Asbury Manor-SY 970403FUGRO-McCLELLAND (SOUTHWEST), INC.
GEOPHYSICAL SURVEY RESULTS
12.694-ACRE RESIDENTIAL SUBDIVISION
COPPELL, TEXAS
RYLAND HOMES
DALLAS, TEXAS
04-17-97 P03:49 IN
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(SOUTHWEST) -
. FUGRO - McCLELLAND , INC.
Report No. 0401-3705
Apdl 3, 1997 6100 Hillcroft (77081)
P.O. Box 740010
Houston, Texas 77274
Ryland Homes Phone: 713-778-5533
Three Metro Square Fax : 713-778-5544
12000 Ford Road, Suite 320
Dallas, Texas 75234
Attn: Mr. Fred Phillips
Land Manager
Geophysical Survey Results
12.694-Acre Residential Subdivision
Coppell, Texas
Introduction
Fugro-McClelland (Southwest), Inc. is pleased to present the results of our geophysical survey
conducted for the 12.694-acre property located in Coppell, Texas. The geophysical technology
applied for this project provided non-destructive methods for attempting to identify and locate
buded debris, trash, metal, and other subsurface anomalies from the existing ground surface
throughout the site. Work was performed in general accordance with our Proposal No. 0401-3705,
dated March 14, 1997. This project was verbally authorized by Mr. Fred Phillips oi Ryland Homes
on March 20, 1997. Site orientation services and aerial photos were provided by Mr. Tom Kline of
Kline and Company.
Project Description. We understand that single-family residential development is planned for the
above-mentioned property. Ryland Homes has identified a need to identify and locate areas within
the property that may contain accumulations of buried debris. Buried debris could be any
combination of subsurface rubble, concrete, trash, metal, or other man-made materials. We
understand that Ryland Homes intends to excavate and remove accumulations of buried debris
identified by our geophysical survey prior to further site development.
Executive Summary. Electromagnetic (EM) surveys were conducted within the 12.694-acre
property on a 25-ft-grid spacing. The electromagnetic data acquired in the survey area was
complex; most likely due to the historical use of the property dating back to the early 1980's as
evidenced by air photos. Our method of interpretation is defined in the report and utilizes both the
conductivity and in-phase readings acquired during EM survey procedures. Based on our
interpretative method, we have identified 5 anomalous areas exhibiting significant conductivity
and/or in-phase (metallic) readings indicating the possible presence of buried debris.
A member of the Fugro group of companies with offices throughout the world.
Report No. 0401-3705 ~._=,.,e,_._
Site Description. The site was generally rectangular in shape, about 430-ft-wide and 1,300-ft-long
in dimension, and was enclosed by barbed-wire fence with gates. Prior to our arrival on-site, Client
representatives placed stakes on a 50-ft-spacing around the perimeter of the site and through the
long axis (east-west) to assist us with establishing our EM survey measurement grid.
The ground surface was covered mostly with grass, with some trees and scrub brush, and a few
areas of exposed dirt. Surficial trash and debris.were noticed throughout the site at the time of our
surveys. Partially-buried metal debris was noted at some locations of the site and identified by our
field crew by placing yellow-colored pin flags into the ground adjacent to these areas.
Purpose and Scope. Fugro-McClelland (Southwest), Inc. conducted an electromagnetic (EM)
survey within the site to attempt to locate and identify areas containing significant amounts of
buried rubble.
The scope of work included:
1. Monitoring EM survey progress on a base map of the site provided by the Client.
2. Conducting field surveys using electromagnetic conductivity technologies.
3. Interpreting raw geophysical data in the field to guide the implementation of
electromagnetic surveys.
4. Recording electromagnetic survey results to a data-logging device for further
computer processing, modeling, and interpretation in the office.
5. Conducting a technical review of EM survey procedures.
6. Preparing a report summarizing our findings and conclusions.
Electromagnetic Conductivity
Electromagnetic Conductivity (EM) methods were used as the investigative tool for acquiring
geophysical data within the survey area. The EM unit consists of a transmitter coil and a receiver
coil mounted at the ends of a rigid "beam" with a central console unit. The coils are housed in
white cylindrical (plastic) tubes and, when connected to the console, the entire unit is about 12 ft in
length and is carried by a shoulder harness.
Basically the technique consisted of energizing a (transmitter) coil to induce an electromagnetic
field into the ground and measuring the ground response with another (receiver) coil. The
instrument measured (1) the bulk soil conductivity in units of millisiemens per meter [mS/m] and (2)
the in-phase component of the induced magnetic field. The in-phase measurement is the ratio of
..- the induced 'secondary' magnetic field (generated by metallic objects) to the 'primary' magnetic
field (generated by the unit) measured in parts per thousand [ppt].
Report No. 0401-3705 _-r-Mo~o
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The relative advantages and limitations of the electromagnetic conductivity (EM) test method are
listed as follows:
Advantages: · Acquires real-time data in the field and is capable of recording digital readings.
· Locates large metallic objects quickly and effectively allowing for large area coverage.
· Determines the general orientation of linear targets (useful for mapping pipelines).
· Can perform measurements over water.
Limitations: · Detection depth is limited by the electrical conductivity of the local soil.
· Difficult to distinguish between closely-spaced metallic targets.
· Interference may occur over heavily steel-reinfomed pavement sections.
Survey Technique
The geophysical instrument was calibrated to site conditions in the survey area prior to data
acquisition procedures. Measurement levels were adjusted to appropriate settings for detecting
accumulations of buried debris. We conducted the EM survey using a 25-ft survey grid spacing.
This spacing interval is typically acceptable for detecting accumulations of buried debris on the
order of about 15 to 20 ft in diameter..Targets with smaller dimensions may als, o be detected at
--- this grid spacing, but with a lesser degree of certainty. Some 10-ft-grid spacing EM data was
recorded in areas with significantly complex readings.
The end-points_and mid-point of each survey line were marked on the existing ground surface by
stakes placed (byothers) on a 50-ft-spacing around the perimeter and through the long axis (east-
west) of the site. Measurements were made on a station-by-station basis on a 25-ft-gdd spacing
using the survey stakes for reference. Any additional surveying of the geophysical data should be
performed by a Registered Professional Land Surveyor and should be done in coordination with
our office.
The EM instrument was positioned with the shoulder strap adjusted so the operator could read
both the control console and polycorder device (used to record the data) during survey procedures.
Measurements were acquired by physically moving to each station, allowing the reading to
stabilize, and then recording data in both east-west and north-south orientations. The data was
downloaded to computer for further processing and interpretation in the office upon completion of
the surveys.
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Data Processing
Electromagnetic data acquired from the survey area was downloaded to computer using software
provided with the data-logging unit. The station and line number for each field survey point was
processed into corresponding northing and easting coordinates for mapping purposes. Instrument
measurements of (1) ground conductivity and (2) in-phase readings were acquired at each survey
gdd point with the instrument oriented in the north-south and east-west directions. Contour maps
of corresponding electromagnetic data were developed for the site as follows:
Description Plate No.
Ground conductivity for east-west instrument orientation 1
Ground conductivity for north-south instrument orientation '~
In-phase reading for east-west instrument orientation 3
In-phase reading for north-south instrument orientation 4
The contour maps of processed EM data provide the basis for developing interpretations regarding
the possible existence of buried debris. Each map contains a color scale bar indicating the
measurement level of the reading to allow for visual interpretation of the geophysical data. The
electromagnetic conductivity and in-phase contour maps may be used to identify and locate areas
of high (red) and Iow (blue) conductivity and in-phase readings.
Interpretative Method
Large and/or abrupt changes in conductivity readings may indicate the presence of conductive
materials in the subsurface (such as metal, fluid, salt, or very high clay content). Large variations
with in-phase readings typically indicate the presence of buried metal. Abrupt changes in
conductivity readings with corresponding large changes of in-phase readings may be interpreted as
a significant buried metallic mass in a specific area.
Large changes in conductivity readings without corresponding in-phase readings may be
interpreted as (1) abrupt changes in the subsurface stratigraphy (fill material, buried sand channel,
trash, etc.) and/or (2) the local presence of a significant amount of conductive fluid present in the
soil (brine, other staturants, etc.). Negative conductivity readings generally indicate interference of
the induced electromagnetic field by surface and/or buried materials exhibiting sic~nificantly different
electromagnetic properties from the surrounding soil medium.
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Report No. 0401-3705
Survey Results
Vadous interpreted electromagnetic anomalies are identified and located throughout the survey
area. Our interpretations of buded anomalies are based on the field electromagnetic data acquired
for this project using the methods described in the preceding sections. The electromagnetic
conductivity (EM) methods were generally effective at acquiring bulk soil conductivity and in-phase
(metallic) readings to an estimated depth up to about 20-ft below existing grade.
The conductivity maps provided on Plates I and 2 have very similar contour patterns and color
schemes. The consistency of the conductivity readings show that the conductivity measurements
obtained at the site are generally independent of the equipment orientation (i.e. no isolated linear
target such as a buded metallic pipeline was detected). Areas of interest in the conductivity maps
include the extreme high readings (red) and extreme Iow readings (blue) that are generally located
from about E6+50 to E9+75 throughout the site.
The in-phase maps provided on Plates 3 and 4 indicate the presence of multiple buried metallic
targets. These targets are shown by sharp contour closures (bulls-eyes) and are located
throughout th~ site from about E3+50 to El1+50. These targets indicate scattered areas of
isolated metal (trash) buried in the subsurface.
Based on our review of the EM survey results, we find strong evidence of buried debds throughout
a relatively large portion of the site. We recommend that excavations be conducted in some of the
more cdtical (or congested) areas to identify and remove buried debris. There are other areas
throughout the site that exhibit slightly anomalous in-phase and/or conductivity readings. These
areas may contain some limited scattered debris.
Areas with strong evidence of buried debris are identified on Plate 5 and are further described as
follows:
Area 1: Several neqative conductivity readings were obtained in this area indicating the presence
of buded materials exhibiting significantly different electromagnetic properties from the
surrounding soil. This anomaly is located north and immediately adjacent to the linear
feature (possible trench) identified in the air photos, We understand that buried vehicles
are suspected to be located in this area. The large Iow to negative conductivity readings
with accompanying in-phase disturbances indicate a distinct area of buried metal.
Area 2: Multiple measurements of large higMow conductivity and in-phase readings were
obtained throughout this area indicating the presence of buded debds, Some of the
conductivity and in-phase readings do not necessarily correspond, indicating that some of
the debris may be non-metal. Visual observations during field surveys noted some
surficial metal debds located in this area.
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Area 3: The existence of several relatively closely-spaced in-phase anomalies and a marked
change in conductivity (E5+00, N1+50) identify this area to possibly contain
accumulations of buried debris.
Area 4: This isolated area (El1+25, N0+40) exhibited both high and Iow in-phase readings as
well as a lower-than-normal conductivity measurement, indicating a possible
accumulation of buried debris.
Area 5: This isolated area (E10+25, N3+20) exhibited both high and Iow in-phase readings as
well as a lower-than-normal conductivity measurement, indicating a possible
accumulation of buried debris.
Limitations
The results of our electromagnetic survey are based on our interpretation of recorded geophysical
data and should not be construed as fact. We performed the services in a manner consistent with
the level of care and skill ordinarily exercised by members of the geophysical profession currently
conducting work under similar conditions. We do not warrant nor guarantee that acquisition,
compilation, and analysis of acquired geophysical data will yield desirable or anticipated results.
Ground Truth. We recommend that physical checks for buried objects be performed wherever
possible to verify the location of interpreted underground anomalies. The Owner or Excavation
Contractor should perform his own survey to satisfy himself as to the accuracy and completeness
of our results. The results of our electromagnetic surveys do not relieve the Owner or Excavation
Contractor of their responsibility to take all necessary care and precautions in order to protect the
safety of personnel, equipment, and property during excavation operations.
Theoretical. The precision of our geophysical measurements are limited by inherent theoretical
considerations of the geophysical methods applied for this study. The objective of our
electromagnetic survey was to attempt to locate and define the existence and configuration of
features to depths allowed by the resolution of the equipment which is controlled by local geologic
properties, equipment capabilities, and subsurface features. These anomalies include natural and
man-made objects, are composed of various materials, and may bear a highly complex
relationship to the electromagnetic measurements recorded by our survey. We do not warrant that
all buried facilities were located by our electromagnetic surveys due to these complex
relationships.
Quality Control
A third-party technical review of this electromagnetic survey was conducted by Dr. Thomas
Dobecki of Dobecki Earth Sciences, Inc. His review generally consisted of (1) examining survey
procedures, (2) evaluating the overall quality of the EM data, and (3) independently processing the
EM data in order to compare interpreted survey results.
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Report No. 0401-3705 -r~.J~o
The following illustrations are attached and complete this report:
Plate
East - West Conductivity Results ................................................................ 1
North - South Conductivity Results ............................................................. 2
East- West In-Phase Results ..................................................................... 3
North - South In-Phase Results .............................................................. ;... 4
Interpreted Survey Results ........................................................................ ~- 5
Closing ·
We appreciate this opportunity to be of service to Ryland Homes. We will be pleased to help you
with any questions that may arise regarding this study and look forward to working with you on
future projects.
Sincerely,
FUGRO-McCLELLAND
(SOUTHWEST), INC.
Robert C. Gauer, P.G.
Project Manager
Robert P. Ringholz, P.E.
Chief Engineer
Copies Submitted: Addressee (4)
Repo~ No. 0401-3705 .-r-iJ~o
ILLUSTRATIONS
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