Lower Cascade Canal Groundwater Monitoring Program
August 14, 2012
Nevada Irrigation District (District) is in the process of improving its facilities to enhance the
reliability of water deliveries. As part of this process, pipelines such as the Banner/Cascade
Pipeline will replace the older canal system. These improvements, however, have precipitated
concerns regarding a potential reduction in groundwater recharge adjacent to the canals. The
potential reduction in recharge may affect the volume of groundwater available to private
shallow wells near the canal. To evaluate these concerns, a detailed monitoring program was
developed to assist the District with assessment of the potential influence of reduced flows in
the Lower Cascade Canal (LCC) on nearby wells, and to determine if any mitigation measures or
other actions are appropriate.
The LCC groundwater monitoring program is based on the following objectives:
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Be scientifically defensible and reproducible;
Provide a clear definition of baseline, or pre-project, conditions;
Have the ability to provide results quickly without lengthy delays for laboratory analysis;
Be cost-effective; and
Allow for District staff to conduct the monitoring, where appropriate, once the baseline
relationships are established.
. The LCC groundwater monitoring program includes two main components. The first
component involves the measurement of water levels in eight private wells located both
upslope and downslope of the canal, in two springs that are used for domestic supply and are
located downslope of the canal, and within four piezometers installed immediately adjacent to
the canal. Changes in water levels in the wells, springs, and piezometers are compared with
rainfall patterns and fluctuations in flow within the LCC to assess potential correlations. The
second component includes the evaluation of general water quality parameters and fieldmeasured parameters to evaluate whether there is a correlation between changes in canal or
meteorological conditions and changes in well conditions.
The following activities were conducted to collect the data used for the LCC groundwater
monitoring program:
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Installation of four new piezometers;
Modification of well heads on seven private wells;
Installation of downhole pressure transducers and dataloggers in the four new
piezometers, eight private wells, and two spring boxes;
Routine download of water-level data from the dataloggers; and
Collection and laboratory analysis of water samples for general mineral parameters.
The monitoring program was initially scheduled to occur from September 2010 to October
2011. During that period, however, the rainfall was approximately 40 percent greater than
average. To evaluate whether or not the high rainfall amounts may have a substantial influence
on the results, the water level monitoring was continued at all locations through late January
2012. At seven of these locations (five wells, one spring, and one piezometer), the monitoring
will continue through September 2012.
The piezometer construction details are summarized in Table 1.
Table 1
Piezometer Construction Details
Lower Cascade Canal Monitoring Program 2010-2011
Nevada Irrigation District
Location
Total Depth Drilled
Soil Conditions
PZ-1
20'
0-17' dry red clayey soil
15' becomes damp
PZ-2
25'
0-15' dry red sandy clay
15'-20' damp red sandy clay with
cobbles to 3"
20'-25' wet red sandy clay with
cobbles to 3"
15'-25'
13'-25'
11'-13'
Dry
12'
None (concrete 50' downstream)
17'-20' wet tan sandy clay
Screened Interval
14'-19'
Sand Pack Interval
12'-19'
Bentonite Seal
10'-12'
Initial Water Level
Dry
Distance from Canal
16'
Concrete
Canal Liner
All depths are in feet below ground surface
All piezometers completed with neat cement from top of bentonite to ground surface
Locking steel monument placed over all piezometers
Installed September 22, 2010
PZ-3
20'
0-10' dry red clay
PZ-4
18'
0-9' red clay
10'-15' damp red clay
7' becomes damp
15'-20' very wet tan clayey sand
10'-20'
8'-20'
6'-8'
Dry
6'
None
9'-18' wet tan clayey sand
10'-15'
8'-15'
6'-8'
13.59'
3'
None
The construction and pumping details for the wells and springs are summarized in Table 2.
Table 2
Well Construction Details
Lower Cascade Canal Monitoring Program 2010-2011
Nevada Irrigation District
Hydrofocus
Well No.
W2
W5
W6
W17
W23
W24
W51
W33
W34
W35
Datalogger
Levelogger
Levelogger
WL-15
WL-15
Levelogger
Levelogger
Levelogger
WL-15
Levelogger
WL-15
September 2010 Well Tests
Static Water
Final Water October Hydrofocus
Total
Pump Level Prior
Level at End
2011
Percent
Midspike
Depth Intake
to Test
Pump Rate
of Test (ft
Pump
Canal
Percent
(ft bgs) (ft bgs)
(ft bgs)
(gpm)
Duration
bgs)
Rate
Water
Decline
90
80
50
17
50
18
0%
54%
560
550
123
6 (decr to 3.5)
3 hrs
319
3.8
51%
179%
93
85
48
15
2 hrs
50
15
51%
83%
spring
66%
59%
200
180
40
2
6
43%
93%
71
65
44
11 (decr to 5.2) 1 hr 35 min
65
5.4
40%
87%
83
80
50
2.3
2
0%
61%
30
16
14
8
14
8
0%
27%
80
70
18
16.5
1 hr
20
16.5
83%
54%
spring
25
25
35%
30%
Water samples were collected at two different
time. Samples were collected in September and
October 2010 to evaluate conditions at the end of
the dry season. Samples were collected in May
2011 to evaluate conditions at the end of the wet
season. The water quality data were evaluated
using standard geochemical plots, examples of
which are shown below, and by comparison of
chemical concentrations with location relative to
the LCC and the underlying geology. Overall, the
water quality data does not show a consistent
correlation with location relative to the LCC and is
not correlated with the underlying geology. The
water quality results, however, do indicate
influences from human activities (e.g. septic
systems, landscape irrigation, water softeners),
which could affect the results of other types of
studies, such as the use of stable isotopes.
Water levels were recorded using electronic dataloggers at each monitoring location. At most
locations, water levels were recorded every hour. At some locations, water levels were
recorded once per day. In either case, thousands of water level measurements were recorded
for this study. In particular, for each well that is still being monitored, over 15,000 water-level
measurements have been recorded since the program started in late 2010. The water-level
data for each monitoring location have been plotted on charts referred to as hydrographs. To
evaluate the potential correlation of changes in canal flow rates and variation in rainfall on
water levels, these parameters were also plotted on the hydrographs. Examples of these charts
from one of the locations in the monitoring program are shown below.
40
40
35
35
30
30
25
25
20
20
15
15
10
10
5
5
0
0
Oct-10 Dec-10 Feb-11 Apr-11 Jun-11 Aug-11 Oct-11 Dec-11 Feb-12 Apr-12 Jun-12 Aug-12
Groundwater Level
Canal Flow
Canal Flow (cfs)
Groundwater Level (ft)
Groundwater Level vs Canal Flow
40
80
35
70
30
60
25
50
20
40
15
30
10
20
5
10
Cumulative Rainfall (in)
Groundwater Level (ft)
Daily Rainfall (in)
Groundwater Level vs Rainfall
0
0
Oct-10 Dec-10 Feb-11 Apr-11 Jun-11 Aug-11 Oct-11 Dec-11 Feb-12 Apr-12 Jun-12 Aug-12
Groundwater Level
Daily Rainfall
Cumulative Rainfall
Both the daily rainfall amounts and the cumulative rainfall for the water year are shown. A
water year extends from October 1 a calendar-year through September 30 of the subsequent
calendar-year. A water year provides a better representation of rainfall conditions than a
calendar year does because of the nature of seasonal weather patterns in California. The
average annual rainfall in the Grass Valley area is approximately 54 inches per year. In the
2010-2011 water year, the rainfall total was about 40 percent above normal. So far in the
2011-2012 water year, the rainfall total is about 15 percent below normal. These differences
are reflected in the cumulative rainfall amounts on the chart above.
Specific details regarding the monitoring data for each location will be presented and available
for review at the August 14, 2012 meeting. The results for each location, however, are
consistent with the examples shown above, independent of whether the monitoring locations
was a well, a spring, or a piezometer. Overall, there is no clear or consistent correlation
between canal flows and water levels at the monitoring locations. In contrast, there is a very
strong correlation between rainfall and water levels. This correlation is especially apparent in
the cumulative rainfall curves. With each major storm event, indicated by a sharp rise in the
cumulative rainfall curve, the water level also rises. Between storm events, or at the end of the
rainy season, (represented by flat periods in the cumulative rainfall curve) water levels decline.