Attachment 1
Community Greenhouse Gas Emissions Inventory Methodology
OVERALL METHODOLOGY
Mountain View’s communitywide greenhouse gas (GHG) emissions inventories are prepared using the U.S. Community Protocol for Accounting and Reporting of Greenhouse Gas Emissions (the Protocol), a national standard developed by ICLEI —Local Governments for Sustainability.
The Protocol provides reporting requ irements and accounting guidance for local gover nments to quantify and report communitywide GHG emissions.
The inventory includes emissions from five sectors: energy use, transportation, waste, water and wastewater, and off -road mobile sources. Emissions are estimated from available energy, transportation, waste, and water data. Where measured City -level data is not available, standardized GHG accounting methodologies are used to estimate emissions at the County level and adjust the results to a City scale. Emissions are reported in metric tons of carbon dioxide equivalent (MT CO₂e), which allows emissions from different greenhouse gases to be expressed using a common unit and facilitates the quantification and comparison of total GHG emissions across the inventory.
Inventories are estimates and are subject to change as methodologies and available information evolve. Changes in global warming potentials (values used to compare the climate impacts of different greenhouse gases), data sources, analytical tools, or accou nting protocols may affect inventory results. Historical inventory results may therefore be updated over time to improve consistency and accuracy. Key methodological differences across inventory years are described in the applicable sector sections below.
The Protocol does not fully account for lifecycle emissions from food, air travel, and purchased goods and services, which can be captured through a Consumption -Based Emissions Inventory.
In response to community interest, the City considered conducting a Consumption- Based Emissions Inventory for Mountain View and presented its analysis to the City Council on December 3, 2019. Council approved the staff recommendation not to conduct ongoing City - level inventories of this type because of challenges associated with obtaining accurate data, the staff time and expense required, and the inventory’s limited ability to capture the effects of initiatives in Mountain View.
EMISSIONS SECTORS
The following sections provide additional information on the methodology used to estimate emissions from each sector and explain differences in methodology across inventory years.
Transportation
Staff estimates on- road transportation emissions based on the amount of vehicle travel, measured as vehicle miles traveled (VMT), and emission factors for different vehicle types. Staff obtains County-level emissions data from the California Air Resources Board (CARB) through its EMFAC tool, which provides emission factors for passenger cars, trucks, motorcycles, buses, and other on-road vehicles. Staff adjusts these results to a City scale using Mountain View’s VMT, service population, and share of the County’s freight jobs. Service population is the combined residential and worker population and helps account for the people traveling to, within, and from the City. The share of the County’s freight jobs helps account for medium- and heavy-duty vehicle activity through the City.
The sources and data used for these inputs have evolved as new sources and tools have become available. The 2017–2019 inventories used a per -capita VMT metric from the City’s 2018 travel demand model, developed by Fehr & Peers as part of the East Whisman Precise Plan transportation analysis . For the 2020– 2024 inventories, staff has used VMT data from the Metropolitan Transportation Commission (MTC) for inventory calculations. The share of the County’s freight jobs is estimated using U.S. Census Bureau data and updated as new data become available. The 2023 and 2024 inventories use 2022 data, which were the most recent data available at the time the inventory data were collected.
CARB has also released updated versions of the EMFAC tool over time. The City uses the version applicable to each inventory and, when feasible, updates previous inventory years to incorporate newer tools and data and improve consistency across inventories.
VMT is an important component of the transportation inventory, and the City continues to refine how it estimates VMT as new data and tools become available. Staff continues to evaluate emerging data sources, including vehicle navigation data from built- in GPS and location -based services data from cell phones, to validate transportation emissions estimates and travel demand model outputs. The City is also in the process of up dating its travel demand model, which will provide an opportunity to further improve VMT estimates used in future community GHG emissions inventories.
Beginning with the 2022 inventory, the City has also included emissions associated with Caltrain service. Staff estimates Mountain View’s share of Caltrain emissions using annual systemwide fuel-use data and ridership data for the Caltrain stations in Mountain View, including Downtown Mountain View and San Antonio. Mountain View’s share of total Caltrain ridership is used to attribute a corresponding share of systemwide emissions to the City . Caltrain began fully electrified revenue service between San Francisco and San Jose in September 2024, replacing diesel-powered service along the main corridor. As a result, Caltrain emissions are expected to decrease in future inventories as the effects of electrification are reflected in the underlying fuel- use and emissions data.
Energy
Staff estimates emissions from building energy use by applying emission factors to electricity and natural gas consumption. The inventory also includes electricity use associated with electric vehicle charging and light rail service in Mountain View.
Several data sources feed into the calculation of emissions from electricity. Silicon Valley Clean Energy (SVCE) provides electricity consumption data for residential and nonresidential customers. For the 2023 and 2024 inventories, the City also obtained electricity consumption data for several large electricity users through the State’s building energy benchmarking program. This data allowed staff to calculate more specific emissions estimates for these users using their reported electricity consumption and applicable emission factors. The benchmarking data also enabled SVCE to provide the remaining electricity consumption data needed to calculate emissions that could not previously be reported due to the California Public Utility Commission’s 15/15 rule regarding customer confidentiality. The 15/15 rule requires publicly disclosed energy usage data to be aggregated so that it includes at least 15 customers, with no single customer’s usage accounting for more than 15 percent of the total consumption reported.
The sources and data available for calculating electricity emissions have evolved over time. In several previous inventories, the City was unable to obtain sufficient electricity consumption data because of the 15/15 rule. As a result, the City used alternative methods to estimate emissions for electricity consumption that could not be directly reported. The availability of benchmarking data represents a significant improvement to the inventory by allowing the City to use more specific electricity consumption data and obtain the remaining aggregate consumption data needed to calculate emissions.
For electricity consumption that is not separately reported through the benchmarking data, staff applies emission factors based on the electricity provider and customer category, including SVCE, PG&E, and Direct Access. For Direct Access electricity, the 2023 and 2024 inventories assume approximately 62 percent of the electricity is supplied from carbon- free sources, based o n information provided by SVCE regarding large Direct Access customers that publicly report purchasing 100 percent carbon-free electricity.
For natural gas, SVCE provides total residential and nonresidential natural gas usage in therms.
Residential and nonresidential natural gas usage is combined in the inventory due to the California Public Utility Commission’s 15/15 rule.
Off-Road Mobile Equipment
Staff estimates emissions from off -road mobile equipment using County -level emissions data from the California Air Resources Board (CARB) and its EMFAC tool. The inventory includes equipment used for construction, lawn and garden activities, commercial and industrial activities, portable equipment, and other activities. Examples include excavators, cranes, loaders, and paving equipment for construction; lawn mowers, leaf blowers, trimmers, and chainsaws for
lawn and garden; forklifts, aerial lifts, and sweepers for industrial activities; and generators, compressors, and other portable equipment.
Staff adjusts the County -level emissions estimates to a City scale using three scale factors. For construction equipment, staff uses Mountain View’s share of Santa Clara County’s housing permits; for lawn and garden equipment, the share of County households; and for commercial, industrial, and other equipment, the share of County jobs. These factors estimate the share of County-level emissions attributable to activity in Mountain View.
The data and tools used for the inventories have evolved as new sources and tools have become available. The City uses the most current EMFAC tool available from CARB for each inventory and, when feasible, updates previous inventory years to incorporate newer tools and data and improve consistency across inventories. The 2023 and 2024 inventories use 2022 jobs data because it was the most recent data available from the U.S. Census Bureau at the time the inventory data were collected.
Waste
Staff estimates emissions from solid waste based on the amount of waste sent to landfills and the amount of organic material in the waste stream. Organic materials, including yard trimmings, food scraps, and food- soiled paper, are the primary contributors to emissions fr om landfilled waste because their decomposition produces methane, a greenhouse gas.
The data used to estimate the amount of organic material sent to landfills has changed over time.
The 2017–2021 inventories use waste characterization data from a 2017 study to estimate the percentage of organic material remaining in the waste stream after sorting at the SMaRT ® Station. As a result, these inventories do not capture additional organic waste diversion associated with the City’s residential food scraps collection program, which was implemented in July 2017 and expanded to multifamily residences in 2021. The 2022 –2024 inventories use updated waste characterization data from October 2022.
Beginning with the 2022 inventory, staff also included emissions from the Shoreline Landfill to improve alignment with the U.S. Community Protocol. Although the Shoreline Landfill has been closed since the early 1990s, organic material remaining in the lan dfill continues to produce methane as it decomposes. Methane and other landfill gases are expected to be generated through approximately 2042, with emissions gradually decreasing over time. The landfill has a highly efficient gas collection system that captures approximately 93.7 pe rcent of the methane produced. Some of the collected gas is used by microturbines to generate on- site power for the City’s sewage pump station, flare station, and irrigation pump station, while the remainder is combusted through flaring, significantly reducing the resulting emissions.
Water
This sector includes emissions from the energy used to treat wastewater and to extract, convey,
treat, and distribute potable water. Staff estimates these emissions by applying energy-intensity values specific to the local water supply to each step in the water and wastewater process.
The methodology has changed over time. Inventories prior to 2017 used average energy-intensity estimates that were higher than those specific to Mountain View’s local water supply. For the charts in the “Water” section of the CSC memo, total water and wastewater emissions have been updated to reflect the current methodology.
Wastewater emissions are estimated using data provided by the Palo Alto Regional Water Quality Control Plant (RWQCP), including activity and emissions -related data for wastewater treatment and related processes. Because the RWQCP serves multiple jurisdictions, emissions are allocated to Mountain View based on its share of the service population. The inventory includes emissions associated with energy use, biosolids management, process nitrous oxide, and other wastewater treatment processes. In 2019, the RWQCP decommissioned its biosolids incinerators and transitioned to dewatering and off- site processing of biosolids, resulting in a significant change in the facility’s emissions profile.