Public Inquiries & Responses

Submission #5

On the evening of October 27, 2021, the Safety Ombudsman email received the following question: “I am not sure if this role is still active, but if it is, can you please tell us if there is a leaking gas well at the Aliso facility right now?”


The Ombudsman provides this summary here but refers the reader to the full detailed report, available here.

The requestor’s question as stated is broad and applicable to the entire Aliso Canyon gas storage facility, so the Safety Ombudsman (“Ombudsman”) confirmed with the requestor that the Ombudsman role is active and asked for clarification as to whether the requestor had something more specific in mind. The requestor confirmed they were asking a general question about whether there is any well in the field that is experiencing any uncontrolled release at the time of the request. 

The Ombudsman reviewed immediately available information and informed the requestor that review of available information could only allow that to the Ombudsman’s knowledge, nothing was “currently leaking”, but that the Ombudsman would seek additional information from SoCalGas.  The Ombudsman prepared and sent a November 5, 2021 request to SoCalGas for specific well data, covering a one month period from October 5, 2021 to November 5, 2021, inclusive, that could be reviewed for anomalies that might indicate an issue with well integrity. 

After review of the data supplied by SoCalGas in response to the Ombudsman’s request, the Ombudsman did not see evidence of an obvious, significant, or persistent issue of well integrity. However, the Ombudsman’s additional review, trend analysis, and linking of methane monitoring, wellhead pressure, and annulus pressure information resulted in the Ombudsman’s opinion that additional questions to SoCalGas were necessary. Therefore, on December 13, 2021, the Ombudsman sent a follow-up data request to SoCalGas, focused on information regarding wells for which the Ombudsman was not able to be satisfied that there were no issues of concern based solely on the information provided in response to the November 5, 2021 data request. The Ombudsman received SoCalGas’ responses dated January 26, 2022.


The Ombudsman did not observe in the data provided by SoCalGas any safety-threatening well integrity issue in the Aliso Canyon storage field during the period October 5, 2021, to November 5, 2021. SoCalGas, in their responses to the Ombudsman’s requests, stated that they did not observe any findings in the monitoring, logging, or testing data at or near surface or downhole in wells that, in accordance with their standards, would indicate any abnormality or leak.

Submission #4

I have severe problems breathing when I am on the hill adjacent to your Aliso Canyon facility. Please tell me what chemicals are escaping into the air so I may give to my Pulmonologist.


The Safety Ombudsman received the following request for assistance on July 14, 2020: “I have severe problems breathing when I am on the hill adjacent to your Aliso Canyon Facility. Please tell me what chemicals are escaping into the air so that I may give to my pulmonologist. Thank you”.

Chemicals which may possibly result in some degree of respiratory irritation include both current natural gas emissions (which is predominantly methane but also contains trace amounts of mercaptans as an odorant for leak detection purposes), and chemicals which may have been emitted at some prior point in time and were deposited on the surface and possibly remain persistent.

After the gas leak from the Aliso Canyon SS-25 well, SoCalGas installed equipment at the Aliso Canyon Facility (Facility) to detect the leakage of natural gas using three different independent systems. These include:

  1. SoCalGas’ “fence line” monitoring system, which consists of eight stations where methane emissions are monitored and recorded using a laser-based system. This system records methane emissions in parts-per-million (ppm) and the data is posted to a website where anyone can access the data via this link:;
  2. An ambient air monitoring system which includes five different stations, three of which are located on the south side of the Facility and two on the north side. This system also monitors and records methane emissions in ppm using laser-based detection technology; and
  3. Methane monitoring equipment at each active well and its connecting pipeline lateral. This system also monitors and records methane emissions in ppm, but utilizes infrared-based technology. 

Another potential source of contaminants relates directly to the leak event itself and the fluids that were released into the atmosphere during that period. Based on records SoCalGas provided to the California Public Utility Commission (CPUC), it is possible, though perhaps unlikely, that some of the chemicals released into the atmosphere during the leak were deposited on the ground and remain persistent.

A data request was subsequently submitted to SoCalGas to obtain information related to the three methane monitoring systems and the chemicals and fluids used during attempts to bring the SS-25 well under control after it blew out. This data may identify chemicals associated with the Facility and which may result in some respiratory irritation. This data may, in turn, assist in resolving this issue. The information requested from SoCalGas included the following:

  1. Please provide me with the dates on which SoCalGas’ fence line methane monitoring system detected any methane emissions since October 14, 2019; please include with the dates the actual emission levels for each of the eight monitoring stations, including those below the threshold reporting level of 25 ppm averaged over 30 minutes.
  2. Please provide me with the dates on which any of the five area methane monitors (3 on the south side of the Aliso Canyon property and 2 on the north side) registered methane emissions since these monitors were placed into service on August 6, 2019. Please include the actual emission levels for each monitor and for the duration of the emission period.
  3. Please provide me with a listing of any well which detected methane emissions from either the wellhead lower explosive limit (LEL) sensor or the adjacent lateral pipeline LEL sensor since the date of installation of these wellsite monitors. Please include the actual LEL readings to the extent those readings are recorded.
  4. Please provide me with a copy of all material safety data sheets (MSDS) for all chemicals, additives, and materials (both solid and liquid) that were used in making any fluids which were pumped into the SS-25 well during the seven attempts to kill that well between October 23, 2015 and February 11, 2016, and any fluids which were pumped into the P-39A relief well for the purpose of killing the SS-25 well.

SoCalGas provided a response to each of the above four questions on October 6, 2020. In reviewing their response, particularly the data they supplied as part of their response, it became clear that additional questions would need to be addressed to clarify what the data reflect. Thus, a subsequent request (Data Request 7A) was made to SoCalGas seeking such clarification. That request was made on October 16, 2020 and a response was received on October 30. A copy of their response to Data Request 7A may be viewed via these two links: Click Here and Click Here. The data supplied by SoCalGas in response to each question is discussed in some detail below. 

Question 1 – Fence Line Methane Monitoring Data

SoCalGas provided the requested data from all eight of the methane monitoring stations at the Facility. The requested data includes all events where methane emissions exceeded normal background level, which is about 2 ppm, and covers the period from October 14, 2019 through August 4, 2020 (methane emission events prior to October 14, 2019 are addressed below). Normal background level was established independently by studies performed by the California Air Resources Board (CARB). There were 35 events during this period when methane emissions exceeded normal background level. In all instances, the peak exceedance was well below the regulatory reporting threshold (which includes readings in excess of 25 ppm averaged over 30 minutes) and the duration extended over a relatively short period of time – typically 10-15 minutes – though several events lasted between 25-65 minutes. A copy of the data supplied by SoCalGas may be viewed via this link: Click Here. The “Peak Methane Value” is, as the heading suggests, the highest methane level that was recorded during the time interval when the methane level exceeded background level.

As noted above, SoCalGas is required to report methane emission events to CARB when emission readings exceed 25 ppm averaged over 30 minutes. SoCalGas is also required to provide notice to the public of all such events and maintains a website, which is available to the public, for documenting such events. The link to the website is:

The methane monitoring system was installed and became operational in July 2017. From August 2017 through October 13, 2019 there were seven events when methane emissions temporarily spiked above normal background level. These include the following:

DATE Reported Concentration – ppm 
August 11, 2017  10 ppm
September 3, 2017 7 ppm
October 13, 2017 25 ppm & 18 ppm
December 1, 2017 minor elevated reading
December 18, 2017 66 ppm
June 21, 2018  8 ppm
October 11, 2029 68 ppm

Several of these exceedances were attributed to high humidity/fog at the time of the event. The October 11, 2019 event was attributable to heat and smoke associated with the Saddle Ridge fire which burned through a portion of the Facility. The methane sensors can and sometimes do indicate false methane emissions due to high humidity/fog. During these events, SoCalGas conducts manual confirmation readings by deploying crewmembers to survey the affected area using infrared sensors.

In summary, methane emissions recorded by the fence line monitoring system at the Facility generally indicate emissions which are at or only slightly above background level. While there have been numerous events registering methane readings above background level, peak levels have remained well below threshold reporting levels for the most part, and in several instances, the methane readings were not, in fact, due to methane leakage but rather to high humidity/fog.

Question 2 – Ambient Methane Monitors

SoCalGas provided the requested data from all five of the ambient methane monitoring stations at the Facility. Three of the monitors are located on the south side of the facility property and the other two on the north side. These monitors utilize the same technology (laser-based) as the fence line methane monitoring system. This system was installed in August 2019. The system records methane levels on a continuous basis in ppm. SoCalGas reported the figures as a 60-minute average. As with the fence line monitoring system, background methane level is approximately 2 ppm. The data provided by SoCalGas may be accessed via this link: Click Here. Raw data from each of the monitors is presented graphically on five separate tabs to better illustrate methane emission levels over time. With few exceptions, all readings for each of the five monitors remain at or near background levels. While each monitor has recorded elevated readings for very brief periods, peak levels have remained below 10 ppm in all instances.

Question 3 – Wellhead and Lateral Line Methane Sensors

There are two wellsite monitors at each active well; one adjacent to the wellhead and the other adjacent to the lateral line which connects to each well. The wellsite monitors utilize infrared technology to detect the concentration of methane emissions in ppm. This equipment was installed beginning in July 2019 and was operational shortly thereafter. SoCalGas provided an Excel file containing the requested data, which included any methane emissions from the time of installation up through the date of the data request. The data may be accessed via this link: Click Here.

The readings are recorded on a continuous basis and are reported as a five-minute average in ppm except when the readings fall to zero, in which case no reading is recorded for that five-minute period. A graph of the historical data has been prepared for each well and lateral to show graphically the trend in methane emissions in ppm as a function of time; the graphs are immediately above the columns which contain the emission readings. As can be seen from the graphs, there is considerable variability in emission levels from well-to-well. Some wells tend to show relatively low emission levels while others, during the same period show higher levels. Also, there does not appear to be any correlation of leakage levels at any specific wellhead and its associated lateral line connection. Sharp declines in readings may be attributable to leakage repair efforts, although in several instances wells which experienced a sharp decline often exhibit a sharp increase later.

As of January 1, 2020, CARB instituted new reporting thresholds for methane emissions. For emissions of 1,000 – 9,999 ppm, repairs must be made within 14 calendar days; for those of 10,000 – 50,000 ppm, repairs must be made within 2 calendar days.

Question 4 – Materials Used in Making Well Kill Fluids Pumped into the SS-25 Well

Seven attempts were made to kill the SS-25 well between the period of October 2015 – December 2015 by pumping water-based fluids into the well. The well was finally killed during an eighth attempt via a relief well drilled specifically for that purpose in February 2016. A variety of different chemicals and additives were used to formulate the kill fluids. According to SoCalGas’ records, the chemicals used in formulating the kill fluids include the following (some of which are trade names):

  • Amberguard-215
  • Desco CF
  • DrisPac SL
  • GeoZan
  • Polytek+
  • Calcium chloride
  • Calcium carbonate
  • Potassium chloride
  • Barite
  • Caustic Soda
  • Nut shells
  • Saw dust

Some of the kill fluids were ejected into the atmosphere during at least one kill attempt and so there is a question as to whether the ejected fluids may have presented a health hazard to nearby residents. In response to a data request from the CPUC dated July 25, 2017, SoCalGas provided a copy of the MSDS sheets for all chemicals/additives used in formulating the kill fluids. SoCalGas provided a link to that same data in response to the Safety Ombudsman’s request for information concerning this issue. That data may be accessed via this link: The link to the MSDS sheets themselves may be accessed via the following links: Click Here and Click Here.

According to a report dated May 22, 2018, issued by the Office of Environmental Health Hazard Assessment (OEHHA), California Department of Conservation Geologic Energy Management Division (CalGEM) inspectors who were on site during kill attempts on the SS-25 well observed that some of the injected kill fluids migrated back to the surface via a vent that formed close to the well-bore and were ejected into the air. OEHHA aided state and local agencies during the leak event; they evaluated the potential public health impacts from exposure to the natural gas plume and its trace organic constituents including benzene, mercaptan, and residual hydrocarbons. A copy of the OEHHA report may be accessed via this link: Click Here.

In their report, OEHHA notes that the Los Angeles County Department of Public Health (LADPH) was alerted by Porter Ranch residents of oily brown spots on outdoor surfaces around their homes in December 2015. The oily spots were attributed to oily mist escaping from the leaking well and transported via wind currents. The highest concentration of oily spots was found north of the Highlands neighborhood of the Porter Ranch community. SoCalGas collected surface-wipe samples from affected cars and tested them from the presence of hydrocarbons and benzene, toluene, ethybenzene, and xylene (BTEX). The samples indicated the presence of heavy hydrocarbons consistent with crude oil; however, BTEX was not detected in any of the samples.

A section of the OEHHA report also addresses potential toxic hazards from inhalation and oral exposure to the chemicals used in the well kill fluids. The report states that most of the chemical additives are non-volatile substances and would not be expected to have a significant exposure hazard to downwind residential areas, given the relatively small quantities of material that were used. One additive, glutaraldehyde, was noted as being semi-volatile with short-term exposure of the vapor to humans resulting in eye, nose, and respiratory tract irritation. OEHHA indicated that if glutaraldehyde were present in air emissions during well control operations it may have contributed to respiratory and other symptoms reported by some residents residing downwind of the leak. However, they concluded that since it is reactive and readily biodegradable, glutaraldehyde would not be expected to persist in surface deposits and would not represent an ongoing oral exposure hazard.

OEHHA concludes their report by indicating that no long-term health consequences would be expected from exposure to the constituents used in the well kill fluids; rather, that sustained release of odorants (specifically mercaptans) in the natural gas during the leak appears to have been more likely to cause respiratory issues for exposed residents. Footnote 16 in the report includes this link to an earlier OEHHA gas-leak hazard assessment which addresses the natural gas plume and trace organic chemicals – There are several other useful links embedded within this earlier assessment, including a summary of expert advisor input regarding public health measures.

Submission #3

“Residents living near the Aliso Canyon facility reported rumbling sounds coming from the facility during several evenings during the first week of May.   Can the Safety Ombudsman please investigate and identify the cause?”

SAFETY OMBUDSMAN RESPONSE: Contact was made with Aliso Canyon station personnel regarding this request.  SoCalGas is not aware of any unusual sounds coming from the facility.   SoCalGas equipment was inspected and operated as normal during this time.  Further, SoCalGas has not identified any safety issues as defined by the Consent Decree, which includes those relating to well integrity and maintenance and associated unintended leak prevention.

Submission #2

“I am not sure if your role is limited to inside the fence at Aliso.  If it is, then please just let me know.  If not, residents have asked me about the public notice they found on this website which is a published SoCalGas press release about pipe inspection work to be done on a street in Granada Hills.  People are asking why this is being done now in a residential street when school is in session and not during the summer break.  If this is necessary, then is it really just an inspection as the press release says?  How can one get the proper information?  You can understand that neither the community nor I trust an answer from SoCalGas’ customer-service people, so I am asking others who may know.”

SAFETY OMBUDSMAN RESPONSE: My role is limited exclusively to the Aliso Canyon facility.   Unfortunately I am not able to offer you any insight into the work being performed by SoCalGas.

Submission #1

“Concern about toxic gases escaping from Southern calif gas storage facility due to faults and fissures inherent in the geology of the area and the lack of adequate gas monitoring. Kew (1929) and Hansen (1984) describe a geologic area riddled with faults that make gas excaping a certainty. The oils wells that were there previously contain toxic materials, including benzene (a known carcinogen) and other petroleum products that, mixed with natural gas, pose a Hazzard should they escape. Placement of gas monitors has not been shown to coincide with known faults nor has gas analysis been done periodically to show the gases do not contain hazardous materials. All these concerns should be monitored.”

SAFETY OMBUDSMAN RESPONSE: There are basically four issues embedded within this concern including:

Issue 1) The concern that Kew, in 1929, characterized the geologic region as riddled with faults that make gas escaping from the storage field a certainty;
Issue 2) The oils that were previously native to the storage reservoir contain toxic materials including benzene and other petroleum products that when mixed with natural gas pose a hazard in the event they escape from the storage formation;
Issue 3) Placement of gas monitors has not been shown to coincide with known faults; and,
Issue 4) Gas analysis has not been done periodically to show the gases do not contain hazardous materials.

Each issue is addressed separately below.

Issue 1 – The Geologic Region is Riddled with Faults That Make Gas Escaping from the Storage Field A Certainty

The paper authored by Kew in 1929 discusses the general nature of the geologic region surrounding the Aliso Canyon Facility, including the existence of several faults, and specifically the Santa Susanna fault.  Kew also mentions the existence of a number of hydrocarbon seeps that were discovered in the area, though given the complexity of the local geology there is no practical means of linking those seeps to a particular hydrocarbon reservoir, including the reservoir used by SoCalGas for gas storage purposes.   

The storage formation operated by SoCalGas exists between approximately 7,000 and 10,000 feet below the surface.  There are multiple porous and permeable formations at shallower depths, some of which also contain hydrocarbons, and some of which may also still be under production by third parties other than SoCalGas.  Thus, as noted above, there is no way of determining the actual source of the hydrocarbon seeps mentioned by Kew.  The natural hydrocarbon seeps could very well have been associated with one or more of the shallower hydrocarbon-bearing formations or a deeper formation below the zone used by SoCalGas for its operations.

Pursuant to DOGGR Order No. 1118, dated July 19, 2017, SoCalGas was required to, among other things, perform a seismic risk study including a comprehensive assessment of the geotechnical hazards present at the Aliso Canyon Facility.   SoCalGas assembled a team of renowned independent experts to examine these hazards and their associated risks.  Where the paper authored by Kew discusses the geologic complexity on a more regional basis, the studies performed pursuant to DOGGR Order No. 1118 examine the geotechnical hazards specific to the Aliso Canyon Facility.  As such, the reports discussed below provide a much more comprehensive and up to date assessment of geotechnical risks associated with the storage facility.

A total of ten hazard assessments were completed which examined the wells at the facility and the facility’s geology.  The reports are numbered 1-10 and address hazards associated with:

Report 1 Landslide Hazard Report;

Reports 2 & 3 Stability Analysis of Landslide-prone Slopes and Wellbore Landslide Loading Assessment;

Report 4 Geologic and Geomechanical Study;

Report 5 Probabilistic Seismic Hazard Analysis;

Report 6 Probabilistic Fault Displacement Hazard Analysis;

Reports 7 & 8 Wellbore Loading Assessment and Shear Testing and Finite Element Analysis of 1:10 Scale Pipe Samples;

Report 9 Well Flow Modeling; and

Report 10 Dynamic Gas Flow Analysis

Collectively, these reports assess the hazards and associated risks due to ground motion and fault displacement, subsurface leaks due to well casing failure resulting from displacement and, potential gas flow rates and volumes through geologic structures and wells, all as a result of earthquake induced damage.  

The proposed scope of work for each of these assessments was reviewed by the California Department of Conservation, Geologic Energy Management Division (CalGEM, formerly DOGGR) and independent technical experts from Lawrence Berkley, Lawrence Livermore, and Sandia National Laboratories (the National Labs), whose feedback was used to extend and improve the technical assessments.  Collectively, these assessments and the reports associated with each speak extensively to the geologic complexity of the region in which the Aliso Canyon Facility exists, and the potential geologic, seismologic, and geomechanical risks associated with the facility.   Overall, the studies indicate that seismic risks at the Aliso Canyon Facility are relatively low and can be reasonably managed and/or mitigated.

An overview of the entire study, a draft summary of the results of each report, and a draft of the entirety of each of the ten individual reports may be accessed by clicking this link. The draft reports were submitted to DOGGR and the National Labs for review and comment in March 2019.

Issue 2 – Oils Native to The Storage Reservoir Contain Toxic Materials Including Benzene and Other Petroleum Products That When Mixed with Natural Gas Pose a Hazard in The Event They Escape from The Storage Formation.

Natural gas itself is considered a hazardous material by the federal government as well as the State of California.   It may indeed pose a hazard if it escapes from surface piping or the Aliso Canyon gas storage reservoir and migrates to the surface or to shallower aquifer systems; the same is true for natural gas leaks in general irrespective of the leak source.  That said, natural gas associated with SoCalGas’ storage operations is normally contained and, as such, does not pose an unacceptable level of risk so long as it remains contained.  SoCalGas is subject to strict new State and Federal safety regulations that were implemented in large part due to the Aliso Canyon incident.  These new state and federal regulations require SoCalGas to develop a program for managing risks associated with their storage operations, including risks associated with gas leakage, and to perform comprehensive storage well integrity demonstration, verification, and monitoring.  They also impose immediate reporting obligations for gas leaks and routine periodic reporting obligations related to facility integrity, which together provide a comprehensive framework to help ensure against future leaks from the facility.  A PDF copy of the State of California Department of Conservation, Geologic Energy Management Division (CalGEM) underground gas storage regulations may be accessed by clicking this link.

A copy of the US Department of Transportation’s Pipeline and Hazardous Materials Safety Administration’s (PHMSA) Interim Final Rules related to underground gas storage may be accessed by clicking this link.

Issue 3 – Placement of gas monitors has not been shown to coincide with known faults

There are eight fence-line methane monitoring stations (sensors) at the Aliso Canyon Facility.  SoCalGas investigated several potential sites to place the methane sensors to ensure optimal detection of methane while minimizing the impact to the community as much as possible. The criteria for site selection was primarily based on the geographic terrain, environmental factors, equipment accessibility, proximity to residential neighborhoods and likely dispersion of any gas leaks. Known faults were not considered in determining the placement of the fence-line methane monitors as the system would not be significantly impacted by the location of such faults.

The location of the monitors can be viewed by clicking on this link.

A data request was submitted to SoCalGas requesting information concerning the on-line versus off-line status of the fence-line methane sensors.  The request covered the period coincident with the activation of the sensors (July 2017) through July 2019. SoCalGas tracks and records the reliability of its fence-line methane monitoring stations – i.e. the number of hours or days when each station is on-line and actively monitoring methane emissions versus off-line due to maintenance and/or repair.  They categorize the off-line periods according to the nature of the causative factors.  The Fence-Line Methane Monitoring System is offline when there is a “Weather Hold,” a “Beam Block Mode”, when “Maintenance Mode” is enabled, or when there is an “IT Outage or Outage Due to Other Factors”.  Table 1 below provides a summary of the off-line hours covering the two-year period from July 2017 – July 2019. 

It is important to note that “Total Days” as referenced for each of the eight area sensors listed in the tables below is a mathematical calculation based on the “Total Hours”; “Total Days” are equal to “Total Hours” divided by 24.  Thus, the figures listed in Table 1 do not necessarily reflect that a sensor was off-line for a continuous 24-hour period during any given day.  For example, early morning fog could result in a sensor being off-line for a period of hours.  When fog dissipates and relative humidity falls below the 80 percent threshold, the sensors are designed to automatically resume on-line status and recording of methane concentrations.

Table 1

“Weather Hold” automatically occurs when relative humidity levels are 80% or greater consistent with the manufacturers’ general recommendation.  Humidity levels above 80% may result in false readings caused by the interference of humidity in the open path of the infrared detectors. For a Weather Hold to be disabled, humidity must remain below 80% for 10 minutes.

“Maintenance Mode” is enabled by the Storage Operations Room personnel to allow for instrument technicians to perform repairs or calibrations. “0 PPM” values are displayed while Maintenance Mode is enabled.

“IT Outage & Other Factors” refers to when IT maintenance is performed on the server or unplanned outages occur due to various disconnection reasons.  Examples of IT outages include such things as temporary network loss, monitors being reset, servers being reset, and IT maintenance mode.

“Beam Block Mode” automatically occurs when beam block levels are 50% or greater. For a “Beam Block Mode” to be disabled, beam block levels must remain below 50% for 10 minutes. “Beam Block” is interference with the fence line monitor infrared signal commonly caused by fog.

In the event of an outage due to Weather Hold, Beam Block Mode, or Maintenance Mode which persists for a period of six hours or greater, Storage Operations personnel conduct field surveys using portable methane detectors to verify methane concentrations.  If the outage extends for 12 hours or greater the manual surveys are conducted every six hours thereafter until the problem which caused the outage is corrected.  Manual readings are not posted on the Fence line Monitoring website.

It is noteworthy that Areas 1 and 2 share a common relative humidity sensor as do Areas 3 and 4.  The total offline hours for all monitors will be different based on which offline event is active.  When multiple offline events occur simultaneously, not all will be recorded.  For example, if a monitor has a Weather Hold triggered, but goes offline during the Weather Hold due to a Maintenance Mode or IT/Other Factor outage, the offline mode other than Weather Hold will be recorded.  This will lead to shared sensors for Areas 1 and 2 and Areas 3 and 4 to record different total Weather Hold hours.

Table 1 above provides a summary of the off-line status of each of the eight methane sensor stations from the time they were first placed into service in July 2017 through July 2019.  During the period of July 2017 – July 2018 the eight sensors were off-line an average of 1792 hours each (the equivalent of about 75 days), or approximately 20 percent of the time.  Approximately 95 percent of the off-line time (an average of about 1704 hours for each sensor) was reportedly due to “Weather Hold” status when relative humidity exceeded 80 percent.  Off-line time due to “Maintenance Mode” and “IT Outages & Other Factors” accounted for only 51 hours and 38 hours, respectively, or about one percent combined.  During the period of July 2018 – July 2019, the eight sensors were each off-line an average of 2364 hours, or approximately 27 percent of the time.  Like the year prior, most of the off-line time (an average of 2242 hours for each sensor) was reportedly due to “Weather Hold” status.  Off-line time due to “Maintenance Mode” and “IT Outages & Other Factors” accounted for an average of only 64 hours and 60 hours, respectively.  Combined, this again amounts to a little over one percent of the operating time.  These figures strongly suggest that relative humidity levels above 80 percent, which are clearly weather related, were responsible for most of the system off-line time since the methane monitoring sensors were installed.  Routine maintenance and other factors resulted in the system being off-line approximately one percent of the operating time since installation of the system, which appears to be within reason from a reliability perspective.

A supplemental data request was made to SoCalGas for a listing of each day (or partial day) when the methane monitoring sensors were off-line due to “Weather Hold” status, or relative humidity above 80 percent.  The purpose of this request was to confirm whether all eight of the sensors were detecting relative humidity levels above 80 percent during the same periods (days or partial days), recognizing that the sensors are in fairly close proximity to one another.  While acknowledging that local terrain/topography can have some impact, one would expect relative humidity readings to be uniform across a small regional area such as the area within which the fence line methane monitoring system exists.  SoCalGas provided the requested information, and that information is summarized in Table 2, which can be found here.

The data in Table 2 illustrate that all eight sensors were off-line 81 percent of the time when any of the sensors (one or more) was off-line due to relative humidity levels above 80 percent.   In other words, in eight out of ten instances, if one of the sensors went off-line due to relative humidity above 80 percent, the remaining sensors detected the same condition and went to off-line status as well.  Given the localized terrain, it’s conceivable that small, highly localized fog conditions could trigger an off-line condition at a single sensor while relative humidity conditions at the next nearest sensor remains slightly below the 80 percent relative humidity threshold.  Thus, the off-line status correlation between all eight sensors appears reasonable, particularly given the local terrain/topography in which the sensors are located.      

In summary, since placing the methane monitoring sensors into service in 2017, most of the off-line time associated with the system is attributable to weather related conditions and not a failure of the system per se.  Actual off-line time due to maintenance and IT issues amounts to the equivalent of approximately 4-5 days per year or a little over one percent of the time, which appears within reason.

Issue 4 – Gas analysis has not been done periodically to show the gases do not contain hazardous materials

As noted above in response to Issue 2, natural gas itself is considered a hazardous material.  SoCalGas has a written standard which outlines the requirements for obtaining compositional analysis of gas samples from its underground storage facilities, including the Aliso Canyon facility.  The written standard has been in place since October 2017, however periodic gas sampling from Aliso Canyon has taken place since the 1970’s.   Generally speaking, SoCalGas’ gas sampling standard indicates they conduct gas sampling and analysis on select wells at their storage facilities on a scheduled basis and on an ad-hoc basis to determine the gas composition for purposes of monitoring for evidence of gas migration, gas leakage, corrosivity, and for purposes of verifying stored gas inventory.   When gas is withdrawn from the Aliso Canyon facility, it is processed and analyzed for C1-C6+, CO2, and air, and this information is used for analysis to determine gas heating value and calculate the WOBBE index of the gas.  The scope of this analysis (the target hydrocarbon and inert components referenced above) is generally consistent with gas storage industry practice in determining the chemical composition of stored gas for use in measurement calculations and storage gas inventory verification.  It is also consistent with SoCalGas’ internal gas standards noted below.  An analysis of the gas injected into the storage reservoir is submitted to the California Department of Conservation, Geologic Energy Management Division (CalGEM) on an annual basis. 

SoCalGas also has a gas standard which specifies the testing of gas samples to determine proper gas quality, heating value, and for pipeline integrity.  This standard applies to supplier gas entering the SoCalGas system.  Prior to flowing gas into the SoCalGas system, 24-hour testing is conducted at a supplier custody transfer point to ensure the gas complies with SoCalGas’ gas quality requirements.   This testing is not performed on gas being injected into the Aliso Canyon facility since the gas has already been tested upstream of the storage facility.

Table 2: Weather Hold Normalization