10 Data sources
10.1 MPCA SCORE
The Minnesota Pollution Control Agency collects an annual inventory, SCORE, of solid waste, recycling and organics as reported by counties across the state. For this project, we used MPCA data for the nine Minnesota counties for the year 2021. SCORE is named for the Governor’s Select Committee on Recycling and the Environment, which first proposed funding laws in 1989 (MPCA 2023a).
The SCORE data is a high-quality government dataset submitted annually by solid waste staff in each county of Minnesota, as a part of Minnesota’s SCORE laws to support waste reduction and calculate the cost of managing waste and recycling. The data provided includes the total short tons of waste generated in each county within each “Method” category, described below.
The data was accessed through the SCORE tool’s Tableau dashboard, then filtered to include only the 9-county Minnesota portion of the region studied in this report.
10.1.0.1 Data distribution
To check if the data is reasonable, we can start by visualizing the tons of waste generated for each county, broken into categories.
We would generally expect waste from landfills to be greater than recycling, and both landfill and recycling waste to be greater than compost (or “organics”). We can see that this expectation largely holds true, with the exception of Ramsey County, where compost outstrips both recycling and landfill. Part of the explanation for this may lie in the fact that, like Hennepin and Washington, a large portion of Ramsey County’s waste is managed in Waste-to-Energy facilities rather than landfills. This is consistent with waste management strategies of the metropolitan areas within Ramsey, Hennepin and Washington counties (Alexander 2020).
We also note that only two counties, Chisago and Sherburne, processed waste through onsite waste processors in 2021.
We would expect that the total amount of waste generated would be generally positively correlated with county area.
We see that this correlation holds loosely. The major outlier is Ramsey County, which includes the St. Paul metropolitan area.
We would expect that counties with large populations would generate more waste, and we observe a strong positive correlation.
10.1.1 Data characteristics
This data includes MSW Compost as a category, but since all values for this category in the area and year needed were 0, we excluded it from our analysis.
Uncertainty was not included in the dataset given, nor does the EPA offer guidance for estimating uncertainty of solid waste emissions factors.
10.1.2 Waste management classification
The MPCA SCORE report classifies waste management by two management methods and, within those categories, five sub-methods (MPCA 2023b). Within the management methods, “MMSW”, or “Mixed Municipal Solid Waste”, refers to garbage, organic refuse, or other solid waste aggregated for collection, while “Combined Recycling and Organics” refers to separated recyclable and composted materials, including traditional recyclables, source-separated compostable materials, and yard trimmings.
MMSW includes the subcategories of Landfill, Waste to Energy (WTE), Onsite, and MSW Compost. Landfill is all material disposed of in a landfill. WTE refers to waste combusted in an energy recovery facility or incinerator. Onsite refers to burning or burying MSW (MPCA 2023b). No metropolitan counties reported any MSW Compost in the year 2021. Only Sherburne and Chisago counties reported waste managed on-site.
Combined Recycling and Organics includes the subcategories Recycling and Organics. Organics, as compared to MSW Compost, refers to source-separated and direct compost streams. All compost data in this report comes from this category.
After comparing with federal tools like the EPA’s Waste and Recycling National Overview and the expectations of a greenhouse gas inventory, we chose to summarize SCORE’s data into three categories: Landfill, Recycling, and Organics. Landfill includes, in addition to MPCA-reported Landfill data, the categories of Onsite and WTE management.
10.1.2.1 Alignment with EPA Emissions Factors
We used emissions factors from the EPA’s Emission Factors Hub to calculate emissions based on the totals reported by the MPCA. These emissions factors come from the EPA’s Waste Reduction Model.
We selected for each management subcategory the emissions factor most aligned with the waste type as reported in SCORE. These emissions factors do not take into account emissions savings associated with a particular management method, for example energy savings from waste to energy facilities.
| MPCA Management Method | MPCA Method | Our Category | Emissions Factor Name | Emissions Factor |
|---|---|---|---|---|
10.1.3 Limitations
- As mentioned above, EPA emissions factors do not account for emissions saved through Waste to Energy conversions, as contrasted with Wisconsin emissions, which do.
- There is wide variation between emissions factors for waste of various kinds within the same category. Because we do not have a detailed breakdown of the makeup of every category, we have assumed each one is adequately represented by the “Mixed MSW”, “Mixed Organics”, and “Mixed Recyclables” factors respectively.
- This estimation method generates emissions for all waste generated in 2021. However, waste in landfills and composting facilities does not release all emissions at once. This method tends to overestimate emissions for a given year (Fong et al. 2021).
10.2 Wisconsin Greenhouse Gas Emissions Inventory
Waste emissions for Wisconsin counties were unavailable in the same detail as the MPCA data. Thus, we estimated total waste emissions based on statewide emissions estimates, allocated by population.
The most recent Wisconsin Greenhouse Gas Emissions Inventory was done in 2018 by the Wisconsin Department of Natural Resources. Included in the solid waste data for this source are emissions from landfills and waste combustion, taking into account the emissions reduced by landfill gas collection for gas-to-energy use or flaring. This inventory does not, however, include emissions generated from composting or recycling.
The emissions for solid waste in this report were calculated using the EPA’s State Inventory and Projection Tool, a tool designed to help states calculate greenhouse gas emissions (USEPA 2024a). Default values provided by the tool were used except in the case of default Mixed Solid Waste population tonnage values, which were replaced by data from the Wisconsin state DNR Annual Waste Tonnage Report (Wisconsin DNR 2021).
For 2018, the Wisconsin DNR reported 2.2 million metric tons carbon dioxide equivalent (MMTCO2e) generated through landfilling and solid waste management.
In the process of analysis, this statewide estimate was apportioned to the county level based on county population data, as detailed in Section 9.2.
10.2.1 Limitations
- Since data reported directly from the counties was unavailable for Wisconsin, the solid waste data used here reflects a disaggregation of state-level data and may not be reflective of the specific mix of waste generated by Pierce and St. Croix counties.
- Data collected in Wisconsin’s emissions inventory only represents waste disposed of in landfills or waste combustion facilities, and does not include organics or recycling. Recycling and composting data is unavailable for Wisconsin counties.
10.2.2 Comparison to similar datasets
The US EPA completes yearly state-level estimates of emissions for each state, which combined sum to the totals reported in the US Greenhouse Gas Emissions Inventory. The data for these estimates and the US inventory can be explored at the GHG Inventory Data Explorer. The EPA’s total of landfill emissions for Wisconsin for 2018 was 2.450 MMTCO2e, not far off from the Wisconsin DNR’s 2.2 MMTCO2e. The EPA’s estimate for 2021 was 2.422 MMTCO2e. More details can be found in Section 9.5.
Since the EPA completes an inventory for the entire US and its methods may not reflect the specific nuances of emissions in each state, we elected to use the data from the Wisconsin DNR for this inventory.
10.3 Wastewater
We explored three sources for wastewater emissions: the EPA state inventory and projection tool, the Minnesota Pollution Control Agency (MPCA) emissions inventory, and Metropolitan Council Environmental Services emission estimates. Because only the EPA’s estimate extends to Wisconsin and Minnesota, we are reporting those data for consistency, but explore all three below where they have geographic overlap.
The EPA estimate is a high-quality government dataset that models emissions using state population, biochemical oxygen demand, fraction of wastewater anaerobically digested, fraction of population on septic, estimated protein content, and biosolids used as fertilizer to estimate CH4 and N2O emissions (USEPA 2024b). These inputs are modifiable and will be explored further in the CCAP. We apportioned the state level emission estimates to county levels by population percentage.
The EPA tool provides outputs in metric tons CO2e. We confirmed that the global warming potentials (GWP) used are from AR5 (IPCC and Core Writing Team 2014). We used the most recent version of the tool released in January 2024, version 2024.1.
We are currently using default input values provided by the EPA, though will refine these based on our knowledge of local wastewater treatment in the future.
You can access the EPA tool on the EPA website and the MPCA data through their Tableau Dashboard. You can also read full methodologies for MPCA (Claflin et al. 2023) and EPA (USEPA 2024a) in their respective documents.
10.3.1 Data characteristics
There are many sources of uncertainty in these estimates due to multiple activity data inputs required for CH4 and N2O emission estimates. The EPA wastewater module does not offer guidance on quantifying these sources of uncertainty, only describing the potential sources themselves. We have not included any uncertainty estimates in our final values.
10.3.2 Limitations
- In order to have homogeneous comparisons among counties, we are relying on default EPA state inventory and projection tool data which may miss particularities about how wastewater is processed in our narrower county scope.
- We are assuming EPA default input values are appropriate representations of the 11 county MSA region and that we can scale to county levels by population given that we are estimating municipal wastewater treatment.
10.3.3 Comparison with similar datasets
The Metropolitan Council, MPCA, and EPA source data leads to different estimates of emissions in the common seven county region. The Metropolitan Council does not process all wastewater in the seven county region. Additionally, they report CO2 emissions from combustion of stationary fuels for infrastructure used in directly processing wastewater, unlike EPA estimates which are CH4 and N2O emissions from municipal wastewater treatment of organic matter.
| Data source | Geographic scope |
|---|---|
EPA GHG Inventory and Projection Tool |
Minnesota and Wisconsin, scaled to county population |
MPCA GHG Inventory |
Minnesota, scaled to county population |
Metropolitan Council Wastewater Emissions Estimate |
7-county Minnesota metro area |
The Metropolitan Council area covers most of the 7-county Twin Cities area, but no areas in Wisconsin (Metropolitan Council 2020). The Met Council environmental services division provided us with a city and county breakdown of wastewater emissions for their service area.
Overall, the EPA estimate for each county proved highest, followed by the MPCA estimate and then Met Council estimate. We used the EPA estimate in our overall emissions estimate.
Code reviewer: Liz Roten