GS4GG PAA M400-XX — Draft Methodology for Public Consultation
🔗 Read the consultation on Gold Standard →The Safe Sanitation Services (SASS) methodology quantifies GHG emission reductions from activities that collect, transport, and safely treat human faecal waste (faecal sludge and septage) that would otherwise decompose anaerobically in unmanaged containment or as open defecation.
The methodology uses a standardised baseline approach with four recognised baseline pathways:
| Baseline Pathway | MCF | Description |
|---|---|---|
| Open Defecation (Suppressed Demand) | 0.5 cap | No facility; uses suppressed-demand counterfactual (basic pit latrine) |
| Unimproved Pit Latrine (dry / low water table) | 0.1 | Dry pit, minimal anaerobic activity |
| Unimproved Pit Latrine (wet / high water table) | 0.7 | Saturated conditions, significant CH₄ generation |
| Unmanaged Septic Tank / Open Trench | 0.5 | Sealed tank never emptied, or open trench/drain |
Demonstrated via a three-pronged test (Section 6):
The methodology models sanitation as a complete service chain. Credits are only generated when all links are verified:
The Operational Fraction (OFy) and Collection Compliance Factor (CCy) ensure that only waste actually collected and safely treated is credited.
Emission reductions are calculated as:
Where:
| Parameter | Description | Source |
|---|---|---|
| Bo (m³ CH₄/kg BOD) | Max methane-producing capacity | IPCC 2019 default: 0.6 |
| BOD (kg/person/day) | Per-capita organic load | IPCC 2019 by region (0.037–0.085) |
| MCFBAU,i | Methane correction factor per baseline pathway | IPCC defaults (0.1–0.7) |
| UAF | Uncertainty adjustment factor | Default 0.66 (applied to unadjusted baseline) |
| GWPCH4 | Global warming potential of biogenic methane | AR5: 28 |
Accounts for all GHG emissions from operating the sanitation service:
Covers embodied (life-cycle) emissions of equipment and infrastructure, calculated as:
Default cradle-to-gate factors are provided in Annex 2 (e.g., HDPE: ~2.5 kg CO2e/kg, steel: ~1.5 kg CO2e/kg). A 5% market-leakage deduction (LEmarket) applies to streams where mass-balance chain-of-custody cannot be demonstrated.
Multiple layers of conservativeness are built in: UAF (0.66), suppressed-demand cap, operational fraction, collection compliance, 5% market leakage, and the DAF.
A back-of-envelope estimator for a SASS project's annual credits, following the methodology's structure: net emission reductions = (baseline methane avoided − activity emissions − leakage), then scaled by the operational, collection-compliance, and ambition factors. All values are editable and the results update instantly. This is a planning sketch, not a registration-grade calculation.
Enter the population served in each baseline condition and its Methane Correction Factor (MCF). For open defecation, suppressed-demand rules cap the MCF at 0.5.
| Baseline pathway | People served | MCF |
|---|---|---|
| Open defecation (suppressed demand, cap 0.5) | ||
| Unimproved pit latrine — wet / high water table | ||
| Unimproved pit latrine — dry / low water table |
Emissions from running the service. Diesel is converted at 2.68 kg CO₂e per litre; electricity uses your grid factor.
The pre-loaded project serves 20,000 people: 8,000 transitioning from open defecation (MCF capped at 0.5), 7,000 from wet pit latrines (MCF 0.7), and 5,000 from dry pit latrines (MCF 0.1).
(8,000 × 0.5) + (7,000 × 0.7) + (5,000 × 0.1) = 4,000 + 4,900 + 500 = 9,400 effective person-units.
9,400 × 0.037 kg/p/d × 0.6 kg CH₄/kg BOD × 365 d × 28 GWP = ≈ 2,133 tCO₂e of raw baseline methane. Applying the UAF (× 0.66) gives BE ≈ 1,408 tCO₂e.
Activity emissions (transport + generator + electricity + process) ≈ 61 tCO₂e; leakage (8 embodied + 5% market) ≈ 78 tCO₂e. Net ≈ 1,269 tCO₂e.
1,269 × 0.90 × 0.95 × 0.92 ≈ 998 credits/yr, worth ≈ $8,000/yr at $8/tCO₂e.
Simplifications: Bo is treated as a mass yield (kg CH₄/kg BOD) per IPCC convention; suppressed-demand caps must be entered manually in the MCF column; the 5% ADJSD suppressed-demand deduction and per-batch product-safety gate are not separately modelled. Use for scoping only.
| ID | Parameter | Frequency | Method |
|---|---|---|---|
| SASS 6 | Served population (Pi,y) | Continuous | 100% census of enrolled units via UIDs |
| SASS 7 | Monitoring days (Dy) | Annual | Commissioning dates & downtime logs |
| SASS 8 | Operational Fraction (OFy) | Annual | Statistically representative field survey |
| SASS 9 | Collection Compliance (CCy) | Continuous | Mass-balance chain-of-custody assessment |
| SASS 10 | Equity coverage indicator | Each period | From activity database & benefit-sharing plan |
| SASS 11 | Product safety / discharge compliance | Per batch/quarterly | Lab testing (E. coli, helminth eggs, heavy metals) |
A binary gate applies: if a batch of treated output (compost, biochar, effluent) fails pathogen limits (national standards or WHO), emission reductions for that batch are forfeit (ERy = 0 for that fraction). This protects public health outcomes.
Developers must track the fraction of vulnerable or hard-to-reach households served, supporting the SDG reporting and equitable-sharing principle.
SASS is classified as an avoidance activity: the methane was never generated, so physical reversal is structurally impossible. Therefore:
5 years, renewable twice (max 15 years). At each renewal:
The methodology supports both standalone activities and PoA structures:
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The methodology caps the MCF for suppressed-demand (open defecation) populations at 0.5 and applies a further 5% deduction (ADJSD). This is based on the assumption that the counterfactual is a basic pit latrine. For many MWA member contexts in Sub-Saharan Africa, this cap significantly reduces creditable emissions. Consider whether the 0.5 cap is overly conservative for wet/tropical environments where pit latrines with high water tables (MCF = 0.7) would be the realistic counterfactual.
The 0.66 UAF is applied to the entire unadjusted baseline. Combined with the suppressed-demand cap, MCF conservativeness, the 5% SD deduction, and the DAF, the cumulative conservativeness may reduce creditable volumes to the point where projects become financially unviable. The methodology should clarify how these multiple layers interact and whether double-discounting occurs.
The methodology requires a Baseline Scenario Survey (BSS) at 90/10 precision to determine pathway proportions. For organisations operating across diverse geographies (e.g., multiple cities or countries), conducting a compliant BSS for each area is resource-intensive. Clarity is needed on whether existing sector studies (e.g., JMP data, government WASH surveys) can supplement or replace primary BSS data collection.
CCy requires a mass-balance chain-of-custody assessment reconciling volumes collected at containment against volumes received at treatment. This is operationally challenging for many FSM service providers, particularly those using manual emptying or operating in informal settlements. The alternative — a flat 5% market-leakage deduction — may be more practical, but the methodology positions CCy as the primary mechanism.
OFy must be determined via a statistically representative field survey confirming that containment units are active, functional, and in regular use. Units that are abandoned, destroyed, or where users have reverted to open defecation are counted as non-operational (OF = 0). The sample frame must include all distributed units on record, not just active users, and units that cannot be located are conservatively coded as non-operational.
If a treated batch fails pathogen limits, the entire batch's emission reductions are forfeit (ERy = 0 for that fraction). This binary gate is an important safeguard, but raises questions about proportionality: a minor exceedance on one parameter results in the same penalty as a major failure. It also means the methane avoidance (which did occur) goes uncredited because of a downstream treatment quality issue.
The IPCC 2019 default BOD values are applied by broad region (Africa = 0.037 kg/person/day). This relatively low value may underestimate organic load in some sub-regions. The methodology allows developers to use measured values but does not specify the protocol for doing so. For projects seeking to demonstrate higher-than-default BOD, clearer guidance on acceptable measurement methodologies would be beneficial.
At crediting period renewal, if a state-funded municipal sewer network has expanded into the activity boundary providing safely managed waterborne sanitation, those households' baselines shift to zero-methane and credits stop. This is appropriate in principle, but the trigger definition could be problematic: many municipal sewer expansions in LMICs are partial, non-functional, or lack treatment. Clarity is needed on what constitutes "reasonable access to a functional municipal sewer system."
Pooled sampling across VPAs is limited to 10 unless homogeneity is demonstrated and validated. For large-scale service providers operating uniform CBS systems across 20+ cities, this cap could be unnecessarily restrictive and increase MRV costs. The requirement to demonstrate homogeneity across technology type, geography, and system age is reasonable, but the hard cap of 10 seems arbitrary.
Annex 2 provides indicative cradle-to-gate embodied-carbon factors from the ICE database (UK-centric). For projects manufacturing containers or infrastructure in LMICs (e.g., HDPE containers made in East Africa), actual embodied carbon may differ. The methodology allows project-specific EPDs, but obtaining these is expensive. Consider whether the UK-based defaults are appropriate for projects operating in different manufacturing contexts.
The DAF is applied per GS4GG Tool 05 to encourage ambition over time. While the concept is sound, sanitation services already face thin margins. The DAF compounds with the UAF, SD cap, and other deductions. The methodology should clarify whether any of these conservativeness measures are considered sufficient to satisfy the ambition function, potentially allowing a reduced or waived DAF for sanitation.
Annex 1, which should contain the detailed monitoring schedule and requirements, is listed as "To be added in the final version." This is a significant gap in the public consultation draft, as it prevents stakeholders from reviewing the practical implementation timeline for monitoring activities.
The additionality test requires demonstrating that safe sanitation is "not yet the norm" in the target area. However, the methodology does not define quantitative thresholds for common practice. In rapidly urbanising LMIC contexts, some form of pit latrine emptying may be common, but safe treatment of collected sludge is extremely rare. The methodology should distinguish between the prevalence of emptying services (which may be common but unsafe) and truly safely managed sanitation chains (which are almost universally non-common practice in target geographies).
At crediting period renewal, developers must demonstrate "ongoing financial need" for carbon finance. The methodology does not define how OFN is assessed or what level of financial dependency qualifies. For sanitation services that have grown partly due to carbon revenue, does their improved financial position at renewal risk disqualifying them — even though withdrawing carbon finance would collapse the service?
Plain-language definitions of the technical terms, acronyms, and equation symbols used throughout this methodology and review. Carbon-finance and sanitation work both carry a lot of specialist shorthand; this page is meant to make the rest of the site readable without prior background.
| Term | Plain-language meaning |
|---|---|
| MCF Methane Correction Factor | The fraction of the organic matter in a sanitation system that breaks down without oxygen (anaerobically) and therefore makes methane. It runs from about 0.1 (a dry pit latrine, little methane) to 0.7 (a wet pit with a high water table, lots of methane). A higher MCF means a higher methane baseline and more credits. It is the single most influential, and most debated, parameter in the methodology. |
| Bo Max methane-producing capacity | The most methane that can theoretically be produced per kilogram of organic load. IPCC default: 0.6 m³ CH₄ per kg BOD. |
| BOD Biochemical Oxygen Demand | A standard measure of how much organic material is in waste (here, kilograms per person per day). More BOD means more potential methane. |
| UAF Uncertainty Adjustment Factor | A built-in conservativeness multiplier (default 0.66) applied to the whole baseline to account for estimation uncertainty. In effect it removes about 34% of the calculated baseline before crediting. |
| DAF Downward Adjustment Factor | A Gold Standard "ambition" discount (set via GS4GG Tool 05) that further reduces the credited amount so that crediting tightens over time. A recurring concern in the feedback is that the DAF stacks on top of the UAF and other deductions. |
| GWP Global Warming Potential | How much a gas warms the planet compared with the same mass of CO₂ over a set period. Used to convert methane into "CO₂-equivalent." |
| AR5 | The IPCC's Fifth Assessment Report, the source used here for methane's 100-year GWP of 28. |
| CH₄ / N₂O / CO₂e | Methane / nitrous oxide / carbon-dioxide-equivalent (a common unit that expresses any greenhouse gas in terms of the equivalent warming from CO₂). |
| BE / AE / LE / ER | The four building blocks of the credit calculation: BE Baseline Emissions (methane that would have happened), AE Activity Emissions (from running the service, e.g. truck fuel), LE Leakage Emissions (embodied emissions of equipment), and ER Emission Reductions (the credited result: ER = BE − AE − LE, then adjusted down). The subscript "y" just means "in year y." |
| OFy Operational Fraction | The share of installed toilets/containment units that are actually working and in use, confirmed by field survey. Abandoned or missing units count as zero. |
| CCy Collection Compliance Factor | The share of waste that is genuinely collected and delivered to safe treatment, proven by a "mass balance" (what went in vs. what arrived). Only waste that is verifiably treated earns credits. |
| Suppressed Demand (SD) | A crediting principle for very poor populations: instead of using their current near-zero situation (e.g. open defecation) as the comparison, you use the basic service they would realistically use (a simple pit latrine). This avoids penalising projects that serve the poorest. |
| ADJSD | The extra 5% conservativeness deduction applied specifically to suppressed-demand baselines, on top of the MCF cap. |
| Pi,y / Dy | Served population in baseline pathway i during year y / the number of monitored days in the year. |
| Term | Plain-language meaning |
|---|---|
| Gold Standard / GS4GG | A leading voluntary carbon-credit certification body. "GS4GG" is its current rulebook, the Gold Standard for the Global Goals, which ties credits to broader Sustainable Development Goals. |
| GS4GG PAA M400-XX | The catalogue/reference code identifying this particular draft methodology within the Gold Standard document set (the "XX" is a placeholder pending finalisation). |
| Additionality | Proof that the emission reductions would not have happened anyway, i.e. the activity genuinely needs carbon finance to exist. |
| Baseline / counterfactual | The "what would have happened without the project" scenario against which reductions are measured. |
| Leakage | Emissions that the project causes outside its own boundary (here, mainly the embodied carbon of manufacturing equipment and containers). |
| Avoidance methodology | A method that credits emissions prevented (methane never made) rather than carbon physically removed from the air. Because the methane never existed, it cannot be "re-released," so no reversal buffer is needed. |
| Buffer pool / reversal | In removal projects, a shared reserve of credits held back in case stored carbon is later lost (a "reversal"). Not required here, since avoidance cannot reverse. |
| Crediting period | The window during which a project can issue credits, here 5 years, renewable twice (15 years maximum). |
| OFN Ongoing Financial Need | A test at each renewal requiring the project to show it still depends on carbon revenue to keep operating. |
| CDM Clean Development Mechanism | The UN's original (Kyoto Protocol) carbon market. Its calculation "Tools" and methodologies are reused by SASS for activity and leakage emissions. |
| ACM0014 / TOOL05 / TOOL13 / TOOL14 | Specific CDM consolidated methodologies and tools that SASS borrows for calculating emissions from wastewater treatment, project energy use, composting, and biogas systems respectively. |
| IPCC | Intergovernmental Panel on Climate Change, the UN scientific body whose default values (Bo, BOD, MCF, GWP) underpin the calculations. |
| DW Precedent / TPDDTEC | "DW" is the Gold Standard Safe Drinking Water methodology (technical name TPDDTEC). The MWA TWG already filed consensus feedback on it, and several of those arguments are flagged here as directly relevant to SASS. |
| WQR Water Quality Risk | A penalty concept from the drinking-water methodology (cited as a parallel), where water-quality failures forfeit credits. |
| Term | Plain-language meaning |
|---|---|
| SASS Safe Sanitation Services | The name of this Gold Standard methodology: crediting the safe collection, transport, and treatment of human waste. |
| WASH | Water, Sanitation and Hygiene, the umbrella term for the sector. |
| FSM Faecal Sludge Management | Emptying, transporting, and treating the sludge that builds up in pit latrines and septic tanks (as opposed to piped sewers). |
| CBS Container-Based Sanitation | Toilets that collect waste in sealed, swappable containers, which are regularly picked up and taken to a treatment site. |
| Faecal sludge / septage | The accumulated waste inside pits and septic tanks; "septage" specifically refers to what is pumped out of a septic tank. |
| Open defecation | Defecating in fields, bushes, or water bodies rather than using a toilet, the lowest rung of the sanitation ladder. |
| Pit latrine (dry vs. wet) | A basic toilet over a pit. A "wet" pit (high water table or flooding) stays saturated and produces far more methane than a "dry" pit, which is why the two have very different MCF values. |
| Service chain | The full path waste must travel to count: containment → emptying/collection → transport → safe treatment → reuse/disposal. Credits require every link to be verified. |
| JMP Joint Monitoring Programme | The WHO/UNICEF programme that produces the official global water and sanitation statistics and defines the "safely managed / basic / unimproved" service ladder used as a benchmark. |
| MICS / DHS | Two large, standardised household survey programmes (UNICEF's Multiple Indicator Cluster Surveys and USAID's Demographic and Health Surveys) often used as secondary data on sanitation practices. |
| WHO | World Health Organization, whose pathogen limits are referenced for treated-product safety. |
| LMIC | Low- and Middle-Income Country. |
| SDG | Sustainable Development Goal, the 17 UN global goals; SASS links especially to SDG 6 (water and sanitation). |
| Helminth eggs | Parasitic worm eggs; a standard indicator (alongside E. coli) for whether treated sludge is safe enough to reuse. |
| Term | Plain-language meaning |
|---|---|
| MRV | Monitoring, Reporting and Verification, the system of measuring, documenting, and independently auditing the claimed reductions. |
| PoA Programme of Activities | An umbrella programme that lets many similar small projects be added over time under one registration, instead of registering each separately. |
| VPA | An individual project component added under a PoA. Pooled sampling across VPAs is capped at 10 unless they are shown to be near-identical. |
| CME Coordinating / Managing Entity | The organisation that runs a PoA, maintains the central database, and adds new VPAs. |
| UID Unique Identifier | A unique code assigned to each enrolled toilet/household so it can be tracked and audited. |
| BSS Baseline Scenario Survey | A field survey establishing what mix of baseline sanitation conditions exists in the project area, required at "90/10 precision." |
| 90/10 precision | A sampling-quality standard: 90% confidence with a margin of error no wider than ±10%. |
| Mass balance / chain-of-custody | Reconciling the volume of waste collected against the volume received at treatment, to prove none was dumped along the way. |
| EPD Environmental Product Declaration | A verified, standardised report of a product's life-cycle (embodied) emissions; an alternative to using default factors. |
| ICE database | The Inventory of Carbon and Energy, a UK-based reference set of embodied-carbon factors used here for default equipment emissions. |
| Cradle-to-gate | Life-cycle emissions counted from raw-material extraction up to the point a product leaves the factory. |
| HDPE | High-Density Polyethylene, the durable plastic used for many sanitation containers; its embodied carbon is around 2.5 kg CO₂e per kg. |
| MWA / TWG | Millennium Water Alliance (the coalition behind this review) and its Climate Finance Technical Working Group (the expert group preparing the feedback). |
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