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Coal tar remediation in an urban environment: a model for community collaboration.


Cleaning up a Superfund site in an urban environment presents complex challenges for regulators, business interests, engineers, and nearby residents. The cleanup of the former Minneapolis Gas Works site in downtown Minneapolis provides a useful model of how sensitive environmental health issues can be managed in an urban setting. Currently, an administration and training facility is located on the site. Formerly, however, the site was occupied by a gas-manufacturing facility that left soil and groundwater contaminated. It was essential to develop effective methods for cleaning up the contamination and addressing community concerns.

Site Description

The former Minneapolis Gas Works site is located on the bluffs of the Mississippi River in downtown Minneapolis, Minnesota. The site passes below two bridges, one of which carries a busy freeway [ILLUSTRATION FOR FIGURE 1 OMITTED]. An adjacent area to the west incorporates hiking and biking trails and the Stone Arch Bridge, a recently renovated historic structure. The site is also adjacent to the Mississippi River. To the east and west, recreational parkways run along both sides of the river. Also nearby are high-rise apartment and condominium complexes, low-income housing units, buildings owned by the University of Minnesota (located on both sides of the river to the east), and many small retail and manufacturing businesses. A thin strip of shoreline along the northern border of the site provides access to a lock-and-dam facility Minnegasco, the utility company that currently owns the site, operates a propane air facility on the western edge of the property The propane air mixture is used to supplement natural gas supplies at peak demand times. Minnegasco also maintains an office building on the site.

Before natural gas became available, gas was manufactured from coal or oil. Nearly 90 years of gas manufacturing at the Minneapolis site resulted in coal tar contamination of the soil and bedrock. Dissolved polycyclic aromatic hydrocarbon (PAH) compounds were also present in the groundwater (1). Underground structures associated with the gas-manufacturing plant still remained. The contaminants of greatest concern included PAHs, volatile organic compounds (VOCs), cyanide, and heavy metals (2-4). The contamination posed a threat to public health and the environment. When the cleanup process began, there were also large areas of general construction debris and spent oxide box filler - wood chips that had been coated with iron oxide dust and exposed to raw manufactured gas to remove impurities from the gas.

Site History

Minnegasco's predecessor constructed a large manufactured-gas plant on the site in 1870. The plant continued to operate through the 1960s. This plant was the only source of gas for Minneapolis residents and businesses until the early 1930s. From the 1930s to the 1960s, the plant was used to supplement natural gas supplies. The facility was demolished in the early 1960s, and dirt was brought in to bring the land surface up to its present grade. In 1966, an interstate-highway bridge (I-35W) was constructed over the Mississippi River and across a portion of the site. After construction of the bridge was completed, the remainder of the site was not much used until the early 1980s, when environmental investigations began.

In early 1983, Minnegasco completed a preliminary groundwater investigation. The information from that investigation led to a more comprehensive investigation, designed to characterize the nature and extent of the contamination. From 1986 to 1989, investigators drilled 33 bore holes to test the soil and installed 15 groundwater-monitoring wells (1).

The first large-scale phase of the remediation process began in 1991, with the excavation of the spent oxide box filler waste. The excavation was ordered by the Minnesota Pollution Control Agency (MPCA), the regulatory agency overseeing the cleanup. Starting in 1992 and continuing through 1993, the community raised concerns about odors, noise, and possible health effects from the excavation of the spent oxide box filler. During this period, new procedures were established to address the community's concerns. These measures included enclosure of the equipment used to process the waste material, regular monitoring of air around the perimeter of the site, and establishment of an open and ongoing dialogue with the community (5).

The first phase of the cleanup was completed in late 1993. The second phase, completed in 1996, included development of a collection system and a treatment facility for the contaminated groundwater. Treatment of the groundwater will continue for at least 30 years. The third and final phase of the cleanup, completed in early December of 1997, involved the excavation and on-site thermal desorption of soil contaminated with coal tar.

Future Use

A portion of the site will become part of the West River Parkway in Minneapolis - the last remaining link in the Great River Road project, which will provide a continuous link from the headwaters of the Mississippi River in northern Minnesota all the way to New Orleans (6). The parkway, which will connect greenbelt areas to the east and west in a continuous corridor along the river bank, will include a bike trail, a hiking trail, and a picnic area. It will form an important part of the overall Minneapolis park system.

Public Health Concerns

Exposure to contamination at the site could occur in a number of ways, including inhalation, ingestion, and direct skin contact. The Minnesota Department of Health (MDH) evaluated these possible routes of exposure. The analysis addressed the type and amount of contamination, its toxicity, and the location of the release. MDH also looked at whether any completed exposure pathways existed and whether any completed exposure pathways might exist in the future. To minimize the potential for exposure, various options were developed for cleaning up the contamination.

MDH concluded that there were no complete exposure pathways and, consequently, that there was no immediate threat to public health (7,8). Nevertheless, contamination was present at the site and would continue to be present, so it was concluded that completed exposure pathways could be a concern in the future. Potential exposure pathways included exposure to contaminated well water through ingestion or skin contact; skin contact with any contaminated soil that might be brought to the surface; and inhalation of vapors released by excavation activities, from stockpiles, or during the handling of soil contaminated with coal tar.

While members of the community expressed concern about PAHs found on the site, some of which are carcinogenic, they were most worried about odor problems related to naphthalene, a noncarcinogenic PAH. The effects of naphthalene, which has an odor similar to that of mothballs, can vary widely Naphthalene vapor is known to cause headaches, lethargy, respiratory tract irritation, nausea, and vomiting (9). At an air concentration of 15 parts per million (ppm), it has been reported to cause eye irritation. Most people can detect the odor of naphthalene at concentrations between 0.01 ppm and 0.80 ppm (10). This variability in odor detection threshold indicates that sensitivity to naphthalene varies.

The odor detection threshold for naphthalene is very near the laboratory detection limit, which ranges from less than 0.017 ppm to less than 0.51 ppm (9). Some individuals may smell naphthalene at levels that are not detected in the laboratory. Sensitive people may experience headaches or nausea when others in the same environment are not affected (11,12). In the case of the former Minneapolis Gas Works site, this variation in sensitivity complicated efforts to characterize public health risks, set priorities for handling complaints from citizens, and communicate information on environmental health issues.

Environmental Investigation and Cleanup

MPCA was responsible for overseeing cleanup activities at the site. MDH characterized public health risks and assisted MPCA in responding to community concerns. Minnegasco was responsible for the cost of investigation, remediation, and cleanup. Minnegasco also assumed primary responsibility for community relations activities, taking a flexible and proactive approach to the management of issues and concerns related to remediation. This active involvement on the part of Minnegasco helped ensure that the cleanup was conducted in accordance with all state and federal rules. As the project continued, all of the parties worked together to establish trust, maintain effective communication, promote respect for each other's varying needs and goals, and ensure progress toward the common goal of cleaning up the site and reclaiming it for use as a valuable park space.

Phase I

Starting in July 1991, approximately 14,000 cubic yards of spent oxide box filler was excavated, screened, and stockpiled on site. The screened spent oxide box filler was then taken to a local utility for use as a supplemental fuel in the generation of electricity. During that year, nearby residents occasionally complained of offensive odors. These odors were reported to be very strong at times, depending on excavation activity at the site, wind direction, and the distance over which the spent oxide box filler was transported. Models that address indoor odor problems are available, but at the time this project was initiated, there was no readily available model for evaluating the ambient odor problems associated with large, open excavations of odorous materials (13).

Despite the lack of an appropriate model, it was clear that area residents had legitimate concerns about odors from the excavation and material-processing activities. The Community [TABULAR DATA FOR TABLE 1 OMITTED] Advisory Council (CAC) worked with Minnegasco, MPCA, and MDH to develop criteria for determining the severity of odor problems emanating from the site and for changing site operations. The result was a response model: the "Real Time Air Monitoring and Odor Response Decision Tree" [ILLUSTRATION FOR FIGURE 2 OMITTED] (5).

Soil Contamination Cleanup Goals

 Cleanup Goal Cleanup Goal
Chemical for 0 to 4 Feet(a) for 4 to 0 Feet(a)

Acenaphthylene 8,000 16,000
Acenaphthene 8,000 16,000
Anthracene 28,000 48,000
Benz[g,h,i]pyrene 1,980 3,960
Fluoranthene 2,640 5,280
Fluorene 3,770 7,540
Naphthalene 5,200 10,400
Phenanthrene 28,000 48,000
Pyrene 1,980 3,960
Total carcinogenic PAHs 32 92
Cyanide 100 100
Lead 400 800

a MPCA risk-based calculations in milligrams per kilograms.

According to this model, the source of the complaint - a casual passerby, an individual working in the area, or someone who lives in the area - is critically important in determining an appropriate response. Also important is the type of complaint - a simple inquiry about an odor, a nuisance complaint, or an actual report of sensitivity or illness. Other important factors are the source of the odor; the severity of the complaint (mild, moderate, or severe); wind speed and direction; and ambient temperature.

The model facilitated timely response to citizen complaints, minimized releases of odor-causing agents to the ambient air, and provided Minnegasco with specific guidance for work practices. Whenever high-risk conditions were identified, excavation and processing activities were halted until emissions from the site could be reduced to acceptable levels.

Steps taken to minimize the release of contaminants to ambient air included

* confining the process of crushing and screening spent oxide box filler to the interior of a specially constructed building with an air filtration system, so that dust and odor-causing agents could be collected and removed;

* covering the stockpiles of screened spent oxide box filler with high-density polyethylene tarpaulins to prevent volatilization and to minimize the release of dust; and

* transporting the spent oxide box filler in covered trucks.

Phases II and III

The temporary building in which the box filler was crushed and screened was a conical structure covered with heavy plastic fabric. The entire structure was under negative pressure and had a carbon air filtration system. A conveyor system was used to move contaminated material from the stockpile outside, into a hopper, and into the building. Workers inside the building were required to wear respiratory protection and hearing protection.

After the spent oxide box filler was excavated, an estimated 40,000 cubic yards of contaminated material, including coal tars and contaminated soils, still remained at the site. MPCA developed cleanup goals for surface soil to a depth of 4 feet (Table 1). These goals were based on the likelihood of exposure under a scenario that assumed use of the site as a park or recreational area.

A parkway is being constructed to provide a barrier that will prevent future human exposure to any remaining contamination. The use of the recreational-exposure scenario was discussed with CAC members. MPCA also developed a secondary set of standards, for soil from 4 to 10 feet below the surface, based on a scenario of possible exposure of construction and utility workers. No standard was set for soil more than 10 feet below the surface since direct human contact with soil at this depth is highly unlikely.

Topsoil sufficient to support grass, ground cover, or trees and shrubs was assumed. MDH and MPCA calculated surface soil standards, assuming 65 days of exposure per year over a period of 10 years. These values reflect the mobility of urban populations (which limits the duration of potential exposure) and the harsh winter weather of the area (which limits exposure frequency). To calculate the standards, MDH and MPCA used a target cancer risk of one in 100,000 - that is, no more than one extra case of cancer in a population of 100,000, assuming lifetime exposure. MDH policy considers this target to represent a negligible cancer risk. The target also falls within the range defined as acceptable by the U.S. Environmental Protection Agency (U.S. EPA), which has specified a lifetime cancer risk of one in 10,000 to one in 1,000,000 (14).

Groundwater at the site is contaminated with PAHs and VOCs. Although groundwater in the region flows into the Mississippi River, where dilution brings contaminants to nondetectable levels, it was determined that installation of a groundwater treatment system would be appropriate to protect both people and the environment. A groundwater collection system, which pumps 3 to 10 gallons of contaminated water per minute to the groundwater treatment facility, began operation in the fall of 1996. (A typical garden hose discharges 5 to 6 gallons per minute.) At the treatment plant, oil and water are separated and solids are removed. The groundwater then is exposed to ultraviolet light and is oxidized with hydrogen peroxide. The groundwater treatment facility is located on site and is housed near the river and next to a bridge. Treatment of the groundwater prevents contamination from entering the Mississippi River.

Under the final remediation plan for soils, soil at the site must - at a minimum - meet the MPCA cleanup goals (1). Contaminated soil was excavated, crushed, and screened before being subjected to the thermal desorption process. An on-site thermal desorption unit was used to heat the soil to 1,100 [degrees] F in an oxygen-deficient environment. A high-temperature after-burner destroyed volatilized organic contaminants before emissions were released through a stack. Some transient odors may have been associated with this operation.

The procedures outlined above addressed the problem of contact with contaminated soil and contaminated groundwater. The long-term effectiveness of these remediation measures, however, depends on the maintenance of appropriate site conditions. In other words, a good vegetation cover must be maintained, and erosion along the river must be prevented. Since some contamination still remains at the site, a significant change in site conditions or land use could create a new exposure pathway. Any future property owner therefore must maintain site conditions as specified.

This final phase of the remediation project began in 1996. Work was completed in December of 1997.

Community Interactions

When excavation of the spent oxide box filler began in 1991, there was an outcry from local residents about odors from the site. The intensity of the odors was variable, but it was significantly worse during excavation and handling of materials that contained naphthalene. The odors, community concerns about possible health effects, and lack of access to regulatory decision makers created a high degree of mistrust in the community. The initial response from the community included protests, fliers, demonstrations, property damage, and numerous complaint calls about the remediation activities.

In response, Minnegasco and MPCA invited MDH and other interested groups to serve on a Community Advisory Council (CAC) beginning in the fall of 1994. Participating groups initially included three residential associations, three business and neighborhood improvement organizations, the University of Minnesota, the Minneapolis Mayor's office, the Minneapolis City Council, the Minneapolis Community Development Association, and the Minneapolis Park and Recreation Board. Staff from Minnegasco, MPCA, and MDH, as well as consultants employed by Minnegasco, attended CAC meetings as nonvoting members, providing technical assistance and community-relations expertise to CAC.

CAC meetings were facilitated by a neutral party from the Minnesota State Office of Dispute Resolution to ensure that issues were addressed in an orderly manner. The presence of a facilitator helped defuse confrontational elements, allowing discussions to focus on solutions rather than the bureaucratic process or "turf." Incentives for participation included the provision of child care for neighborhood residents, scheduling of meetings in the early evening, and provision of light snacks and soft drinks at each meeting. The importance of CAC as a mechanism for resolving disputes was strongly emphasized. Meeting summaries provided a thorough account of all discussions and significant decisions.

CAC greatly improved the flow of information between all interested parties. Groups that were previously antagonistic developed a better understanding of the reasons for decisions and positions adopted by other groups. Residents were informed about the extent of cleanup activities needed at the site and the complexity of decisions to be made. Minnegasco developed a better understanding of community concerns and desires and was therefore in a better position to respond. Regulators understood better that it was necessary to explain the relationships between regulatory requirements, protection of health and the environment, and community concerns. Residents who were vocally opposed at the beginning of the project became some of its strongest supporters.

Participants in CAC came to respect each other's views and positions. This respect was an essential factor in keeping people actively involved in the process, and it encouraged a strong commitment to resolving the complex issues that arose during the cleanup process. For example, the community came to accept the legitimacy of Minnegasco's concern about costs, as long as they felt that the utility was actively considering appropriate protective measures. Residents with young children generally sought the highest degree of protection. The community also came to understand that government agencies were both empowered and restrained by the laws governing cleanup action. So long as each participant recognized that the positions taken by others were reasonable and legitimate, a respectful basis for negotiation was maintained.

CAC discussions addressed the following issues:

* the location of the groundwater treatment facility (nearby residents had concerns about the size and shape of the building, construction materials, arrangements for maintenance and repair, and general site security);

* features to be included in the park (the inclusion of desirable features had to be balanced against the possibility of creating an "attractive nuisance");

* specific details associated with day-to-day cleanup operations (issues included work interruptions for holidays, seasonal and daily starting and ending times, truck routes, rapid access to emergency information, easy access to general information, and effective procedures for reducing noise and odors); and

* the specific technology to be used for the final phase of the soil cleanup (in developing its recommendations for soil cleanup technology, CAC used a descriptive matrix that incorporated information on available techniques and other issues of concern).

Technology options were listed along the left margin of the matrix. Options included no action, thermal desorption, incineration, blending, recycling, and use as fuel in a utility boiler. Factors affecting the desirability of an option were listed across the top of the matrix under two broad headings. "Disturbance" factors included noise, odor, and visual impact. "Traffic" factors included project duration, regulatory requirements, useful by-products, material handling requirements, long-term liability, total cost, and impact on parkway development.

Decision matrices of this type generally are developed as part of a regulatory document such as the U.S. EPA Superfund "Record of Decision." They are not commonly used to communicate with community groups. Nevertheless, the matrix helped CAC members grasp the essentials of each alternative and make informed recommendations. The thermal desorption option was recommended by CAC, approved by MPCA, and implemented by Minnegasco.

Instead of holding a public meeting with formal presentations and question-and-answer periods, Minnegasco and the CAC sponsored several open houses to discuss site status, provide information to the public, and receive feedback from the community at large. Several groups were invited to staff information tables at the open houses. Minnegasco, the Minneapolis Park Board, MPCA, MDH, the remediation contractor, and various interest groups were among those taking part. Members of the public were able to address questions to staff at each table.

An e-mail link was established for employees at a nearby University of Minnesota office building, so that they could communicate with Minnegasco, MPCA, and MDH simultaneously. Although the e-mail link was needed for only a short time, it proved to be an effective vehicle for rapidly informing decision makers about potential problems and getting targeted information to concerned individuals. For example, when employees noticed particularly strong odors around their parking ramp one morning, air monitoring was conducted within the hour. The odors were found to come from a roofing operation several blocks away from the site.

Minnegasco set up a dedicated community-information phone line to provide citizens with updates on the cleanup. The phone line was generally checked daily and updated weekly to ensure that residents and business owners received quick responses to their inquiries. Callers were able to get concise information about the site, request that additional data be sent to them, and give feedback to Minnegasco, MPCA, and MDH.


The overall success of this project can be attributed to the following factors:

* the establishment and operation of CAC;

* the development and implementation of the odor response paradigm;

* regular air monitoring and reporting;

* recommendation and implementation of an on-site cleanup technology for this urban location;

* the establishment of a community information line: and

* the use of open houses rather than formal public meetings as a communication vehicle.

Participants from Minnegasco and the regulatory agencies demonstrated a willingness to spend time on the project up front to ensure that project development was consistent with long-term site goals. Those goals required flexibility on the part of regulators; state agencies were called on to make allowance for Minnegasco's innovative long-term land use goals - such as the development of the West River Parkway - in plans for the initial remediation project. Flexibility and responsiveness to public input helped generate trust and encourage long-term participation.

A number of lessons were learned:

* Involve all interested parties at the earliest practical point in the process, and identify the optimal degree of involvement for effective communication. Not all parties may wish to receive all of the available information about every issue. It is crucial to identify all potential stakeholders early in the process and determine the level of involvement they desire. Opportunities for involvement and responses to community concerns can then be tailored to needs. If issues are addressed early, a consensus can be reached more quickly. Delays and misunderstandings among affected parties can be avoided.

* All parties must strive for trust and credibility in order to foster consensus and promote long-term acceptance of decisions affecting the cleanup. Consensus is difficult to achieve if the community has not been involved from the beginning of the process. Information must be communicated completely and accurately, as soon as it becomes available. There can be no hidden agendas. Limitations must be honestly described, expectations must be honestly expressed, and decisions should be revisited only when absolutely necessary.

* Parties often have legitimately different viewpoints and goals for the project. These differences must be recognized and respected so that useful alternatives can be formulated and consensus achieved. Each participant brings a unique perspective to the process, reflecting the concerns of business, regulators, or individual citizens. Views may differ, but all participants must be heard and respected.

* Early participation by all interested parties can help improve the final product, yielding a clean and usable property. By involving stakeholders early, respecting their various positions and perspectives, and achieving consensus on long-term expectations, technical planners place themselves in a better position to formulate remediation alternatives. Projects that are understood and accepted by people in the community can be implemented more efficiently

Many factors contributed to an effective and efficient remediation of this highly contaminated site. Spent oxide box filler and coal tar-contaminated soil were excavated and treated, a groundwater treatment facility was installed, and a parkway was constructed on the site. As a result, human exposure to contaminants has been prevented. A supportive environment has been created through the thoughtful application of community relations tools, including the CAC process, the odor response model, quick responses to issues raised by community members, and a broad commitment to involve all stakeholders in the project. This positive environment allowed engineers and decision makers to develop plans consistent with long-term goals for the site, as well as with community expectations. The methods used to remediate the contamination and address community concerns at the site provide a model for dealing with environmental health issues in an urban setting.

Acknowledgement: This study was supported by MDH and the U.S. Agency for Toxic Substances and Disease Registry via Cooperative Agreement U50/ATU500010.

Corresponding Author: Lisa Pogoff, Minnesota Department of Health, 121 E. 7th Place, Suite 220, St. Paul, MN 55101.


1. Minnegasco (1996), Remedial Action Plan - Soils, Waterloo, Ontario, Canada: Conestoga-Rovers & Associates, Ref. #1662 (89).

2. Minnegasco (1991), Baseline Public Health Evaluation, Waterloo, Ontario, Canada: Conestoga-Rovers & Associates, REf. #1662-10 (31).

3. Minnegasco (1992), Health Risk Review, St. Paul, Minn.: Minnesota Department of Health.

4. Minnegasco (1993), Public Health Consultation, St. Paul, Minn.: Minnesota Department of Health.

5. Minnegasco (1996), Air Sampling and Action Plan, Arden Hills, Minn.: Delta Environmental Consultants, Inc., Delta Project A095-210.

6. Final Comprehensive Management Plan, Environmental Impact Statement (1994), Minneapolis, Minn.: Parks and Recreation Board, Vol. 56, pp. 27-31.

7. Minnegasco (1995), Public Health Consultation, St. Paul, Minn.: Minnesota Department of Health.

8. Site Review and Update - Former Minneapolis Gas Works Site (1996) St. Paul, Minn.: Minnesota Department of Health.

9. U.S. Department of Health and Human Services (1995), Toxicological Profile for Naphthalene: Update, Atlanta, Ga.: Agency for Toxic Substances and Disease Registry.

10. Verschueren, K. (1983), Handbook of Environmental Data on Organic Chemicals, 2nd ed., New York: Van Nostrand Reinhold, p. 892.

11. Shusterman, D.,J. Lipscomb, R. Neutra, and K. Satin (1991), "Symptom Prevalence and Odor-Worry Interaction Near Hazardous Waste Sites," Environmental Health Perspectives, 94:25-30.

12. Shusterman, D. (1992), "Critical Review: The Health Significance of Environmental Odor Pollution," Archives of Environmental Health, 47:76-87.

13. Cone,J.E., and D. Shusterman (1991), "Health Effects of Indoor Odorants," Environmental Health Perspectives, 95:53-59.

14. Office of Research and Development, National Center for Environmental Assessment (1989), Exposure Factors Handbook, EPA/600/8-89/043, Washington, D.C.: U.S. Environmental Protection Agency.
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Author:Messing, Rita B.
Publication:Journal of Environmental Health
Date:Mar 1, 1999
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