How the 2011 airport EIR treated forecast growth in operations

A sourced account of what the environmental review for the Charles M. Schulz – Sonoma County Airport runway extension said, and did not say, about the growth in operations built into its own analysis.

By Malcolm Crawford

This record reflects the public documents available as of August 2026. This brief distinguishes between what the available record states, what can be calculated from it, and what remains unresolved. It draws on the 2011 Draft EIR together with the available Final EIR addenda and responses to comments, archived at Sonoma Air Record's STS EIR 2011 archive since the county's own document links no longer resolve. A companion piece, the airport review tested the runway project, not the growth behind it, sets out what these facts may mean for residents.

The finding

In 2011, Sonoma County's environmental review of a runway extension at Charles M. Schulz – Sonoma County Airport forecast substantial growth in aircraft operations, and placed that same forecast in both halves of its central comparison: the scenario with the runway extension, and the scenario without it. The review therefore measured the modeled environmental difference between the two scenarios, against a future in which the forecast growth was already assumed to occur regardless.

It did not test whether the runway extension might itself contribute to that growth. When a Planning Commissioner asked the county to analyze an alternative involving fewer operations, the county declined, saying that the forecast level was already assumed and that a lower-operations alternative would underestimate the project's potential impacts.

What follows documents that finding against the primary sources, and states what it does and does not establish.

Why the runway was proposed

The airport's public FAQ lists three objectives for the runway project: compliance with a congressional mandate (Public Law 109-115) requiring Runway Safety Area standards at commercial-service airports by 2015; decoupling the co-located approach ends of Runways 14 and 19; and, third, providing "sufficient runway length to accommodate regional jet operations."

The Draft EIR's own project description gives the same account in more detail. After the airport lost scheduled service in 2001, the county marketed the airport to airlines, who reported the existing runway too short for the regional jets that would serve the market. A runway-length analysis found 6,000 feet the minimum needed for those jets to reach destinations including Los Angeles, Phoenix, Salt Lake City, and Denver, and the extension — from 5,115 feet — "will permit various models of regional jets to operate from the Airport." Both documents state the project's purpose, in substantial part, as enabling scheduled regional-jet service the existing runway could not reliably support.

The Draft Environmental Impact Report (EIR) covering this project was released August 5, 2011; the Board of Supervisors certified it and approved the Master Plan on January 24, 2012.

How the comparison was constructed

Appendix E of the Draft EIR develops the Master Plan's aviation activity forecast. The adopted scenario — Moderate Growth: Mainline Dominant — gives 2025 figures of 7,716 commercial operations and 262,373 enplaned passengers, and 2030 figures of 8,665 commercial operations and 299,739 enplaned passengers (Table 2-8). Chapter 5.3.1 states that airport development is designed to accommodate this forecasted demand. Chapter 5 also contains a "Growth Inducing Impacts" analysis, but it addresses regional population and economic growth; it treats aviation demand as forecast background rather than asking whether the runway project could affect aviation activity.

The Draft EIR's significance threshold for noise (section 3.10.1.2) measures a project's impact by comparing conditions with the project against conditions without it, in the same future year. The air quality analysis uses the same structure. Under Impact 3.3.8, the Draft EIR records 173,785 annual operations for 2030 — approximately a 91 percent increase over the 2009 baseline of 90,660 (Table 2-1) — and states plainly that "this increase is anticipated to occur with or without the implementation of the Proposed Project." The 2015 passage (Impact 3.3.2) originally used the identical construction; the Final EIR addenda later revised it, after Comment C97-27 from a Planning Commissioner questioning whether impacts really were identical either way, from "this increase" to "an increase" — a wording change the county's response tied to the with/without tables, not to any change in the underlying figures.

The noise tables show the same pattern. Table 3.10-21 gives 2030 CNEL contour areas of 2,881 acres without the project and 2,851 with it; Table 3.10-23 records CNEL increases from 2009 to 2030 of between 2.2 and 3.5 dB at every monitored receptor, in both cases. The GHG tables show a comparable pattern in emissions: 2009 emissions of 5,668.96 metric tons CO2e (Table 3.3-4) grow to 10,261.80 without the project and 11,408.57 with it by 2030 (Tables 3.3-27, 3.3-28) — a tested net change of 1,146.77 against a 1,100-ton BAAQMD threshold (Table 3.3-29). The growth between 2009 and the 2030 no-project figure, 4,592.84 metric tons, is about four times the tested increment and appears identically on both sides of the comparison.

One sentence in the record complicates this account. The GHG impact narrative (Impacts 3.3.3 and 3.3.9) attributes the increase partly to "the increase in aircraft operations that would occur as a result of the Proposed Project" — different wording from the parallel criteria-pollutant impacts (3.3.2, 3.3.8), which attribute the identical underlying increase to "growth in activity that is expected to occur," without tying it to the project. The available record does not reconcile the two.

What the county's public materials say about fleet mix

The airport's FAQ complicates the fleet-mix question specifically. Asked what future aircraft would use the airport, it states the mix "will be identical whether or not the project is implemented, except that regional airline jets would be unlikely to use the Airport without the proposed improvements." Elsewhere, asked whether the Master Plan would increase aviation activity, it answers that the plan "does not cause or result in an increase in aviation activity," while separately forecasting an increase, and states its own forecast is in fact lower than earlier forecasts used for the General Plan.

These statements are not necessarily incompatible — a document can hold that overall activity would grow regardless of the project while holding that regional jet service specifically depends on it. But nothing in this record states how they fit together, and whether the operations totals used identically in the with-project and without-project scenarios also assumed the same fleet composition is not established here.

What happened when lower activity was suggested

A Planning Commissioner asked, in comments recorded as C97-5, whether the EIR should analyze an alternative limiting airport activity. The county's response gave two reasons: that the project's impacts, given the already-assumed 21 daily departures, were not significant, so CEQA did not require a lesser-impact alternative; and that analyzing an alternative with fewer operations "would underestimate the potential impacts that could occur." The response did not analyze a lower-operations alternative, and does not address whether the project itself could affect how much of the allowed activity would actually occur.

Substantially the same answer went to at least four other commenters, including the Sierra Club (response B4-8): that the analyses assume the level of activity already approved under the General Plan, and that the project does not increase it. Several of these responses point to Master Response G, in Section 4 of the Final EIR, for a fuller account of the approved flight levels. That file could not be obtained for this brief: it has been unreachable from the county's own site since at least July 2022, the Internet Archive holds no capture of it at any date, and its content is not established here. Printed copies of the Final EIR were placed in county libraries and public offices in 2011.

The cumulative-noise test asked a different question

The Draft EIR did examine the cumulative change in noise between 2009 and the future years — a separate test from the with-project/without-project comparison above — and found significant cumulative effects in mapped areas both for 2015 and 2030, addressed through acquiring the affected homes in one case and an ongoing noise-monitoring and mitigation program (Mitigation Measure 3.10.5) in the other. But this test did not isolate the portion of the increase attributable to the growth common to both scenarios, determine whether the runway itself contributed to that growth, or compare the adopted plan against a lower-operations alternative. It examined a real question. It was not this one.

The resulting limit

Taken together: the Draft EIR calculated future noise, emissions, and other environmental conditions using its forecast growth. It compared those conditions with the runway project against the same conditions without it, and used that comparison to make significance findings about the project's incremental effects. It did not test whether the runway extension might itself contribute to the forecast growth, and when a lower-operations alternative was proposed, it was not analyzed.

What is not established in this record

• The content of Master Response G.
• Whether the with-project and without-project scenarios used the same fleet mix.
• A separate federal environmental review concluded with a Finding of No Significant Impact and Record of Decision on July 19, 2013 (confirmed via Federal Register notice); the Environmental Assessment and the FONSI/ROD's reasoning have not been examined here.

Sources

• Charles M. Schulz – Sonoma County Airport, Draft Environmental Impact Report, July 2011. Chapter 1, Introduction. Chapter 2, Proposed Project, section 2.2.3 and Table 2-1. Chapter 3.3, Air Quality: section 3.3.1.2, Impacts 3.3.2, 3.3.3, 3.3.8, and 3.3.9, Tables 3.3-4, 3.3-27, 3.3-28, and 3.3-29. Chapter 3.10, Noise: section 3.10.1.2, Impacts 3.10.2 and 3.10.5, Tables 3.10-21 and 3.10-23, Mitigation Measure 3.10.5. Chapter 5, Impact Overview, section 5.3, including 5.3.1. Appendix E, Aviation Activity Forecasts, Table 2-8.
• Final EIR – Response to Comments Document, November 2011. Section 3, Addenda to the Draft EIR (the "this increase"/"an increase" revision is at Draft EIR page 3.3-23; the Chapter 5.1 revision is at page 5-1). Response to Comment Letter B4 (Sierra Club) and responses to individual commenters tracked as C24, C30, C31, and C61. Responses to Comment Letters C96 and C97 (oral comments of Planning Commissioners, September 2011 hearings), including Comment C97-27 and C97-5.
• Federal Register notice, Department of Transportation/Federal Aviation Administration, confirming a Finding of No Significant Impact and Record of Decision for the Runway Safety Area project on July 19, 2013; the notice itself concerns a later, separate conservation-easement matter and references the 2013 FONSI/ROD in passing.
• Charles M. Schulz – Sonoma County Airport, Frequently Asked Questions (FAQ) — DEIR and Master Plan, sonomacountyairport.org.
• Sonoma Air Record, STS Airport Master Plan EIR 2011 (archive), airport.mmalc.com/sts-eir-2011/. Primary access point for the Draft EIR and the Final EIR Response to Comments documents used throughout this brief, since the county's own document links no longer resolve; includes a documented retrieval methodology and manifest.
• Master Response G, Section 4 of the Final EIR. Unreachable from the county's site since at least 2022 and never captured by the Internet Archive; not held in the archive above or used for this brief.

Colophon: researched and drafted in collaboration with Claude (Anthropic).