GENERAL33297

• Permit No: M1983194
• IBM Index Class Name: General Documents
• Doc Name: COVER SHEET 3 TEXT CHANGES TO DRAFT EIS
• Media Type: D
• Archive: No

3. TEXT CHANGES
hydrologic system have not been measured in actual field
conditions, monitoring of the perchal and the A-groove
of the upper aquifer, and the B-grocrve and base of the
lower aquifer will be required prior to and during mining
operations to verify predictions and quantify impacts. Lower
aquifer zones will require more frequent monitoring than
upper aquifer zones until such time that subsidence is detected
and quant~ed. At such time, the authorized officer may
require more frequent monitoring in the upper aquifer.
4.4.5 Groundwater QuaBty
Potentially significant impacts to groundwater quality
would occur az the result of expected mine cavity roof
collapse under the commercial-state alternatives. As
predicted in this analysis, the collapse zone would extend
53 feet above each cavity up through the dissolution surface
(Rock Quality section). This would establish a physical
connection between the base of the lower aquifer and the
brines in the cavities resulting in an increase in the area
at the base of the lower aquifer in contact with saline
minerals. This could significantly degrade the water quality
al the base of the lower aquifer by increasing the total
dissolved solids concentration.
4.4.5.1 Common to AU Alternatives
The most significant potential impact to water resources
from the sodium mice operations would be to groundwater
quality. This impact could occur as a result of brine leaking
through well casings, improper hydreiilic seal between the
mine cavity and the lower aquifer, and through breachirg
of a solution cavity during collapse of the mine zone. There
is also the slight potential that the perched aquifer would
be contaminated by percolation from dte septic system leach
field. However, because the Surface nxharge and permea-
bility of the Uinta Formation on lease ee low and the distance
from the ]each field to water in the perched aquifer zone
of the upper aquifer would be 300 to 400 feet, the risk
of contamination to the perched aquift:r is very low.
Contamination of the aquifers could occur from the
breaching of a well casing because of corrosion or improper
installation and failure of the hydraulic seal between the
ravines and the lower aquifer. If this happened, saline brines
could leak into the groundwatu system. WRC's proposed
leak detection system far the production wells, az described
on page 2-8 of the draft EIS, Section 2.2.12.2, should detect
any leak in excess of 3 gallons per minute (Jones 1985).
f(a leak were detected, use of the welt would be suspended
until repaired, and significant impacts to the quality of the
groundwater should not occur.
Casing leaks into the upper aquifer are not expected to
be a problem, because the proposed opereting prooedtues
would not allow mining fluids to rist: up into the annular
region of the casing within the upper aquifer.
Casing leaks (less than 3 gpm) in the upper part of the
lower aquifer would be undetected by WRC's proposed
groundwater monitoring system, batause it would only
measure the base of the lower aquifer. Over the life of
a cavity, this could cause the introduction of a significant
amount (about lacre-foot) of brine into the lower aquifer
of the groundwater system. This potential impact net:essitates
the monitoring of the &groove and base of the lower aquifer.
This will ensure that all casing leaks are detected and that
remedial actions, such az well repair, ran be taken before
significant impacts to groundwater quility occur.
WRC believes that the likelihood of a physical connection
occurring between the mine zone and the groundwater
system would be low because of the presence of the "rubber
beds" and competent oil shale between the mine zone and
the base of the aquifers. Although the "rubber beds" may
have some mitigative effect, they are thin and would weaken
when subjected to thermal conditions of the solution mining
process, and therefore, would probably not be effective at
sealing the mine cavities from the baze of the lower aquifer
if roof collapse aceurted. This analysis predicts that roof
collapse would take place in a gradual manner over all
cavities under commercial-scale development (see the Rock
Quality section in the draft EIS).
Assuming this, if hydraulic communication were
established between the mine cavities and the lower aquifer,
the brines within the cavities would naturally tend to remain
isolated from the water in the base of the lower aquifer,
because the brines would be more dense and more viscous
than these waters. Each collapsed cavity would be a steep
sided bazin in the base of the saturated zone, causing the
brines to remain ponded in the ravines. The water of the
lower aquifer would tend to stratify with the brines in the
cavities. Mixing of the lower aquifer and brines would occur
by continuous groundwater flow across the cavity tops,
natural dissolution, and diliusion. These processes, which
would lake place at very slow rates, would cause an increase
in total dissolved solids at the base of the lower aquifer.
More significant impacts to the quality of the lower aquifer
could also occur in the unlikely event of a catastrophic
or rapid roof collapse. This would take place over several
hours and could be fast enough to cause turbulent conditions
within the collapse zone. These conditions could allow for
a more rapid mixing at the base of the lower aquifer with
the brines in the cavity. Over the very long term (200 to
1,000 years), this could cause an increase in dissolved solids
to the White River by az much az 5.0 mg/I or a maximum
of I percent for the 500,000 TPY Alternative. This would
be a total of 10,270 tons per year contributed to the Colorado
River or an increase of.935 mg/I at Imperial Dam (Progress
Report No. 12, USDI, Bureau of Reclamation 1983).
However, az previously stated, this analysis predicts gradual
roof collapse, not rapid roof collapse.
3-17