Erosion and Sediment Pollution Control Program Manual.pdf

GEOTHERMAL WELL DRILLING
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363-2134-008 / March 31, 2012 / Page 351
Drilling, testing, and development of high
capacity geothermal wells can, if not
properly managed, result in significant
sediment pollution to receiving surface
waters. This is especially true where well
fields are installed, either during initial
construction or as a retrofit to an existing
site. Providing access to drill sites, as
well as staging areas, should be
addressed using the standards provided
in Chapters 3 and 4.
The large volumes of water produced
from each well can be quite turbid
depending upon aquifer and surface
conditions. Therefore care should be
taken to protect surface waters during
construction and development of
geothermal wells.
A fact sheet describing typical erosion
control BMPs during well drilling has
been developed by the Department and
is included in this manual as Appendix K.
The standards set forth in that fact sheet
should be incorporated into all water well
drilling operations, including geothermal
wells. Since the volumes of water
produced by geothermal wells are
typically much greater than for water
supply wells, some additional precautions may be necessary depending upon
discharge rates, sediment content, and site conditions.
On sites where a sediment basin or sediment trap is available to receive the discharges, these may be
used as long as the water level within the basin or trap does not rise above the sediment clean-out
elevation. Where sediment basins or traps are not available, control BMPs specific to the well drilling
should be provided. Stormwater detention and/or retention ponds that are functioning as such may not
be used as sediment removal BMPs for well drilling. Where flocculants are needed to meet effluent
requirements, they may be approved on a case-by-case basis.
It is recommended that a test well be drilled with appropriate sediment removal BMPs in place in a
proposed well field to determine the anticipated flow rate for each well in the well field. BMPs for the
well field should then be designed to provide treatment for the total number of wells being drilled at any
one time (i.e. test well flow rate X number of wells). It should be noted that flow rates will likely vary
significantly from one well to the next. Therefore, the capacity of the BMPs provided should exceed the
calculated required capacity by at least 1.5 times. Large well fields may require several test wells.
Designers should meet with conservation district staff prior to submitting applications that involve
geothermal well testing and drilling in order to discuss site constraints and to develop an appropriate
E&S plan. It is also recommended that well drilling contractors meet with conservation district prior to
beginning drilling operations in order to discuss proper implementation of the E&S plan.