Bristol Township Chemical Spill

PWD’s Sample Collection in Response to Bristol Township Chemical Spill

The Philadelphia Water Department (PWD) was first alerted of a chemical spill on a Delaware River tributary in Bristol Township, Bucks County, on Saturday, March 25, 2023. From March 25 through April 4, our water quality experts collected over 200 samples in response.

Samples were collected throughout PWD’s Baxter Water Treatment Plant (WTP), from the river all the way through to the entry point of treated drinking water into the drinking water distribution system. Samples were analyzed by independent, accredited laboratories to monitor for butyl acrylate, ethyl acrylate, methyl methacrylate, and styrene.

No chemicals of concern from the Bristol Township spill were detected in any of the 200-plus samples collected by PWD and analyzed by independent, accredited laboratories, confirming that Philadelphia’s drinking water was not impacted by the chemical spill.

After initial river screening samples on March 25 PWD employed two general sampling strategies to ensure that no chemicals of concern were present in either the river water being brought into the Baxter plant or throughout the treatment process.

These two strategies are termed “intake monitoring” and “process monitoring.” Between these two sampling strategies, samples were collected from all 12 sampling locations shown in the Baxter treatment plant schematic below during PWD’s response.

• Intake Monitoring: This monitoring strategy focused on collecting samples from the river in front of Baxter WTP’s intake where water enters the raw water basin, and within the raw water basin, where water is stored before entering the treatment process. These sample locations are 1-3 shown in the schematic. Intake monitoring was performed during periods in which the intake was opened to ensure that the water supplied from the river was not impacted by the chemical spill. This sampling strategy was employed every time that Baxter brought in new water from the river from the time the spill occurred through when all models showing the flow of water moving down the river indicated that any chemicals related to the spill had passed by Baxter WTP.
• Process Monitoring: This monitoring strategy focused on collecting samples throughout the overall treatment process from the river and raw water basin all the way through the entry point into PWD’s drinking water system (sample Locations 1-12 shown in the schematic). This sampling method was performed to ensure that no chemicals of concern had made it into PWD’s WTP and through our treatment processes. This sample strategy was employed multiple times each day during PWD’s response to the chemical spill.

Over the week following the spill, PWD modified the locations and times used during these two sampling strategies based on internal and external sample results, hydrological and hydraulic models, and plant operations. Again, no chemicals of concern from the Bristol Township spill were detected in any of the samples.

In addition to the samples collected in response to this event, PWD continued all its routine process control and regulatory sampling both at Baxter WTP and throughout PWD’s drinking water distribution system, ensuring that Philadelphia’s drinking water continued to be of the highest quality.

Health Reference Levels and Laboratory Detection Thresholds

An important consideration when assessing risks such as the Bristol Township chemical spill are the health reference levels and laboratory detection thresholds for the specific chemicals of concern. The health reference levels below are from the U.S. Environmental Protection Agency (EPA) and the Agency for Toxic Substances and Disease Registry (ATSDR). These health reference levels are in parts per billion (ppb) and reflect the level at which, if exceeded, these chemicals could pose a health risk in drinking water.

• Butyl Acrylate: 560 ppb (provided by ATSDR)
• Ethyl Acrylate: 100 ppb (provided by EPA)
• Methyl Methacrylate: 9,800 ppb (provided by ATSDR)
• Styrene: 100 ppb (EPA’s regulatory limit for drinking water)

Samples collected by PWD during PWD’s event response were analyzed by four independent, accredited laboratories . Many of the samples were also analyzed in duplicate by PWD’s Bureau of Laboratory Services as a screening and quality control measure. The laboratories’ detection thresholds for these chemicals (the concentration of a chemical at which the lab would be able to detect the chemical) ranged from 0.5 - 10 ppb. All detection thresholds were far below the individual health reference levels for these chemicals, and none of the accredited laboratories analyzing PWD’s samples detected the presence of any of these chemicals.

Enhanced Monitoring Sampling Results

Laboratories generally send reports of analytical results 2-3 weeks following receipt of samples. Due to the emergency nature of PWD’s response to the chemical spill on the Delaware River, the accredited, independent laboratories that were helping PWD test samples were working around the clock for the first few days.

Immediately upon generation of the results and review of the analytical quality control, the laboratories called PWD with a verbal report of the results. PWD has now received and compiled the final written reports from each laboratory into the summary data report below.