Yosemite Creek Sediment

Description and History

The Yosemite Creek Sediment site, also known as the Yosemite Slough site (“Site”), is an inlet channel tidally connected to central San Francisco Bay in southeastern San Francisco, California. The Site is located in San Francisco’s Bayview-Hunters Point neighborhood between the Hunters Point Naval Shipyard to the north and the Candlestick Point State Recreational Area to the south. The boundary of the Yosemite Slough site includes contaminated sediments in the 1,600-foot long slough channel and portions of contaminated sediments under deeper bay waters (South Basin) at the mouth of the slough. At low tide, the majority of the sediments in the inlet channel are exposed creating a mudflat.
Yosemite Slough once consisted of natural marine habitat including wetlands, marshlands, and tidal mudflats. Portions of San Francisco Bay such as Yosemite Slough were historically utilized by Native Americans due to the temperate climate and abundant natural resources. Between 1900 and 1970, Yosemite Slough underwent significant narrowing by placement of fill soils and debris in wetlands and along the original edges of the Slough. By the 1950’s, the area surrounding the Slough was characterized by mixed residential, commercial, and industrial use. According to 2010 census data, the population within a 1 mile radius of the Yosemite Slough Site is approximately 30,000.

Due to upland development and installation of storm water and sanitary sewer systems, there is no longer a direct connection between the slough and historic surface water flows from Yosemite Creek. Until 1962, combined sanitary sewer and stormwater flows discharged directly to the slough through three separate outfall pipes. In 1963, the Yosemite Pump Station began operation and all dry weather flows were thereafter transported to the Southeast Wastewater Pollution Control Plant, which is operated by the San Francisco Public Utilities Commission (SFPUC). However, all combined wet-weather (storm) flows, during precipitation events exceeding 0.02 inches per hour, were still discharged to the Site through the three outfall pipes. In 1965, the three outfalls were consolidated into a single system. As a result of mandates promulgated under the 1972 Clean Water Act, the City of San Francisco upgraded its sewage collection and treatment facilities, leading to significant reductions in pollutant loadings by the mid 1980’s. In order to minimize the number and magnitude of wet weather overflows throughout the city, SFPUC built large storage and treatment boxes to contain combined flows during wet weather events. A transport and storage box designed to contain wet weather flows went into operation in 1990 and the outfall located at the end of Yosemite Street was replaced by an overflow weir located near the point where the former Yosemite Creek connected to the Site. By 1991, the combined sewer collection system had reached its current configuration. These infrastructure improvements have reduced total suspended solids in the slough, and the number of annual overflows discharging to the Site has dropped from approximately 46 per year to an average of one per year.

Contaminants and Risks

In 2009, EPA collected and analyzed 191 sediments samples from 36 locations at depths of 0 to 5 feet throughout Yosemite Slough. Primary contaminants found in slough sediments are:

• Polychlorinated Biphenyls (PCBs)
• Petroleum Hydrocarbons
• Metals such as Lead and Mercury

Pesticides were not detected or reported in the May 2011 report but are believed to be present and collocated with the PCB contamination and were likely masked by the high PCB contamination during sediment sample analysis. A 2004 City of San Francisco report reported the following pesticides in slough sediments: Chlordane, Dieldrin, and DDT. Polychlorinated biphenyls (PCBs) are a family of chemicals that were widely used from the 1930s to the 1970s. In the United States, PCBs were sold as mixtures known as “Aroclors.” In 1979, a federal ban was imposed on the sale and production of PCBs in the United States. This ban was based on evidence of PCB presence and persistence in the environment, their strong tendency to accumulate in the food chain, and their known toxicity to humans and wildlife. Unsafe levels of PCBs can cause toxic symptoms including developmental abnormalities and growth suppression, disruption of the endocrine system, impairment of immune function, and cancer. EPA classifies PCBs as a probable human carcinogen.

The primary risks presented by Site contamination are potential impacts to marine organisms, including plant and animals receptors that live in, near or periodically visit Yosemite Slough. Human exposure pathways to Site contaminants may be present via accumulations of contaminants (e.g. PCBs) in the food chain (e.g. consumption of fish and shellfish). Local residents have been known to fish within and near the Yosemite Slough. In addition, the State Parks Wetlands Restoration Project will attract additional ecological and human activity near and in the slough.

Who is Involved

San Francisco Bay Regional Water Quality Control Board
In 1989, the California State Legislature added to and modified the California Water Code to establish the Bay Protection and Toxic Cleanup Program (BPTCP). Objectives of this program included identifying locations in enclosed bays and estuaries that were potential toxic hot spots. In August of 1998 the BPTCP published its Final Technical Report for Sediment Quality and Biological Effects in San Francisco Bay. In that report Yosemite Creek was found to have the third highest concentration of Polychlorinated Biphenyls (PCBs) in sediment in the Bay. Subsequently, the San Francisco Regional Water Quality Control Board directed the San Francisco Public Utilities Commission (SFPUC) to investigate sediments in Yosemite Creek. The SFPUC studies are described below. The Water Board has maintained significant interest in Yosemite Slough and is the lead regulatory agency overseeing the California State Parks wetland restoration project, an on-going project located adjacent to the slough.

San Francisco Public Utilities Commission
The SFPUC prepared two sediment studies at Yosemite Slough which investigated sediment chemistry, the nature and extent of the contamination, and biotic toxicology and bioaccumulation. The SFPUC study found that the contamination is primarily contained within the top three feet of sediment. SFPUC maintains a significant interest in solving contaminant concerns in Yosemite Slough and to prevent future flows of contamination from City sewers into the slough.

California State Parks
In 1979, the California Department of Parks and Recreation purchased land immediately adjoining the Slough to expand the Candlestick Point State Recreational Area. In 2006, California State Parks prepared a site assessment and wetlands restoration plan for 35 acres of land surrounding the entire shoreline of Yosemite Slough. The first phase of construction of the park and wetlands habitat restoration project on the north side of the Slough was completed in 2011 with wetland plants to be planted in 2012. Currently, State Parks plans to construct the second and final phase of its park and wetlands restoration project on the southside of the Slough in 2014.

California Department of Toxic Substances Control
The California Department of Toxic Substances Control (DTSC) enforced and oversaw the remediation of the former Bay Area Drum (BAD) facility in 2003. BAD was a drum reconditioning business operated by several companies from 1947 until 1987. The BAD facility was situated on a 35,000 square foot lot, at the northwest corner of the intersection of Thomas Avenue and Hawes Street, which is approximately 800 feet from the Slough. EPA believes that operations at the BAD facility included discharges of hazardous substances into the SFPUC sewer system which subsequently periodically overflowed and discharged contaminants into Yosemite Slough. For more information on the BAD facility, visit DTSC’s website at: http://www.dtsc.ca.gov/SiteCleanup/Projects/Bay_Area_Drum.cfm .

Cleanup Results to Date

To date, there has not been any chemical contaminant cleanup work in the Slough. EPA’s preliminary best case schedule estimates that the Slough cleanup to commence in the summer of 2014.

Potentially Responsible Parties

Potentially responsible parties (PRPs) refers to companies that are potentially responsible for generating, transporting, or disposing of the hazardous waste found at the site.

EPA has conducted enforcement investigations to identify PRPs for the Yosemite Slough Site. These efforts have identified over 70 PRPs who have received enforcement notice letters called “General Notice Letters” under CERCLA also known as the federal Superfund law. Many of the PRPs have formed a Yosemite Slough PRP Group to organize and coordinate the actions of the group members. After completion of the EECA document, EPA intends to reach a legal settlement under which the PRPs would conduct the design and implement the cleanup remedy selected by the EECA. All PRP work would be pursuant to EPA review and approval.

Community Involvement

Public Meetings: The Community Involvement Plan guides EPA’s outreach and community involvement activities for the Yosemite Slough sediment cleanup project. A copy of the Community Involvement Plan is provided above in the Documents and Reports section of this website.

Additional Links

California State Parks website on Candlestick Point State Recreational Area

U.S. Navy Website on Hunters Point Shipyard

ARC Ecology Website on Yosemite Slough

DTSC Website on Bay Area Drum site