Sinkhole progression at the Weeks Island, Louisiana, Strategic Petroleum Reserve (SPR) site Page: 6 of 20
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dence of the now dismantled townsite of the Morton Salt Company, but this history appears unre-
lated to the sinkhole origin.
The relatively small size of the initial sinkhole and lack of diagnostic evidence linking it to
the SPR mine caused little concern at first. Sinkholes have formed at other mines in domal salt
(Neal, 1994), and they also may occur as a result of natural processes (Autin, 1984). The location
near both the edge of the dome and anomalous features in the salt stock, including a salt valley,
suggested an entirely natural origin was possible (Neal, et al., 1993), although Martinez (1992)
insisted from the very beginning that mine-induced factors were likely involved. During the origi-
nal mining, black salt, gas blowouts, and minor brine seeps were noted beneath the vicinity where
the sinkhole developed, and Magorian (1987) later mapped a shear zone just south of the mine
boundary. The latter effectively may have influenced the southerly extent of the original mining.
A watch and wait position was adopted, and in March 1993 fluoroscein dye was placed in
the sinkhole as a means of detecting connections with the underground mine, or to the surface
downdip of the sinkhole. But by mid-1993 it was apparent that the sinkhole was deepening, and
monitoring data suggested that the brine influx into the mine was increasing. The evidence for
increasing dissolution caused sufficient concern by late 1993 to initiate more detailed diagnostic
study, in addition to engineering planning to address actions to decrease the risk of continued oil
storage, and/or relocating the inventory to another site. Safety concerns also necessitated filling
the sinkhole with sand as its depth of more than 12 m (40 ft) and location 15 m (50 ft) from the
main access road had become hazardous.
As plans to move oil were being formulated in early 1995, a second and smaller sinkhole
was identified on the northwest boundary of the mine in a similar geologic and stress-field envi-
ronment that was seen in the first sinkhole. While the second sinkhole was only 4.3 m wide and 3
m deep (14 and 10 ft), its occurrence confirmed the progressive development of processes causing
them and the necessity of expedient mitigation.
A combination of geophysics, drilling, and hydrologic studies were undertaken in 1994 to
provide decisive information needed to establish appropriate action and schedules, consistent with
perceived environmental risks. In addition, salt mechanics modeling and solutioning processes
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Neal, J.T.; Bauer, S.J. & Ehgartner, B.L. Sinkhole progression at the Weeks Island, Louisiana, Strategic Petroleum Reserve (SPR) site, article, November 1, 1995; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc620914/m1/6/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.