Chlordane and Dieldrin Total Maximum Daily Loads for Tumon Bay, Guam

Scenic Tumon Bay is a designated Marine Preserve located at the heart of Guam’s tourist area. The waterbody is critical to the island’s economy but is listed on the Territory’s 303(d) list as impaired for chlordane and dieldrin, which are both hazardous and toxic to human health. The U.S. Environmental Protection Agency’s Region 9 hired ERG to develop a pollution budget—also known as a Total Maximum Daily Load or TMDL—for pollution sources within the watershed to assist in bringing the waterbody back into attainment with water quality standards.

ERG began this work by sampling surface water, groundwater, and fish tissue in the waterbody and surrounding watershed to supplement existing data sets and confirm the waterbody’s impairment status. We also identified all known sources of chlordane and dieldrin within the watershed and developed a model linking the source loadings to the waterbody. We then developed a TMDL for all sources to ensure restoration of the waterbody, along with a long-term monitoring plan. The TMDL was approved and went into effect in 2024.