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Depue/New Jersey Zinc/Mobil Chemical

Site Summary

June 2016

DePue, Illinois                                    
Bureau County                                    
Illinois EPA 0110300003                                    
Rockford Region

Site Description

Total Acreage: 950

Lead Agency: Illinois EPA

NPL Listing: June 9, 1999

Congressional District 16                       

House 76 / Senate 38             

The DePue/New Jersey Zinc/Mobil Chemical Corporation site is located along the north side of the Village of DePue and constitutes roughly one half of the village land area. Initial plans for investigation and cleanup of the site were organized by unit, e.g., plant site soils, Interim Water Treatment Plant, Phosphogypsum Stack, Zinc Slag Pile, Lithopone Ridges and South Ditch. As the cleanup plans for the South Ditch progressed, this organization was found to be inappropriate for the complex site and the site was divided into five operable units (OUs) for investigation and remediation:

  • OU 1: South Ditch Contaminated Sediments
  • OU 2: Phosphogypsum Stack
  • OU 3: Former Plant Site Area (FPSA)
  • OU 4: Off-site Soils
  • OU 5: Lake DePue Sediments and the Flood Plain

The South Ditch, OU 1, is a drainage canal that feeds into Lake DePue and received discharges of contaminated groundwater and surface water from the site. The northern 120 to 150 feet of the ditch is incised into fill consisting of placed soil and slag material. The remainder of the ditch traverses marshy lowlands adjacent to Lake DePue. These discharges resulted in unnatural sediment containing total metals in concentrations up to 200,000 mg/kg each of copper and zinc. Pursuant to a 2003 Record of Decision, removal of contaminated sediment from the South Ditch was accomplished in 2005. The ditch and its immediate vicinity are included in the Lake DePue investigation.

The Phosphogypsum Stack, OU 2, is a large waste pile of phosphogypsum (resulting from conversion of phosphate rock into diammonium phosphate fertilizer), and its associated water control structures including drainage swales, clearwater dam, and constructed treatment wetland. The stack has been partly covered with native prairie vegetation and partly covered with fescue grass. A final closure plan is under development.

The Former Plant Site Area (FPSA), OU 3, includes the plant site property where the smelter operations and fertilizer production occurred, and adjacent bluffs. The Interim Water Treatment Plant, which treats and discharges collected surface and groundwater, is located in one of the former plant buildings. Soil and groundwater investigations, including an assessment of human health risk have been completed. The ecological risk assessment is underway.

Off –site soils within the surrounding community, OU 4, have yet to be investigated systematically. A Pilot Study was conducted in 2013 and 2014, which included sampling 41 residential properties, to determine the types and concentrations of metals present in residential yards. A Scoping Document, which outlines anticipated remedial action to address residential area contamination was approved in 2015. The Scoping Document outlines actions to address contamination in soils associated with residential yards, parks, the school, and Village alleys. Other open spaces within the Village and outlying agricultural fields and natural areas will be addressed in a separate effort.

Lake DePue, a large backwater lake and its associated floodplain, OU 5, have been the focus of intense study in recent years. Recreational use of the lake has been degraded by accumulation of sediment from the Illinois River. (see The remedial investigation, including the human health risk assessment, has been completed. The ecological risk assessment will require an additional sampling effort before it can be completed.

Site History

Mineral Point Zinc Company originally developed the site in 1905 as a primary zinc smelter producing slab zinc for use in the automobile and appliance industries. In addition, the site has at various times been the location of sulfuric acid manufacturing, paint pigment production, ammonium phosphate fertilizer manufacturing, refining and recovery of secondary metals from zinc ore (e.g., cadmium), secondary zinc smelting and zinc dust production. Between 1905 and 1989, portions of the site were owned and operated by New Jersey Zinc Company, Mobil Oil Corporation, Gulf & Western Industries, Horsehead Industries, and the Zinc Corporation of America. In 1990, the facility ceased operation and shortly after that, New Jersey Zinc demolished most of the remaining structures. Through various corporate mergers, acquisitions and the bankruptcy of Horsehead, responsibility for the site has fallen to Viacom International Incorporated/CBS and the ExxonMobil Corporation. These two companies have formed an entity known as “The DePue Group,” which collectively represents the potentially responsible parties (PRPs) for the site. In 1995, the DePue Group entered into an interim consent order with Illinois EPA and the Illinois Attorney General’s Office (IAGO) for investigation of the site and evaluation of possible remedial actions.

Investigative History / Contaminants

Environmental concerns were created by waste disposal activities and discharges from the former smelter, sulfuric acid plant, paint pigment plant and the diammonium phosphate fertilizer plant. These activities produced a primary zinc smelter slag pile in excess of 702,000 cubic yards or 570,000 tons; several ridges of paint pigment plant waste, sometimes referred to as the lithopone ridges, containing in excess of 64,000 tons; a layer of industrial waste varying from 6 inches to several feet over the entire 195-acre former plant site; a more than 140-acre Phosphogypsum Stack; discharges of wastewater and sediment to Lake DePue; and many other impoundments and waste piles. Significant discharges of metals to groundwater and surface water have occurred. All sources were found to contain elevated levels of metals including zinc, lead, arsenic, cadmium, chromium, and copper. In addition to metals contamination, there are elevated concentrations of sulfate, ammonia, and other compounds in the groundwater and surface water. The following investigations and actions have taken place.

  • December 1980 - A preliminary assessment was completed.
  • July 1983 - A second preliminary assessment was conducted.
  • March 1992 - The Illinois EPA conducted an expanded site inspection.
  • 1994 to 1996 – A perimeter air monitoring study was conducted. The study verified that airborne metals were not being released off-site.
  • 1995 to 1997 - The Remedial Investigation/Feasibility Study (RI/FS) for the South Ditch was conducted.
  • 1999 – A site-wide remedial investigation work plan was developed and approved. Site efforts were re-organized into separate efforts for each operable unit; however, this work plan has provided the basis for much of the work in OU3.
  • 2006 – 2007 – Soil sampling from the DePue area was conducted to establish background conditions and support the forthcoming off-site soils investigation.
  • 2006 - 2009 – The remedial investigation for Lake DePue was conducted.
  • 2000 – 2014: The hydrogeologic investigation of the Phosphogypsum Stack was conducted including sampling in off-site areas.
  • 2007 – 2014 – Consistent with the 1999 work plan, a remedial investigation for the plant area was completed.
  • 2013: Soil sampling within the Village was conducted to support remedy selection and preliminary design for OU4.
  • 2015: A Closure Plan for the phosphogypsum stack was submitted, and is currently under review.

Investigation and cleanup is conducted pursuant to the consent order, the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the National Oil and Hazardous Substances Pollution Contingency Plan (NCP).

Human Health Risks

Risks are evaluated in two ways. For carcinogens, risks are evaluated as a range of risks, from 1 in 1,000,000 at the low end of the range to 1 in 10,000 at the high end of the range. Risks below the low end generally do not require remediation and risks above the high end require remediation. Risks within the range may or may not require action based on site-specific circumstances. For non-carcinogens, chemicals are evaluated against a target hazard index of 1. Hazards below 1 generally do not require remediation.

Human health risks from the site have been formally evaluated at OUs 1, 3, 4 and 5. For these OUs, metals are the primary contaminants responsible for human health risks. The sediments in OU1, the South Ditch, were determined to exceed the upper end of the CERCLA risk range (i.e., 1 x 10-4, or 1 in 10,000) for soil ingestion and dust inhalation for both child trespassers and on-site construction workers under current and potential future exposures. These sediments were removed from the South Ditch in 2005.

At OU3, the human health risk assessment indicated that carcinogenic risks within the CERCLA risk range and above the upper end of the range from arsenic and/or polynuclear aromatic hydrocarbons (PAHs), and non-carcinogenic hazards from metals, particularly arsenic and lead, are present to all receptors evaluated, though some risks and hazards are localized.

At OU4, risks and hazards were evaluated by comparing concentrations from samples taken from residential yards to human health screening criteria. The screening criteria represented hazards below 1 and carcinogenic risk within the acceptable risk range. This comparison served as a human health baseline risk assessment and evaluated current and potential future risks to adults, children, and construction workers potentially exposed to soils in OU4. Exceedance of these screening criteria was used as an indication that unacceptable human health risks and hazards may be present which would require remediation.

At OU5, twenty-six receptor-specific routes of exposure were evaluated in the human health risk assessment. The assessment concluded that cancer risks from soil, sediment, and surface water were generally lower than or within the CERCLA target risk range. Non-cancer hazards for all scenarios and receptors were below the CERCLA target hazard index of 1. An evaluation of risks from lead concluded that lead did not present a risk under any scenario.

Ecological Risks

Ecological risks from the site have been formally evaluated at OU 1. The ecological risk assessments for OU3 and OU5 are underway. The ecological risk assessment for OU4 is yet to be planned.

At the South Ditch, OU1, results of the benthic organism testing indicated acute toxicity of South Ditch sediments to the test organisms. Numerous fish species, great blue herons, egrets and certain other waterfowl rely on these benthic organisms as food sources. In addition, some waterfowl, (e.g., mallard ducks) are dabblers and could ingest the contaminated sediments. These sediments were removed from the South Ditch in 2005.

At OU3, the FPSA, concentrations of metals in soil are being investigated for their potential to present ecological risks. Results of the assessment are not yet available.

At OU5, Lake DePue, elevated concentrations of metals associated with the South Ditch, Division Street Outfall, and an area near Lake Park are contributing or may be contributing to increased risks to ecological resources, including plants, soil invertebrates, benthic organisms, fish, and mammals. Risks from other areas of the lake, such as the formerly dredged area are still being assessed. The role of other contaminants or conditions in the lake are still being assessed.

A fish advisory has been issued for Lake DePue for carp, white bass, and channel catfish due to detections of PCBs in fish tissue samples. In addition, there is a state-wide fish advisory for methyl mercury in predator fish. The Superfund site is not thought to be a significant contributor to the lake of PCBs and methyl mercury.

Remediation Acitvities

The major sources of contamination from the New Jersey Zinc site have been intercepted and prevented from entering Lake DePue. The DePue Group or property owners have completed the following remedial activities:

  • Constructed a permeable reactive barrier south of the Zinc Slag Pile, known as the Iron-Rich Material trenches, to remove zinc and copper from the groundwater
  • Constructed the Interim Water Treatment Plant to collect and treat contaminated runoff and groundwater that previously flowed uncontrolled to the South Ditch. Operation of the treatment plant is ongoing.
  • Constructed a Surface Water Redirection and Protection System to segregate water in a 40-acre off-site drainage basin from contact with waste on the Plant Site
  • Reestablished vegetation on most of the plant site to mitigate dust generation and migration
  • Capped the Phosphogypsum Stack
  • Excavated grossly contaminated unnatural sediments in the South Ditch. Contaminated sediments were placed in an on-site corrective action management unit (CAMU) on the plant site.

Completed in 1994:

  • Initiated daily dust inspections and dust suppression with water truck
  • Fenced the plant site area
  • Implemented perimeter air monitoring plan, including sampling for PM-10 dust
  • Implemented draft dust suppression plan
  • Regraded Phosphogypsum Stack and seeded northwest quadrant

Completed in 1995:

  • Regrading of Phosphogypsum Stack
  • Authorized work for design of sump and piping for Interim Water Treatment Plant

Completed in 1996:

  • Continued placement of compost and final grading on Phosphogypsum Stack
  • Completed second treatability study for Interim Water Treatment Plant
  • Conducted field work for South Ditch Focused Remedial Investigation/Feasibility Study
  • Completed construction of South Interceptor Trench

Completed in 1997:

  • Construction of the Interim Water Treatment Plant

Completed in 1998:

  • Modified Lift Station so it would operate during a 25-year flood
  • Submitted Site-Wide Remedial Investigation Work Plan for Soil and Groundwater 

Completed in 1999:

  • Upgraded the Interim Water Treatment Plant

Completed in 2000:

  • Regraded the southwest evaporation basin in the Phosphogypsum Stack Area
  • Groundwater sampling for the Phase 1 Remedial Investigation
  • Discharge from Interim Water Treatment Plant diverted to Illinois River
  • Completed stormwater management improvements north and south of Route 29

Completed in 2001:

  • Scoping documents for the Presumptive Remedy at the South Ditch
  • Closure work for the Phosphogypsum Stack Area

Completed in 2002:

  • Illinois EPA prepared the Proposed Plan for the South Ditch
  • Submittal of Draft Phase 1 Remedial Investigation Report for Soil and Groundwater

Completed in 2003:

  • Ongoing field work in accordance with the Closure Plan for the Phosphogypsum Stack Area
  • Illinois EPA issued Record of Decision for the South Ditch

Completed in 2004:

  • Lower Swale Investigation implemented
  • Removed beaver dams from South Ditch
  • Remedial Design/Remedial Action Design for the South Ditch
  • Corrective Action Management Unit (CAMU) Investigation Work Plan

Completed in 2005:

  • Closure and final grading of the last pond at the Phosphogypsum Stack
  • Completion of the earthwork components of a treatment wetland at the Phosphogypsum Stack
  • Construction of a 2.5-acre Corrective Action Management Unit (CAMU) at the plant site for storage of 8,000 cubic yards of contaminated sediments from the South Ditch Remedial Action
  • Sampling of 17 residential properties within the Village

Completed in 2006:

  • Re-vegetation of the Phosphogypsum Stack, including pilot testing of native prairie grass establishment on approximately 75 acres
  • Phosphogypsum Stack treatment wetland
  • Phase I Plant Site Remedial Investigation Report

Completed in 2007:

  • Remedial Investigation sampling of Lake DePue
  • Reseeding portions of the Phosphogypsum Stack
  • Repaired erosion problems caused by excessive precipitation in OU 2
  • Completed background soil sampling at OU 4

Completed in 2008:

  • Completed Background Soil Sampling Report for OU 4

Completed in 2009:

  • Completed Lake DePue Remedial Investigation Report
  • Planting of a native shrub hedge around the Phosphogypsum Stack wetland as an alternative to traditional chain-link fencing

Completed in 2010:

  • Conducted a controlled burn of the prairie established on the Phosphogypsum Stack
  • Conducted a Five Year Review of the South Ditch
  • Completed field sampling for the Phase III Phosphogypsum Stack groundwater contamination study

Completed in 2011:

  • Finalized Removal Action Limit Assessment Report for OU4, off-site soils
  • Finalized Background Soil Sampling Report
  • Conducted test pits at the six-acre municipal dump area near the South Ditch

Completed in 2012:

  • Completed Comprehensive Hydrogeological Report for Phosphogypsum Stack

Completed in 2013:

  • Conducted off-site sampling to support groundwater model for OU2
  • Conducted Pilot Study field work, including sampling of 41 residential properties for OU4

Completed in 2014:

  • Phase 2 Remedial Investigation Report for OU3
  • Screening Level Ecological Assessment for the Bluff Area
  • Human Health Risk Assessment for OU5

Completed in 2015:

  • Second Five Year Review for OU1
  • Human Health Risk Evaluation for OU3
  • Pilot Study Report for OU4
  • Scoping Document for OU4

Future Remedial Acitvities

  • Complete the Lake DePue Ecological Risk Assessment and initiate the Feasibility Study
  • Complete sampling and remediation of OU 4, off-site soils
  • Complete the ecological risk assessment for OU3, and initiate a Feasibility Study
  • Complete investigation and remediation, as needed, for remaining areas of OU4

Community Involvement

The Illinois EPA helped the community re-establish a community advisory group (CAG) in 2010. The Illinois EPA project manager and community relations coordinator attend the CAG meetings to brief the community on work being done and to answer attendees’ questions. Illinois EPA also meets periodically with the Hispanic community. Representatives of the DePue Group also attend these meetings.

The CAG has received technical support from USEPA through a Technical Assistance Services for Communities (TASC) contractor who has provided information about the risk assessment process and ongoing work at OU4.

Illinois EPA maintains the information repository/administrative record at the Selby Township Library by providing relevant documents, correspondence, and guidance on compact disc. Illinois EPA’s site file has been digitized and is available on Illinois EPA’s web site Documents are provided to the Village of DePue and the CAG for their review and comment.

Illinois EPA conducts community availability sessions as needed, and public meetings as required by CERCLA and the NCP. Such sessions and meetings have addressed the investigation results for Lake DePue and the OU4 Pilot Study. The public meeting to receive comment on the OU4 Proposed Plan is scheduled for June 29, 2016.

Reuse Efforts

The Village of DePue was awarded a grant of services in July 2002 by the U. S. EPA. The purpose of the grant was to assist the community in developing a set of future land use recommendations for the DePue/New Jersey Zinc/Mobil Chemical Superfund site. The consultant team guiding this process was E2 Inc. who, after meeting twice with Village officials and residents, released a project report in August 2004 with the following recommendations:

  • Adapt the former New Jersey Zinc plant facility as a museum of history and industry that showcases DePue’s natural and industrial heritage
  • Promote DePue as a tourist destination and emphasize ecotourism
  • Create recreational opportunities at the site and link the site to regional recreational amenities
  • Provide opportunities for ecological restoration, wildlife habitat enhancements and general environmental education
  • Create new economic opportunities in DePue

The report outlines challenges to site reuse and resources that can help DePue reach its redevelopment goals.

Illinois EPA provided a $50,000 Brownfields Grant to the Village of DePue to hire a contractor.

Current Issues

Illinois EPA has issued a Proposed Plan presenting Illinois EPA’s preferred remedy for certain portions of Operable Unit 4, Off-Site Soils, of the New Jersey Zinc/Mobil Chemical Superfund Site, and to solicit public review and comments on the alternatives considered. An availability session will be held on June 22, 2016 and a public meeting on June 29, 2016 on the proposed plan. Illinois EPA, in consultation with USEPA, will select a final remedy for the portions of Operable Unit 4 addressed by this Proposed Plan after reviewing and considering public comments submitted during the public comment period, from June 14 through July 14, 2016. The final plan will be announced in a Record of Decision (ROD). The public’s comments will be considered and addressed in the Responsiveness Summary included in the ROD. The Public Notice of the Availability Session and Public Meeting, Fact Sheet 17 (in both English and Spanish), the Proposed Plan, and Comment Form Mailers (in both English and Spanish) are all available by clicking on the document at the right.


Charlene Falco

Illinois EPA Project Manager

(217) 785-2891
Jennifer Elkins

U.S. EPA Project Manager

(312) 353-4627
Jay Timm

Illinois EPA Community Relations

(217) 557-4972
Patricia Krause

U.S. EPA Community Involvement Coordinator

(312) 886-9506