Trend analysis shows how legislation and behavior influence our environment.
Two years have passed since Prince George’s County (PGC) implemented the “Better Bag Bill” in January 2024. Immediately after the ban went into effect, the Anacostia Watershed Society (AWS) observed a sharp decline in the number of plastic grocery bags entering Nash Run, a stream where AWS operates a trash trap.
Now that the entire Anacostia watershed – spanning Washington, DC, Montgomery County, and Prince George’s County – is covered by bag fee or ban legislation, it is time to examine the trends.
While the long-term trends will be explained in detail later, first take a close look at the data in the graph below from January 2024.
Just after the Prince George’s County Bag Ban implementation in January 2024, the number of plastic bags per weight (kilogram) of trash declined sharply.
Because the raw number of plastic bags is heavily influenced by the total weight of trash collected per cleanup and the intensity of precipitation, Figure 1 tracks the concentration of plastic bags (number of bags per weight (kilogram) of trash). This provides a more accurate trend analysis than raw counts alone.
Before diving into a detailed explanation of the trends throughout the monitoring period, let’s look at the location of the Nash Run sub-watershed within the Anacostia system.
The Nash Run sub-watershed covers about 0.7 square miles of drainage area along the border between the District of Columbia and Prince George’s County. Roughly one-third of the watershed lies within Prince George’s County; therefore, activities in both jurisdictions influence the water quality of Nash Run. Additionally, the Anacostia Parkway, a busy highway, runs through the area, meaning litter from passing vehicles also significantly affects the stream. Because our trash trap is located at the mouth of Nash Run, it captures trash from this entire drainage area.
Now that you understand the location, let’s examine the data in detail. Figure 3 shows the trend graph again for the entire monitoring period, annotated to explain the changes over time.
There are four distinct trend patterns in the graph, plus one “extraordinary” period circled in yellow.
Pattern 1 (Brown)
Before DC’s bag fee law, there was an increasing trend in plastic bags. The law was implemented in January 2010, and about six months later, the numbers started to drop. The existence of a time lag makes sense; because it is a fee legislation rather than a ban, it took time to educate retailers and the public and to fully implement the system throughout DC.
Pattern 2 (Green)
Following that initial lag, the number of bags decreased gradually until about July 2013. Although Montgomery County (MOC) implemented its own bag fee law in January 2012, we did not see a significant immediate impact from it in this specific data set. This is likely because this sub-watershed is located primarily in DC and PGC. However, the MOC law must have influenced streams within its own borders.
Pattern 3 (Blue)
From July 2013 to January 2017, there was a gradual increasing trend. It is likely that Prince George’s County contributed to this increase, as there was no bag fee or ban in that jurisdiction at the time.
It is also worth mentioning that the Nash Run Restoration Project took place during this time (construction began in January 2016 and finished in June 2016). This project, located upstream from our trash trap, included the installation of a Bandalong Trap. However, this restoration did not appear to significantly alter the ratio of plastic bags per weight (kilogram) of trash.1
The Extraordinary Period (Yellow Circle)
From January 2017 through June 2021, the data shows extraordinarily high numbers. While we cannot pinpoint a single cause, a combination of several factors explains this surge:
- 2017: The Self-Checkout Boom. Major grocery stores on the DC/MD border (Giant, Safeway) rolled out self-checkout kiosks. These relied on an “honor system” for bag fees. Unlike manned registers where a cashier enforces the fee, self-checkout prompts like “How many bags did you use?” are easily bypassed. Many customers likely entered “0” while taking several bags, promoting usage.2
- 2018: Record Rainfall. 2018 was the wettest year in recorded history for the region (66.28 inches of rain). Heavy rain washes more trash into the stream. Lightweight trash like plastic bags also becomes wet and heavy, making it less likely to blow away and more likely to get trapped in the stream.
- 2016-20211: Third-Party Delivery Apps. The rise of services like UberEats and DoorDash increased packaging waste, compounded by the lack of bag regulations in Prince George’s County.3
- 2020: The COVID-19 Pandemic. During the surge, reusable bags were discouraged for safety, enforcement of bag fees was suspended, and delivery volume tripled.
Our monitoring clearly detected all these behavioral and environmental changes and we re-affirmed that behavior change is very important to reduce the amount of trash coming to the river.
Pattern 4 (Orange)
Immediately following the “extraordinary” period, the numbers returned to “normal,” aligning back with the previous Trend #3 (Blue), which was gradually increasing. However, as soon as PGC implemented the grocery bag ban in January 2024, AWS observed a sharp decline in the number of plastic bags per weight (kilogram) of trash. This is very encouraging.
One might note that the numbers after January 2024 are still slightly higher than those in 2013. This is likely because many jurisdictions outside of DC, MOC, and PGC still lack bag legislation, and litter from passing vehicles on busy highways continues to contribute to the problem.
Annual Trends
As mentioned earlier, counting plastic grocery bags on a per-event basis can be inconsistent because results often fluctuate depending on specific weather conditions. However, using annual totals allows for a more reliable comparison, as the variations in yearly rainfall tend to even out over time – even though some years will still be naturally wetter or drier than others.
Since the passage of the DC Bag Fee law, the actual annual number of plastic bags has been steadily decreasing, with the exception of the extraordinary period from 2017 to 2020. After the PGC Bag Ban implementation in 2024, the numbers declined even further.
This graph also demonstrates that the Total Maximum Daily Load (TMDL) for Trash is working. A TMDL is essentially a “pollution diet” for a specific body of water. Under the U.S. Clean Water Act, it defines the maximum amount of a pollutant (like trash, bacteria, or sediment) a river can “digest” while still meeting water quality standards for fishing, swimming, and drinking.
Once this limit is set, the allowable amount of pollutants are allocated to specific sources like Municipal Separate Storm Sewer Systems (MS4s). The EPA then issues permits limiting the discharge of pollutants, helping to reduce trash in a meaningful way. Since the Anacostia River Trash TMDL was established in 2010, the annual amount of trash has been steadily decreasing thanks to the agencies and organizations tirelessly working to remove trash and educate the public.
Conclusion
This trend analysis illustrates one clear fact: Laws and policies curtail the use of plastic bags successfully and our behavior influences the environment significantly .
We saw an increasing trend stop and reverse after the DC Bag Fee law. We saw it creep back up due to a lack of legislation in neighboring counties. We saw it spike due to self-checkouts, delivery apps, and the pandemic. And finally, we saw it plummet again when Prince George’s County banned plastic bags.Now that we know our legal actions and behavior change our local environment, we must take the next step to stop pollution at the source. The next big opportunity is the Bottle Deposit Bill. Plastic bottles still make up a large amount of the trash captured by our traps. Implementing a Bottle Deposit Bill is the necessary next step to reduce plastic bottle trash and protect our streams.
Support the Bottle Deposit Bill
- DC: Get action alerts from 3RC (the bill leads in DC) at 3rcfordc.org.
- Maryland: Sign the Sierra Club petition to pass the bill in MD: Petition Link.
Acknowledgements
We would like to extend our gratitude to the District Department of Energy and the Environment (DOEE) for the trash trap program. This initiative enabled AWS to accumulate the critical data used to identify these trends. We also thank the Anacostia Riverkeeper for serving as the principal contractor of DOEE from 2023 to 2025; their partnership ensured our data collection continued seamlessly.
- Prior to the restoration, the Nash Run was scoured and the stream was trenched without access to the floodplain. The restoration removed a large amount of soil and created a new and accessible floodplain. The Bandalong trap removes floatable trash like bottles (reducing the total weight captured by the Nash Run trap, or the “denominator”), while the vegetation on the constructed floodplain captures plastic bags (reducing the number of bags, or the “numerator”). Because both the numerator and denominator decreased, the ratio remained relatively stable. ↩︎
- Retail industry data from 2017 indicates a ‘tipping point’ for self-service technology, with shipments to top U.S. retailers increasing by 155% that year (PYMNTS, 2017). Locally, Safeway’s parent company, Albertsons, reversed its anti-self-checkout stance in late 2017, initiating a massive rollout that replaced manned express lanes with kiosk clusters. This shift reduced the presence of ‘human gatekeepers’ responsible for enforcing the DC Bag Law, potentially contributing to the ‘bag leakage’ observed in Nash Run trash traps between 2017 and 2019. ↩︎
- Third-party delivery platforms began rapid suburban expansion in 2016; UberEats’ global revenue grew from $0.6B in 2017 to $8.3B by 2021. Delivery orders typically defaulted to single-use plastic bagging and unsolicited cutlery. ↩︎
