Attachment A: Palo Alto 2024 Citywide Greenhouse Gas Emissions Inventory
1.a. Overview of Methodology for Quantifying Greenhouse Gas Emissions Cities represent the single greatest opportunity for tackling climate change, as they are responsible for 70% of global energy-related carbon dioxide emissions, with transportation and buildings among the largest contributors.1 The first step for cities to realize their potential is to identify and measure the sources of their emissions. Best practices for identifying these sources and quantifying emissions are to utilize a standardized GHG inventory.
There are two types of Greenhouse Gas (GHG) emissions inventories:
1.Generation-based GHG inventory – This measurement method helps a community understand its level of emissions based on community energy use. It includes 1) direct consumption of energy, 2) consumption of energy via the electrical grid, and 3) emissions from the treatment/decomposition of waste. This is the industry-accepted methodology for quantifying community GHG emissions, with emissions reported by emission source category.2
2.Consumption-based GHG inventory – This measurement method helps a community understand its level of emissions based on consumption. It offers an alternative, more holistic, approach for quantifying emissions within a community, quantifying consumption of goods and services (including food, clothing, electronic equipment, etc.) by residents of a city, with emissions reported by consumption category.
In 2014, World Resources Institute, C40 Cities Climate Leadership Group (C40) and ICLEI – Local Governments for Sustainability (ICLEI)3 partnered to create a global standard protocol for generation-based GHG inventories. The Global Protocol for Community-Scale GHG Emissions Inventories (GPC) provides a robust framework for accounting and reporting city-wide GHG emissions for a generation-based inventory. The GPC Protocol is the official protocol specified by the Global Covenant of Mayors and defines what emissions must be reported and how. In addition, this inventory draws on methods from the U.S. Community Protocol,4 which provides more detailed methodology specific to the U.S. It seeks to:
Help cities develop a comprehensive GHG inventory to support climate action planning Help cities establish a base year emissions inventory, set reduction targets, and track their performance
Ensure consistent and transparent measurement and reporting of GHG emissions between cities, following internationally recognized GHG accounting and reporting principles
1 See UN Environment Programme, ”Cities and Climate Change,” https://www.unep.org/explore-topics/resource- efficiency/what-we-do/cities/cities-and-climate-change
2 There are two reporting frameworks commonly used by cities: the U.S. Community Protocol and the Global Protocol for Communities (GPC). Palo Alto uses the GPC framework. 3 Formerly the International Council for Local Environmental Initiatives, renamed in 2003 to ICLEI – Local Governments for Sustainability.
4 U.S. Community Protocol; https://icleiusa.org/us-community-protocol/
Enable city inventories to be aggregated at subnational and national levels Demonstrate the important role that cities play in tackling climate change, and facilitate insight through benchmarking – and aggregation – of comparable data Palo Alto’s first generation-based citywide inventory was completed for 2005 and then extrapolated for 1990 (the baseline year). Beginning in 2010, new citywide GHG inventories were completed annually, enabling Palo Alto to track progress over time.
The 2024 Palo Alto Citywide GHG inventory, completed by Rincon Consultants, follows the calculation and reporting standards outlined in the GPC BASIC reporting level.9 Inventory calculations were performed using Rincon’s GHG Inventory tool and uploaded into ClearPath
2.0,10 a software platform designed for creating generation-based GHG inventories.
GHG emissions from community activities are classified into three main sectors:
•Stationary Energy (e.g., building electricity consumption, fugitive natural gas emissions) •Transportation (e.g., on-road passenger vehicles, off-road equipment) •Waste (e.g., solid waste disposal, wastewater treatment and discharge) Activities taking place within a city can generate GHG emissions that occur inside the city boundary as well as outside the city boundary. To distinguish among them, the GPC groups emissions into three categories based on where they occur:
Scope 1: GHG emissions from sources located within the city boundary, such as stationary fuel consumption.
Scope 2: GHG emissions occurring due to the use of grid-supplied electricity, heat, steam, and/or cooling within the city boundary.
Scope 3: All other GHG emissions that occur outside the city boundary as a result of activities taking place within the city boundary.
This inventory follows the city-inducted framework in the GPC protocol, which totals GHG emissions attributable to activities taking place within the geographic boundary of the city.11 Under the Basic reporting level as defined by the GPC protocol, the inventory requirements cover scope 1 and scope 2 emissions from stationary energy and transportation, as well as all emissions resulting from waste generating within the city boundary. While the 2024 Inventory follows GPC BASIC reporting standards and aligns with previous GHG emissions inventories, minor updates to calculation methodologies were included in the 2024 Inventory and previous inventories following the GPC protocol were corrected as well. Of note, the 1990 Inventory was updated to follow GPC BASIC reporting standards and align with GHG emissions inventories from 2019 through 2024. Previously excluded emissions sources were added, including: Airport Emissions, Off-Road Vehicles and Equipment, Caltrain Commuter Rail, Composting, Palo Alto Landfill Gas Flaring, and Wastewater Biosolid Treatment. 9 GPC Executive Summary; https://ghgprotocol.org/sites/default/files/2022-12/GPC_Executive_Summary_1.pdf 10 ClearPath 2.0 tool; https://icleiusa.org/clearpath-2/ 11 GPC Protocol; https://ghgprotocol.org/sites/default/files/standards/GHGP_GPC_0.pdf
The City did not complete a consumption-based GHG inventory. The California Air Resources Board (CARB) has been tasked with developing an implementation framework and accounting to track consumption-based emissions over time.15 In particular, this framework needs to address how to account for the embodied emissions in the food, goods, and services the community purchases not covered by generation-based GHG inventories.
1.b. Palo Alto’s 2024 GHG Emissions
In 2024, Palo Alto emitted an estimated 397,791 metric tons (MT) of carbon dioxide equivalent (CO2e) from the residential, commercial, industrial, transportation, waste, water, and municipal sectors. In comparison to the 1990 base year emissions (which have increased to 798,868 MT from the previously calculated 780,119 MT due to corrections in methodology and additions of excluded emissions sources), these emissions represent a 50.2% decrease in total community emissions, despite a population increase of 22% during that same period. Emissions in 2024 equated to 5.9 MT per capita. The California Air Resource Board’s 2017 Scoping Plan Update recommends a goal for local governments of 6 MT CO2e per capita by 2030 and 2 MT CO2e per capita by 2050.8 In order to achieve 80 x 30, Citywide GHG Emissions need to be at 160,000 MT CO2e (corrected from the previous target of 156,024 MT CO2e).
Of the GHG emissions reductions to date, 46.4% came from providing carbon free for the City’s electricity portfolio, 23.4% from declines in transportation emissions, 16.7% from reduction in natural gas (methane) consumption, 11.5% from declines in solid waste emissions, and 1.9% from declines in wastewater-related emissions.
For citywide GHG emission sources in 2024, 64.1% of GHG emissions were from Transportation and Mobile Sources, 31.9% from Natural Gas (Methane) Use, and the remainder are from other sources. A comparison of 1990 and 2019 through 2024 Citywide GHG emissions is shown in Figure 1. The full comparison between the inventories can be found in Attachment B Historical Comparison of Citywide GHG Emissions by Sector.
Total GHG emissions steadily decreased between 1990 and 2021. However, emissions increased between 2021 and 2022 and slightly increased between 2022 and 2023. The main driver of the increase in 2022 was On-Road Transportation, in part due to the shift away from pandemic- level (reduced) driving frequency, returning to the office after working from home, and economic recovery. These effects likely continued into 2023 as employers continued to change hybrid work policies and economic and travel activities continued to shift.
GHG emissions decreased by 4% between 2023 and 2024. This decrease was primarily driven by reductions in Natural Gas (Methane) Use: residential natural gas GHG emissions decreased by
14.2%, commercial by 10.9%, and industrial by 20.1% since 2023. 15 Executive Department State of California. (2019). Executive Order B-55-18 to Achieve Carbon Neutrality. https://www.ca.gov/archive/gov39/wp-content/uploads/2018/09/9.10.18-Executive-Order.pdf.
Figure 1: Palo Alto Citywide Greenhouse Gas Emissions by Sector, 1990 and 2019 - 2024 As shown in Figure 2, the two largest categories of emissions are Transportation and Mobile Sources (including On-Road Transportation, Airport Emissions, Off-Road Vehicles and Equipment, and Caltrain Commuter Rail) and Natural Gas (Methane) Use (including Residential, Commercial, and Industrial).
Transportation and Mobile Sources include emissions from private, commercial, and fleet vehicles driven within the City’s geographical boundaries, as well as the emissions from public transit vehicles and the City-owned fleet. Off-Road Vehicles and Equipment include airport ground support, construction and mining, industrial, light commercial, portable equipment, and transportation refrigeration units.
Natural Gas (Methane) Use includes emissions that result from natural gas (methane) consumption in both private and public sector buildings and facilities, and residential, commercial, and industrial sources. Fugitive emissions related to natural gas (methane) consumption are calculated separately and are discussed in Section 1.d. The City’s electricity supply has been carbon free since 2013, when the City Council approved a Carbon Neutral Electric Resource Plan, committing Palo Alto to pursuing only carbon-neutral electric resources and effectively eliminating all GHG emissions from the City's electric portfolio.
Figure 2: 2024 Palo Alto Citywide Greenhouse Gas Emissions by Sector
1.c. Transportation and Mobile Sources
In 2024, Transportation and Mobile Sources accounted for 64.1% of total citywide GHG emissions in Palo Alto. GHG emissions from Transportation and Mobile Sources are estimated to have increased slightly (by less than 1%) between 2023 and 2024 but remain 27% lower than 1990 transportation and mobile emissions. Within Transportation and Mobile Sources, On-Road Transportation increased slightly (less than half a percent). However, this estimate is preliminary due to lack of data. Vehicle miles traveled (VMT) data for 2024 were not yet available when the 2024 GHG inventory was prepared. City staff and external experts calculated a preliminary estimate of 2024 VMT by scaling 2023 per capita VMT based on 2024 population for passenger vehicles and service population for commercial vehicles and buses. This estimate reflects demographic growth and may not capture actual VMT trends. The largest increase between 2023 and 2024 was from Airport Emissions, which increased 22.4% from 2023. The largest increase from 1990 was from Off-Road Vehicles and Equipment, which increased 173%.
As shown in Table 2, transportation and mobile sources consist of:
On-Road Transportation – This includes all daily vehicular trips made entirely within the Palo Alto city limits (in-boundary trips), one-half of daily vehicular trips with an origin within Palo Alto city limits and a destination outside of Palo Alto city limits (outbound trips; this assumes that Palo Alto shares half the responsibility for trips traveling from other jurisdictions), and one-half of daily vehicular trips with an origin outside Palo Alto
city limits and a destination within Palo Alto city limits (inbound trips; this assumes that Palo Alto shares the responsibility of trips traveling to other jurisdictions). Vehicular trips through Palo Alto (such as commuters on Highway 101) are not included because Palo Alto cannot solely implement policies that influence the trip-making behavior.
Rather, through trips are assigned to other jurisdictions that can influence either the origin or destination side of the trip-making behavior. Airport Emissions – This includes emissions from take-offs and landings from trips that start and end at Palo Alto Airport. This includes emergency services helicopters, sightseeing helicopters, and training flights. Flights that take-off from Palo Alto Airport but land elsewhere, and flights that land in Palo Alto Airport but take-off from elsewhere are not included per GPC Basic Protocol.
Off-Road Vehicles and Equipment - This includes airport ground support (based on take- offs and landings), construction and mining, industrial (based on employment data), light commercial (based on employment data), portable equipment, and transportation refrigeration units (based on service population).
Caltrain Commuter Rail – This includes emissions from Caltrain travel within Palo Alto.
Table 2: Transportation and Mobile Sources GHG Emissions by Subsector (MT CO2e) Subsector 1990 2019 2020 2021 2022 2023 2024
% of
Total
2024
GHG
On-Road
Transportation 331,840 293,413 217,279 185,925 221,923 225,387 226,019 64.1% Airport
Emissions 3,096 2,192 1,664 2,641 1,837 1,935 2,369 0.6% Off-road
Vehicles 7,431 14,634 15,029 18,961 20,191 19,129 20,287 5.1% Caltrain
Commuter Rail 6,390 4,842 4,552 3,876 7,272 6,377 6,331 1.6% Total MT CO2e 348,757 315,081 238,523 211,403 251,223 252,828 255,006 61.2% Note: Percentages and MT CO2e may not add to the total due to rounding The main driver of GHG emissions from Transportation and Mobile sources is fuel combustion from internal combustion engine (ICE) vehicles, specifically passenger vehicles, commercial vehicles, and buses (69%, 18%, and 2% of all transportation GHG emissions, respectively). Since electricity in the City is carbon-neutral, there are no GHG emissions attributed to passenger, commercial, or bus EVs.
The 2024 inventory utilized vehicles miles traveled (VMT) data from Google’s Environmental Insights Explorer (EIE) and VMT-weighted emission factors from the California Air Resources
(CARB) Emission FACtor (EMFAC) model17 to estimate GHG emissions from all passenger, commercial, and bus ICE vehicles. Because 2024 VMT data is not yet available from Google EIE, City staff and external experts calculated a preliminary estimate of 2024 VMT by scaling 2023 per capita VMT based on 2024 population for passenger vehicles and service population for commercial vehicles and buses. When the Google EIE data becomes available, the City will update 2024 VMT accordingly. In 2023, 46% of VMT was from inbound trips, 45% from outbound trips, and 9% from in-boundary trips.
To determine the EV share of passenger VMT, data from CEC’s Zero Emissions Vehicle (ZEV) Statistics database was pulled for the City’s zip codes. Passenger VMT data was then multiplied by the EV share percentage to determine electric VMT (EVMT) of passenger vehicles allocated to the City. All EVMT was then multiplied by a passenger vehicle energy factor, or electricity (kWh) per mile (EPM), generated from CARB’s EMFAC model to determine the total electricity consumption of passenger EVs.
For commercial and bus VMT, Santa Clara County and San Mateo County boundaries were set in CEC’s ZEV Statistics database to determine the average EV share percentage of these vehicle categories.18 Commercial and bus VMT data were then multiplied by their respective EV share percentages to determine EVMT of these vehicle categories.
All electricity consumption from passenger, commercial, and bus EVs were multiplied by the City of Palo Alto Utilities (CPAU) electricity emission factor (zero MT CO2e/kWh) to determine GHG emissions from on-road, EV transportation.
On-road Transportation accounts for approximately 56.8% of Palo Alto’s total emissions, a
31.9% decrease from 1990, but a slight 0.3% increase from 2023. This increase is primarily driven by increased on-road vehicle miles traveled (VMT) in commercial vehicles and buses.
Off-Road Transportation and Equipment accounts for approximately 5.1% of Palo Alto’s total emissions, a 6.1% increase from 2023. GHG emissions from lawn and garden equipment specifically - which are predominantly gasoline-powered equipment - account for less than 1% of total emissions. It is important to note that most of the off-road transportation emissions are based on models at the County level that do not reflect Palo Alto-specific variations. The 2024 inventory sourced Santa Clara County fuel consumption from CARB’s OFFROAD model,19 including airport ground support, construction, mining, industrial, light commercial, portable equipment, and transportation refrigeration units. All attribution factors used to allocate 17 CARB EMFAC v1.0.1.; https://ww2.arb.ca.gov/our-work/programs/msei/on-road-emfac 18 While these percent EV share estimates also come from CEC’s ZEV Statistics database, only county-level data is available for medium- and heavy-duty (i.e., commercial and bus) ZEVs. The average percent EV share for Santa Clara and San Mateo County was used as a proxy for Palo Alto because Palo Alto shares one zip code (94303) with San Mateo, and much I-E/E-I EVMT attributed to Palo Alto is assumed to be between these two counties 19 CARB OFFROAD v1.0.5.; https://arb.ca.gov/emfac/offroad/
countywide fuel consumption to Palo Alto in 2024 remained the same as previous inventories,23 except airport ground support. Attributed fuel consumption from each off-road sector was then multiplied by its respective GHG emissions factor (MT CO2e/gallon) depending on fuel type (i.e., gasoline, diesel, or natural gas) to estimate GHG emissions.
Airport Emissions account for approximately 0.6% of Palo Alto’s total emissions, a 22.4% increase from 2023, but a 23.5% decrease from 1990.
Caltrain Commuter Rail emissions account for approximately 1.6% of Palo Alto’s total emissions, a 0.7% decrease from 2023 and 0.9% decrease from 1990. For the 2024 Inventory, the most recently available Caltrain ridership data included calendar year 2024 (CY24) total system annual AWR and fiscal year 2025 (FY25) (November and December only) Palo Alto stations’ AWR. In the 2024 Inventory, commuter rail fuel consumption was scaled down and attributed to Palo Alto by dividing the sum of FY25 Palo Alto stations’ AWR by CY22 total system annual AWR. Due to no response from the Peninsula Corridor Joint Power Board, Caltrain commuter rail diesel fuel consumption in the 2024 Inventory uses 2022 diesel fuel consumption from Caltrain’s 2023 Sustainability Report as the most recently available data.24 It is assumed that the total fuel consumption and allocation methodology described above is comparable to Palo Alto’s share of Caltrain commuter rail emissions in 2024. This estimation method results in the highest emissions to remain conservative. Caltrain electrification is a key component of the Caltrain Modernization program,25 with Caltrain electrified in late September 2024. Now that the Caltrain Modernization program is complete, most of the Caltrain commuter rail emissions will be eliminated in future Citywide GHG Emissions Inventories.
1.d Natural Gas (Methane) Use
In 2024, Natural Gas (Methane) Use emissions accounted for 31.9% of total 2024 Citywide GHG emissions in Palo Alto, a 13.2% decrease from 2023 and a 34.5% decrease from 1990.
Residential and commercial natural gas (methane) use contributed nearly equally to GHG emissions in the natural gas sector (44% and 45% of emissions from Natural Gas (Methane) Use, respectively), with a remaining 7% of the emissions attributed to industrial natural gas use. As shown in Table 3, Palo Alto’s total natural gas (methane) consumption in 2024 was 23,781,222 therms. Commercial natural gas (methane) use accounts for 15.0% of total emissions, residential accounts for 14.6% of total emissions, and industrial accounts for 2.4% of total emissions. In 2024, Natural Gas (Methane) Use decreased 10.9% in the commercial sector,
20.1% in the industrial sector and 14.2% in the residential sector compared to 2023. These reductions reflect lower overall natural gas consumption, which can fluctuate based on weather conditions, energy efficiency improvements, and occupant behavior. January 2024 was the warmest January on record, which could account for some of the reductions. Other sources for the reductions could be because residents replaced more gas appliances with electric 23 Attribution factors are based off demographic data such as population, employment, and service population (except for airport ground support).
24 Caltrain 2023 Sustainability Report; https://www.caltrain.com/media/33109 25 Caltrain Modernization Program; https://calmod.org/
appliances. Overall, Natural Gas (Methane) Use emissions remain far below 1990 levels (34.5% decrease).
The City Council unanimously approved Palo Alto’s Carbon Neutral Natural Gas Plan on December 5, 2016. The Natural Gas Plan, implemented on July 1, 2017, achieves carbon neutrality for the gas supply portfolio by 1) purchasing high-quality carbon offsets equivalent to our City and community natural gas (methane) emissions; 2) pursuing efficiency strategies to reduce natural gas (methane) use, and 3) seeking opportunities to fund local offsets that finance actual emissions reductions in Palo Alto and the surrounding region. As a bridging strategy, carbon offsets are being purchased in an amount equal to the GHG emissions caused by natural gas (methane) use within the City. Carbon offsets are not included in this inventory. 1Table 3: Natural Gas (Methane) Consumption by Subsector (Therms) Subsector 2019 2020 2021 2022 2023 2024 % of Total
2024 GHG
Commercial 12,954,768 10,061,842 10,468,041 11,729,819 12,502,216 11,144,038 15.0% Residential 13,565,360 12,952,262 12,756,160 13,037,423 12,686,165 10,884,832 14.6% Industrial 2,707,034 2,253,641 2,294,119 2,372,902 2,193,781 1,752,352 2.4% Total
Therms 28,867,162 25,267,739 25,518,320 27,140,144 27,382,162 23,781,222 31.9% Note: Percentages and Therms may not add to the total due to rounding Natural Gas (Methane) Fugitive Emissions
Natural gas is mainly methane (CH4), some of which escapes during the drilling, extraction, and transportation processes. Such releases are known as fugitive emissions. The primary sources of these emissions may include equipment leaks, evaporation losses, venting, flaring, and accidental releases. Methane is a potent greenhouse gas – approximately 25 times more powerful than carbon dioxide over a 100-year timescale.
In 2024, Natural Gas (Methane) Fugitive Emissions accounted for 1% of total citywide GHG emissions in Palo Alto, a decrease of 13.2% from 2023 and a decrease of 12.5% from 1990. Per the GPC, fugitive emissions from natural gas (methane) are based on overall community consumption and a leakage rate of 0.03%.
As mentioned in Section 1.a., the GPC Basic methodology includes GHG emissions attributable to activities taking place within the geographic boundary of the city. As such, the 2024 GHG inventory does not include a category of emissions that are called “upstream emissions,” which includes emissions from extraction of natural gas (methane) and its transportation across the western United States through California to Palo Alto. Leaks during gas extraction and transportation can be very significant, so the actual impacts of natural gas (methane) use can be much more significant than is represented in a formal Citywide GHG inventory.
1.e. Solid Waste
In 2024, Palo Alto's solid waste diversion rate was 88%, far exceeding the 50% mandate for local jurisdictions. “Diversion” includes all waste prevention, reuse, recycling, and composting activities that “divert” materials from landfills. The City uses the diversion rate to measure progress on waste reduction and resource conservation goals. The diversion rate of 88% is an improvement from the 62% rate in 2007, 81% rate in 2019, and 84% rate in 2022 and 2021.
However, it is a decrease from the 91% rate in 2022 and 2023 due to increased waste landfilled in 2024. As part of the 2016 S/CAP Framework, the City Council adopted a goal of 95% diversion of materials from landfills by 2030.29
Solid Waste emissions accounted for 2.3% of total 2024 citywide GHG emissions in Palo Alto, a
6.4% decrease from 2023 and an 83.4% decrease from 1990. As shown in Table 4, the 2024 inventory included emissions from solid waste generated in the City but treated biologically outside of the city. This includes composting emissions at the Zero Waste Energy Development Company’s (ZWED) Dry Fermentation Anaerobic Digestion (AD) Facility in San Jose, CA, composting emissions at the Synagro El Nido Central Valley Composting (CVC) facility in Dos Palos, as well as Palo Alto Landfill Gas Flaring Emissions. 2Table 4: Solid Waste GHG Emissions by Subsector (MT CO2e) Subsector 1990 2019 2020 2021 2022 2023 2024
% of
Total
2024
GHG
Organic Waste
Composting 0 731 1,154 843 1,142 1,242 1,308 0.3%
Landfill Gas
Flaring 226 281 316 237 233 186 176 0%
Landfill Gas
Fugitive 24,325 n/a30 n/a n/a n/a n/a n/a n/a
Landfill
Methane 30,732 5,519 4,721 5,029 5,297 6,702 7,715 1.9% Total MT CO2e 55,283 6,531 6,191 6,110 6,672 8,130 9,199 2.3% Note: Percentages and MT CO2e may not add to the total due to rounding Solid Waste emissions increased slightly in 2024, with landfill methane emissions increasing by
15.1% compared to 2023 but remaining 74.9% lower than 1990 levels. Organic Waste Composting emissions also increased slightly (5.3%) compared to 2023, continuing the trend driven by state-mandated organic waste diversion programs such as SB 1383. 29 Sustainability and Climate Action Plan Framework, November 2016; https://www.cityofpaloalto.org/civicax/filebank/documents/64814 30 Not included because the Palo Alto landfill was closed
Waste emissions result from organic material decomposing in the anaerobic conditions present in a landfill and releasing methane (CH4) – a greenhouse gas much more potent than CO2.
Organic materials (e.g., paper, plant debris, food waste, etc.) generate methane within the anaerobic environment of a landfill while non-organic materials (e.g., metal, glass, etc.) do not.
This is why diverting waste from landfills is so important. In 2016, Governor Brown signed Senate Bill 1383 (SB 1383) to reduce GHG emissions from a variety of short-lived climate pollutants, including methane from organic materials disposed in landfills. SB 1383 is the largest and most prescriptive waste management legislation in California since the California Integrated Waste Management Act of 1989 (AB 939) and aspires to reduce statewide disposal of organic waste 75% by 2025 and recover at least 20% of the currently disposed edible food for human consumption by 2025. Palo Alto is in compliance with many of SB 1383 requirements due to the City’s progressive zero waste programs and initiatives and is continuing to take initiatives to further reduce organic materials from being disposed in landfills.
1.f. Wastewater Treatment
As shown in Table 5, in 2024 the Regional Water Quality Control Plant (RWQCP) wastewater- related emissions accounted for 0.6% of total 2024 GHG emissions in Palo Alto, a 2.2% decrease from 2023 and a 76.2% decrease from 1990. RWQCP GHG emissions originate from electricity, natural gas (methane), and landfill gas usage required to treat the wastewater, as well as GHGs that are emitted from the wastewater itself either during treatment or after (effluent). The nitrogen within wastewater is subject to transformation to nitrous oxide at varying stages in the treatment process as well as after it has been discharged to a receiving water (effluent). These emissions are included in the RWQCP totals.
3Table 5: Wastewater-Related GHG Emissions by Subsector (MT CO2e) Subsector 1990 2019 2020 2021 2022 2023 2024
% of Total
2024
GHG
Wastewater
Biosolid
Treatment33
1,606 403 0 0 0 0 0 0%
Wastewater
Treatment 380 381 346 86 82 85 0%
Wastewater
Effluent
8,504
1,005 1,007 915 2,344 2,163 2,077 0.5%
Wastewater
Sludge
Composting
409 469 412 185 218 247 0.1%
Total MT CO2e 10,110 2,197 1,857 1,674 2,615 2,463 2,409 0.6% Note: Percentages and MT CO2e may not add to the total due to rounding 33 Sludge incineration
As shown in Figure 3, RWQCP operations achieved significant GHG reductions in 2019 when the facility’s sewage sludge incinerators were replaced with the more environmentally friendly Sludge Dewatering and Truck Loadout Facility. Previously, RWQCP incinerators were the City’s largest facility-related GHG source. The updated biosolids treatment process has and will continue to reduce GHG emissions by approximately 15,000 MT of CO2e per year when compared to the emissions from incineration. This approximates the carbon dioxide emissions of 3,000 passenger cars. The dewatered sludge is used as agricultural soil supplements.
Figure 3: Regional Water Quality Control Plant Historical Total Greenhouse Gas Emissions