NCD991278953_19870201_National Starch & Chemical Corp._FRBCERCLA RA_Geophysical Survey Report-OCR

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rn INTERNATIONAL
TECHNOLOGY
CORPORATION
GEOPHYSICAL SURVEY REPORT
NATIONAL STARCH & CHEMICAL CORPORATION RI/FS
SALISBURY, NORTH CAROLINA
February 1987
by
IT CORPORATION
KNOXVILLE, TENNESSEE
Regional Ollice
3 I 2 Directors Drive• KnoXVJlle. Tennessee 37923.615-690-32 t I
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rn. INTERNATIONAL
TECHNOLOGY
°CORPORATION
GEOPHYSICAL SURVEY REPORT
NATIONAL STARCH &·CHEMICAL CORPORATION RI/FS
SALISBURY, NORTH CAROLINA
;;-ebruary 1987
by
IT:CORPORATION
KNOXVILLE, TENNESSEE
·.R~gional Ot:ice
312 DirectauDrive-: Kno)f,(i_\le, ,'.[e.nnerii;ee 37923. 615-696sti11
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NATIONAL STARCH AND CHEMICAL CORPORATION
Geophysical Report
During October 1986 IT Corporation (IT) conducted geophysical surveys
at the National Starch and Chemical Corporation (NSCC) facility in
Salisbury·, North Carolina. The surveys were conducted in the known trenched
area (Figure 1) and included the trench area, the area south of the trenches
toward the aeration basin, and the section west of the trench area. The
purpose of the investigation was to detect and map conductive. leachate
plume(s) due to the trenched area and to locate buried metal.
Two types of geophysical surveys were utilized at NSCC; . an electromagneUc
conductivity survey and a reconnaissance magnetic survey. Electromagnetics
(EM) is used to define are.as in the subsurface with di.fferi.ng
electro-conductive properties, i.e. leachate plume versus surrounding
subsurface. Reconnaissance magnetics is used to measure magnetic field
strength produced by magnetic objects, i.e. buried metallic drums. EM
results are stated as millimhos per meter (mmho/m) and magnetic data is
expressed as gamma per meter (gamma/ml.
EM and magnetic data were contoured and anomalous areas identified. A
statistical analysis of each data set was conducted to detennine t.he
probability_that an anomalous value existed between data points.
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conductivity zone. The southern and western portions are not as well
defined. The interior of the anomalous zone includes several smaller
areas of extremely large EM conductivity highs.
highs are located in areas with no vegetation.
Soioe of these smaller
These conductivity anomalies show up on .air photos as a series of east•west
striations, which are probably trenching scans. There is also a noticeable
topographic change at the northern end of the large anomaly in which the
land · surface sinks in the vicinity of a east·west line along·
north-coordinate 400. Based on these features, and the magnetics data,
the large EM conductivity anomaly is probably due to a series of trenches.
This zone is the most likely location of buried wastes and contaminated
soils.
MAGNETIC/SURVEY RESULTS
The magnetic anomalies indicated in Figure 3 are probable locations of
buried magnetic· materials. With one exception, the magnetic anomalies
are in the same location as the EM anomalies.
A magnetic anomaly at this particular site is considered to be any measured
value with at. least an absolute value of greater than 20 gaDDDa/m. In
some areas, absolute values greater than 20 gaDDDa/m were not considered
to be anomalies due to surrounding surface interferences or a very large
anomaly due to a nearby buried metal object. Also, due to the computer
contouring system, the contour lines around a very large value may cover
background• values and the anomaly will appear larger than it actually
is.
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:Moat of the outlined anomalies on ·Figure 3 indicate magnetic materials
·randomly disposed of throughout the trench zone and buried less than 15
feet from "the surface. These anoinali:es cannot be ranked. o'r prioritized
according .. to absolute value... A. large object buried at fifteen feet. would
appear .. very.•. simi_lar .i:o a sinall object buried at five feet . on inagne.tic
inapa of i:his nature.
The i:wo ,anoinaliea marked A and B are pr~bably due to a large concentration
of me_tai.a very close to the surface. Examples are reinforcing bars. or
crushed drums. just under the surface·. Overall, the magnetic data indf.cate
that buried metal exists throughout i:he probable trenched zone defined
by EM.
i.eii P.lacement
The monitoring wells discussed in the RI/FS work plan wiii be positioned
outside and aiong the perimeter of these EM and magnetic anomaiies. With
the• exception of wells NS-10 and NS-ll, which will be instailed inside
a large EM anomaly:
This placement wili ensure that the ground water upgradierit aricl doifu.gradient
of the EM, and magnetic arioinalies noted on Figures :i and 3 wtii be nionitorecl
iri weiis NS-01 through NS-17.
Furtiier .. Field Investigation
Areas A and B, as . shown ori Figure 3, should be excavated tci detenriine
if ariy buried metai objects exist iit these two poiiits;
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Likewise, five other magnetic a_nomalies should_ be ei<ca,vated to determine
th_e nature and extent of additio_nal · b_ur_ied obje_c~s. . Th_e, locations of
the_se additional_ excavation_s_ sho_uld. be_ determined in . th_e_ .· _fi,e,ld by . the
IT i_nvestigator and the EPA on~s_ite coordinator and. wHl be scattere_d
throughout the trench area._
The excavations should be attempted with a ba_c;khoe and . should_. not e_xtend
below the depth of ten feet. If no bur-ie,d objects are encountered_ above
that depth, the exca_va.tion wi,ll be terminated. Sin_c.e n_o _t_renching occur-red_
below the_ depth of ten feet, it will be assu:me_d_ tha_t no dee,per exc_avations.
will l!e. necessary.
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