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The 13-acre Montrose Chemical Co. site in Los Angeles, California, was the location of a dichloro-diphenyl-trichloroethane (DDT) manufacturing facility from 1947 to 1982. Various hazardous substances entered the environment through several pathways during this time. EPA is investigating the extent of contamination in certain media and has finished cleanup for others. Cleanup, operation and maintenance activities, and monitoring are ongoing.

The contaminations at Montrose are addressed through seven different Operable Units (OUs) as follows:

  • OU1:  Former Montrose plant property soils and some specified nearby “off-property” areas, focusing on shallow soils and soil vapor (< 10 ft bgs)
  • OU2:  Current Stormwater Pathway - includes Torrance Lateral, Dominguez Channel and Consolidated Slip in LA Harbor
  • OU3:  Montrose/Del Amo Dual-Site Groundwater- includes chlorobenzene, benzene and various chlorinated solvents
  • OU4:  Historic Stormwater Pathway - NorthHistoric Stormwater Pathway - North
  • OU5:  Palos Verdes Shelf - offshore DDTs and PCBs deposit

The Palos Verdes Shelf (PV Shelf) site is a large area of DDT- and PCB-contaminated sediment located in the ocean off the coast  of the Palos Verdes peninsula near Los Angeles, California. The offshore site stretches from Point Fermin in the southeast to Palos Verdes Point in the northwest, a distance of about 15 kilometers. The shelf varies in width from approximately 1 to 6 km, begins in water depths of 30 meters and gently slopes to water depths of approximately 70 to 100 meters, where the shelf breaks. At the shelf break, the slope increases to 13 to 18 degrees, leading to the ocean floor at depths of over 800 meters.

DDT is present in the Palos Verdes sediments largely as a result of wastewater discharges from the former Montrose Chemical Corporation DDT manufacturing plant in Torrance, which operated from 1947 to 1983. Wastewater containing significant concentrations of DDT was discharged from the Montrose plant to local sewers and conveyed to the Joint Water Pollution Control Plant (JWPCP) owned and operated by the County Sanitation Districts of Los Angeles County. Wastewater from the JWPCP is discharged to the Pacific Ocean through submarine outfalls located off White Point on the Palos Verdes peninsula. It is estimated that over 1,700 tons of DDT were discharged by the JWPCP from the late 1950s to the early 1970s.

PCBs from several sources in the greater Los Angeles area were also discharged into the sewer system and released through the White Point outfalls. Much of the DDT and PCBs released through the outfalls settled out on the ocean floor along with the suspended solids and other contaminants in the JWPCP effluent, forming what is referred to as an effluent-affected sediment layer. The DDT- and PCB-contaminated sediment deposit covers portions of both the continental shelf (the Palos Verdes Shelf) and continental slope off the Palos Verdes peninsula and ranges in thickness from 5 centimeters (cm) to greater than 60 cm. The total volume of the effluent-affected sediment deposit is over 9 million cubic meters, with approximately 70% of this volume on the continental shelf (i.e., in water depths less than 100 m). In its 1994 report, the U.S. Geological Survey (USGS) characterized an area of 44 km2 (17 sq. miles) on the PVS with elevated levels of DDT and PCBs in surface sediments. Subsequent data showed that the effluent-affected DDT- and PCB- contaminated sediments covered a larger area, and EPA expanded the PVS study area to include sediments from Point Fermin in the southeast to the southern edge of the Redondo canyon, northwest of the Palos Verdes peninsula. EPA's evaluation of potential cleanup actions is focusing on the areas of highest contamination. 

  • OU6:  Historic Stormwater Pathway-South:  Historic Stormwater Pathway-South
  • OU7:  Jones Chemical Company - operating on former Montrose plant property

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What Has Been Done to Clean Up the Site?

The site is being addressed through federal and potentially responsible party (PRP) actions.

OU 5 Palos Verdes Shelf:

  • Since 2004, EPA and its key stakeholders have been carrying out strategic planning of the Palos Verdes Shelf Institutional Controls Program which has demonistrated success in reducing human exposure to contaminated white croaker.  The institutional controls program has three major elements: public outreach and education, fish monitoring, and enforcement. The public outreach and education program is being implemented by EPA in collaboration with several federal, state and local agencies, environmental groups and community-based organizations. To facilitate coordination and cooperation among these entities, EPA created Fish Contamination Education Collaborative, which guides the implementation of EPA's PV Shelf programs.  The goal of the program is to conduct education for the most affected populations, so they can make informed decisions about fish contamination issues. The outreach efforts have been conducted in English, Spanish, Cambodian, Chinese, Filipino, Korean, Vietnamese, Chamorro, Samoan, Marshallese and Tongan.  The current program focus is to measure risk reduction through the ICs program implementation. EPA, with assistance from all stakeholders, put together a road map for the Institutional Controls Program which outlines the numeric objectives and associated strategies and tactics for the program.  For more information on the Fish Contamination Education Collaborative is available on
  • On September 30, 2009, the EPA signed an interim Record of Decision (ROD) that selected an initial remedial action for PV Shelf of capping, monitored natural recovery, and institutional controls.  However, the results of the 2009 Baseline Sediment Monitoring Report and the First Monitored Natural Recovery Report- data collection 2013-2016, indicated that the site condition has changed and the interim remedy may no longer be effective for the site.  Therefore, EPA is in the process of developing a Feasibility Study in support of the final site remedy selection.


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What Is the Current Site Status?

EPA is addressing site cleanup in phases that align with the contaminated media:

  • Soils on, and at properties next to, the former Montrose plant property
  • Non-aqueous phase liquid (NAPL) at the former Montrose plant property
  • Groundwater contamination
  • Residential soils and produce
  • DDT-contaminated soils and sediments in the Kenwood Stormwater Drainage Pathway
  • DDT-contaminated sediments in the existing stormwater pathway
  • DDT-contaminated sediments in sanitary sewers: a removal action in 1988 removed over 175 tons of contaminated sediments from a sanitary sewer line near the former Montrose plant
  • DDT-contaminated sediment at Palos Verdes Shelf

Initial Actions

Initial actions in 1985 included dismantling of the plant and construction of a temporary asphalt cover over contaminated areas. EPA required that the site’s potentially responsible party (PRP) enlarge the asphalt cover twice. The PRP inspects the asphalt cap monthly.

Soils on, and at, Properties next to the Former Montrose Plant Property: A feasibility study to identify remedial alternatives is underway. Other site studies to determine the treatability of contaminants are ongoing. The draft feasibility study identified capping and excavation, treatment and disposal of contaminated soil as possible remedial alternatives.

NAPL at the Former Montrose Plant Property: A feasibility study to identify remedial alternatives is underway. The draft feasibility study identified hydraulic displacement and thermal treatment as the primary active remedial alternatives.

Residential Soils and Produce Investigation: EPA conducted an investigation between 1994 and 2000 in residential areas to look for DDT and other chemicals that may be present in residential yards and produce. EPA found higher-than-usual levels of DDT in soil on one residential street and did a removal action, or short-term cleanup, to address the area. EPA cleaned up two other properties from 1996 to 1998 because the yards contained DDT-contaminated fill material.

Remedy Selected

Groundwater: The long-term remedy for groundwater contamination included dissolved phase cleanup and the hydraulic isolation of NAPL. The PRP installed additional monitoring wells from 2004 to 2006. A feasibility study for NAPL treatment is ongoing.

OU5 Palos Verdes Shelf:  On September 30, 2009, the EPA signed an interim Record of Decision (ROD) that selected an initial remedial action for PV Shelf of capping, monitored natural recovery, and institutional controls.  However, the results of the 2009 Baseline Sediment Monitoring Report and the First Monitored Natural Recovery Report- data collection 2013-2016, indicated that the site condition has changed and the interim remedy may no longer be effective for the site.  Therefore, EPA is in the process of developing a Feasibility Study in support of the final site remedy selection.

Cleanup Ongoing

OU 5 Palo Verdes Shelf:  Based ont he 2009 Baseline Sediment Report results, EPA suspened the capping component of the remedy.  EPA continues to implemented the Monitored Natural Recovery and the institutional controls components of the remedy.

  • Monitored Natural Recovery  (MNR):  EPA collected and analyzed fish tissue, sediment, and water samples between 2013 and 2016 to establish a baseline for the Monitored Natural Recovery program.  The results of the MNR effort indicated that the DDTs are dechlorinating and the concentrations of DDTs and PCBs in fish, sediment, and water column are generally decreasing.
  • Institutional Controls:  With the assistance of the local government agencies, universities, none profit community groups, and California Fish and Wildlife, EPA continues to: 1) implement existing public outreach and education efforts to increase awareness and understanding of the existing fish consumption advisories and fishing restriction, 2) evaluate and track contaminant concentrations in fish (mainly white croaker) caught at or near the site as well as those sold in retail fish markets and served in restaurants, 3) Enforce the existing commercial and recreational restrictions on white roaker fishing established by the California Department of Fish and wildlife.
  • First Five Year Review Report: On August 28, 2014, EPA completed the first Five Year Review Report for Palos Verdes Shelf. The report concluded that "the interim remedy at Montrose Chemical Corporation Operable Unit 5 (Palos Verde Shelf) is protective of human health and the environment. Institutional controls are in place and are effective in protecting users of PV Shelf. Results of sampling programs and research by EPA and others indicate that natural recovery processes are occurring. While the necessity of an isolation cap is further assessed, the combination of institutional controls and monitored natural recovery is effective and is progressing towards attaining the specific interim cleanup goals and timelines set forth in the Interim Record of Decision. 

Cleanup Complete

Kenwood Stormwater Drainage Pathway: Voluntary cleanup by 24 homeowners began in 2001. The removal action excavated and stored about 10,000 cubic yards of contaminated soil. Cleanup finished in 2002. An additional removal action at one property took place in 2008.

DDT-contaminated Sediments in the Existing Stormwater Pathway: Cleanup is complete at this site.

Sediments in Sanitary Sewers: In 1996, EPA removed and incinerated about 106 tons of sediments. Removal of the rest of the contaminated sediments finished in 1998. Cleanup is now complete.

DDT-Contaminated Fill Material: EPA removed contaminated soil at six residences but was unable to remove all of it. EPA temporarily relocated 30 families in 1994. In 1999, EPA removed and incinerated the rest of the DDT-contaminated fill material at the residences.


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Activity and Use Limitations

At this site, activity and use limitations that EPA calls institutional controls are in place. Institutional controls play an important role in site remedies because they reduce exposure to contamination by limiting land or resource use. They also guide human behavior. For instance, zoning restrictions prevent land uses – such as residential uses – that are not consistent with the level of cleanup.

For more background, see Institutional Controls.

  • OU5 Palos Verdes Shelf: 
    • Fish Consumption Advisory:  California EPA’s Office of Environmental Health Hazard Assessment (OEHHA) has issued health warnings for consumption of certain fish off Palos Verdes and other Southern California sites in 2009.
    • White Croaker Commercial Fishing Ban:  In 1990, the California Department of Fish and Game closed commercial fishing of white croaker on the Palos Verdes Shelf and nearby areas due to health risks posed by DDT and PCB contamination. Commercial fishing for other species of fish is permitted.
    • White Croaker Bag Limit:  In 1998, the Department of Fish and Game established a bag limit for white croaker on the Palos Verdes Shelf and nearby aras to address the concern that sport fishermen may be illegally selling their white croaker catch to markets.

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Sampling and Monitoring

OU5 Palos Verdes Shelf:

In support of the capping and monitored natural recovery components, EPA conducted a Baseline Sediment Study in 2009. Surprisingly, these results indicate that an interim sediment cap may be unnecessary since the post cap installation sediment goals for DDTs and PCBs appear to have been achieved. Therefore, EPA suspended the sediment cap design efforts.

Between 2013 and 2016, EPA collected and analyzed fish, sediment, and water samples as a part of the Monitored Natural Recovery effort.  The results indicate that  Overall, conditions at PV Shelf regarding COC contamination in sediment appear to be improving – concentrations in the 0-2-cm bed-depth interval continue to decline, and concentrations in the 0-8-cm  bed-depth interval were lower than the performance objectives related to the interim cap described in the IROD, even without the cap. However, significant areas of sediment remain highly contaminated, and COC concentrations in samples of water and fish exceeded the associated IROD cleanup goals, both for DDTs and PCBs. EPA will continue the MNR sampling program to evaluate the effectiveness of MNR and to develop final remediation alternatives for PV Shelf cleanup.

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