Supplemental Environmental Impact Statement

for the

International Boundary and Water Commission

International Wastewater Treatment Plant

Interim Operation

September 6, 1996

The International Wastewater Treatment Plant (IWTP) and South Bay Ocean
Outfall (SBOO) are currently under construction as identified in the
Final Environmental Impact Statement and Record of Decision signed in
May 1994. The purpose of the project is to provide new wastewater
control facilities to safeguard the public health, environment, public
beaches, water quality, and economy of San Diego, California. In
conjunction with actions taken by Mexico, this project would minimize
dry‑weather flow of untreated sewage from the municipality of Tijuana,
Baja California, Mexico, into the United States. Currently, such flows
cause chronic and substantial pollution in the Tijuana River valley,
national reserve estuary, and coastal areas used for agriculture and
public recreation and as designated critical habitat for federal and
state listed endangered species. In the Record of Decision, the federal
agencies decided to build a secondary wastewater treatment facility and
ocean outfall.

The purpose of this Supplemental Environmental Impact Statement (SEIS)
is to evaluate proposed project changes to operate the plant as an
advanced primary treatment facility on an interim basis. Unless the
facility is operated during this period, dry‑weather flows of sewage
could continue to pollute the river, estuary, and coastal waters in the
U.S. This Interim Operation SEIS evaluates alternatives for using the
IWTP as an advanced primary treatment works until the SBOO is completed.
It also evaluates the effects of discharge of advanced primary effluent
through the SBOO until alternatives to secondary treatment are
evaluated. Alternatives for providing secondary level treatment of
sewage at the IWTP will be the subject of an additional SEIS.

Lead Agencies

U.S. Environmental Protection Agency, Region IX

International Boundary and Water Commission, U.S. Section

Technical Oversight

U.S. Army Corps of Engineers

Technical Preparation

RECON (Regional Environmental Consultants)

Felicia Marcus, Regional Administrator, EPA Region IX

John M. Bernal, Commissioner, U.S. Section IBWC

TABLE OF CONTENTS

List of Acronyms vii

Executive Summary xi

1\. Purpose and Need for Action 1

2\. Consideration of the Alternatives 51

3\. Affected Environment 115

3.1 Hydrology and Water Quality 115

3.2 Oceanography 135

3.3 Terrestrial Biology 144

3.4 Estuarine Biology 147

3.5 Marine Biology 159

3.6 Geological Resources 177

3.7 Public Health 182

3.8 Air Quality and Odors 186

3.9 Land Use and Socioeconomics 192

4\. Environmental Consequences 199

4.1 Hydrology and Water Quality 200

4.2 Oceanography 214

4.3 Terrestrial Biology 258

4.4 Estuarine Biology 263

4.5 Marine Biology 272

4.6 Geological Resources 282

4.7 Public Health 287

4.8 Air Quality and Odors 292

4.9 Land Use and Socioeconomics 298

4.10 Effects Not Reevaluated for the SEIS 302

5\. Environmental Commitments 305

6\. Compliance with Applicable Environmental Laws and

Regulations 309

7\. Consultation with Others 317

8\. List of Preparers and Their Qualifications 327

9\. References Cited 331

FIGURES

1‑1: Regional Location of the Project 3

1‑2: Tijuana River Watershed Boundaries 7

1‑3: Location of Proposed Action 9

1‑4: Aerial Photograph of Tijuana River Valley 13

1‑5: Municipal Tijuana, B.C., Mexico 17

1‑6: Existing Mexican Sewage Facilities 23

1‑7: Existing Mexican Pumping and Conveyance Facilities 25 1‑8: San
Antonio de los Buenos Treatment Plant 31

1‑9: Major Elements of the IWTP 35

1‑10: South Bay Ocean Outfall 39

2‑1: Alternative 1: No Action 61

2‑2: Sewer Flows/Distribution Hierarchy for IWTP Interim Treatment,

Alternative 1: No Action 63

2‑3: Alternative 1 Hydrograph, Average Flow Day ‑ Year 2001 65

2‑4: Alternative 2: Operate IWTP 73

2‑5: Sewer Flows/Distribution Hierarchy for IWTP Interim Treatment,

Alternative 2: Operate IWTP 75

2‑6: Alternative 2 Hydrograph, Average Flow Day ‑ Year 2001 77

2‑7: Alternative 3: Operate IWTP with Detention Basin 83

2‑8: Alternative 3, Schematic IWTP with Detention Basin 85

2‑9: Sewer Flows Distribution Hierarchy for IWTP Interim Treatment

Alternative 3: Operate IWTP with Detention Basin 87

2‑10: Alternative 3 Hydrograph, Average Flow Day ‑ Year 2001 89

2‑11: Alternative 4: Operate IWTP and Discharge to Mexico 93

2‑12: Proposed Additional Mexican Conveyance Facilities 95

2‑13: Sewer Flows/Distribution Hierarchy for IWTP Interim Treatment,

Alternative 4: Operate IWTP and Discharge to Mexico 97

2‑14: Alternative 4 Hydrograph, Average Flow Day ‑ Year 2001 99

2‑15: Alternative 5: Operate IWTP and Discharge to SBOO 105

2‑16: Sewer Flows/Distribution Hierarchy for IWTP Interim Treatment,

Alternative 5: Operate IWTP and Discharge to SBOO 107

2‑17: Alternative 5 Hydrograph, Average Flow Day ‑ Year 2001 109

FIGURES (cont.)

3.1‑1: North Draining Canyons and Gullies 121

3.1‑2: Tijuana River National Estuarine Research Reserve 131

3.2‑1: TOES Model Current Patterns 137

3.4‑1: Habitats within the Tijuana Estuary 149

3.6‑1: Regional Fault Map 179

4.2‑1: Annual Average Effluent Dilution Contours, No Project
Alternative,

Year 2001 221

4.2‑2: Predicted Coliform Counts at the International Boundary, No
Project

Alternative, Year 2001 223

4.2‑3: SBOO Annual Average Dilution Contours 247

4.2‑4: Predicted Coliform Counts near the Imperial Beach Kelp Bed,

Ocean Layer 3 251

4.2‑5: Annual Average Deposition Rates of Total Suspended Solids 255

PHOTOGRAPHS

1‑1: Pump Station One

1‑2: Conveyance Canal

1‑3: Shoreline Discharge Channel

1‑4: Shoreline Discharge Point

TABLES

S‑1: Summary of Significant Adverse Effects for IWTP Interim Operation

Alternatives xx

2‑1: No Action Alternative Projected Flows 59

2‑2: Year 2001 Diurnal Flows for the No Action Alternative 67

2‑3: Interim Operation of the IWTP 72

2‑4: Interim Operation of the IWTP with 5.5 Million Gallons Flow Storage
81

2‑5: Operate IWTP with New Conveyance to Mexico Using the Emergency
Connection 92

2‑6: IWTP with the South Bay Ocean Outfall 103

3.1‑1: Maximum Discharge of the Tijuana River near Nestor between
1884‑1984 119

3.1‑2: 1990 and 1995 Pollutant Loading of Tijuana River 123

3.1‑3: 1990 and 1995 Pollutant Loading at Pump Station One 125

3.4‑1: Listed and Proposed Endangered and Threatened Species and
Candidate

Species That May Occur in the Area of the Tijuana River Estuary 148

3.5‑1: Fish Species Observed in Nearshore and Offshore Areas Off
Imperial

Beach and the Tijuana River 164

3.5‑2: Marine Mammals Observed or Stranded from 1966 to 1986 169

3.5‑3: Common Seabirds of the Southern California Bight 171

3.5‑4: Shorebirds Observed on Sandy Beaches near Tijuana Estuary 173

3.5‑5: Threatened and Endangered Species 175

3.8‑1: Ambient Air Quality Standards 187

3.8‑2: Summary of Air Quality Data for the San Diego Air Basin 188

3.8‑3: Number of Days Air Quality Standards Were Exceeded at Chula Vista

Monitoring Station 189

TABLES (cont.)

4.1‑1: Wastewater Influent and Effluent Pollutant Concentrations 206

4.2‑1: Simulated Effluent Dilutions at International Border, Surf
Discharges

in Mexico: No Project Alternative, Year 2001 220

4.2‑2: Total Coliform (per 100 ml) at the International Border, Shore
Discharge

Model: No Project Alternative, Year 2001 226

4.2‑3: Compliance with Body‑Contact Standards, Surf Discharges in

Mexico: No Action Alternative, Year 2001 228

4.2‑4: Simulated Effluent Dilutions at International Border, Surf
Discharges

in Mexico: Operate IWTP with New Conveyance to Mexico Using Emergency
Connection, Year 2001 234

4.2‑5: Simulated Effluent Dilutions at International Border, Surf
Discharges

in Mexico: Operate IWTP with New Conveyance to Mexico Not Using

Emergency Connection, Year 2001 234

4.2‑6: Total Coliform (per 100 ml) at the International Border, Shore
Discharge

Model, Operate IWTP with New Conveyance to Mexico Alternative

Using Emergency Connection, Year 2001 235

4.2‑7: Total Coliform (per 100 ml) at the International Border, Shore
Discharge

Model, Operate IWTP with New Conveyance to Mexico Alternative Not Using
Emergency Connection, Year 2001 236

4.2‑8: Compliance with Body‑Contact Standards, Surf Discharges in

Mexico: Operate IWTP with New Conveyance to Mexico

Alternative Using Emergency Connection, Year 2001 238

4.2‑9: Compliance with Body‑Contact Standards, Surf Discharges in

Mexico: Operate IWTP with New Conveyance to Mexico

Alternative Not Using Emergency Connection, Year 2001 239

4.2‑10: Simulated Effluent Dilutions at International Border, Surf
Discharges

in Mexico: Operate IWTP with Discharge to SBOO, Year 2001 240

4.2‑11: Total Coliform (per 100 ml) at the International Border, Shore
Discharge

Model, Operate IWTP with Discharge to SBOO, Year 2001 242

4.2‑12: Compliance with Body‑Contact Standards, Surf Discharges in

Mexico: Operate IWTP with Discharge to SBOO, Year 2001 243

4.2‑13: Simulated Effluent Dilutions at SBOO Zone of Initial Dilution:

Operate IWTP with Discharge to SBOO, Year 2001 249

4.2‑14: Total Coliform (per 100 ml) at the Imperial Beach Kelp Bed,
Ocean

Discharge Model: Operate IWTP with Discharge to SBOO, Layer 3,

Year 2001 253

4.8‑1: Significance Thresholds 293

APPENDIXES

A: USIBWC/EPA flow memo

B: Estuarine biology technical report

C: Marine biology technical report

D: Summary of environmental laws of Baja California

E: IBWC Minutes

List of Acronyms

AB Assembly Bill

APCD Air Pollution Control District

AQAP Air Quality Attainment Plan

ASBS Area of Special Biological Significance

BOD biological oxygen demand

CAAQS California ambient air quality standards

CARB California Air Resources Board

CDFG California Department of Fish and Game

CEQ Council on Environmental Quality

CPFV commercial passenger fishing vessel

D/T dilution over threshold

dB decibel

DHS (California) Department of Health Services

EA Environmental Assessment

EDL elevated data levels

EIS Environmental Impact Statement

EPA (U.S.) Environmental Protection Agency

FEIS Final Environmental Impact Statement

FONSI Finding of No Significant Impact

HEC‑RAS Hydraulic Engineering Center‑River Analysis System

IWTP (South Bay) International Wastewater Treatment Plant

lps liters per second

mgd million gallons per day

MHHW mean higher high water

MLLW mean lower low water

MM Modified Mercalli

MPN minimum probable number

MSL mean sea level

NAAQS national ambient air quality standards

NMFS National Marine Fisheries Service

NOAA National Oceanic and Atmospheric Administration

NPDES National Pollutant Discharge Elimination System

NWR (Tijuana Slough) National Wildlife Reserve

PAH Poly(cyclic) aromatic hydrocarbons

PERL Pacific Estuarine Research Laboratory

PM‑10 Particulate matter less than 10 microns

ppb parts per billion

ppm parts per million

ppt parts per thousand

RAQS Regional Air Quality Strategies

RMPP Risk Management Prevention Plan

ROD Record of Decision

ROV remotely operated vehicle

RV recreational vehicle

RWQCB Regional Water Quality Control Board

SANDAG San Diego Association of Governments

SBLO South Bay Land Outfall

SBOO South Bay Ocean Outfall

SCAQMD South Coast Air Quality Management District

SCCWRP Southern California Coastal Waters Research Project

SDAB San Diego Air Basin

SDM Shore Discharge Model

SEDUE Secretariat of Urban Development and Ecology

SEIS Supplemental Environmental Impact Statement

SWRCB State Water Resources Control Board

TCM transportation control measures

TDS total dissolved solids

TJVCWD Tia Juana Valley County Water District

TOES Tijuana Oceanographic Engineering Study

TRNERR Tijuana River National Estuarine Research Reserve

TSS total suspended solids

USACE United States Army Corps of Engineers

USDA United States Department of Agriculture

USFWS United States Fish and Wildlife Service

USIBWC International Boundary and Water Commission, United States
Section

ZID zone of initial dilution

Executive Summary

Scope of the SEIS

The South Bay International Wastewater Treatment Plant (IWTP) and South
Bay Ocean Outfall (SBOO) are currently under construction as identified
in the Final Environmental Impact Statement (FEIS) and Record of
Decision (ROD) signed in May 1994. The purpose of the project is to
provide new wastewater control facilities to safeguard the public
health, environment, public beaches, water quality, and economy of San
Diego, California. In conjunction with actions taken by Mexico, this
project would minimize dry‑weather flow of untreated sewage from the
municipality of Tijuana, Baja California, Mexico, into the United
States. Currently, such flows cause chronic and substantial pollution in
the Tijuana River valley, national reserve estuary, and coastal areas
used for agriculture and public recreation and is designated critical
habitat for federal and state listed endangered species. In the 1994
ROD, the federal agencies decided to build a secondary wastewater
treatment facility and ocean outfall.

The purpose of this Supplemental Environmental Impact Statement (SEIS)
is to evaluate proposed project changes to operate the plant as an
advanced primary treatment facility on an interim basis. Unless the
facility is operated during this period, dry‑weather flows of sewage
could continue to pollute the river, estuary, and coastal waters in the
U.S. This Interim Operation SEIS evaluates alternatives for using the
IWTP as an advanced primary treatment works until alternatives to
secondary treatment are evaluated and the SBOO is completed.
Alternatives for providing secondary level treatment of sewage at the
IWTP will be the subject of an additional SEIS.

The development of the IWTP and SBOO and the proposed interim operation
of the facilities is a collaborative effort of the U.S. and Mexico
through the International Boundary and Water Commission, U.S. Section
(USIBWC), U.S. Environmental Protection Agency (EPA), State Water
Resources Control Board, Regional Water Quality Control Board, and the
City of San Diego.

Purpose and Need for Action

The Tijuana River and nearshore coastal waters of the United States have
been contaminated with raw sewage since the 1930s. Due to the
physiographic setting and proximity of the city of Tijuana to the United
States untreated sewage flows into the United States via the Tijuana
River or through north‑draining canyons and gullies. Untreated sewage is
also discharged to nearshore ocean waters in Mexico, 5.6 miles (9 km)
south of the international border, which may affect the quality of ocean
waters in the U.S. The contamination has been the result of Tijuana\'s
rapid and constant population growth coupled with a lack of
corresponding sewerage infrastructure.

From 1980 to 1991, however, there were sustained perennial flows of
wastewater in the Tijuana River. Flow data measured by the USIBWC
indicated that the average wastewater flow into the U.S. was 13 million
gallon per day (mgd) (569 liters per second \[lps\]) in 1990. In 1991
Mexico installed a collector in the Tijuana River to divert up to 13 mgd
of dry‑weather flows to the sewage system. More recently, estimates are
that in 1993, 3 mgd (131 lps) of wastewater was in the river and in
1995, 1 mgd (44 lps).

These untreated sewage flows have caused chronic quarantines of public
beaches along the south San Diego coastline (Border Field State Park,
City of Imperial Beach, Silver Strand State Beach, and City of Coronado)
and substantially and adversely affected the residents of the Tijuana
River valley and the environmental quality of the Tijuana River estuary,
a National Estuarine Research Reserve.

The USIBWC/EPA have developed estimates of future sewage generation from
Tijuana through the year 2001 based upon an annual growth rate of 4.8
percent. The estimates indicate that if no action is taken, the
capability of Mexico\'s current sewage collection system would be
exceeded by 1.1 mgd (48 lps) to 3.5 mgd (153 lps) by the end of 1996. By
the planning horizon year of 2001, the system\'s capacity would be
exceeded by 5.6 mgd (245 lps) to 9.5 mgd (416 lps). Unless action is
taken, these untreated sewage flows would enter the U.S. and pollute the
Tijuana River and nearshore coastal areas.

Additionally, the capacity of the San Antonio de los Buenos treatment
facility in Mexico is currently being exceeded and untreated flows of
sewage are being discharged to the shoreline in Mexico. The volumes of
untreated sewage being discharged at the shoreline are estimated to be
19 mgd (832 lps) in 1996 and would increase to 22.9 mgd (1,003 lps) by
2001.

The IWTP will be operational as an advanced primary treatment works
before secondary treatment is available or the ocean outfall is
operational. The IWTP can detain and treat peak flows in the interim
period that may otherwise be discharged untreated to the Tijuana River
and nearshore ocean waters in Mexico. These flows, in excess of the
Mexican pump station or treatment works capacities, could be diverted
for treatment to advanced primary levels at the IWTP, beginning in 1997.
Therefore, consideration of the earliest possible operation of the IWTP
is of urgent necessity.

Current and Planned Facilities in Mexico and the U.S.

The chronic contamination has been acknowledged in numerous declarations
by local, state, and federal legislative bodies and commissions and has
been the subject of international agreements between the U.S. and
Mexico. To address this international problem, the U.S. and Mexico have
considered various alternatives for increasing the quantity and level of
sewage treatment and discharge options. The U.S. and Mexico subsequently
entered into binational agreements (Minute Nos. 270 and 283) to
construct in both countries new facilities to collect, treat, and
dispose of sewage.

Mexico\'s Facilities

The Stage I facilities proposed under Minute No. 270 substantially
comprise the current facilities in Mexico. These facilities include:

Concentration of the Tijuana River basin\'s wastewaters at

Pump Station One, improved to provide a 50 mgd (2,190 lps) peak
capacity, 36 mgd (1,576 lps) average capacity.

Conveyance of the wastewaters via a 42‑inch (1.07 m) force main with a
peak capacity of 62 mgd for discharge to the existing conveyance canal.

Collection, pumping, and conveyance from canyon areas for

disposition in the conveyance canal.

Pumping and conveyance from the Playas de Tijuana area to

the conveyance canal.

Conveyance via a covered and open canal for disposal of wastewaters 5.6
miles (9 km) south of the international boundary.

Construction of two secondary treatment facilities (Modules 1 and 2),
each with a capacity of between 17 and 25 mgd (745 and 1,095 lps)
utilizing aerated facultative lagoons at a location four miles (6.4 km)
south of the international boundary.

Most of these facilities, including the San Antonio de los Buenos
treatment works (Module 1, but not Module 2), have been completed and
are being operated by Mexico.

In October 1991, Mexico completed construction of and operates a
diversion structure in the Tijuana River in Mexico, about 325 feet (100
m) upstream of the international border. A mixture of river flows and
sewage can be captured and diverted to Pump Station One. During dry
weather, up to 13 mgd (569 lps) of sewage‑contaminated flows can be
pumped from the concrete, low‑flow river channel into Mexico\'s
collection system and to Pump Station One if capacity is available.
Wet‑weather and storm flows are allowed to pass through to the U.S.,
even if contaminated with sewage.

U.S. Facilities

Emergency Connection

An emergency connection between Pump Station One and the City of San
Diego\'s South Metro Interceptor sewer has been in existence since 1966.
This connector consists of a 30‑inch (0.76 m) sewer trending north from
Pump Station One to the 36‑inch (0.91 m) San Ysidro Interceptor; the San
Ysidro Interceptor ties into a 42‑inch (1.09 m) segment of the South
Metro Interceptor. The existing emergency connection can accept up to 13
mgd (569 lps) peak flows, which are treated and disposed of at the
City\'s Point Loma advanced primary treatment plant and ocean outfall.

The availability of the emergency connection to accept flows from Mexico
is limited and will not continue indefinitely into the future, however.
The emergency connection is also susceptible to being washed out by
flood flows in the Tijuana River.

South Bay International Wastewater Treatment Plant and Ocean Outfall

In keeping with Minute No. 283, the EPA and the USIBWC circulated an EIS
and signed an ROD in May 1994 for new federal facilities to treat
sewage. Construction has begun of a 25 mgd (1,095 lps) federal treatment
works known as the South Bay IWTP and the SBOO, a 200‑foot‑deep (65 m)
tunnel connecting with a wye diffuser located 18,700 feet (5.7 km)
offshore in 93‑foot‑deep (28 m) ocean waters to dispose of the treated
wastewater.

The IBWC project includes the following major elements:

The advanced primary portion of the IWTP (under construction); The
activated sludge portion of the IWTP (which has been designed, but
construction has been postponed until an additional SEIS has been
finalized);

Facilities for capturing and pumping sewage‑contaminated flows from
Stewart\'s Drain, Silva Drain, Canyon del Sol, Smuggler Gulch, and Goat
Canyon (under construction) and utilization of Mexico\'s existing
dry‑weather collector in the Tijuana River;

The South Bay Land Outfall (completed in 1993); and

The South Bay Ocean Outfall (under construction).

The headworks are designed to handle up to 100 mgd (4,380 lps) including
screening and degritting. The primary treatment facilities are designed
to treat average daily flows of 25 mgd (1,095 lps) with peak flows up to
75 mgd (4,117 lps) during high flow days. The activated sludge
facilities are designed to treat a constant flow of 25 mgd (1,095 lps).

Wastewater flows from east Tijuana are collected via the Tijuana
wastewater collection system and conveyed to Pump Station One, where
they are mixed with wastewater from central Tijuana. From Pump Station
One, wastewater will be directed to the IWTP in the United States or San
Antonio de los Buenos in Mexico. Wastewater flows from the Playas de
Tijuana, Matadero (Smuggler Gulch), and Laureles (Goat Canyon) pump
stations in Mexico will continue to be routed through the Mexican
conveyance system to the San Antonio de los Buenos treatment plant.

The outfall is designed to carry a maximum average daily flow of 174 mgd
(7,621 lps) and a peak daily flow of 333 mgd (14,585 lps) to enable use
of the outfall by both the IWTP and future City of San Diego Otay and
South Bay treatment works. The outfall is currently scheduled to be
completed by June 1998.

The advanced primary treatment works and ocean outfall are scheduled to
be completed in 1997 and 1998, respectively. Once completed, the IWTP
and ocean outfall would treat and dispose of sewage from Mexico that may
otherwise enter the U.S. untreated to safeguard the public health,
environment, public recreation, water quality, and economy of San Diego
and nearshore coastal waters.

Alternatives Considered

EPA and USIBWC are considering operating the IWTP as an advanced primary
treatment works prior to the completion of the ocean outfall and the
secondary treatment process trains to minimize the risk of discharges of
raw sewage or treated effluent into the Tijuana River. In considering
this action, alternatives for the discharge of advanced primary effluent
during the interim period prior to completion of the ocean outfall and
secondary treatment at the IWTP have been identified. The IWTP could
begin operation prior to completion of the ocean outfall with interim
discharge to the emergency connection, Mexico, the Tijuana River, or a
combination of these.

The potential effects of discharge of advanced primary effluent through
the outfall to the year 2001, the interim period, are also being
evaluated to allow for further consideration of the design and
construction of the secondary treatment facility.

Evaluation of Alternatives

The alternatives being considered by EPA and USIBWC are related to the
proposed operation of the IWTP as an advanced primary treatment works
for a limited period of time. Environmental effects from the
construction and operation of the IWTP as a secondary treatment works
and land and ocean outfall were considered in the 1994 FEIS. For interim
operation, no major additional facilities in the U.S. would be required,
although Mexico may construct additional pumping and conveyance
facilities in Mexico.

Estimated Sewage Flows from Mexico

Future Tijuana wastewater flow estimates were developed by USIBWC/EPA
based upon flow data collected by IBWC at the emergency connection and
the main wastewater conveyance canal in Tijuana during February to
December, 1995. These flows include all wastewater generated in Tijuana
except the uncollected flows that spill into the Tijuana River or
north‑draining canyons.

Total Tijuana flows were projected through the year 2001, as a
worst‑case scenario for completion of the SBOO and other facilities.

These flow projections were used to estimate the potential for discharge
of untreated sewage to the river and, given the existing treatment
capacity at San Antonio de los Buenos, the assumed untreated discharges
that could occur at the shoreline in Mexico. The projections also assume
continued use of the emergency connection to Point Loma.

Because of the limitations associated with the data available on past
flow conditions and the uncertainties in growth rate for the Tijuana
sewage, the USIBWC/EPA considers their flow projections to be rough
estimates. Overall, USIBWC/EPA tried to be conservative in their
assumptions and interpretations of available data, but actual flows
could be higher or lower than different from the projections, especially
by 2001.

Modeling of Effluent Discharge Effects

To assess the impacts to ocean water quality, marine biota and public
health from discharge of treated and untreated effluent to the shoreline
in Mexico and of advanced primary effluent through the ocean outfall,
Parsons Engineering Science has modeled the effects of the discharges
including coliform concentrations, dissolved oxygen, and transport
(dilution) of organic and inorganic constituents.

The modeling was based upon current data collected during the Tijuana
Oceanographic Engineering Study, which covered both Mexican and U.S.
waters surrounding the SBOO.

The USIBWC/EPA flow estimates for Tijuana sewage generation were used
and applied to the alternatives under consideration for the years 1996
and 2001. To provide a conservative analysis, the seasonal high flow
rates were used, which provide a worst‑case analysis.

The models provide a screening level analysis for water quality effects
for the shoreline and outfall discharges. The assumptions used for
current conditions, effluent quality, and flow rates are all
conservative estimates. As such, the model results are not definitive
predictions of the actual concentrations that would result from the
discharges once the IWTP or outfall is operational.

For purposes of the EIS, the model results are compared to the State
Ocean Plan as a threshold of significance. This should be understood as
a tool in evaluating alternatives and not as a determination of
compliance or noncompliance with standards during operations.

Alternative 1: No Action

In accordance with the May 1994 ROD, the IWTP would not be operated
until the secondary treatment works are completed and the ocean outfall
is operational. Flows from Tijuana would continue to be conveyed from
Pump Station One through Tijuana\'s existing system to its treatment
works at San Antonio de los Buenos, with flows in excess of 17 mgd (745
lps) discharged untreated to nearshore ocean waters. Flows to Pump
Station One would also be conveyed through the existing emergency
connection to the City of San Diego\'s system. Peak flows of raw sewage
in excess of the combined capacity of Pump Station One and the emergency
connection would be discharged into the Tijuana River in the U.S. via
Stewart\'s Drain. Based upon the USIBWC/EPA flow projections, these
untreated flows are estimated to be between 1.1 mgd (48 lps) average
daily flow and 3.0 mgd (131 lps) seasonal high daily flow in 1996 and
between 5.6 mgd (245 lps) to 9.7 mgd (425 lps) in 2001. Untreated flows
discharged to nearshore ocean waters in Mexico would reach 20 mgd (876
lps).

Alternative 2: Operate IWTP

The IWTP would be operated to provide advanced primary treatment before
completion of the ocean outfall. The IWTP would treat up to 25 mgd
(1,095 lps) average daily flow of untreated sewage from Mexico. Mexico
would continue to convey flows up to 38 mgd (1,664 lps) of untreated
sewage from Pump Station One to San Antonio de Los Buenos and excess
flows up to 13 mgd (569 lps) (during peak flow periods of the day) to
the emergency connection to Point Loma. Treated flows would be returned
from the IWTP to the emergency connection. It is possible that a small
amount of effluent could be returned from the IWTP to Pump Station One
during low‑flow periods of the day, but the emergency connection would
be the primary discharge point for the IWTP effluent.

During periods of peak flows, effluent treated at the IWTP that cannot
be discharged through the emergency connection would be discharged into
the Tijuana River in the U.S. These treated flows are estimated to be
between 1.4 mgd (61 lps) average daily flow in 1999 and 4.7 mgd (206
lps) seasonal high flow. Year 2001 flows would range between 3.6 mgd
(158 lps) and 7.5 mgd (329 lps).

Alternative 3: Operate IWTP with Detention Basin

The IWTP would be operated as an advanced primary plant, as in
Alternative 2. A 5.5 million gallon (20,900 m3) detention basin for
effluent storage would be constructed at the IWTP site to provide flow
equalization for diurnal and wet‑weather peak flows. The earthen
detention basin would be lined, with a depth of 10 to 15 feet (3.0 to
4.6 m) and covering an area of 1 to 2 acres (0.4 to 0.8 ha). Treated
flows would be stored within the detention basin to be released to Pump
Station One or the emergency connection during off‑peak hours. If the
capacity of the Mexican system, emergency connection and detention basin
would be exceeded, then the excess treated flows would be discharged to
the Tijuana River in the U.S.

It is anticipated that no untreated or treated flows would be discharged
to the Tijuana river prior to the scheduled completion of the ocean
outfall in 1998. If the SBOO were not available, there would be no flows
to the Tijuana River during average day flows through the year 2001;
during seasonal high flow days, there would need to be a discharge of
0.7 mgd (31 lps) in the year 2000 and 2,0 mgd (88 lps) in 2001.

Alternative 4: Operate IWTP with New Conveyance to Mexico

A new pumping and conveyance system would be constructed by Mexico as a
parallel backup facility for the existing Mexican conveyance system,
with a capacity of 50 mgd (2,150 lps), to convey flows from Pump Station
One to the discharge point in Mexico. These backup facilities would
provide an additional pumping and conveyance system and would allow
maintenance to be performed on the existing facilities, once the SBOO is
placed into service.. During the interim period, the IWTP would treat
flows up to 25 mgd (1,095 lps) from Tijuana. Once treated, the effluent
would be sent to Tijuana via the new pump station and conveyance
pipeline for discharge in Mexico, near the San Antonio de los Buenos
treatment plant. The existing pumping and conveyance system to the
treatment works in San Antonio de los Buenos would continue to operate.

No discharge of untreated or treated flows to the Tijuana River in the
U.S. is anticipated. No discharge of untreated sewage to the shoreline
in Mexico would occur until 1999 with average flow conditions.

Alternative 5: Operate IWTP with Discharge to SBOO

The South Bay Ocean Outfall is currently under construction. Once
completed in 1998, 25 mgd (1,095 lps) of advanced primary effluent from
the IWTP would be discharged to the ocean. No discharge to the Tijuana
River or through the emergency connection would be necessary.

Alternative 6: Phased Alternative

The previous alternatives have been evaluated as stand‑alone
alternatives to taking no action through the year 2001. It is also
reasonable to evaluate the use of these individual alternatives in a
phased approach.

The logical phasing scheme would begin with Alternative 2, operate the
IWTP to detain up to 2 million gallons (7,600 m3) of flow and treat
additional flows from eastern Tijuana as needed with discharge to the
emergency connection. When it appears that the total average dry‑weather
flows from eastern Tijuana or higher seasonal high peak flows would
result in discharge of treated effluent from the IWTP to the Tijuana
River (expected by 1997 or 1998), then either Alternative 3 (Operate
IWTP with Detention Basin) or Alternative 4 (Operate IWTP with New
Conveyance to Mexico) could be implemented. Either of these two
alternatives could provide a means to avoid discharging treated effluent
from the IWTP into the Tijuana River. When the SBOO is completed, all
treated effluent from the IWTP would be discharged through the SBOO.
Once the SBOO is available, neither the earthen detention basin nor the
additional conveyance system in Mexico would be needed to discharge
treated effluent from the IWTP.

An additional consideration for Alternative 6 is the time required to
construct the facilities. The IWTP will be operational by early 1997.
The 5.5 million gallon (20,900 m3) lined earthen detention basin would
take 9 months to construct and could be available by September 1997. The
new Mexican pumping and conveyance system, is expected to take 15 months
to complete once agreement with Mexico has been reached. These
facilities are not expected to be available for use until 1998. The SBOO
is currently under construction and would not be available for use until
the spring of 1998.

The impacts of the phased alternative would be equal to or less than the
stand‑alone alternatives as analyzed above. The phased alternative would
reduce the impacts from discharge of treated effluent to the Tijuana
river, since each facility would be used in an attempt to avoid
discharge of treated effluent into the Tijuana River. However, the
USIBWC/ EPA flow projections are estimates, and the flows sent from
Mexico may exceed the discharge capacity before these facilities are
available. If this occurs, discharge of treated effluent into the
Tijuana River will be unavoidable and the adverse environmental impacts
will be similar to those discussed for Alternative 2.

Significant Environmental Effects of the Alternatives

The alternatives were assessed for significant environmental effects,
including direct, indirect, adverse, and beneficial. The evaluation of
alternatives is based upon estimates of future flows from Mexico and
sewage characteristics, estimates of both IWTP and San Antonio de los
Buenos effluent quality, and modeling of the effects of ocean
discharges. In the summary Table S‑1, many effects are designated as
&quot;potentially significant adverse.&quot; This indicates that the
future effects can only be estimated within a range of values, within
which range significant adverse effects could result. This lack of
certainty is unavoidable given the information available.

Preferred Alternative

The goal of the action is to avoid the discharge of untreated sewage and
minimize the effects of the discharge of treated effluent to sensitive
areas such as the Tijuana River, estuary, shoreline, offshore kelp beds,
and active recreation and commercial areas. As discharges from the
shoreline in Mexico may affect U.S. coastal waters, the alternative that
provides the maximum level of treatment to the greatest volume of sewage
prior to discharge, whether the discharge occurs in Mexico or the U.S.,
would be preferred. However, selection of a preferred alternative is
also subject to considerations of environmental effects of the
alternatives, cooperation with Mexico, timeliness to implement, and
costs.

For the interim operations period, the preferred approach alternative
would be to phase alternatives as described for Alternative 6.

TABLE S‑1

SUMMARY OF SIGNIFICANT ADVERSE EFFECTS FOR IWTP INTERIM OPERATION
ALTERNATIVES

Tijuana Tijuana River River Ocean Land Use Alternativ Surface Valley
Waters Estuarine Marine Geology Odors Health and and e Water Groundwater
Quality Biology Biology Safety Socioeconomi Quality Quality cs

Alternativ Significant Significant Significant Significant Significant
No effect Significant Significant Significant e 1: No unavoidable
unavoidable unavoidable unavoidable unavoidable unavoidable unavoidable
Action adverse adverse adverse unavoidable adverse adverse adverse
adverse effects effects effects adverse effects effect effect effects
(discharge (discharge (discharge effects (discharge (discharge
(contaminati (contaminati of of of (discharge of of on and on of
untreated untreated untreated of untreated untreated ponding of river,
sewage to sewage to sewage to untreated sewage to sewage in sewage in
odors, river) river) shoreline sewage to shoreline river) river ) beach
in U.S. and estuary) in U.S. and closures) Mexico) Mexico)

Al;ternati Significant Significant Significant Significant Significant
No effect Significant Significant Significant ve 2: unavoidable
unavoidable unavoidable unavoidable unavoidable unavoidable unavoidable
Operate adverse adverse adverse unavoidable adverse adverse adverse
adverse IWTP effects effects effects adverse effects effect effect
effects (discharge (discharge (discharge effects (discharge (discharge
(contaminati (contaminati of treated of treated of treated (discharge of
of advanced on and on of effluent to effluent to effluent of untreated
primary ponding of river, river) river) and advanced sewage to effluent
to treated odors, untreated primary shoreline river) effluent in beach
sewage to effluent in U.S. and river) closures) shoreline to Mexico) in
U.S. and estuary) Mexico)

Alternativ No effect No effect Potential No effect Potential Potential
Potential Potential Beneficial e 3: until 2001 until 2001 adverse until
2001 adverse adverse adverse adverse effects Operate (adverse‑dis
(adverse‑dis effect (adverse‑di effect mitigable mitigable effect IWTP
with charge of charge of (discharge scharge of (discharge effect effect
(beach Detention treated treated of treated treated of treated (basin
(cover closures in Basin effluent to effluent to effluent effluent
effluent design basins, U.S. from river) river) and to river) and
consideratio provide discharges untreated untreated ns) odor in Mexico)
sewage to sewage to control) shoreline shoreline in Mexico) in Mexico)

Alternativ No effect No effect Potential No effect Potential Potential
No effect Potential Potential e 4: adverse adverse adverse adverse
beneficial Operate effect effect mitigable effect effects IWTP with
(discharge (discharge effects (beach New of treated of treated (design
closures in Conveyance effluent to effluent to consideratio U.S. from to
shoreline shoreline ns for discharges Mexico in Mexico) in Mexico)
erosion in Mexico) control, seismic upset)

TABLE S‑1

SUMMARY OF SIGNIFICANT ADVERSE EFFECTS FOR IWTP INTERIM OPERATION
ALTERNATIVES

(continued)

Tijuana Tijuana River River Ocean Land Use Alternativ Surface Valley
Waters Estuarine Marine Geology Odors Health and and e Water Groundwater
Quality Biology Biology Safety Socioeconomi Quality Quality cs

Alternativ No effect No effect Potential No effect Potential No effect
No effect Potential Beneficial e 5: adverse adverse adverse effects
Operate effect effect effect IWTP with (exceedance (discharge (beach
Discharge of Ocean of treated closures in to SBOO Plan effluent to U.S.
from standards shoreline discharges for in Mexico) in Mexico)
polyaromatic hydrocarbons ; discharge of treated effluent to shoreline
in Mexico)

Phased No effect No effect Potential No effect Potential Potential
Potential Potential Beneficial Alternativ adverse adverse adverse
adverse adverse effects e effect effect mitigable mitigable effect
(exceedance (discharge effects effects (beach of Ocean of treated
(earthen (earthen closures in Plan effluent to detention detention U.S.
from standards shoreline basin) basin) discharges for in Mexico) in
Mexico) polyaromatic hydrocarbons ; discharge of treated effluent to
shoreline in Mexico)

Starting with operation of the IWTP in 1997, there would not be a need
to discharge treated effluent to the river until 1998, according to the
USIBWC/EPA flow projections for average day flows. No additional capital
costs would be incurred and discharge of effluent to the emergency
connection would not result in adverse impacts to receiving waters in
the U.S. However, to avoid discharge of treated effluent to the Tijuana
River during seasonal high flows in 1997, and average day flows in 1998
and thereafter to 2001, either the detention basin at the IWTP or new
conveyance facilities in Mexico would need to be constructed.

Each of these alternatives avoids discharge of treated effluent to the
Tijuana River. The new conveyance facilities in Mexico would probably
not be available until the middle of the year 1998, and discharges of
treated effluent could occur by that time if the IWTP is operated. The
addition of detention basins at the IWTP could be implemented in time
(September, 1997) to avoid any discharges of treated effluent to the
Tijuana River and does not require additional agreements with Mexico to
implement.

Neither of these interim alternatives is environmentally preferred to
SBOO, as the discharge of treated effluent at the shoreline in Mexico is
not preferable to discharge through the outfall offshore. Under current
schedules, the SBOO and the new Mexican conveyance are not scheduled to
be available until 1998. Assuming these concurrent schedules, the SBOO
would be preferred. However, if the new facilities in Mexico were
available and the SBOO is delayed, then the new facilities in Mexico
could be used to avoid discharges to the river until the SBOO is
available.

Once completed, discharge through the SBOO is the preferred alternative.
Environmental Commitments

The following mitigation measures would reduce or avoid potentially
significant effects of several of the alternatives considered. The
measures are presented as would be appropriate for each stand‑alone
alternative. For the preferred phased alternative, the measures would
still be necessary, but only for the period of time an alternative is
operating as a stand‑alone facility. For example, once the SBOO is
operational, vector control and estuary monitoring required for
Alternative 2 would no longer be necessary.

Alternative 2: Operate IWTP

If treated effluent is routinely discharged during dry weather to the
Tijuana River, a monitoring program will be undertaken. The program will
monitor changes in water quality using indirect indicators of water
source and sewage contamination. These include salinity, dissolved
oxygen, temperature, and coliform bacteria. The monitoring program will
be initiated prior to discharge of the effluent and will continue
through the period that effluent is discharged to the Tijuana River.
Reports of the monitoring will be provided to the Regional Water Quality
Control Board, Tijuana River National Estuarine Research Reserve, and
EPA.

If effluent is discharged to the Tijuana River, the USIBWC, in
cooperation with the County Department of Health Services, will monitor
the river channel during the dry season to ensure that no ponding of
treated effluent occurs within the low‑flow channel of the river. If
ponding does occur, vector control measures will be implemented.

Alternative 3: Operate IWTP with Detention Basin

If a detention basin is constructed at the IWTP, the earthen basin will
be lined with an impermeable liner to avoid percolation of treated
effluent to the groundwater. The liner will be included in design
specifications for the basin by USIBWC.

Site‑specific geotechnical investigations will be performed prior to
construction of the earthen basin to determine soil characteristics,
thickness, and distribution and to develop appropriate soil engineering
parameters for the proposed facility.

Fault evaluation studies will be performed of mapped fault traces in
order to confirm fault locations and activities. In addition, a
geologist shall observe excavations during construction to detect the
presence of unmapped traces in the general vicinity of mapped fault
traces.

Storage of treated effluent in the detention basin may result in
objectionable odors. As the basin would only fill during peak hourly
flow periods, these impacts would be short term. However, if
objectionable odors result, the detention basin would be covered and the
air circulated to an odor control device. IBWC will include an odor
control system in the design of the detention basin, if this alternative
is chosen.

Alternative 4: Operate IWTP with New Conveyance to Mexico

Mexico will conduct design review of the pipeline and pump station as
part of its environmental impact assessment and to their construction
standards. This design should anticipate the effects of ground shaking
and incorporate measures to minimize the risk of failure during seismic
events.

If construction of the pipeline is undertaken during the rainy season,
Mexico should incorporate erosion controls during any grading to prevent
erosion impacts into the U.S.

Alternative 5: Operate IWTP with Discharge to SBOO

Odor control facilities were included in the design for the IWTP. If
advanced primary treated effluent is discharged through the SBOO,
additional odor control facilities will need to be included at a vent
for the energy dissipater located between the plant and the South Bay
Land Outfall. The USIBWC will be responsible for ensuring that
appropriate odor control facilities are provided for discharge of
primary treated effluent through SBOO.

Agency and Public Participation in Decision Making

The SEIS has been prepared to assess the consequences of the
alternatives for proposed interim operation of the IWTP. The
environmental assessment will be used as an aid in decision making by
the USIBWC and EPA in deciding a future course of action. It is only one
of a number of considerations in determining a future course of action,
however. The SEIS will also be used as an informational document by
other federal, state, and local agencies‑including but not limited to
the U.S. Fish and Wildlife Service, State Water Resources Control Board,
California Coastal Commission, and City of San Diego‑in fulfilling their
jurisdictional responsibilities,permitting activities, or other
cooperation in implementing any future actions taken.

The Draft SEIS will be available for public and agency review from
September 6, 1996, through October 21, 1996. Requests for information or
copies of the Management Division, 75 Hawthorne SEIS may be directed to
Ms. Elizabeth Borowiec at EPA Region IX, Water Street, San Francisco, CA
94105, (415) 744‑1165, or Mr. Charles Fisher at the USIBWC San Ysidro
Office, 2225 Dairy Mart Road, San Ysidro, CA 92173, (619) 662‑7600.
Copies of the SEIS and supporting documents have also been made
available at local library branches in the vicinity of the project (San
Diego, San Ysidro, Imperial Beach, Otay Mesa, and Chula Vista). A public
hearing to receive comments to the Draft SEIS has been scheduled for
October 7, 1996, at Southwest High School.

USIBWC and EPA will review written comments to the Draft SEIS received
during the public and agency review period and oral comments at the
public hearing. A Final SEIS will then be prepared, including revisions
to the Draft SEIS and responses to comments on the Draft SEIS The Final
SEIS will be circulated for an additional 30‑day public review period.

The USIBWC and EPA will then prepare a Record of Decision for the action
that will include consideration of environmental factors as well as
other factors that were important in arriving at a decision.

Chapter One

Purpose and Need for Action

The Tijuana River valley and nearshore coastal waters of the United
States have been contaminated with raw sewage since the 1930s. The
contamination has been the result of Tijuana\'s rapid and constant
population growth coupled with a lack of corresponding sewerage
infrastructure. While Tijuana has grown into a city of approximately one
million residents, only about two‑thirds of the city is currently
sewered.

Due to the physiographic setting and proximity of the city of Tijuana to
the United States (Figure 1‑1), sewage that is not collected for
treatment in Mexico flows into the United States via the Tijuana River
or through north‑draining canyons and gullies. Untreated sewage is also
discharged to nearshore ocean waters in Mexico, 5.6 miles (9 km) south
of the international border, which may affect the quality of ocean
waters in the U.S. These untreated sewage flows have caused chronic
quarantines of public beaches along the south San Diego coastline
(Border Field State Park, City of Imperial Beach, Silver Strand State
Beach, and City of Coronado) and substantially and adversely affected
the residents of the Tijuana River valley and the environmental quality
of the Tijuana River estuary, a National Estuarine Research Reserve. The
contamination adversely impacts the quality of life for residents of the
river valley, agricultural production, coastal recreational
opportunities, and sensitive habitat and wildlife.

The chronic contamination has been acknowledged in numerous declarations
by local, state, and federal legislative bodies and commissions and has
been the subject of international agreements between the U.S. and
Mexico. To address this international problem, the U.S. and Mexico have
considered various alternatives for increasing the quantity and level of
sewage treatment and discharge options. The U.S. and Mexico subsequently
entered into binational agreements (Minute Nos. 270 and 283, included in
Appendix E to this SEIS) to construct in both countries new facilities
to collect, treat, and dispose of sewage.

In keeping with Minute No. 283, the U.S. Environmental Protection Agency
(EPA) and International Boundary and Water Commission, U.S. Section
(USIBWC) circulated an Environmental Impact Statement (EIS) and signed a
Record of Decision (ROD) in May 1994 for new federal facilities to treat
sewage. The ROD reflected a decision to construct a 25 million gallon
per day (mgd) (1,095 liters per second \[lps\]) secondary treatment
works and to discharge the effluent through an ocean outfall.
Construction has begun of a federal treatment works known as the South
Bay International Wastewater Treatment Plant (IWTP) and the South Bay
Ocean Outfall (SBOO), a 200‑foot‑deep (65 m) tunnel connecting with a
wye diffuser located 18,700 feet (5.7 km) offshore in 93‑foot‑deep (28
m) ocean waters to dispose of the treated wastewater.

The Final EIS (FEIS) and ROD for the IWTP and SBOO made a commitment to
provide secondary treatment of sewage from the IWTP discharged through
the SBOO. Construction of the treatment works is to be completed in two
phases. The advanced primary treatment works and ocean outfall are
scheduled to be completed in 1997 and 1998, respectively. Activated
sludge secondary treatment components have been designed for the IWTP;
but construction is on hold until further studies examining alternatives
to secondary treatment processes, including advanced integrated pond
systems, have been evaluated.

Once completed, the IWTP and ocean outfall would treat and dispose of
sewage from Mexico that may otherwise enter the U.S. untreated to
safeguard the public health, environment, public recreation, water
quality, and economy of San Diego and nearshore coastal waters. However,
until the new facilities are operational, there is a serious risk of
untreated sewage being discharged to the Tijuana River, estuary, or
coastline. Untreated sewage flows are still occurring in the Tijuana
River in Mexico. Mexico currently generates more sewage than it can
treat and discharges untreated sewage to the ocean surf zone. The
existing Mexican system\'s capability to convey or treat additional
sewage is limited. Significant limitations are due to diurnal (time of
day) and seasonal (wet weather) peak flows exceeding the capacity of the
system.

If no action is taken, given the existing facilities, USIBWC and EPA
estimate that up to 3.5 mgd (153.3 lps) of untreated sewage could be
discharged to the river in 1996 and up to 9.5 mgd (416 lps) could be
discharged by 2001. In addition, up to 22.9 mgd (1,003 lps) of untreated
sewage could be discharged to the surf 5.6 miles (9 km) south of the
international border by the year 2001.

As the discharge of untreated sewage from Tijuana constitutes a health
and safety concern, as well as causing environmental damage to the river
valley and coastal waters, capture and treatment of sewage flows is of
the utmost urgency.

The IWTP will be operational as an advanced primary treatment works
before secondary treatment is available or the ocean outfall is
operational. The IWTP can detain and treat peak flows in the interim
period that may otherwise be discharged untreated to the Tijuana River
and nearshore ocean waters in Mexico. Therefore, consideration of the
earliest possible operation of the IWTP is of urgent necessity.

Figure 1‑1 The USIBWC and EPA are considering potential actions to
reduce the risk of sewage contamination during this interim period until
the new facilities are completed. The general options under
consideration are:

No Action: The IWTP would not be operated until the

ocean outfall is complete and activated sludge facilities are
constructed, as described in the 1994 FEIS. The IWTP would only
discharge effluent treated to secondary standards. Taking no action
could result in flows of untreated sewage in the Tijuana River in the
U.S. in 1996 and thereafter.

Interim Advanced Primary Operation and Discharge: The

IWTP could be operated as an advanced primary treatment works prior to
the ocean outfall being completed. Various treated effluent disposal
options are under consideration, including disposal through the existing
emergency connection with the City of San Diego\'s Point Loma treatment
plant; return to the current Mexican pumping and conveyance system;
return to a new Mexican pumping and conveyance system; discharge to the
Tijuana River; or discharge to uplands, groundwater, or the surf zone in
the U.S. These options could reduce or avoid discharges of untreated
sewage to the Tijuana River in the U.S. and nearshore ocean waters in
Mexico.

Interim Advanced Primary Operation and Discharge through

SBOO: The IWTP could be operated as an advanced primary plant and the
treated effluent discharged through the SBOO. The advanced primary
effluent discharge would continue only until the activated sludge
components or other secondary treatment process becomes operational;
thus, this option is under consideration for a limited duration of three
to five years. This alternative would limit discharge of untreated
sewage in the U.S. and reduce the discharge of untreated sewage to
nearshore ocean waters in Mexico.

The prior FEIS and ROD for the IWTP includes a commitment to prepare
supplemental environmental studies if any future actions involving the
IWTP were to be undertaken which resulted in less than secondary
effluent being discharged through the SBOO. This Supplemental EIS (SEIS)
addresses potential interim operation of the IWTP with less than
secondary treated effluent and various disposal options. It also
addresses interim discharge of primary treated effluent through the
SBOO. The EPA and USIBWC will consider secondary treatment process
alternatives and the effects of continuing the discharge of less than
secondary effluent through the SBOO over a longer period of time in an
additional SEIS.

Background to the Proposed Action

Physical Setting

Tijuana River Watershed

The Tijuana River is an ephemeral stream within a watershed that drains
an area of 1,700 square miles (4,250 km2), of which 455 square miles
(1,138 km2) (about 30%) are in the United States and 1,245 square miles
(1,930 km2) (about 70%) are in Mexico. The fan‑shaped drainage area is
about 75 miles (121 km) long and 50 miles (80 km) wide (Figure 1‑2). The
majority of this watershed is sparsely populated rural lands of natural
open space or rural residential and agricultural uses; however, the
metropolitan city of Tijuana and the city of Tecate are within the
drainage area in Mexico.

The Tijuana River is formed by the confluence of Cottonwood Creek (Rio
El Alamar) and the Rio de las Palmas about 11 miles (17.7 km) southeast
of Tijuana. The Tijuana River flows northward through a 2.7‑mile (4.3
km) concrete flood‑control channel in the city of Tijuana and crosses
the international boundary into California. The flood control channel
flares out into a dissipater basin for 1.0 mile (1.6 km). The flood
control project is of an international character, operated and
maintained under the supervision of the IBWC under Minute No. 283. After
the pilot channel of the river crosses into the U.S., it continues
westward about 5.3 miles (6.9 km) and empties into the Pacific Ocean
about 1.5 miles (2.4 km) north of the international boundary. The
Tijuana River estuary lies at the mouth of the river at the Pacific
Ocean (Figure 1‑3).

The average annual rainfall across the watershed ranges from about 11
inches (28 cm) near the coast to 25 inches (63.5 cm) at the higher
inland elevations. There are distinct wet and dry seasons, with over 90
percent of the mean annual precipitation occurring during the six‑month
period of November through April.

The Tijuana River is an ephemeral stream characterized by low or no flow
for many months of a given year. Intermittent flood flows are highly
variable and are dependent upon rainfall amounts and intensity across
the watershed. Brief periods of very high flows, primarily during the
rainy season, are typically followed by low or no summer flows. The
flood control channel is designed for 135,000 cubic feet per second
(cfs) (3,820 cubic meters per second \[m3/s\]). Since its completion in
December 1978, it has passed floods with instantaneous peak flows of
32,100 cfs (779 m3/s) on January 30, 1980; 33,100 cfs (937 m3/s) on
February 21, 1980; 27,700 cfs (673 m3/s) on March 3, 1983; 32,600 cfs
(792 m3/s) on January 16, 1993; and 20,000 cfs (486 m3/s) on February 2,
1993. The average annual volume crossing the international border
between the years 1936 and 1981 is 33,000 acre‑feet/year (40 m3), with
the highest flow recorded during 1979‑1980 at 586,000 acre‑feet (715 m3)
(Izbecki 1985). Surface storm flows provide recharge to the underlying
unconfined aquifer, which has an estimated storage of 65,000 acre‑feet
(79 m3).

Figure 1‑2

Figure 1‑3

From 1980 to 1991, however, there were sustained perennial flows of
wastewater in the Tijuana River (Zedler, Nordby, and Griswold 1990;
Williams and Swanson 1987). Flow data measured by the USIBWC indicated
that the average wastewater flow into the U.S. was 13 mgd (569 lps) in
1990. In 1991 Mexico installed a collector in the Tijuana River to
divert up to 13 mgd of dry‑weather flows to the sewage system. This
diversion is not operated when sewage flows exceed available conveyance
capacity in Mexico or during wet‑weather river flows, however. More
recently, estimates are that in 1993, 3 mgd (131 lps) of wastewater was
in the river and in 1995, 1 mgd (44 lps). Urban discharges into the
river, such as trash, detergents, oils, fertilizers, and pesticides,
also occur.

Tijuana River Valley

An alluvial floodplain forms the floor of the Tijuana River valley, the
most southwesterly point in the continental U.S. From an elevation of 40
feet (12.2 m) above mean sea level (MSL) at the Mexican border, the
river valley gradually descends westward to its outlet into the ocean.
The valley floor averages about 1.0 mile (1.6 km) in width; it is
bordered by coastal terraces that range from 20 to over 400 feet (6 to
122 m) in elevation. The Tijuana River can be characterized as a braided
alluvial stream that shifts widely across the valley floor during flood
stage (Figure 1‑4).

The existing vegetation along the riparian corridor in the lower Tijuana
River valley is composed primarily of various species of willow and
cottonwood with varied herbaceous species and mule fat. The upland areas
of the river valley are primarily ruderal disturbed vegetation or active
agriculture and coastal sage scrub. Sensitive wildlife that occur in the
valley include the federally listed least Bell\'s vireo, peregrine
falcon, and coastal California gnatcatcher.

The sparsely populated Tijuana River valley is predominantly natural
open space with privately held lands in agricultural, ranching, and
extractive uses. South of the estuary along the shoreline is a public
coastal recreation area, Border Field State Park; to the north is
Imperial Beach Naval Air Station and the city of Imperial Beach. Most of
the remainder of the valley is designated by the County as part of the
Tijuana River Valley Regional Open Space Park or is in private use for
agriculture and ranching. Tijuana Estuary

At the west end of the valley, the Tijuana River braids into a large
estuary, federally designated as the Tijuana River National Estuarine
Research Reserve. The Tijuana River estuary is one of 18 estuarine
research reserves in the United States and one of only two in California
(Seamans 1988). The estuary is the site of one of the United States\'
few long‑term wetlands research programs. In 1982, the Tijuana River
National Estuarine Research Reserve was established by the National
Oceanic and Atmospheric Administration (NOAA) to protect one of the few
remaining large areas of coastal wetland in southern California.

In its natural state, the Tijuana River estuary consisted of about 870
acres (352 ha) of intertidal wetlands. The estuary currently consists of
about 350 acres (141.8 ha) of tidal slough and salt marsh (as measured
from 1986 aerial photographs), which are bounded by coastal uplands to
the north and south and the alluvial floodplain of the Tijuana River to
the east (Philip Williams &amp; Associates 1987:9). A three‑mile‑long
(4.8 km) barrier beach separates the estuary from the Pacific Ocean at
its western boundary. From the estuary entrance channel, tidal flows are
distributed by four channels. Ten distinct habitats occur within the
estuary area: ocean barrier beach; barrier dunes; relict tidal channel;
non‑tidal pickleweed salt marsh; non‑tidal salt pan; brackish marsh;
mule fat scrub; southern willow scrub; Diegan coastal sage scrub; and
ruderal (disturbed) habitat. Sensitive species include the federally
listed California brown pelican, light‑footed clapper rail, California
least tern, and salt marsh bird\'s beak and the state listed Belding\'s
savannah sparrow.

Since 1982, a land acquisition program has been under way for the
estuary. The Tijuana Estuary Management Plan (James Dobbin Associates
1986) established a framework for developing an enhancement plan to
address the serious physical changes affecting the estuary. Ocean
Environment

The South Bay region is characterized as a coastal bight with nearshore
shallow sandy bottom conditions. The currents along the coast are
dominated by the southerly flowing California current, which occurs at
the surface and near the surface along the edge of the continental
shelf, and a northerly flowing undercurrent beneath the California
current and northerly countercurrents at the surface and near the
surface which flow near the coastline. At certain times of the year, a
transient counterclockwise circulation forms south of Point Loma
extending 6.2 to 9.3 miles (10 to 15 km) offshore and 10.6 miles (17 km)
alongshore. This is an intermittent phenomenon and alternating northerly
and southerly currents are the dominant pattern. A kelp bed is located
north of the Tijuana River estuary. Beneficial ocean uses include
coastal recreation, endangered species habitat, diving, sportfishing,
boating, whale watching, commercial fishing, and kelp harvesting.
Commercial shipping lanes are over five miles offshore in this area.

Tijuana and Tecate

The municipality of Tijuana includes an area of 1,381 square miles, with
urbanized areas concentrated along the border and both sides of the
Tijuana River. The 1990 population was 747,000 (San Diego Association of
Governments \[SANDAG\] 1992) and current 1996 estimates are
approximately 1.1 million. In 1990 there were 161,338 occupied housing
units, of which 65 percent were sewered. There were 2,500 industrial
plants, including 463 maquiladoras, or twin plants, engaged in the
assembly of components from other countries. Manufacturing industries of
Tijuana include metal products, machinery, and equipment; chemical
substances and petroleum; minerals, paper, and printing; wood and wood
products; textiles, clothing, and leather; and food and Figure 1‑4
(oversize)

beverage products. Agriculture and livestock are also important sectors
of the local economy. Figure 1‑5 is a view from space of the extent of
urbanization in Tijuana.

The municipality of Tecate is situated approximately 30 miles to the
east within the Tijuana River watershed. The 1990 population was 51,557
persons; Tecate has 120 industrial plants, with mining, agriculture, and
cattle raising as the principal activities. Tecate has a new sewage
treatment works, as does the Tecate brewery, both of which discharge
effluent to the watershed (SANDAG 1992). History of Border Sewage
Contamination

By the mid 1930s Tijuana\'s population was approximately 16,000
residents. Its sewerage consisted of a septic tank system with effluent
chlorination with a capacity for 5,000 inhabitants. The excess
wastewater flows contaminated groundwaters in the Tijuana River valley
north of the border such that truck crops in San Ysidro were prohibited
from sale and well water was contaminated. In 1935, the International
Boundary Commission, U.S. Section, working in cooperation with the
governments of Mexico and the County of San Diego, designed a project
known as the International Outfall. It consisted of trunk sewers serving
the city of Tijuana and U.S. federal buildings in San Ysidro. The trunk
sewers connected with a sewer that followed the Tijuana River west to an
ocean discharge point just north of the international boundary. No
untreated sewage was to be discharged into the outfall.

By 1950 the population of Tijuana had grown to 65,000 and 2.5 mgd (109.5
lps) of sewage was being generated. Partially treated sewage began to be
discharged through the International Outfall. In 1952 the California
legislature adopted a resolution (Joint Assembly Resolution 16) urging
the U.S. government to expedite the development of sewage treatment and
disposal facilities for Tijuana and San Ysidro.

Local and state public health agencies began monitoring ocean water
quality offshore of Imperial Beach in the United States. Soon after, San
Diego County began to disinfect effluent discharged by the International
Outfall. However, by 1957 the population had increased to over 100,000
and the disinfection program for the International Outfall was no longer
sufficient to prevent sewage contamination of beaches north of the
outfall. In August 1959, the County Department of Health Services
quarantined all beaches between the international border and the north
end of Imperial Beach. Water sampling disclosed high bacterial
concentrations extending north to the city of Coronado.

Development of New Facilities

By 1960 the population of Tijuana was 165,000. The government of Mexico
proposed new facilities, including a pump station and a force main to
convey sewage from the existing facilities west to the top of Spooners
Mesa overlooking the Tijuana River and gravity mains to convey the
sewage 10 miles south to oxidation ponds at Agua Caliente. Due to a lack
of funding, Mexico ceased construction of its new canal 5.6 miles (9 km)
south of the border. From there, raw sewage was discharged into arroyo
San Antonio de los Buenos and flowed into the ocean (see Section 1.1.3
for details of the sewer system).

The new system began operating in 1961. As an additional interim
measure, funding was sought and approved from the U.S. government for
construction of temporary oxidation ponds in the Tijuana River north of
the international border to contain and partially treat Tijuana sewage
flows. In 1962 the discharge through the International Outfall was ended
and the sewage was diverted to a temporary oxidation and stabilization
pond in the Tijuana River valley. Following this action, the three‑year
quarantine on local beaches was finally lifted.

In 1965 an agreement was reached to construct a 0.9‑mile‑long (1.4 km),
30‑inch‑diameter (76.2 cm) emergency connection sewer with a capacity of
up to 13 mgd (569.4 lps) to allow Tijuana sewage to be diverted to the
City of San Diego\'s new Metro sewer system for treatment and discharge
at Point Loma. This connection replaced the oxidation ponds. The City of
San Diego agreed to provide Tijuana use of the sewer and any excess
capacity on an emergency, as‑needed basis for 20 years, and Mexico
agreed to pay for use of the facilities on a fixed‑rate basis.

Sewage Contamination Problems Continue

By 1975 the population of Tijuana had grown to 400,000 and sewage
generation had increased to 20 mgd (876 lps). The emergency connection
was used 188 days of the year. Contaminated runoff at the boundary of
the Tijuana River flood‑control channel was extensive. After 16 of 34
U.S. Navy divers became ill during a training exercise in the Tijuana
River estuary, the County posted warnings along the river in Imperial
Beach.

In 1977 construction began on a new aqueduct to convey Colorado River
waters to serve present and future potable water needs for Tijuana. The
system has a planned capacity of 90 mgd (3,942 lps), or 100,000
acre‑feet per year, to serve Tijuana to the year 2010.

In 1978 pipeline failure led to raw sewage spills in Smuggler Gulch. In
1979 a major failure of the pump station led to sewage flows into the
United States in a number of locations. The conveyance canal washed out
3.2 miles (5.1 km) south of the border. Approximately 70 percent of
Tijuana\'s sewage was sent to the emergency connection, but the
remainder escaped as surface flows. In January 1980, heavy rains damaged
the Tijuana pipelines and washed out the emergency connection; and all
22 mgd (963.6 lps) of Tijuana\'s raw sewage was discharged to the
Tijuana River in the United States. The County quarantined four miles
(6.4 km) of beaches through July. Again, two years later, heavy rains
caused failure of the force main between Smuggler Gulch and Goat Canyon.
Figure 1‑5 (oversize)

Five wells in the Tijuana River valley were contaminated and a mile (1.6
km) of beach was quarantined.

International Agreements Toward a Solution

In February 1979, Presidents Carter and Lopez Portillo instructed the
IBWC to develop an agreement for permanent solutions to the border
sanitation problem. The agreement was concluded in IBWC Minute No. 261
of September 24, 1979. This agreement provides the International
Boundary and Water Commission authority to give permanent attention to
solution of border sanitation problems under Article 3 of the 1944 Water
Treaty. Under Minute No. 261, discussion for an international agreement
on the Tijuana problem began in 1980, but was suspended when Mexico
would not agree to construct treatment facilities before ocean
discharges. Mexico continued to work on improvement of the Tijuana
system, which included a new single lift pump station, force main, and
gravity canal with siphons. In the U.S., a committee of federal, state,
and local officials, including the USIBWC, convened to develop a course
of action for a long‑term solution of the sewage contamination problems
that envisioned an international plant in the U.S. to handle Tijuana
sewage.

In 1983 Presidents de la Madrid of Mexico and Reagan of the United
States signed an agreement, &quot;Cooperation for the Protection and
Improvement of the Environment in the Border Area,&quot; of which
Article 2 stipulates: &quot;the parties undertake, to the fullest extent
practical, to adopt appropriate measures to prevent, reduce and
eliminate sources of pollution in their respective territory which
affect the border area of the other.&quot; The agreement also
established several working technical work groups, including a
binational Water Work Group with representation from the EPA, IBWC, and
Mexico\'s Secretariat of Urban Development and Ecology (SEDUE). Both
parties agreed that the solution to the border sanitation problem would
be through the IBWC.

Minute No. 270‑Mexico\'s Integrated Project

In 1984 Mexico\'s SEDUE prepared plans for the Integrated Project for
Potable Water and Sanitary Sewer of Tijuana, funded in large part by the
Inter‑American Development Bank. The Integrated Project provides for
utilization of the Colorado River aqueduct to provide water sufficient
to supply Tijuana\'s needs to the year 2010 and for new and upgraded
sewage conveyance and treatment facilities. The increase in potable
water supply is expected to increase the volume of wastewater from 39
mgd (1,708 lps) in 1993 to about 75 mgd (4,117 lps) by the year 2010.

The Integrated Project also calls for phased improvement and expansion
of the existing sewer system and construction of new treatment works.
The Integrated Project was incorporated into an international agreement,
Minute No. 270. In this international agreement, Mexico committed to
make immediate repairs in case of system breakdown, meet a surf quality
standard at the boundary, and present to USIBWC for review and approval
its long‑term plans to treat sewage exceeding that in Stage I. The Stage
I facilities as designed included:

Concentration of the Tijuana River basin\'s wastewaters at

Pump Station One, improved to provide a 50 mgd (2,190 lps) peak
capacity, 34 mgd (1,489 lps) average capacity.

Conveyance of the wastewaters via a 42‑inch (1.07 m) force main with a
peak capacity of 62 mgd for discharge to the existing conveyance canal.

Collection, pumping, and conveyance from canyon areas for

disposition in the conveyance canal.

Pumping and conveyance from the Playas de Tijuana area to

the conveyance canal.

Conveyance via a covered and open canal for disposal of wastewaters 5.6
miles (9 km) south of the international boundary.

Construction of two secondary treatment facilities (Modules 1 and 2),
each with a capacity of between 17 and 25 mgd (745 and 1,095 lps)
utilizing aerated facultative lagoons at a location four miles (6.4 km)
south of the international boundary.

Most of these facilities, with the exception of the Module 2 treatment
facilities, have been completed by Mexico; however, the operating
capacities are less than originally intended.

Interim U.S. Defensive Measures

In January 1984, the USIBWC completed construction of a temporary
holding pond near Stewart\'s Drain east of Dairy Mart Road in the U.S.,
to provide additional holding capacity until Tijuana could complete
improvements to its sewage facilities (IBWC 1984). This construction
included a pipeline from Tijuana\'s Pump Station One to the temporary
holding pond and to a connecting pipeline to San Diego\'s Metro system.

In 1985 USIBWC constructed a system to intercept, divert, and dispose of
sewage flows entering the United States from Tijuana along Canyon del
Sol, Silva Drain, and Stewart\'s Drain.

In 1987 the USIBWC constructed an interceptor system to collect surface
sewage flows at Smuggler Gulch. The system included a diversion dike and
settling pond located within Mexico and a pump station and 2,000 feet
(610 m) of 12‑inch (30.5 cm) pipeline within the United States to return
dry‑weather flows to Tijuana\'s 42‑inch (1.07 m) pipeline.

Proposals by Mexico

By 1987 Mexico had improved Pump Station One, the 42‑inch (1.07 m) force
main, and constructed the first module of the San Antonio de los Buenos
treatment plant (17 mgd \[745 lps\] average, 25 mgd \[1,095 lps\] peak
capacity) in accordance with IBWC Minute No. 270. Soon after, facilities
to convey wastewater from Playas de Tijuana and Smuggler Gulch
(Matadero) and Goat Canyon (Laureles) to the canal were completed. At
the same time, Mexico proposed modifications to Minute No. 270 that
would enable Mexico to abandon the second module at San Antonio de los
Buenos and, instead, proceed with the planning and design of the
proposed Stage II Rio El Alamar treatment facility in east Tijuana. This
new Rio El Alamar treatment plant would treat those flows that the
second module of the first stage treatment works would have treated. The
treated effluent would be discharged to the Tijuana River watershed and
used for irrigation.

The EPA, the USIBWC, and the State of California opposed the Rio El
Alamar facility because of concerns over the level of treatment and the
adverse impacts this volume of effluent would have on the ecology of the
Tijuana River estuary. It became clear to EPA, USIBWC, and state and
local agencies that existing defensive measures, the proposed Standby
Interceptor Project, and Mexico\'s proposed Rio El Alamar treatment
facility would not be sufficient to safeguard the public health and
environment of the Tijuana River valley and surrounding areas from water
pollution originating in Tijuana, Mexico (IBWC 1987). The U.S.
Government, through USIBWC, opened talks with Mexico for a solution
through an international treatment plant.

After Mexico decided to proceed with their own solution, Congress
directed EPA and USIBWC to design a larger‑scale defensive works project
(also known as the Standby Interceptor Project) to protect against
massive breakdowns in the west Tijuana system. These works would consist
of an interceptor pipeline and a pump station to return excess flows
from Pump Station One to Tijuana\'s westside conveyance and treatment
system (Boyle 1988).

However, by the spring of 1988 it became clear that sewage flows from
east and west Tijuana had substantially increased and would soon surpass
the Mexican system\'s ability to receive return flows from the Standby
Interceptor Project. Specifically, there would be no capacity in the
Mexican conveyance system to receive sewage originating in east Tijuana
and flowing through the Tijuana River. As a result, serious threats to
public health and the environment would remain even if the Standby
Interceptor Project were completed. In view of the future treatment
needs of Tijuana and the city of San Diego, the Standby Interceptor
Project concept was modified to intercept sewage flowing in the Tijuana
River from east Tijuana and enlarged to accommodate increased flows from
Tijuana and San Diego. It became known as the South Bay Land Outfall
(SBLO) project. Minute No. 283‑International Wastewater Treatment Plant
and Ocean Outfall

In response to the inadequacies of the Standby Interceptor Project and
Mexico\'s own proposal to proceed with the Rio El Alamar treatment
facility, the USIBWC, in September of 1988, proposed to Mexico
construction of an international wastewater treatment facility in the
U.S. to treat Tijuana sewage. The proposal would utilize the upsized
interceptor pipeline (SBLO) contemplated for the Standby Interceptor
Project. The proposal was attractive since it would provide full
secondary treatment, and disposal would be unconstrained by the capacity
of the Mexican conveyance system. In lieu of construction of the Rio El
Alamar treatment works, Mexico would contribute its anticipated costs to
construct the Rio El Alamar facility towards the project and provide
operations support.

The IWTP proposal was formally placed for binational consideration in an
exchange of diplomatic notes between both governments in October 1989
and, subsequently, in an international agreement between the United
States and Mexico as an international solution to the long‑standing
border sanitation problem. This agreement is contained in Minute No.
283, Conceptual Plan for the International Solution to the Border
Sanitation Problem in San Diego, California/Tijuana, Baja California,
signed by both governments on July 2, 1990.

Pursuant to this agreement, a 25 mgd (1,095 lps) International
Wastewater Treatment Plant would be constructed in the U.S. with a land
and ocean outfall (SBOO) for discharge of secondary treated effluent in
U.S. waters offshore. The treatment works could be expanded to 100 mgd
(4,380 lps) and rights to future reclamation of wastewater would be
reserved to whichever country contributed sewage. The sludge generated
by the IWTP will be transported to Mexico for disposal. Mexico also
agreed to make significant improvements to its wastewater collection
system and ensure that there are no discharges of untreated industrial
or domestic wastewaters to the U.S. Mexico also agreed to implement an
industrial pretreatment program that will ensure efficient treatment of
wastewater at the IWTP.

Current and Planned Border Sewage Facilities

Mexico\'s Facilities

Mexico\'s sewage collection, conveyance, and treatment facilities are
presented in Figures 1‑6 and 1‑7. Most of the sewage generated in
eastern and central Tijuana is collected at Pump Station One. Other
sewage from central and western Tijuana is collected at other pump
stations (Laureles, Matadero, and La Playa). Sewage is pumped via force
mains to an open canal that traverses south to a treatment works or is
bypassed and disposed of at the shoreline 5.6 miles (9 km) south of the
international border. This flow capacity is augmented by the City of San
Diego\'s emergency connection, which can take sewage from Pump Station
One to the treatment works at Point Loma. Peak flows of sewage from
eastern and central Tijuana that exceed the capacity of the Mexican
pumping and conveyance system and the emergency connection end up in the
Tijuana River in the U.S. The primary components of the system are
described below.

River Diversion Structure

In October 1991, Mexico completed construction of and operates a
diversion structure in the Tijuana River in Mexico, about 325 feet (100
m) upstream of the international border. A mixture of river flows and
sewage can be captured and diverted to Pump. Figure 1‑6 Existing Tijuana
Sewage Collection System

Figure 1‑7 Existing Tijuana Pumping and Conveyance

Station One. During dry weather, up to 13 mgd (569 lps) of
sewage‑contaminated flows can be pumped from the concrete, low‑flow
river channel into Mexico\'s collection system and to Pump Station One
if capacity is available. Wet‑weather and storm flows are allowed to
pass through to the U.S., even if contaminated with sewage.

Collection System

Mexico has made significant improvements to its wastewater collection
system, as agreed to in Minute Nos. 270 and 283. Sewage flows in the
Tijuana River have been substantially reduced and collection, pumping,
and conveyance facilities from canyon areas such as Matadero (Smuggler
Gulch) and Laureles (Goat Canyon) and from a pump station at Playas de
Tijuana on the coast direct sewage towards the conveyance canal.

Sewage flows are collected from central Tijuana along the Tijuana River
and from eastern Tijuana on both north and south sides of the flood
control channel along Rio El Alamar. These flows merge to a 72‑inch (1.8
m) interceptor along the lower Tijuana River to the river collector and
are conveyed to Pump Station One. From Pump Station One, flows are
pumped to the force main and conveyance canal for treatment at San
Antonio de los Buenos or, in the future, to the IWTP.

A section of the main interceptor from the pumping plant at the river
collector (Pump Station CILA) to Pump Station One is undersized for
handling future flows to both Pump Station One and the IWTP. As part of
Minute No. 283, Mexico has agreed to construct the sewage collection
works necessary to convey sewage from a diversion point near Rio El
Alamar to Pump Station One. It is expected that this line will be
constructed prior to the time that the full capacity of the IWTP will be
needed.

Pump Station One

Sewage from the Tijuana River basin is directed to Pump Station One,
which is located at the hydraulic low point in central Tijuana adjacent
to the international border. Sewage from the collection system flows
either to the emergency connection or to a wet well for detention from
which it is pumped to a force main and conveyance canal. Because Pump
Station One was not operated as designed, Mexico upgraded this facility
in 1995.

Currently, there are three operating pumps and one backup pump, which
are estimated by IBWC to have approximately 50 mgd (2,150 lps) peak
capacity (if all four were used) and 36 mgd (1,489 lps) operating
capacity with three pumps operating (Photograph 1‑1).

Photograph 1‑1. Pump Station One.

Emergency Connection

An emergency connection between Pump Station One and the City of San
Diego\'s South Metro Interceptor sewer has been in existence since 1966.
This connector consists of a 30‑inch (0.76 m) sewer trending north from
Pump Station One to the 36‑inch (0.91 m) San Ysidro Interceptor; the San
Ysidro Interceptor ties into a 42‑inch (1.09 m) segment of the South
Metro Interceptor. The existing emergency connection can accept up to 13
mgd (569 lps) peak flows, which are treated and disposed of at the
City\'s Point Loma advanced primary treatment plant and ocean outfall.

The South Metro Interceptor sewer currently has excess capacity to
accept flows from Mexico, but may not have in the near future due to
anticipated growth in the area it serves in San Diego. The capacity is
also affected by wet‑weather conditions when peak flows are higher.
Current wet‑weather capacity of the South Metro Interceptor is 180 to
192 mgd (City of San Diego 1993). By the year 2001, the planning horizon
year, the City projects that the population in the service area will
expand by 91,000 residents and the capacity of the sewer will be
reached.

On account of these factors, availability of the emergency connection to
accept flows from Mexico is limited and will not continue into the
future. The emergency connection is also susceptible to being washed out
by flood flows in the Tijuana River.

Force Main

Conveyance of the wastewaters from Pump Station One is via a 42‑inch
(1.07 m) force main for discharge to the existing conveyance canal on
the mesa approximately 330 feet (100 m) above and to the west of Pump
Station One. Frequent breakdowns with sewage spills to the U.S. have
occurred, and with the single pipeline, it cannot be shut down to
perform necessary maintenance without additional spills to the U.S.

Conveyance Canal

A covered and open canal with an effective capacity of approximately 48
mgd (2,102 lps) conveys wastewaters from the international border 5.6
miles (9 km) south for treatment and disposal. The canal follows a ridge
and crosses five arroyos for which siphons are used to maintain flows.
As there is only the single canal, the entire system must be shut down
to perform maintenance. Accumulations of debris in the canal and siphons
tend to reduce the capacity of the canal to convey flows (Photograph
1‑2).

Photograph 1‑2. Conveyance Canal

Treatment Works

The San Antonio de los Buenos treatment facility is designed to treat an
average of 17 mgd (745 lps) average flow and up to 25 mgd (1,095 lps)
peak flow utilizing aerated facultative lagoons at a location four miles
(6.4 km) south of the international boundary (Figure 1‑8). Sewage in the
conveyance canal flows through a preliminary sediment detention basin
and then pumped to a series of two aerated facultative lagoons and a
final, nonaerated polishing lagoon. The treated effluent is then
disinfected with chlorine and conveyed 1.6 miles (2.6 km) south for
shoreline discharge with untreated effluent or reuse for irrigation.

Mexico is committed to ensuring that the discharge from its treatment
and disposal facilities, including the San Antonio de los Buenos
treatment plant, will maintain the quality of ocean receiving waters at
the international boundary to protect recreational uses of the ocean, as
described in Minute No. 270.

Effluent Discharge

Effluent from the San Antonio de los Buenos treatment plant and any
sewage that bypasses the treatment plant is conveyed in a canal to the
arroyo San Antonio de los Buenos 5.6 miles (9 km) south of the
international border and discharged to the surf zone (Photographs 1‑3
&amp; 1‑4).

Photograph 1‑3. Shoreline Discharge Channel

Photograph 1‑4. Shoreline Discharge Point

Other Actions by Mexico

Under Minute No. 283, Mexico will assure that there are no discharges of
treated or untreated domestic or industrial wastewaters into the Tijuana
River, which crosses the international boundary. Mexico has constructed
a river diversion structure in Mexico to capture dry‑weather flows in
the river up to 13 mgd (569 lps) and has agreed to construct additional
collection and conveyance facilities in central and eastern Tijuana.
These facilities include an interceptor from the Rio El Alamar area to
Pump Station One, which will be necessary to convey future flows to the
IWTP. Mexico has committed to ensuring that discharges of treated
effluent from its existing facilities at San Antonio de los Buenos will
maintain the quality of ocean waters at the international boundary.
Mexico will dispose of sludge generated at the IWTP.

Mexico, under the international agreement in Minute No. 283 and
consistent with its laws, requires its industries to provide appropriate
pretreatment to their discharges to the Tijuana sewage system. Mexico,
in furtherance of its laws (see Appendix D) establishes maximum
allowable pollutant limits as a federal responsibility and delegates the
implementation to the states. In the case of Baja California, the state
passed appropriate legislation in 1992, promulgated rules in 1993, and
has established organizations to implement a source control program. The
process of registering industrial and commercial establishments is under
way and a voluntary compliance program has been initiated.

Malcolm Pirnie Inc. performed wastewater characterization in 1992 and
1993 for USIBWC of Tijuana wastewaters arriving at Pump Station One and
an expanded characterization in 1995 covering additional points near the
boundary and the Tijuana River. Additional monitoring is planned. The
purpose of the program is to identify those pollutants of concern as
they affect the efficiency of the IWTP measured against the
nonconventional pollutant limits established for the ocean discharge in
the United States. In turn, these pollutants of concern provide the
guidance to the IBWC against which the government of Mexico will apply
its laws, based on Mexican standards, to protect the efficiency of the
plant. At the same time, a continuous monitoring program will provide
the IBWC a warning of exceedances or near exceedances of the headworks,
subject to more intense monitoring, for use by Mexican authorities to
determine the source and take corrective actions.

The United States and Mexico are also engaged through various
environmental cooperation mechanisms in efforts to have Mexico
accelerate implementation of Mexico\'s laws that require industries to
provide appropriate pretreatment that may discharge to the Tijuana
sewage system. Mechanisms include training conferences and seminars
developed by EPA regarding United States source control laws and
practices, including model ordinances.

Future Sewage Flows from Mexico

As Mexico expands its collection facilities to unsewered areas to reduce
the risk of untreated sewage being discharged to the Tijuana River, it
may also increase the amount of sewage being brought to Pump Station One
and the treatment works at San Antonio de los Buenos. Flows from central
and eastern Tijuana that are collected at Pump Station One and the
Matadero and Laureles pump stations could ultimately cross the U.S.
border if capacity of the system is exceeded or failures occur.

Figure 1‑8

Flows from western Tijuana are also expected to increase. While these
flows would not affect the U.S. directly, they are conveyed in the canal
to the San Antonio de los Buenos treatment works. If capacity for
treatment is not available, they are bypassed untreated to the shoreline
discharge point and are of concern with respect to ocean water quality.
EPA estimates that the flows from western Tijuana constitute about 10
percent of the flows from eastern and central Tijuana.

The municipality of Tijuana currently limits the availability of potable
water in certain areas of the city to lower wastewater generation. It is
estimated that only 65 percent of residences in Tijuana have sewer
service (SANDAG 1992). The amount of sewage generated in Tijuana could
increase either if the volume of fresh water from the Colorado River is
increased or if sewer service is extended to existing residences not
currently sewered. This generation is in addition to population growth,
which has increased over 60 percent in the last decade and historically
has been higher.

The Mexican State of Baja California Norte is considering the
development of additional treatment facilities for future flows from
Tijuana.

IBWC Facilities

The IBWC facilities agreed to in Minute No. 283 and in the EIS and ROD
signed in May 1994 are currently under construction in the U.S. They
would treat sewage from Tijuana and, in dry weather, any
sewage‑contaminated flows in the canyons and gullies, up to a total of
25 mgd \[1,095 lps\] (average daily flow). Following treatment, effluent
will be discharged into the Pacific Ocean in the U.S. by way of a land
and ocean outfall conveyance system. The general location of the project
is shown in Figure 1‑9.

The IBWC project includes the following major elements:

The advanced primary portion of the IWTP (under construction); The
activated sludge portion of the IWTP (which has been designed, but
construction has been postponed until an additional SEIS has been
finalized);

Facilities for capturing and pumping sewage‑contaminated flows from
Stewart\'s Drain, Silva Drain, Canyon del Sol, Smuggler Gulch, and Goat
Canyon (under construction) and utilization of Mexico\'s existing
dry‑weather collector in the Tijuana River;

The South Bay Land Outfall (completed in 1993); and

The South Bay Ocean Outfall (under construction).

International Wastewater Treatment Plant

A federal wastewater treatment plant is being constructed on an
approximately 75‑acre (30 ha) site in the United States. The Dairy Mart
Road site is located about 300 feet (91.4 m) north of the border across
from Pump Station One, south of the intersection of Dairy Mart and
Monument Roads, near where the Tijuana River crosses the international
border. While designed as a 25 mgd (1,095 lps) secondary treatment plant
using activated sludge, the initial construction is for advanced primary
treatment only.

The headworks are designed to handle up to 100 mgd (4,380 lps) including
screening and degritting. The primary treatment facilities are designed
to treat average daily flows of 25 mgd (1,095 lps) with peak flows up to
75 mgd (4,117 lps) during high flow days. The activated sludge
facilities are designed to treat a constant flow of 25 mgd (1,095 lps).

The advanced primary facilities were designed with the assumption that
there would be a 3:1 diurnal peak in the influent to the IWTP. Current
data indicate that the actual peaking factor in Tijuana was about 1.3:1
in 1995. The 3:1 peak was assumed (due to uncertainties in actual and
projected Tijuana flow rates) in order to ensure that at least advanced
primary treatment would be provided under any foreseeable conditions,
including breakdown of Pump Station One.

Equivalent conservatism in design of the activated sludge facilities was
not practical given project budget constraints. Construction of the
secondary treatment process trains is under additional study by EPA and
IBWC and is only partially funded at this time.

Wastewater flows from east Tijuana are collected via the Tijuana
wastewater collection system and conveyed to Pump Station One, where
they are mixed with wastewater from central Tijuana. From Pump Station
One, wastewater will be directed to the IWTP in the United States or San
Antonio de los Buenos in Mexico (the emergency connection to Point Loma
would no longer be needed). Wastewater flows from the Playas de Tijuana,
Matadero (Smuggler Gulch), and Laureles (Goat Canyon) pump stations in
Mexico will continue to be routed through the Mexican conveyance system
to the San Antonio de los Buenos treatment plant.

In case of breakdowns in Pump Station One or the conveyance system,
flows could be directed to the IWTP on an emergency basis. Peak flows up
to 75 mgd (4,117 lps) would receive primary treatment. Peak flows
between 75 and 100 mgd (4,117 and 4,380 lps) would be screened,
degritted, and disinfected before being discharged through the ocean
outfall.

Operations Agreement

An operations agreement (IBWC Minute) will be negotiated with Mexico
which will set values for long‑term IWTP usage versus in‑country
treatment by Mexico. The agreement will set forth operations and
maintenance (O &amp; M) for the IWTP and funding of ongoing O &amp; M
costs.

Future expansion of the IWTP would be subject to additional agreements
and funding by both Mexico and the United States. The IWTP has been
conceptually designed to be expanded to a maximum average daily flow
capacity of 100 mgd (4,380 lps).

Figure 1‑9

Collection of Sewage‑Contaminated Flows from Canyons

Sewage‑contaminated dry‑weather flows that occur in Mexico and run
overland in a northerly direction into the United States through Goat
Canyon, Smuggler Gulch, Silva Drain, Stewart\'s Drain, and Canyon del
Sol will be captured and routed through proposed facilities to the IWTP
for treatment.

Sewage will be collected at a new Smuggler Gulch facility and conveyed
down through Smuggler Gulch in a buried pipeline that will be
constructed in the bottom of the drainage. A small pump station will be
constructed near the intersection of Hollister Street and Monument Road
that can pump wastewater flows into a small, existing buried pipeline
within the SBLO alignment which will route flows from Smuggler Gulch to
the IWTP.

A similar type of collection, conveyance, and pumping facility will be
constructed in Goat Canyon. The small pump station located just east of
the mouth of Goat Canyon will pump wastewater into a buried pipeline
within the SBLO alignment to the Smuggler Gulch pump station, which will
route it to the IWTP for treatment. The new collection and conveyance
facilities in Goat Canyon and Smuggler Gulch are backup facilities for
those located in and operated by Mexico.

South Bay Land Outfall

Discharge of treated effluent to the ocean will be through a pipeline
consisting of two segments‑the South Bay Land Outfall and the South Bay
Ocean Outfall‑for ultimate discharge into the Pacific Ocean. The SBLO
consists of a 12,300‑linear‑foot (3,444 m) buried pipeline that runs
east to west from Dairy Mart Road to the mouth of Goat Canyon.
Construction of the SBLO was completed in September 1993.

South Bay Ocean Outfall

The South Bay Ocean Outfall will begin as a vertical drop shaft at the
western end of the existing SBLO and will extend westward as a tunnel at
a depth of approximately 200 feet (60.96 m) below the ground surface to
a point 13,600 feet (4.1 km) offshore (Figure 1‑10). At this point, a
vertical riser will be constructed which will connect to a
4,670‑foot‑long (1.4 km) seafloor pipeline and then to a wye‑shaped
diffuser on the seafloor. Each leg of the wye will have a length of
1,974 feet (602 m). Effluent will be discharged through a series of
ports located on the diffuser legs. The average point of discharge will
be 18,700 feet (5.7 km) offshore at a depth of 93 feet (28 m).

The outfall is designed to carry a maximum average daily flow of 174 mgd
(7,621 lps) and a peak daily flow of 333 mgd (14,585 lps) to enable use
of the outfall by both the IWTP and future City of San Diego Otay and
South Bay treatment works. The outfall is currently scheduled to be
completed by June 1998.

Modifications to the IBWC Facilities Since the 1994 EIS and ROD

Secondary Treatment Deferred

The IWTP was designed as an activated sludge secondary treatment works.
The plant was designed in modules to facilitate future expansion from 25
to 100 mgd (1,095 to 4,380 lps). However, it was recognized that there
could be a potential shortfall in funding such that construction of
secondary clarifiers and activated sludge components would be delayed.
In 1993, in response to public outcries for immediate action, a decision
was made to construct the treatment plant in phases so that some
treatment capability could be made available as soon as possible.

Public interest groups had also expressed the need for analysis of
alternative treatment processes to activated sludge on the basis of cost
and resistance to upset of the biological treatment process due to toxic
influent constituents. Later, EPA and USIBWC agreed to defer
construction of the secondary treatment component until additional
studies and an SEIS are completed.

EPA and USIBWC are currently evaluating process alternatives to
activated sludge in a separate SEIS. Even if funding were to be made
available, selection of a treatment process and construction of the
additional components would not be completed for several years.

Ocean Outfall

Modifications were made to the design of the South Bay Ocean Outfall due
to geotechnical constraints and capacity increases requested by the City
of San Diego for their future Otay and South Bay treatment works. The
tunnel segment of the outfall was shortened due to unfavorable
geotechnical conditions and a combination tunnel and surface seafloor
pipeline is now being constructed. Also, the alignment of the tunnel and
seafloor pipeline were moved about 100 feet (30.5 m) north. The
wye‑shaped diffusers were lengthened to accommodate 100:1 dilution for
the increased maximum flows (from 132 mgd to 174 mgd \[5,782‑7,621 lps\]
average flow and from 258 mgd to 333 mgd \[11,300‑14,585 lps\] peak
flows). The points of discharge from the diffuser are in the same
location.

These changes were addressed in a Supplemental Environmental Assessment
(EA) and Finding of No Significant Impact (FONSI) prepared by the U.S.
Army Corps of Engineers (USACE) for the EPA and USIBWC dated August
1995. It should be noted that the SBOO discharge volumes were originally
set at 181 average and 343 mgd (15,023 lps) peak flows in the 1991 Draft
EIS for the project.

Canyon Collectors

Minor design changes have been made to the canyon collector system in
the U.S. that will pump and convey untreated sewage collected in Goat
Canyon, Smuggler Gulch, and Canyon del Sol back to the IWTP. These
changes have been evaluated in a draft EA dated June 1996 prepared by
the USACE for the EPA and USIBWC.

Figure 1‑10

Chlorination

Chlorination and dechlorination facilities are included in the IWTP
design. A dechlorination station was considered for relocation adjacent
to Goat Canyon and a Supplemental EA was prepared by the EPA and USIBWC
in 1996. A decision to chlorinate/dechlorinate the effluent will not be
made until the IWTP is operational. Proposed Action

EPA and USIBWC are considering operating the IWTP as an advanced primary
treatment works in order to minimize the risk of discharges of raw
sewage in the Tijuana River and nearshore coastal waters in Mexico. In
considering this action, alternatives for the discharge of advanced
primary effluent during the interim period have been identified. The
IWTP could begin operation prior to completion of the ocean outfall with
interim discharge to the emergency connection, Mexico, the Tijuana
River, uplands, groundwater, the surf zone, or in combination.

The IWTP would be operated as an advanced primary plant with discharge
through the ocean outfall once it is completed. The discharge would
continue until the activated sludge process or other processes to meet
Ocean Plan standards or other agreed‑to standards become operational.
This period is estimated at three to five years.

The potential effects of discharge of advanced primary effluent through
the outfall through the year 2001 are also being evaluated to allow for
further consideration of the design and construction of the secondary
treatment facility.

Estimated Sewage Flows from Mexico

Interim Flow Agreement

An interim flow agreement has been negotiated with Mexico. Mexico has
agreed to continue to operate Pump Station One consistent with the
capacities and conditions of its existing pumping, conveyance, and
treatment systems and the increasing volumes of wastewaters. Therefore,
Mexico will continue to accept the current (1996) flows through its
existing system until the ocean outfall is completed. Prior to
completion of the SBOO, the IWTP would only treat those flows in excess
of Mexico\'s current flows that could not be accepted by the City of San
Diego through the emergency connection.

Future Tijuana wastewater flow estimates were developed by USIBWC/EPA
(Appendix A) based upon flow data collected by IBWC at the emergency
connection and the main wastewater conveyance canal in Tijuanaduring
February to December, 1995. Flows were reported every five minutes
during the study period. These flows include all wastewater generated in
Tijuana except the uncollected flows that spill into the Tijuana River
or north‑draining canyons. Approximately 1 mgd (43.8 lps) of sewage flow
in the river is included in the estimates.

Total Tijuana flows were projected through the year 2001, as a
worst‑case scenario for completion of the SBOO and other facilities. The
estimates use mean 1995 flows as the base year and the projections are
derived from an estimate by Mexico of a 4.8 percent annual increase in
flows. The flow projections were made in hourly increments with diurnal
(time of day) and seasonal (wet weather) peaking factors. It was found
that Tijuana\'s average day diurnal variation was less than that of
other U.S. cities. Tijuana\'s collection system covers a broad area,
which tends to equalize flows, and Pump Station One and the collection
system provide potential storage estimated at 0.75 million gallons (2.9
m3). The observed average day diurnal peaking factor was 1.3:1 (peak
flow rates are 1.3 times higher than daily average flows) which is lower
that the 1.8:1 identified in Minute No. 270 or estimated for the City of
San Diego. The forecast projections used a more conservative 1.5:1
average diurnal peak and 1.8:1 seasonal high diurnal peak.

These flow projections were used to estimate the potential for discharge
of untreated sewage to the river and, given the existing treatment
capacity at San Antonio de los Buenos, the assumed untreated discharges
that could occur at the shoreline in Mexico. The projections also assume
continued use of the emergency connection to Point Loma.

EPA and IBWC estimate that eastern Tijuana currently generates an
average of 37 mgd (1,620 lps) of sewage. The forecasted average future
flows are, for 1998, 40.8 mgd (1,787 lps) and, for 2001, 46.9 mgd (2,054
lps); wet‑weather seasonal high flow days are forecasted to be higher:
for 1996, 40.3 mgd (1,752 lps); for 1999, 44.2 mgd (1,936 lps); and for
the horizon year 2001, 51 mgd (2,334 lps).

In assessing the likelihood of exceeding the pumping and conveyance
system capacity, leading to discharges of untreated sewage to the U.S.
or Mexican waters, the peaking factors must also be considered. If it is
assumed that the diurnal peak on high flow days is 1.8:1, the peak
hourly flow rate experienced in 1996 would be the equivalent of 73.4 mgd
(3,215 lps) and in 2001, 91.8 mgd (4,021 lps). It is also important to
note that the emergency connection, if available, reduces the flows in
the Mexican system by up to 13 mgd.

The USIBWC/EPA estimates that Mexico\'s Pump Station One capacity would
be exceeded by 1.1 mgd (48 lps) to 3.5 mgd (153 lps) by the end of 1996.
By the planning horizon year of 2001, the pump station and conveyance
capacity would be exceeded by 5.6 mgd (245 lps) to 9.5 mgd (416 lps).
Unless action is taken, these untreated sewage flows would enter the
U.S. and pollute the Tijuana River and nearshore coastal areas. If a 17
mgd (569 lps) average flow capacity for the San Antonio de los Buenos
treatment facility is assumed, untreated excess flows would be
discharged to the shoreline in Mexico. The volumes of untreated sewage
are estimated at 19 mgd (832 lps) in 1996 and 22.9 mgd (1,003 lps) for
2001. These flows, in excess of the Mexican pump station or treatment
works design capacities, could be diverted for treatment to advanced
primary levels at the IWTP.

Because of the limitations associated with the data available on past
flow conditions and the uncertainties in growth rate for the Tijuana
sewage, the USIBWC/EPA considers its flow projections to be rough
estimates. In the prior EIS, it was noted that flow projections for
sewage in Tijuana provided by Mexico and U.S. agencies varied between 45
mgd (1,971 lps) and 100 mgd (4,380 lps) for the year 2010. The
USIBWC/EPA flow model appears to slightly overestimate the amount of raw
sewage overflows into Stewart\'s Drain at Pump Station One, since
overflows were projected for 1995 and 1996, but none have been observed.
Overall, USIBWC/EPA tried to be conservative in its assumptions and
interpretations of available data, but actual flows could be higher or
lower than the projections, especially by 2001. For purposes of
evaluation of the proposed action and alternatives, the average daily
flow is used, as it is considered more representative of year‑round
conditions.

Alternatives Considered

Alternative 1: No Action

In accordance with the May 1994 ROD, the IWTP would not be operated
until the secondary treatment works are completed and the ocean outfall
is operational. Flows from Tijuana would continue to be conveyed from
Pump Station One through Tijuana\'s existing system to its treatment
works at San Antonio de los Buenos, with flows in excess of 17 mgd (745
lps) discharged untreated to nearshore ocean waters. Flows to Pump
Station One would also be conveyed through the existing emergency
connection to the City of San Diego\'s system. Peak flows of raw sewage
in excess of the combined capacity of Pump Station One and the emergency
connection would be discharged into the Tijuana River in the U.S. via
Stewart\'s Drain. These untreated flows are estimated to be between 1.1
mgd (48 lps) average daily flow and 3.5 mgd (153 lps) seasonal high
daily flow in 1996 and between 5.6 mgd (245 lps) to 9.7 mgd (425 lps) in
2001. Untreated flows discharged to nearshore ocean waters in Mexico
would reach 22.9 mgd (1,003 lps).

Alternative 2: Operate IWTP

The IWTP would be operated to provide advanced primary treatment before
completion of the ocean outfall. The IWTP would treat up to 25 mgd
(1,095 lps) average daily flow of untreated sewage from Mexico. Mexico
would continue to convey flows up to 38 mgd (1,664 lps) of untreated
sewage from Pump Station One to San Antonio de los Buenos and excess
flows up to 13 mgd (569 lps) (during peak flow periods of the day) to
the emergency connection to Point Loma. Treated flows would be returned
from the IWTP to the emergency connection.

During periods of peak flows, effluent treated at the IWTP that cannot
be discharged through the emergency connection would be discharged into
the Tijuana River in the U.S. These treated flows are estimated to be
between 1.4 mgd (61 lps) average daily flow in 1999 and 4.7 mgd (206
lps) seasonal high flow. Year 2001 flows would range between 3.6 mgd
(158 lps) and 7.5 mgd (329 lps). Alternative 3: Operate IWTP with
Detention Basin

The IWTP would be operated as an advanced primary plant, as in
Alternative 2. A 5.5 million gallon (20,900 m3) earthen detention basin
would be constructed at the IWTP site to provide flow equalization for
diurnal and wet‑weather peak flows. The basin would be lined, with a
depth of 10 to 15 feet (3.0 to 4.6 m) and covering an area of 1 to 2
acres (0.4‑0.8 ha). Treated flows would be stored within the detention
basin to be released to the emergency connection during off‑peak hours.
If the capacity of the Mexican system, emergency connection and
detention basin would be exceeded, then the excess treated flows would
be discharged to the Tijuana River in the U.S.

It is anticipated that no untreated or treated flows would be discharged
to the Tijuana River prior to the scheduled completion of the ocean
outfall in 1998. If the SBOO were not available, there would be no flows
to the Tijuana River during average day flows through the year 2001;
however, during seasonal high flow days, there would need to be a
discharge of 0.7 mgd (31 lps) in the year 2000 and 2.0 mgd (88 lps) in
2001.

Alternative 4: Operate IWTP with New Conveyance to Mexico

A new pumping and conveyance system would be constructed by Mexico as a
parallel backup facility for the existing Mexican conveyance system,
with a capacity of 50 mgd (2,150 lps), to convey flows from Pump Station
One to the discharge point in Mexico. These backup facilities would
provide an additional pumping and conveyance system and would allow
maintenance to be performed on the existing facilities. During the
interim period, the IWTP would treat flows up to 25 mgd (1,095 lps) from
Tijuana. Once treated, the effluent would be sent to Tijuana via the new
pump station and conveyance pipeline for discharge in Mexico, near the
San Antonio de los Buenos treatment plant. The existing pumping and
conveyance system to the treatment works in San Antonio de los Buenos
would continue to operate.

No discharge of untreated or treated flows to the Tijuana River in the
U.S. is anticipated. No discharge of untreated sewage to the shoreline
in Mexico would occur until 2000 with average flow conditions.

Alternative 5: Operate IWTP with Discharge to SBOO

The South Bay Ocean Outfall is currently under construction. Once
completed in 1998, 25 mgd (1,095 lps) of advanced primary effluent from
the IWTP would be discharged to the ocean. No discharge to the Tijuana
River or through the emergency connection would be necessary.

Alternative 6: Phased Alternative

The previous alternatives are stand‑alone alternatives to taking no
action through the year 2001. It is also reasonable to evaluate the use
of the individual alternatives in a phased approach.

The phasing scheme would begin with Alternative 2, operate the IWTP to
detain up to 2 million gallons (7,600 m3) of flow and treat additional
flows from eastern Tijuana as needed with discharge to the emergency
connection. When it appears that the total average dry‑weather flows
from eastern Tijuana or higher seasonal high peak flows would result in
discharge of treated effluent from the IWTP to the Tijuana River
(expected by 1997 or 1998), then either Alternative 3 (Operate IWTP with
Detention Basin) or Alternative 4 (Operate IWTP with New Conveyance to
Mexico) could be implemented. Either of these two alternatives would
eliminate dry‑weather flows of untreated sewage or treated effluent to
the Tijuana River until the year 2000.

The 5.5 million gallon (20,900 m3) lined earthen detention basin for
Alternative 3 could be constructed by September 1997, which is the
earliest the seasonal high peak flows that would result in discharge to
the Tijuana River are forecast to occur. Alternative 4, the new Mexican
pumping and conveyance system, is expected to take 15 months to complete
once agreement with Mexico has been reached. This alternative is not
expected to be available for use until the spring of 1998.

Alternative 5, Operate IWTP with Discharge to SBOO, would supersede the
need for the earthen basin at the IWTP or the new Mexican conveyance
system for discharge of IWTP effluent. The SBOO is scheduled to be
completed in 1998. If discharge of advanced primary treated effluent is
permitted at that time, it would be used for IWTP discharge. In that
case the phasing of Alternatives 3 and 4 may not be required, depending
on the occurrence of seasonal high peak flows.

Alternatives Considered But Rejected

The following interim discharge alternatives were considered by EPA and
USIBWC but were considered infeasible for technical or other reasons.
Each alternative is briefly described and the reasons for its
infeasibility are provided below.

Expansion of the Emergency Connection to City of San Diego South Metro
Interceptor

The existing emergency interceptor can accept up to 13 mgd (569 lps)
peak flows. Expansion of the capacity of the emergency connection would
allow additional flows from Mexico to be treated at the Point Loma
treatment plant. Expansion of the capacity of the emergency connector
would include the construction of additional pipelines between the IWTP
and the South Metro Interceptor. The South Metro Interceptor system
consists of a series of main sewers that comprise approximately 14.8
miles (23.8 km) and range in size from 42 to 108 inches (1.06 to 2.74
m). The capacity of the South Metro Interceptor is constrained
downstream from the emergency connector and will be reduced due to
anticipated growth in the service area. Significant portions of this
system would require expansion to accommodate additional flows from the
expansion of the emergency connection.

Construction of pipelines would be required through both sensitive
habitats and highly urbanized areas. Impacts to biological resources,
including riparian habitat, wetlands, and listed species (e.g., Pacific
pocket mouse, least Bell\'s vireo, clapper rail), may result. Open
trench construction through an urban setting has the potential to
disrupt existing utilities, disrupt traffic circulation, and expose
receptors at schools and residences to noise and vibration from
construction equipment and public health and safety impacts due to the
increase in construction vehicles and equipment. Costs associated with
expansion would be considerable, especially as an interim measure. As
the expansion would be a temporary measure that would impact natural and
biological resources and may not provide additional capacity due to
other constraints, this option is considered infeasible.

Discharge to Groundwater

Effluent could be conveyed from the IWTP to wells to be injected into
the groundwater basin. The wells could be sited near the plant or
effluent could be conveyed through the SBLO and then diverted for
discharge in the western end of the valley. The Basin Plan establishes
beneficial uses for the groundwater basin east of Hollister Street
(Municipal, Agricultural, Industrial); these limitations do not apply
west of Hollister Street. Hydrogeological factors affect rate of
injection and mixing in the aquifer. The Tia Juana Valley County Water
District has prepared a groundwater management plan for the aquifer
(Dudek 1994a, 1994b, 1995; West 1994).

Solids in the treated effluent place severe constraints on well
injection rates and volume. Any reductions in water quality to sensitive
habitats or for use as irrigation waters would be adverse effects. This
alternative is not considered feasible.

Discharge to Percolation Ponds

This alternative would utilize discharge to land surfaces for
percolation into the groundwater aquifer. The Tia Juana Valley County
Water District Phase III Groundwater Management Plan for the Tijuana
River Valley conducted limited infiltration tests in the eastern portion
of the valley near the IWTP site. The tests were conducted in July,
1994, and utilized river water. The tests resulted in estimated
infiltration rates of 0.011 foot/hour (30 mm/hr) for upland soils and
0.133 foot/hour (4 cm/hr) for river alluvium. The rates would indicate a
need for 12 acres (4.9 ha) per mgd for upland areas and 1 acre per mgd
for the river channel. This method of discharge would be more acceptable
in areas west of Hollister Street and with secondary treated effluent
from a water quality standpoint. However, the infiltration rates may be
much lower in these areas, requiring additional land area. Basin Plan
water quality objectives and standards for discharge would need to be
met.

This alternative would be land intensive and raise concerns for
groundwater quality impacts in the eastern portion of the basin. It does
not appear feasible to dispose of more than a few mgd of effluent given
the land area that would be available. This method of disposal would
probably not be practicable during the wet‑weather season, a significant
limitation. It is not considered feasible, therefore.

Discharge through SBLO to Surf Zone

Advanced primary effluent would be conveyed through the SBLO to a new
temporary 36‑ to 42‑inch‑diameter (0.9‑1.1 m) pipeline aligned down Old
Monument Road to the shoreline for discharge, either at the beach or
about 1,000 feet (307 m) offshore. Effluent would receive an initial
dilution of 10:1 at the surf zone or approximately 30:1 with a nearshore
diffuser. Storm/surge protection would be needed for the discharge
diffuser.

A National Pollutant Discharge Elimination System (NPDES) permit would
be required. The permit would contain effluent limitations based on
Ocean Plan standards for receiving waters, including concerns for
coastal recreation for body contact and fishing, effects to marine biota
and benthos, and discharge conditions to avoid effects to foraging of
least tern, snowy plover, and brown pelican. Construction would require
seasonal restrictions to avoid impacts to sensitive species, such as
California least tern, snowy plover, California brown pelican,
Belding\'s savannah sparrow, and light‑footed clapper rail.

Due to the time needed to design the discharge facilities and seasonal
restrictions on construction and time to collect baseline data on water
quality, benthos, and fish, it is not likely that this alternative would
be operational in time for interim discharge. Due to the potential
impacts on sensitive species and the timing involved in construction,
this alternative is considered infeasible. Rio El Alamar

Another alternative is the construction of a 25 mgd (1,095 lps) pipeline
from the IWTP to a new secondary or tertiary treatment works at a site
in the Rio El Alamar area. Mexico had previously proposed a treatment
works in this general location. As was discussed in the prior EIS, this
concept was based upon potential reuse of the wastewater for irrigation.
The USIBWC, EPA, and other state and local agencies opposed this action
by Mexico due to concerns that the discharge of wastewater within the
watershed would result in flows to the Tijuana River valley and estuary
in the United States and cause adverse impacts to the estuary.

This current alternative was suggested by a private development company
and included the construction of a low‑head pump station and 6.8‑mile
(21.8 km) effluent conveyance main as well as a treatment works at Rio
El Alamar. Once treated at Rio El Alamar, the effluent would be reused
for agricultural purposes. Water quality levels would be determined on
the basis of needs identified by the reuse market. If adequate markets
are not identified, a discharge of secondary or tertiary effluent could
occur to the Alatamar or Tijuana rivers.

This alternative was eliminated from further consideration for several
reasons. First, USIBWC/EPA rejected this alternative from a detailed
evaluation since this proposal is not currently endorsed by the Mexican
government. Mexico has not made any indication to the United States that
Mexico supports this proposal. In addition, the construction of the
conveyance and reclamation facility by a Mexican entity in Mexico is not
subject to U.S. federal environmental regulations. Finally, the
legislation (Section 510 of the 1987 Water Quality Act) that provides
funds for the IWTP does not provide funds for construction of a
reclamation/wastewater facility in Mexico.

Decisions Needed to Implement the Proposed Action

The 1994 Record of Decision for the IWTP and SBOO includes a commitment
to prepare a supplemental environmental evaluation if any effluent
treated to less than Clean Water Act secondary treatment standards would
be discharged from the IWTP or ocean outfall. This Supplemental EIS for
interim operation addresses the effects of operating the IWTP as a
less‑than‑secondary treatment plant, with interim discharge options
prior to completion of the SBOO. In addition, short‑term (three‑ to
five‑year) discharge of less‑than‑secondary effluent through the ocean
outfall is addressed.

The EPA and USIBWC will prepare an additional Supplemental EIS for
(alternatives to activated sludge‑long‑term operation) addressing the
options for providing enhanced wastewater treatment at the IWTP, such as
advanced integrated ponds, activated sludge, or other means. If
activated sludge or another process selected to provide enhanced
treatment of the wastewater would not provide secondary equivalent
treatment of all flows discharged through the outfall, the potential
effects of long‑term discharge of less‑than‑secondary treated effluent
through the ocean outfall will be considered.

Operation of the IWTP as an advanced primary plant and interim effluent
discharge will require coordination with or approvals from other federal
and state agencies. These agencies will rely upon the information
provided in the SEIS in considering the proposed action. These agencies
include, among others, the U.S. Fish and Wildlife Service (endangered
species consultation), California Coastal Commission (Coastal Zone
Management Act consistency), and Regional Water Quality Control Board
(NPDES permit, waste discharge requirements).

Related Environmental Documents

This SEIS supplements the 1994 FEIS for the International Boundary and
Water Commission International Wastewater Treatment Plant and South Bay
Ocean Outfall prepared for EPA and IBWC by RECON (1994).

The original EIS has been supplemented by the following:

Supplemental Environmental Assessment and Finding of No Significant
Impact, International Boundary and Water Commission and Environmental
Protection Agency South Bay Ocean Outfall Modifications prepared for the
EPA and IBWC by USACE, August 1995

South Bay Ocean Outfall Draft Environmental Impact Report

prepared by the City of San Diego, March 1995

The following documents address environmental issues and impacts for
projects in the vicinity of the proposed action:

Environmental Assessment and Finding of No Significant Impact: South Bay
Land Outfall Phase I (Big Pipe), EPA, August 1988 Final Environmental
Impact Report/Environmental Impact Document for South Bay Land Outfall
Phase I, City of San Diego, February 1988

Final Environmental Assessment and Finding of No Significant Impact:
International Agreement for an International Solution to the Border
Sanitation Problem at Tijuana, Baja California, and San Diego,
California, USIBWC, January 1990

City of San Diego\'s and EPA\'s Joint Secondary Treatment and Associated
Sludge Management Facilities Final EIR/EIS for the Clean Water Program,
March 1991

Marine Environmental Impacts of the Proposed Secondary Treatment System,
Technical Appendix M to City of San Diego\'s and EPA\'s Joint Secondary
Treatment Facilities Final EIR/EIS for the Clean Water Program (Kinnetic
1991)

Biological Assessment for Secondary Treatment Facilities,

Technical Appendix B to City of San Diego\'s and EPA\'s Joint Secondary
Treatment Facilities Final EIR/EIS for the Clean Water Program
Biological Assessment for the International Boundary and Water
Commission International Wastewater Treatment Plant, RECON, December
1993

List of Incomplete or Unavailable Information

The SEIS has been prepared with the best information available at the
time of its preparation. However, the analysis of impacts is based upon
estimates of a number of key factors and the analysis includes modeling
procedures. Pursuant to Section 1502.22 of the Council on Environmental
Quality Guidelines, gaps in relevant information or areas where there
may be scientific uncertainty are identified below.

Future Tijuana Sewage Flows: EPA/USIBWC have developed

new estimates of future flows based upon the best available information
at the time of preparation of the SEIS. A number of previous estimates
have been made, based upon population increase, potable water
consumption and other factors. These estimates vary considerably. That
Tijuana is not fully sewered adds additional uncertainty in making
estimates, in that large changes in sewage flows could result from
improvements to the collection system, in addition to growth in the
population or other factors.

Tijuana Sewage Characteristics: As indicated in the

text, samples have been taken by the City of San Diego, Boyle
Engineering, and Malcolm Pirnie Inc. between 1989 and 1993 toassess the
characteristics of Tijuana\'s sewage. Additional sampling was initiated
in 1995 and is ongoing. The sampling to date has not provided values for
all of the criteria pollutants in the Ocean Plan, however.

IWTP Effluent Quality: The sewage samples were used

to estimate the probable characteristics of IWTP effluent using assumed
removal efficiencies for typical advanced primary treatment processes.
Once construction of the plant is completed, operations testing will be
conducted, at which time the removal efficiencies will be able to be
measured relative to actual sewage characteristics and pollutant loads.

San Antonio de los Buenos Effluent: Detailed information

as to the characteristics of the effluent from San Antonio de los Buenos
and the reduction in coliforms from chlorination of the effluent are not
available. The shoreline discharge modeling used conservative worst‑case
assumptions in modeling effluent discharge impacts.

Chapter Two

Consideration of Alternatives

Basis for the Alternatives

The purpose of the overall IBWC project is to treat and dispose of 25
mgd (1,095 lps) flows of sewage from Mexico that may otherwise enter the
U.S. untreated and to safeguard the public health, environment, public
recreation, water quality and economy of San Diego, and nearshore
coastal waters. Sewage contamination affecting the Tijuana River and
nearshore coastal waters in the U.S. results from flows into the Tijuana
River from Mexico or from north‑draining canyons such as Goat Canyon,
Smuggler Gulch, or Stewart\'s Drain. Untreated sewage discharged to the
shoreline in Mexico may also cause contamination of nearshore water in
the U.S.

Excess flows of sewage during wet or dry weather conditions or
interruption of operations at Mexico\'s Pump Station One, Matadero or
Laureles pump stations, force mains, or conveyance system in Tijuana
could result in sewage contamination to the U.S. In addition, any flows
in excess of the capacity of the treatment works at San Antonio de los
Buenos are diverted and discharged, without treatment, to the shoreline
5.6 miles (9 km) south of the international boundary.

The alternatives being considered by EPA and USIBWC are related to the
proposed operation of the IWTP as an advanced primary treatment works
for a limited period of time. Environmental effects from the
construction and operation of the IWTP as a secondary treatment works
and land and ocean outfall were considered in the 1994 FEIS. For interim
operation, no major additional facilities in the U.S. would be required,
although Mexico may construct additional pumping and conveyance
facilities in Mexico.

The goal of the action is to avoid discharge of untreated sewage and
minimize the effects of the discharge of effluent to sensitive areas
such as the Tijuana River and estuary, offshore kelp beds, and active
recreation or commercial use areas. However, attainment of this goal is
constrained by the availability of resources. Assumptions Made in
Evaluating the Interim Discharge Alternatives

System Capacities

Generation of sewage varies during the course of a day; this variation
is referred to as the diurnal variation of flows. Peak flows are the
highest flow rate occurring during a daily cycle and are expressed as a
ratio to the overall average daily flow. Flows also vary seasonally, as
wet weather can result in infiltration of water into the sewers. By
convention, the hourly diurnal flow rates are expressed as an equivalent
in million gallons per day (i.e., the total daily flow volume that would
result if a particular hourly flow rate continued for 24 hours). The
expected peak flows from Mexico on average flow days during the
dry‑weather season are 1.5:1; seasonal high flow days have been
estimated at 1.8:1. Hydraulic capacities are set by these peak diurnal
flow rates, although they are typically described by average flow
volumes. If hourly peak flows exceed component hydraulic capacities
within the system, failures can occur even if the average daily flow
volumes are within described limits.

Mexico\'s facilities to convey wastewater have the following flow
capacities:

Pump Station One: Pump station one is a hydraulic

low point for eastern Tijuana; sewage is collected and conveyed to this
point. The pump station has to provide hydraulic head of 450 feet (92
meters) to reach the gravity‑fed conveyance canal on the mesa to the
west, to which it is connected by a 42‑inch (1.1 m) force main. The pump
station has an average flow capacity of 36.6 mgd (1,603 lps). Although
its peak capacity is rated at 50 mgd (2,190 lps), this capacity is not
available, as it would require the operation of a fourth pump which is
only used as an emergency backup. In evaluating future flows, it is
assumed that the flow capacity of Pump Station One is 36.6 mgd (1,603
lps). Pump Station One also has a 500,000‑gallon wet well that can
provide limited storage for flow equalization.

Conveyance Canal: The conveyance canal has a peak capacity of 62 mgd
(2,716 lps). The conveyance canal receives flows from other smaller pump
stations in eastern Tijuana and from a pump station in western Playas de
Tijuana in addition to flows from Pump Station One. The conveyance
canal\'s capacity is reduced by accumulations of debris in the canal and
siphons, due to the lack of opportunities to perform regular maintenance
(use of the canal can only be halted for very brief periods). The usable
capacity is estimated at 48 mgd (2,102 lps).

San Antonio de los Buenos: The treatment works pump

station, detention basin, and three treatment lagoons have a 17 mgd (745
lps) average flow capacity. The sewage is treated with five days\'
detention, forced aeration, chlorinated, and discharged to the shoreline
south of the plant. Additional flows greater than 17 mgd (745 lps) in
the conveyance canal are bypassed, not treated, chlorinated, and mixed
with treated effluent at the shoreline for discharge.

Emergency Connection: The 30‑inch (0.76 m) emergency

connection from Pump Station One has a 13 mgd (569 lps) peak flow
capacity to divert flows to Point Loma for advanced primary treatment
and offshore discharge to deep ocean water. The emergency connection was
established in the 1960s as a means of avoiding flows of untreated
sewage in the Tijuana River due to either excess flows or upsets to the
system in Mexico. The emergency connection has been washed out by flood
flows several times in the past and is vulnerable to upset from future
flood flows.

As the emergency connection is only used on an as‑needed basis, to
prevent flows of sewage to the river during peak flow hours, a range of
average daily use of approximately 5 to 8 mgd (219 to 350 lps) is
assumed. The capacity of the emergency connection is limited by the
capacity of sewers downstream of the connection; 13 mgd (569 lps) may
not be available during peak wet‑weather conditions and likely will not
be available beyond the year 2001, due to growth in the service area.

The continued use of the emergency connection is assumed in the flow
analysis of the various alternatives below. If the emergency connection
were not available during peak flow periods, the flows through the
emergency connection would be added to the amount of untreated sewage or
treated effluent discharged to the Tijuana River.

Future Flow Estimates

Future Tijuana wastewater flow estimates were developed by USIBWC/EPA
(see Appendix A) based upon data collected by IBWC at the emergency
connection and the main wastewater conveyance canal in Tijuana during
February to December, 1995. Total Tijuana flows were projected for the
year 1996 through the year 2001, as a worst‑case scenario. The estimates
use mean 1995 flows as the base year and the projections are derived
from a 4.8 percent annual increase in flows. The flow projections were
made in hourly increments with diurnal (time of day) and seasonally (wet
weather) variable peaking factors.

The observed peaking factor in Tijuana during 1995 was 1.3:1. The
USIBWC/EPA forecast projections used a more conservative 1.5:1 average
diurnal peak for dry‑weather flows and 1.8:1 seasonal high diurnal peak
for worst‑case, wet‑weather flows.

Peaking factors are important considerations in evaluating future flows
and the ability of the sewer system to manage flows. For 40 mgd (1,752
lps) average daily flow, the peaking factors would be 52 mgd (2,278 lps)
highest hourly equivalent flow rate at 1.3:1; 60 mgd (2,628 lps) at
1.5:1, and 72 mgd (3,154 lps) at 1.8:1. The capacity of Pump Station One
in Mexico is 36.6 mgd (1,603 lps) and of the emergency connection, 13
mgd (569 lps), for a combined capacity of 49.6 mgd (2,172 lps). Thus,
even if the average daily flows appear to be within the system\'s
capacity, peak hour flow rates will lead to exceedances which may result
in flows of untreated sewage to the U.S.

The 1.5:1 peaking factor is assumed to be the more representative of
dry‑weather conditions most of the year; the 1.8:1 peaking factor is a
worst‑case wet‑weather condition for Tijuana. It should be noted that
1.8:1 is more typical for major urbanized areas in the U.S., including
San Diego. The USIBWC/EPA flow memo includes an hourly analysis of flows
using both the 1.5:1 and 1.8:1 peaking factors for the years 1996‑2001
for each alternative; but for simplicity, peak hour flows are presented
for dry‑weather average daily flows in the comparison of alternatives.

These flow projections were used to estimate the potential for discharge
of untreated sewage to the river and, given the existing treatment
capacity at San Antonio de los Buenos, the assumed untreated discharges
that could occur at the shoreline.

In order for the flow projections to reflect anticipated conditions,
USIBWC/EPA assumed that the river diversion will only be used to divert
raw sewage. Since 1994, dry‑weather river flows have typically been a
blend of natural flow and a small amount of Tijuana sewage.
Indiscriminate use of the river diversion under similar conditions in
the future could displace conveyance treatment and disposal capacity
which would otherwise be used for raw sewage.

Because of the limitations associated with the data available on past
flow conditions and the uncertainties in growth rate for the Tijuana
sewage, the USIBWC/EPA considers its flow projections to be rough
estimates. As discussed in the prior EIS, estimates of future sewage
generation in Tijuana vary considerably. Prior estimates by Mexico and
U.S. agencies range from 75 mgd (3,285 lps) to 100 mgd (4,380 lps) by
the year 2010. The USIBWC/EPA flow model appears to slightly
overestimate the amount of raw sewage overflows into Stewart\'s Drain at
Pump Station One, since overflows were projected for 1995 and 1996, but
none have been observed. Overall, USIBWC/EPA tried to be somewhat
conservative in its assumptions and interpretations of available data,
but actual flows could be significantly different from the projections,
especially by 2001.

It should be understood that the USIBWC/EPA flow projections used in the
comparison of alternatives assume a nominal 1 mgd (44 lps) of
sewage‑contaminated flows in the Tijuana River in Mexico. During dry
weather, these flows would be collected at the river collector and
conveyed to Pump Station One. However, there is the potential for other
sewage flows to occur that would enter the U.S. and that are not
accounted for in the model.

During the wet‑weather season (November through March), runoff in the
Tijuana River in Mexico and in major north‑draining canyons to the U.S.
will not be intercepted to maintain the hydraulic regime of the river.
In years of high rainfall, these flows may continue late into the year
or year‑round, as was the case after the 1993 rains. Sewage in these
wet‑weather runoff flows would not be intercepted by the canyon
collectors or the diversion structure in the Tijuana River and would
pollute the river, estuary, and nearshore ocean waters of the U.S., even
with operation of the IWTP.

Other sources of sewage include upset of the existing systems in Mexico
or the U.S. These other sources of sewage pollution are common to the
alternatives considered and could occur no matter which alternative is
selected. If an alternative is able to otherwise reduce or eliminate
nominal USIBWC/EPA forecast sewage flows in the Tijuana River, it does
not mean that potential sewage pollution in the river or estuary will be
eliminated.

Sewage Characteristics

Tijuana wastewater has been sampled over a period of years by the City
of San Diego and Boyle Engineering from their emergency connection
pipeline and by Malcolm Pirnie Inc., consulting engineers for the USIBWC
at Pump Station One. More recent data (June 1995) has been collected for
flows from Colonia 20 de Noviembre (upstream of Pump Station One), Pump
Station One, and the emergency connection. The sewage is generally
characterized as higher in biological oxygen demand (BOD) and suspended
solids than City of San Diego sewage (see Hydrology, Section 3.1).

IWTP Advanced Primary Effluent Quality

Anticipated effluent quality was developed by the design engineer for
the IWTP, Malcolm Pirnie. Based upon the influent samples and assumed
removal efficiencies for various constituents, they have produced a
characterization of advanced primary effluent parameters. The
constituents analyzed were based upon the Ocean Plan, Tables A and B. If
effluent were discharged to the Tijuana River, the Regional Water
Quality Control Board (RWQCB) would set waste discharge requirements
(see Hydrology, Section 4.1). Modeling of Effluent Discharge Effects

To assess the impacts to ocean water quality, marine biota and public
health from discharge of treated and untreated effluent to the shoreline
in Mexico and of advanced primary effluent through the ocean outfall,
Parsons Engineering Science has modeled the effects of the discharges
including coliform concentrations, dissolved oxygen, and transport
(dilution) of organic and inorganic constituents.

The modeling was based upon current data collected during the Tijuana
Oceanographic Engineering Study (TOES), which covered both Mexican and
U.S. waters surrounding the SBOO.

The TOES was conducted in four phases from 1986 to 1988 (Engineering
Science 1988). Sixteen months of data were collected in U.S. and Mexican
waters for water quality, nearshore ocean current data, benthic infauna,
and sediment chemistry. Based on the use of current meters, drogues,
satellite images, and wind and wave data, a flow field model was
produced to simulate yearly ocean patterns.

The USIBWC/EPA flow estimates for Tijuana sewage generation were used
and applied to the alternatives under consideration for the years 1996
and 2001. To provide a conservative analysis, the seasonal high flow
rates were used, which provide a worst‑case analysis.

The models simulated hourly concentrations over a one‑year period along
the shoreline from Mexico to Coronado and in the area offshore
surrounding the SBOO discharge. The model estimates concentrations at
locations and different water depths (&quot;cells&quot;) over the area
that may be affected. For bacterial contamination, cells were selected
at 23 locations along the shoreline from south of the discharge point in
Mexico to Coronado in the U.S. For other constituents, concentrations
were estimated based upon predicted dilution away from the zone of
initial dilution at the point of discharge.

The models provide a screening level analysis for water quality effects
for the shoreline and outfall discharges. The assumptions used for
current conditions, effluent quality, and flow rates are all
conservative estimates. As such, the model results are not definitive
predictions of the actual concentrations that would result from the
discharges once the IWTP or outfall is operational.

If the model results predict chronic exceedances or exceedances for a
number of constituents, then there is less likelihood that the standards
could be complied with once the facilities are operated. However, if the
model results only show sporadic exceedances or for a few constituents,
then it may be possible that under actual conditions the discharge could
meet the standards or could do so with additional modifications.

For purposes of the EIS, the model results are compared to the State
Ocean Plan as a threshold of significance. This should be understood as
a tool in evaluating alternatives and not as a determination of
compliance or noncompliance with standards during operations.

Ocean Currents

Shoreline discharges in Mexico occur 5.6 miles (9 km) south of the
international border. As the effluent is less saline than seawater, it
is lower in density and, along with shoreward wave action, tends to be
carried along the surface waters near the coastline. During the winter,
currents trend north to south and are affected by turbulence from
storms, which increases mixing and dispersion. During the summer,
currents trend south to north and carry the effluent on the surface near
the shoreline with less mixing.

Seawater is denser at deeper levels. Discharges from the SBOO will occur
at a depth of 93 feet (28.5 m) 3.5 miles (5.7 km) offshore. At this
depth, mixing of the lighter effluent with the heavier seawater at a
minimum ratio of 100:1 within the zone of initial dilution produces a
discharge that is close to the density of the receiving waters. This
tends to trap the discharge in deeper, denser waters. The effluent
discharge remains trapped below the surface at depth unless seasonally
induced turbulence mixes the water column sufficiently to eliminate the
trapping effect.

Ocean currents in the area of the SBOO tend to be longshore; that is,
north to south or south to north. These currents reverse direction
throughout the year. There is an additional circulation pattern that is
an eddy; however, this circulation is a transitory phenomenon. It does
not result in a closed, nonmixing water column.

Bacterial Contamination

Bacterial persistence was modeled by Parsons Engineering Science using a
die‑off factor known as T90. T90 refers to the time required for a 90
percent reduction in coliform bacteria. This factor varies according to
sunlight, temperature of the water, and salinity. The model applied T90
rates (four‑hour average) to the coliforms in the initial discharge
according to concentration, time of day, and depth of discharge. The
resulting concentrations (persistence) could then be estimated at select
locations at given hours of the day and season.

Both the Mexican shoreline discharge and SBOO discharge were modeled.
Simulations were run for each hour of the year and the resulting
bacterial concentrations were calculated at 18 selected shoreline
stations from San Antonio del Mar south of the discharge point to
Coronado in the U.S.

Primary treatment does not result in major reductions in coliform
concentration. For the IWTP, the reduction in concentrations was
estimated to be about 20 percent, resulting in an assumed concentration
of 1.6 &#215; 108 total coliforms. Bacterial concentrations from treated
effluent at the San Antonio de los Buenos treatment works that were
modeled also were not assumed to have significant reductions in
bacterial levels from treatment. This analysis is conservative, as
Mexico recently began to chlorinate its effluent from San Antonio de los
Buenos prior to discharge.

The estimated concentrations were compared to the state health
standards‑no more than 20 tests at a location in one month with
concentrations exceeding 1000 coliforms milliliters per liter (ml/L) or
no more than two tests in a location within 24 hours with a value of
10,000 coliforms ml/L in a sample‑to determine whether the location
would be in compliance with the standards.

Constituent Dilutions

The dilution of organic and inorganic constituents in wastewater was
also modeled for the SBOO by Parsons Engineering Science. The outfall
has been designed so that the zone of initial dilution at the outfall
discharge would receive a minimum 100:1 dilution. As the effluent is
dispersed through the receiving waters, concentrations are further
reduced by dilution. This dispersion is subject to trapping, so four
model simulations at approximately 16‑foot (5 m) interval water depths
were run. The area within a given dilution value was mapped for the four
water depth intervals by months of the year.

Comparison of the Alternatives

The alternatives under consideration are evaluated below. For each
alternative, the flow hierarchy is described and portrayed graphically
in a schematic of the system. The resulting maximum flows and diurnal
variations are presented. The diurnal flows are evaluated for average
dry‑weather flow days; however, seasonal peak high flows are also noted.
The period under consideration is from 1996 to the year 2001.

The direct and indirect environmental consequences of each alternative
are evaluated. The alternatives considered relate primarily to operation
of the IWTP as an advanced primary treatment works, rather than its
construction. The operation of the IWTP as a 25 mgd (1,095 lps)
secondary treatment works with discharge through the SBOO was considered
in the 1994 EIS for the project. Operational differences are largely
indirect, as they relate to the difference in discharge of primary
effluent rather than secondary effluent. Even though new discharge
options are considered, most of the consequences are indirect. Where
minor new facilities are required in the U.S. or Mexico, the direct
impacts are considered.

New pumping and conveyance would be constructed and operated in Mexico
under Alternative 4. Mexico has its own environmental impact assessment
requirements and protocols which would need to be completed by Mexico
prior to construction. The SEIS impact assessment identifies issues or
resources of binational concern. Alternative 1: No Action

This alternative assumes the conditions specified in the 1994 ROD: no
operation of the IWTP until a secondary treatment process has been
constructed and discharge of secondary treated effluent through the
SBOO. As these conditions will not be met during the interim period
considered in the SEIS, the No Action alternative evaluates the
consequences from the EPA forecast of increases in sewage flows from
Mexico with the existing Mexican facilities and continued use of the
emergency connection.

Given current facilities in Mexico and use of the emergency connection,
at a 1.3:1 diurnal peaking factor, 38 mgd (1,664 lps) average flow, with
up to 50 mgd (2,190 lps) peak hour flows, can be conveyed and
discharged. Current (1995) flows received at the San Antonio de los
Buenos treatment works average 35 mgd (1,533 lps) and are expected to
average 39.9 mgd (1,748 lps) in 2001.

Flows from eastern Tijuana are of primary concern, because if the
capacity of the Mexican facilities are exceeded, sewage can enter the
U.S. Flows from eastern Tijuana up to 36.6 mgd (1,603 lps) can be
handled by Pump Station One. Excess flows would enter the U.S. Also,
with planned improvements to the collection and conveyance system in
Mexico, the diurnal peaking factor is expected to increase, as the
current system tends to restrict flows. The average day peaking factor
is expected to increase from 1.3:1 to 1.5:1 on average days and up to
1.8:1 on seasonal high flow days.

The anticipated diurnal flows for the No Action alternative for the year
2001 are given in Table 2‑1. The distribution of the flows within the
system is presented in Figures 2‑1 and 2‑2 and the diurnal variation and
excess flows in Figure 2‑3 and Table 2‑2.

Untreated Flows to the River

Discharge of untreated sewage to the Tijuana River would increase from
1.1 mgd (48 lps) in 1996 to 2.6 mgd (114 lps) in 1998 and 5.6 mgd (245
lps) in 2001. During seasonal high peak flow days, 3.5 mgd (153 lps)
could be discharged in 1996, 5.6 mgd (245 lps) in 1998, and 9.5 mgd (416
lps) in 2001. These discharges would occur during the hours between

TABLE 2‑1

NO ACTION ALTERNATIVE PROJECTED FLOWS

(average day flow in mgd)

Year 1996 1997 1998 1999 2000 2001

Eastern Tijuana sewage flows (average 37.1 38.9 40.8 42.7 44.8 46.9 flow
day)

Flows to the emergency connection 3.9 4.4 4.7 5.2 5.7 6.1

Flows to Pump Station One 32.3 32.8 33.5 34.1 34.6 35.2

Untreated flows discharged to the 1.1 1.7 2.6 3.4 4.5 5.6 Tijuana River

Flows from western Tijuana 3.7 3.9 4.1 4.3 4.5 4.7

Flows to San Antonio de los Buenos 35.9 36.7 37.6 38.4 39.1 39.9

Flows treated at San Antonio de los 17.0 17.0 17.0 17.0 17.0 17.0 Buenos

Untreated flows discharged to the 18.9 19.7 20.6 21.4 22.1 22.9
shoreline in Mexico

1 P.M. and 9 P.M., when sewage flows from eastern Tijuana exceed the
capacity of Pump Station One. Points of entry into the U.S. would be at
Stewart\'s Drain, Canyon del Sol, and Silva Drain near the IWTP; flows
could also enter the U.S. at Smuggler Gulch and Goat Canyon. While the
emergency connection is used, it is insufficient to prevent sewage flows
in the river during peak hours. If the emergency connection was not
used, an additional 3.9 to 6.1 mgd (175 to 263 lps) of flows would also
enter the river.

Untreated Flows Discharged in Mexico

Untreated flows would continue to be discharged to the shoreline in
Mexico south of the San Antonio de los Buenos treatment works. The flows
would increase from 18.9 mgd (828 lps) in 1996 to 22.9 mgd (1,003 lps)
in the year 2001.

Hydrology and Water Quality Effects

Discharges of untreated sewage would remain in the low‑flow channel of
the river and would not result in flooding or alteration of the stream
course. The sewage flows may result in dry‑weather ponding, however.

The sewage‑contaminated flows would represent a substantial health risk,
cause objectionable odors, contaminate groundwater, and adversely impact
riparian and estuarine habitat due to elevated levels of BOD, nutrients,
toxic constituents, and metals in the sewage.

This pollution of the river and estuary has historically had substantial
adverse consequences to the quality of ground and surface waters. These
adverse consequences would continue if no action is taken.

The Tijuana estuary has a relatively small tidal prism (defined as the
volume of water in the estuary between mean higher high water and mean
lower low water) estimated at 290 acre‑feet or 97 mg (0.36 Mm3 ).
Because the tidal prism of the estuary is small, dry‑weather sewage
flows conveyed by the Tijuana River can have far‑reaching effects on the
ecosystem. It has been estimated that at 10 mgd (438 lps) flows,
salinity levels would decrease sufficiently to change the species
composition and abundance in the estuary.

Biological Impacts

Dry‑weather flows of sewage have occurred since the 1930s and, more
recently, have been ongoing from 1980 to 1993. These flows have
adversely impacted estuarine and coastal habitats and sensitive
wildlife.

Riparian

The future dry‑weather flows would be confined to the low‑flow channel
of river. The perennial flows in the river can result in additional
recruitment of understory vegetation in the river channel. This
additional plant growth is periodically scoured during flood events,
however.

In the short term, the loading of nitrogen, phosphorus, and potassium in
sewage flows may stimulate production or growth in plants. If excessive
loading occurs, however, it may cause deleterious effects on riparian
plants. The nutrients cause rapid and excessive growth which can result
in shock and die‑back of riparian trees and shrubs. An increase in
understory vegetation may increase the number of insects which sensitive
species such as least Bell\'s vireo feed on.

Impacts to the riparian habitat are not considered to be significantly
adverse.

Figure 2‑1

Figure 2‑2

Figure 2‑3

TABLE 2‑2

YEAR 2001 DIURNAL FLOWS FOR THE NO ACTION ALTERNATIVE

Flows from Flows to Total Flows Excess Flows Flows from Flows Treated
Untreated Eastern Emergency Out from Pump to Tijuana Western Total Flows
at San Antonio Flows to Time Tijuana\* Connection Station One&#134;
River Tijuana in Canal de los Buenos Shoreline

6:00 a.m. 27.29 0.00 27.29 0.00 2.73 30.02 17.00 13.02

7:00 a.m. 29.06 0.00 29.06 0.00 2.91 31.97 17.00 14.97

8:00 a.m. 31.40 0.00 31.40 0.00 3.14 34.54 17.00 17.54

9:00 a.m. 35.15 0.00 35.15 0.00 3.52 38.67 17.00 21.67

10:00 a.m. 40.78 0.00 36.60 0.00 4.08 40.68 17.00 23.68

11:00 a.m. 44.52 0.00 36.60 0.00 4.45 41.05 17.00 24.05

12:00 m. 49.21 6.72 36.60 0.00 4.92 41.52 17.00 24.52

1:00 p.m. 55.30 13.00 36.60 5.76 5.53 42.13 17.00 25.13

2:00 p.m. 62.33 13.00 36.60 12.73 6.23 42.83 17.00 25.83

3:00 p.m. 66.55 13.00 36.60 16.95 6.66 43.26 17.00 26.26

4:00 p.m. 67.96 13.00 36.60 18.36 6.80 43.40 17.00 26.40

5:00 p.m. 69.36 13.00 36.60 19.76 6.94 43.54 17.00 26.54

6:00 p.m. 70.30 13.00 36.60 20.70 7.03 43.63 17.00 26.63

7:00 p.m. 69.36 13.00 36.60 19.76 6.94 43.54 17.00 26.54

TABLE 2‑2

YEAR 2001 DIURNAL FLOWS FOR THE NO ACTION ALTERNATIVE

(continued)

Flows from Flows to Total Flows Excess Flows Flows from Flows Treated
Untreated Eastern Emergency Out from Pump to Tijuana Western Total Flows
at San Antonio Flows to Time Tijuana\* Connection Station One&#134;
River Tijuana in Canal de los Buenos Shoreline

8:00 p.m. 64.68 13.00 36.60 15.08 6.47 43.07 17.00 26.07

9:00 p.m. 55.77 13.00 36.60 6.17 5.58 42.18 17.00 25.18

10:00 p.m. 46.87 10.32 36.60 0.00 4.69 41.29 17.00 24.29

11:00 p.m. 42.18 5.52 36.60 0.00 4.22 40.82 17.00 23.82

12:00 p.m. 39.84 3.36 36.60 0.00 3.98 40.58 17.00 23.58

1:00 a.m. 37.03 3.36 36.60 0.00 3.70 40.30 17.00 23.30

2:00 a.m. 33.74 0.00 36.60 0.00 3.37 39.97 17.00 22.97

3:00 a.m. 30.46 0.00 36.60 0.00 3.05 39.65 17.00 22.65

4:00 a.m. 28.59 0.00 34.56 0.00 2.86 37.42 17.00 20.42

5:00 a.m. 27.65 0.00 27.65 0.00 2.77 30.42 17.00 13.42

TOTAL 46.89 6.10 35.16 5.63 4.69 39.85 17.00 22.85 Daily Flow

\*Flows are in equivalent million gallons per day (for actual flow rate
in gallons, divide by 24).

&#134;Includes 0.75 million gallons of storage in Tijuana Pump Station
One wet well and conveyance Table 2‑2

Tijuana Estuary

There is a considerable body of evidence that suggests that sewage flows
in the Tijuana River have impacted the estuarine flora, fauna, and
sediments of the Tijuana estuary. Numerous studies have shown that
increased &quot;freshwater&quot; inflows can produce shifts in the
structure of plant and animal communities of coastal wetland systems.

Zedler et al. (1990) examined the effects of sewage flows in the Tijuana
River on the salt‑marsh vegetation in the estuary. Sewage flows were
linked with reduced soils salinities and exotic plant invasions.

An increase in the availability of nutrients from sewage, primarily
nitrogen, stimulates algal blooms. Algal blooms of sufficient magnitude
could result in fish kills that affect higher‑order consumers, such as
the federal and state endangered least tern. Species richness and
abundance for fishes and benthic macroinvertebrates have declined
throughout a period of prolonged sewage discharge.

There is evidence of heavy metal contamination of the sediments and
fishes of the Tijuana River and estuary. Cadmium was found in elevated
levels in the sediments of both the Tijuana River and the estuary. In
fishes, lead was found at levels exceeding the international standard,
but did not appear to pose a health risk.

Coastal Waters

Discharges of untreated sewage through the Tijuana River have less
effect on coastal ocean waters than the estuary, due to the delay in
transit time through the riverine‑estuarine system. Discharges of
untreated sewage to the shoreline in Mexico are anticipated to have more
substantial impacts to coastal waters. In either case, as the sewage is
fresh water, it is carried on the surface of the more saline,
higher‑density ocean waters and the flows are transported by prevailing
currents in the nearshore zone and disperse offshore.

Fecal coliforms, used as indicators of contamination for humans, do not
necessarily effect aquatic organisms as they do humans. Periodic inflows
of compounds potentially lethal to aquatic organisms could occur
virtually at any time, however. Small fishes, benthic animals, and
bottom feeders may uptake toxins and metals which persist upward through
the food chain. This contamination and uptake may in turn affect fish,
marine mammals, and birds, including the endangered California least
tern, brown pelican, and snowy plover.

Public Health and Safety

Discharges of untreated sewage would contaminate the Tijuana River,
estuary, and coastal areas from the international border north to
Coronado in the U.S. These discharges would result in chronic beach
closures around Border Field State Park and Imperial Beach and
seasonally and episodically affect the Silver Strand and Coronado.

Tijuana River Flows

State health standards require total coliform bacteria concentrations
below 1,000 minimum probable number (MPN) per 100 milliliters. According
to historical statistics from the San Diego County Health Department,
the number of days of beach closures in 1995 were 67 days. In prior
years when flows reached up to 10 mgd, beach closures occurred over half
of the year. The beach closures typically included the general area from
south Silver Strand State Beach to the international border, but have
extended as far north as Coronado. At different times, these closures
were caused by sewage flows in the river and other sources of
contamination from the U.S.

Fecal coliform concentrations in the Tijuana River were measured in
1994‑1995. In general, fecal coliform concentrations were highest at
Dairy Mart Road, Hollister Street Bridge, and Smuggler Gulch, where they
greatly exceeded EPA and State standards for body contact. Densities of
fecal indicator bacteria remained high throughout the rainy period
(November to March) implying that there was a continuous and
concentrated source of fecal loading to the estuary. Levels of fecal
indicators in the Tijuana River east of Dairy Mart Road were equal to or
greater than those found downstream.

Sewage‑contaminated flows in the river also create problems associated
with disease vectors. Standing water during the dry‑weather season
provides mosquito breeding habitat.

Mexican Shoreline Discharge

Discharges of untreated wastewater in Mexico would also affect the
quality of nearshore coastal waters in the U.S. The effects of these
untreated flows being discharged was modeled by Parsons Engineering
Science for 23 shoreline locations. This model only estimated the
effects of the shoreline discharge in Mexico; it did not include other
sources of sewage contamination from the Tijuana River or other episodic
sewage spills due to mechanical breakdowns or wet‑weather infiltration.

Exceedances of bacteriological standards for U.S. waters was predicted
to occur chronically for the months June to September and in November at
the international boundary. Exceedances were also predicted during June,
July, and August at the mouth of the Tijuana River and as far north as
Seacoast Drive in Imperial Beach. The model indicates that shoreline
discharges in Mexico would not result in exceedances north of Seacoast
Drive. However, flows of untreated sewage in the Tijuana River would
extend the area affected northward to Coronado.

Land Use and Socioeconomic Considerations

Overall, most of the land uses in the Tijuana River valley have been
negatively impacted by sewage discharges into the Tijuana River and from
discharges of untreated sewage in Mexico extending north along the
shoreline. Continuous indirect impacts are associated with the area\'s
image and reputation. Use of Border Field State Park, Silver Strand
State Beach, and Imperial Beach coastal properties and businesses have
been negatively impacted by beach closures and the image problem
associated with contaminated beaches.

The beach and the special events which are dependent on clean beaches
represent an important economic stimulus for local business. According
to the Imperial Beach Chamber of Commerce, one of the reasons the Bud
Pro Surf Contest was not held in Imperial Beach was the beach closures
caused by sewage discharges into the Tijuana River.

The major impacts to agriculture occur during flood periods, although
groundwater pollution could also impact agricultural productivity in the
valley. Soils have been contaminated with sewage and condemned by the
County Health Department for a period of six months. Agricultural
employees in the area have also expressed concerns over working in the
vicinity of sewage discharges.

Both fishing from the Imperial Beach Pier and beach anglers using the
beach from the Mexican border to roughly the Silver Strand State Beach
are directly impacted by beach closures due to effluent discharges. The
impact on fishing also affects the bait and tackle shop, as well as some
of the smaller businesses in Imperial Beach.

The salability and value of the residential properties in the Tijuana
River valley have and would continue to be affected by sewage
discharges.

Odors

Sewage‑contaminated flows in the river, especially during the dry
season, have caused incessant complaints of unpleasant odors from local
residents.

Consistency with Plans and Policies

Discharge of untreated sewage to the Tijuana River is inconsistent with
federal, state, and local policies and regulations governing water
quality, health, and safety and is inconsistent with local land use
goals and objectives. The ongoing contamination has also had serious
adverse effects on the quality of life for residents and enjoyment of
the amenities of the area for visitors.

Alternative 2: Operate IWTP

In 1997, once construction of the advanced primary portion of the IWTP
is complete, it will be operational and could provide treatment and
storage of 2 mg (7,600 m3) and treat 25 mgd (1,095 lps) average flows
and 75 mgd (3,285 lps) peak flows. Pump Station One would continue to
send 36.6 mgd (1,603 lps) to the force main and conveyance canal. Any
flows in excess of 36.6 mgd at Pump Station One would be diverted to the
emergency connection. Flows in excess of the combined capacity of Pump
Station One and the emergency connection would be directed to the IWTP,
treated to advanced primary levels, stored, and discharged to the
emergency connection when capacity is available. If no discharge
capacity is otherwise available, the treated effluent would be
discharged to the Tijuana River.

Costs for operating the IWTP in 1997 are estimated at \$5.2 million,
including energy, chemicals, service, and other operations and
maintenance. Costs for using the emergency connection are estimated at
\$1.6 million.

Only sewage which would otherwise overflow into the Tijuana River would
be treated and stored at the IWTP and later discharged to the emergency
connection. Once capacity of the emergency connection is exceeded, this
alternative would result in dry‑weather flows in the Tijuana River, but
the flows would be treated effluent rather than untreated sewage. This
would occur because the peak hour flows between 1 P.M. and 9 P.M. exceed
the combined capacity of Pump Station One, the emergency connection, and
the 2 million gallons (7,600 m3) of flow equalization storage in the
IWTP.

The yearly anticipated flows through the system are provided in Table
2‑3. The distribution of the flows within the system is presented in
Figures 2‑4 and 2‑5, and the diurnal variation and excess flows in
Figure 2‑6.

TABLE 2‑3

INTERIM OPERATION OF THE IWTP

(average flow day in mgd)

Year 1996 1997 1998 1999 2000 2001

Eastern Tijuana sewage flows (average 37.1 38.9 40.8 42.7 44.8 46.9 flow
day)

Flows via emergency connection to Point 5.0 6.1 6.7 7.2 7.7 8.1 Loma

IWTP treated flows to the Tijuana River 0.0 0.0 0.6 1.4 2.5 3.6

Untreated flows to Pump Station One 32.2 32.8 33.5 34.1 34.6 35.2

Untreated flows from western Tijuana 3.7 3.9 4.1 4.3 4.5 4.7

Untreated flows to San Antonio de los 35.9 36.7 37.6 38.4 39.1 39.9
Buenos

Flows treated at San Antonio de los 17.0 17.0 17.0 17.0 17.0 17.0 Buenos

Untreated flows discharged to the 18.9 19.7 20.6 21.4 22.1 22.9
shoreline in Mexico

Treated Flows to the River

The flow volumes to the Tijuana River would be substantially reduced
relative to the No Action alternative. Based upon the USIBWC/EPA flow
projections, no flows are anticipated during average flow conditions
until the year 1998 and would reach 3.6 mgd (158 lps) in 2001. During
seasonal high flows, there would be 1.5 mgd (70 lps) in 1996 and up to
7.5 mgd (329 lps) in 2001. However, the discharge would be advanced
primary effluent rather than untreated sewage. Treated effluent has
significantly reduced concentrations of BOD, solids, and some inorganic
constituents. Coliforms and pathogens would remain a health concern,
however.

Figure 2‑4

Figure 2‑5

Figure 2‑6

Untreated Flows Discharged in Mexico

The untreated flow volumes discharged to the shoreline in Mexico would
be the same as for the No Action alternative.

Hydrology and Water Quality

Discharge of treated effluent to the Tijuana River would have no adverse
consequences to hydrology of the river. The flows would be accommodated
in the low‑flow channel and no dry‑season flooding or scouring of the
channel would occur. Ponding within the channel may result, however. The
infiltration to groundwaters would be minor, given the low flow volumes
anticipated.

The discharge of advanced primary treated effluent to the Tijuana River
does not meet federal or state water quality requirements for discharges
to surface or groundwaters and would not meet water quality objectives
of the Basin Plan. Pollutant loadings from the treated effluent would be
reduced relative to the No Action alternative, however. BOD would be
reduced by 45 percent, total solids by 75 percent, and lead by 50
percent. Nutrients would not be reduced, which is of concern for surface
and ground waters. High nutrient content can cause algal blooms which
adversely affect aquatic life and can cause offensive odors. Reductions
of other metals and inorganic compounds vary.

Treated effluent would result in adverse impacts to the Tijuana River
estuary, due primarily to nutrient enrichment but also from reduction of
salinity in brackish waters and pollutant loadings.

While discharge of advanced primary effluent is preferable to raw
sewage, it would result in impacts to surface and ground waters and the
estuary and would constitute a health risk if not disinfected.
Biological Impacts

Impacts to riparian habitats would be similar to the No Action
alternative and are not considered adverse.

Impacts to the estuary would be incrementally reduced from the No Action
alternative. No treated effluent would need to be discharged to the
river until 1998, except during seasonal peak flows. After 1998,
nutrient enrichment leading to eutrophication could result in adverse
effects during average day flow regimes. Pollutant loadings would be
elevated and salinity levels decreased by seasonal high flows. Impacts
to the estuary after the year 1998, when discharge of treated effluent
would occur, would be adverse from this alternative.

Impacts to marine life and shorebirds would be reduced, relative to the
No Action alternative. Pollutant loads in treated effluent could have
adverse effects to benthic communities, fish, and shorebirds; but these
effects would be localized around the mouth of the Tijuana River.
Discharges of untreated sewage in Mexico would occur at the same volumes
as the No Action alternative, however, and cause adverse effects to
marine life along nearshore waters in Baja. Public Health and Safety

Public health risks from bacterial contamination in the river would
continue to be a major concern. State standards for total coliforms in
water bodies are 1,000 MPN/100 ml.

Primary treatment only reduces bacterial contamination by about 20
percent; the IWTP effluent is expected to have coliform concentrations
of 1.6 &#215; 108 total coliform per 100 ml. Bacterial concentrations
are reduced by natural forces of decay, sunlight, salinity, temperature,
and adsorption to sediments. The estimated transit times of effluent in
the river from the IWTP to the estuary range from 6.0 to 14.4 hours in
1996 and 4.6 to 11.6 hours in 2001. Therefore, the bacterial
concentrations in the effluent discharged to the river and flowing to
the estuary and ocean would exceed health and safety standards.

The IWTP has provision for chlorination/dechlorination of the effluent,
which could reduce the bacterial concentrations of the effluent.
However, it may not be possible to disinfect the effluent to below the
surface water discharge standards of 2.2 coliforms per 100 ml of
effluent. Also, chlorination of effluent poses other risks from
chlorinated compounds to freshwater and marine life and would have to
comply with the receiving water standards for residual chlorine.

Concerns about vectors would continue as for the No Action alternative.
Vector control could be enhanced by a program of eliminating ponding of
treated effluent in the low‑flow channel, however.

Land Use and Socioeconomic Considerations

The operation of the IWTP would have beneficial effects to residents in
the valley and agricultural, recreational, and commercial uses in the
valley and along the coastline but would not eliminate impacts related
to sewage contamination. The treated effluent in the river is not safe
for recreational body contact. It is anticipated that bacterial
contamination along the shoreline would be reduced but may not meet
State standards and beach closures could still occur. There should be a
substantial psychological benefit in that action is being taken to
eliminate the sewage contamination in the river and shoreline by
operating the IWTP. Odors

Primary effluent discharged to the river would result in unpleasant
odors, although it is not as malodorous as untreated sewage. The
potential odors could be reduced by chlorination; but as discussed
above, this is not considered feasible for interim operation of the
IWTP.

Consistency with Plans and Policies

Discharging advanced primary effluent from the IWTP to the river would
not be consistent with federal and state water pollution control laws
and policies, under the federal Clean Water Act and the Water Quality
Control Plan for the San Diego Basin (State of California 1995).

Discharge of treated effluent to the river would not meet the goals for
management of the Tijuana River National Estuarine Research Reserve.

Alternative 3: Operate IWTP with Detention Basin

Up to 5.5 million gallons (20,900 m3) of treated effluent could be
stored in a lined earthen detention basin(s) at the IWTP site for
off‑peak discharge to the emergency connection. The earthen basin(s)
would be 10 to 15 feet (3.0 to 4.6 m) in depth and occupy an area of the
IWTP site of under two acres (0.8 ha).

TABLE 2‑4

INTERIM OPERATION OF THE IWTP WITH 5.5 MILLION GALLONS FLOW STORAGE

(average flow day in mgd)

Year 1996 1997 1998 1999 2000 2001

Eastern Tijuana sewage flows (average 37.1 38.9 40.8 42.7 44.8 46.9 flow
day)

IWTP treated flows to the emergency 5.0 6.1 7.3 8.7 9.2 9.5 connection

IWTP treated flows to Tijuana River 0.0 0.0 0.0 0.0 0.0 0.0

Untreated flows to Pump Station One 32.2 32.8 33.5 34.1 34.6 35.2

Untreated flows from western Tijuana 3.7 3.9 4.1 4.3 4.5 4.7

Total untreated flows to San Antonio de 35.9 36.7 37.6 38.4 39.1 39.9
los Buenos

Flows treated at San Antonio de los 17.0 17.0 17.0 17.0 17.0 17.0 Buenos

Untreated flows discharged to the 18.9 19.7 20.6 21.4 22.1 22.9
shoreline in Mexico

Costs for the addition of detention basin(s) at the IWTP are estimated
at \$2.7 million. Increased use of the emergency connection would
increase operations and maintenance costs to \$7.1 million in 1997.

The IWTP would receive flows after Pump Station One and the emergency
connection\'s flow capacities have been exceeded (generally, 1 P.M. to 9
P.M. in Tijuana). After 9 P.M., the emergency connection would be able
to take flows stored or treated at the IWTP. By storing flows during
peak hours, the system capacity can be extended. This capacity would be
sufficient to prevent discharge to the Tijuana River from the IWTP
during average day flows through the year 2001. During seasonal high
flows days, approximately 2.0 mgd (88 lps) would be discharged in 2001.

This alternative would result in flows of untreated sewage being
discharged at the shoreline in Mexico at the same flow volumes as No
Action and Operate IWTP, however.

The yearly anticipated flows through the system are provided in Table
2‑4. A schematic of the flows and site plan are provided in Figures 2‑7
and 2‑8. The distribution of the flows within the system is presented in
Figure 2‑9 and the diurnal variation and excess flows in Figure 2‑10.

Treated Flows to the River

The discharge of treated effluent to the Tijuana River would not occur
until the year 2001, when 2.0 mgd (88 lps) would be discharged during
seasonal high flow days. If the SBOO becomes operational by 1998‑1999,
all discharges to the river of untreated sewage or treated effluent
could be avoided.

Untreated Flows Discharged in Mexico

The discharge of untreated flows to the shoreline in Mexico would be the
same as for the No Action and Operate IWTP alternatives. Hydrology and
Water Quality

The detention basin would be constructed above the 100‑year floodplain
of the river channel. Therefore, the basin would not significantly
impact the hydrology of the river. As planned, the earthen detention
basin(s) would be lined with an impermeable layer to protect against
percolation through the soil into the groundwater.

Effluent flow rates of 2.0 mgd (88 lps) exiting the IWTP directly into
the river during high flow days in the year 2001 are not expected to
cause flooding, scouring, or channel alteration in the river valley.

However, the flow of primary effluent to the river would degrade the
water quality of the river and Tijuana River estuary. The pollutant load
to the river would be less than would occur under either the No Action
or Operate IWTP alternatives, since this alternative results in a lower
treated effluent flow rate discharged to the river. However, the treated
effluent would not meet the State standards for receiving waters and
would not be in compliance with water quality plans or objectives.

Bacterial counts in the treated effluent would exceed State standards
and result in bacterial contamination.

The storage of treated effluent for long periods of time in the earthen
detention basin could allow pollutants to percolate down into the
groundwater. If this were to occur, groundwater quality could be
adversely impacted. This impact could be avoided by the installation of
an impermeable liner within the basin. Biological Impacts

No significant impacts to the riparian habitats are anticipated.

Impacts to the estuary would be substantially reduced due to the
decrease in flow of treated effluent. No flows would be released during
average day conditions. The discharge of 2.0 mgd (88 lps) of treated
effluent would occur only during high flow day periods in 2001. These
flow volumes of runoff can occur naturally during the dry season after
years with high rainfall and are low enough not to seriously reduce the
salinity levels in brackish‑water areas. Eutrophication in low‑flow
areas of the marshes due to nutrient loads could result, however,
adversely impacting the estuary.

Figure 2‑7

Figure 2‑8

Figure 2‑9

Figure 2‑10

Marine biota and shorebirds would not be adversely affected by the river
discharges of treated effluent, and this alternative would provide
beneficial reductions in pollutant loadings compared to the previous
alternatives. However, discharges of untreated sewage to the shoreline
in Mexico would result, which would have adverse impacts.

Public Health and Safety

Public health and safety impacts would be reduced over the previous
alternatives. Bacterial contamination from IWTP effluent would only
occur in the Tijuana River with the seasonal wet‑weather flow discharges
in the years 2000 and 2001. Residual potential contamination could
result from other discharges of untreated sewage in Mexico, however.

Vector control may also be needed to prevent ponding of effluent in the
river. The detention basin would have fluctuating water levels and would
not be a source for disease vectors.

Geotechnical

The earthen detention basin(s) would be within the footprint of the
IWTP. The basin(s) would need to be built with respect to underlying
geotechnical hazards, such as potential for liquefaction of the soils,
seismic shaking, and slope stability. No conditions exist at the site
that would preclude the construction of an earthen detention basin(s) at
the site.

Land Use and Socioeconomic Considerations

This alternative would significantly reduce impacts from existing sewage
contamination, odors, and beach closures, compared to the No Action
alternative. The discharge of untreated effluent in Mexico would remain,
however, which could affect residents and recreational or commercial
uses in coastal areas.

Odors

Storage of primary treated effluent at the plant site in open basins has
the potential to result in objectionable odors. This potential adverse
impact could be mitigated by providing a cover over the basins and
venting the air through an odor control system prior to release.

Consistency with Plans and Policies

The direct discharge of primary treated effluent to the river would be
inconsistent with the federal Clean Water Act and the Water Quality
Control Plan for the San Diego Basin.

Discharge of treated effluent to the river would not meet the goals for
management of the Tijuana River National Estuarine Research Reserve.

Alternative 4: Operate IWTP with New Conveyance to Mexico

Mexico may complete additional pumping facilities, a force main, and a
conveyance canal parallel to the existing facilities as a backup system.
The additional facilities would have a capacity of 50 mgd (2,190 lps)
average capacity and 75 mgd (3,285 lps) peak capacity. In the interim
period, effluent from the IWTP could be conveyed separately to the
shoreline discharge point in Mexico using these facilities. The
additional facilities are a backup and not a stand‑alone expansion of
the existing system. Its use to convey flows from the IWTP separately
would be temporary.

Use of the emergency connection is not required to avoid discharge of
treated effluent to the Tijuana River as the flow capacities of Pump
Station One and the canal to San Antonio de los Buenos are not exceeded
during peak flow hours. However, to reduce the discharge of untreated
flows at the shoreline in Mexico, the emergency connection could be
operated, but at reduced flows.

Costs for this alternative are estimated at \$16.0 million capital costs
(equipment and construction) and \$8.0 million operations and
maintenance costs. If the emergency connection were used in addition,
the operations and maintenance costs would increase.

The yearly anticipated flows through the system are provided in Table
2‑5. The distribution of the flows within the system is presented in
Figure 2‑11. The location of the proposed facilities is provided in
Figure 2‑12. The diurnal variation is shown in Figure 2‑13 and excess
flows in Figure 2‑14.

TABLE 2‑5

OPERATE IWTP WITH NEW CONVEYANCE TO MEXICO

USING THE EMERGENCY CONNECTION

(average flow day in mgd)

Year 1996 1997 1998 1999 2000 2001

Total sewage flows (average flow day) 37.1 38.9 40.8 42.7 44.8 46.9

IWTP treated flows to new Mexican 23.8 25.0 25.0 25.0 25.0 25.0
conveyance

Flows diverted via emergency connection 0.0 0.8 2.9 5.0 6.3 7.3 to Point
Loma

Untreated flows from Pump Station One 13.3 13.1 12.9 12.7 13.5 14.6

Untreated flows from western Tijuana 3.7 3.9 4.1 4.3 4.5 4.7

Total flows to San Antonio de los Buenos 17.0 17.0 17.0 17.0 18.1 19.3

Mixed flows treated at San Antonio de los 17.0 17.0 17.0 17.0 17.0 17.0
Buenos

Untreated flows discharged to shoreline 0.0 0.0 0.0 0.0 1.0 2.3 in
Mexico

Flows to the River

There would be no untreated sewage or treated effluent discharged to the
Tijuana River under this alternative. Any sewage flows in the river
would be from winter storm runoff or equipment failures.

Figure 2‑11

Figure 2‑12

Figure 2‑13

Figure 2‑14

Untreated Flows Discharged in Mexico

The flows through Pump Station One to San Antonio de los Buenos would be
reduced so that far less sewage would bypass treatment and be discharged
to the shoreline. In 2000, only 1.0 mgd (44 lps) is anticipated to be
discharged untreated, rising to 2.3 mgd (101 lps) in 2001. This is a
substantial reduction from the 22.9 mgd (1,003 lps) that would be
discharged with the previous alternatives.

If the emergency connection is not used, however, the flows in Table 2‑5
directed to it would be sent to San Antonio de los Buenos and may be
discharged untreated to the shoreline in Mexico. This would result in
flow of untreated sewage discharged to the shoreline in 1998 of 2.9 mgd
(127 lps) and increase from 2.3 mgd (101 lps) to 9.6 mgd (420 lps) in
the year 2001.

Hydrology and Water Quality

No hydrological or water quality impacts to the Tijuana River valley
would occur as a result of implementation of this alternative. The
volume of discharge of untreated sewage to the shoreline in Mexico would
be significantly reduced. However, the shoreline discharge of IWTP and
San Antonio de los Buenos treated effluent does not provide for much
dilution of the effluent (approximately 10:1), and being fresh water,
the effluent would remain at the surface along the coastline. Ocean
water quality along the coastline in the U.S. would be improved but may
not meet the Ocean Plan standards during periods with north‑trending
coastal circulation. Biological Impacts

This alternative would have no adverse consequences to riparian and
estuarine habitats or biota. The conveyance canal would be sited through
urbanized areas and along a coastal ridgeline of non‑ native grasslands
in Mexico. Several canyons would be crossed that have either coastal
sage scrub or maritime chaparral communities which are considered
sensitive in the U.S. and may provide habitat for the federally listed
(threatened) coastal California gnatcatcher. Mexico is considering three
alternative alignments and would prepare an impacts assessment prior to
construction.

Significant benefits would result both to the estuary and to nearshore
coastal areas north of the river mouth due to the elimination of
dry‑weather flows of sewage or effluent in the Tijuana River. The
discharge in Mexico of primary treated effluent to the ocean would be
increased by 25 mgd (1,095 lps), which may have adverse effects around
the area of discharge. Only 2.3 mgd (101 lps) of untreated effluent
would be discharged to the shoreline in Mexico in the year 2001. If the
emergency connection is not in use, the discharge of untreated sewage
would be 9.6 mgd (420 lps) by 2001, still well below the No Action
alternative.

The overall reduction in untreated effluent being discharged to the
shoreline in Mexico should have beneficial effects to marine biology
over existing conditions or other alternatives. However, due to the low
initial dilution of the discharge, the increase in the amount of
advanced primary treated effluent would have adverse effects to coastal
waters in the U.S. and Mexico. Public Health and Safety

Existing public health risks from bacterial contamination in the river
and along the shoreline would be substantially reduced. The reduction in
untreated sewage being discharged in Mexico would not substantially
change the extent of the chronic bacterial contamination along its
coastline, and beach closures and public health concerns would remain.
This is because advanced primary treatment only reduces bacterial
concentrations by about 20 percent. Thus, the increase in the ratio of
discharge of treated effluent to untreated sewage does not substantially
reduce the health risks.

Mexico chlorinates its effluent; the effectiveness in reducing pathogens
in ocean receiving waters is not known at this time. It has not been
decided whether or to what extent the IWTP effluent would be chlorinated
prior to discharge in Mexico.

Socioeconomic Considerations

Impacts from this alternative would be of substantial benefit to
residents of the valley, agricultural uses, and public and commercial
recreation in the coastal areas. However, beach closures may still
result from the discharge of treated effluent and untreated sewage to
the shoreline in Mexico.

Consistency with Plans and Policies

The discharge of IWTP effluent and treated and untreated effluent would
be subject to requirements for discharges contained in the Mexican State
Ecology Law and federal Mexican standards for discharges to national
waters. No discharges to receiving waters in the U.S. would result.

Alternative 5: Operate IWTP with Discharge to SBOO

In 1998 the South Bay Ocean Outfall becomes operational, and all of the
sewage treated at the IWTP could be discharged through the ocean
outfall. Average daily flows in Mexico are estimated to be between 43
and 46 mgd (1,883‑2,015 lps) with peak hourly flows of 65 to 84 mgd
(2,847‑3,679 lps). The IWTP would be able to treat up to 25 mgd (1,095
lps), while the treatment plant at San Antonio de los Buenos would treat
up to 17 mgd (745 lps).

Therefore, 3 to 5 mgd (131‑219 lps) of untreated sewage would be
discharged at the shoreline in Mexico. No untreated sewage would be
discharged in U.S. waters. By the year 2001, flows would increase to
between 47 and 51 mgd (2,059‑2,234 lps) average, with peaks between 71
and 92 mgd (3,120‑4,030 lps). Between 9.6 and 12.0 mgd (420‑526 lps) of
untreated sewage would be discharged at the shoreline in Mexico.

The emergency connection would not be required with this alternative to
avoid the discharge of treated effluent to the Tijuana River. Use of the
emergency connection and treatment of Mexican sewage by the City of San
Diego was never intended to be a permanent treatment option; it was
constructed to eliminate overflows of sewage in the Tijuana River.

Costs for operation of the IWTP with discharge through SBOO are
estimated at \$7.5 million. If the emergency connection were used
through the year 2001, additional operations and maintenance costs would
be incurred.

The yearly anticipated flows through the system are provided in Table
2‑6. The distribution of the flows within the system is presented in
Figures 2‑15 and 2‑16, and the diurnal variation and excess flows in
Figure 2‑17.

Treated Flows to the River

Under this alternative there would be no treated (or untreated) average
day dry‑ weather flows to the Tijuana River through the year 2001 using
the USIBWC/EPA flow projections.

Untreated Flows Discharged in Mexico

Untreated flows would continue to be discharged to the shoreline in
Mexico south of the San Antonio de los Buenos treatment works. However,
these flows would be substantially reduced from those that would occur
with the No Action alternative. The flows would increase from 2.9 mgd
(127 lps) in the year 1998 to 9.6 mgd (420 lps) in the year 2001. The
impacts of the shoreline discharge in Mexico would be less than for
Alternative 4, because a lesser volume of effluent would be discharged
overall.

TABLE 2‑6

IWTP WITH THE SOUTH BAY OCEAN OUTFALL

(average flow day in mgd)

Year 1998 1999 2000 2001

Total sewage flows (average flow day) 40.8 42.7 44.8 46.9

IWTP treated flows to South Bay Ocean 25.0 25.0 25.0 25.0 Outfall

Flows diverted via emergency connection 0.0 0.0 0.0 0.0 to Point Loma

Untreated flows from Pump Station One 15.8 17.7 19.8 21.9

Untreated flows from western Tijuana 4.1 4.3 4.5 4.7

Total flows to San Antonio de los Buenos 19.9 22.0 24.3 26.6

Flows treated at San Antonio de los 17.0 17.0 17.0 17.0 Buenos

Untreated flows discharged to the 2.9 5.0 7.3 9.6 shoreline in Mexico

Hydrology and Water Quality Effects

There would be no discharges from the IWTP to the river under this
alternative. Therefore, there would be no adverse hydrological or water
quality impacts in the river valley.

Discharge of advanced primary effluent is not consistent with the
federal Clean Water Act. The modeling and analysis by Parsons
Engineering Science of the advanced primary effluent discharge through
the SBOO, given expected effluent characteristics, initial dilution of a
minimum of 100:1, and the TOES current data indicate that polyaromatic
hydrocarbons may not meet the State Ocean Plan standards at the zone of
initial dilution. In addition, a potential for exceedances of the 10,000
coliforms per 100 ml standards for two samples in a 48‑hour period was
identified by the model at the Imperial Beach kelp bed in 50‑foot (15 m)
water depths. This exceedance is predicted to occur less than one
percent of the time throughout the year, however. If the State Ocean
Plan standards are not met by the SBOO discharge, the effects to ocean
water quality could be significant and adverse.

However, the results of the model also indicate that most constituents
of concern would meet the Ocean Plan standards and that further
dilutions around the outfall would be substantial. The high coliform
levels predicted would be rare events of short duration that would not
be considered a significant public health risk. The water quality
impacts from discharge of primary treated effluent from the IWTP through
the SBOO had the lowest impacts to receiving water quality of any of the
alternatives considered.

Biological Impacts

Terrestrial and Estuarine Biology

There would be no adverse impacts to terrestrial or estuarine biology as
a result of this alternative. The removal of dry‑weather sewage
discharges will reduce the pollutant load to the river and estuary.

Coastal Waters

Impacts from the discharge of advanced primary effluent to the marine
environment would not result in substantial adverse impacts to marine
organisms. The area affected by the interim discharge would be smaller
(135 acres, or 55 ha) than the impact area identified in the FEIS.
Modeling of the dilution from the outfall discharge shows that the
effluent would receive significant additional dilution within about
3,280 feet (1,000 m) of the zone of initial dilution. No impacts to
marine organisms at the Imperial Beach kelp bed are forecast.

Discharges of untreated sewage and treated effluent would result in
Mexico, however, and may adversely affect the nearshore coastal
environment around the discharge point.

Public Health and Safety

Tijuana River Flows

Under this alternative, there would be no dry‑weather discharges to the
Tijuana Figure 2‑15

Figure 2‑16

Figure 2‑17

River. Therefore, fecal coliform and other pollutant levels in the
river, estuary, and nearby coastal waters are anticipated to be
substantially reduced.

The reduction of intermittent dry‑weather flows will decrease the
occurrence of standing water, thus lessening problems associated with
disease vectors such as mosquitoes.

SBOO Discharge

Total coliforms from the effluent discharged through the outfall were
modeled and are expected to meet ocean water quality standards except at
the 50‑foot water depth at the edge of the Imperial Beach kelp bed. The
predicted exceedance is for the 10,000 coliforms per 100 ml in two
samples over a 48‑hour period and would not be a chronic condition
throughout the year. The exceedance would not be a significant adverse
impact, due to the rarity of occurrences and limited potential exposure
to humans. Surface ocean waters at this location would not exceed the
standards, due to trapping of the deeper water layers.

Mexican Shoreline Discharge

Discharges of untreated wastewater in Mexico will be substantially less
than those which occur with the No Action alternative. However, based on
modeling performed by Parsons Engineering Science, contamination from
these reduced sewage discharges could impact nearshore coastal waters in
the U.S.

Socioeconomic Considerations

Historically, beach closures caused by contaminated flows in the Tijuana
River have had a negative economic impact on the surrounding communities
and businesses. Additionally, even in times of no closures, businesses
have been negatively impacted by the perception of a perpetual
contamination problem in the river valley.

The reduction of dry‑weather sewage discharges to the river is
anticipated to substantially reduce the number of beach closures and
will reduce the pollutant load in the river, resulting in a positive
economic impact to the area. Coastal water quality would be enhanced,
although there may be residual impacts from shoreline discharge in
Mexico.

Consistency with Plans and Policies

This alternative would be consistent with the Water Quality Control Plan
for the San Diego Basin, since there would be no discharges of treated
effluent to the Tijuana River. However, the model of the SBOO discharge
resulted in exceedances of the State Ocean Plan standards for
polyaromatic hydrocarbons, which would not be consistent with ocean
water quality objectives. Discharge of primary treated effluent to the
ocean is not authorized by the federal Clean Water Act. The operator
will need to comply with a discharge permit and compliance order issued
by the RWQCB. Alternative 6: Phased Alternative

The previous alternatives have been evaluated as stand‑alone
alternatives to taking no action through the year 2001. It is also
reasonable to evaluate the use of these individual alternatives in a
phased approach.

The logical phasing scheme would begin with Alternative 2, operate the
IWTP to detain up to 2 million gallons (7,600 m3) of flow and treat
additional flows from eastern Tijuana as needed with discharge to the
emergency connection. When it appears that the total average dry‑weather
flows from eastern Tijuana or higher seasonal high peak flows would
result in discharge of treated effluent from the IWTP to the Tijuana
River (expected by 1997 or 1998), then either Alternative 3 (Operate
IWTP with Detention Basin) or Alternative 4 (Operate IWTP with New
Conveyance to Mexico) could be implemented. Either of these two
alternatives could provide a means to avoid discharging treated effluent
from the IWTP into the Tijuana River. When the SBOO is completed, all
treated effluent from the IWTP would be discharged through the SBOO.
Once the SBOO is available, neither the detention basin nor the
additional conveyance system in Mexico would be needed to discharge
treated effluent from the IWTP.

An additional consideration for Alternative 6 is the time required to
construct the facilities. The IWTP will be operational by early 1997.
The 5.5 million gallon (20,900 m3) lined detention basin would take nine
months to construct and could be available by September 1997. The new
Mexican pumping and conveyance system is expected to take 15 months to
complete once agreement with Mexico has been reached. These facilities
are not expected to be available for use until the spring of 1998. The
SBOO is currently under construction and is not currently scheduled to
be available for use until the spring of 1998.

The impacts of the phased alternative would be equal to or less than the
stand‑alone alternatives as analyzed above. The phased alternative would
reduce the impacts from discharge of treated effluent to the Tijuana
River, since each facility would be used in an attempt to avoid
discharge of treated effluent into the Tijuana River. However, the
USIBWC/EPA flow projections are estimates, and the flows sent from
Mexico may exceed the discharge capacity before these facilities are
available. If this occurs, discharge of treated effluent into the
Tijuana River will be unavoidable and the adverse environmental impacts
will be similar to those discussed for Alternative 2.

The Preferred Alternative

The goal of the action is to avoid the discharge of untreated sewage and
minimize the effects of the discharge of treated effluent to sensitive
areas such as the Tijuana River, estuary, shoreline, offshore kelp beds,
and active recreation and commercial areas. As discharges from the
shoreline in Mexico may affect U.S. coastal waters, the alternative that
provides the maximum level of treatment to the greatest volume of sewage
prior to discharge, whether the discharge occurs in Mexico or the U.S.,
would be preferred. However, selection of a preferred alternative is
also subject to considerations of environmental effects of the
alternatives, cooperation with Mexico, timeliness to implement, and
costs.

For the interim operations period, the preferred approach alternative
would be to phase alternatives as described for Alternative 6.

Starting with operation of the IWTP in 1997, there would not be a need
to discharge treated effluent to the river until 1998, according to the
USIBWC/EPA flow projections for average day flows. No additional capital
costs would be incurred and discharge of effluent to the emergency
connection would not result in adverse impacts to receiving waters in
the U.S. However, to avoid discharge of treated effluent to the Tijuana
River during seasonal high flows in 1997, and average day flows in 1998
and thereafter to 2001, either the detention basin at the IWTP or new
conveyance facilities in Mexico would need to be constructed.

Each of these alternatives avoids discharge of treated effluent to the
Tijuana River. The new conveyance facilities in Mexico would probably
not be available until the middle of the year 1998, and discharges of
treated effluent could occur by that time if the IWTP is operated. The
addition of detention basins at the IWTP could be implemented in time
(September, 1997) to avoid any discharges of treated effluent to the
Tijuana River and does not require additional agreements with Mexico to
implement.

Neither of these interim alternatives is environmentally preferred to
SBOO, as the discharge of treated effluent at the shoreline in Mexico is
not preferable to discharge through the outfall offshore. Under current
schedules, the SBOO and the new Mexican conveyance are not scheduled to
be available until 1998. Assuming these concurrent schedules, the SBOO
would be preferred. However, if the new facilities in Mexico were
available and the SBOO is delayed, then the new facilities in Mexico
could be used to avoid discharges to the river until the SBOO is
available.

Once completed, discharge through the SBOO is the preferred alternative.

Chapter Three

The Affected Environment

This chapter profiles the environmental resources in the Tijuana River
valley and vicinity that would be affected by construction or operation
of project facilities. The environmental resources include the relevant
physical, biological, social, and economic conditions that would change
under the implementation of an alternative or that might aid a reader to
understand the alternatives. Hydrology and Water Quality

The information provided in this section is derived from a number of
reports, which are referenced in the text. In particular, the Tijuana
Estuary Enhancement Hydrologic Analysis and technical appendixes
prepared by Philip Williams &amp; Associates (1987), the Tijuana River
Groundwater Study by the U.S. Army Corps of Engineers (1990), the
Hydrogeological Assessment of the Tijuana River Valley by Rick Rempel
(1992), the Groundwater Management Plan for the Tijuana River Basin by
the Tia Juana Valley County Water District (TJVCWD 1994a, 1994b) and
Tijuana River Hydraulics Report (Boyle Engineering Corporation 1996)
contain significant information regarding hydrologic characteristics of
the Tijuana River and estuary. These documents are hereby incorporated
by reference.

Watershed Description

Under natural conditions (i.e., without sewage contributions), the
Tijuana River is an ephemeral stream draining an area of about 1,731
square miles (4,483 km2), of which 470 square miles (1,217 km2) (about
30%) are in the United States and 1,261 square miles (3,266 km2) (about
70%) are in Mexico. The fan‑shaped drainage area is about 75 miles (121
km) long and 50 miles (80 km) wide (see Figure 1‑2). Numerous
tributaries combine to form the Tijuana River. That portion of the river
referred to as the Tijuana River is formed by the confluence of
Cottonwood Creek (Rio El Alamar) and the Rio de las Palmas about 11
miles (17.7 km) southeast of the city of Tijuana. The Tijuana River
flows northward through a 6.6‑mile (10.6 km) concrete flood‑control
channel in the city of Tijuana and crosses the international boundary
into California. Immediately downstream of the border, the USACE has
constructed 0.5 mile (0.8 km) of concrete channel, 2.0 miles (3.2 km) of
levees, and an energy dissipater. After the river crosses into the U.S.,
it continues westward about 5.3 miles (8.5 km) and empties into the
Pacific Ocean about 1.5 miles (2.4 km) north of the international
boundary. The Tijuana River estuary lies at the mouth of the river at
the Pacific Ocean.

An alluvial floodplain forms the floor of the Tijuana River valley. From
an elevation of 40 feet (12.2 m) above MSL at the Mexican border, the
river valley gradually descends westward to its outlet into the ocean.
The valley floor averages about 1.0 mile (1.6 km) in width; it is
incised within a suite of coastal terraces that range from 20 to over
400 feet (6‑122 m) in elevation. The alluvial aquifer underlying the
Tijuana River valley occupies an area of about 5,000 acres (2,023 ha) to
depths of 100 feet (30.5 m) or more. The Tijuana River can be
characterized as a braided alluvial stream that shifts widely across the
valley floor during flood stage.

The climate in the Tijuana River basin is classified as Mediterranean
dry summer subtropical. It is characterized by moderate temperatures
near the coast, with increasing temperature variability inland. The
average annual rainfall across the watershed ranges from about 11 inches
(28 cm) near the coast to 25 inches (63.5 cm) at the higher inland
elevations. Thus, an average rainfall year represents a potential
recharge of up to 4,500 acre‑feet (5.55 Mm3) in the 5,000‑acre (2,023
ha) alluvial aquifer. There are distinct wet and dry seasons, with over
90 percent of the mean annual precipitation occurring during the
six‑month period of November through April when evapotranspiration is at
a minimum. Both the annual and individual storm rainfalls are extremely
variable, which means that the region experiences both extremely wet and
very dry years. The extreme variability in rainfall also produces
variability in annual flow, flood peaks, and sediment discharge in the
Tijuana River and the Tijuana River estuary.

Predominant floodplain soils belong to the Chino and Tujunga series.
Lying along the historic river channel in the eastern portion and along
the present channel in the central portion of the hydrologic subarea,
Tujunga soils are notable for their high infiltration rates.
Flood‑control structures and channelization between the international
border and Shelton Pond have diverted the river westward, away from
Tujunga soils and into the finer silty loams of Chino soils. Chino soils
have a considerable clay content and low infiltration rates.

According to the U.S. Soil Conservation Service, the available water
holding capacity of Tujunga soils is 0.05‑0.07 inch per inch of soil
(0.13‑0.18 cm per cm of soil) and of Chino soils is 0.13‑0.17 inch per
inch of soil (0.33‑0.43 cm per cm of soil) (U.S. Department of
Agriculture \[USDA\] 1973). &quot;Available water holding capacity&quot;
is the capacity of a soil to hold water available for use by most plants
and is commonly defined as the difference between the amount of soil
water at field capacity (where water remaining in a soil has ceased to
drain freely) and the amount at the wilting point of plants, as measured
in inches of available water per inch of soil.

Hydraulics of the Tijuana River

River Flow

Prior to 1980, the Tijuana River was an ephemeral stream characterized
by low or no flow for many months of a given year. Intermittent flood
flows are highly variable and are dependent upon rainfall amounts and
intensity across the watershed. Brief periods of very high flows,
primarily during the rainy season (November through April), were often
followed by low or no summer flows. During periods of groundwater
overdraft, surface waters provided recharge to the aquifer in direct
proportion to the available storage. However, when the aquifer was full
or overflowing, groundwater seepage into the lower Tijuana River would
create &quot;gaining&quot; stream conditions. Such conditions were
apparent when ponds and stream flows in the valley were maintained in
the absence of surface water input from Mexico.

Three dams, the Morena, Barrett, and Rodriguez Reservoirs (see Figure
1‑2), have a significant effect during periods of low or moderate flow
in the river and a smaller effect during large events. The Morena and
Barrett Reservoirs are located on Cottonwood Creek in the United States
and provide a water supply to San Diego. The Rodriguez Reservoir is
located on Rio de las Palmas in Mexico and supplies water to Tijuana. As
a consequence of the three dams, the total flow in the Tijuana River at
Nestor has been significantly reduced (Philip Williams 1987). However,
when storm waters fill the reservoirs, water is released over periods of
months during the dry season.

Flow in the Tijuana River has been measured at 18 gauging stations
within the Tijuana River watershed. Most of these are located within the
United States and monitor flow from relatively small drainage areas. Two
of the gauges, one formerly located at Nestor and the other located at
the U.S.‑Mexico border, measure flow from 98 percent of the watershed
and have recorded flow since 1936.

According to the U.S. Geological Survey (Izbicki 1985), the average
annual discharge in the Tijuana River at the international boundary from
1936 through 1981 was about 33,000 acre‑feet/year (41 Mm3/year),
compared to a &quot;median&quot; discharge of 659 acre‑feet/year (0.8
Mm3/year). The maximum annual discharge was recorded during the 197980
water year when 586,000 acre‑feet (723 Mm3) flowed through the lower
Tijuana River valley (Izbicki 1985).

From 1980 to 1991, however, there have been sustained perennial flows of
wastewater in the Tijuana River (Zedler et al. 1990; Williams and
Swanson 1987). Flow data measured by the USIBWC indicates that from 4.5
mgd (197 lps) to 22 mgd (964 lps) of wastewater flowed into the U.S.;
the average wastewater flow was estimated to be 13 mgd (570 lps) in
1990. Since 1991, when Mexico completed construction of a river
collector structure to divert up to 13 mgd (569 lps) of
sewage‑contaminated river flows into its sewage collection system,
sewage‑contaminated flows have crossed the border only when the river
collector was not in operation. This diversion is not operated during
storm flows, however. Estimates of raw sewage in the Tijuana River are 3
mgd (131 lps) in 1993 and 1 mgd (44 lps) in 1995. Urban discharges into
the river, such as trash, detergents, oils, fertilizers, and pesticides,
also occur.

A hydraulics study to determine the low‑flow characteristics of river
flows was conducted by Boyle Engineering (1996). The study was based on
the U.S. Army Corps of Engineers Hydrologic Engineering Center‑River
Analysis System (HEC‑RAS) and does not incorporate estimates of
evaporation, evapo‑transpiration, or groundwater recharge. Inputs to the
model included detailed channel cross‑section and flow‑line data which
were collected during a four‑day field survey. Flow rates ranging from
1.7 mgd (74.5 lps) to 34.8 mgd (1,525 lps) were modeled to determine the
travel times from Stewart\'s Drain to the Tijuana River estuary for the
selected flows. The predicted travel times varies from a minimum of 4.6
hours at 34.8 mgd (1,525 lps) to a maximum of 14.4 hours at 1.7 mgd
(74.5 lps) (Boyle Engineering 1996). These travel times represent the
estimated time it would take flows in the river at Stewart\'s Drain to
reach the estuary at different total river flow rates.

Flood Peaks

Flood peaks on the Tijuana River show an extreme annual variability.
Table 3.11 shows the estimated historical peak flow events between 1884
and 1937 and measured peak flow events between 1937 and 1984. The
highest estimated historical flow of 75,000 cfs (2,124 m3/s) occurred in
1916. An event of this magnitude is expected to have a recurrence
interval of approximately once per 100 years (Philip Williams 1987).
During the floods of 1993, an equivalent flow of 75,000 cfs (2,100 m3/s)
was experienced in the Tijuana River in Mexico.

Mexico constructed a concrete flood control channel from the
international border upstream approximately 6.5 miles (10.6 km) to the
confluence with Rio El Alamar in the 1970s. The channel was designed to
convey up to 500‑year flood flows of 125,000 cfs (3,500 m3/s). The U.S.
constructed an energy dissipater at the downstream end of the flood
channel. Mexico has designed and completed environmental review to
extend the flood control channel upstream an additional 4 miles (6.5 km)
to below the Abelardo L. Rodriguez Reservoir. This project will effect
flood control for approximately 1,034 acres (422 ha) of the floodplain.
In addition to providing additional protection from flooding in Mexico,
the channel extension is proposed to address problems of surface and
groundwater contamination and ecological, recreational, and social
benefits.

TABLE 3.1‑1

MAXIMUM DISCHARGE OF THE TIJUANA RIVER

NEAR NESTOR BETWEEN 1884 AND 1984

(in descending order of magnitude)

Discharge

Number Date cfs m3/s

1 27 Jan 1916 75,000\* 2,124

2 Feb 1884 50,000\* 1,416

3 17 Jan 1895 38,000\* 1,076

4 21 Feb 1980 33,500 949

5 3 Mar 1983 27,700 784

6 16 Feb 1927 25,000\* 708

7 Dec 1889 20,000\* 566

8 Feb 1891 20,000\* 566

9 7 Feb 1937 17,700 501

10 24 Mar 1906 16,000\* 453

11 26 Dec 1921 15,000\* 425

12 22 Feb 1941 13,800 391

13 23 Feb 1944 11,100 314

14 11 Apr 1941 10,400 294

15 15 Mar 1941 8,620 244

16 3 Mar 1938 6,760 191

17 21 Feb 1914 5,000\* 142

18 17 Mar 1942 2,770 78

19 24 Dec 1940 2,700 76

20 13 Jan 1949 2,600 74

21 7 Jan 1944 2,500 71

22 23 Dec 1944 2,100 59

23 13 Mar 1938 1,600\* 45

24 12 Mar 1918 1,600\* 45

25 18 Feb 1932 1,500\* 42

SOURCE: Philip Williams &amp; Associates 1987:8.

\*Flows reconstructed by the USACE.

As part of the development of the IWTP, the south levee of the Tijuana
River in the U.S. has been modified to protect the IWTP from flood
flows. Additional modifications to the floodplain and low‑flow channel
are proposed by the City of San Diego for its South Bay treatment plant
adjacent to the IWTP site and Dairy Mart Road bridge crossing
improvements to accommodate a 330‑year flood.

Sediment Yield and Transport

Flow in the Tijuana River transports sediment from the watershed and
channel to the estuary and, ultimately, the Pacific Ocean. The amount
and size characteristics of this transported sediment are affected by a
variety of factors, including watershed soils, vegetation, topography,
rainfall, river channel geometry, and man‑made structures.

Annual sediment transport by the Tijuana River varies greatly (Philip
Williams 1987). The percentage of annual sediment trapped by the
reservoirs is also not constant on a yearly basis. The reservoirs tend
to reduce sediment transport by 50 percent or more in the low‑flow years
and only by 20 percent or less in the high‑flow years. Dams have
resulted in a decrease of approximately 30 percent in the total sediment
transported past the Nestor gauge during the period of record.

Water Quality

Until Mexico installed the diversion in 1991, approximately 13 mgd (570
lps) of unsewered wastewater flowed into the Tijuana River and concrete
flood‑control channel in Mexico via gullies and storm drains, which then
flowed into the U.S. to the Tijuana River estuary. Intermittent sewage
spills also occur, entering the U.S. via north‑draining canyons and
gullies identified on Figure 3.1‑1. Other urban discharges into the
Tijuana River include trash and unknown quantities of detergents, oils,
fertilizers, and pesticides. During the public scoping meeting, many
people commented on the quality of the river water, noting that the
smell was invasive and intolerable and that the wastewater flowing in
the river constituted a significant public health risk.

In April 1990, a water sampling program of the Tijuana River was
initiated by the IBWC to evaluate the wastewater flows to be treated at
the proposed IWTP. Water quality samples were taken in two locations,
Tijuana Pump Station One in Mexico and the Tijuana River in the U.S.
Samples were taken for 30 consecutive days at each location and were
analyzed for a number of constituents. Based upon the average measured
constituent concentrations, the level of pollutant loading in the
Tijuana River at an estimated 10 mgd (438 lps) flow rate is shown in
Table 3.1‑2. As shown in the table, over 900 pounds of lead and over 290
pounds of cyanide are being introduced annually into the Tijuana River.
However, no detectable levels of mercury, selenium, arsenic, or cadmium
were found. In a 1990 study of some constituents (Boyle Engineering
1990), it is apparent that the concentrations of some constituents,
especially biological Figure 3.1‑1

TABLE 3.1‑2

1990 &amp; 1995 POLLUTANT LOADING

OF TIJUANA RIVER (AT 10 MGD)

1990 1995

Substance Pounds/Day Kilograms/Day Pounds/Day Kilograms/Day

Nutrients Total nitrogen 2,746 1,246 NA ‑‑ Total phosphorus 850 386 NA
‑‑ Pollutants BOD 10,919 4,953 7,101 3,221 COD 25,386 11,515 20,110
9,122 TSS 17,885 8,113 145,860 66,162 Metals Aluminum 260 118 834 378
Cadmium ND ‑‑ 0.8 0.4 Chromium 3.4 1.5 6.3 2.9 Copper 9.7 4.4 9.8 4.4
Cyanide 0.8 0.4 1.7 0.8 Gold 1.0 0.5 NA ‑‑ Iron 366 166 NA ‑‑ Lead 2.5
1.1 2.1 1.0 Magnesium 4,838 2,195 NA ‑‑ Manganese 23.4 10.6 81.9 37.2
Mercury ND ‑‑ 0.3 0.1 Nickel 5.6 2.5 2.5 1.1 Selenium ND ‑‑ 7.3 3.3
Silver 0.8 0.4 0.5 0.2 Thallium 1.5 0.7 5.0 2.3 Zinc 8.3 3.8 118 53.5
Other Arsenic ND ‑‑ 3.8 1.7 Antimony 0.8 0.4 2.8 1.3 Boron 31.3 14.2 NA
‑‑

COD = chemical oxygen demand; NA = not analyzed; ND = none detected.

oxygen demand, have increased significantly as sewage flow in the river
has increased. Others, such as boron, have remained unchanged.

In addition to the daily sampling in 1990, 12 weekly samples were also
taken. While the results were not markedly different from the daily
sampling results, new &quot;highs&quot; were recorded for several
constituents, including BOD, total dissolved solids (TDS), total
suspended solids (TSS), chromium, and mercury. Detectable levels of
selenium were recorded for the first time.

The 1990 samples from Pump Station One were analyzed to characterize the
wastewater that is expected to be received at the IWTP. Based upon the
average measured constituent concentrations, the level of pollutant
loading at an estimated 10 mgd (438 lps) flow rate is shown in Table
3.1‑3.

Subsequent sampling from Tijuana\'s Pump Station One and the emergency
connector to the San Diego sewer system was analyzed by Malcolm Pirnie
Engineers (1993) for the IWTP concept design.

Data from the 1993 sampling at the Tijuana River are also included in
Table 3.1‑2 (again based on the average measured constituent
concentrations at an estimated 10 mgd \[438 lps\] of flow). As shown in
the table, over 290 pounds (132 kg) of cadmium, 110 pounds (50 kg) of
mercury, 2,665 pounds (1,208 kg) of selenium, and almost 1,390 pounds
(630 kg) of arsenic were introduced annually into the Tijuana River.
None of these substances were detected in 1990. Other constituents
detected in the river in 1993 include over 765 pounds (347 kg) of lead
and approximately 620 pounds (281 kg) of cyanide annually.

Data from the 1993 sampling at Tijuana Pump Station One are also
included in Table 3.1‑3 (again based on the average measured constituent
concentrations at an estimated 10 mgd \[438 lps\] of flow). As shown in
the table, the amounts of cadmium (over 2,225 pounds \[1,009 kg\]) and
cyanide (over 620 pounds \[281 kg\]) flowing through Pump Station One
annually. Additionally, over 2,480 pounds (1,125 kg) of selenium and
over 1,385 pounds (628 kg) of arsenic annually flowed through Pump
Station One (neither of these substances were detected in 1990). Other
constituents detected in the wastewater flows include over 765 pounds
(347 kg) of lead and approximately 110 pounds (50 kg) of mercury
annually.

Source Identification Program

In order to further characterize the wastewater that is expected to be
received at the IWTP and in support of the Mexican Government\'s efforts
to develop an industrial pretreatment program in Tijuana, early in 1995
the U.S. and Mexican Sections of the IBWC developed a continuing
monitoring program. The wastewater collector system in Tijuana was
studied and 11 sampling locations in Mexico were proposed as part of a

TABLE 3.1‑3

1990 &amp; 1995 POLLUTANT LOADING

AT PUMP STATION ONE (AT 10 MGD)

1990 1995

Substance Pounds/Day Kilograms/Day Pounds/Day Kilograms/Day

Nutrients Total nitrogen 4,867 2,208 NA ‑‑ Total phosphorus 1,277 579.2
NA ‑‑ Pollutants BOD 26,351 11,953 29,289 13,285 COD 68,905 31,255
68,507 31,075 TSS 28,602 12,974 22,196 10,068 Metals Aluminum 53.5 24.3
65.4 29.7 Cadmium 0.1 0.05 6.1 2.8 Chromium 2.8 1.3 2.1 1.0 Copper 14.3
6.5 8.2 3.7 Cyanide 0.7 0.3 1.7 0.8 Gold 0.7 0.3 NA ‑‑ Iron 222 101 NA
‑‑ Lead 3.8 1.7 2.1 1.0 Magnesium 3,867 1,754 NA ‑‑ Manganese 10.3 4.7
9.8 4.4 Mercury 0.2 0.1 0.3 0.1 Nickel 3.1 1.4 1.0 0.5 Selenium ND ‑‑
6.8 3.1 Silver 0.8 0.4 0.5 0.2 Thallium 1.6 0.7 5.0 2.3 Zinc 23.0 10.4
78.8 35.7 Other Arsenic ND ‑‑ 3.8 1.7 Antimony ND ‑‑ 2.6 1.2 Boron 32.2
14.6 NA ‑‑

COD = chemical oxygen demand; NA = not analyzed; ND = none detected.

phased monitoring effort. The City of San Diego was commissioned to
perform the sampling for the EPA and the IBWC due to their expertise in
sampling and analysis. The sampling was conducted in strict adherence
with the City of San Diego Wastewater Department\'s guidelines.

The first phase of the monitoring was completed in 1995 and second phase
is scheduled to start in the summer of 1996. The first phase contained
three sampling points plus one additional sampling location at the
Tijuana River in the United States, which was selected in order to
characterize the water quality in the Tijuana River. The sampling sites
were Site 1, the international collector at Tijuana Pump Station One;
Site 2, Tijuana Pump Station One; Site 3, Colonia 20 de Noviembre; and
Site 4, the Tijuana River.

The U.S. and Mexican Sections of the IBWC conducted a wastewater
characterization study during a 15‑day period in the month of June 1995.
Twenty‑four‑hour composite samples were collected for metals and
conventional parameters in order to get a long‑term picture of the
influent. In addition, grab samples were collected for pesticides,
volatile and semivolatile organic compounds, cyanide, oil and grease,
and phenols. Grab samples were used to indicate whether spikes of
contaminants were present in the discharge.

The IBWC U.S. and Mexico Sections are preparing to initiate another
round of sampling in 1996. The goal is to include all of the 11 proposed
sampling locations. Based on the results of the June 1996 data set,
additional phases with additional sampling locations may be needed.
Through this phased sampling effort, industries which may need to
implement source control measures will be identified. Groundwater in
Tijuana River Valley

Groundwater in the lower Tijuana River valley occurs in three zones:
beneath the Nestor Terrace north of the valley, in the alluvial fill
underlying the valley, and in the San Diego Formation beneath the
alluvium (TJVCWD 1994a). Of these three zones, the Tijuana Valley
alluvium is the most studied and utilized.

The unconfined alluvial aquifer is approximately 6.5 miles (10.5 km)
long, is 7,000 to 10,000 feet (2,134 to 3,048 m) wide, and has the
potential to store about 65,000 acre‑feet (80 Mm3) of water. The
thickness of the aquifer, which is composed of unconsolidated sands,
silts, clays, and gravels, varies from 50 to 75 feet (15.2‑22.9 m) in
the east to approximately 150 feet (45.7 m) near the Pacific Ocean. At
the base of the alluvial aquifer is a layer of coarse sand, gravel, and
cobbles (TJVCWD 1994a). Gravel and sand layers are tapped by production
water wells at depths of 20 to over 100 feet (6.1‑30.5 m).

The San Diego Formation is composed of partly consolidated marine sand,
silt, and conglomerate interbedded with volcanic tuff and bentonite. It
is estimated that this formation is at least 1,700 feet (518 m) thick.
Tests on a well approximately 1,400 feet (427 m) deep produced water at
a temperature of 97 degrees Fahrenheit, having a pH of 5.9, and with a
sulfurous smell. These are characteristic of geothermal waters,
indicative of contact with fractures and deeper volcanic material
(TJVCWD 1994a). Groundwater in the San Diego Formation occurs under
confined conditions and does not appear to be in direct hydraulic
contact with groundwater in the overlying alluvium.

The alluvial aquifer of the Tijuana River valley is recharged primarily
by direct rainfall, subsurface inflow from adjacent areas, and
intermittent flood flows (State of California 1967; USACE 1990; Rempel
1992). Surface flows in the river may also provide groundwater recharge
(TJVCWD 1994a). The amount of groundwater inflow from across the
international border has been estimated as 1,580 acre‑feet/year (2.0
Mm3/year) (State of California 1952); 1,208 acre‑feet/year (1.5
Mm3/year) (USACE 1965); and 1,160 acre‑feet/year (1.4 Mm3/year) (IBWC
1976). There is also potential recharge from water‑bearing zones east of
Interstate 5, which has not been estimated.

The chief factors contributing to the reduction of groundwater in
storage are agricultural pumping and evapotranspiration from
phreatophytes (deep‑rooted plants notable for their ability to obtain
water from groundwater or the overlying capillary fringe) and water
hyacinths. There is a possibility of minor outflow from the basin toward
the north during periods of high groundwater. The amount of groundwater
discharging either directly to the ocean or to the lower reaches of the
river has been estimated to be 2,090 acre‑feet/year (2.6 Mm3/year)
during dry years and 2,827 acre‑feet/year (3.5 Mm3/year) during wet
years (TJVCWD 1994a).

It is only when the amount of groundwater removed from a basin
chronically exceeds natural recharge from rainfall, subsurface inflow,
and intermittent flood flows that the groundwater table will begin to
trend downward. The record for the lower Tijuana River valley from
1965‑1978 shows that once the rate of groundwater extractions are
reduced, groundwater levels will recover from storm flows and subsurface
inflows into the basin, even during an extended period of
drier‑than‑normal rainfall and less‑than‑normal runoff, such as occurred
from 1965 to 1978, so long as the natural recharge of groundwater is
greater than the extraction rate.

Groundwater Levels

Water table elevations vary from year to year and between wet and dry
seasons, depending on stream flow, accumulated rainfall, and groundwater
pumping. Seasonal water table measurements, taken in 1914 and 1915
during a relatively dry weather cycle, varied on the average from 5 to
15 feet (1.5‑4.6 m) below the ground surface. Measurements taken during
the dry climatic period of the early 1960s after decades of substantial
groundwater pumping varied from less than 25 feet (7.6 m) near the
estuary to depths between 25 and 50 feet (7.6 and 15.2 m) in the upper
valley. During this time, the water table was lowered to the point where
the hydraulic gradient reversed, drawing seawater up into the valley. By
1967, seawater intrusion had affected most wells up to the U.S.‑Mexico
border.

As production wells depleted groundwater recharge, natural recharge from
flows on the lower Tijuana River was reduced by upstream surface water
diversions and dams. For the period 1936 to 1976, average stream flow
was about 50 percent below expected natural flow; in some years, all
watershed runoff was trapped by the dams.

Increased annual precipitation and runoff between 1978 and 1984 and
greatly reduced groundwater pumping for irrigation since 1970 appear to
have since raised the groundwater levels to within 0 to 15 feet (0 to
4.6 m) of the ground surface throughout the river floodplain (Philip
Williams 1987; Rempel 1992). In deeper portions of the aquifer, fresh
groundwater meets the interface with saline groundwater at about 19th
Street.

Groundwater Quality

The sustained groundwater pumping of the 1950s, at rates twice the
average annual natural recharge or safe yield, resulted in a groundwater
decline of 23‑30 feet (7‑9 m) or more in the Tijuana River valley. By
the early 1960s, groundwater table elevations across much of the valley
had fallen below sea level. Due to this lowering of the groundwater
table, highly saline groundwater from underlying and adjacent marine
sediments and seawater began to invade and to degrade the alluvial
aquifer (State of California 1975b; Rempel 1992). This saltwater
degradation contributed to the declining demand for Tijuana River valley
groundwater in the 1960s. As consumption eventually became less than
natural recharge, the resulting annual surplus of supply began to
overcome years of accumulated deficits, and water levels began
recovering as early as the mid‑1960s.

Today, the quality of groundwater in the Tijuana River valley is still
characterized by high sodium chloride and high total dissolved solids.
These high salinity levels prevent the current use of well water for
irrigation of salt‑sensitive crops cultivated within the valley. As a
result of lowered groundwater levels and seawater intrusion, groundwater
TDS concentrations along the coast have exceeded 27,000 milligrams per
liter (mg/l) (a standard TDS content generally ranges between 1,000 and
1,500 mg/l). In the Department of Water Resources Bulletin 106‑2 (State
of California 1967), the Tijuana River valley groundwater was rated
generally inferior for domestic use due to its high sulfate and high
fluoride concentrations. It was also rated generally inferior for
irrigation purposes because of high electrical conductivity, high
chloride levels, and high percentage of sodium in the Spooners Mesa
area. In addition to seawater intrusion, the poor quality of the
groundwater is also attributed to leakage of sodium chloride from the
San Diego Formation, irrigation return, and groundwater movement from
beyond the international boundary (EPA 1988).

Nevertheless, the Water Quality Control Plan for the San Diego Basin (9)
designates municipal and domestic supply, agricultural supply, and
industrial service supply as beneficial uses for the groundwater east of
Hollister Street, although the area is exempted from the sources of
drinking water policy (State of California 1995). These beneficial uses
do not apply west of Hollister Street. Hydrology of Tijuana River
Estuary

The Tijuana River estuary is one of 18 estuarine research reserves in
the United States and one of only two in California (Seamans 1988). The
estuary is the site of one of the United States\' few long‑term wetlands
research programs. In 1982, the Tijuana River National Estuarine
Research Reserve was established by the NOAA to protect one of the few
remaining large areas of coastal wetland in southern California (Figure
3.1‑2).

Since 1982, a land acquisition program has been under way for the
estuary. However, land acquisition, by itself, cannot provide protection
when major hydrologic changes can drastically affect the intricate and
delicately balanced wetland ecosystems (Williams and Swanson 1987). The
Tijuana Estuary Management Plan (James Dobbin Associates 1986)
established a framework for developing an enhancement plan to address
the serious physical changes affecting the estuary.

The reserve includes approximately 2,500 acres (1,012 ha), with the
estuary consisting of approximately 350 acres (141.6 ha) of tidal slough
and salt marsh (as measured from 1986 aerial photographs) (Philip
Williams 1987:9; Nordby and Zedler 1991). Tidal channels comprise
approximately 148.3 acres (60 ha) of the estuary (Nordby and Zedler
1991). The estuary is bisected by the Tijuana River into a northern arm
and a southern arm and is bounded by coastal uplands to the north and
south and the alluvial floodplain of the Tijuana River to the east. A
three‑mile‑long (4.8 km) barrier beach separates the estuary from the
Pacific Ocean at its western boundary. From the estuary entrance
channel, tidal flows are distributed by four channels. The Oneonta
Slough channel drains the isolated north arm of the estuary. The Tijuana
River Slough, Mid‑Valley Slough, and Old River Slough drain the central
and southern portions of the estuary in the active delta of the Tijuana
River.

The Tijuana River estuary is hydrologically linked to its watershed via
intermittent freshwater river flow, intermittent sewage spills and
flows, and street drains, all of which degrade the estuary (Zedler et
al. 1990).

Natural Functioning of the Estuary

The Tijuana River estuary has become a highly stressed ecosystem, with
both chronic and catastrophic assaults on the coastal habitats (Zedler
et al. 1990). Such stresses include perennial flows of wastewater;
intermittent sewage spills; freshwater discharges from Rodriguez Dam;
sedimentation and sand erosion from the watershed that followed major
floods in 1978, 1980, 1983, 1984, and 1993; and urban runoff.

In its natural state, the tidally influenced portion of the Tijuana
River estuary was considerably larger than at present and consisted of
about 870 acres (352 ha) of intertidal wetland. Tidal slough channels
extended into the estuary over 3,000 feet (914 m) east, 5,000 feet
(1,524 m) north, and 2,000 feet (610 m) south from the entrance channel.
Because of its size, the estuary\'s tidal volume was larger and its
tidal circulation sufficient to maintain an open, subtidal entrance
channel and an extensive network of interior slough channels. In its
natural state (prior to 1852), the potential diurnal tidal prism (the
volume of water in the estuary between the mean higher high water
\[MHHW\] and mean lower low water \[MLLW\]) is roughly estimated to have
been about 1,500 acre‑feet (1.85 Mm3). This meant that the ebb flow
velocities were strong enough to scour away any sand deposited by wave
action in the entrance channel and that the entrance channel was not
closed by sand movement during large storms.

The physical appearance and functioning of the Tijuana River estuary
have changed dramatically since 1852 due to sedimentation and
modification by human activities. Over 60 percent of the original 1852
intertidal wetland has been filled or otherwise modified and removed
from tidal influence. This has resulted in a significant reduction in
the tidal prismabout 80 percent loss since 1852and an even greater loss
in actual tidal exchange and circulation. The estuary now contains about
290 acre‑feet (0.36 Mm3) of potential tidal prism and most of that is
elevated above MSL (Entrix et al. 1991). Because the scouring force of
the tidal currents has greatly diminished, the tidal entrance channel is
now susceptible to closure, slough channels are less efficient
hydraulically, and the existence of tidal saline wetlands in the entire
estuary is threatened.

Sedimentation

Sediment movement through the estuary during floods is dependent on the
magnitude of the flood, the volume of sediment, and the alignment of the
river channel with the entrance channel. During the course of a single
flood, some of the tidal channels can experience sedimentation while
others experience erosion. Consequently, after large floods, tidal
action still occurs in the central part of the estuary.

The north arm of the estuary and, to a lesser extent, the south arm are
protected against the flood‑flow sediment transport on the Tijuana
River. The north arm is isolated from the river channel by an
intervening bluff; its only connection with the river is the mouth of
Oneonta Slough. Sediment delivery to the south arm has increased greatly
due to urbanization near the tributary canyons to the west and road
construction which limits tidal action upstream. The constricting effect
of culverts tends to trap sediment and cause the permanent loss of more
wetland upstream.

Closure of Entrance Channel

The entrance channel in 1987 was approximately 100 feet (30 m) wide at
MHHW compared to about 1,200 feet (366 m) in 1852 (Philip Williams
1987). Figure 3.1‑2

The entrance channel at the Tijuana River estuary has shifted from an
&quot;always open&quot; regime to an &quot;intermittently closed&quot;
regime.

Barrier Beach Migration

The historical movement of the barrier beach is a major cause of the
reduction in tidal prism in the estuary. Sand washed over the barrier
beach has filled slough channels and constricted tidal flows. Between
1852 and 1986, the seaward edge of the barrier beach retreated landward
over 300 feet (91 m) on average on both the north and south segments.
The landward edge has retreated about 400 feet (122 m) on average in the
same period because of washout and flattening of the barrier beach
dunes.

In addition to wave attack, the barrier beach would migrate inland in
response to rising sea level and changes in the supply of sand. The
long‑term inland migration rate with a rise in sea level of 0.6 feet
(0.2 m) per century has been approximately 2.5 feet (0.8 m) per year
(Philip Williams 1987:15). (There are now predictions that the rise in
sea level will accelerate to roughly 4 feet \[1.2 m\] per century due to
global warming. This could accelerate inland migration to about 8 feet
\[2.4 m\] per year.) Dams constructed in the Tijuana watershed appear to
have reduced sand delivery to the beach by about 30 percent. This, too,
causes an increase in the rate of beach migrations.

Decrease in Estuary Salinity

The salinity patterns at the Tijuana River estuary are far from what
would be expected under a natural hydrologic regime. With good
circulation throughout the estuarine channels, the water salinity would
be close to 34 parts per thousand (ppt) except during and shortly after
rainfall events. Instead, the Tijuana River has greatly increased flows
during the dry season, which are largely attributable to wastewater from
Mexico. Tidal flows are strongest in the northern arm of the estuary
(Oneonta Slough), where tidal waters are measurably, but not greatly,
diluted (31 ppt). The patterns of salinity in the channels indicate that
it is sewage inflow from the Tijuana River, rather than local urban
runoff, that is responsible for most of the salinity dilution in Oneonta
Slough. Wastewater is influencing the salt‑marsh habitat in the estuary
(by salinity dilution), and exotic species and brackish‑marsh species
are invading near sources of urban runoff (Zedler et al. 1990).

Channel Flora and Fauna Responses

Fish and invertebrate populations are impacted by the continuous
wastewater flows and periodic closure of the estuary mouth, with fewer
species and individuals than has occurred in previous years (Zedler et
al. 1990; Tierra Environmental Services 1996). The flow of wastewater
into the estuary has resulted in an incremental and significant loss in
the abundance of fish and invertebrates, as much as 50 percent over the
last decade (Jorgenson, California Department of Parks and Recreation,
1990). The lower marsh vegetation (cordgrass) may have increased growth
as a result of the increased nutrient loading and decreased soil
salinities associated with the wastewater.

Groundwater Quality

The U.S. Army Corps of Engineers initiated a groundwater sampling
program in July 1990, partially in response to concerns about heavy
metals in sediments of the Tijuana River estuary.

A study by Gersberg, Trintade, and Nordby (1989) found that despite
continued inflow of sewage containing heavy metals from Tijuana into the
Tijuana River and estuary, only cadmium was found to be elevated in the
sediments of both river and southern estuary sites. In fish, only lead
was found to be present at a level above an international standard, but
not at a level that poses a significant public health risk (Gersberg,
Trintade, and Nordby 1989). However, Zedler et al. (1990) found that
soils in the marsh habitats near the estuary\'s main channels,
downstream of Goat Canyon and in the Oneonta Slough, are contaminated
with heavy metals. Cadmium was the predominant contaminant near the main
estuary channels, while copper was the predominant element in the
slough.

As part of the USACE sampling effort, both soil sediments and water
quality were sampled; however, only water quality tests were performed,
since any contamination present would probably show up in the water
quality tests, making any soils tests redundant (USACE 1990). A summary
of the findings from the report are discussed below.

Six wells were drilled to depths of 45 feet (13.7 m) along the
previously proposed land outfall extension alignment. Silts, silty sand,
and clays were the predominant sediments encountered. Water samples were
collected for testing from three of these wells, all southwest of Goat
Canyon, and a fourth well northeast of Goat Canyon which had been
installed previously. Water quality testing was performed by the USACE
laboratory in Sausalito and the Quality Assurance Laboratory in San
Diego. The State Department of Health Services (DHS), Radiation
Laboratory, Berkeley, checked the water samples for radioactivity; and
the ERCE Bioassay Laboratory, San Diego, performed biological toxicity
tests.

A series of critical life‑stage echinoderm fertilization tests which
used the purple sea urchin (Strongylocentrotus purpuratus) yielded
significant negative results. Fertilization rates for urchins in well
water were significantly lower than for controls. Two additional chronic
tests were performed by the ERCE laboratory in January 1991, utilizing
larval silversides (Menidia beryllinaa fish) and larval mysid shrimp
(Mysidopsis bahia). These tests indicate no toxicity to fish even at
full concentration and no observable effect on shrimp at a 2:1 dilution.

Oceanography

The following discussion is based upon the Tijuana Oceanographic and
Engineering Study (Engineering Science 1988), Marine Environmental
Impacts of the Proposed Secondary Treatment System (Kinnetic 1991), and
Wastewater Discharge Modeling and Analysis of Alternative Interim
Discharge Options (Parsons Engineering Science 1996). Physical
Oceanographic Conditions

The physical oceanographic conditions at the ocean outfall site will
control the amount of dilution and dispersion of the wastewater field
that will be achieved by the marine outfall.

Regional and Local Currents

The currents along the California coast are dominated by the offshore,
southward‑flowing California current. The California current system
consists of (1) a broad, southerly flowing surface and near‑surface
current that flows at the edge of and beyond the continental shelf, (2)
a northerly flowing undercurrent that flows under the southerly current,
and (3) northerly countercurrents at the surface and near‑surface which
flow near the coast.

The position and intensity of the California current varies with the
season and typically shifts onshore in the spring and summer, with the
advent of the persistent northwesterly winds. The countercurrent flows
northward at a depth of 90 feet (27.5 m) from Baja California to beyond
Cape Mendocino in Humboldt County, northern California, and transports
warm, high‑salinity Equatorial Pacific water northward. From early
spring to fall, there is a strong equatorward coastal flow occurring
with the northerly undercurrent due to wind stresses. By September,
because of the weakening of this wind stress, a broad northward surface
current develops within 62 miles (100 km) of the coast, called the
Davidson current. Coastal currents within the California system interact
with seasonal upwelling events that bring cool, dense water to the
surface and influence the dynamics of the flows.

Point Conception represents the northern extreme of the region known as
the Southern California Bight. The eastward indentation of the coastline
to the south of the point results in a separation of the California
current from the coast. The California current itself turns shoreward
offshore northern Baja California, resulting in an eddy flow within the
bight, and generally western flow in the Santa Barbara Channel,
rejoining the California current near Point Conception. This reverse
gyre is, thus, a predominant feature of the coastal currents within the
Southern California Bight. The San Diego region is near the southern
edge of this eddy.

The South Bay region is characterized as a coastal bight and extends
from Point Loma to far northern Baja. The coastal currents in this
southern coastal region were measured for a 24‑month period between 1986
and 1988 for the TOES (Engineering Science 1988). The mean flow was
measured by current meters in 15 stations in U.S. and Mexican waters.
This current meter data were augmented by satellite imagery and other
studies (drogue release studies).

Modeling of the flow patterns was conducted by Hendricks (1988). The
mean flow pattern for the first 12 months was predominately to the
south. The principal pattern was found to be a relatively uniform
longshore flow north and south along the coastline, representing about
60 to 65 in the variance in current measurements. A second, independent
flow pattern consists of a recurring eddy with counterclockwise
circulation south of Point Loma of varying intensity that can extend 6.2
to 9.3 miles (10 to 15 km) offshore and approximately 10.6 miles (17 km)
alongshore. About 87 percent of the variability in current meter data is
accounted for by these two patterns. Figure 3.2‑1 depicts the combined
flows from these two current patterns.

The shoreline circulation is predominantly influenced by waves. During
the late fall, winter, and early spring, swells from northerly storm
systems are most characteristic. Southerly swells occur during summer
and fall as a result of tropical storms and wind patterns. Wave data
from an Imperial Beach monitoring station indicate that the predominant
wave direction is from the west to southwest, with a nearly continuous
northern transport through the Imperial Beach area and along the Silver
Strand.

Ocean Floor Composition

The shore types in the South Bay area are represented by sand beaches,
wave‑cut rocky platforms, and gravel boulder beaches. The area from the
international border north to Zuniga Point, at the entrance to San Diego
Bay, a reach of 22 miles (35.6 km), is sandy beach with a shallow
sloping sandy shelf. Wave‑cut rocky platforms and gravel beaches are
found south of the border in Baja.

The South Bay area is comprised almost entirely of medium‑ to
coarse‑grained sand beach. The only intertidal hard substrate is found
12.9 miles (20.8 km) to the north and consists of the south jetty riprap
at Zuniga Point at the mouth of San Diego Bay. A remote‑operated vehicle
reconnaissance survey of the South Bay outfall area was conducted in May
1990 (Kinnetic Laboratories 1990). Soft bottom habitat characterized the
proposed South Bay outfall alignment with a short stretch of cobble bed
at about 55 feet (16.8 m) depth. Coarse shell debris was observed along
the outfall alignment from 50‑80 feet (15.3‑24.4 m) deep, with finer
sediments inshore and offshore.

A study area one mile north and parallel to the outfall alignment
indicated significantly more low‑relief rocks, boulders, and cobbles
from approximately 48 feet (14.6 m) out to 90 feet (27.5 m) in depth.

Figure 3.2‑1

Seawater Characteristics

The ambient seawater density profile in the vicinity of the diffuser
portion of an ocean outfall determines the trapping depth of an effluent
plume. Also, the relative difference between ambient and effluent
density dictates how effective mixing would be near the diffuser
outlets. Because of this, the local vertical density distribution in the
water column plays an important role in determining the amount of
initial dilution that can be achieved.

In general, density varies on a seasonal basis, as well as in response
to short‑term, large‑amplitude tidal and internal waves which can cause
major perturbations in the density profile. In the South Bay region, the
water column was found to be well mixed during winter months with little
detectable stratification except for a slight increase in density with
depth to maintain stability. During the summer, the water column tends
to be stratified by water temperature and density at depths between 10
and 20 meters (33 and 65 feet).

Marine Water/Sediment Quality

Waste discharges can increase levels of chemical constituents in the
water column, sediments, and body tissues of marine organisms. Sediments
and associated interstitial waters are often more directly affected by
ocean discharges, since sediments act as a repository for particulate
materials that settle to the bottom. As solids settle out from a waste
field plume, the accumulation of nutrients and chemicals in the
sediments tend to select for different types of biological communities
than originally lived in the area. High concentrations of organic matter
and inorganic nutrients from municipal wastes can stimulate bacterial
and phytoplankton growth, leading to oxygen depletion. This results in a
reduction of species diversity of benthic fauna and also reductions in
abundance. The Marine Biology section discusses the marine resources of
the South Bay area in more detail.

Regionally, nutrient concentrations in seawater, both dissolved and
particulate, are generally low. Uptake in the near‑surface waters by
phytoplankton further reduces the concentrations of inorganic nutrients.
Upwelling of nutrients regenerated at depth provides a source for
enhanced plankton production, as does wastewater discharge. The most
recent water quality data for the South Bay area comes from the TOES
(Engineering Science 1988). The seasonal variations in dissolved oxygen
concentrations and pH levels were consistent with the rest of the
California bight.

Sediment samples were also collected during the TOES. Organic carbon,
biological and chemical oxygen demand, sulfides, total nitrogen,
arsenic, lead, nickel, zinc, copper, chromium, cyanide, and DDT were
highest in the northwest areas. Sediments were highest in mercury,
cadmium, silver, and phenol in the central areas, and adjacent to the
Tijuana estuary, higher sediment concentrations were found for nickel,
zinc, copper, chromium, and DDT.

The State Water Resources Control Board has conducted a &quot;State
Mussel Watch&quot; program (SMW) since 1977 throughout California (State
of California 1988). This program maintains a station in the South Bay
area. The program establishes &quot;elevated data levels&quot; (EDLs)
for trace metals and organics. The EDL is a concentration of a toxic
substance in a mussel that equals or exceeds a specified percentage of
all SMW measurements of the toxic substance in the same mussel type
between 1977 and 1987. Although trace metals were found in tissues of
mussels at all stations, no EDLs were reported in mussels collected from
the South Bay area.

LA‑5 Dump Site

Since 1977, the USACE . has permitted disposal of more than three
million cubic yards of sediment at the LA‑5 dump site offshore San
Diego. The U.S. Navy and San Diego Bay shipbuilders (NASSCO, Southwest
Marine) have been the major users of the site in depositing dredged
sediments from south San Diego Bay.

The site is centered five miles (8 km) downcoast of Point Loma and
includes all areas within a 1,000‑yard (915 m) radius of the center,
ranging in depth from about 80 to 110 fathoms (146 to 201 m). Bottom
currents have not been measured at the site. The EPA has recently
documented that the actual radius of the dump site is about 5,000 yards
(4,572 m), presumably due to inaccurate disposal procedures.

Site LA‑5 sediments ranged from sandy silt to silty clay. Measured
sediment metals were characteristically within the range of values for
the southern California shelf reported by Chow and Earl (1977). Measured
values of sediment oil and grease (90 ppm) and DDT (3 ppb) were elevated
above reference site values, but fell well below values associated with
wastewater outfalls. PCB data were inconclusive since levels were below
detection limits for many sediment samples, while being slightly
elevated above reference site values in other samples. Water column
measurements of trace metals and hydrocarbons were below employed
detection limits, similar to reference sites.

Bacterial Contamination

Because of malfunctions in Tijuana\'s pumping and conveyance systems,
EPA previously estimated that 10 to 22 mgd (438 to 964 lps) flows from
Tijuana to San Diego by way of the Tijuana River and estuary (Kinnetic
1990). Mexico has now significantly reduced these flows. Wastewater flow
threatens the environment of the Tijuana River estuary with severe
negative impacts and contaminates much of the southernmost beaches in
San Diego County.

The San Diego County Department of Health Services has data regarding
violations of the bacteriological standards on South County beaches.
From 1980 to present, approximately two miles of beach (from the
international border to the south end of Seacoast Drive) have been under
almost continuous quarantine due to violations of total coliform
standards. Since 1983, these South County beaches has been sampled by
three agencies, the RWQCB, the County of San Diego, and the IBWC. These
efforts result in samples being taken every two to three days, with only
occasional missed sampling dates. The results of coliform monitoring
during January, February, and March of 1990 show that the highest
concentrations of coliform bacteria were located between the U.S./Mexico
boundary and 0.75 mile (1.2 km) north of Imperial Beach, with the
highest of these located at the mouth of the Tijuana River. Total
coliforms exceeded 1,000 minimum probable number (MPN)/100 ml in 60
percent of the samples. The State Ocean Plan requires that no more than
20 percent of the samples exceed this value in a 30‑day period.

Beneficial Uses

Preservation of beneficial uses is the main objective of the California
Ocean Plan that establishes standards to &quot;protect the quality of
ocean waters for use and enjoyment by the people of the state.&quot;
Beneficial uses considered in this section are mainly related to coastal
recreation and commerce.

Recreation

San Diego County\'s 72 miles (116 km) of coastline have 52 designated
beaches and parks, 11 of which occur in the Point Loma‑South Bay area.
Beaches and seaside parks offer a wide variety of recreational
activities.

Although South Bay beaches have good public access, they are not as
popular as others elsewhere in the county because of periodic closure of
these beaches as a result of contamination by sewage from Tijuana. The
DHS has imposed repeated quarantine on beaches from the border to
Imperial Beach and has occasionally had to close beaches as far north as
Coronado. This has had an adverse impact on tourism and recreation in
the South Bay and has damaged local economies.

Diving

San Diego County offers some of the best diving in southern California
and features offshore reefs and kelp beds, wrecks and artificial reefs,
submarine canyons, and underwater preserves. The California Department
of Fish and Game (CDFG) surveyed diver catch at small boat launch ramps
in San Diego Bay and Mission Bay in the early 1980s. Abalone, lobster,
rock scallop, sheephead, and kelp bass were the principal game species
taken (State of California 1981a, 1981b).

The northern South Bay offshore area has a small kelp bed and extensive
cobble beds and reefs. It is distant from San Diego Harbor, however, and
not often dived.

Sportfishing

Over a million people a year (22 percent in San Diego County) sportfish
in southern California\'s marine waters (National Coalition for Marine
Conservation 1985).

Sportfishing is done from private and chartered boats, from shore, and
from jetties and piers. San Diego County accounts for about 22 percent
of all sportfishing in southern California. Sportfishing from privately
owned boats in San Diego County was surveyed by the CDFG. Pacific
mackerel was the most commonly caught species, followed by Pacific
bonito, sand bass, and kelp bass.

Most fishing boats heading south out of San Diego Harbor are bound for
the Coronado Islands. The inshore waters are usually bypassed although
an occasional charter boat will fish the small kelp bed off Imperial
Beach or rockfish grounds in deeper water. Shore and pier fishing are
the prevalent types of fishing in the South Bay. The Imperial Beach
Fishing Pier is two miles north of the proposed outfall alignment.

Boating

Sailing and boating are popular pastimes in San Diego. Most boats are
docked or launched in San Diego and Mission Bays. The South Bay is far
from launch and dock areas in San Diego Bay and is rarely visited by
recreational boats. Sailboats and powerboats usually cruise through the
area well offshore.

Whale Watching

Gray whales migrate through San Diego\'s coastal waters twice a year on
their way between summer feeding grounds off Alaska and calving areas in
the coastal lagoons of Baja California. The whales tend to swim closer
to shore from February to March on their northward migration when calves
are present, than on the southward migration during December to January.
However, whale watching boats only occasionally range down to the South
Bay area. Commercial Fishing

San Diego\'s commercial fishing fleet includes about 500 licensed
vessels and 1,500 licensed fishermen (Kaupp 1986). Although tuna
comprise about 45 percent of the commercial catch brought ashore at San
Diego (4,041,000 pounds \[1,837 metric tons\] valued at \$5,027,000 for
1987), port landings have declined significantly during the last decade
due to the transfer of canning operations overseas.

Commercial fishing generated more than \$60 million in 1987 for the
City\'s economy. Commercial fisheries landings at the ports of Mission
Bay and Oceanside are small compared to the Port of San Diego and have
diminished over the last three years. Most of the nearshore fish and
shellfish harvested by commercial fishermen are taken in the vicinity of
kelp beds.

As with recreational fishing, commercial fishing in the South Bay and
off Sorrento Valley is much less intensive than in more northern areas
of San Diego County. The South Bay, however, does have an emerging
prawn/shrimp fishery (likely to outpace those of other areas in San
Diego County). The only mariculture lease in the project area is a
10‑acre (4 ha) site one nautical mile (1.85 km) off the Silver Strand
State Beach lookout tower, five nautical miles from the proposed South
Bay Ocean Outfall. This site has been used for marine bivalve
aquaculture in the past, but the CDFG had to suspend the operation
because of declining water quality due to intrusion of Mexican sewage
flow.

Kelp Harvesting

The San Diego‑based company Kelco regularly harvests the Macrocystis sp.
(giant kelp) canopy from Point Loma, La Jolla, and in

the North County from Del Mar through Carlsbad. Kelp is gathered by a
specially designed ship that cuts the kelp to a depth of about three
feet (0.9 m) below the surface (McPeak and Glanz 1984). The small kelp
bed off the mouth of the Tijuana estuary has been harvested
intermittently by Kelco in the past, but has not been a significant
resource.

Shipping

San Diego Harbor is a major commercial shipping center for the southwest
United States. Between 1,200 and 1,400 commercial and other vessels
called at San Diego Bay annually during the period 1979‑1983 (EPA 1988).
However, the commercial shipping lanes are over five miles offshore,
well beyond the South Bay outfall area.

Military Use

The Port of San Diego is home base for a large Naval fleet of over 120
ships. San Diego\'s offshore area is used extensively for military
operations, including surface and submarine fleet maneuvers and
antisubmarine warfare training. The maneuvers closest to the South Bay
area are amphibious operations and training, which take place along the
Silver Strand in Coronado.

Research and Education

The Scripps Institution of Oceanography in La Jolla, the National Marine
Fisheries Service, San Diego State University, the University of San
Diego, and the Sea World Marine Institute all conduct ocean studies off
the coast of San Diego. San Diego State University has an extensive
long‑term research program in the Tijuana River estuary, but no
long‑term study sites are located offshore. Areas of Special Biological
Significance

There are two Areas of Special Biological Significance (ASBSs) in San
Diego County. Both ASBSs are located in La Jolla: the San Diego‑La Jolla
Ecological Preserve and the San Diego Marine Life Refuge. The ecological
preserve runs from La Jolla Cove to La Jolla Shores and the marine life
refuge runs from the Scripps Institution of Oceanography to Black\'s
Beach. The California Ocean Plan prohibits discharge of waste into an
ASBS and requires that outfalls be located at a sufficient distance away
from an ASBS to assure the maintenance of natural water quality
conditions. The South Bay outfall area is located approximately 20 miles
(33.3 km) from the ASBSs in La Jolla.

Terrestrial Biology

Descriptions of the vegetation communities and sensitive resources found
in the Tijuana River valley on the U.S. side of the border are contained
in the Final EIS and Biological Assessment (EPA 1994). This section of
the SEIS discusses the freshwater riparian biological resources that may
be affected by the interim discharge alternatives discussed in this
document. Coastal habitats such as coastal salt marsh, brackish areas,
and estuarine intertidal areas are discussed in a separate part of this
document.

Historical Perspective

The interim discharge alternatives include live stream discharge to the
Tijuana River as an option under Alternatives 2 (Operate IWTP) and
possibly 3 (Operate IWTP with Detention Basin). Live stream discharge of
effluent to the river will maintain low flows during the dry season.
These dry‑season low flows could influence the hydrology and riparian
vegetation of the river corridor (i.e., adjacent to the low‑flow
channel). Therefore, a brief discussion of the factors that affect
hydrology and riparian vegetation is presented.

Factors that have affected, and continue to affect, the hydrology and
vegetation of the Tijuana River valley are discussed below. The
hydrologic environment is briefly described and then a brief section on
historical changes in riparian habitat is presented. This information
provides background material to be considered when dealing with the
potential impacts of the project discussed in Chapter 4 of this
document.

Historical Changes in Riparian Habitat

The extent of riparian habitat along the lower reach of the Tijuana
River has changed considerably over the years due to many factors,
including changes in groundwater depth, a shifting river channel, and
adjacent land uses. Periodic flood flows also influence the dynamics of
the riparian vegetation by removing vegetation during high‑velocity,
high‑volume flood events (e.g., 100‑year flood) or by helping to sustain
vegetation on the floodplain during lower‑velocity, lower‑volume flood
events (e.g., 10‑ to 20‑year flood). Perhaps the most significant factor
which has affected the amount of riparian vegetation in the lower
Tijuana River valley is land use.

The riparian habitat in the lower Tijuana River valley has been
influenced by agricultural and grazing practices since the early 1900s.
These intensive land uses typically cleared all riparian habitat in
their wake until much, if not all, of the native riparian habitat was
removed from the valley. This trend continued into the 1960s and,
coupled with an overdraft of the basin groundwater and a degradation of
the groundwater quality, further reduced the extent and possibility for
reestablishment of any riparian vegetation. Large areas of riparian
habitat were cleared in the late 1980s by local operations in the river
valley, but in general, as agricultural fields were abandoned during the
1970s and 1980s and the groundwater table recovered from the overdraft,
areas that once supported native riparian vegetation slowly recovered.

The extent of the existing riparian corridor vegetation (plants growing
or immediately adjacent to the low‑flow river channel) has been
increasing since the late 1970s from about 96 acres (38.9 ha) in 1979 to
approximately 238 acres (96.3 ha) in 1990 (Chambers Group 1990). If the
riparian corridor is combined with habitat in the floodplain and
adjacent canyons, over 700 acres (283.3 ha) of riparian habitat exists
in the valley (Chambers Group 1991). Existing Conditions

The Tijuana River on the U.S. side of the border meanders in a
northwesterly direction to the Pacific Ocean. The current riparian
corridor extends from Dairy Mart Road to the eastern boundary of the
Tijuana River estuary. Within the Tijuana River estuary, there is a
transition from riparian habitat to salt marsh habitat which is
influenced by the tidal prism.

The Tijuana River valley supports the following riparian habitat types:
mule fat scrub, southern willow scrub and woodland, freshwater marsh,
and disturbed floodplain. Black willow (Salix gooddingii), red willow
(S. laevigata), and an occasional cottonwood

(Populus sp.) make up the tree layer while arroyo willow

(S. lasiolepis), narrow‑leaved willow (S. exigua),

and mule fat (Baccharis salicifolia) are the primary large shrub species
present.

The entire floodplain of the river east of Dairy Mart Road is currently
being managed by USIBWC. This management involves the periodic mowing of
the vegetation to control floodwaters. Some areas of the floodplain are
recovering from current disturbances, and these areas are temporarily
vegetated with scattered young willows, mule fat shrubs, and various
herbaceous species.

To the west of Dairy Mart Road are stands of mule fat scrub, southern
willow scrub, and southern willow woodland growing along the low‑flow
channel and out into the floodplain of the river. The riparian habitat
of the floodplain is relatively undisturbed except where agriculture,
migrants, or river scour has impacted the vegetation. Areas of the
low‑flow channel where backwater collects or ponds can support small
stands of freshwater marsh. In addition, several large ponds sustained
by groundwater that support some freshwater marsh vegetation occur just
south of Interstate 5, east and west of Dairy Mart Road.

The riparian habitat of the Tijuana River valley supports a wide variety
of wildlife species. Common wildlife species observed include mule deer
(Odocoileus hemionus), southern pocket

gopher (Thomomys umbrinus), California ground squirrel

(Spermophilus beecheyi), striped skunk (Mephitis mephitis), opossum
(Didelphis virginiana), green‑winged teal (Anas

crecca carolinensis), mallard (Anas platyrhynchos platyrhynchos), scrub
jay (Aphelocoma californica), mourning dove (Zenaida macroura
marginella), loggerhead shrike (Lanius ludovicianus), red‑tailed hawk,
sharp‑shinned hawk (Accipiter striatus velox), Cooper\'s hawk (Accipiter
cooperii), black‑shouldered kite

(Elanus caeruleus), northern harrier (Circus cyaneus

hudsonius), house finch (Carpodacus mexicanus frontalis),

lesser goldfinch (Carduelis psaltria hesperophilus), song

sparrow, common yellowthroat (Geothlypis trichas), Bewick\'s wren
(Thyromanes bewickii), Nuttall\'s woodpecker (Dendrocopos nuttallii),
northern flicker (Colaptes auratus), yellow‑rumped warbler (Dendroica
coronata), white‑crowned sparrow, yellow‑breasted chat (Icteria virens
auricollis), yellow warbler (Dendroica petechia), least Bell\'s vireo
(Vireo bellii pusillus),

orange‑throated whiptail (Cnemidophorus hyperythrus beldingi), and
bullfrog (Rana catesbeiana).

Federal Endangered Species

The U.S. Fish and Wildlife Service (USFWS) provided a list of federal
endangered and threatened species that occur or have the potential for
occurrence within the proposed project area (Kinney 1990a). Federal
endangered or threatened wildlife species that occur or could occur in
the area of the proposed action are Pacific little pocket mouse,
California brown pelican, light‑footed clapper rail, California least
tern, American peregrine falcon (Falco peregrinus anatum), western snowy
plover, coastal California gnatcatcher (Polioptila californica
californica), southwestern willow flycatcher (Empidonax traillii
extimus), and least

Bell\'s vireo. One federal endangered plant species occurs in the area
of the proposed action, salt marsh bird\'s beak. Details of the
population status of each of these species in the Tijuana River valley
are contained in the Biological Assessment for the Final EIS (EPA 1994).

Estuarine Biology

The information provided in this section is derived primarily from the
Biological Impacts of Interim Discharge of Primary Treated Effluent from
the International Wastewater Treatment Plant to the Tijuana Estuary,
prepared by Tierra Environmental Services (1996). This report is
included as Appendix B.

The Tijuana estuary is located in the southwestern corner of the
continental U.S. and has been designated the Tijuana River National
Estuarine Research Reserve by the NOAA. The reserve includes
approximately 2,500 acres (1,012 ha), of which 149 acres (60 ha) are
tidal channels (Nordby and Zedler 1991). The Tijuana River bisects the
estuary into a northern arm and a southern arm and rarely provides
substantial freshwater except during exceptionally wet winters or in
years with sewage‑augmented flows.

The Tijuana estuary supports a diverse assemblage of species and
habitats in response to high variability in topography, tidal influence,
and stream flow. Seven major habitat types have been identified (Figure
3.4‑1), including estuarine channels and tidal creeks, salt marsh,
brackish marsh, intertidal flats, salt pan, transition from upland to
wetland, and dunes and beach (Zedler and Nordby 1986). The habitats that
are most likely to be impacted by raw or treated sewage are the channels
and tidal creeks, intertidal flats, intertidal marsh and, to a lesser
degree, dunes and beaches. For the purpose of this discussion, channels,
tidal creeks, and intertidal flats are considered a single continuous
habitat dominated by water at extreme high tides and intertidal flats
with subtidal refuges during extreme low tide.

A USFWS tabulation of state and federal listed and proposed endangered,
threatened, and candidate species that may occur within the Tijuana
River estuary region is presented in Table 3.4‑1 (Kinney 1990b). The
following discussion summarizes some of the key features of each of the
habitat types and notes sensitive species most likely to be associated
with each.

Estuarine Channels, Tidal Creeks, and Intertidal Flats

Channel habitats are important for a variety of organisms and
communities including phytoplankton, macroalgae, invertebrates, fishes,
and birds (Zedler and Nordby 1986). These habitats are subjected to a
wide range of environmental conditions depending on influences of tidal
flushing and freshwater inflows. Both influence water movement,
salinity, temperature, nutrients, and dissolved gases. Nutrients
imported to the estuary from offshore are more readily available to
organisms near the mouth than to those located farther away.

TABLE 3.4‑1

LISTED AND PROPOSED ENDANGERED AND THREATENED SPECIES

AND CANDIDATE SPECIES THAT MAY OCCUR IN THE AREA

OF THE TIJUANA RIVER ESTUARY

Common Name Scientific Name Code

Federally and State‑listed Species

Birds Western snowy plover Charadrius alexandrinus FT Yellow‑billed
cuckoo nivosus SE Southwestern willow Coccyzus americanus SE/PE
flycatcher occidentalis SE/FE American peregrine falcon Empidonax
traillii extimus SE Belding\'s savannah sparrow Falco peregrinus anatum
SE/FE California brown pelican Passerculus sandwichensis FT Coastal
California beldingi SE/FE gnatcatcher Pelecanus occidentalis SE/FE
Light‑footed clapper rail californicus SE/FE California least tern
Polioptila californica Least Bell\'s vireo californica Rallus
longirostris levipes SE/PE Plants Sterna antillarum browni SE/FE Coastal
dunes rattleweed Vireo bellii pusillus Salt marsh bird\'s beak FE Fish
Astragalus tener var. titi Tidewater goby Cordylanthus maritimus ssp.
maritimus FE Mammals Pacific little pocket mouse Eucyclogobius newberryi
PE Amphibians California red‑legged frog Perognathus longimembris
pacificus Rana aurora draytonii

Federal Candidate Species

Birds Mountain plover Charadrius montanus FC

Status Code

FC = Federal candidate for listing

FE = Federally listed as endangered

FT = Federally listed as threatened

PE = Federally proposed endangered

SE = State listed as endangered

Figure 3.4‑1

from the mouth. This gradient is also evident in terms of temperature,
salinity, and dissolved oxygen, with areas nearest the mouth being less
variable than those located farther from the source of tidal exchange.
These environmental factors influence species composition and
distribution and the population and community dynamics of the channel
organisms.

Algae

Phytoplankton of the Tijuana estuary are highly variable in terms of
species composition and density (Zedler and Nordby 1986).
Dinoflaggelates, diatoms, filamentous blue‑green algae and unidentified
unicells, or &quot;monads,&quot; are present in the water column (Fong
1986). These phytoplankton are also present in nearshore habitats, in
lower densities. Phytoplankton density was found to be highest during
spring/ summer &quot;blooms,&quot; especially in tidal creeks where
current speeds are low and nutrients abundant (Zedler and Nordby 1986).
Experimental manipulation supported the relationship between high
nutrients and phytoplankton blooms (Fong 1986).

Macroalgae

Macroalgae, including genera such as Enteromorpha and Ulva, are
similarly influenced by low tidal velocities and nutrients (Rudnicki
1986). In particular, field sampling demonstrated that macroalgal growth
was stimulated by nutrient input following runoff from rainfall.

Invertebrates

Studies of the invertebrate community of the Tijuana estuary, especially
the benthic community, have included primarily resource inventories and
short‑term or species‑specific studies. Such surveys have documented
more than 75 benthic species (Zedler and Nordby 1986). A long‑term
monitoring program was initiated by researchers at the Pacific Estuarine
Research Laboratory (PERL), San Diego State University, in 1986 and
continues today (1996).

Benthic infaunal distribution is strongly influenced by sediment type.
Most larval settlement is limited by substrate availability, while adult
distributions are influenced by grain size, pH, organic content,
nutrients, and dissolved gases. Filter feeders, such as bivalves, occur
in medium‑sized sediments; deposit feeders are associated with finer
sediments.

The benthic community has been subjected to dramatic environmental
events, such as flooding and mouth closure, that have influenced species
composition. Prior to flooding in 1980, the benthic community at the
Tijuana estuary was dominated by bivalve molluscs, especially purple
clam (Nuttallia \[= Sanquinolaria\] nuttalli),

littleneck clam (Protothaca staminea), false mya (Cryptomya
californica), California jackknife clam (Tagelus californica) and
bent‑nose clam (Macoma nasuta). The results of the

long‑term monitoring program, begun in 1986, suggest that purple clam is
now extinct at the Tijuana estuary and that California jackknife clam
and littleneck clam dominated the bivalve assemblage while the
polychaetes of the families Capitellidae and Spionidae dominated that
assemblage (Nordby and Zedler 1991). In addition, ghost shrimp
(Callianassa ssp.), California horn snail

(Cerethidia californica), lined shore crab (Pachygrapsus

crassipes), and yellow shore crab (Hemigrapsus oregonensis) are abundant
channel invertebrates that often form commensal relationships with other
channel fauna.

Fishes

The fishes of the Tijuana estuary can be typified as estuarine residents
and visitors, or transients. Estuarine residents include species adapted
to primarily marine conditions as well as those that are euryhaline
(exhibit tolerance to a wide range of salinities and associated
conditions.) Transients are marine species that enter the estuary at
high tide and usually exit with the low tide.

Like the benthic invertebrates, fish species composition is influenced
by environmental events such as flooding and mouth closure. Prior to
flooding in 1978 and 1980, and mouth closure and ensuing hypersalinity
in 1984, 29 species of fish were found in the Tijuana estuary. The
community was dominated by gobiids, California killifish (Fundulus
parvipinnis), striped mullet (Mugil cephalus),

and longjaw mudsucker (Gillichthys mirabilis). Following

flooding and mouth closure and periods of high sewage inflows, the fish
assemblage was dominated by arrow goby (Clevelandia ios), topsmelt
(Atherinops affinis), California killifish, and staghorn sculpin
(Leptocottus armatus). Longjaw mudsuckers were apparently very
susceptible to hypersalinity and had not recovered from mouth closure by
1990 (Nordby and Zedler 1991).

Birds

The channels of the Tijuana estuary are important foraging and resting
areas for a number of bird species which prey upon the abundant
invertebrates and fishes (Zedler and Nordby 1986; Zedler et al. 1992).
Numerous shorebirds, including various sandpipers (Caladris spp.),
killdeer (Charadrius vociferus),

dowitchers (Limnodromus spp.), willet (Catoptrophorus

semipalmatus), long‑billed curlew (Numenius americanus),

and marbled godwit (Limosa fedoa), forage for invertebrates in the sand
and mud flats during low tide. Diving birds, such as terns and pelicans,
prey upon fishes. Wading birds, including great blue heron (Ardea
herodias) and common egret (Casmerodius albus), feed upon both
invertebrates and fishes. Other species, such as dabbling ducks, feed
upon vegetation and surface insects.

Several endangered bird species use the channel organisms of the Tijuana
estuary for prey. These include the California least tern (Sterna
antillarum browni), the light‑footed clapper

rail (Rallus longirostris levipes), the California brown

pelican (Pelecanus occidentalis californicus), and the

Belding\'s savannah sparrow (Passerculus sandwichensis beldingi).
Because the birds are dependent upon the fishes and invertebrates for
food, environmental events that affect those food sources have impacts
on these higher level consumers. It was estimated that the mouth closure
of 1984 resulted in a reduction in shorebird abundance of 70 percent (P.
Jorgensen in Zedler and Nordby 1986).

Intertidal Marsh

The intertidal salt marsh of the Tijuana estuary intergrades with
freshwater‑associated riparian habitats to the east along the Tijuana
River; with upland habitats along the southern and northern arms of the
estuary; and with dunes and beaches to the west (see Figure 3.4‑1). The
intertidal salt marsh has been the focus of numerous studies at the
Tijuana estuary, ranging from studies of structure and function to
competition among the dominant vascular plants to estimates of gross
primary productivity of vascular and algal plant components.
Considerably less attention has been paid to the animals of the
intertidal marsh; however, there are some recent studies that have
addressed the faunal assemblages of the marsh (Zedler et al. 1992;
Entrix et al. 1991).

The salt‑marsh vegetation at the Tijuana estuary changes gradually with
elevation. Almost every species has its peak occurrence at a different
elevation band, and the vegetation forms a continuum along the
elevational gradient (Zedler and Nordby 1986). The lower elevations are
dominated by cordgrass (Spartina foliosa). Pickleweed (Salicornia
virginica), saltwort (Batis

maritima), and jaumea (Jaumea carnosa) may be considered

mid‑marsh species. Sea blight (Limonium californicum),

alkali heath (Frankenia grandifolia), shoregrass (Monanthochloe
littoralis), and glasswort (Salicornia subterminalis)

may be considered upper marsh species. The federally endangered salt
marsh bird\'s beak (Cordylanthus maritimus ssp. maritimus) occurs in the
upper salt marsh at the Tijuana estuary.

The salt marsh supports a complex web of animal life including insects,
invertebrates, birds, reptiles, and small mammals (Zedler and Nordby
1986). Insect life includes such beetles as Tachys corax and Eurynephala
maritima and such spiders as

Tetragnatha laboriosa and Pardosa ramulosa. Invertebrates of the
intertidal salt marsh include some of the benthic forms discussed in the
section on estuarine tidal creeks, channels, and intertidal flats, as
well as amphipods, snails such as Assimimea californica and Melampus
olivaceus, and water boatmen

(Trichocorixia spp.). The low, cordgrass‑dominated marsh

supports the federally endangered light‑footed clapper rail. This
species constructs nests of cordgrass and other plant species and
forages along tidal creeks and channels. Birds of the mid‑marsh include
the willet, godwit, long‑billed curlew, great blue heron, and the
state‑endangered Belding\'s savannah sparrow. Birds of the upper marsh
include the white‑crowned sparrow (Zonotrichia leucophrys), song sparrow
(Melospiza melodia), western

meadowlark (Sturnella neglecta), and killdeer. Raptors,

such as red‑tailed hawk (Buteo jamaicensis), forage in

the upper marsh.

The high marsh, and its transition to upland habitats, supports more
terrestrial animal species, including reptiles such as the California
kingsnake (Lampropeltis getulus californiae)

and San Diego horned lizard (Phrynosoma coronatum blainvillei) (Zedler
et al. 1992). Most mammals are, likewise, confined to higher and drier
areas. Small mammals recorded at the Tijuana estuary include western
harvest mouse (Reithrodontomys megalotis), deer mouse (Peromyscus
maniculatus), and house mouse (Mus

musculus). The federal endangered Pacific little pocket mouse
(Perognathus longimembris pacificus) was observed in the

1930s but has not been recorded in the estuary.

Beaches and Dunes

Sewage inflows from the Tijuana River exit the estuary at the mouth and
are dispersed to the beach by the nearshore currents. Often elevated
coliform numbers pose human health risks and result in beach closures.
Although other animals are not necessarily affected by human coliforms,
these organisms act as indicators that sewage, including &quot;fresh
water,&quot; reaches the beach and may impact these habitats. Because
beaches and dunes intergrade, it is difficult to arbitrarily decide
where one habitat ends and the other begins. For the purposes of this
discussion, the beach is assumed to extend from extreme low tide to
extreme high tide, storm tides notwithstanding. Any dune habitat above
that elevation would be affected only by a combination of high tide and
storms, which would greatly dilute any impacts from sewage.

Beaches in southern California are heavily used by people and,
therefore, no longer support the diversity of plants and animals that
they once did. However, invertebrate populations are still seasonally
high which, in turn, support shorebird populations. Sand crabs (Emerita
spp.), amphipods, and isopods are

seasonally abundant invertebrate prey organisms for shorebirds.

The Tijuana estuary is a part of the Pacific Flyway used by the millions
of birds traveling between Arctic and Subarctic breeding areas and lower
latitude wintering sites. The number of migratory birds at the Tijuana
estuary peaks in the fall and is an order of magnitude greater than the
number present in the spring (Zedler et al. 1992). Sanderling (Calidris
alba), willet, marbled godwit, whimbrel (Numenius phaeopus hudsonicus),
and western snowy plover (Charadrius alexandrinus nivosus) were the

most abundant shorebirds observed utilizing beach habitats by Boland
(1981) in his study of Tijuana estuary shorebirds.

Two sensitive bird species utilize the beach habitats of the estuary:
the California least tern and the snowy plover. Least terns nest on the
beach and forage in the nearshore and estuarine waters. Their numbers
fluctuate widely from year to year, depending upon natural mortality and
disturbance from predators and humans. Snowy plovers nest on the beach
at the mouth of the Tijuana estuary. They feed on dipterans and
amphipods in the wrack line deposited by high tides. Like the least
tern, this species is very susceptible to disturbance by humans using
the beach.

Sensitive Species Distributions

All of the species discussed in this section, with the exception of the
mountain plover (Charadrius monotones), are listed

as endangered or threatened by the USFWS and are considered California
State listed endangered species. The mountain plover is a federal
proposed species. Additional information regarding the species discussed
below is found in the biological assessment preparedfor the IWTP (RECON
1993). American Peregrine Falcon

The peregrine falcon is a rare fall and winter visitor to San Diego
County and is casual in late spring and early winter. Individuals have
been seen at the Tijuana River estuary (Newman 1990). Two peregrine
falcons were observed flying over the coastal area of the estuary in
April and May of 1990 (Michael Brandman Associates \[MBA\] 1990).
Peregrine falcons are most frequently seen in San Diego County between
October and March (Unitt 1984).

Salt Marsh Bird\'s Beak

Salt marsh bird\'s beak currently is found at Tijuana Marsh. Salt marsh
bird\'s beak grows in the higher reaches of salt marshes, where it is
inundated with salt water only at the higher tides. Seed germination is
dependent on the salinity of the soil; if the soil salinity is too high,
the seeds fail to germinate (Zedler 1984). The USFWS Salt Marsh
Bird\'s‑Beak Recovery Plan (1985) calls for the protection of the
present sites, the restoration in historic sites, and continued field
monitoring and biological studies.

Light‑footed Clapper Rail

Recent population surveys and field studies of clapper rails have shown
that these birds (especially young) and their nests can be highly
susceptible to predation. Common predators include red‑tailed hawk,
great horned owl, common raven, American crow, ground squirrel, red fox,
feral cat, raccoon, striped skunk, and perhaps certain snake species
(Zembal 1989).

One of only two known large populations of light‑footed clapper rails in
southern California is located in the Tijuana Slough National Wildlife
Refuge (NWR). In 1989, 15 territorial pairs were recorded, plus 19
unpaired individuals, for a total of 49 rails. Most of the unpaired
birds were female. This sex ratio imbalance &quot;could be the result of
breeding inhibition brought on by sibling recognition, abnormally high
predation, or some unknown factor&quot; (Zembal 1989). High noise levels
from regular helicopter overflights could also affect breeding behavior
by reducing the effectiveness of advertising calls and interfering with
the detection of predators. The 1990 surveys of the Tijuana Slough NWR
showed an increase in pairs of 17 pairs of clapper rails detected.

The Tijuana Slough NWR population of clapper rails continues its
recovery from decimation in 1983/1984, when severe weather conditions
and high tides forced the rails to leave. In 1991, light‑footed clapper
rail surveys showed a remarkable increase in the number of pairs
detected (Zembal 1991). A total of 47 pairs of clapper rails were
observed in the refuge. This situation illustrates the need to develop
and sustain large, healthy clapper rail populations in a number of areas
along the California coast, since natural, as well as unnatural,
disasters can destroy entire breeding sites.

In 1988, 1989, and 1993, one pair of clapper rails was found nesting and
foraging in a marsh pond dominated by cattails just west of Dairy Mart
Road, east of the Tijuana Slough NWR.

California Least Tern

Nesting activity during the 1990 breeding season at the Tijuana Slough
NWR (Tijuana River estuary) occurred on two sites, one south of the
Tijuana River mouth and one north of the river mouth, while a single
nesting area occurs within the Border Field State Park approximately 0.6
mile (1 km) north of the international border (Massey 1989; MBA 1990).

Nesting during 1990 was primarily in the sand dune habitat along the
coast. At the site north of the river in the Tijuana Slough NWR, there
were 14 nests observed with an average number of young hatched per nest
of about 0.2 to 0.4; however, the number of fledglings produced per nest
was zero (0). Destruction by human foot traffic and heavy predation by
dogs, cats, gulls, ravens, and northern harriers were major factors
affecting nest and fledgling success (MBA 1990). The NWR south site had
62 nests in 1990, with the number of young hatched per nest at about 0.5
to 0.8 and the number of fledglings produced per nest ranging from 0.1
to 0.4 (8 to 26 chicks fledged). Nest and egg success was affected by
human foot traffic and avian predation. Chick mortality was affected
primarily by avian predation by ravens, kestrels, gulls, harriers, and
herons. The Border Field State Park least tern nesting area produced
about 20 nests in 1990, with the number of young hatched per nest at
about 0.6 to 1.0 and the number of fledglings produced per nest ranging
from 0.3 to 0.6 (5 to 13 chicks). Human, equestrian, and vehicular
traffic all contributed to nest failures in this area. Predation of
chicks by animals already mentioned for the other sites was also common
at this site.

During the 1991 breeding season, the California least tern continued to
use the beach and sand dune habitat both to the north and south of the
river mouth. Of particular significance is the increased use of area to
the south of the river mouth in Border Field State Park. Least tern
nests were observed farther south than the previous year. Seven nests
occurred within 1,600 feet north of the international border. Loafing
least tern adults, fledglings, and chicks were also observed within 550
feet of the international border. California Brown Pelican

In San Diego County the most important region for brown pelicans is the
coastal waters between Mexico and Point Loma. During the 1986 pelican
census, as reported by Jaques and Anderson (1987):

. . . the location of pelicans roosting in the San Diego area was
variable. Hundreds of birds utilized the rock crest of the submerged
jetty at the mouth of South San Diego Bay during low tides, but during
high water they were restricted to a few cement &quot;islands&quot; on
the jetty bearing light markers. The cliffs at Point Loma were used
heavily by perhaps several thousand pelicans during peak abundance of
immature pelicans in the area, but no birds were seen there during
previous or subsequent visits. The Tijuana River mouth contributed to
high counts during one flight (350 pelicans), but only 20 pelicans were
censused there on subsequent flights.

Surveys conducted during 1990 in the Tijuana Slough NWR and Border Field
State Park for brown pelicans resulted in the observance of
approximately 322 pelicans with the majority of the birds seen in the
ocean habitat (MBA 1990). They were seen in a number of habitats,
including the ocean, beach, sandbar, channel, dunes, and river mouth
areas. Directional flight over these areas and roosting were only
observed behaviors, and no nesting or other breeding activities
occurred.

Western Snowy Plover

This species is known to breed on the dunes near the mouth of the
Tijuana River (Unitt 1984). Western snowy plovers build their nests in
dunes using small pieces of shell. They feed almost exclusively on
insects and crustaceans gleaned from the sand surface (County of San
Diego 1972).

In 1990 western snowy plovers were observed foraging on the beach,
sandbars, and mud flats near the mouth of the Tijuana River (MBA 1990).
A total of 144 snowy plovers were observed between April and August. A
minimum of three pairs nested to the north of the Tijuana River mouth,
five pairs south of the river, and two pairs within Border Field State
Park. The majority of the nesting took place in beach habitat. Three of
the nests located each contained three eggs and at least two of the
nests fledged two chicks each. In 1991 a survey counted only 129 snowy
plovers in coastal San Diego County with a mere 57 birds in the south
part of the county. Belding\'s Savannah Sparrow

Survey\'s were conducted for Belding\'s savannah sparrow at the Tijuana
River estuary, including Border Field State Park, in March of 1990. A
total of 289 territorial Belding\'s savannah sparrows were observed,
including 184 singing males and 105 breeding pairs (Kus 1990). Some 219
additional individuals were observed whose sex could not be determined
at the time the birds were seen. These numbers may represent a slight
increase in the population in this part of the range. Approximately 72
percent of the males occurred in the salt marsh habitat south of the
Tijuana River mouth.

In April of 1992 additional surveys for the Belding\'s savannah sparrow
were conducted along a 500‑foot‑wide (152.4 m) section of the salt marsh
immediately north of Monument Road between the 90‑degree turn and the
ocean, and salt‑marsh habitat to the south of Monument Road along the
base of the bluffs (Kus 1992). A total of 10 males and 8 other
individuals of undetermined sex were observed in the study area.

Mountain Plover

The mountain plover is a common localized winter visitor that is usually
found in fields of bare dirt (Unitt 1984). They are known to occur
regularly in the Tijuana River valley, where they arrive in October and
leave by the end of January. This species is threatened by loss of
habitat due to development and disturbance from humans, domestic
animals, and off‑road vehicles.

Marine Biology

The information provided in this section is derived primarily from the
Marine Biological Resources Technical Report for the South Bay Ocean
Outfall prepared by MBC (1996), which is Appendix C to the SEIS.
Information was also drawn from the TOES (Engineering Science 1988),
Marine Environmental Impacts of the Proposed Secondary Treatment System
(Kinnetic 1991), and Wastewater Modeling and Analysis of Alternative
Interim Disposal Options (Engineering‑Science 1996). These reports are
incorporated by reference.

Intertidal Communities

Shores in the South Bay area are composed predominantly of medium to
coarse sand. The riprap of the south jetty at Zuniga Point, at the
entrance to San Diego Bay, is the nearest intertidal hard substrate in
the vicinity. The jetty acts as a barrier to sediment transport along
the shore. Beach sediment is supplied primarily by local rivers and
creeks which have been grouped into distinct sedimentation circulation
cells (State of California 1977). In the South Bay, the Silver Strand
cell is supplied by the Tijuana River.

Biological studies conducted on the beaches from Coronado to the
U.S.‑Mexico border indicate that the most conspicuous organisms are sand
crabs (Emerita analoga), beach hoppers (Orchestoidea spp.), olive snails
(Olivella biplicata), and bean clams

(Donax gouldii) (Clark 1969; Dexter 1977; Parr et al. 1978; Straughn
1982; MBC 1990). Several smaller amphipod and isopod crustaceans and
polychaete annelids also inhabits the shoreline sands. In the spring,
grunions spawn and deposit their eggs on these beaches.

From the international border south to Punta Banderas, the coast is a
narrow coastal plain backed by bluffs. The beaches are primarily sandy
like those of the South Bay project area and presumably have similar
intertidal communities. Rock shores are found further south near Punta
Descanso.

The California State Mussel Watch and National Status and Trends
programs have found increased organic contaminants in California mussels
collected from the Imperial Beach area (State of California 1988, 1994a;
NOAA 1989; O\'Connor and Beliaeff 1995). High concentrations of DDT and
dieldrin suggest agricultural sources of contamination, as opposed to
industrial and marina sources within San Diego Bay. Benthic Communities

Benthic infauna refers to the assemblage of usually small, invertebrate
organisms which live in the soft sediments of the seafloor. Most benthic
organisms live within the upper four inches (10 cm) of sediment and
consume dead organic matter (detritus) or are predators. This community,
which is relatively immobile, is important for its use as a food
resource for epibenthic macroinvertebrates and demersal fish and is
important in the conversion of organic deposits into biomass available
to higher trophic levels.

The magnitude and composition of available detrital material strongly
influences species composition, abundance, and biomass, with biological
densities usually being greater along gradients of increasing detrital
food supply. Community composition is also affected by sediment grain
size, water motion, and sources of planktonic larvae for recruitment.
Sediment characteristics determine biologically meaningful variables
such as porosity, compaction, oxygen tension, water content, and
retention of organic material.

Baseline information on the benthic community of the South Bay,
generally from the mouth of San Diego Bay to the international border
and offshore of far northern Baja California, was collected for the TOES
in 1986 and 1987 (Engineering Science 1988). Abundance and community
composition were found to vary with depth. Along the 66‑ft (20 m) depth
contour, the numerically dominant infaunal species were the polychaete
Magelona sacculata and the

clam Tellina modesta, and at 131‑ft (40 m) depths, the

polychaete Euchone arenae was dominant. In the northern

portion of the area, the brittle star Amphiodia urtica

and the polychaete Spiophanes missionensis were the dominants at 198 ft
(50 m), while to the south, the tube snail Caecum crebricinctum and the
white sea urchin Lytechinus pictus

predominated.

Considerable additional information is being collected for the baseline
monitoring for the SBOO. An ongoing program of sampling, which began in
July 1995, is being conducted by the City of San Diego; several of the
sampling stations both north and south of the international border
reoccupy those of the TOES program.

The importance of sediment grain size is apparent in the distribution of
community composition. As described by Jones (1969), Amphiodia urtica
(brittle star) occurs along most of the southern California coastal
shelf where sediments are fine, usually at depths of over 120 ft (37 m).
However, sediments in the South Bay are variable, with pockets of
coarse, relict red sands, which support a very different community
dominated by species which are adapted to the conditions presented by
the coarse substrate. Brittle star was not abundant in the area of the
SBOO diffusers.

Abundance, species richness (number of species), and species diversity
were generally greater offshore than near shore. Species richness and
diversity followed the same inshore‑offshore and north‑south patterns.

Abundance averaged 108 individuals/0.1 m2 (1.1 ft2) along the 39‑ft
(12‑m) isobath, increasing to 323/0.1 m2 at 197 ft (60 m). Values also
tended to be higher to the north and lower to the south, consistent with
the presence of the coarser sediments.

Richness ranged from an average of 34 species/0.1 m2 at a depth of 39 ft
(12 m) to 83 species/0.1 m2 at 197 ft (60 m). Species diversity was not
as variable as the other parameters, but did show an increase in values,
from 2.99 at 39 ft (12 m) to 3.57 at 197 ft (60 m.)

The Infaunal Trophic Index was developed to assist in the description of
infaunal community feeding structure around point sources of enrichment,
such as wastewater outfalls, and is based on assignment of benthic
organisms into feeding categories (Word 1978, 1980). The index has a
range from 0 to 100, and low values result from a high proportion of
subsurface deposit feeders, which indicate the presence of organic
enrichment.

Infaunal Trophic Index values ranged from an average of 70 at 39 ft (12
m) deep to 84 at 197 ft (60 m). Unlike other parameters, values were
slightly higher in the middle of the area, near the future outfall, than
to the north or south. The lower values inshore suggest the presence of
detrital material carried longshore from kelp beds and the Tijuana
River, while the higher values in the middle of the north‑south range
suggest the presence of coarse sediments which typically contain little
organic material. However, all values were in the range considered to be
unaffected by deposition of significant input of suspended solids.

A remotely operated vehicle (ROV) survey of the South Bay outfall area
conducted in 1990 showed considerable variability in sediment type
(Kinnetic 1990). Cobble beds occur at a depth of about 55 ft (16.8 m),
with coarse shell debris on the surface from 50 to 80 ft (15.2 to 24.4
m). Finer sediments occur both inshore and offshore. About one mile (1.6
km) north of the future outfall, low‑relief rocks, boulders, and cobbles
occur occasionally, including a zone at a depth of approximately 48 ft
(14.6 m) out to about 90 ft (27.4 m).

Invertebrates observed included white sea urchin (Lytechinus pictus),
Kellet\'s whelk (Kelletia kelletii), the sea

pen Stylatula elongata, cancer crabs (Cancer spp.),

spiny sand star (Astropecten armatus), and short‑spined

sea star (Pisaster brevispinus). The red urchin (Strongylocentrotus
franciscanus) and unidentified attached algae dominated the cobble
areas. In deeper areas, hard substrate unaffected by sand scouring was
colonized by red gorgonian (Lophogorgia chilensis), sea fans (Muricea
spp.), jewel anemone (Corynactis californica), and golden cup coral
(Balanophyllia elegans).

Kelp Beds

Small kelp beds occur within the South Bay area. As the giant kelp
(Macrocystis pyrifera), feather boa kelp (Egregia

laevigata), palm kelp (Pterygophora californica), and

other macroalgae which form kelp forests require an attachment
substrate, the occurrence of kelp beds is usually restricted to areas of
subtidal rocks, boulders, and cobble within the photic zone (generally
20 to 60 ft \[6.1 to 18.3 meters\]).

The forest and dense canopy formed on the water surface provide food and
a complex habitat for a highly diverse community of fish, invertebrates,
and other algae (North 1971; Foster and Schiel 1985). Many of these
species are important to commercial and sportfishing. Estimates of kelp
productivity range from 4.5 to 6.1 lbs (wet weight)/ft2/year (22 to 30
kg/m2/year) based on growth estimates or up to 31.0 lbs/ft2/year (152
kg/m2/year) based on physiological estimates (reviewed by Foster and
Schiel 1985). Some kelp enters the food web directly via grazing (by sea
urchin, for example), but the majority of the productivity (estimated as
over 70%) becomes part of the detrital pathway (Gerard 1976).

Kelp populations along the southern California coast vary temporally,
depending on oceanographic and weather conditions. Declines generally
occur during &quot;warm water&quot; periods associated with El
Ni&ntilde;o events or during severe storms. Declines during El
Ni&ntilde;os result from the loss of plant tissue near the surface,
primarily from the lack of nutrients (nitrogen and phosphorus) necessary
for growth (Zimmerman and Kremer 1984). During the last two major El
Ni&ntilde;os (1957‑1958 and 1983‑1984), the canopy in southern
California kelp forests was reduced by up to 90 percent, and some kelp
beds disappeared completely (North and Schaefer 1964; Tegner and Dayton
1987). Storms, which usually occur in winter, decimate kelp beds as
accompanying large waves tear off kelp frond or dislodge entire plants.
Grazing sea urchins can also reduce kelp beds if drift kelp, their usual
food source, is in short supply (Dean et al. 1984; Harrold and Reed
1985).

Two small patches of kelp bed, referred to as the Imperial Beach bed,
occur off the Imperial Beach Pier and near the Tijuana Slough mouth,
about 2.5 and 1.0 miles (4.0 and 1.6 km) north, respectively, of the
future outfall pipeline corridor. The Imperial Beach bed is attached to
boulders and cobbles, as opposed to consolidated reef. Giant kelp was
reportedly abundant at these sites prior to 1939, but only a few
scattered patches were observed from the mid‑1950s through the
mid‑1980s, in spite of several restoration efforts (North 1973,
Engineering Science 1988). Kelp reappeared in 1985 and reached a peak in
1987 with more than 173 acres (0.7 km2), but most was lost during storms
in January 1988 (McPeak, pers. com. 1991). The beds rebounded strongly
in 1989 and 1990. Recent surveys have shown that the bed is maintaining
a small canopy, with the most recently available figures indicating a
canopy area of about 24.7 acres (0.1 km2) (MBC 1995). Additional kelp is
also found in small patches to the south along the Mexico coastline off
Tijuana (North, pers. com.; Dearn, pers. com., in Engineering Science
1992b).

Reasons for both the absence of kelp at the Imperial Beach bed for over
40 years and for the sudden resurgence of kelp are not known. Unstable
substrate, coupled with high abundance of grazers and high rates of
sedimentation, made kelp colonization difficult. Suggestions have been
made that the lack of kelp at the site was due to sewage contamination
from Tijuana, but that is unlikely, as kelp returned when sewage flow in
the Tijuana River was increasing. Also, observations at the Point Loma
kelp bed showed that the 1992 spill of sewage from the storm‑damaged
Point Loma outfall pipeline had little adverse effect on the kelp bed,
and the high ammonia concentrations may actually have benefited the
kelp, as the spill occurred during an episode of reduced nutrients
accompanying an El Ni&ntilde;o event (Tegner et al. 1995).
Recolonization of kelp at the Imperial Beach bed may have been due in
part to a reduction in urchin densities from commercial urchin
harvesting (Kinnetic 1991).

Just south of the international border, ephemeral kelp beds have
occurred, probably on cobble substrate similar to the Imperial Beach
beds. However, these beds have not been reported since the 1950s. Small
beds occur south of Punta Banderas near Punta Descanso. Kelp beds
previously occurring around the Coronado Islands were almost extirpated
by sea urchin divers and are not recovering due to a lack of recruitment
from current‑borne spores from the south (Tegner, pers. com. 1996).

Fish Populations

Fifty‑one species of fish have been observed at depths of 30 to 120 ft
(9.1 to 36.6 m) in surveys of the Imperial Beach kelp bed, offshore over
soft bottoms (Southern California Coastal Water Research Project
\[SCCWRP\] n.d.; City of San Diego 1995), and in a description of San
Diego recreational fishing areas (Squire and Smith 1977). Twenty‑eight
of the species are found primarily on soft bottoms, 16 on hard bottoms
and in kelp beds, and 7 are pelagic (Table 3.5‑1).

Pelagic species feed primarily on zooplankton and other fish. Yellowtail
(Seriola lalandi), white seabass (Atractoscion

nobilis), Pacific barracuda (Sphyraena argentea), and

Pacific bonito (Sarda chiliensis) are important predatory

pelagic species caught by recreational fishermen. Other small, pelagic
species which occur in the area, occasionally in abundance, but may not
be captured in trawl surveys include northern anchovy (Engraulis
mordax), Pacific mackerel (Scomber japonicus),

Pacific sardine (Sardubios sagax), Pacific saury (Cololabis saira), and
Pacific hake (Merluccius productus) (Kinnetic

1991). The smaller of these species (anchovies, smelt), when they school
near shore and into bays and estuaries, are prey for seabirds, such as
the endangered California least tern. Migratory pelagic species such as
Pacific mackerel are known to occasionally congregate above wastewater
outfalls (Smith 1974; SCCWRP 1973; County Sanitation District of Orange
County 1986).

Fish species associated with sand bottom and reef habitats are more
localized in their movements than pelagic species. Fish assemblages
which occupy kelp beds and reefs are dominated by perches, basses,
rockfishes, wrasses, and gobies. In diver surveys in 1986 and 1987, 27
species of fish were observed in the Imperial Beach kelp bed, of which
the most common species were senorita (Oxyjulis californica), halfmoon
(Medialuna calaforniensis), and rainbow seaperch (Hyspurus caryl)
(Engineering Science 1988).

TABLE 3.5‑1

FISH SPECIES OBSERVED IN NEARSHORE AND OFFSHORE AREAS

OFF IMPERIAL BEACH AND THE TIJUANA RIVER

Common Name Scientific Name

Pelagic

topsmelt Atherinops affinis

jacksmelt Atherinopsis

californiensis

yellowtail Seriola lalandi

jack mackerel Trachurus symmetricus

white seabass Atractoscion nobilis

Pacific barracuda Sphyraena argentea

Pacific bonito Sarda chiliensis

Kelp Beds and Hard Bottoms

leopard shark Triakis semifasciatus

coralline sculpin Arteduis corallinus

kelp bass Paralabrax clathratus

opaleye Girella nigricans

halfmoon Medialuna californiensis

kelp perch Brachyistius frenatus

black perch Embiotoca jacksoni

rainbow seaperch Hyspurus caryi

rubberlip seaperch Rhacochilus toxotes

pile perch Rhacochilus vacca

rock wrasse Halichoeres semicinctus

senorita Oxyjulis californica

California sheephead Semicossyphus pulcher

stripedfin ronquil Rathbunella hypoplecta

giant kelpfish Heterostichus rostratus

blackeye goby Coryphopterus nicholsii

Shallow (10‑40 m) Soft Bottom

thornback Platyrhinoidis

triseriata

shovelnose guitarfish Rhinobatos productus

round stingray Urolophus halleri

California Scorpaena guttata

scorpionfish

barred sand bass Paralabrax nebulifer

California halibut Paralichthys

californicus

C‑O sole Pleuronichthys coenosus

speckeled sanddab Citharichthys stigmaeus

fantail sole Xystreurys liolepis

California lizardfish Synodus lucioceps

TABLE 3.5‑1

FISH SPECIES OBSERVED IN NEARSHORE AND OFFSHORE AREAS

OFF IMPERIAL BEACH AND THE TIJUANA RIVER

(continued)

Common Name Scientific Name

plainfin midshipman Porichthys notatus

gulf sanddab Citharichthys fragilis

roughbacked sculpin Chitonotus pugetensis

Deep (60 m) Soft Bottom

Pacific argentine Argentina sialis

calico rockfish Sebastes dallii

shortspine combfish Zaniolepis frenata

longspine combfish Zaniolepis latipinnis

yellowchin sculpin Icelinus quadriseriatus

pink seaperch Zalembius rosaceus

Pacific sanddab Citharichthys sordidus

longfin sanddab Citharichthys

xanthostigma

bigmouth sole Hippoglossina stomata

English sole Pleuronectes vetulus

hornyhead turbot Pleurocichthys

verticalis

California tonguefish Symphurus atricauda

stripetail rockfish Sebastes saxicola

bay goby Lepidogobius lepidus

Dover sole Microstomus pacificus

Some of the species encountered are pelagic species not usually
associated with kelp beds.Shallow rocky reefs lacking kelp typically
have lower abundance and diversity of fish species (Larson and De
Martini 1984). Remote video surveys in the cobble and rocky areas near
the future outfall found California scorpionfish (Scorpaena guttata) as
the dominant species (Kinnetic 1990). At depths below 100 ft (30.5 m),
the shallow water reef and kelp assemblage is replaced by a greater
diversity of rockfish species.

Kelp beds are important sportfish areas. Kelp bass (Paralabrax
clathratus) and California sheephead (Semicossyphus pulcher) are the
most important kelp bed and hard‑bottom species in the area for
recreational fishermen (Squire and Smith 1977). North (1971) estimated
that 90 percent of the southern California sportfishing party boat catch
of kelp bass and sand bass (Paralabrax nebulifer) and 70 percent of the
entire party boat catch came from kelp beds. In addition to fish,
recreationally important invertebrates found in the Imperial Beach kelp
bed include red abalone (Haliotis rufescens), California spiny lobster
(Panulirus interruptus), and sheep crab (Loxorhynchus grandis)
(Engineering Science 1988).

Within the kelp bed, bottom‑dwelling species browse or forage for mobile
prey, while species of the kelp canopy also feed on open‑water plankton
(Choat 1982). Many of these demersal species feed at the benthic
boundary layer, and, in areas of wastewater discharge, they may be
exposed to particulates settling to the bottom. Consequently, demersal
fish have been a concern of wastewater monitoring programs in southern
California.

Soft‑bottom demersal fish are typically more associated with the benthic
boundary than are kelp bed and reef fish. Common shallow‑water species
trawled from the depth of the future outfall include speckled sanddab
(Citharichthys stigmaeus), longfin sanddab (Citharichthys xanthostigma),
English sole (Pleuronectes vetulus),

hornyhead turbot (Pleurocicthys verticalis), yellowchin

sculpin (Icelinus quadriseratus), and California lizardfish (Synodus
lucioceps) (City of San Diego 1995). Barred sand bass (Paralabrax
nebulifer) and California halibut (Paralicthys californicus) are also
encountered at shallow depths and are important to recreational
fishermen (Squire and Smith 1977). Most halibut are fished along the
sandy beaches north of the Tijuana River mouth, while barred sand bass
are taken more offshore between depths of 75 and 120 ft (22.9 and 30.6
m).

In deeper waters (greater than 120 ft), the most abundant demersal fish
are Pacific sanddab (Citharichthys sordidus), English sole, and pink
seaperch (Zalembius rosaceus) (SCCWRP n.d.). Plankton Community

Plankton includes small organisms which drift with the currents and
includes phytoplankton (plants) and zooplankton (animals). Zooplankton
includes species which reside permanently in the water column, as well
as larval forms of benthic invertebrates (meroplankton) and fishes
(ichthyoplankton). In nearshore waters, close proximity of the entire
water column to the bottom promotes greater benthic‑pelagic interaction
than is possible in deeper oceanic regions, and, in general,
productivity is elevated.

Species composition and relative abundance patterns vary on a seasonal
basis and in relation to fluxes of nutrients which affect phytoplankton
productivity. Plankton frequently make daily vertically migrations in
the water column in response to changing light levels. They may also
congregate near the surface, where photosynthesis occurs, or near the
bottom, where resuspended particulate matter and epibenthic food sources
are available.

In the San Diego area, nearshore phytoplankton are usually limited by
nitrogen availability (Kinnetic 1991). Studies near the Point Loma
discharge have shown increases in phytoplankton stocks in response to
excess levels of ammonia and available nitrogen. Phytoplankton
assemblages are dominated by diatoms in winter and spring, in response
to increased nutrients, and by dinoflagellates in summer, when nutrient
levels are lower.

Nearshore zooplankton include microscopic animals, protozoans, and
larval forms of benthic invertebrates. A number of species of copepod
and mysid crustaceans, as well as other larger zooplankton, serve as a
major food source for fish (Kinnetic 1991). Species found in the
vicinity of the future outfall include the copepods Coryceaus anglicus,
Paracalanus parvus, and Oithona

plumifera; the cladocerans Evadne nordmanni and Penilia

avirostris; and the arrow worm Sagitta euneritica.

Other organisms which also may occur include gastropod veligers and fish
eggs. Ichthyoplankton found in the area include northern anchovy,
queenfish (Seriphus politus), white croaker (Genyonemus lineatus), and
rockfish (Sebastes spp.).

Marine Mammals

The Southern California Bight contains the largest and most diverse
populations of marine mammals in temperate waters of the world, with as
many as 31 species (Norris et al. 1975). Most are seasonal migrants and
are widely distributed throughout the bight. The most abundant species
are California gray whale (Eschrichtius robustus), Risso\'s dolphin
(Grampus griseus), common

dolphin (Dephinus delphis), and California sea lion (Xalopus
californianus) (Schulberg et al. 1989). All marine mammals are protected
against harassment, injury, or taking by the Marine Mammal Protection
Act of 1973.

Twenty‑four species of cetaceans (whales, dolphins, and porpoises) are
found in the Southern California Bight, six of which are listed as
endangered (the gray whale was recently removed from the endangered
list). Only the gray whale and the bottlenose dolphin (Tursiops
truncatus) occur frequently near shore in the vicinity of

South Bay. All species are either transient or migratory in the area.
Most cetaceans feed on fish and squid, although bottlenose dolphins also
take crabs and mollusks (gray whales also feed on bottom invertebrates,
but only in their summer grounds in the Bering Sea) (Dohl et al. 1981).

Aerial surveys and shore observations of gray whales were conducted
offshore of San Diego County by the U.S. Navy to determine migration
corridors (Schulberg et al. 1989). Four southbound migratory corridors
were found to converge in the vicinity of Point Loma, extending only
about five miles (8.0 km) offshore. Two of three northbound corridors
also approached Point Loma but were much broader, extending almost 12
miles (19.3 km) offshore. The southern migration appeared to approach
the near shore of the South Bay more closely than did the northern
route. Southern migration through the area occurred in January and
February, while northern migration occurred from February through March.

A number of studies have been conducted to evaluate the effect of noise
on cetaceans. Because whales produce sound for echolocation or
communication, there has been concern that noise created by commercial
activity might disrupt the behavior of some whales. In a study off the
coast of Monterey, California, migrating gray whales showed short‑term
avoidance behavior at sound levels of 110 to 130 decibels (dB) (Malme et
al. 1984). A Standardized Exposure Rating Model was developed for
potential responses to offshore oil and gas development noise exposure.
The predicted noise level required for a 50 percent probability of
avoidance response in gray whales was 117 to 125 dB at a distance of 985
feet (300 m) from the noise source. The types, spectra, and volume of
noise generated by oil and gas construction activities would differ
substantially from that expected for the outfall project, although
underwater noise and shock waves are anticipated.

A summary of cetaceans stranded in San Diego County was compiled by
National Marine Fisheries Service (NMFS) Southwest Fisheries Center for
the 20‑year period from 1966 to 1986 (Bernard et al. 1988). Common
dolphin and bottlenose dolphin were most frequently stranded. Gray
whales were stranded at the rate of about one a year (Table 3.5‑2).
Based on analysis of tissues taken from marine mammals stranded in the
Southern California Bight, high levels of contaminants were found
(Schafer et al. 1984). Highest contaminants were found in blubber
tissue. Concentrations of 2,070 ppm total DDT (wet weight) and 128 ppm
PCB were present in bottlenose dolphin. Other studies found even higher
levels (2,695 ppm DDT and 400 ppm PCB) in stranded Dall\'s porpoise
(Phocoenoides dalli) (O\'Shea et al. 1980). Efforts to link high
contaminants in stranded animals with specific sources of contaminants
have not proven possible, as cetaceans have large home ranges. However,
there may be a correlation between diet and contaminant levels.
Bottlenose dolphin, for example, feed on fish that are known to have
high levels of contaminants, such as white croaker.

Six species of pinnipeds (seals and sea lions) may be found in the
Southern California Bight (Bonnel 1985). Pinnipeds reproduce on land and
also &quot;haul out&quot; to rest for various periods of time. The
nearest hauling grounds for pinnipeds are the Coronado Islands,
approximately 7.5 miles (12 km) south of the international border. These
islands are considered minor hauling grounds for California sea lions,
harbor seals (Phoca vitulina), and northern elephant seals (Mirounga
angustirostris). They prey principally on schooling fish and squid.
California sea lion is the most abundant species, accounting for 50 to
90 percent of all pinnipeds (Bonnel et al. 1981).

TABLE 3.5‑2

MARINE MAMMALS OBSERVED OR STRANDED FROM 1966 TO 1986

Common Name Species Observed Stranded

gray whale Eschrichtius robustus 261 23

Risso\'s dolphin Grampus griseus 76 2

common dolphin Delphinus delphis 52 122

California sea lion Xalophus californianus 50 0

white‑sided dolphin Lahenorhynchus 13 23 obliquidens

bottlenose dolphin Tursiops truncatus 2 42

blue whale Balaenoptera musculus 2 1

spinner dolphin Stenella longirostris 2 0

false killer whale Pseudoorca crassidens 2 0

pilot whale Clobicephala sp. 2 0 (melaena)

Dall\'s porpoise Phocoenoides dalli 1 9

Brydes\'s whale Balaenoptera edem 1 0

beaked whale Mesoplodon sp. 1 0

harbor seal Phoca vitulina 1 0

elephant seal Mirounga angustirostris 1 0

N. right whale Lissodelphis borealis 1 3 dolphin

right whale Balaena glacialis 1 0

Hector\'s beaked Mesoplodon hectori 0 4 whale

Pacific pilot whale Glabicephala 0 4 macrorhyncus

long‑beaked dolphin Stenella coeruleolaba 0 3

Cuvier\'s beaked Xiphius cavirostris 0 2 whale

finback whale Balaenoptera physalus 0 2

pygmy sperm whale Kogia breviceps 0 2

humpback whale Megaptera novaeangliae 0 1

Hubb\'s beaked whale Mesoplodon carlhubbsi 0 1

sperm whale Physter macrocephalus 0 1

minke whale Balaenoptera 0 1 acutorostrata

unidentified 0 1 mystecete

unidentified 0 1 delphinid

TOTAL 469 248

Sea lions are most abundant during summer and autumn, while elephant
seals and harbor seals are most abundant in winter and spring. The San
Diego basin is used as a foraging area by a few animals associated with
the Coronado Islands\' rookery. It may also be part of a migratory route
used by animals from Mexican colonies moving to and from the islands in
the Southern California Bight (Bonnel et al. 1981).

Marine Birds

The seabird fauna of the Southern California Bight is comprised of
approximately 80 species (excluding shorebirds), only 30 of which are
relatively numerous (Bender et al. 1974; Briggs et al. 1981). Nearly
half of the species are winter visitors, present principally from
October through April. These include loons, grebes, sea ducks, gulls,
terns, jaegers, and alcids (murres, auklets, and puffins). A few species
are transients, and a small number of strays are recorded each year.
Subtropical species in particular may arrive in late summer and autumn,
swelling the avifauna diversity.

Six species are summer visitors: three nest to the south in Baja
California, two nest in the Southern Hemisphere and spend their winter
in southern California, and sooty shearwaters (Puffinus griseus) are
summer visitors. Year‑round visitors do not

breed in southern California but can occur somewhere in the bight at any
time of year. Three species, California least tern (Sterna antillarum),
caspian tern (Sterna caspia), and elegant

tern (Sterna elegans), nest on mainland beaches and in

estuaries. Eleven species regularly nest on the Channel Islands, seven
of which are year‑round residents of the bight. Seabird abundance
differs with habitat: 50 to 95 percent of birds were associated with
open water, 5 to 10 percent with mainland beaches, and 1 to 4 percent
with island beaches.

Many seabirds exhibit nest site fidelity, and nesting areas tend to be
located near predictable, seasonal food supplies (Table 3.5‑3). However,
they are also likely to follow their food supply, which consists
primarily of fish, squid, shrimp, and other crustaceans. Three seabird
nesting colonies occur in or near the South Bay area (nesting sites in
Baja California were not included) (Sowls et al. 1980). Three sites for
California least tern, a federal‑ and California‑listed endangered
species, occur in Mission Bay, north San Diego Bay, and near the Tijuana
River mouth. Western gulls also nest in San Diego Bay.

Stranded seabirds found on South Bay beaches showed that approximately
10 percent were oiled (Briggs et al. 1981; Ainley and Bontrager 1981).
Most were found in early winter, and most were Brandt\'s cormorants
(Phalacrocorox penicillatus) and western gulls

(Larus occidentalis). Generally, the trends were consistent with the
species\' breeding, wintering, and migratory habits.

Shorebirds also use the shores and waters of the South Bay area. Most
available information on shorebirds is based on surveys in coastal
lagoons, marshes, and mud flats, but they may also feed on adjacent
beaches (Table 3.5‑4). Two protected habitats, south San Diego Bay and
the Tijuana estuary, are immediately adjacent to the South Bay.

TABLE 3.5‑3

COMMON SEABIRDS OF THE SOUTHERN CALIFORNIA BIGHT

Bird Group/Common Name Scientific Name Status

Loons and Grebes

common loon Gavia immer FLR

Arctic loon Gavia arctica FLR

red‑throated loon Gavia stellata FLR

horned grebe Podiceps auritus FR

eared grebe Podiceps nigricollis F

western grebe Aechmophorus occidentalis F

red‑necked grebe Podiceps grisegena F

pied‑billed grebe Podilymbus podiceps X

Shearwaters and Petrels

northern fulmar Fulmarus glacialis F

sooty shearwater Puffinus griseus F

Pelicans and Cormorants

brown pelican Pelecanus occidentalis F

white pelican Pelecanus erythrorhynchos X

double‑crested cormorant Phalacrocorax auritus F

Brandt\'s cormorant Phalacrocorax penicillatus F

pelagic cormorant Phalacrocorax pelagicus F

Herons

great blue heron Ardea herodias F

Geese, Scoters, Mergansers, and Ducks

brant Branta bernicla X

surf scoter Melanitta perspicillata FLR

white‑winged scoter Melanitta fusca deglandi FLR

black scoter Melanitta nigra FLR

common merganser Mergus merganser F

red‑breasted merganser Mergus serrator F

green‑winged teal Anas crecca X

greater scaup Aythya marila F

lesser scaup Aythya affinis F

bufflehead Bucephala albeola F

oldsquaw Clangula hyemalis F

ruddy duck Oxyura jamaicensis X

Phalaropes

northern phalarope Phalaropus lobatus F

red phalarope Phalaropus fulicaria F

TABLE 3.5‑3

COMMON SEABIRDS OF THE SOUTHERN CALIFORNIA BIGHT

(continued)

Bird Group/Common Name Scientific Name Status

Gulls, Terns, and Jaegers

parasitic jaeger Stercorarius parasiticus F

glaucous‑winged gull Larus glaucescens F

western gull Larus occidentalis X

herring gull Larus argentatus X

Thayer\'s gull Larus thayeri X

California gull Larus californicus F ring‑billed gull Larus delawarensis
X

mew gull Larus canus F

Heermann\'s gull Larus heermanni FL

Bonaparte\'s gull Larus philadelphia F

Franklin\'s gull Larus pipixcan

blacked‑legged kittiwake Rissa tridactyla F

common tern Sterna hirundo F

Caspian tern Sterna caspia F

elegant tern Sterna elegans F

Forster\'s tern Sterna forsteri F

least tern Sterna antillarum F

black tern Chlidonias niger

royal tern Sterna maxima F

Murres, Auklets, and Puffins

common murre Uria lomvia FLR

pigeon guillemot Cepphus columba F

Xantus\' murrelet Synthliboramphus hypoleucus F

Craveri\'s murrelet Synthliboramphus craveri F

ancient murrelet Synthliboramphus antiquus F

Cassin\'s auklet Ptychoramphus aleuticus F

rhinoceros auklet Cerorhinca monocerata F

tufted puffin Fratercula cirrhata F

F ‑ feeding or foraging

L ‑ loafing

R ‑ roosting

X ‑ unknown activities

TABLE 3.5‑4

SHOREBIRDS OBSERVED

ON SANDY BEACHES NEAR TIJUANA ESTUARY

Bird Group/ Common Name Scientific Name 1989 1990

Plovers, Turnstones, and Surfbirds

western snowy plover Charadrius alexandrinus + + nivosus

semipalmated plover Charadrius semipalmatus + +

black‑bellied plover Pluvialis squatarola + +

ruddy turnstone Arenaria interpres +

Sandpipers

long‑billed curlew Numenius americanus +

whimbrel Numenius phaeopus + +

marbled godwit Limosa fedoa + +

sanderling Calidris alba + +

western sandpiper Calidris mauri + +

white‑rumped Calidris fuscicollis + sandpiper

dunlin Calidris alpina + +

Shorebirds feed on a variety of prey, including mol‑lusks (clams,
snails), worms, crustaceans (crabs, amphipods, isopods), insects (adults
and larvae), and other invertebrates. They feed by capturing visible
prey, probing in the sand for buried organisms, or prying open sessile
organisms on rocks.

The majority of coastal shorebirds are migratory and are typically
absent in summer. However, a few‑such as western snowy plover (federally
listed threatened), long‑billed curlew (California species of concern),
black oystercatcher (Haematopus bachmani), whimbrel, and marbled
godwit‑are present year‑round and may breed locally. The most abundant
species include western sandpiper (Calidris mauri), least sandpiper
(Calidris minutilla),

dowitchers, willet, marbled godwit, American avocet (Recurvirostra
americana), sanderling, and semipalmated plover (Charadrius
semipalmatus) (Warnock et al. 1989). Seabirds, such as gulls, terns, and
pelicans, may use the same habitats as shorebirds for resting and
nesting.

Endangered, Threatened, and Other Species of Special Concern

The South Bay area potentially contains a large number of species which
are considered to be of concern because of loss of breeding habitat,
reduction or contamination of food supply, or other impacts from human
activities (Table 3.55). Thirteen species are listed as endangered by
the federal government and five by the State of California. Four species
are federally listed as threatened and one is state‑listed. In addition,
nine species are listed as species of special concern by the federal
government or the state.

California brown pelican populations declined in the 1950s and 1960s due
to eggshell thinning caused by high body burdens of chlorinated
hydrocarbon compounds, especially DDT. With reductions in DDT discharges
to the marine environment, brown pelicans have rebounded and are
currently limited in southern California by availability of prey,
principally anchovies (Southern California Association of Governments
1988).

California least terns nest on salt flats of southern San Diego Bay and
on dunes of the nearby beaches. In 1995, about 500 pairs nested in this
area, fledging about 250 young; 225 pairs nested on the beach near the
Tijuana River mouth, fledging 60 young (Jurek, pers. com. 1996). Least
terns forage for small fish in the estuary and shallow nearshore waters,
but conditions in the estuary, such as closure of the entrance to tidal
flushing, appear to strongly affect nesting success (Zedler et al.
1992).

Western snowy plovers nest in the same habitat as least terns, but
forage for small insects and crustaceans along the shorelines of the
Tijuana estuary and South Bay. Snowy plover populations along the entire
coast have been declining, prompting their recent listing. In the past,
about 100 nesting pairs were typically seen on the dunes and beaches
around the Tijuana River mouth.

TABLE 3.5‑5

THREATENED AND ENDANGERED SPECIES

Marine Mammals Status Birds Status Sea Turtles Status

blue whale FE American peregine FE,CE green sea FE falcon turtle

finback whale FE Belding\'s savannah CE leather‑backed FE sparrow turtle

Guadalupe fur FT,CT California black rail CT loggerhead sea FT seal
turtle

humpback whale FE California brown FE,CE Pacific ridley FE pelican

Pacific right FE California least tern FE,CE whale

Sei whale FE light‑footed clapper FE,CE rail

southern sea FT southern bald eagle FE,CE otter

sperm whale FE western snowy plover FT

longbilled curlew CSC

common loon CSC

doubled‑crested CSC cormorant

northern harrier CSC

osprey CSC

California gull CSC

black skimmer CSC

elegant tern CSC

gull‑billed tern CSC

FE: federally listed endangered

FT: federally listed threatened

CE: California‑listed endangered

CT: California‑listed threatened

CSC: California species of concern

By 1990, only 10 nesting pairs were counted, and in 1991, only four
adults were seen in the spring (Page and Stenzel 1981; Page et al.
1991). Counts at Rosarito Beach in Baja California also were declining
(Page et al. 1986). Regular surveys for snowy plovers began in 1994.
Five nests were laid near the Tijuana River mouth in 1994, but no young
fledged; in 1995, 11 nest fledged a total of seven young (Powell, pers.
com. 1996). An average of 18 snowy plovers were seen in the winter
surveys of 1994‑1995 and 23 in 1995‑1996. In the case of both California
least terns and western snowy plovers, disturbance of the habitat by
human activities is a major factor in nesting success.

Areas of Biological Significance

Five areas adjacent to South Bay are protected: Point Loma Ecological
Preserve, Cabrillo National Monument, Tijuana River Estuary Sanctuary,
Tijuana Slough National Wildlife Refuge, and Border Field State Park and
National Wildlife Refuge. All of these extend into tidal waters.

Geological Resources

Adverse environmental effects from the construction and operation of the
IWTP and land and ocean outfall as designed were considered in the 1995
Final EIS. This SEIS addresses the potential impacts of several interim
discharge alternatives of advanced primary effluent for a limited period
of time resulting from operation of the IWTP. The following discussion
is a summary of the geology of the river valley and ocean floor in the
vicinity of the ocean outfall taken from an engineering report prepared
by Woodward‑Clyde in the Engineering Science Conceptual Design Reports,
prepared and updated in 1992 and 1993. This document is hereby
incorporated by reference, pursuant to Section 1502.21 of the Council on
Environmental Quality (CEQ) Guidelines.

Regional Geology

The project area is located within the coastal plain geomorphic
subprovince of the Peninsular Range province. This nearly
rectangular‑shaped coastal plain is characterized by a series of
wave‑cut terraces which extend inland for approximately 10 miles (16
km). These terraces have been dissected by various rivers forming a
series of wide alluvium‑filled valleys. The Tijuana River valley, formed
by the Tijuana River, is typical of these alluvium‑filled valleys.
Alluvial soils found within these valleys consist primarily of poorly
consolidated stream deposits of silt, sand, and cobble‑sized particles
originating from bedrock sources in the vicinity.

The river valley and nearshore geology are a result of changes in sea
level and fluvial processes. About 18,000 to 20,000 years ago, sea level
was approximately 280 feet (85.4 m) lower than today. Major river
channels draining west cut into the coastal plain. As sea levels rose,
the river courses backfilled their channels with sediments. At the same
time, during rising sea levels erosional retreat and coastal processes
resulted in broad depositions of sand across the inner shelf. The
paleochannel of the river extends out about 10,000 feet (3 km) from the
shoreline parallel to the south rim of the present river valley and then
trends southerly.

The geologic setting of the river valley is characterized by broad
alluvium deposits. Underlying the alluvium and exposed in the bluffs of
the Border Highlands to the south and east are Tertiary‑age deposits of
the San Diego Formation. The Tertiary‑age sediments are estimated to
range in thickness from 3,000‑4,000 feet (915‑1,220 m) at the mouth of
the Tijuana River. This formation is locally underlain by a thin veneer
of early Pleistocene nonmarine sediments of the Lindavista Formation,
deposited on the upper terraces. Lower terraces are mantled by late
Pleistocene deposits of the Bay Point Formation that also overlie the
San Diego Formation.

In general, the geologic setting of the offshore area can be thought of
as a broad cover of unconsolidated, fine‑grained late Pleistocene to
Holocene sediment that varies in depth with relation to the position of
the paleochannel. The deeper portions of the unconsolidated sediments
within the channel are fluvial, whereas the upper sediments have been
transported and redeposited by waves and currents. The consolidated
formations underlying the unconsolidated sediments offshore are thought
to be comprised of generally the same Tertiary and Quaternary
sedimentary formations as the uplands flanking the river valley.

Local Faulting

The project area is within a seismically active region subject to the
effects of moderate to large earthquake events along major faults. The
regional faults that may affect the project area include the Rose
Canyon, Coronado Bank, Coronado Shelf, Elsinore, San Jacinto, and San
Andreas faults. Those faults nearest to the project area are the Rose
Canyon, Coronado Banks, Coronado Shelf, and Silver Strand (Figure
3.6‑1).

The Rose Canyon fault is a north‑to‑northwest‑trending, complex zone of
onshore and offshore faults. It extends across the San Diego Bay and end
of Mission Bay before continuing up Rose Canyon and out to sea north of
La Jolla approximately 14 miles (22.5 km) north of the project vicinity.
The offshore Rose Canyon fault zone includes many small‑ to
medium‑length faults. The actual number is not well known; however, they
are presumed to be in the area of the proposed ocean outfall.

A secondary extension of the Rose Canyon fault zone complex is known as
the La Nacion‑San Ysidro fault zone and extends north and northeast of
the Tijuana River valley. Mapped fault traces also extend south into
Mexico as the Los Buenos faults. These faults are last identified as
active during the late Pleistocene and are considered potentially
active.

The Coronado Bank fault zone is located approximately 7.5 miles (12 km)
offshore. It is a complex zone of faults and folds thought to extend
onshore in the Los Angeles and Ensenada areas. Various faults within
this fault zone are thought to be active (based on Holocene‑age
displacement of sediments near the ocean floor).

The Coronado Shelf fault zone is located about 2.5 miles (4 km) west of
the outfall end and consists of a series of northwest‑trending faults
which extend from several miles southwest of the tip of Point Loma to
the area several miles offshore from Tijuana. The zone of faults appears
to consist of two relatively continuous strands which extend about 10
miles (16 km) across the inner shelf off San Diego.

The Silver Strand fault is the principal fault in the study area. The
activity of this fault is based on seismic reflection data; however,
much existing data suggest a strong possibility of Holocene faulting,
which is consistent with the repeated Holocene activity seen on the
adjoining onshore segment of the Rose Canyon fault zone to the north.

Figure 3.6‑1

Historical Seismicity

The historical seismicity of the San Diego area within a 50‑mile (80 km)
radius is low, with only a limited number of small earthquakes having
been reported since early mission days (late 1700s). Some strong shaking
and minor damage has been experienced in San Diego, but none of the
events have been very destructive because the earthquakes originated at
long distances from San Diego, generally from locations in the Imperial
Valley or northern Baja California. Earthquakes in 1800, 1862, and 1892
appear to have had the strongest intensities in downtown San Diego.
These earthquakes are estimated to have been a maximum Modified Mercalli
(MM) intensity of VII, VI‑VII, and VI, respectively. Recently,
seismographs have recorded many small to moderate magnitude earthquakes
in the area. The largest earthquake occurred in July 1986 (magnitude
5.3). In conclusion, based on historical records of earthquake activity,
the seismic hazard in coastal San Diego is difficult to quantify.

The Rose Canyon fault zone is the closest major active fault zone.
Estimates of the maximum potential earthquake range from magnitude 6.5
to 7.25, with a maximum 7.0 earthquake typically considered in local
seismic hazard evaluations. Significant traces of the Rose Canyon fault
zone are mapped at distances ranging from about 0.5 mile to about 3
miles (0.8‑4.8 km) from the project area. Recent probabilistic seismic
hazard analyses for the San Diego‑Tijuana coastal region indicated that
the level of seismic shaking associated with a 10 percent probability of
exceedance for a 75‑year period ranges from about 0.45 g to 0.48 g.

Seafloor Conditions

About 20 to 40 feet (61 to 12.2 m) of finer‑grained sands, silts, and
sparse clay layers underlie the eastern two‑thirds of the ocean outfall
alignment. A varying thickness of up to 40 feet of gravelly and sandy
alluvial deposits underlies the upper material. Varying depths of deeper
unconsolidated sediments underlie the sandy layers. These soils are
subject to liquefaction and settlement due to ground shaking and
significant wave height. Tertiary sediments of the San Diego Formation
are found at depths of approximately 115 feet (35 m).

Public Health

Background

As discussed previously in the 1994 FEIS, the Tijuana River is highly
contaminated by continuing spills from the Tijuana sewerage system and
by drainage of sewage from large populated areas within the city of
Tijuana that are not served by any sewer system. Sewage flows from
Tijuana have been reduced since 1991 and the conditions that currently
exist in the valley have improved. However, continuing sewage flows pose
environmental and health concerns, including vector‑borne disease.

Beach Quarantines

Discharge of untreated or treated sewage into the marine environment may
cause a variety of public health risks including bacteria, viruses, and
toxic or carcinogenic constituents. Water quality criteria for marine
waters are defined by the State Water Resources Control Board (SWRCB) in
the Water Quality Control Plan: Ocean Waters of California (State of
California 1990a), known as the Ocean Plan. Of greatest concern are
pathogenic organisms (bacteria and viruses), as their effects may lead
to direct harm to humans. Concerns for the effects of toxics, metals,
and carcinogens that may be discharged with sewage or treated effluent
are usually directed to marine biota and would be harmful to humans
through uptake in food sources.

Pathogens may be natural inhabitants of seawater (autochthonous) or
introduced through sewage or other means to the marine environment. Both
varieties of bacteria can affect human health. Autochthonous bacteria
are not present in sewage or effluent, but their existing concentrations
can be increased by the discharge of elevated levels in treated
effluent. Risks associated with autochthonous bacteria include
infections of the ear, swimmer\'s itch, and, potentially,
gastroenteritis. These complaints are typically due to contact between
bathers in the water and not ingestion of water (Kalichman and Conway
1989).

Allochthonous pathogens are discharged with wastewater into the marine
environment and can affect humans through ingestion or skin contact or
by consumption of fish or shellfish. Bacteria such as salmonella,
streptococci, and enterococci; enteric, rota, and parvo viruses; and
protozoa and helminths are all of concern (EPA 1985). Enterococci is
most strongly associated with complaints of gasroenteritis but fecal
coliforms and Norwalk virus are also indicated (Cabelli et al. 1983).

The bacterial standards vary somewhat based upon beneficial uses, with
body contact zones, defined as the area within 1,000 feet (304.8 m) of
the shoreline or 30 feet (9.1 m) of water depth and kelp beds, having
the most stringent requirements. The water contact standards provide
that the density of total coliform organisms must not exceed 1,000 per
100 ml for more than 20 percent of samples in any 30‑day period (or
10,000) and that fecal coliforms may not exceed a geometric mean of 200
per 100 ml in any 5 samples during a 30‑day period nor exceed 400 fecal
coliforms per 100 ml in 10 percent of samples taken during a 60‑day
period.

The San Diego County Department of Health Services has data regarding
violations of the bacteriological standards on South County beaches.
From 1980 to 1991, approximately two miles (1.2 km) of beach (from the
international border to the south end of Seacoast Drive) have been under
almost continuous quarantine due to violations of total coliform
standards. The intent of the quarantine is to reduce exposure and thus
risk to public health. The Department of Health Services has also
occasionally quarantined beaches as far north as Coronado, prior to 1985
(Melbourn, pers. com. 1991). Once the river diversion structure was
installed by Mexico in 1991, the quarantines were placed on an
intermittent basis north of the mouth of the river, extending as far as
the Silver Strand.

In addition to the public health threat caused by sewage‑contaminated
river flows, limited monitoring studies performed by Engineering Science
in 1991 resulted in data which indicate that the beach discharge of
effluent from the San Antonio de los Buenos treatment plant may result
in exceedances of water quality standards in U.S. waters (Engineering
Science 1991). Effluent discharged onto the beach travels northward with
the nearshore ocean current. Sampling in Mexico near the U.S./Mexico
border has shown that the total coliform standard in the Ocean Plan
would have been exceeded 58 percent of the time.

Parsons Engineering Science has conducted a recent study of the probable
effects of the discharge of untreated sewage in Mexico with respect to
bacterial concentrations along the coastline from south of the discharge
point in Mexico to Coronado. As part of their study, records of
monitoring of bacterial levels at various locations in the U.S. and
Mexico were compiled. These data were collected from various sources,
including the County of San Diego, City of San Diego, and IBWC.

The available data, while extremely limited, indicate that ocean
standards would be violated as far north as the beaches of Imperial
Beach and the kelp bed offshore from the discharge in Mexico.

Other sources of bacterial contamination to coastal waters exist,
however (storm flows, urban runoff, sewer breaks in the U.S., etc.), and
the frequency and relative contribution of the various sources have not
been determined or the individual significance evaluated. Standards for
water quality for human health and safety are established in the Water
Quality Control Plan for the San Diego Region (Basin Plan). The Tijuana
River is designated for non‑body contact recreation. Bacterial
concentrations for any 30‑day period shall not exceed 2,000 fecal
coliforms per 100 ml and shall not exceed 4,000 per 100 ml for 10
percent of samples taken in a 30‑day period. Mexico has committed to
ensuring that the quality of the Tijuana River and U.S. ocean waters
will be maintained.

Vectors

The Tijuana River valley is host to at least 14 of 24 mosquito species
known to occur in San Diego County, including those capable of
transmitting diseases. The lack of adequate water drainage and waterway
maintenance and the constant flow of wastewater into the Tijuana River
valley has created an environment where mosquito breeding is rampant.

There are several issues which must be considered when assessing vector
problems in the Tijuana River valley. Basic considerations include the
physical features (water quality, topography, and groundwater
hydrology), the augmented surface flows resulting from sewage from
Mexico, chemical features associated with the sewage flows (stimulation
of excessive plant growth and deleterious effects on mosquito fish and
other aquatic vertebrates and invertebrates), and the constraints from
environmental regulation on mosquito breeding prevention.

Natural and man‑made obstructions divert the sewage flows, resulting in
the flooding of large areas overgrown with vegetation. This creates
ideal breeding conditions for mosquitoes; mosquitoes that act as vectors
in the transmission of malaria occur in significant numbers. Mosquitoes
that act as vectors in the transmission of viral encephalitis (sleeping
sickness) have been counted in greater numbers in the Tijuana River
valley than anywhere else in San Diego County. These mosquito
populations are highest during the summer months.

These conditions have also reduced the effectiveness of predators, both
introduced and natural. High biological oxygen demand and ammonia in
wastewater can stress or eliminate fish and insects which feed on
mosquitoes. The access of natural avian predators that normally feed on
mosquito larvae and adults is inhibited by dense vegetation.

San Diego County Mosquito Abatement Program

No cases of viral encephalitis or malaria have been documented within
the Tijuana River valley, though all of the parameters necessary for
transmission of these vector‑borne diseases are present. To prevent
potential outbreaks of these diseases through vector‑borne disease
transmission, the County Environmental Health Services has engaged in
various mosquito abatement programs. These programs have included
stocking ponds with mosquito fish, placing larvaecidal oil on bodies of
standing water, and spraying with chemicals agents. None of these
measures have resulted in substantial reductions in the mosquito
population. Fogging with chemical sprays has not proved effective due to
the dense vegetation which limits access by truck‑mounted or hand‑held
fogging equipment and which prevents dispersion of the fog. Aerial
spraying would be ineffective for the same reason. In addition, concerns
have been raised by USFWS regarding the effects of chemical spraying on
least Bell\'s vireo, a federally listed endangered species, and on the
ecological system in general.

Public Concerns

The vast majority of the comments raised by the public at the public
scoping meeting focused on concerns that the wastewater flowing through
the Tijuana River valley posed a significant public health risk.
Residents complained that mosquitoes were a year‑round problem that
posed a major health hazard to themselves, their children, and their
pets. Many indicated that children were not allowed outside after dusk,
to prevent mosquito bites that may result in malaria or encephalitis.
They strongly voiced the need for an immediate solution to the problem,
including aerial spraying of pesticides and channelizing the river or
other solutions that would allow water to flow more freely. Commenters
also indicated that the IWTP was the only long‑term solution to this
problem, but that it was taking too long to implement.

Hazardous Materials/ Risk of Operational Upset

A Risk Management Prevention Plan (RMPP) is required by the County
health department for any facility in which hazardous substances will be
used during operations. The RMPP must include procedures for the
handling, storage, and use of listed substances; employee training and
safety procedures; and procedures to be followed in event of a spill or
other accidental release.

If an emergency involving hazardous materials were to occur, the Hazmat
Response Team (three trained personnel and a response vehicle) would
respond. Emergency vehicles would be provided direct access to the
project site by taking Interstate 5 to Dairy Mart Road. The site is
located south of both Interstate 5 and the intersection of Monument and
Dairy Mart Roads. Existing land uses surrounding the site include rural
residential, agriculture, and open space uses. The community plan
designates the treatment plant site and lands to the north and east for
agricultural use. Immediately west of the site, land is designated for
commercial recreation. The Mexican border lies within 300 feet (91.4 m)
of the site\'s southern boundary.

Air Quality and Odors

Climate

The project area, like the rest of San Diego County\'s coastal areas,
has a cool semiarid steppe climate characterized by warm, dry summers
and mild, wet winters. The dominating permanent meteorological feature
affecting the region is the Pacific High Pressure Zone, which produces
the prevailing westerly to northwesterly winds. The project area has a
mean annual temperature of 62 degrees Fahrenheit (&#176;F) (16.7 degrees
Celsius \[&#176;C\]) and an average annual precipitation of 9.5 inches
(24.1 cm), falling primarily from November to April. Winter low
temperatures in the project area average about 45 &#176;F (7.2 &#176;C),
and summer high temperatures average about 75 &#176;F (23.9 &#176;C)
(U.S. Department of Commerce 1992; Pryde 1976).

Prevailing conditions along the coast are modified by the daily sea
breeze/land breeze cycle. Fluctuations in the strength and pattern of
winds from the Pacific High Pressure Zone interacting with the daily
local cycle produce periodic temperature inversions that influence the
dispersal or containment of air pollutants in the San Diego Air Basin
(SDAB). The afternoon temperature inversion height, beneath which
pollutants are trapped, varies between 1,500 and 2,500 feet (457 and 762
m) above MSL. The altitude beneath the inversion layer is the mixing
depth for trapped pollutants. In winter, the morning inversion layer is
about 800 feet (244 m) above MSL. Project area elevations range from sea
level to an approximate high of 45 feet (13.7 m) above MSL. In summer,
the morning inversion layer is about 1,100 feet (335 m) above MSL. A
greater change between morning and afternoon mixing depth increases the
ability of the atmosphere to disperse pollutants. Generally, therefore,
air quality in the project area is better in winter than in summer.

The predominant pattern is sometimes interrupted by the socalled Santa
Ana conditions, when high pressure over the NevadaUtah area overcomes
the prevailing westerlies, sending strong, steady, hot, dry
northeasterly winds over the mountains and out to sea. Strong Santa Anas
tend to blow pollutants out over the ocean, producing clear days.
However, at the onset or breakdown of these conditions, or if the Santa
Ana is weak, air quality may be adversely affected. In these cases,
emissions from the South Coast Air Basin to the north are blown out over
the ocean, and low pressure over Baja California draws this
pollutantladen air mass southward. As the high pressure weakens,
prevailing northwesterlies reassert themselves and send this cloud of
contamination ashore in the SDAB. There is a potential for such an
occurrence about 45 days of the year, but San Diego is adversely
affected on only about 5 of them. When this event does occur, the
combination of transported and locally produced contaminants produces
the worst air quality measurements recorded in the basin.

Regulatory Framework

The federal Clean Air Act was enacted in 1970 and amended in 1977 and
1990 \[42 U.S.C. 7506(c)\]. In 1971, the EPA promulgated national
ambient air quality standards. The six pollutants of primary concern for
which national standards have been established are sulfur dioxide, lead,
carbon monoxide, nitrogen dioxide, ozone, and suspended particulate
matter (PM‑10).

The EPA allows the states the option to develop different (stricter)
standards, which the California Air Resources Board (CARB) has adopted.
Table 3.8‑1 lists the federal and California state standards.

TABLE 3.8‑1

AMBIENT AIR QUALITY STANDARDS

Maximum Concentration Averaged over Specified Time Period

Pollutant State Federal Standard Standard

Oxidant (ozone) 0.09 ppm 0.12 ppm (180 mg/m3) (235 mg/m3) 1 hr. 1 hr.

Carbon monoxide 9.0 ppm 9 ppm (10 mg/m3) (10 mg/m3) 8 hr. 8 hr.

Carbon monoxide 20.0 ppm 35.0 ppm (23 mg/m3) (40 mg/m3) 1 hr. 1 hr.

Sulfur dioxide 0.04 ppm 0.03 ppm (105 mg/m3) (80 mg/m3) 24 hr. Annual
Average

Nitrogen dioxide 0.25 ppm 0.053 ppm (470 mg/m3) (100 mg/m3) 1 hr. Annual
Average

Lead 1.5 mg/m3 1.5 mg/m3 30‑day Calendar Average Quarter

Suspended particulate matter 50 mg/m3 150 mg/m3 (PM‑10) 24 hr. 24 hr.

SOURCE: State of California 1994.

ppm = parts per million; mg/m3 = micrograms per cubic meter.

The San Diego Air Pollution Control District (APCD) is the agency which
regulates air quality in the SDAB. The APCD has prepared the updated
1991/1992 Regional Air Quality Strategies (RAQS) in response to the
requirements set forth in Assembly Bill (AB) 2595. The updated draft was
adopted, with amendments, on June 30, 1992 (County of San Diego 1992).
The required triennial update of the RAQS was adopted on December 12,
1995. The RAQS and transportation control measures (TCM) plan set forth
the steps needed to accomplish attainment of state and federal ambient
air quality standards.

The APCD has also established a set of rules and regulations initially
adopted on January 1, 1969, and periodically reviewed and updated. The
rules and regulations define requirements regarding stationary sources
of air pollutants and fugitive dust.

Existing Air Quality

The project area is within the SDAB. Air quality at a particular
location is a function of the kinds and amounts of pollutants being
emitted into the air locally and throughout the basin and the dispersal
rates of pollutants within the region. The major factors affecting
pollutant dispersion are wind speed and direction, the vertical
dispersion of pollutants (which is affected by inversions), and the
local topography.

Air quality is commonly expressed as the number of days in which air
pollution levels exceed state standards set by the CARB and federal
standards set by the EPA (see Table 3.8‑1). The concentration of
pollutants within the SDAB is measured at 10 stations maintained by the
APCD and the CARB. The station nearest the project area measuring a full
range of pollutants is in Chula Vista. This station does not monitor
lead concentrations. However, the 1993 lead levels measured at other
monitoring stations in the SDAB were well below both federal and state
standards.

Table 3.8‑2 summarizes the number of days annually from 1989 to 1993
during which state and federal standards were exceeded in the SDAB
overall, while Table 3.8‑3 lists these data for the Chula Vista
monitoring station.

TABLE 3.8‑2

SUMMARY OF AIR QUALITY DATA

FOR THE SAN DIEGO AIR BASIN

Number of Days Over Standard

State Federal

Pollutant 1989 1990 1991 1992 1993 1989 1990 1991 1992 1993

Oxidant 158 139 106 97 89 55 39 27 19 14 (ozone)

Carbon 6 1 0 0 0 6 0 0 0 0 monoxide

Sulfur dioxide 0 0 0 0 0 0 0 0 0 0

Nitrogen 0 0 0 0 0 0 0 0 0 0 dioxide

Lead 0 0 0 0 0 0 0 0 0 0

Particulates 28/75 11/80 20/83 7/75 14/76 0/75 0/80 0/83 0/75 0/76
(PM10)\*

SOURCE: State of California 1990b, 1991, 1992, 1993, 1994b.

\*Number of samples over standard/number of samples collected.

Table 3.8‑3

Ozone

The air basin is currently designated a state &quot;serious&quot;
nonattainment area and a federal &quot;serious&quot; nonattainment area
for ozone. Even though peak ozone concentrations have steadily declined
since 1978 (SANDAG 1994), in 1991, 1992, and 1993, the SDAB exceeded the
federal ozone standard on 27, 19, and 14 days, respectively. During the
same three years, the state ozone standard was exceeded on 106, 97, and
89 days, respectively.

Ozone presents special control strategy difficulties in the SDAB because
of climatological and meteorological factors. Ozone is the end product
of the chain of chemical reactions that produces photochemical smog from
hydrocarbon emissions. A major source of hydrocarbon emissions is motor
vehicle exhausts. In the SDAB, only part of the ozone contamination is
derived from local sources; under certain conditions, contaminants from
the South Coast Air Basin (such as the Los Angeles area) are windborne
over the ocean into the SDAB. When this happens, the combination of
local and transported pollutants produces the highest ozone levels
measured in the basin.

At the Chula Vista station, the federal standard was exceeded on 1 day
in September and the state standard for ozone was exceeded on 12 days in
1993.

In 1992, pollution transported from the Greater Los Angeles area was
responsible for 11 out of 19 days over federal standards. On average,
approximately 42 percent of the days over state standards since 1987
were attributable to pollution transported from Los Angeles (SANDAG
1994:249‑250). The 1994 Regional Transportation Plan concludes that
ozone remains the major primary pollutant in the San Diego region.

Local agencies can control neither the source nor the transportation of
pollutants from outside the basin. The APCD\'s policy, therefore, has
been to control local sources effectively enough to reduce locally
produced contamination to clean air standards.

Carbon Monoxide

No violations of the state standard have been recorded for carbon
monoxide since 1990 and the basin is classified as a state attainment
area for carbon monoxide. The basin currently is classified as a federal
nonattainment area for carbon monoxide; however, no violations of the
federal standard have been recorded since 1989. The APCD is currently in
the process of applying for reclassification of the basin as a federal
attainment area for carbon monoxide. Moreover, it should be noted that
the state standard for carbon monoxide is more stringent than the
federal standard.

Particulates (PM‑10)

Particulates within the respirable range (10 microns in size or less)
are reported as both an annual average and a 24‑hour average. The basin
overall is currently in attainment of the federal standard but has not
met the more stringent state standard. For several reasons hinging on
the area\'s dry climate and coastal location, the SDAB has special
difficulty in developing adequate tactics to meet present particulate
standards.

Nitrogen Dioxide, Sulfur Dioxide, and Lead

The basin is in attainment for these pollutants.

Odors

Odors are not regulated under emissions standards, rather they are
regulated under the APCD\'s Regulation IV, Rule 51 (the
&quot;nuisance&quot; rule).

Complaints of odors result primarily from the perceived intensity of the
odor sensation and the frequency of occurrence. People judge the
intensity of odors they consider unpleasant as higher than those they
consider pleasant or normal to their environment. The range in olfactory
sensitivity in people of normal acuity can vary up to four orders of
magnitude relative to measured concentrations. Few odors are
attributable to a single compound.

A method of quantitatively assessing odors has been devised by the
American Society of Testing Materials (ASTM, Standard Method D 1391),
which considers how many times an air sample must be diluted with
&quot;clean&quot; air before the odor is no longer detectable to an
average adult with average odor sensitivity. The number of dilutions
needed to reach this threshold level is referred to as a &quot;dilution
to threshold&quot; (D/T) factor. A threshold level of perception for an
odor is 2 D/T (two parts of fresh air to one part of odorous air); at
this value approximately 50 percent of people can detect the presence of
an odor. The South Coast Air Quality Management District (SCAQMD) uses a
value of 10 D/T as a screening threshold for determining significant
impacts due to odor (SCAQMD 1993:63). However, there is no established
correlation between odor threshold values and annoyance.

The IWTP is in a rural area of the Tijuana River valley surrounded by
agricultural and livestock activities and a few isolated residences.
However, Tijuana is 300 feet (91 m) south and has mixed residential and
industrial uses. The only odors detected during previous odor surveys
for the IWTP (Odor Science and Engineering 1990) were manure odors from
a local farm, which measured less than 2 D/T. Since release of the Draft
EIS for the IWTP, the City of San Diego approved a new residential
development for the Tijuana Street site. This approval would add
sensitive receptors approximately 1,700 feet (0.5 km) northeast of the
IWTP.

While the odor surveys found the ambient odor conditions in the project
vicinity to be acceptable, comments received at previous public meeting
indicated that the existing odor of the Tijuana River was foul and
unacceptable. Also, foul‑smelling odors have been detected by USIBWC
personnel at the IWTP site, ostensibly from Tijuana Pump Station One,
located adjacent to the site on the Mexican side of the border
(McMicheaux, USIBWC, 4/17/91). Land Use and Socioeconomics

This section profiles the existing socioeconomic conditions in the
Tijuana River valley and Imperial Beach that could be affected by the
Tijuana River or SBOO discharges. The information provided in this
section is derived from an updated review conducted by CIC Research,
Inc. (1996).

Existing Conditions

This section discusses the existing activities within the defined study
area (potential affected area). This area includes roughly the entire
Tijuana River valley and the coastal strip which runs just south of
Silver Strand State Beach in Coronado to the Mexican border. A drive‑by
visual field survey within the study area was conducted.

Land Use Plans and Policies

The Tijuana River valley is within the Coastal Zone. The Coastal Zone
Management Program for the area is made up of the California Coastal Act
Policies and Plan, Local Coastal Program, and Tijuana River National
Estuarine Sanctuary Management Plan.

The California Coastal Plan (State of California 1975a) identifies the
coastal area of the Tijuana River valley as Subregion 12 of the San
Diego Coast Region. The plan highlights this area as follows:

Tijuana Estuary and River valley‑Preserve and protect resource and
habitat values and agricultural lands. Prevent urban encroachment.
Complete the acquisition of land and improve in a manner consistent with
estuarine preservation. Retain and restore the estuary to tidal action.

The Tijuana River Valley Plan and Local Coastal Program Addendum (City
of San Diego 1977) covers the major portion of the Tijuana River valley.
The overall goals of the plan are to provide flood protection, to
protect and preserve diminishing natural coastal areas, to conserve and
enhance agricultural productivity, and to provide visual and passive
relief from continuous urbanization. The specific objectives of the
agricultural element are to restore the rich floodplain to more
productive agricultural use, to preserve open space, and to conserve
valuable natural deposits of alluvium and river bed sand. The part of
the Tijuana River floodplain which lies between the levee paralleling
Interstate 5 and 19th Street is designated in the plan as an
agricultural preserve. Stated benefits from the preserve include food
production for an increasing population, aesthetic satisfaction
resulting from maintained open space, educational benefits of model farm
operations, and experimental plant hybridization. In addition to model
farms and experimental hybridization programs, horse farms, nurseries,
and orchards are desirable uses in the agricultural preserve.

The Tijuana River National Estuarine Sanctuary Management Plan
encompasses 2,531 acres (1,025 ha) in the western portion of the river
valley and shoreline including the Border Field State Park area. The
management plan addresses land use concepts, maintenance of
environmental quality, natural and cultural resources protection and
enhancement, public recreation, research, and sanctuary area management.

South of Monument Road, between Old Dairy Mart Road and Border Field
State Park is an upland formation containing sand and gravel resources
that is known as the Border Highlands area. An addendum to the Tijuana
River Valley Land Use Plan and Local Coastal Program was adopted in
1982. The addendum addresses the phased extraction of mineral resources
for this area and reclamation of mined areas for future open space and
commercial recreation uses.

The County Department of Parks and Recreation is currently acquiring
property in the Tijuana River valley for inclusion in the planned
Tijuana Valley Regional Park. The focused planning area for the park was
adopted by the County Board of Supervisors and encompasses the area west
of Interstate 5, east of the Border Field State Park and Tijuana River
National Estuarine Research Reserve, south of Imperial Beach. To avoid
possible land speculation, a specific park boundary has not yet been
determined. Ultimately, the park will be comprised of 1,100 acres (446
ha) centered along the Tijuana River. The park could take a decade to
complete. It is being paid for in part with \$9.8 million from a state
bond act approved by voters in 1988 for parks and wildlife preservation.
The primary goal of the park is agricultural and wildlife preservation;
its location would provide protection for that portion of the river
system which lies within the jurisdiction of the United States. Lands
which are considered high priority for acquisition are those which
presently provide viable habitat for sensitive bird species,
agricultural land with which sensitive bird species are also associated,
and biologically marginal land for the more active uses of the park.

Residential Uses

The Tijuana River valley is characterized by rural, sparsely scattered
homes including single‑family homes and private ranches. According to
the U.S. Census Bureau, 52 percent of the area\'s residents are
Caucasian and roughly 36 percent are of Hispanic origin. SANDAG has
estimated the 1990 population base within the Tijuana River Valley
Community Planning Area at 165. Population growth is expected to be
minimal and reach 170 by 2015. An estimated 51 total housing units (1990
base) are within the area. These residences have an average of 3.2
persons per household.

The portion of the study area which includes the coastal sections of
Imperial Beach include numerous oceanfront condominium and apartment
developments. Although the actual number of housing units in this
coastal area could not be determined, this area is expected to have a
high percentage of the total 5,518 (January 1995) multi‑family units in
Imperial Beach. These units range in value from roughly \$110,000 to
\$400,000 and rent from \$400 to \$1,300 per month. Some of the units
are used as vacation rentals and vacation homes. The south end of Sea
Coast Drive includes more owner‑occupied condominiums compared to the
northern end, which has more resident and vacation rentals. The northern
end is close to the Imperial Beach Fishing Pier and is the location of
the annual tourist events.

Business Uses

Business uses in the Tijuana River valley are primarily agricultural and
equestrian related. Numerous equestrian businesses exist in the valley,
including horse rentals, boarding, or breeding. The rental businesses
operate all year and utilize the nearby trails and beaches. SANDAG
estimates the total 1990 employment base in the Tijuana River Valley
Community Planning Area was 189 and forecasted to reach 286 by 2015.

According to a recent (1995) survey conducted by members of the Tijuana
River Valley Equestrian Association and Mounted Assisted Unit and
Citizens Against Recreational Eviction, the area has a total of 876
horses. The area has three rental stables with a total of roughly 150
rental horses. These rental horses represent an estimated 20,000 horse
rides per year in the valley. The area also includes three thoroughbred
breeding ranches and five full‑time boarding stables. Horse riders have
access to numerous trails and are allowed on the beaches in the valley
vicinity. The valley has 27 miles (43.5 km) of trails as well as trail
access to the Otay Mesa area. Based on the above‑mentioned survey, total
ridership in the valley and to Otay Mesa include roughly 100,000 trips
per year.

The businesses within the coastal area of Imperial Beach include mostly
small local serving uses with a few tourist‑oriented shops. These
businesses include roughly two small motels, restaurants, clubs,
minimarket, surf shop, and a bait and tackle/snack shop located at the
end of the Imperial Beach Pier. The bait and tackle/snack shop and surf
shop are heavily dependent on ocean activities. The motels (Seacoast Inn
and Hawaiian Gardens Suite Hotel) have a total of roughly 78 rooms and
offer seasonal rates from \$45 to \$140. These hotels rely on tourists
visiting the beaches. According to the owners, the hotels are always
booked for the major local events (sand castle, triathlon, and chili
cook‑off/jazz festival). According to the Imperial Beach Chamber of
Commerce, the restaurants, clubs, and convenience market receive
significant support from beach tourists and especially around the major
tourist events.

According to the Imperial Beach Chamber of Commerce, the sand castle
event, which is held on July 26, 27, and 28 is the largest event, with
an estimated attendance of 250,000. The chili cook‑off and jazz festival
(held the second week in May) attracts an estimated 15,000 persons. A
triathlon event (which is held on August 17 and 18) attracts an
estimated 5,000 to 7,000 persons. In the past, the city beaches were
home to the Bud Pro Surf Contest, which was held on Memorial Day. This
five‑day event attracted roughly 5,000 persons. However, this event is
no longer held in Imperial Beach. These events are heavily dependent on
access to the beaches and ocean and offer significant support to local
businesses.

Agricultural Uses

The Tijuana River valley is agricultural, with a diverse array of
agricultural operations represented. Row cropping, sod farming,
greenhouse operations, and horse breeding and boarding have been the
primary agricultural uses in this area. Recently, there has been a
grower who specializes in native plant production for revegetative
projects and an organic grower who specializes in sprout production.
Another use in the Tijuana River valley is a sand and gravel extractive
operation.

The Tijuana River Valley Plan calls for agricultural preservation and
enhancement of agricultural values and productivity. Retention of
agricultural values also is meant to stem urban encroachment in this
region. The Plan\'s agricultural element calls for restoration of the
rich floodplain to more productive agricultural use, to preserve open
space, and to conserve valuable national deposits of alluvium and river
bed sand. Part of the floodplain itself is designated an agricultural
preserve.

Soil resources in the study area include Chino silt loam (saline),
Visalia sandy loam, Tujunga sand, and tidal flats. Both the Chino silt
loam and Visalia sandy loam are considered prime agricultural land,
while Tujunga sand is classified as a soil of statewide importance.
Tidal flats are not suitable for agriculture and are suited instead to
wildlife habitat.

Recreational Uses

Recreational use and preservation of natural coastal resources account
for the bulk of the Tijuana River valley acreage. Specific recreational
areas include Border Field State Park, Tijuana River National Estuarine
Sanctuary, Silver Strand State Beach, Tijuana Slough National Wildlife
Refuge, Imperial Beach Pier, and all of the beach areas. Some smaller
recreational areas include the Chula Vista Model Airplane and Radio
Control Club and the YMCA Camp Surf in Imperial Beach.

Tijuana River National Estuarine Reserve and Border Field State Park

The Tijuana River National Estuarine Research Reserve is located to the
west and north of the Tijuana River valley. It is part of a system which
includes 20 estuaries. This park has been preserved by the NOAA.

The reserve has a visitor center located at its northern edge, within
the community of Imperial Beach. The center has an exhibit hall,
library, theater, and bookstore, and offers educational classes.

Border Field State Park is part of the Estuarine Reserve and is located
at the westernmost end of the Tijuana River valley, at the southwest
corner of the continental United States. This park is one of the few
remaining U.S. beaches to allow horseback riding, and riding is a
popular form of recreation in this park. Other activities include
bicycling, hiking/walking, picnicking, and nature viewing. The park is
open for day use only. Border Field State Park offers a unique view of
the border and Tijuana bullring, as well as views of the Los Coronados
Islands and Playas de Tijuana. No camping is allowed in the park.
Visitor attendance at Border Field State Park has grown from 78,000 in
1992/93 to 217,000 in the 1994/95 fiscal year, the most current year
available for visitor statistics. While it appears that attendance
almost tripled during that period, 1992/93 was a period of severe
flooding, requiring a significant number of beach closures.

Silver Strand State Beach

Silver Strand State Beach is located along a seven‑mile (11.3 km)
stretch of wide sandy beach connecting the communities of Coronado and
Imperial Beach. On its western edge is the Pacific Ocean and its eastern
border is formed by San Diego Bay. This beach is well known as one of
the most beautiful beaches in southern California.

This beach offers a variety of recreational opportunities, including
swimming, sunning, picnicking, bicycling, surfing, and ocean fishing.
Recreational vehicle (RV) camping is allowed for a fee of \$16.00 per
night. Day use fees are \$4.00 per vehicle.

Silver Strand State Beach has several rest rooms and showers, a snack
bar, and a beach equipment rental concession. There are 124 RV spaces in
the campground.

Visitor attendance at Silver Strand has increased from roughly 249,000
in the 1992/93 fiscal year to 358,000 in the current (1995/96) fiscal
year. This represents a healthy 44 percent increase in visitation in a
relatively short period of time.

The Chula Vista Model Airplane and Radio Control Club has a relatively
small site in the river valley used for flying model airplanes. The club
recently moved from Border Field State Park to a site just west of the
IWTP. According to a club member, the club has a total of 112 members.
Actual activity levels could not be identified, but the site includes
parking for 23 cars and is typically full on the weekends.

The YMCA Camp Surf is located in North Imperial Beach, just south of
Silver Strand State Beach. The camp operates all year and offers
environmental education classes for school children during the spring
and fall school seasons. The environmental classes utilize the beach,
and during the summer months the camp offers additional recreational
activities to all children. The activities include pier fishing,
surfing, and arts and crafts. The YMCA camp, which remains relatively
full when open, is dependent on the nearby ocean for most of their
activities/business.

Sportfishing Uses

Sportfishing is an important recreational outlet for San Diego
residents. Used by a variety of socioeconomic segments, sportfishing as
a recreational activity is enjoyed by many people. The subject area
provides ample access to marine recreational fishing through pier,
beach, and nearby offshore boat fishing.

Pier fishing is an important aspect of recreational fishing as it allows
the easiest and lowest cost access for the angler. According to the
NMFS\'s Southern California Sportfishing Economic Survey (1991), pier
fishing requires the smallest average

cost per trip of any mode of marine fishing. In addition, on the
average, pier anglers travel the shortest distance to participate in
their fishing activity as compared to other modes of fishing. Pier
fishing attracts anglers with lower household incomes due to its
affordability. In addition, pier fishing appeals to young anglers since
it is a readily accessible method of recreation, especially in the
summer months.

The Imperial Beach Fishing Pier is owned and maintained by the San Diego
Port District. However, the City of Imperial Beach actively promotes the
pier as an attraction. Located at the end of the pier is a tackle/snack
shop that is leased from the Port District. During weekdays in
non‑summer months, the pier attracts approximately 10 to 50 anglers in
the morning, many of whom are subsistence anglers. Weekday non‑summer
afternoon anglers number from 50 to 75 anglers. During weekend and
summer months the number of anglers increases to several hundred.
According to the NMFS in 1991, there were roughly 21,394 angler trips
from the Imperial Beach Pier.

A second mode of fishing found in the subject area is beach fishing.
Beach fishing also allows easy and low cost access for the angler. Beach
anglers are able to collect bait on the beach (sand crabs), as well as
purchase bait nearby. One of the drawbacks to beach fishing is the
interaction of anglers with other people using the shore for recreation.
Consequently, beach fishermen tend to use the shore for angling when the
beach is not used for other forms of recreation (i.e., early morning or
late evening). The difficulties in beach fishing coupled with a lower
catch rate than other modes of fishing tend to make beach anglers rare.
The number of beach anglers using the Imperial Beach area is estimated
to be roughly 7,847 per year (NMFS 1991).

Private boat anglers and commercial passenger fishing vessels (CPFV) use
the area immediately offshore of Imperial Beach, especially during the
spring and summer months. There has been an attempt (unsuccessful to
date) to attract a CPFV operation to run out of the Imperial Beach Pier.
According to the CDFG, there are approximately 400 annual boat trips
accounting for roughly 10,000 angler trips using the fishing grounds
that extend 12 miles (19.3 km) from the shoreline between Imperial Beach
and the Mexican border.

Chapter Four

Environmental Consequences

This chapter discusses the potential environmental impacts resulting
from implementation of each of the alternatives considered in this SEIS.
Each alternative is considered as a stand‑alone alternative that would
be used during the interim period from 1996 to the planning horizon year
of 2001. Each alternative considered is a means to reduce the
environmental impacts relative to the No Action baseline. The phasing of
the individual alternatives, discussed as Alternative 6 in Chapter 2, is
not given separate evaluation here, as the impacts are considered by
each alternative.

The term impacts is used interchangeably with the term

effects and is defined as adverse or beneficial changes

or consequences of the project taken as a whole. Effects include changes
that are ecological, economic, social, or health related and can be
direct or indirect and of short‑ or long‑term duration, if not permanent
(irreversible). The effects considered are primarily related to the
discharge of advanced primary effluent from the IWTP over a five‑year
period of time. The effects of construction and operation of the IWTP
and SBOO and discharging up to 100 mgd of secondary treated effluent
were evaluated in the previous EIS for the project.

Direct effects are caused by the action and occur at the same time and
place. Direct effects may result from new construction or operation of
the facilities. Indirect effects are caused by the action or the
combined effects of the action and other future actions and occur later
in time or are removed in distance.

A significant effect on the human environment means a substantial, or
potentially substantial, adverse change in any of the physical,
economic, or social conditions in the area affected by the project
including land, air, water, minerals, flora, fauna, ambient noise, and
objects of historic or aesthetic significance.

CEQ regulations require consideration of the cumulative impact of a
proposed action on the environment. This is defined as that which
results from the incremental impact of the action when added to other
past, present, and reasonably foreseeable future action. Cumulative
effects can be individually minor but collectively significant. For this
SEIS, the primary cumulative impact would be the discharges in Mexico of
treated effluent and untreated sewage with respect to discharge of
treated effluent from the IWTP.

Hydrology and Water Quality

This section describes the hydrological and water quality impacts
anticipated to result from implementation of each alternative.
Regulatory Standards

Federal Clean Water Act

Section 402 of the Clean Water Act establishes the NPDES permitting
program. Subsection (a)(5) of Section 402 specifies that the
Administrator (EPA) may delegate authority to issue permits for
discharges to the State. As allowed per this subsection, the EPA has
delegated NPDES permitting authority to the RWQCB.

All point‑source dischargers are required to obtain and comply with the
provisions of an NPDES permit for any discharge of pollutants into
waters of the U.S. (e.g., oceans, lakes, or streams). NPDES permits must
contain discharge limitations based on the more stringent of the
applicable technology‑based requirements and water quality standards.
RWQCB will be the authority issuing the NPDES permit for operation and
interim discharge of effluent from the IWTP.

Additionally, Section 301 of the Clean Water Act specifies effluent
limitations. Under this section, discharge of less than secondary
treated effluent to marine waters is not authorized.

Porter‑Cologne Water Quality Act

Under the Porter‑Cologne Act, the RWQCB issues waste discharge
requirements to sources of pollutants to state waters. Because the IWTP
discharges into state waters, the RWQCB will issue waste discharge
requirements for the IWTP discharge. The waste discharge requirements
will be based on the Basin Plan and Ocean Plan. The waste discharge
requirements will likely be contained in a joint document with the NPDES
permit.

Water Quality Control Plan for the San Diego Basin

The San Diego Regional Board\'s Basin Plan (State of California 1995) is
designed to preserve and enhance water quality and protect the
beneficial uses of all regional waters. Specifically, the Basin Plan:
(1) designates beneficial uses for surface and ground waters; (2) sets
narrative and numerical objectives that must be attained or maintained
to protect the designated beneficial uses and conform to the state\'s
antidegradation policy; (3) describes implementation programs to protect
the beneficial uses of all waters in the region; and (4) describes
surveillance and monitoring activities to evaluate the effectiveness of
the Basin Plan. Additionally, the Basin Plan incorporates by reference
all applicable State and Regional Board plans and policies.

Beneficial uses are defined as the uses of water necessary for the
survival or well‑being of man, plants, and wildlife. These uses of water
serve to promote the tangible and intangible economic, social, and
environmental goals of mankind. Existing beneficial uses for the Tijuana
River in the Tijuana River valley west of Interstate 5 are Non‑contact
Water Recreation (REC‑2), Warm Freshwater Habitat (WARM), Wildlife
Habitat (WILD), and Rare, Threatened, or Endangered Species (RARE).
Potential beneficial uses specified for the river include Industrial
Service Supply (IND) and Contact Water Recreation (REC‑1). It is noted
that the Tijuana River is exempted from the Municipal (MUN) beneficial
use designation.

Existing beneficial uses for the Tijuana River estuary include all of
those mentioned above (i.e., REC‑1, REC‑2, WARM, WILD, RARE, and IND)
except MUN, as well as Commercial and Sport Fishing (COMM), Preservation
of Biological Habitats of Special Significance (BIOL), Estuarine Habitat
(EST), Marine Habitat (MAR), Migration of Aquatic Organisms (MIGR), and
Shellfish Harvesting (SHELL).

Groundwater beneficial uses for the Tijuana River valley include MUN,
IND, and Agricultural Supply (AGR).

These beneficial uses are defined as follows:

Contact Water Recreation (REC‑1): Includes

uses of water for recreational activities involving body contact with
water, where ingestion of water is reasonably possible. These uses
include, but are not limited to, swimming, wading, waterskiing, skin and
scuba diving, surfing, white water activities, fishing, or use of
natural hot springs.

Non‑contact Water Recreation (REC‑2):

Includes uses of water for recreational activities involving proximity
to water but not normally involving body contact with water, where
ingestion of water is reasonably possible. These uses include, but are
not limited to, picnicking, sunbathing, hiking, beachcombing, camping,
boating, tide pool and marine life study, hunting, sightseeing, or
aesthetic enjoyment in conjunction with the above activities.

Municipal and Domestic Supply (MUN):

Includes uses of water for community, military, or individual water
supply systems including, but not limited to, drinking water supply.

Agricultural Supply (AGR): Includes

uses of water for farming, horticulture, or ranching including, but not
limited to, irrigation, stock watering, or support of vegetation for
range grazing.

Industrial Service Supply (IND): Includes

uses of water for industrial activities that do not depend primarily on
water quality including, but not limited to, mining, cooling water
supply, hydraulic conveyance, gravel washing, fire protection, or oil
well repressurization.

Warm Freshwater Habitat (WARM): Includes

uses of water that support warm‑water ecosystems including, but not
limited to, preservation or enhancement of aquatic habitats, vegetation,
fish, or wildlife, including invertebrates.

Wildlife Habitat (WILD): Includes uses

of water that support terrestrial ecosystems including, but not limited
to, preservation and enhancement of terrestrial habitats, vegetation,
wildlife (e.g., mammals, birds, reptiles, amphibians, invertebrates), or
wildlife water and food sources.

Rare, Threatened, or Endangered Species (RARE):

Includes uses of water that support habitats necessary, at least in
part, for the survival and successful maintenance of plant or animal
species established under state or federal law as rare, threatened, or
endangered.

Commercial and Sport Fishing (COMM):

Includes the uses of water for commercial or recreational collection of
fish, shellfish, or other organisms including, but not limited to, uses
involving organisms intended for human consumption or bait purposes.

Preservation of Biological Habitats of Special Significance (BIOL):
Includes uses of water that support designated

areas of habitats, such as established refuges, parks, sanctuaries,
ecological reserves, or ASBSs, where the preservation or enhancement of
natural resources requires special protection.

The Tijuana River National Estuarine Research Reserve is designated a
national estuarine research reserve by the NOAA.

Estuarine Habitat (EST): Includes uses

of water that support estuarine ecosystems including, but not limited
to, preservation or enhancement of estuarine habitats, vegetation, fish,
shellfish, or wildlife (e.g., estuarine mammals, waterfowl, shorebirds).

Marine Habitat (MAR): Includes uses

of water that support marine ecosystems including, but not limited to,
preservation or enhancement of marine habitats, vegetation such as kelp,
fish, shellfish, or wildlife (e.g., marine mammals, shorebirds).

Migration of Aquatic Organisms (MIGR):

Includes uses of water that support habitats necessary for migration,
acclimatization between fresh and salt water, or other temporary
activities by aquatic organisms, such as anadromous fish.

Shellfish Harvesting (SHELL): Includes

uses of water that support habitats suitable for the collection of
filter‑feeding shellfish (e.g., clams, oysters, and mussels) for human
consumption, commercial, or sport purposes.

In order to protect the designated beneficial uses, water quality
objectives have been specified by the Regional Board. These water
quality objectives are described in detail in Chapter 3 of the Basin
Plan (State of California 1995).

Additionally, the Basin Plan specifies that discharges of wastewater to
surface water must meet the effluent limitations prescribed in the NPDES
permit issued by the Regional Board. Effluent limitations are based on
the following criteria:

Secondary treatment effluent limitations defined by the U.S. EPA
contained in 40 CFR 133, unless a waiver to the secondary treatment
standards is obtained (more stringent effluent limitations than
secondary treatment may be imposed by the Regional Board if necessary).

Applicable water quality objectives and beneficial uses contained in the
Basin Plan and State Board Water Quality Control Plans. Applicable
public health protection standards for total and fecal coliform.

Assimilative capacity of the receiving water.

The terms and conditions of the federal Antidegradation Policy (40 CFR
131.12) and the State Antidegradation Policy (Resolution No. 68‑16).

Anti‑backsliding provisions described in Clean Water Act Section 404.

Land disposal or recycling of sludge as a soil amendment.

As such, the live stream discharge of less than secondary treated
effluent to the Tijuana River would not be in compliance with the Basin
Plan and, consequently, the Clean Water Act.

Chlorination/Dechlorination

Chlorination of wastewater prior to discharge is used for disinfection
and may also be used for control of odors. The IWTP was designed with
the capability to chlorinate/dechlorinate effluent. However, the final
design for the South Bay Ocean Outfall may provide sufficient initial
dilution to avoid the need for chlorination of effluent. At this time,
USIBWC/EPA are uncertain if chlorination/dechlorination will be required
for discharge of treated effluent in the U.S. For general discussion
purposes, the regulatory standards and potential environmental concerns
are presented below.

Both state and federal standards for chlorine discharge are based on
known toxicity to aquatic organisms. The most sensitive organisms and
life stages tested to date (such as sea urchin sperm or oyster larvae)
have toxic effects at about the concentrations of the state standards
for daily maximum and six‑month median limits. Freshwater and estuarine
aquatic organisms have similar sensitivities.

Regulatory Standards

If chlorination of ocean discharge is required to control coliform
concentrations, then the California Ocean Plan (1990) has receiving
water limitations for total residual chlorine as follows:

Six‑month median 2 &#181;g/l

Daily maximum 8 &#181;g/l

Instantaneous maximum 60 &#181;g/l

These Ocean Plan standards will apply to any marine discharge and allows
for effluent dilution at the point of discharge from the diffuser. These
limits may be met with or without dechlorination, as necessary to keep
calculated total residual chlorine in receiving waters below the water
quality objectives.

The latest EPA criteria (1986) for chlorine‑produced oxidants in
seawater is 7.5 &#181;g/l as a four‑day average and 13 &#181;g/l as a
one‑hour average (in practice, usually applied as a daily limit). These
values are similar to those used by the State of California.

Environmental Concerns

The chlorination of wastewater and discharge to the estuarine and marine
environment has the potential to cause adverse effects. Any chlorine
that is not neutralized by dechlorination is extremely toxic to most
freshwater, estuarine, or aquatic biota. Concerns for the effects of
chlorination to freshwater or marine organisms include mutagenicity
(production of mutations), toxicity, and bioaccumulation in tissues.

Chlorine can be added to effluent in one of several forms. Uncomplexed
chlorine oxidant (without nitrogen or carbon) is termed free chlorine.
Total residual chlorine includes other oxidants formed by the
chlorination process, such as chloramines. When the water contains
ammonia, as in the case of sewage effluent, monochloramine,
dichloramine, and nitrogen trichloride are also formed. These and a few
other oxidizing species formed by chlorination are collectively known as
total residual chlorine. Other halogenated organics, such as bromoform
and chloroform, and various trihalomethanes, among others, are also
formed.

The rapid dissipation of these oxidants in the environment should render
concentrations nontoxic outside of the zone of initial dilution, as long
as State effluent limits are met. With a dilution ratio of 100:1, the
SBOO would have to maintain an effluent concentration of total residual
chlorine of less than 200 &#181;g/l, on average, to remain below. the
State Ocean Plan limit of 2 &#181;g/l for receiving waters.

Alternative 1: No Action

Impacts

Under this alternative, raw sewage flows in excess of the combined
capacity of Tijuana Pump Station One and the emergency connector would
flow into the Tijuana River via Stewart\'s Drain. As shown in Table 2‑1,
these excess sewage flows are estimated to be 5.6 mgd (245 lps) average
day flows with 9.5 mgd (416 lps) highest day peak flows by the year
2001. From a hydrological perspective, this is a low flow rate for the
river. Therefore, no flooding, scouring, or channel alteration is
expected to occur in the river valley as a consequence of continued
sewage flows to the river.

However, the flow of untreated raw sewage to the river will degrade the
water quality of the river and Tijuana River estuary. A wastewater
quality sampling program was initiated by USIBWC in 1990 to determine
the typical composition of the wastewater. An additional round of
sampling was conducted in 1992 (see Section 3‑1). The wastewater was
analyzed for a variety of substances including heavy metals, pesticides,
and nutrients. Results of this testing are shown in Table 4.1‑1 in the
influent concentration columns for both maximum observed concentrations
and sample average concentration. The Basin Plan standards for the
Tijuana River are also provided in Table 4.1‑1. Clearly, the untreated
sewage does not comply with water quality standards and objectives for
surface, ground, or ocean waters.

Additionally, the &quot;freshwater&quot; flows would also continue to
negatively impact the Tijuana River estuary as described in Chapter 3 of
this SEIS and in the Estuarine Biology impacts section below (Chapter
4.4).

Significance of Impacts

Under the No Action alternative, untreated dry‑weather sewage flows and
associated pollutants would enter the Tijuana River in Mexico and flow
into the U.S., eventually reaching the Pacific Ocean. Significant,
unavoidable adverse effects to the surface water, groundwater, estuary,
and nearshore ocean waters would result.

Mitigation

No additional mitigation is available for the No Action alternative.
Therefore, significant adverse impacts to water quality in the Tijuana
River and Tijuana River estuary would result.

Alternative 2: Operate IWTP

Impacts

Under this alternative, raw sewage flows in excess of the combined
capacity of the emergency connection and Pump Station One would flow to
the IWTP and be treated to primary standards. Effluent would then be
pumped to the emergency connection and the City of San Diego Point Loma
treatment plant. Effluent flows in excess of the capacity of the
emergency connection would be discharged directly to the Tijuana River.
The excess effluent flow is estimated to be 3.6 mgd (158 lps) by the
year 2001.

The typical composition of the wastewater influent to be received by the
IWTP is shown in Table 4.1‑1. Based on these influent concentrations,
the composition of the IWTP effluent was estimated by Malcolm Pirnie
Inc., the design engineers of the facility, using assumed removal
efficiencies for various constituents with advanced primary treatment.
The resulting effluent concentrations are also shown in Table 4.1‑1.

As indicated in Table 2‑3, beginning in 1998, treated effluent flow
rates of 0.6 mgd (26 lps) would be discharged on a daily basis and
increase to 3.6 mgd (158 lps) in the year 2001. Up to 9.5 mgd (416 lps)
would be discharged on peak high flow days in the year 2001. These flow
volumes are not expected to cause flooding, scouring, or channel
alteration in the river valley.

TABLE 4.1‑1

WASTEWATER INFLUENT AND EFFLUENT POLLUTANT CONCENTRATIONS

Calculated Calculated Calculated Calculated Measured Measured Effluent
Effluent Effluent Effluent Influent Influent Maximum Maximum Average
Average Basin Plan Ocean Ocean Parameter Daily Average Concentrati
Concentrat Concentratio Concentrat Maximum for Plan Plan Maximum
Concentrati on Before ion n Before ion River Daily 6‑Month Concentrat on
Dilution 100:1 Dilution 100:1 Discharge Maximum Median ion (mg/l) (mg/l)
Dilution (mg/l)\* Dilution (mg/l) (mg/l)&#134; (mg/l)&#134; (mg/l)
(mg/l) (mg/l)

Grease and oil ‑ 89 NA ‑ 46 0.46 &#167; 40# 25\*\* (mg/l)&#135;

BOD5 (mg/l)&#135; ‑ 370 NA ‑ 204 2.04 ‑ ‑ ‑

Suspended solids ‑ 350 NA ‑ 88 0.88 ‑ &#134;&#134; &#134;&#134;
(mg/l)&#135;

Cadmium 4 2 3.4 0.034 2 0.02 5&#135;&#135; 4 1

Copper 216 94 168.5 1.685 73 0.73 1,000&#135;&#135; 12 3

Lead 1,770 50 761 7.61 22 0.22 ‑ 8 2

Mercury 1.3 0.3 1.2 0.012 0.3 0.003 2&#135;&#135; 0.16 0.04

Nickel 162 21 139 1.39 18 0.18 100&#135;&#135; 20 5

Silver 67 10 54 0.54 8 0.08 100&#135;&#135; 2.8 0.7

Zinc 725 262 529 5.29 191 1.91 5,000&#135;&#135; 80 20

Ammonia‑nitrogen 40,400 35,800 40,400 404 35,800 358 25 2,400 600

Phenolic compounds ‑ 820 57 754 7.54 52 0.52 1&#135;&#135; 120 30 phenol

HCH 18.6 0.2 16 0.16 0.2 0.002 ‑ 8 4

Chlorinated 15 2 12.2 0.122 2 0.05 ‑ 4 1 phenolics

Bis(2‑ethylhexyl) ‑ 52 NA ‑ 52 0.52 4&#135;&#135; ‑ 3.5\*\* phthalate

Polyaromatic ‑ 9 NA ‑ 9 0.09 ‑ ‑ 0.0088\*\* hydrocarbons

Settleable solids 13.4 4.4 NA ‑ NA ‑ ‑ 1.5# 1.0\*\* (ml/L)&#135;

Turbidity (NTU)&#135; 150 130 NA ‑ NA ‑ 5&#135;&#135; 100# 75\*\*

pH (pH units)&#135; 6.0 to 6.0 to 7.7 NA ‑ NA ‑ &#167;&#167; \## \## 7.7

Arsenic 10 3 NA ‑ NA ‑ 50&#135;&#135; 32 8

Antimony ‑ 60 NA ‑ NA ‑ 6&#135;&#135; ‑ 1,200\*\*

Chromium (III) ‑ 16 NA ‑ NA ‑ 50&#135;&#135; ‑ 190,000\*\*

Ethylbenzene ‑ 4 NA ‑ NA ‑ 700&#135;&#135; ‑ 4,100\*\*

Toluene ‑ 20 NA ‑ NA ‑ 150&#135;&#135; ‑ 85,000\*\*

Trichloroethane ‑ 5 NA ‑ NA ‑ 200&#135;&#135; ‑ 540,000\*\* (1,1,1‑)

Di‑n‑butylphthalate ‑ 7 NA ‑ NA ‑ ‑ ‑ 3,500\*\*

Dichlorobenzenes ‑ 34 NA ‑ NA ‑ 600&#135;&#135; ‑ 5,100\*\*

Diethylphthalate ‑ 36 NA ‑ NA ‑ ‑ ‑ 33,000\*\*

Dimethylphthalate ‑ 47 NA ‑ NA ‑ ‑ ‑ 820,000\*\*

Dichloromethane ‑ 13 NA ‑ NA ‑ 5&#135;&#135; ‑ 450\*\*

Tetrachloroethylene ‑ 10 NA ‑ NA ‑ 5&#135;&#135; ‑ 99\*\*

Benzene ‑ 2 NA ‑ NA ‑ 1&#135;&#135; ‑ 5.9\*\*

Dichlorobenzene ‑ 7 NA ‑ NA ‑ 5&#135;&#135; ‑ 18\*\* (1,4‑)

Halomethanes ‑ 12 NA ‑ NA ‑ ‑ ‑ 130\*\*

Trichloroethylene ‑ 2 NA ‑ NA ‑ 5&#135;&#135; ‑ 27\*\*

SOURCE: Malcolm Pirnie Inc. 1996.

NA Effluent concentrations are not available for these pollutants.

\* Effluent average concentrations shown are undiluted.

&#134; Effluent limitations shall be imposed in a manner prescribed by
the SWRCB such that the concentrations specified shall not be exceeded
in the receiving water upon completion of initial dilution.

&#135; These substances have concentrations in the units shown.

&#167; Waters shall not contain oils, greases, waxes, or other materials
in concentrations which result in a visible film or coating on the
surface of the water or on objects in the water or which cause nuisance
or which otherwise adversely affect beneficial uses.

\# 7‑day average (weekly).

\*\* 30‑day average (monthly).

&#134;&#134; Dischargers shall, as a 30‑day average, remove 75% of
suspended solids from the influent stream before discharging wastewaters
to the ocean, except that the effluent limitation to be met shall not be
lower than 60 mg/l. RWQCBs may recommend that the SWRCB (Chapter VI.F.),
with the concurrence of the EPA, adjust the lower effluent concentration
limit (the 60 mg/l above) to suit the environmental and effluent
characteristics of the discharge. As a further consideration in making
such recommendation for adjustment, RWQCBs should evaluate effects on
existing and potential water reclamation projects.

If the lower effluent concentration limit is adjusted, the discharger
shall remove 75% of suspended solids from the influent stream at any
time the influent concentration exceeds four times such adjusted
effluent limit.

&#135;&#135; Objective applies to waters designated for use as domestic
or municipal supply (MUN)

&#167;&#167; Changes in normal ambient pH levels shall not exceed 0.2
unit in waters with designated marine (MAR) or estuarine (EST) or saline
(SAL) beneficial uses. Changes in normal ambient pH levels shall not
exceed 0.5 unit in fresh waters with designated cold freshwater habitat
(COLD) or warm freshwater habitat (WARM) beneficial uses. In bays and
estuaries, the pH shall not be depressed below 7.0 or raised above 9.0.
In inland surface waters. the pH shall not be depressed below 6.5 or
raised above 8.5.

\## pH within limits of 6.0 and 9.0 at all times.

However, the flow of primary effluent to the river will degrade the
water quality of the river, groundwater, and Tijuana River estuary,
although the pollutant concentrations of the effluent from advanced
primary treatment would be less than would occur under the No Action
alternative.

The reduction in concentrations can be seen by comparing the influent
pollutant concentrations (which are equivalent to the pollutant
concentrations in untreated sewage flowing to the river under the No
Action alternative) to the estimated IWTP effluent concentrations before
dilution, shown in Table 4.1‑1. As the lower Tijuana River is not
considered a high‑quality water body, the Basin Plan does not contain
numerical standards that would apply to discharges further upstream.

Bacteria counts in the wastewater are not substantially reduced by
primary treatment. Disinfection of the IWTP effluent could reduce the
coliform concentrations and other pathogens. However, no dilution of the
effluent with river discharge is expected during dry weather with the
river discharge. Residual chlorine and associated by‑products are
extremely toxic to aquatic organisms. To avoid substantial additional
impacts to the river and estuary aquatic biota from residual chlorine
impacts, the level of disinfection that could be achieved with
chlorination/ dechlorination of the effluent may not be sufficient to
reduce coliform concentrations to meet health standards. South Bay
beaches would be subject to quarantine. Additionally, the freshwater
flows would also continue to negatively impact the Tijuana River estuary
as described in Chapter 3 of this SEIS and in the Estuarine Biology
impacts section below (Chapter 4.4).

Significance of Impacts

Beginning in 1998 and through the year 2001, primary treated effluent
flows and associated pollutants would enter the Tijuana River, flow
through the estuary, and eventually reach the Pacific Ocean. Significant
adverse impacts to water quality in the Tijuana River and Tijuana River
estuary would occur, although at a reduced level from that which would
occur under the No Action alternative. Adverse effects to the estuary
and nearshore ocean waters in the South Bay region are considered
significant.

Additionally, the direct discharge of primary treated effluent to the
river is not authorized by the federal Clean Water Act and the Water
Quality Control Plan for the San Diego Basin. An NPDES permit would be
required from the RWQCB, as well as wastewater discharge requirements.
The direct discharge of primary treated effluent to the river is a
significant impact.

Mitigation

No mitigation is available for this alternative. To avoid the
significant effects from the discharge of advanced primary effluent to
the river beginning in 1998, additional storage capacity would be
necessary, as discussed under Alternative 3. Implementation of this
alternative would be inconsistent with the federal Clean Water Act and
the Water Quality Control Plan for the San Diego Basin.

Alternative 3: Operate IWTP with Detention Basin

Impacts

Under this alternative, raw sewage flows in excess of Tijuana Pump
Station One capacity would flow to the IWTP and be treated to primary
standards. Effluent would then be pumped to the emergency connection for
further treatment at the Point Loma treatment plant. Effluent flows in
excess of emergency connection capacity would be discharged to a 5.5
million gallon (20,900 m3) lined earthen detention basin. Effluent
stored in the basin would be pumped to the emergency connection during
off‑peak hours.

If the detention basin is filled to capacity before the emergency
connection is able to receive the total effluent flow, flow to the basin
would be diverted and discharged directly into the Tijuana River. The
USIBWC/EPA estimates there would be no treated effluent discharged to
the Tijuana River through the year 2001. There could be episodic
discharges of up to 2.0 mgd (88 lps) on seasonal high flow days in the
year 2001, however.

The detention basin would be constructed above the river channel.
Therefore, the basin would not impact the hydrology of the river.
Periodically, effluent flow rates of 2.0 mgd (88 lps) could exit the
basin directly into the river but are not expected to cause flooding,
scouring, or channel alteration in the river valley. Any discharge of
primary effluent to the river would degrade the water quality of the
river and Tijuana River estuary, even though the discharge volume and
frequency of occurrence and resultant pollutant load to the river,
groundwater, and estuary would be greatly reduced in comparison to
either the No Action or Operate IWTP alternatives.

As indicated above, bacterial counts in primary treated effluent would
remain high. South Bay beaches could be subject to quarantine when
effluent is discharged to the river. Additionally, the freshwater flows
would negatively impact the Tijuana River estuary as described in
Chapter 3 of this SEIS and in the Estuarine Biology impacts section
below (Chapter 4.4).

A significant impact could also occur if pollutants were to enter the
groundwater from the detention basin. The basin would be lined, which
would avoid this impact.

Significance of Impacts

Under this alternative, primary treated effluent flows and associated
pollutants would only enter the Tijuana River on high flow days in the
year 2001. Prior to 2001, no treated effluent flows would be discharged
to the river. This action would be beneficial to river, groundwater,
estuarine, and ocean waters relative to No Action and avoid most of the
adverse effects to water quality associated with operation of the IWTP.

Adverse effects to the estuary, beaches, and ocean in the South Bay
region caused by the discharge of primary treated effluent on high flow
days in the year 2001 are considered significant. Additionally, the
direct discharge of primary treated effluent to the river would be in
violation of the federal Clean Water Act and the Water Quality Control
Plan for the San Diego Basin. An NPDES permit would be required from the
RWQCB, as well as wastewater discharge requirements. The direct
discharge of primary treated effluent to the river is a significant
impact.

Mitigation

Lining the detention basin with an impermeable barrier would prevent
pollutants from percolating from the basin into the groundwater.

No other mitigation is available for this alternative. The amount of
discharge through the emergency connection would be exceeded during
seasonal high flows in 2001 and some treated flows would have to be
discharged to the river, even if the size of the detention basin were
increased. The significant adverse impacts to water quality are
unavoidable.

Alternative 4: Operate IWTP with New Conveyance to Mexico

Impacts

Under this alternative, raw sewage flows in excess of 17 mgd (745 lps)
in Mexico would flow to the emergency connection IWTP and be treated to
primary standards. Effluent would then be pumped back to a new
conveyance system in Mexico for discharge at the shoreline. No effluent
would be discharged to the Tijuana River. Therefore, no hydrological or
water quality impacts to the Tijuana River valley would occur as a
result of implementation of this alternative.

This alternative assumes continued use of the emergency connection.
Whether the emergency connection to Point Loma is utilized through the
year 2001 or not, there would be a substantial reduction in the volume
of untreated sewage discharged to the shoreline in Mexico with this
alternative. However, Parsons Engineering Science modeling of shoreline
transport of treated effluent indicates that coliforms resulting from
the increased discharge of treated wastewater at the shoreline in Mexico
could pollute beaches north of the international border.

Disinfection of the IWTP effluent could reduce the coliform
concentrations and other pathogens. Effluent from the San Antonio de los
Buenos facility in Mexico is currently chlorinated, although there has
not been sufficient time to assess its effectiveness in reducing
pathogens. However, the initial dilution of the effluent with shoreline
discharge is only estimated at 10:1. Residual chlorine and associated
by‑products are extremely toxic to marine organisms. To avoid
substantial additional impacts to the nearshore coastal waters and
biota, the level of disinfection that could be achieved may not reduce
coliform concentrations sufficiently to prevent exceedances of the Ocean
Plan standards for U.S. waters.

Significance of Impacts

No significant impacts to the Tijuana River valley would occur with
implementation of this alternative. However, the potential for nearshore
pollution of ocean waters and beach closures from the increased volume
of discharge to the shoreline in Mexico could be significant. This would
result in adverse effects to ocean water quality in Mexico and the U.S.

Mitigation

No mitigation is available for this alternative for impacts to U.S.
waters. Disinfection of the effluent by chlorination could further
reduce coliform concentrations in effluent from the IWTP but would
result in additional significant adverse impacts to coastal waters in
Mexico and would not eliminate the potential for exceeding coliform
standards of the Ocean Plan. Discharges of treated effluent or untreated
sewage in Mexico are the responsibility of Mexico.

Alternative 5: Operate IWTP with Discharge to SBOO

Impacts

Under this alternative, raw sewage flows in excess of San Antonio de los
Buenos treatment plant capacity would flow to the IWTP and be treated to
primary standards. Effluent would then be pumped to the SBOO for
discharge to the ocean. Under this scenario, no impacts to the Tijuana
River valley, estuary, or local beaches would result from the outfall
discharge.

Parsons Engineering Science modeled the effects of the discharge of
advanced primary effluent on ocean water quality, which is discussed in
detail in Section 4.2. The results of the modeling found that the only
constituent of the treated effluent that would exceed Ocean Plan
standards given the level of initial dilution (100:1) at the point of
discharge would be polyaromatic hydrocarbons. Only one location along
the shoreline at the edge of the Imperial Beach kelp bed was identified
as having the potential for exceedances of the Ocean Plan coliform
standards. The 10,000 coliform per 100 ml over 48 hours standard might
be exceeded less than one percent of the time at the 50‑foot (30 m)
water depth adjacent to the kelp bed.

The discharge of effluent at the shoreline in Mexico would have
potential adverse consequences to ocean waters in the U.S. Coliform
standards could be exceeded.

However, the SBOO will not be available until sometime in 1998. Prior to
that time, one of the other four alternatives would be implemented. The
impacts discussed above for each of the other four alternatives would
apply, although at a reduced level due to the lower sewage or effluent
flows which would reach the river prior to the SBOO becoming
operational.

Significance of Impacts

No significant direct hydrological impacts to the Tijuana River valley
would occur as a result of implementation of this alternative once the
SBOO is operational in 1998.

The SBOO discharge may not meet Ocean Plan standards for all criteria
pollutants, however, which could result in significant adverse impacts
to ocean water quality. Discharge at the shoreline in Mexico could
result in adverse impacts to nearshore coastal waters in Mexico and the
U.S. Additionally, the direct discharge of primary treated effluent to
the ocean is not consistent with the Clean Water Act or the Ocean Plan.

Mitigation

No hydrological mitigation measures would be required after the SBOO
becomes operational in 1998. Mitigation required prior to this time is
dependent on the alternative chosen for implementation in the interim.
Mitigation measures are discussed above under each alternative.

However, as indicated above, ocean water quality standards may not be
met for this discharge. The direct discharge of primary treated effluent
to the ocean is inconsistent with the Clean Water Act and Ocean Plan.
This is an unavoidable impact.

Oceanography

The information provided in this section is derived primarily from the
wastewater discharge modeling and analysis report prepared for the
project and alternatives (Parsons Engineering Science 1996). This
document is hereby incorporated by reference, pursuant to Section
1502.21 of the CEQ Guidelines.

Definition of Impact Criteria

The significance criteria for discharges that could affect water quality
and sediment are presented below.

Magnitude of change compared to natural backgrounds

Area of change (small, local, regional)

Comparison of change with applicable standards or with known toxic
concentrations

Duration of change (short‑ or long‑term)

Potential to cause change in indigenous marine populations

For water and sediment quality, impacts are judged based on the
regulatory standards along with consideration of changes from natural
levels. The significance of beneficial use impacts is based on the
impact to water quality and/or biological resources depending on the
type of use involved.

Regulatory Standards and Criteria

State Ocean Plan

The primary regulatory standards applicable to marine water and sediment
quality are contained in the Water Quality Control Plan: Ocean Waters of
California (Ocean Plan). The State of California originally adopted a
Water Quality Control Plan for ocean waters in July of 1973. This plan
has been revised in 1978, 1983, 1988, and most recently in 1990. This
Ocean Plan regulates the discharge of wastewater within the
three‑nautical‑mile (5.6 km) territorial limit of California
jurisdiction.

Limitations on major wastewater effluent constituents and properties
(such as grease and oil, suspended solids, settleable solids, turbidity,
pH, and toxicity concentration) are specified in the Ocean Plan.
Limitations on toxic materials are, however, specified in the Ocean Plan
in terms of concentrations in the receiving waters. Many of these
standards are shown in Table 4.1‑1.

For discharges through the SBOO, the actual use of the Ocean Plan to set
limits for toxic compounds for the undiluted wastewater effluent
requires the use of a state‑approved dilution model that will calculate
the &quot;minimum probable initial dilution&quot; near the mixing zone
around the outfall diffuser. For this purpose, the EPA initial mixing
models are used. Data on effluent quality can then be combined with the
initial dilution achieved by the outfall diffuser in order to calculate
the expected ambient concentrations of any toxic constituent for
comparison with the Ocean Plan standards.

For the surf discharges at the shoreline in Mexico 5.6 miles (9 km)
south of the international border, which is outside the waters of the
United States, the dilution of effluent at the first contact with
California waters (i.e., the international border) is calculated. The
pollutant concentrations resulting from the dilutions are then compared
to the Ocean Plan standards to determine impacts using a dispersion
model appropriate for surf discharges.

Bacteriological standards for marine waters for the State of California
are also specified in the Ocean Plan. These standards apply to body
contact zones, defined as those areas outside an area of initial
dilution about a discharge point at a distance of 1,000 feet (305 m)
from the shoreline or those areas within the 30‑foot (9.15 m) depth
contour, whichever is further, and for all kelp beds. These water
contact standards specify that the density of coliform organisms must
not exceed 1,000 per 100 ml for more than 20 percent of the samples in
any 30‑day period, nor shall a single sample, when verified by a repeat
sample taken within 48 hours, exceed a maximum of 10,000 per 100 ml. As
with toxic compounds, for the surf discharges in Mexico, the dilutions
at first contact with California waters were calculated for comparison
with the bacteriological standards in the Ocean Plan.

In addition, the Ocean Plan defines the beneficial uses of the ocean
waters of the state that shall be protected. These include industrial
water supply, water contact, and noncontact recreation, including
aesthetic enjoyment, navigation, commercial and sportfishing,
mariculture, preservation and enhancement of Areas of Special Biological
Significance, rare and endangered species, marine habitat, fish
migration, fish spawning, and shellfish harvesting.

Additional requirements of the Ocean Plan are defined water quality
objectives, including those regarding physical characteristics (such as
floating particulates, visible oil and grease, natural light reductions,
or deposition of inert solids such as to degrade benthic communities).
Chemical characteristics are also generally defined, for example,
depression of dissolved oxygen, a change from natural pH, and excessive
nutrient materials. Protected biological characteristics are marine
communities, including vertebrate, invertebrate, and plant species.
Taste, odor, and color of fish, shellfish, or other marine resources
used for human consumption shall not be altered. Neither shall the
concentrations of toxics or organic materials in marine resources used
for human consumption bioaccumulate to levels that are harmful to human
health. Clean Water Act

Section 402 of the Clean Water Act establishes the NPDES permitting
program. Subsection (a)(5) of Section 402 specifies that the
Administrator (EPA) may delegate authority to issue permits for
discharges to the State. As allowed per this subsection, the EPA has
delegated NPDES permitting authority to the RWQCB.

All point‑source dischargers are required to obtain and comply with the
provisions of an NPDES permit for any discharge of pollutants into
waters of the U.S. (e.g., oceans, lakes, or streams). NPDES permits must
contain discharge limitations based on the more stringent of the
applicable technology‑based requirements and water quality standards.
Because of the diffuser location, effluent from the IWTP that is
discharged through the SBOO will be discharged into state waters.
Therefore, RWQCB will be the authority issuing the NPDES permit for
operation of the IWTP.

Section 403(c) of the Clean Water Act establishes requirements for
discharges into federal ocean waters. For discharges to state waters,
review is delegated to the RWQCB. For the discharge through the SBOO
from the IWTP, EPA will use the Ocean Plan to satisfy the requirements
of Section 403(c). Thus, the Ocean Plan will be the primary source of
water quality standards applicable to the IWTP discharge.

For publicly owned treatment works such as the IWTP, the applicable
technology‑based requirements are the secondary treatment requirements.
Secondary treatment is defined by the EPA on the basis of three
characteristics of wastewater: BOD, a measure of how much oxygen will be
required by microorganisms to break down the organic material in
wastewater into carbon dioxide and water; TSS, the concentration of
solids in the discharge; and pH, a measure of acidity. The secondary
treatment requirements for BOD and TSS are more stringent than those set
forth in the Ocean Plan. However, secondary treatment will not be
available with the interim operation of the IWTP as described in this
SEIS.

Porter‑Cologne Water Quality Act

Under the Porter‑Cologne Act, the RWQCB issues waste discharge
requirements to sources of pollutants to state waters. Because the IWTP
discharges into state waters, the RWQCB will issue waste discharge
requirements for the IWTP discharge. The waste discharge requirements
will be based primarily on the Ocean Plan. The waste discharge
requirements will likely be contained in a joint document with the NPDES
permit. The RWQCB will issue the waste discharge requirements and the
NPDES permit for the interim operation of the IWTP.

Alternative 1: No Action

Impacts

Under the No Action alternative, the IWTP would not be operated until
the ocean outfall is complete and would only discharge effluent treated
to secondary standards. Under this alternative, raw sewage flows in
excess of the combined capacity of Tijuana Pump Station One and the
emergency connection would flow into the Tijuana River via Stewart\'s
Drain. These average excess sewage flows are estimated to be 5.6 mgd
(245 lps) by the year 2001, with high flow days reaching 9.5 mgd (416
lps). Additionally, by the year 2001, an average 17 mgd (745 lps) of
treated flows from San Antonio de los Buenos and an average of 22.9 mgd
(1,003 lps) of untreated flows would be discharged to the surf in Mexico
south of Punta Banderas.

Surf Discharges in Mexico

Modeling of the surf discharges in Mexico was performed by Parsons
Engineering Science, Inc. (1996) to determine the dispersion and
dilution of pollutants discharged with the wastewater. The results of
this modeling are compared with the Ocean Plan standards to determine
impacts.

Model Selection. A number of methods and models have been developed to
assess the fates of materials introduced into the surf zone. These
methods range from the relatively simple (e.g., Jirka 1990) to the
highly complex (see Proceedings of the 4th International Conference on
Estuarine and Coastal Modeling, American Society of Coastal Engineers
1995). However, no existing models are appropriate for the time‑ and
length‑scales associated with an assessment of the Mexican shoreline
discharge. The processes that determine the transport and fates of this
wastewater involve time‑scales ranging from seconds to years and
length‑scales ranging from meters to tens of kilometers. As a result, a
new, time‑dependent, two‑dimensional simulation model was developed for
this type of discharge and is referred to as the &quot;Shore Discharge
Model&quot; (SDM).

The model is driven by time‑series data on the coastal currents, wave
conditions, and effluent discharge. It partitions the coastal waters
into three zones‑the surf zone, the offshore

zone, and a transition zone. The properties of the

surf zone at any time are determined by the characteristics of the waves
at that time, while dispersion in the offshore zone is determined by the
coastal ocean currents and associated eddies. These two zones are
separated by a transition zone, where dispersion is associated with both
the waves (e.g., rip currents and undercurrent) and the ocean currents.

Oceanographic Data Used for Modeling. The primary force

driving circulation within the surf zone is energy from incident waves;
this energy varies in its direction and magnitude with incident wave
height, wave period, and wave direction. Wave data for the model
simulations were synthesized from a time‑series of historical wave
information for the Southern California Bight and developed specifically
for the discharge site using a wave refraction‑propagation model.

Periodic rip currents can be important factors in the exchange of
constituents between the surf zone and the offshore zone. A simplified
representation of this process was incorporated into the model, with the
rate of exchange related to the strength of the wave‑induced currents in
the surf zone (Inman et al. 1968).

Since the primary areas of interest in determining the potential impacts
of the effluent discharge are distances of kilometers to tens of
kilometers away from the discharge point, simplified representations
were used for the processes that are important in determining the
patterns of wastewater dispersion in the immediate vicinity of the
discharge in order to reduce the computation time. As a result, the
model does not accurately reproduce wastewater distributions close to
the discharge point. However, the mass input of wastewater is included
in the simulation to ensure that wastewater concentrations in the ocean
cannot exceed the initial effluent concentration

Data used in the input for offshore advective currents was based on
current meter measurements made during the baseline studies for the SBOO
work (Engineering Science 1988).

Effluent Quality. The San Antonio de los Buenos treatment facility is
designed to treat 17 mgd (745 lps) average daily flow and up to 25 mgd
(1,095 lps) using aerated facultative lagoons. Flows from the conveyance
canal flow through a preliminary sediment basin and then are pumped to a
series of two aerated facultative lagoons and a final, nonaerated
polishing lagoon. The treated effluent is then conveyed 2.6 kilometers
south for shoreline discharge with the bypassed untreated effluent. A
portion of the treated effluent is used for irrigation.

No increases in treatment capacity at the San Antonio de los Buenos
facility were assumed for discharge scenarios simulated in the year
2001. The simulation took into account the known diurnal flow
fluctuation at the San Antonio de los Buenos plant in determining the
percent volume of wastewater bypassed and discharged untreated. Effluent
quality was determined by the extent of wastewater treatment received by
the components of the combined discharge stream. Appendix A of the
discharge modeling report (Parsons Engineering Science 1996) details the
calculation used to specify the quality of effluent discharged.

Based on limited sampling conducted by Malcolm Pirnie Inc. in June 1996,
a bacteria concentration in the wastewater influent of 2 &#215; 108
total coliform per 100 ml was assumed at San Antonio de los Buenos. No
reduction in numbers of bacteria as a result of wastewater treatment was
assumed and no chlorination of the effluent from San Antonio de los
Buenos was assumed for the modeling. This analysis is conservative, as
the effluent from San Antonio de los Buenos is currently chlorinated
prior to discharge, although its effectiveness is not documented.

Discharged Bacteria. Bacteria discharged into the marine

environment undergo a bacterial disappearance (T90) concentration
reduction as a result of exposure to environmental factors such as salt
water, temperature, exposure to sunlight, predation,
flocculation/sedimentation, abrasion, and so on. This bacterial
disappearance rate, expressed as the time (in hours) required for 90
percent of the bacteria to die (T90), varies with respect to these
environmental factors, as well as with the depth of discharge. The
reduction in bacteria concentration (or apparent dilution) is computed
according to:

Dilution (T90) = 10 elapsed time/T90

Review of the literature (see Parsons Engineering Science 1996 for
discussion) regarding T90 rates resulted in the assumption of a rate of
four hours as a daily average in the surf zone into which the San
Antonio de los Buenos effluent is released. For the offshore zone, due
to low rates of vertical diffusion compared to horizontal mixing, the
effluent is assumed to be confined to the upper few meters of the water
column where bacteria are most susceptible to higher mortality rates.
Therefore, the rate assumed in the offshore zone of the model was the
same as for the surf zone.

The value of T90 represents a daily average value that varies diurnally.
The model simulations take this variation into account as it determines
the concentration of bacteria over time.

Effluent Dilution Contours. Wastewater effluent

discharged at the shoreline at Punta de los Buenos enters the surf zone
and is dispersed into the ocean by the action of waves and currents. The
SDM simulates the movement and resulting dilution of the effluent over
time. At any time during the simulation, the dilution of discharged
effluent can be determined (and, as a result, its concentration, by
dividing the initial concentration by the calculated dilution factor).
Constituents of concern in the discharge include metals, organics, and
other constituents that are transported with the movement of water along
the coast or offshore. Except for bacteria (for which T90 die‑off rates
are included), the model assumes that all constituents are
&quot;conservative&quot;; that is, that the concentration of the
pollutant changes only as a function of dilution and is not affected by
chemical or biological processes such as photodegradation. Thus, the
model may overestimate the concentrations of some constituents that are
subject to additional processes of reduction.

Figure 4.2‑1 displays the annual average dilution contours of
conservative constituents discharged in Mexico in the year 2001 for the
No Action alternative. Additionally, Table 4.2‑1 indicates the simulated
effluent dilutions at the international border resulting from the surf
discharges. Dividing the concentration in the effluent of any Ocean Plan
regulated constituent by the dilution factor in Table 4.2‑1 will yield
the concentration of that constituent at the international border for
the period selected. The dilutions shown in Table 4.2‑1 under the
&quot;Toxic Materials&quot; heading are for use in evaluating impacts
relative to the Ocean Plan objectives for the protection of marine
aquatic life. Those shown under the &quot;Others&quot; heading (i.e.,
the 30‑day average dilutions) are for evaluation of impacts relative to
the Ocean Plan standards for the protection of human health.

Based on the concentrations of substances that were detected during
influent testing (see Table 4.1‑1), no compounds are predicted to exceed
the daily maximum Ocean Plan standards at the international border.
Additionally, the only detected substances that may exceed the Ocean
Plan 30‑day average concentration standard are polyaromatic hydrocarbons
(PAHs).

TABLE 4.2‑1

SIMULATED EFFLUENT DILUTIONS AT INTERNATIONAL BORDER

SURF DISCHARGES IN MEXICO

NO PROJECT ALTERNATIVE, YEAR 2001

Toxic Materials Others‑

Nominal Instantaneous Daily 6‑Month 30‑Day

Month Minimum Minimum Median Average

January 48 59 111 358

February 34 46 152 250

March 12 112 473 1,219

April 33 60 663 1,107

May 111 124 8,584 6,793

June 15 29 2,509 473

July 11 18 328 336

August 14 17 176 301

September 14 16 93 381

October 20 25 83 1,131

November 21 39 75 1,388

December 12 19 80 1,268

SOURCE: Parsons Engineering Science, Inc.

NOTE: Dilutions expressed as ratio of parts of diluting water per one
part

of discharge effluent, e.g., 198:1.

Distribution of Discharged Bacteria. The distribution

of concentrations of bacteria in discharged effluent is similar to that
discussed for conservative constituents in the effluent. Average
concentration patterns of bacteria differ from those of conservative
constituents due to the disappearance of bacteria that is ongoing during
their dispersion with the discharged effluent. The concentration of
discharged bacteria at each station location addressed in the SDM is
expressed as a time‑series of hourly concentration over the year of
simulation.

An example of the time‑series of bacteria concentration is shown here as
Figure 4.22. At the international boundary, under the No Project
alternative, bacteria concentrations show occasional &quot;spikes&quot;
related to the upcoast transport of water by wave‑driven currents. These
concentrations rise and fall depending on the current regime and the
time of day. For example, during a period when waves cause rapid upcoast
transport, higher concentrations will most likely be found in the early
morning hours. This is because during the proceeding nighttime hours,
the bacterial reduction rate is low to nonexistent. During periods of
slower transport, the exposure to daylight will tend to even out the
concentration spikes. Based on wave predictions, wave‑induced upcoast
transport during June, July, and August is especially strong.

Figure 4.2‑1

Figure 4.2‑2

In general, as would be expected, the concentration of both the
conservative and nonconservative constituents is lower for simulation
stations located further away from the release point. The time‑series of
bacteria concentration figures for each modeled station may be found in
the modeling report (Parsons Engineering Science 1996).

From these time‑series, a table of monthly and annual bacteria
concentration at the international boundary was compiled and is included
as Table 4.2‑2. Tables for each modeled station may be found in the
modeling report (Parsons Engineering Science 1996). Table 4.2‑2 includes
the minimum and maximum hourly bacteria concentration, geometric mean
and median of hourly concentration, and number of occurrences with
concentrations greater than 1,000 per 100 ml during each month. The data
displayed in the tables are for the hours of 8:00 A.M. to 5:00 P.M.
daily, corresponding to the time of day when samples for compliance with
bacteria standards are generally collected.

A post‑processing numerical model was developed to determine the
potential for noncompliance with body‑contact standards for bacteria in
receiving waters. This &quot;compliance screening&quot; model was based
on the following criteria defined in the Ocean Plan:

Sample of water from each sampling station shall have a density of total
coliform organism less than 1,000 per 100 ml (10 per ml); provided that
not more than 20 percent of the samples at any sampling station, in any
30 day period, may exceed 1,000 per 100 ml (10 per ml), and provided
further that not a single sample when verified by a repeat sample taken
within 48 hours shall exceed 10,000 per 100 ml (100 per ml).

The model determined compliance or noncompliance for each simulated
station individually. As the first part of compliance, the model read
five hourly sample values during five different days of the month,
spaced five days apart, from a monthly set of input data. The input data
used was for the time period between 8 A.M. and 5 P.M., the time when it
is most likely that actual samples would be collected in the field. Each
of the five samples occurred at the same time of day. The process was
repeated 100 times (the total number of sampling combinations available
for that month) for a total of 500 samples in any 30‑day period. The
model determined what percentage of the sample values exceeded the
standard in the given month. If more than 20 percent of the samples
exceeded the standard, the program returned a value of &quot;NO&quot;
for noncompliance. If 20 percent or less of the samples exceeded the
standard, the program returned a value of &quot;YES&quot; for
compliance.

TABLE 4.2‑2

TOTAL COLIFORM (PER 100 ML) AT THE INTERNATIONAL BORDER

SHORE DISCHARGE MODEL

NO PROJECT ALTERNATIVE, YEAR 2001

Nominal Number of Geometric Observations Month1 Data Minimum Mean3
Median Maximum &gt;1,000/100 ml Points2 (%)

All 3,600 0 10 0 490,000 14

January 300 0 2 0 19,300 4

February 300 0 6 0 148,400 9

March 300 0 5 0 78,800 10

April 300 0 4 0 220,400 6

May 300 0 3 0 15,200 5

June 300 0 36 20 171,200 22

July 300 0 121 180 353,600 34

August 300 0 41 40 176,000 22

September 300 0 9 0 173,400 10

October 300 0 7 0 399,000 13

November 300 0 23 20 490,000 17

December 300 0 7 0 266,200 13

SOURCE: Parsons Engineering Science, Inc.

1To correspond to compliance requirements, months are considered as 12
consecutive, 30‑day periods.

2Hourly data from 8 A.M. to 5 P.M.

3In order to calculate geometric mean, all zero values were changed to 1
for this calculation.

Table 4.2‑2

For the second part of the screening (a standard of 10,000 per 100 ml),
the model read each sample from the 8 A.M. to 5 P.M. input data set
until it encountered the first sample with a value equal to or greater
than 10,000. At that point, it checked for the occurrence of a value
greater than 10,000 within the next 48 hours. If another such value was
encountered, a &quot;NO&quot; was recorded for noncompliance; otherwise,
the next value greater than 10,000 was located, if one existed.

The process was repeated until all the values in the input data files
were read. This procedure was then repeated for each of the stations
addressed by the model.

Further evaluation of the model found that these exceedances of 10,000
coliforms per 100 ml occurred less than three percent of the time at
stations north of the border. Also, the model is extremely sensitive in
that it executes as if it were a continuous coliform monitoring station.
The occurrence of the predicted spikes has not been observed in actual
coliform monitoring at several locations. Given that the exceedances are
probably only detectable by modeling, rare in frequency of occurrence,
and of limited duration, the potential exposure health risks are not
considered to be significantly adverse, as would be the case for
stations exceeding the 1,000 coliforms per 100 ml 20 times in a 30‑day
period. While the exceedances are noted for full and fair disclosure,
these exceedances in and of themselves are not considered to be
significant and adverse water quality impacts or human health risks.

Results of the evaluation of compliance are shown in Table 4.2‑3 for
three stations: the international border, the Tijuana River mouth, and
the Imperial Beach Pier. Compliance tables for all other modeled
stations are contained in the modeling report (Parsons Engineering
Science 1996). As seen in Table 4.2‑3, at the international boundary the
No Project alternative is out of compliance with both the 1,000 and the
10,000 standards during the months of June, July, August, and November.
During the remaining months, the No Project alternative is in compliance
with the body‑contact standards of 1,000/100 ml, but not with the
10,000/100 ml standard. Stations farther north tend to have fewer
periods of noncompliance, as would be expected.

Figure 4.2‑2 showed the 30‑day, 80‑percentile superimposed on the
time‑series of the concentration. The 80‑percentile curve is a graphic
&quot;comparison&quot; with the 1,000 MPN total coliform per 100 ml
standard in the sense that &quot;. . . 20 percent or less shall exceed
1,000 MPN per 100 ml.&quot; If the curve indicates less than 103, most
likely the month was in compliance with the standard. The curve is only
an indicator of possible compliance and has the advantage of showing the
annual trend. In an attempt to simulate the results of a sampling
program, the 80‑percentile was calculated only on the 8 A.M. to 5 P.M.
landings. The results indicated by the 80‑percentile curve are only to
be used as an indicator of compliance and may differ from the compliance
results shown in Table 4.2‑3 due to the following reasons:

All of the values between 8 A.M. and 5 P.M. were used in deriving the
80‑percentile, while Table 4.2‑3 results were computed as the average of
100 five‑sample sets per month.

The results in Table 4.2‑3 also incorporate the 10,000 total coliform
per 100 ml standard.

TABLE 4.2‑3

COMPLIANCE WITH BODY‑CONTACT STANDARDS

SURF DISCHARGES IN MEXICO

NO ACTION ALTERNATIVE, YEAR 2001

Location January February March April May June

International N border

Tijuana River Y Y N mouth

Imperial Beach Y Y Y Pier

Location July August September October November December

International N N N border

Tijuana River N N mouth

Imperial Beach Y Pier

Not in compliance with body‑contact standards of 1,000/100 ml. N

In compliance with body‑contact standards of 1,000/100 ml, but exceeded
coliform concentrations of 10,000/100 ml in model runs. Exceedance of
the 10,000/100 ml standard occurs less than 3 percent of the time.

Y In compliance with body‑contact standards of 1,000/100 ml and
10,000/100 ml.

Discharges to the Ocean from the Tijuana River

As indicated previously, by the year 2001 an estimated average 5.6 mgd
(245 lps) of untreated sewage flows would be dis charged directly to the
Tijuana River. High flow day discharges are estimated to reach 9.5 mgd
(416 lps). These flows would then travel to the Tijuana estuary, with
estimated travel times ranging from approximately 8 to 10 hours. The
wastewater would then mix with and be diluted by the water in the
estuary. The current tidal prism of the Tijuana estuary is estimated at
290 acre‑feet (0.36 Mm3). The diluted wastewater would then be
discharged to the ocean through the mouth of the river/estuary.

Ocean modeling of the discharged wastewater from the Tijuana River has
not been performed. However, discharges of untreated wastewater would be
inconsistent with the Clean Water Act and the State Ocean Plan.
Concentrations of pollutants in excess of Ocean Plan standards would
likely reach the ocean where they would be dispersed up and down the
coast. Additionally, high bacteria coliform counts could continue to
impact local beaches by forcing beach closures. Significance of Impacts

Significant oceanographic impacts would occur nearshore in the vicinity
of the Tijuana River mouth due to the direct discharge of untreated
wastewater to the Tijuana River. Pollutant concentrations in excess of
Ocean Plan standards may reach the ocean, and high bacteria coliform
counts would continue to significantly impact local beaches in the
United States.

Additionally, the discharge of both treated and untreated wastewater at
the shoreline in Mexico is expected to result in bacteria coliform
counts that could exceed the Ocean Plan standards in U.S. waters up to
the Tijuana River. This would continue to significantly impact local
beaches in the United States. Of the potential pollutants detected
during influent testing, only PAHs are expected to reach U.S. waters in
concentrations exceeding Ocean Plan standards. Nevertheless, if this
were to occur, it would be a significant impact.

Mitigation

Under the No Action alternative, mitigation is not available. The
discharges in Mexico are the responsibility of Mexico in coordination
with the IBWC under the provisions of Minute No. 270. The effects of the
discharges of sewage on oceanographic resources are considered
significant and unmitigated.

Alternative 2: Operate IWTP

Impacts

Under this alternative, in 1997 the IWTP will be operational and could
provide advanced primary treatment for 25 mgd (1,095 lps) average and 50
mgd (2,190 lps) peak flows. Raw sewage flows in excess of Tijuana Pump
Station One and the emergency connection capacity would flow to the IWTP
and be treated to primary standards. Effluent would then be pumped to
the emergency connection for further treatment at the Point Loma
treatment plant. Treated flows in excess of emergency connection
capacity would be discharged directly to the Tijuana River. The excess
effluent flow is estimated to be 3.6 mgd (158 lps) by the year 2001,
with high flow days reaching 7.5 mgd (329 lps). Additionally, by the
year 2001, 17 mgd (745 lps) of treated sewage and 22.9 mgd (1,003 lps)
of untreated sewage will be discharged to the shoreline in Mexico.

Surf Discharges in Mexico

The Mexican surf discharge flow volumes and impacts are identical with
those discussed above under the No Action alternative.

Discharges to the Tijuana River

The oceanographic impacts in the vicinity of the mouth of the Tijuana
River are similar to those discussed above under the No Action
alternative. However, rather than discharging untreated sewage to the
river, the excess flow discharged to the river will be advance primary
effluent. Additionally, in the year 2001 excess flows to the river are
anticipated to average 3.6 mgd (158 lps) of advance primary effluent as
compared to the 5.6 mgd (245 lps) flow of untreated sewage which flows
to the river under the No Action alternative. Therefore, oceanographic
impacts associated with implementation of the Operate IWTP alternative
are expected to be less than those which would occur under the No Action
alternative. Nevertheless, the direct discharge of advanced primary
effluent to the river and the resulting flow to the ocean would not be
authorized by the Clean Water Act and the Ocean Plan.

Significance of Impacts

Impacts associated with surf discharges in Mexico are identical with
those which would occur under the No Action alternative. Concentrations
of PAH pollutants reaching U.S. waters in excess of Ocean Plan Table B
standards, as well as bacteria coliform counts in excess of Ocean Plan
standards up to the mouth of the Tijuana River, would be a significant
impact.

Significant oceanographic impacts would occur nearshore in the vicinity
of the Tijuana River mouth and north to Imperial Beach due to the direct
discharge of advanced primary effluent to the river. Although these
impacts are anticipated to be less than those which would occur under
the No Action alternative, they nevertheless would be significant.

Mitigation

Under the Operate IWTP alternative, mitigation is not available.
Chlorination of the effluent is not considered feasible, due to the
potential toxic effects to aquatic organisms in the river, estuary, and
nearshore coastal waters. The discharges in Mexico are the
responsibility of Mexico in coordination with the IBWC under the
provisions of Minute No. 270. Mexico will determine if additional
measures are to be taken. The effects of the sewage and advanced primary
effluent on oceanographic resources are considered significant and
unmitigated.

Alternative 3: Operate IWTP with Detention Basin

Impacts

The IWTP would be operated as an advanced primary plant, as in the
Operate IWTP alternative. A 5.5 million gallon (20,900 m3) earthen
detention basin would be constructed at the IWTP site (Dairy Mart Road)
to provide flow equalization for diurnal and wet‑weather peak flows.
Treated flows would be stored within the detention basin to be released
to the emergency connection during off‑peak hours. If the capacity of
the Mexican system, emergency connection and detention basin would be
exceeded, then the excess treated flows would be discharged directly to
the Tijuana River in the U.S.

On average, through the year 2001, it is estimated that no advanced
primary effluent would be discharged to the Tijuana River under this
alternative. However, on high flow days up to 2.0 mgd (88 lps) of
advanced primary effluent could be discharged to the river.

Flows discharged at the shoreline in Mexico would be similar to those
which occur under the No Action and Operate IWTP alternatives (i.e., 17
mgd \[745 lps\] treated, 22.9 mgd \[1,003 lps\] untreated). Therefore,
oceanographic impacts due to the discharges in Mexico would be the same
as those discussed above for the No Action and Operate IWTP
alternatives.

Significance of Impacts

Impacts associated with surf discharges in Mexico are similar to those
which would occur under the No Action and Operate IWTP alternatives.
Concentrations of PAH pollutants reaching U.S. waters in excess of Ocean
Plan Table B standards, as well as bacteria coliform counts in excess of
Ocean Plan standards, would be a significant impact.

Dry‑weather discharges of advanced primary effluent to the Tijuana River
would only occur on high flow days with implementation of this
alternative. Therefore, although they would be considered significant,
nearshore oceanographic impacts in the vicinity of the Tijuana River
mouth are anticipated to be less than would occur under the No Action
and Operate IWTP alternatives.

Mitigation

Under the Operate IWTP with Detention Basin alternative, mitigation is
not available. The effects of the discharge of treated effluent on
oceanographic resources are considered significant and unmitigated. The
discharges in Mexico are the responsibility of Mexico in coordination
with the IBWC under the provisions of Minute No. 270.

Alternative 4: Operate IWTP with New Conveyance to Mexico

Impacts

A new pumping and conveyance system would be constructed by Mexico as a
parallel backup facility for the existing Mexican conveyance system,
with a capacity of 50 mgd (2,190 lps), to convey flows from Pump Station
One to the discharge point in Mexico. During the interim period, the
IWTP would treat flows up to 25 mgd (1,095 lps) from Tijuana. Once
treated, the effluent would be sent to Tijuana via the new pump station
and conveyance pipeline for discharge in Mexico, near the San Antonio de
los Buenos treatment plant. The existing pumping and conveyance system
to the treatment works in San Antonio de los Buenos would continue to
operate.

Additionally, there are two operation scenarios under this alternative.
In the first scenario, the emergency connection would continue to
receive untreated wastewater flows up to capacity for conveyance to
Point Loma. In the second scenario, the emergency connection would not
be utilized.

Under this alternative, no direct dry‑weather discharges to the Tijuana
River would occur.

In the year 2001, continued use of the emergency connection would result
in 17 mgd (745 lps) of San Antonio de los Buenos treated flows, 25 mgd
(1,095 lps) of IWTP treated flows, and 2.3 mgd (101 lps) of untreated
flows being discharged in Mexico (44.3 mgd \[1,941 lps\] total). On high
flow days, 17 mgd (745 lps) of San Antonio de los Buenos treated flows,
27 mgd (1,183 lps) of IWTP treated flows, and 4.6 mgd (202 lps) of
untreated flows would be discharged to the shoreline (48.6 mgd \[2,129
lps\] total).

Not utilizing the emergency connection would result in 17 mgd (745 lps)
of San Antonio de los Buenos treated flows, 25 mgd (1,095 lps) of IWTP
treated flows, and 9.6 mgd (421 lps) of untreated flows being discharged
in Mexico (51.62 mgd \[2,260 lps\] total). On high flow days, 17 mgd
(745 lps) of San Antonio de los Buenos treated flows, 27 mgd (1,183 lps)
of IWTP treated flows, and 12 mgd (526 lps) of untreated flows would be
discharged to the shoreline (56 mgd \[2,453 lps\] total).

As with the No Action alternative, the impacts due to the Mexican
shoreline discharges were modeled by Parsons Engineering Science using
the SDM. In addition to the increased flows discharged relative to the
No Action alternative, the quality of the discharges is different due to
the advanced primary treatment at the IWTP.

IWTP Effluent Quality

In the year 2001, the IWTP was assumed to treat a maximum annual daily
average volume of 25 mgd (1,095 lps). Treatment was assumed to consist
of advanced primary treatment without chlorination. The IWTP was assumed
to have a diurnal flow fluctuation, but the fluctuation was not assumed
to affect treatment quality.

The efficiency of constituent removal during the treatment process at
IWTP was assumed based on information on the type of treatment and known
efficiencies at treatment plants in the United States. At the IWTP, a 20
percent reduction in bacteria concentration was assumed as a result of
wastewater treatment. This resulted in a discharge concentration of
bacteria of 1.6 &#215; 108 total coliform per 100 ml.

Effluent quality for the San Antonio de los Buenos treatment plant and
for the untreated wastewater is as discussed above under the No Action
alternative.

Effluent Dilution Contours

The annual average dilution contours of conservative constituents
discharged in Mexico in the year 2001 for this alternative are very
similar to those presented in Figure 4.2‑1 for the No Action
alternative. The dilution contour figures for the scenarios with and
without the emergency connection may be found in the modeling report
(Parsons Engineering Science 1996). Table 4.2‑4 indicates the year 2001
simulated effluent dilutions at the international border resulting from
the surf discharges for the scenario utilizing the emergency connection;
Table 4.25 indicates the results for the scenario not utilizing the
emergency connection (also at the international border).

Review of the data in Tables 4.2‑4 and 4.2‑5 indicates that operation
without the emergency connection results in the worst‑case condition
(lower dilutions). This is due to the greater untreated sewage flows
that are discharged at the shoreline in Mexico when the emergency
connection is not utilized.

Based on the concentrations of substances that were detected during
influent testing (see Table 4.1‑1), no compounds are predicted to exceed
the daily maximum Ocean Plan standards at the international border.
Additionally, the only detected substances that could exceed the Ocean
Plan 30‑day average concentration standard at the international border
are PAHs.

Distribution of Discharged Bacteria

The time‑series of bacteria concentration in the year 2001 at each
modeled station is similar to that shown for the international border in
Figure 4.2‑2 for the No Action alternative. The time‑series of bacteria
concentration figures for each modeled station with and without the
emergency connection may be found in the modeling report (Parsons
Engineering Science 1996).

As with the No Action alternative, tables of monthly and annual bacteria
concentration at each modeled station were compiled. Table 4.2‑6 shows
the year 2001 results at the international border for the scenario
utilizing the emergency connection; Table 4.2‑7 shows the results for
the scenario not utilizing the emergency connection. Tables for each
modeled station may be found in the modeling report (Parsons Engineering
Science 1996). Comparison of the results in Table 4.2‑6 with those shown
in Table 4.2‑7 indicates that not utilizing the emergency connection
results in higher bacteria counts than would occur if the emergency
connection were utilized.

By comparing the results with Table 4.2‑2 (No Action alternative) it can
be seen, in general, that the Operate IWTP with New Conveyance to Mexico
alternative results in larger maximum bacteria coliform counts at the
international border than the No Action alternative.

TABLE 4.2‑5

SIMULATED EFFLUENT DILUTIONS AT INTERNATIONAL BORDER

SURF DISCHARGES IN MEXICO

OPERATE IWTP WITH NEW CONVEYANCE TO MEXICO ALTERNATIVE

NOT UTILIZING EMERGENCY CONNECTION, YEAR 2001

Toxic Materials Others‑

Nominal Instantaneous Daily 6‑Month 30‑Day

Month Minimum Minimum Median Average

January 52 62 114 375

February 38 50 168 262

March 11 118 485 1,235

April 34 70 590 1,202

May 132 149 6,086 7,369

June 14 26 1,920 491

July 14 21 338 348

August 15 18 190 315

September 15 17 99 398

October 16 23 88 1,179

November 28 43 76 1,411

December 14 22 84 1,382

SOURCE: Parsons Engineering Science, Inc.

NOTE: Dilutions expressed as ratio of parts of diluting water per one
part

of discharge effluent, e.g., 198:1.

TABLE 4.2‑4

SIMULATED EFFLUENT DILUTIONS AT INTERNATIONAL BORDER

SURF DISCHARGES IN MEXICO

OPERATE IWTP WITH NEW CONVEYANCE TO MEXICO ALTERNATIVE

UTILIZING EMERGENCY CONNECTION, YEAR 2001

Toxic Materials Others‑

Nominal Instantaneous Daily 6‑Month 30‑Day

Month Minimum Minimum Median Average

January 68 82 150 523

February 49 65 217 347

March 15 156 646 1,646

April 45 90 824 1,574

May 171 193 9,606 9,852

June 19 35 2,730 650

July 18 28 459 458

August 20 23 251 414

September 20 22 129 524

October 20 30 115 1,542

November 37 59 100 1,895

December 18 28 110 1,796

SOURCE: Parsons Engineering Science, Inc.

NOTE: Dilutions expressed as ratio of parts of diluting water per one
part

of discharge effluent, e.g., 198:1.

TABLE 4.2‑6

TOTAL COLIFORM (PER 100 ML) AT THE INTERNATIONAL BORDER

SHORE DISCHARGE MODEL

OPERATE IWTP WITH NEW CONVEYANCE TO MEXICO ALTERNATIVE

UTILIZING EMERGENCY CONNECTION, YEAR 2001

Nominal Number of Geometric Observations Month1 Data Minimum Mean3
Median Maximum &gt;1,000/100 ml Points2 (%)

All 3,600 0 16 0 1,079,140 18

January 300 0 3 0 61,660 6

February 300 0 8 0 369,740 11

March 300 0 7 0 248,780 13

April 300 0 6 0 495,480 10

May 300 0 4 0 39,400 8

June 300 0 71 40 428,580 28

July 300 0 290 400 866,640 41

August 300 0 84 60 457,720 29

September 300 0 13 0 464,360 15

October 300 0 11 0 970,340 15

November 300 0 43 20 1,079,140 24

December 300 0 10 0 720,980 15

SOURCE: Parsons Engineering Science, Inc.

1To correspond to compliance requirements, months are considered as 12
consecutive, 30‑day periods.

2Hourly data from 8 A.M. to 5 P.M.

3In order to calculate geometric mean, all zero values were changed to 1
for this calculation.

TABLE 4.2‑7

TOTAL COLIFORM (PER 100 ML) AT THE INTERNATIONAL BORDER

SHORE DISCHARGE MODEL

OPERATE IWTP WITH NEW CONVEYANCE TO MEXICO ALTERNATIVE

NOT UTILIZING EMERGENCY CONNECTION, YEAR 2001

Nominal Number of Geometric Observations Month1 Data Minimum Mean3
Median Maximum &gt;1,000/100 ml Points2 (%)

All 3,600 0 19 0 1,260,660 19

January 300 0 3 0 73,720 7

February 300 0 9 0 440,920 11

March 300 0 8 0 287,160 13

April 300 0 7 0 584,320 10

May 300 0 5 0 47,500 9

June 300 0 84 60 524,480 29

July 300 0 377 480 1,005,560 43

August 300 0 103 80 538,420 30

September 300 0 16 0 544,560 16

October 300 0 13 0 1,162,640 17

November 300 0 53 40 1,260,660 26

December 300 0 11 0 805,620 16

SOURCE: Parsons Engineering Science, Inc.

1To correspond to compliance requirements, months are considered as 12
consecutive, 30‑day periods.

2Hourly data from 8 A.M. to 5 P.M.

3In order to calculate geometric mean, all zero values were changed to 1
for this calculation.

This is due to the larger discharge flow volumes in Mexico which result
from implementation of this alternative.

Compliance tables were also generated for this alternative at the
international border, the Tijuana River mouth, and the Imperial Beach
Pier. The results are shown in Tables 4.2‑8 and 4.2‑9. Compliance tables
for all other modeled stations are contained in the modeling report
(Parsons Engineering Science 1996). As seen in these tables, at the
international border, this alternative is out of compliance with both
the 1,000 coliforms and the 10,000 coliforms standards during the months
of June, July, August, and November for both operation scenarios. During
the remaining months, this alternative is in compliance with the
body‑contact standards of 1,000/100 ml, but not with the 10,000/100 ml
standard. Stations farther north tend to have fewer periods of
noncompliance, as would be expected.

Significance of Impacts

Under the Operate IWTP with New Conveyance to Mexico alternative, no
direct dry‑weather discharges to the Tijuana River would occur.

However, oceanographic impacts to U.S. beaches and waters associated
with surf discharges in Mexico would be significant. High bacteria
coliform counts associated with the surf discharges could result in
continued and additional beach closures in the United States. Mitigation

No mitigation is required for the Tijuana River.

Under the Operate IWTP with New Conveyance to Mexico alternative,
mitigation for the surf discharges is not available to EPA and USIBWC.
Chlorination of the effluent is not considered feasible, due to the
potential toxic effects to aquatic organisms in nearshore coastal
waters. The effects of the treated effluent and untreated sewage on
oceanographic resources are considered significant and unmitigated. The
discharges in Mexico are the responsibility of Mexico in coordination
with the IBWC under the provisions of Minute No. 270. Mexico will
determine if additional measures are to be taken.

Alternative 5: Operate IWTP with Discharge to the SBOO

Impacts

The SBOO is currently under construction and is expected to be completed
in 1998. Once completed, an average 25 mgd (1,095 lps) of advanced
primary effluent from the IWTP would be discharged to the ocean. No
discharge to the Tijuana River or through the emergency connection would
be necessary.

Additionally, 17 mgd (745 lps) of San Antonio de los Buenos treated
flows and 9.8 mgd (429 lps) of untreated flows would be discharged to
the surf in Mexico (26.6 mgd \[1,165 lps\] total). On high flow days, 17
mgd (745 lps) of San TABLE 4.2‑8

COMPLIANCE WITH BODY‑CONTACT STANDARDS

SURF DISCHARGES IN MEXICO

OPERATE IWTP WITH NEW CONVEYANCE TO MEXICO ALTERNATIVE UTILIZING
EMERGENGY CONNECTION, YEAR 2001

Location January February March April May June

International N border

Tijuana River Y Y N mouth

Imperial Beach Y Y Y Pier

Location July August September October November December

International N N N border

Tijuana River N N mouth

Imperial Beach Y Pier

Not in compliance with body‑contact standards of 1,000/100 ml. N

In compliance with body‑contact standards of 1,000/100 ml, but exceeded
coliform concentrations of 10,000/100 ml in model runs. Exceedance of
the 10,000/100 ml standard occurs less than 3 percent of the time.

Y In compliance with body‑contact standards of 1,000/100 ml and
10,000/100 ml.

TABLE 4.2‑9

COMPLIANCE WITH BODY‑CONTACT STANDARDS

SURF DISCHARGES IN MEXICO

OPERATE IWTP WITH NEW CONVEYANCE TO MEXICO ALTERNATIVE

NOT UTILIZING EMERGENGY CONNECTION, YEAR 2001

Location January February March April May June

International N border

Tijuana River Y Y N mouth

Imperial Beach Y Y Y Pier

Location July August September October November December

International N N N border

Tijuana River N N mouth

Imperial Beach Pier

Not in compliance with body‑contact standards of 1,000/100 ml. N

In compliance with body‑contact standards of 1,000/100 ml, but exceeded
coliform concentrations of 10,000/100 ml in model runs. Exceedance of
the 10,000/100 ml standard occurs less than 3 percent of the time.

Y In compliance with body‑contact standards of 1,000/100 ml and
10,000/100 ml.

Antonio de los Buenos treated flows, and 12 mgd (526 lps) of untreated
flows would be discharged to the shoreline (29 mgd \[1,270 lps\] total).
This is substantially less total flow discharged to the surf than would
occur under any of the other four alternatives.

As with the No Action and Operate IWTP with New Conveyance to Mexico
alternatives, the impacts due to the Mexican discharges were modeled by
Parsons Engineering Science using the SDM. Additionally, the discharges
through the SBOO were also modeled.

TABLE 4.2‑10

SIMULATED EFFLUENT DILUTIONS AT INTERNATIONAL BORDER

SURF DISCHARGES IN MEXICO

OPERATE IWTP WITH DISCHARGE TO SBOO, YEAR 2001

Toxic Materials Others‑

Nominal Instantaneous Daily 6‑Month 30‑Day

Month Minimum Minimum Median Average

January 71 84 165 579

February 52 68 239 357

March 14 160 755 1,717

April 45 104 1,016 1,701

May 178 205 16,181 11,442

June 21 42 4,517 709

July 16 34 490 504

August 20 23 271 428

September 20 22 141 557

October 20 29 127 1,583

November 32 65 112 2,135

December 18 31 122 1,883

SOURCE: Parsons Engineering Science, Inc.

NOTE: Dilutions expressed as ratio of parts of diluting water per one
part of discharge effluent, e.g., 198:1.

Surf Discharges in Mexico

Effluent Quality. The year 2001 effluent quality used

in the simulation for the shore discharges is basically the same as that
described above under the No Action alternative.

Effluent Dilution Contours. The annual average dilution

contours of conservative constituents discharged in Mexico in the year
2001 for this alternative are very similar to those presented in Figure
4.2‑1 for the No Action alternative. The dilution contour figure for
this alternative may be found in the modeling report (Parsons
Engineering Science 1996). Table 4.2‑10 indicates the year 2001
simulated effluent dilutions at the international border resulting from
the surf discharges.

Comparison of the data in Table 4.2‑10 with the data in Tables 4.2‑1,
4.2‑4, and 4.2‑5 indicates that, in general, the highest dilutions of
the surf discharge are obtained with this alternative. This is because
the Operate IWTP with Discharge to SBOO alternative results in the
lowest flow discharged in Mexico.

Based on the concentration of substances that were detected during
influent testing (see Table 4.1‑1), no compounds are predicted to exceed
the daily maximum Ocean Plan standards at the international border.
Additionally, the only detected substances that could exceed the Ocean
Plan 30‑day average concentration standard at the international border
are PAHs.

Distribution of Discharged Bacteria. The time‑series of

bacteria concentration in the year 2001 at each modeled station is
similar to that shown for the international border in Figure 4.2‑2 for
the No Action alternative. The time‑series of bacteria concentration
figures for each modeled station with and without the emergency
connection may be found in the modeling report (Parsons Engineering
Science 1996).

Monthly and annual bacteria concentration at each modeled station were
compiled and are shown in Table 4.2‑11 at the international boundary.
Tables for each modeled station may be found in the modeling report
(Parsons Engineering Science 1996).

A compliance table was also generated for this alternative at the
international border, the Tijuana River mouth, and the Imperial Beach
Pier and is shown in Table 4.2‑12. Compliance tables for all other
modeled stations are contained in the modeling report (Parsons
Engineering Science 1996). As seen in Table 4.2‑12, at the international
border this alternative is out of compliance with both the 1,000
coliform and 10,000 coliform standards during the months of June, July,
August, and November. During the remaining months, this alternative is
in compliance with the body‑contact standards of 1,000/100 ml, but
concentrations of coliforms above 10,000/100 ml could occur. Stations
farther north are within the 1,000 coliform standard year‑round.

SBOO Discharges

Advanced primary effluent discharges through the SBOO were modeled by
Parsons Engineering for this alternative. Modeling of the effluent
dispersion and dilution involved the use of the following five models:

Initial Dilution Model. The initial dilution model (RSB‑TSI) used in
this study was a modified version of the RSB computer model, the primary
initial dilution model recommended by the EPA. This model was developed
by Dr. Philip Roberts and is based on the experimental results conducted
under contract with the EPA. The initial dilution model used in this
study was derived from the RSB model by using the same algorithms with
two minor modifications that enable the model to run time‑series and to
converge more efficiently. The model was fully tested and was the basic
tool used in the recent city of San Diego Point Loma 301(h) Waiver
Application for Modification of Secondary Treatment Requirements (City
of San Diego, April 1995). In that study, the model results were
verified by EPA independent contractors.

TABLE 4.2‑11

TOTAL COLIFORM (PER 100 ML) AT THE INTERNATIONAL BORDER

SHORE DISCHARGE MODEL

OPERATE IWTP WITH DISCHARGE TO SBOO, YEAR 2001

Nominal Number of Geometric Observations Month1 Data Minimum Mean3
Median Maximum &gt;1,000/100 ml Points2 (%)

All 3,600 0 11 0 767,020 14

January 300 0 2 0 41,280 5

February 300 0 7 0 240,560 10

March 300 0 5 0 168,440 9

April 300 0 4 0 320,900 8

May 300 0 3 0 26,840 6

June 300 0 43 20 294,360 23

July 300 0 158 180 572,460 34

August 300 0 47 20 302,920 25

September 300 0 9 0 305,060 12

October 300 0 7 0 672,940 11

November 300 0 20 0 767,020 18

December 300 0 8 0 485,920 13

SOURCE: Parsons Engineering Science, Inc.

1To correspond to compliance requirements, months are considered as 12
consecutive, 30‑day periods.

2Hourly data from 8 A.M. to 5 P.M.

3In order to calculate geometric mean, all zero values were changed to 1
for this calculation.

TABLE 4.2‑12

COMPLIANCE WITH BODY‑CONTACT STANDARDS

SURF DISCHARGES IN MEXICO

OPERATE IWTP WITH DISCHARGE TO SBOO, YEAR 2001

Location January February March April May June

International N border

Tijuana River Y Y mouth

Imperial Beach Y Y Y Pier

Location July August September October November December

International N N N border

Tijuana River N N mouth

Imperial Beach Y Pier

Not in compliance with body‑contact standards of 1,000/100 ml. N

In compliance with body‑contact standards of 1,000/100 ml, but exceeded
coliform concentrations of 10,000/100 ml in model results. Exceedance of
the 10,000/100 ml standard occurs less than 3 percent of the time.

Y In compliance with body‑contact standards of 1,000/100 ml and
10,000/100 ml.

Current Flow Model. A diagnostic flow model that interpolates and
extrapolates the flows measured at the current meter moorings to the
region of the study area was used to reproduce the currents at the
mooring locations, preserve the continuity condition, and incorporate
the dominant terms in the governing equations of flow (the Navier‑Stokes
equations). This model was previously used in the initial analysis of
the oceanographic data collected during the SBOO studies.

Hydrodynamic Model. A finite‑element, two‑dimensional,

hydrodynamic numerical flow model (RMA2) was used to produce the
detailed flows (at four depths) within the study area, based on the
general flow patterns generated from the diagnostic model. Versions of
this model have been used to simulate ocean flows in a variety of
studies around the world.

Sediment Transport and Deposition Model. In the particle

deposition model (DEP), imaginary particles are released at the location
of the outfall, then tracked over many time‑steps as their motion is
simulated. While this method can be used for a dissolved or suspended
constituent, its particular advantage is in the simulation of settleable
particulates. The flexibility of the method permits simulation of the
range of particle sizes and the associated distribution of settling
velocities in treated sewage effluent.

Tracking and Water Quality Model. The tracking and water

quality model used in this study was an updated version of the TRACKER
model described in Appendix D of the South Bay Outfall Preliminary
Planning Study (Engineering Science 1990). The puff‑tracking model
simulates the advection and spreading of the effluent plume as a
sequence of discrete &quot;puffs&quot; of effluent. This model is
capable of tracking the wastefield and calculating physical
characteristics and bacterial concentrations in the wastefield as it
moves under the influence of the currents.

The SBOO simulation area extends approximately 8.7 miles (14 km) south
and 20 miles (32 km) north from the border with Mexico. The latter lies
approximately 10 miles (16 km) north of Point Loma. The area extends
about 6.2 miles (10 km) offshore from the coast at the northern boundary
and 10.5 miles (17 km) from the coast at the southern boundary.

Oceanographic Data Used for Modeling. All the simulation

models require information on the ocean currents. The initial dilution
simulations require information on the currents within the entrainment
region of the water column during the initial dilution process; the
transport simulations; and the properties of the currents at the water
depths occupied by the wastefield formed by the discharge. Both types of
information were provided by a year of time‑series measurements of
currents at multiple depths collected at an array of moorings located
within the study area (Engineering Science 1988).

The initial dilution simulations also require information on the density
structure of the water column. A year of hydrographic data, collected
monthly with an electronic conductivity‑temperature‑depth profiler at an
array of stations, was used to provide this information.

The initial dilution simulations used the current meter data collected
in the lower half of the water column at the mooring closest to the
terminus of the proposed discharge (after decimating to hourly
intervals). The transport modeling used the collective set of data from
all the moorings. The raw data was initially filtered into new
time‑series based on the time‑scales of the fluctuations (supertidal,
tidal, and subtidal + net flow frequency bands), analyzed for persistent
or energetic flow patterns (using empirical orthogonal function analysis
on the subtidal frequency fluctuations), then extended over the study
area using the stream function‑based diagnostic model. The resulting
one‑year‑long hourly time‑series for the dominant flows were used to
provide the boundary conditions for the RMA2 hydrodynamic simulations. A
year‑long hourly time‑series of the supratidal, tidal, and residual
subtidal (i.e., not part of the dominant flows) fluctuations in the
cross‑shore component of the currents measured between the discharge and
the coast was also used by the RMA2 model to drive the simulated
cross‑shore flows.

Model Assumptions. In addition to assumptions regarding

the quantity and characteristics of the discharged effluent and the
mortality of bacteria present in the wastewater as required for the SDM,
additional assumptions were required for the SBOO modeling. Suspended
solids present in the effluent were assumed to settle in the ocean as
discrete particles (i.e., the effects of aggregation were minimal over
the time‑scales characterizing the deposition in the immediate vicinity
of the discharge‑the area with the greatest impacts).

A number of assumptions were also required about the characteristics of
the ocean currents. First, it was assumed that the currents measured
during the year‑long study were representative of the currents typically
present in the area. It was also necessary to partition the
density‑stratified water column into multiple layers (by depth) in order
to assess the potential for the intrusion of discharged wastewater to be
carried into inshore protected waters. Therefore, flow simulations were
carried out for four discrete layers (0‑5 m, 5‑10 m, 10‑15 m, and &gt;15
m \[0‑17 ft, 17‑34 ft, 34‑50 ft, and &gt;50 ft\]). Based on the
similarity of the dominant flows measured at various depths in the water
column, it was assumed that the two identified dominant flows in the
current meter data could be used as the boundary conditions for each
layer in the hydrodynamic model (RMA2). In general, these dominant flows
do not include substantial contributions from cross‑shore motions‑but
these flows could be important for the cross‑shore transport of
wastewater into nearshore protected waters. Therefore, it was assumed
that a simplified cross‑shore flow, driven by the measured currents,
could be added to the RMA2 flows to simulate this cross‑shore transport
(see Parsons Engineering Science 1996 for more details).

Effluent Characteristics and Quality. In general, assumptions regarding
effluent characteristics and quality are the same as those for the SDM
discussed above under the No Action alternative. However, review of the
literature regarding T90 rates resulted in the assumption of a rate of
eight hours as a daily average in the offshore area where the SBOO is
proposed. This rate is different from that assumed for the SDM; the
effluent discharged at SBOO is released and distributed deeper in the
water column, where bacteria are less susceptible to higher mortality
rates than in the surf zone and upper layer of the water column.

Effluent Dilution Contours. Effluent dilution contours

represent an average dilution of discharged effluent over some period of
time. Figure 4.2‑3 presents annual average dilution contours for
effluent discharged from the proposed SBOO for each of the four water
layers evaluated in this scenario. Each layer is simulated separately;
the initial dilution simulation partitions the effluent plume into each
layer depending on water column conditions at the time of discharge.
Water currents in the four layers, although generally very similar in
magnitude and direction, differ in proximity of the coast as a result of
the differing bathymetry.

The evaluation of effluent dilution and the concentration of
conservative constituents included the potential effect of reentrainment
of effluent discharged from the outfall at an earlier time, which was
carried by advection back to the area near the outfall and was subject
to being entrained again into the effluent plume.

Effluent dilution contours for each water column layer during each month
of the year of the simulation are presented in the modeling report
(Parsons Engineering Science 1996).

These contours represent the amount of dilution simulated for
conservative constituents in the effluent (bacteria concentrations are
evaluated separately, below). As discussed in the No Action alternative
section, the physical dilution process was assumed to be the only factor
determining the concentration of conservative constituents, rather than
biological, physical, or chemical processes. As can be observed from
Figure 4.2‑3, the additional dilution beyond the zone of initial
dilution (ZID) is substantial, with annual average values of 50,000:1 at
the surface above the discharge and 100,000:1 approaching the shoreline.
In deeper waters, the additional dilution in the immediate area (3,281
feet, or 1,000 m) around the ZID is 2,000:1.

Ocean Plan compliance for toxic pollutants present in the proposed SBOO
discharge must be met at the edge of the ZID, as defined by the Ocean
Plan. Table 4.2‑13 indicates the year 2001 simulated dilution of
discharged effluent at the edge of the ZID for each month of the year in
intervals corresponding to the requirements of the Ocean Plan. Based on
the concentrations of substances that were detected during influent
testing (see Table 4.1‑1), no compounds are predicted to exceed the
daily maximum Ocean Plan standards at the ZID. Additionally, the only
detected substances that may exceed the Ocean Plan 30‑day average
concentration standard at the ZID are PAHs.

Distribution of Discharged Bacteria. The distribution

of pathogenic bacteria in the receiving waters of the study area is
dependent on initial concentrations following discharge and initial
dilution of effluent, magnitude and direction of waterFigure 4.2‑3

TABLE 4.2‑13

SIMULATED EFFLUENT DILUTIONS AT SBOO ZONE OF INITIAL DILUTION

OPERATE IWTP WITH DISCHARGE TO SBOO, YEAR 2001

Toxic Materials Others‑

Nominal Instantaneous Daily 6‑Month 30‑Day

Month Minimum Minimum Median Average

January 198 495 326 605

February 179 260 358 490

March 175 279 364 331

April 156 192 360 236

May 100 127 350 211

June 117 151 295 247

July 117 153 269 255

August 122 198 253 265

September 122 214 248 273

October 140 259 264 324

November 130 243 281 315

December 186 319 309 566

Dilution 100 100 100 100

to be

achieved

SOURCE: Parsons Engineering Science, Inc.

NOTE: Dilutions expressed as ratio of parts of diluting water per one
part

of discharge effluent, e.g., 198:1.

Dilutions to be achieved is based on requirements in Engineering

Science 1993.

currents, and the mortality rate of the bacteria. The dispersion model
simulates the distribution of bacteria in four layers of the water
column. The resulting distribution of bacteria can differ significantly
from location to location and between water column layers.

Concentrations of bacterial indicators are of regulatory concern
primarily in areas where body‑contact recreation occurs. In this
analysis, a total of 23 locations were selected for examination, based
on water depth, location near kelp beds, or location near other
sensitive areas.

The distribution of discharged bacteria at each station location
addressed in the ocean discharge model is expressed as a time‑series of
concentration over the year of simulation. The time‑series displays the
concentration of bacteria on an hourly basis at that station.

An example of the time‑series of bacteria concentration is shown here as
Figure 4.24. In water column layer 3 (depth range 10 to 15 m \[34‑50
ft\]) at Station D8 (the station in the Imperial Beach kelp bed closest
to the proposed outfall location), bacteria concentrations show
occasional &quot;spikes&quot; related to the inshore transport of water
by advective currents. These concentrations rise and fall depending on
the current regime and the mortality rate of the bacteria.

Time‑series were generated for each of the four water column layers at
each of the 23 stations addressed by the model (except where the maximum
station depth was less than the depths encompassed by each layer). These
time‑series, grouped by station, are available in the modeling report
(Parsons Engineering Science 1996).

From these time‑series, a table of monthly and annual bacteria
concentration for each station and each layer was compiled. Each table
includes the minimum and maximum hourly bacteria concentration,
geometric mean and median of hourly concentration, and number of
occurrences with concentrations greater than 1,000 per 100 ml during
each month, which is the most common requirement period of compliance.
The data displayed in the tables is for the hours of 8:00 A.M. to 5:00
P.M. daily, corresponding to the time of day when samples for compliance
with bacteria standards are generally collected.

An example of the monthly bacteria concentration table is shown here as
Table 4.2‑14. The example is for Station D8 in layer 3 (near the
Imperial Beach kelp bed as described above), corresponding to the
bacteria concentration time‑series shown in Figure 4.2‑4. The table
includes the minimum and maximum hourly bacteria concentration,
geometric mean and median of hourly concentration, and number of
occurrences with concentrations greater than 1,000 per 100 ml during
each month. The data displayed in the tables is for the hours of 8:00
A.M. to 5:00 P.M. daily, corresponding to the time of day when samples
for compliance with bacteria standards are generally collected.

Tables of bacteria concentration for all stations and water column
layers are included in the modeling report (Parsons Engineering Science
1996).

The potential for noncompliance with body‑contact standards for bacteria
in receiving waters was computed using a numerical model similar to that
discussed under the No Action alternative for the SDM. Only modeled
station D8 (near the Imperial Beach kelp bed), layers 3 and 4, exceeded
the 10,000/100 ml Ocean Plan standard during the months of February,
November, and December. As this occurred in less than three percent of
the samples, it is not considered to represent a health risk. All other
modeled stations, as well as modeled station D8 during the remaining
months, met both the 1,000 and 10,000 standards.

The compliance results for all modeled stations are included in the
modeling report (Parsons Engineering Science 1996).

Change in pH of Receiving Waters. Ocean Plan requirements state that the
change in receiving water pH as a result of the effluent discharge must
be no more than 0.2 unit everywhere, with the exclusion of the ZID. The
time‑series of effective initial dilution simulated by the model was
used as the basis for the evaluation.

Figure 4.2‑4

TABLE 4.2‑14

TOTAL COLIFORM (PER 100 ML) NEAR THE IMPERIAL BEACH KELP BED OCEAN
DISCHARGE MODEL

OPERATE IWTP WITH DISCHARGE TO SBOO, LAYER 3, YEAR 2001

Nominal Number of Geometric Observations Month1 Data Minimum Mean Median
Maximum &gt;1,000/100 ml Points2 (%)

All 3,600 16 21 16 182,440 2

January 300 16 20 16 90,806 2

February 300 16 23 16 182,440 4

March 300 16 17 16 3,823 1

April 300 16 19 16 4,137 1

May 300 16 25 16 15,817 3

June 300 16 16 16 17 0

July 300 16 18 16 633 0

August 300 16 18 16 6,638 1

September 300 16 17 16 134 0

October 300 16 23 16 58,522 2

November 300 16 35 16 175,055 9

December 300 16 24 16 83,377 2

SOURCE: Parsons Engineering Science, Inc.

NOTE: Depth, 10‑15 meters.

1To correspond to compliance requirements, months are considered as 12
consecutive, 30‑day periods.

2Hourly data from 8 A.M. to 5 P.M.

Values for receiving water pH were taken from baseline studies in the
SBOO area (Engineering Science 1988); effluent pH was assumed based on
historical effluent data from Point Loma. Point Loma data was used for
pH, since no definitive pH values were available for the various Tijuana
wastewater characterizations thus far prepared. For each month of the
year, the instantaneous minimum, monthly average, and monthly maximum
dilution values were used to determine potential changes in pH resulting
from these conditions. Available data indicate that the maximum change
in receiving water pH would be 0.09 occurring during the month of May.
Therefore, the requirements of the Ocean Plan for changes in receiving
water pH would not be violated.

A more detailed discussion of the assumptions and calculations for
determining compliance with Ocean Plan requirements for pH is included
in the modeling report (Parsons Engineering Science 1996).

Dissolved Oxygen Levels. The Ocean Plan requires that:

The dissolved oxygen concentration shall not at any time be depressed
more than 10 percent from that which occurs naturally, as the result of
the discharge of oxygen demanding waste material.

The modeling report prepared for the project (Parsons Engineering
Science 1996) presents calculations of the dissolved oxygen depression
due to the release of oxygen demanding waste materials from the SBOO.
Separate calculations were performed for water column, sediment
resuspension, and steady‑state. All three analyses indicated that the
dissolved oxygen depressions would be within the 10 percent standard
specified in the Ocean Plan.

Deposition and Accumulation of Suspended Solids. The depositional
pattern and rates of deposition of effluent and natural particles
depends on the mass distribution of their settling speeds, the strength
and spatial and temporal variability of the ocean currents, and the
distance they must settle to reach the ocean bottom. At the time of
discharge, wastewater normally contains particles with a wide range of
settling speeds. For primary treated effluent, this range can extend
from settling speeds faster than 0.01 cm/sec to slower than 10‑4 cm/sec.

A complete discussion of the sediment deposition modeling is presented
in the modeling report for the project (Parsons Engineering Science
1996).

Results of the modeling indicate that the annual average deposition rate
adjacent to the outfall is on the order of 2 g/m2/day. This deposition
rate occurs over an area of approximately 39.5 acres (16 ha) (Figure
4.2‑5). This is of sufficiently small magnitude that erosion due to wave
and storm action will prevent the buildup of any significant amount of
material around the outfall. Monthly sediment deposition contour plots
are presented in the modeling report.

Significance of Impacts

As with the other alternative, impacts associated with surf discharges
in Mexico would be significant. Concentrations of PAHs could reach U.S.
waters in excess of Ocean Plan standards. Additionally, bacteria
coliform counts in excess of Ocean Plan standards will continue to
occur. These impacts are unavoidable.

Figure 4.2‑5

No dry‑weather discharges to the Tijuana River are forecasted to occur
with implementation of this alternative.

Concentrations of PAHs in the zone of initial dilution of the SBOO in
excess of Ocean Plan standards could potentially occur. This would be a
significant impact. Additionally, bacterial coliform counts in excess of
the 10,000 coliform per 100 ml Ocean Plan standards could occur at a
depth of 50 feet (15 m) near the Imperial Beach kelp beds during certain
months. As the likelihood of this exceedance occurring is under one
percent of all samples taken during the year, the potential for
exceedance is not considered a significant impact. Mitigation to reduce
the impacts to below a level of significance (i.e., to achieve the Ocean
Plan standards) may be feasible, however.

The discharge of advanced primary effluent to the ocean through the SBOO
is not authorized by the federal Clean Water Act. The operator will
comply with a discharge permit and compliance order issued by the RWQCB.
This is a significant unavoidable impact.

No significant impacts would occur to the pH of the receiving waters or
to the dissolved oxygen content in the vicinity of the SBOO.
Accumulation of deposited solids near the outfall would not be
significant.

Mitigation

Mitigation for the impacts due to the surf discharges in Mexico is not
available to EPA or USIBWC for the Operate IWTP with Discharge to SBOO
alternative. The effects of the discharge of treated effluent and sewage
on oceanographic resources are considered significant and unmitigated.
The discharges in Mexico are the responsibility of Mexico in
coordination with the IBWC under the provisions of Minute No. 270.
Mexico will determine if additional measures are to be taken.

Bacterial coliform impacts due to discharge of advanced primary effluent
from the SBOO would not be significant and do not require mitigation
measures.

Impacts due to PAHs concentrations can only be mitigated by source
identification and reduction. As indicated in the previous EIS, Mexico
has agreed to implement a source reduction program, which is under
development. However, until a program is implemented, this impact is
considered significant and unmitigated.

No other mitigation is required. However, as indicated above, the direct
discharge of advanced primary effluent to the ocean is not authorized
under the federal Clean Water Act.

Terrestrial Biology

The following section is an assessment of potential impacts to
terrestrial biological resources within the riparian corridor of the
Tijuana River that may occur due to the implementation of any of the
proposed interim discharge alternatives. A discussion of potential
sources of impacts to the riparian corridor is presented. How these
impact sources apply to each of the interim discharge alternatives is
discussed separately below.

Potential Impact Sources

The discussion of potential impacts to the riparian corridor of the
Tijuana River is relevant in those situations where the discharge of
sewage or treated effluent is made directly to the river. Under this
condition, the major factors that may have an effect on the riparian
habitat include nutrient additions, shifts in the biological oxygen
demand, and introduction of toxic elements. Nutrient Loading

The discharge of less than tertiary treated sewage effluent will contain
relatively high concentrations of certain nutrients. Most notably with
regard to plants is the concentrations of inorganic nitrogen and
phosphorus. Excessive inputs of these nutrients can alter the growth of
plants. High nitrogen levels can cause an increase in above ground
productivity (shoots and leaves), reduced root development, and a
general yellowing of the leaves. Elevated phosphorus levels tend to
increase root production relative to above ground productivity and
produce leaves that are dark green. When one or the other nutrient is
elevated these symptoms can have a dramatic effect on the long‑term
vigor of the plant. When elevated together, they tend to counteract the
effects of each other, up to a point, increasing overall plant
productivity. However, chronic long‑term exposure to elevated levels of
nitrogen and phosphorus ultimately may negatively affect the vigor of
plants decreasing their resistance to other environmental factors (i.e.,
disease, water stress).

Increases in nutrient levels of streams, especially elevated levels of
nitrogen and phosphorus, can result in the eutrophication of this
aquatic system. Eutrophication involves increases in nutrient levels
with a corresponding increase in aquatic plant and animal productivity
and decreases in dissolved oxygen levels of the water. Although this
process is most prevalent in the succession of lakes, stream
eutrophication can occur near the mouths of rivers and streams where
nutrient loads and sedimentation are greatest.

The addition of nitrogen and phosphorus from sewage discharged to the
river may have only a limited effect on the riparian habitat within the
corridor. Losses of nitrogen can be substantial due to leaching. Large
accumulations of these two nutrients in the soils of the river channel
are unlikely in the long term due to the seasonally flooding of the
river that transports large sediment loads to the ocean, thus removing
excess nutrient levels.

Increased BOD

Advanced primary treated sewage has a relatively high organic matter
content. Discharge of this type sewage to a stream or river can increase
the BOD of the aquatic system for some distance from the discharge
point. Bacterial decomposition of the elevated organic material levels
in the sewage coupled with potential increases in algae increases the
BOD and reduces the dissolved oxygen content of the water. As the flows
get further from the discharge point, the water gets aerated naturally
and the BOD decreases. The extent or distance this &quot;oxygen
sag&quot; occurs in the river is dependent on the flow rate, organic
content of the sewage, and rate of natural aeration of the water.

High BODs can have a detrimental effect on aquatic wildlife. Certain
fish species and aquatic insects can be eliminated from areas of high
BOD and replaced with less desirable species that have lower oxygen
demands. This impact would be most evident in the estuarine system near
the mouth of the river where sewage may become trapped in tidal
channels. Areas of the Tijuana River that could be most effect by
potentially high BOD would be backwater areas where water may pond for
long periods of time.

Toxic Elements

Sewage effluent may contain varying concentrations of toxic elements,
particularly heavy metals. Elements such as cadmium, lead, arsenic, and
selenium are examples of toxic elements that could be present in the
sewage effluent. Although in certain cases these elements may be
concentrated in the soil and eventually wind up in the food chain, the
uptake of these elements by the riparian plants of the Tijuana River
corridor to toxic levels is unlikely. Cadmium, lead, selenium, and
arsenic are mostly unavailable to plants for uptake due to the ionic
state these elements are in within the soil environment. Transfer of
these elements up the food chain is more likely to occur in aquatic
plants and fish that feed on these plants, rather than in more
terrestrial plants such as willows. Alternative 1: No Action

Impacts

Under this alternative raw sewage would flow in the Tijuana River
channel. These flows would carry the increased nutrient levels, the
highest organic matter contents, and highest concentrations of toxic
elements through the system. Most of these constituents flow through the
riparian area to the estuary and ocean at the mouth of the river.
Potential concentration of nutrients, organic matter, and toxic elements
would only be evident in backwater areas where water ponds for long
periods of time. These ponds may pose a human health hazard due to fecal
coliform contamination , the potential for mosquito breeding areas, and
transmission of diseases (e.g., encephalitis).

In the short term, effects on the riparian habitat of the Tijuana River
in these areas may be beneficial through the addition of supplemental
water and nutrients. This condition could cause an increase in
recruitment of riparian plants along the low‑flow channel. However, it
is doubtful that any habitat created will remain due to seasonal flood
scour which recontour the low‑flow channel annually. No impacts to
federal endangered or threatened species are anticipated.

Significance of Impacts

No significant adverse impacts to terrestrial habitat or sensitive
species are anticipated.

Mitigation

No mitigation measures in addition to commitments made in the previous
EIS and Biological Opinion for the project are required. Alternative 2:
Operate IWTP

Impacts

Under this alternative, the IWTP would operate to detain and treat the
captured sewage to advanced primary levels prior to discharge to the
emergency connection or, if no capacity is available, the Tijuana River.
This process will remove up to 75 percent of the solids (organic
matter), some level of the toxic elements (those levels absorbed to the
solids, grease, and oil that are removed), and little if any nutrients.

Potential effects to the riparian habitat of the river are expected to
be the same as the No Action alternative, but at a much slower rate due
to lower BODs and toxic elements. No adverse impacts are anticipated.

Significance of Impacts

No significant adverse impacts to terrestrial habitat or sensitive
species are anticipated.

Mitigation

No mitigation measures in addition to commitments made in the previous
EIS and Biological Opinion for the project are required. Alternative 3:
Operate IWTP with Detention Basin

Impacts

Under this alternative, the IWTP would treat the sewage to advanced
primary levels and store the effluent in a lined earthen detention basin
for later discharge to Point Loma through the emergency connection.
Discharges to the Tijuana River under this alternative are not expected
during average dry‑weather conditions through the year 2001, but up to
2.0 mgd (88 lps) could occur during seasonal high flows in 2001 when
excess effluent will need to be put in the river.

The long‑term effects of the reduction of dry‑weather flows in the
Tijuana River in the U.S. was evaluated in the previous EIS. Until the
year 2001, this alternative would result in the conditions evaluated
previously. During 2001, the effects to the riparian habitat of the
Tijuana River would be similar to the Operate IWTP alternative; however,
the flows will be substantially less decreasing the rate at which any
effects may be observed.

Significance of Impacts

No significant adverse impacts to terrestrial habitat or sensitive
species are anticipated.

Mitigation

No mitigation measures in addition to commitments made in the previous
EIS and Biological Opinion for the project are required. Alternative 4:
Operate IWTP with New Conveyance to Mexico

Impacts

Under this alternative the IWTP would treat and detain the sewage to
advanced primary levels prior to discharge of the treated effluent to a
new conveyance system in Mexico for discharge to the ocean.

The pumping and conveyance would be built in urbanized central Tijuana
and extend west up to Spooners Mesa and south above the coastal toll
road to the existing shoreline discharge point 5.6 miles south of the
international border. Mexico is considering several alternatives,
including one that follows the route of the existing canal and one that
would be within the right‑of‑way for the toll road. Both routes would
impact disturbed grassland habitat, but the existing canal also crosses
several naturally vegetated canyons that have coastal sage scrub and
maritime chaparral. These native communities may provide habitat for
sensitive species of binational concern, such as the federally listed
(threatened) coastal California gnatcatcher.

Any environmental impacts incurred due to the construction of the
conveyance system in Mexico would be evaluated in environmental review
under the Mexican State Ecology Law. No impacts to the riparian habitat
of the Tijuana River in the U.S. are anticipated. Significance of
Impacts

Adverse impacts to native habitat and sensitive wildlife could result
from construction of the new conveyance in Mexico. Mexico will conduct
the environmental review for the conveyance and select an alignment. No
significant adverse impacts to terrestrial habitat or sensitive species
in the U.S. are anticipated.

Mitigation

No mitigation measures in addition to commitments made in the previous
EIS and Biological Opinion for the project are required. Alternative 5:
Operate IWTP with Discharge to SBOO

Impacts

Under this alternative the IWTP would treat the sewage to advanced
primary levels and discharge the effluent to the ocean via the South Bay
Ocean Outfall. No impacts to the riparian habitat of the Tijuana River
are expected from this alternative.

Significance of Impacts

No significant adverse impacts to terrestrial habitat or sensitive
species are anticipated.

Mitigation

No mitigation measures in addition to commitments made in the previous
EIS and Biological Opinion for the project are required. Estuarine
Biology

The information provided in this section is derived primarily from the
Biological Impacts of Interim Discharge of Primary Treated Effluent from
the International Wastewater Treatment Plant to the Tijuana Estuary,
prepared by Tierra Environmental Services (1996). This report is
included as Appendix B.

Impacts of Sewage Inflows at the Tijuana Estuary

The Tijuana estuary has been characterized as having a small tidal prism
(defined as the volume of water in the estuary between MHHW and MLLW).
The estuary\'s tidal prism has been calculated at 290 acre‑feet (0.36
Mm3) (Entrix et al. 1991). Because the tidal prism of the estuary is
small, sewage conveyed by the Tijuana River can have far‑reaching
effects on the ecosystem.

The plants and animals that inhabit southern California lagoons and
estuaries are adapted to the saline conditions that exist during most of
the year. The channel organisms, including fishes and invertebrates, are
primarily marine, although many display an ability to withstand a wide
variation in salinity. Similarly, the plant species that inhabit coastal
salt marshes are adapted to hypersaline soil conditions that exclude
species that might otherwise outcompete them under less saline
conditions (Zedler 1982). Any modification of a wetland\'s hydrology
that results in an increase in &quot;freshwater&quot; inflows can result
in large‑scale shifts in species composition. For the purpose of this
section, &quot;fresh water&quot; is defined as nonsaline water rather
than a measure of potability.

The potential impacts of sewage inflows on the phytoplankton and
macroalgae of the Tijuana estuary are primarily related to population
dynamics and effects on other organisms. An increase in the availability
of nutrients from sewage, primarily nitrogen, could stimulate algal
blooms. Depending on the magnitude and duration of such blooms, water
quality conditions could deteriorate to the point that channel fauna are
impacted. Algal blooms and reduced dissolved oxygen levels have been
correlated with fish kills at San Elijo Lagoon in San Diego County
(Nordby 1990). Algal blooms of sufficient magnitude could result in fish
kills that affect higher‑order consumers, such as the federal endangered
least tern.

The impacts of sewage flows on channel organisms in the Tijuana estuary
are difficult to quantify given the lack of baseline data. However, a
long‑term monitoring program, initiated by PERL researchers in 1986,
identified several trends in species composition that have been
attributed to sewage inflows (Nordby and Zedler 1991). Species richness
and abundance for fishes and benthic macroinvertebrates declined
throughout a period of prolonged sewage discharge; population structures
were skewed toward young animals; and assemblages were dominated by
species with early reproductive maturity and prolonged spawning periods.
The sampling station located farthest from the mouth of the estuary and,
subsequently, farthest from the source of sewage acted as a refuge for
species that were eliminated at the mouth.

The effects of increased freshwater inflows and hypersalinity from mouth
closure on the functioning and structure of the salt marsh of the
Tijuana estuary have been well documented (Zedler and Nordby 1986;
Zedler et al. 1992). Heavy mortality of the cordgrass‑dominated low
marsh was documented following mouth closure in 1984; however, the
pickleweed‑dominated mid‑marsh actually expanded during this time
(Zedler et al. 1992). Conversely, cordgrass growth (measured in total
stem length) increased following flood events of 1980 and 1983, while
pickleweed growth (measured in percent cover) decreased. Field
observations and experiments have suggested that cordgrass is commonly
under stress due to hypersaline soils and low nitrogen concentrations.
Freshwater inflows to the marsh stimulate increased growth by reducing
soil salinities. Freshwater inflows that are high in nitrogen may also
stimulate increased growth. Timing of freshwater inflows is important:
inflows in winter have resulted in increased height and density; inflows
in summer have resulted in increased vegetative reproduction.

Zedler et al. (1990) examined the effects of sewage flows in the Tijuana
River on the salt‑marsh vegetation in the estuary. Several a priori
hypotheses were formulated regarding salt‑marsh vegetation responses to
wastewater. These included (a) lower salt‑marsh plants (i.e., cordgrass)
would have increased foliar nitrogen and greater biomass with proximity
to wastewater flows and (b) exotic plant species would be linked to
areas of prolonged &quot;freshwater&quot; flows and artificially
prolonged periods of salinity reduction. No direct correlations were
demonstrated for wastewater inflows and soil nitrogen, foliar nitrogen,
or growth of cordgrass. Sewage flows were linked with reduced soil
salinities and exotic plant invasions.

Equally difficult to measure are the effects of the constituents of
sewage on wetland plants and animals. Fecal coliforms, used as
indicators of contamination for humans, do not necessarily affect
aquatic organisms as they do humans. Similarly, sewage constituents have
been measured from within the City of Tijuana\'s conveyance system, but
not within the estuary itself. Periodic inflows of compounds potentially
lethal to aquatic organisms could occur virtually at any time.

The magnitude and spatial distribution of microbial contamination of the
Tijuana estuary during both wet and dry weather under a range of tidal
conditions was recently investigated (Zedler et al. 1995). Densities of
fecal indicator bacteria were determined in water collected during the
period of November 1994 through June 1995. Fourteen sites were sampled,
extending from the approximate location of the IWTP to the Pacific
Ocean. In general, fecal coliform concentrations were highest at Dairy
Mart Road, Hollister Street Bridge, and Smuggler Gulch, where they
greatly exceeded EPA and state standards for body contact. Densities of
fecal indicator bacteria remained high throughout the rainy period
(November 1994‑March 1995), implying that there was a continuous and
concentrated dry‑weather source of fecal loading to the estuary and,
apparently, no first‑flush phenomenon. Levels of fecal indicators in the
Tijuana River east of Dairy Mart Road were equal to or greater than
those found downstream, suggesting that the main river, entering the
U.S. from Tijuana, is contaminated with fecal material before receiving
flows from Smuggler Gulch and Goat Canyon.

In a parallel study, Zedler et al. (1995) measured water salinity and
dissolved oxygen as indirect indicators of sewage inflows to the
estuary. As demonstrated in the Estuarine Biology section of the
Affected Environment chapter of this SEIS (Chapter 3.4), numerous
studies have shown that increased &quot;freshwater&quot; inflows can
produce shifts in the structure of plant and animal communities of
coastal wetland systems.

Salinity in the northern arm of the estuary, known as Oneonta Slough,
was highly variable in terms of seasons, months, weeks, days, and tidal
cycles. Of particular interest was the preponderance of dates with
salinities below seawater (34 ppt). Oneonta Slough was brackish
throughout most of the sampling dates and became saline only in July
when sewage flows were low enough to be diverted to the emergency
connector. Based on these assertions, flows of raw sewage from the city
of Tijuana are capable of impacting the farthest reaches of the Tijuana
estuary, particularly during the wet season.

Evidence of heavy metal contamination of the sediments and fishes of the
Tijuana River and estuary is presented by Gersberg, Trintade, and Nordby
(1989). In that study, 55 sediment sampling stations were tested for
levels of toxic metals: cadmium, chromium, copper, zinc, lead, and
nickel. In addition, several species of fish collected from three sites
within the Tijuana estuary were tested. Cadmium was found in elevated
levels in the sediments of both the Tijuana River and the estuary. In
fishes, only lead was found at levels exceeding the international
standard, but did not appear to pose a health risk. In general, surface
sediments were found to contain higher levels of cadmium in the southern
portion of the estuary, influenced by renegade sewage spills from Goat
Canyon, and in the river. Lower cadmium levels were detected in the
northern arm of the estuary (Oneonta Slough).

In summary, there is a considerable body of evidence that suggests that
sewage flows in the Tijuana River have impacted the estuarine flora,
fauna, and sediments of the Tijuana estuary; however, quantifying those
impacts is difficult. Lacking baseline data, it is difficult to
demonstrate cause and effect relationships.

Indirect measurements, such as water salinity and heavy metal
accumulation, point to river‑borne sewage as the causative agent. For
example, in a USACE study examining the future treatment of Mexico\'s
sewage (USACE, EPA, IBWC, SWRCB, and City of San Diego 1990), it was
determined that daily sampling of sewage inflows may be required to
measure events that most affect the estuary. Daily samples taken from
Dairy Mart Road showed high variation between April 13 and May 2, 1990.

Forty‑four physical variables, including temperature, were measured with
individual values ranging as much as 30 times the mean for the 30‑day
period. On one date‑April 4, 1990‑following a rainfall event of
approximately 0.4 inch (1 cm) measured in nearby Chula Vista, high
values were measured for aluminum (5.9 mg/l), chromium (0.22 mg/l),
copper (0.62 mg/l), iron (74.8 mg/l), lead (0.8 mg/l), manganese (1.72
mg/l), mercury (0.003 mg/l), nickel (0.18 mg/l), silver (0.8 mg/l), zinc
(1.68 mg/l), antimony (0.26 mg/l), and cadmium (0.1 mg/l). Total
suspended solids were greater than 12 times the average and chemical
oxygen demand was more than 5 times higher than average.

These data suggest that the April 4 event was a major one, with water
concentrations more than 28 times the month\'s average in antimony, 25
times more lead, 18 times more aluminum, and 17 times more iron and
zinc. The potential that there are many one‑day events such as this
illustrates the difficulty in characterizing the effects of sewage
inflows on the system.

Hydraulic Modeling of Flows

The USIBWC and EPA (1995, Appendix X) estimated future sewage flows from
Tijuana through the year 2001 using mean 1995 flows as the base year and
using a 4.8 percent rate of growth for Tijuana\'s population. The focus
of that analysis was to estimate future wastewater flow rates from
Tijuana and determine how those flows can be conveyed and treated given
each interim alternative.

In order to address the impacts on the Tijuana estuary of discharging a
given volume of sewage to the Tijuana River, a number of parameters must
be estimated or assumed. These include the amount of time required for a
given volume to travel from the point of origin to the estuary; the
amount of flow lost to evapotranspiration and groundwater recharge as
the sewage flows through the vegetated channel of the river; the timing
of the release of the sewage flows; and the tidal condition of the
estuary (i.e., high tide versus low tide).

In a simplified example, sewage released from the IWTP would require a
certain period of time to reach the estuary. A certain volume of sewage
would be lost to groundwater effects and evapotranspiration (if release
occurred during the daytime). This reduced volume of sewage would reach
the estuary where, during an extreme low tide, it would be transported
offshore or, during an extreme high tide, retained within the estuary
for a given period of time. It is during the period of retention within
the estuary that potentially environmentally damaging effects could
occur.

Boyle Engineering (1996) prepared a hydraulics report that predicted
travel times for flows of sewage entering the river at the IWTP site and
flowing to the estuary via the low‑flow channel, currently maintained by
the City of San Diego. Using the USACE HEC‑RAS model, Boyle estimated
the low‑flow travel times for a range of low flows. The study was based
on projections of future wastewater production rates by the city of
Tijuana provided by the USIBWC/EPA in their model. Boyle evaluated a
worst‑case scenario using the high‑flow‑day values for the years 1996
and 2001, representing present conditions and a conservative estimate of
the conditions after which the outfall would become operational,
respectively. The model does not incorporate estimates of evaporation,
evapotranspiration, or groundwater effects.

For 1996, travel time from Stewart\'s Drain to the entry to the estuary
(+6 feet MSL) for the highest flow (26.7 cfs \[0.8 m3/s\]) was 6.0
hours, while that for the lowest flow (2.67 cfs \[0.08 m3/s\]) was 14.4
hours. Corresponding travel rates for the highest peak flow rates for
2001 (53.8 cfs \[1.5 m3/s\]) were 4.6 hours while travel rates for the
lowest flow (5.38 cfs \[0.2 m3/s\]) were 11.6 hours.

The study also included a simple model of the estuary (USACE HEC‑1) to
simulate the hydraulic effects of sewage flows in the estuary. The model
treated the estuary as a reservoir with an outlet, with sewage inflows
included as storage capacity and outgoing tides modeled as dam breaches
(Boyle Engineering 1996). The estuarine model also included 1996 tidal
data to project how tides would affect the 1996 sewage flows that were
estimated in the HEC‑RAS model to reach the estuary. A best‑case and
worst‑case scenario were analyzed.

The best‑case scenario would occur when a very high high tide is
followed by a very low low tide. This would result in a large
&quot;reservoir&quot; of water within the estuary to dilute the
inflowing sewage and allow for the greatest amount of subsequent tidal
flushing. The worst‑case scenario is one in which a low high tide is
followed by a high low tide and both are low. This would result in a
small reservoir of estuarine water and greatly reduced tidal flushing.

The model predicted that, under the best‑case scenario, essentially all
of the sewage inflows would be transported out of the estuary during the
seven hours between high and low tide. Of the 10.7 acre‑feet (13,200 m3)
representing high‑flow‑day volumes that entered the estuary in 1996, 10
acre‑feet (12,350 m3) exited during the best‑case scenario. Similarly,
of the 29.33 acre‑feet (36,200 m3) entering the estuary in 2001, 24
acre‑feet (29,600 m3) would exit during low tide.

The worst‑case scenario results in retention of significant volumes of
sewage in the estuary over the tidal period. For the 10.7 acre‑feet
(13,200 m3) entering the estuary in 1996, 7 acre‑feet (8,650 m3)
remained after the low tide. Similarly, of the 29.33 acre‑feet (36,200
m3) entering the estuary in 2001, 15 acre‑feet (18,500 m3) would remain
after low tide.

The retention times calculated using this model suggest that discharging
sewage to the Tijuana River as a viable interim solution to the use of
the ocean outfall could result in significant deleterious environmental
impacts. Upon examination of 1996 tidal data, the optimal, or best‑case,
scenarios of a high high tide followed by a low low tide are limited,
primarily, to the spring tides of summer and winter. Tidal fluctuations
are dampened during the spring and fall neap tides. Therefore, any
continual discharge of wastewater would have to occur under suboptimal,
if not worst‑case, conditions.

Retention of up to 7 acre‑feet of wastewater over a given tidal cycle
complicates the mechanics of tidal exchange on ensuing cycles. It is
possible that the diluted reservoir would remain within the estuary and
be transported to tidal creeks and channels, rather than flow out to sea
with the next low tide. As sewage inflows continued through the rising
tide, those flows would be added to the volumes retained, resulting in
cumulative impacts. The end result could be a reservoir that, once
diluted, does not return to the undiluted state.

Indeed, the data collected by Zedler et al. (1995) suggest that
long‑term retention of wastewater currently occurs at the Tijuana
estuary, with reduced salinities measured at the extreme northern end of
Oneonta Slough. Continued long‑term retention from the proposed interim
discharge alternatives may result in community shifts similar to those
discussed in Chapter 3.4. For example, Nordby and Zedler (1991)
suggested that a prolonged discharge of between 5 and 20 mgd (219‑876
lps) of untreated sewage during the period of September 1986‑March 1987
resulted in the shift of dominant estuarine fishes to short‑lived
species with protracted spawning seasons and rapid rates of maturity.
The projected 1996 eight‑hour average of 10.47 mgd (459 lps) falls
within that range.

Both the HEC‑RAS and HEC‑1 models illustrate the complexities in
attempting to &quot;pulse&quot; discharges to reduce impacts to
estuarine resources. This technique has been proposed for other projects
resulting in artificial increases in freshwater discharge to southern
California streams and estuaries, specifically &quot;live stream&quot;
discharge of treated effluent. Pulsed discharge, in its simplest form,
would involve storage and timed release of effluent so that discharges
would reach the estuary at low tide and flow, unhindered by the tides,
out to the ocean. As illustrated in the HEC‑RAS model, the discharge of
sewage at the highest 1996 hourly rate of 26.74 cfs (0.8 m3/s) requires
six hours transit time to the estuary. Except on dates that approximate
the best‑case scenario, this period exceeds the time between outgoing
low tide and incoming high tide. Release of sewage at lower rates would
require a longer transit time.

Alternative 1: No Action

Impacts

USIBWC/EPA predict a seasonal high discharge to the Tijuana River of
9.52 mgd (417 lps) of wastewater by the year 2001 with no action taken
to correct the current condition. Peak hourly flows would double from
1996 to 2001 (26.74 cfs to 53.84 cfs). Transit time from the IWTP to the
estuary would decrease with increased flows; however, tidal conditions
would preclude efficient discharge to the ocean, except on a few
seasonal days with optimal tides. Prolonged exposure to freshwater and
sewage constituents would likely continue the impacts to biological
resources documented in previous studies of the estuary.

Significance of Impacts

Impacts to the Tijuana River estuary would be significant and adverse.
Dry‑weather sewage‑contaminated flows would result in elevated pollutant
loadings, eutrophication, and the reduction of salinity levels which
could cause substantial adverse impacts. Mitigation

No mitigation measures are available for the No Action alternative to
EPA and USIBWC.

Alternative 2: Operate IWTP

Impacts

The USIBWC/EPA model predicts the mean daily discharge of 0.6 mgd (26
lps) of treated wastewater to the Tijuana River beginning in 1998,
rising to 3.6 mgd (158 lps) average flows and 7.5 mgd (329 lps) seasonal
peak flows by 2001 The discharge of average flows would be year‑round,
while the seasonal high flows would occur during wet‑weather periods
when there would probably be seasonal or flood flows in the river.

Discharge of 0.6 mgd to 3.6 mgd (26‑158 lps) of dry‑season flows of
treated effluent would have impacts to the estuary due primarily to
nutrient loads. These flow volumes could induce eutrophication; and the
seasonal high flows could reduce salinity levels and cause pollutant
loadings that would affect species composition or abundance relative to
current conditions. As with the No Action alternative, prolonged
exposure to freshwater and sewage constituents would likely continue or
exacerbate the shifts in estuarine plants and animal communities
documented in recent studies. These flow rates would require
approximately nine and eight hours transit time to reach the estuary,
respectively, a time period that exceeds even the most optimal window
for pulsed discharge.

Significance of Impacts

Impacts under this alternative are substantially reduced from those
anticipated under the No Action alternative. However, any discharge to
the estuary of a point source that does not meet the receiving waters
standards would be a significant impact. Mitigation

If treated effluent is routinely discharged during dry weather to the
Tijuana River, a monitoring program will be undertaken. The program will
monitor changes in water quality using indirect indicators of water
source and sewage contamination. These include salinity, dissolved
oxygen, temperature, and coliform bacteria. The monitoring will be
conducted using automatic data loggers, hand‑held salinity, dissolved
oxygen and temperature meters, and standard methods for the examination
of water and wastewater. The monitoring program will be initiated prior
to discharge of the effluent and will continue through the period that
effluent is discharged to the Tijuana River. Reports of the monitoring
will be provided to the RWQCB, Tijuana River National Estuarine Research
Reserve, and EPA.

Operate IWTP with Detention Basin

Impacts

Incorporating a 5.5 million gallon (20,900 m3) detention basin into the
project design results in no discharges of treated effluent to the
Tijuana River during average flow days through the year 2001. A
discharge of 0.6 mgd (26.3 lps) to 2.0 mgd (88.5 lps) could occur on
seasonal high peak flow days in 2001. Transit time for 0.66 mgd to reach
the estuary is approximately 15 hours, which would overlap with the
following day\'s peak flows and resultant discharges. Therefore, a
nearly constant volume of wastewater would flow in the river.

Operation of the detention basin would reduce impacts to the estuary
relative to the No Action and Operate IWTP alternatives. Under average
day conditions, no flows are anticipated. However, during seasonal high
flows, retention of wastewater in the estuary would continue to impact
biological resources as previously documented, though the volume of flow
would be substantially reduced. Because these flows are more likely to
be encountered during the wet‑weather season, the flows may be mixed
with other flows in the river from runoff.

Significance of Impacts

Impacts to the estuary from this alternative are not substantially
different from current conditions and are well below forecasts for the
No Action and Operate IWTP alternatives. While the only discharges
expected to occur would be during the wet‑weather season and may be
mixed with other runoff, any discharge to the estuary of a point source
that does not meet the receiving waters standards would be a significant
impact.

Mitigation

If treated effluent is routinely discharged during dry weather to the
Tijuana River, a monitoring program will be undertaken as described for
the Operate IWTP alternative. If, however, the only discharges that
would occur are during the wet‑weather season and are mixed with other
flows, a monitoring program for the effluent discharge would not be
practical.

If required, the monitoring program will be initiated prior to discharge
of the effluent and will continue through the period that effluent is
discharged to the Tijuana River. Reports of the monitoring will be
provided to the RWQCB, Tijuana River National Estuarine Research
Reserve, and EPA.

Alternative 4: Operate IWTP with New Conveyance to Mexico

Impacts

Constructing and operating a 50 mgd (2,190 lps) parallel pipeline and
pump station would eliminate the need to discharge treated or untreated
flows to the Tijuana River. Therefore, there would be no direct impacts
to the estuary under this alternative. Significance of Impacts

No significant adverse impacts to the estuary would result from this
alternative.

Mitigation

No mitigation measures for impacts to the estuary would be necessary.
Operate IWTP with Discharge to SBOO

Impacts

Operating the IWTP and discharging treated effluent to the Pacific Ocean
via the South Bay Ocean Outfall would eliminate the need to discharge to
the Tijuana River. Therefore, as with Alternative 4, no direct impacts
to the estuary would result under this alternative. Significance of
Impacts

No significant adverse impacts to the estuary would result from this
alternative.

Mitigation

No mitigation measures for impacts to the estuary would be necessary.
Marine Biology

Dry‑weather flows of sewage in the river have occurred for many years
and were chronic between 1980 and 1993 at approximately the flow volumes
projected for the No Action alternative (up to 9.6 mgd \[420 lps\]).
Thus, existing conditions reflect the impacts of sewage discharges to
the nearshore environment. None of the alternatives evaluated below
would eliminate sewage‑contaminated flows in the river during the
wet‑weather season or floods, and residual contamination of the
nearshore environment could continue, regardless of the alternative
chosen.

Alternative 1: No Action

Impacts

Under the No Action alternative, the IWTP would not be operated until
the ocean outfall is complete and would only discharge effluent treated
to secondary standards. During the interim period, dry‑weather flows of
untreated sewage in the Tijuana River would increase, up to 5.6 mgd (245
lps) average daily flow and 9.5 mgd (420 lps) seasonal high daily flow.
This flow of untreated sewage adversely affects the estuary and
nearshore ocean environment.

Increases in sewage flows would also result in increases in the volume
of untreated sewage discharged at the shoreline in Mexico 5.6 miles (9
km) south of the international border. These untreated flows would
increase up to 23 mgd (1,007 lps) by 2001 if no action is taken.

Intertidal Communities

Beaches adjacent to the Tijuana River mouth and along the Mexican
shoreline may experience organic enrichment. This should not impact
sandy shores, but rocky shoreline communities may shift toward less
species diversity and greater seasonal fluctuation (Littler and Murray
1975, Murray and Littler 1978).

Studies on sandy and rocky shores have focused on the immediate zone of
the discharge and have not evaluated low‑level chronic exposure. Algae
may actually be enhanced by low levels of nutrients, but organisms such
as mussels may accumulate toxins and bacteria and become a hazard to
human health if consumed.

Benthic Communities

As with the sandy intertidal communities, benthic organisms in the
nearshore zone may respond to gradually increasing organic loading with
a shift in community dominants. However, little is known of these
communities in the South Bay area. Sampling of the benthos has been
conducted at depths as shallow as 39 ft (12 m), but effects of
concentrations of nutrients and suspended materials should be widely
dispersed through the surf zone, with little making its way to deeper
waters.

Kelp Beds

The Imperial Beach kelp beds are not anticipated to be affected by
discharges into the Tijuana River and Mexico. The greatest impact would
be from turbidity, which reduces water transparency and, therefore,
photosynthesis. Settling of suspended material on kelp fronds would have
the same effect. The decline of the Palos Verdes kelp beds during the
1960s has been partially attributed to the inshore accumulation of
wastewater solids from the Palos Verdes outfalls (Mearns et al. 1977).
Longshore currents would carry the Tijuana River sewage flows upcoast,
toward the kelp beds. However, the river discharge is anticipated to be
dispersed in the surf zone. The shoreline discharge in Mexico is distant
enough from the kelp bed that impacts are unlikely.

Fish Populations

Fish populations in the estuary may be significantly affected by the
sewage contamination and lowered salinity levels. It is unlikely that
the pelagic or demersal fish community would be substantially affected
by the untreated river and shore discharges due to the dispersion of
pollutants prior to reaching deeper waters.

Plankton Community

It is unlikely that the ocean plankton community would be affected by
the river and shore discharges due to the dispersion of pollutants prior
to reaching deeper waters.

Marine Mammals

The discharges resulting from this alternative are not anticipated to
have significant effects on marine mammals, as they are mobile and not
usually found in the vicinity of these discharges. The main concern
would be uptake of chlorinated hydrocarbons or metals such as mercury
from prey species of fish or crustaceans. These effects would be
localized around the points of discharge. Marine Birds

Shorebirds could be affected if intertidal prey organisms were
influenced, either negatively or positively. If populations of
intertidal organisms were depressed by the Tijuana River and Mexican
shoreline discharges, prey availability would be lowered. If these
populations were increased due to the discharges, the result would be
beneficial to shorebirds. However, if these increases were accompanied
by increases in tissue burdens of contaminants, the shorebirds would be
negatively affected.

Significance of Impacts

Significant and adverse marine biological impacts are assessed for the
No Action alternative due to the continued and increasing amount of
sewage from Tijuana polluting waters (including the Tijuana River,
estuary, and Pacific Ocean) and beaches in the United States. The
effects of these discharges are already reflected in existing
conditions, however, due to the preceding years of chronic flows of
sewage, and any changes due to the increases in volume of flow would be
incremental.

Mitigation

Under the No Project alternative, mitigation is not available.
Alternative 2: Operate IWTP

Impacts

Under this alternative, in 1997 the IWTP will be operational and could
provide advanced primary treatment for 25 mgd (1,095 lps) average and 75
mgd (3,285 lps) peak flows. During this interim period, any flows
diverted to the IWTP would be treated and discharged to the emergency
connection. If capacity is not available, the treated effluent would be
discharged to the Tijuana River.

It is projected that the effluent flow volumes to the Tijuana River
would be 3.6 mgd (158 lps) average and 7.5 mgd (328 lps) seasonal high
daily flow by the year 2001. However, the discharge would be advanced
primary effluent. Treated effluent has significantly reduced
concentrations of BOD, solids, and some inorganic constituents. Coupled
with the additional aeration during the travel time downriver, filtering
and sorbing of constituents by plants and sediments, and reduction in
solids by detention in the estuary, the quality of the effluent would be
enhanced relative to untreated sewage flows.

Intertidal or benthic communities, fish, or shorebirds around the mouth
of the Tijuana River may still be adversely affected by the effluent
discharge. These effects are anticipated to be localized and would not
adversely affect the Imperial Beach kelp bed north of the river.

The flows of untreated sewage discharged in Mexico would be the same as
for the No Action alternative. The effects of this discharge are
substantially adverse in Mexican waters, and some residual impacts are
anticipated in U.S. waters between the international border and the
Tijuana River.

Significance of Impacts

The discharge of treated effluent as opposed to untreated sewage during
the dry‑weather season would reduce impacts to the intertidal and
benthic communities, fish, and shorebirds around the mouth of the
Tijuana River. Impacts are anticipated to be beneficial relative to the
No Action alternative. Localized adverse impacts to intertidal and
benthic communities, fish, and shorebirds around the mouth of the
Tijuana River would remain, however. Impacts along the coastline in
Mexico would be substantially adverse and the same as for the No Action
alternative.

Mitigation

No mitigation measures are necessary for the effects to marine biota
from the discharge of treated effluent to the Tijuana River. Mitigation
is not available for the residual effects of the discharges in Mexico on
the intertidal and benthic communities, as well as shorebirds. These
existing effects are considered significant and unmitigated.

Alternative 3: Operate IWTP with Detention Basin

Impacts

The IWTP would be operated as an advanced primary plant, as in the
Operate IWTP alternative. A 5.5 million gallon (20,900 m3) earthen
detention basin would be constructed at the IWTP site to provide flow
equalization for diurnal and wet‑weather peak flows. Treated flows would
be stored within the detention basin to be released to the emergency
connection during off‑peak hours. If the capacity of the Mexican system,
emergency connection and detention basin would be exceeded, then the
excess treated flows would be discharged to the Tijuana River in the
U.S.

It is projected that no treated effluent would be discharged on average
dry‑weather flow days and that treated effluent discharges to the
Tijuana River would only occur during seasonal high flow days after the
year 2000. These flows would be less than 2.0 mgd (88 lps). However, the
flows of untreated sewage discharged at the shoreline in Mexico would be
the same as for the No Action and Operate IWTP alternatives.

Impacts would be further reduced compared to the Operate IWTP
alternative, since the treated flows discharged to the river under this
alternative would only occur during the wet‑weather season and would be
reduced in volume. The magnitude of the impacts is not considered
significant to intertidal or benthic communities, the Imperial Beach
kelp bed, fish communities, marine mammals, or shorebirds.

The flow of raw sewage discharged in Mexico would be the same as with
the No Action and Operate IWTP alternatives. Therefore, the impacts to
the shoreline and nearshore environment would be the same as for the No
Action and Operate IWTP alternatives. Significance of Impacts

No significant adverse impacts to the intertidal and benthic
communities, kelp beds, fish, marine mammals, or shorebirds would result
from the discharge to the Tijuana River under this alternative. The
impact would be beneficial relative to existing conditions. Impacts from
discharges of untreated sewage to the shoreline in Mexico would continue
and are considered adverse.

Mitigation

Mitigation for the effects of ongoing discharges of untreated effluent
in Mexico under this alternative is the responsibility of Mexico.

Alternative 4: Operate IWTP with New Conveyance to Mexico

Impacts

A new pumping and conveyance system would be constructed by Mexico as a
parallel backup facility for the existing Mexican conveyance system,
with a capacity of 50 mgd (2,150 lps), to convey flows from Pump Station
One to the discharge point in Mexico. During the interim period, the
IWTP would treat flows up to 25 mgd (1,095 lps) from Tijuana. Once
treated, the effluent would be sent to Tijuana via the new pump station
and conveyance pipeline for discharge in Mexico, near the San Antonio de
los Buenos treatment plant. The existing pumping and conveyance system
to the treatment works in San Antonio de los Buenos would continue to
operate.

Under this scenario, no flows would be discharged to the Tijuana River;
the discharge of treated effluent from the San Antonio de los Buenos
treatment plant would be unchanged at 17 mgd (745 lps); and an
additional 25 mgd (1,095 lps) of advanced primary effluent from the IWTP
would be discharged at the shoreline in Mexico.

The discharge of untreated effluent to the shoreline in Mexico could be
substantially reduced. If the emergency connection continues to be used,
only 2.3 mgd (101 lps) of untreated sewage would be discharged on an
average flow day in the year 2001, with up to 4.6 mgd (201 lps) on
seasonal high flow days. If the emergency connection is not used, the
volume of untreated sewage discharged in Mexico would be 9.6 mgd (420
lps) and 12.0 mgd (526 lps) on seasonal high flow days, respectively.

No adverse impacts would result from this alternative to intertidal or
benthic communities, plankton, the Imperial Beach kelp beds, fishes,
marine mammals, or shorebirds in U.S. ocean waters.

Impacts to the beaches and coastline in Mexico would be reduced relative
to other alternatives. The flow of raw sewage would be significantly
less than would occur with the first three alternatives. However, the
flow of advanced primary effluent discharged at Punta Banderas would be
greater than with the first three alternative. The treated effluent
would travel along the coastline and receive dilutions of up to 1,000:1
prior to entering U.S. waters. This dilution should be sufficient to
lower concentrations of suspended solids, organic and inorganic
constituents, and dissolved oxygen. However, the Parsons Engineering
Science modeling suggested that PAH concentrations may exceed Ocean Plan
standards in U.S. waters. The localized effects around the discharge
point in Mexico would continue to be adverse to intertidal and benthic
communities and shorebirds, however.

Significance of Impacts

No significant impacts would occur in the vicinity of the Tijuana River
mouth. No significant impacts are anticipated to occur to marine life in
U.S. waters. There is a potential for PAH concentrations to exceed Ocean
Plan standards, however, which could have an adverse effect on marine
organisms. Impacts to the intertidal and benthic communities, as well as
shorebirds in Mexico would be reduced, but localized impacts around the
point of discharge from treated effluent would be significant.

Mitigation

No mitigation is required for U.S. marine waters.

Mitigation for impacts to marine life in Mexico from the discharge of
untreated effluent is the responsibility of Mexico. Mexico has committed
to an industrial source pretreatment and source reduction program, which
could reduce the concentrations of PAHs in their effluent.

Alternative 5: Operate IWTP with Discharge to SBOO

Impacts

The SBOO is currently under construction and is expected to be completed
in 1998. Once completed, 25 mgd (1,095 lps) of advanced primary effluent
from the IWTP could be discharged to the ocean approximately 3.5 miles
(5.7 km) offshore in 87 feet (26.5 m.) of water. No discharge to the
Tijuana River or through the emergency connection would occur.

The discharge of treated effluent in Mexico would be unchanged, and the
discharge of untreated sewage would be reduced as for Alternative 4.
This untreated discharge is substantially below the flow forecast
volumes for the other alternatives.

The area surrounding the SBOO discharge is sandy bottom and
characterized by benthic communities of filter feeders and deposit
feeders. With the outfall discharge, there is an increase in deposition
of organic solids which tends to shift the benthic community towards
species that feed on detritus on and in the sediments.

Assuming a mass emission of 3,000 metric tons/year of suspended solids
(80% organic) for a discharge of 25 mgd (1,095 lps) of advanced primary
effluent, the affected area of benthos around the outfall would be
approximately 135 acres (54.6 ha) (Word and Mearns 1979). This area is
less than the total area of approximately 175 acres (71.1 ha) that was
estimated to be affected in the FEIS for the SBOO from discharge of 181
mgd (7,928 lps) of secondary effluent, which was not considered a
significant impact.

Detectable elevations in BOD, chemical oxygen demand, trace metals, and
chlorinated hydrocarbons may be expected in these sediments, extended in
a longshore elliptical pattern from the diffuser based upon prevailing
currents. The diffuser is in relatively shallow water where waves can
induce resuspension and current transport is more prevalent than further
offshore.

Parsons Engineering Science modeled the discharge dispersion and
settling. The dilution of the effluent beyond the zone of initial
dilution is anticipated to meet the California Ocean Plan standards.
Their study results showed that the effects of trapping at approximately
49‑foot (15 m) water depths due to seawater density would limit the
dispersed effluent from reaching the shoreline most of the year. When
trapping breaks down, due to storm turbulence or other factors, the
dilutions of the effluent are at least 5,000:1 at the surface above the
discharge and over 20,000:1 away from the discharge. The dilutions are
sufficient such that bacterial, organic, or inorganic contaminants are
not an issue.

Intertidal Communities

The offshore discharge, three miles from shore, would result in no
impacts to the beaches adjacent to the Tijuana River mouth.

Impacts to the beaches adjacent to the shoreline discharge in Mexico
would be similar to those discussed above under Alternative 4. The
magnitude of the impacts to the beaches adjacent to the discharge point
in Mexico are anticipated to be less than would occur for the first
three alternatives and localized around the point of discharge.

Benthic Communities

Benthic communities around the outfall discharge will experience greater
sedimentation, organic loading, and turbulence.

During the three‑year period in which the Encina Water Pollution Control
Facility discharged advanced primary treated effluent at up to 22 mgd,
little effect was observed on the benthic infaunal community (MEC 1992).
Suspended solids, BOD, and ammonia increased, and dissolved oxygen
decreased near the outfall. Some groups of organisms (polychaete worms
and crustaceans) were more abundant or diverse near the outfall, and
Amphiodia was significantly less abundant, but other groups such as
mollusks were not affected.

The most apparent response of benthic communities to wastewater
discharge is a shift from dominance by suspension‑feeding species to
dominance by abundant deposit‑feeding species.

Generally, species abundance and biomass increase near the outfall while
species richness and diversity are not substantially affected. The
infaunal trophic index also declines, reflecting the shift in feeding
strategies. Low index values have been shown to correlate with high BOD
at several southern California wastewater discharges. Some of these
community changes may occur at the South Bay outfall, depending on mass
emissions and dispersion. Maps of projected dilution ratios suggest that
the depositional footprint will be long‑coast north and south of the
discharge, with little inshore or offshore movement. Benthic infauna
would be altered only in the immediate vicinity (135 acres \[54.6 ha\])
of the discharge.

Impacts adjacent to the shoreline discharges in Mexico would be similar
to those discussed above under the Operate IWTP with New Conveyance to
Mexico alternative.

Kelp Beds

The kelp beds are unlikely to be affected by the offshore discharge,
more than two miles away. Although a larger volume than the river
discharges, this effluent is expected to be dispersed north and south of
the discharge, with little inshore component. At present, a kelp bed
exists at the Point Loma outfall. Data suggest that the Point Loma
discharge has not degraded the kelp beds in that area. Therefore,
impacts from the South Bay outfall would be unlikely.

Fish Populations

Studies of fish populations around outfalls have shown that some fish
and invertebrates are more abundant around outfall sites, while other
species are less abundant (Mearns and Young 1983). The most notable
differences were the low numbers of young‑of‑the‑year at outfall sites
compared to control sites. At small discharges, no differences were
distinguishable. Overall, the effects appear to be limited and not as
easily documented as for the benthic infauna.

Fin erosion is the only disease conclusively linked to wastewater
discharges. The precise cause of the disease is unknown, but high
sediment and tissue concentrations of PCBs and contact with highly
contaminated bottom sediment (as with flatfish) appear to be required.
At some locations off Palos Verdes, fish tissues exceed the USDA
standard for DDT and are unfit for human consumption (Mearns and
Sherwood 1977).

Bioaccumulation of chlorinated hydrocarbons in fish collected in the
Southern California Bight is highest near Los Angeles and declines
dramatically away from Los Angeles. Representative fish collected near
Point Loma had body burdens one to two orders of magnitude lower than
found around the Palos Verde and Hyperion Los Angeles wastewater
outfalls. Scorpionfish, which were the most common species noted along
the SBOO alignment, also had lower body burdens along San Elijo Lagoon
and Ensenada, B.C., Mexico (Kinnetic 1991).

Demersal fish, living in close contact with the sediment along sandy
bottoms and reef habitats, are more localized in their movements and
most likely to be affected by ocean disposal of wastewater. In areas
surrounding the SBOO wastewater discharge, species such as croaker,
sculpin, scorpionfish, turbot, sole, and sanddabs may be in regular
contact with particulates that settle to the bottom. Pelagic species
(e.g., mackerel and smelt), which feed on water column particulates,
have been observed to congregate around discharges; and reef‑associating
species, such as surf perch, sand bass, and rockfish, may be attracted
to the physical structures of the seafloor pipeline and rock ballast.

Fish taken at the Encina Water Pollution Control Facility are similar to
those in the South Bay (MEC 1992). During the period of advanced primary
treatment, no spatial or temporal trends in the fish community
composition or fish tissue contaminants were observed relative to the
outfall.

Most of the fish taken in 1995 in trawl surveys at the outfall depth
were flatfish (speckled sanddab, longfin sanddab, English sole). These
fish would be most susceptible to contaminants occurring on the sediment
surface. However, these species would unlikely be prey for birds and
mammals, reducing the probability of bioaccumulation through the food
chain.

Pelagic species which may school around the turbulent zone of the
discharge would be more likely to contribute to contamination through
the food web. The decline in California brown pelican populations has
been attributed to eggshell thinning caused by tissue accumulations of
DDT. Coastal cetaceans such as bottlenose dolphins have also been found
to have high levels of DDT and PCBs, which have been suggested as the
cause of death but so far have not been confirmed.

At discharge rates high enough to contaminate fish, effects of the
discharge would be considered adverse and significant. However, the
magnitude of the proposed discharge would be unlikely to have an effect
or, therefore, to be significant.

It is unlikely that the fish community would be significantly affected
by the shoreline discharges in Mexico due to the reduction in the volume
of discharge and the dispersion of pollutants prior to reaching deeper
waters. Parsons Engineering Science modeling found that dilutions of
1000:1 would typically occur in the nearshore zone and would increase in
deeper waters offshore. Additionally, the discharges of untreated sewage
at Punta Banderas would be less than would occur with the first three
alternatives.

Plankton Community

Several studies have confirmed that the plankton community has responded
to some of the larger wastewater discharges (Mearns and Young 1983).
Evidence suggests that nutrients were entering the mixing layer and
contributing to plankton growth. Consistently higher phytoplankton
standing crops and productivity were found in Santa Monica Bay than at
other equivalent sites (Eppley et al. 1978). Attempts to determine
responses of fish populations to this potential resource increase have
been inconclusive. Under conditions of high turbidity, phytoplankton
populations would be depressed.

This alternative, with nutrients discharged at greater volumes in a
localized area, could enhance phytoplankton productivity and potentially
zooplankton populations also. Therefore, this alternative would have a
beneficial but negligible impact on the plankton community.

It is unlikely that the plankton community would be affected by the
shore discharges in Mexico due to the dispersion of pollutants prior to
reaching deeper waters. Additionally, the discharges of untreated sewage
in Mexico would be less than would occur with the first three
alternatives.

Marine Mammals

The potential for biomagnification of chlorinated hydrocarbons
discharged through the outfall would suggest that marine mammals,
especially dolphins which feed on fish, might be affected by the
discharge of additional contaminants into South Bay. The area within
which these constituents might be bioaccumulated by benthic organisms
and consumed by demersal or pelagic fish is very limited, however, and
the potential significance of this effect for a 25 mgd (1,095 lps)
discharge is considered insignificant. It is unlikely that gray whales,
other large whales, or pinnipeds would be affected. Therefore, the
potential, although small, exists for negative impacts to some marine
mammals.

The discharges in Mexico resulting from this alternative would have
little potential for adverse effect on marine mammals, as they are not
usually found in the vicinity of these discharges.

Marine Birds

Shorebirds in the vicinity of the Tijuana River mouth would not be
affected by the outfall. Marine birds, on the other hand, could
potentially be impacted by the offshore outfall. If pelagic fish such as
anchovies were to experience increased body burdens of chlorinated
hydrocarbon contaminants, these could be passed on to surface‑feeding
birds such as California brown pelicans, California least terns, elegant
terns, and gulls. However, these species are unlikely to be impacted to
any significant degree, based on the anticipated dilution of the
discharge and the low potential for biomagnification.

Potential impacts at the discharge point in Mexico would be similar to
those discussed for Alternative 4. The discharges of untreated sewage
would be less than would occur with the first three alternatives.
Significance of Impacts

In U.S. waters, impacts to the intertidal and benthic communities, fish,
and marine mammals due to discharges from the ocean outfall would not be
significant.

Impacts to the intertidal and benthic communities, as well as shorebirds
in Mexico, are adverse and potentially significant. However, the
magnitude of these impacts is anticipated to be less than would occur
for the first three alternatives due to the reduced flows of untreated
sewage discharged to the shoreline. This is a beneficial impact relative
to existing or future conditions under the No Action alternative.

Mitigation

Mitigation for impacts to marine life in U.S. waters is not necessary
for this alternative. The effects of the discharges from the ocean
outfall on the benthic communities and marine mammals are not
anticipated to be significantly adverse.

As part of the NPDES permit for the outfall discharge, a comprehensive
baseline monitoring program has been initiated and will continue during
the period of the interim discharge. This program will monitor
sediments, benthos, water quality, fish, and the Imperial Beach kelp
bed. If significant changes were to occur, the monitoring program would
identify problems and the discharge would be required to be modified to
conform to the Ocean Plan or other requirements.

Mitigation for impacts to marine life in Mexico from discharges of
untreated effluent are the responsibility of Mexico.

Geological Resources

The geology of the ocean floor in the vicinity of the ocean outfall was
studied in engineering reports prepared by Engineering Science and
Woodward‑Clyde consultants entitled South Bay Ocean Outfall, Basis of
Design Report (1991) and Conceptual Design Reports (1992a, 1993). The
prior EIS for the IWTP and SBOO considered geotechnical hazards,
including seismic events, in the siting, construction, and operation of
the facilities.

The potential for seismic‑related impacts to the ocean outfall include
damage from fault rupture, seismic ground shaking, seafloor instability,
liquefiable soils surrounding the outfall pipe, and wave‑induced
liquefaction. Each of these potential impacts are described below as
they pertain to each alternative.

Alternative 1: No Action

Impacts

Impacts under this scenario were evaluated in the FEIS for the IBWC
International Wastewater Treatment Plant and Outfall Facilities
(February 1994). Thus, no additional impacts from geologic constraints
that were not already evaluated would result if the No Action
alternative is implemented.

Significance of Impacts

Since no actions not already evaluated would be taken under this
alternative, no new significant geological impacts would occur.
Mitigation

Under the No Action alternative, mitigation is not applicable.
Alternative 2: Operate IWTP

Impacts

Under this alternative, in 1997 the IWTP will be operational and could
provide advanced primary treatment for 25 mgd (1,095 lps) average flows.
The ocean outfall connection would not be completed until 1999, so
during this interim two‑year period, any flows diverted to the IWTP
would be treated and stored and discharged to the emergency connection.
If no capacity is otherwise available, the treated effluent would be
discharged to the Tijuana River. Potential impacts to the existing
emergency connection and Pump Station One were evaluated in the FEIS for
the IBWC International Wastewater Treatment Plant and Outfall Facilities
(February 1994). Thus, no additional impacts from geologic constraints
that were not already evaluated would result if the interim operation
alternative is implemented. Discharges of advanced primary treated
effluent to the Tijuana River have no geologic constraints.

Significance of Impacts

Since no actions not already evaluated or new actions not constrained by
geologic resources would be taken under this alternative, no new
significant geological impacts would occur.

Mitigation

No additional mitigation, beyond that already committed to as described
in the prior EIS, is necessary.

Alternative 3: Operate IWTP with Detention Basin

Impacts

The IWTP would be operated as an advanced primary plant, as in the
Operate IWTP alternative. A 5.5 million gallon (20,900 m3) earthen
detention basin(s) would be constructed at the IWTP site (Dairy Mart
Road) to provide flow equalization for diurnal and wet‑weather peak
flows. Treated flows would be stored within the detention basin to be
released to the emergency connection during off‑peak hours. If the
capacity of the Mexican system, emergency connection, and detention
basin would be exceeded, then the excess treated flows would be
discharged to the Tijuana River in the U.S.

Geologic conditions at the Dairy Mart Road project site are evaluated in
the FEIS for the IBWC International Wastewater Treatment Plant and
Outfall Facilities (February 1994). The on‑site geologic and seismic
hazards include potentially compressible on‑site topsoils not suitable
for the support of proposed fill or building loads; a potential for
landslides on the southern portion of the site; fault traces mapped near
the site which are not considered active; and potential for ground
shaking from an earthquake on a regionally active fault that could
affect on‑site structures.

Since the mapped fault traces are not considered active, the potential
for surface rupture (ground breakage along fault traces) is low.

A maximum probable earthquake of a 6.5 magnitude on the Coronado Bank
fault zone may produce a horizontal peak ground acceleration of 0.18 g
at the Dairy Mart Road site. A maximum probable earthquake of 7.0
magnitude on the less seismically active Rose Canyon fault may produce a
horizontal peak ground acceleration of 0.25 g on the site.

Significance of Impacts

The IWTP is currently under construction; landslide‑prone formations
have been considered in its construction. Nevertheless, the existence of
compressible soils and expansive clays could significantly impact
construction activities of the earthen detention basin at the IWTP site.

Mitigation

Implementation of the mitigation measures identified for Alternative 2
of the FEIS for the IBWC International Wastewater Treatment Plant and
Outfall Facilities (February 1994) and established by the ROD will
reduce geologic impacts to the proposed earthen detention basin at the
IWTP site to below a level of significance. Design measures for the
proposed detention basin that would reduce potential geologic impacts to
below a level of significance include the following:

Perform site‑specific geotechnical investigations (including subsurface
exploration, slope instability calculations, laboratory testing of
representative soil samples, and geotechnical analysis) prior to
construction to determine soil characteristics, thickness, and
distribution and to develop appropriate soil engineering parameters for
the proposed facilities.

Perform fault evaluation studies of mapped fault traces in order to
confirm fault locations and activities. In addition, a geologist shall
observe excavations during construction to detect the presence of
unmapped traces in the general vicinity of mapped fault traces.

Alternative 4: Operate IWTP with New Conveyance to Mexico

Impacts

A new pumping and conveyance system would be constructed by Mexico as a
parallel backup facility for the existing Mexican conveyance system,
with a capacity of 50 mgd (2,150 lps), to convey flows from Pump Station
One to the discharge point in Mexico. During the interim period, the
IWTP would treat average dry‑weather flows up to 25 mgd (1,095 lps) from
Tijuana. Once treated, the effluent would be sent to Tijuana via the new
pump station and conveyance pipeline for discharge in Mexico, near the
San Antonio de los Buenos treatment plant. The existing pumping and
conveyance system to the treatment works in San Antonio de los Buenos
would continue to operate.

Portions of the proposed Mexican conveyance system traverse areas with
mapped fault traces. Potential impacts of ground shaking with velocities
similar to those expected at the IWTP and SBLO could result (0.25 g).
Substantial movement could rupture or damage pipelines to such an extent
that they become unusable.

Grading of hillsides for pipeline construction could result in
sedimentation and erosion impacts in north‑facing canyons draining
towards the U.S.

Significance of Impacts

The proposed Mexican conveyance system would be subject to seismic
ground shaking, which is considered a potential geologic impact.
Mitigation

Mexico will conduct design review of the pipeline and pump station as
part of its environmental impact assessment and to their construction
standards. This design should anticipate the effects of ground shaking
and incorporate measures to minimize the risk of failure during seismic
events.

If construction of the pipeline in any north‑draining canyons is
undertaken during the rainy season, Mexico should incorporate erosion
controls during any grading to prevent erosion impacts into the U.S.

Alternative 5: Operate IWTP with Discharge to SBOO

Impacts

The South Bay Ocean Outfall is currently under construction and is
expected to be completed in 1998. Once completed, an average of 25 mgd
(1,095 lps) of advanced primary effluent from the IWTP would be
discharged to the ocean. No discharge to the Tijuana River or through
the emergency connection would be necessary. Discharge of advanced
primary effluent to the ocean is discussed in Chapter 4.2, oceanographic
impacts, of this SEIS.

The SBOO tunnel will be excavated through the consolidated sediments of
the San Diego Formation underlying the unconsolidated sediments along
the ocean floor. Special problems with differential settlement may
develop at the bend structure, the wye structure, and at any point where
the thickness of the underlying sediment changes abruptly, such as at
the wall of the buried paleochannel.

A review of the proposed alignment reveals at least eleven (11) active
fault crossings offshore from the beach. Depending upon its starting
point, a tunnel outfall will cross an additional two or three
north‑trending faults between the Border Highlands and the coast,
although these faults may not have been active in the last 11,000 years
(Holocene age).

For conceptual design, it should be assumed that each fault crossed by
the alignment and mapped as &quot;potentially active&quot; is capable of
fault displacements averaging between 0.8 to 2.5 feet (0.24‑0.76 m) in
either horizontal or vertical direction. The possible maximum
displacement estimate is 8.2 feet (2.5 m) for a 31‑mile‑long (49.9 km)
fault rupture.

The potential for the outfall to move during a seismic event exists. The
pipeline would be constructed with a flexible steel sleeve to allow
seismic‑induced motion without rupture. These potential geologic impacts
are evaluated and appropriate mitigation measures recommended in the
FEIS for the IBWC International Wastewater Treatment Plant and Outfall
Facilities (February 1994) and established by the ROD.

Significance of Impacts

The potential for the outfall to move during a seismic event has been
evaluated in the 1994 FEIS and the outfall tunnel design includes the
construction of steel sleeves in crossing faults to reduce potential
seismic impacts to a level below signifiicance. No new significant
geologic impacts are anticipated due to implementation of this
alternative.

Mitigation

No mitigation is required other than the tunneling of the SBOO and the
inclusion of steel sleeves in the tunnel where it crosses existing
mapped faults.

Public Health

This section evaluates impacts from vectors for each of the
alternatives. The issue of pathogens as human health risks is evaluated
in Section 4.1, Hydrology and Water Quality, and Section 4.2,
Oceanography. These evaluations are based upon modeling of coliform
concentrations from discharges at the shoreline in Mexico and the SBOO.
Discharges of untreated and treated effluent to the Tijuana River are
included.

Operation of the IWTP also involves use of hazardous substances for the
plant\'s treatment processes. This issue was evaluated in the prior EIS
for the IWTP. No additional chemicals or risks from hazardous substances
are anticipated for the interim operations period.

Alternative 1: No Action

Impacts

Under the No Action alternative, the IWTP would not be operated until
the ocean outfall is complete and would only discharge effluent treated
to secondary standards. Impacts under this scenario were evaluated in
the FEIS for the IBWC International Wastewater Treatment Plant and
Outfall Facilities (February 1994).

The Tijuana River valley would receive dry‑weather sewage flows from
Mexico which could result in ponding of surface water in the river
low‑flow channel. The presence of dry‑weather flows historically has
caused a mosquito‑ and vector‑borne disease potential. Implementation of
this alternative would result in contamination of the valley, ponded
areas where mosquito breeding is unchecked due to inaccessibility for
mosquito control measures, and reduced survival of mosquito‑eating fish
which cannot tolerate the sewage‑laden water.

Significance of Impacts

The potential for significant impacts to public health due to mosquito
breeding would exist as the sewage flows from Tijuana increase and
chronic dry‑weather flows occur in the river. Public beaches could be
quarantined.

Mitigation

In coordination with the County of San Diego, dry‑weather flows to the
river should be monitored to ensure that no ponding of effluent occurs
that could provide breeding areas for mosquitoes. If ponding does occur,
the area should be drained or modified to return flowing water
conditions. Stocking of ponded areas that cannot be drained with
mosquito fish would also reduce impacts from the No Action alternative.

Alternative 2: Operate IWTP

Impacts

Under this alternative, in 1997 the IWTP will be operational and could
provide advanced primary treatment for 25 mgd average and 50 mgd peak
flows. The ocean outfall connection would not be completed until 1998,
so during this interim two‑year period any flows diverted to the IWTP
would be treated and discharged to the emergency connection. If no
capacity is otherwise available, the advanced primary treated effluent
would be discharged to the Tijuana River.

The discharge of advanced primary effluent to the Tijuana River would
not significantly reduce health risks to residents in the valley from
bacterial contamination or vectors. The effluent could provide mosquito
breeding habitat by ponding in the river channel. Impacts would be
similar to the No Project alternative.

Under this alternative, urban runoff from the surrounding areas and
effluent spills from the conveyance canal to the Mexican treatment plant
at San Antonio de los Buenos could still result in contamination and
closures. Limited monitoring data and modeling by Parsons Engineering
Science indicate that the discharge from the Mexican treatment plant
could periodically cause contamination of some U.S. beaches.

Significance of Impacts

Discharge of advanced primary effluent to the Tijuana River would result
in significant human health risks from pathogens, including disease
vectors.

Mitigation

The discharges to the river should be monitored to ensure that no
ponding of effluent occurs that could provide breeding areas for
mosquitoes. If ponding does occur, the area should be drained or
modified to return flowing water conditions. Stocking of ponded areas
that cannot be drained with mosquito fish would also reduce impacts from
this alternative.

Alternative 3: Operate IWTP with Detention Basin

Impacts

The IWTP would be operated as an advanced primary plant, as in
Alternative 2. A 5.5 million gallon (20,900 m3) earthen detention
basin(s) would be constructed at the IWTP site (Dairy Mart Road) to
provide flow equalization for diurnal and wet‑weather peak flows.
Treated flows would be stored within the earthen detention basin to be
released to Pump Station One or the emergency connection during off‑peak
hours. If the capacity of the Mexican system, emergency connection and
detention basin would be exceeded, then the excess treated flows would
be discharged to the Tijuana River in the U.S.

Public health impacts under this alternative are less than under
Alternative 2, because 5.5 million gallon (20,900 m3) effluent will be
stored for approximately eight hours (1pm to 9 pm) and not released to
the Tijuana River but sent to Pump Station One or the emergency
connection. Treated flows in excess of 5.5 million gallon (20,900 m3)
would still be discharged to the Tijuana River and have the potential to
contaminate U.S. beaches; however, this potential impact would only
occur during seasonal high flow days in 2001.

This alternative would reduce the potential for dry‑weather flows in the
river, which would reduce the potential for pathogen exposure, including
disease vectors. However, it would not eliminate the potential health
risks from mosquitoes and may result in periodic discharges of effluent
from the IWTP, which is not suitable for body contact.

Significance of Impacts

Potential public health impacts from contamination and disease‑bearing
vectors would be reduced by this alternative, but any discharges of
treated effluent to the river could result in significant adverse human
health risks.

Mitigation

The discharges to the river should be monitored to ensure that no
ponding of effluent occurs that could provide breeding areas for
mosquitoes. If ponding does occur, the area should be drained or
modified to return flowing water conditions. Stocking of ponded areas
that cannot be drained with mosquito fish would also reduce impacts from
this alternative.

Alternative 4: IWTP with New Conveyance to Mexico

Impacts

A new pumping and conveyance system would be constructed by Mexico as a
parallel backup facility for the existing Mexican conveyance system,
with a capacity of 50 mgd (2,150 lps), to convey flows from Pump Station
One to the discharge point in Mexico. During the interim period, the
IWTP would treat flows up to 25 mgd (1,095 lps) from Tijuana. Once
treated, the effluent would be sent to Tijuana via the new pump station
and conveyance pipeline for discharge in Mexico, near the San Antonio de
los Buenos treatment plant. The existing pumping and conveyance system
to the treatment works in San Antonio de los Buenos would continue to
operate.

Existing public health impacts to the Tijuana River Valley are
beneficial under this alternative. Mosquito breeding potential will be
greatly reduced as no effluent would be discharged to the Tijuana River.

The volume of treated effluent discharged to the shoreline in Mexico
would increase under this alternative. The volume of untreated sewage
discharged in Mexico would decrease if the emergency connection
continued in use. However, impacts to coastal waters in the U.S. would
result from the discharges. Mexico is committed to ensuring that the
discharge from its treatment plant will not cause violations of the
Ocean Plan standards established to protect recreational uses of U.S.
beaches. Assuming that Mexico complies with Minute No. 270 and Annex 1,
the impacts of the discharge from the San Antonio de los Buenos
treatment plant will not be significant. Significant impacts to public
health would occur if Mexico does not comply with Minute No. 270 and
Annex 1.

Significance of Impacts

Impacts to human health risks in the Tijuana River valley would be
beneficial under this alternative. There would be no discharge of
treated effluent to the river and the additional facilities in Mexico
would decrease the likelihood that an upset of their system would result
in spills of untreated sewage into the U.S. The discharge of treated
effluent to the shoreline in Mexico would increase, however, and may
result in public health risks in coastal waters of the U.S. This would
be a significant impact.

The combined surf discharge from San Antonio de los Buenos and the IWTP
may impact U.S. coastal recreation areas, however. Assuming that Mexico
complies with Minute No. 270 and Annex 1, the impacts of the discharge
from the San Antonio de los Buenos treatment plant will not be
significant. Significant impacts to public health would occur if Mexico
does not comply with Minute No. 270 and Annex 1.

Mitigation

No mitigation is necessary for the interim operation of the IWTP for
vector control in the Tijuana River valley. Existing control programs
will need to be continued, however. Monitoring of coastal areas in the
U.S. with public notification and closure of contaminated areas for
public use could reduce health risks.

Alternative 5: Operate IWTP with Discharge to SBOO

Impacts

The South Bay Ocean Outfall is currently under construction and is
expected to be completed in 1999. Once completed, 25 mgd (1,095 lps) of
advanced primary effluent from the IWTP would be discharged to the
ocean. No discharge to the Tijuana River or through the emergency
connection would be necessary. Discharge of advanced primary effluent to
the ocean is discussed in Section 4.2, Oceanography, of this SEIS.

Public health impacts in the Tijuana River Valley (pathogens and
mosquitoes) and at southern San Diego beaches (pathogens) would not
result from any effluent discharges using the South Bay Ocean Outfall.
Potential discharge impacts from the San Antonio de los Buenos treatment
plant would be reduced, but discharge of untreated sewage would still
occur.

Significance of Impacts

This alternative reduces potential public health impacts from discharge
of IWTP effluent to below a level of significance. Residual impacts from
shoreline discharge in Mexico are considered potentially significant and
adverse, however.

Mitigation

As a condition of the NPDES permit for the project, monitoring of the
discharge will be required. If exceedances of health and safety
standards are identified, the affected areas can be identified and steps
taken to avoid public use of the area until corrective action can be
taken.

Air Quality and Odors

Impact Standards and Criteria

Federal Clean Air Act

As indicated in Section 3.8.2, the Clean Air Act establishes national
standards for six criteria pollutants. Significant air quality impacts
would result if implementation of the project would (1) cause a
violation of the California ambient air quality standards (CAAQS) or
national ambient air quality standards (NAAQS), whichever is strictest;
(2) create a substantial contribution to an existing or projected
violation of CAAQS or NAAQS; or (3) contribute to a delay in attainment
of a CAAQS or NAAQS according to the local Air Quality Attainment Plan
(AQAP). As indicated in Section 3.8.2 of this SEIS, California has
adopted stricter standards than those specified by the EPA. In San
Diego, the AQAP is the 1991/1992 RAQS and attached TCMs.

CARB Guidelines

For short‑term emissions of criteria pollutants (e.g., construction
emissions), the SCAQMD has established daily emissions significance
thresholds (Table 4.8‑1). These thresholds have generally been accepted
by the San Diego APCD. The CEQA Air Quality Handbook (SCAQMD 1993) also
provides a screening table to determine whether a proposed project has
the potential to generate construction‑related emissions greater than
the standards.

For long‑term emissions of criteria pollutants, the direct impacts of a
project can be measured by the degree to which the project is consistent
with regional plans to improve and maintain air quality. The regional
plan for San Diego is the 1991/1992 RAQS and attached TCM plan. The CARB
provides criteria for determining whether a project conforms with the
RAQS (State of California 1989), which include the following:

Is a regional air quality plan being implemented in the project area?

Is the project consistent with the growth assumptions in the regional
air quality plan?

Does the project incorporate all feasible and available air quality
control measures?

The proposed alternatives are located in the SDAB, which is covered by
the 1991/1992 RAQS as indicated above. Additionally, none of the
proposed alternatives are growth inducing. Therefore, criteria 1 and 2
above are satisfied. Air quality control measures are discussed under
each alternative below. The San Diego APCD is responsible for issuing
air quality permits for operation of the IWTP.

SIGNIFICANCE THRESHOLDS

Source/

Pollutant Threshold

Operation

ROC 55 lbs/day

NOx 55 lbs/day

CO 550 lbs/day

PM‑10 150 lbs/day

SOx 150 lbs/day

Constructi

on

ROC 2.5 tons/qtr or 75

lbs/day

NOx 2.5 tons/qtr or 100

lbs/day

CO 24.75 tons/qtr or 550

lbs/day

PM‑10 6.75 tons/qtr or 150

lbs/day

SOx 6.75 tons/qtr or 150

lbs/day

SOURCE: SCAQMD 1993:6‑2 and 6‑4.

ROC = reactive organic compounds; NOx =

nitrogen oxides; CO = carbon monoxide;

PM‑10 = 10‑micron particulates; SOx =

sulfur oxides.

Odor impacts would be considered potentially significant if the proposed
project or alternatives would noticeably change existing conditions in
areas where sensitive receivers occur or are proposed (e.g.,
residences).

Alternative 1: No Action

Impacts

Under this alternative, raw sewage flows in excess of the combined
capacity of Tijuana Pump Station One and the emergency connector would
continue to flow into the Tijuana River via Stewart\'s Drain. These
sewage flow, currently estimated at 1.1 mgd (48 lps), are expected to
grow to 5.6 mgd (245 lps) by the year 2001.

No additional emissions of criteria pollutants would occur under this
alternative. However, offensive odors would continue to be emitted from
the river which could impact surrounding sensitive receivers. Odors
associated with Tijuana Pump Station One would remain unchanged.

Significance of Impacts

Odors emanating from the river could continue to be a public nuisance if
these odors are detected by sensitive receivers in the area. This is a
significant adverse impact.

Mitigation

No mitigation is available for the No Action alternative. Odor impacts,
if they occur, would be significant and unmitigated. Alternative 2:
Operate IWTP

Impacts

Under this alternative, raw sewage flows in excess of the combined
capacity of Tijuana Pump Station One and the emergency connection would
flow to the IWTP and be stored or treated to primary standards. Effluent
would then be pumped to the emergency connection for further treatment
at the Point Loma treatment plant. Effluent flows in excess of emergency
connection capacity would be discharged directly to the Tijuana River.
The excess treated effluent flow is estimated to be 3.6 mgd (158 lps)
for average day flows by the year 2001.

The IWTP was designed with air pollution and odor control equipment and
the effects from operation are covered in the prior EIS. No additional
emissions of criteria pollutants would occur under this alternative.

However, primary effluent would be discharged directly to the river.
Odors associated with primary treated effluent are generally less than
those associated with raw sewage. However, they still can be offensive.
Therefore, odor impacts to sensitive receivers in the vicinity of the
Tijuana River could occur. Odors associated with Tijuana Pump Station
One would remain unchanged.

Significance of Impacts

Odors emanating from the river could constitute a public nuisance if
these odors are detected by sensitive receivers in the area. This is a
potentially significant impact.

Mitigation

Odors emanating from the advanced primary effluent could be reduced by
chlorination, although they would not be eliminated entirely. However,
this is currently not included in the proposed IWTP operation under this
alternative. Odor impacts, if they occur, would be significant.

Alternative 3: Operate IWTP with Detention Basin

Impacts

Under this alternative, raw sewage flows in excess of Tijuana Pump
Station One capacity would flow to the IWTP and be treated to primary
standards. Effluent would then be discharged to the emergency connection
to the Point Loma treatment plant. Effluent flows in excess of emergency
connection capacity would be discharged to a 5.5 million gallon (20,900
m3) detention basin. Effluent stored in the basin would be pumped to the
emergency connection during off‑peak hours.

If the detention basin is filled to capacity before the emergency
connection is able to receive the total effluent flow, flow to the basin
would be diverted and the excess flow would be discharged directly into
the Tijuana River. It is estimated that the effluent flow rate directly
discharged to the river would be 0.6 to 2.0 mgd (26 to 88 lps) and would
only occur during seasonal high flows in the years 2000 and 2001.

Construction Impacts

Construction of the 5.5 million gallon (20,900 m3) detention basin(s)
would generate fugitive dust (PM‑10) and construction equipment exhaust
emissions. The basins are anticipated to cover one to two acres (4,050
to 8,100 m2). According to the SCAQMD screening manual, grading of a
one‑acre (0.4 ha) area results in 55 lbs/day of emissions without dust
control measures. The federal standard for emissions of PM‑10 is 150
lbs/day. The SCAQMD uses a threshold of 177 acres (716,000 m2) for
potentially significant impacts from grading activities with dust
controls. Therefore, given the small size of the detention basins, no
significant construction‑related emissions are anticipated.

Operation Impacts

No additional emissions of criteria pollutants would occur under this
alternative. However, primary effluent would be stored in the 5.5
million gallon (20,900 m3) detention basin as well as discharged
directly to the river. Odors associated with primary treated effluent
are generally less than those associated with raw sewage. However, they
still can be offensive. Therefore, odor impacts to sensitive receivers
in the vicinity of the Tijuana River, and especially adjacent to the
detention basin, could occur. Odors associated with Tijuana Pump Station
One would remain unchanged. Significance of Impacts

Odors emanating from the river and detention basin could constitute a
public nuisance if these odors were detected by sensitive receivers in
the area. This is a potentially significant impact.

Mitigation

Aerating the detention basin(s), covering them, and equipping them with
appropriate odor control equipment would mitigate odors emanating from
the detention basins to below a level of significance. Odor control
measures shall be incorporated into the design of the detention basins.

Odors emanating from the advanced primary effluent discharged directly
to the river could be reduced by chlorination, although they would not
be eliminated entirely. However, this is currently not included in the
proposed IWTP operation under this alternative. Odor impacts, if they
occur, would be significant.

Alternative 4: Operate IWTP with New Conveyance to Mexico

Impacts

Under this alternative, raw sewage flows in excess of Tijuana Pump
Station One capacity would flow to the IWTP and be treated to primary
standards. Effluent would then be pumped back to a new conveyance system
in Mexico for discharge at Punta Banderas. No effluent would be
discharged to the Tijuana River.

Construction Impacts

Under this alternative, no significant construction‑related emissions
would occur in the United States. Emissions of criteria pollutants would
occur during the construction of the new conveyance system in Mexico.
However, these emissions would not be subject to U.S. regulation. Since
detailed design of the new conveyance system is not currently available,
it is not possible to estimate the resulting construction emissions at
this time. However, due to the prevailing northwesterly winds, these
construction emissions would not be expected to significantly affect the
air quality north of the border.

Operation Impacts

Under this alternative, no additional criteria pollutant emissions will
occur. Additionally, discharges to the river would cease. Therefore,
odor impacts in the Tijuana River valley as a result of dry‑weather
sewage flows would be eliminated with implementation of this
alternative.

Significance of Impacts

No significant air quality or odor impacts are expected to occur with
implementation of the Operate IWTP with New Conveyance to Mexico
alternative.

Mitigation

No mitigation is required for the Operate IWTP with New Conveyance to
Mexico alternative.

Alternative 5: Operate IWTP with Discharge to SBOO

Impacts

Under this alternative, raw sewage flows in excess of Tijuana Pump
Station One capacity would flow to the IWTP and be treated to primary
standards. Effluent would then be pumped to the SBOO for discharge to
the ocean.

No additional criteria pollutant emissions would occur under this
alternative. Additionally, discharges to the river would cease.
Therefore, odor impacts as a result of dry‑weather sewage flows in the
river would be eliminated with implementation of this alternative.

The IWTP was designed with odor control facilities, and the impacts of
its operation are not anticipated to be adverse. However, there will be
an energy dissipater between the plant and the South Bay Land Outfall
pipe, which is vented to the atmosphere. If secondary treated effluent
were being discharged, odor control facilities would not be necessary.
However, if primary treated effluent is being discharged, odor control
at the vent would be necessary to avoid odor impacts to residents and
visitors.

Odors associated with Tijuana Pump Station One would remain unchanged.
Significance of Impacts

Potential nuisance odors could result from the energy dissipater vent
structure should the IWTP be operated as an advanced primary treatment
plant and effluent discharged through SBOO. Odor controls are feasible
to implement that would reduce this impact to a level below
significance. No other significant air quality or odor impacts are
expected to occur with implementation of the Operate IWTP with Discharge
to SBOO alternative.

Mitigation

The energy dissipater vent will be provided with odor control equipment
if the IWTP is operated as an advanced primary plant and effluent is
discharged to the SBOO.

Land Use and Socioeconomics

Alternative 1: No Action

Currently, raw sewage from unsewered areas of Tijuana collects in the
Tijuana River. Overall, most of the land uses in the Tijuana River
valley have been negatively impacted by sewage discharges into the
Tijuana River. These impacts include direct impacts resulting from
discharges during dry weather and rainy periods and impacts from
discharges of untreated sewage in Mexico extending north along the
shoreline. Continuous indirect impacts are associated with the area\'s
image/reputation. Use of Border Field State Park and Imperial Beach
coastal properties and businesses have been negatively impacted by beach
closures and the image problem associated with unclean beaches.

According to historical statistics from the San Diego County Health
Department, the number of days of beach closures were recorded at 187
days for 1993, 36 days for 1994, and 67 days in 1995. The beach closures
typically included the general area from South Silver Strand State Beach
to the international border. In 1995 the cause of these closures was
primarily related to rain and sewage. For seven days in April and May of
1995 the recorded cause was a shutdown at Pump Station One in Tijuana.

Residential Impacts

The salability and value of the residential properties in the Tijuana
River valley have and will continue to be affected by sewage discharges.
According to the Imperial Beach Chamber of Commerce, oceanfront
condominium sales and rental values have also been negatively affected
by the discharges. Overall, the area\'s image due to the discharge
problem has had a negative affect on the salability and values of the
residential units in the valley and along the Imperial Beach coast.

Business Impacts

The equestrian rental businesses in the river valley have experienced an
image problem associated with the sewage discharges. The Equestrian
Association indicated that horse rentals are easier to market to
out‑of‑town visitors, as opposed to locals, because of the river
valley\'s reputation. Also, during beach closure days, the horse rental
business is directly impacted.

Although the small businesses within the coastal areas of Imperial Beach
receive some year‑round support from local residents, beach visitors,
particularly during major events, represent a profitable support source.
According to the Imperial Beach Chamber of Commerce, one of the reasons
the City was not selected to host the Bud Pro Surf Contest was the beach
closures caused by sewage discharges into the Tijuana River. The beach
and the special events which are dependent on clean beaches represent an
important economic stimulus for local businesses.

The sales realized by the above‑mentioned businesses have been
occasionally impacted by beach closures and continuously affected by
image problems.

Agricultural Impacts

Based on the limited number of agricultural businesses in the valley,
and on an informal survey of a few of these businesses, the major
impacts to these businesses occur during flood periods. One grower
indicated the combination of flooding and effluent discharge has had a
significant impact. The soil on the growers\' property was contaminated
and condemned by the County health department for a period of six
months. Agricultural employees in the area have also expressed concerns
over working in the vicinity of sewage discharges.

Recreational Impacts

Recreational activities are an important amenity to the California
lifestyle. According to a 1992 California Outdoor Recreation Survey
conducted by the California Department of Parks and Recreation, 69
percent of California\'s population participates in beach activities, 16
percent ride horses, and 56 percent participate in nature study and
viewing. These statistics indicate the importance of recreational areas
in general.

Based on visitor attendance at Border Field State Park and Silver Strand
State Beach, this area represents an important recreational area. Based
on County health department statistics, the beach from the international
border to Silver Strand State Beach has incurred numerous days of
closure due to effluent discharges. These closure days directly affect
water sports (surfing, swimming), as well as beach activities. During
most beach closure days, the camping areas at Silver Strand State Beach
have remained open for camping, hiking, picnicking, and land activities.
Although the discharges did not close these parks, it is assumed that
attendance was impacted.

The YMCA Camp Surf is also dependent on open, clean beaches. The camp
has had to cancel some activities in the past and is continuously
affected by the image problem associated with effluent discharges.

The Tijuana River Valley Regional County Park has no facilities
developed for public recreation.

Sportfishing Impacts

According to the California Department of Parks and Recreation survey,
25 percent of Californians have participated in saltwater fishing within
the last two years, which indicates the importance of the ocean as a
recreational amenity. Both fishing from the Imperial Beach Pier and
beach anglers using the beach from the Mexican border to roughly the
Silver Strand State Beach are directly impacted by beach closures due to
effluent discharges. The impact on fishing also affects the bait and
tackle shop, as well as some of the smaller businesses in Imperial
Beach. Offshore fishing typically is well beyond the surf line and,
therefore, is minimally affected by discharges from the Tijuana River.

Significance of Impacts

Existing conditions have had a significant adverse effect upon residents
of the Tijuana River, adjoining communities, and public recreational
opportunities. These impacts would continue under the No Action
alternative.

Mitigation

No mitigation measures are available to EPA or USIBWC.

Alternative 2: Operate IWTP

Interim operation of the IWTP will eliminate discharge of dry‑weather
flows of untreated sewage to the Tijuana River. Discharge of treated
effluent to the Tijuana River may be necessary on a regular basis from
1998 to 2001, however, and the discharge of untreated sewage 5.6 miles
south in Mexico would continue.

The effects to residential, business, agricultural, and recreational
uses would be beneficial. Dry‑weather flows in the river would be
treated effluent. Although not treated to body contact recreation
standards, contamination, pollutant loading, and odors would be reduced.
The potential for summer restrictions on coastal water recreation uses
would be lessened, although residual impacts from untreated discharges
in Mexico would remain.

Significance of Impacts

Existing adverse effects on residents, commercial enterprises, and
public recreation would be reduced under this alternative but will still
be considered adverse.

Mitigation

No additional mitigation measures are available to EPA or USIBWC.
Alternative 3: Operate IWTP with Detention Basin

Storage of 5.5 million gallons (20,900 m3) of treated effluent at the
IWTP would eliminate the discharge of dry‑weather sewage flows and
reduce the potential of discharge of treated effluent to the Tijuana
River. This alternative would also have substantial beneficial impacts.
Residual impacts from untreated sewage discharges in Mexico would
remain, however.

Significance of Impacts

Impacts to the river valley from this alternative would not have a
significant impact on land use or socioeconomic conditions. However,
residual impacts would continue from seasonal beach closures.

Mitigation

No mitigation measures are available to EPA or USIBWC. Residual impacts
from discharge of untreated swage in Mexico is the responsibility of
Mexico.

Alternative 4: Operate IWTP with New Conveyance to Mexico

This alternative would eliminate dry‑weather flows of untreated sewage
or treated effluent in the Tijuana River and reduce the flows of
untreated sewage discharged in Mexico. This alternative would further
incrementally reduce the risk of sewage contamination to coastal areas
and enhance coastal recreation, dependent businesses, and residential
areas in the U.S. and Tijuana.

Significance of Impacts

Impacts to the Tijuana River valley or shoreline communities in the U.S.
would be beneficial. Residual impacts from discharge of untreated sewage
in Mexico to U.S. coastline areas would remain.

Mitigation

No mitigation measures are available to EPA or USIBWC. Residual impacts
from discharge of untreated swage in Mexico is the responsibility of
Mexico.

Alternative 5: Operate IWTP with Discharge to SBOO

This alternative would have the most beneficial impacts of the
alternatives. There would be further improvement to ocean water quality
in the U.S. and Mexico. Discharge of treated effluent offshore in deeper
water discharge results in greater dilution and dispersion of treated
effluent and is preferable to shoreline discharge.

Significance of Impacts

Impacts to the Tijuana River valley or shoreline communities in the U.S.
would be beneficial. Impacts from operation of the SBOO were covered in
the 1994 FEIS for the project.

Mitigation

No additional mitigation measures beyond those identified in the 1994
FEIS are necessary.

Effects Not Reevaluated for the SEIS

The EPA and IBWC circulated an EIS and signed a Record of Decision in
May 1994 for new federal facilities to treat sewage from Mexico in the
Tijuana River valley. The EIS analyzed several alternatives for
potential impacts to the physical, biological, and socioeconomic
environments. As such, 15 separate issues relating to those three
environments were discussed. They included hydrology, geological
resources, scenic and visual resources, noise, air quality, odor,
oceanography, terrestrial biology, estuarine biology, marine biology,
cultural resources, paleontology, land use, traffic and transportation,
and public health.

The Interim Operation SEIS addresses operational alternatives for the
IWTP and SBOO. As such, no new major facilities or construction are
required. Many issues previously addressed in the 1994 EIS were found
not to have new potentially significant effects and, consequently, are
not discussed in detail in the preceding environmental impact analysis.
These are briefly explained below.

Scenic and Visual Resources

The effects of the IWTP construction were addressed in the 1994 EIS. No
new visual impacts would result from interim operation of the IWTP.

Noise

The effects of construction and operation of the IWTP and collector pump
stations were addressed in the 1994 EIS and Biological Assessment. No
new impacts would result from interim operation of the IWTP. Cultural
Resources

Cultural resources have been addressed according to a Memorandum of
Understanding with the State Office of Historic Preservation for the
project. No new facilities are proposed in the U.S. that would impact
significant cultural resources.

Paleontology

Paleontological impacts for the project were addressed in the 1994 EIS.
No new impacts would result from interim operation of the IWTP.

Traffic and Transportation

Operation of the IWTP was covered in the 1994 EIS. Supplemental EAs have
been prepared by the USACE for modifications to the design and
construction of the SBOO (USACE 1995) and dechlorination facilities
(USACE 1996). No additional traffic or transportation impacts would
result.

Cumulative Effects

Cumulative effects‑including to hydrology, scenic and visual resources,
air quality and odors, oceanography, terrestrial and marine biology,
noise, cultural resources, paleontological resources, and land uses‑were
considered in the prior EIS for the No Action alternative and the
operation of the IWTP as a secondary treatment works of up to 100 mgd
(4,380 lps) with discharge through the SBOO. The effects of the
discharge through the SBOO were considered with effluent to be
discharged from other future City of San Diego treatment works in the
South Bay.

The specific potential cumulative effects relevant to interim discharge
of advanced primary treatment to the river or through the SBOO with the
shoreline discharge in Mexico are analyzed in the Oceanography section
of the SEIS. Potential adverse effects to marine biota, ocean water
quality, public health, and land use and socioeconomics are identified
for the Interim Operation SEIS.

Growth Inducement

The growth‑inducing effects of the long‑term operation of the IWTP with
discharge of up to 100 mgd through the SBOO was considered in the prior
EIS. No additional growth‑inducing effects are anticipated for the
interim operation of the IWTP as an advanced primary plant through the
year 2001.

Relationship of Local Short‑term Uses of the Environment and the
Maintenance and Enhancement of Long‑term Productivity

The adverse effects of the No Action alternative and the short‑term
impacts of construction and operation of the IWTP with discharge of up
to 100 mgd through the SBOO and benefits to maintaining the quality of
surface and ocean waters in the U.S. were considered in the prior EIS.
No additional impacts are anticipated for the interim operation of the
IWTP as an advanced primary plant through the year 2001.

Significant Irreversible Environmental Changes

The prior EIS identified significant irreversible impacts to biota, land
uses, scenic and visual quality, energy consumption, cultural resources,
paleontological resources, and the ocean from construction and operation
of the IWTP and SBOO. The additional interim treatment and discharge
alternatives would not result in additional irreversible commitments or
changes to the affected environment.

Chapter Five

Environmental Commitments

Hydrology and Water Quality

Effluent Chlorination

Treated effluent that would be discharged to the Tijuana River or
through Mexican facilities to the shoreline can be chlorinated prior to
discharge to reduce odor impacts and reduce health risks from coliforms.
However, chlorination of effluent may be of limited effectiveness and
pose concerns for water quality impacts from residual chlorinated
compounds. This decision will be made after consultation with the Air
Pollution Control District, RWQCB, and San Diego County Health Services
Department.

Detention Basin

If an earthen detention basin is constructed at the IWTP, the basin will
be lined with an impermeable liner to avoid percolation of treated
effluent to the groundwater. The liner will be included in design
specifications for the basin by USIBWC.

Estuarine Biology

Monitoring Program

If treated effluent is routinely discharged during dry weather to the
Tijuana River, a monitoring program will be undertaken. The program will
monitor changes in water quality using indirect indicators of water
source and sewage contamination. These include salinity, dissolved
oxygen, temperature, and coliform bacteria. The monitoring will be
conducted using automatic data loggers; hand‑held salinity, dissolved
oxygen, and temperature meters; and standard methods for the examination
of water and wastewater. The monitoring program will be initiated prior
to discharge of the effluent and will continue through the period that
effluent is discharged to the Tijuana River. Reports of the monitoring
will be provided to the RWQCB, Tijuana River National Estuarine Research
Reserve, and EPA.

Geotechnical

Detention Basin

Site‑specific geotechnical investigations will be performed prior to
construction of the earthen detention basin to determine soil
characteristics, thickness, and distribution and to develop appropriate
soil engineering parameters for the proposed facility.

Fault evaluation studies will be performed of mapped fault traces in
order to confirm fault locations and activities. In addition, a
geologist shall observe excavations during construction to detect the
presence of unmapped traces in the general vicinity of mapped fault
traces.

New Pumping and Conveyance in Mexico

Mexico will conduct design review of the pipeline and pump station as
part of its environmental impact assessment and to their construction
standards. This design should anticipate the effects of ground shaking
and incorporate measures to minimize the risk of failure during seismic
events.

If construction of the pipeline is undertaken during the rainy season,
Mexico should incorporate erosion controls during any grading to prevent
erosion impacts into the U.S.

Public Health

Vector Control

If effluent is discharged to the Tijuana River, the USIBWC, in
cooperation with the County Department of Health Services, will monitor
the river channel during the dry season to ensure that no ponding of
treated effluent occurs within the low‑flow channel of the river. If
ponding does occur, vector control measures will be implemented.

Odors

Storage of treated effluent in the detention basin may result in
objectionable odors. As the basin would only fill during peak hourly
flow periods, these impacts would be short term. However, if
objectionable odors result, the detention basin would be covered and the
air circulated to an odor control device. IBWC will include covers and
an odor control system in the design of the detention basin, if this
alternative is chosen.

Odor control facilities were included in the design for the IWTP. If
advanced primary treated effluent is discharged through the SBOO,
additional odor control facilities will need to be included at a vent
for the energy dissipater located between the plant and SBLO. The USIBWC
will be responsible for ensuring that appropriate odor control
facilities are provided for discharge of primary treated effluent
through SBOO.

Chapter Six

Compliance with Applicable Environmental Laws and Regulations Federal
Laws and Regulations

National Environmental Policy Act of 1969, as Amended

The EPA and USIBWC have prepared this SEIS to assess impacts associated
with the interim operation of the IWTP in the Tijuana River valley just
north of the U.S./Mexico border in San Diego County. During this interim
period, the plant will be operational as an advanced primary treatment
works before secondary treatment is available or the ocean outfall is
operational. Since the FEIS for the IBWC wastewater treatment plant and
outfall facilities did not anticipate such an interim operational
period, this SEIS has been compiled and prepared in accordance with the
National Environmental Policy Act of 1969, as amended (42 U.S.C. 432 et
seq.).

Clean Water Act of 1977, as amended (Public Law 95‑217)

Section 402 of the Clean Water Act establishes the National Pollutant
Discharge Elimination System permitting program. All point source
dischargers are required to obtain and comply with the provisions of an
NPDES permit for any discharge of pollutants into waters of the U.S.
(e.g., oceans, lakes, or streams). NPDES permits must contain discharge
limitations based on the more stringent of the applicable state or
federal technology‑based requirements and water quality standards. Due
to the location of the diffusers, the discharge from the IWTP will occur
in state waters. Therefore, EPA and/or RWQCB will be the authorities
issuing the NPDES permit for the IWTP.

Section 402 of the Clean Water Act establishes the NPDES permitting
program. Subsection (a)(5) of Section 402 specifies that the
Administrator (EPA) may delegate authority to issue permits for
discharges to the state. As allowed per this subsection, the EPA has
delegated NPDES permitting authority to the RWQCB. Thus, the Ocean Plan
will be the primary source of water quality standards applicable to the
IWTP discharge, regardless of whether EPA and/or RWQCB issues the NPDES
permit for the discharge.

Discharge of primary treated effluent to the ocean is not authorized by
the federal Clean Water Act. If a discharge is to occur, the discharger
will comply with a discharge permit and compliance order issued by the
RWQCB.

Antidegradation Policy of the Clean Water Act (40 CFR 131.12)

This policy requires that an antidegradation analysis be performed for
projects which will result in a lowering of water quality. A project
which lowers the quality of the receiving waters cannot be allowed if
the receiving waters do not meet state water quality standards. The
applicable water quality standards are found in the California Ocean
Plan and the San Diego Basin Plan. Ocean waters are designated
high‑quality waters; however, the Tijuana River does not meet the Basin
Plan standards and is not considered a high‑quality receiving water.

Because the discharge is to high‑quality ocean waters, the project meets
the antidegradation requirements if the following conditions are
satisfied:

The project is necessary to accommodate important economic or social
development in the area in which the waters are located. Water quality
will remain adequate to assure water quality sufficient to fully protect
existing uses.

The highest statutory and regulatory requirements for all

new and existing point sources and all cost‑effective best management
practices for non‑point source control will be achieved.

The proposed action satisfies the first condition since the project
would prevent dry‑weather sewage flow in the Tijuana River that has
impaired economic and social development in the area and has limited the
use of the river and the ocean adjacent to its mouth.

The proposed action satisfies the second condition because the NPDES
permit for the discharge will contain effluent limitations based on the
Ocean Plan and other applicable standards.

The proposed action satisfies the third condition because the IWTP will
collect and treat existing untreated non‑point source discharges from
Mexico. RWQCB of San Diego is already regulating existing point and
non‑point sources in the U.S.

Discharges to the Tijuana River and estuary of treated effluent would
not meet the goals of this policy, however.

Endangered Species Act of 1973, as Amended

Potential impact to federal listed species requires consultation with
the USFWS or NMFS, as stated under Section 7 of the federal Endangered
Species Act. If the USFWS or NMFS advises a federal agency that a listed
species may be present in the area of a proposed agency action, the
agency must conduct a biological assessment to determine whether its
proposal is likely to affect any listed species. If the assessment
concludes that a protected species may be adversely affected, the agency
must initiate formal consultation with USFWS or NMFS. Based upon the
results of the formal consultation, USFWS or NMFS must issue a written
biological opinion. Informal consultation has been initiated by EPA and
USIBWC with USFWS. Interagency Cooperation Endangered Species Act of
1973, as Amended; Final Rule

This final ruling, effective July 3, 1986, establishes the procedural
regulations which govern interagency cooperation under Section 7 of the
Endangered Species Act of 1973. The act requires federal agencies, in
consultation with and with the assistance of the secretaries of the
Interior and Commerce, to insure that their actions are not likely to
jeopardize the continued existence of endangered or threatened species
or result in the destruction or adverse modification of the critical
habitat of such species.

Formal consultation was completed for the IWTP and SBOO. The USFWS
originally expressed concern that the removal of dry‑weather sewage
flows in the Tijuana River might reduce the area and quality of riparian
habitat supporting least Bell\'s vireo. The State Water Resources
Control Board (SWRCB) provided supplementary evidence to the USFWS that
the contribution of dry‑weather surface sewage flows to groundwater
levels in the Tijuana River did not provide substantial support for
riparian habitat in the river valley. The IBWC has committed to a
groundwater and soil moisture monitoring program along the riparian
corridor in conformance with the terms and conditions of the Biological
Opinion provided by the USFWS.

The proposed action is in compliance with this ruling. The EPA is
coordinating with the USFWS in accordance with Section 7(a)(2) of the
Endangered Species Act.

Clean Air Act, as Amended

The federal Clean Air Act, as amended, was enacted for the purposes of
protecting and enhancing the quality of the nation\'s air resources to
benefit public health, welfare, and productivity. The only major
construction proposed is for the earthen detention basin under
Alternative 3. This construction would not cause exceedance of any
priority pollutants. The proposed action to discharge advanced primary
treated effluent into the Tijuana River and/or the ocean or through the
SBOO would not require additional review or compliance beyond that
already proposed and evaluated in the EIS.

National Historic Preservation Act

The National Historic Preservation Act (NHPA) is managed in the state of
California by the State Office of Historic Preservation. The NHPA
requires an assessment of historic properties which may be located on a
project site. Because the proposed action includes only operational
changes during a short interim period and no new major construction
would occur outside the boundaries of areas already evaluated, no
historic properties would be affected. Coastal Zone Management Act

This act was passed in 1972 to preserve, protect, develop, and, where
possible, restore and enhance U.S. coastal resources. To achieve this,
Congress required that states wishing to participate in the national
program would have to develop management programs that would fulfill the
goal of the act. California enacted the California Coastal Act.

A Coastal Consistency Determination was approved by the California
Coastal Commission for the IWTP and SBOO in 1994.

The USIBWC will submit a supplemental Coastal Consistency Determination
to the California Coastal Commission for the proposed operational
changes. The proposed action would fulfill the goals of the Coastal Zone
Management Act by improving the water quality in the Tijuana River
valley and in the ocean waters near the mouth of the river from current
water quality levels.

Farmland Protection Policy Act

This act requires a federal agency proposing a major federal action to
examine the effects of the action using the criteria of the act and, if
any adverse impacts are identified, consider alternatives to lessen them
and ensure that the action is consistent with state, local, and private
programs to protect farmland. Impacts to farmland were considered in the
Socioeconomic section of the EIS. The short‑term (three to five years)
discharge of advanced primary effluent into the Tijuana River would not
adversely affect adjacent farmland.

Marine Mammal Protection Act

The Marine Mammal Protection Act provides protection for marine mammals
by prohibiting the taking (including harassment, disturbance, capture,
or death) of any marine mammals except as set forth in the act. In
addition, many species are also listed as threatened or endangered and
are thereby protected under the Endangered Species Act. The EPA and
USIBWC, in coordination with the NMFS, must determine that marine
mammals will not be affected by the proposed action.

Executive Orders

Executive Order 11988‑Flood Plain Management

This act requires a federal agency to consider alternatives to avoid
adverse effects and incompatible development in the floodplain. The
proponent agency must also design or modify the action to minimize
potential harm within the floodplain, in coordination with the federal
Water Resources Council and the Federal Emergency Management Agency. The
interim discharge would be of a low volume relative to normal flood
flows and would not affect the Tijuana River floodplain.

Executive Order 11990‑Protection of Wetlands

This act states that the proponent agency will avoid funding new
construction located in wetlands unless the agency finds that there is
no practicable alternative to such construction and that the proposal
contains all practicable measures to minimize harm to wetlands. The SEIS
evaluates the effects of the short‑term discharge of advanced primary
effluent and does not include any new construction.

Executive Order 12114‑Environmental Effects Abroad of Major Federal
Actions

This order, signed January 4, 1979, establishes procedures for federal
agencies including EPA to consider the significant effects of their
actions on the environment outside the U.S. consistent with foreign
policy and national security policies of the U.S. For purposes of the
order, &quot;environment&quot; means the natural and physical
environment‑including global commons (oceans and the Antarctic),
emissions or effluent discharges regulated by federal law in the U.S.
because of their potential toxic effects on the environment to create a
serious public health risk, and natural and ecological resources of
global importance designated for protection or protected by
international agreement‑and excludes social, economic, and other
environments.

Executive Order 12898‑Environmental Justice

This order, signed February 11, 1994, requires agencies to incorporate
environmental justice into their missions by identifying and addressing
disproportionately high and adverse human health or environmental
effects of their programs and policies on minorities and low‑income
populations and communities.

The Tijuana River valley has been impacted for many years by flows of
sewage from Mexico. The action to collect, treat, and discharge sewage
offshore that would otherwise enter the U.S. and contaminate the Tijuana
River valley and public coastal recreation areas is consistent with this
policy directive.

State Laws and Regulations

California Environmental Quality Act

The proposed interim discharge is not subject to CEQA. No state permits
are required, other than review of the proposed interim discharge by the
State Water Resources Control Board and Regional Water Quality Control
Board. Their review is not subject to CEQA. Porter‑Cologne Water Quality
Act

In 1949, California enacted the Porter‑Cologne Water Quality Act, which
created a State Water Resources Control Board and nine Regional Water
Quality Control Boards with broad powers to protect water quality by
regulating discharges to ground and surface waters of the state,
including discharges by publicly owned treatment works, to rivers,
streams, lakes, or ocean waters. Discharges to surface or ground waters
are subject to consistency with the Basin Plan and specific conditions
and limitations set by the RWQCB, known as waste discharge requirements.
Discharges to ocean waters are subject to standards promulgated by State
Water Resources Control Board in 1990, which are known as the state
Ocean Plan.

Ocean Plan standards address constituents in effluent discharged to
receiving waters such as grease and oil, suspended solids, settleable
solids, turbidity, pH, and over 20 species of toxic pollutants,
including heavy metals. The Ocean Plan sets standards for maximum
average concentrations and instantaneous levels for both effluent and
receiving waters.

All effluent discharged to ocean waters must meet the standards in the
Ocean Plan or the RWQCB will issue an order to cease and desist.

California Air Toxics Act of 1987 (Assembly Bill 2588)

As required by AB 2588, publicly owned wastewater treatment plants with
a wastewater flow of more than 20 million gallons per day must conduct a
toxic air emission inventory/health risk assessment. The sources of
volatile organic compounds, hydrogen sulfide, and as many as 135 other
toxic compounds must be identified and inventoried and the emissions,
regardless of how small, have to be quantified.

Air Pollution Control District Rules and Regulations

Existing APCD regulations (Rule 10) require that the IWTP facility
obtain Authority to Construct and/or Permit to Operate permits from the
APCD. This review will include air quality modeling of pollutants and
requirements for best available control technology or lowest achievable
emissions reduction based upon emissions thresholds. No new sources of
emissions from the IWTP are proposed for interim discharge.

California Coastal Act of 1976

This act was developed to fulfill the goals of the Coastal Zone
Management Act in the state of California. The California Coastal
Commission implements the regulations of the California Coastal Act.

Because the IWTP involves federal funding, it is exempt from obtaining a
state‑mandated Coastal Development Permit. Instead, the IBWC must submit
a Consistency Determination to the California Coastal Commission (15 CFR
930). The California Coastal Commission can either concur or object to
the proposed action and can make suggestions on how to minimize impacts
to the Coastal Zone.

The IBWC completed a Coastal Consistency Determination for the IWTP and
SBOO which was accepted by the California Coastal Commission in 1994,
but the Coastal Commission will further consider the action with respect
to short‑term discharge of advanced primary effluent within the Coastal
Zone.

California Endangered Species Act

Potential impacts to California state listed endangered or threatened
species would require the issuance of a 2080 permit by the California
Department of Fish and Game as stated under Section 2080 of the
California Fish and Game Code. The Tijuana estuary provides habitat for
listed plant and animal species.

Surface Mining and Reclamation Act of 1975

The IWTP site is located in two Mineral Resource Zones. The proposed
action does not include any construction or site improvements that would
affect these zones.

California Fish and Game Code Sections 1601‑1603

The proposed discharge of advanced primary effluent during the three‑ to
five‑year interim time period will not impact a stream course or
drainage that would require a 1603 Streambed Alteration Agreement be
issued by CDFG as stated under Sections 1601‑1603 of the California Fish
and Game Code prior to project approval. California Code of Regulations
Section 15000 and CEQA Section 21167(a)

A lease was granted by the California State Lands Commission to cross or
build the SBOO facility on state‑owned public land. No new facilities
are proposed for the interim discharge SEIS.

Chapter Seven

Consultation with Others

Persons and Agencies Consulted

An ongoing program of coordination with interested individuals, groups,
and agencies has been conducted by EPA and USIBWC for the IWTP and SBOO
project. Information meetings have been held monthly. Attendees included
the following.

Focus Group

Jack McCabe, Private Citizen

Bob Coates, Private Citizen

Carolyn Powers, C.A.R.E.

Rina Kelly, C.A.R.E.

David Gomez, C.R.A.P.

Robert Simmons, Sierra Club

Thomas Penfield, Sierra Club

Craig Adams, Sierra Club

Rory Wicks, Surfrider Foundation

Gary Sirota, Surfrider Foundation

Kimberley Collins, San Diego State University

Mike Richmond, Senator Dianne Feinstein

Liza Hirsch Medina, Congressman Bob Filner

Scott Vydra, Assemblyman Baldwin

Marco Cortes, Supervisor Greg Cox

Doc Doolittle, U.S. Border Patrol

Nan Valerio, San Diego Association of Governments

Homer Bludau, City of Coronado

Diane Rose, City of Imperial Beach

Don Hall, City of Imperial Beach

Ric Repasy, County of San Diego Parks and Recreation

Mike Devine, County of San Diego Environmental Health

Moise Mizrahi, County of San Diego Environmental Health

Horace Ketcham, County of San Diego Environmental Health

Dave Schlesinger, City of San Diego Metropolitan Wastewater Department

Rolf Lee, City of San Diego Metropolitan Wastewater Department Richard
Enriquez, City of San Diego Metropolitan Wastewater Department

Tom Weeks, Air Pollution Control District

Mike Coleman, Otay Water District

Resources Agencies

Bill Paznokas, California Department of Fish and Game

Martin Kenney, U.S. Fish and Wildlife Service

Mark Helvey, National Marine Fisheries Service

Joanne Kerbavaz, Tijuana River National Estuarine Research Reserve

Lee McEachern, California Coastal Commission

Susan Hector, County of San Diego Parks and Recreation

Jennifer Maxwell, City of San Diego

Rolf Lee, City of San Diego Metropolitan Wastewater Department Bruce
Nyder, San Diego State University

Carolyn Powers, Tia Juana Valley County Water District

Art Letter, Tia Juana Valley County Water District

Scoping of Issues and Concerns

An official public and agency workshop to introduce the proposed project
alternatives and solicit comments regarding the scope and content of the
SEIS was hosted by EPA and USIBWC on August 31, 1995, in San Diego,
California. Panel members represented the following agencies:

U.S. Environmental Protection Agency

International Boundary and Water Commission

U.S. Army Corps of Engineers

City of San Diego

Public Meeting

The following six individuals provided verbal comments during the
meeting:

William E. Claycomb, Save Our Bay, Inc.

David Gomez, Citizens Revolting Against Pollution

Carolyn Powers, Tia Juana Valley County Water District

Diane Rose, Imperial Beach City Councilmember

Lori Saldana, Sierra Club

Danny Marshall, Resident, Tijuana River Valley

A presentation was made by the EPA and USIBWC representatives and
questions answered regarding the project background, purpose and need,
existing flows from Mexico, existing and proposed facilities, project
schedule, and costs. That two supplemental EISs would be prepared, one
covering interim operation of the IWTP and discharge alternatives and
the other covering treatment process alternatives and long‑term
operation and discharge. The EPA noted that the Interim Operation SEIS
was to be at a level of detail to allow construction of alternative(s)
selected but that perhaps no alternative would be implemented to the
exclusion of all others, and there could be combinations of
alternatives, which would also be analyzed in the EIS.

Verbal comments regarding issues to be addressed in the SEIS were
received. Although not specifically relevant to the project
alternatives, a primary concern voiced was that none of the alternatives
presented dealt with the flow of raw sewage into the Tijuana River
during the wet season. Concern was also expressed that all but one of
the proposed alternatives would result in discharges to the Tijuana
River, which is a violation of the Clean Water Act.

Other concerns expressed included a fear that the Mexican government
would not follow through on its promises; the overall cost of the
project; a belief that the infrastructure in Mexico is so weak and
overtaxed that future failures and sewage spills to the river from
across the border are inevitable regardless of the alternative chosen;
the impact of increased sewage flows (treated or untreated) into the
ocean; and a fear that funding for construction of the secondary
treatment facility would not be pursued. An opinion was expressed that
money might better be spent by diverting funds from the project to
improve infrastructure in Mexico.

It was mentioned that the SEIS should address how each of the proposed
alternatives would affect alternative secondary treatment facilities. It
was also felt that reclamation of water from the sewage flows should be
pursued. One individual indicated that ponds should be included as an
alternative in the long‑term SEIS, while another individual expressed
concern that ponds would be breeding grounds for mosquitoes and result
in objectionable odors.

Most individuals expressed their support for alternative 6 (operating
the IWTP and pumping the treated effluent to the discharge point just
south of Punta Banderas through a new pipeline constructed by Mexico).
Finally, studies were requested to determine the disbursement of the
discharges from Punta Banderas.

Resource Agencies Meeting

Agency representatives present included:

Jewel Bennett, USFWS

Mike Elling, City of San Diego

Peter Goodwin, Owens Associates

Mark Helvey, NMFS

Rachel Kamman, Owens Associates

Martin Kenney, USFWS

Horace Ketcham, County Environmental Health Services

Joanne Kerbavaz, Tijuana River National Estuarine Research Reserve

Art Letter, Tia Juana Valley County Water District

Carolyn Powers, Tia Juana Valley County Water District

Kristin Schwall, RWQCB

Mari von Hoffman, USFWS, Tijuana Slough NWR

Joy Zedler, SDSU Research Lab

County Health asked about leakage from the gates at Rodriguez Reservoir
in Mexico and whether repairs there would reduce flows. USIBWC noted
that leakage at Rodriguez, at Barrett Reservoir, and from the city of
Tecate, combined with improved capture of renegade flows in Tijuana,
made a complicated equation for identifying flows in the Tijuana River.
IBWC and EPA\'s projections were based on measured flows from all
sources at a certain time.

The TVCWD requested clarification regarding the issue of institutional
arrangements with Mexico and their relationship to the feasibility of
the subalternative. NMFS asked about the &quot;surf zone&quot; as
related to Mexican discharge. EPA clarified that Mexican effluent was
discharged into an arroyo and flowed across the beach into the ocean; at
times contamination from that source did occasionally and intermittently
come north. The SEIS would cover this topic. Concern was expressed about
stopping the analysis at the international border; that the analysis of
discharge in Mexico would probably be limited, and that the question of
obligations for analysis in another nation would have to be explored.

It was noted that the SDSU Estuary and Research Lab has been studying
the Tijuana River estuary and has collected a great deal of information
on it, including a wide‑scale water quality and salinity monitoring
program and a study of coliform bacteria in the estuary. The reports
will be made available to IBWC.

Discussion of Alternatives

Tijuana River National Estuarine Research Reserve would not support any
alternatives that involve interim discharge into the Tijuana River
because of the possible effect on the estuary.

No Action Alternative: The TJVCWD is on record opposing

no action. Environmental Health concurred because of concerns for health
effects of sewage on the beaches and bays and potential for mosquitoes,
high‑nutrient waters, and pollution.

Pond Detention of Untreated Sewage: Several agencies voiced concerns
that that community and political opposition would be likely to be high
and vocal, that there would be odor problems, and that mosquito control
in raw sewage would be a control problem. TVCWD expressed concerns that
earthen basins would not be favorably viewed due to groundwater impacts
or if the detention pond was lined because of possible accidents. Any
excess flows reaching the river would be unacceptable.

IWTP as Advanced Primary Plant: A question was raised

about the statement that the IWTP would have to receive at least 10 mgd
(440 lps) to operate. EPA explained the plant was designed to operate at
a minimum flow of 10 mgd (440 lps) and would not operate properly with
less. A question was asked about the capacity of the emergency
connection, if that would not just about take up its capacity, which is
13 mgd (569 lps). But the alternative would relieve pressure on
Mexico\'s system and allow it to handle increased flows for a while.
TVCWD noted that since excess flows would go to the river, some points
made about other alternatives applied. It opposed discharge of such
sewage, even if treated, into the river. EPA noted discharge would be
treated (advanced primary only); the treatment level would be about the
same for BOD as what Point Loma receives, but suspended solid levels
would be considerably less. Recent monitoring of Mexican sewage would be
done so the composition of Mexican sewage can be better understood,
which will be included in the EIS. Mexico has said they would not accept
treated sewage at Pump Station One.

IWTP with Pond Storage of Effluent: The Tia Juana Valley

County Water District has the same concerns as for storage of untreated
effluent. County Health noted mosquito control could be managed and
capacity would be greater than operating the IWTP without storage. The
advantage would be in the spring, when waiting for flows to drop below
13 mgd (569 lps) so emergency bypass could be turned on, and some of
early heavy flows could be taken and stored. The detention basin would
allow better management of odors and mosquitoes; it would also allow
storage of peak flows and discharge when peak flows are past at night.

Return to Sender Alternative: In response to questions,

it was noted that Mexico would build the facilities but in exchange
would be forgiven their share of IWTP costs. Cost would be about \$16
million by Mexican estimate and IBWC is trying to refine. The Mexican
pipeline would take 16 months to build. But IBWC will need to evaluate
plans to assure feasibility. IBWC would supervise the construction in
Mexico. After construction, it would be operated by the U.S. for the
interim period, then be turned over to the Mexican government. It would
then act as a parallel system with crossovers to the existing system and
help provide protection against system failures in Mexico. The IWTP
operation during interim discharge would be under IBWC\'s supervision,
until the SBOO outfall system was completed, when the facilities would
become wholly controlled by Mexico, probably with stipulations that
Mexico would be required to do maintenance on their existing system.
Mexico would have their own legal requirements that they would have to
comply with. Negotiations with Mexico are ongoing.

The TVCWD supports a return to sender alternative, as it best meets
needs for alternative discharge, assuming institutional and financial
arrangements can be worked out. The USIBWC noted that the timing could
be different, and a combination of alternatives could be needed if, for
instance, the return to sender facilities took longer than 16 months to
build. USFWS asked about benefits of alternative 6 after the interim
discharge period. Mexico would derive considerable benefits in
protecting against future failures in the Mexican system. It could also
be useful if Mexico in the future decides to reclaim effluent from the
IWTP.

The NMFS, County Health, TVCWD, and TRENERR expressed concern with the
discharge point for the return to sender alternative and its effects on
marine resources and public health issues, which were not confined by
the border. This was noted as a concern for the whole bioregion. A
question was asked if money was not available from the U.S. for the
return to sender pipeline, could Mexico find their own money for an
ocean outfall?

Discharge of IWTP Advanced Primary Effluent through SBOO: TVCWD asked if
it would be possible to construct return to sender and use it until the
ocean outfall was completed and then switch to the outfall. The water
district would support use of the outfall, even if using it extends the
interim discharge time frame. IBWC would look at effect of discharge on
the ocean at a hundred to one dilution. EPA noted that the SBOO
discharge, and all other U.S. discharge alternatives, would not be in
compliance with the Clean Water Act, but the Mexican discharge would not
require a U.S. waiver.

EPA stated that it did not have a preferred alternative and was awaiting
the analysis in the EIS. In response to a question, IBWC indicated they
did not plan to institute new studies. TRNERR urged that IBWC
incorporate existing studies of the estuary. USFWS asked about secondary
treatment and its alternatives. EPA responded that it would be addressed
through the long‑term SEIS. It was strongly recommended an agency
meeting for the alternatives to activated sludge SEIS be held also. EPA
stated that would be the case. Frustration was expressed by TVCWD at
legal constraints and with any studies that would take more money and
time.

Notice of Availability and SEIS Distribution

On September 6, 1996, EPA published a Notice of Availability of the
Supplemental EIS in the Federal Register. Public notices were also
placed in three newspapers with circulation in the South Bay area: San
Diego Union Tribune, Chula Vista Star News, and the Coronado Journal.
Copies of the SEIS were made available in local libraries or through the
San Diego office of the EPA or the U.S. Army Corps of Engineers. Copies
of the SEIS were sent to the following persons, organizations, and
agencies:

ELECTED OFFICIALS

Senator Barbara Boxer, U.S. Senate

Senator Dianne Feinstein, U.S. Senate

Congressman Randy Cunningham, U.S. House of Representatives, District 51

Congressman Bob Filner, U.S. House of Representatives, District 49

Congressman Duncan Hunter, U.S. House of Representatives, District 52

Congressman Ron Packard, U.S. House of Representatives, District 48

Congressman Brian Bilbray, U.S. House of Representatives, District 49

Senator, David Kelley, California State Senate, District 37

Senator Lucy Killea, California State Senate, District 39

Senator Steve Peace, California State Senate, District 40

Assemblywoman Dierdre Alpert, California State Assembly, District 78

Assemblywoman Steve Baldwin, California State Assembly, District 77

Assemblywoman Denise Moreno Ducheny, California State Assembly, District
79

Assemblyman Susan A. Davis, California State Assembly, District 76

FEDERAL AGENCIES

Environmental Protection Agency, Region IX

Ms. Nancy Woo; Ms. Elizabeth Borowiec; Mr. Doug Eberhardt, Water
Management Division; Mr. Dave Farrel, Federal Activities Branch

Federal Environmental Management Agency, Region IX

Mr. Ray Lenaburg, Mitigation Division

International Boundary and Water Commission, U.S. Section

Mr. C. W. Ruth, Mr. Charles Fischer, Mr. Steve Tencza

National Marine Fisheries Service

Mark Helvey

National Oceanic and Atmospheric Administration

Ms. Nina Garfield

U.S. Army Corps of Engineers, Regulatory Branch, San Diego Field Office

Mr. David Zoutendyk

U.S. Border Patrol, Imperial Beach Sector

Chief Patrol Agent Doc Doolittle

U.S. Customs, Rudy Camacho, District Director

U.S. Department of Agriculture, Soil Conservation Service

Mr. Jason Jackson

U.S. Fish and Wildlife Service, Carlsbad Field Office

Mr. Martin Kenney

Naval Command Control &amp; Ocean Surveillance, RDT &amp; E Division

Commanding Officer

Naval Amphibious Base, Coronado

Lieutenant Smith, Staff Civil Engineer

U.S. Coast Guard, Air Station San Diego

Commanding Officer

STATE

California Coastal Commission

Mr. Lee McEachern

State Clearinghouse, Office of Planning and Research

California Resource Agency

Ms. Carol Whiteside

California Coastal Conservancy

Mr. Michael Fischer

California Department of Fish and Game

Mr. Bill Paznokas

California State Parks, Southern Service Center

Mr. Clay Phillips, Manager

California State Parks, San Diego Coast District

Mr. Ed Navarro

California Department of Parks and Recreation, Tijuana Estuary Visitors
Center

Ms. Joanne Kerbavaz

California State Water Resources Control Board

Mr. Bart Christensen

California State Water Quality Control Board, San Diego Region

Ms. Kristin Schwall

Caltrans ‑ District 11

Environmental Review Coordinator

Governor\'s Office of California‑Mexico

Mr. Rudy Fernandez

Pacific Estuarine Research Lab

Ms. Joy Zedler

State Historic Preservation Officer, Department of Parks and Recreation

State Resources Agency

Ms. Cherlyn Widell

State Lands Commission, Division of Environmental Planning Management

Mr. Dwight E. Sanders

COUNTY

County of San Diego, Department of Planning and Land Use

Mr. Mark Carroll

San Diego Air Pollution Control District

Mr. Tom Weeks

County of San Diego, Department of Parks and Recreation

Ms. Susan Hector

County of San Diego

Mr. Michael Devine

Chief, Environmental Health Services

County of San Diego, Chief Administrator Officer

Mr. Lawrence Prior

San Diego County Board of Supervisors, Chair

Tia Juana Valley County Water District

Mr. Art Letter, General Manager

District Council, R.J. Klitgadd

San Diego Association of Governments

Mr. Kenneth Sulzer, Executive Director

Imperial Irrigation District

Mr. Michael Remington

CITY

City of Coronado, City Manager

City of Chula Vista, City Manager

City of Imperial Beach, City Manager

City of National City, City Manager

City of San Diego

Mayor Susan Golding

City Manager

Mr. Larry Monserrate, Principal Planner, Development Services Department

Mr. Geoffrey Bogart, Binational Affairs

Mr. Dave Schlesinger, Metropolitan Wastewater Department

Mr. Leonard Wilson, Water Utilities Dept.

San Diego Unified Port District

Mr. Ralph Hicks, Environmental Management Coordinator

PRIVATE INTEREST GROUPS

Aqualogic, Mr. Allyn Feinberg

Audubon Society, San Diego Chapter, Mr. Jim Peugh

Bay Users Group of San Diego

Border Community Town Council

California‑American Water Company

California Native Plant Society, San Diego Chapter

California United Mexican Americans, Mr. Alberto R. Garcia

Centers for Disease Control, Special Programs Group

Citizens Against Recreational Eviction, Ms. Carolyn Powers

Citizens Coordinate for Century 3

Citizens Revolting Against Pollution, Ms. Rosemary Nolan, Chairperson

David Gomez

Environmental Health Coalition

Glorietta Bay Users/Concerned Public

Greenpeace, Mr. Jim Lawrence

Otay Mesa/Nestor Community Planning Group, Ms. Ruth J. Schneider

Otay Mesa Recreation Council, Mr. Val Guerra

Otay Water District, Mr. Keith Lewinger, General Manager

Pacific Institute, Mr. Santos Gomez

Parsons Engineering Science, Mr. Luciano Meiorin

San Diego Bay Coalition

San Diego Council of Divers, Inc., Mr. Lee Olson, President

San Ysidro Community Planning Group, Ms. Mirna Perez

San Ysidro Chamber of Commerce

Sierra Club, San Diego Chapter

Sierra Club Legal Defense Fund, Mr. Larry Silver

Southwest Wetlands Interpretative Association, Mr. Larry Kadlecik

Surfrider Foundation, San Diego Chapter

INTERESTED INDIVIDUALS

CalMat Company, William Walker

Nelson and Sloan Contractor, Mr. Ken Monson

Swanson Oswald Associates, Mr. Edwin W. Lee

Mr. William E. Claycomb

Mr. Alejandro Flores

Mr. Wendell Gayman

Mr. Monty Griffin

Ms. Rachel Hanlon

Mr. Ken Jackman

Mr. Robert Simmons

PUBLIC LIBRARIES

Central Library, Reference Section

Chula Vista Library, Reference Section

Coronado Library, Reference Section

Imperial Beach Library, Reference Section

National City Library, Reference Section

Otay Mesa Branch Library, Reference Section

San Ysidro Library, Reference Section

Chapter Eight

List of Preparers and Their Qualifications

International Boundary and Water Commission, U.S. Section

Lead Agency responsible for SEIS; IWTP project management and
coordination. Key personnel include:

Charles Fisher, Environmental Specialist

C. W. Bill Ruth, Chief, Office of Construction Activities

Steve Tencza, Environmental Engineer

Responsibilities: Technical review of SEIS; public and

agency coordination.

International Boundary and Water Commission, Mexico Section

The United States Section has coordinated the technical preparation of
the SEIS with the following representatives of the Mexican Section,
IBWC.

Roberto Espinoza, Resident Engineer, Tijuana

Luis Antonio Rascon Mendoza, Principal Engineer

J. Arturo Herrera Solis, Commissioner

State Water Resources Control Board

State cooperating and funding agency.

Bart Christensen, California/Mexico Border Coordinator

Responsibilities: Technical review of SEIS.

U.S. Environmental Protection Agency, Region IX

Lead Agency responsible for SEIS; management and coordination for EPA.
Key personnel include:

Elizabeth Borowiec, AICP, Environmental Planner

Doug Eberhardt, Border Water Coordinator

Terrence Fleming, Life Scientist

Sheldon Gen, Presidential Management Intern

Ben Machol, Project Engineer

Bob Moyer, Legal Counsel

Norwood Scott, San Diego Project Office

Nancy Woo, Project Manager

Responsibilities: Technical review of SEIS; development

of flow estimates; public and agency coordination.

U.S. Army Corps of Engineers

Provided assistance to EPA in their lead agency responsibilities. Key
personnel include:

Jennifer Altergott, Ecologist, Project Manager

Hayley Lovan, Ecologist

Responsibilities: Technical review of SEIS; public and

agency coordination.

Regional Environmental Consultants (RECON)

Responsible for preparation of the SEIS. Key personnel include:

Scott Fulmer, Senior Project Manager

Qualifications: Twenty years\' experience preparing and

processing environmental documents. B.A. Anthropology. Certified by the
Society of Professional Archeologists.

Responsibilities: SEIS preparation and quality assurance.

David Gottfredson, Environmental Analyst

Qualifications: Two years\' experience in noise and environmental
analysis. B.S. Chemical Engineering.

Responsibilities: SEIS preparation.

Gerry Scheid, Ecologist

Qualifications: Seventeen years\' experience conducting

biological surveys. Twelve years\' experience assessing project‑related
impacts to biological resources and preparing mitigation
recommendations. M.S. Ecology, B.S. Biology.

Responsibilities: SEIS preparation.

Additional RECON staff who assisted in production of the SEIS include:

Loretta Gross, Production Supervisor, document design and editing

Stacey Higgins, Production Specialist, document editing

Harry J. Price, Senior Technical Illustrator

Mike Scott, Technical Illustrator

Boyle Engineering Corporation

Rick Bottcher, Senior Civil Engineer

Jeff Garvey, Principal Engineer

Responsibilities: Technical evaluation of alternatives;

review of SEIS.

CIC Research

Mark Crooks

Qualifications: Twelve years\' experience preparing socioeconomic impact
analyses. B.A. Market Research.

Responsibilities: Socioeconomic impacts assessment.

MBC Environmental

Carol Paquette, Senior Scientist

Qualifications: 18 years\' experience in marine research

and impact assessment. B.A. Biology.

Chuck Mitchell, President

Qualifications: 26 years in marine research and impacts

assessment. B.A. Zoology.

Responsibilities: Marine biological impacts assessment.

Parsons Engineering Science Inc.

Gilbert Bogle

Qualifications: 3 years as postdoctoral fellow at CALTECH specializing
in water modeling. B.Sc. Mathematics and Physics, Ph.D. Engineering.

David Connaly, M.A. Oceanography

Terry Hendricks. Ph.D. Physics

Luciano Meiorin, Ph.D. Engineering

Responsibilities: Ocean discharge modeling studies.

Tierra Environmental Services

Chris Nordby, Principal Biologist

Qualifications: Over 17 years\' experience specializing

in wetlands ecology. M.S. Biology.

Responsibilities: Tijuana estuary biology technical report.

Chapter Nine

References Cited

Ainley, D. G., and D. R. Bontrager

1981 Beached Bird Census, 1977‑1978, with Comparison to Previous Years.
In Summary of Marine Mammal and Seabird Surveys of the Southern
California Bight Area, 1975‑1978. University of California, Santa Cruz.
Prepared for Bureau of Land Management, U.S. Department of the Interior.

American Society of Coastal Engineers

1995 Proceedings of the 4th International Conference on Estuarine and
Coastal Modeling. October.

Bender, K. E., C. T. Collins, and S. L. Warter

1974 Marine and Shore Birds. In Biological Environment.

A Summary of Knowledge of the Southern California Coastal Zone and
Offshore Areas, vol. 2, edited by M. D. Daily, B. Hill, and H. Lansing.
Prepared by Southern California Ocean Studies Consortium of California
State Universities and Colleges. Prepared for Bureau of Land Management,
U.S. Department of the Interior.

Bernard, H. J., J. W. Gilpatrick, Jr., L. J. Hansen, and J. R. Henderson

1988 Cetacean Strandings along the San Diego, California, Coast from
1966 through 1986. Draft report, February. National Marine Fisheries
Service, Southwest Fisheries Center, La Jolla.

Boland, J. M.

1981 Seasonal Abundances, Habitat Utilization, Feeding Strategies and
Interspecific Competition within a Wintering Shorebird Community and
Their Possible Relationships with the Latitudinal Distribution of
Shorebird Species. M.S. thesis, San Diego State University, San Diego.

Bonnel, M. L.

1985 Sea Birds. In Cities Service Project (P‑0409), Northern Santa Maria
Basin, Marine Biology Technical Appendix. URS Corporation, Santa
Barbara.

Bonnel, M. L., M. O. Pierson, T. P. Dohl, R. C. Guess, K. T. Briggs, E.
W. Chu,

D. B. Lewis, and G. L. Hunt, Jr.

1981 Synthesis of Findings. In Summary of Marine Mammals and Seabird
Surveys of the Southern California Bight Area, vol. 2. NTIS PB
1‑177‑164. Springfield, Virginia.

Boyle Engineering Corporation

1988 EPA Standby Interceptor Project Phase 1B Concept Design Report for
Parts A, B, D, and E. Prepared for USACE, EPA, IBWC, SWRCB, and City of
San Diego. Contract Number DACW‑09‑87‑C‑0035. August.

1990 International Wastewater Treatment Plant, San Diego County,
California. Preliminary Report. Prepared for IBWC, EPA, USACE, SWRCB,
and City of San Diego. Contract Number DACW‑09‑87‑C‑0035. November.

1996 Tijuana River Hydraulics Report for the United States Army Corps of
Engineers and Environmental Protection Agency.

Briggs, K. T., E. W. Cuy, D. B. Lewis, W. Breck Tyler, R. I. Pitman, and
L. Hunt, Jr.

1981 Summary of Marine Mammal and Seabird Surveys of the Southern
California Bight Area, 1975‑1978. Vol. 3, Final Report. In part 3,
Investigator\'s Reports, of Book 1, Seabirds: Distribution, Numbers, and
Seasonal Status of Seabirds of the Southern California Bight. NMS No.
PB81‑248197.

Cabelli, V. J., M. A. Levin, and A. P. Dufour

1983 Public Health Consequences of Coastal and Estuarine Pollution:
Infectious Diseases. In Ocean Disposal of Municipal Wastewater: Impacts
on the Marine Environment, vol. 2, edited by E. P. Meyers. NOAA Sea
Grant Program.

California, State of

1952 Progress Report on Tijuana Basin as of April 1, 1952. Division of
Water Resources memorandum, Department of Public Works.

1967 Department of Water Resources Bulletin 106‑2 regarding Tijuana
River valley groundwater.

1975a California Coastal Plan. January.

1975b Sea Water Intrusion in California: Inventory of Coastal Ground
Water Basins. Bulletin 63‑5. Department of Water

Resources.

1977 Assessment and Atlas of Shoreline Erosion along the California
Coast. California Department of Navigation and Ocean Development, The
Resources Agency. July.

1981a Southern California Marine Sport Fishing from Privately Owned
Boats: Catch and Effort for April‑June 1981. Department of Fish and
Game.

1981b Southern California Marine Sport Fishing from Privately Owned
Boats: Catch and Effort for July‑September 1981. Department of Fish and
Game.

1988 California State Mussel Watch: Ten Year Data Summary, 1977‑1987.
Water Quality Monitoring Report No. 87‑3. State Water Resources Control
Board.

1989 Guidelines for Air Quality Impact Assessments for General
Development and Transportation‑Related Projects. Page 8.

June.

1990a Water Quality Control Plan: Ocean Waters of California. State
Water Resources Control Board. March.

1990b Annual Summary of 1989 Air Quality Data, Gaseous and Particulate
Pollutants, California (Vol. XXI). Air Resources Board.

1991 Annual Summary of 1990 Air Quality Data, Gaseous and Particulate
Pollutants, California (Vol. XXII). Air Resources Board.

1992 Annual Summary of 1991 Air Quality Data, Gaseous and Particulate
Pollutants, California (Vol. XXIII). Air Resources Board.

1993 Annual Summary of 1992 Air Quality Data, Gaseous and Particulate
Pollutants, California (Vol. XXIV). Air Resources Board.

1994a State Mussel Watch Program, 1987‑1993. Data Report 94‑1WQ. State
Water Resources Control Board.

1994b Annual Summary of 1993 Air Quality Data, Gaseous and Particulate
Pollutants, California (Vol. XXV). Air Resources Board.

1995 Water Quality Control Plan for the San Diego Basin (9). State Water
Resources Control Board, Regional Water Quality Control Board, San Diego
Region. April 26.

Chambers Group

1990 Final Review and Analysis of Drought Tolerance of Riparian and
Estuarine Species. Prepared for the Department of the Army, Corps of
Engineers, Los Angeles District.

1991 Review and Analysis of Drought Tolerance of Riparian and Estuarine
Species. Prepared for the U.S. Army Corps of Engineers. January.

Choat, J. H.

1982 Fish Feeding and the Structure of Benthic Communities in Temperate
Waters. Ann. Rev. Ecol. Syst. 13:423‑449.

Chow, T. J., and J. E. Earl

1977 Trace Metals in Sediments. In Southern California Baseline Study.
Bureau of Land Management.

CIC Research, Inc.

1996 Interim Discharge Supplemental Environmental Impact Statement,
Socioeconomic Analysis. June 21.

Clark, M. B.

1969 Distribution and Seasonal Dynamics of Animal Population in San
Diego Beaches. Thesis, San Diego State College.

County Sanitation Districts of Orange County

1986 Marine Monitoring. In 1986 Annual Report, vol. 3.

Dean, T. A., S. Schroeter, and J. Dixon

1984 Effects of Grazing by Two Species of Sea Urchins
(Strongylocentrotus franciscanus and Lytechinus anamesus) on Recruitment

and Survival of Two Species of Kelp (Macrocystis pyrifera

and Pterygophora californica). Marine Biology 78:301‑313.

Dexter, F.

1977 Biological Baseline Studies of the Imperial Beach Erosion Control
Project Area. Contract No. DAC09‑76‑M‑1423. U.S. Army Corps of
Engineers, Los Angeles District.

Dohl, T. P., K. S. Norris, R. C. Guess, J. D. Bryant, and M. W. Honig

1981 Summary of Marine Mammal and Seabird Surveys of the Southern
California Bight Area, 1975‑1978. Vol. 3, Final Report. In part 2,
Investigator\'s Reports, Cetacea of the Southern California Bight.
Prepared for U.S. Bureau of Land Management, Contract AA550‑CT7‑36.

Dudek and Associates

1994a Groundwater Management Plan for the Tijuana River Basin Phase II.
Report prepared for the Tia Juana Valley County Water District. April.

1994b Groundwater Management Plan for the Tijuana River Basin Phase III.
Report prepared for the Tia Juana Valley County Water District. October.

1995 Groundwater Management Plan for the Tijuana River Basin Phase IV.
Report prepared for the Tia Juana Valley County Water District.
February.

Engineering Science, Inc.

1988 Tijuana Oceanographic and Engineering Study. Engineering Studies
Report, vols. 1 and 2.

1990 South Bay Land Outfall Preliminary Planning Study. Tijuana
Oceanographic Engineering Study ‑ Phase IV. Prepared for the City of San
Diego. May.

1991 South Bay Ocean Outfall, Basis of Design Report. Tijuana
Oceanographic Engineering Study ‑ Phase IV. January.

1992a South Bay Land Outfall Extension and Ocean Outfall Conceptual
Design Report. April.

1992b South Bay Land Outfall Extension and Ocean Outfall Supplemental
Ocean Outfall Planning Study: Initial Dilution and Outfall Length
Analysis. July.

1993 South Bay Land Outfall Extension and Ocean Outfall Revised
Conceptual Design Report. July.

Entrix, Inc., Pacific Estuarine Research Laboratory, and PWA Ltd.

1991 Tijuana Estuary Tidal Restoration Program. Draft Environmental
Impact Report/Environmental Impact Statement. 3 vols. California State
Coastal Conservancy (SCC) and U.S. Fish and Wildlife Service, Lead
Agencies. SCC, Oakland.

Eppley, R. W., W. G. Harrison, S. W. Chisolm, and E. Stewart

1978 Particulate Organic Matter in Surface Waters off Southern
California and Its Relation to Phytoplankton. Journal of Marine Research
35:671‑696.

Fong, P.

1986 Monitoring and Manipulation of Phytoplankton Dynamics in a Southern
California Estuary. M.S. thesis, San Diego

State University, San Diego.

Foster, M., and D. Schiel

1985 The Ecology of Kelp Forests in California: A Community Profile.
U.S. Fish and Wildlife Service Biological Report 85(7.2).

Gerard, V.

1976 Some Aspects of Material Dynamics and Energy Flow in a Kelp Forest
in Monterey Bay. Ph.D. dissertation, University of California, Santa
Cruz.

Gersberg, R., F. Trintade, and C. Nordby

1989 Heavy Metals in Sediments and Fish of the Tijuana Estuary. Border
Health 5(3).

Harrold, C., and D. Reed

1985 Food Availability, Sea Urchin Grazing, and Kelp Forest Community
Structure. Ecology 66:1160‑1169.

Hendricks, T. J.

1988 Modeling of Flow Fields and Effluent Trajectories in the San Diego
Bight. In Tijuana Oceanographic Engineering Study, prepared by
Engineering Science.

Inman, D., R. Tait, P. Komar, and C. Nordstrom

1968 Dispersion of Water and Sediment in the Surf Zone. University of
California, Scripps Institution of Oceanography. SIO Reference 68‑4.

International Boundary and Water Commission

1976 Final Environmental Statement for the Tijuana River Flood Control
Project, San Diego County, California. United States Section. May.

1984 Environmental Memorandum. Tijuana Sewage ‑ Emergency Regulating
Pond. United States Section. October 25.

1985 Minute No. 270. Recommendations for the First Stage Treatment and
Disposal Facilities for the Solution of the Border Sanitation Problem at
San Diego, California‑Tijuana, Baja California. April 30.

1987 Position Paper. Tijuana/San Diego Sanitation Problem. October.

1990 Minute No. 283. Conceptual Plan for the International Solution to
the Border Sanitation Problem in San Diego, California‑Tijuana, Baja
California. Signed by both governments, July 2.

Izbicki, John A.

1985 Evaluation of the Mission, Santee, and Tijuana Hydrologic Subareas
for Reclaimed Water Use, San Diego County. U.S. Geological Survey Water
Resources Investigation Report 85‑4032.

James Dobbin Associates Incorporated

1986 Tijuana River National Estuarine Sanctuary Management Plan.
Prepared for State of California, Coastal Commission; U.S. Department of
Commerce, National Oceanic and Atmospheric Administration Sanctuary
Programs Division; and Tijuana River National Estuarine Sanctuary
Management Authority. February.

Jaques, D. L., and D. W. Anderson

1987 Conservation Implications of Habitat Use and Behavior of Wintering
Brown Pelicans (Pelicanus occidentalis californicus). Public Service
Research and Dissemination Program, University of California, Davis.

Jirka, G. H.

1990 Tijuana Beach Discharge Evaluation, Final Report. Prepared for the
U.S. Environmental Protection Agency, Region IX. March.

Jones, G. F.

1969 The Benthic Macrofauna of the Mainland Shelf of Southern
California. Allan Hancock Mon. in Mar. Biol. No. 4.

Jurek, R. M.

1996 Personal communication, July 24. California Department of Fish and
Game, Sacramento.

Kalichman, S. G., and J. B. Conway

1989 San Elijo Ocean Outfall Improvement Project: Public Health Issues.
City of Escondido and San Elijo Lagoon Joint Powers Authority.

Kaupp, S. E.

1986 Commercial Fishing. Report of a Symposium by the

San Diego Oceans Foundation. Scripps Institution of Oceanography.

Kinnetic Laboratories, Inc.

1990 Deep Water Ocean Outfall ROV Reconnaissance Survey, South Bay and
San Diego River Sites. Report prepared for City of San Diego Clean Water
Program.

1991 Marine Environmental Impacts of the Proposed Secondary Treatment
System. Appendix M to Secondary Treatment System and Associated Sludge
Management Facilities. Prepared for the City of San Diego.

Kinney, M.

1990a Personal communication. Biologist, Ecological Services, U.S. Fish
and Wildlife Service, Laguna Niguel, CA.

1990b Tabulation of Federal Lists and Proposed Endangered, Threatened,
and Candidate Species in Tijuana River Valley and Estuary. Biologist,
Ecological Services, U.S. Fish and Wildlife Service, Laguna Niguel, CA.
May.

Kus, B.

1990 Status of the Belding\'s Savannah Sparrow at the Tijuana Estuary,
1990. Prepared for the Department of the Army, Los Angeles District,
Corps of Engineers, Los Angeles.

1992 Status of the Belding\'s Savannah Sparrow at Border Field State
Park. Prepared for the Department of the Army, Los Angeles District,
Corps of Engineers, Los Angeles.

Larson, R. J., and E. E. De Martini

1984 Abundance and Vertical Distribution of Fishes in a Cobble‑Bottom
Kelp Forest Off San Onofre, California. Fish Bulletin 82:37‑53.
California Department of Fish and Game.

Littler, M. M., and S. N. Murray

1975 Impact of Sewage on the Distribution, Abundance, and Community
Structure of Rocky Intertidal Macro‑organisms. Marine Biology
30:277‑291.

Malcolm Pirnie Engineers

1993 Draft Conceptual Design Report, South Bay International Treatment
Plant. November.

Malme, C. I., P. R. Miles, C. W. Clark, P. Tyack, and J. E. Bird

1984 Investigations of the Potential Effects of Underwater Noise from
Petroleum Industry Activities on Migrating Gray Whale Behavior. Phase
II: January 1984 Migration. Report No. 5586. Prepared for Minerals
Management Service, U.S. Department of the Interior, Anchorage, AK.

Massey, B. W.

1989 California Least Tern Field Study, 1989 Breeding Season. Prepared
for the California Department of Fish and Game.

MBC Applied Environmental Sciences

1990 IBWC International Wastewater Treatment Plant Data Report. Prepared
for Engineering‑Science, Inc. March.

1995 San Diego County Region Nine Kelp Survey Consortium, 14 November.

McMicheaux, Dion

1991 Personal communication, April 17. International Boundary and Water
Commission, United States Section.

McPeak, R. H.

1991 Personal communication.

Mearns, A. J., and M. J. Sherwood

1977 Distributions of Neoplasms and Other Diseases in Marine Fishes
Relative to the Discharge of Wastewater. In Aquatic Pollutants and
Biological Effects with Emphasis on Neolasia, edited by H. F. Kraybill,
D. J. Dawe, J. C. Harshbarger, and R. G. Tariff. Annals of New York
Academic Sciences, vol. 298.

Mearns, A. J., and D. R. Young

1983 Characteristics and Effects of Municipal Wastewater Discharges to
the Southern California Bight: A Case Study. In Ocean Disposal of
Municipal Wastewater: Impacts on the Environment, vol 2, edited by E. P.
Meyers. MIT Sea Grant College Program, MITSA‑83‑33, Cambridge, MA.

Melbourn, John

1991 Personal communication, January 24. County of San Diego.

MEC Analytic Systems

1992 Encina Receiving Water Monitoring Summary Report: July 1985‑June
1991. Prepared for Encina Water Pollution Control Facility, Carlsbad,
CA.

Mearns, A. J., D. A. Hanan, and L. Harris

1977 Recovery of Kelp Forest off Palos Verdes. In Coastal Water Research
Project Annual Report 1977. U.S. Department of Commerce, NTIS No.
PB274463/AS.

McPeak, R. H., and D. Glanz

1984 Harvesting California\'s Kelp Forests. Oceanus 27(1):19‑26.

Michael Brandman Associates (MBA)

1990 Estuarine Impacts. Appendix P to Secondary Treatment System and
Associated Sludge Management Facilities EIR/EIS. Prepared for the City
of San Diego.

Murray, S. N., and M. M. Littler

1978 Patterns of Algal Succession in a Perturbated Marine Intertidal
Community. J. Phycol. 14:506‑512/

National Coalition for Marine Conservation

1985 Economic Assessment of Marine Recreational Fishing in Southern
California. Prepared for National Marine Fisheries Service.

National Marine Fisheries Service

1991 Southern California Sportfishing Economic Survey.

National Oceanic and Atmospheric Administration

1989 A Summary of Data on Tissue Contamination from the First Three
Years (1986‑1988) of the Mussel Watch Project: Progress Report. NOAA
Tech. Mem. NOS OMA 49. Rockville, MD.

Newman, J.

1990 Personal communication. Ecologist, Regional Environmental
Consultants (RECON), San Diego.

Nordby, C. S.

1990 Biological Monitoring of San Elijo Lagoon. Final Report to the San
Diego County Department of Parks and Recreation.

Nordby, C. S., and J. B. Zedler

1991 Responses of Fish and Macrobenthic Assemblages to Hydrologic
Disturbances in Tijuana Estuary and Los Pe&ntilde;asquitos Lagoon,
California. Estuaries 14: 180193.

Norris, K. S., G. L. Hunt, E. J. LeBoeuf, M. Bonnel, K. Briggs, D.
Dettman, T. Dohl, J. Hail, L. Hobbs, L. Jones, D. Lewis, N. Quarmen, and
B. Tuyler

1975 The Distribution, Abundance, Movement and Reproduction of Birds,
Crustaceans and Pinnipeds in the Southern California Bight: A Six Month
Monitoring Report to the BLM‑OCS Program. Contract No. 08550‑CT5‑25.
University of California, Santa Cruz and Irvine.

North W. J. (editor)

1971 The Biology of Giant Kelp Beds (Macrocystis) in California. Nova
Hedwigia 32:1‑600.

1973 Kelp Habitat Improvement Project Annual Report, 1 July 1972 to 30
June 1973.

North, W. J., and M. B. Schaefer

1964 An Investigation of the Effects of Discharged Waste on Kelp.
California Water Quality Control Board Publication

26\.

O\'Connor, T. P., and B. Beliaeff

1995 Recent Trends in Coastal Environmental Quality: Results from the
Mussel Watch Program. National Status and Trends Program. Marine
Environmental Quality. U.S. Department of Commerce, National Oceanic and
Atmospheric Administration, National Ocean Service, Office of Ocean
Resources Conservation and Assessment, Coastal Monitoring and Bioeffects
Assessment Division, Silver Springs, MD.

Odor Science &amp; Engineering

1990 Secondary Wastewater Treatment Facility Odor Impact Study. Appendix
E to Secondary Treatment System and Associated Sludge Management
Facilities EIR/EIS. Prepared for the City of San Diego.

O\'Shea, T. H., R. L. Brownell, D. R. Clark, W. A. Walker, M. L. Gay,
and T. G. Lamont

1980 Organochlorine Pollutants in Small Cetaceans from the Pacific and
South Atlantic Oceans, November 1968‑June 1976. Pesticides Monitoring
Journal 14:35‑46.

Page, G. W., and L. E. Stenzel

1981 The Breeding Status of the Snowy Plover in California. Western
Birds 12(1):140.

Page, G. W., F. C. Bidstrup, R. J. Ramer, and L. E. Stenzel

1986 Distribution of Wintering Snowy Plovers in California and Adjacent
States. Western Birds 17(4):145‑170.

Page, G. W., L. E. Stenzel, W. D. Shuford, and C. R. Bruce

1991 Distribution and Abundance of the Snowy Plover on Its Western North
American Breeding Grounds. J. Field Ornithology 62(2):245‑255.

Parr, T. D., D. Diener, and S. Lacy

1978 Effects of Beach Replenishment on the Nearshore Sand Fauna at
Imperial Beach, California. Mis. Report No. 78‑4. USACE Coastal
Engineering Research Center, VI.

Parsons Engineering Science, Inc.

1996 Wastewater Discharge Modeling and Analysis of Alternative Interim
Disposal Options for the Supplemental Environmental Impact Statement for
the International Boundary and Water Commission International Wastewater
Treatment Plant Interim Operation. Prepared for Boyle Engineering
Corporation. July 18.

Philip Williams &amp; Associates

1987 Tijuana Estuary Enhancement Hydrologic Analysis.

Powell, A.

1996 Personal communication, July 26. National Biological Service, San
Diego State University.

Pryde, Philip R.

1976 San Diego: An Introduction to the Region. Kendall/Hunt, Dubuque.

RECON

1993 Biological Assessment for the International Wastewater Treatment
Plant. Prepared for the Environmental Protection Agency, Region IX.
December 7.

1994 Final Environmental Impact Statement, International Boundary and
Water Commission International Wastewater Treatment Plant and Outfall
Facilities. Prepared for USIBWC and EPA. February.

Rempel, Rick

1992 Hydrogeological Assessment of the Tijuana River Valley. California
State Water Resources Control Board. February 26.

Rudnicki, R.

1986 Dynamics of Macroalgae in Tijuana Estuary: Response to Simulated
Wastewater Addition. M.S. thesis, San Diego State University, San Diego.

San Diego Association of Governments (SANDAG)

1992 INFO Baja California Demographic Profile. May‑June 1992.

1994 1994 Regional Transportation Plan. February.

San Diego, City of

1977 Tijuana River Valley Plan and Local Coastal Program Addendum.
March.

1993 South Metro Interceptor Facilities Design Preliminary Report.
Metropolitan Wastewater Department. May.

1995 Point Loma 301(h) Waiver Application for Modification of Secondary
Treatment Requirements. April.

San Diego, County of

1972 Natural Resource Inventory of San Diego County: Section 5A, Coastal
Zone Ornithology. Environmental Development Agency Integrated Regional
Environmental Management Project.

1992 1991/1992 Regional Air Quality Strategies. Air Pollution Control
District. June.

Schafer, H. A., R. W. Gossett, C. F. Ward, and A.M. Westcott

1984 Chlorinated Hydrocarbons in Marine Mammals. In SCCWRP Biennial
Report 1983‑1984, edited by W. Bascom. Southern California Coastal Water
Research Project, Long Beach, CA.

Schulberg, S., I. Shaw, and D. Van Schoik

1989 Results of the 1987‑1988 Gray Whale Migration and LCAC Interaction
Study Program. Prepared by Southwest Research Associates for Western
Division, Naval Facilities Engineering Command, San Bruno, CA. U.S. Navy
Contract No. N62474‑87‑C‑8669.

Seamans, P.

1988 Wastewater Creates a Border Problem. Journal WPCF

60(10):1799‑1804.

Smith, G.

1974 Some Effects of Sewage Discharge to the Marine Environment. Ph.D.
dissertation. University of California, San Diego.

South Coast Air Quality Management District (SCAQMD)

1993 CEQA Air Quality Handbook. April.

Southern California Association of Governments

1988 The State of the Santa Monica Bay. Santa Monica Bay Project. 3
vols.

Southern California Coastal Water Research Project

n.d. Unpublished data.

1973 The Ecology of the Southern California Bight: Implications for
Water Quality Management. Three‑year report.

Sowls, A. L., A. R. DeGange, J. W. Nelson, and G. S. Lester

1980 Catalog of California Seabird Colonies. U.S. Fish

and Wildlife Service FWS/OBS‑80‑37.

Squire, J. L., Jr., and S. E. Smith

1977 Angler\'s Guide to the United States Pacific Coast. U.S. Department
of Commerce, NOAA, NMFS, Seattle, WA.

Straughn, D.

1982 Inventory of the Natural Resources of Sandy Beaches in Southern
California. Allan Hancock Foundation Technical Report No. 6.

Tia Juana Valley County Water District

1994a Groundwater Management Plan for the Tijuana River Basin, Phase II.
Prepared by Dudek &amp; Associates, Inc. April.

1994b Groundwater Management Plan for the Tijuana River Basin, Phase
III. Prepared by Dudek &amp; Associates, Inc. October.

Tegner, M. J.

1996 Personal communication, July 22. Scripps Institution of
Oceanography.

Tegner, M. J., and P. V. Dayton

1987 El Ni&ntilde;o Effects on Southern California Kelp Forest
Communities. Advanced Ecological Research 17:243‑279.

Tegner, M. J., P. K. Dayton, P. B. Edwards, K. L. Riser, D. B. Chadwick,
T. A. Dean, and L. Deysher

1995 Effects of a Large Sewage Spill on a Kelp Forest Community:
Catastrophe or Disturbance? Marine Environmental Research

40(2):181‑224.

Tierra Environmental Services

1996 Biological Impacts of Interim Discharge of Primary Treated Effluent
from the International Wastewater Treatment Plant to the Tijuana
Estuary. July 3.

Unitt, P. A.

1984 Birds of San Diego County. Memoir No. 13. San Diego Society of
Natural History.

U.S. Army Corps of Engineers (USACE)

1965 Proposed International Flood Control Project, United States and
Mexico, Tijuana River Basin in California and Baja California. July.

1990 Endangered Species Act Biological Assessment. South Bay Land
Outfall Project: Phase I Tijuana River Valley, South Bay, San Diego.

1995 Supplemental Environmental Assessment and Finding of No Significant
Impact, South Bay Ocean Outfall Modifications. Prepared for the U.S.
Environmental Protection Agency and International Boundary and Water
Commission by the U.S. Army Corps of Engineers. August.

1996 Environmental Assessment for International Wastewater Treatment
Plant Project, Goat Canyon Pumping Plant and Dechlorination Facility.
Prepared for International Boundary and Water Commission, United States
Section. June.

U.S. Army Corps of Engineers, U.S. Environmental Protection Agency,
International Boundary and Water Commission, California Water Resources
Control Board, and City of San Diego

1990 Data obtained by Boyle Engineering Corporation for the EPA Standby
Interceptor Project Alternatives Study‑Bi‑national Wastewater Treatment
Project. Contract No. DACW‑09‑87‑C‑0035. February.

U.S. Department of Agriculture (USDA)

1973 Soil Survey, San Diego Area, California. Soil Conservation Service
and Forest Service. December.

U.S. Department of Commerce

1992 Monthly Station Normals of Temperature, Precipitation, and Heating
and Cooling Days, 1961‑1990, California. Climatography of the United
States No. 81. National Climatic Data Center, National Oceanic and
Atmospheric Administration. January.

U.S. Environmental Protection Agency (EPA)

1985 Preliminary Assessment of Environmental Effects of Sewage on San
Diego Beaches. Prepared by Earth Metrics for EPA Region 9.

1988 Environmental Assessment and Finding of No Significant Impact:
South Bay Land OutfallPhase I (Big Pipe). Project No. C‑06‑1092‑21.
August.

1994 Biological Assessment for the International Wastewater Treatment
Plant. In Final Environmental Impact Statement for the International
Boundary and Water Commission International Wastewater Treatment Plant
and Ocean Oufall Facilities. February 1994.

1995 Memorandum Regarding Treatment/Conveyance Abilities of the Interim
Operation SEIS Alternatives.

U.S. Fish and Wildlife Service (USFWS)

1985 Salt Marsh Birds‑Beak Recovery Plan.

Warnock, N., S. Griffin, and L. E. Stenzel

1989 Results of the 22‑23 April 1989 Shorebird Census in Coastal
Wetlands of San Diego County and Northern Baja California. Point Reyes
Bird Observatory Report.

West Consultants Inc.

1994 Flood Control Study for the Tijuana River Valley. Prepared for Tia
Juana Valley County Water District.

Williams, P., and M. Swanson

1987 Tijuana Estuary Enhancement Hydrologic Analysis. Prepared for San
Diego State University Foundation. February.

Word, J. Q.

1978 The Infaunal Trophic Index. Southern California Coastal Water
Research Project Report 1978, pp. 19‑39.

1980 Classification of Benthic Invertebrates into Infaunal Trophic Index
Feeding Groups. Southern California Coastal

Water Research Project Biennial Report 1979‑1980, pp. 103‑122.

Word, J. Q., and A. J. Mearns

1979 60‑Meter Control Survey Off Southern California.

Southern California Coastal Waters Research Project Report TM 119.

Zedler, Joy B.

1982 The Ecology of Southern California Coastal Salt Marshes: A
Community Profile. U.S. Fish Wildl. Serv. Biol. Serv. Program
FWS/OBS‑81/54.

1984 Salt Marsh Restoration: A Guide Book for Southern California.
California Sea Grant College Program, Institute of Marine Resources,
University of California, A‑032, La Jolla, California. Sea Grant Report
No. T‑CSGCP‑009, pp. 39‑41.

Zedler, Joy B., C. Nordby, and T. Griswold

1990 Linkages: Among Estuarine Habitats and with the Watershed. National
Oceanic and Atmospheric Administration Technical Memorandum. June.

Zedler, J. B., C. S. Nordby, and B. E. Kus

1992 The Ecology of Tijuana Estuary, California: A National Estuarine
Research Reserve. NOAA Office of Coastal Resource Management,
Sanctuaries and Reserves Division, Washington, D.C.

Zedler, J. B., J. Callaway, B. Nyden, D. Stow, R. Gersberg, P. Goodwin,
and R. Kammen

1995 Restoring Coastal Wetlands. Annual Report for Year

Ending June 30, 1995. U.S. National Biological Service, Pacific
Estuarine Research Laboratory and San Diego State University Foundation.

Zedler, Joy B., and C. Nordby

1986 The Ecology of Tijuana Estuary, California: An Estuarine Profile.
U.S. Fish and Wildlife Service Biological Report 85(7.5).

Zembal, R.

1989 Light‑footed Clapper Rail Census and Study, 1989. Prepared for the
California Department of Fish and Game.

1991 Light‑footed Clapper Rail Census and Study, 1991. Preliminary
report to the California Department of Fish and Game.

Zimmerman, R. C., and J. N. Kremer

1984 Episodic Nutrient Supply to a Kelp Forest Ecosystem in Southern
California. J. Mar. Res. 42:591‑604.