2011_0216_CAR_Geotech_Desk_Study_FINAL.pdf

J017065.01 City-Arch-River Geotech Desk Study FINAL.doc

GEOTECHNICAL DESK STUDY

THE CITY + THE ARCH + THE RIVER 2015

JEFFERSON NATIONAL EXPANSION MEMORIAL

ST. LOUIS, MISSOURI

Prepared for:

THE CITY + THE ARCH + THE RIVER 2015 FOUNDATION

St. Louis, Missouri

Prepared by:

GEOTECHNOLOGY, INC.

St. Louis, Missouri

Geotechnology, Inc. Project No. J017065.01

February 16, 2011

J017065.01

THE CITY + THE ARCH + THE RIVER 2015

TABLE OF CONTENTS

Page

I. INTRODUCTION AND SCOPE OF SERVICES

Project Description Site Description Purpose and Scope of Services

II. DOCUMENT REVIEW

Historical Maps and Photographs Soil Survey Coal and Clay Mines Caves, Sinkholes, and Quarries

III. GEOLOGY

Stratigraphy Structural Geology Top of Rock

IV. SUBSURFACE EXPLORATIONS

V. SUBSURFACE CONDITIONS

Museum of Westward Expansion North Entrance South Entrance Gateway Mall St. Louis Riverfront Illinois Overlook Poplar Street Bridge

VI. SITE DEVELOPMENT CONSIDERATIONS

Rubble Fill Environmentally Impacted Soils and Groundwater Soft Soils Swelling Clay Seismicity and Liquefaction New Fill Karst Groundwater

TABLE OF CONTENTS

-Continued-

Page

VII REFERENCES

VIII. REPORT LIMITATIONS

ILLUSTRATIONS

Plate

Site Location and Topography Plan of Site and Boring Data Locations in Missouri Plan of Site and Boring Data Locations in Illinois

APPENDICES

Appendix

Important Information About Your Geotechnical Engineering Report........................................A Selected Historical Maps ...............................................................................................................B Historical Pictorial – Downtown St. Louis 1895 Topography 1930’s Topography Selected Subsurface Data...............................................................................................................C Downtown St. Louis Bedrock Surface Surface & Bedrock Profile, Market-Pine Section JNEM Test Borings & Schedule Subsurface Profile – East Riverfront Subsurface Profile – Laclede’s Landing Station Subsurface Profile – Eighth and Pine Station Subsurface Profile – Stadium Station Soil Liquefaction Potential

SECTION I - INTRODUCTION AND SCOPE OF SERVICES

PROJECT DESCRIPTION

The City + The Arch + The River 2015 project includes redevelopment of the Jefferson National Expansion Memorial (JNEM), namely the Arch grounds, the Gateway Mall and Kiener Plaza, and the Mississippi riverfront in Missouri, and the Arch Viewing Stand and Gateway Geyser on the east side of the river in Illinois. The goal of the redevelopment is to connect the JNEM with the City of St. Louis and east riverfront by making inviting entrances that are unobstructed by the surrounding highways and by building new attractions to draw people into the area. Proposed changes include:

Arch Grounds. A landscaped structural deck will be built over the depressed section of Interstate 70 to connect the Arch grounds with the Gateway Mall to the west. The Museum of Westward Expansion under the Arch will be enlarged, and the entrance will be changed to face west towards the Gateway Mall. A plaza and restaurant will be constructed south of the Old Cathedral entrance. The Arch grounds will be landscaped to include lawn, meadow, shrub woodlands and wetlands, and new pedestrian paths will be provided.

The parking garage at the north entrance to the JNEM will be demolished and replaced with underground parking covered by a neighborhood park with common ground and play areas.

Walkways will connect to Laclede’s Landing through existing, arched openings under the Eads Bridge. The south entrance from Chouteau’s Landing will include an oval park and roundabout under the Poplar Street Bridge, with underground parking and amenities such as a farmer’s market, dog run, beer garden, ice rink, and art exhibits on existing Arch grounds to the north. Glass-enclosed pavilions at the north and south overlooks will be constructed along the riverfront.

Gateway Mall. The Gateway Corridor between Walnut and Pine Streets will be converted into an unofficial pedestrian zone by narrowing the streets and providing greener streetscape. Luther Ely Smith Square will be refurbished and extend across the I-70 deck into the Arch grounds. Kiener Plaza will be rebuilt as a new landscaped urban park.

Riverfront. The cobblestone levee will be refurbished and a pedestrian/vehicular corridor will replace the existing Leonor K. Sullivan Boulevard. 60-foot tall, lighted, river gauges will mark flood levels along the riverbank at six locations.

The City + The Arch + The River 2015 Foundation J017065.01

Illinois Overlook. The Malcolm W. Martin Memorial Park, south of the Arch viewing platform and Gateway Geyser, will be developed as a wetland reserve including wetland hydrology and avian research centers. A 35-foot tall, stilt-supported canopy trail will connect with the viewing platform.

SITE DESCRIPTION

The site boundaries and general topography of the area from the U.S.G.S. map of the vicinity are shown on Plate 1. The Gateway Arch is situated on a bluff about 30 feet above the Mississippi River. East of the Arch, the terrain drops abruptly to the river landing; the slope is covered by the grand staircase in front of the Arch, grass lawn north and south of the staircase, and concrete flood walls at the north and south ends of the park. West of the Arch, the ground slopes downward towards a north-south-trending valley that includes Memorial Drive. The area west of the Arch includes two lakes/reflecting pools, one north and one south of the Arch. A parking garage and maintenance building are located at the north and south ends of the park, respectively.

Downtown St. Louis slopes downward towards the east and south from high ground north and west of Kiener Plaza at about El 4751. The terrain begins to drop off steeply east of the Old Court House on Fourth Street to low ground along Memorial Drive and the depressed section of Interstate 70.

The Arch grounds consist mostly of lawns with trees planted along several walkways, particularly those north and south of the Arch legs. The Terminal Railroad passes through a tunnel along the staircase and slope east of the Arch. The Gateway Mall and Kiener Plaza are generally covered with concrete walks and plazas with intervening lawn areas.

The Illinois side of the JNEM is floodplain near El 400. As such, the site is relatively flat and covered with brush, weeds, and trees. Along the centerline of the Arch, a lawn area extends east from the river past the Arch Viewing Stand to the Gateway Geyser. The McArthur Bridge and railroad embankment form the east boundary of the property. The Casino Queen is north of the project, with the Eads and Martin Luther King Memorial Bridges further to the north. The Poplar Street Bridge will form the south boundary of the project. A rail yard and levee run parallel to the river in the western portion of the property. West of the railroads, the riverbank drops approximately 20 feet to the river. Several mooring dolphins and grain loading facilities are situated in the river along the riverbank.

1 Elevations used herein are in units of feet and referenced to mean sea level (msl) datum.

PURPOSE AND SCOPE OF SERVICES

The purpose of Geotechnology’s services was to conduct a geotechnical desk study to identify potential geotechnical site development issues for The City + The Arch + The River 2015 project. The desk study will assist the design team in identifying potential ground hazards and corresponding primary risks at an early stage, so that these risks can be better managed during the design and construction processes. The results of the desk study will also be used to optimize the costs of the subsequent subsurface explorations.

Briefly, our services consisted of site reconnaissance, review of available in-house and publicly-held geotechnical reports and published literature, data interpretation, and preparation of this report. Important information regarding geotechnical engineering reports has been prepared by the Association of Engineering Firms Practicing in the Geosciences (ASFE) and is included in Appendix A for your review.

SECTION II - DOCUMENT REVIEW

Several existing documents pertaining to surface and subsurface conditions were reviewed and are discussed in this section.

HISTORICAL MAPS AND PHOTOGRAPHS

USGS Quadrangle Map. We reviewed the USGS Quadrangle Maps for Granite City and Cahokia, Illinois, issued in 1954 (photo revised 1993). Depicted on Plate 1, the existing topography varies from El 390 to El 470 on the Missouri side and from El 390 to El 420 on the Illinois side of the JNEM. The land use designation is urban for most of the project area, except for a wetland in the vicinity of the Gateway Geyser.

1930’s Topographic Map. The 1930’s topographic map of the Missouri side of the

JNEM, as shown on Appendix B, indicates the topography in the project area sloped gradually downward towards the east and south from a hill top of El 475 at the intersection of Broadway and Market. East of about Third Street, the slope is more gradual below approximately El 445.

The street grid terminates at the Terminal Railway at the wharf line at approximately El 415.

The wharf terminates at the Mississippi River which is shown at El 390.

The topography shown on the 1930’s map is fairly regular with no apparent disruptions from excavations, ponds, or sinkholes. Comparing the topography from the 1930’s with the present topography shown on the USGS Quadrangle Map, there is little change in the topography other than the reflecting pools, below-grade parking garage and maintenance building, and the riverside slope and floodwall.

1895 Topographic Map. The street layout from 1895, presented in Appendix B, is essentially the same as that shown on the 1930’s topographic map, except for the presence of alleys between many streets.

1875 Pictorial Map. A pictorial map of St. Louis was published by Camille N. Dry in 1875 that presents a topographic survey depicting streets and buildings in perspective view.

Presented in Appendix B, the Arch grounds were a commercial district comprised mostly of warehouses, factories, and banks. The buildings were generally 3- to 5-stories tall, situated on a regular grid pattern from the top of the wharf, designated as Levee Street, to Third Street.

The commercial district extended northward beyond the Eads Bridge. The south end of the Arch grounds contained more industrial facilities, including forges, lead and zinc works, chemical works, lumber yards, breweries, distilleries, and a railroad depot. West of Third Street were more governmental and social buildings including the chamber of commerce, court house, custom house, post office, meeting halls, hotels, and churches. Luther Ely Smith Square contained Dr. McLean’s building, Walker& Kershaw, and the Missouri State Museum of Anatomy. Kiener Plaza was occupied by the Laclede Hotel, and the Nathan Card and David Nicholson buildings.

Sanborn Maps. Sanborn fire insurance maps provide a history of commercial development in the project area. Maps of St. Louis were prepared in 1908, 1932, 1950, and 1989. We refer the reader to the Phase I Environmental Report2 for a detailed discussion of findings from these maps.

Aerial Photographs. Geotechnology reviewed aerial photographs provided by

Environmental Data Resources, Inc. (EDR) (circa 1952, 1958, 1965, 1971, 1974, 1979, 1986, 1992, 1994, 1997, 1998, 2005, and 2006) to assist with determining past land usage on the Arch grounds and Illinois overlook. Copies of the aerial photographs are included in Geotechnology’s Phase I Environmental Site Assessment report. A summary of the aerial photograph observations is included below.

The photographs from 1952 and 1958 indicate the Arch grounds were mostly cleared of buildings, except for the Old Cathedral and a single warehouse at the northeast corner of 2nd Street and Clark Avenue. A large parking lot occupied the northern half of the grounds. By 1958, construction trailers occupy the southern portion of the grounds. Several riverboats with accompanying parking occupied the wharf in those years.

2 Phase I Environmental Site Assessment, The City + The Arch + The River 2015, 38 Washington Avenue, St. Louis, Missouri, Prepared for The City + The Arch + The River 2015 Foundation; Geotechnology, Inc., Report No.

J017065.03 not finalized as of this date.

The 1958 photograph depicts the Illinois overlook site as predominantly occupied by several railroad switch yards. Adjacent and surrounding properties contain manufacturing, industrial, or transportation related facilities. By 1986, the tracks in the railroad switch yard had been removed or covered. The 2005 and 2006 photographs indicate the rail switch yard has been either paved or covered with gravel and is occupied by several storage containers or semi trailers.

SOIL SURVEY

The USDA Soil Survey maps of the Missouri and Illinois project areas were reviewed for relevant project information. The Soil Survey of St. Louis County and St. Louis City, Missouri, shows one map unit for the Arch grounds, Gateway Mall, and St. Louis riverfront: Symbol 7B, Urban Land, Upland, 0 to 5 Percent Slopes. The map unit is described as more than 85 percent covered by asphalt, concrete, buildings, or other impervious material. The depth of cuts and fills ranges from 6 feet on flatter landscapes to more than 30 feet on steep slopes. Soil types are highly variable and require detailed onsite exploration to determine.

The Soil Survey of St. Clair County, Illinois, shows one map unit for the Illinois overlook and Malcolm W. Martin Memorial Park: Symbol 533, Urban Land. The map unit is described as more than 75 percent paved areas and buildings with high runoff into storm drainage systems.

Most of the area is nearly level to gently sloping.

COAL AND CLAY MINES

The Arch grounds and Gateway Mall are underlain by Mississippian-aged limestone bedrock that is not amenable to coal or refractory clay mine operations. Geotechnology reviewed the 1987 coal and clay mine map3; no coal or clay mines have been recorded in these areas.

The Illinois project area is underlain by thick alluvial deposits that are also not amenable to mining of coal, clay, or limestone products. The Illinois State Geological Survey’s collection of County Coal Mine Maps and Directories shows no record of mining activity in the project area.

CAVES, SINKHOLES, AND QUARRIES

Karst features, including caves and sinkholes, occur in the St. Louis region where Mississippian limestone is at or very near the bedrock surface, such as under the Arch grounds and Gateway Mall. Karst is often associated with bedrock drainageways such as Mill Creek and

3 “Underground Coal and Clay Mines in the City of St Louis, Missouri,” by Mimi Garstang, MDNR Division of

Geology and Land Survey, OFM-87-238-MR, 1987.

a northern tributary of Mill Creek that runs through downtown along 4th Street and Broadway, and then turns northwest to the intersection of 8th and Market Streets (Saeger, 1975).

Sinkholes averaging 50 to 60 feet deep occur in the City of St. Louis (Saeger, 1975);

almost all have been naturally or artificially filled. Within the limits of the Gateway Mall, Saeger listed one filled karst area or sinkhole, 138 feet deep, on 7th Street between Market and Walnut Streets. Saeger did not list any filled quarries in the project area.

Numerous caves are located within the City of St. Louis. Most are located south and west of the project area, particularly in the area of the Anheuser Busch brewery. The cave nearest to the Arch grounds is reported4 to be the St. Louis Brewery cave, located on Franklin Avenue between Second Street and Broadway. The Indian Mound, Kerzinger’s, Hyde Park, and Bremen caves are located further north on Broadway. Little is reported on the St. Louis Brewery cave, but the largest room in the Indian Mound cave was reported to be 20 feet square and 7 feet high. The nearest cave west of the project area is the Winkleman and Excelsior cave, located at Market between 17th and 18th Streets. In 1959, development over this cave resulted in a collapse measuring 38 by 22 feet at the ground surface and 25 feet deep. In 1960, a sunken sidewalk in front of the post office at 18th and Market Streets revealed a hole 38 feet deep.

SECTION III - GEOLOGY

STRATIGRAPHY

Carbonate rocks of the Mississippian System form the bedrock surface in both the Missouri and Illinois areas of the site. Quaternary deposits lie unconformably over the bedrock at the Illinois overlook and St. Louis riverfront. The Illinois overlook is located within a portion of the Mississippi River floodplain that is locally referred to as the American Bottoms.

Landforms commonly associated with mature river deposits, such as meander scars and oxbow lakes, are present within the floodplain.

Mississippian System. The Mississippian bedrock is between 450 to 1,000 feet in thickness in the area and is comprised mostly of carbonate rocks with some prominent shale and siltstone formations (Jacobs, 1971). The St. Louis Limestone is the uppermost formation beneath the Arch grounds, Gateway Mall, and Illinois overlook. The St. Louis Limestone is described as a light gray to gray, micritic to fine-grained limestone that commonly contains chert (Wilman et al, 1975). In downtown St. Louis, the formation is approximately 180 feet in thickness, thick bedded to massive with blue and bluish-gray shale seams (Saeger, 1975). The underlying Salem formation is 100 to 160 feet thick and consists of argillaceous oolitic limestone, bluish-gray to white with depth. The Salem is underlain by the Warsaw formation, a

4 Lost Caves of St. Louis, A History of the City’s Forgotten Caves, by Hubert and Charlotte Rother, 1996.

very shaley, fine to coarse crystalline fossiliferous limestone. The Salem grades gradually into the overlying St. Louis Limestone and the underlying Warsaw.

Quaternary System. Quaternary System deposits include all of the unconsolidated deposits between the bedrock surface and the ground surface. Two formations of the Pleistocene Series, the Henry Formation and the Cahokia Formation, represent most of the deposits in the Mississippi River Valley floodplain.

The Henry Formation is the older of the two formations and represents glacial outwash deposits of the Wisconsin Stage. The Henry Formation is described as stratified sand and gravel that can contain lenses of silt, clay, organic debris, and wood. Paleozoic carbonates are the most common pebble type, although Paleozoic sandstones/shales, igneous and metamorphic rocks are also common. The Henry Formation can display lateral and vertical variations in grain size, sorting, and bedding (Hansel and Johnson, 1996).

The Cahokia Formation is the younger of the two formations and represents post-glacial fluvial deposits of the Holocene. The Cahokia Formation is described as poorly sorted silt, clay, and silty sand that can contain lenses of sand and gravel. The Cahokia Formation can vary in thickness, but rarely exceeds 50 feet (Wilman et al, 1975).

In the East St. Louis area, the thickness of the Cahokia Formation is approximately 25 feet, while the Henry Formation is nearly 100 feet thick (Piskin and Bergstrom, 1975).

STRUCTURAL GEOLOGY

In general, the bedrock in St. Louis dips slightly to the east-northeast, influenced by the Ozark Dome to the southwest and the Illinois Basin to the east. The main structural features impacting local geology are the 12th Street and Dupo Anticlines. The 12th Street Anticline is a small flexure near 12th and Spruce Streets which trends northwest and becomes the Florissant Dome in north St. Louis County (Saeger, 1975). The Dupo Anticline runs underneath the town of Dupo, located south of the Illinois overlook, and trends northwest-southeast (Jacobs, 1971).

TOP OF ROCK

A deep-filled depression or erosional valley occurs within the bedrock surface in downtown St. Louis. The depression is bounded roughly by Third Street, Twelfth Street, Chouteau Avenue, and Washington Avenue. A bedrock surface map of downtown St. Louis is presented in Appendix C. The deepest part of the depression, at approximately El 325, is located at Market Street between 7th and 8th Streets. The bedrock surface rises abruptly towards the east and forms a north-south-trending ridge between El 415 and El 430 on the Arch grounds parallel to the former Second Street. East of the Second Street ridge, the bedrock surface drops down steeply to the base of the Mississippi River channel (Saeger, 1975).

The bedrock depth at the Illinois overlook is greater than 130 feet. Borings drilled for the neighboring Casino Queen project to the north encountered rollerbit refusal on apparent bedrock at a depth of 136 feet (El 274).

SECTION IV - SUBSURFACE EXPLORATIONS

Geotechnology reviewed site subsurface data in our files for the following projects within or adjacent to the Arch grounds, Gateway Mall, and Illinois overlook. The project locations with reference to the project limits of The City + The Arch + The River 2015 are shown on Plates 2 and 3.

SUBSURFACE EXPLORATIONS IN GEOTECHNOLOGY’S RECORDS

Project No. Project Title Borings, Depth

4095 Planet Hollywood 4 borings, 2 to 12 feet 5889 Casino Queen 19 soil borings, 30 to 136 feet 6311 Carr Street Pump Station 4 soil/rock borings, 19 to 30 feet 6634 Gateway Arch Grand Staircase 3 soil/rock borings, 26.5 to 48.5 feet 8093 Pet Building Renovation 5 soil borings, 5 to 30 feet 8242 Lumiere Casino & Tunnel 23 soil/rock borings, 5 to 66 feet 8698 Fountain Viewing Stand 2 soil borings, 108 to 130 feet 8834 902 South 4th Street 2 soil borings, 36 to 38 feet 8846 I-64 Eastbound Widening at 6th Street 1 soil/rock boring, 75 feet 9006 Port St. Louis Condominiums 9 soil/rock borings, 4 to 26.5 feet 10797 Ball Park Village 15 soil/rock borings, 65 to 102.5 feet 11428 Peavy Grain Company 2 soil borings, 40 feet F-16 Spanish International Pavilion 11 soil/rock borings, 118 to 140 feet F-22 500 North Broadway 8 soil/rock borings, 90 to 100 feet

M-114 First National Bank 11 soil/rock borings, 50 to 113 feet M-515 St. Louis Place 8 soil/rock borings, 74 to 86.5 feet M-518 JNEM Parking Garage 9 soil/rock borings, 21 to 37.5 feet MC-30 Boatmen’s Tower 10 soil/rock borings, 57.5 to 89 feet

Geotechnology also requested boring information from the following agencies:

IDOT: We received boring data on the approaches to the Poplar Street Bridge, Eads Bridge, Martin Luther King Memorial Bridge, and the proposed new alignment of Illinois Route 3.

MESD: Geotechnology performed cone penetrometer (CPT) soundings along the centerline of the Metro East Sanitary District (MESD) levee, located east of the Mississippi River in the Illinois overlook area. We have data from sixteen CPT soundings, spaced 100 to 2,000 feet apart.

METRO: We received boring data for METRO stations at Busch Stadium, 8th and Pine Streets, and Laclede’s Landing. In Illinois, we received boring data along the METRO track alignment from the Eads Bridge east to Illinois Route 3. We also received river bottom elevation data for soundings made in the Mississippi River next to Eads Bridge Piers 9, 10, and 11 in 1974.

MODOT: We received boring data from the Walnut, Market, Chestnut, and Pine Street Bridges over Interstate 70, the Third Street Viaduct over the approaches to the Eads Bridge and Martin Luther King Memorial Bridge, and the Poplar Street Bridge piers and approach ramps.

NPS: The National Park Service provided a plan of the Arch grounds depicting the locations of 154 test borings and a schedule of bedrock elevations at most of the boring locations. The NPS has also provided boring information for the maintenance building located at the south end of the Arch grounds.

USACE: We requested but have not received boring data from the U.S. Army Corps of Engineers on the St. Louis floodwall in Missouri and the MESD levee in Illinois. A subcontractor provided data from two borings made along the St. Louis floodwall, one near the Poplar Street Bridge and the other at the foot of Carr Street.

SECTION V – SUBSURFACE CONDITIONS

Anticipated subsurface conditions within specific areas of the project, based on boring data from subsurface explorations listed in the previous report section, are discussed below.

Selected subsurface plan and profile data are presented in Appendix C.

MUSEUM OF WESTWARD EXPANSION

Based on MODOT borings made along Memorial Drive, the stratigraphy in the area of the proposed museum expansion consisted of rubble fill, 3 to 25 feet deep, underlain by silty clay, silty sand, sandy clay, and clay. The cohesive soils were soft to stiff; the sand was loose.

Groundwater was noted in one boring at a depth of 23 feet.

Limestone bedrock occurred at depths of 33 to 50 feet. The top of rock was generally highly weathered, solutioned, and pinnacled. Within the footprint of the museum, the bedrock surface generally decreased towards the west from approximately El 425 at the Arch to El 415 at Memorial Drive. The bedrock surface also decreased from north to south along Memorial Drive.

NORTH ENTRANCE

The stratigraphy consisted generally of uncontrolled fill, 6 to 27 feet deep, underlain by clayey silt, silty clay, sandy silt, and silty sand. Auger refusal occurred at depths of 12 to 60 feet.

Groundwater was observed during drilling at depths of 13.5 to 33.5 feet. Groundwater was measured at depths of 20.4 to 22.3 feet in piezometers installed at Lumiere Place Casino, located north of the Martin Luther King Memorial Bridge.

The fill consisted generally of stone and brick rubble, wood, and glass in a matrix of silt, silty clay, or sand and gravel. The underlying cohesive soils, where present, were generally soft to medium stiff in consistency, underlain by medium dense, sandy silt to silty sand.

Bedrock cores consisted of hard, gray, lithographic to fine-grained limestone with brown clayey shale partings. The rock was generally thin to medium bedded with some cavities.

RQD’s5 of 0 to 100 percent were recorded in the cores. A solutioned, calcareous siltstone layer occurred at depths of 10 to 15 feet below top of rock in cores made at 500 North Broadway. The rock was also solutioned, with little or no recovery, in the upper 3 to 12 feet of cores made in three borings at the Lumiere Place.

SOUTH ENTRANCE

The stratigraphy consisted generally of uncontrolled fill, 3 to 35 feet deep, underlain by silty clay and clayey silt with layers of silty sand and clay. Auger refusal on bedrock occurred at depths of 9 to 55 feet (El 425 to El 373). However, the depth to bedrock has been reduced by subsequent cuts in ground elevations during construction of the Arch maintenance facility.

Groundwater was observed during drilling at depths of 8 to 29 feet in several borings.

Groundwater was typically found perched within the fill.

The fill consisted of limestone blocks, concrete, brick, glass, and rebar in a matrix of sand, gravel, and silty clay. The underlying silty clay and silt layers were generally soft to medium stiff. The silty sand was loose to medium dense. Bedrock consisted generally of hard, gray, finely crystalline to micritic, medium bedded, highly weathered to fresh limestone with stylolites and gray, shaley clay seams. The upper 2.5 to greater than 7 feet was highly weathered. RQD’s in the core ranged from 51 to 93 percent.

5 Rock quality designation is the ratio of the sum of the pieces of core measuring 4 inches or larger to the total length of the cored interval, expressed as a percentage.

GATEWAY MALL

The stratigraphy consisted generally of uncontrolled fill, 2 to 25 feet deep, underlain by soft to stiff, silty clay and clay with layers of sandy silt and silty sand. Auger refusal on bedrock occurred at depths of 40 to 125 feet. The depth to rock decreases from west to east; the shallowest is at the intersection of Chestnut Street and Memorial Drive. Groundwater was measured in piezometers at depths of 21 to 40 feet.

The fill consisted of concrete and brick rubble with wood and glass in a matrix of cinders, ash, and sand. The upper 20 to 30 feet of the underlying soil consisted of modified loess comprised of soft to stiff silt, silty clay, and clay of low to high plasticity. The loess was underlain by alluvial soils consisting of soft to medium stiff, silty clay and clay stratified with loose to dense silt, silty sand, and fine sand.

Bedrock cores consisted of gray, lithographic to finely crystalline, limestone, stylolitic, with brown to blue shale and shaley clay partings. The limestone was generally hard to very hard, thin to medium bedded, slightly weathered, and dense. RQD’s were recorded in the range of 60 to 100 percent in borings made for the Boatmen’s Tower; the top 5 feet of the core were highly weathered with poor RQD in several of the borings.

ST. LOUIS RIVERFRONT

The stratigraphy consisted of uncontrolled fill, 3 to 27 feet deep, underlain by silt, silty clay, clay, and fine- to medium-grained sand. The fill consisted of silty clay and silt with brick and stone rubble, asphalt, cinders, sand, and gravel. The underlying cohesive soils, where present, were soft to stiff in consistency, and the sand was medium dense. Auger refusal on bedrock occurred at depths of 8 to 40 feet. Groundwater was observed during drilling at depths of 14 to 38.5 feet.

Bedrock consisted of hard, gray, very finely crystalline, massive, moderately to slightly weathered limestone with clay seams and cavities. RQD’s ranged from 18 to 93 percent. Rock cores made along the riverfront north of the Eads Bridge encountered several cavities 6 to 18 inches thick. Bedrock is deepest at the south overlook and adjacent to the Eads Bridge.

Bedrock typically occurs at depths of 10 to 20 feet under most of the riverfront.

ILLINOIS OVERLOOK

The stratigraphy consisted generally of uncontrolled fill, 4 to 25 feet deep, underlain by soft to stiff, silt and silty clay to depths of 20 to 27 feet, underlain in turn by very loose to medium dense, silty sand. Medium dense to very dense, fine- to medium-grained sand generally occurred at depths below 20 to 60 feet. Groundwater was encountered during drilling at an approximate depth of 29 feet, but is anticipated to rise and fall with Mississippi River levels.

The fill consisted generally of silty clay or sand and gravel with cinders. Brick and concrete rubble with silty clay occurred in the southern part of the Casino Queen site, north of the viewing stand and fountain. Underlying layers of very loose to loose, silty sand and fine-grained sand could be potentially susceptible to liquefaction.

Rollerbit refusal on apparent bedrock occurred at an approximate depth of 136 feet

(El 274) at the Casino Queen site. Rock coring was not performed to determine the type and quality of the bedrock.

CPT soundings on the MESD levee indicated interbedded layers of silty clay and clay occur within the silt and silty sand, mostly in the top 25 to 55 feet of the soundings. Particularly thick layers of silty clay and clay occur along the levee near the Arch Viewing Stand and the Poplar Street Bridge.

POPLAR STREET BRIDGE

West Abutment, Pier 1. The soil stratigraphy consisted generally of uncontrolled fill, 3 to 15 feet deep, underlain by silty sand, fine sand, and fine to coarse sand. The fill consisted generally of sand, clay, boulders, brick, and cinders with some wood. Rollerbit refusal on apparent bedrock occurred at approximate depths of 37 to 39 feet (El 376 to El 378). Bedrock consisted of gray, cherty limestone. Core recoveries ranged from 80 to 100 percent.

Groundwater was encountered during drilling at approximate depths of 20 to 23 feet, but is anticipated to rise and fall with Mississippi River levels.

River Piers 2 through 5. The river bottom varied from approximately El 380 at western

Pier 2 to El 365 at middle Pier 3 to El 353 at middle Pier 4 to El 380 at eastern Pier 5. The soil stratigraphy consisted generally of fine sand with variable amounts of gravel on the west, to fine to coarse sand and gravel on the east. Rollerbit refusal on apparent bedrock occurred at approximately El 355 at western Pier 2 to El 323 at middle Pier 3 to El 298 at middle Pier 4 to El 288 at eastern Pier 5. Bedrock consisted of gray, fine- to medium-grained limestone, some with few thin shale seams. Core recoveries ranged from 58 to 100 percent.

East Abutment, Pier 6. The soil stratigraphy consisted generally of 2 to 5 feet of uncontrolled, sand and cinder fill underlain by fine to coarse sand with gravel. Rollerbit refusal on limestone bedrock occurred at depths of 129 to 135 feet (El 282 to El 287). Core recoveries ranged from 78 to 98 percent.

SECTION VI - SITE DEVELOPMENT CONSIDERATIONS

Geotechnical field explorations and related analyses will be required once preliminary plans are prepared for proposed individual structures. The comments included in this report should only be used for conceptual planning. Subsurface and surface features that could influence the geotechnical approach to site development include the following:

RUBBLE FILL

Fill is likely to be present as a result of previous alterations to the topography. Most of the fill is likely to be uncontrolled and poorly compacted. Rubble fill can be expected in basement areas of previously demolished structures and was noted in many of the existing borings. Non-engineered fills can settle excessively and would therefore require remediation for use of shallow-bearing foundations. Rubble fill, free of deleterious material, can often be processed and reused on site.

ENVIRONMENTALLY IMPACTED SOIL AND GROUNDWATER

The southern section of the Illinois overlook was previously used as a locomotive repair facility and rail yard. A metal fabrication facility was previously located on the northern portion of the site. Additionally, a review of previous environmental reports for subject property revealed the past presence of an underground storage tank. The tank was reportedly removed and surrounding contaminated soil was removed. The reader is referred to Geotechnology’s Phase I Environmental Site Assessment report for further details.

These and other activities on the site could have generated hazardous substances and petroleum products. Therefore, the possibility exists that localized areas of contaminated soil and groundwater could be encountered.

SOFT SOILS

Soft, compressible soils were observed in some borings, particularly in areas with deeper soil profiles such as the Gateway Mall and the proposed south entrance to the Arch grounds.

When loaded, these soils could take several months to more than a year to fully consolidate. Soft soil below structures could require removal and replacement with compacted fill, preloading with wick drains or settlement monitoring during fill placement, or ground improvement such as aggregate columns.

The Sanborn Maps indicate former sludge ponds south of Trendley Avenue and a pond in the northeast portion of the Illinois side of the JNEM. Soft soils can be expected at these and other backfill locations.

Soft, silty soils can quickly decrease in strength if disturbed. It could be necessary to use wide-track equipment and vary traffic patterns to reduce disturbance and resultant softening of these soils. During site grading, substantial moisture-conditioning of these soils could also be required to achieve required compaction.

Soft, wet, sensitive soils might also require a special grading approach to establish a stable subgrade. These soils often must be overexcavated using a trackhoe and backfilled with crushed rock, pushed into the excavation with the equipment working on top of the rock platform. A biaxial geogrid might also need to be placed on the excavation bottom before placing the crushed rock.

SWELLING CLAY

Moderate to high plasticity soils were generally not observed at shallow depth in the existing borings. However, these clays commonly occur within the St. Louis region. High plasticity clay has a swell potential and can cause distress to lightly loaded foundations, floor slabs, and pavements. Remedial alternatives include partial removal and replacement or treatment with hydrated lime or lime byproducts.

SEISMICITY AND LIQUEFACTION

During an earthquake, pore water pressures increase within saturated soil deposits due to seismic shaking. Loose, saturated, cohesionless soil deposits in which the increased pore water pressure exceeds the effective overburden pressure could experience a sudden loss of strength, sometimes resulting in loss of bearing capacity, permanent lateral displacement, and settlement of the ground. This phenomenon is called soil liquefaction.

The project area is located in a region of the country that has a significant seismic risk due to the presence of the New Madrid Seismic Zone (NMSZ) in southeastern Missouri and the Wabash Valley Seismic Zone (WVSZ) in southeastern Illinois and southwestern Indiana. The NMSZ is the site of three of the largest magnitude earthquake events (estimated surface-wave magnitudes greater than or equal to 8.0) to strike North America in recorded history (December 1811 through February 1812). Researchers predict that the WVSZ is capable of producing large earthquakes similar in magnitude to the 1811-1812 NMSZ earthquakes. Seismologists predict that there is a reasonable probability that an earthquake of damage-causing magnitude could occur during the lifetime of the proposed structures.

The stratigraphy in the Illinois project area and the St. Louis Riverfront contain cohesionless silts and sands that could be susceptible to liquefaction during a strong ground motion event. The magnitude of risk depends on soil type, soil density, and the magnitude of the earthquake. A regional map depicting areas with high liquefaction potential is presented in Appendix C. Liquefaction can result in lateral movement and settlement of shallow-bearing structures and steep slopes, and loss of lateral support of piles and other deep foundation systems.

NEW FILL

Fills greater than 10 feet thick are planned at the north and south entrances to the Arch grounds. Significant fill-induced settlement of the underlying soil could occur in these areas.

Settlement plates can be used to monitor dissipation of movement, prior to construction of surface features on the new fills. In areas where the anticipated settlement delay is extensive, wick drains or ground improvement can be used to increase the rate of settlement and reduce the delay.

Negative skin friction (downdrag) can reduce the capacity of deep foundations installed in areas where relatively thick fills are placed. Cohesive soils that settle under fill loads can produce downdrag on pile and drilled pier foundations. Pre-drilling holes for the piles through the new fill and underlying cohesive deposits might be required to reduce downdrag forces.

Piles could also be coated with bitumen to reduce downdrag.

KARST

The site topography and historical records do not feature sinkholes or caves indicative of karst activity on the Arch grounds. However, the long history of man-made fills in downtown St. Louis would tend to mask karst features.

Solution features, including thin voids and clay seams, were observed in existing rock cores, generally limited to the upper 3 to 5 feet of the St. Louis Limestone. Solution activity appears to be more common in the northern part of the site (Laclede’s Landing), the Gateway Mall, and the Museum of Westward Expansion. Drilled pier foundations bearing on karstic limestone would require probe borings to check for the presence of voids or clay layers below the pier bottom.

GROUNDWATER

In the upland areas of the project in Missouri, the boring data indicate that groundwater generally occurs within sandy layers at depths below 20 feet or is perched on the bedrock.

However, groundwater can also occur at shallower depth within porous, existing fill materials.

Groundwater can normally be controlled in shallow excavations with pumps and sumps.

Excavations that extend into deeper sandy layers connected to the river could require active dewatering with well points or deep wells. Perimeter drains and, in some cases, underdrains are generally specified for basement construction in St. Louis.

Saturated sand occurs at relatively shallow depth within the floodplain of Illinois and along the St. Louis riverfront. Groundwater levels in the sand will vary with the Mississippi River stage. As such, some form of local dewatering is often required to complete excavations in these areas. Deeper excavations would require an active dewatering system using well points or deep wells.

SECTION VII - REFERENCES

Bergstrom, R.E. and Walker T.R. 1956, Groundwater Geology of the East St. Louis Area, Illinois. Illinois State Geological Survey, Report of Investigations 191, 44 p.

Jacobs, A.M. 1971, “Geology for Planning in St. Clair County, Illinois.” Illinois State Geological Survey, Circular 465, 35 p.

Piskin, K. and Bergstrom, R.E. 1975, “Glacial Drift Thickness in Illinois: Thickness and Character.” Illinois State Geological Survey, Circular 490, 34 p.

Saeger, W.E, “Geologic and Subsurface Investigation of the St. Louis Missouri Metropolitan Area (for a Proposed Rapid Transit System),” Washington University Department of Earth Sciences Graduate School Thesis, May 1975.

SECTION VIII - REPORT LIMITATIONS

This report has been prepared on behalf of and for the exclusive use of the client for specific application to the named project as described herein. If this report is provided to prospective contractors, the client should make it clear that the information is provided for conceptual planning only and not as a warranty of subsurface conditions included in this report.

The comments given in this report are based on interpretation of limited published data and Geotechnology's experience. Subsurface exploration and geotechnical evaluation must be performed for detailed site evaluation. Geotechnology will not be responsible for improper use of the comments herein or failure by others to recognize conditions that could be detrimental to the successful design of the project.

Geotechnology has endeavored to conduct the services described herein in a manner consistent with that level of care and skill ordinarily exercised by members of the profession currently practicing in the same locality and under similar circumstances as this project.

Geotechnology makes no other warranty, expressed or implied. The comments contained in this report are professional opinions.

APPENDIX A

IMPORTANT INFORMATION ABOUT

YOUR GEOTECHNICAL ENGINEERING REPORT

APPENDIX B

SELECTED HISTORICAL MAPS

HISTORICAL PICTORIAL – DOWNTOWN ST. LOUIS

1895 TOPOGRAPHY

1930’s TOPOGRAPHY

APPENDIX C

SELECTED SUBSURFACE DATA

DOWNTOWN ST. LOUIS BEDROCK SURFACE

SURFACE & BEDROCK PROFILE, MARKET-PINE SECTION

JNEM TEST BORINGS & SCHEDULE

SUBSURFACE PROFILE – EAST RIVERFRONT

SUBSURFACE PROFILE – LACLEDE’S LANDING STATION

SUBSURFACE PROFILE – EIGHTH AND PINE STATION

SUBSURFACE PROFILE – STADIUM STATION

SOIL LIQUEFACTION POTENTIAL