH adjustments, coagulants and flocculants, are introduced into the drill spoils, which cause the solid particles to clump together into larger aggregates to improve the liquid/solids separation process. The material is then introduced into a mechanical separation device such as a horizontal decanting centrifuge, which spins at speeds high enough to exert as much as 3,000 times the force of gravity on the material in order to facilitate liquid/solids separation.

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