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Long Term Treatment Options Supplemental EIS Fact Sheet
Long Term Treatment Options
Supplemental EIS
Fact Sheet
November 1997
Introduction
The U.S. Environmental Protection Agency (EPA) and the U.S. International Boundary and Water Commission (IBWC) are currently preparing a Supplemental Environmental Impact Statement (SEIS) to evaluate wastewater treatment alternatives for the South Bay International Wastewater Treatment Plant (IWTP). This fact sheet describes the Long Term Operation SEIS and outlines additional studies to evaluate the impacts of each alternative.
Overview
The wastewater treatment system for the City of Tijuana, Mexico, has not kept pace with the city's growing population. Tijuana's inadequate infrastructure has resulted in raw sewage flows to the Tijuana River and the Pacific Ocean. Although Mexico is working to improve this situation, the overflows persist. Consequently, the EPA, the IBWC, the City of San Diego, the State Water Resources Control Board, and the Mexican government have jointly participated in the South Bay IWTP and the South Bay Ocean Outfall. IWTP's advanced primary wastewater treatment facilities were completed in the Spring of 1997. The ocean outfall will discharge the plant's treated wastewater 3.5 miles offshore at a depth of 93 feet. The outfall's scheduled completion is the fall of 1998.
Alternatives in the SEIS
The treatment of wastewater replicates the natural process of decomposition through the use of physical and biological processes. Typically, municipal wastewater treatment involves two levels of treatment: primary and secondary. It also includes the disposal of the treated wastewater and sludge by-products. The objective of primary treatment is the removal of large solids from wastewater. Secondary treatment is the removal of the remaining pollutants using a biological process. This SEIS will evaluate alternatives for secondary treatment for the IWTP, including activated sludge process, treatment ponds, and no treatment beyond the present level of advanced primary. The advanced primary facilities at the IWTP are operating on an interim basis until planning, design and construction for any additional treatment facilities are complete.
Operate the IWTP with Advanced Primary Treatment Facilities
One alternative considered in the SEIS is the continued operation of the IWTP at the advanced primary level. Presently at the IWTP, the wastewater first undergoes grit removal and screening. Advanced primary facilities then use chemicals to facilitate the settling of the remaining solids in the wastewater. Sampling conducted by the IBWC indicates that wastewater discharged from the IWTP may meet California Ocean Plan standards. Therefore, maintaining the IWTP at the advance primary level is considered a viable alternative, provided a waiver to the secondary Clean Water Act requirements is approved.
Build Activated Sludge Treatment Facilities
Another alternative is the construction of activated sludge treatment facilities to follow the advanced primary facilities discussed above. The activated sludge process, a secondary treatment process, uses microorganisms to break down organic matter in the wastewater. This removes additional pollutants from the wastewater. The SEIS considers four options that use activated sludge technology. The major difference among these options is the level of treatment available for the peak flow of sewage.
Construct Pond Treatment Facilities
Another alternative being considered in the SEIS supplements the advanced primary treatment facilities with secondary treatment ponds. Ponds allow further sedimentation and decomposition of wastewater pollutants by natural processes. Algae or mechanical aeration devices can accelerate treatment by the ponds. The evaluation of this alternative includes the analysis of two possible sites for the ponds near the IWTP, the Hofer and the Spooner's Mesa sites.
Supporting Studies
Each alternative in the SEIS will be evaluated using a variety of criteria, including the potential for impacts to the environment and public health, as well as the ability to achieve all water quality and sludge standards.
The following studies will be used in the development of the SEIS in order to provide comprehensive analysis of the alternatives:
Hofer Property Site Assessment
Metals and other contaminants have been identified at the Hofer property, a site considered for two of the alternatives being studied in the SEIS. A site assessment has been prepared to identify remediation activities required if the Hofer site is selected.
Pond Studies
The Pond Study Phase I appraised the feasibility of using ponds for secondary treatment and assessed possible locations for the ponds. The Pond Study Phase 2 evaluated which pond treatment technology is best suited for the Hofer and Spooner's Mesa sites.
Analysis of Ocean Discharge
This analysis will identify the impacts on the marine environment and public health of a discharge through the South Bay Ocean Outfall. This will include the effects of suspended sediments in the ocean and sedimentation on the ocean floor. The analysis will also estimate environmental effects from the discharge and compare these to requirements of the California Ocean Plan and the Clean Water Act.
Ecological Risk Assessment
This study will gauge the potential risks associated with each alternative including the effects of the discharge on migratory marine mammals, kelp-bed communities, and other species and their habitat.
Community Input
A draft of the SEIS will be released in early 1998 and a final version in the Spring of 1998. Your input on the SEIS is encouraged. Monthly public meetings and quarterly evening meetings are being held during this process. If you would like more information about the SEIS or the meetings, please contact:
U.S. Environmental Protection Agency
San Diego Office
David Fege
(619) 235-4769
International Boundary and Water Commission
San Ysidro Field Office
Charles Fischer
(619) 662-7600