VA Diesel Spill Community Updates – City of Palo Alto, CA

The fire department continues to consider the incident at Matadero Creek stable. Soil remediation continues on the VA property, while regular creek monitoring at 16 locations indicates Matadero Creek is largely remediated with no observed impacts to fish or wildlife. Sampling data continues to show that the boom system is still keeping the tailings contained. All work is carried out to ensure that wildlife remains protected throughout the remediation.

The Palo Alto Fire Department remains under Unified Command, which means the Hazmat Office of the Palo Alto Fire Department is working as a cohesive unit through all phases of this incident with the VA healthcare system. Palo Alto, City of Palo Alto Stormwater staff, California Department of Fish and Wildlife, San Francisco Regional Water Board, Santa Clara Valley Water District, and third-party remediation and environmental experts.

Representatives from regulatory agencies continue to meet to review all aspects of the incident, including the cause of the release, the continued containment of the diesel, and the remediation of soil and water. Action plans continue to evolve based on monitoring results and expert recommendations.

Planned next steps include the application of bioremediation additives to enhance the natural microbial degradation of oil remaining in the soil along the creek. Soil samples will be taken before and after application to monitor degradation. Additionally, areas of algal buildup are monitored by methods approved by the Fish and Wildlife Service.

At the VA Hospital, remediation work is underway and will soon include cleaning of the impacted storm sewer, including the drainage outlet to the creek. This work will be closely monitored by representatives of the Unified Command.

Buildup of algae identified during treatment

It has been observed that natural algae seem to be blocked from flowing downstream and are accumulating in a few places along the dam network. Algae buildup occurs naturally in other areas of the stream where water collects and stagnates. Since algae growth and subsequent decomposition can reduce the oxygen concentration in the water, the remediation contractor obtained approval from Fish and Wildlife to use pool skimming equipment to reduce the growth. algae only in areas where the accumulation is next to the dams.

The public asked not to disturb the creek

The Department of Fish and Wildlife asks the public to refrain from moving any material in the affected section of the creek, as any adjustment could affect the rate and direction of water flow, which which could inadvertently cause water to come into contact with contaminated soil or direct flow of water around the dam system. Also, from a public health perspective, in principle, any material from the affected part of the creek is considered hazardous unless it is established that it is not hazardous by laboratory analysis.


There is still visible muskrat activity along the creek, demonstrating that restoration efforts do not appear to be interfering with wildlife. Fish and Wildlife representatives want to assure the public that although algal buildup is reduced to prevent oxygen depletion in the water, muskrats (and other mammals) do not have been affected by the presence of algae since their source of oxygen comes from the air above. the surface of the water.

Continuous stream monitoring

Throughout the remediation, Matadero Creek was monitored at 16 locations for multiple diesel-related chemicals:

  1. Total petroleum hydrocarbons in the form of diesel (TPH-Diesel) – a measure of the suite of hydrocarbon compounds that typically make up diesel fuel.
  2. Polyaromatic hydrocarbons (PAHs) – individually measured compounds for which the Water Board has a specific water quality objective for each compound based on toxicity data.
  3. Benzene, toluene, ethylbenzene and xylene (BTEX) – four compounds found in gasoline and diesel for which the Water Board also has specific water quality objectives for each compound based on toxicity data.

Throughout monitoring, the major constituent consistently detected was that of the overall TPH-diesel measurement, rather than individual PAH or BTEX species. Based on discussions with the Department of Fish and Wildlife, this is a positive result as it is the individual PAH and BTEX compounds that are expected to impact wildlife.

TPH-Diesel results

Analysis continues to show periodic TPH-Diesel sample results outside normal limits between W-008 and W-006, as well as occasionally just downstream at W-005. Third-party experts suggest this may be due to limited exposure to sunlight, higher density of plants, and natural obstruction of the creek to water flow. This combination of conditions may have trapped small portions of the initial spill; therefore, limited processing was initiated at this unique location. Meanwhile, according to Fish and Wildlife staff, these TPH-diesel values, while above the Water Board’s target of 640 ug/L, are not the typical indicator of possible impact. on wildlife. Rather, it is the more specific diesel compounds, PAHs and BTEX, that are of greatest concern from a habitat perspective.

In mid-July, sites W-012 and W-013 observed a slight increase in TPH, with analytical values ​​higher than those observed at either site since May 11. Since this particular lab analysis can detect organic materials other than TPH, including organics (eg, humus) and petroleum breakdown products, the analysis of both samples is repeated using a process that first removes non-TPH hydrocarbons. The (pending) results will be compared to the original results. In addition, these sites will continue to be monitored to ensure values ​​return below the Water Board’s target.

HAP results

To date, more than 14 species of PAHs have been analyzed on more than 220 water samples. As can be seen from the data tables, of approximately 2,900 combined analytical results for these PAH species, only two PAH species had a combined total of four values ​​above the Board’s habitat objective. waters, and no such value has been observed since the middle of the year. June.

BTEX results

As can be seen in the data tables, although there have been over 200 tests for BTEX, there was only one discovery of xylene in early May at one location, and more recently a detection minor toluene elsewhere; both were well below the Water Board’s habitat objective.

Soil treatment

There are residual diesel residues in the ground along the creek bank near the outfall. The Department of Fish and Wildlife, VA staff and consultants assessed options for improving bioremediation. Planned next steps include additional light tillage and the application of bioremediation additives to enhance the natural microbial degradation of oil remaining in the soil along the creek. Soil samples will be taken and analyzed before and after application to monitor the biodegradation process. The goal of the project is to accelerate natural processes to maximize clearance before a major rainfall event, while minimizing disturbance to the creek bank and vegetation.

Stream data and map update

As noted above, the boom areas the team is keeping a close eye on are between W-006 and W-008 on the map, and solely due to TPH-Diesel values. All data is available by downloading the latest data table below.

To download: Stream Water Sampling Tables 1 and 2 with map as of August 13, 2021(PDF, 471 KB)

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