Central Transport -GW Assmt Dec 92-OCR

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December 28, 1992
SECTION 1 . INTRODUCTION
1.01 Background
O'Brien & Gere Engineers, Inc. (O'Brien & Gere), has been retained by Central
Transport, Inc. to prepare a response to a letter dated November 12, 1992 from the State
of North Carolina, Department of Environment, Health and Natural Resources, Division
of Solid Waste Management (State). This letter requires CTI to develop a ground water
assessment plan "to define the vertical and horizontal extent of the plume" which has been
detected in the vicinity of MW-7. This monitoring well is near two former lagoons located
at the Central Transport, Inc. (CTI) Charlotte, North Carolina terminal site.
Briefly restated, the results of the previous investigations have demonstrated two flow
patterns existed on the eastern side of lagoons 1 and 2 at the site. The "non-pumping" flow
pattern is the natural flow pattern on the eastern portion of the site. The pumping
condition resulted when CTI operated its production well. The practical effect of pumping
the production well was to create a hydraulic gradient away from the lagoons, and toward
the production well. Since Westinghouse Remediation Services, Inc. completed the lagoon
excavation (in January 1992), CTI has not used its production well. Shutting off the
production well allows the ground water flow direction to return to its natural, generally
southward trend.
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December 28, 1992
During non-pumping conditions, two ground water flow regimes are present at the
site. The direction of ground water flow in the eastern flow regime is to the southwest. For
this reason, wells MW-6, MW-7, and MW-8 are hydraulically upgradient of the lagoons.
In addition to the horizontal flow direction data, vertical flow data was collected
during previous investigations. A fracture trace analysis was conducted and the results were
summarized in a report dated November 1990. Briefly restated, the results of this analysis
suggest that one fracture lineation is present at the Charlotte site and apparently underlies
the naturally occuring depression in which Pond 3 and former Lagoon 2 are situated. The
general ground water gradient in the fracture at the site is from north to south and the
fracture system forms a significant permeability barrier to the ground water flowing from
the west and ground water from the east should not flow further west than the fracture. The
two flow regimes on the site likely coalesce in this fracture and then turn southward as
ground water leaves the site. Wells MW-11, MW-13, and MW-16 are in a low area of the
site where this change in direction is believed to occur which suggests that wells MW-11,
MW-13, and MW-16 are downgradient wells. Groundwater is at a higher elevation in the
deeper well at each well nest (i.e., the ground water elevation in MW-12 and MW-16 is
higher than the elevation in MW-11 and MW-13, respectively). The higher ground water
elevations in the deeper wells indicates upward flow potential. The vertical hydraulic
gradient is probably the hydraulic response to the discharge of bedrock ground water to the
stream south of lagoon 2. Figure 1 shows the location of the wells installed on the site.
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December 28, 1992
Ground water sampling has been conducted at the site on at least nine occasions
beginning in October 1989. Details of these activities are included in previous reports
including the Hydrogeologic Investigation, June 1990, the Supplemental Phase 1
Hydrogeologic Investigation, July 1990, and a subsequent letter reports dated January 17,
1992, and September 15, 1992. Ground water samples were analyzed for volatiles, base
neutral/acid extractables, pesticides/PCBs, and metals. Constituents detected in MW-8
samples included acetone, methylene chloride, 1,1,1-trichloroethane, and 1,1-dichloroethane
at a range of nondetectable (ND) to 43 ppb. No constituents have been detected in MW-8
since March 1991, and, prior to March 1991 these constituents were detected only
irregularly. Constituents detected in MW-7 included 1,4-dichlorobenzene, vinyl chloride,
benzene, 1, 1-dichloroethylene, ethylbenzene, toluene, 1, 1, 1-trichloroethane, xylenes, and 1,2-
dichloroethene at a range of ND to 110 ppb. As presented on Figure 1, MW-7 and MW-8
are east of lagoon I and 2 and were downgradient only when the production well was in
operation. Analysis of the samples from wells located south and west of the lagoons did not
indicate the presence of contamination. In one sample from MW-16, which appears to be
aberrational, ethylbenzene was detected at 25 ppb.
1.02 Objective
The purpose of this ground water assessment plan is to outline an additional
hydrogeologic investigation that will further define the vertical and horizontal extent of
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December 28, 1992
ground water contamination in the vicinity of MW-7 and MW-8. Specifically, there are two
objectives:
1 ). verify the eastern edge of the plume, and
2). assess whether the contamination near MW-7 extends into the deeper bedrock
aquifer.
Sampling of the production well will be utilized to delineate the eastern edge of the
plume. A newly installed bedrock well (designated MW-17) will be utilized to further define
the vertical extent of contamination in the vicinity of MW-7. Installation of well MW-17 is
more fully described in Section 2.01.
1.03 Description of Ground Water Monitoring System
The ground water monitoring system will consist of wells MW-6, MW-7, MW-8, MW-
9, MW-10, MW-11, MW-13, MW-16, the production well and a newly installed bedrock well
designated MW-17. Figure 1 is a site map which shows the locations of the monitoring
wells, the proposed location of MW-17, and other site features, including the former waste
management units (the lagoons.)
The ground water monitoring system is required to include at least one monitoring
well hydraulically upgradient of MW-7 and MW-8; the proposed system includes four
upgradient wells, MW-6, MW-9, MW-10, and the production well. The ground water
monitoring system is required to include at least three wells in the vicinity of MW-7 and
hydraulically downgradient of the lagoons; the proposed system includes six downgradient
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December 28, 1992
wells, MW-7, MW-8, MW-11, MW-13, MW-16,and the newly installed MW-17 are provided.
Two of these are installed in the "deep bedrock" (MW-16 and MW-17)
Table 1 contains well specifications. The table includes the following data for each
well (except where noted): the screened interval; the elevation of the measuring point (for
water level measurement); and the elevation of the land surface. Data in Table 1 is
accurate to the nearest 0.01 foot, except where noted.
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December 28, 1992
SECTION 2 -MONITORING AND COLLECTION PROCEDURES
2.01 Additional Well Installation
In order to assess the potential for vertical ground water contamination in the vicinity
of MW-7, one additional bedrock monitoring well (MW-17) will be installed at the site. The
well will be located adjacent to monitoring well MW-7 so that a well nest is formed. The
additional well will be deeper than MW-7. MW-17 will be completed at a depth which is
a minimum of approximately 25 feet deeper than MW-7 in the first water bearing zone
encountered at or below the minimum depth. A zone will be considered to be water
bearing if it yields a minimum of approximately 1 gallon per minute.
The well installation will be completed using the air rotary drilling method, with a
nominal six-inch diameter bit. The drill cuttings will be inspected in the field for lithology
and moisture content. Once the desired depth has been reached, the monitoring well will
be constructed by lowering an assembly of two-inch inside diameter, flush joint threaded,
PVC well screen and riser casing into the borehole. The well assembly will consist of 10
feet of PVC screen, with 0.020-inch slot size, attached to an appropriate length of riser
casing. A clean sand pack will be installed in the annular space between the well screen
and the borehole. The sand pack will extend two feet above the top of the well screen. A
two-foot thick bentonite seal will then be placed on top of the sand pack. The remaining
annular space between the borehole wall and the well casing will be filled with a cement
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December 28, 1992
2.02 Sampling Methods
One round of ground water samples will be collected from the following wells: MW-
6, MW-7, MW-8, MW-9, MW-10, MW-11, MW-13, MW-16, the production well and a newly
insitalled bedrock well designated MW-17. Ground water purging or sampling procedures
will not be initiated at MW-17 until a minimum of 24 hours after its development.
Ground water sampling procedures will be according to the Sampling and Analysis
Plan dated December 1992 which is being submitted along with this Ground Water
Assessment plan.
2.03 Analytical Methods
Ground water samples will be analyzed in accordance with the Sampling and Analysis
Plan dated December 1992 which is being submitted along with this Ground Water
Assessment plan.
2.04 Evaluation Procedures
Background arithmetic means, variances and standard deviations for indicator
parameters from upgradient wells will be calculated. Based on an evaluation of ground
water quality data collected at the site since 1989, an appropriate statistical procedure for
comparing upgradient and downgradient wells will be selected. The statistical procedure
will be selected in accordance with the US Environmental Protection Agency Guidance
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December 28, 1992
entitled " the Statistical Analysis of Ground Water Monitoring Data at RCRA Facilities",
lnt<~rim Final Guidance Office of Solid Waste, dated February 1989. As stated in Section
5 of the referenced guidance document, if more than 50% of the observations are below the
detection limit then the appropriate method is a test of proportions. If the proportion of
detected values is 50% or more, then an analysis of variance procedure will be used. A
statistical analysis will be performed on any constituent analyzed that has been detected
above the detection limits at least once.
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December 28, 1992
SECTION 3 • SCHEDULE FOR IMPLEMENTATION
The investigations outlined in this ground water assessment plan will be implemented
in accordance with the following schedule:
Acceptance of Plans by State
Installation of MW-17
Sampling of wells
Submittal of Report
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Weeks following acceptance of
Sampling and Analysis Plan and
Ground Water A~sessment Plan
0 weeks
4 weeks
5 weeks
11 weeks
O'BRIEN & GERE