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Interim Operation–Supplemental Environmental Impact Statement
FACT SHEET
March 1996
The purpose of this fact sheet is to provide the community with information on the Interim Operation Supplemental Environmental Impact Statement (SEIS). It includes details on the alternatives being evaluated in the SEIS, as well as the analysis that will be completed to identify the impacts associated with each alternative.
Background
To address the long-standing problem of cross-border sewage flows into the Tijuana River Valley, the U.S. Environmental Protection Agency (EPA), the International Boundary and Water Commission (IBWC), the City of San Diego, and the State Water Resources Control Board are cooperating on a project to build the South Bay International Wastewater Treatment Plant (IWTP) and the South Bay Ocean Outfall (ocean outfall). The advanced primary wastewater treatment facilities of the IWTP are now under construction and are scheduled for completion by January 1997. Construction of the ocean outfall is scheduled to begin shortly and is expected to be completed in 1998. Secondary treatment facilities have been designed, but will not be completed until after the outfall is constructed.
Since the advanced primary treatment facilities of the IWTP are scheduled to be completed prior to the secondary treatment facilities and the South Bay Ocean Outfall, the EPA and IBWC are now preparing a SEIS to evaluate alternatives for discharge of treated effluent during this interim period (2-5 years). A second SEIS will be prepared next year to address alternatives to the present activated sludge design for secondary treatment. The draft Interim Operation SEIS is expected to be available for public comment in August/September of 1996.
Alternatives For Interim Operation
Alternative 1: No Action - This alternative describes the current situation. The IWTP would not be operated until the secondary treatment facilities and the ocean outfall are completed. The City of Tijuana would continue to convey and treat sewage to their treatment facility at San Antonio de Los Buenos Treatment Plant, with excess flows being sent to the City of San Diego's Point Loma Treatment Plant via the Emergency Connection. Flows over the capacity of the Emergency Connection (13 million gallons per day or mgd of peak flows) would overflow into the Tijuana River.
Alternative 2: Operate the IWTP - Flows up to 13 mgd sent to the U.S. would be conveyed through the Emergency Connection to the Point Loma Treatment Plant. During peak periods, flows over 13 mgd would be treated and stored at the IWTP and then discharged through the Emergency Connection and/or through an existing pipeline (with a capacity of 1-2 mgd) back to Mexico during off-peak times. We estimate the IWTP could store flows up to 2 mgd. Excess flows that could not be conveyed would be discharged into the Tijuana River.
Alternative 3: Operate the IWTP with Earthen Storage Basin - As in Alternative 2, flows up to 13 mgd conveyed to the U.S. would be sent through the Emergency Connection to the Point Loma Treatment Plant. Flows over 13 mgd would be treated at the IWTP and then discharged through the Emergency Connection and/or through an existing pipeline (with a capacity of 1-2 mgd) back to Mexico during off-peak times. The construction of an earthen basin at the IWTP would provide additional storage for treated wastewater above the 2 mgd accommodated by the IWTP. Any excess flows not conveyed or stored in the earthen basin would be discharged into the Tijuana River.
Alternative 4: Operate the IWTP and Return to Mexico - The IWTP would treat flows up to 25 mgd from Tijuana. Once treated, the effluent would be sent back to Tijuana via a new pump station and new conveyance pipeline for discharge in Mexico, near the San Antonio de Los Buenos Treatment Plant. The new pipeline would run parallel to the existing Mexican conveyance system.
Alternative 5: Operate the IWTP and Discharge through the Ocean Outfall - Upon completion in 1998, the IWTP would be operated to provide advanced primary treatment to flows averaging 25 mgd. Treated effluent would be discharged through the ocean outfall.
Alternative 6: Operate the IWTP with a Phased Discharge Approach - Alternative 2 would be used when flows from Mexico exceeded the capacity of the Emergency Connection. Alternative 3 would be used once flows exceeded the capacity of Alternative 2. Finally, once the ocean outfall is completed, Alternative 5 would be implemented.
Additional Analysis
Each alternative in the SEIS will be evaluated based upon a variety of criteria including the potential impacts to the environment and public health. However, in order to consider all the impacts, further analysis will be required to determine the state of the environment prior to and after discharge. This additional analysis will include:
- A baseline inventory of current conditions at the site including an assessment of the Tijuana River and the Pacific Ocean.
- An analysis of the impacts of short-term discharge of primary treated effluent to the Tijuana River, as identified in Alternatives 1, 2, and 3. The SEIS will use a computer model to project the time required for effluent discharged into the river to reach the ocean. This effort will help determine the best time and rate of discharge into the river, taking into consideration tidal influences.
- Analysis of the impacts of short-term ocean discharge from the ocean outfall (Alternative 5). The SEIS will use a model to evaluate the dilution, dispersion, and migration of advanced primary treated effluent once it is discharged into the ocean through the outfall.
- Analysis of the impacts of short-term ocean discharge of unchlorinated advanced primary treated effluent to the surf zone near the San Antonio de Los Buenos Treatment Plant in Mexico (Alternative 4). The SEIS will analyze the migration of treated effluent discharged into the ocean. In addition, the SEIS will examine the effects of the discharge on the U.S. coastline, since effluent released in Mexico may travel north.
- The study of impacts from the construction of a new disposal pipeline through Mexico (Alternative 4). Although no new studies will be conducted, the SEIS will examine existing data available on land uses and natural and cultural resources along the proposed pipeline alignment in Mexico, in accordance with Mexican laws and regulations.
- An analysis of the potential range of sewage flows from Tijuana that may be conveyed to the IWTP once advanced primary facilities are completed. The analysis will be based on 1994 average sewage flows taking into account Tijuana's projected population growth rate of 4.8%; the highest flow that could be expected is 25 mgd.
For More Information
The U.S. EPA and IBWC are hosting monthly meetings concerning the IWTP. If you would like to attend these meetings or have any questions or concerns regarding the project, please contact:
U.S. Environmental
Protection Agency
Dave Fege
San Diego Border Office
(619) 235-4769
International Boundary and
Water Commission
Linda Allen
San Ysidro Field Office
(619) 662-7600