SURFACE GEOPHYSICAL SURVEYS · The magnetic survey consiste odf 425 station s on a 10-foot by 10-foot grid in all of the open areas of the Site. The GPR survey covered mos oft the

HAGER-RICHTERGEOSCIENCE, INC

SURFACE GEOPHYSICAL SURVEYSSOLVENTS RECOVERY SERVICEOF NEW ENGLAND, INC. SITESOUTHINGTON, CONNECTICUT

Prepared for:

NUS Corporation187 Ballardvale StreetSuite A-100Wilmington, Massachusetts 01887

Prepared by:

Hager-Richter Geoscience, Inc8 Industrial Way - DIGSalem, New Hampshire 03079

File 91D04April, 1991

HAGER-RICHTER GEOSCIENCE, INC.

Surface Geophysical Surveys SRSNE Site Southington, Connecticut File 91D04 April. 1991

O. EXECUTIVE SUMMARY

Hager-Richter Geoscience, Inc. conducted surface geophysical surveys at the Solvents Recovery Service of New England, Inc. (SRSNE) Site, Southington, Connecticut for NUS Corporation in April, 1991. The geophysical surveys were conducted under Subcontract No. S90-117-011 from NUS and are part of a larger Phase II RI/FS by NUS for the US-EPA.

Two complementary geophysical techniques were used at the Site: magnetics and ground penetrating radar (GPR). The objectives of the geophysical surveys were to detect and accurately locate buried metal objects, buried concrete structures and pads, and, if possible, to determine the depth and lateral extent of filled lagoons on the Site property.

The magnetic survey consisted of 425 stations on a 10-foot by 10-foot grid in all of the open areas of the Site. The GPR survey covered most of the open areas of the Site and consisted of over 8500 feet of traverse.

The data from both geophysical techniques indicate that few buried buried metal objects other than known utilities are present at the SRSNE Site. Almost all of the anomalies identified in the magnetic survey correlate with metallic surface objects or known utilities. The GPR records for areas of isolated magnetic anomalies do not indicate the presence of buried metal objects at those locations, indicating either a surface cause for the anomaly or that the object is small and not directly under the line of GPR traverse.

GPR signal penetration at the Site was limited to the upper few feet. One possible UST, located at the southeast corner of the processing building, was identified on the basis of the GPR data. The GPR records indicate that much of the asphalt paved area may be underlain by concrete. The approximate location of a former secondary lagoon at the southeast part of the Site was outlined on the basis of the GPR records, but the former primary lagoon was not detected by GPR. The location of a former incineration pit reportedly located near groundwater collection well number 6 could not be determined from the geophysical data.

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Surface Geophysical Surveys SRSNE Site Southington, Connecticut File 91D04 April, 1991

TABLE OF CONTENTS

0. Executive Summary i

1. Introduction 1

2. Equipment and Procedures 2 2.1 Magnetic Survey 2

2.1.1 General 2 2.1.2 Site Specific 2

2.2 Ground Penetrating Radar Survey 3 2.2.1 General 3 2.2.2 Site Specific 4

3. Results and Discussion 5 3.1 General 5 3.2 Magnetic Survey 5 3.3 Ground Penetrating Radar Survey 6

4. Conclusions 9

FIGURES

1. Site location. 2. SRSNE, Inc. facility. 2. GPR system. 3. GPR record for a traverse crossing the location of a

former secondary lagoon. 4. GPR record for a traverse on a concrete pad. 5. GPR record for a traverse crossing a water line.

PLATES

1. Site Plan 2. Magnetic Survey 3. GPR Survey 4. Interpretation of Geophysical Data

APPENDIX

Graph of diurnal variation monitoring data

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HAGER-RICHTER GEOSCIENCE. INC.


1. INTRODUCTION

Hager-Richter Geoscience, Inc. conducted surface geophysical surveys at the Solvents Recovery Service of New England, Inc. (SRSNE) Site in Southington, Connecticut for NUS Corporation of Wilmington, Massachusetts. The geophysical surveys were conducted under Subcontract No. S90-117-011 from NUS and are part of a Phase II RI/FS by NUS for the United States Environmental Protection Agency.

The SRSNE Site is located on the south side of Lazy Lane in a suburban industrial area of Southington (Figure 1) . SRSNE reportedly operated an industrial solvents processing facility at the Site until the end of March, 1991. The 2.5 acre property is entirely surrounded by a chain link fence and is open except for a wooded slope in the southwest corner of the Site. Plate 1 and Figure 2 show many of the existing and former features of the Site. Although Figure 2 shows concrete pavement covering much of the Site, Plate 1 is more nearly correct in showing the current pavement conditions. The area between the above ground tank farm and the system of 25 ground water recovery wells along the east edge of the property is currently paved with asphalt except for two well defined concrete drum pads.

The objective of the geophysical surveys was to detect and accurately locate subsurface metal objects and former structures at the Site. In particular, NUS was interested in determining the locations of the former primary and secondary lagoons and a former incineration pit, approximate locations shown in Figure 2, for which there is no current surface expression.

Two complementary geophysical methods were used at the SRSNE Site: magnetics and ground penetrating radar (GPR). Jeffrey Mann and Jonathon Puliafico of HagerrRichter conducted the magnetic survey on April 3 and the GPR survey on April 4-5, 1991. The field operations were coordinated with and observed in part by Mr. Walter Martin of NUS. All field operations meet or exceed the specifications of the subcontract and were conducted under level D personal protection. The data were analyzed and interpreted at the Hager-Richter offices.

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2. EQUIPMENT AND PROCEDURES

2.1 Magnetics

2.1.1 General. The magnetic survey was conducted using two EG&G Model G856 Proton Precession Portable Magnetometers. The G856 is a microprocessor controlled instrument with a resolution of 0.1 gamma, an accuracy of 1 gamma, and a memory capable of storing data for approximately 3000 stations. The data are transferred to a computer at the end of each field day.

One magnetometer was used as a base station, recording the total magnetic field at one-minute intervals during the magnetic survey. Such data are necessary to correct the survey data for the temporal variation of the earth's magnetic field and to check for sudden fluctuations due to magnetic storms that may adversely affect the quality of the survey data.

The other magnetometer was used with a gradiometer option to collect the survey data. With the gradiometer option, two sensors are mounted on a staff at 4' 5 3/4" and 9' 3/4" above ground level. Upon command, the magnetometer records the total magnetic field measured by each sensor sequentially within 4 seconds. Computer software subsequently separates the data for analysis. All magnetic field data, including gradiometer data, were corrected for diurnal variation prior to plotting and contouring.

The total magnetic field data were contoured using the top sensor magnetic values. Gradiometer data were processed by subtracting the top sensor value from the bottom sensor value and dividing by the distance between the sensors.

2.1.2 Site Specific. At the SRSNE Site, NUS specified the limits of the magnetic survey area and established a 50-foot grid in a 100-foot by 400-foot area, shown on Plate 1. Magnetic data were collected at 10-foot intervals along lines spaced 10 feet apart, at a total of 425 stations.

The recording base station was located in the empty field immediately to the east of the Site. A graph of the diurnal variation monitoring data is included in the Appendix.



2.2 Ground Penetrating Radar

2.2.1 General. A Geophysical Survey Systems, Inc. Model SIR-3:VDU-38 ground penetrating radar system was used for the survey. The system consists of an electronics unit, graphic recorder, color video display unit and transmitting/receiving antenna. Figure 3 shows the basic setup of the GPR system. The antenna is housed in a box that is moved across the surface. The antenna transmits electromagnetic signals into the subsurface and then detects and amplifies the reflected signals. The reflections are displayed in real-time on a graphic recorder and a color video monitor. The result is a radar record of the subsurface. The data are also recorded on a tape recorder for later computer processing, if necessary to interpret the data.

The maximum depth of penetration of the GPR signal and the resolution of the reflected signals are controlled in part by the frequency of the antenna used and in part by the electrical properties of the subsurface. The total time during which radar signals are recorded can be varied from a few to 1,000 nanoseconds (nsec). However, there is a trade-off between total time, corresponding to depth range, and resolution. As the total time of recording is increased, the resolution of the GPR records decreases. For a given site, the total time window is set to detect features located somewhat below the maximum expected target depths.

The horizontal axis of a GPR record is distance across the surface and the vertical axis is round-trip travel time of the radar signals. The round-trip travel time can be converted to approximate depth by correlating with reflections from targets of known depth or by using handbook values of velocities for materials in the subsurface. For those sites where the subsurface is electrically inhomogeneous, the travel times of the radar signal may be different in the various materials, and the vertical scale for the radar records is npt necessarily uniform with depth.

The reflections in a GPR record are produced by spatial changes in the physical properties (e.g., type of material, subsurface fluids, porosity, etc.) and related changes in the electrical properties (dielectric constant) of the subsurface materials in the path of the signals. The greater the difference in electrical properties between two materials in the subsurface, the stronger the reflection observed on the GPR record.

HAGER-RICHTER GEOSCIENCE INC


The size, shape, and amplitude of the GPR reflections are the characteristics that are considered in the interpretation of the data from any site. Metal USTs, utilities, and conduits have electrical properties very different from the soils in which they are buried; they thus produce GPR reflections with high amplitude and distinctive shapes. Metal USTs can be detected in a soil subsurface with a high degree of reliability with GPR. Fiberglas tanks can also be detected with GPR, but the strength of the reflected signals is weaker. Underground utilities can be recognized on plots of GPR reflections by linear arrays of sharp hyperbolic reflections. The coincidence of manholes, grates, drains, and similar materials with projections of such possible utilities identified from the GPR data increases confidence in the identification. Most other objects, although readily detectable, require "ground truth" for identification. Only excavations provide positive identification for most such objects identified in GPR surveys.

2.2 Site Specific

The GPR data for the survey at the SRSNE Site were recorded with a 500 MHz antenna. This antenna provides the best size and depth resolution for objects buried less than about 12-15 feet deep. Trial GPR traverses were also recorded at the SRSNE Site with a 300 MHz antenna in order to try to increase the depth of penetration of the GPR signal. The general quality of the radar records was judged to be lower for the trial GPR traverses made with the 300 MHz antenna, and with the concurrence of the NUS representative, the 500 MHz antenna was used for the survey.

Orthogonal GPR traverses were spaced ten feet apart in most of the open areas of the Site, using the same coordinate system established by NUS for the magnetic survey. Such a spacing between profiles is sufficient to detect utilities with a high degree of confidence. The GPR antenna was towed behind a vehicle for most of the survey and pulled by hand for some lines of restricted length. Fifty-seven GPR traverses were recorded for a total length of over 8500 feet.

The GPR data were recorded with a 60 nsec time window. Using a handbook time-to-depth conversion of 5-6 nsec/foot for unsaturated sand, the 60 nsec window represents a maximum depth of exploration of about 10-12 feet. However, water table at the Site was estimated by the NUS representative to be about 8-10

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feet below the surface. Since the travel time of the GPR signal in saturated sand is about 9-10 nsec/foot, the maximum depth of exploration for the GPR survey was probably no more than 10 feet.

3. RESULTS AMD DISCUSSION

3.1 General

The results of the surface geophysical surveys at the SRSNE Site are presented in Plates 2 - 4 . The magnetic data are contoured in Plate 2. Plate 3 shows the locations of the GPR traverses, and Plate 4 is an interpretation map that incorporates the results from the magnetic and GPR surveys.

3. Magnetic Survey

Plate 2A is a contour map of the total magnetic field measured at the SRSNE Site. The magnetic field data are presented as the total intensity relative to 54,000 gammas, an arbitrary value near the "undisturbed" total magnetic field for the Site. A 50-gamma contour interval was used. Contours for values higher than 1000 gammas and lower than -200 gammas were not plotted in order to avoid having black spots on the map. The locations of the magnetic stations are shown on the map as small x's.

Plate 2B is a contour map of the vertical magnetic gradient measured at the SRSNE Site. Vertical magnetic gradient data, also commonly called gradiometer data, can be used to interpret the relative depth of burial of metal objects. In general, an object at or near the ground surface, such as a UST, produces a much greater magnetic effect at the lower sensor than at the upper sensor. The result is a steep vertical magnetic gradient. If a magnetic object is deeply buried, the magnetic field measured by both sensors is nearly the same, and the vertical gradient is near zero. Therefore," steep vertical magnetic gradients indicate the presence of near-surface metallic objects.

The anomalies in Plates 2A and 2B correlate well with one another and, in general, with surface objects and known utilities. The several anomalies within the area defined by the corner coordinates (0,50), (50,50), (0,100), and (50,100) at the southeast corner of the survey area correlate with debris piles containing metallic objects, and one of the groundwater recovery wells (number 5). A 30-foot long portable steel loading ramp was

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parked along the eastern edge of the survey area near coordinates (90,100). Magnetic effects from the plant building, steel roofed storage area, dumpster, and overhead power lines likely produced the anomalies at the northwest corner of the survey area.

At the north end of the survey area (between 350 - 400), several high amplitude anomalies occur in the vicinity of a known drainage outfall and other utilities and are tentatively correlated with them. The amplitude of the anomalies is somewhat higher than one might expect for the utilities, however. As discussed in section 3.3 below, the GPR records indicate the presence of only utilities in that area.

Smaller magnetic anomalies on Plate 2 also correlate with surface objects such as the raised curbing of the concrete drum storage pads and associated pipes and valves. The generally higher magnetic field and large number of gradient anomalies in the southwest part of the survey area correlates with the location of a concrete drum storage pad; thus they appear to be a magnetic effect due to the mesh in the concrete pads. However, there is no magnetic effect evident at the location shown on Plate 1 as "old foundations."

The magnetic anomalies caused by surface features such as those described in the paragraphs above may mask magnetic anomalies produced by subsurface objects located nearby. Thus, the correlation of magnetic anomalies with surface features does not eliminate the possibility that buried objects are also present at the Site. In particular, the location of a former incinerator, reportedly near groundwater collection well number 6, could not be confirmed on the basis of the magnetic data due to the metallic debris nearby.

3.3 Ground Penetrating Radar Survey

Plate 3 shows the locations of the GPR traverses for the SRSNE Site. The traverses were located along lines that coincided with the grid used for the magnetic survey and were extended into areas in and around the buildings at the Site.

The general quality of the GPR records for the SRSNE Site is only fair, but the data provide information to complement the magnetic survey, nevertheless. GPR is a geophysical technique that is variable (i.e., site specific) in the quality of its data. The dielectric properties of the materials through which the GPR signals are directed strongly affect the quality of the data that

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data that can be obtained. Evidently the subsurface materials at the SRSNE Site are sufficiently conductive that GPR reflections are not received for depths greater than a few feet. The consistent attenuation of the GPR signal at the Site may be due to the thickness and properties of the pavement, a relatively high clay content in the till overburden at the Site, and possibly to residual conductive fluid in the vadose zone or to some combination of these factors. The pavement appears to be at least a significant factor in the signal attenuation, because the GPR signal penetration for those few lines or portions of lines on gravel near the eastern border of the Site exhibit reflections from significantly greater depths. For most of the SRSNE Site, however, GPR reflections were not detected for times greater than about 30 nsec., or about 6 feet. In many areas, the signal penetration was only about 20 nsec., or about 4 feet.

The GPR records for the SRSNE Site have two general types of patterns. One type exhibits multiple reflections (ringing), and the other type exhibits severe attenuation of the GPR signal below the pavement.

The first type of GPR pattern is best displayed in a limited area in the southeast part of the Site. This area, outlined on Plate 4 by a dotted line, occurs in the approximate location of the former secondary lagoon shown in Figure 2. The edges of the areas exhibiting such a pattern are fairly sharply defined in the GPR records; however, the edges exhibit sloped reflections commonly associated with filled areas in the GPR records for traverses oriented west-east (Figure 4). Based in part on the information available about the location of former primary and secondary lagoons at the SRSNE Site (Figure 2), we tentatively correlate the region characterized by consistent multiple GPR reflections with the secondary lagoon. The depth of the former lagoon, however, cannot be clearly determined from the GPR records.

We searched for similar patterns in the GPR records for traverses in the vicinity of the former primary lagoon shown in Figure 2, but did not find such a pattern. Thus, we cannot confirm the location of the primary lagoon based on the GPR records.

The second type of GPR pattern, with strong attenuation of the GPR signal below the pavement, is characteristic of most of the rest of the SRSNE Site. Such patterns characterize traverses on both asphalt and concrete pavement. Older concrete pavement is visible at the edges of the asphalt pavement at the southeast

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Surface Geophysical Surveys SRSNE Site Southington, Connecticut File 91D04 April_, 1991

corner of the Site, and Figure 2 indicates that large areas of the Site were paved with concrete at some time. We infer, then, that the patterns of GPR signal attenuation are consistent with the presence of concrete underlying much of the asphalt pavement. In the GPR records for some locations, the concrete exhibits reflections from rebar (Figure 5) , but for most areas, there is no strong pattern of rebar reflections in the GPR records.

Faint GPR reflections characteristic of a UST are present in the records for two GPR traverses near the southeast corner of the processing building. Figure 5 shows the reflections from the possible UST under the concrete pad. The faintness of the reflections may be due to such causes as the attenuation of the signal by the concrete or deterioration (rusting) of the possible tank. The location and orientation of the object with respect to the building is suggestive of it being a tank; however, there are no vent pipes or other surface evidence of a tank and the GPR records for the nearby cross-traverses do not contain reflections characteristic of a tank. The identification of the object as a tank is therefore tentative.

The GPR records contain a few reflections that are likely caused by isolated buried metal objects and utility lines. The locations of such objects are marked on Plate 4 by x's. Figure 6 is an example of the GPR record for the storm drain and water line at the north end of the Site. The GPR records for the traverses near the groundwater collection wells on the east side of the Site do not indicate the presence of utilities oriented perpendicular to the line of wells.

The isolated objects indicated on Plate 4 appear to be small and buried at a shallow depth; they may be miscellaneous debris. In particular, the objects do not produce the distinctive high amplitude hyperbolic GPR reflections indicating the presence of buried metal storage tanks and/or drums.

We specifically examined the GPR records for those areas that produced magnetic anomalies to determine whether we could identify buried metallic objects as the cause of the anomalies. In every case, the GPR records did not contain reflections that would be caused by large metallic objects. We infer that the objects that caused the magnetic anomalies are either surface objects or small buried metal objects that were not sufficiently near the lines of GPR traverse. The location of the former incinerator reportedly located near groundwater collection well number 6 was not confirmed by the GPR records.

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HAGER-RICHTER GEQSCIENCE, INC.


Bedrock at the SRSNE Site is estimated to be located at a depth of about 20 feet. The GPR signal penetration at the SRSNE Site was not sufficient to obtain reflections from that depth, so no information regarding the depth and configuration of bedrock can be determined from the GPR records.

4. CONCLUSIONS

The results of the surface geophysical survey at the SRSNE Site in Southington, Connecticut indicate that:

1. Few buried buried metal objects other than known utilities are present at the Site.

2. One possible UST located near the southeast corner of the processing building was identified on the basis of the GPR records.

3. Much of the area now paved with asphalt may be underlain by concrete.

4. The approximate location of the former secondary lagoon at the southeast part of the survey area was outlined on the basis of the GPR records, but the location of the former primary lagoon could not be confirmed.

4. The location of a former incinerator reportedly located near groundwater collection well number 6 could not be determined from the geophysical data.

Surface Geophysical Surveys HAGER-RICHTER SRSNE Site GEOSCIENCE, INC Southington, Connecticut File 91DQ4 April. 1991

G T O v -V

S ] W\\\, • '• ^ LI /. /HcMJ I/IM'

mm .

1000 2000 3000 «000 MOO 6000 7000 SCALE 1000

SOURCE : US GEOLOGICAL SURVEY 7.5 HINUTE SERIES TOPOGRAPHIC HAPS. CONNECTICUT QUADRANGLES (SOUTHINGTOH 1968, photorevised 1984; MERIDEH. 1967, p.r. 1984; NEW BRITAIN. 1966, p.r. 1984; BRISTOL. 1966, p.r. 1984)

Figure 1. Site location. I CONNECTICUT

SOLVENTS RECOVERY SERVICE OF NEW ENGLAND, INC. SITE SOUTHINGTON. CONNECTICUT

Map courtesy of NUS Corporation.

i



l£GEMQ

Figure 2. SRSNE, Inc. facility. Plan (courtesy of NUS Corporation) shows the approximate locations of former primary and secondary lagoons, a former incinerator, and former limits of concrete pavement.



COLOR VIDEO PULSE DISPLAY UNIT TRANSMITTER

GROUND SURFACE

TRANSMITTED PULSE REFLECTED PULSE

TARGET

Figure 3. The GPR system.

HAGER-RICHTER GEOSCIENCE. INC


Distance (feet) w 80 90 100 110

0

CD CD

CL

x oL_

Q_CL

tWa«,yM1 <•*--'* *•• JV

10

Figure 4. GPR record for a traverse over the location of a former secondary lagoon. The edge of the filled lagoon appears to be located between 85 and 90 feet along the line. The vertical scale is approximate because the velocity of the GPR signal in the subsurface materials is variable. Portion of the west-east Line 130.

HAGER-RICHTER GEOSCIENCE INC


Distance (feet) N

320 330 335 0

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>• ~ jflBr. '-—L_ • M-'gME--" -«P—-«— fo EgSar^râlffPâacsarrrâsa:L_ L'% , -.^fW^T&ffiS1"^*^^^^^ !Q_ . a f - **-,**^*^ Q_

10-1

Figure 5. GPR record for a traverse on a concrete pad. The concrete has produced distinctive GPR reflections characteristic of rebar. Faint reflections possibly due to a UST are present at about 323 feet. The vertical scale is approximate because the velocity of the GPR signal in the subsurface materials is variable. Portion of the south-north traverse along Line 0, east side of the existing plant building.



CD O>

Q_ (D Q

•

X ol_ Q_O_

Distance (feet) N

375 4-00

0

2

.,»»l'.r. ». . l . . W i f. * w 4V '*^ *Vk _^ |V*A'IV^BM 4

6

Figure 6. GPR record for a traverse crossing a storm drain and water line. The water line produced high amplitude reflections with a hyperbolic shape, the common GPR signature of a metal pipe. The reflections from the drainage outfall are weaker. The vertical scale is approximate because the velocity of the GPR signal in the subsurface materials is variable. Portion of south-north Line 20.



APPENDIX



o o o^ tn

650-1

CO CO LU

600

CO <

<

550 7 8

I I I T [ I

10 TIME

I

11 I I I I

12 I I I \

Graph of diurnal monitoring data.

0 20 40

Base map provided by NUS Corporation SCALE (feet)

A: TOTAL MAGNETIC FIELD

50 100 v H H H H ^ H v H H

100

B: VERTICAL GRADIENT

Legend

PLATE 2A. Contour Interval 50 gammas Contours = Total Magnetic Field - 54,000 gammas Contour Range Plotted >-200 gammas and <1000 gammas

PLATE 2B. Contour Interval 20 gammas/ft.

Contour Range Plotted >-200 gammas/ft. and <200 gammas/ft.

x Magnetic Survey Station

0 20 40

SCALE (feet)

i%-

_ _ — —

Legend

UNDERGROUND UTILITIES

•50 4

0 -

50 -

100-

\- -50

OVERHEAD POWERUNE

PORTABLE METAL LOADING RAMP

STEEL GAS CMJNDEF RACK

O X

Approx. Extent of Secondary Lagoon

Magnetic Anomaly 0 20 40

GPR Anomaly

Possible UST

SCALE (feet)

PLATE 4 INTERPRETATION OF GEOPHYSICAL DATA

SRSNE SITE SOUTHINGTON, CONN.

File 91D04 April, 1991

HAGER-RICHTER GEOSCIENCE, INC. 8 Industrial Way Unit D-10

Salem, NH 03079

Documents

SURFACE GEOPHYSICAL SURVEYS · The magnetic survey consiste odf 425 station s on a 10-foot by 10-foot grid in all of the open areas of the Site. The GPR survey covered mos oft the