Theme: 06. Petroleum and Heavy Hydrocarbon Site Strategies

Topic Area: 6c. LNAPL Recovery/Remediation Technology Transitions

Formatted Title:

Remediation of a Petroleum Release in an Urban Setting, Successful Closure, and Managing Future Risk

Background/Objectives:

The subject site is located in Metro Manila, Philippines. Light non-aqueous phase liquid (LNAPL) was discovered seeping through basement walls of a large building on 12 July 2010.The building has four levels of underground parking. The level 4 basement is the deepest structure in the area and contains a drainage system on the exterior walls. The maintenance of a “dry” basement by pumping groundwater caused LNAPL to preferentially flow towards the basement. The source of the leak was an adjacent petroleum product pipeline. Approximately 1,800,000 L of LNAPL may have leaked from the pipeline into the soil and groundwater. The extent of mobile LNAPL observed in monitoring wells was approximately 10,000 sqm, and over 1.5 m vertically. When the project started, foreign standards were adopted in the absence of applicable Philippine specific comparison criteria. In 2017, the Philippines released Site Characterization and Remediation Guidelines.

Approach/Activities:

A multi-phase extraction (MPE) system for the remediation of the area affected by the petroleum leak from the pipeline was installed. On 9 May 2012, the MPE system commenced operations by initially receiving extracted groundwater from pumping operations at the basement of the Building. The building basement water was impacted with petroleum hydrocarbon and required treatment via the MPE system prior to discharge into the nearby creek. Additionally, the MPE system began to extract water from 28 of the 42 MPE wells installed within the area containing hydrocarbon impacts.

The MPE system operated continuously (i.e., 24 hours per day, 7 days per week) for over five years until its shutdown in August 2017 when it had reached asymptotic removal rates. The MPE system treated approximately 581,260,000 liters of impacted water and removed approximately 265,000 liters of light non-aqueous phase liquid (LNAPL). Since operations commenced, the MPE system also met the required discharge requirements of the Department of Environment Natural Resources (DENR) and local regulatory requirements for operation and safety. After the MPE system was shut down, a rebound study was performed and was followed by a monitored natural period.

Results/Lessons Learned:

All wells have met the benzene remediation goal of 528 µg/L for construction worker, and by April 2023, all monitoring wells had met the 5 µg/L benzene criteria that was required by the regulators. Due to the lack of a complete exposure pathway, there is no current health risk to receptors (community residents and workers) at the site. A final Environmental Site Assessment for the site is planned which comprises a comprehensive groundwater monitoring wells which includes sampling of the existing 31 monitoring wells at the site.

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Edmund Alan Jr Piquero