This is a summary of a report that reviews the available information on the natural resources potentially impacted by the Chino Hills oil spill which took place during the week of March 13, 1994, and was discovered on or about March 20, 1994.   During the week of March 13, 1994, approximately 14 barrels of crude oil were released on an unnamed tributary of Aliso Creek from a separator operation owned at that time by Taylor-McIlhenny of Dallas, Texas.  The spilled crude oil was apparently covered with fresh soil by the operator, but leeched out with the rains that followed on or about March 20, 1994.  The crude oil impacted a 3 to 4-mile stretch of the downstream portion of the tributary and entered Aliso Creek within the Chino Hills State Park above its confluence with the Santa Ana River.  Impacts to the Santa Ana River could not be determined with the high water flows which followed the rain.  An initial site visit was made by US Fish and Wildlife Service (USFWS) personnel on March 22, 1994.

Several agencies besides the U.S. Fish and Wildlife Service (USFWS) responded to the spill. When the spill was initially discovered, most of the cleanup efforts focused on control of the source - the oil pooled around the separator and the contaminated soil.  Due to anticipated rains, the contaminated soil was covered with plastic in an attempt to minimize further run-off.  Two coffer dams were constructed to trap the crude oil in places where vacuum trucks could remove it from the stream.  Vacuum operations at the Aliso Creek site continued for several days after the initial response to the spill, but the upstream site was abandoned after only a few days.  The spill  was federalized after an EPA Technical Assistance Team, the USFWS, and the California Department of Fish and Game. (CDFG) toured the site on March 28, 1994.  Once the pooled oil and the contaminated soils underneath had been removed from Aliso Creek, efforts focussed on cleanup of the impacted stream course.  Hand crews removed oiled vegetation and debris, and pooled oil. USFWS  personnel assisted with direction of cleanup efforts on April 1-6, 1994.  Cleanup was conducted using sorbent pads and pom poms. EPA made a decision not to excavate contaminated soils from the hillside below the spill site.  A semi-permanent mortar dam was constructed in the tributary just below the site to allow for pooling of water in the creek and removal of any floating oil which may have been carried from the contaminated soils by subsequent rain events.  The USFWS  was concerned that this structure would not be properly maintained and pooled oil would become a hazard to wildlife.  The California Department of Oil and Gas (CDOG), after discussions with EPA,  agreed to take the responsibility for maintenance of the dam.

The tributary portion of the spill course is a narrow stream that is steep and rocky in places.  In several places the banks were quite steep, with no vegetation at water level.  In areas where the stream course was wider, dense vegetation grew up to the stream channel.  Because it is an intermittent stream, during most months of the year there is no flow. However, after rainstorms, the flow in this stream course can be quite strong.  High volume flow damaged the coffer dam in the tributary after a rainstorm following the initial response to the spill. Aliso Creek is larger than the tributary and includes portions which are supplied by underground springs and thus have water year-round.  Most of the portion in which the spill occurred dried up during the summer months.  Much of this area is comprised of a wide riparian zone with a meandering stream course.  It is located at the base of a wider valley than the tributary, and the portion of its length within the park does not include narrow, rocky stretches. Approximately 3 to 4miles of stream were oiled as a result of the spill.  Smaller amounts of oil may have traveled into the Santa Ana River before the coffer dams were constructed.  Standing product was found in pockets on the surface of the tributary and Aliso Creek.  This material remained in the creek for up to 17 days when hand crews completed their work.

The vegetation along both the tributary and Aliso Creek is dominated by riparian species such as willows and mulefat.  Cottonwoods (Populus sp.) which occur sporadically along both stream courses, although they are more frequent along Aliso Creek.  In places the tributary was surrounded by a dense cover of poison oak.  Surrounding vegetation is dominated by annual grassland with patches of coastal sage scrub.  There are many species of wildlife possibly at risk in the area, but that may not have been seen during the course of sampling activities.  No oiled birds were located in the course of the spill response.  However, several species are known to use the area including the federally endangered Least Bell’s vireo (Vireo bellii pusillus).  No oiled mammals were found in the course of response to the spill.  Some mammal species which may occur there include: mountain lion (Felis concolor), bobcat (Felis rufus), coyote (Canis latrans), mule deer (Odocoileus hemionus), raccoon (Procyon lotor), and opossum (Didelphis virginiana).  In the course of response activities, the following reptiles were observed:  the southwestern pond turtle (Clemmys marmorata pallida) has been found in Aliso Creek during previous surveys, including the area which was oiled.  One turtle was found oiled in Aliso Creek.  It died during rehabilitation efforts. A southern alligator lizard (Elgeria multicarinatus) was noted along the tributary.  While specific species surveys were not conducted in response to the spill event, surveys had previously been conducted for the southwestern pond turtle in Aliso Creek.  Two rattlesnakes were seen in the course of conducting the March 28 walk through:  the southern Pacific rattlesnake (Crotalus viridis helleri) and a red diamond rattlesnake (Crotalus ruber). Tadpoles were seen in Aliso Creek.  These were most likely tadpoles of the western toad (Bufo boreas).   Fish and aquatic invertebrates were found within the oiled portion of the stream course.  Two species of fish were observed:  arroyo chub (Gila orcutti) and fathead minnow (Pimephales promelas).  Contaminated fish and invertebrates in this stream system could be consumed by southwestern pond turtles and bird species known from the area such as snowy egrets (Egretta thula), green herons (Butorides striatus) and possibly great blue herons (Ardea herodias).

The general trend observed from the chemical analysis was that the heaviest oiling occurred along the downstream portion of the tributary, and moderate oiling occurred along the portion of Aliso Creek between the confluence with the tributary and just upstream of where it exits Chino Hills State Park. Total resolved petroleum hydrocarbon (TRPH) concentrations in the April sediments were higher for sites within the oiled portions of the tributary and Aliso Creek than at the respective reference sites.  However, the distribution appeared to be somewhat patchy as one of three sites on the tributary, and one of two sites on Aliso Creek were only slightly above values for the reference sites.  Based on the information gathered for this preassessment screen report, the USFWS determined that the uncontrolled release of oil on or about March 20, 1994, into riparian habitat on an unnamed tributary and Aliso Creek in Chino Hills State Park did not result in quantifiable impacts to wildlife resources and their habitat beyond the initial impact and cleanup. 

Find out more by reading the full report:Roberts, C., Preassessment Screen for the Chino Hills Oil Spill, Chino Hills, California, April, 1996 (Division of Environmental Contaminants: Carlsbad Field Office)

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