Regulatory
Citation(s):
78.83.
Surface and coal protective casing and cementing procedures.
(c) The operator shall drill to approximately
50 feet below the deepest fresh groundwater or at least 50 feet into
consolidated rock, whichever is deeper, and immediately set and permanently
cement a string of surface casing to that depth…
Question:
Questions have come up recently about what we
mean by deepest fresh groundwater, as we do not have a numerical
definition. One particularly complicated
aspect of this issue is that concerns can arise on both ends of the
spectrum. For example, the operator of a
public water supply well field where groundwater is characterized by relatively
low total dissolved solids (TDS) water may desire a surface casing set depth that
does not allow cementing across both their aquifer and deeper zones of marginal
water quality (e.g., zones with TDS in excess of 500 mg/L), whereas someone
considering future uses of groundwater in the same area may be of the opinion
that setting surface casing to a depth that isolates only groundwater-bearing
intervals characterized by 500 mg/L TDS or less can’t possibly protect future groundwater
reserves.
What is the appropriateness of casing and
cementing across water-bearing zones characterized by different
chemistries? Are there any scenarios
where setting two water protective strings in succession would be appropriate,
or have such well designs ever been employed?
Is the fact that surface casing strings must be cemented to the surface
sufficient to ensure zonal isolation of water-bearing zones characterized by
different chemistries?
Response:
The SWRO has seen the use of two water
protective strings in certain instances.
The first, shallower casing string is run to the base of currently utilized
fresh groundwater in consideration of water wells in the vicinity of the
drilling location. The second water
protective string is installed to a depth protective of the deepest fresh
groundwater formation locally. The
regulations, however, currently allow one surface casing string to be set to
isolate the deepest fresh groundwater formation from underlying water bearing
zones.