Pacific Southwest, Region 9: Superfund
Serving Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations
Montrose Chemical Corp
EPA #: CAD008242711
County: Los Angeles
City: Los Angeles
Congressional District: 36
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Description and History
NPL Listing History
NPL Status: Final
Proposed Date: 10/15/84
Final Date: 10/04/89
Montrose Chemical Corporation of California (Montrose) manufactured the technical grade of the pesticide DDT (dichloro-diphenyl-trichloroethane) from 1947 until 1982 at a plant located at 20201 Normandie Avenue, Los Angeles, near the City of Torrance. The 13-acre former plant property is located in the Harbor Gateway, a narrow half-mile-wide strip of land extending southward from Los Angeles proper to the Los Angeles Harbor. The plant was historically called the Torrance Plant because of its immediate proximity to Torrance. The former plant operations included manufacturing, grinding, packaging, and distributing the DDT pesticide. Various locations on the former plant property were used for storing chemical raw materials, DDT and waste products. In 1982, after Montrose ceased operations, the plant was disassembled and removed from the property. In 1985, Montrose regraded and paved the majority of the former plant property with asphalt. This temporary measure has prevented DDT in surface soils from being dispersed by the wind or stormwater while EPA completes the selection of permanent cleanup remedies for the site. The Montrose Chemical Corporation plant property is undeveloped and unoccupied at this time. Approximately 3,000 people live or work within 1/4 mile of the former plant property. The Del Amo Superfund site is located immediately adjacent to the Montrose Chemical Corporation and groundwater contamination from the two sites has commingled (overlapped).
Various hazardous substances, pollutants or contaminants entered the environment via several pathways over the 35 years of operation of the former Montrose plant. These pathways included, but were not limited to, releases of non-aqueous phase liquid (NAPL) and wastewaters to the ground, releases to the stormwater drainage pathways, discharge of hazardous substances to sanitary sewers and to the Pacific Ocean, aerial dispersion of DDT dust, and disposal of DDT in soil fill materials. EPA has been conducting investigations into whether, where, and how much of this contamination persists today from these mechanisms. Where appropriate, EPA is selecting cleanup actions to address contamination from the former Montrose plant site.
The following discussions provide an overview of the components of the Montrose Chemical Corporation project. For more detailed and specific discussions, please use the links, or review this section and then proceed to Cleanup Approach, below.
NAPL. In the DDT production process, Montrose used large quantities of monochlorobenzene (chlorobenzene) as a raw material in the process of making DDT. In its pure form, chlorobenzene is a dense non-aqueous phase liquid, known as a dense "NAPL," meaning it is heavier than water and dissolves little in water. Chlorobenzene entered the ground at the former Montrose plant by way of trenches and a settling and recycling pond. The pond and trenches were used for process wastes and were initially unlined, then lined with acid resistant brick or concrete. Chlorobenzene also entered the ground within the former plant property by way of a rework facility, leaks from valves and clogged lines, and other elements of the DDT manufacturing process. Most of the chlorobenzene DNAPL is located under the former Central Process Area in the north-central portion of the former plant property. Significant quantities of DDT remain dissolved in the chlorobenzene in the ground. For more site-specific information about NAPL at the Montrose site, see below or click here.
Groundwater at the Montrose site is contaminated. EPA is addressing the groundwater from the Montrose Chemical Corporation and Del Amo sites with a cleanup action for groundwater at both sites at the same time in what is called a Dual-Site Remedy. Groundwater contamination from the former Montrose site occurs in six (interconnected) aquifer units and extends more than 1.3 miles from the former Montrose site. No one is presently drinking or using this water. However, the groundwater is considered a municipal drinking water supply beneficial use under the Regional Water Quality Board Basin Plan. The closest drinking water well is located 1.5 miles southwest of the former Montrose site and draws water from the two deepest aquifers. EPA is concerned about ensuring that people are not exposed to the contaminated groundwater in the future and that the groundwater resource is preserved. See below or click here for more detailed information on groundwater at the Montrose site.
Surface soils at the former Montrose plant property are contaminated with DDT at high concentrations. For more information about soil contamination at and adjacent to the former Montrose plant property, see below or click here.
During the Montrose operations, some DDT was dispersed by wind into the surface soils in residential neighborhoods immediately southeast and southwest of the Montrose property. However, extensive investigation by EPA indicates that levels of DDT in residential soils within 30 square blocks of the former Montrose plant property are very similar to levels of DDT in soils in background areas, 2-4 miles from the former Montrose plant (a previous exception was soils in the Kenwood Stormwater Drainage Pathway, see below). This sampling indicates that low levels of DDT are ubiquitous in the south LA area, most likely due to former widespread use of DDT in the United States before its sale was banned in 1972. This means that the amount of residual DDT from historical areal dispersion of DDT dust from the plant site is small. In the areas tested, DDT in residential soils is present at levels that do not pose a significant health risk For more detailed information about DDT in residential areas and areal dispersion of dust at the Montrose site, see below or click here.
Stormwater Pathways. Contaminated surface water from the Montrose site occasionally flowed off the property along a surface water drainage pathway. This contamination originally flowed in an open ditch, called the Kenwood Ditch, which ran paralleled to Kenwood Avenue. EPA refers to this pathway as the Kenwood Stormwater Drainage Pathway. The Kenwood stormwater drainage emptied into a slough, or marshy area south of Torrance Boulevard, where it turned eastward and entered the Dominguez Channel. EPA found high levels of DDT in soil in residential yards along the Kenwood Stormwater Drainage Pathway, and has conducted a cleanup action to remove this soil and restore the yards. More detailed information is provided below, or click here.
In the 1970s, Los Angeles County filled the Kenwood Ditch and replaced it with the Kenwood Drain, an enclosed pipe buried under Kenwood Avenue. The slough was filled and the Kenwood Drain now empties into the Torrance Lateral storm water collection system. About 10 miles downstream from the former Montrose plant property, the Dominguez channel empties into the Los Angeles Harbor about 10 miles from the Montrose plant (7 miles direct). EPA is evaluating the potential for DDT-contaminated sediments along the existing stowmwater pathway and any associated ecological risks (the potential for DDT in the pathway to cause harm to wildlife and water organisms). For more detailed information about the existing stormwater pathway, see below or click here.
Palos Verdes Shelf and the Sanitary Sewers. Montrose discharged wastes containing DDT, chlorobenzene, and caustic scrubber wastes/liquors, into the sanitary sewers during much of the history of its operations. Sediments in the sanitary sewers were contaminated by this discharge. For more information, see below or click here. The sanitary sewers flowed into the Joint Water Pollution Control Plant and then into the Pacific Ocean at the White's Point Outfall. Sediments on the ocean floor of the Palos Verdes Shelf are contaminated with DDT. During its later years of operations, Montrose disconnected almost all plant operations from the sanitary sewers except for showers and toilets. During these years, Montrose hired companies to haul large quantities of the wastes already mentioned, as well as waste acids and acid tars, to hazardous material landfills in the areas used for hazardous materials. Some were also sent out to sea by barge and then dumped in the Pacific Ocean. For more information on the DDT in ocean floor sediments associated with the Montrose Chemical Corporation plant, please leave this site overview and go to the separate overview for the Palos Verdes Shelf.
In the early-to-mid 1950s, EPA believes that Montrose also hauled DDT-contaminated material from its property to a ravine between 204th Street and Del Amo Boulevard. Additional (clean) fill was subsequently brought into this area and additional residences built. EPA found bowling-ball-sized pieces of technical grade DDT in this fill material. EPA has subsequently removed the DDT-contaminated material on 204th Street from the site. For more information, see below or click here.
Contaminants and Risks
- Surface Water
- Soil and Sludges
- Environmentally Sensitive Area
The discussion in this section is basic and general. The section on Cleanup Approach and status below contains more detail and also projected schedule information.
What are the Contaminants?
The two primary contaminants associated with the Montrose Chemical Corporation site are the following: the pesticide DDT , the raw material, chlorobenzene, the raw material that Montrose used to make DDT, benzene hexachloride, and the manufacturing by-product parachlorobenzene sulfonic acid, or pCBSA. Other, contaminants are present at the former plant site as well, including benzene, benzene hexachloride, trichloroethylene, perchloroethylene, chloroform, and others.
DDT was a very widely-used pesticide in the United States until its sale was banned in 1972. It is still used in some countries to fight malaria spread by mosquitoes. DDT is a persistent organic chemical, meaning that once it is put on soil it lasts a long time (often for decades) because it breaks down very slowly. It usually is present as particles that stick strongly to soil. DDT can bioaccumulate in the food chain. Animals in higher trophic levels - i.e., higher up on the food chain - can have more DDT stored in their bodies than the animals they eat. DDT tends to be stored in the fat tissues of animals (including humans) that have ingested it.
Unlike DDT, chlorobenzene tends to evaporate when in open air. While it dissolves only a little in water, it takes only a small amount of chlorobenzene to dissolve in water for EPA to consider the water unsafe for drinking. In its pure form, chlorobenzene is called a "dense non-aqueous phase liquid," or DNAPL, because it is heavier than water and tends to sink. In an aquifer, however, it takes only a small amount of dissolved chlorobenzene for EPA to consider the water unsafe for drinking. For more information about NAPL see discussions below.
Benzene Hexachloride, or BHC, is another pesticide which was present at the former Montrose plant during its operations. As with DDT, BHC is also a fairly persistent chemical that likes to stick strongly to soil particles.
Another chemical in groundwater is para-chlorobenzene sulfonic acid, or "pCBSA." This chemical is rare and is found only in association with DDT manufacture. It is a by-product of the manufacturing process and is not a listed hazardous substance. Unlike chlorobenzene or DDT, it is very soluble in water (it dissolves readily and completely)
Where are the Contaminants?
DDT has been found in 1) soils at the former Montrose plant site and surrounding commercial properties, 2) sediments and soils in residential areas and the historical stormwater pathway, 3) in the sanitary sewer system where Montrose historically discharged wastes from its operation, 4) on the ocean floor on the Palos Verdes Shelf, and 5) in groundwater very close to the former plant property. DDT has also been found in residential areas that EPA has subsequently cleaned up.
BHC is present primarily in soils under the former Montrose plant property and to a lesser extent in nearby storm drainages.
EPA has found the pure form of chlorobenzene in soil under the former Montrose plant property. There chlorobenzene is stuck in the soils and continues to very slowly dissolve into the groundwater. The portion of a plume of dissolved chlorobenzene has spread through in the groundwater and travelled about 1.3 miles from the former Montrose plant property. It has also passed through six different hydrogeologic layers, or aquifers, reaching as deep as 250 feet below the ground. People are not presently in contact with this contaminated water.
BHC is present primarily in soils under the former Montrose plant property and to a lesser extent in nearby storm drainages.
Nearly all of the pCBSA associated with the Montrose site is found in the groundwater fairly exclusively.
See more detailed discussion about these contaminants in the later sections of this update.
Is DDT only found in soils and sediments near Montrose?
No. DDT can be found in soil at low levels in southern Los Angeles County because DDT was widely used in the past. EPA took more than 70 samples of surface soil in residential areas two or more miles away and upwind from the former Montrose plant. The sampling showed that it is common to find 1-3 ppm and as much as 8-10 parts per million (ppm - a measure of how much DDT is in soil) even in soil not close to Montrose. These are very low levels of DDT that do not pose a health concern. This is called background DDT. EPA's investigations -- in residential areas especially -- have been checking to see on where there might be DDT from the former Montrose plant at levels higher than the background DDT. EPA also has evaluated whether such higher levels in soils might pose a health risk.
What levels of DDT are a problem?
To cause harm to people, DDT generally must be swallowed, or dust with DDT must be inhaled, trapped on the mucosa and then swallowed. DDT in soil is not readily absorbed into the body through direct contact with skin. Persons are not in contact with soil that is deep under the ground. In its evaluation of DDT risks, EPA considers not only whether the top soil is a problem, but also whether deeper soils might be a problem if they were dug up in the future.
The acute (short term) toxicity of DDT is generally considered to be relatively low compared with many pesticides in its class, know as organochlorine pesticides. In general, DDT in soil does not pose a danger from short-term or casual contact until DDT levels in the soil are at least 500 ppm.
Persons exposed to DDT in soil over much longer periods may experience health effects at lower DDT levels. This is called chronic (long-term) toxicity. When assessing the possibilities, or risks, of health effects from exposure to chemicals, EPA evaluates both acute and chronic toxicity. EPA considers the risks of health problems from exposure to DDT in soil at concentrations below 170 ppm to be low, even to someone swallowing the soil every day for 30 years. Generally speaking, EPA's Superfund cleanups seek to ensure 1) that levels of contamination are reduced to a low enough level that the risk of long-term health effects is not significant, or 2) that persons cannot come into contact with contamination.
EPA's residential Preliminary Risk Goal (PRG) for DDT in soil is 1.7 ppm. The industrial PRG is 13 ppm. EPA treats DDT as a carcinogen. Additionally, several studies are being performed to evaluate other potential health effects of DDT. Among these is whether DDT may be what is called an "endocrine disrupter" which refers with a chemical that mimics or interferes with natural hormones in the body.
What levels of chlorobenzene are a problem?
Chlorobenzene is found primarily directly in the deep soils and groundwater under the Montrose plant property and in the groundwater. By regulation, chlorobenzene is not allowed in drinking water at levels higher than 70 parts per billion (ppb). This level is called the Maximum Contaminant Level, or "MCL" for chlorobenzene in water. EPA treats chlorobenzene as a non-carcinogen; that is, it has not been shown to cause cancer in human or animal studies. However, it can cause other non-cancer health effects if ingested at sufficiently high concentrations.
What is "Non Aqueous Phase Liquid" or "NAPL" and how is it a problem?
Part of EPA’s study and cleanup for Montrose is for NAPL under the ground at the former Montrose plant property. NAPL is a technical word which means “Non-Aqueous Phase Liquid”, which is used to describe a chemical that dissolves only a little in water. For instance, unlike sugar, only a very small amount of salad oil will dissolve into water, while the rest stays separated from the water. The oil exhibits the properties of a NAPL. In general, NAPL and water don't like to "mix."
Below ground surface, certain types of waste liquid chemicals behave in the ground like salad oil in water. These chemicals are NAPLs when they are in their pure, highly-concentrated form. Once released at the ground surface, NAPL drips down through the soil in strings, fingers and globs -- which are called ganglia. The ganglia are trapped in spaces between the soil particles. Below the water table, both NAPL and water are in the spaces between the soil particles.
NAPL can be extremely difficult to remove from the ground. Because water does not mix well with the NAPL, it does not flush away most of the NAPL but flows around it. An analogy is running water on a sponge that is filled with oil-based paint. The water coming out of the sponge has paint in it, but the sponge stays filled with oily paint for a very long time. If you imagine the ground under the Montrose plant property as a sponge 90 feet high and 13 acres wide with oily paint in it, you can see why it could take a very long time for all of the NAPL to dissolve away in the groundwater. Groundwater moves much more slowly than water from a faucet.
As groundwater slowly moves into the area with NAPL, the NAPL very slowly dissolves. NAPL dissolves enough into groundwater to make the groundwater very contaminated and extremely toxic to drink. However, most of the NAPL stays in place. Unless it can be removed, it can indefinitely thwart efforts to clean up contaminated groundwater. Sometimes contaminated groundwater must be pumped to the surface with extraction into wells for an extremely long time to keep it from spreading further.
Why is cleanup necessary?
Without cleanup, the chlorobenzene, which contains dissolved DDT, may continue to migrate in the groundwater in all six aquifers, potentially reaching drinking water wells and threatening the loss of the groundwater resource. Also, no one will be able to drill wells and use the water in the area of groundwater already contaminated. Without further action, NAPL at the Montrose site may compromise the long-term effectiveness and health protectiveness of the groundwater cleanup remedy that EPA selected in March 1999. It may be impossible to keep the contaminated groundwater from escaping during the extremely long time it would take for the chlorobenzene at the plant property to dissolve away into the water. Without further action, soil contamination at the former Montrose property may become a long-term health threat to persons living around the plant or making use of redeveloped land at or near the plant site, particularly if the asphalt cover degrades. The contamination in the soil may also make the plant property permanently unusable for most purposes.
If EPA had not taken action, soils and sediments along the former Kenwood Stormwater Drainage Pathway could have posed a health threat to residents, particularly if the deeper soils with higher concentrations of DDT were dug up and brought to the surface by future residential activities. If EPA had not taken action, sediments in the sanitary sewer system heavily laden with DDT, monochlorobenzene, and tars could have been dislodged and swept downstream to the sewage treatment plant and ultimately onto the ocean floor off the coast of Palos Verdes, where they could pose toxic threats to marine organisms.
Who is Involved
The lead agency lead for this site is EPA. This site is being addressed through federal and potentially responsible parties' actions. EPA and Montrose Chemical Company of California, Inc. have signed an Agreement on Consent that requires Montrose to perform a remedial investigation and feasibility study, and EPA has issued various unilateral orders to Montrose for other actions. At times, EPA has assumed completion of some work that Montrose has refused to perform or has inadequately performed.
EPA has issued general notice of potential liability under the Superfund Law to the following parties with respect to the Montrose Superfund Site. EPA may issue future such notices to additional parties.
> Montrose Chemical Corporation of California
> Chris-Craft Industries
> Zeneca Corporation, Inc.
> Rhone Poulenc, Inc.
> Atkemix Thirty-Seven, Inc.
> Stauffer Management Company
> Jones Chemicals, Inc.
- > Boeing Realty Corporation
> Shell Oil Company, Inc.
> Dow Chemical Company, Inc.
> Cadillac Fairview/California, Inc.
> Goodyear Tire and Rubber Company
> Minnesota Mining and Manufacturing Company
> Uniroyal, Inc.
> United States General Services Administration
> Montrose Chemical Corporation of California
> Bayer CropScience
> Stauffer Management Company
> News Publishing Australia Ltd.
> Shell Oil Company, Inc.
> United States General Services Administration
> JCI Jones Chemicals, Inc.
> The Boeing Company
> Weatherford Artificial Lift Systems, Inc.
> PACCAR, Inc.
> BP Amoco Chemical Company
> American Polystyrene Corp.
> Dianorys, Inc.
Investigation and Cleanup Activities
The discussion in this section is more detailed and specific than the more general discussions above. Projected schedule information also appears in this section.
EPA is performing multiple investigations for this site, aligned with the types of contaminated media. EPA has selected and conducted several cleanup actions and anticipates selecting additional cleanup actions at differing points in time, to address the entire site. EPA is using both remedial and removal authority to accomplish cleanup of the site. The areas being investigated, and which may receive cleanup actions, are as follows:
1. Soils on, and at properties adjacent to, the former Montrose plant property.
2. Non aqueous phase liquid (NAPL) at the former Montrose plant property.
3. Groundwater contamination. EPA is addressing groundwater contamination at the Montrose Site jointly with groundwater contamination at the Del Amo Site, as a dual-site operable unit.
4. Residential Soils and Produce. EPA has investigated a 30-block residential area near the former Montrose plant property as well as background areas many miles from the former Montrose plant property.
5. DDT-contaminated soils and sediments in the Kenwood Stormwater Drainage Pathway.
6. DDT-contaminated sediments in the existing storm water pathway, including the present Kenwood Drain, Torrance Lateral, and Dominguez Channel.
7. DDT-contaminated sediments in sanitary sewers. A removal action, completed in 1998, removed more than 175 tons of contaminated sediments from a sanitary sewer line near the former Montrose plant.
In 1985, Montrose dismantled the plant and built a temporary asphalt cover over the majority of the contaminated soil areas at the former plant. EPA required that Montrose enlarge this temporary cover on two occasions to ensure that the high concentrations of DDT in surface soils at and near the former Montrose DDT plant cannot be disturbed or entrained by wind or conveyed off property in stormwater runoff. Montrose inspects the asphalt cap monthly and prepares inspection reports for EPA, conducting repairs as needed. The former plant property is presently vacant.
Soils at the former Montrose plant property, primarily in the first four to six feet below the ground surface, are contaminated with DDT at soil levels averaging about 1000-2000 ppm and up to several tens of thousands of ppm. When the plant site was regraded after plant closure, the soil and DDT was mixed and spread across larger areas by the grading equipment. The result was that the property became more uniformly contaminated over most, if not all, of the former plant property area. Before the grading, sample results for DDT as high as 710,000 ppm were recorded in individual locations. There are a series of trenches in the center of the property into which Montrose buried old plant footings and debris. These extend to as much as 12 feet below the ground surface.
Until 1998, Montrose, under EPA oversight, had been conducting an investigation to determine the nature and extent of contamination at the Montrose plant site. Because of inadequacies in Montrose's work on the remedial investigation of the site, EPA took over the work of completing the remedial investigation in January 1998. This report, which contains information on the nature and extent of contamination of soils and NAPL at/near the former plant property, was completed in May 1998. The 1998 RI Report was used in support of the remedy selection for the dual site groundwater (see below). The report was subsequently appended in April 2001 to incorporate data related to residential areas. Since that time, a large amount of additional soil sampling data has been collected to support the remedy selection for the soils cleanup at and near the plant property. In 2005 Montrose completed a major sampling effort that included more than 800 soil samples from 152 borings to supplement preexisting data. Montrose has continued to conduct site investigations that include soil borings, soil gas samplings, and indoor air samplings to further characterize the site for the ongoing risk assessment and FS document.
Montrose continues to work to complete the Feasibility Study for Soils at the former plant property, and on immediately adjacent properties where soils are contaminated due to the former plant operations. The Feasibility Study for Soils will develop and compare several alternatives for cleanup actions to address the soils at the former Montrose property. Some of the general possibilities being considered would involve:
1) Placing a permanent cap over the contaminated plant property; and/or
2) Digging up contaminated soil, treating it, and putting it back on the property; and/or
3) Treating soil while in place at the former plant property, without excavating it; and/or
4) Excavating contaminated soil and hauling it away for treatment..
Montrose has completed work on several treatability tests that provide results needed for the Feasibility Study for Soils. Among these tests are a soil vapor extraction test for volatile chlorinated contaminants, a biological treatment test for DDT, and a soil gas survey. The Feasibility Study for Soils will be issued to the public with EPA's proposal for the cleanup action. EPA will open a public comment period and hold a hearing on the proposal to explain it and obtain comments. EPA will then issue a Record of Decision (ROD) which will select the cleanup action for soils at the former Montrose plant property. As part of the FS process, Montrose will also be preparing a Human Health Risk Assessment (HHRA) that will address potential risks associated with shallow on and near-property soils. The HHRA will evaluate extensive soil and soil vapor sampling data and help guide the development of alternatives for site remediation.
NAPL At the Former Montrose Plant Property:
Non Aqueous Phase Liquids (NAPL) is a topic of some technical complexity. If you are unfamiliar with NAPL and how it poses a problem, see the section "What is Non-Aqueous Phase Liquid and Why is It A Problem" above, or click here.
The chemical chlorobenzene under the Montrose plant property behaves as a NAPL in its pure form. There are chlorobenzene ganglia in soils under the plant. Some of the NAPL has dissolved into the groundwater and moved with the groundwater more than a mile away from the plant. No one is in physical contact with, or othewise being exposed to, the chlorobenzene NAPL now. EPA is preparing a feasibility study of options for removing chlorobenzene from the ground, so that the cleanup of the groundwater can be made more effective (see groundwater, next section). Because the NAPL is the continuous source of the dissolved chlorobenzene in the groundwater, it is possible that removal of this source will shorten the groundwater cleanup time, or make it more certain that the groundwater cleanup will be successful. EPA will present the feasibility study to the public for comment, along with a proposal for the cleanup, to help us decide how to address the NAPL.
Montrose submitted a revised draft Feasibility Study Report in December 2011. A draft final version incorporating EPA's comments is anticipated in early 2013.
The NAPL feasibility study and remedy selection process will lead to a determination as to whether and to what degree NAPL will be recovered, or removed, from the ground. The remedy selected to address NAPL likely will be considered an amendment to the groundwater remedy. The groundwater remedy addresses the dissolved contamination and hydraulically isolates NAPL, but does not address NAPL recovery itself (see the next section).
The primary active remedial alternatives (as opposed to no-action) for NAPL in the draft FS include hydraulic displacement and thermal treatment. There are two types of thermal treatment under closest consideration given the nature of the site: electrical resistance heating and steam injection. Under hydraulic displacement, NAPL is removed from the ground as a liquid by pumping of wells. Under steam treatment, steam propagates through the ground and heats the NAPL, which turns to vapor and is captured/sucked out in vapor and groundwater extraction wells. Under electrical resistance heating, electrodes installed in the ground heat the subsurface to vaporize contaminants which are captured and removed by extraction wells.
Groundwater Layers and Extent of Contamination
There are several contaminated ground layers, or "hydrostratigraphic units" under the Montrose Chemical Corporation site. These units bear different names in some documents; the aliases are mentioned below. The term "unit" when used below refers to one of these layers. In general, groundwater is not an underground river but rather water pushing its way through soil and rock. The way that groundwater behaves depends on the type of soil or rock through which it moves. The type of soil can change as one goes deeper into the ground. Water may move faster in some layers, or units, and slower in other units that lie above or below. Groundwater, and the contamination in it, can move horizontally or vertically, or both.
The upper-most Groundwater layers are referred to as the Middle Bellflower B-Sand ("MBFB Sand") unit, which also appears in Montrose documents with the alias Upper Bellflower Aquitard ("UBA"). This is a fine-grained, interbedded stratigraphic unit with very slow groundwater flow. While an aquifer is a permeable water bearing zone, an aquitard functions as a confining layer between aquifers. The strata in this unit are heterogeneous, consisting of a number of thin, mixed, different geologic deposits of fine sands, silts and clays. The water table occurs at about 60 feet below land surface. The unit extends to about 90 feet below land surface.
Below the MBFB Sand/UBA lies the Middle Bellflower C-Sand ("MBFC Sand") which also appears in Montrose documents with the alias "Bellflower Sand." This is a coarser and more uniformly sorted sand with a faster groundwater flow (higher hydraulic conductivity). This unit extends from about 90 feet to 135 feet, though its thickness is variable.
Below the MBFC/Bellflower Sand lies the Lower Bellflower Aquitard ("LBA"). This unit has been shown to be intermittent and/or thinner in some areas, which allows downward migration of contaminants.
Below the LBA lies the Gage Aquifer. Like the MBFC/Bellflower Sand, the Gage Aquifer consists of medium to coarse sands and is less heterogeneous than is the MBFB/UBA. The unit extends variably from about 145 to 190 feet in depth.
Below the Gage Aquifer lies the Gage-Lynwood Aquifer and the Lynwood Aquifer. The latter begins at about 210-225 feet below land surface. The Lynwood Aquifer is actively screened for drinking water by water purveyors.
Groundwater contamination from Montrose has been found in all of these units. Concentrations of chlorobenzene up to almost 400,000 parts per billion (ppb) and of pCBSA over 1 million ppb have been found in the MBFB / UBA. Due to this unit's slow groundwater flow - i.e. very small horizontal hydraulic gradient - contamination has not moved far from the former plant property. The greatest lateral extent of contamination is in the MBFC / Bellflower Sand, where chlorobenzene is present at concentrations up to about 75,000 ppb, and pCBSA is present at concentrations up to about 100,000 ppb. The chlorobenzene plume in this unit is about 1.3 miles long and about 0.75 miles wide. Chlorobenzene is present in the Gage Aquifer at concentrations up to about 16,000 ppb and pCBSA is present at concentrations up to about 25,000 ppb. The chlorobenzene plume in the Gage aquifer has three distinct lobes; one directly downgradient of the Montrose plant property; one to the west of the first, and one downgradient (southeast) of both the first and second.
As previously mentioned, groundwater contamination from the Del Amo site is being addressed together with the Montrose groundwater contamination. Concentrations of benzene have been detected at that site at up to 1.7 million ppb in the water table and up to 380,000 ppb in the MBFC Sand.
Selected Remedial Action for Groundwater: Completed
The groundwater contamination from the Montrose Chemical plant has commingled with a portion of the groundwater contamination from the former Del Amo Rubber plant, which lies adjacent and to the east of the former Montrose plant. Remedial actions for groundwater at these two Superfund sites are related. EPA has selected a single remedial action to address groundwater at both the Montrose Chemical and Del Amo Superfund sites. The remedy applies to what EPA calls the Dual-Site Operable Unit. This operable unit covers dissolved phase cleanup and the hydraulic isolation of NAPL at both sites.
EPA completed the Joint Groundwater Feasibility Study (JGWFS) in May 1998, and issued a Proposed Plan on June 2, 1999. EPA issued a Record of Decision (ROD) for the Dual Site Groundwater Operable Unit on March 30,1999. This ROD can be downloaded in Adobe Acrobat (pdf) format from this website.
Groundwater in the immediate vicinity of the NAPL cannot be cleaned up in a reasonable and definite timeframe, because the NAPL continues to dissolve in it. Some, but not enough of the NAPL can be recovered from the ground. This water may stay contaminated for hundreds of years. A feasibility study for NAPL is being performed to evaluate whether and to what degree NAPL should be removed from the ground. Technologies for NAPL removal have been steadily improving. In the meantime, the strategy of EPA's cleanup remedy is designed to indefinitely contain the water near the NAPL in a containment zone, so that this contamination can no longer spread. The remedy then cleans up the groundwater outside the containment zone which can then be cleaned to drinking water standards.
More technically, the ROD selects remedial actions that will:
1. Contain the principal threat by containing the dissolved-phase groundwater contamination that surrounds the NAPL, thereby isolating the NAPL;
2. Reduce the concentrations of dissolved contaminants in groundwater, outside the area of groundwater being contained, to levels that no longer pose an unacceptable health risk; and
3. Prevent human exposure to groundwater contamination at these Superfund sites.
The ROD requires that the containment zone be created by (1) hydraulic extraction and treatment (with aquifer injection) for a portion of the contaminated groundwater, and (2) reliance on intrinsic biodegradation for another portion of the contaminated groundwater.
The ROD also requires that the cleanup of dissolved contaminants outside the containment zone be accomplished by hydraulic extraction, treatment, and aquifer injection, in which the treated water is injected back into the ground. The ROD specifies the projected rates of cleanup and other performance requirements. Provisions for institutional controls, monitoring, additional data acquisition, acceptable forms of groundwater treatment, and waivers of certain ARARs based on technical impracticability, also apply to the selected remedial action and are specified by the ROD. Groundwater cleanup outside the containment zone is expected to take decades to complete.
EPA anticipates selecting a separate cleanup remedy for NAPL recovery. This will be done after the feasibility study for NAPL is completed.
Remedial Design Status for Groundwater: Completed
The remedial design for groundwater was completed on September 19, 2012. This provides the planning, specifications, drawings, modeling, testing, cost estimating and analysis that is necessary in order to construct a remedial system that will meet the standards and requirements for the cleanup that were selected in the groundwater ROD. The cleanup system will pump contaminated water to the ground surface, treat it in a treatment system to remove the contaminants, and then pump clean water back into the ground.
The major elements of the ongoing remedial design are as follows: (1) additional sampling and data collection, 2) pilot scale aquifer extraction and injection testing, 3) extensive groundwater modeling with automated calibration, 4) wellfield and pump rate optimization, 5) formal pen-to-paper design of the treatment system(s), wells and conveyances, 6) establish development of long-term monitoring and compliance procedures, and 7) bench scale and pilot scale testing for VOC treatment.
In 2003, EPA issued unilateral enforcement orders to Montrose Chemical Corporation and Shell Chemical requiring that they perform the steps 1, 2 and 4 of the remedial design, as shown above. In 2008, EPA issued an additional unilateral enforcement order requiring Montrose and Shell to perform the formal pen-to-paper design, step 5 above. Montrose and Shell continue to perform the work under these orders under EPA oversight. EPA completed the computer modeling, step 3, with input from Montrose and Shell.
Many additional monitoring wells were installed and sampled in 2004-2006 by Montrose Chemical Corporation and by Shell Chemical Oil Company to refine the knowledge of TCE and PCE contamination that is present within the chlorobenzene and benzene plumes, and to support modeling activities. In addition, the modeling revealed the possibility of chlorobenzene contamination in an area of the Gage Aquifer not previously sampled. When new monitoring wells were installed and sampled in that area, chlorobenzene contamination was confirmed and Montrose installed and sampled a new series of monitoring wells in order to redefine the edge of the chlorobenzene and pCBSA contamination in the Gage Aquifer. In June 2010, temporary wells were installed west of Western Avenue to look for chlorobenenze. No contamination was found and thus the wells were formally abandoned. Additional groundwater monitoring was completed in 2012, 2014, and in 2015..
Residential Soils and Produce Investigation:
EPA conducted an extensive investigation between 1994 and 2000 in residential areas. Our sampling looked for DDT and other Montrose chemicals that might have: 1) blown off the Montrose plant as dust when the plant was operating (this is called, "aerial dispersion"), 2) floated away in drainage water that ran off the plant property, 3) been dumped by Montrose in waste fill material, and 4) been absorbed into homegrown fruits, vegetables, and eggs. Since 1999 alone, we have collected and analyzed more than 2000 surface and underground soil samples for DDT and other Montrose chemicals in residential areas within 30 square blocks to the south, southeast, and southwest of the former Montrose plant property. EPA also collected more than 70 soil samples in "background" areas far from the Montrose plant. Soil samples were collected both from surface soils, and in many areas, from borings that allowed EPA to evaluate DDT levels at soil depths of 0 to 4, and sometimes up to 8 feet below the ground surface depending on the location. EPA has results for 41 samples of homegrown fruits and leafy vegetables and 12 samples of homegrown chicken eggs.
These are highlights of EPA’s findings:
-- EPA found higher than usual DDT levels in soil along a stormwater drainage pathway on Kenwood Avenue. EPA has now performed a cleanup (removal action) of that pathway - see the next section - which is referred to as the Kenwood Stormwater Drainage Pathway discussed further below.
-- Outside of Kenwood Avenue, levels of DDT in soil were very similar to the low background DDT levels (mostly one to three ppm, up to 10 ppm). These low DDT levels do not pose a health risk.
-- In 1994, EPA found two properties on 204th Street which had DDT-contaminated fill material from Montrose. These properties were cleaned up in 1996 to 1998.
-- No additional DDT-contaminated fill was found in other parts of the neighborhood.
-- No DDT was found in homegrown fruits and leafy vegetables in the neighborhood.
-- EPA found DDT in all homegrown chicken eggs sampled. DDT can build up in chicken eggs, so even very low background DDT in soil may result in some DDT in homegrown chicken eggs. Residents wishing to consume homegrown eggs may wish to consult a Fact Sheet by the California Department of Health Services (DHS) issued in 2000. EPA has copies of this fact sheet as does DHS.
-- EPA found three yards with higher than usual levels of DDT outside of Kenwood Avenue. However, DDT was applied as a pesticide on these yards by owners in the past. There is no evidence the DDT in these yards came from Montrose. EPA did not clean up soils in these yards.
-- A sampling by the Agency for Toxic Substances and Disease Registry (ATSDR) of more than 700 blood samples from local residents showed no higher levels of DDT in blood than are present on average in the U.S. population.
Some of these findings were presented in more detail in a November 1999 fact sheet issued by EPA.
EPA has issued a Remedial Investigation Addendum: Residential Soils and Produce (April 2001) which summarizes EPA's sampling efforts in residential areas. Appendix K of this Addendum contains EPA's human health risk assessment for residential soils associated with the Montrose site. A risk assessment is a document which EPA uses to assist in selecting cleanup actions. It estimates the possibility of health effects in the future to hypothetically exposed individuals. It does not evaluate the possibility of health effects from exposures to contaminants in the past, nor evaluate whether health effects existing today are the result of contamination. For more information on these past exposure issues, we encourage visitors to contact the Agency for Toxic Substances and Disease Registry.
Kenwood Stormwater Drainage Pathway
With input from long-time residents, EPA discovered the remnants of a former storm-water drainage ditch that came from Montrose and used to run through residential front yards on the west side of Kenwood Avenue. In 2000, EPA collected more than 1000 samples along the stormwater drainage there. These samples showed that there were higher-than-usual levels of DDT in some soils in the front yards on the west side of Kenwood Avenue. Between the 1940s and 1970s, this ditch carried drainage water from the former Montrose DDT plant. The water sometimes contained DDT. There was no evidence of a drainage ditch or elevated DDT levels on the east side of Kenwood Avenue. EPA took additional samples in several back yards where owners said soil was possibly moved. No elevated DDT levels were found in back yards.
With a few exceptions, most of the elevated DDT on Kenwood Avenue was in soils deeper than 1.5 feet below the ground. EPA offered to remove DDT-contaminated soil from all 25 properties within the storm water pathway. The goal of the cleanup was to remove the soil that had elevated DDT levels because of the former storm water pathway. EPA signed an action memorandum selecting and authorizing the removal action on May 7, 2001.
The cleanup was voluntary, and EPA obtained signed agreements from each homeowner before starting the cleanup. Twenty-four home-owners chose to have their yards cleaned up and restored. One homeowner decided to leave some DDT 4 feet down under a permanent structure.
Starting in July 2001, EPA began the removal of soils in front yards of homes along Kenwood Avenue. The steps of the cleanup included the following: 1) preparation and protection of the yard, 2) excavation of the DDT-contaminated soil, 3)backfill of the hole with clean soil, and 4) restoration of landscaping, concrete, asphalt, fencing, retaining walls and other yard features. EPA performed extensive dust suppression and extensive air/dust monitoring during the excavation work. This monitoring showed that there were no significant releases of dust from the excavations and the cleanup work was safe.
EPA placed the dug up soil into secure containment cells at the former Montrose property. Each containment cell consists of an enclosed berm (a raised mound). The soil sits inside the berm in a sealed wrap of polypropylene liners and geotextile fabric, like the contents of a burrito sit inside a tortilla. Montrose is maintaining the cells and the former plant property, with EPA oversight. EPA plans to store the soil in these cells temporarily (perhaps 2 to 4 years) until EPA decides how to clean up all the soil at the Montrose plant property.
EPA removed 10,000 cubic yards of material in this cleanup action, which is approximately 1300 large truckloads of material.
The Kenwood Avenue cleanup was finished in February 2002. Completion letters were sent to homeowners detailing the work that was done on their property. EPA’s cleanup made these properties safe for residential purposes with respect to DDT.
In 2008, EPA conducted a new cleanup action at the one property with elevated DDT levels at which the original property owner refused EPA access during the removal action in 2001/2002. The ownership of the property had changed at least twice since the completion of the removal, and the new property owner asked EPA to complete the cleanup work. This work was conducted in essentially the same fashion as the 2001/2002 cleanup action for the Kenwood Stormwater Drainage Pathway.
Sediments in Sanitary Sewers:
In September 1992, EPA approved a removal action to address DDT contamination in sediments in the sanitary sewer within about 1/2 mile of the Montrose site. The objective of this action was to remove contaminated sediments to prevent them from washing downstream to the treatment plant and the ocean, as well as to protect routine sewer workers from exposure. The removal action was delayed until the installation of a replacement sewer line was completed by the County of Los Angeles. In the summer of 1996, about 106 tons of sediments containing an average of 24% DDT by weight, as well as chlorobenzene, was removed and sent to a permitted off-site incineration facility for destruction as a hazardous waste. Approximately 60 tons of additional and extremely viscous material remained between the two manholes closest to the former Montrose facility. In 1997, about 8 tons of material were removed during a pilot test. In 1998 the remaining 52 tons of viscous material was removed by full-scale down hole hand-removal and disposed in the same manner as the material removed in 1996. This action is now complete. However, should additional DDT contamination in other reaches of the sewers be found, EPA will evaluate at that time whether additional investigation or cleanup is warranted.
Periodically, and especially between 1947 and 1955, waste water from the Montrose plant mixed with rain water and backed up, flowing into the storm water pathway leading from the plant. This pathway left the Montrose plant at the southeast corner, flowed along a ditch along Kenwood Avenue, and opened into a slough south of Torrance Boulevard and ultimately emptied into the Dominguez Channel. In the late 1960s and early 1970s, the Kenwood Ditch was replaced by the Kenwood Drain, and the Slough was filled in and replaced by the Torrance Lateral. The Kenwood Drain and Torrance Lateral are buried, engineered drain structures.
The current stormwater pathway refers to the drainage pathway that exists today from the former Montrose facility to the Los Angeles Harbor, which includes the Normandie Avenue Ditch, the Kenwood Drain, the Torrance Lateral, the Dominquez Channel, and the Consolidated Slip.
DDT-Contaminated Fill Material:
In 1993, EPA found technical grade DDT at six residences along 204th Street. At that time, EPA removed some of the contaminated soil, but was unable to remove all of it. In 1994, EPA temporarily relocated 30 families from their homes on 204th Street. After an extensive sampling program, EPA found contamination only in three lots where the DDT fill was located. None of the other properties of relocated residents was shown to be contaminated. In September 1998, EPA completed a removal action which excavated the DDT-contaminated fill material. This material was incinerated at a permitted off-site incinerator facility. This removal action is now complete.
Negotiations between the responsible parties and the residents resulted in an agreement by which the residents were permanently relocated by the Del Amo responsible parties. This buyout of land was completed in February 1998 and the affected homes were demolished according to the agreement. Planning by local community and other entities for the buyout to become a community park is underway. Planning for the park is primarily between Los Angeles County and local residents. In September 1998, EPA completed a removal action which excavated the DDT-contaminated fill material. This material was incinerated at a permitted off-site incinerator facility. This removal action is now complete.
In 1983, EPA issued an Administrative Order requiring Montrose Chemical to cease all discharges of DDT and to initiate a study to determine the nature and extent of contamination. In 1985, 1987, and 1989, the EPA and Montrose signed additional consent orders requiring Montrose to expand its studies and to perform a remedial investigation and feasibility study for the site. In 1994, EPA ordered Montrose to perform the cleanup of DDT-contaminated fill from the backyards of residents on 204th Street. A health clinic for community members was established with a grant from the Agency for Toxic Substances and Disease Registry (ATSDR). The clinic was located near the Del Amo Facility and Montrose Chemical Corp. sites. The clinic evaluated approximately 600 residents for possible historical exposure to site-related chemicals and offered treatment referrals where appropriate. The clinic opened for residents in January 1995 and was closed in January 1998. As of 2011, EPA has initiated enforcement negotiations for a Consent Decree with several parties to construct and operate the groundwater extraction and treatment system.
Cleanup Results to Date
The construction of the asphalt cover has reduced the potential of exposure to contaminated soil at the Montrose site while studies are taking place and interim and final cleanup activities are being planned.
EPA issued the joint (dual site) ROD for groundwater contamination at Montrose and Del Amo sites in March 1999.
The DDT-contaminated sediments have been removed from certain sanitary sewers, and additional sewer cleanup is under consideration.
The DDT contamination in fill material in the 204th St. neighborhood has been removed.
The DDT in residential soils in the Kenwood Stormwater Drainage Pathway have been removed and the yards restored with clean soil.
Investigations, treatability studies, and feasibility studies for soils on and near the former Montrose plant property, NAPL at the former Montrose plant property, and the extended stormwater pathway are ongoing at this time (see above).
The groundwater extraction and treatment remedy is currently in design, and construction is anticipated to begin in 2012.
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.
See above - "Who Is Involved" section.
Documents and Reports
Public Meetings: On May 26, 2016 from 6-9 p.m., EPA hosted a Community “Open House” Event. This informal event was organized as multiple “booths” or “poster sessions” to allow people to learn about all aspects of the Superfund sites at their own pace. This structure also allows people to have one-on-one conversations with EPA Remedial Project Managers (RPMs) about the cleanup work. EPA had updates for the Del Amo & Montrose Superfund Sites on the following topics:
- - Five Year Review
- Vapor Intrusion Investigation
- Del Amo Superfund Site Soil and NAPL cleanup design work
- Soil Removal on the ECI property
- Groundwater Treatment System
- Anti-Degradation Policy Analysis
The handouts from the meeting can be viewed here.
We are planning our next Community Open House Event in early November (before Thanksgiving). Please contact Yolanda Sanchez, the Community Involvement Coordinator if you have suggestions regarding the next event: 415-972-3880 or email@example.com.
Public Information Repositories
The public information repositories for the site are at the following locations:
Carson Public Library,
151 East Carson Street,
Carson, CA 90745
Torrance Public Library,
3301 Torrance Blvd.,
Torrance, CA 90503
EPA Site Manager
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Community Involvement Coordinator
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Public Information Center
After Hours (Emergency Response)