Folsom City Council
June 23, 2026

06/23/2026 Item No.18.

IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-2
List of Figures
Figure S1: Locations of PM2.5 air monitoring stations (blue) in relation to study homes (red).... 8 Figure S2. Results of side-by-side deployment of indoor and outdoor MetOne photometers at each house, typically outdoors........................................................................................................ 9 Figure S3: Distribution of ACH50 from Envelope Leakage Measurements................................ 21 Figure S4: Bathroom Exhaust Fan Measured Flow Rates............................................................ 23 Figure S5: Total Estimated Air Exchange Rate............................................................................ 25 Figure S6: Infiltration and Total Airflow (Mechanical + Infiltration).......................................... 26 Figure S7. Comparison between mean outdoor PM2.5 measured using MetOne photometer and inverse distance weighted ambient monitoring data (N=67). ....................................................... 33 Figure S8: One-Week Integrated NO2, NO, and NOx Concentrations........................................ 34 Figure S9: Overnight (midnight-5am) CO2 measurements in indoor main living space and master bedroom. ....................................................................................................................................... 35 List of Tables
Table S1. Specifications of air pollutant monitoring equipment .................................................... 5 Table S2. Comparison of study design and measurement methods HENGH and CNHS studies of indoor air quality and ventilation in single family detached homes............................................... 6 Table S3. Sampled Homes by Cities and Climate Zones (N=70) ................................................ 16 Table S4. Sampled Homes by Seasons......................................................................................... 16 Table S5. Sampled Homes by Year Built ..................................................................................... 17 Table S6. Age of Homes When Sampled1.................................................................................... 17 Table S7: Sampled Homes by Floor Area .................................................................................... 17 Table S8: Sampled Homes by Number of Stories........................................................................ 18 Table S9: Sampled Homes by Number of Bedrooms................................................................... 18 Table S10: Sampled Homes by Number of Bathrooms................................................................ 18 Table S11: Locations of Gas Fireplaces ....................................................................................... 19 Table S12: Number of Occupants in Sampled Homes ................................................................. 19 Table S13: Number of Occupants in Sampled Homes by Age Group ......................................... 20 Table S14: Total Household Income in Sampled Homes............................................................. 20 Table S15: Education Level of Head of Household in Sampled Homes...................................... 21 Table S16: Whole House Ventilation System Type ..................................................................... 22 Table S17: Whole House Ventilation System Control ................................................................. 22 Table S18: Air Filter MERV Ratings ........................................................................................... 23 Table S19: Time Since Last Air Filter Change............................................................................. 24 Table S20: Condition of Air Filters Observed by Field Team...................................................... 24 Table S21: How Frequently Are Candles Used in the Home ....................................................... 27 Table S22: Number of Furry Pets in Homes................................................................................. 27 Table S23: Self-Reported Average Occupancy (Number of People) When Home Was Occupied ....................................................................................................................................................... 27 Table S24: Self-Reported Average Occupied Hours per Day During Monitoring Week ............ 28

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Table S25: Self-Reported Cooktop Use (Number of Times) During Monitoring Week.............. 28 Table S26: Self-Reported Oven and Outdoor Grill Use During Monitoring Week ..................... 28 Table S27: Average Cooking Activity Duration During One-Week Monitoring, Self-Reported 29 Table S28. CNHS Activities (Table 42 and 43 of Offermann et al. 2009):.................................. 29 Table S29: Comparison of Time-Integrated Formaldehyde Measured with Two Methods......... 30 Table S30. Time-integrated PM2.5 concentrations measured by MetOne and Thermo pDR-1500 photometers compared with gravimetric analysis of co-located filter samples............................ 31 Table S31. Summary statistics (N=67) of the mean outdoor PM2.5 measured using MetOne photometer and inverse distance weighted ambient monitoring data........................................... 32 Table 32. Air quality satisfaction reported by participants........................................................... 36 Table 33. Satisfaction with seasonal temperature conditions by ventilation system status on first visit to home.................................................................................................................................. 36 Table 34. Satisfaction with environmental parameters by ventilation system status on first visit to home.............................................................................................................................................. 37

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Methods
Recruitment and Screening
Most participants were recruited through postcards mailed to addresses identified on a real estate website (Zillow.com), targeting single-family, detached homes built 2011 or later. Some participants learned of the study via referrals. LBNL attempted to contact all who expressed interest through the study website or by telephone. On contact, participant eligibility was confirmed and participant responsibilities, including keeping windows closed, were described.

This process identified 103 eligible and interested candidates and led to monitoring in 72 homes.

Most of the other 31 candidates did not respond to three attempts to schedule visits or withdrew before the first scheduled visit. One consented participant withdrew between the first and second visits. Another was excluded when the field team found during the first visit that the home was built before 2011. These participants received a $75 gift card. Two monitored homes did not have compliant ventilation systems and are not included in the data reported herein.

Information Collected for House and Equipment Characterization  House information: floor area and ceiling heights; number of stories, bedrooms, full and half baths, and other rooms on each floor; attached garage, number of parking spots, etc.  Whole-house mechanical ventilation system. Noted basic design (exhaust, supply, or balanced); type of control; make, model and rated flow; and fan settings.  Other ventilation equipment: bath and toilet room exhaust fans, kitchen range hood, and any laundry exhaust fans. Noted make, model and rated flow, type of control for each fan; and for kitchen note if range hood is microwave or simple range hood.  Heating and cooling system(s). Noted type of system (all were forced air), make and model, capacity (in tons and Btuh) and whether system was zoned. Noted dimensions and location of each return and locations of filter(s) if not at the return air grille. Noted location(s) and types of thermostats. For each filter in a forced air heating or cooling system, recorded make, model and performance rating and visually assessed condition of filter; also took photo.

Identified and characterized thermostat and marked location on floor plan.  Attic. Noted whether it was vented or unvented and the type of insulation. Photographed ductwork, gas furnace, exhaust fans, and vents.
 Gas-burning appliances. Noted make, model and firing rates of all burners or photographed nameplate. Noted locations on floor plans.

Floor plans were generally obtained from builders’ websites; otherwise they were sketched on site. Photos were taken of the home exterior, garage, gas appliances, mechanical ventilation equipment, air filters, and any special features.

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Specification of Air Quality Monitoring Equipment
Table S1. Specifications of air pollutant monitoring equipment Parameter Device make and
model
Range and
Resolution
Accuracy in
Product Literature
Other
Temperature Onset HOBO
UX100-011
Range: -20° to 70°C.

Resolution: 0.024°C at
25°C
±0.21°C from 0° to
50°C
Response time: 4 min in
air moving 1 m/s
Drift: <0.1°C per year
Temperature Extech SD800 0 to 50°C ±0.8°C
Relative
humidity
Onset HOBO
UX100-011
Range: 1% to 95%
(non-condensing);
Resolution: 0.05%
±2.5% from 10% to
90%; up to ±3.5% at
25°C including
hysteresis
Response time: 11 sec to
90% in airflow of 1 m/s
Drift: <1% per year
typical
Relative
humidity
Extech SD800 Range: 10-90% ±4%RH below
70%; 4% of reading
+ 1% for 70–90%
range
Particulate
matter, PM2.5
MetOne ES-642
MetOne BT-645
Range: 0-100 mg/m3.

Resolution: 0.001
mg/m3.
± 5% traceable
standard with 0.6um
PSL
Carbon dioxide,
CO2
Extech SD800 Range: 0-4000 ppm;
Resolution: 1 ppm
±40 ppm under
1000 ppm; ±5%
>1000 ppma
Nitrogen
Dioxide
Aeroqual 500
Series
Range: 0 to 1 ppm ± 0.02 ppm within 0
to 0.2 ppm range
Formaldehyde GrayWolf
(Shinyei)
Multimode
Monitor
20 to 1000 ppb ± 4ppb for <40ppb,
± 10% of reading
for ≥40ppb
30 min resolution; 20
ppb is lowest reliable
value with stated
accuracy
a Extech monitors did not achieve this performance when compared to a calibrated PPSystems EGM-4 in an injection-decay experiment in a small, room-sized chamber during monitoring as described in the text.

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Table S2. Comparison of study design and measurement methods HENGH and CNHS studies of indoor air quality and ventilation in single family detached homes Parameter HENGH CNHS
Number of Homes 70 108
Year Built
(Monitoring)
2011-2017
(Jul 2016 – Apr 2018)
2002-2005
(Aug 2006 – March 2007)
Dwelling Unit
Mechanical
Ventilation
(Operational
Systems)
All 70 homes had systems that met
2008 or later California code:
64 exhaust; 6 supply.
13 homes had systems that met
ASHRAE 62.2-2004:
8 balanced (HRV); 5 with duct
connecting FAU to outdoors and
controller for ventilation.
9 homes had duct connecting FAU
to outdoors but no controller for
ventilation.

Gas Cooking
Appliances
Cooktops: 100%
Ovens 43%
Cooktops: 2%
Ovens: 27%
Natural
Ventilation
Occupants agreed to not use
windows for ventilation.

Occupants asked to use windows
as they do normally.

Duration ~7 days ~24 hour
Locations for IAQ
parameter
measurements
• Living, dining or family room:

PM2.5, CO2, NOX, NO2,
formaldehyde.
• Master bedroom: CO2 and
formaldehyde.
• Other bedroom(s): CO2
• Outside: PM2.5, NOX, NO2,
formaldehyde.
• Living, dining or family room:

VOCs, CO2, CO, formaldehyde in
all homes; PM2.5 in 28 homes; NO2
in 29 homes.
• Outside: formaldehyde at each
cluster of 2-3 homes (n=39); PM2.5
and NO2 at 11 clusters.

Air Contaminant
Measurement
Methods
• Formaldehyde, NO2, NOX: timeintegrated passive samplers. • Formaldehyde: colorimetric
sensor/photometer, 30-min logs
• PM2.5: Estimated by photometry
with indoor adjusted using timeintegrated filter samples. • CO2: Passive, NDIR, 1-min
• Formaldehyde, NO2, 10 VOCs:
time-integrated, pumped samples
• PM2.5: time-integrated pumped
filter samples with size selective
inlets and gravimetric analyses.
• CO2: Passive, NDIR, 1-min
• CO: Passive, Electrochemical, 1-
min

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Parameter HENGH CNHS
• T: thermistor sensor
• RH: Thin film capacitive sensor
• T: thermistor sensor
• RH: Thin film capacitive sensor
Air Contaminant
Measurement
QA/QC
• Formaldehyde, NOX, NO2:
duplicates, field blanks,
manufacturer’s recommended
sampling rate.
• PM2.5: zero at sample start, span
adjustment calculated from
simultaneous gravimetric samples
at 8 indoor locations.
• CO2: baseline and span checks at
middle of study. No adjustment of
field data.
• NO2: baseline and span checks
prior to sampling in most homes.
• T and RH sensors used factory
calibration with no field
calibrations.
• Formaldehyde, PM2.5, NO2, 10
VOCs: duplicates, field blanks,
sampling rate measurements at
start and stop.
• CO2 and CO: zero and span
calibration at start and stop of
sampling at each home and
corresponding adjustment of field
data.
• T and RH sensor calibration prior
to field session and corresponding
adjustment of field data.

Record of natural
ventilation use.

Participant affirmed that windows
would not be used for ventilation,
per study requirements. Loggers on
two most-used doors. No loggers
or signage on windows. Daily log
asked for hours that any windows
were opened but not the amount
opened.

Occupants instructed to operate
windows normally. Loggers on
windows that occupants reported to
use most frequently, and signage
with logs on all windows for
occupants to record hours and
amount opened.

Method to
measure or
estimate outdoor
air ventilation rate
Estimated from measured
mechanical airflows and modeled
infiltration with unbalanced
ventilation.

Measured with perfluorocarbon
tracer (PFT) gas.

Abbreviations: HRV = Heat recovery ventilator; FAU = forced air unit; NDIR = non-disperse infrared.

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Locations of Ambient Air Quality Monitoring Stations Used to Estimate Outdoor PM2.5  San Francisco Bay Area
 Sacramento and Central Valley
Southern California 
Figure S1: Locations of PM2.5 air monitoring stations (blue) in relation to study homes (red).

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Quality Assurance Procedures for Air Quality Monitors
The indoor and outdoor PM2.5 monitors were co-located for roughly one hour during the instrument deployment visit at each home. In most cases the co-location was outdoors at the location of the outdoor monitor. Co-located comparisons were available from 45 homes. In two of the homes, the two monitors measured very different concentrations likely because the outdoor monitor had a heated inlet that was set to activate when relative humidity reached above 60%, and the indoor monitor did not. The heated inlet prevents condensation that could damage the instrument. The indoor monitor did not have a heated inlet because high humidity is generally not a concern when sampling indoors. At the two homes during the one-hour colocation test, the outdoor monitor measured high concentration of PM2.5 (51 and 60 g/m3 at
Home 063 and 068, respectively). Without the heated inlet, the co-located indoor monitor measured 111 and 78 g/m3, respectively. The two homes were sampled in winter (January 2018) in Tracy and Manteca CA, where high humidity condition in the morning likely explained this difference between the co-located indoor and outdoor PM2.5 monitors. Excluding these two cases, the co-located indoor and outdoor PM2.5 monitors agreed to within 1.9 g/m3 on average (median = 0.9 g/m3), with the outdoor monitor reporting lower concentrations than the indoor monitor in 79% of the indoor side-by-side deployments. This is likely because the heated inlet intended to prevent condensation resulted in some volatilization of organics in the outdoor particles. The results of the brief side-by-side deployment of indoor and outdoor MetOne photometers at each home are provided in Figure S2.

Figure S2. Results of side-by-side deployment of indoor and outdoor MetOne photometers at each house, typically outdoors.

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The Extech CO2 monitors were co-located for 1 hour at each home or at a warehouse where the field team prepared equipment before a visit. The field team confirmed that CO2 monitors agreed with one another to within a range of 100 ppm. Extech monitors were also calibrated at LBNL during two breaks in sampling, with 5 units checked during Feb 2017 and 7 units (including two from first round) checked during Dec 2017. On each occasion, the monitors were set up in a well-mixed room along with an EGM-4 gas analyzer (PP systems, Amesbury, MA, USA). The EGM-4 was separately calibrated using standard gas of known CO2 concentrations between 0 and 2500 ppm. During each event, CO2 concentrations in the chamber were raised by injection of pure CO2 then left to decay with air exchange. Hourly concentrations were calculated for each monitor. The first-hour means were 1056 and 1537 ppm for the two events. Decay periods were 26 and 7 hours to final-hour concentrations of 420 and 529 ppm. Hourly average concentrations reported by the Extech units differed (high to low range) by 71–86 ppm during the first spikedecay and 111–168 ppm during the second. Averaged over the full spike-decay intervals, differences between Extech units and the EGM-4 ranged from -20 ppm to 84 ppm.

The Aeroqual 500 NO2 monitor was calibrated before each visit with zero gas and a 1 ppm NO2 standard gas. Monitor response was adjusted to match those values following manufacturer instructions. Despite this calibration step, there was generally a substantial, positive offset in the time-integrated NO2 concentration measured by the Aeroqual when compared with the concentrations measured using the passive sampler. Further processing of the Aeroqual NO2 data is required, which is beyond the scope of this paper.

Weighing of Filters for Gravimetric PM2.5 Determination Gravimetric samples were collected on 37 mm diameter, 2.0 micron pore size, Pall Teflo filters with ring. Prior to deployment, filters were preconditioned for 24 hours at controlled temperature and humidity conditions (47.5 +/- 1.5 % RH and 19.5±0.5 ºC), passed over a deionizing source to remove static charge and weighed twice using a Sartorius SE2-F balance. Pre-weighed filters were loaded into the pDR-1500 photometers and were shipped to GTI for deployment. After a week of monitoring, GTI shipped the pDR monitors back to LBNL. LBNL removed the filters, and repeated the preconditioning and weighing procedures. The collected mass was determined as the post-sampling versus pre-sampling mass difference. The field blank was subtracted from the sample mass. Sampled air volume was taken from the pDR. Mass concentration was calculated as collected PM mass / sample air volume. The sample flow rate of the pDR was checked in the lab before and after each field use.

Passive Sampler Procedures and Quality Assurance
Ogawa samplers were prepared according to manufacturer protocols. Prior to assembly for field deployment, all parts of the samplers were washed thoroughly with deionized water and allowed to dry thoroughly in a laboratory at LBNL. Sample pads were stored in the refrigerator in their original packaging until they were inserted into samplers. After samplers were assembled with new sample pads, they were placed in sealed amber plastic bags (Ziploc) and shipped to the field team in an insulated box with ice packs to keep them cool.

All passive samplers were shipped to LBNL for analysis. To avoid damage to the chemical samplers from extreme temperatures, samplers were mailed in an insulated shipping container

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with ice packs to keep them cool. The samples were extracted and analyzed following the protocols provided by each company (Ogawa & Company 2017; SKC, Inc. 2017). All Ogawa samples were extracted for analysis within 30 days from when the samplers were assembled.

For each NOX and NO2 sample we subtracted the mass determined from the field blank at the same home before calculating the sample period concentrations of NOX, NO2 and NO as the difference between the adjusted NOX and NO2 concentrations. For two homes that did not have a field blank, we subtracted 0.15 micrograms for NO2 and 0.22 micrograms for NOx, which are the mean mass determined from all available field blanks; these masses correspond to 0.9 ppb of NO2 and 1.3 ppb of NOx for a 7-day collection period. Following blank subtraction, 4 indoor and 5 outdoor NO2 samples and 1 indoor and 6 outdoor NOx samples had negative concentrations; the occurrence of negative values results from variability in the blank correction and low sample masses. These negative NO2 and NOx concentrations were retained when calculating summary statistics. Analysis of 64-paired duplicates of indoor samples found that agreement in NO2 concentrations was within 0.6 ppb on average (median = 0.3 ppb). When available, duplicates were averaged to provide a better estimate of the indoor concentrations of NO, NO2, and NOx.

Sampling rates were calculated using co-located temperature and relative humidity measurements following manufacturer instructions.

The formaldehyde concentration determined by passive sampler at each home also was adjusted by the effective sample period concentration determined from the field blank at the same home.

For the eleven homes that did not have a formaldehyde passive sample field blank, we subtracted

0.15 micrograms, which is the mean mass determined from all available field blanks (and corresponds to 0.6 ppb for a 7-day collection period). Sixty-six paired indoor formaldehyde samples agreed to within 1.0 ppb on average (median = 0.7 ppb). When available, duplicates were averaged to provide a better estimate of the indoor concentrations. A sampling rate of 20.4 ml/min were used following manufacturer instructions.

The UMEx contains an internal blank within each sampler that can potentially be used for convenience instead of deploying a separate field blank sampler. However, analysis of the internal blank suggested that even though it was not directly exposed to the sampling air, some formaldehyde was collected, possibly because the compartment isolating the internal blank was not completely airtight. The average analyte mass determined from internal blanks of indoor samples was 0.6 micrograms; this is 4 times the field blank value noted above.

Formaldehyde indoor emission rates E (g/m3-h) were calculated using a simple mass-balance equation assuming well-mixed, steady state condition. The same method was applied by Offermann (2009) to estimate indoor emission rates of formaldehyde and other VOCs.

E = (Ci – Co)AER (1)
Outdoor formaldehyde concentration (Co, g/m3) was subtracted from the indoor concentration (Ci, g/m3) measured at the central location, assuming that there is no loss in formaldehyde as the outdoor air enters through the building envelope. Air exchange rate (AER, 1/h) is assumed to be the only mechanism that removals formaldehyde from the indoor air. Air exchange rate was estimated from natural infiltration airflow and mechanical airflow using sub-additivity, as described later in the Methods.

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-12
Potential Impact of Low Air Speeds on Passive Sampler Data The sampling rates of passive samplers may be impacted by low air speeds at the sampler inlet, as discussed by Offermann and Hodgson (2018)1and papers cited therein. At very low air speeds, diffusive uptake to the passive sampler causes a reduction in analyte concentration at the face of the air sampler relative to the surrounding indoor air, resulting in an effective increase in the diffusive path length and lower sampling rate.

Since air speeds were not measured in HENGH homes, we rely on the data of Mathews et.al. (1989)2to assess the potential for low air speeds to bias the passive sampler measurements in residences. Matthews et al. used a TSI Model 1620 omnidirectional anemometer to measure air speeds during daytime hours in various rooms of six occupied homes and in an unoccupied research house. The overall median air speed measured in the six occupied homes was 318 cm/min. HVAC operation was found to substantially impact air speeds, by a factor of 5 in one house and by roughly a factor of 2 in two other occupied houses. The median measured air speeds with HVAC off in three occupied homes and the research house were 90, 198, 342, and 246 cm/min. Among the rooms studied, air speeds were lowest in the master bedroom, with median values during no HVAC use of 108 cm/min across the three occupied houses. The condition with the lowest measured air speeds was in a bedroom that was completely unoccupied; during HVAC off times median air speeds were 66 cm/min. HVAC operation was not tracked in HENGH; but the median HVAC run time was 1.1 h per 24 h in the CNHS.

Using a TSI Model 8475 omnidirectional anemometer, Offermann and Hodson reported an air speed of 27 cm/min in an unoccupied office overnight with no HVAC operation.

Using the data above as reference points, Offermann provided the following correction factors for the geometries of the UMEx and Ogawa samplers at selected air speeds.

Air Speed (cm/min) UMEx CF Ogawa CF
27 1.21 1.16
66 1.09 1.07
100 1.06 1.04
300 1.02 1.01
Using the daytime airspeeds measured with no HVAC operation and assuming that condition applied roughly half the time in HENGH master bedrooms, and also assuming higher airspeeds with occupancy during nighttime hours, the bias from low air speeds would be on the order of 3% for formaldehyde and 2% for NOX and NO2. A bedroom that is completely unoccupied during the daytime and similar to the one reported in Matthews could have a bias of 4-5% for formaldehyde and 3-4% for NOX and NO2. If any rooms commonly experienced conditions similar to those observed overnight in the Offermann office, the bias would be 8-10%.

1 Offermann, F. J. and A. T. Hodgson (2018). Accurancy of Three Types of Formaldehyde Passive Samplers. Indoor Air 2018, Philadelphia PA, International Society of Indoor Air Quality Sciences. 2 Matthews, T. G., C. V. Thompson, D. L. Wilson, A. R. Hawthorne and D. Mage (1989). "Air velocities inside domestic environments: An important parameter in the study of indoor air quality and climate." Environment International 15: 545-550.

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-13
Adjustments to Formaldehyde Data from FM-801 Monitor
Output of the FM-801 formaldehyde monitor dropped precipitously during events of substantial gas cooking burner use, presumably owing to an NO2 interference as described by Maruo et al.3 FM-801data that were clearly affected by cooking were identified by visual review, considering data from the time-resolved NO2 monitor and the cooktop and oven temperature sensors, and removed. Data marked as “<LOD” because they were below the 10 ppb quantitation limit were assigned a value of 7.3 ppb based on analysis of data from homes with the modified FM801software that provided numerical results below 10 ppb.

Calculation of Outdoor Air Exchange Rate
First, mechanical fan flows were calculated by summing exhaust fan flows (whole house exhaust fan, and other fans in bathroom, range hood, clothes dryer) weighted by their average usage time.

Since it was not practical to directly measure the airflow of the clothes dryers in most homes, we assumed dryer airflow of 125 cfm based on a recent report4.

Airflows from mechanical fans were added to calculate balanced (Qbalance_mech) and unbalanced (Q unbalance_mech) airflows by comparing minute by minute the amount of exhaust and supply air from usage data collected from each home. Next, air infiltration (Qinfiltration) was calculated using the flow coefficients and pressure exponents from average of pressurization and depressurization tests of building envelope leakage, determined as part of the DeltaQ Test, and using stack and wind coefficients following the ASHRAE Fundamentals Enhanced Model. Wind data were obtained from the nearest weather station5. Indoor and outdoor temperatures were monitored onsite. Photos of the house and surroundings were reviewed to determine the appropriate shelter class: either 4 (urban building on larger lots where sheltering obstacles are more than one building height away) or 5 (shelter produced by buildings or other structures that are closer than one house height away). The total ventilation rate was calculated following Equation 2, which uses a superposition adjustment (∅) to account for the sub-additivity of unbalanced mechanical airflows with air infiltration.

𝑄𝑡𝑜𝑡𝑎𝑙 = 𝑄𝑏𝑎𝑙𝑎𝑛𝑐𝑒_𝑚𝑒𝑐ℎ + 𝑄𝑢𝑛𝑏𝑎𝑙𝑎𝑛𝑐𝑒_𝑚𝑒𝑐ℎ + ∅𝑄𝑖𝑛𝑓𝑖𝑙𝑡𝑟𝑎𝑖𝑡𝑜𝑛 (1) ∅=
Qinfiltration
Qunbalance_mech+Qinfiltration
(2)
Field teams measured ceiling heights in the great room, kitchen, living room, dining room, bedrooms, and other parts of the house. Air exchange rate was computed using an approximate house-averaged ceiling height and floor area recorded by the field team.

3 Maruo, Y. Y., T. Yamada, J. Nakamura, K. Izumi and M. Uchiyama (2010). "Formaldehyde measurements in residential indoor air using a developed sensor element in the Kanto area of Japan." Indoor Air 20(6): 486-493. 1 ENERGY STAR reports rated fan flow of clothes dryer typically range between 100 and 150 cfm. https://www.energystar.gov/sites/default/files/asset/document/ENERGY_STAR_Scoping_Report_Residential_Clot hes_Dryers.pdf
5 Data obtained from www.wunderground.com. During periods when wind was reported as “calm”, 1 mph (mile per hour) was assumed for calculating air infiltration rate.

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-14
Estimate of Potential Bias in Calculated Air Infiltration While the ASHRAE Enhanced Model was developed from an extensive set of measured data and has been evaluated in several previous studies6,7,8, it is nevertheless valuable to consider that it could have varied performance in specific applications.

For this study, we used data from the CNHS – which measured time-integrated outdoor air ventilation rates using perfluorocarbon tracer gases (PFTs) – to evaluate the method used to calculate the infiltration portion of air exchange in HENGH, which measured mechanical airflows but calculated infiltration and overall AER.

The analysis looked at 13 CNHS homes that that had no window opening and no continuous mechanical ventilation (just occasional bathroom, kitchen, and clothes dryer exhausts); the overall AERs in these homes were thus dominated by infiltration. For these 13 homes, we calculated infiltration/air exchange in the same manner as was done for the HENGH study. (The only difference was that the calculation was done with 1-minute indoor temperature and intermittent exhaust fan data for HENGH and 15-minute data for CNHS. The calculations used the following parameters:
 default stack and wind coefficients for n=0.67;
 on-site data for indoor air temperature and local Meteorological Station data for outdoor air temperatures and wind speeds;
 setting all 0 mph wind speeds to 1 mph;
 using the interpolated ASHRAE Fundamentals Shelter Factors;  combining any intermittent mechanical airflow with infiltration using sub-additivity;  calculating the weekly integrated AER as the harmonic mean of 15-min estimates.

For each of the 13 CNHS homes, we compared the AER measured by PFT to the calculated AER to determine a correction factor, which we consider to be applicable to the calculated infiltration portion of AER. The median correction factor for the 13 homes was 1.81 with a range of 1.04 –

2.11. While this is high compared to published comparisons of measurements to infiltration model calculations, our hypothesis is that it is mostly due to the difficulty in selecting appropriate wind shelter factors.

Since most of the HENGH homes had continuous mechanical exhaust systems, infiltration accounted for only a fraction of the total outdoor air exchange. To assess the potential impact of infiltration bias calculated for the CNHS homes on the AERs calculated for HENGH homes, we

6 Walker, I.S. and Wilson, D.J., (1998), “Field Validation of Equations for Stack and Wind Driven Air Infiltration Calculations”, ASHRAE HVAC&R Research Journal, Vol. 4, No. 2, pp. 119-140. April 1998. ASHRAE, Atlanta, GA. LBNL 42361.
7 Francisco, P. and Palmiter, L. (1996). “Modeled and Measured Infiltration in Ten Single-Family Homes. Proc.

ACEEE 1996.
8 Wang, W., Beausoleil-Morrison, I. and Readon, J. 2008. Evaluation of the Alberta Air Infiltration Model Using Measurements and Inter-Model Comparisons. Building and Environment, 44. 309-318. doi:10.1016/j.buildenv.2008.03.005c

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-15
adjusted the calculated infiltration rates for all HENGH homes by a factor of 1.81, then used subadditivity to combine the adjusted infiltration rates with the measured mechanical ventilation rates on a home-by-home basis. The median calculated adjustment factor for the total ventilation rates for HENGH homes is 1.18.

In addition to the potential bias from infiltration calculations, the calculated AERs for HENGH homes are also biased in some cases because the calculation assumed no window or door opening; any substantial use of windows or doors for ventilation would further raise AERs relative to calculated values.

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-16
Results
House Characteristics
Table S3. Sampled Homes by Cities and Climate Zones (N=70) Gas
Utility
Service
Cal.

Climate
Zone
Cities (Number of Homes) Homes Total
PG&E 3 Discovery Bay (2), Hayward (2), Oakland (1) 5 48 11 Marysville (1) 1
12 Brentwood (12), El Dorado Hills (10), Elk Grove (6), Manteca (4), Mountain House (2), Pittsburg (2), Davis (1), Dublin (1), Sacramento (1)
39 13 Clovis (3) 3
SoCalGas
8 Irvine (2), Downey (1), Lake Forest (1), Yorba Linda (1) 5 9 Van Nuys (5), Alhambra (1) 6 22
10 Jurupa Valley (5), Chino (4), Corona (1), Eastvale (1) 11 Table S4. Sampled Homes by Seasons
Season Months Number of Homes
Winter Dec-Feb 16
Spring Mar-May 13
Summer Jun-Sep 27
Fall Oct-Nov 14
Total 70

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-17
Table S5. Sampled Homes by Year Built
Year Built Number of Homes
2011 1
2012 7
2013 13
2014 17
2015 15
2016 14
2017 3
Total 70
Table S6. Age of Homes When Sampled1
HENGH Age When
Sampled (years)
HENGH Number of
Homes at Age
CNHS Percentile CNHS Age When
Sampled (years)
<1 2 Min 1.7
1 14 10th 2.4
2 32 25th 3.0
3 14 50th 3.4
4 4 75th 4.0
5 2 90th 4.3
No Response 2 Max 5.5
Total N=70 N=108
1 CNHS data from Table 15 of Offermann et al. (2009)
Table S7: Sampled Homes by Floor Area
Floor Area (ft2) Homes Floor Area (m2) Homes
<1500 5 <150 9
1500–1999 11 150–199 12
2000–2499 16 20–-249 15
2500–2999 16 250–299 22
3000–3499 14 300–349 6
3500 8 3500 6
Total 70 Total 70

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-18
Table S8: Sampled Homes by Number of Stories
Stories Number of Homes
1 27
2 42

2.5 1
Total 70
Table S9: Sampled Homes by Number of Bedrooms
Bedrooms Number of Homes
1 1
2 3
3 20
4 28
5 17
6 1
Total 70
Table S10: Sampled Homes by Number of Bathrooms
Bathrooms Number of Homes
1–1.5 1
2–2.5 24
3–3.5 35
4–4.5 9
5–5.5 1
Total 70

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-19
Table S11: Locations of Gas Fireplaces
Location Homes
Great room or living room 26
California room 3
Courtyard 1
Patio 2
No gas fireplace 38
Total 70
Household Demographics
HENGH homes are compared with data from American Housing Survey (2017 AHS). Data from the Public Use File (PUF)9 were used to compare with demographic data of HENGH homes. The PUF provided data for four California metropolitan areas that were surveyed in 2017: Los Angeles-Long Beach-Anaheim, San Francisco-Oakland-Hayward, Riverside-San BernardinoOntario, and San Jose-Sunnyvale-Santa Clara. The first three of the four metropolitan areas were included in the national survey, and the last one was included in the metropolitan survey. Data from owner-occupied, single-family detached homes built after 2010 were selected from the 2017 AHS data for comparison with HENGH homes in the tables below.

Table S12: Number of Occupants in Sampled Homes
Number of Occupants Number of Homes
in HENGH
% Homes in
HENGH
% Homes in 2017
AHS
1 3 4% 13%
2 29 43% 28%
3 10 15% 18%
4 13 19% 24%
5 6 9% 9%
6 3 4% 5%
7 or more 3 4% 2%
No response 3 -- --
Total 70 100% 100%

9 https://www.census.gov/programs-surveys/ahs/data/2017/ahs-2017-public-use-file--puf-.html

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-20
Table S13: Number of Occupants in Sampled Homes by Age Group Number of
Occupants
Within Age
Group
Homes with Designated Number of Occupants in Designated Age Group Number of HENGH % HENGH Homes % Homes in 2017 AHS
Age
0–17
Age
18–65
Age
65+
Age
0–17
Age
18–65
Age
65+
Age
0–17
Age
18–65
Age
65+
0 41 8 49 60% 12% 72% 59% 12% 74%
1 7 7 10 10% 10% 15% 19% 17% 14%
2 14 41 9 21% 60% 13% 18% 42% 11%
3 3 8 0 4% 12% 0% 4% 15% 0%
4 2 2 0 3% 3% 0% 0% 9% 0%
5 or more 1 2 0 1% 3% 0% 0% 5% 0%
No response 2 2 2 -- -- -- -- -- --
Total 70 70 70 100% 100% 100% 100% 100% 100%
Table S14: Total Household Income in Sampled Homes
Income Range Number of Homes
in HENGH
% Homes in
HENGH
% Homes in 2017
AHS
$35,000–$49,999 1 2% 18%
$50,000–$74,999 2 3% 12%
$75,000–$99,999 5 8% 10%
$100,000–$150,000 29 44% 20%
Greater than $150,000 29 44% 40%
No response 4 -- --
Total 70 100% 100%

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-21
Table S15: Education Level of Head of Household in Sampled Homes Education Level Number of Homes
in HENGH
% Homes in
HENGH
% Homes in 2017
AHS
No diploma 0 0% 6%
Completed high school 1 1% 16%
Some college 5 7% 15%
Associate’s degree 2 3% 7%
College degree 23 34% 30%
Graduate or professional degree 36 54% 26%
No response 3 -- --
Total 70 100% 100%
Air Tightness
Figure S3: Distribution of ACH50 from Envelope Leakage Measurements

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-22
Ventilation and Filtration Equipment
Table S16: Whole House Ventilation System Type
System Type Operation Mode Fan Location(s) Number of Homes Exhaust Continuous Laundry Room 43
Bathroom 9
Attic 3
Intermittent Laundry Room 5
Bathrooms (multiple) 4
Supply Continuous Attic 4
Intermittent None* 2
Total 70
*These central fan integrated supply (CFIS) systems had a duct with motorized damper that connected the outdoors to the return side of the forced air system, but no supply fan.

Table S17: Whole House Ventilation System Control
Whole-House Ventilation Control Controller Labelled? % On As-Found On/Off Switch No (N=42) 5%
Yes (N=12) 58%
Programmable Controller No (N=10) 50%
Thermostat No (N=2) 0%
Breaker Panel No (N=1) 100%
No Controller No (N=3) 100%

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-23
Figure S4: Bathroom Exhaust Fan Measured Flow Rates
Table S18: Air Filter MERV Ratings
MERV Number of Air Filters
6 2
7 2
8 57
10 17
11 22
12 1
13 9
14 1
Total 111

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Table S19: Time Since Last Air Filter Change
Marked or Estimated Time Number of Air Filters
0 to 2 Months 33
3 to 5 Months 16
6 to 8 Months 17
12 to 15 Months 8
Never Changed 11
Total 85
Table S20: Condition of Air Filters Observed by Field Team Air Filter Condition Number of Homes Number of Air Filters Clean or Like New 20 39
Used or Dirty 29 65
Very Dirty 18 24
Total 67* 128
* Total excludes one home (113) without a central forced air system (this home had a minisplit heat pump with no filter for air quality), one home (127) without any air filters installed in the return air registers, and one home (117) for which field observations were missing.

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-25
Figure S5: Total Estimated Air Exchange Rate
This plot includes estimates for 63 homes. It excludes four homes that used supply ventilation because the mechanical airflow could not be determined. The plot also excludes three homes with missing DeltaQ test result because building envelope airtightness is required to calculate air infiltration (part of total ventilation). There are six homes (*) where opening of the house-to-patio and/or garage door(s) for more than 3 hours per day on average may have increased the overall AER substantially.

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-26
Figure S6: Infiltration and Total Airflow (Mechanical + Infiltration) Mechanical airflow rates were calculated by summing all exhaust fans in a home. The estimated total outdoor airflow rates include both mechanical airflow and air infiltration. Data are plotted for 63 homes same as in Figure S5.

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-27
General Occupancy and Sources – From Survey
Table S21: How Frequently Are Candles Used in the Home
Number of Homes
Never 13
A few times a year 23
A few times a month 16
A few times a week 11
Every day 5
No response 2
Total 70
Table S22: Number of Furry Pets in Homes
Occupancy and Sources During Week of Monitoring
Table S23: Self-Reported Average Occupancy (Number of People) When Home Was Occupied Average Occupancy Number of Homes Average Occupancy Number of Homes 1 to <2 People 23 5 to <6 People 4
2 to <3 People 20 6 to <7 People 3
3 to <4 People 14 No Response 2
4 to <5 People 4 Total 70
Number of Pets Number of Homes
0 20
1 17
2 12
3 3
4 or more 2
No response 16
Total 70

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-28
Table S24: Self-Reported Average Occupied Hours per Day During Monitoring Week Number of Occupied Hours Number of Homes
> 23 Hours 16
20 to <23 Hours 27
16 to <20 Hours 17
12 to <16 Hours 3
6 to <12 Hours 3
< 6 Hours 2
No Response 2
Total 70
Table S25: Self-Reported Cooktop Use (Number of Times) During Monitoring Week Number of Cooktop Use Number of Homes
None 2
1–3 Times 16
4–6 Times 16
7–14 Times 26
15–21 Times 6
More than 21 Times 2
No Response 2
Total 70
Table S26: Self-Reported Oven and Outdoor Grill Use During Monitoring Week Number of Homes
Number of Uses Oven Outdoor Grill
None 16 52
1 Time 14 9
2–3 Times 21 7
4–5 Times 11 0
6–8 Times 6 0
No Response 2 2
Total 70 70

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-29
Table S27: Average Cooking Activity Duration During One-Week Monitoring, Self-Reported Number of Homes
Use Duration Cooktop Oven Outdoor Grill
Less than 10 Minutes 3 3 0
10–30 Minutes 40 20 5
30–60 Minutes 20 24 8
>60 Minutes 3 5 3
No Usage Reported 2 16 52
No Response 2 2 2
Total 70 70 70
Table S28. CNHS Activities (Table 42 and 43 of Offermann et al. 2009):
- Toasting: n=50, median of 5 min
- Frying or sautéing: n=36, median of 17 min
- Baking: n=33, median of 45 min
- Broiling: n=11, median of 19 min
- Other cooktop: warming/boiling, n=47, median of 20 min - Vacuuming: n=16, median of 25 min
- Sweeping or dusting: n=16, median of 12 min
- Candle burning, n=4 events, median of 165 min.
- Aerosol air fresheners or personal care products: n=30 - Large party or dinner gathering: n=3
- Other activities: dust, smoke or fumes: n=3, median 30 min

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-30
Air Pollutant Concentrations: Formaldehyde
Table S29 presents a comparison of formaldehyde measurements made at the main indoor site with the UMEx-100 time-integrated sampler and the weeklong average of the half-hourly resolved data obtained with the FM-801 monitor. Statistical significance tests suggest no difference in formaldehyde concentrations measured using the two methods: p-value = 0.09 (Student’s paired t-test).

Table S29: Comparison of Time-Integrated Formaldehyde Measured with Two Methods SKC UMEx-100
Passive Sampler
GrayWolf FM-801
Monitor
Indoor Main (ppb) N = 68 N = 69
Mean 19.8 18.9
Median 18.2 18.8
10th–90th Percentile 13–28 10–27
Similar to the finding (reported in the main paper) that formaldehyde measured by the UMEx was higher in the bedroom than at the main indoor site, FM-801 data collected in the bedroom also indicated higher period-averaged formaldehyde compared to data collected in the main indoor site (p-value = 4.5e-5 using Student’s paired t-test). Among the 65 homes with valid FM801 data in both locations, formaldehyde in the bedroom was >10% higher than in the living room in 35 homes and less than 90% in 4 homes. The median and 10th–90th ratios of bedroom to living room concentrations were 1.13 and 0.97–1.44. Using data from the FM-801, overnight concentrations in the bedroom were higher than the period-average at that location (p-value =

5.4e-6 using Student’s paired t-test). Formaldehyde in the bedroom overnight was >10% higher than the period-average living room in 38 homes and less than 90% in 3 homes. The median and 10th–90th ratios of bedroom overnight to period-average living room concentrations were 1.19 and 0.97–1.52.

06/23/2026 Item No.18.

IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-31
Air Pollutant Concentrations: PM2.5
A comparison of time-integrated PM2.5 measured with the MetOne and Thermo pDR photometers and co-located gravimetric samples are provided in Table S30. Table S30 Table S30. Time-integrated PM2.5 concentrations measured by MetOne and Thermo pDR-1500 photometers compared with gravimetric analysis of co-located filter samples.

House City Dates MetOne pDR Filter Filter/
MetOne
Filter/
pDR
Indoor PM2.5 (ug/m3)
025 Hayward 2017-03-23 to 03-30 3.7 4.5 4.7 1.3 1.1
026 Davis 2017-04-18 to 04-25 2.8 4.3 4.2 1.5 1.0
040 Discovery Bay 2017-05-23 to 05-30 2.1 3.2 2.8 1.3 0.9 029 Brentwood 2017-06-09 to 06-16 3.1 3.8 3.7 1.2 1.0
047 Clovis 2017-10-12 to 10-19 31.9 30.1 23.5 0.7 0.8
046 Clovis 2017-11-08 to 11-15 5.1 6.9 5.0 1.0 0.7
068 Manteca 2018-01-24 to 01-31 2.6 4.2 3.6 1.4 0.9
066 Manteca 2018-02-05 to 02-12 2.7 4.3 4.0 1.4 0.9
Outdoor PM2.5 (ug/m3)
025 Hayward 2017-03-23 to 03-30 NA 5.6 4.1 NA 0.7
026 Davis 2017-04-18 to 04-25 NA 3.4 4.4 NA 1.3
040 Discovery Bay 2017-05-23 to 05-30 4.5 5.1 4.8 1.1 0.9 029 Brentwood 2017-06-09 to 06-16 3.0 3.9 3.4 1.1 0.9
047 Clovis 2017-10-12 to 10-19 25.5 30.3 19.6 0.8 0.6
046 Clovis 2017-11-08 to 11-15 6.0 NA NA NA NA
068 Manteca 2018-01-24 to 01-31 20.2 18.2 10.6 0.5 0.6
066 Manteca 2018-02-05 to 02-12 14.0 12.4 5.6 0.4 0.4
Analysis of Regulatory Air Monitoring Data to Estimate PM2.5 Outside of HENGH Homes We investigated the possibility of using regulatory ambient air monitoring station data to develop correction factors for photometers outside of the homes. We identified up to three regulatory air monitoring stations near each of the study home. Figure S1 show locations of the air quality monitoring stations in relationship to the study home. The air monitoring stations were all located within 30 km of the study home, selected to broadly represent the air quality at that location. Air monitoring stations sited to monitor near-road concentrations (located within 100 m of a major roadway) were excluded to avoid biases from traffic emissions. The daily mean PM2.5 were obtained from AQMIS.

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-32
We applied inverse distance weighting to calculate the daily mean PM2.5 at the study home, and calculated the mean PM2.5 for the monitoring period (~6 days). Results of the inverse distance weighted ambient monitoring data are compared with the outdoor PM2.5 measured using MetOne photometer in Error! Reference source not found..

Table S31 shows the differences in mean PM2.5 measured using the MetOne photometer and inverse distance weighted ambient monitoring data. Because the ambient monitoring data obtained from AQMIS are daily means, the results presented in Table S31Table S31 considered only days with full 24-h data as monitored by the MetOne photometer (i.e., partial days on first and last day of monitoring were excluded). The mean, median, and 10th percentile estimates of PM2.5 measured by the MetOne photometer were less than what was measured at the corresponding ambient monitoring station. This suggests that the MetOne photometer may have underestimated the outdoor PM2.5 relative to the ambient monitoring data at some of the homes.

However, the reverse is true for other homes such that the MetOne photometer measurements were higher than the ambient monitoring data when compared at 90th percentile. No correction factor is applied to outdoor MetOne because of a lack of consistency when compared with the ambient monitoring data.

Table S31. Summary statistics (N=67) of the mean outdoor PM2.5 measured using MetOne photometer and inverse distance weighted ambient monitoring data.

MetOne photometer
(ug/m3)
Nearby ambient air quality
monitoring stations (ug/m3)
Mean 9.3 10.5
Median 6.8 9.7
10th–90th 2.7–18.1 5.3–16.7

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-33
Figure S7. Comparison between mean outdoor PM2.5 measured using MetOne photometer and inverse distance weighted ambient monitoring data (N=67).

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-34
Air Pollutant Concentrations: Nitrogen Dioxide and Nitric Oxide Figure S8: One-Week Integrated NO2, NO, and NOx Concentrations Ranked ordered by indoor concentrations (blue circles), with corresponding outdoor concentrations plotted as black crosses.

06/23/2026 Item No.18.

IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-35
Air Pollutant Concentrations: CO2
Figure S9: Overnight (midnight-5am) CO2 measurements in indoor main living space and master bedroom.

06/23/2026 Item No.18.

IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-36
IEQ Satisfaction by Ventilation System Operation
Tables S33 to S35 present air quality and comfort satisfaction reported by participants, divided by whether the dwelling unit ventilation system was operating when the research team arrived to the home. The Fisher’s exact test for count data was performed to determine if there is an association between the ventilation system operating at that time and satisfaction. Survey responses for satisfaction were scored using a scale between 1 and 9. For the Fisher’s test, satisfaction responses were classified into four groups: dissatisfied (1–4), neutral (5), satisfied (6–7), and very satisfied (8–9). Survey responses for frequency of a discomfort were provided using a 5-level scale: (i) never, (ii) a few times a year, (iii) a few times a month, (iv) a few times a week, and (v) every day. For the Fisher’s test, frequency responses were classified into two groups: infrequent (i, ii, or iii) and frequent (iv or v).

Table 32. Air quality satisfaction reported by participants.

To what extent are you
satisfied or dissatisfied with
indoor air quality in your
home?
How would you rate the
outdoor air quality where
you live?
How would you rate your
home in protecting you
from outdoor air pollution?
Ventilation
As-Found
Off On Off On Off On
Dissatisfied 3 3 11 8 3 2
Neutral 13 3 9 2 18 3
Satisfied 17 4 17 6 15 6
V. Satisfied 17 8 10 2 14 7
p-value 0.375 0.413 0.444
Table 33. Satisfaction with seasonal temperature conditions by ventilation system status on first visit to home.

Winter / Some
rooms are too hot1
Winter / Some
rooms are too cold1
Summer / Some
rooms are too hot1
Summer / Some
rooms are too cold1
Ventilation
As-Found
Off On Off On Off On Off On
Infrequent 41 13 36 10 37 9 45 15
Frequent 6 4 12 8 13 9 2 1
p-value 0.435 0.144 0.081 1
1 Survey question: In [season], how often is the temperature in your home uncomfortable to any occupants because [condition]?

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-37
Table 34. Satisfaction with environmental parameters by ventilation system status on first visit to home.

Too much air
movement
Not enough air
movement
Indoor air is
too dry
Indoor air is
too damp
Indoor air has
musty odor
Ventilation
As-Found
Off On Off On Off On Off On Off On
Infrequent 48 18 41 11 43 17 49 18 48 17
Frequent 1 0 8 7 5 1 1 0 1 0
p-value 1 0.094 1 1 1
1 Survey question: How often do the following conditions affect the comfort of occupants in your home? Frequent is on weekly or daily basis.

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-38
Recruitment Postcard

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-39
Daily Activity Log
Provided below is the top page of the activity log. Participants were asked to complete a log table for each calendar day during which measurements were being made in the home. Participants were provided with paper sheets containing a log for each day.

Healthy Efficient New California Homes Study
Occupancy and Indoor Activities Data Log
Instructions: Please fill out this data log each day, or on the following day.

Please enter your best estimates. If you are unsure, please provide your best guess.

Do not list the names of any people.

Code number for home _________
Day 1: Date __________________ Date completed _______________ Midnight
to 7am
7am to
11am
11am to
1pm
1pm to
5 pm
5pm to
9pm
9pm to
Midnight
Number of people
in home
Cooktop use
Number of minutes
Oven use
Number of minutes
BBQ/outdoor grill
Number of minutes
Vacuuming
Number of minutes
Window Use
Number of minutes
Other notable*
indoor/outdoor events
* For example, use of fireplace, candle, air freshener, air cleaner, humidifier, unusual outdoor air quality (wood smoke, wildfire), and so on.

06/23/2026 Item No.18.

IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-40
Occupant Survey
Welcome to the 2015 California New Homes Survey!
This survey is part of a research study on new homes in California. This research will help inform how new homes can provide adequate ventilation and good indoor air quality, while reducing air infiltration and energy use.

This survey takes about 15 minutes to complete. It asks questions about your home, household activities, and demographics. You can skip questions that you do not want to answer.

This research is being conducted by Lawrence Berkeley National Laboratory (LBNL) with funding from the California Energy Commission. Results will be used only for research on how to provide adequate ventilation and improve indoor air quality. In order to protect your privacy, the data will be encrypted and password protected.

Please return your completed survey in the envelope provided.

If you have questions about the research study, please contact:

Max Sherman, Ph.D.

Principal Investigator, Residential Building Systems Group Lawrence Berkeley National Laboratory
[email protected] (510) 486 4022
Code number for home _________ Date completed _______________

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IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-41
Please answer to the best of your knowledge. You can skip any questions that you do not want answer.

A. Home and Household Characteristics

1. What year was your house built?
Year Built: ………………

2. What is the size (floor area) of your home?
Square Feet: ………………

3. What year did you move into this home?
Year Moved In: ……………….

4. Do you own or rent your home?
……. Own (If yes  5, skip otherwise)
……. Rent
……. Other

5. Are you the first owner of the property? Yes / No

6. How many people currently live in your home?
Number of People: ……………..

B. Air Quality In and Around Your Home

7. To what extent are you satisfied or dissatisfied with the indoor air quality in your home? Very
Dissatisfied
Neutral Very
Satisfied
☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐

8. How would you rate the outdoor air quality near where you live? Very
Poor
Neutral Excellent
☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐

9. How would you rate your home in protecting you from outdoor air pollution? Very
Ineffective
Neutral Very
Effective
☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐

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C. Comfort Level in Your Home

10. In winter, how often is the temperature in your home uncomfortable to any occupants because some room(s) are too hot or too cold?
Never Few times
a year
Few times
in a month
Few times
a week
Every
day
Too hot in some room(s). ☐ ☐ ☐ ☐ ☐
Too cold in some room(s). ☐ ☐ ☐ ☐ ☐

11. In summer, how often is the temperature in your home uncomfortable to any occupants because some room(s) are too hot or too cold?
Never Few times
a year
Few times
a month
Few times
a week
Every
day
Too hot in some room(s). ☐ ☐ ☐ ☐ ☐
Too cold in some room(s). ☐ ☐ ☐ ☐ ☐

12. How often do the following conditions affect the comfort of occupants in your home? Never Few times
a year
Few times
a month
Few times
a week
Every
day
Too much air movement. ☐ ☐ ☐ ☐ ☐
Not enough air movement. ☐ ☐ ☐ ☐ ☐
Indoor air is too dry. ☐ ☐ ☐ ☐ ☐
Indoor air is too damp. ☐ ☐ ☐ ☐ ☐
Indoor air has musty odor. ☐ ☐ ☐ ☐ ☐

06/23/2026 Item No.18.

IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-43
D. Natural Gas Appliances and Mechanical Ventilation

13. Which of the following heating appliances are used in your home? Select all that apply. ..….. Central gas furnace
……. Gas fireplace/ log set
….... Gas wall furnace
……. Freestanding gas heater
……. Central electric heating or heat-pump
……. Baseboard electric wall heater
……. Freestanding electric heater
……. Wood fireplace
……. Freestanding propane heater
……. Freestanding kerosene heater
……. Other. Please describe: ...………………………….
……. Don’t know

14. How often is the kitchen range hood or kitchen exhaust fan used when cooking with a cooktop?
……. Always (5 out of 5 times)
……. Most of the Time (4 out of 5 times)
……. Sometimes (2 to 3 out of 5 times)
……. Rarely (1 out of 5 times)
……. Never (0 out of 5 times)
……. Don’t know

15. If the kitchen range hood or kitchen exhaust fan is NOT always used, what are the reasons for not using it? Select all that apply.
……. Forget to turn it on
……. Not needed for what is being cooked
……. Too noisy
……. Doesn’t seem to remove cooking fumes or odors
……. Open window instead
……. Uses too much energy
……. Other. Please describe: ……………........................................

16. Was the operation of the mechanical ventilation system explained to you when you bought or moved into the home?
……. Yes
……. No
……. Don’t know

17. Do you feel you understand how to operate your mechanical ventilation system properly? ……. Yes
……. No
……. Not Sure

06/23/2026 Item No.18.

IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-44

18. To what extent are you satisfied or dissatisfied with your mechanical ventilation system? Very
Dissatisfied
Neutral Very
Satisfied
☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐ ☐

19. If you are NOT very satisfied with your mechanical ventilation system, what are the reason(s) for dissatisfaction? Select all that apply.
……. Too noisy
……. Too drafty
……. Difficult to operate
……. Difficult to maintain
……. Uses too much energy
……. Brings in dust, odor, or air pollutants from outdoor ……. Not effective
……. Other. Please describe: ………………………………….

E. Occupancy and Indoor Activities

20. On average, how many hours per day is your home occupied by at least one person, including day and night hours?
Fewer than 8
hours per
day
8 to 12 hours
per day
12 to 16
hours per
day
16 to 20
hours per
day
More than 20
hours per
day
Weekday ☐ ☐ ☐ ☐ ☐
Weekend ☐ ☐ ☐ ☐ ☐

21. On average, how many times per week is your cooktop and/or oven used for cooking, including boiling water?
0 time
per week
1 to 2 times
per week
3 to 4 times
per week
5 to 6 times
per week
7 times
per week
Breakfast ☐ ☐ ☐ ☐ ☐
Lunch ☐ ☐ ☐ ☐ ☐
Dinner ☐ ☐ ☐ ☐ ☐
Other cooking ☐ ☐ ☐ ☐ ☐

06/23/2026 Item No.18.

IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-45

22. On average, how many times per week do the following activities occur inside your home? Enter “0” if occurrence is less frequent than once a week.

Use shower (Times per week) …………………
Use bath or indoor Jacuzzi (Times per week) …………………
Use dishwasher (Times per week) …………………
Use washing machine (Loads per week) ………………..

Hang clothes to dry indoors (Loads per week) ………………..

F. Window Opening

23. On average, how many hours per day are your windows open? 0 hour per
day
1 to 2 hour
per day
2 to 8 hours
per day
8 to 16
hours per
day
More than 16
hours per day
Summer ☐ ☐ ☐ ☐ ☐
Fall ☐ ☐ ☐ ☐ ☐
Winter ☐ ☐ ☐ ☐ ☐
Spring ☐ ☐ ☐ ☐ ☐
G. Indoor Activities

24. On average, how often do the following activities occur inside your home? Never Few times
a year
Few times
a month
Few times
a week
Every
day
Smoking ☐ ☐ ☐ ☐ ☐
Burn candle or incense ☐ ☐ ☐ ☐ ☐
Vacuuming ☐ ☐ ☐ ☐ ☐
Use cleaning agent for floor
cleaning
☐ ☐ ☐ ☐ ☐
Use spray air freshener ☐ ☐ ☐ ☐ ☐
Use pesticide spray ☐ ☐ ☐ ☐ ☐
Use paints, glue, solvents (e.g.,
hobbies, home repairs)
☐ ☐ ☐ ☐ ☐
Use humidifier ☐ ☐ ☐ ☐ ☐
Use dehumidifier ☐ ☐ ☐ ☐ ☐

06/23/2026 Item No.18.

IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-46
H. Other Indoor Sources

25. Are plug-in or stick air fresheners, or other scented decorations, used in your home? ……. Yes
……. No
……. Don’t know

26. Do occupants wear shoes in your home?
……. Yes
……. No
……. Don’t know

40. How many dogs, cats, or other furry pets are in the home? Number of Pets: ………………
I. Use of Air Cleaners

27. Do you use a stand-alone (portable) air filter, air purifier, or air cleaner in the home? ……. Yes
……. No
……. Don’t know

28. Where is your stand-alone (portable) air filter, air purifier, or air cleaner located in your home? Select all that apply.
……. Master bedroom
……. Other bedroom(s)
……. Living room
……. Home office
……. Other. Please describe: ……………........................................

29. Has anyone in the household been diagnosed with asthma? ……. Yes
……. No
……. Don’t know

30. Has anyone in the household been diagnosed with allergies? ……. Yes
……. No
……. Don’t know

06/23/2026 Item No.18.

IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-47
J. Demographic Information
The next questions will help us interpret the results of the survey. All responses will be kept confidential.

31. Please indicate the number of household member(s) in the following age categories.

Number of household member(s)
0 to 17 Years Old ……………………
18 to 65 Years old ……………………
Over 65 Years old ……………………

32. What is the highest education level of head of household? …….. No schooling completed
…….. 1 to 8th grade
…….. 9th to 12th grade
…….. Completed high school (high school diploma, GED credential) …….. Some college
…….. Associate’s degree
…….. College degree (Bachelor’s degree)
…….. Graduate degree (Master’s, Professional school, Doctorate degree)

33. Please indicate all races and/or ethnicities of people living in your household. …….. American Indian, Alaska Native
…….. Asian or Pacific Islander
…….. Black, African American
…….. Hispanic/ Latino
…….. White, Caucasian
…….. Other, specify: ………………….
…….. Mixed race, specify: ………………….

34. What is the total income of all member(s) of your household combined? …….. Less than $35,000
…….. $35,000 to $ 49,999
…….. $50,000 to $ 74,999
…….. $75,000 to $ 99,999
…….. $100,000 to $150,000
…….. Greater than $150,000
K. End of Survey
Thank you for filling out this survey! Your data is very valuable to our understanding of indoor air quality and mechanical ventilation in new California homes.

Please return your completed survey in the envelope provided.

If you have any questions about the survey, please contact: [LBNL contact provided]

06/23/2026 Item No.18.

IAQ in Mechanically Ventilated U.S. Homes INA-19-10-297-R2 04-April-2020 SI-48

06/23/2026 Item No.18.

Attachment 26
Buchalter/ECORP Comment Response Letter,
Dated June 15, 2026

06/23/2026 Item No.18.
425 Market Street
Suite 2900
San Francisco, CA 94105
415.227.0900 Phone
415.227.0770 Fax
BUCHALTER 110892766v1
110892766v2
415.227.3508 Direct
aguerra@buchalte r.com June 15, 2026
Jessica Brandt, Principal Planner
Planning Department
City of Folsom
50 Natoma Street
Folsom, CA 95630
Re: Toll Brothers’ Response to Late-Submitted Comments of Laborers Union of North America, Local Union 185 for Toll Brothers at Alder Creek Project, File # MSTR25-00084
Dear Ms. Brandt:

Buchalter, LLP, (“Buchalter”) represents Toll Brothers, Inc. (“Toll Brothers”) as land use counsel regarding its project to develop 1,424 single-family homes and associated infrastructure (the “Alder Creek Project” or “Project”) on an approximately 464.2-acre project site (the “Property”) located in the Folsom Plan Area Specific Plan (“FPASP”) in the City of Folsom (the “City”). The Toll Brothers Alder Creek Project includes 1,488 lots for the development of 1,424 dwelling units and private recreation, parks, landscaping, open space, roadways, fire stations, and an elementary school. Since early last year, Toll Brothers applied for and has been processing with the City a Small Lot Vesting Tentative Map, Planned Development Permit, Design Guidelines, Landscape Guidelines, and a Minor Administrative Modification to develop the Project (the “Project Approvals”).

The purpose of our letter is to respond to late hit comments from Lozeau Drury LLP that were submitted to the City of Folsom on behalf of the Laborers International Union of North America, Local Union 185 (“LIUNA”) regarding Agenda Item No. 10 of the June 9, 2026 City Council hearing for the Toll Brothers at Alder Creek Project (File #MSTR25-00084). Never having participated in any City proceedings concerning any FPASP projects since its adoption 15 years ago, now LIUNA, has shown up at the end of the approval process for Toll Brothers’ Project even though it is consistent with the FPASP. At the eleventh hour, LIUNA improperly claims the Project requires further environmental review under the California Environmental Quality Act (CEQA) based on supposed new information and changed circumstances which

06/23/2026 Item No.18.

Jessica Brandt
June 15, 2026

BUCHALTER 110892766v1
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LIUNA contends requires supplemental environmental review, even though the only information LIUNA provides is information generated by LIUNA that does not apply to the Project as further explained below. LIUNA has not provided any substantial evidence to support any of the claims raised in LIUNA’s June 8, 2026 Letter as demonstrated in the attached memorandum entitled, “Alder Creek – Conformity Analysis,” prepared by ECORP Consulting, Inc. dated June 12, 2026 (“ECORP Memorandum”). For the reasons discussed in this letter and the attached, we respectfully request that the City Council disregard LIUNA’s comments and approve the Alder Creek Project based on the Alder Creek Conformity Analysis.

The City Conducted Prior CEQA Review of the FPASP and Concluded that the Alder Creek Project Would Not Require a Supplemental EIR Because There are No New Significant or Substantially Greater Environmental Impacts.

The Project is located in the FPASP area and was previously subject to an Environmental Impact Report/Environmental Impact Statement (EIR/EIS) for the Folsom South of U.S.

Highway 50 Specific Plan Project. The City of Folsom and U.S. Army Corps of Engineers (USACE) jointly prepared an EIR/EIS to fulfill requirements of the California Environmental Quality Act (CEQA) and National Environmental Policy Act, respectively. The City filed a Notice of Determination (NOD) for the EIR on June 15, 2011 (State Clearinghouse [SCH] #2008092051), and the USACE filed a Record of Decision for the EIR/EIS on August 12, 2011, (SPK-2007-02159). The City prepared and adopted a Mitigation Monitoring and Reporting Program (MMRP) when it adopted the FPASP. The approved MMRP outlines mitigation measures required for the projects located in the FPASP, including the Alder Creek West Project.

The City later prepared and adopted an Initial Study (IS) and Mitigated Negative Declaration (MND) for the FPASP Backbone Infrastructure (“BB IS/MND”) and filed an NOD on February 25, 2015 (SCH #2114122018). The BB IS/MND outlines mitigation measures specifically for the Backbone Infrastructure development.

The City has relied on the FPASP EIR for the approval of subsequent specific residential projects consistent with the FPASP in accordance with Government Code Section 65457. As a specific project proposed in conformance with the FPASP, the Project is subject to a statutory CEQA exemption because the Project was subject to the prior Specific Plan EIR, and subsequent environmental review did not result in the identification of significant and unavoidable environmental impacts. Moreover, CEQA Guidelines section 15182(c) states that "Where a public agency has prepared an EIR on a specific plan after January 1, 1980, a residential project undertaken pursuant to and in conformity to that specific plan is exempt from CEQA if the project meets the requirements of this section. Residential projects covered by this section include but are not limited to land subdivisions, zoning changes, and residential planned unit developments." The 15182 exemption does not apply if an event described in Section 15162 occurs, which is not the case here.

06/23/2026 Item No.18.

Jessica Brandt
June 15, 2026

BUCHALTER 110892766v1
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ECORP Consulting prepared the attached August 2025 Alder Creek Conformity Analysis to examine the Project under the FPASP EIR/EIS, pursuant to CEQA Guidelines Section 15182, to determine if any of the events described in CEQA Guidelines Section 15162 have occurred, and were not considered in the FPASP.

Despite the extensive technical information prepared for the Project Conformity Analysis, LIUNA requested that the City prepare a new “supplementary” EIR for the Project Tentative Map due to two primary unsubstantiated claims. First, LIUNA claims with respect to the evaluation of biological resource impacts, that new information of substantial importance exists that was not known at the time the 2011 FPASP EIR was certified, and that the new information will have significant effects not discussed in the EIR. The LIUNA Letter claims that there is substantial evidence of the presence of a special-status species, which has the potential to result in significant impacts to the species, is cause for requiring a supplemental EIR. Second, LIUNA claimed that CEQA requires a new EIR when new air quality mitigation measures become available after the 2011 FPASP EIR/EIS was certified. The June 12th ECORP Memorandum confirms that the LIUNA Letter did not identify any new significant impacts warranting supplemental environmental review as further discussed below and in the attached ECORP Memorandum.

Substantial Evidence Supports the Alder Creek Conformity Analysis.

CEQA requires that an EIR include adequate information to ensure informed decisions are made about a project. CEQA further requires that the lead agency evaluate whether or not a proposed project will result in a significant environmental impact based on substantial evidence.

Under Public Resources Code Section 21082.2(c), substantial evidence includes facts, reasonable assumptions predicated upon facts, and expert opinion supported by facts. Argument, speculation and unsubstantiated opinion are not substantial evidence. The substantial evidence standard of review applies to disagreements concerning the methodology used for studying an impact, and the reliability or accuracy of the data upon which the EIR relied. Even when commenters suggest that different conclusions should be reached, or different methods of gathering and compiling statistics could have been used, that does not constitute substantial evidence. The issue is not whether other methods might have been used, “but whether the agency relied on evidence that a reasonable mind might accept as sufficient to support the conclusion reached in the EIR.” North Coast Rivers Alliance v. Marin Municipal Water Dist. Bd. Of Directors, 216 Cal.App.4th 614, 615 (2013). Moreover, when an agency prepares an EIR (and subsequent environmental documents relying upon them), the issue is whether substantial evidence supports the agency’s conclusions, not whether others might disagree with those conclusions (North Coast Rivers Alliance v. Marin Municipal Water Dist. Bd. Of Directors, 216 Cal.App.4th 614, 624 (2013)).

Contrary to LIUNA’s unsubstantiated claims, the FPASP EIR was based on substantial evidence in the administrative record as documented in the ECORP Conformity Analysis and

06/23/2026 Item No.18.

Jessica Brandt
June 15, 2026

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extensive technical reports upon which that analysis is based. Since the City certified the EIR in 2011, the City has relied on this evidence for its approval of the subsequent entitlements necessary to implement the FPASP. As the ECORP Memorandum explains, substantial evidence supports the City’s reliance on the prior FPASP EIR for the Project Approvals the results of which are documented in the Conformity Analysis.

The City Council Must Approve the Project in Accordance with the Housing Accountability Act.

The Legislature has long recognized that “housing is of vital statewide importance,” and the provision of suitable housing for every Californian is “a priority of the highest order.” (Gov.

Code § 65580(a).) But California is in the midst of a housing crisis, and to address California’s severe housing shortage, the Legislature enacted the Housing Accountability Act (“HAA”) to significantly limit a local government’s ability to deny, reduce the density of, or make infeasible housing development projects that provide affordable housing units. (Gov. Code § 65589.5(d).) Toll Brothers predecessor in interest obtained entitlements for the FPASP Project along with associated infrastructure for the 464.2 acre Project site as part of five permit areas: Mangini Ranch, Alder Ranch (also known as Folsom 560 and Hillsborough), Carpenter Ranch, Javanifard and Zarghami Property (J & Z Property) (see Conformity Analysis, page 2-3). The Alder Creek Project Approvals include the Small Lot Vesting Tentative Map for 1,424 residential lots consistent with the General Plan land use designations and FSASP designations. Under the HAA, the City may not deny, reduce the density of or make the Project infeasible unless there is a preponderance of the evidence demonstrating that the housing development will result in a significant public health and safety impact.

That could not be further from the case here. LIUNA’s comments address only the existence of the listing of species which is not a new impact under CEQA, and new mitigation measures to address operational air quality impacts that are typical of mobile source and construction source emissions associated with other residential projects in the community. There is no evidence whatsoever that approval of the specific Project Approvals for the Alder Creek Project would result in any public health and safety impacts. For that reason, the City Council should uphold the Planning Commission’s recommendation for Project approval in accordance with the HAA, and reject LIUNA’s last minute unsubstantiated efforts to hold the residential project hostage to study impacts that were already evaluated and mitigated by the Project’s implementation of the FPASP EIR mitigation measures.

Substantial Evidence Supports the City’s Determination that the Project would not Trigger any New Significant Environmental Impacts and would not Require Subsequent Environmental Review under Public Resources Code § 21166.

06/23/2026 Item No.18.

Jessica Brandt
June 15, 2026

BUCHALTER 110892766v1
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CEQA defines an approval as the decision by a public agency committing the agency “to a definite course of action in regard to a project intended to be carried out.” (CEQA Guidelines, § 15352(a).) For private projects, an approval “occurs upon the earliest commitment to issue” some discretionary entitlement. (CEQA Guidelines, § 15352(b).) CEQA further limits the situations in which an activity will be subject to additional CEQA review, after a lead agency has already satisfied the environmental review requirements. Under Public Resources Code section 21166 and CEQA Guidelines section 15162, if a lead agency has already certified an EIR for a project, a subsequent discretionary approval will not be subject to CEQA review unless:
(1) substantial changes are proposed in the project which will require major revisions of the EIR;
(2) substantial changes occur with respect to the circumstances under which the project is being undertaken which will require major revisions in the EIR; or (3) new information which was not known and could not have been known at the time the EIR was certified as complete, becomes available.
(Pub. Res. Code, § 21166; CEQA Guidelines, § 15162.)
Once an EIR has been certified for a Project CEQA does not require a new EIR unless there are new significant or substantially more severe impacts associated with a subsequent discretionary approval in accordance with Public Resources Code Section 21166 and CEQA Guidelines Section 15162. Even if changed circumstances occur (which is not the case here per the ECORP Memorandum and the 2025 Conformity Analysis), subsequent environmental review will not be required if the resulting environmental impacts were already addressed in the prior EIR or if the changed circumstances will not result in effects that are substantially more severe than those previously evaluated. (Committee for Re-Evaluation of the T-Line Loop v. San Francisco Mun. Transp. Agency (2016) 6 Cal.App.5th 1237, 1255-56.) In this case, the City complied with CEQA when it certified the 2011 EIR, and then when it adopted an IS/MND in 2015 for the Backbone Infrastructure for the FPASP area. When the City adopted the Specific Plan, the City committed to the Project as part of the entire development of the FPASP area, a portion of which included the Alder Creek Project 1,424 units included in the FPASP. It was at that time that the City could (and did) impose conditions of approval and mitigation measures to reduce the Project’s environmental impacts evaluated in the 2011 EIR.

Even though the City Council is now considering approval for the Project’s Small Lot Vesting Tentative Map and other Project Approvals consistent with the prior 2011 Specific Plan, none of the circumstances exist (described above) that would require subsequent CEQA review, especially under the statutory exemption pursuant to Government Code section 65674 and CEQA Guidelines Section 15182. The LIUNA letter did not identify any new information associated with the Project Approvals that would show that there are significant changes in the Project or circumstances under which it was approved that would result in new significant or substantially greater impacts than the previously identified Project impacts already evaluated the

06/23/2026 Item No.18.

Jessica Brandt
June 15, 2026

BUCHALTER 110892766v1
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2011 EIR. Since nothing about the Project or how it is being developed has changed, and because the Project will not result in any new substantial environmental impacts, no additional CEQA review is required as a result of the City Council’s approval of the Project Approvals.

The City’s reliance on the 2011 EIR to approve the Project Approvals therefore complies with CEQA.

There is No Evidence that Residents will be Subject to Sustained Elevated Indoor Formaldehyde Levels.

Public Resources Code Section 21166 and CEQA Guidelines Section 15162 provide that no subsequent EIR shall be prepared unless the lead agency determines on the basis of substantial evidence, that new information of substantial importance, which was not known and could not have been known with the exercise of reasonable diligence at the time the previous EIR was certified as complete or the Negative Declaration was adopted, shows that the Project would result in new significant impacts. As addressed in the ECORP Memorandum, LIUNA mistakenly claims the City must prepare another EIR for the Project because of some speculative assertion that residents would be exposed to indoor levels of formaldehyde purportedly resulting in new impacts since the City certified the 2011 FPASP EIR. LIUNA has not provided any substantial evidence to support their claim that the Project will be constructed with building materials with significant amounts of formaldehyde.

The California Air Resources Board (“CARB”) and Sacramento Metropolitan Air Quality Management District (“SMAQMD”) do not require the evaluation of indoor formaldehyde emissions from building materials and practices for residential uses. Nonetheless, as the ECORP Memorandum states, the Project is required to and will comply with applicable California Air Resources Board (“CARB”) and Sacramento Metropolitan Air Quality Management District (“SMAQMD”) requirements. Consequently, LIUNA fails to provide any evidence that the Project would result in any new significant impacts associated with formaldehyde levels.

The Availability of New Air Quality Mitigation Measures does not Require Preparation of a Supplemental EIR.

As analyzed in the ECORP Memorandum, LIUNA mistakenly claims the City must prepare another EIR for the Project because EV charging infrastructure and battery storage systems for each new residence would substantially reduce significant and unavoidable air quality and greenhouse gas emissions (“GHG”) impacts previously identified in the FPASP EIR.

With respect to the existence of possible new air quality mitigation measures (assuming they are feasible), Public Resources Code Section 21166 and CEQA Guidelines Section 15162 provide that no subsequent EIR shall be prepared unless the lead agency determines on the basis of substantial evidence, that:

06/23/2026 Item No.18.

Jessica Brandt
June 15, 2026

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(a)(3) New information of substantial importance, which was not known and could not have been known with the exercise of reasonable diligence at the time the previous EIR was certified as complete or the Negative Declaration was adopted, shows any of the following:
(D) Mitigation measures or alternatives which are considerably different from those analyzed in the previous EIR would substantially reduce one or more significant effects on the environment, but the project proponents decline to adopt the mitigation measure or alternative. (Emphasis added.) The LIUNA Letter asserts that a “supplementary” EIR is required to include new mitigation measures such as installing Level 2 EV charging infrastructure and battery storage systems at each residence and suggests that the City can just revise the 2011 EIR mitigation measures to improve on the prior measures that the City already adopted and for which conditions of approval were incorporated into the prior Project approvals to address significant and unavoidable air quality and GHG impacts. However, the California Building Code requirements already address EV capable infrastructure and the Project is required to comply with State law. LIUNA misstates CEQA’s requirements. The mere availability of new mitigation measures does not, by itself, trigger a subsequent or supplemental EIR. That is not what CEQA requires. Rather, pursuant to CEQA Guidelines Section 15163, a subsequent EIR is required if, and when “project proponents decline to adopt” the newly available mitigation measures. In this case, Toll Brothers agreed to incorporate the prior required mitigation measures into its Project, and there is no evidence to suggest that it won’t comply with the applicable conditions of approval. There is no substantial evidence in the record indicating that Toll Brothers declined to adopt any applicable mitigation measures included in the 2011 EIR.

With respect to the Project Approvals, LIUNA has not provided any evidence that the City’s approval of the Small Lot Vesting Tentative Map, Planned Development Permit, Design Guidelines, Landscape Guidelines, and a Minor Administrative Modification included in the certified 2011 EIR would have otherwise required new or different mitigation measures. They are unable to do so because the Project includes the same number of dwelling units compared to the approved Project and there are no new or substantially greater air quality impacts associated with building the same number of housing units evaluated in the 2011 EIR. Because there are no new impacts or substantially greater air quality impacts compared to the prior EIR analysis, CEQA does not require that the City change the mitigation measures it already adopted when it approved the 2011 FPASP and the Project.

LIUNA has failed to demonstrate that there is substantial evidence requiring that the City replace the prior adopted mitigation measures with new measures to mitigate the same impacts caused by the Project. CEQA does not require a new EIR simply because a project opponent prefers that the lead agency replace mitigation measures that were already effective in reducing

06/23/2026 Item No.18.

Jessica Brandt
June 15, 2026

BUCHALTER 110892766v1
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the impact to a less than significant level. Accordingly, CEQA allows the City to rely on the prior 2011 EIR for the Project Approvals.

We respectfully request that the City Council disregard LIUNA’s comments on the Project and uphold the Planning Commission’s approval of the Project. Based on the substantial evidence in the administrative record, the City Council may – and should in accordance with the statutory Specific Plan exemption -- properly rely on the 2011 EIR and approve Project in accordance with the HAA.

Toll Brothers appreciates the City’s consideration of the attached ECORP Memorandum and looks forward to the City Council’s approval of the Project at its upcoming meeting.

Sincerely,

BUCHALTER LLP
Alicia Guerra
Partner
AG:nj
Attachments
cc: City Clerk
Sari Myers Dierking, Interim City Attorney
Demond Parrington, Planning Manager
Martin Nivinski
Andrew Gunson
Scott Esping
Greg Van Dam

06/23/2026 Item No.18.

2024-012.01/Alder Creek Property 2025
Rocklin ♦ Redlands ♦ Irvine ♦ San Diego ♦ Chico ♦ Santa Fe ♦ Fresno ♦ ecorpconsulting.com

MEMORANDUM
TO: Martin Nivinski
CC: Jessica Brandt
FROM: ECORP Consulting, Inc.

DATE: June 12, 2026
RE: Alder Creek – Conformity Analysis

SUMMARY
In August 2025, a CEQA Guidelines Section 15182 and 15162 Conformity Analysis was prepared for the Toll Brothers Property, Alder Creek Subdivision Tentative Map. The Conformity Analysis evaluated the approval of a Small Lot Vesting Tentative Map, Planned Development Permit, Design Guidelines, Landscape Guidelines, and a Minor Administrative Modification. The project area covers approximately 464.2 acres and includes 1,424 single-family dwelling units of varying densities. Additionally, various parcels are designated for land uses such as private recreation, parks, landscaping, open space, roadways, fire stations, and an elementary school, creating a total of 1,488 lots.

On June 8, 2026, Lozeau Drury LLP submitted a letter to the City of Folsom on behalf of the Laborers International Union of North America, Local Union 185 (“LIUNA”) regarding Agenda Item No. 10 of the June 9, 2026 City Council hearing for the Toll Brothers at Alder Creek Project (File #MSTR25-00084). The letter focuses on compliance with the California Environmental Quality Act (CEQA) and argues that new information and changed circumstances require subsequent or supplemental environmental review.

CALIFORNIA ENVIRONMENTAL QUALITY ACT COMPLIANCE
CEQA applies to proposed projects initiated by, funded by, or requiring discretionary approvals from state or local government agencies. As such, the proposed project constitutes a project as defined by CEQA (California Public Resources Code, Section 21000 et seq.). CEQA Guidelines Section 15367 states that a “Lead Agency” is “the public agency which has the principal responsibility for carrying out or approving a project.” Therefore, the City of Folsom (City) is the lead agency responsible for compliance with CEQA for the proposed project. An Environmental Impact Report/Environmental Impact Statement (EIR/EIS) for the Folsom South of U.S. Highway 50 Specific Plan Project was prepared jointly by the City of Folsom and U.S.

Army Corps of Engineers (USACE) to fulfill requirements of the California Environmental Quality Act (CEQA) and National Environmental Policy Act, respectively. A Notice of Determination (NOD) for the EIR

06/23/2026 Item No.18.

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was filed by the City of Folsom on June 15, 2011 (State Clearinghouse [SCH] #2008092051), and a Record of Decision for the EIR/EIS was filed by the USACE on August 12, 2011, (SPK-2007-02159). A Mitigation Monitoring and Reporting Program (MMRP) was prepared and adopted with the Folsom Plan Area Specific Plan (FPASP) and is a binding document applicable to the Alder Creek Property development (see Appendix A of the Conformity Analysis). The approved MMRP outlines mitigation measures required for all projects located within the FPASP. An Initial Study (IS) and Mitigated Negative Declaration (MND) was prepared for the FPASP Backbone Infrastructure (BB IS/MND), and an NOD was filed by the City of Folsom on February 25, 2015 (SCH #2114122018). The BB IS/MND outlines mitigation measures specifically for the Backbone Infrastructure development. The mitigation measures in the BB IS/MND mirror the original EIR/EIS with some modifications. The Conformity Analysis was prepared to examine the project in light of the FPASP EIR/EIS (City of Folsom 2011), pursuant to CEQA Guidelines Section 15182, to determine if any of the events described in CEQA Guidelines Section 15162 have occurred, and were not considered in the FPASP.

The CEQA Guidelines section 15182(c) states that "Where a public agency has prepared an EIR on a specific plan after January 1, 1980, a residential project undertaken pursuant to and in conformity to that specific plan is exempt from CEQA if the project meets the requirements of this section. Residential projects covered by this section include but are not limited to land subdivisions, zoning changes, and residential planned unit developments." The 15182 exemption shall not apply if an event described in Section 15162 occurs, which includes the following circumstances:
“(1) substantial changes are proposed in the project which will require major revisions of the previous EIR or negative declaration due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified significant effects; (2) substantial changes occur with respect to the circumstances under which the project is undertaken which will require major revisions of the previous EIR or Negative Declaration due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified significant effects; or
(3) New information of substantial importance, which was not known and could not have been known with the exercise of reasonable diligence at the time the previous EIR was certified as complete or the Negative Declaration was adopted, shows any of the following:

A. The project will have one or more significant effects not discussed in the previous EIR or negative declaration;
B. Significant effects previously examined will be substantially more severe than shown in the previous EIR;
C. Mitigation measures or alternatives previously found not to be feasible would in fact be feasible, and would substantially reduce one or more significant effects of the project, but the project proponents decline to adopt the mitigation measure or alternative; or

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D. Mitigation measures or alternatives which are considerably different from those analyzed in the previous EIR would substantially reduce one or more significant effects on the environment, but the project proponents decline to adopt the mitigation measure or alternative.”
For purposes of the conformity analysis, however, because the proposed project implements and is consistent with the FPASP, and none of the factors set forth in CEQA Guidelines Section 15162 are present or have been identified, pursuant to CEQA Guidelines Section 15182, the City finds that the project is exempt from further CEQA compliance. The City further finds that the project is also exempt pursuant to Government Code Section 65457.

Biological Compliance
The Project would not result in a new significant impact to special-status species.

The primary issue raised in the comment letter for biological resources is the contention that new information of substantial importance exists that was not known at the time the previous EIR was prepared, and that the new information will have significant effects not discussed in the EIR. The letter states that substantial evidence of the presence of a special-status species, which has the potential to result in significant impacts to the species, is cause for requiring a supplemental EIR.

Exhibit A, Table 1, of the comment letter includes a list of special-status wildlife species occurring “at or near” the Project Site. It defines “nearby” as within 1.5 to 4 miles, and “in region” as within 4 to 30 miles, and “in range” as within the species’ geographic range. The letter identifies several of these species as having new status designations that afford them additional consideration under CEQA.

ECORP Consulting, Inc. (ECORP) disagrees that substantial information exists to demonstrate there would be new significant impacts to special-status species. All of the species on the list provided by the commenter were evaluated by ECORP biologists and species experts for their potential to occur in the Project Area using reliable sources of information, including queries of state and federal agency species’ occurrence records and published reference materials (Appendix A). We note that two of the references cited in the comment letter, eBird and iNaturalist, contain unverified records submitted by members of the public who may or may not accurately identify species. ECORP references these sources for general information, but in practice, they cannot be assumed to be a reliable source of validated species occurrences, comparable to the verified databases provided by California Department of Fish and Wildlife (CDFW) and U.S. Fish and Wildlife Service (USFWS).

The letter specifically cites foothill yellow-legged frog (Rana boylii) and western yellow-billed cuckoo (Coccyzus americanus occidentalis) as being species that were listed as endangered or threatened under the federal Endangered Species Act (ESA) or California ESA (CESA) since the 2011 EIR was prepared and are “likely present in the Project Area.” Based on literature reviews and field investigations conducted by ECORP, neither of these species has potential habitat or is likely to occur in the Project Area.  Foothill yellow-legged frog – This species was evaluated during the biological resources literature review and field surveys conducted in support of the Conformity Analysis. The species occurs in

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shallow foothill and mountain streams with cobble substrates. Aquatic features in the Project Area have been extensively surveyed, and suitable habitat does not occur in the Project Area. The historic range of the “South Sierra” Distinct Population Segment of this species roughly corresponds to the El Dorado County boundary eastward (USFWS 2023). The nearest occurrence of species, as documented by the CDFW’s California Natural Diversity Data Base (CNDDB) is approximately 4 miles to the northeast, at an elevation more than 200 feet above the Project Area, observed in 1972 and now considered extirpated (CDFW 2026a). All other CNDDB occurrences are limited to higher elevation streams farther east. Foothill yellow-legged frog is not expected to occur in the Project Area.
 Western yellow-billed cuckoo – This species was not specifically evaluated because it does not appear on standard species searches conducted for the Project Area through the CNDDB or U.S.

Fish and Wildlife Service’s Information for Planning and Consultation (iPAC) online search tool.

Western yellow-billed cuckoo requires expansive blocks of tracts of streamside riparian habitats with dense vegetation (USFWS 2014). The Project Area contains only small, isolated patches of riparian vegetation that do not meet the necessary habitat requirements for this species.

Additionally, the Project Area is not within the current range of the species, as reported by the USFWS’ online interactive species range map (USFWS 2026) or the CDFW’s species range data set (CDFW 2026b). The nearest validated historical occurrence is approximately 19 miles away along the Sacramento River and is based on an observation from 1877 and is believed to be extirpated (CNDDB 2026). Thus, further review of this species’ habitat requirements and geographic range confirm that Western yellow-billed cuckoo is not expected to occur in the Project Area.

The letter states that three invertebrates species that have been identified as candidates for listing since preparation of the 2011 EIR – Monarch butterfly (Danaus plexippus), western bumble bee (Bombus occidentalis), and Crotch’s bumble bee (Bombus crotchii) – are “expected to occur in the Project Area.”  Monarch butterfly - This species was evaluated during the biological resources literature review and field surveys conducted in support of the Conformity Analysis. Within California, overwintering populations of Monarch butterfly are the focus of the USFWS listing petition (USFWS 2024). Overwintering in California occurs at sites along the Pacific Coast, where they roost in eucalyptus, Monterey pines, and Monterey cypress trees. Occurrences outside of this range are not tracked by the CNDDB. Herbaceous vegetation within the Project Area is dominated by nonnative annual grasses with a very low coverage of nectar resources required by Monarchs during the breeding season. Only a few individual milkweed plants, the obligate host plant for larval Monarch butterflies, were observed. Monarch butterflies have not been observed in the Project Area despite multiple surveys conducted by ECORP biologists throughout the Project Area since the species were proposed for listing. ECORP invertebrate specialists were involved in full transect special-status plant surveys providing 100 percent visual coverage of the Project Area on May 1 and 2 and June 25 and 26, 2025. Incidental observations of special-status wildlife species were recorded and mapped when encountered. No monarch butterflies were observed. Given the

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low availability of foraging resources and lack of observations, Monarch butterfly is not expected to occur in the Project Area.
 Western bumble bee - This species was evaluated during the biological resources literature review and field surveys conducted in support of the Conformity Analysis. The Project Area is outside of the known current and historic geographic range of Western bumble bee based (CDFW 2023, 2026c). The Western bumble bee occurs at higher elevations in the foothills and mountains of the Sierra Nevada and Coast Ranges. The nearest CNDDB documented occurrence is approximately 12 miles away at an elevation of approximately 1,200 feet above mean sea level (CNDDB 2026).

Western bumble bee is not expected to occur in the Project Area.  Crotch’s bumble bee – This species was evaluated during the biological resources literature review and field surveys conducted in support of the Conformity Analysis. Three occurrences of Crotch’s bumble bee are documented in the CNDDB within 5 miles of the Project Area (CDFW 2026a), and the Project Area may provide suitable foraging and nesting habitat. However, the species has not been detected in the Project Area despite multiple field surveys conducted since the species was identified as a candidate for listing by CDFW. ECORP invertebrate specialists participated in walking transect special-status plant surveys of the Project Area on May 1 and 2 and June 25 and 26, 2025. These survey dates fall within the colony active period for Crotch’s Bumble Bee, the time period with the highest probably of detection of the species (CDFW 2023). During the survey, incidental observations of special-status wildlife species were recorded and mapped when encountered. No bumble bees of any species were observed. Further, herbaceous vegetation within the Project Area is dominated by nonnative annual grasses with a very low coverage of floral resources, estimated at less than 5 percent. Bumble bees rely on a rich supply of flowers to provide foraging resources during the colony’s entire life cycle (Xerces Society 2018). Thus, the habitat in the Project Area is potentially suitable, but habitat quality is low, minimal foraging resources are present, and the species has not been observed during multiple rounds of field surveys. Therefore, Crotch’s bumble bee is not expected to occur in the Project Area.

The Project will be required to undergo review by CDFW during the notification process for the 1602 Streambed Alteration Agreement. As discussed in the Conformity Analysis, CDFW may require surveys for Crotch’s bumble bee prior to the commencement of construction. If the species is observed, avoidance measures will be developed in coordination with CDFW to avoid the potential for “take” of this species during Project construction. Avoidance of take is a non-discretionary statutory requirement under CESA and protects state listed or candidate species at an individual level. Compliance with CESA, in coordination with CDFW, would assure no direct take of Crotch’s bumble bee.

The remainder of the letter focuses on special-status bird species that are not state or federally listed as threatened or endangered, and are not candidates for listing.

The letter cites Aleutian cackling goose (Branta hutchinsii leucopareia) as a species that has been identified as a special-status species since the 2011 EIR was prepared. Aleutian cackling goose, a subspecies of cackling goose, was removed from ESA listing in 2001, and in 2018 was added to the CDFW

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Watch List. CDFW Watch list species are taxa that were previously considered by CDFW to be Species of Special Concern (SSC) but do not currently meet SSC criteria, and for which there is concern and a need for additional information to clarify status (CNDDB 2026). The species is not considered to be threatened, endangered, or rare pursuant to CEQA. Further, there are no CNDDB documented occurrences of Aleutian cackling goose in the Project Area or a 12-quad search radius (Appendix A). Occurrences documented in eBird and iNaturalist are associated with open water habitats such as Lake Natoma. Aleutian cackling goose is not expected to occur in the Project Area.

The letter mentions 14 other bird species that the USFWS has identified as Birds of Conservation Concern (BCC) since 2011. These include:
 Western grebe (Aechmophorus occidentalis)
 Franklin’s gull (Leucophaeus pipixcan)
 Clark’s grebe (Aechmophorus clarkii)
 Heermann’s gull (Larus heermanni)
 Calliope hummingbird (Selasphorus calliope)
 Western gull (Larus occidentalis)
 American avocet (Recurvirostra americana)
 Wrentit (Chamaea fasciata)
 Pectoral sandpiper (Calidris melanotos)
 California thrasher (Toxostoma redivivum)
 Lesser yellowlegs (Tringa flavipes)
 Cassin’s finch (Haemorhous cassinii)
 Willet (Tringa semipalmata)
 Bullock’s oriole (Icterus bullockii)
The letter contends that, because USFWS has identified these species as BCC, they are special-status species as defined by the CEQA Guidelines. We note that the BCC designation does not establish that a species is "rare" pursuant to CEQA (CEQA Guidelines §15380). The goal of the Birds of Conservation Concern 2021 report is to identify the migratory and non-migratory bird species (beyond those already designated as federally threatened or endangered) that represent the highest conservation priorities (USFWS 2021). The 2021 USFWS report states, “this list makes no finding with regard to whether [the species] warrant consideration for ESA listing.”
In Nassiri v. City of Lafayette, the plaintiff contended that the City of Lafayette had failed to identify a significant impact because the site had value for two BCC species, Oak titmouse and Nuttall’s

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woodpecker. The court held that a “special concern” designation is not equivalent to being deemed “rare” under CEQA, and that there was nothing in the record to support a claim that the two bird species were likely to be candidates for listing under the ESA/CESA, were rare or unique to the region, or existed in such small numbers throughout all or a significant portion of their ranges that they may become endangered.

The identification of 14 new BCC species does not result in a new significant impact because the new BCC species are either not expected to occur in the Project Area and/or do not meet the definition of a rare species pursuant to CEQA. ECORP conducted species searches through the CNDDB, iPaC, eBird, and iNaturalist for occurrences of the 14 new BCC species. None of the species appear within a standard 12- quad search of the CNDDB (Appendix A). Nine of the species – Western grebe, Clark’s grebe, American avocet, Pectoral sandpiper, Lesser yellowlegs, Willet, Franklin’s gull, Heermann’s gull, and Western gull – are birds found in aquatic habitats, including lakes, ponds, rivers, and associated freshwater wetlands.

There are no reported occurrences in eBird or iNaturalist of these species in the Project Area. Nearby occurrences are associated with large open water features such as Lake Natomas, Folsom Lake and the American River, with many cited as migrant or vagrant observations. These species are not expected to occur in the Project Area.

The were also no occurrences reported in the CNDDB 12-quad search area of the remaining new BCC species – Calliope hummingbird, Wrentit, California thrasher, Cassin’s finch, and Bullock’s oriole. Other databases, including eBird and iNaturalist, contain scattered occurrences within a 5-mile radius. Only Wrentit and Bullock’s Oriole have reported observations from within the Folsom Plan Area. The oak woodlands and riparian habitats and in the Project Area represent potentially suitable habitat. However, the potential presence of Wrentit and Bullock’s oriole in the Project Area does not indicate a new significant impact.

Bullock’s oriole and Wrentit are common residents of California where suitable habitat occurs (Appendix B). They are known to be regionally or locally abundant in California including Sacramento Valley and/or Sierra Nevada foothills. Impacts to these species would not trigger a significant impact under CEQA unless the impact had the potential to result in substantial adverse effects such as population declines or range restrictions of these species. The Project Area comprises a small proportion of the species’ total geographic range and distribution. The small amount of impact that would occur to oak woodland and riparian habitats in the Project Area would not have the potential to result in a new significant impact to these species pursuant to CEQA.

Air Quality Compliance
The commenter suggests installation of Level 2 electric vehicle (EV) charging infrastructure and battery storage systems for each residence. However, the commenter provides no substantial evidence demonstrating that these measures would substantially reduce the significant and unavoidable air quality and greenhouse gas impacts identified in the FPASP EIR. Since certification of the FPASP EIR in 2011, California has adopted increasingly stringent Building Code a requirements requiring new residential

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development to incorporate EV capable infrastructure. As a result, the Project would already be required to comply with applicable State requirements related to electric vehicle readiness.

While EV charging infrastructure may facilitate future electric vehicle ownership, vehicle purchasing decisions are made by future residents and are outside the control of the Project. Installation of charging infrastructure does not ensure the purchase or operation of electric vehicles and therefore does not provide an assured or quantifiable reduction in operational emissions. The commenter provides no quantitative analysis, emissions calculations, or modeling demonstrating that the proposed measures would substantially reduce operational air pollutants or greenhouse gas emissions.

The commenter also proposes the use of super-compliant architectural coatings containing a maximum volatile organic compound (VOC) content of 10 grams per liter. The Project is already required to comply with applicable California Air Resources Board (CARB) and Sacramento Metropolitan Air Quality Management District architectural coating regulations. The commenter provides no substantial evidence demonstrating that coatings with VOC contents below applicable regulatory standards would substantially reduce the significant and unavoidable operational air quality impacts identified in the FPASP EIR. In addition, no quantitative analysis or emissions calculations are provided demonstrating that the proposed measure would result in a meaningful reduction in regional emissions. Accordingly, the proposed measure does not constitute substantial new information requiring additional environmental review.

The commenter further asserts that future residents could be exposed to indoor formaldehyde concentrations associated with composite wood products used in residential construction. The Project would be required to comply with all applicable State regulations governing formaldehyde emissions from composite wood products, including CARB's Airborne Toxic Control Measure for Composite Wood Products. The commenter has not provided project-specific evidence demonstrating that the Project would result in significant health risks beyond those addressed through existing regulatory programs.

Furthermore, the cited cancer risk threshold was developed for evaluation of outdoor exposures and is not intended for evaluation of indoor residential air quality conditions. Therefore, the commenter has not identified substantial new information demonstrating a new significant environmental effect or a substantial increase in the severity of a previously identified impact.

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CONCLUSION
Based on the foregoing analysis, the Proposed Project implements and maintains consistency with the FPASP. The City of Folsom, acting as the Lead Agency, has evaluated the Project in accordance with CEQA Guidelines Sections 15182 and 15162.

Because the Project is a residential development undertaken in conformity with a certified Specific Plan, and because the Conformity Analysis demonstrates that none of the triggers for subsequent environmental review under Section 15162 have occurred—specifically, there are no substantial Project changes, changed circumstances, or new information revealing a substantially more severe significant environmental impacts—the Project qualifies for a statutory exemption.

Consequently, the City of Folsom finds that the Proposed Project is fully exempt from further environmental review pursuant to CEQA Guidelines Section 15182 and Government Code Section 65457.

The Project remains subject to all applicable binding mitigation measures outlined in the FPASP MMRP and the FPASP Backbone Infrastructure Initial Study/Mitigated Negative Declaration (BB IS/MND).

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REFERENCES
California Department of Fish and Wildlife. 2023. Survey Considerations for California Endangered Species Act (CESA) Candidate Bumble Bee Species. June 6, 2023.
_____. 2026a. RareFind Natural Diversity Data Base Program. Version 5. California Department of Fish and Wildlife. California Natural Diversity Database. https://wildlife.ca.gov/Data/CNDDB/MapsandData. Accessed February 1, 2023, March 18, 2025, and June 10, 2026. _____. 2026b. Yellow-billed Cuckoo Range - CWHR B259 [ds940] in CDFW Open Data Portal. https://datacdfw.opendata.arcgis.com/datasets/CDFW::yellow-billed-cuckoo-range-cwhr-b259- ds940/explore?location=38.619094%2C-120.675640%2C9. Accessed June 10, 2026. _____. 2026c. Western Bumble Bee Range – CDFW [ds3097]. https://www.arcgis.com/apps/mapviewer/index.html?layers=c0b86d57ea4e4c54900409d37d2685 e2. Accessed June 10, 2026.

California Natural Diversity Database (CNDDB). 2026. Special Animals List. California Department of Fish and Wildlife. Sacramento, CA. April 2026.

City of Folsom. 2011. Folsom Plan Area Specific Plan Environmental Impact Report/Environmental Impact Statement. June.

U.S. Fish and Wildlife Service. 2026. Yellow-billed Cuckoo (Coccyzus americanus) | Map | U.S. Fish & Wildlife Service | FWS.gov. https://www.fws.gov/species/yellow-billed-cuckoo-coccyzus-americanus/map.

Accessed June 10, 2026.
_____. 2024. Endangered and Threatened Wildlife and Plants; Threatened Species Status With Section 4(d) Rule for Monarch Butterfly and Designation of Critical Habitat. 50 Code of Federal Regulations Part

17. December 12, 2024.
_____. 2023. Species status assessment report for the foothill yellow legged frog (Rana boylii), Version 2.11.

U.S. Fish and Wildlife Service, Sacramento Fish and Wildlife Office, Sacramento, California. April 2023.
_____. 2021. Birds of Conservation Concern 2021. United States Department of the Interior, U.S. Fish and Wildlife Service, Migratory Birds. Falls Church, Virginia. http://www.fws.gov/birds/management/ managed-species/birds-of-conservation-concern.php. Accessed June 11, 2026. _____. 2014. Endangered and Threatened Wildlife and Plants; Determination of Threatened Status for the Western Distinct Population Segment of the Yellow-billed Cuckoo (Coccyzus americanus); Final Rule (50 Code of Federal Register Part 17). October 3, 2014.

Xerces Society. 2018. A Petition to the State of California Fish and Game Commission to List the Crotch Bumble Bee (Bombus crotchii), Franklin’s Bumble Bee (Bombus franklini), Suckley Cuckoo Bumble Bee (Bombus suckleyi), and Western Bumble Bee (Bombus occidentalis occidentalis) as Endangered

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under the California Endangered Species Act. Submitted by The Xerces Society for Invertebrate Conservation, Defenders of Wildlife, Center for Food Safety. October 2018.

06/23/2026 Item No.18.

LIST OF APPENDICES
Appendix A – CNDDB and IPaC Database Queries
Appendix B – Species Accounts

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APPENDIX A
CNDDB and IPaC Database Queries

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Element Code Species Federal Status State Status Global Rank State Rank Rare Plant
Rank/CDFW
SSC or FP
AAAAA01181 Ambystoma californiense pop. 1
California tiger salamander - central California DPS
Threatened Threatened G3T3 S3 WL
AAABF02020 Spea hammondii
western spadefoot
Proposed
Threatened
None G2G3 S3S4 SSC
AAABH01022 Rana draytonii
California red-legged frog
Threatened None G2G3 S2S3 SSC
AAABH01055 Rana boylii pop. 5
foothill yellow-legged frog - south Sierra DPS
Endangered Endangered G3T2 S2
ABNFD01020 Nannopterum auritum
double-crested cormorant
None None G5 S4 WL
ABNGA04010 Ardea herodias
great blue heron
None None G5 S4
ABNGA04040 Ardea alba
great egret
None None G5 S4
ABNKC01010 Pandion haliaetus
osprey
None None G5 S4 WL
ABNKC06010 Elanus leucurus
white-tailed kite
None None G5 S3S4 FP
ABNKC10010 Haliaeetus leucocephalus
bald eagle
Delisted Endangered G5 S3 FP
ABNKC12040 Astur cooperii
Cooper's hawk
None None G5 S4 WL
ABNKC19070 Buteo swainsoni
Swainson's hawk
None Threatened G5 S4
ABNKC19120 Buteo regalis
ferruginous hawk
None None G4 S3S4 WL
ABNKC22010 Aquila chrysaetos
golden eagle
None None G5 S3 FP
ABNKD06030 Falco columbarius
merlin
None None G5 S3S4 WL
ABNME03041 Laterallus jamaicensis coturniculus
California black rail
None Threatened G3T1 S2 FP
ABNSB10010 Athene cunicularia
burrowing owl
None Candidate
Endangered
G4 S2 SSC
ABPAU01010 Progne subis
purple martin
None None G5 S3 SSC
Query Criteria: Quad<span style='color:Red'> IS </span>(Buffalo Creek (3812152)<span style='color:Red'> OR </span>Folsom (3812162)<span style='color:Red'> OR </span>Roseville (3812173)<span style='color:Red'> OR </span>Rocklin (3812172)<span style='color:Red'> OR </span>Pilot Hill (3812171)<span style='color:Red'> OR </span>Clarksville (3812161)<span style='color:Red'> OR </span>Folsom SE (3812151)<span style='color:Red'> OR </span>Carbondale (3812141)<span style='color:Red'> OR </span>Sloughhouse (3812142)<span style='color:Red'> OR </span>Elk Grove (3812143)<span style='color:Red'> OR </span>Carmichael (3812153)<span style='color:Red'> OR </span>Citrus Heights (3812163))
Report Printed on Thursday, June 11, 2026
Commercial Version -- Dated May, 31 2026 -- Biogeographic Data Branch Page 1 of 4 Information Expires 11/30/2026
Selected Elements by Element Code
California Department of Fish and Wildlife
California Natural Diversity Database

06/23/2026 Item No.18.

Element Code Species Federal Status State Status Global Rank State Rank Rare Plant
Rank/CDFW
SSC or FP
ABPAU08010 Riparia riparia
bank swallow
None Threatened G5 S3
ABPBXA0020 Ammodramus savannarum
grasshopper sparrow
None None G5 S3 SSC
ABPBXB0020 Agelaius tricolor
tricolored blackbird
None Threatened G3 S2 SSC
AFCHA0209K Oncorhynchus mykiss irideus pop. 11
steelhead - Central Valley DPS
Threatened None G5T2Q S2 SSC
AMACC02010 Lasionycteris noctivagans
silver-haired bat
None None G4 S3S4
AMACC10010 Antrozous pallidus
pallid bat
None None G4 S3 SSC
AMAFJ01010 Erethizon dorsatum
North American porcupine
None None G5 S3
AMAJF04010 Taxidea taxus
American badger
None None G5 S3 SSC
ARAAD02031 Actinemys marmorata
northwestern pond turtle
Proposed
Threatened
None G2 SNR SSC
ARADB36150 Thamnophis gigas
giant gartersnake
Threatened Threatened G2 S2
CTT37D00CA Ione Chaparral
Ione Chaparral
None None G1 S1.1
CTT42110CA Valley Needlegrass Grassland
Valley Needlegrass Grassland
None None G3 S3.1
CTT44110CA Northern Hardpan Vernal Pool
Northern Hardpan Vernal Pool
None None G3 S3.1
CTT44132CA Northern Volcanic Mud Flow Vernal Pool
Northern Volcanic Mud Flow Vernal Pool
None None G1 S1.1
CTT45310CA Alkali Meadow
Alkali Meadow
None None G3 S2.1
CTT45320CA Alkali Seep
Alkali Seep
None None G3 S2.1
CTT61430CA Great Valley Valley Oak Riparian Forest
Great Valley Valley Oak Riparian Forest
None None G1 S1.1
ICBRA03030 Branchinecta lynchi
vernal pool fairy shrimp
Threatened None G3 S3
ICBRA03150 Branchinecta mesovallensis
midvalley fairy shrimp
None None G2 S2S3
ICBRA06010 Linderiella occidentalis
California linderiella
None None G2G3 S2S3
ICBRA10010 Lepidurus packardi
vernal pool tadpole shrimp
Endangered None G3 S3
Report Printed on Thursday, June 11, 2026
Commercial Version -- Dated May, 31 2026 -- Biogeographic Data Branch Page 2 of 4 Information Expires 11/30/2026
Selected Elements by Element Code
California Department of Fish and Wildlife
California Natural Diversity Database

06/23/2026 Item No.18.

Element Code Species Federal Status State Status Global Rank State Rank Rare Plant
Rank/CDFW
SSC or FP
ICBRA23010 Dumontia oregonensis
hairy water flea
None None G1G3 S1
IICOL48011 Desmocerus californicus dimorphus
valley elderberry longhorn beetle
Threatened None G3T3 S3
IICOL5V010 Hydrochara rickseckeri
Ricksecker's water scavenger beetle
None None G2? S2?
IIHYM24252 Bombus occidentalis
western bumble bee
None Candidate
Endangered
G3 S1
IIHYM24260 Bombus pensylvanicus
American bumble bee
None None G3G4 S2
IIHYM24480 Bombus crotchii
Crotch's bumble bee
None Candidate
Endangered
G2 S2
IIHYM35030 Andrena blennospermatis
Blennosperma vernal pool andrenid bee
None None G2 S1
IIHYM35210 Andrena subapasta
An andrenid bee
None None G1G2 S1S2
IIPLE23020 Cosumnoperla hypocrena
Cosumnes stripetail
None None G2 S2
ILARA14020 Banksula californica
Alabaster Cave harvestman
None None GH SH
PDAPI0Z0P0 Eryngium pinnatisectum
Tuolumne button-celery
None None G2 S2 1B.2
PDAST11061 Balsamorhiza macrolepis
big-scale balsamroot
None None G2 S2 1B.2
PDAST1P090 Calycadenia spicata
spicate calycadenia
None None G3? S3 1B.3
PDAST8H1V0 Packera layneae
Layne's ragwort
Threatened Rare G2 S2 1B.2
PDAST9X0D0 Wyethia reticulata
El Dorado County mule ears
None None G2 S2 1B.2
PDCAM060C0 Downingia pusilla
dwarf downingia
None None GU S2 2B.2
PDCAM0C010 Legenere limosa
legenere
None None G2 S2 1B.1
PDCIS020F0 Crocanthemum suffrutescens
Bisbee Peak rush-rose
None None G2?Q S2? 3.2
PDCON040H0 Calystegia stebbinsii
Stebbins' morning-glory
Endangered Endangered G1 S1 1B.1
PDERI04240 Arctostaphylos myrtifolia
Ione manzanita
Threatened None G1 S1 1B.2
PDONA05053 Clarkia biloba ssp. brandegeeae
Brandegee's clarkia
None None G4G5T4 S4 4.2
Report Printed on Thursday, June 11, 2026
Commercial Version -- Dated May, 31 2026 -- Biogeographic Data Branch Page 3 of 4 Information Expires 11/30/2026
Selected Elements by Element Code
California Department of Fish and Wildlife
California Natural Diversity Database

06/23/2026 Item No.18.

Element Code Species Federal Status State Status Global Rank State Rank Rare Plant
Rank/CDFW
SSC or FP
PDPGN080F1 Eriogonum apricum var. apricum
Ione buckwheat
Endangered Endangered G2T1 S1 1B.1
PDPGN080F2 Eriogonum apricum var. prostratum
Irish Hill buckwheat
Endangered Endangered G2T1 S1 1B.1
PDPLM0C0X1 Navarretia myersii ssp. myersii
pincushion navarretia
None None G2T2 S2 1B.1
PDRHA04190 Ceanothus roderickii
Pine Hill ceanothus
Endangered Rare G1 S1 1B.1
PDROS0W0C0 Horkelia parryi
Parry's horkelia
None None G2 S2 1B.2
PDRUB0N0E7 Galium californicum ssp. sierrae
El Dorado bedstraw
Endangered Rare G5T1 S1 1B.2
PDSCR0J0D1 Chloropyron molle ssp. hispidum
hispid salty bird's-beak
None None G2T1 S1 1B.1
PDSCR0R060 Gratiola heterosepala
Boggs Lake hedge-hyssop
None Endangered G2G3 S2 1B.2
PDSTE03030 Fremontodendron decumbens
Pine Hill flannelbush
Endangered Rare G1 S1 1B.2
PMALI040Q0 Sagittaria sanfordii
Sanford's arrowhead
None None G3 S3 1B.2
PMCYP03M60 Carex xerophila
chaparral sedge
None None G2 S2 1B.2
PMJUN011L1 Juncus leiospermus var. ahartii
Ahart's dwarf rush
None None G2T1 S1 1B.2
PMJUN011L2 Juncus leiospermus var. leiospermus
Red Bluff dwarf rush
None None G2T2 S2 1B.1
PMLIL0G020 Chlorogalum grandiflorum
Red Hills soaproot
None None G3 S3 4.2
PMLIL0V010 Fritillaria agrestis
stinkbells
None None G3 S3 4.2
PMPOA4G050 Orcuttia tenuis
slender Orcutt grass
Threatened Endangered G2 S2 1B.1
PMPOA4G070 Orcuttia viscida
Sacramento Orcutt grass
Endangered Endangered G1 S1 1B.1
Record Count: 77
Report Printed on Thursday, June 11, 2026
Commercial Version -- Dated May, 31 2026 -- Biogeographic Data Branch Page 4 of 4 Information Expires 11/30/2026
Selected Elements by Element Code
California Department of Fish and Wildlife
California Natural Diversity Database

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APPENDIX B
Species Accounts

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Folsom City Council Meeting
Additional Information
Transmittal
Instructions to staff: Deliver original and 30 stapled/double-sided copies to the City Clerk’s Department; City Clerk’s Department will distribute via email and hardcopy to City Council, City Manager, City Attorney, and City Clerk.

Updated: Jan 2026
MEETING DATE: 6/23/2026
AGENDA SECTION: Public Hearing

STAFF REPORT TITLE
Toll Brothers at Alder Creek - south of Alder Creek Parkway, east and west of Oak Avenue Parkway, north of Mangini
Parkway, and east of Prairie City Road, in the Folsom Plan Area (MSTR25-00084)- Resolution No 11643 - A Resolution of the City Council Determining that the Toll Brothers at Alder Creek Project is Exempt from CEQA pursuant to CEQA Guidelines Section 15182 and Approving a Small-Lot Vesting Tentative Subdivision Map, Planned Development Permit,
Inclusionary Housing Plan, and Minor Administrative
Modification (Continued from June 09, 2026)
FROM: Community Development Department
Staff is providing the attached additional information for the above-referenced agenda item. • Comment Letter from Environmental Council of Sacramento and California Native Plant Society

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www.ecosacramento.net
June 22, 2026
Mayor and Council, City of Folsom
Sent via email to: [email protected]
Re: Toll Brothers at Alder Creek Environmental Documentation, Agenda Item #18 Dear Mayor and Council:

Environmental groups in our region are increasingly concerned with the rapid destruction of oak woodlands.

We have been reviewing projects that would impact oak woodlands to determine cumulative impacts of numerous separate land use authorities. The Folsom City Planning Commission recently reviewed (and approved) Toll Brothers at Alder Creek, a 464 acre residential development, with the Council hearing expected soon.

The documents on the agenda website do not adequately disclose the environmental impacts of the project.

We are asking for additional environmental documentation prior to the presentation of this project at a public hearing before the Council.

The only environmental document made public on this project is the City of Folsom Environmental Information Form, completed by the applicant. This document does not state the number of blue oaks on the property, how many oaks will be removed, the size of the canopy to be removed, and how many oaks and the size of the canopy to be permanently preserved on the site. This document does not explain how the project complies with Measure W's requirement for 30 percent permanent open space in the south of 50 annexation area.

Measure W is a landmark 2004 ballot initiative in Folsom, California, that authorized the city's annexation and development of 3,500 acres of land south of Highway 50. Measure W requires that thirty percent of the total land area must be permanently preserved as natural open space, oak woodlands, and sensitive habitats. How does the project affect the achievement of this goal?
The Environmental Information Form for this project sites various environmental documents and specifically refers to a 2011 EIR that outlines mitigation projects for projects in this area. There is in fact no independent environmental assessment of whether this project as presented for approval is consistent with the prior EIR assumptions. How does the project differ from the project site as described in the 15 year old EIR? We are specifically concerned with the lack of documentation about the direct and cumulative impacts on the oak resource. The Project Narrative at pp. 9-10, submitted by the applicant, refers to an Arborist Report and working with ECORP. Although an arborist report is listed by the applicant as a submitted document, that report is not available on the Planning Department's website. The project narrative acknowledges that the exact impacts to the oak woodlands and specific important individual oaks will not be disclosed prior to project approval. It states (p. 9):

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www.ecosacramento.net

"The purpose of the Arborist Report is to quantify the amount of oak woodland area within the project area and provide an assessment of the size and health condition of the individual trees. The Report does not intend to provide a final quantity of oak woodland impact area, and the reason is detailed immediately below.

There are 73 isolated oak trees on the project site, and oak woodland areas up to an estimated maximum of 100.48 acres. Once final project improvement plans are prepared, the information in the Arborist Report will be used to assess the precise oak woodland impact area, the precise individual free‐ standing oak tree impacts, and will develop a final mitigation requirement pursuant to FPASP policies.

Final boundary conditions as determined by the improvement plan level of detail may dictate that slightly less or slightly more oak woodland area may be impacted. At this time, (Vesting Tentative Map level of detail) it would be imprecise to state with certainty the amount of impact that may occur.

Additional tree survey data will be collected as needed to support evaluation of individual tree impacts, ground verification of oak woodland, and applications for tree work permits or tree removal permits." This strikes us as deferred mitigation. Moreover, nothing in the documentation for this project presents to the public the appliable performance standards and evidence that the mitigation will be consistent with performance standards established in the earlier EIR.

The Environmental Information Form is not an independent environmental review for consistency, is prepared by the applicant, and no evidence is presented that further CEQA review is not required at this time as asserted.

The Project Narrative, by the applicant, states "ECORP has determined that based on the current project design, additional CEQA review is not required at this time." However, no ECORP document is included for public review.

Please respond via email to: [email protected].

Sincerely,
Heather Fargo
President of the ECOS Board of Directors
Carol W. Witham
California Native Plant Society, Sacramento Valley Chapter Sean Wirth
ECOS Board of Directors

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