The Effects of Current Artificial Recharge Practices on...

ARTIFICIAL RECHARGE AS POSSIBLE CAUSES OF OBSERVED

LONG –TERM CHANGE IN TRANSMISSIVITY OF THE SAN PEDRO FORMATION AQUIFERS, CENTRAL BASIN OF THE GREATER LOS ANGELES BASIN, CALIFORNIA

____________________________________

A Thesis

Presented to the

Faculty of

California State University, Fullerton

In Partial Fulfillment

Of the Requirements for the Degree

Master of Science

In

Geology

By

Sean Hunt

Approved by: Dr. William Laton Date Department of Geological Sciences Dr. John Foster Date Department of Geological Sciences Dr. Jeff Kuo Date Department of Civil and Environmental Engineering

ii

ABSTRACT Transmissivity values for the aquifers of the Upper San Pedro Formation of the Central Basin

of the greater Los Angeles Basin have increased since the implementation of artificial recharge.

To determine if the water used for artificial recharge is related to the observed increase in

transmissivity, a groundwater data collected from the Water Replenishment District of

Southern California (WRD) and the United States Geological Survey (USGS) from 1995 to

2002 was compared to the historical groundwater data collected by Piper and Garrett in 1953.

The results indicate that the hydrochemical facies of the groundwater of the aquifers of the

upper San Pedro Formation have been altered by the implementation of artificial recharge

particularly by water imported from the Colorado River and Northern California, not

reclaimed waters. These waters are characterized by higher calcium, sulfate, and total dissolved

solids (TDS). Although some mineral dissolution may be occurring, the evidence does not

support this process as a mechanism for increased transmissivity. Therefore, the increase in

transmissivity is more likely due to the physical changes to the aquifers and aquitards of the

Central Basin caused by extensive drilling, seasonal fluctuations and long-term over-pumping,

rather than a chemical change.

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TABLE OF CONTENTS ABSTRACT .......................................................................................................................................... ii

LIST OF FIGURES ............................................................................................................................ vi

LIST OF TABLES ............................................................................................................................... viii

ACKNOWLEDGMENTS ................................................................................................................ x

Chapter 1. INTRODUCTION .................................................................................................................. 1

2. DESCRIPTION OF AQUIFER SETTINGS ................................................................... 7

Basin Description ............................................................................................................... 7 Geological Description ...................................................................................................... 9 Basin Aquifers .................................................................................................................... 13

3. PREVIOUS WORK ................................................................................................................. 16

4. CENTRAL BASIN GROUNDWATER CONDITIONS .............................................. 20

Groundwater Recharge (Native/Artificial).................................................................... 20 Central Basin Groundwater Budget ................................................................................ 25 5. METHODS AND RESULTS ................................................................................................ 28

Transmissivity Map and Concentration Maps ............................................................. 28 Mixing Graphs ................................................................................................................... 30 Results .................................................................................................................................. 40 6. DISCUSSION............................................................................................................................ 49

Physical Indicators ............................................................................................................ 49 7. CONCLUSIONS ...................................................................................................................... 54

Conclusions ........................................................................................................................ 54

8. FUTURE RESEARCH Future Research .................................................................................................................... 56

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APPENDIX A CURRENT AND HISTORICAL CONCENTRATION GRAPHS ......... 57 Figure 1 – Site Map indicating the well location of the wells installed by the USGS and WRD from 1995 to 2002. ........................................................................................................... 58 Figure 2 -Current concentration of calcium (mg/L) within the groundwater of the aquifers of the San Pedro Formation (Contour Interval = 10 mg/L) ............................... 59 Figure 3 – Current Concentration of Magnesium (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Contour Interval = 5mg/L). ................................ 60 Figure 4 - Current Concentration of Sodium (mg/L) of the groundwater of the San Pedro Formation (Contour Interval = 10 mg/L) ......................................................... 61 Figure 5– Current Concentration of Bicarbonate (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Contour Interval = 10 mg/L). ............................ 62 Figure 6 - Current Concentration of Chloride (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Contour Interval = 10 mg/L) ............................. 63 Figure 7 – Current Concentration of Sulfate (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Contour Interval = 5 mg/L). ............................... 64 Figure 8 - Current Concentration of Total Dissolved Solids (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Contour Interval = 10 mg/L) ....................... 65 Figure 9 – Site Map indicating the well location of the wells used in Poland’s work Native and Contaminated Groundwater from Torrance to Santa Ana (Piper and Garrett, 1953. ........... 66 Figure 10 - Historical Concentration of Calcium (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953) ........................................ 67 Figure 11 – Historical Concentration of Sodium (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953). ........................................ 68 Figure 12 - Historical Concentration of Magnesium (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953) ........................................ 69 Figure 13– Historical Concentration of Bicarbonate (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953). ....................................... 70 Figure 14 - Historical Concentration of Chloride (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953) ......................................... 71 Figure 15 – Historical Concentration of Sulfate (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953). ........................................ 72 Figure 16 - Historical Concentration of Total Dissolved Solids (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953) ............ 73

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APPENDIX B MIXING GRAPHS ................................................................................................ 74 Figure 1 – Magnesium concentrations found in the nested groundwater monitoring wells for the Montebello Forebay Area of the Central Basin....................................................... 75 Figure 2 – Bicarbonate concentrations found in the nested groundwater monitoring wells for the Montebello Forebay Area of the Central Basin. ................................ 76 Figure 3 – Magnesium concentrations found in the nested groundwater monitoring wells for the Northern Pressure Area of the Central Basin. ......................................................... 77 Figure 4 – Bicarbonate concentrations found in the nested groundwater monitoring wells for the Northern Pressure Area of the Central Basin. ................................... 78 REFERENCES .................................................................................................................................... 79

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LIST OF FIGURES

Figures Page Figure 1- Los Angeles Central Basin Site Location Map .............................................................. 2 Figure 2 – Changes in Transmissivity Map...................................................................................... 6 Figure 3 - Hydrologic Sub-divisions of the Central Basin ............................................................ 8 Figure 4 - Site Map ............................................................................................................................... 11 Figure 5 - Generalized cross-section of the Central Basin ........................................................... 12 Figure 6 - Tritium concentrations in groundwater sampled in the Los Angeles ........................................................................................................................................... 18 Figure 7 Groundwater Elevation Contour Map for Fall 2001 ................................................... 21 Figure 8 - Generalized model of the hydrological system of the native and artificial recharge of the aquifers of the Central Basin, Los Angeles, California ...................................... 22 Figure 9 – Comparison of anion, cation and pH concentrations of Piper and Garrett’s (1953), Whittier Narrows, the Spreading Centers (Rio Hondo and San Gabriel) of the Montebello Forebay. ................................................................................................................ 24 Figure 10 – Comparison of total dissolved solids (TDS) concentrations of Piper and Garrett’s (1953), the Spreading Centers (Rio Hondo and San Gabriel) and the Montebello Forebay. ........................................................................................................................... 25 Figure 11 - Sulfate concentrations found in the nested groundwater monitoring wells for the Southern Pressure area of the Central Basin .................................................................... 34 Figure 12 - Sulfate concentrations found in the nested groundwater monitoring wells for the Northern Pressure area of the Central Basin. .................................................................... 35 Figure 13 – Calcium concentrations found in the nested groundwater monitoring wells for the Montebello Forebay of the Central Basin. ........................................................................ 36

vii

Figure 14 – Calcium concentrations found in the nested groundwater monitoring wells for the Northern Pressure Area of the Central Basin. ................................................................. 37 Figure 15 – Sodium concentrations found in the nested groundwater monitoring wells for the Montebello Forebay of the Central Basin. ........................................................................ 38 Figure 16 – Sodium concentrations found in the nested groundwater monitoring wells for the Northern Pressure Area of the Central Basin. ................................................................. 39 Figure 17 - Comparison of Historical and the Present Average Groundwater Chemical Signatures in the Montebello Forebay ............................................................................ 41 Figure 18 – Comparison of Historical and the Present Average Groundwater Chemical Signatures in the Northern Pressure Area ..................................................................... 42 Figure 19 – Current pH levels of the groundwater of the Aquifers of the San Pedro Formation .............................................................................................................................................. 44 Figure 20 - Sulfate vs. Chloride Concentrations found in the nested groundwater monitoring wells in the Southern Pressure Area of the Central Basin. ...................................... 47 Figure 21 – Central Basin San Pedro Formation Aquifer Piper Diagram. ................................ 48 Figure 22 – Generalized Cross-Section/Screen Interval ion ....................................................... 51 Figure 23 – Aquitard Thickness Map ............................................................................................... 53

viii

LIST OF TABLES Table Page 1 – Average Annual Water Balance 1970/71 – 1999/2000 (afy); 2000/01 Water Budget (afy). ......................................................................................................................................... 26 2 – Endmemebers – The concentration of the each of the analytes for the water entering into the Central Basin ........................................................................................................................ 32 3 - Represent the average concentration for each of the analytes within each of the four hydrochemical facies of the Central Basin. ............................................................................. 33

ix

With thanks to

Dr. William Laton Dr. John Foster

Dr. Jeff Kuo Dr. Diane Clemens-Knott Ted Johnson (WRDSC)

Michel Land (USGS) Rene Perez

Otto Figueroa and

Dr. Grace J. Fu

for their contributions and support.

1

CHAPTER 1

INTRODUCTION The demand for fresh water began to exceed the supply of surface water and shallow

groundwater as the land use within the Los Angeles Region changed from primarily agriculture

to urban residential and industrial. The completion of the Los Angeles aqueduct through the

San Fernando Valley in 1926 increased the supply of fresh water to the Los Angeles Region

(LARWQCB, 1989). Even with the additional water provided by the Los Angeles Aqueduct,

in the 1940s groundwater pumping had lowered the water table below sea level and altered the

groundwater flow dynamics of the Los Angeles Basin (Figure 1) (Poland et al., 1959a).

In 1948, additional water was delivered to the Los Angeles region via the Colorado River

Aqueduct, and artificial recharge with imported water in the Montebello Forebay began during

1949. Prior to artificial recharge, groundwater recharge of the Central Basin was dependent

upon surface water from inflow Los Angeles, Rio Hondo, and San Gabriel Rivers, surface run-

off and the groundwater underflow from the San Gabriel Basin to the north.

2

Figure 1 – Los Angeles Central Basin Site Location Map. CB = Central Basin; WCB = West Coast Basin; HB = Hollywood Basin; OC = Orange County; SGB = San Gabriel Basin; SFB = San Fernando Basin; SG = San Gabriel Mountains; MH = Merced Hills; PH = Puente Hills; NIFZ = Newport Inglewood Fault Zone; LAR = Los Angeles River; RHR = Rio Hondo River; SGR = San Gabriel River.

Despite the additional imported water, it was not until the responsibility for the protection and

management of groundwater of the Central and West Coast Basins was placed under the

direction of the newly formed Water Replenishment District of Southern California (WRD) in

1959 that over-drafting of the aquifers ceased. By reducing the overall pumping of

groundwater and increasing the volume of Colorado River water placed into the spreading

3

centers, WRD was able to increase and stabilize groundwater elevations throughout the Los

Angeles Basin (Riechard et al., 2002). However, the demand placed upon the groundwater

resources of the Los Angeles Basin still outweighed the supply.

Reclaimed water was introduced as an alternative source of groundwater recharge in

1961 and has increased from 5% to nearly 40% of total water recharged into the Montebello

Forebay (Water Replenishment District’s Regional Groundwater Monitoring Report Water

Years 1971-72 through 2001-2002). Reclaimed water is supplied by three Water Reclamation

Plants (WRP): Whittier Narrows WRP, San Jose Creek East and West WRP, and Pomona

WRP. In 1970, the State Water Project was completed and began delivering an additional 1.9

billion liters (430 million gallons) a day to the City of Los Angeles. With the exception of

seasonal fluctuations as observed by Bawden et al. (2001), the stabilization of the groundwater

levels has been achieved through the management of pumping and the addition of imported

and reclaimed water.

Though numerous studies have been conducted on possible health effects of using

reclaimed water (Toze et al., 2004; Schroeder and Andres, 2003; Dilon, 2002; Sumner and

Bradner, 1996; Sloss et al., 1994; Wilson et al., 1993; Asano, 1992; Bull et al., 1990; and Roberts

and Reinhard, 1982), the feasibility, groundwater “flow paths” and capacity of recharge basins

(Avisar and Clark, 2005; O’Reilly, 2004; Leserman and Ferry, 1997; Davisson et al., 1996;

Guymon et al., 1992; and Brose and Dozer, 1989) saltwater intrusion (Kulshan, 2002); and the

effects of seasonal groundwater fluctuations on tectonic movement within the Los Angeles

Basin (Bawden et. al., 2001), no studies have investigated the potential for artificial recharge to

induce mineral precipitation or dissolution and thereby affect the transmissivity of the aquifers

of the San Pedro Formation in the Los Angeles Basin.

4

As artificial recharge has increased in use globally, studies investigating the effects of

artificial recharge (Guo and Wang, 2004; Stuyfzand and Juhasz-Holterman, 2004; and Rinick-

Pfeiffer et al., 2002) on the distinct zones that have cation and anion concentrations

characterized within the defined composition categories known as the hydrochemical facies of

the groundwater has also increased (Freeze and Cherry, 1998), Such scientific studies have not

yet be compiled for the Central Basin. In addition, there have been no studies that have

investigated the possible degradation of the aquifers through mineral dissolution or

precipitation induced by the practice of artificial recharge and how this affects the hydrologic

conductivity of the aquifers within the Los Angeles Central Basin.

Figure 2 shows a plot of the difference between the transmissivity values recorded in

California State Departments of Water Resources Planned Utilization of the Ground Water Basins of

the Coastal Plan of Los Angeles County Bulletin 104A (commonly referred to as Bulletin 104A)

(DWR, 1961) to the transmissivity values observed today. In the Montebello Forebay,

transmissivity values have increased anywhere from 1,736 square meters per day (m2/day)

(14,000 gallon per foot per day (g/ft/d)) to 12,400 m2/day (100,000 g/ft/d). Along the

boundary between the Montebello Forebay and the Northern Pressure Area, transmissivity

values have increased a maximum of 24,304 m2/day (196,000 g/ft/d).

This paper presents evidence that artificial recharge of the Central Basin may have

altered the native hydrochemical facies of the Upper San Pedro Formation fresh water

aquifers. The objective of this thesis is to determine if the alteration of the native

hydrochemical facies induced by the practice of artificial recharge is directly related to the

observed increases in Upper San Pedro Formation aquifers transmissivity (see Figure 2) within

the Montebello Forebay and the Northern Pressure Area of the Central Basin.

5

Data collected by Piper during the 1950s (Piper and Garrett, 1953), the United States

Geological Survey (USGS) and the WRD between 1995 and 2003 (Riechard et al., 2003; and

Riechard et al., 2002), and the City of Whittier between 2000 and 2002 (City of Whittier Water

Quality Flyer, 2000 & 2002), were used in this study to model the hydrochemical conditions of

the Central Basin. The results of the modeling were used to produce cation-anion

concentration contour maps and mixing plots. The maps and graphs were used to determine

if mineral dissolution/ precipitation is occurring in the fresh water aquifers of the Upper San

Pedro Formation and therefore resulting in the observed change in transmissivity.

6

Figure 2 –Change in Transmissivity Map – Represents the difference in the values of transmissivity reported in Bulletin 104A and the transmissivity values recorded in well completion logs between 1990 and 2000 (WRD Files).

7

CHAPTER 2

DESCRIPTION OF AQUIFER SETTINGS

Basin Description

The Los Angeles Coastal Plain is the region bounded on the northwest by the Santa

Monica Mountains, on the north by the San Gabriel Mountains, on the east by the Puente

Hills, and the Pacific Ocean on the south and southwest. This area is divided into four

groundwater basins: Santa Monica, Hollywood, Central Basin and West Coast Basin (Riechard

et al., 2002; and DWR, 1961) (Figure 1).

The Central Basin is the largest basin within the Los Angeles Coastal Plain, covering

approximately 717 square kilometers (227 square miles). The Central Basin is by the

Hollywood Basin to the north; the Elysian, Repetto, Merced and Puente Hills (listed from

north to south) to the northeast; the Newport-Inglewood Fault Zone to the west and

southwestern Orange County to the east. The Newport-Inglewood fault zone is considered

the hydrologic boundary between the Central and West Coast Basin (Riechard et al., 2003; and

DWR, 1961).

The Central Basin has five sub-divisions: Los Angeles Forebay, Montebello Forebay,

Whittier Area, Northern Pressure Area, and Southern Pressure Area (Figure 3). The

designation of the boundary between the Los Angeles and Montebello Forebays or the “non-

pressure area” and the “pressure area” that lies to the south of the two Forebays, was first

noted by Mendenhall (1905a) and was later delineated by the California Department of Water

8

Resources Bulletin 104A (DWR, 1961). This boundary represents a change in hydrological

parameters of the underlying aquifers from a unconfined (non-pressure area) to a confining

aquifer system (pressure area). The Central Basin aquifers become deeper toward the south

from the Montebello Forebay to the Southern Pressure Area. Therefore, induced by ancient

oscillating shorelines, the aquitards between the aquifers of the San Pedro Formation, increase

in thickness and are more continuous within the pressure areas of the Central Basin.

Figure 3 - Hydrologic Sub-divisions of the Central Basin; Los Angeles Forebay, Montebello Forebay, Whittier Area, Northern Pressure Area, and the Southern Pressure Area. (NIFZ = New Port Inglewood Fault Zone)

9

Geological Description

Nearly continuous block downwarping of the Central basin and uplift of the hills of

the Los Angeles basin occurred until the mid-Miocene. Since that time the Central Basin has

experienced approximately 7.25 vertical kilometers (km) (4.5 vertical miles (mi)) of subsidence,

over a horizontal distance of 12.8 km (8 mi) (Yerkes et al., 1965). The depth of the

embayment increased by approximately 1.83 km (1.14 mi), with up to 1.53 km (0.96 mi) of

organic rich sediment, during the Late Miocene to Early Pliocene (5.3 ma) (DWR, 1961).

Rapid uplift of the marginal blocks at the end of the Pliocene (1.6 ma) , brought about by a

rapid transition from extension to oblique contraction and the deposition of large volumes of

coarse sediments in both the newly formed San Gabriel Basin and the Central Basin (Wright,

1991; Yerkes et al., 1965; and DWR, 1961).

During the Pleistocene, shallow basin conditions caused deposition to be more

responsive to sea-level change. In addition, rapidly uplifting mountains to the east formed

alluvial plains that moved the shoreline progressively to the west and south (Quinn, 1992).

Rivers, such as the ancestral San Gabriel and Rio Hondo, transported sand, gravel, cobble and

boulder sized sediment from the igneous and metamorphic rocks of the San Gabriel and San

Bernardino Mountains (Moran and Wiebe, 1992). Clastic sediments were effectively trapped

by uplift along the Newport-Inglewood Fault Zone (Quinn, 1992; and Harding, 1973).

The lower San Pedro Formation (early Pleistocene) is a sequence of coarse sands and

gravels interbedded with lenses of silt and clay is called the Sunnyside Aquifer (Callison, 1992).

The sediments of the Late Pleistocene to Holocene represent the transition from inner neritic

to nonmarine deposition (Callison, 1992) of unconsolidated sands, gravels, silts, clays and

marine sediments that make up the Upper San Pedro Formation aquifers (Silverado, Lynwood,

10

Jefferson, Hollydale) (Figure 4 and 5). Core samples collected by the USGS (Riechard et al.,

2002) indicate that the general mineral assemblages of the Lower and Upper San Pedro

Formation include plagioclase feldspar, potassium feldspar, quartz, mica, calcite, hornblende,

chlorite gypsum, kaolinite, smectite, and sepiolite at various percentages throughout the basin.

If mineral dissolution is occurring in the Montebello Forebay, increases in bicarbonate,

sodium, calcium, sulfate and magnesium would be in agreement with the mineral assemblage

of the Forebay.

Natural systems tend to move towards equilibrium; thus, if the solution (groundwater)

is undersaturated, minerals will be more likely to dissolve into the groundwater. As the

introduction of reclaimed recharge water has increased, it has resulted in the change of an

average pH value of the groundwater in the Montebello Forebay from a pH of 8 to 7.2 (Figure

19). This observed change in pH, from a basic to a neutral value, has possibly disrupted the

“equilibrium’ by increasing the solubility of the groundwater therefore resulting in the

dissolution of mineral within the matrix of the aquifers of the San Pedro Formation. For

example, the dissolution of calcite (calcium carbonate) into groundwater would result in the

increased concentrations of calcium and bicarbonate by means of the following reaction:

CaCO3 + H2O Ca2+ + HCO3- + OH-

CO2 + H20 HCO3- + H+

11

A

A’

Figure 4 – Site Map: The cross-section is presented in Figure 5.

12

Figure 5 – Generalized cross-section of the Central Basin (Adapted from WRD, 2001)

13

Basin Aquifers

Sunnyside Aquifer: The Sunnyside Aquifer of the Lower San Pedro Formation (Figure

5) are marine, blue of hard to soft, coarse-grained sands, gravels and clays, interbedded with

fine-grained layers of sandy clay and clay (DWR, 1961). Drilling logs indicate that Sunnyside

sediments are weathered, and generally have medium specific yields and transmissivity values

(DWR, 1961).

The Sunnyside Aquifer is approximately 90 meter (m) thick [300 feet (ft)]. Hydraulic

communication with the overlying aquifers is sporadic throughout the Central Basin. The

Sunnyside Aquifer is normally separated from the overlying Silverado Aquifer by the Timms

Point Silt and the Lomita Marl (DWR, 1961).

The sediments that make up the overlying aquifers were deposited during the Mid-to-

Late Pleistocene Epoch, (approximately 950,000 to 150,000 ybp [Stage 4 (Lajoie, 1992)] and

generally reflect marine regression associated with glacial stages (DWR, 1961). As each

glaciation event ended and continental ice sheets melted, sea levels rose to heights averaging 30

m (100 ft) above present day sea level. This in-turn led to major transgression of the coastlines

around the world, which alternately inundated and exposed the basin surfaces to erosion

(DWR, 1961).

Silverado Aquifer: The Silverado Aquifer (Figure 5) is composed of both terrestrial

and marine sediments deposited 960, 000 to 860,000 ka [Stage 4 (Lajoie, 1992)] (DWR, 1961)

by the ancestral Rio Hondo and San Gabriel rivers (Herndon, 1992; and DWR, 1961). Other

source areas of continental sediments came from the Elysian Hills, Santa Monica Mountains,

and Palo Verdes Hills (Herndon, 1992).

14

The Silverado Aquifer is composed of yellow to brown, coarse to fine sands and

gravels with interbedded yellow to brown silts and clays. Silverado Aquifer marine sediments

are primarily blue to gray sand, gravel, silt, and clay. Uncemented sands, fossils, and wood

fragments are also noted in boring logs of the marine sediments within the Silverado Aquifer

(DWR, 1961). Generally, the Silverado aquifer has high values of transmissivity ranging from

75,700 to 757,100 liters per foot per day (L/m/day) (20,000 to 200,000 g/ft/d).

The Silverado aquifer continuously underlies the Central Basin and is considered to be

in hydraulic conductivity at various locations with the overlying, Lynwood, and underlying,

Sunnyside, aquifers of the San Pedro Formation (DWR, 1961).

The Silverado Aquifer is separated from the underlying Sunnyside Aquifers by the

Timmus Pt. silt and Lomita Marl. Overlying fined-grained sediments separate the Silverado

from the Lynwood Aquifers.

Lynwood, Jefferson, and Hollydale Aquifers: The Lynwood, Jefferson and Hollydale

Aquifers (Figure 5) overlie the Silverado Aquifer. These aquifers are separated by layers of silts

and clays that underlie the Lakewood Formation of the Upper Pleistocene.

The Lynwood Aquifer is composed of a combination of continental and marine

sediments. The continental deposits are located in the vicinity of the Montebello Forebay and

are composed of yellow, brown and red coarse gravels, sands, silts, and clays. Based on drilling

logs, it is apparent that the major sources of the continental deposits were in the upper reaches

of the Rio Hondo and San Gabriel River watersheds (DWR, 1961). The marine sediments,

characterized by blue, gray, and black silts and clays, sands and gravels, are located in the area

within the basin surrounding the Montebello Forebay. Several sections, ranging in aerial extent

between less than 0.40 square kilometers (km2) [0.154 square miles (mi2)] to approximately 18.2

15

km2 (7.0 mi2), within the marine deposits of the Lynwood Aquifer are composed of fine-

grained sediment. In addition to these low hydraulic conductivity zones, some sections of the

marine sand and gravel deposits are moderately to highly cemented. These sediments appear

to have been deposited in shallow marine conditions (DWR, 1961).

The Jefferson and Hollydale Aquifers are mostly composed of fine-grained sediments;

however, gravel deposits within these aquifers are extensive within the area of the Whittier

Narrows and somewhat scattered throughout the basin (DWR, 1961). The sediments of the

Jefferson and Hollydale Aquifers were transported from their sources in the San Fernando and

San Gabriel valleys via the Los Angeles and San Gabriel Rivers into the Central Basin (DWR,

1961). The discontinuous nature of the sediments that make up the aquifers in the Central

Basin indicate that extensive erosion has occurred.

16

CHAPTER 3

PREVIOUS WORK Poland et al. (1959a), comprehensively characterized the aquifer system of the Los

Angeles coastal basins (Riechard et al., 2003). The California State Departments of Water

Resources Bulletin 104A (DWR, 1961) further characterized the groundwater systems of the

Los Angeles Basin. Bulletin 104A (DWR, 1961), identifying the compositions aquifers of the

Upper San Pedro Formation (Silverado, Lynwood, Jefferson, and Hollydale), along with their

corresponding aquifer thicknesses and transmissivity values. These two bodies of work

provide insight into the hydrochemical facies and hydrological properties of the freshwater

aquifers of the Upper San Pedro Formation prior to the implementation of the practice of

artificial recharge in the Central Basin.

Between 1961 and the early 1990s research into the hydrological characteristics of the

Central Basin focused on two areas: pumping/recharging activities and water quality issues.

The WRD (Water Replenishment District’s Regional Groundwater Monitoring Report Water

Years 1971-72 through 2001-2002) focused its research mainly in pumping and recharging

effects within the Central Basin. The WRD maintained vigilant monitoring activities that

included recording recharge levels, regulating pumping activities, and collecting some water

quality data. Water quality research focused on the health concerns and potential biological

ramifications brought about through the increase use of reclaimed water for the purpose of

artificial recharge (Sloss et al., 1994; Wilson et al., 1993; Asano, 1992; and Bull et al., 1990).

17

In 2002, the USGS released the Geological, Hydrological, and Water Quality Data from

Multiple-Well Monitoring Sites in the Central and West Coast Basin; Open-File Report 01-277

(Riechard et al., 2002) providing information on the geological, hydrological, and water quality

data from multiple-well monitoring sites in the Central and West Coast Basin from 1995 to

2000. Building on Open-File Report 01-277, the USGS published Geohydrology, Geochemistry, and

Groundwater Simulation-optimization of the Central and West Coast Basins in 2003 (Riechard et al.,

2003). Using tritium data collected from 1995-2000, the USGS determined the lateral and

vertical extent at which artificial recharge water has infiltrated the lower aquifer systems of the

Central Basin (Figure 6). Tritium, an unstable isotope used in a quantitative manner to

determine if the groundwater was in the atmosphere as water vapor either pre or post 1953,

allowed the USGS to determine the extent at which the recharge water from the Los Angeles

and Montebello Forebay has infiltrated into the Central Basin. The pattern of the distribution

of tritium data (Figure 6) is similar to that of the pattern of the change in transmissivity values

presented in Figure 1.

Model (Rinick-Pfeiffer et al., 2002) and field studies (Stuyfzand and Juhasz-Holterman,

2004) found that changes in transmissivity values may be due to mineral dissolution and

precipitation brought about by changes in the source water used for the recharge of aquifers.

Rinick-Pfeiffer et al. (2002) studied the interrelationships between biological, chemical and

physical processes as an analog to clogging in Aquifer Storage and Recovery (ASR) wells to

understand and predict bore-hole clogging issues in Southern Australia. Using laboratory

18

Figure – 6. Tritium concentrations in groundwater sampled in the Los Angeles Basin. The shaded gray areas show the approximate extent of recent water (>1TU) in the low aquifer systems, dashed where uncertain (Adapted from Riechard et al., 2003)

models simulating continuous injection of recycled water into an aquifer matrix, Rinick-

Pfeiffer et al. (2002) showed that hydraulic conductivity increased due to calcite dissolution in

19

the inlet end of the columns and decreased due to mineral precipitation of calcite in the

effluent zone of the model.

Stuyfzand and Juhasz-Holterman (2004), Guo and Wang (2004), have shown that

alterations in the hydrochemical facies induced by human activity (e.g., artificial recharge) have

the potential to induce geochemical reactions within fresh water aquifers and reduce water

quality. Stuyfzand and Juhasz-Holterman (2004) found that the displacement of native

groundwater resulted in the dissolution of various minerals (i.e., calcite). Guo and Wang

(2004), using the geochemical modeling code PHREEQC found that the hydrolysis of

bedrock within the alluvial aquifers of the Datong Basin, China, has been induced by

agricultural and industrial run-off. For example, concentrations of calcium have increased

from 114.9 milligrams/liter (mg/l) to 790 mg/l and concentrations bicarbonate increase from

324.8 mg/l to 6,375 mg/l. This has resulted in the oversaturation of groundwater with

calcium, sulfate, bicarbonate and sodium and is inducing mineral precipitation down-gradient

of the points of mineral dissolution.

20

CHAPTER 4

CENTRAL BASIN GROUNDWATER CONDITIONS The following section describes the natural and artificial recharge conditions of the

aquifer system. To put these conditions into perspective, the groundwater budget for the

Central Basin is also described. The impact of artificial recharge can then be accurately

assessed and the flow path defined.

Groundwater Recharge (Natural/Artificial) Prior to major artificial recharge (pre-1960s) and major urban development of the Los

Angeles Basin, groundwater recharge of the basin occurred by means of discharge of the Los

Angeles, San Gabriel and Rio Hondo Rivers into the Los Angeles and Montebello Forebay

(Figure 7) (DWR, 1961).

The Los Angeles River flows from the northeast to southwest entering the Central

Basin via the Los Angeles Narrows (Figure 2). The concrete-lined banks and channel bottom

of the Los Angeles River limit recharge into the Central Basin aquifers. Both the San Gabriel

and Rio Hondo Rivers enter the Central Basin through the Whittier Narrows of the Puente

Hills and on into the Montebello Forebay area. Additional sources of recharge occurred by

means of aerial recharge, surface run-off from the surrounding hills (Reppetto, Merced, etc.),

and underflow from the north of the basin via the Whittier Narrows from San Gabriel Basin.

In general, groundwater recharge of the Central Basin percolates into the aquifers of the

21

Montebello Forebay and flows towards the southwest-south to the eastern edge hydrological

barrier of the Newport-Inglewood Fault Zone (Figure 3, 7 and 8) (Riechard et al., 2002).

Figure 7- Groundwater Elevation Contour Map for Fall 2001. (Adapted from WRD’s Regional Groundwater Monitoring Report, Water Year 2001-2002)

22

Figure 8 – Generalized model of the hydrological system of the natural and artificial recharge of the aquifers of the Central Basin, Los Angeles, California (Adapted from WRD’s Regional Groundwater Monitoring Report, Water Year 2001-2002).

23

The coarse-grained sediments, merging of the aquifers, and synclinal structure of the

Central Basin makes the Montebello Forebay the main point of recharge for the aquifers for

the Central Basin. Recognizing the importance of the recharge capabilities of the Montebello

Forebay, two large spreading centers were constructed along the banks of the Rio Hondo and

San Gabriel Rivers for the purpose of artificial recharge from three main sources the Colorado

River, Northern California via the State Aqueduct and reclaimed water from three treatment

facilities (Figure 7 and 8) (DWR, 1961). Water imported for the Colorado River began to flow

into the basin via the Colorado aqueduct in the late 1940s and currently supplies roughly

14,487,000 cubic meters (m3) [11,725 acre/foot (acre/ft)] of water per year (Table 1) (WRD’s

Regional Groundwater Monitoring Report, Water Year 2003-2004). In 1961, reclaimed water

composed of 5% of the total artificial recharge and in 2004 comprises nearly 40% of the total

water used for recharge. The California State Water Project (beginning in 1970) supplies on

average an additional 24,280,000 m3 (19,650 acre/ft) for the purpose of artificial recharge of

the basin over the last 30 years (WRD’s Regional Groundwater Monitoring Report, Water

Year 2003-2004; Riechard et al., 2003; and DWR, 1961). Illustrated by Figure 8 are the

percentages of the water that make up the current total volume of the recharge water used for

the Central Basin which is further explained in detail in section 3.1 Central Basin Groundwater

Budget.

The chemical characteristic of the water imported into the basin varies from the native

chemical characteristics as recorded by Joseph Poland (Riechard et al., 2003; and Poland et al.,

1959a). Figure 9 below graphs the 30-year average concentrations of cations and anions and

pH of the water that is entering the Central Basin via the Montebello Forebay and compares

these concentrations to the data collected by Joseph Poland (1959a). The chemical

24

characteristics of the Colorado River, Northern California, and reclaimed water are represented

by the chemical concentrations recorded in the spreading centers.

0

50

100

150

200

250

Calcium Magnesium Sodium Bicarbonate Sulfate Chloride pH

Cation and Anion

Con

cent

ratio

n (p

pm)

Spreading Centers (30-year Average)

Montebello ForebayGroundwater (30-yearaverage)

Whittier Narrows (2003)

Piper and Garrett(1953)

Figure 9 – Comparison of anion, cation and pH concentrations of Piper and Garrett’s (1953), Whittier Narrows, the Spreading Centers (Rio Hondo and San Gabriel) of the Montebello Forebay. *Bicarbonate concentrations for the groundwater of the Whittier Narrows where not available in the literature provided by the City of Whittier. Figure 10 illustrates the 30-year average of total dissolved solids (TDS) for the

groundwater of the Montebello Forebay and the Spreading Centers and is compared to the

TDS concentrations recorded by Piper and Garrett (Piper and Garrett, 1953). Both figures 9

and 10 illustrate the difference in chemical characteristics between the native and imported

25

waters and the change in the hydrochemical facies of the groundwater of the Montebello

Forebay.

0

100

200

300

400

500

600

TDS

Con

cent

ratio

n (p

pm)

Spreading Centers(30-year Average)

Montebello ForebayGroundwater (30-yearaverage)

Piper and Garrett(1953)

Figure 10 – Comparison of total dissolved solids (TDS) concentrations of Piper and Garrett’s (1953), the Spreading Centers (Rio Hondo and San Gabriel) and the Montebello Forebay. *TDS concentrations for the Whittier Narrows where not available in the literature provided by the City of Whittier.

Central Basin Groundwater Budget Through coordination with the USGS (Riechard et al., 2003) and the WRD, these two

26

organizations have compiled the following 30-year average (1970/1971 to 1999/2000) and the

2000/2001 surface water inflow for the Central Basin:

Table 1 – Average Annual Water Balance 1970/1971 – 1999/2000 (afy); 2000/2001 Water Budget (afy) (Riechard et al., 2003).

Spreading Centers

Inflow Stormflow Imported Recycled Areal Recharge (Rain)

Barrier Injection

Net Underflow

Total (Inflow)

Central Basin (Average 1971-2000)

48,825 39,305 34,770 32,300 5,300 44,680 205,180

Percentage (Average 1971-2000)

23.79% 19.16% 16.95% 15.74% 2.58% 21.78% 100%

2000/2001 47,071 23,451 43,781 34,100 5,200 45,000 198,603 Percentage 23.70% 11.81% 22.0% 17.17% 2.61% 22.66% 100%

The significance of this table is its illustration of the amount of imported and recycled

water that has been used on average for the purpose of groundwater recharge over the last 30

years. Focusing on the water budget for the spreading centers, roughly 1.5x108 m3 (122,900

acre/ft) of water is placed into the spreading centers per year. Of the total volume of recharge

water, 9.1x107 m3 (74,100 acre/ft), 60% comes from imported sources or recycled water

(Riechard et al., 2003; and WRD’s Regional Groundwater Monitoring Report, Water Year

2000-2001). The water budget for the 2000/2001 water year shows that imported and recycled

water make-up 62% of the total water used for artificial recharge. Furthermore, the

2000/2001 water budget shows the increase in the use of recycled water for the purpose of

artificial recharge.

27

The water budget for the entire Central Basin indicates that on average, 40% of the

total water that is used for aquifer recharge of the basin is from the imported and reclaimed

sources. This estimation of 40% is excluding the percentage of the net underflow that is

composed of imported and recycled water. Therefore, the hydrochemical facies of the aquifers

becomes more characteristic of the imported and recycled water and as shown by previous

research. This change in hydrochemical facies could lead to geochemical reactions resulting in

the degradation of the physical properties of the aquifers.

28

CHAPTER 5

METHODS AND RESULTS

Transmissivity Map and Concentration Maps

Transmissivity is a measure of the amount of water that can be transmitted

horizontally through a unit width by the fully saturated thickness of the aquifer under a

hydraulic gradient of one (Fetter, 2001). Transmissivity (T) is the product of the hydraulic

conductivity (K) and saturated thickness (b) of the aquifer (T=Kb). Transmissivity can also be

determined during the development of groundwater production wells by measuring the

specific capacity [m3/d (gallons per minute {gpm})] divided by the amount of drawdown upon

the top of the water column in the well. This method was used to construct the transmissivity

maps in Bulletin 104 (DWR, 1961) (WRD Technical Bulletin, 2005).

To remain consistent with Bulletin 104 (DWR, 1961), 20 development logs of

production wells installed and screened in the Upper San Pedro Aquifers (Lynwood and

Silverado Aquifers) of the Central Basin from 1990 to present were used to construct a

“current” transmissivity map of the Central Basin. Each well log contained the production rate

in m3/day (gpm) produced by well, the duration of the aquifer test (minimum of 33 hours) and

the amount of drawdown the well experienced. Transmissivity was then calculated using the

following equation (Batu, 1999; Thomasson et al., 1960):

29

T= 1.042 (Q/Sw); for unconfined aquifers; (T=1500*Q/s)

T= 1.385 (Q/Sw); for confined aquifers; (T=2000*Q/s)

T= Transmissivity in m2/d (gpd/ft)

Q/s= Specific Capacity in m3/d (g/m/ft) divided by drawdown

Sw = drawdown in the pumped well after 1 day

Using the State Well Identification to locate the wells, the 20 production wells were

plotted onto a geocoded digital map of the Central Basin. A “current” transmissivity (CT)

contour map was then configured using the data available for the production wells. The CT

contour map was converted into a grid map by interpolating the transmissivity data with the

Geographical Information System (GIS) extension tool Vertical Mapper (version 2.5). The

method used for the interpolation was the Simplified Natural Neighbor Interpolation. The

settings for the interpolation were set at smoothed, with no overshoot, cell size of 1.52 meters

(m) (5 ft), an aggregation distance of 1.66 m (5.5 ft), and a grid dimension of 594 X 416.

Historical transmissivity data gathered from California Department of Water Resources

Bulletin 104A (DWR, 1961) was also gridded using the same procedures described above. The

transmissivity data was analyzed by overlaying the two grid maps and calculating the

differences between the two. Transmissivity values for the CT grid were subtracted from

those of the California Department of Water Resources Bulletin 104A (DWR, 1961) grid using

the GIS tools. These results were interpolated using the Natural Neighbor method (e.g.,

Figure 1).

30

The same grid method was used to construct the anion, cation, pH and total dissolved

solids (TDS) concentration contour maps for both the “current” and “historical” data sets,

(Appendix A).

Mixing Graphs

To determine if mineral dissolution/precipitation of calcite or gypsum was occurring

in the Upper San Pedro Aquifers, mixing graphs were constructed using the groundwater data

collected from USGS Open File Report 01-277 (Riechard et al., 2002), the WRD (WRD’s

Regional Groundwater Monitoring Report, Water Years 1971-1972 through 2002-2003), Piper

and Garrett (Piper and Garrett, 1953), and the City of Whittier (City of Whittier Technical

Bulletin 2000 and 2002). First, the possible end members or groundwater recharge sources of

hydrochemical facies were plotted onto a graph for each of the major cations and anions: the

historical groundwater signature (“native”) for the Central Basin provided through Piper and

Garrett’s work in the 1948-52 (Piper and Garrett, 1953); imported water from the Colorado

River and Northern California; recycled water (reclaimed water); the spreading centers (San

Gabriel and Rio Hondo rivers); and the underflow between the Whittier Narrows. This

analysis only enables one to assess whether the groundwater data are consistent with mixing

between plausible endmembers (Faure, 1995). If the data are not consistent, then other

processes (i.e., mineral dissolution/precipitation) should be considered and tested by modeling

using mineral stabilities (i.e., PHREEQ).

The endmembers, presented in Table 2, define the boundaries of possible water

signatures for a given anion or cation for the Central Basin. Second, the data obtained from

the USGS (Reiechard et al., 2002) and WRD (WRD’s Regional Groundwater Monitoring

Report, Water Years 1971-1972 through 2002-2003) databases (Table 2) were plotted on the

31

mixing graphs. If a datum was to plot outside the range of these specified end members, then

it would be possible that mineral precipitation or dissolution was occurring at that point within

the Central Basin (Figures 11–16 and Appendix B) (Faure, 1995).

This method was used for observing the groundwater at depth by aquifer (i.e.

Hollydale, Jefferson, Lynwood, Silverado, and Sunnyside) and by distance away from the

spreading centers (i.e., Montebello Forebay, Northern Pressure Area, and Southern Pressure

Area).

32

Table 2 – “End Members” – The concentration of the each of the analytes for the water entering into the Central Basin *X25 and X75 represent the variation from the mean.

Source TDS Ca Mg Na HCO3 SO4 Cl pH

Reclaimed Water

Average 572 61 18.79 111 270 110 114 7.12 Median 571 56 15.74 111 275 112 112 7.1 X25 558 55 15.37 108 250 102 107 7.08 X75 579 58 16.59 114 283 115 115 7.22 Standard Deviation 46.1 20.1 12.4 6.2 18.9 8.2 23.4 0.1

Imported Water

Average 435 47 19.97 69.7 121 152 73.5 8.16 Median 430 48 20.25 67.8 121 147 73.4 8.15 X25 409 45 18.27 63.3 118 137 64.7 8.06 X75 465 49 21.5 76.9 124 162 86.6 8.25 Standard Deviation 42.8 2.4 2.1 10.9 6.4 27.7 15.7 0.1

Spreading Centers

Average 471 58 16.64 78.1 172 132 77.8 7.67 Median 464 57 16.8 79.9 168 128 79.6 7.62 X25 446 55 15.87 72.9 156 120 73.4 7.32 X75 507 62 17.51 81.5 184 134 82.5 7.99 Standard Deviation 47.5 6.2 1.5 8.2 20.3 20.4 7.4 0.4

Montebello Forebay Groundwater

Average 486 79 15.73 58.5 195 62.7 129 7.7 Median 487 80 15.79 58.8 200 65.3 122 7.69 X25 453 72 14.56 54.1 194 56.4 114 7.59 X75 523 84 17.19 62.6 205 69 136 7.84 Standard Deviation 39.8 7.3 2.9 6.0 15.6 8.0 22.5 0.2

Piper and Garrett (1953)

Average 287 43 12.38 44.6 71.7 14 12.4 NA Median 273 48 13.6 34.8 75.1 11.8 10.6 NA X25 236 33 7.25 28.2 61.6 7.35 7.4 NA X75 330 55 18.05 60.1 82.9 22.2 15.4 NA Standard Deviation 68.9 17.6 6.7 23.0 14.5 9.0 6.6 NA

Whittier Narrows Underflow

Values NA 60.7 17.5 83.3 NA 107.3 60.7 NA

33

The data presented in Table 3 represent the general groundwater characteristics for each of the

four hydrochemical facies in the Central Basin.

Table 3 - Represent the average concentration for each of the analytes within each of the four hydrochemical facies of the Central Basin. *X25 and X75 represent the variation from the mean.

Section TDS Ca Mg Na HCO3 SO4 Cl pH

Montebello Forebay

Average 475.5 72.8 19.8 60.3 249.8 88.7 74.1 7.6 Median 523.5 83.9 17.0 58.8 215.0 125.4 68.8 7.4 X25 469.5 70.9 14.4 45.0 189.3 114.8 57.5 7.3 X75 573.0 99.1 19.2 74.1 241.8 143.8 88.0 7.7 Standard Deviation 101.1 20.9 7.2 20.3 40.0 21.7 55.6 0.1

Los Angeles Forebay


Northern Pressure Area


Southern Pressure Area


34

Figure 11 - Sulfate concentrations found in the nested groundwater monitoring wells in the Montebello Forebay of the Central Basin.

Mon

tebe

llo F

oreb

ay: S

ulfa

te v

s C

hlor

ide

(mg/

L)

050100

150

200

250

020

4060

8010

012

014

0

Chl

orid

e (m

g/L)

Sulfate (mg/L)

Pipe

r and

Gar

rett

(195

3)

Mon

tebe

llo F

oreb

ay

Spre

adin

g C

ente

rs

Whi

ttier

Nar

row

s

Impo

rted

Wat

er

Rec

laim

ed

Sulfa

te

35

Figure 12 - Sulfate concentrations found in the nested groundwater monitoring wells in the Northern Pressure area of the Central Basin.

Nor

ther

n Pr

essu

re A

rea:

Sul

fate

vs

Chl

orid

e (m

g/L)

020406080100

120

140

160

180

020

4060

8010

012

014

016

018

020

0

Chl

orid

e (m

g/L)

Sulfate (mg/L)

Pip

er a

nd G

arre

tt (1

953)

Mon

tebe

llo F

oreb

ay

Spr

eadi

ng C

ente

rs

Whi

ttier

Nar

row

s

Impo

rted

Wat

er

Rec

laim

ed

Sul

fate

36

Figure 13 – Calcium concentrations found in the nested groundwater monitoring wells in the Montebello Forebay of the Central Basin.

Mon

tebe

llo F

oreb

ay: C

alci

um v

s C

hlor

ide

(mg/

L)

020406080100

120

140

160

020

4060

8010

012

014

0

Chl

orid

e (m

g/L)

Calcium (mg/L)

Pipe

r and

Gar

rett

(195

3)

Mon

tebe

llo F

oreb

ay

Spre

adin

g C

ente

rs

Whi

ttier

Nar

row

s

Impo

rted

Wat

er

Rec

laim

ed

Cal

cium

37

Pipe

r and

Gar

rett

(195

3)

Mon

tebe

llo F

oreb

ay

Spre

adin

g C

ente

rs

Whi

ttier

Nar

row

s

Impo

rted

Wat

er

Rec

laim

ed

Cal

cium

Figure 14 – Calcium concentrations found in the nested groundwater monitoring wells in the Northern Pressure Area of the Central Basin.

Nor

ther

n Pr

essu

re A

rea:

Cal

cium

vs

Chl

orid

e (m

g/L)

050100

150

200

250

300

020

4060

8010

012

014

016

018

020

0

Chl

orid

e (m

g/L)

Calcium (mg/L)

38

Pip

er a

nd G

arre

tt (1

953)

Mon

tebe

llo F

oreb

ay

Spr

eadi

ng C

ente

rs

Whi

ttier

Nar

row

s

Impo

rted

Wat

er

Rec

laim

ed

Sod

ium

Figure 15 – Sodium concentrations found in the nested groundwater monitoring wells in the Montebello Forebay of the Central Basin.

Mon

tebe

llo F

oreb

ay: S

odiu

m v

s C

hlor

ide

(mg/

L)

050100

150

200

250

300

350

020

4060

8010

012

014

0

Chl

orid

e (m

g/L)

Sodium (mg/L)

39

Figure 16 – Sodium concentrations found in the nested groundwater monitoring wells in the Northern Pressure Area of the Central Basin.

Nor

ther

n Pr

essu

re A

rea:

Sod

ium

vs

Chl

orid

e (m

g/L)

050100

150

200

250

300

020

4060

8010

012

014

016

018

020

0

Chl

orid

e (m

g/L)

Sodium (mg/L)

Pipe

rand

Gar

rett

(195

3)

Mon

tebe

llo F

oreb

ay

Spre

adin

g C

ente

rs

Whi

ttier

Nar

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s

Impo

rted

Wat

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Rec

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Sodi

um

40

Results

Comparing the groundwater data collected by Piper and Garrett from 1948 to 1952

(Piper and Garrett, 1953) to the data collected by the WRD and the USGS from 1995 to 2002

for the Montebello Forebay and the Northern Pressure Area to investigate the possibility of

the mineral dissolution of gypsum, halite and/or calcite induced by the current practice of

artificial recharge. The Southern Pressure Area was excluded from investigations based on the

tritium data findings published by the USGS in 2003 (Riechard et al., 2003) that indicated that

the water used for artificial recharge has not infiltrated the area (Figure 10).

Figures 17 and 18 indicate that the concentrations of the specified analytes have

increase in concentration over the last 45 years. The most significant increase is in the

concentrations of total dissolved solids and sulfate concentrations at 65% and 719%,

respectively, for the Montebello Forebay and 58% and 668 %, respectively, for the Northern

Pressure Area. Bicarbonate concentrations have increase on average by 22% in the Montebello

Forebay and by 318% in the Northern Pressure Area. The increases in anion, cation and TDS

concentrations are similar to the findings of Rinick-Pfeiffer et al. (2000), Stuyfzand and Juhasz-

Holterman (2004), and Guo and Wang (2004).

41

65

91

18

68

17

208

321

6983

17

70

123

256

530

0

100

200

300

400

500

600

Na Ca Mg Cl SO4 HCO3 TDS

Cations and Anions

Con

cent

ratio

n (m

g/L)

MF-1

MF-2

Figure 17 - Comparison of Historical and the Present Average Groundwater Chemical Signatures in the Montebello Forebay (MF1 – Historical Average; MF2 Current Average).

42

3153

15 12 14

74

280

5272

17

60

91

228

440

0

100

200

300

400

500

600

Na Ca Mg Cl SO4 HCO3 TDS

Cantions and Anions

Con

cent

ratio

n (m

g/L)

NPA-1

NPA-2

Figure 18 – Comparison of Historical and the Present Average Groundwater Chemical Signatures in the Northern Pressure Area (NPA1- Historical Average; NPA2 Current Average). Figure 19 illustrates the range of groundwater pH values for the San Pedro aquifers

across the Central Basin. The modeled distribution of the pH values is similar to that of the

tritium data (Figure 10) collected by the USGS (Riechard et al., 2003 and Riechard et al., 2002).

This appears to indicate a correlation between the pH of the groundwater and the extent at

which the artificial recharge water has infiltrated into the basin. In addition, the pH values of

the Southern Pressure Area (pH 8.2 to 8.9) likely represents the pH value of the native

43

groundwater of the Central Basin as artificial recharge water has not infiltrated into this region

of the basin. Furthermore, the distribution presented in Figure 19 is reflected in the majority

of the contour concentrations maps of calcium, bicarbonate, sulfate and sodium for the

aquifers of the San Pedro Formation (Appendix A). Lowering of the pH values would

increase the solubility of the groundwater and therefore increase the possibility of mineral

dissolution within the aquifers of the Montebello Forebay and Northern Pressure Area.

Figure 19, displayed above, and the concentration contour maps attached in Appendix

A, show that groundwater concentrations of the specified analytes and the pH values have

increased over the last 45 years. To investigate further into whether these increases are due to

mineral dissolution, the mixing graphs were composed (Figures 11 through 16). If mineral

dissolution is occurring, the plotted concretions of the specified ion will lie outside of the

range of the ion concentrations of the native groundwater, imported water, recycled water, the

water flowing between the Whittier Narrows from the San Gabriel Basin (Figures 11 through

16). The error bars (X25 and X75; Table 2) represent the measured range of concentrations

from each of the waters described.

44

Figure 19 – Current pH levels of the groundwater of the Aquifers of the San Pedro Formation (Contour Interval = 0.1). The patterns or location of the project points plotted on Figures 11 through 16

indicated that there is no reason to invoke significant mineral dissolution/precipitation to

45

explain the temporal variation (Figure 21) in the chemistry of the groundwater for the

Montebello Forebay and Northern Pressure Area. If mineral dissolution was occurring in the

Central Basin, the projected points would plot outside of the range of the end members within

multiple figures. The few “outliers” that are plotted along the chloride axes represent the

introduction of reclaimed water into the system. Other outliers along the sulfate (Figure 11)

and calcium (Figure 12) axes in the Montebello Forebay are still within the plausible range of

the imported water and do not consistently lie outside of the plausible range within the other

figures (Figures 13 through 16) to suggest mineral dissolution.

Figures 11 and 12 plot the concentrations of sulfate to chloride ratios recorded for the

groundwater samples obtained from the groundwater monitoring wells located in the

Montebello Forebay and the Northern Pressure Area. The majority of project well points for

sulfate plotted in Figure 11 are clustered around the point plotted for the Spreading Centers

were as the project well points for sulfate plotted in Figure 12 are plotted between the plotted

spreading centers point and the plotted point of Piper’s and Garrett’s data (Piper and Garrett,

1953). The visual pattern displayed in these two figures indicates that the hydrochemical facies

of the groundwater within the individual aquifers of the Lower and Upper San Pedro

Formation is more related to the distance from the spreading centers than the depth of the

aquifer. This is in accordance with the geology of the Montebello Forebay, as there are no or

very few confining layers in the Montebello Forebay between the aquifers. Furthermore the

aquifers of the Lower and Upper aquifers shallow and in some regions merge in the

Montebello Forebay as indicated in Figures 5 and 8. For example, the pattern plotted in

Figure 11 indicated that the hydrochemical facies of the groundwater in the Montebello

Forebay is more representative of the water placed in the spreading centers than that of the

46

hydrochemical facies of that recorded by Piper and Garrett (Piper and Garret, 1953). Moving

down gradient or away from the spreading centers, located in the Montebello Forebay, into the

northern pressure area of the basin, the pattern of plotted points indicate that of mixing

between the water of the spreading center and that of “original” groundwater characteristics.

This same pattern of the plotted points shown in Figures 11 and 12 is repeated in Figures 13

and 14 (Calcium vs. Chloride) and Figures 15 through 16 (Sodium vs. Chloride).

To expand upon this observation, only the project well plot points of sulfate vs.

chloride concentrations in the Southern Pressure Area (Figure 20). As indicated in the tritium

data collected by the USGS (Riechard et. al, 2003) and pattern of mixing indicated by Figures

11, 12, 20, and 21 show that the hydrochemical facies of the groundwater of the Upper and

Lower San Pedro Formation is more characteristic of the “native” groundwater of the central

basin than that of the water of the spreading centers.

The observed pattern of mixing is again supported by the piper diagram displayed

below (Figure 21). This figure illustrates the phase of mixing between the artificial recharge

water and that of the nature hydrochemical facies of the Central Basin recorded by Piper and

Garrett (Piper and Garrett, 1953). Over a given period of time, the groundwater of the

aquifers of the San Pedro Formation within the southern pressure area will become more

representative of the hydrochemical facies of the water used for artificial recharge than that of

the hydrochemical facies observed by Piper and Garrett in the late 1940s and early 1950s.

47

Pipe

r and

Gar

rett

(195

3)

Mon

tebe

llo F

oreb

ay

Spre

adin

g C

ente

rs

Whi

ttier

Nar

row

s

Impo

rted

Wat

er

Rec

laim

ed

Sulfa

te

Figure 20 - Sulfate vs. Chloride Concentrations found in the nested groundwater monitoring wells in the Southern Pressure Area of the Central Basin.

Sout

hern

Pre

ssur

e Ar

ea: S

ulfa

te v

s C

hlor

ide

(mg/

L)

020406080100

120

140

160

180

050

100

150

200

250

Chl

orid

e (m

g/L)

Sulfate (mg/L)

48

Northern Pressure Area

Montebello Forebay

Figure 21 – Central Basin San Pedro Formation Aquifer Piper Diagram. The hollow squares represent the hydrochemical facies of the groundwater in the Montebello Forebay; the solid circles represent the hydrochemical facies of the groundwater found in the Northern Pressure Area; and the crosses represent the hydrochemical facies of the groundwater found in the Southern Pressure Area. The arrow represents the hydrologic flow of the groundwater from the Montebello Forebay to the Southern Pressure Area.

49

CHAPTER 6

DISCUSSION

Physical Indicators

Long-Term Pumping: Studies on the effects of long-term pumping on changes in

transmissivity were conducted by the USGS, in cooperation with the Arkansas Geological

Commission and the Arkansas Soil and Water Conservation Commission (Stanton et al.,

2000). The test was designed to replicate an aquifer test performed in 1947, thereby enabling

evaluation of any changes in hydraulic properties (transmissivity) and possible compaction of

the Sparta aquifer over the intervening 52 years of intensive water use. The results of the study

indicated that the transmissivity values computed from the 1999 aquifer test (drawdown and

recovery data) are in close agreement with the 1947 transmissivity values. The results of this

study indicate that there is no significant change in transmissivity due to long-term pumping.

Seasonal Fluctuations: Bawden et al. (2001), using satellite imaging, observed seasonal

fluctuations in the surface elevation of the Los Angeles Basin induced by season pumping

trends of groundwater. Such seasonal elevation oscillation brought about by the dewatering or

depressurizing the major aquifers of the basin could potentially result in the re-organization,

“packing” or fracturing of the matrices aquifers affecting the hydraulic conductivity of the

aquifers (Bawden et al., 2001). The fluctuation in elevation could also affect the thickness of

the aquifers which would intern influence the transmissivity of the major aquifers in the basin.

However, with a maximum gain in elevation of 2.3 m (7.6 ft) in various areas of the basin this

50

increase in potential thickness of the aquifers does not mathematically match the observed

change in transmissivity. Furthermore, it is not possible to determine which set of aquifers

were swelling based upon the data collected by Bawden et al. (2001).

Screen Intervals and Well Construction: There are approximately 550 production

wells throughout the Central Basin. A review of 440 groundwater production well records

obtained through the Department of Health Services, WRD and USGS, indicated that

approximately 75% of these wells are screened across multiple aquifers and have been active

for a minimum of 10 years. Pumping rates of the wells vary from the lower 545 m3/day too

26,160 m3/day (100s to 4,800 gpm). Based upon personal communications with the WRD

and the USGS (WRD communicate, June 2004), the activity of drilling and instillation of these

wells has perforated what hydraulic boundaries that exists between the “semi-confined

aquifers” between the transitional boundary of the Montebello Forebay and Northern Pressure

Area. These points of perforation have therefore become “new” points of hydraulic

communication between permeable matrixes (aquifers) that had not previously existed as

illustrated by Figure 22.

51

Figure 22 – Generalized Cross-Section/Screen Interval - Represents a generalize cross-section that illustrates how the installation of groundwater well screens across multiple aquifers could act as hydraulic conduits and affect the calculated transmissivity values recorded during an aquifer test.

52

Chapuis and Chenaf (2003) published a paper on the effects of monitoring wells and

pumping well pipe capacities on aquifer tests in confined aquifers. The findings of this study

indicated that the calculated transmissivity value based upon data collected from

pumping/aquifer tests can be influenced by water storage in monitoring and pumping wells

and can be used as a hydraulic conduit between aquifers. Therefore, the data collected during

a prolonged aquifer test could be potentially influenced by such an effect and would result in

unrepresentative data of the true values for transmissivity.

Further possible influences that could effects the data collected during the aquifer tests

is the added variable of screen intervals of other productions wells within the vicinity of the

cone of depressions (sphere of influence) of the well that is being pumped. These wells,

screened across multiple aquifers (Jefferson, Lynwood, etc.), would draw water from additional

aquifers and further influence the data collected during the duration of the aquifer test.

Comparing the modeled transmissivity map (Figure 2) to the Aquitard Thickness Map (Figure

23) that illustrates the hydrologic confining layer between the Silverado and the Lynwood

Aquifers, an observed pattern of increase in transmissivity is similar to the aquitard thickness

map.

53

Figure 23 – Aquitard Thickness Map represents the aquitard between the Silverado and Lynwood Aquifers across the Central Basin. The zones represent the thickness of the aquitard between the two aquifers. Therefore, the data used to construct the transmissivity map are possibly influenced by

the installation of multiple wells across the basin over the last seventy years and do not truly

reflect the true transmissivity of the aquifers of the San Pedro Formation.

54

CHAPTER 7

CONCLUSIONS

Conclusions

The findings of this thesis indicate that:

• The chemistry of artificial recharged waters does not appear to be of sufficient pH to

induced mineral dissolution or precipitations of gypsum, feldspars, calcite or halite in

the aquifers of the San Pedro Formation of the Central Basin.

• The hydrochemical facies of the Montebello Forebay represent the water

characteristics of the imported where the groundwater in the Northern Pressure Area

represents a broad zone of mixing between the native groundwater and the water

being used for artificial recharge (Figures 11 through 16, Figures 20 and 21, and

Appendix B).

• There is no supporting evidence of a direct relationship between the observed change

in transmissivity in the Silverado and Lynwood aquifers of the San Pedro Formation

(Figure 2) and mineral dissolution induced by the practice of artificial recharge in the

Central Basin.

• The observed changes in transmissivity are more likely due to the numerous wells in

the Central Basin being screened across multiple aquifers. Therefore, in areas where

the confining units are thin between the major aquifers of the San Pedro Formation, it

55

is more likely to affect the values recorded during pump tests that in turn affect the

calculated value of transmissivity, resulting in a false inflation in the values recorded for

transmissivity.

56

CHAPTER 8

FUTURE RESEARCH

Future Research In conclusion the observed change in transmissivity is not related to geochemical

reactions and therefore it must be related to physical changes that have occurred within the

Central Basin over the last seventy years. Plausible physical changes that could affect

transmissivity values are long-term pumping, the installment of numerous wells screened

across multiple aquifers, and seasonal groundwater fluctuations. Another plausible factor to

consider is how the technological advancements in groundwater well construction and drilling

methods would affect the values recorded during aquifer testing. Further investigation into the

hydraulic properties and physical parameters of the aquifers of the San Pedro Formation are

needed to fully understand and assess the observed results presented in this thesis for the

betterment of Southern California’s potable groundwater supply.

57

APPENDIX A

Current and Historical Concentration Graphs

Appendix A Figure 1 – Site Map indicating the well location of the wells installed by the USGS and WRD from 1995 to 2002. The information from these wells were used to model the “current concentration maps.”

59

Appendix A Figure 2- Current concentration of calcium (mg/L) within the groundwater of the aquifers of the San Pedro Formation (Contour Interval = 10 mg/L).

60

Appendix A Figure 3 – Current Concentration of Magnesium (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Contour Interval = 5mg/L).

61

Appendix A Figure 4 – Current Concentration of Sodium (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Contour Interval = 10 mg/L).

62

Appendix A Figure 5 – Current Concentration of Bicarbonate (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Contour Interval = 10 mg/L).

63

Appendix A Figure 6 – Current Concentration of Chloride (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Contour Interval = 10 mg/L).

64

Appendix A Figure 7 – Current Concentration of Sulfate (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Contour Interval = 5 mg/L).

65

Appendix A Figure 8 – Current Concentration of Total Dissolved Solids (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Contour Interval = 10 mg/L).

66

Appendix A Figure 9 – Site Map indicating the well location of the wells used in Poland’s work Native and Contaminated Groundwater from Torrance to Santa Ana (Piper and Garrett, 1953). The information from these wells were used to model the “historical concentration maps.”

67

Appendix A Figure 10 – Historical Concentration of Calcium (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953). (Contour Interval = 10mg/L).

68

Appendix A Figure 11 – Historical Concentration of Sodium (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953) (Contour Interval = 5 mg/L).

69

Appendix A Figure 12 – Historical Concentration of Magnesium (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953) (Contour Interval = 10 mg/L).

70

Appendix A Figure 13 – Historical Concentration of Bicarbonate (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953) (Contour Interval = 10 mg/L).

71

Appendix A Figure 14 – Historical Concentration of Chloride (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953) (Contour Interval = 10 mg/L).

72

Appendix A Figure 15 – Historical Concentration of Sulfate (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953)(Contour Interval = 5 mg/L).

73

Appendix A Figure 16 – Historical Concentration of Total Dissolved Solids (mg/L) of the groundwater of the Aquifers of the San Pedro Formation (Piper and Garrett, 1953) (Contour Interval = 200 mg/L).

74

APPENDIX B

MIXING GRAPHS

75

Appendix B Figure 1 – Magnesium concentrations found in the nested groundwater monitoring wells for the Montebello Forebay Area of the Central Basin.

Mon

tebe

llo F

oreb

ay: M

agne

sium

vs

Chl

orid

e (m

g/L)

05101520253035

020

4060

8010

012

014

0

Chl

orid

e (m

g/L)

Magnesium (mg/L)

Pip

er a

nd G

arre

tt (1

953)

Mon

tebe

llo F

oreb

ay

Spr

eadi

ng C

ente

rs

Whi

ttier

Nar

row

s

Impo

rted

Wat

er

Mag

nesi

um

Rec

laim

ed

76

Appendix B Figure 2 – Bicarbonate concentrations found in the nested groundwater monitoring wells for the Montebello Forebay Area of the Central Basin.

Mon

tebe

llo F

oreb

ay: B

icar

bona

te v

s C

hlor

ide

(mg/

L)

0

100

200

300

400

500

600

700

800

900

020

4060

8010

012

014

0

Chl

orid

e (m

g/L)

Bicarbonate (mg/L)

Pip

er a

nd G

arre

tt (1

953)

Mon

tebe

llo F

oreb

ay

Spr

eadi

ng C

ente

rs

Impo

rted

Wat

er

Bic

arbo

nate

Rec

laim

ed

77

Pip

er a

nd G

arre

tt (1

953)

Mon

tebe

llo F

oreb

ay

Spr

eadi

ng C

ente

rs

Whi

ttier

Nar

row

s

Impo

rted

Wat

er

Mag

nesi

um

Rec

laim

ed

Nor

ther

n Pr

essu

re A

rea:

Mag

nesi

um v

s C

hlor

ide

(mg/

L)

05101520253035

020

4060

8010

012

014

016

018

020

0

Chl

orid

e (m

g/L)

Magnesium (mg/L)

78

Appendix B Figure 3 – Magnesium concentrations found in the nested groundwater monitoring wells for the Northern Pressure Area of the Central Basin.

Appendix B Figure 4 – Bicarbonate concentrations found in the nested groundwater monitoring wells for the Northern Pressure Area of the Central Basin.

Nor

ther

n Pr

essu

re A

rea:

Bic

arbo

nate

vs

Chl

orid

e (m

g/L)

0

100

200

400

500

600

020

4060

8010

012

014

016

018

020

0

Chl

orid

e (m

g/L)

Bicarbona (mg/L)

Pip

er a

nd G

arre

tt (1

953)

Mon

tebe

llo F

oreb

ay

Spr

eadi

ng C

ente

rs

Impo

rted

Wat

er

Bic

arbo

nate

Rec

laim

ed

300

te

79

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