HomeMy WebLinkAbout; Proposed Revision Basin Plan Objectives; Hydrology Report; 1980-11-02PROPOSED REVISION BASIN PLAN OBJECTIVES
CARLSBAD HYDROGRAPHIC SUBAREA
November 2, 1980
LUKE-DUDEK, Civil Engineer
700 Second Street Suite E Encinitas, California
7141942-5147
TABLE OF CONTENTS
CHAPTER
. 1.
2.
3.
4.
5.
6.
PAGE -
IDENTIFICATION OF STUDY AREA .................... 1
A. Introduction ................................ 1
LAND USE ........................................ 3
A. Introduction ................................ 3 B. 1968 Land Use ............................... 5 C. 1980 Land Use ............................... 6
D. 2000 Land Use ............................... 6
DESCRIPTION OF BENEFICIAL USES OF GROUND- WATER IN THE STUDY AREA ........................ 11
A. Past Beneficial Uses ....................... 11 B. Present Beneficial Uses .................... 12
C. Future Beneficial Uses ..................... 12
DESCRIPTION OF GROUND AND SURFACE WATER QUALITY ........................................ 14
A. Historic Groundwater Quality ............... 14 B. Present Groundwater Quality ................ 17 C. Future Groundwater Quality ................. 20 1. Introduction ........................... 20 2. Summary of Geohydrologic Conditions Buena Vista Basin ...................... 20
4. Future Groundwater Quality 27 3. Groundwater Movement 23
5. Effects of a Reclamation Program ....... 28
D. Surface Water Quality ...................... 29
................... .............
DESCRIPTION OF REQUESTED CHANGES ............... 32
A. Introduction ............................... 32
DEMONSTRATIONS OF CONSISTENCY BETWEEN THE
REQUESTED AND THE STATE'S NONDEGRADATION
POLICY ......................................... 37
A. Introduction ............................... 37 B. Summary of State's Nondegradation Policy ..................................... 37 C. Implications of the Requested Changes to the Groundwater Objectives for
Subarea 4.21 ............................... 38
TABLE OF CONTENTS (Cont ' d)
CHAPTER PAGE -
6. CON" ' D
D. Population Group 1 - Existing and Potential Groundwater Users ................. 40 1. Evaluation of Economic Benefit
vs Detriments for the Group 1
Population 41
Detriment for the Group 1 Population .............................. 42
of Reclaimed Water .......................... 42 1. Economic Benefits vs Detriment for
2. Social Benefits vs Detriment for the Group 2 Population 43
the Group 2 Populations ................. 43
.............................. 2. Evaluation of Social Benefit vs
E. Population Group 2 - Potential Uses
..................
F. Population Group 3 Residents Within the Costa Real Water District and
1. Economic Benefit vs Detriment for
2. Social Benefits vs Detriment for
City of Oceanside ........................... 44
...................... Group 3 Population 45
the Group 3 Population .................. 47
LIST OF FIGURES
FIGURE - PAGE
1-1 Study Area .......................... 2
2-1 Past Land Use ....................... 8
2-2 Present Land Use (1980) ............. 9
2-3 Future Land Use (2000) ............. 10
4- 1 Sampling Locations ................. 16
4- 2 Hydro-geologic Representations Subarea 4.21 ....................... 22
LIST OF TABLES
TABLE
2-1
2-2
4- 1
-
4- 2
4- 3
4- 4
5-1
5-2
6-1
6-2
6- 3
6-4
PAGE -
Land Use Acreage Estimates Subarea 4.21 ........ 4
Population Estimates Subarea 4.21 .............. 4
Carlsbad Hydrographic Subarea 4.21 Historical Well Sampling Data ................. 15
Recent Well Sampling Data ..................... 18 Carlsbad Hydrographic Subarea 4.21
Vista Groundwater Basin 1980 Conditions 25 Estimated Underdrainage to the Buena
Carlsbad Hydrographic Subarea 4.21
.......
Buena Vista Creek Sampling Data ............... 31
Groundwater Quality Objectives for the : Bista Hydrographic Subunit .................... 34
Proposed Groundwater Quality Objectives for the Carlsbad Hydrographic Subarea ......... 36
Economic Benefits vs Detriments for Group 1 Population Caused by Easing Groundwater Objectives .................................... 41
Potential Users of Reclaimed Water ............ 43
Projected Population and Water Use for Carlsbad "Ll and City of Oceanside ............ 46
Energy Saving of Reclaimed Water Progr am...... 48
CHAPTER 1
IDENTIFICATION OF STUDY AREA
A. Introduction
The study area for which groundwater objectives
revision is prepared, is shown in Figure 1-1. This hydro-
logic area is defined as the portion of the Carlsbad
Hydrographic Subarea (Subarea 4.21) east of Interstate 5.
Subarea 4.21 is located within the Vista Hydrographic
Subunit of the Carlsbad Hydrographic Unit as defined by
the “Comprehensive Water Quality Control Plan Report San
Diego Basin 9“ (Basin Plan), prepared for the State Water
Resources Control Board and the San Diego Regional Water
Quality Control Board in 1975. Drainage within Subarea
4.21 flows to Buena Vista Creek which then empties into
Buena Vista Lagoon. The northern and southern boundaries
parallel State Highway 78 from just west of Melrose Drive
in the City of Vista, westerly to the Pacific Ocean. Sub-
area 4.21 lies within the corporate boundaries of the
Cities of Vista, Oceanside and Carlsbad, and a portion lies
within the County of San Diego.
CHAPTER 2
LAND USE
A. Introduction
The lower Buena Vista drainage basin is roughly
split in half lengthwise by the Oceanside-Carlsbad city
limit. The area has been marked in the last decade by a
rapid conversion from undeveloped-rural land use to a pre-
dominately urban landscape. Land use projections predict
the urbanization process will be completed within the next
10 to 20 years.
Agricultural activities which have developed after
the introduction of imported water supplies (about 1950) will
gradually lose ground to urban development. In its place, open
space areas are planned to maintain the natural aesthetic
qualities of the landscape. Irrigation of the open space
corridors with reclaimed water will further enhance the verdant
qualities of the area.
An estimation of the land use acreages for the vears
1968, 1980 and 2000 have been compiled for the study area, and
are listed in Table 2-1. Population and dwelling unit data
are shown in Table 2-2 for these years, based on San Diego
Comprehensive Planning Organization figures. Land use acreages
were taken from information provided by the U.S. Geological
Survey, City of Carlsbad, San Diego Comprehensive Planning
Organization and aerial photographs. Because some of the
land use data is conflicting, a rational estimate of each
land use boundary was determined.
TABLE 2-1 Land Use Acreage Estimates Subarea 4.21*
YEAR URBAN AGRICULTURAL OPEN SPACE
(acres) (acres) (acres)
1968 1,965 153 4,382
1980 4,611 115 1,774
2000 6,009 0 491
* Does not include those areas west of Interstate 5.
TABLE 2-2 Population Estimates Subarea 4.21*
YEAR POPULATION DWELLING UNITS
1968
1980
2000
13,000
22,180
40,000
5,200
8,870
16,000
* Based on extrapolated data from the Comprehensive Planning Organization
Series IV-B Prpjections, and excluding those areas west of Interstate 5.
Three land use classifications are shown for this
study. These are: urban areas; including commercial, industrial
and sewered residential zones; agricultural areas, and open
space areas. The latter land use type includes all undeveloped
lands, parks, golf courses, sparsely populated rural areas
(sewage disposal by septic tanks) and those portions of Buena
Vista Lagoon within the study area.
B. 1968 Land Use
The 1968 land use acreages were compiled from the U.S.
Geological Survey, 15 minute, San Luis Rey quadrangle dated 1968,
and from aerial photographs. The locations of each land use type
are shown in Figure 2-1.
Urban areas consisting of the Cities of Oceanside,
Carlsbad and Vista, and a portion of the County of San Diego
add up to 1,965 acres within the immediate study area. Agricultural
areas amounted to 153 acres in 1968, while the remaining open
space areas made up approximately 4,382 acres. This gives a total
of 6,500 acres within this drainage basin.
As can be seen from Table 2-1 and Figure 2-1, the
majority of land within Subarea 4.21 was considered open space
in 1968. Urbanization was beginning to spread easterly along
State Highway 78 from the coastal cities of Carlsbad and Oceanside
toward the community of Vista on the eastern end of the study
area. Likewise, urbanization is spreading westerly along Highway 78
toward the coast from Vista. Population figures for 1968 are
13,000 persons with 5,200 dwelling units (DUs) based on 2.5 persons
per DU.
Agricultural areas along Buena Vista Creek reportedly
consisted of orchard crops irrigated from Buena Vista Creek
in the past. Field crop agriculture existed in the other areas
shown in the south-central portion of the study area. The
small amount of agriculture practiced within Subarea 4.21 is
thought to be mainly due to the limitedquantity and quality
of ground and surface waters within the basin, as well as
progressing urbanization of prime agricultural lands.
C. 1980 Land Use
The 1980 land-use acreages were compiled from the
U.S. Geologic Survey, 1968 San Luis Rey 15-minute quadrangle
(photorevised 1975), the San Diego Comprehensive Planning
Organization's recent survey maps shaving sewered areas within
the basin, and from recently shot aerial photographs of the
study area. Land use configurations for 1980 are shown in Figure
2-2.
Those areas classified as urbanized in 1968 have
grown to approximately 4,611 acres in 1980. Agricultural and
open space areas have shrunk to 115 and 1,774 acres, respectively.
Figure 2-2 shows that urbanization has increased rapidly since
1968, becoming the major land use type in 1980. Developed
areas have continued to grow inward along Highway 78 from both
ends of the study area. Agricultural lands have been urbanized
along Buena Vista Creek and are yielding to urbanization in the
south-central portions of Subarea 4.21. Population figures for 1980
have increased to 22,180 persons with 8,870 DUs.
D. 2000 Land Use
The year 2000 land use acreages were based on the City
of Carlsbad's "Land Use Plan" and from development trends evident
in past and present land use data. The Plan represents the
expected land uses in the City of Carlsbad at some future period
of time at "total Saturation". Based on existing trends and
current planning practices, we expect total saturation to occur
before the year 2000, for not only the City of Carlsbad, but
for the nearby Cities of Oceanside and Vista as well. As shown
in Figure 2-3, urbanization will have extended, by that time,
entirely across the drainage basin along Highway 78. No major
agricultural operations will exist at that time, only small
orchards and gardening at individual homesites. Some open
space areas will be spared from development for the enjoyment
of the population existing at that time. Population in year
2000 is expected to be 40,000 persons in the study area, with
16,000 DUs.
CHAPTER 3
DESCRIPTION OF BENEFICIAL USES
of
GROUNDWATER IN THE STUDY AREA
A. Past Beneficial Uses
A field survey and literature search was conducted
of the basin to determine past and present beneficial uses
of groundwater. A U.S. Geological Survey map published in
1898 showed nine scattered buildings along laver Buena Vista
Creek. Groundwater was presumably used to serve the needs
of the residents, although a record of only one well remains.
A U.S.G.S. "Water-Supply Paper" identifies the well located
about 2 miles east of the mouth of Buena Vista Creek. On
October 25, 1914 the water level was 10.1 feet below the
surface of the ground. A windmill supplied water for
"domestic supply and to a small extent for irrigating a
small vegetable garden".
Evidence was found of other historic uses of the
groundwater. El Camino Golf Course reportedly used a shallow
well and a windmill for landscape irrigation. Long-time
residents spoke of one or two wells which were used to
irrigate small orange groves. Other than the remains of
windmills now used for decorative purposes, no evidence of
the wells could be found. In the recent past, South Coast
Asphalt Co. used' groundwater for non-potable uses at the
plant. This well has recently been abandoned.
While groundwater has in the past been used for
domestic supply, agricultural and landscape irrigation, and
industrial service supply, in all cases the quantity of
water used was extremely small. As will be discussed more
thoroughly in Chapter 4, the groundwater transmissivity of
the basin is quite low. Historic evidence suggests, and
aquifer testing appears to confirm, that all the wells
drilled in the basin were low yield (less than 5 gallons
per minute). No evidence was found of any well which either
had a high yield or had been put to a beneficial use requiring
considerable quantities of water, such as large scale agri-
cultural irrigation.
B. Present Beneficial Uses
Currently, only one functioning well is known to
exist in the basin. This well serves the Caron residence.
Water is used for non-potable uses within the house and
for small amounts of outside irrigation. Bottled water is
used for drinking water.
The residents report that the well is capable of
yielding a maximum of 1000 gallons per day. The residents
expressed fears that the water is contaminated due to high
salts and nearby sewer lines and septic tank leach fields.
Well water continues to be used only because of the expense
of bringing municipal water to the home.
c. Future Beneficial Uses
Two factors severely limit the future beneficial
uses of the groundwater, poor quality and low yield. Both
of these factors are discussed in detail in Chapter 4.
Other than the limited uses now being made by the Caron well,
constructive use of the basin's groundwater has essentially
ended.
With the widespread availability of imported water
there is no compelling reasons for residents of the area to
use groundwater for domestic supply. The high TDS violates
the California Department of Health's secondary standards
for domestic water. As such, it is highly doubtful that the
Department of Health would permit the water to be used in
the future for drinking water.
The aquifers low yield and high total dissolved
solids preclude the water from being used for most agricultural
purposes. If a severe water shortage should occur, it is pos-
sible that individual homeowners could use the groundwater on
a limited basis for irrigation of landscape or salt-tolerant
pasture grasses.
The groundwater could potentially be used for
industrial service supply in the future, even though the
prospect seems unlikely. Since quality is not a major con-
sideration for this use, any revision of the groundwater
objectives will not prevent this beneficial use. The basin's
low yield probably would discourage any major future indus-
trial use. During a water shortage the water could conceivably
be used for minor purposes such as wash-down water and dust
control.
CHAPTER 4
DESCRIPTION OF GROUND AND SURFACE WATER QUALITY
A. Historic Groundwater Quality
In the late 1950's and early 1960's the State De-
partment of Waters Resources (DWR) conducted a well sampling
program within Subarea 4.21. A portion of the results of
this program are shown in Table 4-1, listing data for calcium
(Ca), sodium (Na), sulfate (SO4), chloride (Cl), boron (B),
total dissolved solids (TDS), nitrate (NO3), and electrical
conductivity (EC).
Three wells were sampled within Subarea 4.21 by DWR,
llS/4W-33F, 11S/4W-33G, and 11S/4W-32C. These wells are shown
on Figure 4-1, as W-1, OW-2, and OW-1, respectively. Well
W-1 is located adjacent to Buena Vista Creek near an existing
residence owned by the Robert Caron family, approximately one
mile east and upstream of the El Camino Real bridge. Well
OW-2 was located approximately another 1,500 feet upstream
along Buena Vista Creek on South Coast Asphalt Company proper-
ty. Well OW-3 was located on property approximately 1,000
feet east of El Camino Real, presently belonging to the El
Camino Country Club, just north and adjacent to State Highway
78.
Based on the results of DWR's well sampling data,
shown in Table 4-1, the groundwater quality of Subarea 4.21
can be rated as locally fair to poor regarding mineral content.
TDS concentration varied from 950 mg/l at well OW-2 on June 18,
1964 to 1,660 mg/l at well OW-1 on September 7, 1960.
The Basic Plan states the following regarding the
coastal-plains section of the Carlsbad Hydrographic Unit, which
includes Subarea 4.21:
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brackish waters that occur in the lagoons; of this water is probably the result of
however, it may be the result of sea water or connate water migrating into the allu- vium filled valley areas because of over- extractions at the groundwater reservoir. These waters were probably relatively poor historically although very few analyses are available prior to 1958."
Bulletin 106-2 published by the DWR in 1967 shows groundwater
quality along Buena Vista Creek as marginally poor quality,
with sodium and chloride representing the major cation and
anion, respectively.
B. Present Groundwater Quality
The only known well within Subarea 4.21 presently
being used is Well W-1, which is the Caron Well. The well
is thought to have a low yield (less than 1 GPM) and is
reportedly about 150 ' deep. Well OW-2 was abandoned ap-
proximately 12 years ago, and the grounds supervisor at
the El Camino Country Club (Well OW-1) indicated the use
of well water for irrigation purposes was discontinued sev-
eral years ago due to high mineral concentrations. Although
this study team consulted local water and irrigation district
personnel, as well as long-time residents to determine the
existence of any additional wells within Subarea 4.21, no
additional well sites were located.
Well W-2, however, was drilled by this study team
in April 1980 as a test boring into the Buena Vista Creek aqui-
fer. This test hole, located approximately 1% miles upstream
from Buena Vista Lagoon (Figure 4-l), was drilled to depth
of approximately 23 feet. A groundwater sample was collected
from Well W-2 on May 14, 1980, and its chemical constituents
are quantified in Table 4-2.
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Well W-1 was also sampled recently for mineral analy-
sis, and the laboratory results are shown in Table 4-2.
One of the samples was collected in December 1977, and
reported in the "Preliminary Design Report for Lake
Calavera Hills Waste Water Treatment Plant," in March
1978. Another sample was collected in March 1980 by this
study team. Both samples were taken during the winter-
spring rainy season, when the mineral concentration of
waters collected near the ground surface may have been lowered
by storm runoff water percolating into the ground.
Based on the data shown in Table 4-2, it appears
that groundwater quality in Subarea 4.21 has not changed
appreciably at Well W-1 since the early 1960's. The TDS
concentration of the three historical samples averaged
approximately 1,300 mg/l in the early 1960's while recent
samples collected from Well W-1 averaged a TDS concentra-
tion approximately 1,100 mg/l. Well W-2, however, had a
TDS concentration greater than 5,000 mg/l. This may be
due to strictly localized conditions, by salt water in-
trusion since the ground surface elevation is less than 40
feet at that point, or by conditions described in section
C. 3 of this Chapter.
The Basin Plan states the following regarding the
groundwater quality in the coastal-plains section of the
Carlsbad Hydrographic Unit, which contains Subunit 4.21:
use in the coastal-plains section "Ratings of groundwater for domestic
range from suitable to inferior. The marginal and inferior ratings are due to a high TDS content along with high nitrate or high sulfate in local areas."
use in this unit are generally marginal "Ratings of groundwater for irrigation
to inferior because of the high electri- cal conductivity and high chloride."
More specifically, the Basin Plan states the following
regarding the groundwater basin paralleling Buena Vista
Creek :
the Carlsbad Region is located along
"The northernmost groundwater basin of
and near Buena Vista Creek. This small groundwater basin has not been extensiveiy developed nor studied. In general, the quality of water exceeds l,OOOmg/l TDS and therefore is not widely used as a domestic supply. The chloride concen- tration of water in this basin exceeds 350 mg/l and therefore renders the water inferior for use as agricultural irriga- tion water. Because this basin is in
extensive mining of the basin could limited hydraulic contact with the sea,
result in salt water intrusion. This area is being urbanized and it is not expected that this groundwater basin will be extensively developed within the time-frame of this study".
C. Future Ground Water Quality
1. Introduction
The present groundwater quality of the basin was
described in the previous section. A geohydrologic study of
the basin is contained in Appendix A. This section utilizes
the data to project future water quality of the basin, consid-
ering the impacts of changing land use patterns, the proposed
water reclamation program, and the aquifer characteristics.
2. Summary of Geohydrologic Conditions
Buena Vista Basin
The Buena Vista Basin consists of three main geologic
features. A small ribbon of unconsolidated clays parallels
Buena Vista Creek at an estimated average depth of 20 feet.
This recently deposited alluvium is saturated, but has very little
capacity to transport or store groundwater.
Underlying the alluvial clays are beds of
sandstone and silty claystone deposits known as the Santiago
Formation. The depth of the formation varies in thickness
from 0 to 100 feet depending on location, but average
approximately 40 feet. The sedimentary deposits are
saturated at depth though the permeability is quite low.
A massive formation of meta-volcanic, meta-
sedimentary, and granitic rocks underlie the Santiago
Formation. Judging from exposures of this basal formation
elsewhere in the County, the upper several hundred feet are
weathered and fractured. Varying quantities of ground-
water are generally found within this zone. While wells
that intercept the larger fractures are typically capable
of producting usable quantities of groundwater, no such
wells are found in Subarea 4.21.
The soil borings conducted in the study area
showed the basin is currently well-saturated with ground-
water. All of the test holes showed water at a shallow
depth. Further evidence of this comes from the fact that
Buena Vista Creek flows year round. Figure 4-2 shows a
conceptual model of the basin's geology and groundwater.
It should be pointed out that while much of the
basin's sediments are thought to be saturated, the area
cannot be considered a groundwater basin in the normal
sense. The horizontal and vertical permeability of the
Santiago sediments is quite low, in the order of 0.2
feetlday. A well drilled in these sediments would have
an extremely low yield. To pump a reasonable quantity
of water, a series of closely spaced wells would be
required, each contributing a small fraction of the total
water.
The low permeabilities also preclude the use
of subsurface flow as a source of groundwater recharge.
Using transmissivity values obtained by well pump tests,
and the hydraulic gradient established by the static water
levels in exploratory borings. the subsurface flow was
calculated to be 0.05 acre-feet per year, which is negligible.
Theoretically, a well could also be drilled into
the underlying fractured basement rock. By intercepting
a fracture zone, usable quantities may be obtained. How-
ever a search of well records in the basin does not reveal
the existence of a well of this type. The Caron well, which
is 150' deep may draw water from the basement rock, although
the well has a very low yield.
A study of the hydrogeologic conditions of the
basin by Allied Geotechnical Engineers, Inc. (see Appendix)
computed the groundwater in storage to be approximately
79,000 acre-feet. Of this amount approximately 27,000
acre-feet consist of saltwater and brackish groundwater.
The annual safe yield of the basin is estimated to be
approximately 47.2 acre-feetlyr.
3. Groundwater Movement
The information presented in this section
represents the author's opinion of the groundwater hydrologic
conditions within the basin. Wherever possible, the opinions
are supported by field data, calculations and references.
However, the complexity of mechanisms involved in groundwater
movement require a degree of subjective judgement. As such,
this section should be regarded as learned opinion not in-
disputable fact.
Using the geologic model shown in figure 4-2,
it is possible to hypothesize how future land use changes
will affect groundwater quality.
TO do so, however, it is necessary to establish how groundwater
migrates within the basin.
Currently, evidence obtained by field testing
suggests the alluvium, the laser portion of the Santiago
sediments, and the fractured basement rock are saturated.
In essence, the groundwater basin appears to be "full" and
holds all the water it is capable of holding.
The very low permeability exhibited by the soils
of the basin inhibits the movement of groundwater. These
physical conditions then limit the soils' recharge potential.
Recharge from the percolation of precipitation is estimated
to be 47.2 acre-feet per year. Subsurface inflow is calculated
to be .02 acre-feet per year. The high groundwater table pre-
vents significant recharge from stream percolation.
By far the largest contributor to the groundwater
basin is imported irrigation water which percolates into the
underlying sediments. Previous studies* in the area show
that approximately .32 acre-feet per year per dwelling unit
is used for landscape irrigation. Agriculture irrigation
rates vary between 2.5-3.5 acre-feet per year per acre.
Applied irrigation water will be'partially consumed by
plant transpiration and evaporation. However, anywhere from
10% to 40% will pass the root zone and will percolate into
the underlying strata (called irrigation underdrainage or
return waters). The irrigation process will concentrate
dissolved salts passing the root zone. Table 4-3 shows
fiat underdrainage water contributes some hG5 acre-feet per
year to the groundwater basin.
*City of Carlsbad, "Waste Water Reclamation Master Plan
Study", 917 9 (Lowry & Associates).
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Leaching irrigation water percolates downward
until reaching either an impervious horizontal strata or
the water table. If an impervious strata is encountered,
the water will migrate in a slightly dipping horizontal
direction along the impervious strata. It will eventually
intersect either the ground surface as seepage or flow into
the groundwater reservoir.
Irrigation underdrainage which reaches the ground-
water reservoir will cause a mounding of the water table there.
The mounding effect increases the water table gradient which in
turn causes a lateral migration of water. Without a
mechanism for groundwater mixing, the inflows of excess
irrigation water would not readily co-mingle with the main
portion of the groundwater reservoir. Rather, the irrigation
underdrainage would tend to migrate down gradient to a
surface drainage course.
Again due to the low permeability of the soils
within this basin, irrigation water migration is quite slow.
During summer months phreatophytes, long-rooted plants that
absorb water from the groundwater table, consume a portion
of the water, which further concentrates the dissolved salts.
The effect of poorer quality irrigation water entering the
groundwater basin is reflected in the groundwater samples
collected from the basin. Samples collected from the upper
layers of the groundwater reservoir registered TDS concen-
trations of approximately 5,000 mg/l. Water drawn from the
underlying Santiago sediments indicated a TDS concentration of
about &200 mgll. The introduction of irrigation water
combined with the concentrating effects of phreatophyte con-
sumption appear to have created a vertical water quality gradient
The presence of poor quality summer flows in Buena Vista Creek
(Table 4-4) also attests to the presence of migrating irrigation
water.
During the winter rainy season there is some
evidence to suggest that the irrigation water migration process
is accelerated. Several weeks after a major rainfall, the
TDS concentration in Buena Vista Creek has been found to
be about 1500 mg/l. After higher quality rainfall runoff
leaves the basin a winter "baseflow" is established in the
Creek. The baseflow is the result of groundwater draining
from the watershed. The relatively poor quality of the
water indicates that salts, which were presumably introduced
by irrigation underdrainage, are being leached out of the
soil into the watercourse.
4. Future Groundwater QuaXty
Chapter 2 projected that by the year 2000 the
basin would be completely urbanized. Only a few designated
areas would remain as open space. At that time an estimated
16,000 dwelling units would be located within the imediate
study area. Using the same assumptions contained in the notes
for Table 4-3, it is estimated 5000 acre-feet/year will be
used for irrigation, of which 1000 acre-feet of water will
leach into the underlying sedimentary soils.
With the basin's low transmissivfty, and no
significant extractions of groundwater anticipated, the water
table is expected to remain at current high levels, As pre-
viously discussed, this level represents a full groundwater
bas in.
If some mechanism were available to completely
mix the incoming irrigation underdrainage, the basin would
quickly match the quality of the underdrainage water, an
estimated 2200 mg/l. If no groundwater mixing is assumed, the
leaching irrigation water would follow the mounding-horizontal
migration mechanism described earlier. In this case, the
existing groundwater quality would be maintained. The salts
contained in the irrigation underdrainage would continually
leach to the surface watercourse, presumable mostly as
winter baseflow. In reality, some groundwater mixing pro-
bably does occur. However, the basin's physical character-
istics would seem to indicate that the no-mixing condition
much more closely represents the true condition.
It is concluded that near future groundwater quality
will remain essentially the same as presently exists. The
existing vertical water quality gradient, varying between
5000 mg/l at the surface to 1200 mg/l at depth, will be
maintained. Poor quality year-round baseflows are expected
to increase as urbanization progresses. The quality of
the baseflows may improve slightly in response to improved
imported water quality. Should an areawide water shortage
occur, irrigation efficiencies could be increased which
would, in turn, reduce the baseflow but increase its TDS
concentration. In any event the underlying groundwater in
storage would be maintained essentially unchanged.
Over a long period of time (ie. hundreds of years),
groundwater mixing may occur, slowly degrading the water
in storage to an estimated TDS concentration of 2200 mg/l.
This process may be hastened if groundwater extractions are
increased, which would promote the mixing of groundwaters
and underdrainage.
5. Effects of a Reclamation Program
The City of Carlsbad is currently seeking
to implement a reclaimed water program in the lower Buena
Vista Basin. Reclaimed water could begin to be distributed
for landscape irrigation within a year. The City of Ocean-
side also has long-term plans to distribute reclaimed water
to portions of the watershed within its city limits. It is
estimated that approximately 1,440 acre-feet of reclaimed
water could be distributed in the area by the year 2000.
Reclaimed water would be used as a substitute
for a portion of the total irrigation water required (an
estimated 5,000 acre-feet) at ultimate development. Using
the 1,440 acre-feet per year of reclaimed water with a TDS
concentration of 1,000 mg/l would increase the overall salt
loading to the basin by 30%.
Because of the apparent lack of groundwater mixing,
the additional salt load is not expected to significantly
degrade the groundwater in storage. If groundwater mixing
does occur, the overall groundwater quality would approach
the average quality of the irrigation underdrainage water.
Using the assumptions listed in Table 4-3, and considering
irrigation with both potable and reclaimed water sources,
the average quality of the underdrainage is calculated to
be 2,850 mg/l. Therefore, if groundwater mixing does occur,
the water quality of the basin would reach an estimated
2,850 mg/l.
D. Surface Water Quality
Staff of the San Diego Regional Board conducted an
extensive surface water sampling program inside Subarea
4.21 in 1975 and early 1976. Table 4-4 shows the results
of laboratory analysis of samples collected from Buena
Vista Creek just upstream from the Buena Vista Lagoon
adjacent to the Jefferson Street bridge. This sampling
location is shown in Figure 4-1 as S-0. Also listed in
Table 4-4 are data from samples collected from Buena Vista
Creek by this study team in March 1980. These samples are
designated S-1, S-2 and S-3 progressing upstream, and their
locations are shown in Figure 4- 1.
The data in Table 4-4 indicates that the TDS concentration
of stream flow in Buena Vista Creek averaged approximately
1,400 mg/l during 1975, and about 1,350 mg/l on March 21, 1980.
Lower values of 492 mg/l and 333 mg/l in February and April
1975 are related to rainstorms occurring shortly before
these two samples were collected.
Regional Board staff analyzed several surface
water samples collected from Buena Vista Lagoon for mineral
constituents between May and November 1979. TDS concentrations
varied from approximately 1,400 mg/l near the termination of
Buena Vista Creek, to over 3,000 mg/l near the mouth of the
lagoon.
TABLE 4-4 Carlsbad Hydrographic Subarea (4.21) Buena Vista Creek Sampling Data
CHEMICAL CONSTITUENTS (mg/l)
LOCATION SAMPLED SAMPLE DATE Ca Na so4 c1 8 TDS NO3 EC1
I
s-0 02-10-75
03-05-75
03-25-75
04-08-75
06-10-75
06- 18- 75
07-17-75
08-29-75
09-19-75
10-02-75
10-28-75
12-02-75
01-16 75
s-1 03-21-80
S-2 03-21-80
s-3 03-21-ao
44 73
140 240
148 256
30 60
108 256
124 176
144 279
192 284
160 270
129 262
- 210
124 228 - 264 - 215 - 215
200
53 141
211 484
175 513
43 107
198 371
170 380
195 504
213 534
198 519
213 465
180 481
267 3a5
198 489
280 362
290 360
298 344
0.33 492 4.9
0.85 1.440 14
0.75 1,560 21
0.94 337 5.4
0.60 1.264 1.2
0.62 1,200 20
0.55 1,430 5.8
0.40 1,420 0.3
0.63 1,550 5.3
0.40 1,408 6.2
0.44 1,380 9.7
0.50 1.350 13
0.19 1,380 15
0.25 1.360 43
0.26 1,360 49
0.30 1.340 44
-
-
-
-
-
2,260
2.260
2,200
CHAPTER 5
DESCRIPTION OF REQUESTED CHANGES
A. Introduction
The Basin Plan lists beneficial uses of groundwater
in the Vista Hydrographic Subunit, which includes Subarea 4.21,
as follows:
o Municipal and Domestic Supply,
o Agricultural Supply,
o Industrial Service Supply.
As noted in Chapter 4, a survey of all known wells
in Subarea 4.21 revealed that only one well, Well W-1 owned
by Robert Caron and used for domestic supply (for washing
and yard irrigation only), was presently in use. Two other
historic wells were abandoned because of poor quality ground-
water and lack of capacity or use. No other wells are used
for domestic, agricultural or industrial purposes at this
time, and it does not appear that any new wells will be
drilled in the future for these purposes.
The following has been determined about the study
area :
o Groundwater quality is relatively poor,
o Good quality imported water is available for
water users,
o Local water purveyors have no plans to develop
the basin's groundwater supplies.
It has also been stated that, although no present
industrial uses and only very minor agricultural and domestic
use (Caron family) of groundwater occurs in the study area,
future use of groundwater for industrial purposes or for
irrigation of salt-tolerant crops may be possible. Future
domestic use of the basins groundwater appears to be impractical
due to the small quantities and poor mineral quality.
It is therefore requested that, for the portion of
the Carlsbad Hydrographic Subarea that presently retains
designated groundwater beneficial use classifications (areas
east of Interstate 5), the following revisions be incorporated
into the Basin Plan:
1. The beneficial use "Municipal and Domestic Supply" (MUN) be designated a potential beneficial use.
2. The beneficial use "Agricultural Supply" (AGR) be designated a potential beneficial use.
3. The beneficial use "Industrial Service Supply" (IND) be designated a potential beneficial use.
With these requested changes, the beneficial uses of ground-
water in Subarea 4.21 east of Interstate 5 would be as follows:
o Municipal and Domestic Supply (potential)
o Agricultural Supply (potential)
o Industrial Service Supply (potential)
Present groundwater quality objectives for Subarea
4.21, excluding those areas west of Interstate 5 are listed in
Table 5-1.
(33)
Luke-DWek
TABLE 5-1 Groundwater Quality Objectives for the Vista Hydrographic Subunit
Parameter Objective*
as noted) (mg/l or
Total dissolved solids 1,000
Chloride 400
Percent sodium(%) 60
Sulfate 500
Nitrate
Iron
10
0.3
Manganese 0.05
Methylene blue active substances 0.5
Boron 0.5
Odor
Turbidity(JTU)
none
5
Color (Units) 15
Fluoride 1.0
* Concentrations not to be exceeded more than 10% of the time during
any one year period.
(34)
Present quality of groundwater within Subarea 4.21 does
not meet these objectives based on recent sampling data.
It is requested the groundwater quality objectives
for this basin be changed in the following manner:
1. Total dissolved solids from 1000 to 3500 mg/l,
2. Chloride from 400 to 800 mg/l,
3. Nitrate from 10 to 45 mg/l,
4. Boron from 0.5 to 2.0 mg/l.
These revisions would allow the use of secondarily
treated reclaimed water within Subarea 4.21. With these changes
the proposed groundwater quality objectives for Subarea 4.21,
excluding areas west of Interstate 5, would be as listed in
Table 5-2.
(35)
TABLE 5-2 Proposed Groundwater Quality Objectives for the Carlsbad Hydrographic Subarea
Parameter Objective*
as noted) (mgll or
Total dissolved solids 3,500
Chloride 800
Percent sodium(%) 60
Sulfate 500
Nitrate 45
Iron 0.3
Manganese 0.05
Methylene blue active substances 0.5
Boron 2.0
Odor
Turbidity(JTU)
Color(Units)
Fluoride
none
5
15
1.0
* Concentrations not to be exceeded more than 10% of the time during
any one year period.
CHAPTER 6
DEMONSTRATION OF CONSISTENCY BETWEEN THE REQUESTED
AND THE STATE'S NONDEGRADATION POLICY
A. Introduction
The State Water Resources Control Board's Resolution
No. 68-16, "Statement of Policy with Respect to Maintaining
High Quality Waters in California" (known as the State's Non-
degradation Policy) establishes the basic policy for setting
and changing water quality objectives. Any request for revision
of groundwater objectives must demonstrate that the revision
requested is consistent with the Nondegradation Policy.
This chapter examines the provisions of the Non-
degradation Policy. The effects of making the requested re-
visions are then examined to show the changes are consistent
with the provisions of Resolution No. 68-16.
B. Summary of State's Nondegradation Policy
Resolution No. 68-16 states, in part,
"1. Whenever the existing quality of water is
better than the quality established in policies . . . . ,
such existing high quality will be maintained until it has
been demonstrated to the State that, (1) any change will be
consistent with maximum benefit to the people of the state,
(2) will not unreasonable affect present and anticipated
beneficial use of such water, and (3) will not result in
water quality less than that prescribed in the policies."
(37)
The Nondegradation Policy further states that,
"2. . . . waste discharge requirements (must be
established) to assure that (a) a pollution or nuisance will
not occur and (b) the highest water quality consistent with
maximum benefit to the people of the State will be maintained.
In a letter dated November 29, 1979 to Lake Calavera
Hills, the staff of the Regional Board explains what specifically
must be considered to demonstrate consistency with the State's
Nondegradation Policy. This letter states, "The demonstration
must include an assessment of the impacts of the requested
modifications on beneficial uses and an assessment of the
benefits of the requested modifications. The assessment of
the benefits of the requested modifications must, as a minimum,
be based on the following: (1) Identification of affected
populations and evaluations of hardship vs. benefit for each
group; (2) evaluation of economic benefit vs.detriment; and
(3) evaluation of social benefit vs.detriment. 1,
C. Implications of the Requested Changes to the Groundwater
Objectives for Subarea 4.21
The following discussion addresses the consistency of
the requested groundwater objective modifications with the
State's Nondegradation Policy. Chapters 4 and 5 discuss the
projected impact of revising the water quality objectives on
future water quality and future beneficial uses. Briefly, it
was concluded that changing groundwater objectives would
result in only minimal groundwater degradation. However, for
the purposes of analyzing a "worst case" alternative, it is
assumed the TDS concentration does reach the objective of
3,500 mg/l.
Revising the basirls groundwater objectives will DOSsib,y
be detrimental to some groups of people and be beneficial to
other groups. The affected populations have been classified
into three basic groups; (1) Existing and potential ground-
water uses, (2) Potential users of reclaimed water, and (3)
Citizens residing within the boundaries of the Carlsbad
Municipal Water District and the City of Oceanside. These
three population groups represent the range of people who
may be impacted. An evaluation will be made of the hardship
versus benefit for each of these population groups. The
analysis will consider both economic and social factors.
It should be noted that the economic analysis
presented below uses current imported water prices. Because
of increasing power costs it is expected the price of im-
ported water will rise considerably faster than the rate
of inflation. If this fact were considered in the analysis,
using reclaimed water would offer an even greater economic
advantage. However, to analyze a "worst case" situation
for reclaimed water, the chances of rapidly rising imported
water costs were not included in the analysis.
D. Population Group 1 - Existing and Potential Groundwater
Users
Only one functioning well is known to exist within
Subarea 4.21. This well (Well W-1) supplies a single family
residence with non-potable water. Water is used for domestic
uses, (excepting drinking water) and a minor amount of
irrigation adjacent to the residence.
It is conceivable that in the future others will
seek to utilize the limited groundwater supplies found within
the basin. The beneficial uses for relatively poor quality
groundwater are limited to agricultural or landscape irrigation
of salt-tolerant crops and industrial process water, such as
sand and gravel wash water. Plainly, no reasonable method
exists to determine how much groundwater will be utilized in
the future. Land use projections show that landscape irrigation
could consume relatively large quantities of groundwater if a
suitable distribution system were installed. However, the
hydrogeologic investigation showed the "safe" perennial yield
of the basin from natural recharge is 47.2 acre-feetlyr. For
(39)
the purposes of this study, it is assumed, all of the safe
yield (as calculated by natural recharge) will be used for
irrigation water.
1. Evaluation of Economic Benefit vs Detriments for the
Group 1 Population
Lowering the groundwater objectives for the lower
Buena Vista Basin may be detrimental to the one family which
now utilizes groundwater for non-potable domestic use. Al-
though the reclaimed water to be distributed throughout the
basin will consist of highly treated secondarily treated
wastewater, it is possible that the groundwater basin could
become increasingly mineralized. Should the total dissolved
solids concentration rise to the proposed water quality ob-
jective of 3500 mgll, the water would probably not be suitable
for either non-potable domestic uses or landscape irrigation.
Whether the groundwater basin would actually de-
grade to the 3,500 mg/l level is highly doubtful. Assuming
the basin does degrade to the 3,500 mg/l level, the existing
groundwater uses would be degraded for the family presently
using well water. A new water supply source may be required.
Connecting the house to the Costa Real Water District's lines
would cost about $30,000 for pipelines, meters, etc. Water
consumed would cost about $175.00/acre-foot. For a single
family using 1 acre-footlyear and paying $4.40/month for
meter fees, the yearly water bill would be about $230/yr.
The cost of an alternative water source for this
single family is too high. To mitigate the high cost, the
cost of the connecting water line should be included in the
cost of providing a reclaimed water distribution system.
Doing so would bring the annual water costs paid by the family
down to the same level paid by other water users in the area.
However, installing municipal water service would allow the
family to discontinue buying bottled water, saving them an
estimated $130/yr. Therefore the total economic loss to
existing groundwater users would be about $100/yr.
The economic loss to potential users of groundwater
can also be calculated. The assumption is made that if the
(40)
Luke- Dud&
groundwater objectives are revised, 47.2 acre-feetlyear
(the basin's safe-yield) would be lost as a potential source
of irrigation water. Losing this source of irrigation water
would mean that potential irrigators would have to pay about
$7,725 per year to buy water from the water district. Ground-
water could probably be supplied at about $lO/acre-foot or
$444 per year. The potential users of groundwater would there-
fore suffer a net loss of about $7281/year. The total economic
benefit versus detriment to the Group 1 population is listed
in Table 6-1.
TABLE6-1 Economic Benefits versus Detriments for Group 1
Population Caused by Easing Groundwater Objectives
Group 1 Population Benefit Detriment
Existing Groundwater $0 Users
Potential Groundwater $0 Users
2. Evaluation of Social Benefit vs Detriment for the
Group 1 Population
Permitting the groundwater quality in Subarea 4.21 to
degrade would affect the water supply to the family now using
the groundwater. To mitigate this problem, a new connection to
a municipal water supply system would be provided. The new
source of water would be both more reliable and of higher water
quality. The family would benefit from a better quality water
source.
The groundwater basin could also be degraded as a
future source of irrigation water. The social implications of
this loss are small. The basin storage and annual safe yield
capabilities are very limited. It is doubtful that this water
supply would actually be utilized significantly in the future.
Many property owners who could have used the groundwater for
irrigation purposes will have access to reclaimed water for
the same purpose. The domestic water supply system is also
fairly well developed in the area. As such, no property Owner
will be deprived of the use of his land because of a lack of
a suitable water supply.
Overall, revising the groundwater objectives is
expected to have minimal social impact on the existing and
potential future users of groundwater. Providing an alter-
native water supply to the family now using groundwater will
benefit this user from water quality, reliability and health
aspects. Providing a reclaimed water distribution system
for property owners who need irrigation water in the area
will offset possible future impacts of a degraded groundwater.
- E. Population Group 2 - Potential Users of Reclaimed Water
Changing groundwater objectives are expected to
- encourage the use of reclaimed water within the Lower Buena
Vista basin (Subarea 4.21). Both the City of Carlsbad and
the City of Oceanside are actively planning to distribute
reclaimed water to the area. -
It is difficult to accurately predict which markets
will be served. The exact quantity of reclaimed water to be
used depends upon a variety of factors, including the avail-
ability and cost of potable water, the proximity of reclaimed
water distribution lines, and the aggressiveness with which
reclaimed water is marketed. However, it is reasonable to
expect the markets outlined in Table 6-2 will be served within
the basin.
TABLE 6-2 Potential Users of Reclaimed Water
Market Estimated Irrigable Estimated Average Use
Land (acres) (acre-feetfyear)
1. Landscape irrigation
within Lake Calaver
Hills Development 200 .
2. Golf Course irrigation
at El Camino Country
Club 125
3. Landscape irrigation at
Mira Costa College 50
4. Landscape irrigation at
Tri-City Hospital 25
5. Miscellaneous landscape
distribution pipe
irrigation adjacent to
50
640
400
160
80
160
Total 450 1440
Note: Irrigation water use is estimated at 3.2 acre-feet/year.
1. Economic Benefits vs Detriment for the Group 2 Population
Changing gromdwater objectives in Subarea 4.21 is
expected to enable a variety of landscaped areas to be irrigated
with reclaimed water. As shown in Table 6-2, approximately 1,440
acre-feetfyear of reclaimed water could be reused within the
basin. Assuming reclaimed water is sold at $130/acre-foot
(equivalent to 75% of domestic water supply cost), the total
water revenue for irrigation use would be $187,20O/year. If
reclaimed water were not available, the cost for irrigation water
from the Costa Real Water District would be $250,60O/yr. The
irrigators would realize a net savings of $63,40O/year.
2. Social Benefits vs Detriment for the Group 2 Population
Providing reclaimed water for irrigation Purposes
within Subarea 4.21 would have a variety of social benefits for
the Group 2 population. Perhaps the most signigicant benefit
is the availability of a new water source. Prospects of a
severe water shortage occurring in Southern California are
continually growing. Should a water shortage occur in the near
future, it could have serious consequences for businesses re-
quiring irrigation water. During a drought, stringent restric-
tions are generally placed upon using water for irrigation.
Similiar restrictions would not be placed on using reclaimed
water. By using reclaimed water, water-intensive irrigation
activities such as golf courses would be able to avoid both the
loss of business and damage fairways and greens. Hydrogeologic
studies indicate the existing groundwater basin would be in-
capable of providing a significant contribution of irrigation
water. Therefore, revising groundwater objectives to permit
reclaimed water to be utilized in the basin would be a significant
benefit to the Group 2 population. A possible social detriment
may be associated with developing a reclaimed water distribution
system within the-basin. Using treated wastewater increases the
risk of water users being exposed to a waterborne pathogenic
organism. While both treatment and operation regulations
established by public agencies stringently protect against such
problems, health risks can not be totally eliminated.
Another problem inherent with a reclaimed water
system is the possibility of equipment failure. A broken
distribution main could result in reclaimed water temporarily
flowing to Buena Vista Lagoon. A malfunctioning chlorinator
could result in the distribution of inadequately disinfected
water.
Currently, regulatory agencies require back-up
equipment for critical treatment and distribution functions.
The stringent regulations essentially eliminate the oppor-
tunities for major public health problems.
F. Population Group 3 Residents Within the Costa Real Water
District and City of Oceanside
The reclamation projects proposed for Subarea 4.21
would provide a supplemental or alternate supply of water to a
portion of the Costa Real Water District and the City of Ocean-
side. If reclaimed water is provided for landscape irrigation,
the two districts may delay or avoid the construction of some
capital facilities necessary to expand the potable water system.
In addition, using secondarily treated wastewater for irrigation
water saves energy which would be needed to import alternative
potable water supplies.
The 1979 population of the Costa Real Water District
was 31,000 people with a water consumption of 11,135 acre-feetlyear
(.36 acre-feet/year/person). The City of Oceanside had a 1979
population of 72,400* people, who consumed a total of 18,310
acre-feetlyear (.25 acre-feet/year/person). Table 6-3 lists
the projected population and water use for the two water
districts.
1. Economic Benefit versus Detriment for Group 3 Population
Implementing a water reclamation program in Sub-
area 4.21 would provide 1,440 acre-feet/year of water as a
supplemental or alternative water supply to portions of the ,
Costa Real Water District and City of Oceanside. It is difficult
to estimate the true economic worth of an additional water supply
to the residents of the area. Initially, it appears public
agencies will not be able to initially distribute reclaimed
water for a profit. Initial projections for the Carlsbad area
project the expense of operating the system will about equal
the revenues produced from reclaimed water sales.
The economic benefits could increase markedly in
the future. When contracts to supply imported water through
the California Aqueduct are renegotiated in 1983, the price of
imported water is expected to rise substantially.**
*County Water Authority Estimate
**Metropolitan Water District, "1979 Water Pricing Study," 8/79
(45 1
TABLE 6-3 Projected Population and Water Use For
Carlsbad MWD and City of Oceanside
Costa Real City of Year Parameter W.D. Oceanside Total
~~
19 79 Population 31,000 72,400 103,400
Water Consumption 11,135 18,310 29,445 (acre-feet)
1985 Estimated Population 51,100 78,400 129,500
Water Consumption 18,400 19,600 38,000 (acre-feet)
1995 ,Estimated Population 77,800 107,400 185,200
Water Consumption 28,000 26,850 54,850 (acre-feet)
As ,the price of imported water rises, the sales price of reclaimed
water can also be raised proportionately. This should result in
a net income for the public agencies distributing reclaimed water,
which would benefit the residents of the area.
2. Social Benefits versus Detriment for the Group 3
Population
Revising groundwater objectives and constructing a
water reclamation system would have significant social benefits
for residents of the Carlsbad and Oceanside area. Supplying
an additional 1,440 acre-feet/year of reclaimed water as a
supplemental or alternative water source for irrigation reduces
the dependence on imported water supplies. The reclaimed water
program would supply an amount equivalent to water used by 4,720
people. Producing this supply locally would not only lessen
the overall demand on imported water supplies, but also would
reduce the amount of energy necessary to deliver the water.
Table 6-4 shows the total energy savings by treating and reusing
1,440 acre-feetlyear of reclaimed water is 2,600,000 kilowatt-
hourslyear. This is equivalent to saving a total of 4,400 barrels
of crude oil per year.
(47) LuUe-Dud&
TABLE 6-4 Energy Saving of Reclaimed Water Program*
Energy Source Energy Requirement
(kwh/acre-feet)
Energy required for imported water (50/50 blend)
Energy required for secondary
treatment
Energy required for chlorination
(including production)
2,700
400
100
Energy required for distribution
pumping (300 ft. head) 400
900 Total energy required for reclaimed
water system -
Net energy savings by using reclaimed
water 1,800
Total annual energy savings in Buena Vista
Basin (1,440 acre-feet/year) 2,600,000 kwhlyear
*Data extracted from Roberts and Hagan, "Energy Requirements of Alternatives in Water Supply, Use and Conservation", December 1975.
HYDROGEOLOGIC INVESTIGATION
Prepared By:
Allied Geotechnical Engineers Inc. 8624 Cuyamaca Street Suite F Santee, California 7141449-5900
Project No 14D3 Page i
TABLE OF CONTENTS
INTRODUCTION
HISTORIC DATA AND PREVIOUS WORK PERFORMED BY OTHERS
PROJECT LOCATION
SITE PHYSIOGRAPHY
GEOLOGY
RESIDUAL SOILS
GEOLOGIC STRUCTURE
FIELD INVESTIGATION
A. Field Reconnaissance Mapping and Existing
B. Well Drilling
C. Trench Excavations and Stream Gaging
D. Seismic Refraction Survey
E. Aquifer Testing
Water Well Inventory
LABORATORY TESTING
A. Determination of Specific Retention
B. Determination of Water Quality
BASIC CLIMATOLOGIC DATA COLLECTION AND REDUCTION
A. Precipitation Data Analysis
B. Evaporation Data Analysis
C. Recharge Analysis
GROUNDWATER IN STORAGE
A. Agua Hedionda Basin Study Area
B. Buena Vista Basin Study Area
PAGE NO
1
2
2
3
4
7
7
8
8
9
1 D
12
12
14
14
15
16
16
20
21
24
24
26
C. Saltwater In Storage Within The Basin Study Area.5 27
GROUNDWATER SUBSURFACE FLOW 28
SAFE YIELD 29
CONCLUSIONS 30
. - Project No 14D3 Page ii
TABLE OF CONTENTS
LIST OF TABLES
Table 1 : Inches of Retention
Table 2 : Adjusted 104-Year Rainfall Record
For Palomar Airport Station
Table 3 : Monthly Precipitation Data Represen- tative of Precipitation Events,
Palomar Airport (1875 - Present)
Table 4 : Weighting of Precipitation Events
Table 5 : Mean Monthly Potential Evapotranspiration Lake Hodges (1920 - Present)
Table 6 : Long Term Annual Groundwater Recharge
LIST OF FIGURES
PAGE NO
15
17
19
20
21
23
Figure I : Location Map
Figure II* : Plot Plan showing boundaries of basin study areas, Lake Calaveras Hills Associates property. approximate locations of existing and explora- tory wells, trenches, stream gaging stations,
and seismic traverses.
Figure III*: Geologic Map
Figure IV* : Soils Map
Figure V : 104-Year Rainfall Graph (on Page 18)
Figure VI : Rainfall Correlation Graph
*NOTE : Figures 11, 111, and IV are located in the map case
011 the rear cover of this report. ~
LIST OF APPENDICES
Appendix A : Boring Log Sheets (8 sheets)
Appendix B : Trench Log Sheets (7 sheets)
Appendix C : Stream Flow Measurements (4 sheets)
(Appendices not included in this report)
Project No 14D3
TABLE OF CONTENTS
LIST OF APPENDICES (Continued)
Appendix D : Seismic Traverses(7 sheets)
Appendix E : Well Recovery Versus Time Graph(2 sheets)
Appendix F : Monthly Rainfall Analysis(7 sheets)
Appendix G : References(2 sheets)
(Appendices not included in this report)
Page iii
PRELIMINARY HYDROGEOLOGIC INVESTIGATION
INTRODUCTION
At the request and direction of Luke-Dudek Engineers of Encinitas,
California, we have conducted and completed a Preliminary Hydrogeologic
Investigation of the Buena Vista and Aqua Hedionda basins located
in the Carlsbad area in northern San Diego County, California.
- 1 The purpose of this hydrogeologic investigation was to determine
and evaluate the aquifer characteristics of the two basins in terms
of water quality, storage, safe yield, and long-term recharge. The
findings and conclusions derived from our field and laboratory work,
an analysis of basic climatologic data, and a review of available
maps and literature pertinent to the geology of the general project
study area, as presented in this report, are to be used as a basis
for the report prepared by Luke-Dudek Engineers in connection with
the request of Lake Calaveras Hills Associates to revise the ground-
water objectives of the two basins.
-
-
It is our understanding that Lake Calaveras Hills Associates intends
to develop its property into a master planned residential community
which utilizes its own on-site located sewage treatment facilities.
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 2
Prior to our commencement of the investigation, we have discussed
the general procedures and objectives of our study with Mr. Dennis
O'Leary of Lowry and Associates, the water quality consultant to the
City of Carlsbad, and with Messrs. Ladin H. Delaney and Art Coe, rep-
resentatives of the California Regional Water Quality Control Board
in San Diego. Throughout our investigation, we have coordinated our
activities with Messrs. Greg Luke and Frank Dudek of Luke-Dudek
Engineers.
HISTORIC DATA AND PREVIOUS WORK PERFORMED BY OTHERS
- Previous geologic mapping in the project study area was done by
Benjamin F. Jones (1959) and Kenneth Wilson (1972) as part of their
Master's Thesis work. Geologic mapping of those portions of the San
Luis Rey Quadrangle which are located within the City of Carlsbad mun-
icipal boundaries by Burkland and Associates (1973) as part of a
-
- geotechnical planning study commissioned by the City of Carlsbad i was also used.
More recent work performed by Irvine Soils Engineering, Inc. (1977)
and San Diego Soils Engineering, Inc. (1979) have focused on defining
the soil percolation characteristics of two tributary drainage basins
to the Buena Vista and Aqua Hedionda drainages.
PROJECT LOCATION
The project study area is located to the east of the currently devel-
oped portion of the City of Carlsbad, California (Fig. I). The major-
ity of the project study area lies to the east of El Camino Real and
is bounded by State Highway 78 to the north, Calaveras Lake to the
east, and the Aqua Hedionda drainage to the south and southeast.
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 3
The boundaries of the Lake Calaveras Hills Associates property are
shown on Figure 11. However, as the joint effort between Luke-Dudek
Engineers and our firm is primarily concerned with the request by
Lake Calaveras Hills Associates to the California Regional Water
Quality Control Board in San Diego to revise its groundwater objec-
tives for portions of both the Buena Vista and Aqua Hedionda basins,
the boundaries of our project study area as indicated on Figure I1
actually encompass a larger geographic area than the property cur-
rently owned and proposed for development by Lake Calaveras Hills
Associates. The boundaries of this larger study area were specified
by Luke-Dudek Engineers and do not correspond to hydrologic boundaries
in all cases.
SITE PHYSIOGRAPHY -
The project study area is located in the coastal plain of the Penin-
sular Ranges geomorphic province in San Diego County and is bordered
to the north by Buena Vista Creek. The southern boundary is defined
" (,
~- by the Agua Hedionda drainage. Both drainages, and the gently rolling
hills located between them, form the major tppographic features of the
project study area. Elevations within the study area range from a low
of approximately 10 feet above mean sea level to approximately 440
feet above m.s.1. at the base of the existing water tank in the north-
eastern portion of the project study area.
-
Access to the project area is by means of several rough graded private
easements roads, which generally run in a northerly and easterly direc-
tion off of El Camino Real. El Camino Real forms the western boundary
of the Buena Vista basin for the purpose of our investigation (Fig. 11).
Access along any of these private graded roads is fair to moderately
good in order to reach any portion of the project study area.
Project NO. 14D3 L,uke-Dudek Engineers 6/17/80 Page 4
The natural vegetation cover within the project study area consists
predominantly of chaparral and annual grasses. The south-facing hill-
sides are dominated by the chaparral and the grassy vegetation cover
is more widespread on the north-facing slopes. Well developed, mature
trees are found along the major drainage alignments, and a row of
mature eucalyptus trees trends along the western boundary of the
Lake Calaveras Hills Associates property.
Surface drainage within the project study area is channeled primarily
along the numerous tributary drainages which feed into either Buena
Vista Creek to the north or into Agua Hedionda Creek to the south.
Both drainages terminate at their western end in salt marshes which
are a part of the Buena Vista and Agua Hedionda lagoons.
GEOLOGY
( Geologic Formations
The project study area and its immediate vicinity is underlain by five
different geologic formations, which are listed and discussed in chron-
ologic order, starting with the oldest formation:
Basement Complex: Basement rock units in the area consist of a wide
variety of metavolcanic hnd metasedimentary rocks of Jurrasic age, which
are better known as the Santiago Peak Volcanics after Larsen (1948).
The metavolcanic rocks exhibit a wide compositional range. Andesites,
dacites, and quartz latites are the most common (Wilson, 1972).
In some areas, these metavolcanic and metasedimentary rock units are
intruded by plutonic rocks of the southern California batholith, which
range in composition betwen gabbro and granite (Wtlson, 1972). These
plutonic rocks are generally considered to be Upper Cretaceous in age.
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 5
Lusardi Formation: Unconformably overlying the basement rock complex
is a boulder conglomerate with interbedded coarse-grained sandstone
beds of the Lusardi Formation of Cretaceous age. Exposures of this
formation have been mapped to the east and southeast of the project
study area. This formation reportedly provides a good aquifer for the
Sintorosa Country Club wells located outside the southeastern portion
of our study area.
Santiago Formation: This formation consists predominantly of inter-
bedded sandstones and silty claystones of Eocene age which were first
recognized in the Carlsbad-Encinitas area and studied in detail by
Wilson (1972).
-
Within the project study area, these formational units consist pre-
dominantly of light to dark gray, silty clays and clayey sandstones
varying in thickness from 0 to 30 feet along the roadcuts (Wilson,
1972) and up to 100 feet thick in the Aqua Hedionda basin, as indicated
on bridge foundation boring log data obtained from the County of San
Diego Materials and Laboratory (Lough, 19801.
-
-
The Santiago Formation lies unconformably upon the basement rock com-
plex and the Lusardi Formation (Wilson, 1972).
Lindavista Formation: This formation commonly consists of a gravel and
pebble conglomerate set in a reddish brown sandstone matrix and is
generally considered to be early Pleistocene in age.
This formation is generally found as a thin (less than 50 feet thick)
terrace deposit on elevated terraces in western San Diego County.
Exposures of the Lindavista Formation have been mapped by Wilson (19721
along the ridgetop which follows the western boundary of the Lake
Calaveras Hills Associates property. During our geologic reconnaissance
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 6
mapping of the area, however, most of these terrace cap deposits
had been removed as a result of grading activity on the adjacent
property to the west of the Lake Calaveras Hills Associates property.
Quaternary Alluvium and Slopewash: Within the project study area,
Recent alluvial deposits were encountered only along the major drain-
age basins to an average depth of 20 feet, as derived from our well
borings (Refer to Appendix A) and verified by the seismic refraction
survey traverses (Appendix Cl .
These alluvial deposits predominantly consist of dark brown to dark
grayish black, clayey fine sands and sandy silty clays with an organic-
rich, approximately 6-inch t.hick topsoil layer.
Due to their limited areal extent and depth, the alluvial deposits are
not considered as a significant hydrologic unit.
A maximum 6-inch thick layer of coarse-grained sandy alluvial materials
were encountered in two well borings just to the west of College Boule-
vard on the South Coast Asphalt plant property. These coarse-grained
sands have apparently been "washed into" the basin from the nearby
located cut slope and graded road during the most recent floods.
'Directly underlying these coarse sandy deposits, the same clayey fine
sands and silty clays were encountered to the extent of the borings.
Recent slopewash deposits within the project study area are found
primarily in the Buena Vista basin, along the north side of State
Highway 78. As these slopewash materials have been derived from the
Santiago Formation, they are similar in composition to the underlying
formational mudstones and claystones. The color of these slopewash
deposits vary from light gray to grayish brown to tan brown, depending
on the organic material content of the soils, the depth of weathering,
and freshness of the cut slopes.
" .
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 7
A generalized geologic map of the project study area has been com-
piled on the basis of previous work performed by Wilson (1972) and
Burkland and Associates (1973), as well as our own field reconnais-
sance mapping of the area (Fig. 111).
RESIDUAL SOILS
The project study area is basically underlain by three major soil
types, known as the Diablo Clay and the Las Flores loamy fine sand,
which have both been predominantly derived from the Santiago Forma-
tion, and the Friant rocky sandy loam, which has been derived from
the basement complex rock units (primarily the metavolcanic and
metasedimentary rock units). Figure IV represents a generalized soil
map of the project study area based on the U.S. Department of Agri-
culture Soil Survey of the San Diego area. This map indicates the
existence of several smaller patches of different soil types, but
all of these smaller soil types can be classified as a sub-group of
one of the major soil types due to similarities in composition, slope
gradient, and vegetation cover.
GEOLOGIC STRUCTURE
Faulting in the general project area generally strikes between north
30° east and north 50° west and dips steeply (60 to 90 degrees) either
east or west (Wilson, 1972). The majority of these faults occur toward
the eastern boundary of Wilson's mapping area in both the San Luis Rey
and Encinitas Quadrangles. Only one lineation, which reportedly trends
north 14O east from a point about 1,600 feet west of Calavera Lake and
follows a trend toward the intersection of El Camino Real and Calavera
Road (mapped as Fault C on Wilson's geologic map), appears to traverse
the project study area.
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 8
Folding in the area is on a broad scale with pre-Tertiary rocks
showing north-south trending fold axes. The post-upper Cretaceous
sequences have been tilted to the west almost exclusively (Wilson,
1972). Wilson's geologic map indicates average dips between 5 and
15 with local maximum dips up to 30°.
0
0
The structure of the project study area is dominated by the relief
of the Jurassic basement complex rocks, which were covered by marine
sediments during the transgressive phase of the transgression-regres-
sion sequence which occured during the middle to late Eocene epochs
(Wilson, 1972). Wilson further stated that the Oligocene-Miocene
depositional history of his thesis mapping area is not preserved,
and assumes that this represents a time of non-deposition and probably
extensive erosion of great quantities of the Eocene deposits. The
high relief areas were eroded and "rounded-off'' at that time, and it
was not until the early Quaternary period when renewed deposition
occured in the general project area as indicated by the presence of
-
-
-. Pleistocene age terrace deposits.
FIELD INVESTIGATION
- The field investigation phase of our study was conducted in several
stages, each of which is discussed in more detail in chronological
order below and on the following pages:
A. Field Reconnaissance Mapping and Existing Water Well Inventory
This initial stage of our field investigation was conducted to
inspect and map geologic outcrops and surface soil exposures in
order to determine suitable well boring and trench locations.
At thesame time we also surveyed existing water wells in the
project study area and contacted the individual well and property
owners to secure permission to collect water samples and/or
perform drilling operations on their property.
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 9
The collection of the well water samples was coordinated with
and partially conducted by Mr. Frank Dudek of Luke-Dudek Engin-
eers, who also collected surface water samples at several
locations in both the Buena Vista and Aqua Hedionda basins.
The approximate locations of the existing water wells are
indicated on Figure 11. This initial stage was conducted and
completed during the period from March 25 to April 1, 1980.
B. Well Drillinq
The subsequent stage of our field investigation consisted of
the drilling operation of a total of eight exploratory well
borings with a truck-mounted continuous flight auger drill rig
The drilling operation took two days to complete, and was con-
ducted on April 3 and 4, 1980.
The approximate locations of the well borings are indicated on
Figure 11. A continuous log of the various soil strata encoun-
tered in each excavation was recorded at the time of drilling,
and are shown on the "Boring Log Sheets" presented as Appendix
A. Bulk samples of the representative soil types were collected
for visual and textural classification in the laboratory.
The depth of alluvial deposits encountered in these well borings
range from approximately 16 to 23 feet, with the exception of the
two attempted well borings (Boring NOS. 7 and 8) drilled in the
eastern portion of the Buena Vista basin, off of College Boule-.
vard. The underlying formational materials were considered as
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 10
bedrock and represent firm claystone and clayey sandstone
beds of the Santiago Formation of Eocene age. The water
table encountered in the well borings ranged from 8 feet in
Boring No. 1, which was drilled just off El Camino Real in
the Agua Hedionda basin, to approximately 2 feet in Boring
Nos. 2 and 3, which were drilled about 3,000 feet further
to the west in the same basin. In Boring No. 4, at the west-
ern end of Haymar Drive (Caron's residence), the water table
was encountered at a depth of 9 feet, whereas in Boring Nos.
5 and 6, which were drilled on the south side of Haymar Drive,
just to the east of the Carlsbad Plaza Shopping Center, the
water table was encountered at a depth of approximately 6 feet.
In the two attempted well borings (Boring Nos. 7 and 8) the
water table occurred at a depth of less than 8 inches below
the ground surface.
Upon completion of the drilling of each boring, a 5-inch
diameter PVC casing was lowered and installed and subsequently
capped. The maximum depths reached in the borings ranged from
20 to 30 feet below the ground surface. The bottom one-third
portion of the casing was perforated to allow stabilization
of the static water level. It is noted that no casing was
installed in Boring Nos. 7 and 8 since these wells were drilled
primarily to establish depth to bedrock. This concluded our
preparations of the exploratory borings for pump testing oper-
ations to be conducted as a subsequent stage.
C. Trench Excavations and Stream Gaging
On April 12 and 13, 1980, a total of seven exploratory trenches
were excavated with a tractor-mounted backhoe at the approximate
Project NO. 14D3 Luke-Dudek Engineers 6/17/80 Page 11
locations shown on Figure 11. The purpose of these excava-
tions was to determine the effective rooting depth of the
native vegetation types in the project study area and to
collect samples of the various on-site soil types for labor-
atory testing. The laboratory procedures are briefly dis-
cussed under "Laboratory Testing" in a subsequent section of
this report.
The soil exposures observed in each excavation were also
recorded at the time of digging and are presented on the
"Trench Log Sheets", attached as Appendix B to this report.
Concurrent with our trenching operations, we performed stream
flow measurements with a Pygmy current meter in both the Buena
Vista and Agua Hedionda drainages. Measurements were taken at
"upstream" and "downstream" locations within the project study
area. Care had to be exercised in performing these measure-
ments in order to minimize potential errors due to increased
runoff within the drainage basins since the project area did
experience moderately heavy rainstorms at that time.
The results of our stream flow measurements are presented in
tabulated form as Appendix C. Our measurements indicated a
flow rate of 8.85 cu.ft./sec. at the "upstream" end of the
Buena Vista basin, and 5.11 cu.ft./sec. at the "downstream"
end. The Agua Hedionda drainage flowed at a rate of 5.80
cu.ft./sec. at our "upstream" gaging station, whereas the
"downstream" measurements indicated a flow rate of 6.25 cu.
ft./sec. In summary, our stream flow measurements appear to
indicate the presence of a losing stream in the Buena Vista
basin, i.e.a stream which loses water to the basin sediments
as it flows through the basin. On the other hand, the Agua
Project No. 14D3 Luke-Dudek Engineers 6/17/80
Hedionda appears to represent a gaining stream.
D. Seismic Refraction Survey
Page 12
In order to arrive at a more accurate projection of the sub-
surface geometry of the groundwater basins within the project
study area, a seismic refraction survey was conducted using a
Nimbus ES-125 Signal Enhancement Seismograph. Our seismic
survey consisted of a total of five 100-foot long traverses,
one 180-foot long traverse, and one 250-foot long traverse
across the Buena Vista and Agua Hedionda basins at the approxi-
mate locations plotted on Figure 11.
The seismic traverses were performed on April 19 and 20, 1980,
and an attempt was made to correlate the data derived from
these traverses with the subsurface information derived from
the exploratory well borings. The correlation with respect to
the depth to the alluvium-bedrock interface between the seis-
mic traverses and well borings appears fairly good in both.
basins. In the Buena Vista basin, two of the seismic traverses
were able to only identify the interface between the nonsat-
urated and saturated alluvial deposits.
The data from our seismic survey is presented as Appendix D
to this report.
E. Aquifer Testing
The final stage of our field investigation consisted of pump
tests performed on several well borings in both the Buena Vista
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 13
and Agua Hedionda basins. The pump tests were performed on
May 3, 4 and 6, 1980.
The equipment used for this testing program consisted of a
14 HP Tee1 submersible water pump with a gasoline powered
portable 230 Volt generator as a power source. The well dis-
charge was channeled by means of a 100-foot long flexible
hose and collected in a calibrated container to permit accu-
rate discharge measurements.
Due to the very rapid drawdown experienced in all tested well
locations, it became impractical to conduct conventional well
pump tests, and it was therefore decided to perform slug
withdrawal tests instead. The test results have been tabu-
lated and "Recovery Versus Time'' graphs have been prepared,
as shown in Appendix E to this report. Recovery of the wells
in the Agua Hedionda basin were much more rapid compared to
those wells tested in the Buena Vista basin. The transmiss-
ivities of the alluvial deposits in both basins, as derived
from our well recovery tests and analyzed using type curves!
are on the order of 0.2 ft /day. The test run on Well Boring
No. 2 in the Agua Hedionda basin, however, indicated a much
higher transmissivity, on the order of 113 ft /day. This is
interpreted as being due to a coarse, granular, porous layer
at approximately 15-foot depth. This layer is considered to
represent either a paleo stream channel or lens of coarse
granular, porous materials. A cross section of as large a
basin as the Agua Hedionda basin would probably yield the
existence of many such lenses or paleo stream channels within
the relatively impermeable clayey alluvial deposits.
2
2
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 14
Upon completion of the well recovery tests, water samples were
collected from the wells for laboratory testing. The test
results are briefly discussed under "Laboratory Testing" in
the following section of this report. The complete data
obtained from the chemical analyses performed on all water
samples collected during this investigation are included in
the report prepared by Luke-Dudek Engineers.
LABORATORY TESTING
A. Determination of Specific Retention
During our trenching operation, relatively undisturbed core
samples were collected in order to determine the specific
retention of the major soil types. 'The samples were satur-
ated in the laboratory and left to dry in a shady cool area
over a period of 1+ weeks. The samples were then weighed
wet, dried in an oven, and subsequently weighed dry. The
difference between the wet and dry weights was considered .
as the weight of the water retained. Specific retention is
defined as volume of water retained divided by total volume
of soil, and expressed as a percentage figure. The density of
water was taken to be 1 gram/cm , and the volume of the soil
sample was measured in the laboratory.
3
The specific retention of the Diablo Clay series and Las Flores
series was determined to 31%, and the specific retention of
the Friant rocky sandy loam group was determined to be 27.5%
(Refer to Table 1 on the following pagel.
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 15
Diablos
TABLE I
INCHES OF RETENTION
Sample Wet Dry Weight Specific Soil
Volye Weight Weight of Water Retention Moisture*
cm grams grams grams percent Capacity
& Las Flores 9.0 27.20 24.30 2.90 31.0 8.5 in.
Series
Friant rocky
sandy 11.33 30.60 27.50 3.10 27.5 7.6 in. loam series
*Derived by using 70 cm of effective evaporation depth, which was
obtained from Table 1-3, Harr (1962).
B. Determination of Water Quality
Water samples collected during our field investigation were.
sent to Environmental Engineering Laboratory in San Diego for
an evaluation of their total dissolved solids (TDS) content,
conductivity, and other chemical parameters. The test results
of the only existing well which is being used in the Buena
Vista basin (Caron's residence off the western end of Haymar
Drive) indicates a TDS content on the order of 1200 ppm. The
water sample collected from our exploratory well boring in the
same basin has a TDS content of approximately 5000 ppm. In the
Aqua Hedionda basin, water samples collected from existing
wells indicate a TDS range of 1300 ppm to 2000 ppm, and the
tests run on water samples collected from our well borings came
up with a TDS content of approximately 6000 ppm to 6600 ppm.
The complete water sample test data are included in the report
prepared by Luke-Dudek Engineers. It is noted that the high
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 16
TDS water samples collected from our exploratory well borings
were drawn from the alluvium, whereas the existing wells report-
edly penetrate the fractured basement rock aquifer (Kelly,
1980).
BASIC CLIMATOLOGIC DATA COLLECTION AND REDUCTION
A. Precipitation Data Analysis
The nearest rainfall gaging station to the project study area
is located at Palomar Airport. This particular station, how-
ever, has only 16 years of recorded precipitation data (County
of San Diego Department of Sanitation and Flood Control). In
order to obtain a longer rainfall record for our analysis,
these 16 years available data were compared and adjusted with
the 104-year rainfall record collected at the Escondido rain-
fall gaging station, which is located approximately 12 miles
inland from Palomar Airport.
A comparison of the two rainfall records yielded a correlation
of :y = 1.14 + 0.77~; where y = rainfall at Palomar Airport
and x = rainfall in Escondido (Figure VI). This linear re-
gression formula was used to construct a 104-year rainfall graph
for the Palomar Airport Rainfall Station (Figure V). The ad-
justed rainfall record for the project study area is presented
in Table 2.
Based on this adjusted 104-year precipitation record for the
project study area (Table 2). a rainfall graph has been con-
structed as shown on Figure V (Page 18). From this rainfall
graph, loo-, SO-, 40-, 30-, 25, 20-, 18-, and 1-year rainfall
events were extracted as shown on Table 3.
Project No. 14D3 Luke-Dudek Engineers 6/17/80
Rainfall Year
1875-1876 76- 77 77- 78
78- 79 79- 80
80- 81
81- 82 82- 83
83- 84
84- 85 85- 86
86- 87
87- 88
88- 89 89- 90 90- 91 91- 92
92- 93 93- 94
94- 95
95- 96 96- 97 97- 98
98- 99 1899-1900 1900-1901
01- 02 02- 03 03- 04
05- 06
04- 05
06- 07
07- 08 08- 09 09- 10
TABLE 2
ADJUSTED 104-YEAR RAINFALL
RECORD FOR PALOMAR AIRPORT STATION
Rainfall (Inches)
17.16 7.58
21.81
7.70
16.60
9.36
9.09 7.07 25.83
8.38
17.20
9.24
13.35 15.36 17.07 12.65 10.07 15.28
15.79
5.73
12.31
7.23
7.82
8.93 11.84 12.27
10.11 14.76
19.22 7.42
20.72 14.91 11.55 15.16 15.64
Rainfall Year
1910-1911
11- 12 12- 13 13- 14 14- 15 15- 16 16- 17
18- 19 17- 18
19- 20 20- 21 21- 22 22- 23 23- 24
24- 25 25- 26
26- 27
27- 28
28- 29 29- 30
30- 31 31- 32 32- 33 33- 34 34- 35 35- 36 36- 37 37- 38 38- 39 39- 40 40- 41
41- 42 42- 43 43- 44
44- 45
Rainfall
(Inches)
13.03
12.46
15.85 9.08
20.67 22.67 14.26
11.66
10.58 12.82
23.39 9.92
7.81
9.31
17.65 9.86
20.14 12.27 11.05 14.23 12.34 20.79 14.65
8.13 17.86 11.93
27.79 15.92
12.81
25.57 15.68
15.55 13.79 13.86 12.87
Rainfall Year
1945-1946 46- 47 41- 48 48- 49 49- 50 50- 51 51- 52
53- 54 52- 53
54- 55 55- 56 56- 57 57- 58
58- 59
59- 60
60- 61
61- 62
62- 63 63- 64
64- 65
65- 66 66- 67 67- 68 68- 69 69- 70
71- 72 70- 71
72- 73
73- 74
74- 75
75- 76
76- 71
77- 78
78- 79
Page 17
Rainfall
(Inches)
11.76
10.16 8.05 12.07
9.68
20.48 8.72
10.33 12.47 8.95
8.20 11.72 18.51
12.03 6.46
14.26 5.84
6.85 9.57 10.52
15.03
15.26
11.19 15.36 7.26 9.81 7.51 14.53 9.10 12.33 10.18 11.76
17.46 19.16
>
I
Page 18
U z - .
U
I I
D z
z m
Project No 14D3 Luke-Dudek Engineers
ui
I
. ..
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 19
EVENT
MONTH -
- Oct.
NOV . - Dee .
Jan.
- Feb.
Mar.
Apr .
-I ,, May
Jun.
Jul.
Aug .
Sep .
-
-
Total
NOTE : -
1-Yr
(in.)
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
TABLE 3
MONTHLY PRECIPITATION DATA
REPRESENTATIVE OF PRECIPITATION EVENTS
PALOMAR AIRPORT (1875 - Present)
18-Yr
(in.)
1.09
1.69
4.17
3.82
4.19
3.32
1.77
0.42
0.12
0.01
0.19
1.31
22.10
20-Yr (in.)
1.13
1.74
4.30
3.93
4.33
3.43
1.82
0.43
0.12
0.01
0.20
1.35
22.80
25-Yr (in.)
1.15
1.77
4.41
4.04
4.44
3.52
1.87
0.44
0.12
0.02
0.21
1.40
23.39
30-Yr (in.)
1.20
1.86
4.58
4.20
4.61
3.65
1.94
0.46
0.13
0.02
0.21
1.44
24.30
40-Yr (in.)
1.26
1.95
4.82
4.42
4.85
3.85
2.04
0.48
0.14
0.02
0.23
1.52
25.58
50-Yr
(in.
1.27
1.97
4.87
4.46
4.90
3.89
2.06
0.49
0.14
0.02
0.23
1.53
25.83
100-Yr
(in.)
1.37
2.12
5.24
4.80
5.27
4.18
2.22
0.52
0.15
0.02
0.24
1.65
27.70
The 1-Year precipitation event is be definitation 0.00 inches
will occur every year of 100% of the time. of precipitation, since 0.00 inches or greater of precipitation
These rainfall events were then combined and weighted according to
their probable occurrence during a 100-year rainfall cycle. For
example, a 25-year rainfall event is expected to occur four times
Project NO. 14D3 Luke-Dudek Engineers 6/17/80 Page 20
every 100 years; however, the four 25-year rainfall events
also include the 30-, 40-, 50-, and 100-year precipitation
events. Therefore, in order to determine the weighted amount
of rainfall for the 25-year rainfall event, the 30-, 40-, 50-,
and 100-year events must first be subtracted from.the 25-year
events, yielding an individual occurrence of 0.67 for the
25-year events. These individual occurrences are then divided
by the time interval (cycle) in which they occurred, which in
this case is 100 years. Thus, the weighted factor is calculated
to be 0.67/100 = 0.0067. Sample calculations determining the
weighting factors of each rainfall event used in our study are
presented in Table 4 below:
TABLE 4
WEIGHTING OF PRECIPITATION EVENTS
Cumulative No. Individual NO. Weighting of
of Occurrences of Occurrences Events
Events(Yr.1 in 100 years in 100 years Column 3/100
100
50
40
30
25
20
18
1
1.0
2.0
2.5
3.33
4.00
5.00
5.56
100
1.0
1.0
0.5
0.83
0.67
1.0
0.56
94.44
0.01
0.01
0.005
0.0083
0.0067
0.01
0.0056
0.9444
B. Evaporation Data Analysis
The evaporation data used for this study was taken from the
Lake Hodges evaporation station (California Department of
-
-, \
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 21
Water Resources, 1974), which is located approximately 14
miles to the southeast of the project study area. This is
the nearest evaporation station for which adequate recorded
evaporation data is available, and assumed to exhibit evapo-
ration characteristics similar to the project study area.
The evaporation of water from a pan has been found to be
greater than the actual evaporation from a reservoir or sat-
urated soil, and therefore potential evaporation can be com-
puted by multiplying standard pan coefficients by the pan
evaporation values provided in a particular evaporation sta-
tion's record. Estimated monthly potential evaporation values
have been computed using the Lake Hodges station data and a
pan coefficient of 0.7, as shown in Table 5 below:
TABLE 5
MEAN MONTHLY POTENTIAL EVAPOTRANSPIRATION
LAKE HODGES (1920 - Present)
- MONTH Oct. Nov. Dec. Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep.
P.E.T. 3.23 2.32 1.83 1.54 1.52 2.37 2.90 4.00 4.63 5.46 5.50 4.29 (in.)
- Total = 39.57 inches
C. Recharge Analysis
Rainfall infiltration results in groundwater recharge after evap-
oration and soil moisture capacity have been satisfied. Ground-
water recharge for each precipitation event is estimated by the
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 22
following "Water Budget" formula (Refer to Monthly Rainfall
Infiltration Calculation Sheets, Appendix F):
Ri = Pi + SRi - ROi - SDi - ET - SM
where, Ri = Recharge of i event
Pi = Precipitation of i event
SRi = Subsurface recharge of i event*
SDi = Subsurface discharge of i event*
ROi = Runoff of i event
ET = Potential Evapotranspiration
SM = Soil Moisture Holding Capacity
*NOTE: - SDi and SRi are assumed to be equal and will cancel each other.
The long term annual rate of groundwater recharge occurring in
the project study area was computed by the following formula,
and the results are presented in Table 6:
8
RL= (Ri) (Wi)
i=l
Where, RL = The long term annual rate of groundwater recharge
Ri = Recharge of the i event
Wi = Weighting of the i event
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 23
Event Year -
100
50
40
30
25
20
18
1
TABLE 6
LONG TERM ANNUAL GROUNDWATER RECHARGE
Cummulative Individual Weighted Inches
currences currences
NO. of OC- NO. of OC- Factor Infil-
Wi (in.) Ri (in.) tration
1.0
2.0
2.5
3.33
9.5
14.05
18.81
100
1.0 0.01
1.0 0.01
0.5 0.005
0.83 0.0083
4.0 0.0067
5.0 0.001
5.56 0.0056
0.9444 0.9444
4.23
2.68
2.50
1.60
0.97
0.55
0.06
0.00
Weighted
Infiltra-
tion(inches1 (Ri) (Wi)
0.0423
0.0268
0.0125
0.0133
0.0065
0.0055
0.0003
0.0000
Total = Long term annual groundwater recharge = 0.107 inches
= 0.009 acre-feet per acre per year
It is noted that this recharge estimate of approximately 0.009 acre-
feet per acre per year represents maximum recharge as runoff is com-
pletely ignored (assumed = 0). The estimated total annual recharge
for the Buena Vista basin study area has been computed to be approxi-
mately 72.0acre-feet, and for the Aqua Hedionda basin study area, the
annual recharge has been estimated to be approximately 19-lacre-feet.
However, as the eastern boundary of the Aqua Hedionda basin study area
is not a hydrologic boundary, an unknown amount of additional recharge
may flow across this boundary into the basin study area from the up-
stream located portions of the basin.
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 24
GROUNDWATER IN STORAGE
-
As a first step in estimating the amount of groundwater in storage
- in those portions of the Buena Vista and Agua Hedionda basins which
are located within the project study area, the total surface area
within each basin was determined. The basin boundaries for the
purpose of this investigation were provided by Luke-Dudek Engineers
and are outlined on Figure 11. By counting sections within each
-
- basin, it was determined that the interception areas of the Buena
- acres, respectively.
Vista and Agua Hedionda basin study areas are 8,000 acres and 2,120
- Groundwater storage estimates were then computed €or each basin
study area on the basis of the above discussed interception areas
and the subsurface information derived from our exploratory well
Dorings, the El Camino Real bridge foundation boring logs provided
by Lough 119801, and the verbal well log information of the existing
-
-8 mobile home park water well (located on the east side of El Camino
- In addition, our groundwater storage computations also relied on
', Real, opposite Calaveras Road) provided by Mr. Allan Kelly (1980).
the information derived from the seismic traverses and estimated
formational unit thicknesses based on the data provided by Wilson
(1972) and our own field reconnaissance mapping. -
A. Agua Hedionda Basin Study Area
In the Agua Hedionda basin study area, the Quaternary alluvial
deposits cover an area of approximately 372 acres along the
bottom of the basin, and extends to a depth of approximately
20 feet (Appendices A and D). Based on our examination of the
road cut exposures and the information supplied by Wilson (1972),
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 25
an average thickness of 20 feet is estimated for the residual
soil mantle (i.e. the Diablo Clay series) and the underlying
Santiago Formation units which cover the sloping areas within
the Agua Hedionda basin study area. The formational materials
also underlie the Quaternary alluvial deposits in the basin
to a depth of approximately 80 feet (Lough, 1980, and Kelly,
1980). Estimated porosities of 30% for the saturated Quaternary
alluvial and 32% for the Santiago Formation were used in our
groundwater storage calculations. These porosity values were
obtained from a "Porosity Versus Seismic Wave Velocity Plot"
(Zohdy, et.al., 1974) by correlating the seismic velocities
derived from our seismic traverses (Appendix D) to the estimated
porosities shown on this plot.
Storage within the basement complex rock units which underlie
the entire basin study area was determined by using the crys-
talline bedrock storage parameters discussed by Mayo and Lower
(1976). In San Diego County, most groundwater circulation and
storage in fractured crystalline bedrock occurs within 400 feet
of the surface (Mayo and Lower, 1976), and a specific yield
(the amount of water per unit volume of rock that such rock
will yield) of 0% to 3% may be used (Davis and Dewiest, 1966,
and Mayo and Lower, 1976). For the purpose of our groundwater
storage computations, a "thickness" of 300 feet of fractured
basement rocks and a specific yield (effective porosity) of 1%
was used, though average porosities are likely much lower.
Storage within the Agua Hedionda basin study area is estimated
to be on the order of 29,000 acre-feet.
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 26
B. Buena Vista Basin Study Area
The Buena Vista basin study area is much larger than the Aqua
Hedionda basin. Quaternary alluvial deposits along its bottom
cover an area of approximately 211.5 acres and extend to a depth
of approximately 20 feet as encountered in the well borings
(Kppendix A). The residual soil mantle (Diablo clay series and
Las Flores series) and underlying units of the Santiago Form-
ation have an estimated total thickness on the order of 20 feet
based on our inspection of road cuts and the information pre-
sented by Wilson (1972). An estimated thickness of 40 feet has
been used for the Santiago Formation units which underlie the
Quaternary alluvial deposits along the bottom of the basin.
Although there is no subsurface information which supports this
estimate, it is our judgement that the 40 feet is conservative
and adequate for the purpose of groundwater storage computations
based on the relatively small size of the basin and the shallow
depth of the basement complex rocks within the basin (dacite
outcrops are exposed at the surface on the South Coast Asphalt
plant property).
The same porosities of 30% for the saturated alluvium and 32%
for the Santiago Formation were used in our groundwater storage
calculations for the Buena Vista basin. Furthermore, the same
storage parameters for the fractured crystalline basement rocks
as discussed on the preceding page were also used in our ana-
lysis of groundwater storage for this basin. Estimated ground-
water storage within the Buena Vista basin study area is
calculated to be on the order of 79,000 acre-feet.
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 27
C. Saltwater in Storage within the Basin Study Areas
Salt marshes comprise the westernmost portions of the basin
study areas as indicated by the presence of saltwater lagoons
in each basin. Salt marsh-type vegetation (e.g. Saltwart,
Marsh Rosemary and Marshgrasses) indicate that a saline environ-
ment exists a significant distance landward from the coastline.
Water in the salt marsh areas can be construed for all intents
and purposes to be "saltwater", i.e. water with 10,000+ parts
per million of total dissolved solids content.
The salt marsh areas comprise approximately 2,755 and 689 acres,
respectively, for the Buena Vista and Agua Hedionda basin study
areas. Saltwater in storage within the Buena Vista basin study
area was calculated to be approximately 27,166 acre-feet. The
saltwater in storage within the Agua Hedionda basin study area
is estimated to be 18,406 acre-feet, or approximately 63% of
the total storage within the basin study area. It is noted that
the Agua Hedionda basin study area is dominated by the basin
bottom which contains most of the storage, and which is almost
entirely occupied by salt marsh.
The saltwater in storage in both basin study areas is unusable
for domestic or agricultural use and should be subtracted from
the totalgroundwater in storage estimates for both basin study
areas in order to properly evaluate the amount of "usable" water
in storage. It is also noted that any precipitation occurring
in the salt marsh areas is rendered unpotable immediately, and
should therefore not be used in calculating safe yield of the
basin study areas.
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 28
GROUNDWATER SUBSURFACE FLOW
Subsurface flow of groundwater within the basin study areas can be
estimated by using the transmissivity values obtained from our well
tests (Appendix E) and the hydraulic gradient established by the
static water levels in the exploratory well borings (Appendix A).
For this purpose, Darcy's formula: Q = KAi has been used, where Q
represents the estimated amount of subsurface flow; K = permeability,
which is equal to the transmissivity divided by the aquifer thick-
ness; A = cross-sectional area of the basin study area: and i = the
hydraulic gradient, which is determined by dividing the difference
in the static water levels by the length of the flow path.
For the Agua Hedionda basin study area, the cross-sectional area:
A = 300,000 ft2; the hydraulic gradient: i = 0.1; and the permea-
bility: K = 0.0023 ft/day. Thus, the amount of subsurface flow:
Q- was calculated to be approximately 6.21 ft /day = 2,266.7 ft /year=
0.05 acre-feet per year.
3 3
For the Buena Vista basin study area, our calculations indicated an
estimated amount of subsurface flow of approximately 0.02 acre-feet
per year.
The subsurface flow estimates indicate that the groundwater is not
flowing through the basin sedimentary deposits at any appreciable
rate. It is our judgement that the groundwater flows primarily
through the upper portions of the fractured crystalline basement
rock complex underlying both basins study areas. This tends to
explain the high yield of the Kelly well and the mobile home park
wells located off of El Camino Real which reportedly penetrate the
crystalline basement rock aquifer. Furthermore, the fact that water
samples collected from those existing wells have a TDS content on
the order of 4,000 part per million less than the water samples
Project No. 14D3 Luke-Dudek Engineers 6/17/80 Page 29
collected from our exploratory well borings (refer to Luke-Dudek
Engineers report), which only penetrate the alluvial deposits, also
appears to indicate that the majority of groundwater within the
basins is flowing within the fractured basement rock aquifer under-
neath the alluvial materials.
SAFE YIELD
The safe yield of a basin is defined as the amount of water that
can be safely removed from the basin through pumping of wells located
in that particular basin without "mining" of the available ground-
water in storage. When groundwater is extracted at rates in excess
of the safe yield of that particular basin, groundwater mining
occurs, resulting in the eventual depletion of the local groundwater
resources.
Safe yield for the purpose of this report, is determined by multi-
plying the surface area of the freshwater portion of. the study area
(in acres) by the average annual recharge of the basin study areas
(in acre-feet per acre). The safe yield of the Buena Vista basin
study area was found to be 47.21 acre-feet per year, whereas the
safe yield for the Agua Hedionda basin study area was calculated
to be 12.9 acre-feet per year.
Project No 14D3 Luke-Dudek Engineers 6/17/80 Page 30
CONCLUSIONS
1. The groundwater in storage in the Buena Vista basin study area
is estimated to be approximately 79,000 acre-feet, and for the
Agua Hedionda basin study area it is estimated to be 29,000
acre-feet. It should be noted that these storage estimates
include the estimated amounts of saltwater in storage in each
basin study area, which is approximately 27,166 acre-feet and
18,406 acre-feet, respectively, within the Buena Vista and Agua
Hedionda basin study areas.
2. The safe yield of the freshwater portions of each basin study
area has been estimated to be approximately 47.2 acre-feet per
year for the Buena Vista basin study area, and approximately
12.9 acre-feet per year for the Agua Hedionda basin study area.
3. The transmissivities of the alluvial deposits and underlying
formational materials of the Santiago Formation within both
basin study areas are on the order of 0.2 feet2 per day, which
accounts for the fact that the majority of the wells drilled
in these basins have practically been failures(kelly, 1980).
It is noted that our test of well boring No 2 in the Agua
Hedionda basin study area revealed the presence of porous,
moderately permeable lenses or strata, which are believed to
represent paleo stream channels.
4. The transmissivity values obtained from our well tests(Appen-
dix E) indicate that groundwater recharge within the basin
study areas does not flow through the alluvial deposits;
Project No 14D3 Luke-Dudek Engineers 6/17/80 Page 31
Subsurface flow of groundwater probably occurs in a general
east to west direction underneath the alluvial deposits, and
most likely occurs within the upper portions of the fractured
basement rock complex underlying the basin study areas.
5. The presence of a losing stream in the Buena Vista basin study
area indicates that there probably is less storage in that
basin than what our calculations indicate, as the water level
is below stream level.
6. Both basin study areas terminate at their western end in salt
marshes as indicated by the extensive growth of marsh grass,
saltwart, and marsh rosemary, which are indicative of a salt-
water environment. The high TDS content(on the order of 6000
ppm) obtained from the water samples collected from the explo-
ratory well,borings, however, are not necessarily considered
as an indication of saltwater intrusion. We suspect that this
high TDS content reflects the leaching process of salts within
the basimsediments. Our suspicion finds at least partial
support in the fact that the chlorine content of the well
water samples does not match the chlorine content of sea water
according to Mr. Bob Chambers of Environmental Engineering Lab-
oratoryCRefer to chemical analyses results - Luke-Dudek Engin-
eers report).
SUPPLEMENT TO HYDROGEOLOGIC INVESTIGATION
ROBERT CHAN
Civil Eng1ne.r
8624 CUYAMACA STREET
SUITE F
SANTEE, CALIFORNIA 92071
TEL: (714) 449-5900
ALL REPORTS APE SUBMITTED AS THE CONFIDENTIAL PROPERTY OF CLIENTS. AUlHORlZATION FOR PUBLIC4TION OF OUR REPORTS. CONCLUSIONS, EXTRACTS
FROM OR REGARDING THEM IS RESERVED PENDING OUR WRITTEN APPROVAL AS A MUTUAL PROTECTION TO CLIENTS. THE WBLlC AND OURSELVES.
October 31, 1980
Mr. Greg Luke Luke-Dudek Civil Engineers
700 Second Street, Suite E Encinitas, California 92024
Subject: Project NO. 14D3
relative to our preliminary hydrogeologic Response to comments raised by the CRWQCB
investigation report of the Buena Vista And Agua Hedionda basin study areas
Carlsbad area, San Diego County, California
Dear Mr. Luke:
This is to acknowledge receipt of your letter dated August 26, 1980,
Water Quality Control Board addressed to Your office, dated August
and the accompanying copy of a letter from the California Regional
22, 1980. a result of our subsequent discussions regarding the project, we have scheduled a meeting with representatives of the
CRWQCB to resolve their concerns.
more detail in your letter and at the meeting with Messrs. Art Coe
In response to the questions raised by the CRWQCB, as discussed in
and Ladin Delaney and yourself on October 24, 1980, we would like to present the following comments with respect to the question concerning the safe yield of the Aqua Hedionda Basin. We should emphasize that
basin. The safe yield computation presented in our report pertains our report did not present any safe yield estimates for the entire
within the basin study area, which encompasses approximately 2,120
only to the .amount of recharge from precipitation which occurs
acres as defined by your office.
In this context, please refer to Page 23 of our report which states: "...the eastern boundary of the Aqua Hedionda basin study area is not a hydroLogic boundary....". Furthermore, on Page 24 we stated
basin study areas are 8,000 acres and 2, 120 acres, respectively." that "...the interception areas of the Buena Vista and Agua Hedionda
promise approximately 2,755 and 689 acres, respectively for the
Subsequently, on Page 27 we stated that "The salt marsh areas com-
Buena Vista and Agua Hedionda basin study areas." This leaves ap- proximately 1,431 acres of rainfall interception area within the
Agua Hedionda basin study area to provide on-site fresh water recharge.
-
reject NO. 14D3 Luke-Dudek Engineers 10-31-80 Page 2
Using a calculated annual recharge rate of 0.009 acre-feet a safe yield of 12.9 acre-feet per year was calculated for the Hedionda basin study area.
project (presumably the work performed by Dr. Huntley referred to
Dr. Huntley's report, prepared for the Shadow Ridge Water Reclamation
in Your letter) was concerned with the entire Agua Hedionda Hydrologic sub-unit, encompassing an area of apporximately 18,963'
acres. In his report, Dr. Huntley assumed a minimum soil moisture
capacity of 2 inches and calculated a maximum recharge rate of 0.06 acre-feet/acre/year to yield a maximum calculated.recharge of 1, 140
acre-feet per year for the entire Agua Hedionda Hydrologic sub-unit.
The actual soil moisture holding capacity, determined through our
trenching operations and laboratory work, was 8.2 inches. This higher soil moisture capacity decreases the estimated recharge rat.= of 0.06 acre-feet/acre/year to 0.009 acre-feet/acre/year and yields a recharge.of approximately 171 acre-feet per year for the entire Aqua Hedionda Hydroloqic sub-unit.
IC should be noted that tne rechdrgb computations presented in our report as well as in the above mentioned report prepared by Dr. Huntley pertain only to groundwater recharge derived from precipitation and exclude any recharge from stream seepage and/or entire
Agua Hedionda Hydrologic sub-unit.
With respect to current groundwater usage in the Agua Hedionda basin,
Park is for irrigation of the golf course and is estimated to be on it should be noted that the water use at Rancho Carlsbad Mobile Home
the order of 300 acre-feet per year. Assuming that at least one-
third (and probably more) is returned to the groundwater system,
acre-feet per year. The combination of recharge from precipitation the actual consumptive use is estimated to be on the order Of 200
(estimated to be 171 acre-feet/year), streamflow infiltration (which
probably represents the major source of recharge to the wells in the
wells in the basin without producing a decline in the Water table. basin), and from up-gradient irrigation would easily Supply the existing
With respect to your question concerning our groundwater subsurfwe
flow estimates, we would like to refer you to Pages 28, 29, 313 and 31 of our report, which clearly indicate that the computed subsurface
flow rates of 0.05 acre-feet/year and 0.02 acre-feet/year for the
Agua Hedionda and Buena Vista basin study areas, resPecttvelY, 9 represent the estimated amount of subsurface flow occurfng withln
materials of the Santago Formation). No transmisstvity could be the sedimentary deposits (i.e. the alluvial deposits and fonational
determined for the fractured crystalline bedrock aquifer based on the
subsurface data collected during our investigation. It is Our OPhion, Aqua Hedionda~and Buena yista basins occur within.the upper portions
of the underlying fractured basement rock complex.
In order to estimate the underflow through the fractured Crystalline .. ..
ALLIED GEOTECHNICAL ENGINEERS INC. - 8624 Cuyamaca Street, Suite F, Santee. California 92071
Project No. !4D3 Luke Dudek Engineers 10-31-80 Page 3
bedrock, a cross-section was selected at the topographic constriction that occurs in the basin along El Camino Real. The subsurface
of 0.01. Groundwater flow through fractured crystalline rock gradient, as determined during our investigation, is on the order
has been noted to be a shallow depth phenomenon. Estimates are that it occurs within 400 feet of the crystalline rock surface
overburden materials). (i.e. the interface between the relatively anweathered bedrock and
a typical crystalline hydraulic conductivity of 1 foot/day, Darcy's Selecting a cross-section at the topographic constriction, and using
Law: Q=KAi (where (.)=amount of flow: A=cross-sectional flow area;
a figure of 134.16 acre-feet per year of throughflow beneath the and i=hydraulic gradient) was applied. This calculation yields
Aqua Hedionda Study area. This estimate can be considered to be
the maximum amount of water flowing through the crystalline rock in this area, because of the nature of the calculations performed.
The same calculations were performed for the Buena Vista Basin and throughflow of 301.86 was obtained.
at your convenience. If you have any questions, please feel free to .contact our office
Respectfully submitted,
Staff Hydrogeologist
Reviewea::%y,
CEG #lo12
tS
ALLIED GEOTECHNICAL ENGINEERS INC. - 8624 Cuyamaca Street. Suite F, Santee, California 92071