All lanes are back open after crews have worked around the clock to clear debris from a massive landslide that blocked Marine Corps Drive in East Hagatna and caused heavy traffic earlier this week. The Guam Environmental Protection Agency is now investigating the cause and working to mitigate further landslides as the result of further erosion.

While roads are now open, the aftermath of Wednesday's cliffside collapse is still visible, from sediment in the bay to efforts to prevent further erosion. Guam EPA acting administrator Glenn San Nicolas says an investigation has been launched to find out what caused the landslide and its potential environmental impacts.

"Both agencies are working together to determine the cause of the landslide and to assess the damage to the Tiyan storm water system," he told KUAM News. "This will help to determine the responsible party or parties for the landslide, who will then be held responsible for subsequent losses, damages, cleanup and restoration efforts."

Water quality sampling in the bay has already begun to see if runoff from the landslide has impacted the marine ecosystem and if potential contamination poses a public health hazard. "At this time, the public is advised to stay away from the cliffside due to loose soil and rock," San Nicolas stated. "Additionally, we’re waiting for lab results from GEPA’s EMAS program.

"Depending on the lab results, EMAS may issue advisories to the public to avoid swimming in the areas due to contamination."

The agency issued a stop work order to the Palisades Estates while the investigation is ongoing and is requiring them to safely discharge runoff from sediment ponds, away from the cliffside and the ocean.

They must comply with some conditions, as San Nicolas explained, "So Day 1, which starts [Friday], immediately drain sediment ponds filled with runoff water away from cliffs and affected areas. Day 2, submit written plans to Guam EPA outlining mitigation measures for discharge and damage to the buried drainage system – such as cleaning ponds, increasing pond capacity, and implementing dewatering plans for review and approval. Day 5, complete the installation of approved mitigation measures. And Day 6, provide Guam EPA access to inspect the site once measures are installed."

As reported, Tasi Vista Development, the company behind the nearby Palisades project, says the erosion stemmed from an aging concrete storm drain, not the construction site itself.

They said the underground infrastructure at the site was designed to handle heavy weather, with temporary drainage and containment basins already in place under Guam EPA's direction. But the aging storm drain caused runoff to spill onto the highway, following heavy rains from a passing tropical disturbance.

Plans for further clean up is in the works.

"Additionally, Guam EPA is looking to engage in the Department of Agriculture Aquatics and Wildlife Resources to develop plans for beach cleanup, removal of sediment and silt already present from the landslide debris," said San Nicolas.

In the meantime, DAWR says "this recent disaster is a clear reminder of the ridge to reef connection– what happens on land directly affects our ocean. By caring for our ridges, we protect the reefs and marine life that sustain our island.”