Technical Memorandum- OK.ERFO.10301(1).Kerr Reservoir.2020.FINAL.PDF

To: Dorothy Eisenbraun, Project Manager, CFLHD, Lakewood CO

From: James M. Arthurs, Geotechnical Engineer, CFLHD, Lakewood CO

Through: Marilyn D. Dodson, Lead Geotechnical Engineer CFLHD, Lakewood CO

Subject: Evaluations and Recommendations for the Kerr Reservoir Powerhouse Parking Lot, Le Flore County, Oklahoma, OK ERFO RS KERR 10301(1)

1 PROJECT BACKGROUND INFORMATION

This geotechnical memorandum presents the field evaluation results and recommendations for the reconstruction of the Robert S. Kerr Reservoir Powerhouse Parking Lot. The facility was damaged during high flow events along the Arkansas River during the spring of 2019. Repairs are planned as part of the Emergency Relief for Federally Owned Roads (ERFO) program.

The Kerr Reservoir Powerhouse Parking Lot Project is in La Flore County, Oklahoma, within U.S.

Army Corps of Engineers (USACE) land (Figure 1). The site is located approximately 8 miles south of the City of Sallisaw. The parking lot is located on the south bank of the Arkansas River, immediately downstream of the Robert S. Kerr Dam. Based on discussions with USACE personnel, and interpretation of the failure areas, we understand that high flows eroded and damaged the asphalt paved parking lot and related improvements.

Traffic or daily usage counts are not available, but are assumed to be low based on the capacity of the parking lot. The lot is generally used for fishing access. At the time of the initial site visit, the river access road that extends from the parking lot northeast towards U.S. Highway 59 was closed.

Guardrail and riprap throughout the area was also damaged during the high flows.

Technical Memorandum

Date: July 22, 2020

Figure 1:- Project location map.

2 GEOLOGY

2.1 Regional Geology

The site is located in the Arkansas Valley Section of the Ouachita Province. This area is located between the Ozark Mountains to the north and the Ouachita Mountains to the south (Foti, 2019).

The Arkansas River is the major geographic feature of this Section. Dissected plateaus and folded ridges are common features, along with isolated steep sided mesas. Topographic relief in this area is generally low.

The site is mapped as underlain by Quaternary Alluvium described as containing gravel, sand, silt, and clay (Marcher, 1969; Heran et al., 2003). Based on published maps, the bedrock is likely to belong to one of the following three map units: Boggy Formation (IPbg), McAlester and Hartshorn Formations (IPmh), or Atoka Formation (IPa). All three of these units are of Pennsylvanian age and described as combinations of shale and sandstone with coal. Bedrock is not expected to be encountered during reconstruction of the project parking area. A map of the regional geology is presented in Figure 2.

Figure 2:- Regional geologic map.

2.2 Site Geology

A geomorphological and geoarchaeological study was performed in the vicinity of the project area by URS (Ahr and Turner-Pearson, 2012). This study included collecting soil cores to an approximate depth of 20 feet below the existing ground surface. In the vicinity of the project area, these borings encountered fill materials overlying a buried soil profile and native alluvial deposits.

The fill materials are reported as containing coarse sand, clay, gravel, and shale fragments.

The parking lot may be underlain by fill related to construction and maintenance of the dam. Based on publicly available well logs in the region, bedrock is anticipated to be present at depths of 40 to 50 feet below the ground surface (OWRB, 2020). A review of two water well boring logs in the vicinity note the upper 10 feet of alluvium consist of dark clays, fine to coarse grained sands, and spoils from river dredging. Geotechnical borings were also completed in the area on behalf of the Oklahoma Department of Transportation, likely pertaining to construction of the U.S. Highway 59 bridge over the Arkansas River. However, no lithologic data was reported to the Oklahoma Water Resources Board.

The Sequoyah Fuels site, located near the City of Gore, processed uranium for nuclear reactor fuel and currently serves as a temporary storage site for waste materials (Rowley, 2017). A series actions by various site owners have led to the potential for radioactive contamination of the Arkansas River. Fill materials at the site, especially dredging material collected between the Sequoyah Fuels site and the Kerr dam, could potentially be contaminated.

2.3 Seismicity

No seismic source or Quaternary faults are mapped within 40 miles for the project (U.S. Geological Survey, 2020).

At this time, no structures are planned for inclusion in this project. The American Association of State Highway and Transportation Officials (AASHTO) criteria for recommended seismic response parameters are based on the AASHTO LRFD Bridge Design Specifications, 7th Edition, 2014, and represents horizontal peak ground acceleration (PGA) with a 7 percent probability of exceedance in 75 years (approximate 1000-year return period). The 1000-year return period uniform hazard spectrum for Kerr Reservoir powerhouse parking area (35.344815° N latitude and 94.772862° W longitude) was obtained in accordance with the AASHTO ground motion maps.

The site was classified as “Class D” according to site class definitions specified in Table 3.10.3.1- 1 of AASHTO and soil profile assumptions based on geologic mapping of the project vicinity. The recommended spectral acceleration coefficient values for probabilistic design are summarized on Table 1.

Table 1:- Summary of Seismic Parameters Corrected for Site Class D

Peak Seismic Ground Acceleration Coefficient (As) 0.085

Horizontal Response Spectral Acceleration at Period of 0.2 sec (SDS) 0.195

Horizontal Response Spectral Acceleration at Period of 1.0 sec (SD1) 0.116

Site Factor at Zero-Period of Acceleration Spectrum (FPGA) 1.600

Site Factor at Short-Period of Acceleration Spectrum (Fa) 1.600

Site Factor at Long-Period Range of Acceleration Spectrum (Fv) 2.400

Based on the long acceleration coefficient SD1 value of 0.116, the site is assigned to Seismic Hazard Zone 1, in accordance with Table 3.10.6-1 of AASHTO. Based on this designation, seismic conditions are assumed to not control design of structures at the project site.

3 FIELD EVALUATION

To evaluate the field conditions, a CFLHD team visited the project site and conducted limited field measurements and observations on December 3, 2019. This team included Dorothy Eisenbraun (Project Manager), Kelly Terrell (Roadway Designer), Lisa Hemesath (Environmental Protection Specialist), Nathan Marshall (Bridge Engineer), and James Arthurs (Geotechnical Engineer). The CFLHD team met with representatives of USACE including Amanda Palmer and Gerald Treadwell.

Field observations focused on evaluating the existing parking area conditions and soil properties.

Evaluations and recommendations presented in this memorandum are based on visual observations and limited measurements taken during the site visit. Due to ERFO project time and budget constraints to expedite project delivery and relatively low risk (pavement only, no structures planned), no subsurface investigations were conducted.

An annotated aerial photo is presented in Figure 3. The existing parking area is nearly flat lying with a gradual slope towards the Arkansas River (Figure 4). The banks of the river are approximate 1V:3H and armored with riprap. A post-and-beam guardrail system is present between the edge of the parking area and the river bank and was damaged during the flood event. The parking area is accessed from U.S. Highway 59 via a two-lane paved roadway. This roadway was generally above the flood level with only approximately 125 feet of the roadway adjacent to the parking area damaged. A concrete vault toilet and sun shelter are located at the southwest edge of the parking area. (Figure 5) Neither structure appeared to be damaged. A river access road extends from the parking area northeast along the Arkansas River towards US 59. This road and the associated post-and-beam rail was severely damaged by the flooding (Figure 6). At the time of our site visit, the river access road was barricaded to prevent public access.

Figure 3: Annotated Aerial Photo of the Powerhouse Parking Lot and related infrastructure.

From the site visit and office discussions, we understand that USACE plans to permanently close and abandon the river access road. In addition, we discussed the possibility of relocating the parking area to higher ground southeast of the existing footprint (Figure 3). USACE personnel report that dredge material was previously placed in this location without moisture-density control.

A brief surface reconnaissance of this area indicated that the ground was very soft and wet.

Figure 4: Existing Parking Lot and Guardrail

Figure 5: Parking Lot and Vault Toilet.

Figure 6: Damage to River Access Road.

4 RECOMMENDATIONS

4.1 Parking Area

If the parking lot and related structures are to be relocated to the southeast, there is significant risk of poor performance due to the wet, soft dredge materials present in that area. In addition, these materials have potentially been contaminated by activities at the Sequoyah Fuels site. No subsurface geotechnical investigation was performed to evaluate the potential limits (horizontal or vertical) of the dredge materials. To reduce the risk of poor performance, a reinforced fill section should be constructed on top of the existing ground surface, after clearing and grubbing. The reinforced fill section should consist of material meeting the criteria of Backfill Material (704.03(b)). The fill section should be supported by a geotextile separator and one layer of reinforcing geogrid placed between the existing ground and the fill materials. Construct the reinforced fill according to Section 204 of the FP-14 and project SCR’s. The reinforced fill should extend two feet laterally beyond the edge of pavement for the parking area.

If guardrail with wooden posts is to be placed within the reinforced fill footprint, special effort should be made to prevent displacement of the geogrid and geotextile during guard rail construction. This could include placement of blockouts (such as sonotube) during fill construction, or hand digging and cutting the geosynthetics prior to guardrail post installation.

Metal posts may be driven through the geogrid and geotextile, provided that there is at least 12 inches of fill soil cover on the geosynthetics. The contractor should provide their guardrail installation plan for review by a CFLHD geotechnical representative.

If the existing dredge materials can be shown to not be contaminated, subexcavation can be considered as an alternative to the reinforced fill section. The dredge materials should be subexcavated beneath the pavement footprint and replaced with moisture-density controlled fill according to Section 204 of the SCR and FP-14. The subexcavation should extend two feet below the pavement section as shown in Special 204-A. For the parking area, the subexcavation should extend laterally 2 feet beyond the edge of pavement. If unstable materials are encountered at the bottom of the subexcavation, additional remediation should be performed according to Section 208.08(d) of the FP-14. Alternatives such as reinforcing geosynthetics (geogrid or geotextile) can be considered with review by the CFLHD geotechnical representative and approval of the Contracting Officer.

4.2 Structures

We recommend that structures not be founded on the dredge materials. If relocation of the vault-toilet and shade structure are proposed, geotechnical subsurface exploration consisting of borings or test pits should be performed to evaluated the subsurface conditions and inform foundation analysis. Shallow foundations may be feasible, but would likely require significant subexcavation to reduce settlements and improve bearing resistance of the foundation soils.

4.3 Erosion Protection

Riprap damaged or removed during the flooding event should be replaced according to the recommendations presented in the CFLHD Hydraulics Report.

4.4 Construction Observations

A CFLHD geotechnical representative should be on-site during construction to evaluate the subsurface conditions encountered during subexcavation, if performed.

5 DISCLAIMERS/LIMITATIONS CLAUSE

Subsurface exploration was not performed as a part of this scope of work. Interpretation of surface and subsurface conditions is based on limited field reconnaissance and surface mapping of soil and rock outcrops. The Recommendations section of this report includes interpretations and recommendations developed by the Government in the process of preparing the design. These interpretations are not intended as a substitute for the personal investigation, independent interpretation, and judgement of the Contractor.

Prepared by:

James Arthurs, Ph.D., P.E.

Geotechnical Engineer, CFLHD

Reviewed by:

Todd G. Hansen, P.E.

Geotechnical Engineer, CFLHD

Approved by:

Marilyn D. Dodson, P.E.

Lead Geotechnical Engineer, CFLHD

6 REFERENCES

Ahr, S.W. and Turner-Pearson, K. (2012). “Geomorphological and Geoarchaeological Investigations on Portions of the McClellan-Kerr River Navigation System, LeFlore, Muskogee, Rogers, Sequoyah, and Wagoner Counties, Oklahoma.” URS Group Miscellaneous Reports, Report of Investigations Number 150

American Association of State Highway and Transportation Officials (AASHTO). “AASHTO LRFD Bridge Design Specifications.” Seventh Edition, 2014.

Foti, T. (2019). “Arkansas Valley”. <http://www.encyclopediaofarkansas.net/entries/arkansas-valley-441/>.

Heran, W.D., Green, G.N., and Stoeser, D.B. (2003). “A Digital Geologic Map Database for the State of Oklahoma”. 1:500,000. Open File Report 03-247.

Marcher, M.V. (1969). “Reconnaissance of the Water Resources of the Fort Smith Quadrangle, East-Central Oklahoma”. 1:250,000. U.S. Geological Survey, Map HA-1.

Oklahoma Water Resources Board (OWRB). Water Well Records.

<https://www.owrb.ok.gov/wd/search/search.php> Accessed on 8 June 2020.

Rowley, S. (2017). “Legal battle of long-shuttered Sequoyah County uranium plant still ongoing.”

The Southwest Times Record

U.S. Department of Transportation, Federal Highway Administration (FHWA). (2014). “Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects, FP-14.”

Publication No. FHWA-FLH-14-001.

U.S. Department of Transportation, Federal Highway Administration (FHWA). (2009). “Design and Construction of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes.”

Publication No. FHWA-NHI-10-024.

U.S. Geological Survey (2017). “Quaternary Fault and Fold Database of the United States.” USGS Earthquake Hazards Program, <http://earthquake.usgs.gov/hazards/qfaults/>

U.S. Geologic Survey (2017). “U.S. Seismic Design Maps.” USGS Earthquake Hazards Program, <http://earthquake.usgs.gov/designmaps/us/application.php> https://www.owrb.ok.gov/wd/search/search.php