Executive Summary
The City of Santa Monica operated a landfill from 1948 to 1970. The facility was closed and capped with three to five feet of cover soil in 1970. In order to comply with new regulatory requirements for landfills, a Landfill Gas Control and Treatment System (LFG Control System) was installed in 1998 to monitor and control methane and other landfill gases. This report provides a summary of the inactive landfill site located beneath Gandara Park and portions of the Municipal City Yards located at 2500 Michigan Avenue and a description of the LFG Control System, the regulatory requirements, and recent monitoring results. The LFG Control System has been in continuous operation since 1998 to monitor methane levels and to maintain safe environmental conditions for nearby residents, park users, and City staff who work at the Yards. Oversight of the LFG Control System is performed by a licensed independent contractor, Montrose Environmental, that maintains, operates, and manages the LFG Control System in strict accordance with permits from the County of Los Angeles Department of Public Health (LADPH) and the South Coast Air Quality Management District (SCAQMD). The permits require routine monitoring and maintenance of a perimeter probe network, LFG extraction wells, and the LFG Control System. Additionally, the air above the landfill surface and the interiors of the City Buildings are monitored for LFG. Compliance reports are submitted to the LADPH and SCAQMD on a quarterly basis.
Over the past 20 years, the LFG monitoring results indicate predominantly safe methane levels in all of the system’s 37 subsurface LFG detection probes, including a network of monitoring probes that specifically monitor methane levels adjacent to the Mountain View Mobile Home Park. In several instances, anomalies have been recorded at a handful of locations that exhibit temporary increases in methane levels that exceed the regulatory threshold of 5% by volume. These anomalies can generally be remedied by adjustments to the LFG mechanical network, or through expansion of the control system. A planned expansion is currently underway to address a recent anomaly associated with utility work and construction activities at the City Yards.
Background
Landfill Background
In 1904, the Simons Brick Company established a factory to manufacture pottery, brick, tile and clay shingles alongside the Southern-Pacific tracks and adjacent to the Sunset Brick and Tile Manufacturing Company. The operations included a large clay mining pit located at present day Gandara Park and portions of the City Yards. This local resource provided materials for the construction of many buildings in the Bergamot area and West Los Angeles.
Following the closure of the clay mine in the 1940’s, the site transitioned to a landfill that was primarily used for the disposal of construction debris composed of wood, cement, metal, gypsum, and other construction related materials. Based on the historic aerial photos it appears that municipal solid waste (residential trash) was disposed at this location from approximately 1949 to 1952. The western portion of the pit remained unfilled until approximately 1964, at which time it also appears to have been predominantly filled with construction debris. At the time of the landfill’s closure in 1970, it is estimated that it contained approximately 300,000 cubic yards of refuse. It is estimated that the pit was a maximum of 30 to 35 feet deep at its southern edge and considerably shallower along the northern edge (about 3 to 5 feet deep.) A layer of approximately 3 to 5 feet of soil was reportedly used as a landfill cover material at the site.
Figure 1: Approximate Boundary of the Landfill from 1977 Discussion
The City has been actively monitoring methane levels at the former landfill site since 1996. California Title 27 regulations for control of LFG adopted in 1997 required a LFG Control System to be installed to control gases generated by the decomposition of the landfill material. An interim LFG Control System was installed in 1998. Construction of the permanent LFG Control System that incorporated the interim system was completed in the fourth quarter of 2000. The primary LFG components are methane and carbon dioxide. Methane gases are the primary subject of this report, as methane is flammable and thus presents safety considerations.
The objectives of the LFG Control System are:
• Reducing methane concentrations within the landfill;
• Reducing methane concentrations in native soils surrounding the landfill; • Reducing methane concentrations in identified utility trenches; and • Maintaining methane concentrations in perimeter subsurface detection probes outside the landfill below the regulatory action level of five percent methane by volume or 50,000 parts per million.
Five percent represents the lower flammability limit (LFL) for methane, which is the lowest concentration of gas capable of producing a spark or flash of fire in the presence of an ignition source. With methane concentration levels below the LFL, the gas would be too lean to burn.
LFG Control System – How it Works
The system includes the following major components:
• Monitoring Probe Network: consisting of 37 subsurface probes for monitoring LFG.
• Extraction Well Network: consisting of ten vertical wells that extract LFG from the landfill.
• Conveyance Piping: consisting of underground piping to collect and transport LFG from the extraction wells to the treatment compound. • Treatment Equipment: consisting of multiple systems that treat the collected LFG before it is discharged to the atmosphere through a 26-foot-high stack.
Regulatory Compliance – Why We Have the Landfill Gas Control and Treatment System
Policy decisions made 80 years ago provided for a landfill to be located in the presentday Pico Neighborhood. Operations at the landfill ceased in 1970 and, in 1996, the City was compelled to begin monitoring the site due to changes in the California Code of Regulations. In order to control exposure to potential LFG emissions, the LFG Control System was installed in 1998 and expanded in 2000. The LFG Control System was approved and permitted by the SCAQMD and LACDPH. These permits require the following monitoring and maintenance activities:
• Bi-weekly Activities:
o Check the treatment vessels outlet for volatile organic compounds (VOCs) and schedule a media replacement if VOCs exceeds 20 parts per million (ppm).
o Check the blower and equipment for any LFG leaks and to ensure it is operating properly.
o Check the condensate tank for remaining capacity to ensure it will be pumped out and hauled away.
• Quarterly Activities:
o Monitor the vacuum methane, oxygen, carbon dioxide, and hydrogen sulfide in all 10 LFG extraction wells and make adjustments, if necessary. o Monitor the methane and pressure in all 37 probes (many of which have multiple depths).
o Collect a composite sample of air from within three inches of the ground throughout Gandara Park and have it analyzed by a certified laboratory for methane and VOCs to ensure the total methane emissions in the park do not exceed 25 ppm.
o Conduct instantaneous surface monitoring (ISM) for methane within three inches of the ground surface throughout Gandara Park.
o Conduct ISM indoors throughout the City Yards buildings to check for LFG in the buildings.
o Report findings to SCAQMD and LACDPH.
• Annual Activities:
o Collect LFG system outlet and inlet samples and have a certified laboratory analyze them for hydrogen sulfide, methane, and VOCs to check the functioning of the treatment system and ensure it is working properly.
o Collect a perimeter probe sample for VOC analysis at a certified laboratory.
The continuous monitoring of the former landfill site has produced a record going back nearly 25 years. As a whole, this record demonstrates that methane levels – both underground and in the ambient air environment – are generally below the regulatory compliance threshold of 5%, with a few isolated exceptions that are described in this report in more detail. Overall, the site generates a low volume of methane. This can be attributed to the landfill being over 50 years old and to the composition of the waste landfilled, which was predominantly construction debris such as concrete blocks, bricks, and wood. Based on the volume and type of waste in place and the known time the landfill was in operation, landfill modelling indicates that the landfill’s ability to generate methane is very low and will continue to decrease over time.
Community Concerns About Methane and Environmental Justice Over the years, concerns have been expressed by the community over the presence of LFG and its potential impact on the human environment. As part of the former landfill sits beneath a public park, concerns have been raised about the effects of emissions on families and children and the potential for the vented methane to combust. Similar concerns have been expressed by the neighboring residential community living adjacent to the former landfill site at Mountain View Mobile Home Park.
The City closely monitors the LFG to track methane levels to a high degree of accuracy, provide a historical record, and ensure a stable and safe human environment. The LFG system’s network of monitoring probes and gas extraction wells help to form a barrier against any potential methane leaks, and effectively monitor and extract landfill gasses near sensitive residential areas including the Mountain View Mobile Home Park, as well as Gandara Park. The compliance reporting requirements that are satisfied by a licensed contractor, Montrose Environmental, ensure independent professionals continually evaluate the system for changing conditions. The current scope of services with Montrose Environmental covers preventive maintenance, proactive upgrades, and field monitoring of the landfill gas extraction system to ensure optimum operation and performance of the components in extracting landfill gases. This allows the City to go above and beyond the regulatory requirements set by the LADPH and SCAQMD.
Members of the public may request copies of the City’s Quarterly LFG Operations, Maintenance, and Monitoring Reports from CalRecycle (Attachment A) or from SCAQMD (Attachment B).
Subsurface Methane Levels
Since the LFG control system began operation, required monitoring of subsurface vapor probes has documented that methane concentrations in native soils surrounding the landfill are generally below regulatory action levels. Similarly, the network of trench probes that exists at the site have not contained methane in excess of the regulatory action limit, with the exception of trench probe TP-2 located in the City Yards that is described below. Multi-depth vertical monitoring probes are installed along the perimeter of the landfill. A total of 37 probe clusters are used to detect any landfill gas that may be traveling through the subsurface soil. The probe clusters each contain shallow, intermediate, and deep probe depths.
Monitoring at Mountain View Mobile Home Park
LFG monitoring equipment installed between the landfill and the Mountain View Mobile Home Park consists of eight perimeter probe clusters, eight landfill gas extraction wells, and two sumps. These are located along the northeast perimeter of the mobile home park to detect and prevent LFG migration. There were also ten former monitoring probes situated within the Mountain View Mobile Home Park. After LFG was consistently not detected (0.0 ppm) for an extended number of years, the regulatory agencies no longer required the City to test and sample monitoring wells MVP1 through MVP10.
Figure 2: Map of Shallow Probes In Compliance with LADPH and SCAQMD Requirements Ambient Air Methane Levels
The SCAQMD permits require a composite air sample be collected quarterly within three inches of Gandara Park for methane and VOC analysis. The results of these samples in recent years have been consistently below the SCAQMD limit of 25 ppm.
Compliance with Regulatory Requirements
Quarterly compliance reports detailing methane levels throughout the monitoring and control system are submitted to SCAQMD and there have been no non-compliance violations recorded against the City of Santa Monica. Quarterly compliance reports are also submitted to the LADPH. An inspector from the LADPH has inspected the site quarterly for the past 20 years. During that time there have been no enforcement actions for the Santa Monica Landfill. There have been “Areas of Concern” or minor “Violations” noted on the inspection reports, most of which occurred back in the late 1990s and early 2000s when the LFG Control System was being installed and later expanded. The most recent of these occurred in 2018 and 2019. They were due to water ponding in the City Yards and exceedances of 5% methane detected in the nearby subsurface probe PP-6. This exceedance was noted on June 13, 2019, when
5.1% methane was detected in probe PP-6B. Subsequent inspections of PP-6 consistently indicate no exceedances of 5% methane.
Anomalies in Historically Low Methane Levels
Methane concentrations exceeding 5% have occurred sporadically in certain Rule 1150.1 compliance probes. These elevated concentrations have been controlled through LFG extraction well adjustments and upgrades on aging LFG equipment.
Upgrades have included installing new well heads and sump pumps, improving compressor operation, and keeping the vacuum system continually running with a new variable frequency drive which allows the City to control the vacuum system and blower.
Two anomalies identified in the continuous system monitoring warrant further discussion in this report, as they demonstrate the City’s commitment to transparency and to maintaining tight oversight of LFG emissions.
• Trench Probe #2– Potential Sewer Utility Off-Gassing
Only the methane concentrations in trench probe TP-2, which is located on the north side of the City Yards in front of the Water Resources Division’s facilities, have consistently exceeded the Rule 1150.1 limits. The methane readings collected from this compliance monitoring probe have been higher than most of the landfill gas extraction wells, ranging from 22.3% to 38.4% by volume in air since 2016. Montrose believes the gas detected in probe TP-2 may not be originating from the landfill, but instead is the product of a nearby sewer utility.
Montrose conducted gas sample fingerprinting during the first quarter of 2020 by comparing laboratory analysis of vapor samples collected from probe TP-2 and the closest LFG extraction well (LFG-7). The analytical results indicate the gases are different and that TP-2 may not be detecting LFG but may be detecting sewer gas from a nearby sewer line in the trench. LADPH is aware of the history of this probe and there have been no violations issued for trench probe TP-2, which is located in the City Yards area.
• Perimeter Probe Anomalies
There have been sporadic exceedance of the 5% methane detected in the subsurface perimeter monitoring probes over the past 10 years. When elevated levels of methane are detecting in perimeter probes, corrective actions are performed. This usually includes checking and adjusting the nearby LFG extraction wells.
Some of the perimeter probes are located very close to the edge of the landfill waste and also to the LFG extraction wells. This close proximity to LFG sources, makes it more likely to periodically have readings that exceed 5% methane. In order to monitor the probe, it has to be evacuated by connecting it to a pump. By putting the probe under vacuum to collect a sample, LFG from the surrounding soil may be drawn towards and into the probe. Therefore, one-time anomalous elevated methane readings in the perimeter probes may be due to sampling errors and are not necessarily an indication that LFG is migrating beyond the site’s border.
The following maps show all the perimeter monitoring probes at the site. Next to each probe is either a green dot or yellow dot. The green dots indicate that probe has not exceeded 5% in the past five years of quarterly readings (20 monitoring events). The yellow dot indicates that the probe has had one or more exceedances of 5%. Since each probe has 3 depths, the shallow, intermediate, and deep probes are shown on three separate maps.
Figure 3: Shallow Probe Map (Green Dots = No Readings Over 5% and Yellow Dots = 1 or More Readings Over 5% in Past 5 Years)
Figure 4: Intermediate Probe Map (Green Dots = No Readings Over 5% and Yellow Dots = 1 or More Readings Over 5% in Past 5 Years)
Figure 5: Deep Probe Map (Green Dots = No Readings Over 5% and Yellow Dots = 1 or More Readings Over 5% in Past 5 Years)
• Recent Anomalies at City Yards Construction Site – Expansion of the LFG System
As a result of recent utility work and construction activities of the new Fleet Maintenance building located at the City Yards, several new anomalies were recently identified. The City was contacted by Southern California Gas Company in June 2021 regarding the results of their aerial methane mapping survey, which identified two locations with detectable levels of methane in the City Yards.
Asphalt and concrete were removed at these two locations during construction, and planters and electrical conduit boxes were installed.
Based on a thorough investigation involving surface monitoring at multiple areas in the City Yards, it was determined that two subsurface electrical conduit boxes had elevated methane readings. To reduce the methane detected in these locations, Montrose increased the vacuum at the nearest two LFG extraction wells and the City contractor capped open conduits within the boxes. This reduced the methane concentrations in the utility boxes. These locations have been added to the routine monitoring program and will continue to be inspected.
In addition, Public Works is installing an additional vertical LFG extraction well to reduce and capture methane near the surface in these areas. This work is covered by existing contracts. Staff is preparing to submit applications and obtain permits from the LACDPH and SCAQMD for the installation of the new well and all necessary trenching and piping connections to the existing LFG header. A Work Plan and Health and Safety Plan will be prepared to describe the proposed construction activities and safety protocols to be performed at the site.
Figure 6: Proposed Location of Additional LFG Extraction Well and Piping System Maintenance
The LFG system has performed well over the past twenty-four years, owing to a routine maintenance schedule that continuously evaluates the condition of all mechanical equipment. Repairs are performed when necessary, or when the opportunity to improve the system with upgraded components is presented through advances in technology or science. Routine maintenance and repairs are covered in the City’s existing contract with Montrose.
Conclusion
The City maintains an inactive landfill site located beneath Gandara Park and portions of the Municipal City Yards in the Pico Neighborhood with a Landfill Gas Control System. The LFG Control System has been in continuous operation since 1998 to monitor methane levels and to maintain safe environmental conditions for nearby Pico Neighborhood residents, park users, and City staff who work at the Yards. Oversight of the LFG Control System is performed by a licensed independent contractor, Montrose Environmental, that maintains, operates, and manages the LFG Control System in strict accordance with permits from the County of Los Angeles Department of Public Health (LADPH) and the South Coast Air Quality Management District (SCAQMD).
Montrose performs biweekly system inspections to confirm the LFG Control System is running properly and provide maintenance to the mechanical equipment. Montrose also monitors the landfill surface and the LFG detection and collection system quarterly. By regularly monitoring the 37 perimeter and trench probe clusters for LFG detection in the subsurface soil, staff can identify elevated methane and perform adjustments or repairs on the LFG extraction wells. The LFG extraction wells are monitored to ensure they are providing the maximum LFG control at the site. The entire landfill surface is monitored for LFG emissions and repairs and updates are made as necessary to ensure the health and safety of the public and City workers.
Financial Impacts and Budget Action
There is no immediate financial impact or budget action necessary as a result of this action. Staff is using existing funds for installation of an additional vertical LFG extraction well. City Council approved funds to award a contract with Montrose Environmental for services related to the operation, maintenance, and compliance sampling and reporting for the City’s Landfill Gas Control System at the July 27, 2021 meeting. The total contract amount was $715,211 of which $137,990 was approved for FY 2021-22.