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Restoring Gasoline-Tainted Marshes

On January 6, 1994, unleaded gasoline seeped from an underground pipe into a tidal channel on Chevron property in the East Bay city of Richmond. The gasoline, which daylighted in Gertrude Ditch near Wildcat Creek, was successfully contained, but a small area of Pacific cordgrass was injured. Clean-up and repair operations further altered the landscape when excess clean fill was accidentally placed on an adjacent seasonal marsh. A typical response to an accident such as this includes containment of the spilled material, clean-up, and restoration, but then, as ENTRIX's Ted Winfield comments, "After you get sign-off, everyone walks away." But a Chevron restoration team chose instead to find ways to increase the survival of the wetland species. Chevron researchers Lucinda Jackson and Gary Rausina worked with Winfield and Cal Fish & Game's John Tarpley to develop a long-term restoration and monitoring plan that would do more than just fix the immediate problem.

The restoration team tackled two project sites: the banks of Gertrude Ditch, where the initial spill occurred, and a predominantly pickleweed marsh where the unused fill material had been dumped. To restore the pickleweed marsh, workers removed fill dirt in September of 1994 and recontoured the area. The following spring, the team established plots for two restoration strategies, and depended on the natural seed bank in the soil to supply the wetland plants. Assisted restoration plots received periodic irrigation with bay water and removal of weedy upland species. Natural restoration sites were left alone, and reference plots were defined in unaffected areas. After one year, the team found wetland plants thriving in the assisted restoration area, achieving 94% of total cover, as compared to 60% for the reference sites and 23% for the natural restoration area. Irrigation with bay water favored salt-tolerant wetland species. However, after two growing seasons, the wetland plant cover in the natural restoration areas compared favorably to that of the reference sites.

At the second restoration site in Gertrude Ditch, the soil still contained relatively high levels of BTEX and TPH-gasoline when planting began in May 1995. Researchers expected that cordgrass planted in an insulating mix of sand, peat moss and gravel would out-perform plants placed directly in contaminated soil. Surprisingly, the petroleum residue didn't affect cordgrass success-all assisted plots approached 100% survival. The researchers were also pleasantly surprised with the recovery of cordgrass in the other plots. "I didn't think the natural restoration would look as good as it did," says Jackson. Although assisted restoration efforts in each area promoted the success of wetland species, the natural restoration areas are not far behind. The damage caused by people trampling about, trucking in soil, and removing vegetation may outweigh the benefits attained in the clean-up effort. "We should look at natural restoration as a viable alternative to any invasive clean-up activity," says Winfield.

Contact: Lucinda Jackson (510)242-1047

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