Geosciences –
Geophysics, Seismology and Engineering

expanded PGDP & vicinity geophysical data coverage and successfully applied two iterations of state-of-the-art data processing methods to  define the upper and lower surfaces of the Lower Continental Deposits comprising the Regional Groundwater Aquifer (RGA).  Both projects re-processed data collected by Langston (1998) and collected additional data on focused targets.

Through the additional data collection and use of two iterations of improved analytical software the Projects: 1) correlated shallow subsurface displacement  features with the lateral extent of PGDP’s off-site Northwest and Northeast Plumes in the Regional Gravel Aquifer; 2) Utilized electrical resistivity along seismic lines to identify areas of decreased resistivity that correlate with structural features  3) Utilized electrical resistivity to identify a very shallow area of lower resistivity coincident with contaminated groundwater seep discharges in Little Bayou Creek; and 4) Applied a birefringence approach to identify ‘fast’ and ‘slow’ flow directions in the RGA material (see Al-Mayahi, 2013).

The Code of Federal Regulations (CFR), Subtitle D, Title 40, Part 258, subpart B (258.13) requires that disposal facilities (such as the C-746-U landfill and possible expansions) be located more than 200 feet from a fault that has had surface displacement within Holocene time (i.e., the past 11,000 years).

The planned expansion is located directly north of the present-day C-746-U landfill. Previous geophysical studies (Blackhawk 2003) within the PGDP site and vicinity identified possible northeast-striking faults beneath the proposed landfill expansion (Below).  Prior to this investigation the existence, locations, and ages of these inferred faults have not been confirmed through independent subsurface exploration.

The Holocene Investigation geologic assessment included (a) review of relevant geologic and geotechnical data from the site vicinity, (b) analysis of detailed aerial photography, (c) field reconnaissance of the site vicinity and other important sites of previous investigations, (d) collection and stratigraphic analysis of 86 subsurface sediment cores, (e) laboratory chronological (age-dating) analyses, and (f) preparation of this report. These activities were completed at or above the accepted standard-of-practice for geologic investigations in the mid-continent region; overall this investigation represents an effort that exceeds previous levels of investigation for site-specific fault-rupture assessments in the mid-continent.

The investigation was completed as a collaborative effort involving local, regional, and national paleoseismology subject-matter experts; William Lettis & Associates, Inc., Earth and Environmental Sciences (Geology) Department of the University of Kentucky, and the University of Chicago.

Technical peer review of the approach, methods, preliminary results and final conclusions of this study have been provided by geoscientists and paleoseismic technical experts with the Kentucky Geological Survey, the Illinois Geological Survey, the University of Memphis, the University of Illinois – Champaign, Science Applications International Corporation (SAIC), and M. Tuttle & Associates.

Based on extensive data collection and analysis followed by paleoseismic subject-matter-expert review there is NOT evidence of Holocene Displacement in the study area, i.e. displacement of materials within the last 11,000 years.  If late Quaternary displacement has occurred beneath the site, the most-recent displacement occurred following deposition of the Unnamed Intermediate Silt between approximately 53,600 and 75,500 years ago.

The Holocene Investigation Report presents the findings of a fault hazard investigation for a proposed expansion of the C-746-U landfill located at the Paducah Gaseous Diffusion Plant (PGDP), in Paducah, Kentucky.

the Great New Madrid Earthquakes of 1811-12.  More than 1,000 earthquakes occurred during those 2 years with the strongest up to magnitude 8.  The ground liquefied, sand boiled to the surface, the mighty Mississippi flowed backwards and the bootheel of Kentucky, across the river from New Madrid, raised and fell depending upon where you were standing.  The largest earthquakes of 1811-12 remain the strongest earthquakes to have occurred in the continental U.S. away from plate margin subduction zones.

The PGDP and the city of Paducah are located 55+ miles northeast of New Madrid, Mo. and straddle 3 known seismic zones: the Wabash Valley Seismic Zone (WVSZ), Fluorspar Area Fault Complex (FAC or FAFC) and the NMSZ.

The FAC, which is the zone in closest proximity to the PGDP, has not been active in the last 55,000 years.  Portions of the WVSZ have been active in the last 6,000 years and the  NMSZ remains active today. PGDP’s location relative to known seismic zones prompted the 1988 installation of seismic joints in enrichment process piping to ensure system integrity in the event of modern seismic events in the region.

For public officials, engineers, seismic scientists, and local folk, intrigue may be replaced by the challenges of defining and understanding the history and occurrence of earthquakes in the region, their likelihood of recurrence, and the bedrock to surface response at given locations.  Defensible and actionable characterization of the seismic hazards and resultant risks inherent to specific locations remain a challenge for all, especially the technical and regulatory community.

KSSMN can monitor any earthquake with a magnitude 2.0 or larger within Kentucky and includes monitoring of significant blasts, mine collapses, and explosions.

Data from 12 seismic stations are continuously recorded as part of the “near” real-time monitoring system.  The system “triggers” to record events of note to be reviewed.  The real-time network utilizes the Kentucky Early Warning System (KEWS) for data transmission.

Data from remaining stations are downloaded weekly via modem (weekly) or are downloaded manually on a quarterly basis and reviewed.

KSSMN recorded numerous earthquakes since January 1, 2006. Instruments are available to rapidly begin aftershock studies for large events.

The 1900-foot deep CUSSO installation located at Sassafras Ridge, near the “bootheel” of Kentucky, is instrumented to monitor three (3) subsurface horizons.  Data collected from CUSSO will be used to refine models used by architects and engineers to design ground-motion safety features.

After 15 years of operation, CUSSO received maintenance upgrades in 2020 and 2021.  The KGS Hazards Section publishes semi-annual reports summarizing CUSSO and network data collection efforts and research findings.