HomeMy WebLinkAboutNC0001422_DRAFT_GA140527_ADD01_LVSutton_I&A Report_20150805
Prepared for
Duke Energy
526 South Church Street
Charlotte, North Carolina 28202
DATA INTERPRETATION AND
ANALYSIS REPORT
ADDENDUM NO. 1
CONCEPTUAL CLOSURE PLAN
L.V. SUTTON PLANT
Prepared by
Geosyntec Consultants of NC, PC
1300 South Mint Street, Suite 110
Charlotte, North Carolina 28203
Project Number GC5592
August 2014
GC5592/GA140527_ADD01_LVSutton_I&A Report.docx i 08.08.14
TABLE OF CONTENTS
1. INTRODUCTION ................................................................................................ 1
2. LOLA INVESTIGATION .................................................................................... 2
2.1 Overview and Background .......................................................................... 2
2.2 Field Investigation ....................................................................................... 2
2.2.1 Groundwater Monitoring ................................................................ 2
2.2.2 Soil and CCR Investigation ............................................................ 3
3. ADDITIONAL INVESTIGATION IN THE 1971 BORROW AREA ................ 5
3.1 Overview ..................................................................................................... 5
3.2 Geotechnical Index Properties ..................................................................... 5
3.2.1 Foundation Soils ............................................................................. 5
3.2.2 CCRs .............................................................................................. 6
3.3 Analytical Tests ........................................................................................... 6
3.3.1 Total Concentrations ...................................................................... 6
3.3.2 SPLP Concentrations ...................................................................... 6
4. REFERENCES ..................................................................................................... 7
LIST OF FIGURES
Figure 2.F1: DPT Investigation and Groundwater Monitoring Well Locations
Figure 2.F2: Shallow Water Table Elevation Isocontour Map of LOLA
Figure 2.F3: Bottom Elevations of CCR in LOLA
Figure 2.F4: Isopach Thickness of CCR in LOLA
GC5592/GA140527_ADD01_LVSutton_I&A Report.docx 1 08.08.14
1. INTRODUCTION
Geosyntec Consultants of North Carolina, P.C. (Geosyntec) has been evaluating
conceptual closure options for the coal combustion residuals (CCR) ponds located at the
L.V. Sutton Plant using: (i) available information from historical documents and
drawings; (ii) data obtained from the field investigations conducted by Geosyntec in
May 2014; and (iii) laboratory testing results for the samples collected from the
referenced Geosyntec investigations.
Two additional field tasks were identified during a meeting in early June 2014 to: (i)
delineate the vertical boundaries of the CCR materials within the Lay-of-Land-Area
(LOLA) located to the south of the CCR ponds and collect water quality information
from monitoring wells located within the LOLA; and (ii) refine the horizontal and
vertical delineation of CCR materials located below the 1971 Pond and address the new
information gathered from the Geosyntec field investigation conducted in May 2014.
The additional field investigations were implemented in late June and early July 2014
and results were presented in the addendum to the Preliminary Site Investigation Data
Report (Data Report Addendum 1) [Geosyntec, 2014a].
This current report includes interpretation of the data presented in the Data Report
Addendum 1 and is provided as an addendum to the Data Interpretation and
Analysis Report (Report 2) [Geosyntec, 2014b] submitted to Duke Energy
Corporation (DEC) on 25 July 2014.
The remaining sections of this report are organized as follows:
Section 2 presents the interpretation of the LOLA investigation results;
Section 3 presents the interpretation of the results from the additional
investigation below the 1971 Pond; and
Section 4 presents the cited references.
GC5592/GA140527_ADD01_LVSutton_I&A Report.docx 2 08.08.14
2. LOLA INVESTIGATION
2.1 Overview and Background
The LOLA is located between the discharge canal and the coal pile. It is believed that
the observed presence of CCR in this area may have been due to the plant operations
between approximately 1954 and 1972. Geosyntec understands that the LOLA may be
on the North Carolina Inactive Hazardous Waste Sites Priority List and may at some
point have been under the North Carolina Department of Environment and Natural
Resources (NCDENR) Department of Waste Management (DWM) Inactive Hazardous
Sites Branch’s voluntary program.
2.2 Field Investigation
2.2.1 Groundwater Monitoring
Figure 2.F1 depicts the monitoring well locations (as well as the boring locations)
within the LOLA. Water level measurements were summarized in Table 2.T1 of the
Data Report Addendum 1. Based on these water level elevations, a potentiometric
surface map was developed, which is presented on Figure 2.F2. As can be seen on this
figure, the flow direction within the LOLA is consistent with previous depictions of the
flow direction from the northeast to the southwest towards the discharge canal.
Water quality samples were collected from all existing monitoring wells within the
LOLA, including MW-13, MW-13D, MW-14, MW-15, MW-15D, MW-16, MW-16D,
MW-20 and MW-20D. During purging of the wells, field parameters were collected
and the readings were summarized in Table 2.T2 of the Data Report Addendum 1.
As can be seen from this table, pH conditions were relatively uniform and circum-
neutral to slightly acidic and redox conditions were generally mildly reducing. This is
consistent with other monitoring locations throughout the Site (including background
conditions), even though many locations across the Site appear to have somewhat more
oxidizing conditions. The difference might be related to the input from natural organic
matter (e.g., decaying leaf litter within the densely vegetated areas in the northern part
of the LOLA) and/or potential historical impacts of petroleum hydrocarbon around the
former aboveground storage tank (AST) area within the southern part of the LOLA.
The analytical results were presented in Table 2.T3 of the Data Report Addendum 1.
Consistent with historical sampling results, the arsenic concentration in MW-13
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(shallow well) was substantially elevated (218 µg/L), but the boron concentration was
only slightly elevated (935 µg/L). On the other hand, the deep well at this location
(MW-13D) indicated a low arsenic concentration (9.6 µg/L), but a substantially
elevated boron concentration (2,350 µg/L), which likely did not originate within the
LOLA, but from the upgradient deeper zones within the 1971 Pond area. Shallow
monitoring well MW-15, which appears to be located at the previously established
compliance boundary around the LOLA, indicated an arsenic concentration of 31.2
µg/L, exceeding the groundwater standard of 10 µg/L. Manganese and iron
concentrations were substantially elevated throughout the LOLA, which is consistent
with conditions across the Site (including background conditions).
2.2.2 Soil and CCR Investigation
A preliminary, screening-level assessment of the soils and CCR materials within the
LOLA was conducted and the boring locations are shown on Figure 2.F1. A subset of
soil and/or CCR samples was collected from the borings and submitted for chemical
analysis.
The analytical results were presented in Table 2.T4 (total metals, pH, and % moisture)
and Table 2.T5 (SPLP) of the Data Report Addendum 1. The analytical results were
used to evaluate levels of constituents of interest (COI), assess the current leachability
potential, and supplement the visual identification of CCR materials to confirm that the
vertical extent of CCR materials has been reached.
Using both the analytical results and the visual identification of CCR materials, boring
logs were developed that were included in Appendix 2.A3 of the Data Report
Addendum 1. Figure 2.F1 includes descriptions of the depth increments that appeared
to contain CCR materials. Based on visual identification, the observed CCR materials
appeared to include a range of grain sizes, which might indicate the presence of both
bottom ash and fly ash within the LOLA.
Based on this investigation alone it cannot be confirmed that a continuous soil layer is
present over CCR and/or CCR sand mixtures across the entire LOLA and additional
confirmatory shallow borings are recommended to evaluate shallow soil (cover)
conditions across the area. However, the main purpose of this current investigation was
to evaluate the vertical extent of CCR materials. The elevations (NAVD 88) for the
bottom of CCR materials are presented on Figure 2.F3, while Figure 2.F4 depicts
isopach contours of the thickness of CCR materials within the LOLA. Note that the
GC5592/GA140527_ADD01_LVSutton_I&A Report.docx 4 08.08.14
horizontal extent of the LOLA has changed from previously depicted delineations, but
is subject to further adjustments. As can be seen on Figure 2.F4, the thickness of CCR
varies considerably across the LOLA, but appears to be thickest within the northwestern
corner of the LOLA and thinnest within the southeastern corner.
The chemical characterization summarized in Table 2.T4 of the Data Report
Addendum 1 indicates relatively low concentrations of arsenic (up to a maximum of 42
mg/kg), boron (up to 25 mg/kg), chromium (up to 25 mg/kg), and iron (up to 16,200
mg/kg) compared to the CCR materials characterized in the 1971 and 1984 Ponds. The
chemical signatures do indicate a contribution of CCR materials when arsenic, iron, and
chromium were detected at appreciable concentrations, but the levels are more
consistent with a CCR/soil mixture than pure CCR materials.
The SPLP data summarized in Table 2.T5 of the Data Report Addendum 1 indicate
that this CCR/soil mixture within the LOLA does not leach COIs at elevated
concentrations. Again, this is in contrast to the CCR materials characterized within the
1971 and 1984 Ponds.
The chemical characterization of the deeper CCR materials below the 1971 Pond is
discussed in Section 3 below.
GC5592/GA140527_ADD01_LVSutton_I&A Report.docx 5 08.08.14
3. ADDITIONAL INVESTIGATION IN THE 1971 BORROW AREA
3.1 Overview
The additional investigation in the 1971 Pond with focus on the 1971 Borrow Area
consisted of 14 geoprobe borings, and geotechnical and analytical laboratory tests for
selected samples collected during the geoprobe borings. Based on the additional
investigation results, the horizontal and vertical delineation of CCR materials in the 1971
Pond (i.e. 1971 Pond and 1971 Borrow Area) was refined from that developed using the
Geosyntec May 2014 investigation results. The refined interpreted horizontal and vertical
delineation of CCRs in the 1971 Pond will be included in the “Closure Options Feasibility
Analysis Report” (Report 3) to be submitted to DEC. Also, the estimated thickness of
CCRs in the 1971 Pond will be graphed as isopachs, which are contours connecting points
of equal thicknesses, in Report 3.
The sections below present the interpretation of the laboratory test results including: (i) the
geotechnical index properties; and (ii) the analytical tests (total and SPLP concentrations).
3.2 Geotechnical Index Properties
3.2.1 Foundation Soils
One geoprobe boring was conducted on the dike separating the 1971 Pond from the 1984
Pond. As observed from other dike borings conducted during the Geosyntec May 2014
investigation, the Dike Fill and Foundation Soils are generally sandy. However, some
Foundation Soil samples appeared to be different from the sandy Foundation Soils. Two
grain size distribution tests [ASTM D 422] (both of which included a hydrometer test
[ASTM D 422]) and six Atterberg Limits tests [ASTM D 4318] were conducted on those
samples as part of Geosyntec’s laboratory testing program. The grain size distribution data
and measured Atterberg Limits were presented in Table 3.T1 of the Data Report
Addendum 1. The grain size test results indicate that the tested samples consist of 44% to
59% sand and 41% to 56% fines (i.e., silt and clay). Also, the Atterberg Limits tests
indicate that one sample is non-plastic and that the rest of the samples tested have liquid
limits ranging from 26 to 126, plastic limits ranging from 22 to 60, and plasticity indices
ranging from 4 and 66. These test results are consistent with visual observations in the field
and indicate that the Foundation Soil at the investigated location is clayey and sandy soil
and not CCRs.
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3.2.2 CCRs
As part of Geosyntec’s laboratory testing program, seven Atterberg limits tests were
conducted on CCR samples collected from locations depicted on Figure 3.F1 of the Data
Report Addendum 1. The samples were collected from deep locations (1971 Borrow
Area) and the results were summarized in Table 3.T1 of the Data Report Addendum 1.
The data indicate that the tested CCR samples are non-plastic, which is consistent with their
field identification as CCR. In addition, visual observations indicated that these materials
would classify as predominantly fly ash.
3.3 Analytical Tests
In order to supplement the visual and geotechnical characterization of the CCR within the
1971 Borrow Area, samples were collected for chemical analysis. Both total concentrations
of COIs and SPLP concentrations were analyzed in nine CCR samples and the results were
summarized in Tables 3.T2 (total concentrations) and 3.T3 (SPLP) of the Data Report
Addendum 1.
3.3.1 Total Concentrations
Total concentrations of many COIs indicate that the tested samples are CCR materials and
not soils, which is consistent with the visual and geotechnical characterization of these
samples. Consistent with the results from the May 2014 investigation, the samples
exhibited substantially elevated concentrations of arsenic and iron, which appear to be the
most important “CCR indicator parameters” of the materials found within the 1971 Borrow
Area. Arsenic concentrations ranged up to 155 mg/kg, a result obtained from the deepest
sample submitted (MB2 at 76-80 ft bgs), and iron concentrations ranged up to 43,400
mg/kg. In comparison, site-specific soil samples discussed in Report 2 exhibited non-
detect results for arsenic and iron concentrations that were generally below about 1,000
mg/kg.
3.3.2 SPLP Concentrations
Leaching tests using the SPLP method indicate that the CCR materials located within 1971
Borrow Area have the potential to leach arsenic at elevated concentrations. Arsenic
concentrations of up to 316 µg/L were measured in SPLP extracts, and there is a good
apparent correlation between total arsenic and SPLP arsenic concentrations. Other
“typical” CCR indicator parameters such as boron, iron, chromium, manganese, and
selenium do not leach at elevated concentrations from the CCR materials submitted for
analysis.
GC5592/GA140527_ADD01_LVSutton_I&A Report.docx 7 08.08.14
4. REFERENCES
ASTM Standard D 422 (2007), "Standard Test Method for Particle-Size Analysis of
Soils," ASTM International, West Conshohocken, PA, DOI: 10.1520/D0422-
63R07, www.astm.org.
ASTM Standard D 4318 (2010), "Standard Test Methods for Liquid Limit, Plastic
Limit, and Plasticity Index of Soils," ASTM International, West Conshohocken,
PA, DOI: 10.1520/D4318-10, www.astm.org.
Geosyntec Consultants, Inc. (2014a), "Preliminary Site Investigation Data Report
Addendum No. 1. Conceptual Closure Plan, L.V. Sutton Plant”.
Geosyntec Consultants, Inc. (2014b), "Data Interpretation and Analysis Report.
Conceptual Closure Plan, L.V. Sutton Plant”.
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Pa
t
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Bottom Elevations of CCR in LOLA
L.V. Sutton Plant
Figure
2.F3
Project No. GC5592
August 2014
Notes:
1.LOLA indicates Lay-of-Land Area
2.FDPT indicates direct-push technology boring location
3.Bottom elevations are in feet relative to North American Vertical Datum of 1988 (NAVD88)
4.Horizontal coordinate system North American Datum 1983 (NAD83)
Pa
t
h
:
Isopach Thickness of CCR in LOLA
L.V. Sutton Plant
Figure
2.F4
Project No. GC5592
August 2014
Notes:
1.LOLA indicates Lay-of-Land Area
2.FDPT indicates direct-push technology boring location
3.Isopach thickness is denoted in feet
4.Elevations are in feet relative to North American Vertical Datum of 1988 (NAVD88)
5.Horizontal coordinate system North American Datum 1983 (NAD83)