Petroleum Vapors at Intersection of Gentile and Angel
Layton City

What is Vapor Intrusion?

What are the potential health effects of petroleum vapors?

Notification area: Gentile St. to 500 South and Angel St. to Denver & Rio Grande Western Trail

More Information

Safety concerns

• Layton City Public Works (801) 336-3720
• Layton City Fire Department (801) 336-3940

Health concerns

• Davis County Environmental Health Department (801) 525-5128

Investigation information

• Utah Department of Environmental Quality (801) 536-4123

Background

Residents in a small area near the intersection of Gentile and Angel streets in Layton City reported petroleum odors on Feb. 14, 2019. This initiated an investigation to determine the source and extent of the vapors. Reports were made to the Davis County Health Department (DCHD) and the Utah Department of Environmental Quality (DEQ). Since the initial reports, state, county, and local officials have actively investigated potential sources, pathways, and extent of the vapors. Water sampling and vapor monitoring are ongoing.

Attention: Due to the ongoing nature of the investigation, this page will be updated as new data become available. Please check back regularly for the latest sample results and findings.

Updated March 2023

Gentile Street Chevron

Between January 28-30, 2023,  a groundwater monitoring event was completed at the site. This report may be viewed at the link below

• Groundwater Monitoring Report, January 28-30, 2023

Updated December 2022

Gentile Street Chevron

Between October 18-20, 2022, a groundwater monitoring event was completed at the site. This report may be viewed at the link below.

• October 2022 Groundwater Monitoring Report

Updated August 2022

Gentile Street Chevron

On June 8, 2022, a mobile high vacuum extraction unit completed a 37-day event in the cul-de-sac of the Angel Crossing neighborhood to address the dissolved petroleum contamination in the groundwater. The unit removed and treated an estimated 240,000 gallons of contaminated groundwater.

On July 18, 2022, a groundwater monitoring well sampling event was performed to determine the extent and concentration of the groundwater contamination remaining after the event was completed.

Below is a link to the August 2022 report for the July 2022 sampling event which includes a summary report from the operation of the mobile high vacuum extraction.

• August 2022 – Post Remediation Event Sampling and Summary Report

Update July 2022

Gentile Street Chevron

On May 2, 2022, a mobile high vacuum extraction unit abatement and began in the cul-de-sac of the of the Angel Crossing neighborhood to address the dissolved petroleum contamination in the groundwater. The unit operated until June 8, 2022, for a total of 37 days and removed and treated an estimated 240,000 gallons of contaminated groundwater.

On May 7, 2022, an air sparge system was added to the existing vapor extraction system (SVE), at the station property and began operation. The air sparge system is an additional remedial measure implemented at the source of contamination (Triple Stop Chevron) to further remove dissolved and absorbed phase groundwater contamination that is contributing to the impacts moving into the neighborhood. This system is anticipated to be run for at least 6 months, however, if it is successful in meeting cleanup standards sooner, it will be discontinued.

On June 8, 2022, the most contaminated groundwater monitoring well in the neighborhood and at the gas station property were sampled. These two groundwater monitoring wells both showed dramatic decreases in contamination levels. No groundwater contamination was detected in the neighborhood well and the well on the gas station property had met acceptable risk-based screening levels. Below is a table of these two historical groundwater contamination results:

MW-10 Gas Station Monitoring Well

Air Sparge System on Gas Station Started on May 7, 2022

MW-42 Neighborhood Monitoring Well

Mobile Treatment Unit Started on May 2, 2022

A comprehensive sampling of all previously contaminated groundwater monitoring wells will be performed in the first week of July, 2022. Additional sampling rounds will be required in 2022 to insure no rebound of groundwater contamination is present.

Update May 2022

Gentile Street Chevron

May 2022 groundwater sampling continues to show a general decrease in contamination concentrations throughout the plume. However, these numbers are still above the Division of Environmental Response and Remediation’ s (DERR) cleanup screening levels. The contamination plume continues to migrate in a southwestward direction in the neighborhood, but does not cross 75 South.

On May 2, 2022, a mobile high vacuum extraction unit abatement and pilot test began in the cul-de-sac of the northern boundary of the Angel Crossing neighborhood to address the dissolved petroleum contamination in the groundwater. This unit will most likely operate until June, however, if it is successful in lowering contamination levels sooner, it will be discontinued, and all wells in the neighborhood will be resampled to confirm that screening levels are met.

On May 7, 2022, an air sparge system was added to the existing vapor extraction system (SVE), at the station property and began operation. The air sparge system is an additional remedial measure implemented at the source of contamination (Triple Stop Chevron) to further remove dissolved and absorbed phase groundwater contamination that is contributing to the impacts moving into the neighborhood. This system is anticipated to be run for at least 6 months, however, if it is successful in lower contamination levels sooner, it will be discontinued, and all wells in the neighborhood will be resampled to confirm that screening levels are met.

Update April 2022

Gentile Street Chevron

January 2022 groundwater sampling continues to show a decrease in contamination concentrations throughout the plume. The contamination plume continues to migrate in a southwestward direction, but does not cross 75 South.

A Corrective Action Plan (CAP) was approved for an air sparge system to be added to the existing vapor extraction system (SVE). This will begin operation in May 2022. The air sparge system is an additional remedial measure implemented at the source of contamination (Triple Stop Chevron) to further remove dissolved and absorbed phase groundwater contamination that is contributing to the impacts moving into the neighborhood.

Around this same time (May 2022), a mobile high vacuum extraction unit abatement and pilot test will be performed in the Angel Crossing neighborhood to address the dissolved petroleum contamination currently present at some of the properties in the neighborhood.

• January 2022 Triple Stop Site Map – Dissolved Benzene
• January 2022 Triple Stop TPH Contour Map
• January 2022 Triple Stop Historical Groundwater Table

Update December 2021

Gentile Street Chevron

A Corrective Action Plan (CAP) was approved for a vapor extraction system (SVE) and began operation in July 2020. As of August 4, 2021, the system has recovered 2,252 equivalent gallons of gasoline in the vapor phase plus the 2,545 gallons from the mobile high vacuum system for a total of 4,797 gallons equivalent of gasoline recovered. Additionally, approximately 30 gallons of LNAPL has been recovered from MW-10 through manual bailing of the well. Additional remedial measures are being implemented at the source of contamination (Triple Stop Chevron) to include an air sparge system that will operate 6 sparge wells, four located in Gentile Street and two on the Chevron property. The purpose is to further remove dissolved and absorbed phase that is contributing to the contamination flowing into the neighborhood. The system is expected to be operational in early 2022.

Additionally, in the early Spring of 2022, a mobile high vacuum extraction unit abatement and pilot test will be performed in the Angel Crossing neighborhood to address the dissolved petroleum contamination.

Update October 2021

• October 2021 Groundwater Monitoring Report (6.6 MB)

Update August 2021

• July 2021 Groundwater Monitoring Report (20.4 MB)

Update June 2021

Gentile Street Chevron

• April 2021 GW Monitoring Event and High Resolution Site Characterization (HRSC) Report (9.5 MB)

Update April 2021

Gentile Street Chevron

A groundwater sampling event was conducted in January 2021 to evaluate concentrations of dissolved petroleum hydrocarbons and groundwater elevations at the site. Historic sampling events have reported an overall general decrease in groundwater contamination, both in areal extent and mass. This can be observed in the January 2021, Groundwater Monitoring Report, dated April 2, 2021. The groundwater was sampled again in early April and those results should be reported within the next month.

Sub-slab vapor samples were collected from the six homes with sub-slab vent systems in November and December, 2020, and again in March 2021. Vapor concentrations remain below the residential screening levels at each or the residential sampling locations.

The Soil Vapor Extraction Remediation System was started on July 9, 2020. To date, the system has recovered, as vapor, approximately 2000 gallons of product.

A High-Resolution Site Characterization was completed at the site in late March 2021, to help determine the cleanup approach moving forward. The results are currently being reviewed and a report detailing its findings and recommendations will be submitted within the next month or two.

Overall, the site cleanup is progressing well and overall decreases in groundwater contamination have been observed.

• Sub-slab soil gas sampling, first quarter report from Terracon (April 09, 2021, 2.4 MB)
• January 2021, GWM Report (April 02, 2021, 14 MB)

Update February 2021

Gentile Street Chevron

A groundwater sampling event was conducted in October of 2020 evaluating concentrations of dissolved petroleum hydrocarbons and groundwater elevations at the site. Currently, the plume is no longer delineated to the southwest in the direction of the groundwater flow. A work plan to install additional groundwater monitoring wells to delineate the downgradient extent of the plume is in the approval process.

Although some monitoring well locations have increased in concentration since the April 2020 sampling event, the overall groundwater concentrations have continued to decrease across the impacted area.

Sub-slab vapor samples were collected from the six homes with sub-slab vent systems in November and December. Vapor concentrations remain below the residential screening levels at each home.

The Soil Vapor Extraction Remediation System was started on July 9, 2020. To date, the system has recovered, as vapor, approximately 1800 gallons of product.

The DERR is hosting an evening virtual neighborhood meeting on February 9th to discuss the results of the sub-slab sampling, groundwater monitoring, and updates to the corrective action plan and remediation system. If you’re interested in joining the neighborhood meeting, please contact Therron Blatter (tblatter@utah.gov).

Additional sub-slab vapor monitoring pins were installed in several residences to ensure that a vacuum extended throughout the sub-slab.

• Sub-Slab Gas Sampling Report (11 MB)
• Groundwater Monitoring Report (12 MB)

Update August 21, 2020

Since the initial reports on Valentine’s Day 2019, state, county, and local officials have actively investigated potential sources, pathways, and extent of the vapors. Water sampling and vapor monitoring are ongoing.

The 37 monitoring wells installed to identify the source of the petroleum plume in a Layton neighborhood offered compelling evidence that the plume originated from the Chevron gas station property on the corner of Gentile and Sugar Streets and migrated to the southwest under the nearby subdivision.

Temporary vapor venting systems were installed around the foundations of three homes affected by the petroleum plume. These systems began operating on March 1, 2019, and proved highly effective in removing the petroleum vapors beneath the structures. In the spring of 2020, the temporary systems were replaced with permanent systems that draw air and petroleum vapors out from under the foundation of the home referred to as sub-slab vent systems.  Sub-slab vent systems were also placed in two additional residents in close proximity to the plume as a precautionary measure.  The Division of Environmental Response and Remediation (DERR) continues to evaluate the impact of petroleum vapors from this release on the homes in the area to ensure the systems are effective.

In March 2020, the installation of a Soil Vapor Extraction (SVE) system began.  This system consists of a blower connected to a number of wells within the plume.  As the blower exerts a vacuum on the wells, petroleum contamination is extracted from the liquid phase and turned into vapors by volatilization and is then burned off by using a high heat source. Installation of the SVE system was completed in early July and began operation on July 8.  Initial estimates of contamination removal rates, by vapor, is approximately 30 gallons per week or 120 gallons per month.

• Aug. 2020, Soil Vapor Extractions Operations Data Report
• April 2020, Groundwater Monitoring Report

Update April 16, 2019

The 37 monitoring wells installed to identify the source of the petroleum plume in a Layton neighborhood offered compelling evidence that the plume originated from the Chevron gas station property on the corner of Gentile and Sugar Streets and migrated to the southwest under the nearby subdivision.

The gas station owner is proceeding with the cleanup of the plume and has hired Terracon as his environmental consultant. The owner applied for coverage under the Petroleum Storage Tank (PST) Fund. DERR has had regular contact with Terracon, and the consultant is moving forward with arrangements to have a CalClean dual-phase extraction truck on site as soon as possible to begin abatement activities.

Update April 5, 2019

The Division of Environmental Response and Remediation (DERR) received the preliminary result for a tracer test conducted on the underground storage tanks (USTs) at a gas station near the intersection of Gentile and Angel Streets. The initial test indicates that there is not an ongoing release from the UST system at the facility. The tracer test is at least 10 times more accurate than the typical tests that are conducted for compliance purposes on these tanks and has an accuracy of .005 gallons per hour, or about 44 gallons per year.

The field investigation conducted over the past month points to the station as the source of the gasoline plume in the groundwater, but scientists still cannot find a clear nexus between the facility and the release, or how and when it occurred.

DERR will continue to look into the issue but plans to move forward with remediation efforts at the site.

Update March 25, 2019

Scientists from DEQ’s Division of Environmental Response and Remediation (DERR) have identified a gas station on Gentile Street as the probable source of a petroleum plume that has infiltrated the soil, groundwater, and storm drains in a nearby Layton neighborhood. DERR has scheduled additional testing to further identify the source and define the extent of the release.

DERR and their contractor have, to date, drilled and sampled 30 investigative monitoring wells. Data collected from these monitoring wells indicate that the plume extends from the corner of Gentile and Sugar Streets and flows in a southwesterly direction. Several more monitoring wells will be drilled later this week to fully determine the extent of the plume.

Investigators believe that once the petroleum enters the sandy soil in the area, it migrates through the soil until it reaches the shallow groundwater. The petroleum-contaminated groundwater then flows along a natural pathway toward the neighborhood at the intersection of Gentile and Angel Street. The groundwater also likely follows a secondary flow path through the fill material of a nearby sewer trench where it intersects the 40-year-old storm drain that travels south along Angel Street.

Volatile organic compounds (VOCs) in the petroleum products off-gas from the impacted groundwater and accumulate in the storm drains and beneath the homes in the area. Area land drains that are used to keep the groundwater from reaching basements also provide a pathway for the VOCs to migrate and accumulated beneath the homes.

DERR has notified the gas station owner of its investigative findings and his responsibilities. In the meantime, DERR continues to investigate and abate the release.

• View Sampling Data (38 KB)

Monitoring Well Installation and Sampling (DERR)

• March 20, 2019 – Monitoring wells MW 27 through MW-30 were installed. DERR staff gauged, developed, and sampled six groundwater monitoring wells (MW-10, MW-22 through MW-25, and MW-27 through MW-30).
• March 19, 2019 – Monitoring wells MW-22 through MW-26 were installed.  DERR staff gauged, developed, and sampled three groundwater monitoring wells (MW-3, MW-4, MW-26).
• March 15, 2019 – Monitoring wells MW-18 through MW-21were installed.  DERR Staff gauged, developed, and sampled 21 groundwater monitoring wells (MW-1 through MW-21).
• March 14, 2019 – Monitoring wells MW-14 through MW-17 were installed.
• March 12, 2019 – Monitoring wells MW-11 through MW-14 were installed. Monitoring well MW-10 was gauged, developed, and sampled. Sub-slab sampling was conducted at one additional home on Angel Street.
• March 11, 2019 – Monitoring wells MW-8 through MW-10 were installed.
• March 8, 2019 – Monitoring wells MW-5 through MW-7 were installed. Indoor air sampling data was sent to four homeowners with a Utah Department of Health (UDOH) narrative about exposure risks.
• March 6, 2019 – Sub-slab vapor monitoring points were resampled along with the indoor air in three homes with initial vapor impacts.
• March 5, 2019 – Monitoring wells MW-1 through MW-4were installed.
• March 2, 2019 – Sub-slab vapor sampling was installed and collected at two homes along with indoor air sampling at one home.
• March 1, 2019 – Vapor mitigation system installation was completed, and systems were operational at three homes with vapor impacts.
• February 26-27, 2019 – Eight additional Geoprobe borings were installed in the right-of-way near the gas station to collect soil and groundwater samples (SB-3 to SB-10).
• February 26, 2019 – Sub-slab sampling was conducted at three homes with initial vapor impacts to determine if the vapors were entering the house from the sub-slab. (The sub-slab consists of soil or fill material located under buildings). Because the air pressure in most homes is lower than the pressure in the surrounding soil, vapors can be drawn into the house through cracks or openings in the foundation. The installation of sub-slab mitigation systems began at three homes. A total of three ventilation points were scheduled to be installed at each home near the rooms with the highest vapor impacts based on indoor photoionization detector (PID) readings. Two Geoprobe (soil) borings (SB-1 & SB-2) were installed near the homes to gauge the depth to groundwater and collect samples.

Update March 8, 2019

Groundwater samples have been collected in the area around the intersection of Angel and Gentile Streets in Layton. Groundwater was typically encountered approximately nine feet below ground surface and likely flows to the southwest. This likely directional flow may be affected by subsurface drainage in the area. The results of the groundwater samples are compared to Regional Screening Levels (RSL’s) for petroleum contamination. The groundwater collected on the south side of Gentile Street indicated petroleum contamination. These groundwater samples were further screened against Vapor Intrusion Screening Levels. The samples collected south of Gentile Street near the rail trail and near the intersection of Sugar and Gentile Streets contained concentrations of certain hydrocarbons in the groundwater that could result in vapor intrusion to residences.

The Division of Environmental Response and Remediation (DERR) continues to sample groundwater in these areas in an effort to pinpoint the source(s) and determine the size of the contamination plume.

• View the Groundwater Samples

Update March 5, 2019

Underground Storage Tank Tests

Tank and line tightness tests were performed on February 27, 2019, for the underground storage tanks and piping at the gas station. The diesel and premium tanks both passed, as did all of the piping. The unleaded tank initially failed the tightness test. On March 1, 2019, it was determined that the spill bucket on the unleaded tank was cracked, causing the tank to fail the tightness test. The spill bucket was replaced, and the tank passed a tank tightness test late in the day on March 1, 2019. The cracked spill bucket had minimal soil staining in the surrounding backfill immediately around the bucket, but nothing to suggest a large release.

Vapor Mitigation Systems

The vapor mitigation systems installed in the three homes have been operating since March 1, 2019. The Division of Environmental Response and Remediation (DERR) continues to evaluate the impact of vapor intrusion on the homes in the area to ensure the systems are effective.

The 417 Investigation

The investigation continued on March 5, 2019, with the installation of groundwater monitoring wells to delineate the extent of the groundwater contamination to the southwest under the subdivision. DERR will continue its investigation to determine the source of the groundwater contamination found near the gas station and is reaching out to the property owner to secure access.

Stormwater Data

Stormwater samples collected for lab analysis indicate petroleum contamination at several sample locations. Concentrations of certain volatile organic compounds (VOCs) found in some samples exceeded Regional Screening Levels.

February 25, 2019

Employees of the Division of Water Quality (DWQ) and Layton City Public Works collected water samples at six locations in west Layton. Four of those samples were collected from the storm drains in the area of Gentile and Angel Streets, while the other two were collected from Kays Creek and the outfall where the storm drain system flows into the creek. This sampling followed an initial sampling of the outfall at Kays Creek by the Davis County Health Department and Layton City on February 23, 2019.

The samples were analyzed for concentrations of organic compounds present in diesel fuel and gasoline and also for dozens of other VOCs, particularly benzene, toluene, ethylbenzene, xylenes, and naphthalene.

The samples collected from a storm drain upstream near 196 North Sugar Street and a storm drain in a catch basin at approximately 30 North Sugar Street did not contain detectable concentrations of any of these compounds. However, samples collected from the storm drains at the intersection of Angel Street and Gentile Street and the intersection of 75 South Street and Angel Street contained some of these compounds in concentrations that exceeded Regional Screening Levels (RSLs) and indicated petroleum contamination.

The sample collected at the storm drain outfall near Heritage Elementary School on Weaver Lane in Layton still contained detectable concentrations of volatile organic compounds, of which the concentration of benzene exceeded the Regional Screening Level.

February 27, 2019

As a follow-up to the previous sampling, employees of DWQ, Layton City Storm Water, and the Utah National Guard collected samples from three locations in the storm drain system. Samples were collected at the upstream control site, at the intersection of 75 South Angel Street, and at the storm drain outfall on Kays Creek and analyzed for the same contaminants as the previous samples.

The sample collected at the upstream control site did not contain any detectable concentrations of volatile organic compounds, but diesel-range organic compounds were detected in the sample. Concentrations of diesel- and gasoline-range organic (GRO) compounds were detected in the other two samples, along with several volatile organic compounds. In general, the concentrations detected in these samples were greater than those collected on February 25, 2019. This is thought to be due to the rain that fell in the area before and during the time the samples were collected.

• View the Storm Water Samples (26 KB)

Update March 1, 2019

Groundwater

Groundwater samples (72 KB) have been collected in the area around the intersection of Angel and Gentile streets in Layton. Groundwater was typically encountered approximately nine feet below ground surface and likely flows to the southwest but may be affected by subsurface drainage in the area. The results of the groundwater samples are compared to Regional Screening Levels (RSL’s) for petroleum contamination. The groundwater collected on the south side of Gentile Street indicated petroleum contamination. These groundwater samples were further screened against Vapor Intrusion Screening Levels. The samples collected south of Gentile Street indicate concentrations in the groundwater that could result in vapor intrusion to residences.

• View the Groundwater Samples (72 KB)

Stormwater

On February 25, 2019, employees of the Utah Division of Water Quality (DWQ) and Layton City Public Works collected water samples at six locations in west Layton (64 KB). Four of those samples were collected from the storm drains in the area of Gentile and Angel Street, while the other two were collected from Kays Creek and the outfall where the storm drain system flows into the creek. This sampling followed an initial sampling of the outfall at Kays Creek by the Davis County Health Department (DCHD) and Layton City on Saturday, February 23, 2019.

The samples were analyzed for concentrations of organic compounds that are present in diesel fuel and gasoline and also for dozens of other volatile organic compounds (VOCs), particularly benzene, toluene, ethylbenzene, xylenes, and naphthalene. The samples collected from a storm drain upstream near 196 North Sugar Street and a storm drain in a catch basin at approximately 30 North Sugar Street did not contain detectable concentrations of any of these compounds.

However, samples collected from the storm drains at the intersection of Angel Street and Gentile Street and the intersection of 75 South Street and Angel Street contained some of these compounds in concentrations that exceeded Regional Screening Levels and indicated petroleum contamination.

The sample collected at the storm drain outfall near Heritage Elementary School on Weaver Lane in Layton still contained detectable concentrations of volatile organic compounds, of which the concentration of benzene exceeded the Regional Screening Level.

• View the Stormwater Samples (64 KB)

Surface Water

The sample collected from Kays Creek (36 KB) at the Bridge Creek Lane Bridge approximately 100 yards downstream contained detectable concentrations of gasoline-range organic compounds (GROs), toluene, and xylenes, none of which exceeded any screening levels. This sample indicates that the contamination is diluted sufficiently such that the creek does not pose a health risk to the public. DWQ will be further analyzing Kays Creek data for impacts to aquatic life.

• View the Surface Water Samples (36 KB)

Update February 27, 2019

Coordinated sampling continued in the affected area. After the informational flyer was distributed to residents, the Layton City Fire Department received reports of two additional households in the area with gas fumes. Utah’s National Guard provided technical assistance to help with investigation efforts.

Division of Environmental Response and Remediation (DERR) activities

Fieldwork for the 417 Subsurface Investigation began today with the collection of soil and groundwater samples from several Geoprobe (groundwater monitoring) boreholes along the west and south sides of the gas station. The analytical results from these samples should be available on February 28, 2019.

Division of Water Quality (DWQ) data

DWQ received the following lab results from samples collected February 25, 2019:

• The control samples collected in storm drains upstream and in the flood basin directly to the west of the gas station on Sugar Street did not contain detectable levels of gasoline, diesel, or any other volatile organic compound.
• The sample collected at the intersection of Angel Street and Gentile Street contained concentrations of diesel range organics (DROs) that are likely to exceed screening levels and concentrations of benzene that exceeded DWQ groundwater standards.
• The sample collected at the intersection of 75 South and Angel Street contained concentrations of diesel range organics (DROs) and gasoline range organics (GROs) that exceed screening levels and concentrations of benzene that exceeded DWQ groundwater standards. The highest contaminant concentrations of all the samples collected were detected at this location.
• The sample collected at the storm drain outfall at Kays Creek contained concentrations of benzene that exceeded DWQ groundwater standards.
• The sample collected at Kays Creek (approximately 100 yards downstream from the outfall) contained detectable concentrations of gasoline, toluene, and xylenes, but none exceeded screening levels or groundwater standards.

Division of Drinking Water (DDW) data

DDW received lab results for the eight homes that were sampled by Layton City Public Works on February 23, 2019. All drinking-water samples were non-detect for VOCs.

Additional test data will be posted as soon as it becomes available.

Time Line

February 26, 2019

DEQ and Layton City assembled and distributed a flyer about the petroleum vapors to residents in the affected area. The flyer included a brief synopsis of the issue, a map of the area, and contact numbers for health and safety information.

DEQ’s Division of Water Quality (DWQ) collected samples from six storm drain locations:

• Upstream control samples north of the gas station
• Near the gas station
• The intersection of Angel Street and Gentile Street
• The intersection of 75 South and Angel Street
• Storm drain outfall into Kays Creek
• Kays Creek at Bridge Creek Lane

The DWQ Spills Coordinator collecting the samples reported the strongest gasoline odors at the Gentile and Angel Street intersection and the 75 South and Angel Street intersection. Test results are expected back on February 27, 2019.

A preliminary groundwater sample was collected from the backyard of one of the affected residences on February 25, 2019. Groundwater was encountered approximately nine feet below ground surface.

DEQ personnel met with a DEQ-contracted consultant to install a subsurface vapor removal system at three residences. Three perforated PVC casings were installed adjacent to the three houses that reported petroleum vapor odors inside their homes. The vapor extraction system will remove petroleum vapors from beneath the houses. In addition, sub-slab soil-gas samples were collected from under each of the three houses, and the analytical results from the samples should be received on February 28, 2019. The source of the petroleum vapors is not currently known.

February 25, 2019

DEQ, Layton City, Layton Fire Department, and Davis County Health Department (DCHD) continued to coordinate their activities to identify the source of the gasoline vapors. The pipeline company dug up additional portions of the pipeline. DERR installed Geoprobe groundwater monitoring wells in the front yards of two of the residences and collected water samples from the wells.

One sample collected on February 23, 2019, at the outfall in Kays Creek showed elevated levels of benzene.

February 23, 2019

Layton City worked with the Davis County Health Department (DCHD) to sample the stormwater outfall that enters Kays Creek. Sampling was requested by the Division of Water Quality (DWQ).

February 22, 2019

Another homeowner contacted Layton City Public Works to report a strong smell of gasoline from the storm drain in front of her house located approximately a quarter-mile from the other houses with reported vapor impacts. Layton City reported that the storm sewer is a 33-inch concrete drain at a depth of 16 feet. The Air Force installed the storm sewer in the 1950s.

DERR’s contractor, DERR staff, the Layton City Public Works Director, and the Layton City Fire Battalion Chief conducted a survey of the storm drain to check for petroleum vapors. DERR staff indicated they smelled gasoline vapors at the Kays Creek discharge point and in a manhole slightly upgradient of the creek. No sheen or gasoline was observed in the creek. The investigation moved north to check storm drains upgradient from the gas station and impacted homes. Vapors were not detected in the manholes north of the gas station on Sugar Street. The sanitary sewer was also checked near the same area and no petroleum impacts were detected.

Pipeline personnel began a new excavation on the north side of Gentile Street to check the pipeline and determine if there were any petroleum impacts in the area.

February 21, 2019

The pipeline company began excavating an area around their pipeline in the backyard of one of the impacted homes. There was no visual evidence of impacts to the soil from the pipeline, but they were unable to excavate to depth without shoring. The DERR contractor was on site to collect samples and observe the excavation as well as begin planning for the installation of a vapor abatement system for the impacted homes.

DEQ Executive Director Alan Matheson authorized the use of Hazardous Substance Mitigation Act (HSMA) funds to take emergency actions to abate the imminent threat to the three affected homes. Vapor monitoring equipment is scheduled to be installed shortly.

February 20, 2019

Petroleum vapors were detected in the basements of the three homes by a photoionization detector (PID), a portable vapor and gas detector that can identify the presence of a variety of organic compounds.

February 19, 2019

The Davis County Health Department (DCHD) reached out to DEQ’s Division of Environmental Response and Remediation (DERR) and Division of Water (DWQ) for assistance. DERR and DWQ began work to identify the source(s) of the vapors and the extent of the impact on the community. DERR initiated a 417 Subsurface Investigation into the incident because a gas station with underground storage tanks is located upgradient of the homes experiencing the vapor intrusion. DERR and DCHD met with residents and entered the homes to monitor the vapors.

February 17, 2019

The DERR contractor took nine soil vapor readings and collected four soil samples for laboratory analysis. No volatile organic compounds (VOCs) or Gasoline Range Organics (GROs) were detected, and very minimal Diesel Range Organics (DROs) were detected.

Stand-up pressure tests were conducted on the petroleum pipelines. Pressure tests passed and both pipelines were restarted.

February 16, 2019

DERR received a report from the original homeowner that the smell had become much worse since his previous call. Two other neighbors had noticed the gas smell in their houses. Several homeowners decided to leave their houses because the gas smell was permeating their entire house.

DERR reviewed the ATG records from the previous three months to ascertain whether the leak detection system had failed. The records indicated there was no gasoline leak from the underground storage tanks.

An additional report from the National Report Center (NRC) indicated that a pipeline company was investigating a possible hydrocarbon release from an eight-inch petroleum pipeline. Both pipelines were shut down pending further tests.

February 14, 2019

A homeowner living at the intersection of Gentile and Angel Street in Layton contacted DEQ’s Division of Environmental Response and Remediation (DERR) to report that he and a neighbor had smelled gasoline vapors in their basements. The caller first noticed the odor two weeks before but noted that the smell had become stronger since that time.

DERR contacted the nearby gas station to request automatic tank gauging (ATG) records. An ATG is an electronic device that monitors the fuel level in an underground storage tank over a period of time to see if the tank is leaking.

The Davis County Health Department (DCHD) and Layton City Fire Department visited the home, and DCHD tested the indoor air in the home with a volatile organic compound (VOC) monitor (photoionization detector or PID). Homeowners were concerned about a possible gas leak. The report was entered into the DERR Environmental Incidents Notifications database for investigation.

What are the potential health effects of petroleum vapors?

Petroleum vapors contain volatile organic compounds (VOCs), a large and diverse group of chemicals that evaporate easily in air. Some, like benzene and toluene, can have harmful health effects when inhaled at high levels.

Many VOCs have a strong or distinctive smell, often chemical or gasoline-like. People can smell some VOCs at very low levels, often below the levels associated with health effects from breathing them for a short period. Different VOCs have different health effects and levels of risk. However, there are some typical health effects that can result from short-term inhalation:

• Eye, nose, and throat irritation
• Headache
• Dizziness or light-headedness
• Loss of coordination
• Difficulty concentrating
• Nausea

Individuals experiencing health effects they suspect are caused by inhaling VOCs should seek fresh air and consider contacting their health care provider or the Utah Poison Control Center at (800) 222-1222.

If the health effects are serious, it’s recommended that people call 9-1-1.

For more information on possible health impacts from gasoline, consult the Agency for Toxic Substances and Disease Registry (ATSDR) fact sheet on gasoline health effects.