HomeMy WebLinkAbout1403_FoothillsMSWLFLIned_ASD_DIN27386_20161104
PREPARED FOR:
REPUBLIC SERVICES OF NORTH CAROLINA, LLC
D.B.A. FOOTHILLS ENVIRONMENTAL
2800 CHERAW ROAD
LENOIR, NORTH CAROLINA 28645
FOOTHILLS REGIONAL LANDFILL
PERMIT NO. 14-03
ALTERNATE SOURCE DEMONSTRATION
FOR COBALT
AND REQUEST TO USE BACKGROUND AS THE GPS
NOVEMBER 2016
PREPARED BY:
2211 WEST MEADOWVIEW ROAD, SUITE 101
GREENSBORO, NORTH CAROLINA 27407
NC LICENSE NUMBER C-0782
PHONE: (336) 323-0092
FAX: (336) 323-0093
JOYCE ENGINEERING PROJECT NO. 00890.1601.12
______________________________________________________________________________
Alternate Source Determination for Cobalt Joyce Engineering
Foothills Regional Landfill, Permit No. 14-03 November 2016
i
Alternate Source Determination for Cobalt
and Request to use Background as the GPS
Foothills Regional Landfill, Permit No. 14-03
TABLE OF CONTENTS
1.0 INTRODUCTION..............................................................................................................1
1.1 Site Description and Background ................................................................................ 1
1.2 Compliance Monitoring History .................................................................................. 1
1.3 Hydrogeologic Setting ................................................................................................... 1
2.0 COBALT CONCENTRATIONS IN GROUNDWATER ..............................................2
21 Comparisons to Groundwater Standards ................................................................... 2
2.2 Statistical Evaluation of Background ......................................................................... 3
2.0 NATURAL SOURCES OF COBALT .............................................................................3
3.0 CONCLUSIONS ................................................................................................................4
4.0 REFERENCES ...................................................................................................................4
TABLE
Table 1: Historical Cobalt Detections
CHART
Chart 1: Cobalt Concentrations vs. Time
DRAWING
Drawing 1: Potentiometric Surface Contour Map (July 2016)
APPENDICES
Appendix A: Statistical Analysis Worksheets & Summary
Appendix B: Cobalt in NC Stream Sediments
______________________________________________________________________________
Alternate Source Determination for Cobalt Joyce Engineering
Foothills Regional Landfill, Permit No. 14-03 November 2016
1
1.0 INTRODUCTION
On behalf of Republic Services of North Carolina, LLC (Republic), Joyce Engineering (JOYCE)
presents this Alternate Source Demonstration (ASD) for the Foothills Regional Landfill in
accordance with 15A NCAC 13B .1633(c)(3). This ASD addresses recent and historic
detections of cobalt above groundwater protection standards (GPS), as requested in a Letter from
the NCDEQ to Republic dated August 8, 2016.
1.1 Site Description and Background
The Foothills Regional Landfill is located approximately two miles northwest of Lenoir, North
Carolina in Caldwell County at 2800 Cheraw Road. The landfill is bounded to the north and east
by mainly wooded and agricultural properties, to the south by Cheraw Road, and to the west by
rural residential/wooded properties and Abingdon Road. The location of the facility is shown on
the inlay on Drawing 1. The facility is a lined Subtitle D municipal solid waste landfill which
began operating in 1998 under Permit Number 14-03, issued by the North Carolina Department
of Environmental Quality (NCDEQ). The approximately 230-acre facility is maintained and
operated by Republic Services of North Carolina, LLC.
1.2 Compliance Monitoring History
Groundwater monitoring at the facility was initiated in 1998 under the Detection Monitoring
Program for municipal solid waste landfills. The facility’s current monitoring network is
comprised of nine monitoring wells: MW-1R (background), MW-2R, MW-3R2, MW-4, MW-5,
MW-6, MW-7, MW-8, and MW-10, which monitor the uppermost aquifer beneath the facility.
In addition, four surface water sampling points are sampled semiannually: upstream surface
point SW-1; and downstream surface points SW-2, SW-3, and SW-4. Two underdrains are also
sampled semiannually: UD-1, the underdrain for Cell 1; and UD-2, the underdrain for Cells 4
and 8A. The locations of all sampling points are shown on Drawing 1.
The facility was in an Assessment Monitoring Program in 2006. An Alternate Source
Demonstration (ASD), for volatile organic compounds (VOCs) detected in wells MW-3 and
MW-3R, was approved by NCDEQ on December 14, 2006, and the facility reverted to a
Detection Monitoring Program.
1.3 Hydrogeologic Setting
Geologically, the facility is located in the northwestern portion of the Inner Piedmont Belt of the
Piedmont Physiographic Province, approximately 20 miles east of the thrust belt (Brevard Shear
Zone) delineating the boundary between the westerly Blue Ridge Belt and the easterly Inner
Piedmont Belt. The metamorphic rocks of the Inner Piedmont Belt generally group within the
sillimanite facies of the amphibolite metamorphic sequence. Locally, the bedrock underlying the
facility has been mapped as migmatitic granitic gneiss of the Ordovician and older Cambrian
______________________________________________________________________________
Alternate Source Determination for Cobalt Joyce Engineering
Foothills Regional Landfill, Permit No. 14-03 November 2016
2
Periods. These rocks are described as ranging in composition from granitic to quartz dioritic with
smaller biotite gneiss and amphibolite facies present locally. The unit as a whole exhibits a
variable massive to foliated fabric (NCGS, 1985).
The uppermost aquifer beneath the facility is present within weathered bedrock saprolite and
fractured bedrock. The saprolite ranges in texture from clayey silt in the upper, most weathered
sections to micaceous sandy silt in the lower sections. Immediately above the competent
bedrock surface, a variable thickness transitional zone composed of highly weathered and
degraded friable bedrock is present.
The uppermost aquifer is laterally continuous across the site, with depth to water ranging from
less than 31 feet in low-lying areas to greater than 77 feet beneath topographic highs.
Groundwater in the uppermost aquifer generally flows from recharge areas associated with broad
gently sloping topographic areas towards topographically lower areas that are generally
delineated by the presence of stream channels, some of which are perennial receiving streams
(groundwater discharge areas) and others of which are intermittent discharging streams. In the
vicinity of the facility, the general groundwater flow direction is towards the south and west.
Groundwater elevations obtained during the July 28, 2016, monitoring event are summarized in
Table 1 and were used to prepare a potentiometric surface map presented as Drawing 1. The
groundwater flow in the uppermost aquifer beneath the site is toward south and west in the
direction of Abingdon Creek. The potentiometric surface map and interpreted flow directions are
consistent with previously submitted potentiometric surface maps for this facility.
2.0 COBALT CONCENTRATIONS IN GROUNDWATER
21 Comparisons to Groundwater Standards
For most constituents, the Groundwater Protection Standards (GPS) are the standards found in
15A NCAC 2L.0202 (NC2L Standards); however, the NCDEQ Solid Waste Section (SWS) has
established alternate groundwater protection standards for constituents with no listed NC2L
standard, referred to herein as the GWPS. The SWS has also established reporting limits for
constituents, referred to as the Solid Waste Section Limits (SWSL), below which detections are
considered estimated (not quantified).
There is no NC2L standard established for cobalt. The SWS GWPS for cobalt is 1 µg/l;
however, this is less than the SWSL of 10 µg/l. Estimated detections (below the SWSL) are not
considered exceedances, so the effective GPS is the SWSL.
Cobalt was detected in MW-4 above the GWPS and SWSL during the most recent (July 28,
2016) monitoring event with a concentration of 18.7 µg/l. No other inorganic constituents were
detected at quantified concentrations above their respective NC2L or GWPS during the July 28,
2016, monitoring event. These results are consistent with historical detections of cobalt at the
facility. The full results, including laboratory analytical reports, of the July 2016 sampling event
______________________________________________________________________________
Alternate Source Determination for Cobalt Joyce Engineering
Foothills Regional Landfill, Permit No. 14-03 November 2016
3
have been presented in the Second Semiannual Water Quality Monitoring Report of 2016, dated
September 2016.
Cobalt in MW-4 has been consistently above the GWPS and SWSL, with the highest historical
concentration of 27 µg/l in July 2009. Historically, there have also been periodic quantified
exceedances for cobalt in UD-1 and UD-2. Table 1 presents all of the historical cobalt detections
for the Foothills Landfill from August 1998 through July 2016, and Chart 1 shows a graph of the
cobalt concentrations vs. time. There do not appear to be any consistent trends in the cobalt
concentrations with time.
2.2 Statistical Evaluation of Background
The data were evaluated through the use of the Shapiro-Wilk Test, Parametric Prediction Limits,
Parametric Tolerance Intervals, Aitchison’s Adjustment, Non-parametric Prediction Limits, and
Poisson Prediction Limits, as appropriate. Background data, tests for normality, outliers,
Aitchison’s adjustment, tolerance interval, or prediction limits are used, as appropriate based on
the background data. The statistical test by which downgradient data are compared to facility
background data is based upon the nature of the data and the number of data values that are less
than the laboratory limit of detection. All statistical tests are evaluated at the 0.05 level of
significance, 95% confidence level, and are conducted as one-tailed tests.
MW-1 was the upgradient background well for the facility from August 1998 through the July
2015 sampling event. MW-1, was abandoned in preparation for construction of Cell 5A and a
new background well, MW-1R, was installed in October 2015. The data used for statistical
analysis of the background consists of all the data available for both MW-1 and MW-1R from
August 1998 through July 2016.
Cobalt was detected in MW-4 at quantified concentrations above the GWPS during the July 28,
2016, monitoring event. The cobalt detections were statistically evaluated in accordance with
the procedures outlined in 15A NCAC 13B.1632.(g) and (h) to determine if the quantified
concentration exceeded the facility background concentration. Statistical analysis indicated a
background level of 44.1 µg/l for cobalt. The statistical worksheets and summary table are
presented in Appendix A. There have been no detections of cobalt above the statistical
background in the history of the facility.
2.0 NATURAL SOURCES OF COBALT
Cobalt is a common element occurring naturally in minerals commonly found in the bedrock,
soil, and sediments in the North Carolina Piedmont. Appendix B presents a plate from A
Geochemical Atlas of North Carolina (Reid, 1993), which shows the distribution of cobalt in
stream sediments across the state. Caldwell County has been highlighted. Note that cobalt is
found at concentrations as high as 10 mg/kg throughout Caldwell County; however there is a
significant amount of variability. Metals in the soil and bedrock can easily leach into the
groundwater, especially if the groundwater is acidic (pH < 7.0). The pH of groundwater samples
______________________________________________________________________________
Alternate Source Determination for Cobalt Joyce Engineering
Foothills Regional Landfill, Permit No. 14-03 November 2016
4
from the Foothills Landfill during the July 2016 sampling event averaged 5.2, and the pH of the
sample from MW-4, which had the highest cobalt concentrations, was 4.78. Also, since metals
analyses required for the facility are for total metals, any suspended or dissolved sediment in the
collected groundwater sample will be detected and included in the reported results.
3.0 CONCLUSIONS
Cobalt is a naturally-occurring element if the bedrock, soil, and sediment in the region, and is
therefore, expected to be naturally-occurring in the groundwater. The variations in cobalt
concentrations in the groundwater are believed to reflect natural geologic variation at the site.
Based on statistical evaluation, the cobalt detections at this facility are not statistically significant
and are considered representative of historical background concentrations. The facility requests
that the background value of 44.1 µg/l be considered the applicable groundwater protection
standard for cobalt at the Foothills Landfill in accordance with 15A NCAC 13B.1634.(g).(5).
4.0 REFERENCES
North Carolina Geologic Survey, 1985, Geologic Map of North Carolina; North Carolina
Department of Natural Resources and Community Development, Geological Survey Section;
scale 1:500,000.
Reid, Jeffery C., 1993. A Geochemical Atlas of North Carolina. North Carolina Geological
Survey, Bulletin 93. May 1991, Revised 1993.
Table
TA
B
L
E
1
:
H
i
s
t
o
r
i
c
a
l
C
o
b
a
l
t
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t
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t
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o
n
s
Sa
m
p
l
e
An
a
l
y
t
e
Da
t
e
DL
R
L
Co
b
a
l
t
08
/
1
0
/
9
8
--
-
10
ND
--
-
--
-
--
-
--
-
--
-
--
-
--
-
--
-
--
-
---------------------
01
/
2
7
/
9
9
-
-
-
10
ND
--
-
--
-
--
-
--
-
--
-
--
-
--
-
--
-
--
-
---------------------
GW
P
S
=
1
µ
g
/
l
07
/
1
9
/
9
9
-
-
-
10
ND
--
-
ND
--
-
ND
--
-
--
-
ND
--
-
--
-
---------------------
09
/
0
7
/
9
9
-
-
-
10
--
-
--
-
--
-
--
-
--
-
--
-
--
-
--
-
--
-
--
-
---------------------
SW
S
L
=
1
0
µ
g
/
l
09
/
0
9
/
9
9
-
-
-
10
ND
--
-
ND
--
-
ND
--
-
--
-
ND
--
-
--
-
---------------------
10
/
1
2
/
9
9
-
-
-
10
--
-
--
-
ND
--
-
ND
--
-
--
-
ND
--
-
--
-
---------------------
Ba
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g
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=
4
5
.
2
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g
/
l
1
2
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0
6
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9
9
-
-
-
10
--
-
--
-
ND
--
-
ND
--
-
--
-
ND
--
-
--
-
---------------------
01
/
2
5
/
0
0
-
-
-
10
ND
--
-
ND
--
-
ND
--
-
--
-
ND
--
-
--
-
---------------------
07
/
2
1
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0
0
-
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10
ND
--
-
ND
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ND
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ND
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-
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------------------ND
01
/
0
9
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1
-
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10
ND
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07
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1
7
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-
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11
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1
4
1
0
.
0
10
.
0
ND
--
-
--
-
ND
--
-
--
-
0
.
6
0
J
22
.
6
ND
6
.
8
2
J
1
.
0
5
J
3
.
5
5
J
-
-
-
---------ND
07
/
2
2
/
1
4
0
.
3
10
.
0
ND
--
-
--
-
ND
--
-
--
-
1
.
8
4
J
21
.
2
ND
4
.
4
8
J
1
.
7
0
J
2
.
2
4
J
-
-
-
---
7
.
1
0
J
11.9 ND
01
/
2
6
/
1
5
0
.
2
6
10
.
0
ND
--
-
--
-
ND
--
-
--
-
0
.
3
9
J
19
.
0
ND
4
.
8
8
J
1
.
4
0
J
3
.
5
3
J
-
-
-
---
7
.
3
4
J
16.0 ND
07
/
2
8
/
1
5
0
.
2
9
10
.
0
ND
--
-
--
-
ND
--
-
--
-
ND
19
.
0
ND
4
.
6
0
J
0
.
7
0
J
1
.
0
5
J
-
-
-
---
6
.
9
6
J
16.0 ND
01
/
2
8
/
1
6
0
.
2
9
10
.
0
--
-
0
.
5
5
J
-
-
-
ND
--
-
--
-
0
.
3
7
J
19
.
1
ND
4
.
9
4
J
0
.
6
2
J
4
.
1
9
J
-
-
-
1
.
8
5
J
10.3 8.9
J
N
D
07
/
2
8
/
1
6
0
.
2
9
10
.
0
--
-
ND
--
-
ND
--
-
--
-
ND
18
.
7
ND
5
.
0
1
J
1
.
1
1
J
1
.
6
6
J
1
.
8
1
J
0
.
5
4
J
2
.
3
J
d
r
y
N
D
No
t
e
s
:
DL
=
M
e
t
h
o
d
D
e
t
e
c
t
i
o
n
L
i
m
i
t
.
Al
l
c
o
n
c
e
n
t
r
a
t
i
o
n
s
a
r
e
r
e
p
o
r
t
e
d
i
n
m
i
c
r
o
g
r
a
m
s
p
e
r
l
i
t
e
r
(
µ
g
/
l
)
.
J
= Estimated concentration above the DL but below the RL.
RL
=
R
e
p
o
r
t
i
n
g
L
i
m
i
t
=
P
Q
L
p
r
i
o
r
t
o
2
0
0
7
a
nd
S
W
S
L
s
t
a
r
t
i
n
g
J
a
n
u
a
r
y
2
0
0
7
.
ND
=
N
o
t
d
e
t
e
c
t
e
d
a
b
o
v
e
t
h
e
D
L
.
B = Blank-qualified data - analyte detected at a similar conentration in a quality-control blank.
PQ
L
=
P
r
a
c
t
i
c
a
l
Q
u
a
n
t
i
t
a
t
i
o
n
L
i
m
i
t
.
Bl
a
n
k
s
=
H
i
g
h
e
s
t
c
o
n
c
e
n
t
r
a
t
i
o
n
d
e
t
e
c
t
e
d
i
n
f
i
e
l
d
,
t
r
i
p
a
n
d
/
o
r
m
e
t
h
o
d
b
l
a
n
k
s
.
dry = insufficient water to sample.
SW
S
L
=
N
C
-
D
E
Q
S
o
l
i
d
W
a
s
t
e
S
e
c
t
i
o
n
L
i
m
i
t
.
Al
l
d
a
ta
p
r
i
o
r
t
o
2
0
1
2
t
a
k
e
n
f
r
o
m
p
r
e
v
i
o
u
s
r
e
p
o
r
t
s
b
y
G
o
l
d
e
r
A
s
s
o
c
i
a
t
e
s
N
C
,
I
n
c
.
--- = No data.
NC
2
L
=
G
r
o
u
n
d
w
a
t
e
r
S
t
a
n
d
a
r
d
es
t
a
b
l
i
s
h
e
d
i
n
1
5
A
N
C
A
C
2
L
.
0
2
0
2
Bold = Concentrations above the NC 2L or Groundwater Protecti on standards (GWPS).
GW
P
S
=
N
C
D
E
Q
S
o
l
i
d
W
a
s
t
e
S
e
c
t
i
o
n
G
r
o
u
n
d
w
a
t
e
r
P
r
o
t
e
c
t
i
on
S
t
a
n
d
a
r
d
f
o
r
c
o
n
s
t
i
t
u
e
n
t
s
w
i
t
h
n
o
l
i
s
t
e
d
N
C
2
L
.
Blanks
MW
-
3
R
M
W
-
3
R
2
M
W
-
4
M
W
-
5
M
W
-
6
M
W
-
7
M
W
-
8
M
W
-
9
M
W
-
1
0
U
D
-
1
U
D
-
2
MW
-
1
M
W
-
1
R
M
W
-
2
M
W
-
2
R
M
W
-
3
Fo
o
t
h
i
l
l
s
R
e
g
i
o
n
a
l
L
a
n
d
f
i
l
l
Pe
r
m
i
t
#
1
4
-
0
3
Joyce Engineering
Chart
Fo
o
t
h
i
l
l
s
R
e
g
i
o
n
a
l
L
a
n
d
f
i
l
l
Pe
r
m
i
t
#
1
4
-
0
3
Joyce Engineering
05101520253035404550
J
u
l
‐
9
9
J
a
n
‐
0
0
J
u
l
‐
0
0
J
a
n
‐
0
1
J
u
l
‐
0
1
J
a
n
‐
0
2
J
u
l
‐
0
2
J
a
n
‐
0
3
J
u
l
‐
0
3
J
a
n
‐
0
4
J
u
l
‐
0
4
J
a
n
‐
0
5
J
u
l
‐
0
5
J
a
n
‐
0
6
J
u
l
‐
0
6
J
a
n
‐
0
7
J
u
l
‐
0
7
J
a
n
‐
0
8
J
u
l
‐
0
8
J
a
n
‐
0
9
J
u
l
‐
0
9
J
a
n
‐
1
0
J
u
l
‐
1
0
J
a
n
‐
1
1
J
u
l
‐
1
1
J
a
n
‐
1
2
J
u
l
‐
1
2
J
a
n
‐
1
3
J
u
l
‐
1
3
J
a
n
‐
1
4
J
u
l
‐
1
4
Jan‐15 Jul‐15 Jan‐16 Jul‐16
C
o
b
a
l
t
C
o
n
c
e
n
t
r
a
t
i
o
n
(
µ
g
/
l
)
Ch
a
r
t
1:
Co
b
a
l
t
Co
n
c
e
n
t
r
a
t
i
o
n
s
vs
.
Ti
m
e
MW ‐3R2 MW ‐4 MW ‐6 MW ‐7 MW ‐8 MW ‐9 MW ‐10 UD ‐1 UD ‐2 GWPS SWSL Background
Drawing
Appendix A
Statistical Analysis Work Sheets and Summary
JOYCE Project:Foothills Regional Landfill
Project No: 890.1601.12
Task No:02
Date: October 2016
Analyte:Cobalt
Concentration RL
Sample No. Sample Date Location (µg/L)(µg/L)
1 10-Aug-98 MW-1 ND 10
2 27-Jan-99 MW-1 ND 10
3 19-Jul-99 MW-1 ND 10
4 9-Sep-99 MW-1 ND 10
5 25-Jan-00 MW-1 ND 10
6 21-Jul-00 MW-1 ND 10
7 9-Jan-01 MW-1 ND 10
8 17-Jul-01 MW-1 ND 10
9 22-Jan-02 MW-1 ND 10
10 15-Jul-02 MW-1 ND 10
11 30-Jan-03 MW-1 ND 5
12 30-Jul-03 MW-1 ND 5
13 15-Jan-04 MW-1 ND 10
14 16-Jul-04 MW-1 ND 10
15 28-Jan-05 MW-1 ND 10
16 21-Jul-05 MW-1 ND 10
17 18-Jan-06 MW-1 ND 10
18 26-Jul-06 MW-1 ND 10
19 23-Jan-07 MW-1 ND 10
20 25-Jul-07 MW-1 ND 10
21 7-Jan-08 MW-1 ND 10
22 23-Jul-08 MW-1 ND 10
23 6-Jan-09 MW-1 ND 10
24 8-Jul-09 MW-1 ND 10
25 19-Jan-10 MW-1 ND 10
26 27-Jul-10 MW-1 ND 10
27 24-Jan-11 MW-1 ND 10
28 25-Jul-11 MW-1 ND 10
29 5-Jan-12 MW-1 ND 10
30 3-Jul-12 MW-1 ND 10
31 30-Jan-13 MW-1 ND 10
32 15-Jul-13 MW-1 ND 10
33 30-Jan-14 MW-1 ND 10
34 22-Jul-14 MW-1 ND 10
35 26-Jan-15 MW-1 ND 10
36 26-Jul-15 MW-1 ND 10
37 28-Jan-16 MW-1R 0.55 J 10
38 29-Jul-16 MW-1R ND 10
Number of Data: 38
Number of Truncated Data: 37
Percentage of Truncated Data: 97%
Upper Poisson Prediction Limit: 44.1 µg/L
All concentrations in micrograms per liter (µg/L).
ND = Not detected above the method detection limit (truncated).
J = Estimated concentration below the RL.
RL = Reporitng Limit (PQL or SWSL).
Joyce Project:Foothills Regional Landfill
Project No: 890.1601.12
Task No: 02
Date: October 2016
Upper Poisson Prediction Limit
Analyte:Cobalt
Background Data Discrete
Concentration RL Half Poisson
Sample No. Sample Date Location (µg/l) (µg/l) RL Count
1 10-Aug-98 MW-1 ND 10 5 5
2 27-Jan-99 MW-1 ND 10 5 5
3 19-Jul-99 MW-1 ND 10 5 5
4 9-Sep-99 MW-1 ND 10 5 5
5 25-Jan-00 MW-1 ND 10 5 5
6 21-Jul-00 MW-1 ND 10 5 5
7 9-Jan-01 MW-1 ND 10 5 5
8 17-Jul-01 MW-1 ND 10 5 5
9 22-Jan-02 MW-1 ND 10 5 5
10 15-Jul-02 MW-1 ND 10 5 5
11 30-Jan-03 MW-1 ND 5 2.5 2.5
12 30-Jul-03 MW-1 ND 5 2.5 2.5
13 15-Jan-04 MW-1 ND 10 5 5
14 16-Jul-04 MW-1 ND 10 5 5
15 28-Jan-05 MW-1 ND 10 5 5
16 21-Jul-05 MW-1 ND 10 5 5
17 18-Jan-06 MW-1 ND 10 5 5
18 26-Jul-06 MW-1 ND 10 5 5
19 23-Jan-07 MW-1 ND 10 5 5
20 25-Jul-07 MW-1 ND 10 5 5
21 7-Jan-08 MW-1 ND 10 5 5
22 23-Jul-08 MW-1 ND 10 5 5
23 6-Jan-09 MW-1 ND 10 5 5
24 8-Jul-09 MW-1 ND 10 5 5
25 19-Jan-10 MW-1 ND 10 5 5
26 27-Jul-10 MW-1 ND 10 5 5
27 24-Jan-11 MW-1 ND 10 5 5
28 25-Jul-11 MW-1 ND 10 5 5
29 5-Jan-12 MW-1 ND 10 5 5
30 3-Jul-12 MW-1 ND 10 5 5
31 30-Jan-13 MW-1 ND 10 5 5
32 15-Jul-13 MW-1 ND 10 5 5
33 30-Jan-14 MW-1 ND 10 5 5
34 22-Jul-14 MW-1 ND 10 5 5
35 26-Jan-15 MW-1 ND 10 5 5
36 26-Jul-15 MW-1 ND 10 5 5
37 28-Jan-16 MW-1R 0.55 10 5 0.55
38 29-Jul-16 MW-1R ND 10 5 5
Note: All sample concentrations are micrograms per liter (µg/L)
Using the background data, the upper Poisson Prediction Limit, y*, is determined by:
y* =
c y + [(t^2) c / 2] + t c [y (1 + (1/c)) + ((t^2) / 4)]^0.5
where:
c = k / n
y = Poisson count
t = t(n-1, 0.95), Student's t-distribution
n-1 = degrees of freedom (number of samples - 1)
k = number of downgradient samples per event (7)
.95 = confidence interval
n = number of background samples
For:
c = 0.184
k = 7 = 7 d.g. MW's
y = 180.55
t = 1.689
n = 38
y* = 44.1 µg/L
Co
n
s
t
i
t
u
e
n
t
S
W
S
L
N
C
2
L
G
W
P
S
Da
t
a
Di
s
t
r
i
b
u
t
i
o
n
St
a
t
i
s
t
i
c
a
l
M
e
t
h
o
d
u
s
e
d
t
o
Es
t
a
b
l
i
s
h
B
a
c
k
g
r
o
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n
d
Ca
l
c
u
l
a
t
e
d
Ba
c
k
g
r
o
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d
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n
t
r
a
t
i
o
n
Sa
m
p
l
e
Lo
c
a
t
i
o
n
Sample Result SSI
Co
b
a
l
t
1
0
N
/
E
1
9
7
%
T
r
u
n
c
a
t
e
d
U
p
p
e
r
P
o
i
s
s
o
n
P
r
e
d
i
c
t
i
o
n
L
i
m
i
t
-
I
n
t
e
r
w
e
l
l
4
4
.
1
M
W
-
4
1
8
.
7
N
O
No
t
e
s
:
Co
n
c
e
n
t
r
a
t
i
o
n
s
a
r
e
i
n
m
i
c
r
o
g
r
a
m
s
p
e
r
l
i
t
e
r
(
µ
g
/
L
)
.
SW
S
L
=
N
C
D
E
Q
S
o
l
i
d
W
a
s
t
e
S
e
c
t
i
o
n
R
e
p
o
r
i
t
n
g
L
i
m
i
t
.
NC
2
L
=
N
o
r
t
h
C
a
r
o
l
i
n
a
G
r
o
u
n
d
w
a
t
e
r
S
t
a
n
d
a
r
d
e
s
t
a
b
l
i
s
h
e
d
i
n
1
5
A
N
C
A
C
2
L
.
0
2
0
2
.
GW
P
S
=
G
r
o
u
n
d
w
a
t
e
r
P
r
o
t
e
c
t
i
o
n
S
t
a
n
d
a
r
d
e
s
t
a
b
l
i
s
h
e
d
b
y
t
h
e
D
E
N
R
-
S
W
S
.
SS
I
=
S
t
a
t
i
s
t
i
c
a
l
l
y
s
i
g
n
i
f
i
c
a
n
t
i
n
c
r
e
a
s
e
o
v
e
r
b
a
c
k
g
r
o
u
n
d
.
N/
E
=
N
o
t
e
s
t
a
b
l
i
s
h
e
d
.
Su
m
m
a
r
y
o
f
S
t
a
t
i
s
t
i
c
a
l
B
a
c
k
g
r
o
u
n
d
A
n
a
l
y
s
e
s
Fo
o
t
h
i
l
l
s
R
e
g
i
o
n
a
l
L
a
n
d
f
i
l
l
Pe
r
m
i
t
N
o
.
1
4
-
0
3
Joyce Engineering
Appendix B
Cobalt in NC Stream Sediments