GEOPHYSICS GPR INTERNATIONAL INC.A number of geophysical methods were employed to characterize the subsurface conditions at specified traverse locations at the site (Fig. 2). The methods

1.3- __.

GEOPHYSICS GPRINTERNATIONAL INC.

SDMS DocID 268552

GEOPHYSICAL INVESTIGATION

GENERAL ELECTRIC NEWELLSTREET PARKING LOT SITE

PnrSFIELD, MASSACHUSETTS

Prepared for:

BLASLAND, BOUCK & LEE, INC.6723 Towpath Road

Syracuse, New York 13214

Prepared by:

GEOPHYSICS GPR INTERNATIONAL, INC.13 Highland Circle, Suite E

Needham Heights, Massachusetts 02194

May 8, 1996 B96121

GEOPHYSICS GPR INTERNATIONAL INC. 13 Highland Circle Su"e ENeedham Heights, MA Tel.: (617) 455-018502194-3031 Fax: (617) 455-0522

May 8, 1996 Our Project No. B96121Your Project No. 201.37#2

Blasland, Bouck & Lee, Inc.6723 Towpath RoadSyracuse, NY 13214-0066

Attention: Lynette Mokry

In accordance with your General Contract, Geophysics GPR International, Inc. has conducteda geophysical investigation at the General Electric Newell Street Parking Lot site, Pittsfield,Massachusetts.

This report contains the results of our findings, and is intended for the use of Blasland, Bouck&Lee.

Sincerely,

GEOPHYSICS GPR INTERNATIONAL, INC.

Lester M. Tyrala,District Manager

LMT/hpAtt - 3 copies


GENERAL ELECTRIC NEWELLSTREET PARKING LOT SITE

PITTSFIELD, MASSACHUSETTS

Presented to:

BLASLAND, BOUCK & LEE, INC6723 Towpath Road

Syracuse, New York 13214

Presented by:

GEOPHYSICS GPR INTERNATIONAL, INC.13 Highland Circle, Suite E

Needham Heights, Massachusetts 02194

May 8, 1996 B96121

CONTENTS

1.0 INTRODUCTION 1

2.0 SITE AND AREA CONDITIONS 1

3.0 METHODS OF INVESTIGATION 13.1 Ground Penetrating Radar 33.2 Seismic Refraction Survey 33.3 Seismic Reflection Survey 3

4.0 DATA ACQUISITION 54.1 Equipment 54.2 Survey Design and Procedures 5

5.0 INTERPRETATION 6

6.0 RESULTS 66.1 Ground Penetrating Radar 76.2 Seismic Reflection and Refraction 76.3 Precision and Limitations 76.4 Geophysical Traverse Lines 10

7.0 CONCLUSIONS 12

FIGURES

Figure 1. Site Location Plan Map, Pittsfield, Massachusetts 2Figure 2. Geophysical Traverse Line Positions Map 4Figure 3. Ground Penetrating Radar Record, Line 5 8

LIST OF MAPS

Profiles, L-l to L-7 foldout, pocket

APPENDIX

Seismic Reflection Method (with Reflection Profiles) ASeismic Refraction Method B

1.0 INTRODUCTION

Geophysics GPR International, Inc., under a directive of Blasland, Bouck &Lee, Inc. (BBL),performed several geophysical methods at the General Electric Newell Street Parking Lot site.The plan of activities are set out in our proposal of April 4, 1996.

Ground penetrating radar, seismic reflection, and seismic refraction surveys were conductedunder the direction of a BBL representative at specified locations at the site. These surveyswere conducted during the period of April 16 to 19, 1996. The primary objectives of thesesurveys were to delineate and map a silt layer occurring in the glacial overburden and determinethe depths to the bedrock surface. The area investigated by the methods is flatlying and wasfree of obstructions during the time of the survey.

The Newell Street Parking Lot site is located on Newell Street, Pittsfield, Massachusetts. Thesite is generally bounded on the northerly side by the Housatonic River, the easterly andwesterly sides by residential properties, and the southerly side by Newell Street (Fig. 1).

2.0 SITE AND AREA CONDITIONS

The site is flatlying with a gentle northeasterly slope toward the river. The site consists of anasphalt paved parking area, grassy areas, and wooded patches adjacent to the river and alongthe westerly side of the site.

The surficial materials consist of loose, graded sand and gravel and unconsolidated glacialmaterials away from the parking lot. The area is well drained and the underlying materialsconsist of a sequence of glacial deposits occupying a valley generally coincident with the courseof the river. The water table is about ten feet below ground surface with the depth ofoverburden ranging up to sixty feet. Cultural disturbance has slightly altered the naturaltopography and soil composition within the top few feet at the site.

The bedrock at the site consists of metasedimentary rocks. The provided boring logs of the siteborings did not penetrate to bedrock. This information was taken from data provided by BBLand observed conditions.

3.0 METHODS OF INVESTIGATION

A number of geophysical methods were employed to characterize the subsurface conditions atspecified traverse locations at the site (Fig. 2). The methods were selected on the basis ofconversations with BBL and provided subsurface information.

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DRAWN BY

A. Beaudoin

CHECKED BY

C. Robillard

APPROVED BY

L. Tyrala

TITLE

LOCATION PLAN MAP FORGEOPHYSICAL TRAVERSES

BLASLAND, BOUCK & LEE, INC.PROJECT

GENERAL ELECTRIC NEWELLSTREET PARKING LOT SITE,

PITTSFIELD, MASSACHUSETTSDRAWING DATE

04/25/96

SCALEFig. 1

3.1 Ground Penetrating Radar Method

Ground penetrating radar (GPR) employs high resolution radar to detect buried objects andsubsurface stratigraphy. Many of the principles of GPR are similar to that of the seismicreflection method used in oil and gas exploration. The transmitting antenna emits brief pulsesof electromagnetic energy into the ground, then pauses between pulses with the receivingantenna recording energy which has been reflected back to the surface.

Radar waves are reflected by interfaces between media with differing dielectric constants, suchas geologic contacts, buried objects, or voids. The dielectric constant is controlled by factorssuch as water content, density, and composition. The depth of penetration is limited by theoperating frequency of the transmitter and the electrical conductivity of the ground.

The GPR unit records the two-way travel time and the amplitude of the reflected signals. Thetypical radar anomaly produced by a layer of stratum is a coincidence of radar wave formsproducing a defined reflector in the records as a band. The source of the radar anomaly islocated at the upper surface of the stratum.

3.1 Seismic Refraction Survey

A 24-channel digital seismograph, an EG&G SmartSeis, was used and set up in the seismicrefraction mode with a geophone spacing of about eight feet. The objectives of the refractionsurvey were to try to profile the silt layer and determine the depths to the bedrock surface.These traverses were coincident with the reflection traverses with five to seven energy points(shots) along each spread for our quality control of field data collection: forward and reverseoffset (far) shots, end shots, a center shot, and quarter shots. A two geophone overlap was laidout for contiguous spreads.

The offset (far) shots allow detailed calculation of the profile and velocity of the bedrock, whilethe shots within the spread provide information on the lateral variation in the velocity of theoverburden, which is required to determine the depth to bedrock (see App. A).

3.2 Seismic Reflection Survey

The same 24-channel digital seismograph was employed, an EG&G SmartSeis, and configuredfor a reflection survey. The seismic reflection survey, about an eight foot spacing at alllocations, was configured to determine the silt layer in the glacial overburden and define thebedrock surface. Interfaces which exhibit a contrast in acoustic impedance (the product ofvelocity and density) will reflect seismic energy back to the surface. Seismic reflection has thepotential of detecting units of glacial strata and the detailed configuration of the bedrock surface(see App. B).

LECBm

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MONITORING WELL

PIEZOMETER

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APPROXIMATE STE BOUNDARY

APPROXIMATE EXISTING FENCELOCATION

APPROXIMATE PARCEL BOUNDARY

NOTES:

1. THE BASE MAP FEATURES PRESENTED ON THIS FIGUREWERE PHOTOGRAMMETR1CALLY MAPPED FROM APRIL 1990AERIAL PHOTOGRAPHS.

2. ALL SAMPLING LOCATIONS ARE APPROXIMATE.

100'

SCALE: r-1001

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GENERAL ELECTRIC COMPANYPITTSFIELD, MASSACHUSETTS

NEWELL STREET PARKING LOT/USEPA AREA SB

BBL BUSUND. BOUCK & lie. INC.•nglnitr* * scl»ntl*1*

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The performed seismic reflection survey employed common depth point (CDP) data acquisitionwith multi-fold coverage (up to 12-fold (1,200% coverage)). Refer to Appendix B for eachprofile displaying the fold coverage.

4.0 DATA ACQUISITION

Each geophysical method utilized at this site had its own requirement for equipment and mannerof conducting the survey. The surveys required laying out traverse lines to control datacollection points.

4.1 Equipment

The GPR survey was performed with a GSSI SIR System-10 radar system, with a 100 mHzhigh-power antenna. Lower frequency antennas permit greater depths of exploration whilereducing spatial resolution. All field data were viewed on a monitor and stored on magnetictape.

A digital seismograph was employed for this investigation. Amplification of the signals fromthe geophones is accomplished using integrated floating point technology, which allowsmaximum trace size throughout the record. Each seismogram is recorded digitally on theseismograph hard drive, transferred to floppy disk, and printed onsite.

For the seismic reflection survey, a roll-along switch was used to select the appropriate 24geophone position for each shotpoint from the total 48 geophone positions laid out as onespread. This switch allows for "rolling in and out" of the spread to efficiently increase the foldcoverage and for continuous common-midpoint recording within the spread. For the refractionsurvey, a 24 geophone array was used.

A sledge hammer was used for the refraction and reflection surveys. Typically, ambientacoustic noise was at acceptable levels and, where at higher levels, overcome by stacking andfiltering of the seismic records.

4.2 Survey Design and Procedures

Trial traverse lines were performed at selected locations using ground penetrating radar as thefirst method to determine its application at this site. The method showed an inconsistent anddiscontinuous response from the top of the silt layer. As was the schedule of activities, aseismic refraction survey was then performed to test its application to the detection of the siltlayer and bedrock. The results of the method did not define the silt layer, but did determinethe top of water saturated zone and the bedrock surface.

Seismic reflection was then performed with the field records indicating detection of reflectorsat depth. Based upon these results, the specified traverse lines were completed using seismicreflection and refraction (at no additional cost) with some fill radar traverses run at thecompletion of the specified program (at no additional cost).

Traverse lines were established at the specified locations. Areas within the parking lot and openground were investigated with the methods, and referenced to fixed structures and monitoringwell locations.

The specified program for the site required that traverses be performed at several locations (seepocket map). The seismic surveys were performed with an 8 1/4 foot geophone spacing alongthe specified locations, yielding a spread length of 190 feet.

5.0 INTERPRETATION

The results of the geophysical surveys were correlated with the relevant borehole data at thetime of the interpretation of the data. Not all of the borings that were consulted during theinterpretation were plotted on profiles, primarily due to its distance from a traverse line and/orshallow depth of the boring.

Preliminary interpretation of the seismic refraction data was accomplished with the cross-overdistance method. This method provides the depth to significant interfaces beneath theshotpoints. The reciprocal method of L.V. Hawkins (also known as Hawkins Method) was usedto provide the detailed interpretation. Unlike the cross-over distance method, the reciprocalmethod allows the calculation of the depth to bedrock beneath each geophone. The concurrentuse of both interpretive methods provides an important means of checking the validity of theinterpretation.

The interpretation of the seismic reflection data involved 2-D inverse computer modeling. FullCDP data processing was accomplished including normal move out (NMO), filtering, and terraincorrection. Each trace on the processed seismic section was spaced at one-half of the geophonespacing and represent the summation of the traces that receive reflections from the samesubsurface point. Depth conversion for the seismic reflection data was performed by usingaverage velocities derived from the refraction data and calibrated with the relevant boreholeinformation.

6.0 RESULTS•

Overall, the methods used at this site, when combined and integrated, gave very good results.The silt layer was imaged with ground penetrating radar and seismic reflection, and the bedrockwas determined with seismic refraction, seismic reflection, and radar.

6.1 Ground Penetrating Radar

Radar records obtained in the field are time sections. In order to convert the two-way traveltimes to depth, the velocity of radar waves in the subsurface must be determined. Velocitiescan be calculated by surveying objects of known depth or by materials velocity averaging.Depth calibration at this site was accomplished by surveying over monitoring well NS-31 atwhich the silt layer is at a known depth.

This velocity determination was used in generating the depth scales for the cross-sections.While the estimated depths are expected to be accurate in unsaturated materials, the sitecondition, the depth scale will be less accurate below the water table, where the velocity of radarwaves is considerably slower. The average depth of our GPR penetration across the site was15 feet (at the parking lot) to 55 feet (at the grassy areas at the western side of the site).

In general, GPR data of good quality were collected at the site (Fig. 3). The composition ofthe placed fill and natural materials allowed for good penetration of the GPR signal within aportion of the site. However, for most of the site where the radar trial was conducted themethod could not achieve the required penetration. Typically, a stratigraphic layer isdistinguished by its continuity as a flatlying radar reflector.

6.2 Seismic Reflection and Refraction Surveys

Approximately 1,825 linear feet of combined seismic reflection and refraction profiling wasaccomplished along four line traverses during the field surveys (foldout map, pocket). Theseismic surveys were performed at specified locations and modified in the field, as required, toconform to the specified positions with a BBL representative present for this fieldwork.Information provided by relevant boring logs were integrated into the final geophysicalinterpretation.

The results of the seismic refraction and reflection surveys are presented as integrated cross-sections (foldout map). A layer of dry surficial soils was determined along all traverses withdeeper unconsolidated overburden being fully water saturated. The top of this layer is welldefined continuously as a reflector in the reflection records and as a higher velocity layer in therefraction records. The top of the silt layer was imaged to a moderate degree on every traverse.The velocities of the bedrock are in distinct contrast to the overlying materials. Due to thelengths and orientations of the reflection and refraction traverses, the subsurface layers couldbe contoured, if desired, in a meaningful way.

6.3 Precision and Limitations

The typical velocities for sound, unweathered metasedimentary in southern New England rangefrom 7,500 to 15,000 ft/s and for weathered and/or fractured metasedimentary from 6,000 to

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GROUND SURFACE

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^ GEOPHYSICS GPRy£ INTERNATIONAL INC.

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DRAWN 8V

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C. Rob.llard

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L. Tyrala

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GROUND PENETRATING RADARLINE 5, 2 + 40 TO 3+10

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BLASLAND, BOUCK & LEE. INC.rnojicr

GENERAL ELECTRIC NEWELLSTREET PARKING LOT SITE.

PITTSRELD. MASSACHUSETTSDRAWWG D*TC SCALE

04/25/96 Record Marks '9

10,000 ft/s. The bedrock velocity values are shown on the profiles, and those in parenthesesare interpolated values.

The precision of a ground penetrating radar survey depends upon the subsurface conditionswithin the interval of the traverse where the survey was performed. The precision for a radartraverse is based upon the accuracy of electromagnetic travel time measurement, accuracy ofthe reflector (anomaly) selection, and accuracy of the depth conversion process. Typically, aradar traverse with quality records will yield a high precision of ±7 to 10 percent, and withmoderate quality records will yield a moderate precision of ±10 to 12 percent. The precisionat this site is high to moderate for the reflection traverses.

The precision of seismic reflection and refraction surveys depends upon the conditions withinthe interval of the traverse where the reflection and/or refraction was performed. The precisionfor a reflection traverse is based upon the accuracy of acoustic travel time measurement,accuracy of the reflector (time pick) choice, and accuracy of the depth conversion process.Typically, a reflection traverse with all shots collected and high quality records will yield a highprecision of ±8 to 10 percent, and with most shots and/or moderate quality records will yielda moderate precision of+.10 to 12 percent. The precision at this site is high to moderate forthe reflection traverses.

Typically, a refraction traverse with all seven shots collected and high quality records will yielda high precision of ±7 to 10 percent for depths greater than thirty feet and a precision of ±3to 5 percent for bedrock velocities, and with five to seven shots and/or moderate quality recordswill yield a moderate precision of ±10-15 percent for depths greater than thirty feet and aprecision of ±4 to 6 percent for bedrock velocities. The precision at this site is high tomoderate for the refraction traverses.

Altogether, the quality of the interpretation for this combined seismic reflection and refractioninvestigation at this site is high to moderate, due to the combination of the methods andcorrelation with the results of previous borings. Calculated depths to bedrock correlated withinthree feet with the cross seismic spreads. As explained in the Appendices, each method doeshave certain constraints with respect to detection of particular layers.

As with all geophysical methods, there are minimum detectible limits. Major limitations forseismic reflection and radar are thickness and/or size of the objectives, and for seismic refractionare velocity inversions and hidden layers (see App. B). Calibration with borehole data candefine and overcome most of these limitations. With respect to widths of low velocity bedrockintervals that could correlate to open fracture zones, widths greater than ±five feet should bedetectible with the refraction configuration that was used here.

For the surveys at this site, the minimum thickness of a layer that could be defined is about fivefeet near-surface and about 15 feet within the deeper portions of the investigated area. Thisresolution corresponds to the minimum thickness of more or less parallel layers which allow

10

detection of the lower interface. Thinner dipping layers and fracture zones ±two feet or morein width should be recognizable in the records.

6.4 Geophysical Traverse Lines

Geophysical trial traverse lines 1, 2, and 2A were conducted with radar only. Geophysicaltraverse lines 1 to 4 were conducted using all three methods, while traverse lines 5 to 7 wereconducted using radar only as an addition and at the completion of the survey.

Traverse Line 1

The subsurface horizons mapped on Line 1 (west to east), chainage 0+00 to 8+60, are derivedprimarily from the seismic refraction and reflection methods, as the ground penetrating radardid not yield good results along this traverse. Chainage 0+00 is positioned on the grass nearthe large wooded area at the western end of the site adjacent to the riverbank, and the traverseextends more or less parallel to the river, mostly on the paved surfaces, to the eastern end ofthe site.

The overburden portion of the profile shows about 12 to 18 feet of placed fill and unsaturatedsurficial soils (1,300 ft/s), 10 to 17 feet of saturated sediments (5,000 ft/s), and the top of thesilt layer. The silt surface appears to be nearly horizontal having minor topographic relief withdepths below ground surface ranging from 26 to 34 feet. The silt layer appears well definedin the reflection records and was imaged almost continuously as a seismic reflector.

The bedrock surface, from west to east, is at a depth of about 60 feet, inclined slightly upwardto a depth of 42 feet at about chainage 5+60, then is inclined downward to 70 feet at the endof the traverse at chainage 8+60. A good correlation was obtained by both seismic methodsin determining the bedrock surface. This line shows a moderate bedrock velocity (10,500 to13,500 ft/s) indicative of sound, unweathered bedrock. The depths show a good correlation toour crossline L-4.

Traverse Line 2

The subsurface horizons mapped on Line 2 (northwest to southeast), chainage 0+00 to 4+65,are derived from the seismic refraction and reflection methods, and the ground penetrating radaras it did yield some results along this traverse. Chainage 0+00 is positioned near the largewooded area at the western end of the site adjacent to the riverbank (southerly of chainage0+00 on Line 1), and the traverse extends on the grassy area nearly to Newell Street.

The overburden portion of the profile shows about 10 to 16 feet of placed fill and unsaturatedsurficial soils (1,300 ft/s), 7 to 16 feet of saturated sediments (5,000 ft/s), and the top of the silt

11layer. The silt surface appears to be inclined to the north having some topographic relief withdepths below ground surface ranging from 22 to 38 feet. The silt layer appears marginallydefined in the reflection records and discontinuously in the radar records.

The bedrock surface, from northwest to southeast, is at a depth of about 50 feet, horizontal toabout chainage 3+90, then is inclined upward to 45 feet at the end of the traverse at chainage4+65. A good correlation was obtained by the seismic refraction and radar methods indetermining the bedrock surface. This line shows a moderate bedrock velocity (10,200 to12,500 ft/s) indicative of sound, unweathered bedrock. The depths show a good correlation toboring F-l and to our crosslines, L-3, L-6, and L-7.

Traverse Line 3

The subsurface horizons mapped on Line 3 (southwest to northeast), chainage 0+00 to 2+35,are derived from the seismic refraction and reflection, and the ground penetrating radar method.No one method mapped the silt or bedrock surface continuously along this traverse. Chainage0+00 is positioned on the grass near the end of Line 2 and the traverse extends across the edgeof the parking lot.

The overburden portion of the profile shows about 7 to 15 feet of placed fill and partiallysaturated surficial soils (1,300 to 3,600 ft/s), 14 to 18 feet of saturated sediments (5,000 ft/s),and the top of the silt layer. The silt surface appears to be inclined slightly to the east havingsome topographic relief with depths below ground surface ranging from 26 to 32 feet. The siltlayer appears marginally defined in the reflection and radar records.

The bedrock surface, from southwest to northeast, is at a depth of about 52 feet, and nearlyhorizontal within this short interval. A correlation was obtained by the seismic refraction andradar methods in determining the bedrock surface. This line shows a moderate bedrock velocity(10,200 to 12,500 ft/s) indicative of sound, unweathered bedrock. The depths show a goodcorrelation to our crosslines, L-2, L-4, and L-5.

Traverse Line 4

The subsurface horizons mapped on Line 4 (north to south), chainage 0+00 to 3+30, arederived from the seismic refraction and reflection, and the ground penetrating radar method.As with Line 3, no one method mapped the silt or bedrock surface continuously along thistraverse. Chainage 0+00 is positioned on the grass near the end chainage of Line 2 and thetraverse extends across the edge of the parking lot to the site property line.

The overburden portion of the profile shows about 15 to 19 feet of placed fill and partiallysaturated surficial soils (1,300 to 3,600 ft/s), 13 to 17 feet of saturated sediments (5,000 ft/s),and the top of the silt layer. The silt surface appears to be nearly horizontal having no

12

topographic relief with depths below ground surface ranging from 32 to 36 feet. The silt layerappears marginally defined in the reflection and radar records.

The bedrock surface, from north to south, is at a depth of about 50 feet, and nearly horizontalwithin this short interval. A correlation was obtained by the seismic refraction and radarmethods in determining the bedrock surface. This line shows a moderate bedrock velocity(12,100 ft/s) indicative of sound, unweathered bedrock. The depths show a good correlationto borings NS-9, 11, 12, and 14 and to our crosslines, L-l and L-3.

Traverse Lines 5. 6. and 7

The subsurface horizons mapped on Lines 5, 6, and 7 were acquired with ground penetratingradar only. The silt layer could be mapped fairly consistently along these three lines. The dataappears to be of better quality in areas closer to the river. Line 5 (northwest to southeast)chainage 0+00 is positioned on the grass near the start of Line 1 and the traverse extends acrossthe grassy area almost to the end of line 2. Lines 6 and 7 (southwest to northeast) chainages0+00 are positioned on the grass near the wooded area and extend almost to the parking lot.

The overburden portions of the profiles show about 19 to 37 feet of placed fill, partially andfully saturated surficial soils and sediments on top of the silt layer. The silt surfaces displaysome inclination and relief; Line 5 shows a slight inclination to the north, Line 6 shows a nearlyhorizontal surface, and Line 7 shows a slight inclination to the south. There were nointerpretable radar reflections from the bedrock along these three lines.

7.0 CONCLUSIONS

The specified objectives of this geophysical investigation were to identify geologic surfaces, suchas the silt layer and bedrock. The results of this investigation identified and traced thesefeatures. Overall, the combination of the three methods detected the top of the water saturatedzone, the top of the silt layer, and bedrock surface.

A certain amount of stratigraphic detail was defined within the overburden. The lack ofcontinuity of several of these layers in the seismic and radar records is probably due to thediscontinuous nature of these layers recognized in the borings.

o Overall, the silt layer is overlain by placed fill and glacial deposits with a totalthickness ranging from 19 to 36 feet.

o Most of the traverse lines detected a continuous silt layer, displayed as a reflector inthe seismic reflection and/or ground penetrating records.

13

o The ground penetrating radar method located intermittently the top of the watersaturated zone, silt layer, and the bedrock surface.

o The complementary nature of ground penetrating radar, seismic reflection, andseismic refraction surveys defined, with a high to moderate degree of precision, layersin the overburden and the bedrock surface.

o Seismic reflection and refraction and radar imaged several different overburden layersas well as the bedrock surface.

o Seismic Refraction and reflection delineated the top of the water saturated zone.

o The seismic refraction and reflection surveys showed that the overburden at this siteconsists of unsaturated and saturated glacial materials overlying the silt layer. Theseoverburden layers have a velocity range of 1,300 ft/s to 5,000 ft/s.

o Overall, relatively sound bedrock is overlain by placed fill and glacial deposits witha total thickness ranging from 42 to 63 feet.

o The bedrock velocities are generally indicative of sound rock (10,200 to 13,500 ft/s).

o The bedrock surface was generally shown to have moderately uniform and gentlerelief.

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I THE RESULTS PRESENTED ON PROFILES SL- I , SL-2 , SL-3 AND SL-4 ARE A COMBINATION OF 3 METHODS , SEISM IC REFRACTION,

SEISMIC REFLECTION AND GEORADAR SURVEYS

2 THE GEOPHYSICAL SURVEY WAS PERFORMED BETWEEN THE 16th AND 19th OF APRIL 1996

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CHECKED BY

M Poul in, geol

C. Robi l lard, geoph

APPROUVE PARAPPROVED BY

L Tyrala , geol

N° CONTRATCONTRACT Nc B-96I2I

ECHELLE Hor I 50SCALE Vert l" 50 '

DATE May , 1996

N° DESSIN

DRAWING N*9 6 - 0 5 - 2 0 0

CLIENT' CLIENT!

BLASLAND, BOUCK S LEE INC.

PROJET GENERAL ELECTRIC NEWELL STREET PR0JK

PITTSFIELD. MASSACHUSETTSTITRE TITLE


APPROUVE PARAPPROVED BY

DATE

APPENDIX A

THE SEISMIC REFRACTION METHOD

The seismic refraction method is used to infer subsurface conditions on the basis of contrastingseismic wave velocities. The primary goal of the seismic survey is to rapidly and efficientlyobtain subsurface information, thereby reducing direct investment costs, such as drilling.Geological information typically obtained from a well-planned and executed seismic refractionsurvey will include: depth and configuration of the bedrock surface, nature and competency ofbedrock (degree of fracturing, alteration, weathering), whether it is faulted or sheared, natureof overburden, and depth to the water table. Modern portable equipment makes the methodaccessible to remote and rough regions. A review of the seismic refraction theory, fieldmethods and interpretational procedures can be found inDobrin (1976) and Telford etal (1990).

INSTRUMENTATION

The instrumentation involved in a seismic refraction survey consists of an acoustic seismicenergy source to generate seismic waves, a line of geophones to detect the seismic energy, anda seismograph which is essentially a highly accurate stopwatch. By measuring the arrival timesof the first seismic waves at various distances from the energy source (shotpoint), depths tointerfaces and seismic velocities can be determined. Seismographs are usually 12 or 24-channel,in that they can simultaneously record the energy arrivals at 12 or 24 geophones. The recordof these vibrations is a seismogram. Digital seismographs (for example, ABEM Terraloc,EG&G SMARTSEIS S24) acquire data with a built-in computer, whereas analog seismographs(e.g ABEM Trio) output the data to photographic paper as it is acquired. The energy sourcemust be coupled to the seismograph so that the instant of detonation or impact can be recorded.Timing marks, at 1 or 2 milliseconds intervals, are provided to permit very accurate estimatesof arrival times.

FUNDAMENTAL PRINCIPLES

The seismic refraction method relies on measuring the transit time of the seismic wave that takesthe shortest time to travel from the shotpoint to each geophone. The fastest seismic waves arethe compressional (P) or acoustic waves, where displaced particles oscillate in the direction ofwave propagation. The energy that follows this first arrival, such as reflected waves ortransverse (S) waves, is not considered under routine seismic refraction interpretation.

Figure 1 shows a simple geological structure, where a layer with a velocity of Vt overlies asecond layer with a higher velocity, V2. Atone end of the spread, an energy source is triggeredand the vibrations at each geophone are recorded. Seismic waves will travel via the direct pathfrom the source to each of the geophones. Waves may also be refracted at some critical anglealong the interface and travel at the higher velocity V2.

1

Geophone No. 1

« Velocity of Upper Layer« Velocity of Lower Layer* Slope of Une Segment" Crossbyer Distance» Intercept Time

or iJJSJL

Principles of Seismic Refraction

Figure 1

Energy is continually transmitted back to the surface as it travels along the interface. A time-distance graph may be constructed, plotting the first arrival transit times as a function of positionalong the seismic line. The first arrival at the closest geophones is the direct wave. However,ai the critical or crossover distance (Xc) the refracted wave which travels along the highervelocity layer overtakes the direct arrival. The inverse slope of a straight line segment of thetime-distance curve is equal to the velocity in that layer. The crossover distance is directlyproportional to the depth of the interface.

INTERPRETATION

The simplest methods of interpretation are illustrated in figure 1. Having determined thevelocity of compressional waves through each layer, the calculation of depths can be doneaccording to crossover distance or the intercept time formulas. The case of a horizontalinterface, illustrated in figure 1, becomes slightly more complicated if the planar interface isdipping. The general case of an irregular interface can be handled by more complexinterpretational calculations, including various delay-time methods, the reciprocal andgeneralized reciprocal methods, and ray tracing. One method may be better suited than anotherto a particular geological environment.

LIMITATIONS

Two important limitations of the seismic refraction method must be kept in mind. First, layersof insufficient thickness and velocity contrast will not produce first arrivals at the surface. Thisis the hidden layer problem. For example, a thin layer of glacial till or weathered bedrockoverlying unweathered bedrock might be such a hidden layer. The presence of a hidden layerwill lead to calculated depths that are too shallow. Secondly, the seismic refraction methodrequires that the velocities of all layers increase with depth. A low velocity layer at depth istermed a blind zone. Such layers will not yield first arrivals because critical refractions cannotoccur. Computed depths will be greater than actual depths in this case. Fortunately, suchvelocity reversals are seldom encountered in shallow surveys. The generalized reciprocalmethod can be used to infer the absence or presence of blind zones and hidden layers.However, correlation with boreholes and uphole surveys may be necessary to accurately gaugethe effects of such layers.

DESCRIPTIVE CLASSIFICATIONOF BEDROCK SEISMIC VELOCITIES WITH RQD VALUES

The following table represents a descriptive classification of bedrock seismic velocities that canbe correlated with RQD (Rock Quality Designation) values. The following table is extractedfrom a study by Coon and Merritt (ASTM STP 477).

This table may proved helpful for the developmental phase of this project, in terms of planning,security, and cost. The seismic refraction method measures the velocity of the bedrock to adepth of approximately 45 feet.

TABLE

mtsisf^ssmQ^^^^Si "^^ m srrcj -ROCK 0)RQD (%)

0- 2525 - 5050- 7575 - 9090 - 100

VELOCITYINDEX

0.00 - 0.200.20 - 0.400.40 - 0.600.60 - 0.800.80 - 1.00

SEISMIC VEL-OCITY (ft/s) w

80008000 - 11400

11400 - 1400014000 - 1600016000 - 22000

DESCRIPTION

Very poorPoorFairGoodExcellent

SEISMICDESCRIPTION

Low velocityLow velocityIntermediateSound rockSound rock

(1) Taken and adapted from: Coon,R.F. and Merritt,A.H.,Predicting in-situ Modulus ofDeformation using Rock Quality Indexes, Determination of the in-situ modulus ofdeformation of rock, ASTM STP 477, American Society for testing and materials 1970,pp. 154-173.

(2) Taking into account a velocity of 18 000 ft/sec for the compressional wave measured inthe laboratory (VJfor a limestone rock.

The classification of Coon and Merritt is based upon the velocity index property of in situ rock,which is a measure of the discontinuities in the rock mass. According to Coon and Merritt, thevelocity index is defined as the square of the ratio of seismic field velocity to laboratorycompressional wave velocities, measured on a core sample, representative of a sound rock. Thefield seismic velocities are normalized by the laboratory results in order to minimize theinfluence of lithology. Hence as the number of joints decreases, the ratio of the velocities willapproach one. This ratio is then squared to make the velocity index equivalent to the ratio ofdvnamic moduli.

APPENDIX B

SEISMIC REFLECTION PROFILES

The interpretation of the seismic reflection data involved 2-D inverse computer modeling. FullCDP data processing was accomplished including normal move out (NMO), filtering, and terraincorrection. Each trace on the processed seismic section was spaced at one-half of the geophonespacing and represent the summation of the traces that receive reflections from the samesubsurface point.

The attached profiles are the processed and interpreted reflection data sets, together with a plotof fold and static values, along each traverse. The prominent reflectors are colored:

• Green marks the top of the saturated layer• Violet marks the top of the silt layer• Orange marks the bedrock surface

The horizontal scale is the distance along the traverse, chainage position 0+00 at mark 1, andeach vertical trace is approximately 4.1 feet apart. The vertical scale is in milliseconds (two-way travel time). The profiles shown on the foldout map (pocket) are the integrated sectionscomposed of the combined seismic refraction, seismic reflection, and radar results.

II0

A

I0

TRAV VRMS VINT8 676 676

22 1148 133431 1398 188550 1587 185466 1673 1917

TRftV VRMS VINT8 676 676

22 1140 133432 1467 200650 1587 178066 1673 1917

TRAV VRMS VINT8 6 7 6 676

23 1037 118534 1312 175251 1518 186266 1673 2116

TRAV VRMS VINT8 676 676

24 1157 133336 1398 1784

52 1673 216769 1759 1999

TRflV VIMS VINT8 676 676

24 1088 124337 1(67 198452 K73 2O9669 1759 1999


24 1157 133335 1553 2180

52 1759 212170 1879 2189


24 1157 133335 1553 2180

52 1759 212170 1879 2189

TRAtf VRHS VINT8 676 676

1- 1 140 138233 1621 210448 1811 217167 1914 2152


21 1226 146533 1621 214348 1811 217167 1914 2152

TRflV VRMS VINT8 676 676

21 1226 146533 1621 214348 1811 217167 1914 2152

TRftV VRHS VINT8 676 676

23 1346 159131 1639 228048 1897 229367 2034 2344

TRSV VRMS VtNT8 676 «76

19 1 1 57 1.10731 1639 219548 1897 Z29367 2034 2.144

SL-4STN 40

93I

91 89 87I

85I

83I

81I

79I

75I

71I

69I

67 65 63I

61 59 55I

53 51 49I

45I

41I

39I

37I

3SI

33 31I

27 25 23I

21I

17I

13I

11I SHOT POINT

prowwrawp OC*>Y t:'>>-j.J,*

sW^W^aWaPm;fei@o!lM: *m

TIME (ns)

COP Number

GEOPHYSIQUE GPR INTERNATIONAL INC.

AREA: GE Pittsfield, Massachusett

LINE : SL- 1

SP 96 EAST SP 1

NORMAL POLARITY

STRUCTURE STACK

Date shot:Instruments:Filter:Spread:

Source:Spacing:Geophones:Spacing:

FIELD PARAMETERS

April 1996EGM60 Hz NOTCH24 trace, 1 - 1 2 X 13 - 24

6O - 2.5 X 2.5 - 60 netreSledgehamner2.S n.Mark Products 40 Hz.2.5 n.

Date:Trace EditsExponential ScalingTrace EqualizationDeconvolution

Equalization ScalingTrace GathersStructure StaticsResidual StaticsVelocity analysisMute

StackFilterTrace EqualizationPost Stack Noise Red.

PROCESSING PARAMETERS

April 1996

A»t*exp(B«t)Mean amplitude scaleSpiking 32ms. operator0.1X Pre-whiteningFirst break region

Relative 980 n., Vr 1 SCO n/s.Shot + Station, hand pickedSenblance6 10 60 n.0 15 40 ns.12 fold70x90 - 280X310 Hz.Mean amplitude scale 10 - 100 ns.Connon signal extraction

SCALE:Horizontal 10 Traces/in Vertical 6O in/second

PROCESSED BY:

GeophysicalApplicationsProcessingServices

GUELPH, ONTARIO

II

1

ft

TRflV VBHS VINT16 641 E4126 1054 149339 1578 227453 1759 228183 1931 2282

TRBV VRMS VINT

13 598 59027 1157 158241 1725 2476GO 2051 261980 2292 2897

TRflV VRMS VINT

i~3598 59024 1888 147343 1484 18676O 1811 245O81 1965 2350

TRftV VRMS VINTT3 590 59027 1157 158243 1484 1913G8 1811 245881 1965 2358

TRflV VRMS VINT13 590 59026 1123 147443 1484 190860 1811 245081 1965 2350

TRflV VRMS VINTT3 590 59026 1123 147439 1673 2423£8 1811 284281 1965 2350

TRflV VRHS VINTi "3598 59026 1123 147437 1604 23816O 1811 210181 1965 235O

SL-S

STN 29

13I

15I

17I

27I

29 33I

37I

47I

49I

51I

53[

55I

SHOT POINT

TIME (us)


AREA: GE Pittsfield, Massachusett

LINE: SL-2

SP 1 NORTH SP 56

NORMAL POLARITY

STRUCTURE STACK

FIELD PARAMETERS

Date shot:I nstr orients:Filter:Spread:


April 1996EGfcGGO Hz NOTCH24 trace, 1 - 1 2 X

GO - 2.5 XSledgehamer2.5 n.Mark Products 40 Hz.2.5 it.

13 -242.5 - GO





April 199G

Attt#exp(BMt)Mean amplitude scaleSpiking 32ns. operator0.1X Pre-whiteningFirst break region

Relative 980 n., Vr 15OO ra/s.Shot + Station, hand pickedSemblanceG 10 GO0 15 4012 fold70/9O - 280/310Mean amplitudeCommon signal e80 msec, operat

Hz.cale 10 - 100 ms.traction

SCALE:Horizontal 10 Traces/in Vertical GO in/second

PROCESSED BY:


GUELPH, ONTARIO

- 20

TRftW VBMS VINT6 727 727

17 1157 133430 1467 179357 1690 190775 1811 2149

TRftv VRMS VINT6 727 727

17 1157 133428 1656 221655 1811 195877 1879 2039

TRflV VRMS VINT6 "727 ~727

17 1209 140334 1725 211858 1948 222580 2O86 2412

SL-2STN 10

SL-4STN 7

27 25 21I

17I

151

11I

A R E A :

SHOT POINT

liimMmmwmm',te ii;


GE Pittsfield, Massachusetts

LINE : SL-3

SP 29 EAST SP 1

NORMAL POLARITY

STRUCTURE STACK



FIELD PARAMETERS

April 1996ma60 Hz NOTCH24 trace, 1 - 1 2 X 13 - 24

60 - 2.5 X 2.5 - 60 netnSledgehanner2.5 n.Mark Products 40 Hz.2.5 n.





April 1996

A*t*exp(B«t)Mean amplitude scaleSpiking 32ns. operator0.1X Pre-whiteningFirst break region

Relative 98O n., Vr 1SOO n/*.Shot + Station, hand pickedSemblance6 1O 60 n.0 15 40 ns.12 fold70/90 - 280/310 Hz.Mean amplitude scale 10 - 100Common signal extraction80 nsec. operator

SCALE:Horizontal 1O Traces/in Vertical 60 in/second

PROCESSED BY:

GeophysicalApplicationsProcessingServicesGUELPH, ONTARIO

TRftV VRMS VINTC 424 424

22 £82 75634 1043 149343 1541 2689et 1954 2695

TRflV VRMS VINT8 527 527

23 716 79835 1026 144443 1387 239460 1713 2343

TRfltf VRMS VINT8 527 527

22 733 82835 1232 178246 1524 220961 1696 2138

SL-3STN 5

13I

17I

19 21 23[

25I

27I

33I

37I

SL-1STN 43

39I SHOT POINT

TIME (us)


AREA: GE Pittsfield, Ma achuse t ts

LINE : SL-4

SP 1 NORTH SP 42

NORMAL POLARITY

STRUCTURE STACK



FIELD PARAMETERS

199GAprilEGS.GGO Hz NOTCH24 trace, 1 - 1 2 X

GO - 2.5 XSledgehammer2.5 n.Hark Products 40 Hz.2.5 m.

13 - 242.5 - GO


Equalization ScalincTrace GathersStructure StaticsResidual StaticsVelocity analysisMute



April 1996

fl*t*exp(B*t)Mean amplitude scaleSpiking 32ms. operator0.1X Pre-whiteningFirst break region

Relative 980 m., Vr 1 SCO «/s.Shot + Station* hand pickedSemblance6 10 GO n.0 15 40 ms.12 fold70/90 - 280/310 Hz.Mean amplitude scale 10 - 10OCommon signal extraction80 msec, opera-tor

SCALE:Horizontal 10 Traces/in Vertical 60 in/second

PROCESSED BY:


GUELPH, ONTARIO

THE SEISMIC REFLECnO >J METHOD

The basic technique of the seismic reflection method cor ;ists of generating energy source wavesand measuring the time required for the waves to t avel from the source to an array ofgeophones place along a straight line directed towards t e energy source. The measurement oftravel time to each geophone or cluster of geophones, tc Aether with the energy wave velocities,allow the reconstruction of the paths of the seismic w ves.

Subsurface structural information is principally derived :rom the energy paths which fall in twomain categories: refracted paths in which the principal ] ortion of the path is along the interfacebetween two rock layers, and reflected paths in which the wave travels downward initially andat some point is reflected back to the surface. The ene -gy travel times depend upon physicalproperties of the rocks and the orientation of transecte 1 strata.

Depths to reflecting interfaces can be determined rom the travel times using velocityinformation that can be obtain from surveys in borings : uch as, uphole or downhole surveys orby using seismic refraction data over the same area.

The reflection method is based on the measurement oi time taken for the acoustic energy totravel from a source (shot location) to a receiver (geopnone) location. The acoustic energy isproduced by a seismic source, which can be either sledgehammer striking a steel plate, weightdrops of different of different weights and designs, or from percussive sources such as, Betsyseisgun, or detonation of explosives.

This energy will travel downward and be reflected back towards the surface from any subsurfaceinterface across which there is a contrast in density and/or seismic velocity.

The arrivals of these seismic waves causes displacements of the ground which are picked up bygeophones and recorded as a function of time by the seismograph. The analysis of these arrivaltimes, which have traveled through the subsurface, will allow identification of subsurfacefeatures.

Typically, the output of the reflection survey is a series of seismic records that are processedto produce a seismic section. The seismic section is a plot of two-way travel time versus thedistance along the ground surface and can be interpreted as a geological cross-section when thetwo-way travel time is converted to a depth scale (the calculation of a depth scale requiresinformation about the seismic velocity).

MULTIPLE COVERAGE IN SEISMIC REFLECTION

When using simple coverage, only one reflection of the subsurface point is recorded (figure 1).Tie sampling of this point is referred to as "fold," in this case, 1-fold and is frequentlyexpressed as a percentage (1-fold equals 100%). When a coverage of 600% is planned (figure2), six reflections are recorded at the same subsurface point. However, the distance betweenthe energy source and each geophone is different. A correction factor is applied to the time ofthe wave travelling path from its shotpoint to the seismograph so that it can be converted to theline of the vertical trajectory by six oblique time measurements. These are then added togetherto obtain the most precise average.

FIGURE 1

100% CoverageSingle-ended spread

FIGURE 2

600% CoverageCommon Depth Point (CDP)

A 1200% coverage involves shotpoints at every geophone along the spread, keeping the samedistance between shots and geophones. A detailed discussion of this technique can be found inTeiford & Al (1976).

FIELD ACQUISITION

When using obtaining a coverage of 300%, the cable and geophone setup remains the same(figure 3). However, three more shotpoints are required.

Therefore, the accuracy of data recording when using multiple coverage is largely dependanton obtaining shotpoints. Data are digitally recorded to facilitate calculations of time values.

FIGURES

SCHEMATIC DIAGRAM FOR 300% COVERAGE

DATA PROCESSING

1) Gather all relative trajectories, referred to as a "gather," corresponding to the samecommon depth point (CDP).

2) Perform all obliquity corrections, referred to as "normal move out." This is done bymaking successive approximations using hyperbolic functions. The best approximatevalue gives the velocity down to the geological unit.

3) Stack the corrected trajectories and take an average.

SEISMIC REFLECTION

ID, V

(

1

D2 V

>» Vr

1 (500m/s)

^INTERFACE Wo 1

2 (2500m/*) ,,NTERFACE No 2

3 (1500 m/»)

/INTERFACE Mo. 3

V 4 (3000m/*)

100% coverage : determines interfaces 1 to 3 and V1600% multiple coverage : determines interfaces 1 to 3, V1 to V4, D1 to D3.

FIGURE 4

SCHEMATIC CROSS-SECTION

ADVANTAGE

The advantages of multiple coverage are very significant:

The quality improvement of reflection quality is generally dramatic since the reflectivityis multiplied by the factor of the fold with the spectrum of random "noise" remaining atinitial levels or cancelling out.

TOPOGRAPHIC CORRECTION

The precision is increased when the influence of topographic corrections is reduced.

P. QP

Resolution with increase depth have been greatly improved. A variation in lateral velocity canthen be identified (figure 4).

INTERPRETATION

The interpretation of seismic data in geological terms is the objective and end product of seismicwork.

The basic task of interpreting seismic records is that of selecting those events on the recordwhich represent primary reflections, translating the arrival times for these reflections into depthsand dips, and mapping the reflecting horizons.

In addition, the interpreter must be alert to other types of events which may yield valuableinformation such as multiple reflections and diffractions.

Recognition and identification of seismic events are based upon different characteristics of thereflected signal, such as its amplitude, its coherence from trace to trace, its frequency contentand its waveform appearance.

Drawing of horizons on the seismic section and conversion to depth yields a two-dimensionalgeological profile of the subsurface.

Documents

GEOPHYSICS GPR INTERNATIONAL INC.A number of geophysical methods were employed to characterize the subsurface conditions at specified traverse locations at the site (Fig. 2). The methods