Talking Trash: Mapping Waste-related sites in the Denver Metro Area

As a new resident of the beautiful and troubled city of Denver, Colorado, one of the first questions I found myself asking was, “Why does a city with an abundance of nature lovers have such an abysmal composting program?” Composting food waste helps divert mass from landfi lls and contributes to a massive reduction in greenhouse gas emissions, and is such an easy way to curb your carbon footprint. I began to wonder what happens to the rest of our garbage here. If we are not yet succeeding as a community in something as simple as composting, what is happening to our waste, and how is our waste affecting the people who live in this rapidly growing city?

In the following pages, I will provide an overview of our current waste management practices, introductory analysis of population within the vicinity of waste-related sites, and a few strides we’ve made towards improving these systems as the region has grown. Beyond residential waste management, industrial and commercial growth has also led to the creation of numerous brownfields and Superfund sites throughout the area. As infill development becomes an increasingly more important strategy in the Denver area, these sites cannot simply be left to succession, and must be remediated. This article will scratch the surface on progress made in this realm as well.

Much of the existing research and literature regarding the use of GIS within the field of waste management focuses on siting practices for landfills, optimization of transportation routes to and from waste processing facilities or storage sites. Table 1 of De Feo and DeGisi’s introduction provide a good overview of examples (2226). However, this article will focus on a few sources discussing land-use allocation and planning strategies regarding waste management facilities and remediation of toxic lands.

Nothing happens in a vacuum, modern life creates a fluid dynamic, and many systems are shared, so this analysis will focus within a 20-mile radius of Downtown Denver, rather than strictly falling within city, county, or various municipal boundaries.

Let’s talk trash.

Literature Review

The question presented in this analysis, “what is happening to our waste, and is our population affected by waste sites in this rapidly growing city?”, is both quite broad, and could be asked of just about any level of geographic entity. When considering this overall question, I thought it pertinent to review research and literature in terms of how GIS is being used within the greater realm of waste management as a whole, rather than attempting to find information specific to the Denver area, or even Colorado, specifically because this research could be applied to any location.

Much of the research in this realm involves techniques for land-use analysis for siting landfill locations, waste processing facilities, and for waste collection transportation route optimization for dispatch.

De Feo and De Gisi’s article, “Using MCDA and GIS for Hazardous Waste Landfill Siting Considering Land Scarcity for Waste Disposal” is a great example of a typical use of GIS within this scope, that takes a slightly different approach, considering land scarcity and the prioritization of available land for alternative uses for which it may be better suited than a landfi ll.

As urban development continues, and social opposition remains strong, land availability for waste management and landfills, in particular, are in short supply. This study uses both GIS and a multi-criteria decision analysis (MCDA), to create a framework for use in siting landfills to first eliminate unsuitable locations, and then analyze data on potential locations remaining. This proposed process optimizes land-use allocation based on the type of waste management that could occur on a site-by-site basis and minimizes the potential “wasting” of land for lower-risk uses (composting, recycling facilities, etc.) better suited for higher risk uses (hazardous waste, landfills, etc.).

Proper land use allocations are vital to the future of healthy cities and continued urban development. As cities expand and experience shortages of space available for new waste disposal sites, particularly for hazardous waste and landfills, utilizing the wealth of data available can help planners make smart choices about siting. Certain areas are better suited to higher risk waste management uses, and when considering the overall scope of waste cities need to manage, especially with increasing density and growth, we must consider what amounts to rankings for land use allocations specifically for types of waste, rather than a lump sum category.

While I do not analyze or designate land use types, or review siting analysis for waste disposal sites of the future in my project, as the Denver Metro Area population increases, so do our needs for waste disposal facilities, and proper siting and land use allocations will be more important than ever.

This is certainly a necessary use, but my area of interest falls more within the realm of waste reduction and landfill diversion, so I focused my search on alternative uses of GIS for waste management. There were a variety of interesting articles, but the next two were the most relevant to my data analysis.

Switching gears to the topic of land remediation in the context of brownfields and superfund sites, Literature Review Thornton, et al.’s article, “Urban Geochemistry: Research Strategies to Assist Risk Assessment and Remediation of Brownfield Sites in Urban Areas” provides an introduction to the role of soil quality and composition in brownfield identification. Urban geo-chemical mapping of soil composition data through GIS presents a great opportunity for identifying contaminated brownfields, and providing data that will determine methods of remediation. Additionally, one is able to determine urban communities at risk of heavy metal intake through urban agriculture, and exposure, particularly as urban development moves into remediated brownfields.

This article uses scientific data collected from soils regarding quality and toxicity, among many other geochemical factors, under consideration when evaluating and determining brownfield status, and later remediation strategies. These specific data points and mineral content analysis are critical in determining health risk to local populations, including potential contamination of produce grown on site, which carries implications for urban agriculture.

While my project does not directly analyze soil quality, these types of GIS applications were likely incorporated in the evaluation of the sites that the Environmental Protection Agency and Colorado Department of Public Health and Environment identified as brownfields and superfund sites, that are now included in my analysis. Mineralogical data such as those explored in this paper can have direct human health impacts on local populations in a variety of ways. As seen in my map analyses, there are high concentrations of brownfield sites within densely populated areas surrounding downtown Denver. Further, this type of information analysis will be helpful in discussing how these sites can be successfully remediated for alternative uses, and which uses would be appropriate based on the measures that can be undertaken. Unfortunately, Denver soil quality is known to be quite poor, but current composition research is severely lacking, and the existing data is piecemeal throughout the region.

Lastly, Abdullahi and Pradhan’s article, “Sustainable Brownfi elds Land Use Change Modeling Using GIS-Based Weights-of-Evidence Approach” proposes that a “weights-of-evidence” statistics approach is the most effective way to incorporate GIS data when modeling and considering potential changes in land use allocations of brownfield sites, both remediated, and candidates for remediation. As urban areas experience rapid growth, we can use GIS to analyze land-use changes that are actively contributing to urban sprawl and reducing available lands for other necessary purposes. GIS modeling can provide geospatial context to a variety of data points needed for consideration when potentially re-classifying remediated brownfield land-use designations and proposing plans for brownfield sites that still need to be remediated going forward.

Similarly to De Feo and De Gisi’s article, this paper presents a critical way of reimagining land use changes in areas with high levels of brownfields, that are also experiencing rapid urban growth and development. There are a variety of methods commonly used for land use change modeling at present, but Abdullahi’s methodology promotes a way to incorporate past land use changes, predicted land uses and development, and also site suitability based on those factors within the “compact city paradigm.” This approach allows for the recommendation of brownfield remediation and development for the most appropriate land uses, with the goals of urban infill density, minimization of “wasted space,” while also reducing the conversion of land better suited to other uses.

The project presented in this article reviews existing brownfields and superfund sites in the Denver area, which is also a rapidly developing area in need of more concentrated infill development to avoid the developing of open spaces. Abdullahi and Pradhan’s approach would be a natural next step for research given the brief introduction to the locations of these sites.

It is the belief of this researcher that the next steps in this field involve similar trains of thought as the three articles previously mentioned, pushing the envelope of current GIS use to analyze the information with an eye towards sustainability, responsible growth, and proper space allocation for resource diversion and non-recoverable waste accumulation. Additionally, more ecologically focused or population focused research on how our waste affects these groups would be valuable.

Methods Report

Introduction

This project involved a visual spatial analysis of where our solid waste ends up within a 20-mile radius of Downtown Denver, CO, in an attempt to answer the general question, “What happens to our waste?” Further, how has the waste production process affected our landscapes in this vicinity? Knowing that Denver is home to multiple superfund sites, brownfields, and landfills, among others, I began to wonder if there were visual relationships between the concentration of those areas and their demographic makeup.

Process & Data Collection:

Research was conducted and maps were produced in May 2022. Additional research and data for 2022 and 2023 likely exists but has not been added to this analysis.

To establish a base, I began by looking for appropriate boundaries to operate within. Ultimately, I decided to focus my area of analysis on a 20-mile radius from Downtown Denver. County boundaries were still too large of an area for analysis, considering that the radius only included parts of each county, and would result in skewed data, so I further subdivided into census tracts for population-based analyses, allowing me to clip to only the census tracts within each county within the radius boundary. This still skews data with tracts that are only partially within the radius, but allows for a broad enough context for a legible map within the scale presented.

With my chosen geographic areas, I began to search for what data was publicly available in this realm. Due to the constraints above, I primarily looked for government agency or state-wide data sources to analyze. This approach allowed me to avoid needing to seek out the same data for each county, knowing that discrepancies in the data collection process or digitizing may be a factor in that case. Next, I gathered shapefiles for the locations of landfills, solid waste, recycling facilities, composting facilities, brownfields, and superfund sites through state and federal level sources, primarily Colorado Department of Local Affairs, Colorado Department of Public Health and Environment, and the Environmental Protection Agency. Many additional datasets were initially collected, regarding wastewater, water sanitation, municipal boundaries, soil quality, and hazardous waste sites to name a few. Ultimately, these data sets were removed as I finalized my geographic question and the best ways to represent the data features that would work well together. Ultimately, I decided to focus on landfills, recycling centers, composting facilities, brownfields, and superfund sites, in addition to census tract level demographic data so that I could analyze the population density and any relevant trends of who lives within the vicinity of these sites. I also wanted to focus on the idea of remediation as a means to transform toxic places into ones suitable for certain uses, or at a minimum, more aesthetically pleasing places, if not still partially toxic, as this type of land development plays a crucial role within our growing city.

Data was organized in my data dictionary (see previous page) and clipped to the 20-mile radius for a variety of analyses and visualizations. Prior to learning how to operate a spatial join or overlay in the course, I opted to manually combine the various tract level census data by county into one master csv file with all counties represented in one. Census data for each tract within the involved counties was combined into one layer, and data points I did not plan to analyze were removed from the data set (sex ratios (M : F), voting age populations, etc.).

Coordinate System:

I chose to represent my maps in the WGS 1984 Coordinate System. The vast majority of the data I collected directly from the state of Colorado was already in WGS 1984, so for ease of use and consistency with the source, I opted to maintain the existing projection. Further, because my analysis did not rely on precision of distance and involved a relatively small area overall, I felt that changing the projection system would ultimately not make much of a diff erence in the visual quality or accuracy of the data.

Analysis & Symbology:

All maps were represented in a similar fashion, with the same hierarchy of line weights delineating county boundaries, the 20-mile radius, and when shown, census tracts, and were designed with a set color scheme to allow for differentiation between features. Counties and the 20-mile radius were labeled throughout to maintain a consistent appearance and ensure the identity of the location should these maps be separated. The only other labeling occurs on the final map to name the locations specifically for discussion. All other features are only identified within their legends.

My initial map, “Wasted Space” was simply displaying a collection of data sets, all clipped to a 20-mile radius boundary to show locations and familiarize the reader with the data we would be analyzing. I opted for graduated symbols for landfills by 2020 volume to show the most active landfills in the area, unique values for Superfund sites to show their status within the process of remediation, and single symbols for all other layers. 2020 values were chosen to chronologically align with the 2020 census data collected for use in later maps.

The second map, “Whose mess is it anyway?” incorporates a population density analysis normalized by square mileage within each census tract, symbolized with graduated colors to show variances in population density.

The third map, “Not in my backyard,” keeps the population density analysis but adds a buffer analysis of 1 mile with dissolved boundaries to represent all landfills, brownfields, and superfund sites, to show which of the most densely populated tracts are within 1 mile of these site locations. Each type was symbolized in a similar fashion but with a slight variance in saturation to allow for distinction and overlap. A one-mile buffer was chosen to represent a potential impact zone of each of these locations. For example, landfill smells may carry in the wind, contaminated soils may travel by tires or wind along roadways, or seep into groundwater reserves nearby and travel much farther distances. Additionally, brownfield sites may not be closed off to the public and could potentially serve as outdoor play spaces for residents within this 1-mile radius, creating unknown exposure to a variety of toxins. The implications deserve much greater research and detail based on the level and type of contamination, but this map is intended to begin a thought process rather than serve as a scientific baseline and should be read as a loose representation, rather than a hard boundary.

The fourth set of maps, “A Sea of Waste,” then takes these buffers into the context of population density by race and ethnicity by census tract. Density was again normalized by square mileage and symbolized by graduated colors in greyscale to allow for a more clear reading. Major racial and ethnicity categories were selected as a representative sampling of our diverse population, and it should be noted that an analysis of other minority groups or those who identify with one or more races may help complete the full picture. The final map, “Time to Clean Up,” symbolizes Superfund sites and brownfields similarly by remediation status, active, completed, or proposed with unique values. This shows where progress is being made and which areas are in need of assistance and focuses on just how much of our space has been affected by contamination in a variety of forms as we’ve developed.

The area of focus for this study includes portions of eight counties that fall within a 20-mile radius of Downtown Denver: Adams County, Arapahoe County, Boulder County, Broomfield County, Denver County, Douglas County, Jefferson County, and Weld County. As is evident in Figure 1, the majority of waste-related sites within this radius are concentrated in the center with landfills falling to the outskirts.

This map includes the locations of EPA-designated Superfund Sites, commercial recycling facilities, the one commercial composting facility, and commercial landfills.

There are four major commercial landfills operating in the Denver area: The Tower Landfill, Foothills Landfill, Denver Arapahoe Disposal Site, and the Front Range Landfill, which accounted for the largest share of municipal solid waste (better known as residential or household waste) disposal in 2021. A fifth, the Denver Regional - South Landfill closed in December 2020 with 1,219,870 cubic yards of waste volume, and is in the process of being capped. (CDPHE, and Weaver Consultants Group, LLC).

In 2021 alone, all four operating landfills accumulated a total of over 2.5 million cubic yards of solid waste from both municipal and industrial solid waste sources. Municipal waste made up approximately 6% of the total 2021 waste disposed at landfills.

According to the Colorado Department of Public Health & Environment, each landfill accumulated the following amount of waste between 2006 and 2021:

• Front Range Landfill - 2,954,008 cubic yards
• Tower Landfill - 11,370,886 cubic yards
• Foothills Landfill - 4,340,910 cubic yards
• Arapahoe Disposal Site - 16,218279 cubic yards

There are 116 recycling facilities within the 20-mile radius, primarily concentrated north of downtown and in a strip leading south.

There is only one commercial composting facility, located in Arapahoe County.

According to an April 2022 article by the Denverite, within the last decade, “Denver reduced landfill waste by 300 pounds per household; replaced dumpsters with trash, recycling and composting carts; automatically sent recycling carts to 96% of the city’s households; increased composting from 1,600 homes in 2010 to over 30,000 homes in 2022; and more.” (Harris).

There are also 281 known brownfields throughout this area. “A brownfield is a property, the expansion, redevelopment, or reuse of which may be complicated by the presence or potential presence of a hazardous substance, pollutant, or contaminant. It is estimated that there are more than 450,000 brownfields in the U.S.” (EPA).

Due to lack of available data and limitations on the legibility of this map series, it should be noted that individual composters, private composting companies, scrap yards, material re-use donation/sale sites (like Habitat for Humanity Restore for example), and many additional solid waste, grease, tire, and electronics processing facilities are not included. Additionally, this analysis does not consider the disposal of medical waste or motor oil. This map represents a small sample of waste management, but provides a quick introduction to where our waste ends up.

According to the Metro Denver Economic Development Corporation, “Metro Denver has a population of more than three million people, and has a growth rate that has consistently outpaced the national rate every decade since the 1930s. The region grew steadily in the past 10 years, and by 2030, Metro Denver’s population is anticipated to increase to more than 3.6 million.”

As evidenced by this statement, the Denver area is quickly growing and our needs for waste disposal, recycling, re-use, and composting will only continue to grow. Additionally, considering the density of brownfields and superfund sites clustered in the areas representing the highest population density, these areas will likely continue to experience growth and require the redevelopment of these land parcels through remediation.

The remediation process, depending on the type and level of contamination, has proven successful in many cases, and allows for the land to be utilized in a variety of means once cleaned up, although it may not be suitable for all uses.

Ultimately, we are all responsible for our own outputs, the decisions we make to create waste, and how we choose to dispose of or re-purpose that waste. However, with the infl ux of new residents, and an existing housing affordability crisis, the development and new construction of residential units are a key factor in our waste generation. The commercial and construction industries create massive amounts of waste, and despite improvements in the realm of green infrastructure and greater popularity of material re-use, “are responsible for more than 80% of the city’s waste and only diverting 36%” (Harris). According to that same article, the city is working to enact regulations that would require recycling and composting for new multi-family units as well as their construction crews. It is yet to be seen if these regulations will go into effect, and if they will drive up housing rates to offset higher building and operation costs.

On a more personal scale, “American consumers waste an estimated 30 million tons of food each year,” and many compost and diversion programs are successful in significant reduction of household food waste entering landfills (Broad Leib, E.M., et al. 5).

New programs have a learning curve which can be improved with community education, but ultimately, community buy-in is a major factor in the effectiveness of any diversion program. The image at the bottom of the previous page (Figure 3) posted to the Town of Erie, Colorado - Government’s facebook page highlights a perfect example. The post aimed to remind Erie citizens that construction waste may contain nails, screws, paint, and other inorganic materials, and does not belong in the yard waste or compost bins. This post illuminates a common issue experienced with well-intentioned citizens and recycling and compost programs.

We each have a role to play in the success of any program, but as private citizens, we are not always in control of our circumstances, or the environment in which we carry out our daily lives. Many Denver-area residents live in poverty and are unable to move to an area less impacted by waste. Further considerations for research would also include where unhoused populations in the Denver area fit into this picture.

The map above (Figure 4) shows the same population density as Figure 2, but represents the previously shown Superfund Sites, brownfields, and landfills with a one-mile buffer around their location. Many areas near downtown are overlapping showing that some of these densely populated census tracts are also within one mile of multiple waste-related sites. Further analysis found that...

...of the 687 Census Tracts,

378 are within one mile of a Brownfi ld,

122 are within one mile of a Superfund Site, and

11 are within one mile of a Landfill.

Over 1.9 million people live in those tracts,

many within more than one site.

1,550,677 people live in a Census Tract that falls within one mile of a Brownfield. 469,367 people live in a Census Tract that falls within one mile of a Superfund Site. 55,825 people live in a Census Tract that falls within one mile of a landfill. It is important to note that some of these census tracts are much larger than others and not the entire population may live within one mile of the site in every tract.

These sites suffer from a variety of environmental hazard concerns, and some are more harmful than others. A one-mile buffer was chosen to represent the potential impact zone of these sites, though in reality, the buffer for some would be much larger than others based on the contamination type and levels that occur there. Additionally, if toxins seep into groundwater reserves, or contaminated soils, or smells blow in the wind, the impact range could vary significantly. Again, some of these sites pose much less of a threat than others.

The following series of maps (Figure 5) dives into population density by major racial or ethnic group, based on 2020 Census data by census tract.

These maps show the distribution of density of those who identify themselves as White, Black or African American, Asian, Native American or Alaska Native, Pacific Islander or Native Hawaiian, and lastly, Hispanic or Latino, a growing segment of Denver’s population.

The map below (Figure 6) shows Superfund Sites, and brownfields identified by the Colorado Department of Public Health & Environment. Brownfields previously included on the initial maps from the EPA’s FRS Interests List are still included although their remediation status was not specified, as such, they are included in the last category, “unknown.”

Of the 281 brownfields shown in this map:

• 3 are known to be in Active Remediation status
• 15 are known to have Completed Remediation
• and 262 are missing data regarding remediation status

It is very likely that many of the unknown 262 have been remediated or are in progress, but further research would be required to determine their status.

The EPA’s main focus in terms of remediation is on Superfund Sites, highly contaminated sites where hazardous waste was “improperly managed” or “dumped”, that pose a major risk to the public. “These sites include manufacturing facilities, processing plants, landfills and mining sites.” The Comprehensive Environmental Response, Compensation and Liability Act, otherwise known as CERCLA is responsible for this focus, and,” allows EPA to clean up contaminated sites. It also forces the parties responsible for the contamination to either perform cleanups or reimburse the government for EPA-led cleanup work. When there is no viable responsible party, Superfund gives EPA the funds and authority to clean up contaminated sites” (EPA).

The largest Superfund Sites in the Denver radius are in the process of remediation, or are in the monitoring phase. Many of these projects completed their initial remediation in the 1980s and are continuing to undergo monitoring at regular intervals.

One success story that demonstrates the power of remediation is The Rocky Mountain Arsenal National Wildlife Refuge. This was the former production site of chemical warfare munitions, rocket fuel, pesticides, and more. After massive clean up efforts between 1989 and 2010, this site now operates as a fully functional and nationally renowned wildlife refuge, although the US Army Corps of Engineers continues treatment of the contaminated groundwater. “It supports hundreds of species of wildlife, including bison, prairie dogs, bald eagles and black-footed ferrets,” and receives a wealth of visitors each year (EPA Region 8).

Even with remediation complete on many of these sites, considering the remaining levels of contamination at certain sites, remediation is still a clear goal, and proper land use allocations for these parcels, once remediated, are critical to our continued growth as a city.

Moving forward, we should continue to utilize GIS as a tool to help solve pressing issues, drive future waste diversion strategies, and plan ahead for proper disposal of and mitigation of hazardous waste substances to minimize the creation of future brownfields and superfund sites.

Discussion

While this analysis enlightened me on the overall scope of our waste and contamination here in Denver, the answer to the question posed is much more complicated than I anticipated. Even with 2020 data, I’ve come to learn that this situation is changing relatively quickly, and we are in a much different situation as of March 2023, than we were in May 2022 when this research project was completed. Ultimately, this research was fairly limited in scope, and has much further room for analysis.

As of May 2022, Denver had proposed many measures to reduce landfill inputs, and was working to increase recycling and composting capacity in the near future.

At that time, I was unable to find data regarding volumes of material processed at waste recovery and scrap yard locations, as well as diversion through private composting companies like Compost Colorado or home-based composting, which is likely a growing segment here in the Denver area. Being able to incorporate waste diversion data may have told a different story about the transition towards more sustainable growth as a city. Further, some construction companies have internal diversion and material recycling/reuse protocols in place that it would have been interesting to include. For example, an analysis looking at new development and their construction diversion rates/offsets would be an interesting thing to consider within this scope.

Additionally, I do feel that the data was limited in scope due to the radius area I selected, and likely would have told a different story had each county’s methods for waste management been analyzed separately. Specific programs run through different neighborhoods, towns/cities/municipalities, and counties provide vastly different services to their residents, and an equity analysis on access to recycling, compost, and diversion programs may also be an opportunity for further study. And looking beyond the existing municipal waste and diversion programs, data looking at facilities that offer drop off for hard-to-recycle items may illuminate opportunities for new drop off locations throughout the metro area.

While much of this story could have been told without the use of GIS, I found it to be a very helpful tool for visualizing the information in a spatial manner and combining varying data sets that exist in silos online. Being able to combine these into one map, or set of maps, helped to tell a more complete picture of a complicated story, that is still unfinished. There are many other tools within GIS, that I also believe would be helpful in more accurately and more precisely answering this question in the future.

This would make an interesting and informative series to show how our waste management has changed over time, and as we continue to evolve the processes in the future.