Appendix O: Tierra Rejada Basin Analysis

Transcription

GROUNDWATER GEOLOGY AND YIELD
ANALYSIS OF THE TIERRA REJADA BASIN
Report Prepared for:
Camrosa Water District
Report Prepared by:
Norman N. Brown, Ph.D., P.G.
December 4, 2009
TABLE OF CONTENTS
EXECUTIVE SUMMARY ............................................................................................................1
INTRODUCTION ..........................................................................................................................1
GROUNDWATER GEOLOGY....................................................................................................2
GEOLOGIC STRUCTURE ................................................................................................................3
GROUNDWATER CONDITIONS...............................................................................................3
GROUNDWATER LEVELS ..............................................................................................................4
GROUNDWATER QUALITY ...........................................................................................................5
PRECIPITATION..........................................................................................................................5
CUMULATIVE DEPARTURE AND BASE PERIOD ANALYSIS ...........................................................5
BASIN YIELD ANALYSIS ...........................................................................................................6
IMPLICATIONS FOR BASIN YIELD ...............................................................................................10
Recent Basin Responses...................................................................................................10
DISCUSSION................................................................................................................................11
ASSESSMENT OF POTENTIAL IMPACT – PROPOSED NEW DISTRICT WELL ................................12
RECOMMENDATIONS..................................................................................................................13
REFERENCES .............................................................................................................................14
Groundwater Geology and Yield
Analysis of the Tierra Rejada Basin
p. i
CONTENTS
December 4, 2009
LIST OF TABLES
(Tables follow the main text)
Table 1. Precipitation stations used for base period analysis.
LIST OF FIGURES
(Figures follow the main text)
Figure 1A-B. Maps of Tierra Rejada basin and surrounding areas.
Figure 2A-R. Water level hydrographs for wells in the Tierra Rejada basin.
Figure 3A-D. Water quality hydrographs for the District’s Tierra Rejada well.
Figure 4. Precipitation cumulative departure for precipitation stations.
Figure 5A-B. Precipitation cumulative departure for, showing base periods.
Figure 6. List of potential uncertainty for components of a basin water balance.
p. ii
CONTENTS
December 4, 2009
EXECUTIVE SUMMARY
Groundwater in the Tierra Rejada basin is derived from bedrock aquifers and
has exhibited greatly differing ranges of water level responses over time in
different portions of the basin. This study was principally conducted to provide a
technical foundation for evaluation of basin yield.
Principal conclusions concerning basin yield are:
♦
Groundwater levels observed over a long-term base period including
two wet-dry climatic cycles shows that average groundwater production
was within the basin yield over the period 1944-1996.
♦
Current and recent conditions indicate that existing production and
possibly new production can be managed within basin yield. It is
unknown if production from a proposed new District well would result
in total basin production greater than or less than the historic average
over the base period 1944-1996.
♦
An increase in basin yield may be possible by active management of
basin storage and pumping distribution.
In addition, hydrogeological findings of the study include:
♦
Bedrock structural geology strongly suggests that the watershed
boundary – traditionally used as the boundary for recharge from
precipitation – does not adequately encompass the larger bedrock
recharge area that may be hydraulically connected with the principal
producing aquifer zones in the Tierra Rejada basin. It is also notable
that the surface watershed of Tierra Rejada valley is substantially larger
than the areal extent of alluvium in the basin.
♦
In the western portion of the basin, long-term climatic trends are readily
observed in corresponding changes in the basin’s groundwater levels,
over a wide range of pumping and precipitation conditions.
♦
In the eastern portion of the basin, long-term groundwater levels have
exhibited more subdued response to climatic cycles, and are now at or
near historic high levels.
♦
Limited water quality data for the basin show increases in TDS, chloride
and sulfate during the last 10 years; concentrations are within drinking
p. ES-1
EXECUTIVE SUMMARY
December 4, 2009
water standards. Nitrate concentrations in 2008 exceeded the drinking
water standard for four wells in the central portion of the basin.
An additional purpose of this study was to examine the possibility of pumping
interference between the District’s proposed new well and other nearby wells.
Based on the aquifer test results following construction of the District’s existing
well, together with consideration of bedrock hydrogeology and characteristics of
wells near the proposed new well, the anticipated pumping interference from a
new pumping well on nearby well sites is expected to be less than 5 feet at a
distance of 1,500 feet or more from the pumping well.
p. ES-2
EXECUTIVE SUMMARY
December 4, 2009
INTRODUCTION
The Tierra Rejada basin is within the Calleguas Creek watershed in Ventura
County, California, and includes the upper reach of Arroyo Santa Rosa.
Groundwater wells in the basin produce drinking water quality groundwater from
volcanic and sedimentary bedrock formations.
This study provides a foundation for evaluating two technical subjects of
interest to Camrosa Water District in the Tierra Rejada basin:
♦
Yield of the basin, and
♦
Potential well interference from a proposed, new District groundwater
supply well.
Work conducted to address these subjects includes:
♦
Collection, processing and analysis of technical data principally
concerning:
›
Groundwater levels,
›
Groundwater quality,
›
Well construction,
›
Well production,
›
Basin geology and structure, and
›
Precipitation.
In addition, technical data from an aquifer pumping test (Schaaf, 1998)
was reviewed and utilized for consideration of potential well
interference associated with the proposed new District well.
♦
Cumulative departure analysis of precipitation data for determination of
base periods (periods of long-term average hydrologic conditions, and
including complete portions of wet and dry climatic conditions)
♦
Analysis of bedrock geology and geological structure, particularly to
identify and characterize geological features that may be important to
mechanisms and pathways of recharge from precipitation, groundwater
p. 1
December 4, 2009
flow and groundwater gradients. This portion of work includes analysis
of individual well completion reports and lithologic logs.
♦
Consideration of potential methods for estimation of yield, and
application of the most appropriate method to evaluate basin yield. This
work includes recommendations of work and data that might be desired
for more quantitative treatments in the future.
The term “yield” as used in this analysis and report refers to the common
notion of perennial yield (e.g., Todd and Mays, 2005), with the understanding that
future improvements in basin management, infrastructure, supplemental water
sources or similar factors can result in changes to basin yield.
Data used for the study includes publicly-available information concerning
groundwater levels and groundwater quality, regional geologic mapping, an
aquifer pumping test using the District’s existing water supply well and a nearby
monitoring well, and previous technical studies conducted for both the regional
geology and groundwater resources of the Tierra Rejada basin. Work for the
study also included acquisition of confidential state water well drillers’ reports for
portions of the study area (Appendix A).
GROUNDWATER GEOLOGY
Work for this study builds on previous technical analyses, in particular a
master’s thesis on the basin’s hydrogeology (Schaaf, 1998). For certain general
and background information, such as descriptions of geologic formations and
basin setting, this report references the previous work rather than reproducing the
complete descriptions.
Geology of the Tierra Rejada basin consists of an uppermost, thin veneer of
alluvium, underlain by bedrock formations that are primarily either sandstone and
related rocks (the Topanga Formation) or volcanic and volcaniclastic units (the
Conejo Volcanics). The Topanga Formation unconformably overlies the Conejo
Volcanics; both formations can have thickness of many hundreds of feet in the
basin. Detailed descriptions of the stratigraphy can be found in Dibblee and
Ehrenspeck (1990, 1992a&b, 1993) and Schaaf (1998). Both of the principal
bedrock formations are water-bearing and host productive groundwater wells with
water quality acceptable for domestic and irrigation purposes.
Beneath the two principal water-producing bedrock units is the Sespe
Formation, which is also oriented with a moderate northward dip. This formation
p. 2
December 4, 2009
is also water-bearing and where it extends upward to the south, it outcrops in the
hills around Lake Bard.
GEOLOGIC STRUCTURE
Groundwater-producing bedrock formations of the Tierra Rejada basin are
mostly organized as layered units which together are tilted moderately down to the
north. At the northern margin of the basin, the units are sharply folded up against
the Simi Fault, a regional east-west trending structure (Figure 1). Other segments
of the Simi-Santa Rosa fault zone have been active in the late Quaternary or
Holocene, based on geological relationships in folded areas transected by the
faults (Blake, 1991).
It is unknown if the fault acts as a barrier to groundwater flow, but any
permeability contrasts in the bedrock units will serve to inhibit northward flow
across the upturned beds, as will fault gouge and related clays that may exist along
the fault zone itself.
GROUNDWATER CONDITIONS
Groundwater levels are known from wells within the Tierra Rejada basin as
well as from nearby, surrounding areas (Figure 1). Based on water level behavior
from historical records together with geological characteristics, the principal
producing aquifers appear to be unconfined in the Tierra Rejada basin.
In this context, recharge from deep percolation of precipitation is of principal
importance to the basin hydrology – in Schaaf’s (1998) analysis, 85% of the
basin’s 6,200 afy of “inflows” are from precipitation. Such previous estimates of
basin precipitation are calculated from rainfall records (see Precipitation section
below) as applied to the surface watershed boundary for the basin. It is likely that
this amount of rainfall, and any associated calculation of percolation and recharge
underestimate actual recharge because of the geologic structure in relation to
surface topography.
South and southeast of the watershed boundary, topographic relief is mild, but
the bedrock formations (principally the Sespe in the areas just south of the
watershed boundary) dip to the north. This geometry, together with the generally
stratified nature of the sedimentary Sespe Formation, suggest that precipitation in
southern regions near the basin but outside its watershed boundary may contribute
p. 3
December 4, 2009
to groundwater recharge and the subsurface flow regime of the Tierra Rejada
basin.
In the main portion of the basin, previous studies have concluded that aquifer
productivity diminishes considerably below about 700 feet depth, based largely on
relatively transmissive units in the upper portion of the Conejo Volcanics, and on
an acoustic well log acquired during construction of the District’s well, which is
one of the basin’s deepest at 640 feet total depth (well 15N3; Schaaf, 1998).
Whereas high-permeability zones such as those observed in the upper Conejo may
not be present beneath existing well completions, it is certainly possible that
deeper portions of the Conejo Volcanics include productive groundwater-bearing
zones with acceptable water quality. The base of the basin’s productive aquifer
may be deeper than the maximum depth of existing wells in the basin.
GROUNDWATER LEVELS
Hydrologic data were acquired and reviewed from a range of sources,
principally the California Department of Water Resources, Ventura County Public
Works and Camrosa Water District.
Several important relationships and characteristics of the study area’s
groundwater regime are noted in water level data:
♦
Long-term water level records from approximately 1945 to present
show basin water level changes of up to 150 feet; this magnitude of
change is observed both as water level declines and increases, even in
the same well over different parts of the historical hydrograph (Figure 2;
see for example well 10R1 in Figure 2E).
♦
Water levels in the eastern and southern portions of the basin exhibit
much less variation in water levels, particularly over several decades
when other parts of the basin experienced greater variation in
groundwater levels (Figure 2; see for example wells 12M3 and 14P1).
♦
Many wells with long-term historical water level records indicate
current conditions are at or near historical high water levels, even for
wells which experienced the greatest declines in water level from
~1945-1970 (Figure 2).
p. 4
December 4, 2009
GROUNDWATER QUALITY
With exception of water quality reporting for the District’s well, limited
information exists from other wells to evaluate changes in water quality over time.
The available data indicate groundwater in the basin is generally acceptable for
domestic and agricultural irrigation uses, except recent data showing nitrate above
the 45 mg/l drinking water standard (for NO3) in four wells in the central portion
of the basin (Ventura County, 2008, see figure 3-26 therein). Based on this result,
the County considers the basin “nitrate impacted”. The four wells with high
nitrate had 2008 results of 52 to 72 mg/l NO3,), but do not have uniformly
distinguishing well construction characteristics (e.g., depth or depth of
perforations).
For the District’s existing well, water quality information reported annually for
the last dozen years shows moderately increasing trends for TDS, sulfate and
chloride, but within drinking water standards (Figure 3). Nitrate concentrations
for the District’s well have been consistently below 5 mg/l (NO3), with no
apparent upward trend. A single result of 61 mg/l in January 2001 appears
anomalous and is not associated with a corresponding change in pumping rate.
Basin groundwater quality is likely also influenced by infiltrating surface water
from creeks flowing though Tierra Rejada basin. A December 2009 surface water
sample from the creek flowing into the basin from the south had acceptable water
quality, with TDS of 1,056 mg/l, chloride of 152 mg/l, and nitrate of 14 mg/l.
PRECIPITATION
Daily precipitation data are available from several gauging stations relatively
near to the Tierra Rejada basin. For this study, analysis of a precipitation station
at Lake Bard was conducted together with evaluation of data from several stations
in Moorpark and Simi valleys, and a station with a relatively long period of record
in Fillmore. At Lake Bard, average annual precipitation for water years 19672008 was 15.1 inches.
CUMULATIVE DEPARTURE AND BASE PERIOD ANALYSIS
Cumulative departure analysis is a valuable tool for viewing long-term trends
in precipitation relative to the associated long-term average. Figure 4 shows the
cumulative departure curves for each of the gauging stations presented in this
p. 5
December 4, 2009
study (numbers associated with the station names are gauging station numbers
assigned by Ventura County).
A long-term period of relatively dry conditions prevailed for several decades
beginning in the mid-1940’s and continuing through the mid-1960’s. This period
of relative drought is seen widely in central and southern California, including a
station with an even longer period of record in Santa Paula. Similarly, the more
recent 1986-1991 drought is prominent in all the precipitation records.
With the benefit of the historical context provided by the station at
Fillmore/Rancho Sespe, which has almost a century-long record, an evaluation of
all nearby gauging locations finds that their periods-of-record include full portions
of wet and dry climatic cycles. Cumulative departure curves were then evaluated
to define “base periods” – a range of years that encompasses both wet and dry
conditions and has long-term average hydrologic characteristics. For precipitation
in the vicinity of Tierra Rejada basin, the base periods selected for study were
(Figure 5):
♦
1944 to 1996 (and potentially also extending to 2001);
♦
1958 to 1998; and
♦
1969 to 2006.
Sufficient water level data exist to examine basin groundwater conditions for
the base periods selected. For the starting and ending years of a base period, the
highest observed water levels in a well are compared to see what if any difference
in water levels exists over the base period of average hydrologic conditions.
BASIN YIELD ANALYSIS
Several basin yield estimation methods are possible for the Tierra Rejada
basin. For a range of technical reasons described below, and consistent with the
project timeline and scope, a Water Level Change method was employed, utilizing
groundwater levels and complementary technical data to describe the
characteristics of groundwater fluctuations and the associated implications for
long-term average basin yield.
Modified Hill Method. Some groundwater basins show a strong correlation
between annual production and groundwater levels, allowing a simple and
straightforward estimate of yield based on long-term water level changes. For the
p. 6
December 4, 2009
Tierra Rejada basin, three considerations limit the utility of the Modified Hill
Method for estimating yield:
♦
The paucity of well production information in the basin, other than from
the District’s relatively new well (15N3),
♦
Significant changes in historical land use and associated water demands,
and
♦
The highly seasonal nature of precipitation, which in turn influences
groundwater recharge and water levels in ways that are not wellaccommodated by the method.
Water Balance Method. A detailed water balance is a commonly-employed
method for quantifying a basin’s main flow components – with implications for
basin yield – but the method is subject to potential uncertainty with each piece of
the equation (Figure 6; Peters, 1981 cited in DWR, 2002). In regard to water
levels or gauged streamflow, such uncertainty might be relatively small, but
components such as subsurface flow, recharge, aquifer storativity and well
production can have potential errors large enough to make this method a poor
predictor of yield. For the Tierra Rejada basin, four components of a water
balance are very poorly known, and any corresponding basin yield estimates could
readily be subject to error of 100% or more. Additional technical work could
produce more accurate estimates for these four components (this subject is
discussed further in the Recommendations section below), but it is not clear that
such work would produce technical benefits to outweigh the uncertainty that
would still remain with this method. Four sources of large potential error for a
water balance approach in the Tierra Rejada basin are:
♦
Basin extractions from well production are largely unknown; regular,
direct measurement of well production is only known for Camrosa
Water District’s existing and relatively recent water supply well
(beginning in 1997). With over 50 years of unknown basin extractions,
during a time that experienced significant land use conversions,
historical water extractions in particular are a highly uncertain quantity.
♦
Recharge to the Tierra Rejada basin includes deep percolation of
precipitation. However, the structural geology of the area’s bedrock
units, which form the principal aquifers for the basin, suggests the
likelihood that the basin’s recharge area is not coincident with, and is
larger than, the basin’s surface watershed. As a result, basin
groundwater recharge, which is already subject to considerable potential
error, is subject to even greater uncertainty for the Tierra Rejada basin.
p. 7
December 4, 2009
♦
In addition to inputs and outputs, groundwater storage changes
comprise the third leg of a water balance analysis. In the Tierra Rejada
basin, aquifer storage is very poorly known because: (i) the base of the
usable aquifer is very poorly defined, and (ii) storativity of the bedrock
aquifer is mostly unknown, and can vary considerably within a bedrock
aquifer.
♦
Subsurface flow into and out of the Tierra Rejada basin is known only
approximately. The uncertainty about this condition is amplified by the
dominance of bedrock structure and geology in the basin and the
likelihood of significant temporal changes of underflows over the
historical record.
Water Level Change Method. An alternative approach to estimating basin
yield relies on long-term water level changes to guide an interpretation of basin
responses to pumping and basin yield. Variations of this method emphasize
periods with no net groundwater level change, and/or the nature of groundwater
level changes over a relatively long-term base period that represents at least one
full climatic cycle of wet and dry conditions (e.g., Yates et al., 2005; Santa Paula
Basin Experts Group, 2003). Because two of the better-known characteristics of
the Tierra Rejada basin during the historical record are groundwater levels and
precipitation, a Water Level Change (Base Period) method was applied in this
study for the evaluation of basin groundwater level changes and implications for
yield.
Analysis of precipitation cumulative departure (see “Precipitation” section
above) shows three periods during which overall climatic conditions included
approximately relatively-equal amounts of wet and dry conditions over at least one
full wet-dry climatic cycle. These base periods are developed from daily
precipitation records from gauging stations at Lake Bard, Simi and Moorpark, as
well as from a station with a longer period of record at Rancho Sespe (Fillmore)
(Table 1). The base periods used in this study are (Figure 5): 1944 to 1996/2001;
1958 to 1998; and 1969 to 2006.
There are adequate groundwater level records to examine overall changes in
basin water levels during each of these periods of approximately average climatic
conditions. In cases where water level conditions are approximately the same at
the start and end of the base period, production during this time is considered to be
within basin yield. If groundwater levels are lower at the end of the base period,
pumping may have been greater than yield.
BASE PERIOD 1944 – 1996/2001. The Fillmore/Sespe Ranch rain gauge
experiences somewhat wetter weather (~20 in/yr average) compared with gauges
p. 8
December 4, 2009
closer to the Tierra Rejada basin (~15 in/yr in Moorpark, Simi and at Lake Bard).
But it is the longest precipitation record in regional proximity to the Tierra Rejada
basin and affords perspective on relatively dry conditions that persisted in much of
central and southern California during two decades beginning in the mid 1940’s.
This base period includes the most recent drought ending in 1991 and includes
two climatic episodes of wet and dry conditions. The end of the base period can
be chosen as 1996, when cumulative departure conditions return to the 1944
benchmark, or 2001 after five additional years with aggregate average
precipitation conditions.
During the roughly half century of this base period, groundwater levels
experienced declines measuring as much as 150 feet (well 10R1) from 1944 until
the 1960’s. Groundwater levels then steadily increased, and by 1996 were at or
near 1994 levels. During this time, groundwater extractions changed
considerably, first with the onset of significant new farming in the basin during the
1940’s and 1950’s, and then later with a reduction in agricultural groundwater
extractions (Schaaf, 1998). A small amount of imported water was also added to
basin supply beginning in the 1960’s. In total, on average over the full base
period, extractions have been accommodated by basin replenishments without
significant change to groundwater levels, and the average extraction rate appears
to be approximately within the basin yield.
BASE PERIOD 1958 – 1998. Detailed precipitation in Moorpark is known only
from about 1950 to present, but includes a 40-year period from 1958 to 1998 with
significant wet and dry periods. For groundwater wells with an adequately long
period of record, this base period is characterized by an overall increase in
groundwater levels in all parts of the basin, suggesting that over this period of
approximately average climatic conditions, average basin pumping was less than
yield.
BASE PERIOD 1969 – 2006. Near the southern basin boundary, a precipitation
station at Lake Bard has recorded daily rainfall since 1966. During a base period
of almost 30 years beginning in 1969, the station experienced many dry years
through 1977, the regional drought during 1986-1991, and a number of relatively
wet years during the 1990’s.
This base period experienced the introduction of imported water to the basin
(together with utilization of Lake Bard for regional water supply management)
and, beginning the 1990’s, new groundwater production from the District’s well in
the basin. Groundwater levels during the full base period experienced an overall
increase in groundwater levels in all parts of the basin, suggesting that over this
p. 9
December 4, 2009
period of approximately average climatic conditions, average basin pumping was
less than yield.
IMPLICATIONS FOR BASIN YIELD
With changes to basin water supply (from imported water and previous
wastewater treatment plant discharges) and particularly because of potentially
significant but unknown historical changes in the amount of groundwater
extractions, only general statements are warranted with regard to long-term
pumping relative to basin yield. However, long-term base periods are still
informative with regard to basin aquifer response. Using the longest available
base period available (1944-1996/2001), which includes two complete sets of
drought and recovery, groundwater levels are clearly able to rebound from periods
of relative depletion, and apparently without adverse physical damage to the basin
(such as from subsidence or influx of poor-quality groundwater).
Because the base period captures elements of both wet and dry climate cycles,
full recovery of groundwater levels from the beginning to the end of the 19441996/2001 period demonstrates that the long-term average groundwater
production during this time can be accommodated by the long-term basin
recharge. The average production rate in this evaluation incorporates both longterm changes in groundwater pumping rates as well as increases to basin recharge
and yield from imported water, through wastewater treatment plant discharges
(which ended approximately 7 years ago) and any irrigation return flows.
Recent Basin Responses
Basin water level changes during the last decade are of special interest because
the District has been producing an average of 540 afy from its well in the basin
during the last five years, with average production of 470 afy since regular
pumping began in 1997 (Figure 2D). Average annual precipitation at Lake Bard
from 1997 to 2008 was 15.0 inches, slightly less than the full station record (15.1”
from 1967 to 2008) or the base period average (15.3” from 1969-2006).
Since 1997, groundwater level declines are observed at the District’s and
others’ wells, but eastern and southern areas of the basin have experienced little
change in groundwater levels (e.g., wells 14P1 and 12M3; Figure 2). In the
eastern Tierra Rejada basin, relatively stable or even rising groundwater levels are
similar to recent water level behavior in western Simi Valley basin. While surface
flow from Simi Valley toward Moorpark and Las Posas basin occurs along Arroyo
Simi to the north of Tierra Rejada basin, there may exist subsurface flow in the
bedrock aquifers from Simi to Tierra Rejada basin.
p. 10
December 4, 2009
At the western margin of Tierra Rejada basin, fluctuations in groundwater
levels at the District well are well-correlated with changes in production rates
(Figure 2D; see, for example, water level responses during increased pumping in
2006). To some degree, water level changes here also reflect the cumulative
departure curve for precipitation (Figure 2B). In this context, it appears that
standard basin management practices could be used to ameliorate local pumping
depressions or potentially also to accommodate increased basin production
without long-term adverse effect in the Tierra Rejada basin.
DISCUSSION
This study makes three principal findings about groundwater yield of the
Tierra Rejada basin, as well as a range of related findings important to the
determination and further quantification of basin yield. Principal conclusions
concerning yield are:
♦
Groundwater levels observed over a long-term base period including
two complete wet-dry climatic cycles shows that average groundwater
production was within the basin yield over the period 1944-1996.
♦
Current and recent conditions indicate that existing production and
possibly new production can be managed within basin yield.
♦
An increase in basin yield may be possible by active management of
basin storage and pumping distribution.
Principal, related findings concerning determination of basin yield are:
♦
Bedrock structural geology strongly suggests that the watershed
boundary – traditionally used as the boundary for recharge from
precipitation – does not adequately encompass a potentially larger
bedrock recharge area hydraulically connected with the principal
producing aquifer zones in the Tierra Rejada basin.
♦
In the western portion of the basin, long-term climatic trends are readily
observed in corresponding changes in the basin’s groundwater levels,
over a wide range of pumping and precipitation conditions.
♦
In the eastern portion of the basin, long-term groundwater levels have
exhibited more subdued response to climatic cycles, and are now at or
near historic high levels.
p. 11
December 4, 2009
♦
Limited water quality data for the basin show increases in TDS, chloride
and sulfate during the last 10 years; concentrations are within drinking
water standards. Nitrate concentrations in 2008 exceeded the drinking
water standard for four wells in the central portion of the Tierra Rejada
basin.
♦
Aquifer depth is poorly constrained and aquifer thickness may be
greater than previously recognized, particularly in permeable structural
zones that act as principal conduits for groundwater at depth.
Previous reports have estimated different components of a water balance, but
none have estimated basin yield (e.g., Schaaf, 1998; DWR, 2004), nor made
reliable groundwater production estimates for the basin.
ASSESSMENT OF POTENTIAL IMPACT – PROPOSED NEW DISTRICT WELL
As discussed above, it is possible that the Tierra Rejada basin can
accommodate additional groundwater extractions within long-term basin yield.
The District’s proposed new well offers both opportunities and uncertainties in
this regard:
♦
The closest known well – 14P1 – has experienced little water level
change over many decades and is now at or near historic high water
level (Figures 2A and 2I).
♦
It is unknown if production from the proposed well would result in total
basin production greater than or less than the historical average over the
base period 1944-1996 (refer to discussion in previous section).
♦
Well interference is possible from a new production well at the
proposed District site, in addition to potential impacts of general water
level lowering associated with potential pumping in excess of basin
yield. In this regard, wells 14P1 and 14R1 are the closest existing wells
that might be impacted (and could be used for monitoring). Based on
the aquifer test results from Schaaf (1998), anticipated impacts from a
new pumping well on water levels at these well sites are on the order of
several feet or less.*
*
Unfortunately, Schaaf’s pumping test was not able to record any water levels in the pumping well (the
District supply well), nor in the observation well after the first 12 hours of test production. Based on the
available data, the observation well, which is ~130 feet from the District supply well, was estimated to
have experienced a total water level decline of 40 feet during approximately 30 hours of pumping at a
p. 12
December 4, 2009
♦
With an existing well in the basin, the District’s proposed additional
well may afford some flexibility for managing basin pumping stresses,
depending on well production characteristics and District infrastructure
interconnections and capacities.
RECOMMENDATIONS
For more quantitative evaluation of hydrologic characteristics of the basin,
three recommendations follow logically from the results of this study:
♦
Estimates of historical groundwater production would be useful for
gauging relative basin pumping stress over time. Such estimates would
likely be most reliably derived from historical aerial photographs, if
available, together with regional crop water use characteristics.
♦
Regular monitoring of a few additional, existing groundwater wells
would improve understanding of basin-wide groundwater levels and
gradients (assuming such wells can be accessed and are suitable for
testing and instrumentation). Regular water quality sampling should be
continued, particularly at locations with known water quality impacts
(e.g., nitrate).
♦
Further quantitative analysis of any potential well interference between
the District’s proposed new production well and other wells could be
conducted, and nearby existing wells in this portion of the basin could
be instrumented for detailed monitoring.
constant rate of ~1,100 gpm. For comparison, the District’s proposed new wellsite is approximately 1,500
feet or more from the nearest wells (e.g., 14P1 and 14R1).
p. 13
December 4, 2009
REFERENCES
Blake, T.F., 1991, Synopsis of the character and recency of faulting along the Simi
– Santa Rosa fault system, in T.F. Blake and R.A. Larson (ed.’s),
Engineering geology along the Simi – Santa Rosa fault system and adjacent
areas, Simi Valley to Camarillo, Ventura County, California: Southern
California section, Association of Engineering Geologists, Field Trip
Guidebook, p. 96-118.
Bredenkamp, D.B. and Y. Xu, 2003, Perspectives on recharge estimation in
dolomitic aquifers in South Africa, in Groundwater recharge estimation in
southern Africa, Y. Xu and H.E. Beekman (ed.’s). UNESCO, p. 73-79.
California Department of Water Resources, 2002, Water resources of the Arroyo
Grande – Nipomo Mesa area, Southern District report.
California Department of Water Resources, 2004, Tierra Rejada groundwater
basin, in California’s Groundwater, Bulletin 118, basin 4-15.
California Division of Mines and Geology, 1997, Seismic hazard zone report for
the Simi Valley East and Simi Valley West 7.5-minute quadrangles,
Ventura and Los Angeles Counties, California: Seismic Hazard Zone
Report 002.
the Thousand Oaks 7.5-minute quadrangle, Ventura and Los Angeles
Counties, California: Seismic Hazard Zone Report 042.
the Moorpark 7.5-minute quadrangle, Ventura County, California: Open
File Report 2000-007.
the Newbury Park 7.5-minute quadrangle, Ventura County, California:
Seismic Hazard Zone Report 055.
Dibblee, T.W., and H.E. Ehrenspeck, 1990, Geologic Map of the Camarillo and
Newbury Park Quadrangles, Ventura County, California, Dibblee
Geological Foundation, map DF-28, scale 1:24,000.
p. 14
December 4, 2009
Dibblee, T.W., and H.E. Ehrenspeck, 1992a, Geologic Map of the Simi
Quadrangle, Ventura County, California, Dibblee Geological Foundation,
map DF-39, scale 1:24,000.
Dibblee, T.W., and H.E. Ehrenspeck, 1992b, Geologic Map of the Moorpark
Quadrangle, Ventura County, California, Dibblee Geological Foundation,
map DF-40, scale 1:24,000.
Dibblee, T.W., and H.E. Ehrenspeck, 1993, Geologic Map of the Thousand Oaks
Quadrangle, Ventura and Los Angeles Counties, California, Dibblee
Geological Foundation, map DF-49, scale 1:24,000.
Peters, H.J., 1981 Groundwater basins, in Concepts of groundwater management,
notes for UC Davis Extension Course, section 3. Reference cited in DWR,
2002.
Santa Paula Basin Experts Group, 2003, Investigation of Santa Paula basin yield.
Report for the Santa Paula Basin Technical Advisory Committee, 63 p.
Schaaf, J.P., 1998, Hydrogeology of the Tierra Rejada groundwater basin, Ventura
County, California: MS Thesis, CSU-Northridge, 141 p.
Todd, D.K., and L.W. Mays, 2005, Groundwater Hydrology (Third Edition). John
Wiley & Sons, 636 p.
Ventura County Watershed Protection District, 2008, Annual Report of the Water
and Environmental Resources Division, Groundwater Section, 137 p.
Yates, E.B., M.B. Feeney and L.I. Rosenberg, 2005, Seaside groundwater basin –
update on water resource conditions. Report for Monterey Peninsula Water
Management District, 123 p.
p. 15
December 4, 2009
CONFIDENTIAL
APPENDIX A – CONFIDENTIAL SUPPORTING INFORMATION
(WELL COMPLETION REPORTS)
Water well drillers’ construction/completion reports were acquired for the
following wells in the study area:
2N-19W- 14D1, 14P1
2N-19W- 15B1, 15F2, 15G1, 15H1, 15H2, 15H3, 15M1, 15N1, 15N2, 15N3**,
15Q1
2N-19W- 10R1, 10R2
2N-19W- 11J1, 11J2, 11J3*
2N-19W- 12F1, 12F2, 12F3, 12F4, 12M1, 12M2*, 12M3, 12M4, 12N1*, 12N2*,
12P1
2N-19W- 21C1, 21C2, 21F2, 21H1
*Only the well “index card” was available from DWR.
**Curiously, the District’s existing well – 15N3 – was not among those
DWR provided for section 15. I have seen this well mislabeled elsewhere as being
in range 20W, and it may be similarly misfiled at DWR. For this study, well
completion information for this well was provided by the District; borehole
electric and acoustic logs are reproduced in Schaaf (1998).
p. A1
APPENDIX A
December 4, 2009
CONFIDENTIAL
Table 1. Precipitation stations used for base period analysis.
Station
Period of Record
(Water Year)
Base Period
Base Period Average
Annual Precipitation (in)
Fillmore / Rancho Sespe
1913-2003
1944-1996/2001
18.8
Moorpark Everett
1956-Present
1958-1998
14.5
Lake Bard
1967-Present
1969-2006
15.3
December 4, 2009
TABLES
Figure 1A. Map showing the Tierra Rejada alluvium-bedrock boundary, surface watershed and nearby groundwater basins.
December 4, 2009
FIGURES
Figure 1B. Tierra Rejada basin map showing groundwater wells.
December 4, 2009
FIGURES
Figure 2. Water level hydrographs for the Tierra Rejada basin. See Figure 1B for well locations.
2A: Water level hydrographs for several wells in the basin.
2B: Water level hydrographs for several wells in the basin, showing also cumulative departure of precipitation.
2C: Water level hydrographs for several wells in the basin, showing also cumulative departure of precipitation and base
periods selected for study.
2D: Hydrograph for District well 15N3, showing also monthly production.
Figures 2E – 2: Individual hydrographs for all wells with historical water level data. All are plotted at the same vertical and
horizontal scale.
2E: Hydrograph for well 10R1.
2F: Hydrograph for well 11J1.
2G: Hydrograph for well 12M3.
2H: Hydrograph for well 14D1.
2I: Hydrograph for well 14P1.
2J: Hydrograph for well 14R1.
2K: Hydrograph for well 15B1.
2L: Hydrograph for well 15F2.
2M: Hydrograph for well 15G1.
2N: Hydrograph for well 15H1.
2P: Hydrograph for well 15H2.
2Q: Hydrograph for well 15N2.
2R: Hydrograph for well 15N3.
December 4, 2009
FIGURES
Figure 2A
Water Level Elevation
700
Groundwater Elevation (ft msl)
600
500
400
300
10R1
12M3
14P1
15F2
15N3 (District Well)
14D1
15B1
-10
Jan
-05
Jan
-00
Jan
-95
Jan
-90
Jan
-85
Jan
-80
Jan
-75
Jan
-70
Jan
-65
Jan
-60
Jan
-55
Jan
-50
Jan
-45
Jan
Jan
-40
200
15G1
December 4, 2009
FIGURES
Figure 2B
10R1
12M3
14P1
15F2
14D1
15B1
15G1
Precip--LakeBard
Precip--FillmoreSespe
-10
Jan
-05
Jan
-00
Jan
Jan
Jan
Jan
Jan
-75
Jan
Jan
Jan
Jan
-55
Jan
Jan
Jan
Jan
-95
-80
-90
200
-85
-40
-80
300
-70
0
-65
400
-60
40
-50
500
-45
80
Cumulative Departure, Precipitation (in)
120
600
-40
700
December 4, 2009
FIGURES
Figure 2C
700
130
120
110
600
90
1944-1996/2001
80
70
60
1958-1998
500
50
1969-2006
40
30
20
10
400
0
-10
-20
300
-30
Cumulative Departure, Precipitation (in)
100
-40
-50
-60
10R1
12M3
14P1
15F2
14D1
15B1
15G1
Precip--LakeBard
Precip--FillmoreSespe
-1 0
Jan
-0 5
Jan
-0 0
Jan
-9 5
Jan
-9 0
Jan
-8 5
Jan
-8 0
Jan
-7 5
Jan
-7 0
Jan
-6 5
Jan
-6 0
Jan
-5 5
Jan
-5 0
Jan
-4 5
-70
Jan
Jan
-4 0
200
December 4, 2009
FIGURES
Figure 2D
700
80
60
Ground Surface ~ 590
500
40
400
20
300
0
Precipitation (Cumulative Departure), Lake Bard (right scale, in.)
Ja
n-1
0
Ja
n-0
9
Ja
n-0
8
Ja
n-0
7
Ja
n-0
6
Ja
n-0
5
Ja
n-0
4
Ja
n-0
3
Ja
n-0
2
Ja
n-0
1
Ja
n-0
0
Ja
n-9
9
Ja
n-9
8
Ja
n-9
7
-20
Ja
n-9
6
Ja
n-9
5
200
December 4, 2009
FIGURES
Monthly production (TRW; af/mo)
Groundwater Elevation (ft)
600
Figure 2E
10R1
800
750
700
650
600
550
500
450
400
350
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
300
Figure 2F
11J1
800
750
700
650
600
550
500
450
400
350
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
300
Figure 2G
12M3
800
750
700
650
600
550
500
450
400
350
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
300
Figure 2H
14D1
800
750
700
650
600
550
500
450
400
350
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
300
Figure 2I
14P1
800
750
700
650
600
550
500
450
400
350
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
300
Figure 2J
14R1
800
750
700
650
600
550
500
450
400
350
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
300
Figure 2K
15B1
800
750
700
650
600
550
500
450
400
350
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
300
Figure 2L
15F2
800
750
700
650
600
550
500
450
400
350
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
300
Figure 2M
15G1
800
750
700
650
600
550
500
450
400
350
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
300
Figure 2N
15H1
800
750
700
650
600
550
500
450
400
350
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
300
Figure 2P
15H2
800
750
700
650
600
550
500
450
400
350
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
300
Figure 2Q
15N2
700
600
500
400
300
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
200
Figure 2R
700
600
500
400
300
December 4, 2009
FIGURES
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
Ja
n-4
5
Ja
n-4
0
200
Figure 3. Water quality hydrographs for the District’s Tierra Rejada well (15N3). See Figure 1 for well locations.
3A: TDS.
3B: Nitrate.
3C: Chloride.
3D: Sulfate.
December 4, 2009
FIGURES
Figure 3A
15N3 TDS
1000
700
900
600
700
TDS (mg/l)
600
500
500
400
400
300
300
200
100
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
200
Ja
n-4
5
Ja
n-4
0
0
December 4, 2009
FIGURES
800
Figure 3B
15N3 Nitrate
700
50
45
600
Nitrate (mg/l NO3)
35
500
30
25
400
20
15
10
300
5
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
200
Ja
n-4
5
Ja
n-4
0
0
December 4, 2009
FIGURES
40
Figure 3C
15N3 Chloride
500
700
450
600
Chloride (mg/l)
350
300
500
250
200
400
150
300
100
50
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
200
Ja
n-4
5
Ja
n-4
0
0
December 4, 2009
FIGURES
400
Figure 3D
15N3 Sulfate
500
700
450
600
Sulfate (mg/l)
350
300
500
250
400
200
150
100
300
50
Ja
n-1
0
Ja
n-0
5
Ja
n-0
0
Ja
n-9
5
Ja
n-9
0
Ja
n-8
5
Ja
n-8
0
Ja
n-7
5
Ja
n-7
0
Ja
n-6
5
Ja
n-6
0
Ja
n-5
5
Ja
n-5
0
200
Ja
n-4
5
Ja
n-4
0
0
December 4, 2009
FIGURES
400
Figure 4. Precipitation cumulative departure for precipitation stations.
Cumulative Departure -- Precipitation
30
20
10
Annual Departure (in)
0
-10
-20
-30
-40
-50
-60
-70
1910
1920
1930
1940
1950
1960
1970
Fillmore Rancho Sespe 039
Moorpark SCS and Co Fire 141
Moorpark Everett 192
Lake Bard 227
1980
1990
2000
Simi Co Fire 154
December 4, 2009
FIGURES
2010
Figure 5A. Precipitation cumulative departure for precipitation at Fillmore/Rancho Sespe, showing base period 1945-1996/2001.
30
Base Period 1944 – 1996/2001
20
10
0
-10
-20
-30
-40
-50
-60
-70
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
Fillmore Rancho Sespe 039
December 4, 2009
FIGURES
2010
Figure 5B. Precipitation cumulative departure for precipitation at Moorpark and Lake Bard, showing base periods 1958-1998 and
1969-2006, respectively.
30
Base Period 1969 – 2006 (Lk Bard Station)
20
Base Period 1958 – 1998 (Moorpark)
10
0
-10
-20
-30
-40
-50
-60
-70
1910
1920
1930
1940
1950
Moorpark SCS and Co Fire 141
1960
1970
Moorpark Everett 192
1980
1990
2000
2010
Lake Bard 227
December 4, 2009
FIGURES
Figure 6. List of potential uncertainty for different components of a basin water balance (from DWR, 2002; after Peters, 1981)
December 4, 2009
FIGURES

Appendix O: Tierra Rejada Basin Analysis

Transcription

Similar documents

Form For Candidates

AN EXPERIENCE OF TARUN BHARAT SANGH

GBYC Volunteer Sign Up Form

The Water Cycle - UN

Sustainable Water Management in the Selenga-Baikal Basin

Physical Geography Water Resources Chapter 9

Page 1 TECTONOSTRATIGRAPHY AND NEOTECT ONIC

Elqui and Limarí river basins at a glance

Field Trip to the Betic Zone and the Carboneras Fault System (SE

Building Code Training – August 30th at Burgundy Basin Inn