Methane Gas Capture and Electricity Production at Kubratovo Wastewater Treatment Plant, Sofia, Bulgaria
GS-719 ↗ · current registry ID: GS4238
#146of 352 in Biomass#1of 6 in Bulgaria#1183of 1801 in Gold Standard (GS)#47of 115 in AMS-I.C
Audit Analysis
A long-operating methane capture and cogeneration project at a Sofia wastewater treatment plant with inherent permanence (no carbon storage), but the verification record reveals extensive material findings, a requirement for a supplementary audit with a different team, and a contradiction on whether additionality was VVB-verified. The project over-delivers relative to its ex-ante estimate, and the grid emission factor discrepancy appears conservative, but data quality issues across documents undermine confidence in the MRV chain.
Red Flags
- The 2025 verification report states additionality was NOT verified by the VVB, while the 2025 monitoring report states it was — an unresolved contradiction on a core integrity criterion
- The verification report requires a supplementary audit with a new team leader and an entirely different team for the next verification, indicating systemic quality concerns in the verification process
- Grid emission factor differs by 2.5× between the 2025 verification report (0.4 tCO₂/MWh) and the 2023 monitoring report (1.019 tCO₂/MWh), with no documented explanation for the discrepancy
- 18 corrective actions remain open, including missing calibration protocols, absent meter documentation, and inconsistent emission-reduction values between the PDD and calculation sheets
- Leakage justification is contradictory: the verification report says 'quantified' while the monitoring report says 'deemed negligible', yet the deduction is 0% in both
Credit Vintages
| Issued | Retired | Available | ||
|---|---|---|---|---|
| 2014 | 44,975 | 44,764 | 211 | |
| 2015 | 58,912 | 58,838 | 74 | |
| 2016 | 67,825 | 58,113 | 9,712 | |
| 2017 | 78,176 | 32,590 | 45,586 | |
| 2018 | 78,957 | 40,622 | 38,335 | |
| 2019 | 69,702 | 65,631 | 4,071 | |
| 2020 | 75,710 | 74,860 | 850 | |
| 2021 | 72,520 | 52,520 | 20,000 | |
| 2022 | 61,642 | 61,642 | 0 | |
| 2023 | 74,610 | 19,149 | 55,461 | |
| 2024 | 15,595 | 0 | 15,595 | |
| Total | 698,624 | 508,729 | 189,895 |
Risk Indicators
Investment test present but VVB verification unconfirmed per 2025 VR
Methane converted to electricity on-site; no storage or reversal risk
0% deduction; justification contradictory between VR and MR
Project-specific measured baseline; reassessed 2021; not jurisdictional
Grievance mechanism and benefit sharing documented; FPIC not stated
CORSIA and CCP status not stated in extracted record
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