20080868 Ver 2_Section III B Wetland Hydrology 2020 PCS Creeks Report_20210701

B. WETLAND HYDROLOGY
Section II-B contains summary information about pre- and post -Mod Alt L hydrology for
Jacks Creek, Jacobs Creek, Drinkwater Creek, Tooley Creek, Huddles Cut, Porter Creek, and
DCUT11 as it pertains to an aspect of one of the six permit questions, while this section
contains additional summary information about hydrology in each monitored creek. While the
study officially began in 1998 and data collection for some parameters occurred in both 1998
and 1999, due to CAMA permits for pier construction, the official start date for some
parameters, including hydrology, was May 1999. Therefore, the first full year of wetland
hydrology data was 2000 and the years with incomplete data are not included in wetland
hydroperiod analysis.
Water depth at most wells appears to be influenced by large amounts of rainfall (>2-3
inches) or small events over several days; however, at many wells, if the water level has been
below 12 inches deep or deeper than the well can record, even rain amounts of 2-3 inches does
not have an effect, or only a marginal effect, on the water level. Large amounts of Tar River
discharge appears to influence water level at some wells, but mostly only the wells closer in
proximity to the Pamlico River.
1.0 Wetland Hydroperiods by Creek
a. Broomfield Swamp Creek
The first year of hydrology data was collected in 2019 and 2019 is the first
pre -Mod Alt L year for Broomfield Swamp Creek. In 2020, total annual rainfall was 64.19 inches
(Table I-F2). Two wells were monitored, both within the floodplain on the south side of the
creek; BSCW2 is approximately 700 feet further downstream from BSCW1. In 2020, the
longest hydroperiod for the upstream well (BSCW1) was 59 days (23.0 percent) and the
hydroperiod for BSCW2 was 136 days (53.1 percent) (Table III-B1).
b. SCUT1
Hydrology data collection in this tributary to South Creek also began in
2019. Rainfall data for SCUT1 was obtained from the same rain gauge as Broomfield Swamp
Creek due to its proximity to the creek. In 2020, total annual rainfall was 64.19 inches (Table I-
F2). Two wells were monitored, both within the floodplain on the west side of the creek;
SCUT1W2 was placed approximately 500 feet downstream of SCUT1W1. Both wells
experienced similar longest hydroperiods in 2020; SC1W1 was 133 days (52.0 percent) and
SC1W2 was 132 days (51.6 percent) (Table III-B1).
c. Jacks Creek
Years of hydrology data included in this report are 2000-2005 and 2011-
2020. Mod Alt L activities began and were completed in the Jacks Creek drainage basin in
2015; all previous years are pre -Mod Alt L. During these years, total annual rainfall ranged from
34.87 (2001) to 61.47 inches (2005) with an average of 47.96 inches (Table I-F2). Total annual
rainfall for 2020 was 67.02 inches, which was 15.94 inches more than the average rainfall for all
years. In 2020, the three most downstream wells on the east prong of Jacks Creek (JW9A,
JW9B, and JW10) recorded a hydroperiod for the entire growing season (Table III-B1 and
Figure III-B1). The longest hydroperiod for the most upstream well on the east prong (JW7A)
was 22.7 percent (58 days) of the growing season. When the longest hydroperiods in 2020
were compared to 2019, JW7B and JW8 increased by 28 days, JW9A, JW9B, and JW10
remained the same with hydroperiods for the entire growing season, and JW7A decreased by 9
days. On the main prong, hydroperiods for JW1, JW2A, and JW2B were 50.8 percent of the
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growing season, JW3 was 30.9 percent of the growing season, and JW4 and JWSA were 48.0
percent of the growing season. The two most downstream wells on the main prong (JWSB and
JW6) recorded hydroperiods for the entire growing season.
d. Jacobs Creek
Two wells in the upper reaches of Jacobs Creek have been monitored
since 2011. Mod Alt L activities in the drainage basin began in 2014 and were completed in
2015. The wells are located within 100 feet of each other, at more or less equivalent
geomorphic positions in the creek system.
Neither of the wells recorded a wetland hydroperiod in 2020, the same as
past years (Table III-B1 and Figure III-B2). The only recorded instance of a wetland
hydroperiod at Jacobs Creek wells was in March 2014, a year with above average rainfall.
While 2015 and 2018 through 2020 total rainfall were also above average, 2014 was the only
year where February, March, and April rainfall were each above the WETS 30-year monthly
averages (Table I-F1); however, March, April, and May of 2018 were all above the WETS 30-
year monthly averages and the Jacobs wells did not record a wetland hydroperiod. To date,
hydroperiods in Jacobs Creek are the shortest among all creeks monitored for this project.
e. Drinkwater Creek
Three wells in Drinkwater Creek have been monitored since 2011. Pre -
Mod Alt L years include 2011 and 2012. As measured by the PA2 rain gauge, total annual
rainfall over the 10 years ranged from 41.60 (2013) to 67.02 inches (2020) with an average of
52.80 inches (Table I-F2). Total annual rainfall for 2020 was 67.02 inches, which was 14.22
inches more than the average rainfall for all years. In 2020, hydroperiods ranged from 16.4
(DWW1C) to 100 (DWW1B) percent of the growing season (Table III-B1 and Figure III-B2).
One of the wells (DWW1B) is in the middle of the stream channel and the other two are outside
of the stream channel on either side of the creek floodplain. In 2020, the longest wetland
hydroperiod at DWW1 B increased to 256 days (100 percent of the growing season) making it
the longest hydroperiod recorded at DWW1B. Hydroperiods at DWW1A throughout the years
ranged from 19 percent (49 days) in 2013 to 34 percent (88 days) in 2012. In 2020, six
hydroperiods were recorded for DWW1A, with the longest being 24.6 percent (63 days) of the
growing season. At DWW1C, hydroperiods ranged 9 percent (24 days) in 2014 to 18 percent
(47 days) in 2018. In 2020, two hydroperiods were recorded for DWW1A, with the longest being
16.4 percent (42 days) of the growing season.
To potentially understand the behavior of DWW1A and DWW1C, relative
elevations across the floodplain between the two wells were collected every 10 feet with a sight
level and stadia rod (a total of nine measurements including the sight -level location). That
exercise showed DWW1C to be approximately 3.5 inches higher in elevation than DWW1A.
LiDAR indicates that the topography perpendicular to the axis of the creek at this monitoring
array is different on either side, which is not uncommon. According to LiDAR, beyond DWW1A,
there are several polygons of somewhat higher elevation compared to the land beyond
DWW1C; these higher features could affect runoff from some rainfall events in the vicinity of
DWW1A and contribute to the different behavior of these two wells.
f. Long Creek (control)
Two wells in two small and narrow branches of a minor prong on the
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south side from the main channel of Long Creek have been monitored since 2011. As
measured by the Tooley Creek gauge (across South Creek), total annual rainfall over the nine
years ranged from 40.61 (2013) to 66.88 (2020) inches with an average of 52.29 inches (Table
I-F2). In 2020, total annual rainfall was 66.88 inches, which was 14.59 inches higher than the
average rainfall for all years. The longest hydroperiod in 2020 for LOCW1B was 100 percent
(256 days) of the growing season (Table III-B1 and Figure III-B3). LOCW2B is located further
upstream on the main branch of the prong and has always had a shorter hydroperiod than
LOCW1A. In 2020, LOCW2B had a hydroperiod for 50.0 percent (128 days) of the growing
season, which was 64 days more than in 2019. The hydroperiods at both wells have been
similar to the other creeks.
g. Tooley Creek
Years of hydrology data included in this evaluation are 2000-2001 and
2010-2020, with 2000-2001 and 2010-2011 as pre -Mod Alt L years. Total annual rainfall ranged
from 35.71 (2001) to 66.88 (2020) inches with an average of 51.74 inches (Table I-F2). In 2020,
total annual rainfall was 66.88 inches, which was 15.14 inches higher than the average rainfall
for all years. In 2020, the two most upstream wells on the east prong had longer hydroperiods
than 2019, TW1 and TW2 (Table III-B1 and Figure III-B4). TW1 had a hydroperiod for 15.2
percent (73 days) of the growing season and TW2 had a hydroperiod for 47.7 percent (122
days) of the growing season. The downstream most well on the east prong, TW3, had a
hydroperiod for 47.7 percent (122 days) of the growing season, which was shorter than the
hydroperiods for 2019. For the west prong, in 2020, the two most upstream wells (TW5 and
TW6) had shorter hydroperiods than 2019. TW5 had a hydroperiod for 46.5 percent (119 days)
of the growing season and TW6 had a hydroperiod for 11.3 percent (29 days) of the growing
season. The downstream most well on the west prong, TW4, had a hydroperiod for 51.2
percent (131 days) of the growing season, which was longer than in 2019.
h. Huddles Cut
Years of hydrology data included in this evaluation are 2000-2002, 2007-
2019; post -Mod Alt L began in 2010. Total annual rainfall over all years ranged from 32.18
(2001) to 68.14 (2003) inches with an average of 49.72 inches (Table I-F2). In 2020, total
annual rainfall was 66.48 inches, which was 16.76 inches higher than the average rainfall for all
years. There have been seven years in the main prong (2000, 2014, and 2016 - 2020) and five
years in the west prong (2016-2020) when every well recorded hydroperiods for 100 percent
(256 days) of the growing season (Figures III-B5 and III-B6).
i. Main Prong
Continuous hydroperiods for all wells over the 15 years ranged
from 27.7 percent (HMW10 in 2011s) of the growing season (71 days) to 100 percent (256
days) with an average of approximately 91.0 percent or 233 days (Figure III-B5). As evident in
Figure III-B5, the longest hydroperiod for more wells was shorter in 2007 through 2011 than in
the years prior and after. In 2013, the hydroperiod for HMW10, a well located downstream on a
small branch east of the other transects in the main prong, decreased to about half of the
growing season while all other wells had hydroperiods for the entire growing season. In 2015,
the year of second highest total rainfall, a well located about midway up the main prong and in a
small crenulation on the west side of the swamp (HMW9), decreased to just over half of the
growing season while all other wells had hydroperiods for the entire growing season. There is
no known explanation for the decreases, but they are not likely related to the deep water well
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pump operations discussed in Section 111.112.0. Wells HMW11 and HMW12, both closer to
deep well pumps, were not affected in 2013, and pumps in the area were off in January 2014,
therefore did not potentially affect 2015 data. Since 2016, all wells recorded hydroperiods for
the entire growing season.
ii. West Prong
Continuous hydroperiods for all wells over the 15 years ranged
from 0 days (HWW9 in 2013, the most upstream well) to 100 percent (256 days) with an
average of approximately 69.5 percent or 178 days (Figure III-B6). Until 2016, the more
upstream wells on the west prong tended to have shorter wetland hydroperiods than the
downstream wells and water levels appeared to be more influenced by rainfall than the wells
further downstream; however, since 2016 all wells recorded hydroperiods for the entire growing
season.
i. Porter Creek
Wetland hydrology data were collected at Porter Creek at six wells in the
beginning of the 2006 growing season for another PCS project and three additional wells were
installed downstream of the other six wells in early 2011. Since no other creek in the study was
monitored in 2006, only Porter Creek well data from 2007 forward was included in this report,
and pre -Mod Alt L years include 2007-2015, the longest pre -Mod Alt L data set among the
creeks in the study. Mine activities in the Porter Creek drainage basin began in 2016, the first
post -Mod Alt L year. Total annual rainfall over the 14 years ranged from 36.16 (2007) to 73.21
(2020) inches with an average of 53.19 inches. In 2020, total annual rainfall was 20.02 inches
higher than the average rainfall for all years. The six most upstream wells had hydroperiods
that ranged from 5.07 percent, (13 days) four wells in 2009, to 26.2 percent, (67 days) three
wells in 2008, with an average of approximately 16.2 percent or 41 days (Figure III-B7).
Hydroperiods have decreased slightly over the past two years (2019 and 2020) at all six
upstream wells. The three downstream units were installed in 2011 with one in the middle of
the creek channel (PCW9B) and two on either side of the creek channel in the wide floodplain
but nearby (PCW9A and PCW9C). Hydroperiods at these three wells were much longer than
other Porter Creek wells for all years since monitoring began; PCW9B had a hydroperiod for the
entire growing season every year since monitoring began. For all years excluding 2017,
PCW9A had longer hydroperiods than PCW9C. The increase in hydroperiod length at PCW9C
in 2017 was likely due to beaver dams that were noticed near the wells; the beaver(s) were
removed in late 2017(Table III-B1). The longest hydroperiod at PCW9C has been decreasing
from year to year since the beavers were removed in late 2017. In 2020, the year with the
highest rainfall since 2007, the longest hydroperiod at PCW9A increased by 142 days from
2019 and the longest hydroperiods at PCW9C decreased by 16 days from 2019.
j. DCUT11
Hydrology data collection in this tributary to Durham Creek began in
2013. Mod Alt L activities occurred in its drainage basin for the first time in 2018. Data from the
Porter Creek rain gauge were used for this creek due to its close proximity. Total annual rainfall
since 2013 ranged from 43.39 (2013) to 73.21 (2020) inches with an average of 56.95 inches;
2020 total was 16.26 inches more than the average of all years (Table I-F2). The eight wells
are in three different arrays along the creek and exhibited a wide range of hydroperiods in 2020
that appear to be influenced by rainfall (Table III-B1 and Appendix B). As would be expected,
the wells located in the channel (DC11 W1 B, DC11W2B, and DC11W3B) all had longer
hydroperiods than the wells of the same array located in the floodplain. The downstream wells
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with hydroperiods ranging from 48.0 percent (123 days) to 100 percent (DC11W3A, DC11W3B,
and DC11W3C) had longer hydroperiods than the more upstream wells. In 2020, all wells
except DC11W3B, which has had hydroperiods that span the entirety of the growing season for
all years, and DC11 W2A, which had an increase in hydroperiod of one day in 2020, had shorter
hydroperiods than 2019 (Figure III-B8). Wetland hydroperiods for the upstream DCUT11 wells
are among some of the shortest of all monitored creeks; in this part of the system, the stream is
incised with a narrow floodplain which is not as well connected to overbank flow events.
k. DCUT19 (control)
Hydrology data collection in this tributary to Durham Creek also began in
2013. Total annual rainfall during monitoring years ranged from 40.09 (2019) to 65.20 (2020)
inches with an average of 50.80 inches (Table I-F2). In 2020, total annual rainfall was 14.40
inches more than the average rainfall for all years. Hydroperiods for the four wells in the two
most upstream arrays (DC19W1A, DC19W1B, DC19W2A, and DC19W2B) were similar to one
another each year from 2013-2019 (Figure III-B9). In 2020, hydroperiods for these four wells
were shorter than any previous year, with hydroperiods that ranged from 8.6 percent (22 days)
to 9.4 percent (24 days) with an average of 9.0 percent (23 days) of the growing season. The
most downstream array of wells (DC19W3A and DC19W3B) had longer hydroperiods than the
more upstream wells (Table III-B1). The hydroperiod for DC19W3A in 2020 was for the entire
growing season, which was 160 days longer than 2019. DC19W3B had a hydroperiod for the
entire growing season for 2014 through 2018, but was reduced to 131 days in 2019, and
increased to a hydroperiod for the entire growing season in 2020.
I. Duck Creek (control)
Hydrology data collection at eight wells in three arrays and one additional
well began in 2011. Total annual rainfall ranged from 36.16 (2013) to 62.73 (2016) inches with
an average of 49.20 inches (Table I-F2). In 2020, total annual rainfall was 54.47 inches, 5.27
inches more than the average rainfall for all years. All of the wells in 2020 at Duck Creek had
longer hydroperiods than 2019 (Figure III-B10). In 2020 DKCW4B had a hydroperiod that
spanned the entire growing season, similar to what was observed at this location in 2016-2018.
Hydroperiods for the remaining seven wells ranged in percentage of the growing season from
23.8 percent (61 days) to 68.8 percent (176 days) (Table III-B1). In 2015, logging began on
land adjacent to the monitoring locations on the north and south prongs. There has been a
noticeable increase in hydroperiod lengths and an increase in the percent of flow events during
field visits at all Duck Creek flow stations since 2015 (Figure III-B10 and Appendix B).
2.0 PCS Deep Wells and Water Levels in CZR Wetland Level TROLLs
Water depth within creeks and wetlands should respond to changes in
environmental conditions. For example, precipitation events should increase the amount of
belowground and aboveground water. The operation of pumps within PCS deep wells near
impact creeks could potentially disrupt how the hydrology of surrounding wetlands responds to
changing environmental conditions. If the relationships between environmental variables and
hydrology change during or after the operation of pumps within deep wells, then some effect of
Mod Alt L activities may be inferred.
a. Methods
Water level data collected from shallow monitoring wells (In Situ Level
TROLLs) in the wetlands and waters of Porter Creek were used to investigate these potential
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changes in relationships. Level TROLLs measure water levels across a range of approximately
5 feet with most data collected from —24 to +24 inches at each location
(configuration/installation varies by site conditions). Information on the operation of pumps
within each 20-inch diameter deep well was provided by PCS. Each deep well is drilled
approximately 250-feet deep through several confining layers in order to depressurize the
Castle Hayne Aquifer under the active mine. Each pump can produce 3,000 gallons/minute.
Daily hydrology data from each Level TROLL were split into three time
periods: pre, during, and post pump operation. For each of these time periods, a dynamic
multiple linear regression model was constructed with hydrology (i.e., water depth) as the
response variable and Tar River discharge, precipitation, wind speed, and wind direction as
predictor variables. Tar River discharge was lagged by 5, 10, 15, and 20 days and precipitation
was lagged by 0.5, 1, 2, 3, 4, and 5 days. Wind direction was converted into a categorical
variable to represent eight directions (north, northeast, east, etc.). Water depth was also lagged
one day and included in all models as another predictor variable; however, this variable was
only included to control for temporal autocorrelation and not for any explanatory purposes.
Larger absolute values for coefficients in Table III-B3 represent stronger correlations and
negative coefficient values show a negative relationship with depth and the listed variable, while
the opposite holds true for positive coefficient values.
A full model with all of the predictor variables was first constructed.
Predictor variables were removed in a step -wise manner based on their significance value (i.e.,
P-value), however, a predictor was not removed if it was the only representative remaining of
the four main predictor types (wind speed, wind direction, discharge, or precipitation). Thus,
each final model included at least one predictor of wind speed, wind direction, discharge, and
precipitation. Final predictor variables were compared to one another using the absolute values
of the calculated t-value. Those variables with the highest t-values for each final model will be
referred to as `important' to distinguish from significant or non -significant variables that did not
produce high t-values. Models were fit using the "dynlm" package in R (Zeileis 2016).
b. Porter Creek Results
The analysis of pump operation in deep wells and wetland hydrology for
Porter Creek was first examined in the 2018 report. Six Level TROLLs (PCW4, PCWS, PCW6,
PCW9A, PCW9B, and PCW9C were used in the 2020 analysis in relation to nearby deep wells
(March 2016 — December 2020 data) with pre, during and post data sets. Locations of deep
wells and Level TROLLs in Porter Creek are shown in Figure III-B11 and operation dates of
pumps are also shown in Table III-B2.
Porter Creek hydrology at six Level TROLLs was examined. Graphs of
the water levels for each Level TROLL from 2016 to 2020 with horizontal bars above the graphs
to show the operation periods of the pumps in deep wells are depicted nearest to the two arrays
of CZR wells Figure III-B12. Pre, during, and post time periods were established for five wells
depending on their on/off dates and proximity to CZR Level TROLLs. At DW-1108, pre data
consisted of January 2016-October 2017, during November 2017-August 2018, and November
2019-August 2020, and post data consisted of September 2018-November 2019 and
September 2020-December 2020 using data from PCW4, PCWS, and PCW6. For DW-1109
and 1110, pre dates included January 2016-Febuary 2017, during included March 2017-October
2018, and post included November 2018-December 2020 also using PCW4, PCWS, and PCW6
data. DW-1113 and DW-1114 pre dates consisted of January 2016-October 2017, during of
November 2017-December 2019, and post of January 2020-December 2020 using data from
PCW9A-C. DW-1108 represents the closest well to PCW4, PCWS, and PCW6, but was
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restarted in November 2019, over a year after the next two closest wells were turned off (DW-
1109 and DW-1110). Because of its proximity and unaligned dates Level TROLL depth
correlations were done separately for DW-1108, DW-1109 and DW-1110. For DW-1113 and
DW-1114, the PCW9A-C wells were used due to their proximity to the deep wells.
Detailed results of all final models are given in Table III-B3. Rainfall (at
either a 0 day or 1 day lag) was among the most important predictors for every Level TROLL
and every time period except at PCW9B during (DW-1113 and DW-1114), where wind speed
was the important predictor. All the coefficient values for the important rainfall predictors were
positive and ranged from 1.09 (PCW9B, post, 0 day lag) to 4.70 (PCW6 During, 0 day lag), an
indication that rainfall increased water depth, more so than discharge and wind. Under both well
operation dates PCW4, PCWS, and PCW6 had important rainfall predictor lags that consisted 1
day in the pre deep well operation, 0 days during deep well operation, and 0 days for post deep
well operation. PCW9A, PCW9B, and PCW9C all followed a similar pattern excluding PCW9B
during. Occasionally rainfall showed a significant negative correlation at 2 or 5 day lags
potentially representing high water levels remaining within the system days after a rainfall event.
Wind speed was a significant predictor in the post in all but two Level
TROLLs, while it wasn't significant as often for during and post in most tested Level TROLLs.
Wind direction appeared to be more impactful at the downstream array (PCW9A-C) with
easterly winds often positively correlated with depth and westerly winds negatively correlated
across all time periods.
Discharge was a significant predictor 10 times across pre, during, and post time periods at all
wells with varying lag days and negative or positive correlations.
c. Conclusions
Rainfall was the most important predictor for almost every Level TROLL
and deep well pump operation time period in Porter Creek. It is clear that rainfall positively
impacted the hydrology of this creek, after controlling for discharge and wind. Furthermore, this
positive effect was present before, during, and after deep well pump operation for all Porter
Creek Level TROLLs. Thus, the operation of pumps in deep wells does not appear to have
affected the positive influence of rainfall on hydrology in Porter Creek.
In Porter Creek, all six Level TROLLS across all timeframes, excluding
PCW9B during, showed a 0-1 day lags during the pre -deep well operation time period, 0-1 day
lags for the during time period, and a 0 day lag for the post time period for rainfall as an
important predictor. This result suggests that the amount of time for a rainfall event to strongly
affect the water levels measured by the Level TROLLs has remained relatively the same since
pumps first began operation. Due to the strong positive results for the rainfall coefficient, pump
operation in the deep wells has not changed the positive impact of rainfall on hydrology.
The pump operation in deep wells does not seem to have had any major
impacts on the hydrologic response of Porter Creek to changes to the external environment (as
measured by the Level TROLLs). Regression models constructed before, during, and after
pump operation in the deep wells were similar (but not identical).
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Jacks Creek
250 -
- JW1
+ JW2A
' JW2B
o JW3
p JW4
* JW5A _
�L
x JW5B m 150 -
o JW6
❑ JW7A
• JW7B
® JW8
O JW9A
X JW9B
® JW10
1 1 Total annual
rainfall
ro
200 -
100 -
50 -
0
13
ED
I
0 • • • • • #F 0 * #F • #f
V
IP
❑ _ *
0 ❑
*
o
ri,o ri,o qo ri,o ri,o ri,o ri,o qo qo ri,o ri,o
100
- - 80
- 60
- 40
- 20
0
Total Annual Rainfall (in)
Year
Figure III-B1. Longest hydroperiod for each well in Jacks Creek by year with total annual
rainfall for each year (PA2 rain gauge).
- JCBW1A
+ JCBW1B
' DWW1A
A DWW1B
✓ DWW1C
1 Total annual
rainfall
Hydroperiod Length (days)
Jacobs and Drinkwater Creeks
250 -
200 -
150 -
100 -
50 -
4.
A
2011 2012 2013 2014
t 1: t
2015 2016 2017
100
- - 80
- - 60
- 40
- 20
2018 2019 2020
0
Total Annual Rainfall (in)
Year
Figure III-B2. Longest hydroperiod for each well in Jacobs and Drinkwater creeks across all
years (2011-2020). Means (dots) and ranges are shown.
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o LOCW1B
x LOCW2B
Total annual
rainfall
Hydroperiod Length (days)
Long Creek
250 -
200 -
150 -
100 -
50 -
0 0 0 0
100
- 80
- 60 2
- m
- 40 c
- Q
m
0
1-
- 20
2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
Year
0
Figure III-B3. Longest hydroperiod for each well by year in Long Creek and total annual rainfall
(Tooley Creek rain gauge).
+ TW1
x TW2
• TW3
o TW4
* TW5
❑ TW6
Total annual
rainfall
Longest Hydroperiod (days)
Tooley Creek
2000 2001 002 200920102011201220132014201520162017201820192020
Year
Total Annual Rainfall (in)
Figure III-B4. Longest hydroperiod for each well by year in Tooley Creek and total annual
rainfall.
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250
HMW1 in
+ HMW2 m 200
A HMW3
✓ HMW4 0
* HMW5 a 150
o HMW6 2
❑ HMW7 �,
® HMW8 =
O HMW9 100
$ HMW10 0)
HMW11
x HMW12 50
I I Total annual rainfall
0
00 0N ��
Huddles Cut Main Prong
• • • • • • * • • • • •
100
- - 80
- 20
000000000000-
Yea r
0
Figure III-B5. Longest hydroperiod for each well in Huddles Cut Main Prong by year and total
annual rainfall.
250
A HWW2 200
✓ HWW3 -o
* HWW4 0
a HWW5 a� 150
O HWW6 0
L
® HWW7 -o
O HWW8 2
$ HWW9 ▪ 100
Total annual
rainfall J
50
Huddles Cut West Prong
O ;p ® ;. • • • • •
V
0
A
® A A
co 0 o 0 ^\ 0 I)` ^�' ^^^< 0 ^^o'1 'b 0 ^^oti0
0 o 0 o o o o o o
100
80
60
40
20
0
Total Annual Rainfall (in)
Year
Figure III-B6. Longest hydroperiod for each well in Huddles Cut West Prong by year and total
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annual rainfall.
- PCW9A
O PCW9B
PCW9C
O PCW4
✓ PCW5
* PCW6
❑ PCW1
• PCW2
• PCW3
Total annual
rainfall
Hydroperiod Length (days)
Porter Creek
250 -
200 -
150 -
100 -
50 -
0 0 0 0 0 0 0 0 0 0_
100
- 80
- 60
- 40
- 20
r r r r r r r r r - 0
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
Year
Total Annual Rainfall (in)
Figure III-B7. Longest hydroperiod for each well in Porter Creek by year and total annual
rainfall.
0
A
v
•
I I
DCUT11
250 -
DC11W1A _
DC11W1B as 200 -
DC11 W2A -
DC11 W2B o _
DC11W2C .a -
DC11 W3A o 150
L
DC11W3B 7, -
DC11 W3C 2 -
Total annual • 100 -
rainfall • -
c
0
J -
50 -
❑ ® ® ® ❑ ❑ ❑ ❑
v
A
v
Y
2013 2014 2015 2016 2017 2018 2019 2020
Year
100
- - 80
- - 60
- - 40
- - 20
- 0
Total Annual Rainfall (in)
Figure III-B8. Longest hydroperiods for each well in DCUT 11 by year and total annual rainfall
(Porter Creek rain gauge).
III-B-11

- DC19W1A
o DC19W1B
' DC19W2A
A DC19W2B
✓ DC19W3A
* DC19W3B
I I Total annual
rainfall
Longest Hydroperiod (days)
DCUT19
250 -
*
200 -
150 -
100 -
50 -
*
100
- 80
- - 60
- 40
- 20
2013 2014 2015 2016 2017 2018 2019 2020
0
Year
Figure III-B9. Longest hydroperiod for each well in DCUT19 by year and total annual rainfall.
Duck Creek
+ DKCW1B
x DKCW2A
o DKCW2B
a DKCW3A
* DKCW3B
❑ DKCW4A
O DKCW4B
- DKCW4C
1 1 Total annual
rainfall
Longest Hydroperiod (days)
250 -
200 -
150 -
100 -
50 -
0 0 0 0
*
R
Total Annual Rainfall (in)
100
- 80
- 60
- 40
- 20
2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
Year
0
Total Annual Rainfall (in)
Figure III-B10. Longest hydroperiod for each well in Duck Creek by year and total annual
rainfall.
III-B-12

MODIFIED ALT L PERMIT BOUNDAR
SEMI -CONTINUOUS WELL
SALINI { /WATER LEVEL STATION
WATER QUALITY STATION
SEDIMENT STATION
FISHIBENTHOS STATIO
BENTHOS STATION
DEEP WELL USED IN ANALYSIS}
DEEP WELL (STILL ON)
III-B-13
1
0
0
0
0
a)
c
0
( Q)
O
<
E
U Q
O 6-
-1 a)
C
LT]
a
Q1
0
. [.1-11.!_Y1_4Li1 Z 1 Zit 1: u!A I.[■1
J
H
4
C
0
w
0
U
O
•• rove • •
0
L
a)
MO
W
N
J
J
0
1-
a)
a)
-o
N
a)
0-
a)
a)
-o
O
U
0
J
a)
LL

-Z
0W1109
01V1110
1,1
PCW4
2016
2017
2018
2019
2020
ourIlams
11'
PCW5
2016
2017
2012
2019 2020
OW LIM
so.
x1
1
'j
)1
1
I
1
kliiirl.
_
PCW6
2016 2017 _018 201 2j2;i
Figure III-B12. Hydrology of Level TROLLs in Porter Creek and times of deep well pump operation. Gray line shows Level TROLL data collected every 1.5 hour and blue line shows a 2-month moving average of hydrology
data. Horizontal lines indicate pump operation dates for 14 deep wells around the mine in Bonnerton.
III-B-14

Table III-B1. Wetland hydroperiods during the 2020 growing season* at Level TROLLS in 12 study
creeks. (m)=manual well
Level TROLL
Dates
Number of
consecutive days
Highest percentage
of growing season
Broomfield Swamp
Creek (BSCW)
BSCW1
3/14-5111; 5/18-6/10; 6112-6/30; 7/2-7/18; 7/29-8127
59; 24; 19; 17; 3D
23.0
BSCW2
3/14-7127; 7/29-11/24
136; 119
53.1
South Creek
Tributary SCUT1
(SCUT1)
SCUTW1
3/14-724; 7126-11/24
133; 122
52.0
SCUTW2
3/14-7/23; 7/26-11/24
132; 122
51.6
Jacks Creek (JW )
JW1 (m)
3/ 14-7/21; 7/25-8/29; 9/12-11/24
130; 36; 74
50.8
JW2A
3/ 14-7/21; 7/25-8/29; 9/12-11/24
130; 36; 74
50.8
JW2B
3/14-7/21; 7/25-8/29; 9/12-11/24
130; 36; 74
50.8
JW3
3/14-5/26; 5/18-5/19; 7/25-8/28; 9/7-11/24
64; 63; 35; 79
30.9
JW4 (m)
3/14-5/16; 5/18-7/20; 7/25-11/24
64; 64; 123
48.0
J W5A
3114-5/ 16; 5118-7120; 7/25-11/24
64; 64; 123
48.0
J W5B
3/14-11/24
256
100.0
JW6 (m)
3/14-11/24
256
100.0
JW7A
3/14al10; 5/18-6/4; 6/13-6/27; 9/14-10/7; 10118-11/5
58; 18; 15; 24; 19
221
JW7B
3/14-7/20; 7/25-8128; 9/6-11/24
129; 35; 80
504
JW8 (m)
3/14-7/20; 7/25-8/28; 9/6-11/24
129; 35; 80
50.4
JW9A
3/14-11/24
256
100.0
J W9B
3/14-11/24
256
100.0
JW10 (m)
3/14-11/24
256
100.0
Jacobs Creek (JCBW)
JCBW1A
no wetland hydropenod
4
N/A
JCBW1 B
no wetland hydropenod
6
N/A
Drinkwater Creek
(DWW )
DWW1A
3/14-5115; 5/18-6I9; 6/12-7/3; 7/29-8/25; 9/18-10114; 10/25-1117
63; 23; 22; 28; 27; 14
24.6
DWW1B
3/14-11/24
256
100.0
DWW1C
3/14-4/24; 5/18-6/2
42; 16
16.4
Tooley Creek (TW)
TW1
3/14-4/21; 5/18-6/6; 6/13-6/28; 8/2-8/25; 9/12-11/24
39; 20; 16; 24; 73
152
TW2 (m)
3/14-5/16; 5/18-7/22; 7/25-11/24
64; 66; 122
47.7
TWO
3/14-5/16; 5/18-7/22; 7/25-11/24
64; 66; 122
47.7
TW4
3/14-7/22; 7/29-11/24
131; 119
51.2
TW 5 (m)
3/ 14-5/ 13; 5/18-7/20; 7/29-1 1 /24
61; 64; 1 19
46.5
TW6
3/30-4l15; 5/18-6/2; 6/30-7/17; 9/12-10/10; 10/12-11/2
17; 16; 18; 29; 22
11.3
Long Creek (LOCW)
LOCW 1 B
3/14-11/24
256
100.0
LOCW2B
3/14-7/19; 7/29-8128; 9/8-11/24
128; 31; 78
50.0
Huddles Main (HMW)
HMW1 (m)
3/14-11/24
256
100.0
H M W2
3/14-11/24
256
100.0
HM W3 (m)
3/14-11/24
256
100.0
HM W4 (m)
3/14-11/24
256
100.0
H M W S
3/14-11/24
256
100.0
H M W6
3/14-11/24
256
100.0
HM W7 (m)
3/14-11/24
256
100.0
HMW 8
3/14-11/24
256
100.0
HMW 9
3/14-11/24
256
100.0
HMW10
3/14-11/24
256
100.0
HMW11 (m)
3/14-11/24
256
100.0
HMW12
3/14-11/24
256
100.0
III-B-15

Table III-B1 (concluded).
Level TROLL
Dates
Number of
consecutive days
Highest percentage
of growing season
Huddles West (I-IWW)
HWW2
3/14-11/24
256
100.0
HWW3 (m)
3/14-11/24
256
100.0
HWW4
3/14-11/24
256
100.0
HWW5 (m)
3/14-11/24
256
100.0
HWW6 (m)
3/14-11/24
256
100.0
HWW7
3/14-11/24
256
100.0
HWW8
3/14-11/24
256
100.0
HWW9 (m)
3/14-11/24
256
100.0
Porter Creek (PCW)
PCW 1
3/14-4/18
36
14.1
PCW2
3/14-4/24
42
16.4
PCW 3
3/14-4/22
40
15.6
PCW4
3/14 4/26; 5/18-6/3; 6/14-6/27
44; 17; 15
17.2
PCW 5
3/ 14 4/27; 5/18-6/4; 6/ 14-6/28
45; 18; 16
17.6
PCW6
3/14 4/26; 5/18-6/3; 6/14-6/27
44; 17; 15
17.2
PCW 9A
3/14-11/24
256
100.0
PCW 9B
3/14-11/24
256
100.0
PCW9C
3/14-5/15; 5/18-7/20; 7/26-8/28; 9/1-11/24
63; 64; 34; 85
25.0
Durham Creek
Tributary DCUT11
(D11)
D11-1A
no wetland hydroperiod
2
N/A
❑11-1B
3/14-4/24; 5/18-6/5; 6/13-6/28; 7/29-8/21
42; 19; 16; 24
16.4
D11-2A
no wetland hydroperiod
5
N/A
D11-2B
3/25-4111; 6/13 6/26
18; 14
TO
❑11-2C
no wetland hydroperiod
13
N/A
D11-3A
3/23-5/12; 5/18-7/21; 7/25-11/24
51; 65; 123
48.0
D11-3B
3/14-11/24
256
100.0
❑11-3C
3/14-5/13; 5/18-7/21; 7/25-11/24
61; 65; 123
48.0
Durham Creek
Tributary DCUT19
(D19)
D19-1A
3/25-4/16; 6/13-6/29
23; 17
9.0
D19-1B
3/25-4/15; 6/13-6/29
22; 17
8.6
D19-2A
3/23-4/15; 6/13-6/27
24; 15
9.4
D19-2B
3/23-4/15; 6/13-6/28
24; 16
9.4
D19-3A
3/14-11/24
256
100.0
D19-3B
3/14-11/24
256
100.0
Duck Creek (DKCW)
DKCW 1 B
3/14 5/ 15; 5/18-7/5; 8/2-8/29; 9/18-10/21; 10/25-11/24
63; 49; 28; 34; 31
24.6
DKCW2A
3/14-9'2; 9'8-11/24
173; 78
67.6
DKCW2B
3/14-9'2; 9'8-11/24
173; 78
67.6
DKCW3A
3/14-5/13; 5/18-6/5; 6/13-6/29; 8/2-8/26; 9/12-11/24
61; 19; 17; 25; 74
23.8
DKCW 3B
3/ 14-6/9; 6/12-7/22; 8/2-8/29; 9/ 12-11 /24
88; 41; 28; 74
34.4
DKCW4A
3/14-9/5; 9/8-11/24
176; 78
68.8
DKCW4B
3/14-11/24
256
100.0
DKCW4C
3/14-9/5; 9/8-11/24
176; 78
68.8
*To properly compare Alt E monitoring hydraperiads to Mad Alt L, the farmer growing season of 256 days (14 March - 24
November) was used with agency approval.
III-B-16

Table III-B2. Operation dates for the pumps within deep water wells in proximity to the Level TROLLs
in Porter Creek.
Deep Well
Date Pump On
Date Pump Off
DW1108*
DW1109
DW1110
DW1113
DW1114
October 2017/November 2019
February 2017
February 2017
October 2017
December 2017
August 2018/August 2020
May 2018
October 2018
December 2019
February 2019
*well turned back on November of 2019, but only the period shown used as During time in the analysis
III-B-17

Table III-B3. Details of the final models for Level TROLLs in Porter Creek. Level TROLL
locations are in order from downstream to upstream. Pre -before pump on; During -pump
operation; Post -after pumps off. DoF = degrees of freedom. Value of the coefficient and the
standard error (in parentheses) are given for discharge, rainfall, and wind speed; significant
wind directions are categorized by positive (+) or negative (-). Bold = significance; number of
asterisks = level of significance: * - < 0.05, ** - < 0.01, *** - < 0.001. Red = variables with the
highest t-values for each Level TROLL and are referred to as "important."
DW-1108
Leve1TROLIlPeriad DoF Disckarge Rainfall
Wind Speed Wind Direction
R=
PCW4
Pre 506 10 days: -0.25 (0.12]*
0 days: 1.24 (0.25)**
1 day: 1.32 (0.25)***
- 0.05 (0.05)
(+): [NONE]
(-): [NONE]
0.97
0 days: 0.98 (0.20)** *
During 556 5 days: -0.45 (0.19)*
0 days: 4.17 (0.29)** *
1 day: 2.97 (0.29)**
5 days: -0.72 (0.30)*
(+): [NONE]
005 (005) (-): W
0.962
Post 587 5 day s: 025 (0.13)
0 days: 2.18 (0.19)** *
1 day: 0.98 (0.18)**
0.09 (0.04)*
(+): [NONE]
t-) [NONE]
0.97
PCW5
Pre
505 10 days: -0.26 (0.12)*
0 days: 1.29 (0.26)**
1 day: 1.61 (0.26)***
2 days:-0.60 (0.25)*
(+): N*
- 0-05 (0-06] (-r NW*
0.971
During
0 days: 1.03 (0.21)***
556 5 days: -0.48 (0.20)*
0 days: 4.25 (0.31)**
1 day:3.32 (0.31)*** 006(005)
5 days:-0.74 (0.32)*
(+): [NONE]
[] W**
0.963
Post
PCW6
587
5 days: 027 (0.14)
0 days: 2.13 (0.20)** *
1 day: 1.19 (0.19)**
0.10(0.01)*
(+): [NONE]
t-) [NONE]
0.97
Pre
505 10 days: -0.2 7 (0.13)*
0 day: 1.25 (0.29)**
1 day: 1.65 (0.28)***
2 days: -0.60 (0.27)*
(+): [NONE]
- 006(O t-]= [NONE]
0.967
During
0 days: 1.09 (0.22)**
556 5 days: -0.49 (0.21)*
0 days: 4.70 (0.33)**
1 day: 3.15 (0.33 )* * * 006 (005)
5day: -081(034)*
(+): [NONE]
[] W*
0.961
Post 587
5 days: 028 (0.14)
0 days: 2.29 (0.20)** *
1 day: 1.07 (0.20)**
0.09 (0.05)
(+): [NONE]
t-) [NONE]
0.97
DW-1109 and DW-1110
PCW4
Pre
295 0 day s: -025 (0.20)
0 days: 0.88 (0.34)**
1 day: 1.47 (0.35r *
- 0.13 (0.09)
(+): N*
t-) [NONE]
0.958
During
578 0 day s: -0-04 (0.09)
0 days: 2.98 (0.21)** *
1 day: 1.92 (0.20)**
0.06 (0.04)
(+): S*
[] w*
0.981
Post 787 20 days: 034 (0.1O)* **
0 days: 2.42 (0.18)** *
1 day: 1.33 (0.18)***
0.07 (0.04)
(+): [NONE]
(-): SW*
0.968
PCw5
Pre
295 0 day s: -025 (0.09)
0 days: 0.94 (0.36)**
1 day: 1.72 (0.37)***
- 0.13 (0.09)
(+): N*
(-): [NONE]
0.959
During
578 0 day s: -0-04 (0.09)
0 days: 3.07 (0.21]*-"
1 day: 2.10 (0.20j** *
0.07 (0.04)*
(+): S**
(-): [NONE]
0.982
Post
PCW6
787 20 days: 036 (011)* **
0 days: 2.36 (0.19)**
1 day: 1.63 (0.19)***
0.08 (0.04)
(+): [NONE]
(-): SW*
0.968
Pre
296 0 day s: -0.19 (0.23) 1 day: 1.85 (0.40)** * -0.08 (0.10)
(+) [NONE]
(-): [NONE]
0.953
During
578 0 day s: -0.04 (0.10)
0 days: 3.31 (0.23)***
1 day: 2.07 (0.22)**
0.06 (0.04)
(+): S**
[-7 w*
0.979
Post
787 20 days: 036 (0.11)*
0 days: 2.58 (0.20)**
1 day: 1.43 (0.20)***
0.07 (0.04)
(+): [NONE]
(-): SW*
0.968
III-B-18

Table III-B3 (concluded).
DW-1113 aid DW-1114
PCW9A
Pre 510
During 744
5 days: -0.01 (0.10)
0 days: 1.76 (0.20)*
1 day: 2.17 (020)***
2 days: -1.33 (0.21)***
(+): [NONE]
0.09 (0.04)* (-): SW**
0.897
15 days: 0.02 (0.06)
0 days: 1.31 (0.13)*** (+):[NONE]
1 day: 0.66 (0.13)*** 0.10 (0.03)*** (-): SE'
2 day: -0.36 (0.13)**
0.954
Post 366
15 days: 0.13 (0.07)
0 days: 1.68 (0.13)* * *
1 day: 0.39 (0.13)**
0.07 (0.02)**
(+): N*
{-) [NONE]
0.810
PCW9B
Pre
During
500 15 days: 0.04 (0.10)
0 day: 1.52 (022)***
1 day: 1.86 (023)*** 0.05 (0.05)
2 day: -1.25 (023)**
(+): NE* * * N**
(-) SW*** NW** 0.85
739 20days:0.14(0.07)
0 days: 0.93 (0.16)* * *
1 day: 0.45 (0.16)* *
2 day: -0.37 (0.16)*
(+): NE**
022 (0.03)*** {-}: SW""" W** 0936
Post
370 10 days: 0.26 (0.13)*
0 days: 1.09(0.21)*** 023 {0.03}*** {+}_E""" NE*** SE* 0.734
1 day: 0.89 (023)* ** (-): NW"" S W *
PCW9C
Pre
513 O days: 0.14 (0.10)
0 day: 1.34 (019)***
1 day: 2.04 (0.19)* ** 0.07 (0.04)
2 day: -1.17 (019)***
(+): N* NE*"*
(-): SW**
0.872
During
749 l0 day s: 0.08 (0.06)
0 days: 1.34 (0.14)* * *
1 day: 0.65 (0.14)***
2 day: -0.40 (0.14)* *
0.11 (0.03)***
(+): E'
(-): SE' SW*
0.918
Post 379 0 days: 0.11 (0.16)
0 days: 1.80 (0.16]* * *
1 day:0.62 (0.16)***
0.08 (0.03)**
(+):N**
(-): SW**
0.802
III-B-19