G.R. No. 171947-48 - Metropolitan Manila Development Authority vs. Concerned Residents of Manila Bay

Petitioners: Metropolitan Manila Development Authority (MMDA), Department of Environment and Natural Resources (DENR), Department of Education (DepEd), Department of Health (DOH), Department of Agriculture (DA), Department of Public Works and Highways (DPWH), Department of Budget and Management (DBM), Philippine Coast Guard (PCG), Philippine National Police–Maritime Group (PNP-MG), Metropolitan Waterworks and Sewerage System (MWSS), Local Water Utilities Administration (LWUA), Philippine Ports Authority (PPA).
Respondents: Concerned Residents of Manila Bay, represented by individual environmental advocates.
January 29, 1999—Complaint filed in RTC Imus, Cavite (Civil Case No. 1851-99) for cleanup, rehabilitation, protection of Manila Bay.

Manila Bay water quality fell below “SB” classification under PD 1152 (Philippine Environment Code).
Pollution caused by cumulative acts of omission/commission of government agencies.
Violations alleged: constitutional right to life, health, balanced ecology; PD 1152; PD 984 (Pollution Control Law); PD 1067 (Water Code); PD 856 (Sanitation Code); PD 825 (Illegal Disposal of Wastes Decree); PD 979 (Marine Pollution Law); EO 192; RA 6969 (Toxic and Hazardous Wastes Law); Civil Code nuisance provisions; trust doctrine; international law.
Prayer: joint and several liability for petitioners; order to submit a consolidated, concrete plan to restore Manila Bay to SB standards fit for swimming and other contact recreation.

Summary hearing at Manila Yacht Club and ocular inspection of Manila Bay.
Evidence: DENR water samples (fecal coliform 50,000–80,000 MPN/ml vs 200 MPN/100 ml standard); MWSS Manila Second Sewerage Project; PPA Linis Dagat project; PPA circulars on ship-generated waste.
RTC Decision (September 13, 2002) ordering agencies, jointly and solidarily, to clean up and rehabilitate Manila Bay and restore SB classification, with DENR as lead agency and specific tasks for each petitioner.

MWSS, LWUA, PPA appealed to the Court of Appeals (CA-G.R. CV No. 76528).
Other agencies filed a Rule 45 petition directly to the Supreme Court, consolidated by the Court in CA-G.R. SP No. 74944.
CA Decision (September 28, 2005) affirmed the RTC in toto, holding that cleanup orders fell within agencies’ statutory functions.

Petitioners argued: Sections 17 and 20 of PD 1152 apply only to specific pollution incidents; cleanup is a discretionary, not ministerial, duty.
Oral arguments were heard on August 12, 2008.

Do Sections 17 and 20 of PD 1152 relate only to cleanup of specific pollution incidents?
Or do they impose a general duty to upgrade and clean water bodies whenever quality deteriorates?

Can petitioners’ cleanup and rehabilitation duties be compelled by writ of mandamus?
Are those duties ministerial or discretionary?