Leading hypothesis ties methane gas in Oxnard water wells to oil and gas extraction - County considering ban of new drilling
By Kimberly Rivers
It is the leading hypothesis of state researchers that gases found in water wells on the Oxnard Plain are linked to oil and gas extraction activity in the area.
“That is the leading hypothesis, why we see what we see,” said Matthew Landon, Program Chief of the California Oil, Gas and Groundwater Program (COGG), part of the United State Geological Survey (USGS) California Water Science Center, conducted in cooperation with the California State Water Resources Control Board. https://ca.water.usgs.gov/projects/oil-gas-groundwater/. He is manager of the program conducting the study and a co-author of the findings. Celia Rosencrans, a USGS hydrologist is the lead author.
Landon is referring to preliminary findings revealing the presence of gases associated with petroleum in three wells in the Oxnard Plain and the sources of those gases. Gases in two of the wells are likely the result of natural migration, whereas Landon said it is likely for the third well, the gases will be found to be linked to the oil and gas extraction activities in the area.
“But [we] can’t confirm right now," said Landon, adding that further analysis is needed to confirm whether the gases in one of the water wells are present due to natural migration or from leaks associated with oil and gas extraction activities in that area. He expects those results this spring (2019).
This study is part of a statewide program resulting from state legislation (SB4) with a goal of taking a broad look at oil and gas extraction and groundwater impacts.
Gases found in the Oxnard water wells include methane and propane, and data confirm these thermogenic gases are associated with petroleum sources – not from microbial processes.
“In these areas with high concentrations of oil and gas activity the primary pathways are those preferential pathways – the ones people make,” said Landon. When considering the Oxnard Plain and the Vaca Tar Sands field he said, “there are a lot of potential [preferential] pathways.”
Two Potential Pathways
Landon said, “isotopic” measurements and ratios confirm the gases in these three wells are associated with petroleum and there are two potential pathways for such gases to find their way into groundwater aquifers and water wells. The next step is to determine which pathway the gas took to get into the water wells.
The two pathways are either “a leak from the oil and gas zones” or from a “preferential pathway [including] a compromised [oil] well casing or a long abandoned well.” Landon said sometimes the “annular space [of an oil well] is not completely sealed,” and results in leaks.
In the case of a leak from the zone, this is deemed a natural migration from the formation that has held the oil and natural gases for millions of years, migrating over time. Landon explained those gases are “usually” found with “high [amounts of] organic compounds,” which are associated with the briny water mixed with the oil and gas naturally underground. This is the case in two of the wells on the Oxnard Plain, and so the likely pathway for the gas in those wells is a natural migration from the oil and gas formation.
But in the third well, Landon said there was a “high concentration (compared to other wells in the study area) of only thermogenic gases” and none of the microbial gases from natural processes in the aquifer.
“While the source of the thermogenic gas in the one well could be the result of natural migration, or flow path, the most common pathway, in the absence of the brine [oil field water] water is from oil extraction activity, [including] casing failure,” said Landon.
Gases are not Contaminants
Landon emphasized, “Methane is not a drinking water contaminate. The presence of methane does not make drinking water contaminated. It is an indicator that there is some kind of connection to the underlying source.” He clarified that from the scientific perspective the word contamination means, “a chemical [is present] rendering [the water] unfit for its intended use.”
He said methane in water is tracked for explosion hazard in closed spaces. “When the water is exposed to the air, methane immediately dissipates. The thresholds found in the wells in Oxnard are well below the explosion hazard [levels].”
Next Steps for USGS study
For the one well with only thermogenic gases further study of data is needed to confirm the source of the gas. That data has been collected and the research team is awaiting the results. The process involves analyzing the “noble gas signatures” in the samples. Landon said those results are expected this spring (2019).
No reports or data from the first portion of the study have been released to the public. The findings are in the peer review process and will be released when complete.
Potential Action by Ventura County Board of Supervisors
Tomorrow, Tuesday, April 9 at 3:00 the Ventura County Board of Supervisors will consider a proposal to pass a 45-day ban on new oil and gas drilling and re-drills of existing oil wells using cyclic steam in areas that overlie groundwater aquifers used for drinking and irrigation.
The proposal is being presented by Supervisor Steve Bennett (Dist. 1), and asks for the Board to approve two directives for the Planning Department. First, to create an “interim ordinance,” which would “temporarily prohibit the County’s approval of new oil and gas wells, and re-drilling of existing oil and gas wells, for oil production that will utilize steam injection in the vicinity of potable groundwater aquifers while the County studies potential regulations for this land use.” That ordinance would be brought before the Board for review and final approval. Second, to “study a potential amendment to the County’s zoning ordinances to require discretionary approval of new development under antiquated oil and gas permits.”
Antiquated oil and gas permits were granted decades ago, prior to the California Environmental Quality Act (CEQA) being approved and usually have no expiration date - meaning the County does not get an opportunity to review the permits or conduct modern environmental review - or have a limit to the number of oil wells that can be drilled.
The proposal letter cites the USGS preliminary findings, and refers to a current pending project for 79 new cyclic steam tar sands wells on the Oxnard Plain as support for the emergency action. A super majority vote of four of the five Supervisors in favor of the action is needed to approve the temporary ban.
Link to agenda for proposal and public written comments submitted – Item #46.
2019 copyright VCInFocus/Kimberly Rivers