Guam DPW: Poor stormwater mitigation system caused Palisades landslide

 By Pacific Island Times News Staff

The Palisades Estates development site in Maite lacked adequate stormwater mitigation infrastructure, resulting in the collapse of a portion of the cliff on Marine Corps Drive last week, the Guam Department of Public Works said.

DPW found that the Oct. 15 cliff’s erosion, which expelled an avalanche of soil that blocked the East Agana segment of Guam’s main thoroughfare, was caused by excessive water and soil overfilling a makeshift receptacle at the site.

“The failure was caused by the overtopping of rainfall runoff from a temporary

detention basin located near the cliff line, created by the placement of sandbags

at the low point of the site," Vincent Arriola, public works director, said in a notice of violation issued to Tutujan Hill Group.

Tutujan Hill is one of the contractors for Tasi Vista Development, the developer of the high-end subdivision owned by the Calvo family.

Arriola said that a subsequent inspection and drone footage showed that a majority of the site's runoff ended up in the detention basin. Clogged downpipes and drainage systems triggered the water buildup.

“The existing Naval Air Station down drain that conveys water from the

top of the cliff to an outfall in Agana Bay and the newly constructed

drainage inlets on the development site were blocked, thus contributing to the volume of overland flow that had nowhere to go other than the detention basin on the top of the cliff,” Arriola wrote in the notice addressed to William Beery, vice president of Tutujan Hill.

When the temporary holding area hit capacity, water overtopped the sandbag impoundment and then burst over the cliff face.

"The hydraulic cut caused by the flooding resulted in changes to the existing cliff face, increasing the slope and causing soil and organic material to detach from the surface," Arriola added.

The Palisades Estates is a “private, gated neighborhood" with 62 single-family home lots on what was advertised as “Guam’s most desirable address for luxury island living” with "thoughtfully designed infrastructure."

The Palisades was a long-running project that began in 2018.

The Guam Land Use Commission approved the developer's petition to rezone on March 20, 2020, and approved the “final subdivision” request on Dec. 14, 2023, paving the way for the project to proceed.

According to the minutes of the GLUC meeting, Jennifer Calvo, who represented Tasi Vista, told the commissioners that “they have complied with all the requirements for the final subdivision."

She said Tasi Vista had been working closely with the Department of Land Management "to work through the issues that they have had," and with the Guam Environmental Protection Agency "to ensure that they comply with all the infrastructure requirements for this project.”

In a memo dated Dec. 1, 2023, Celine Cruz, chief planner for GLUC, recommended the approval of Tasi Vista’s final subdivision application, noting that “the applicant has been coordinating with the various government entities since 2018 to adequately address” the development site’s infrastructure needs, including utilities, sidewalks, streetlights and an adequate stormwater mitigation system.

In a notice issued on Wednesday, Arriola set additional conditions for Tutujan to address the effects of the cliff erosion that “caused significant inconvenience to the people of Guam, damage to the government of Guam assets and expenses to the DPW for the cleanup.”

DPW instructed Tutujan to relocate the detention basin to a safe location away from the cliff face to prevent the recurrence of the Oct. 15 earthfall.

The department also ordered the contractor to unblock the Naval Air Station pipeline and the inlets at the site to accommodate any overflow of surface runoff.

“DPW will require a temporary grading plan and an updated storm water management plan to be developed for review by DPW,” Arriola said.

In April last year, the Occupational Safety and Health Administration, cited another contractor, Giant Construction Corp., for nine violations of federal safety standards while installing sewer lines at the development site.

During a site inspection at a worksite in the Palisades project last year, federal investigators found employees who were installing sewer lines were in trenches deeper than 5 feet without required safety equipment, OSHA said.

Additional DPW conditions are as follows: 
1.      Conduct a land survey to clarify property boundaries and distinguish owner responsibilities from those of the government regarding drainage and cliff conditions.

2.      Perform an engineering survey using LiDAR drone of the cliff face and site to document surface conditions and impacts of site flooding during construction

3.      Perform hydrologic and hydraulic investigation of existing conditions and predicted conditions based on current land use to better document the existing drain system and how the proposed drainage system will function. The study is to consider all off-site contributing areas to the original NAS storm drain and this development.
4.      Perform a geotechnical investigation, focused on slope stability and cliff face integrity with solutions for long-term stabilization. The stabilization recommendations and plan shall factor in the maximum allowable development limits and restrictions for density, height, as well as weight limits permitted for the subject cliff line development, notwithstanding current zoning ordinances and Guam Land Use Commission approvals. These recommendations will guide the review and permitting of construction for the subject area and adjacent properties.
5.      Re-examine the drainage study to determine if implementing a more conservative design would be in the interest of perspective lot owners and the government of Guam as the foundation for both temporary and permanent drainage system designs.

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