Drillers can pour powdered,  inorganic mineral solidification reagent over a slurry pit and mix it in with an excavator or backhoe. CETCO photo.

Even though drill spoils from construction drilling, utility directional drilling, ground sourced heating and cooling, and water well drilling are inherently non-hazardous, options for drilling contractors to dispose of drill spoils are becoming increasingly limited. One alternative is to have a liquid waste disposal company haul the material off, which can be expensive. Another alternative is to try and settle out the material in tanks, which can be minimally effective and time consuming. Centrifuge dewatering works great but requires knowledgeable people to operate such systems. Centrifuge dewatering equipment is expensive and cost can only be justified on very large projects. Solidification can be a viable and cost effective method of dealing with liquid or semi-solid material, and new products and technology are available to ease the burden of drill spoils disposal.

The simple process of solidifying drill spoils involves taking liquid or semi-solid slurry, and then bonding it together with another material so that the end product becomes a solid (no free liquids). The more absorbent a solidification product is, the more effectively that product will perform as a solidifying agent. Wood chips, for example, are frequently used as a solidification agent, but because wood chips are minimally effective as an absorbent, using wood chips as a solidification agent can double the volume of material to be disposed of. The initial price of some solidification agents, such as wood chips, fly ash, cement kiln, dust and sawdust may appear cheap. However, the overall operational cost can be astronomical when you consider costs of trucking the material to the project, trucking the large volume of solidified material away and increased landfill tipping fees.

Untreated slurry is poured from a container on the left. On the right, treated spoils show the absorbency of solidification materials. CETCO photo.

One great product for solidifying drill spoils is a powdered, inorganic mineral formula made from non-biodegradable mineral that is designed specifically for use on such waste. This product can be poured into or across the surface of a waste slurry pit and stirred into the slurry with a backhoe or excavator. The powdered inorganic mineral formula has the ability to absorb seven and a half times its weight in water, therefore calculating dosage requirements is as simple as measuring the density of the drill spoils to be solidified (using a standard mud balance), determining the approximate solids content utilizing simple calculations (7.5 x mud weight – 62.5 = % solids), and then subtracting the calculated solids content to determine the estimated entrapped volume of water. The estimated volume of water is then converted to total weight of water and divided by 7.5 to derive the correct dosage of the inorganic mineral formula solidifying agent. Drill spoils that are higher in density (that is, have more drill solids) require lower dosages of the inorganic mineral formula solidifying reagent.

Another product now available to contractors is a proprietary blend consisting of powered inorganic mineral as well as a super absorbent material that can even solidify clear water with dosages as low as 2 percent by weight. This product can be very cost effective when used with a specially designed mixing unit that precisely meters in the correct dosage. It must also efficiently blend/shear the mixture to maximize utilization of the solidification reagent. The mixing unit will discharge the processed material as a liquid, and within 10 minutes the end product is dry and ready to be back-filled or hauled to a landfill. The processed material can be discharged directly into roll-off boxes or dump trucks, or simply discharged into a burmed area where it can be stockpiled before loading for haul-off or mixed with native soil for onsite disposal. Although the processed material no longer contains free liquids, the material will continually reduce in moisture content and shrink in volume when allowed to set exposed to the sun and wind.

As regulations and restrictions on drill spoils disposal tighten, contractors must become better educated on these regulations and restrictions, as well as the disposal alternatives available.

As previously mentioned, solid-ification can be a viable and cost effective method of dealing with liquid or semi-solid material, and new products and technology are available to ease the burden of drill spoils disposal.  ND