City Of Palo Alto: Matadero Creek/VA Palo Alto Health Care Diesel Spill Community Update

Press release from the City of Palo Alto:

July 19, 2021

July 15, 2021 Community Update

The Fire Department continues to consider the incident at Matadero Creek to be stable. Soil remediation continues on the VA property while regular monitoring of the creek at 16 locations indicates that Matadero Creek is largely remediated with no observed impacts to fish or wildlife. The sampling data continue to show that the boom system has performed optimally. On a recent creek visit, all booms were blue in color (booms turn pink as they absorb petroleum) and there was no diesel odor anywhere along the creek (see fig. 1).

The Palo Alto Fire Department remains in Unified Command, which means the Palo Alto Fire Department Hazmat Bureau is working as a cohesive unit through all phases of this incident with the VA Palo Alto Health Care System, City of Palo Alto Stormwater staff, California Department of Fish and Wildlife, the San Francisco Regional Water Board, the Santa Clara Valley Water District and 3rd party remediation and environmental scientist experts. Representatives from regulatory agencies continue to meet to review all aspects of the incident, including cause of the release, continued containment of the diesel and remediation of the soil and water. Action plans continue to evolve based on monitoring results and expert recommendations.

Throughout the remediation, Matadero Creek has been monitored at 16 locations for multiple chemicals related to diesel:

Throughout the monitoring, the primary constituent consistently detected has been that of the overall measurement of TPH-diesel, rather than the individual PAH or BTEX species. Based on discussions with the Department of Fish and Wildlife, this is a positive outcome in that it is the individual PAH and BTEX compounds that would be expected to impact wildlife.

The analysis continues to show periodic TPH-Diesel sample results outside of normal limits between W-008 and W-006 as well as occasionally just downstream at W-004. Third party experts suggest this may be due to limited sunlight exposure, a higher density of plants, and a natural in-creek obstruction to water flow (see fig. 2). This combination of conditions may have trapped small portions of the initial spill. Therefore limited treatment was initiated at this single location. Meanwhile, according to Fish and Wildlife staff, these TPH-diesel values, while higher than the Water Board goal of 640 ug/L, are not the typical indicator of possible impact to wildlife. Rather, it is the more specific compounds within diesel, that of PAH and BTEX, that are of greater concern from a habitat perspective.

To date, more than 14 PAH species have been analyzed on more than 190 water samples. As can be observed from the data tables, out of about 2,900 combined analytical results for these PAH species, only 2 PAH species had a combined total of 4 values greater than the Water Board’s Habitat Goal and no such value has been observed since mid-June.

As can be observed from the data tables, of the 190 tests for BTEX, only a single finding of Xylene at one location has ever been detected at the site, and it was far below the Water Board’s Habitat Goal.

Due to the lingering TPH-Diesel between W-006 and W-008, the Department of Fish and Wildlife met with third-party industry experts to generate a plan to mobilize the remaining diesel product on the water surface and in the soil adjacent to the water’s edge just upstream of the in-creek obstruction. The work, which was completed July 13th, involved 3 components:

• Vegetation Removal: Using hand tools, vegetation above the water line and along the shore near site W-007 was trimmed (leaving the roots) to mobilize and/or expose any remaining material trapped in the vegetation to aid in natural attenuation.
• Flushing: To encourage water movement in that area, low pressure ambient water was used to mobilize any diesel product remaining on the surface trapped by vegetation or other obstructions. Any observable diesel product was directed toward the boom immediately downstream for collection by the sorbent.
• Light tilling: The top 1-2 inches of soil around site W-007 was lightly scrapped in order to expose the area to sunlight. The work was minimal in scope in order to expose remaining pollutants while preserving the ecosystem and creek banks.

As noted above, the boom areas that the team is closely monitoring are between W-006 and W-008 on the map, and only due to the TPH-Diesel values. All data are available by downloading the latest data table below.

Download: Creek Water Sampling Table 1 and 2 With Map - July 15, 2021(PDF, 796KB)

• Water Quality Data Summary - As of June 15, 2021(PDF, 677KB) (starts on pg. 6)
• Water Quality Data Summary - As of May 28, 2021(PDF, 162KB)

More information will be released as details become available.

Read the initial joint community update on this issue.

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This press release was produced by the City of Palo Alto. The views expressed here are the author’s own.