Page 231 - Trenchless Technology Piping Installation and Inspection

Pr oject Considerations for Horizontal Dir ectional Drilling 195

FIGURE 5.9 Drilling fl uid disposal can be a major operation in Maxi-HDD operations.
(Source: Trenchless Engineering Corporation.)

• Mix with backfill materials
• Transport to landfills

Proper documentation of drilling fluid disposal is usually
required and includes volume removed, results of contamination
testing, property owner agreement, and landfill license (see Fig. 5.9).
In addressing regulatory concerns, it is important to recognize
that HDD drilling fluid is composed typically of water, bentonite,
and drilled spoil. The major component of the fluid is water normally
taken from a waterway or municipal source. For most HDD installa-
tions, the only foreign material introduced to the location is bentonite
(a naturally occurring clay), possibly enhanced with polymers, with
known characteristics and disposal recommendations. Applicable
disposal regulations should be similar to those governing sedimenta-
tion and erosion control, hydrotest water disposal, or general con-
struction spoil disposal.

Recirculation
The primary method of effectively dealing with excess drilling fluid
disposal is to minimize the excess. This is accomplished by recirculat-
ing drilling fluid returns to the extent practical. Recirculation on an
HDD waterway crossing is complicated by the fact that a significant
portion of the drilling fluid returns often occur at the exit point, on
the bank opposite the drilling rig. This requires either two drilling
fluid systems to be utilized or transportation of returns from the exit
point to the drill rig location. Transportation of drilling fluid returns
can be accomplished by truck, barge, or a temporary recirculation
line drilled beneath the bottom of the waterway. Site-specific condi-
tions will determine which system is most advantageous.
Inadvertent Returns
An important HDD task involves management of uncontrolled sub-
surface discharge of drilling fluids. Under ideal circumstances,