News Release

NPS Conducting Dye Tracer Study to Determine Groundwater Pathways

Fluorescent yellow-green dye halps scientists identify the pathways taken by stormwater.

NPS Photo/Malzone

News Release Date: May 22, 2022

Contact: Kathleen Sandt, 570-234-9144

Contact: Jonathan Malzone, 570-296-6952, ext. 26

BUSHKILL, PA- Staff at Delaware Water Gap National Recreation Area are conducting a dye tracer study along US Route 209 near mile marker 17 beginning May 20. This study will help determine the pathway water takes underground. Knowing that pathway will help NPS understand the location of groundwater resources that possibly contribute to the occurrence of landslides along this section of US Route 209. This area has historically been subject to slope failure and landslides. The most recent landslide occurred on April 7, 2022.

While assessing the area to determine what repairs will be needed and how future landslides can be prevented, several investigators have noticed groundwater seeping through the area of the current slope failure. According to park scientist Jonathan Malzone, “It is suspected that this groundwater is either coming from an ephemeral, or intermittent, stream nearby that entirely disappears into the ground or from rerouted drainage that we are currently unaware of.” Ephemeral streams flow as a result of precipitation and cease to flow once stormwater has flushed through the system. “The source of this water needs to be known so that we can understand both the probable cause of the slope failures and which water resource may need to be managed to avoid recurring landslides,” added Malzone. Information gathered from this study will be shared with the Federal Highway Administration.

Park staff will be monitoring the area over the next few days to track and document the path of the dye. Visitors may notice areas along the Delaware River where water has a temporary bright fluorescent yellow-green color. Although the dye used is highly visible, it is a commonly used, environmentally friendly, non-persistent, biodegradable, non-toxic dye that is often used in fish hatcheries. The color will disappear in a matter of hours to days as it dilutes and degrades.