W912QR24R0048_FIO_Vol6_ProjGIR_1of16-0000.pdf

Solicitation For Rough River Dam Safety Modification Project Phase II - New Outlet Works and Cutoff Wall

P2: 145870

Design-Bid-Build

Geotechnical Information Report (GIR) (1of16)

For Information Only

23 September 2024

W912QR24R0048

ARIMS: 1200

Disposition: Permanent

W912QR24R0048_FIO_Vol6_ProjGIR_1of16-0000

FOR OFFICIAL USE ONLY (FOUO)

This document is FOR OFFICIAL USE ONLY (FOUO). It contains information that may be exempt from public release under the Freedom of Information Act (5 USC 552). It is to be controlled, stored, handled, transmitted, distributed, and disposed of in accordance with USACE policy relating to FOUO information and it is not to be released to the public or other personnel who do not have a valid “need to know” without prior written approval of an authorized USACE official.

Rough River Dam (KY03012) Geotechnical Interpretive Report New Outlet Works and Cutoff Wall

ROUGH RIVER, FALLS OF ROUGH, KY

LRL DISTRICT, LRD DIVISION

Report Status: Draft, Date

DRAFT

ii

Introduction Purpose and Limitations of Geotechnical Interpretive Report (GIR) Relation to Contract Documents Organization of Report Project Authorization Project Location and Population at Risk Risk Driving Failure Modes Rough River Dam Safety Modification and DSAC History

Project Overview Existing Conditions

Project Features Dam Embankment Outlet Works Spillway Original Construction Overview

Existing Outlet Works Construction Dam Construction

Groundwater Previous Phases of the Dam Safety Modification (DSM) Project

DSM Phase 1A (Road Relocation) DSM Phase I Intermediate (Automated Instrumentation Installation) DSM Phase IB (Exploratory Drilling and Grouting)

Embankment Cracks Geologic Profile Updates and Overburden Soils

Project Operations Flood Pool Event Frequency

2011 Record Pool Overview of Planned Rehabilitation

Site Specific Soils and Rock Summary of Geologic Data

2018 Phase I Outlet Works Investigation 2019 Phase II Outlet Works Investigation

On-Site Soils Dam Embankment Valley Soils and Overburden Below the Dam Borrow Areas

Left Upstream Abutment Area Left Downstream Abutment Area Upland Disposal and Staging Areas

Old Campground Area Geology

Regional Geology Stratigraphy and Profiles for Cutoff Wall and New outlet Works Karst Potential Abrasivity

On-Site Bedrock iii

Hardinsburg Formation Haney Limestone Big Clifty Sandstone Beech Creek Limestone Elwren Shale

Reelsville Limestone Sample Sandstone Rock Structure

Groundwater Haney Limestone Big Clifty

Seismicity Induced Seismicity Previous Seismic Evaluation Site Classification Seismic Hazard Curve Deaggregation

Work Area Descriptions and Construction Considerations Overview Site Preparation for the New Control Tower

Work Area Description Construction Considerations

Excavation of Approach Channel Work Area Description Construction Considerations

Site Preparation for the New Stilling Basin and Apron Work Area Description Construction Considerations

Excavation and Construction of the Retreat Channel Work Area Description Construction Considerations

Modification of Old Campground Work Area Description Construction Considerations

Construction of Cutoff Wall Working Platform Work Area Description Construction Considerations

Installation of the Cutoff Wall Work Area Description Construction Considerations

Critical Areas B1 & B4 (Overburden in Contact with Haney LS) Critical Areas B2 & B3 (Overburden in Contact with Beech Creek LS) Critical Area A (Conduit)

Spoil Placement, Site Restoration, and Road Relocation Excavation of Outlet Tunnel Construction of the Control Tower Service Bridge Abutment iv

Work Area Description Construction Considerations v

Acronyms AEP Annual Exceedance Probabilities ASCE American Society of Civil Engineers ASTM American Society for Testing and Materials BCLS Beech Creek Limestone CEUS Central and Eastern United Sates DSAC Dam Safety Action Classification DSM Dam Safety Modification DSMR Dam Safety Modification Report DSOG Dam Safety Senior Oversight Group ERDC Engineering and Research Design center FAR Federal Acquisition Regulation FIO For Information Only GBR Geotechnical Baseline Report GDR Geotechnical Data Report GIR Geotechnical Interpretive Report GIS Geographic Information System ICOLD International Commission of Large Dams MCE Maximum Credible Earthquake MDE Maximum Design Earthquake MSL Mean Sea Level NAVD North American Vertical Datum NGVD Nation Geodetic Vertical Datum OATV Optical and Verification Hole Drilling OBE Operating Basis Earthquake OW Observation Well PE Probability of Exceedance PFM Potential Failure Mode PFMA Potential Failure Mode Analysis PGA Peak Horizontal Ground Acceleration PMF Probable Maximum Flood PSHA Probabilistic Seismic Hazard Analysis PZ Piezometer RMR Rock Mass Rating RQD Rock Quality Designation RW Relief well SEI Structural Engineering Institute SOG Senior Oversight Group SQRA Semi-Qualitative Analysis UCS Unconfined Compressive Strength USACE US Army Corps of Engineers USBR US Bureau of Reclamation USGS United States Geologic Survey

Rock Formation Abbreviations Mh Hardinsburg Sandstone Mgh Haney Limestone Mgb Big Clifty Sandstone Mgb (sh-u) Big Clifty-Upper Shale Mgb (ss) Big Clifty-Sandstone Mgb (int) Big Clifty-Interbedded Mgb (sh-l) Big Clifty-Lower Shale Mgc Beech Creek Limestone El Elwren Shale Mr Reelsville Limestone Ms Sample Sandstone

INTRODUCTION

Purpose and Limitations of Geotechnical Interpretive Report (GIR) This report includes subsurface information from field investigations and associated laboratory test results along with USACE’s interpretation of the subsurface conditions to support design efforts for the new outlet works and cutoff wall project and is considered essential information for the establishment of technical requirements and limitations applicable to construction. The design and construction considerations provided herein are for information only (FIO). The GIR is not intended to provide contractual baseline conditions for the entire project as these baseline conditions have been incorporated into the plans and specifications. The appendices contain geotechnical and geological data associated with multiple historic designs, investigations, and rehabilitations to support design assumptions and provide the available historic information for the dam.

Relation to Contract Documents The New Outlet Works and Cutoff Wall GIR is provided FIO in Volume 6 of the technical package. The GIR includes project history, soil and bedrock conditions based on previous investigation for the entire Rough River Dam Project, and applications of this information to design elements essential to the New Outlet Works and Cutoff Wall Design. Nothing in the GIR should be construed as amending or altering the Plans and Specifications, applicable FAR clauses, or other contract requirements or standards for construction. This GIR references the Phase IB Exploratory Grouting Contractor Completion Report also contained in Volume 6 of the technical package as FIO. References to the new tunnel (conduit) are used in this manual only in general terms; details of the tunneling and portals required for this project are covered under a separate Tunneling Geotechnical Baseline Report (GBR) and Tunneling Geotechnical Data report (GDR).

Organization of Report This document has been formatted to include the New Outlet Works information and the cutoff wall information and follows the following outline:

Chapter 1: Introduction (Purpose of Report, Project Location and Assessed Risks) Chapter 2: Project Overview (Project Features, Construction History Summary) Chapter 3: Site Specific Soils and Rock (Properties of Project Soils and Rocks) Chapter 4: Work Area Descriptions and Construction Considerations

Appendix A: Synopsis of Construction History and Performance Appendix B: Boring Location Plans and Boring Logs Appendix C: Soil and Rock Testing and Analyses by Investigation Appendix D: Instrumentation and Monitoring Appendix E: Analysis of Upstream Filter and Dewatering Appendix F: Analysis of Downstream Cofferdam and Dewatering Appendix G: Analysis of Downstream Filter for Stilling Basin Abandonment Appendix H: Analysis of Cutoff Wall Work Platform Appendix I: Analysis of Upland Disposal Area and Archery Berm

Project Authorization The flood protection plan for the Ohio River Basin, which included the construction of the Rough River Dam, was authorized by the Flood Control Act approved 28 June 1938 (Public Law 761, 75th Congress, 3rd Session), revised under a report titled “Rough River and Tributaries, Kentucky” and published as House Document No. 535, 78th Congress, 2nd Session, 1944. Water supply was authorized per the Water Supply Act of 1958 (43 U.S. Code § 390b). Water supply agreements are in place with Leitchfield, KY (120 acre-feet) and Grayson County, KY (260 acre-feet). During the fall and winter months, the lake is kept at a relatively low level (winter pool) to store the runoff from large rainfall events common to that time of year for later release after the swollen streams and rivers below the dam have receded and can receive the release of the stored water without consequences. The pool extends upstream approximately 45 miles when the reservoir is at the spillway crest elevation.

Project Location and Population at Risk Rough River Dam straddles the Breckinridge/Grayson County line in Kentucky on the Rough River, 89.3 miles above its confluence with the Green River. The project is located in south-central Kentucky, approximately 60 miles southwest of Louisville, approximately 30 miles west of Elizabethtown, Kentucky, approximately 35 miles southeast of Owensboro, Kentucky and approximately 20 miles northwest of Leitchfield, Kentucky (Figure 1). The potential dam failure inundation area closest to the dam includes the towns of Dundee, Hartford, and Beaver Dam along the Rough River in Kentucky (exclamation symbols in Figure 1), along with smaller communities in portions of Breckinridge, Grayson, and Ohio counties along the Rough River and some of its tributaries. Outside of these communities, the study area is rural with scattered development. Hartford and Beaver Dam are located approximately 60 miles downstream of the dam with 2010 census population estimates of 2,672 and 3,409, respectively. Livermore (population ~1,365) is located approximately 90 miles downstream from the dam at the confluence of the Rough and Green Rivers.

Figure 1: General location plan for Rough River Dam and associated areas

Risk Driving Failure Modes

A Potential Failure Mode Analysis (PFMA) was completed in 2008 and indicated the foundation of the Rough River Dam posed unacceptable risks from internal erosion failure modes at extreme reservoir loading conditions and produced 4 risk driving failure modes (Figure 2).

21A - Concentrated leak erosion into and along the Haney Limestone on the right abutment 22 - Concentrated leak erosion into and along the Haney Limestone on the left abutment 23A - Concentrated leak erosion of the valley soil along the Beech Creek Limestone 23C - Erosion into the untreated valley center and lower left abutment Beech Creek Limestone

The dam was assigned a Dam Safety Action Classification (DSAC) Classification 2 (High Urgency) ranking. A Dam Safety Modification Report (DSMR) was completed in 2012 in accordance with ER 1110-2-1156 Safety for Dams – Policies and Procedures. Additional risk assessments were completed in 2016 and 2017. The 2017 Risk Assessment indicated that the two primary risk driving failure modes were Potential Failure Mode (PFM) 22 scour (concentrated leak erosion) into and along the left abutment Haney Limestone, and PFM 23A scour (concentrated leak erosion into the right abutment Beech Creek Limestone. These karstic formations are present on both sides of the incised valley.

Figure 2: General locations of risk driving failure modes

Rough River Dam Safety Modification and DSAC History

The purpose of the Dam Safety Modification Project is to reduce risks associated with potential dam failure and the associated loss of life below tolerable risk guidelines. In 2005 Rough River Dam was evaluated through a Screening Portfolio Risk Assessment and was assigned a DSAC Classification 2 (High Urgency) ranking by the Dam Safety Senior Oversight Group (DSOG).

The key risk contributors involve erosion into or along the karstic rock foundation. A PFMA was performed in 2008 which ultimately lead to approval for the 2012 DSMR which recommended completion of an exploratory grouting program and a seepage barrier across the dam foundation and to be saddled around the conduit.

The proejct was broken into phases with Phase IA relocating the existing state highway to the updstream slope of the dam between 2014 and 2015. The Phase IB Exploratory Drilling and Grouting Program began in the fall of 2015 and was completed in 2017. Because grout was observed exiting into the stilling basin in 2016, a Semi-Qualitative Risk Analysis (SQRA) was performed which concluded there was direct evidence of adverse conditions at the project which had the potential to result in unacceptable performance and the possible uncontrolled release of the reservoir. This conclusion was supported and approved by the SOG with formal approval from the Assistant Secretary of the Army for Civil Works to proceed with design for the cutoff wall. A post-grouting risk assessment was conducted upon the conclusion of the Phase 1B

#21A grouting to evaluate the effectiveness of the cutoff wall to reduce the project risk below the tolerable risk guidelines.

The Phase II concrete cutoff wall was fully designed in 2017 with an approach to install the cutoff wall around the existing conduit; however, during a Safety Assurance Review, it was determined the conduit did not have the structural capacity to handle the anticipated increase in loading from the cutoff wall. These concerns ultimately rendered the 2012 DSMR incomplete and resulted in cancellation of the Phase II Solicitation. Alternative methods for installing the cutoff wall in the area of the conduit were evaluated in 2018 and 2019. In 2018, a Constructability Evaluation and an SQRA were conducted to complete the 2012 DSMR. The 2020 DSMR Supplement, prepared in accordance with ER 1110-2-1156 to analyze the effectiveness of the design options, concluded that the most effective approach for installing the cutoff wall required the installation of a new outlet works within the left abutment followed by total abandonment of the original outlet works. During the design of this option, the DSOG discussed the results of the 2017 Post-Grouting Risk Assessment and changed the project classification from a DSAC 2 to a DSAC 3 using the justification that post-grouting instrumentation readings confirmed that conditions within the dam foundation had been improved by the grouting.

PROJECT OVERVIEW

Existing Conditions

Project Features

The major features of the existing Rough River Dam project include an earthen dam, an outlet works positioned at the base of the right abutment, and an emergency spillway near the left abutment (Figure 3).

Figure 3: Plan view of existing Rough River Dam project

Table 1: Pertinent Existing Project-Related Data

Physical Data

Dam Type Earth Core with Rock Fill Maximum Height 130 feet Length 1,590 feet Top Elevation (Does not include pavement section)

553.53 NAVD88; 554 NGVD29 (+5’

parapet wall placed in 2006 = 559)

Spillway Crest Elevation 523.53 NAVD; 524 NGVD Spillway Type Open Cut Spillway Dimensions 65 feet wide; Design Q=22k cfs Control Works 12’ X 12’ semi-elliptical concrete culvert Conduit Invert Elevation 430 ft NGVD (at inlet)

Hydrology

Drainage Area 454 mi2 Total Rainfall from PMP (HMR 51/52) 27.8 inches Probable Maximum Flood (PMF) Peak Inflow 344,700 cfs Maximum PMF Pool Elevation 556.26 NAVD88; 556.69 NGVD29 Maximum recorded Pool Elevation 526.88 NAVD88; 527.35 NGVD29 Maximum Recorded Outflow 6,400 cfs (peak; includes spillway) Maximum Recorded Inflow 36,500 cfs (24-hr average) Average Flow at Dam Site 660 cfs Maximum Conduit Discharge Capacity at Spillway Crest

5,580 cfs

Operating Levels

Pool Elevation

(ft, NGVD29*) Elevation

(ft, NAVD88) Storage (acre-ft)

Winter 470 469.53 29,800 Summer 495 494.53 120,000

Flood Control 470 to 524 469.53 to 523.53 304,600 Top of Dam 554 553.53 775,000

* The project was designed and referenced to the COE Datum, which equals NGVD29 and MSL.

Subtract 0.47 feet from NGVD29 datum to obtain NAVD88.

Dam Embankment The dam consists of a 1,590-foot long, earth-filled embankment having a maximum height of 130 feet above the streambed with a 40 feet wide crest width. The maximum width at the dam base of 819 feet. The original upstream face has 4 feet of dumped riprap stone protection underlain by 12 inches of spalls and choker material. The rock at the downstream toe is limestone that has a top elevation of 460 and an upstream slope of 1.0H:1.0V. A volume of 1,141,400 cubic yards of earth and rock material was required for the original construction. In 2007, the top-of-dam embankment elevation was raised from 554 to 559 using a 5-foot parapet wall which was added to meet current hydrologic requirements. KY Highway 79 (aka Falls of Rough Road), was moved to the upstream crest in 2014 where the roadway is currently trafficked.

The dam embankment consists of low permeability lean and fat clay fill. Internal drainage of the embankment is provided by a 10-foot thick, 1.0H:2.0V inclined drain starting at elevation 495, as well as a 2-foot thick, basal filter blanket on the stripped downstream ground surface extending to the toe of the dam. The structure is founded on residual soils along the left abutment and alluvial soils within the valley center. Three relief wells were installed at the downstream toe in the left bank foundation to reduce uplift pressures and to control the water movement through the soil.

There is no core trench, rock treatment, or grouting between the conduit and the left upper left abutment. Along the right abutment the structure is founded on limestone, in which a special treatment zone was slush grouted and treated with dental concrete and concrete bulkheads at several overhangs and ledges. A comprehensive review of the construction photographs indicated that numerous rock overhangs actually remained in place as embankment material was placed along the right abutment.

Outlet Works The outlet works, located at the base of the right abutment and founded predominately on the karstic Beech Creek Limestone, provides a discharge capacity of 3,000 cubic feet per second (cfs) at conservation pool (elevation 495), and 5,580 cfs at spillway crest level (elevation 524).

The dry-type control tower has three hydraulically-operated 4.75-foot by 9.5-foot vertical lift slide gates (invert elevation of 430) and two 24-inch low-flow bypass pipes (invert elevation of 450), discharging to a 12-foot by 12-foot, semi-elliptical concrete conduit that leads to a stilling basin. The semi-elliptical section of the conduit is 548 feet long and has a drainage gradient of

0.2 percent. There are five seepage collars on 60-foot spacings at the center of the dam. The conduit leads to an energy dissipating stilling basin and directs the flow through a riprap-lined retreat channel to the river’s original course. The stilling basin was originally a 52-foot long dispersal bucket, but an emergency impoundment during embankment construction resulted in high discharges and erosion of the end sill. In 2007, the end sill and apron were removed and extended the stilling basin to 139 feet with five baffle blocks. A 144-foot, simple-span, steel truss service bridge extends from the control tower to a roadway on the right abutment.

Spillway A 65-foot wide, 1,800-foot long uncontrolled, unlined, open rock cut emergency spillway was excavated on a 1H:4V slope roughly 45 feet deep into rock. Water enters the spillway through a natural drainage valley in the left abutment and flows over a 6-foot-wide concrete sill with a crest elevation of 524, installed for grade protection, after which the spillway slopes downstream at 1.5 percent and spills approximately 400 feet beyond the left abutment (Figure 3). The Contractor overshot the rock leaving the ragged appearance in the walls and floor (Figure 4).

Overburden was excavated with 2H:1V side slopes. The spillway is crossed by Kentucky Highway 79 using a single span, simply supported, steel multi-girder bridge with a cast-in-place concrete deck extending approximately 36 feet above the spillway floor. The spillway side slopes are lined only at the bridge location to support the bridge structure. The floor of the spillway is the Haney Limestone and is described in Chapter 3. Performance of the spillway during the 2011 record pool event is discussed in Paragraph 2.3.1.1.

Figure 4: Current spillway condition

Original Construction Overview

Two contracts were awarded to construct the Rough River Dam project. A contract for the tower and outlet works was awarded in 1955. A contract for construction of the dam and spillway was awarded in May 1957 and proceeded concurrently with construction of the outlet works to expedite completion of the project. The embankment was completed in November 1958, and the project was placed in limited operation in October 1959 and into full operation in December 1960. Design of the project features was aided by pre-construction and construction explorations. Key construction items pertinent to the Phase II Project include the original outlet works construction, right abutment dental treatment (Special Treatment Zone), natural alluvium and overburden left and place, and abutment grouting. A summary of key construction information is contained in Figure 6.

Figure 5: Key Construction Summary

Figure 6: Historic grouting at centerline (geology shown is 7.5 feet upstream of centerline)

Existing Outlet Works Construction

Construction of the outlet works began in November 1955 and was completed in January 1958.

The original outlet works construction consisted of a tower monolith, two transition monoliths, 27 conduit monoliths, and the outlet bucket structure. Most of the rock excavation was performed by drilling and blasting complimented by mechanical removal. The tower and approximately two-thirds of the upstream portion of the conduit was founded on the Beech Creek Limestone, while the stilling basin and remaining portion of the conduit was founded on the Big Clifty Lower Shale, which is underlain by the Beech Creek Limestone. During the conduit trench excavation, the limestone was documented to contain a significant number of karstic features (Figure 7). These features were cave sized and ran sub-parallel to the conduit exiting the excavation toward the left (valley side). Where discovered in the limestone, karst features were dentally treated with concrete. Karstic features were not observed in Monoliths 9 through

13. A large karstic feature re-entered the excavation on the left side wall of Monolith 15. It is believed that the karst feature observed exiting out of the riverward side wall of Monolith 8 was the same feature observed that the re-entered excavation in Monolith 15.

Figure 7: Foundation Mapping of Existing Conduit.

The features which were encountered in the base of the tower and conduit excavations were cleaned with an air-water jet to remove clay infilling and dentally treated with concrete. Where the natural dip of the ground caused the excavation to run deeper than designed the limestone foundation received a lean concrete mud mat between 0.5 and 2 feet thick. The shale foundation was covered with a 3-inch thick concrete seal coat prior to placing concrete. The concrete was then placed in approximately 18-inch layers and consolidated with internal vibrators. The left side of the conduit trench was excavated at a 2H:1V slope into native overburden; whereas 20 to 30 feet of rock excavation was required along the right side of the conduit trench to achieve the 1H:4V slope (Figure 8). DRAFT

Figure 8: Construction photos and drawings of the existing conduit.

Dam Construction

Native Overburden and Foundation Drains:

Construction of the dam embankment began in May 1957 and was completed in December 1958.

There was no core trench to rock or foundation grouting between the conduit and lower left abutment. Organics were stripped from the foundation soils and a 6-foot deep inspection trench installed, but it did not extend down to rock. The foundation soils along the right bank (Station 21+00 to 22+45) of the original river channel had a maximum depth of about 30 feet with no natural drainage stratum, so a system of vertical sand drains upstream and downstream of the centerline of the dam was installed to facilitate consolidation of the foundation clays beneath the embankment (Figure 9). No drains were placed within 50 feet of the dam axis. The 12-inch-diameter sand drains were drilled into bedrock on a 13-foot center-to-center spacing, and filter-graded sands were placed via tremie methods. A total of 368 sand drains were installed (141 downstream and 227 upstream of the centerline of the dam). The downstream and upstream vertical sand drains are connected to a 2-foot thick, basal filter blanket (Figure 9).

Left of the conduit the dam is founded on 40 to 50 feet of lean clay and silts that transition to interbedded sands and sandy clays near the historic river channel and incised valley. The original dam designers were concerned with embankment slope stability and considered the natural drainage material which exists left of the historic river channel to be desirable for embankment construction because it is naturally draining. As a result, three relief wells were installed at the downstream left toe to control the seepage and reduce uplift pressures from the left in place material. RW-1 and OW-1 are noted to reflect artesian pressures at seasonal pool and above with flow generally less than 1 gallon per minute.

Figure 9: Drainage Blankets and Relief Drain Configuration

Right Abutment Special Treatment Zone:

Bedrock on the right abutment was stripped to rock which required a series of reinforced concrete bulkheads and dental treatment in the form of slush grouting where exposed. This area is referred to as the “Special Treatment Zone”. This effort was conducted in order to provide a suitable surface against which to place compacted backfill. Internal erosion was not a consideration, so the integrity of the treatment is not clear. The actual area and location of the special treatment area is not known but appears to between approximately elevation 450 (approximate top of fill at conduit) and elevation 524. Based on the detail provided in the original construction drawings and the foundation report, the width of the treatment area at elevation 450 was approximately 70 feet, tapering up to 5 feet at the top of the treatment zone (Figure 10).

Figure 10: Right Abutment Special Treatment Zone

Historic Grouting:

During dam construction in 1958 foundation grouting initially consisted of a single-line grout curtain in the abutments. A total of 15 grout holes were advanced on the right abutment from Station 22+73 to Station 24+14. The holes were advanced at the bedrock contact with soil stripped and removed. Grouting holes were drilled on a 20-foot maximum center-to-center spacing with a 20-degree batter into the abutment to a bottom elevation of 435 (in the Big Clifty Lower Shale). A total of 695 bags of grout were used in 14 of the holes. An additional 135 bags were injected into hole R-1 (nearest the conduit); however, it openly communicated with the adjacent conduit excavation, so it is not certain how much was actually taken by the formation and how much simply flowed into the excavation. From the limited information available about the grouting, it appears that most of the grout takes were associated with vertical stress relief fractures and bedrock that was blast-damaged which was encountered at or below elevation 450.

These stress relief fractures have only been observed on the right abutment and when the formation is at or near the surface. While no rock core was obtained during the grout hole drilling, it would appear the grout takes are primarily associated with the Big Clifty interbedded sandstone and shale and the lower shale formation. This area also was noted to accept grout immediately adjacent to the conduit excavation during the Phase IB Exploratory Grouting.

Grouting on the left abutment consisted of vertical holes spaced on 20-foot centers from Station 13+90 to 11+80 to a bottom elevation of 475 into the Big Clifty Sandstone.

In 1960 additional grouting was performed on the abutments following the discovery of additional bedrock solutioning during excavation for a downstream recreation site access road.

The subsequent foundation grouting was within the left abutment from Station 13+16 (on the downstream edge of the crest) to 6+06 (at the Highway 79 bridge abutment) on 16-foot centers with a 20-degree batter into the abutment, terminating at an elevation of 475 in the Big Clifty Sandstone. During Phase IB grouting grout on the left abutment was extensively encountered exceeding five feet thick. The grout can be distinguished from latter grouting endeavors by identification of fine black aggregates and, in some instances, pea gravel sized coarse aggregate.

Another grout line on roughly 20-foot centers with a 20-degree batter into the right abutment, was advanced into the Haney Limestone from Station 23+90 to 27+46 along the dam centerline to a bottom elevation of 485. Any hole requiring more than 10 bags of cement was split-spaced.

A pictorial of the described grouting is presented in Figure 11 and Figure 12. No documentation was found concerning the conditions encountered during this grouting effort.

Figure 11: Right Abutment Grouting Summary

Figure 12: Left Abutment Grouting Summary

Groundwater

There are multiple sinkholes and springs identified across the project site. Sinkholes have been observed within the spillway floor, behind the project office, along a hiking trail downstream of the project office, and along the campground access road. Springs have been observed upstream of the left abutment, in the tree line downstream from the left embankment toe, and beneath the downstream footprint of the dam on the left abutment.

The groundwater conditions at the site are complex and groundwater encountered across the project site is not consistent. This is attributed to perched groundwater within Haney Limestone overlying restrictive shales (i.e. upper Big Clifty shale) on the left abutment. Instrumentation on the upper left abutment indicates groundwater as high as 545 and as low as 495 in the left dam abutment and is typically well above summer pool levels. This condition is attributed to the void structure within the Haney Limestone, the large upland drainage area to the south of the drainage basin, and the presence of a draped basal filter (inclined chimney and horizontal blanket drains) present along the downstream dam foundation. Groundwater conditions for earthwork on the upper left abutment encountered groundwater a few feet above the top of rock in most locations.

Groundwater in the lower left abutment generally exists at the ground surface during wet periods mostly influenced by rainwater, dam seepage and abutment groundwater influence seeking the valley center. This is evident in a series of test pits advanced along the downstream left abutment in late fall of 2019 which indicated groundwater to exist just below the ground surface in the campground area and recreational area. A seepage area at the base of the left abutment (~Station 18+00 to 18+30) is attributed to a combination of dam seepage, the filter blanket and surface water runoff. A spring present in the left abutment (~200 feet downstream from the dam toe) regularly saturates the area between the existing tailwater recreation area. Relief wells located closer to the valley on the left indicate artesian pressure from Relief Well #1 at the toe of the dam which flows regularly slightly above the riser height at ~446.75 feet. Relief wells #2 and #3 have historically not had any flow.

Groundwater from the right abutment is mainly from surface water runoff. The perched water groundwater found in the Haney Limestone within the left abutment is not found in the right abutment to the same extent. The right abutment Haney groundwater levels are typically found just a few feet above the base of the formation (~495-437 feet). PZ59, installed in late 2011, has read dry since installation. The absence of a perched water table in the right abutment can be attributed to the topography of the catchment basin to the north of the dam. There is a prominent ridge just upstream of the dam that runs roughly parallel to the dam centerline. This ridge is thought to direct the ground water to the north and south parallel to the strike of the abutment that drain away from the area.

During Construction, groundwater was encountered above the base of several of the conduit monoliths. The groundwater was channeled to sumps and removed, diverted, or drained. Water seepage was also observed at the ground surface of the former river channel, downstream of the centerline of the dam, subsequent to the dewatering and stripping operations. Construction photographs indicate that efforts were made to pump and divert the water from the site; however, water remained present prior to fill placement. During stilling basin dewatering in 2012 and 2016 artesian conditions were noticed in the stilling basin indicative of high levels of seepage exiting into the stilling basin. After completion of the 2017 grouting this condition was not observed during dewatering in 2020.

Across the dam foundation the phreatic surface in the dam embankment ranges from approximately 480 on the upstream slope to approximately 445 on the downstream slope controlled by the inclined chimney and horizontal blanket drains. Relief wells and instrumentation indicate seasonal artesian groundwater conditions at the toe of the dam.

Previous Phases of the Dam Safety Modification (DSM) Project The Dam has a long history of previous maintenance and rehabilitation in addition to the previous phases of the Dam Safety Modification Project. A comprehensive listing and summary of previously completed projects is contained Appendix C. Previous design and construction activities which directly pertain to the Phase 2 project are as follows:

Phase 1A – Relocation of SR 79 (2014-2015) Phase 1 Intermediate - Install additional “real-time” instrumentation (2014-2015) Phase 1B – Exploratory Drilling and Grouting (2015-2017) Phase 2 Cutoff Wall Design (2017)

- Solicitation Canceled (critical design flaw discovered)

- New Outlet Works and Cutoff Wall Design (2020)

DSM Phase 1A (Road Relocation)

KY Highway 79 was relocated to the upstream face of the dam to allow traffic to pass during grouting and cutoff wall construction during summer and fall of 2014. The road relocation required altering the upstream slope of the dam between elevations 495 to 550 to a 2H: 1V (Table 2). The modified slope provides a 30 feet wide roadway surface at elevation 550. The slope is tied into the original dumped stone protection in a rock toe trench excavated down to elevation 495. Benches 8 to 10 feet wide and not exceeding 4 feet in height were excavated across the dam. Rock fill was placed and compacted in 2-foot thick lifts. The Contractor advanced both rock fill and riprap simultaneously up to elevation 550 (Figure 13). Special considerations for raising piezometer standpipes and placing rock fill around existing instruments were required. Additional empty manholes were installed on the upstream slope to accommodate future multi-level vibrating-wire piezometers, which occurred in 2015. The overall project placed 36,414 cubic yards (65.5 tons) of rock fill covered by approximately 14,758 cubic yards (22 tons) of KYTC Class III riprap on the dam face. All utilities previously located on the crest of the dam were located from the dam crest and were moved to the new road location.

Table 2: Modified Upstream Slope Geometry Upstream Downstream

Slope Elevation

(feet MSL) Slope

Elevation (feet MSL)

2.0H:1.0V 554-550 2.0H:1.0V 554-539 2.0H:1.0V 550-495 2.5H:1.0V 539-531 3.0H:1.0V 495-471

3.0H:1.0V 531-base 4.0H:1.0V 471-base

The pavement section was approved by KYTC. KYTC No. 2 stone was placed directly on top of the rock fill to a thickness of 5 inches and compacted by 6 full passes of a 10-ton vibratory roller.

Four inches of KYTC Crushed Stone Base was placed on top of the KYTC No. 2 stone and compacted to 95% maximum dry density per ASTM D1557. Non-woven geotextile fabric was used as a separation layer between the roadway section and the riprap face which extended flush to the top of asphalt. Traffic was rerouted onto the new road in the Spring of 2015. Figure 13 depicts a typical road embankment section with benching details.

Figure 13: State Hwy 79 traffic platform

Figure 14: Phase IA Road Relocation (2014).

DSM Phase I Intermediate (Automated Instrumentation Installation)

A total of 58 fully-grouted vibrating wire transducers were installed in 20 boreholes along the upstream and downstream crest of the dam. The system included an Automated Data Acquisition System to monitor effects of the future grout curtain installation on the dam foundation and to aide in design of the cutoff wall.

DSM Phase IB (Exploratory Drilling and Grouting) Detailed information for Phase IB Grouting is contained in Volume 6 Phase IB Exploratory Grouting Contractor’s Construction Report and the USACE Foundation Completion Report, and the boring logs are in “Volume 6: Phase IB Boring Logs”. The Phase IB project consisted of a base contract for exploratory purposes and a modification contract for production drilling and grouting. A summary of Phase IB is provided below.

2015-2016 Phase IB Base Contract:

Rough River Dam Safety Modification Phase 1B – Exploratory Drilling and Grouting was awarded in April 2015. The stated goal of the project was to install two partial grout lines to explore and evaluate subsurface conditions, to determine the extent of the pre-treatment required, and to establish remediation methods in preparation for a future cutoff wall. The base contract included 154 boreholes to be advanced from the dam crest to further define the foundation conditions through soil and rock sampling, water pressure tests, grout takes, instrumentation responses, etc. To define the extents and type of treatment needed for dam remediation. Two partial grout lines were placed parallel and offset upstream and downstream of the contract baseline along the crest of the dam. The grout lines were installed straddling the alignment of the proposed future cutoff wall. The downstream line was 10 feet from the center line (“D- Line”), and the upstream line, which was originally 10 feet from the center line, was ultimately placed 7.5 feet from the center line (“U-Line”). Holes drilled on the U-Line between Station 9+16 and 21+16 were inclined 20 degrees from vertical towards the left abutment. Holes drilled on the U-Line between Station 19+were inclined 20 degrees from vertical towards the right abutment. The base contract boreholes were drilled through the embankment/overburden soils into rock, and to a bottom elevation of 354, or approximately 10 feet into the Sample Sandstone.

The holes were divided into 6 zones (from left to right) depending primarily on the formations that were in direct contact with the embankment/overburden material and other defined project features (Figure 15). There were 3 holes on each side of the existing conduit.

Figure 15: Phase IB Base Contract Boreholes

The dam embankment and underlying overburden was drilled with resonant sonic drills as described in ER 1110-1-1807 (dated 31 July 2014). Grout hole drilling in rock was performed with water-actuated, down-the-hole hammers and standard rotary diamond coring drills. In addition to drilling upstream and downstream lines of grout holes, the Contractor was required to perform optical and acoustic televiewer (OATV) surveying for all lengths of rock drilling for the base contract and verification hole drilling. Borehole stages were assigned by the Government, pressure tested, and pressure grouted utilizing balanced stable grouts. All grouting operations were conducted in accordance with EM 1110-2-3506 (dated 28 February 2013). The project specifications particularly required that instrumented packers be used for all water pressure testing and grout injection. The Contractor was further required to provide and operate an

Automated Grouting Monitoring and Data Collection System to provide daily updated data collection and reporting of volume, pressure, rate of flow during grouting and Lugeon values during pressure testing. All data obtained through the drilling and testing program was made available through a real time geographic information system interface.

Notable Events:

Borehole DXS2192 encountered lean clay overburden overlying weathered shale above the Beech Creek interface from 138 to 141 feet below ground in direction of drilling. During grouting the interface took 591 gallons of grout at 7.5 gpm injected at 52 psi. The grouting was unable to build to the target pressure even moving to a sanded grout mix and closure was not achieved. During the grouting event, PZ-42 located 72 feet downstream of the dam centerline was filled with grout. Reclaiming piezometer PZ-42 by installing a vibrating-wire transducer in the remaining standpipe was attempted, but subsequent monitoring provided meaningless information and the piezometer was ultimately abandoned and replaced by PZ42A in 2017. PZ- 42 historically showed an instantaneous tailwater influence and grout entering the Beech Creek Limestone (BCLS) at the dam centerline could exit into or around the stilling basin. The stilling basin was dewatered before permitting additional grouting. The hole was down-staged and grouting was initiated for the next 15-foot gravity stage in the BCLS. Within 30 minutes of initiating grout operations, grout was observed exiting from a weep-hole and cold joints in the stilling basin/apron area approximately 500 feet downstream from the injection point (Figure 16).

Figure 16: Grout exiting into the stilling basin advanced from borehole DXS2192

Based on the speed and linear relationship of the grout exit location, the grout is thought to have traveled along valley stress relief fractures to the exit point. The stage took 1,914 gallons of grout at gravity pressure with sanded grout mix constituting 400 gallons of the total injected grout volume. The hole confirmed the presence of a continuous interconnected karst network in the BCLS left of the conduit. Any grout exiting the tailwater would typically be unobservable even during moderate conduit release. Therefore, additional events where grout exiting into the stilling basin could not be confirmed without subsequent dewatering. This was not feasible for much of production grouting.

While grouting through borehole DXP2232 in 2016, piezometer PZ35 received enough grout to expel water up through its standpipe onto the ground surface. Dye which had been injected into PZ40 in 2010 was observed exiting the top of PZ35. An effort was made to flush the grout from the piezometer but the bottom 18 feet, which included the screened interval, became permanently grouted and the instrument was taken out of service.

The largest void encountered within the BCLS is attributed to valley stress relief fracture five feet left of the conduit in vertical holes DXP2242-A and UXP2242-2. This is in the vicinity of conduit monolith 12 and the location where a large karst feature was observed to have exited the conduit foundation mapping area below overburden which was not removed during construction.

The feature was noted by rod drops in the tooling encountered at a depth of 133 feet vertically below the dam. The void and infilling varied from 4 to 6 feet across the boreholes. This is consistent with observations from the outlet works foundation report which detailed solution features leaving the conduit excavation during foundation mapping.

The largest and most notable outbreak occurred in the Haney Limestone while grouting DXP2582, with grout exiting into the ravine downstream of the abutment at approximately elevation 535. A smaller grout outbreak was noted while grouting Borehole DXP2462.

Figure 17: Grout exiting the left abutment advanced from borehole DXP2582.

2016-2017 Phase IB Contract Modification:

On the basis of conditions encountered during the initial phase it was determined that a cutoff wall was necessary, and the original contract was modified to consist of a complete two-line grout curtain with an additional 154 boreholes. Beginning in June 2016, the Government issued a series of Contract Modifications requiring that additional production drilling and grouting work be performed. The modification work extended the curtain fully from Station 9+16 to 25+82 along the upstream and downstream portions of the crest. The modification work continued with the upstream and downstream offsets for the production grout lines. Holes drilled on the D-Line between Station 9+26 and Station 21+06 were inclined 20 degrees from vertical towards the left abutment. Holes drilled on the U-Line between Station 19+82 and 25+82 were inclined 20 degrees from vertical towards the right abutment. The work shifted from an exploratory focus to a production emphasis with less rock core obtained, less OA/TV, and prescribed downstage grouting in the left abutment Haney Limestone. DRAFT

Figure 18: Phase IB Modified Contract Boreholes

Phase IB Completion Summary:

Ultimately, the project successfully installed a total of 308 production grout holes and 20 verification holes. These holes required 32,422 linear feet of overburden and embankment drilling, 7,477 linear feet rock coring, 26,058 linear feet percussion rock drilling, and a total of 212,763 gallons (1,053 cubic yards) of grout injected into the dam foundation bedrock. There was a limited amount of additional drilling and grouting associated with abandoned boreholes.

The Phase 1B work was completed in April 2017. A summary of current dam cross section is shown in Figure 19.

Figure 19: Existing Dam Cross Section: Station 20+00

Embankment Cracks Twelve borings encountered embankment cracks while drilling through the embankment.

Generally, the cracks were observed along the periphery of the valley abutments where the embankment is the deepest and appeared to be parallel to the core axis. These cracks ranged in elevation from 512.8 to 479.8, between Stations 18+50 and 19+30 (left of old river channel) and 21+90 and 22+00 (right of old river channel). Three samples were discolored with what appeared to be mineral staining. All the encountered embankment crack locations are summarized in Table 3 from borings drilled in early 2016 as part of the Phase 1B grouting effort.

Table 3: Embankment cracks encountered during Phase 1B grouting

Hole Depth of Fracture

Elevation

(NGVD-29)

Length of Fracture (ft.)

Material From To From To

UXT1871 60 65 498.9 494.2 5 CL

UXS1886 68 75 491.4 484.8 7 CL-ML

UXS1886 67 73 492.3 486.7 6 CL

UXT1891 45 48 513.0 510.2 3 CLg

UXT1891 70 74 489.5 485.8 4 CL

UXS1906 55 65 503.6 494.2 10 CLg

UXS1926 55 60 503.6 498.9 5 CL

UXP1936 55 56 503.6 502.7 1 CL

UXT1941 56.5 62 502.2 497.0 5.5 CL

UXT1951 64 67 495.2 492.3 3 CL

UXS2172 65 67 494.2 492.3 2 CL

DXT2177 67 74 492.3 485.8 7 CL/CH

Other items to note include: UXS1906 showed a 5-foot crack in the center of the 6” core sample from 55 to 65 feet below top of ground (angled); UXS2172 (2 foot crack, elevation 492-494);

and DXT2177 (7 foot crack, elevation 485-492) were both angled right. The cracks are not at the same elevation and are below the inclined filter (elevation 495). The only downstream hole where cracking was encountered is DXT2177. A 2020 crest survey between Stations 18+00 and 20+00 has indicated settlement of the dam crest (occurred post 2007 dam raise).

Geologic Profile Updates and Overburden Soils After Phase IB was completed the upstream and downstream grout line was studied fully to evaluate soil and bedrock stratigraphy across the two grout lines. The geologic profile that is contained in the Phase IB As-Builts has since been adjusted and the content of the left in place alluvial deposits across the valley have been better defined. The upstream and downstream geologic profiles shown in the Geology Section and in the Volume 3 plans is the most up to date stratigraphy and supersedes any previous interpretations or theories documented within the historical record. Some colluvial deposits were encountered along the base of the abutments but continuous boulder zones were not encountered.

Prior to Phase IB grouting, odorless gas was encountered at a depth of roughly 121 feet while installing PZ-77 (Station 20+25) and PZ-79 (Station 21+50) within the sand overburden. Gas was encountered at a depth of 135 feet in the inclined hole of DXP1982 and at a depth of 130 and in the inclined hole of UXP2056 during Phase IB drilling, which roughly corresponds to the location where gas was encountered in PZ-77. In all cases, the gas (suspected to be methane) was encountered in sandy overburden soils with heavy organics approximately 30 to 40 feet above the top of rock and pegged the gas analyzer as explosive (above the Lower Explosive Limit). In order to continue drilling, the drill string was charged with water to suppress the gas.

Prior to encountering the gas during drilling, the reservoir was observed to bubble in an around the control tower at times with a large area observed just upstream and to the left of the control tower. This has not been observed since the gas was encountered during drilling.

Observations from Phase IB Slurry Control Grouting:

Overburden stick logs from Phase IB (Figure 20 and Figure 21) are included in the…