SAN JOAQUIN VALLEY CRUDE OIL SPILL INTO A FRESHWATER STREAM: A CASE STUDY1

Abstract

ABSTRACT In April 1993, a pipeline rupture occurred adjacent to a primary California freeway on the north slope of the Tehachapi/San Emigdio Mountains leading into the San Joaquin Valley. An estimated 6,200 barrels of blended San Joaquin Valley crude oil (27° API gravity) sprayed on the freeway, and flowed downslope and into Grapevine Creek. The crude oil flowed 12 kilometers terminating at a containment dike constructed during the initial response. Cleanup activities were completed and approved by the lead regulatory agency within 21 days of the release. The release occurred at an elevation of 730 meters above sea level, spraying oil on to the northbound lanes of the freeway and closing it for 36 hours. After passing through engineered freeway drainage, the oil entered Grapevine Creek and flowed through 1,525 meters of riparian habitat and 8,500 meters of grassland habitat. Elevation at the terminus was 300 meters. Upper Grapevine Creek supports dense riparian vegetation that may have contributed to significant diurnal flow fluctuations and caused surface flows to retreat 1,500 meters from the terminus during the afternoon and early evening hours during response operations. Typical flow rates in Grapevine Creek during the response operations were less than 0.15 m3/s (less than 5 ft3/s). Cleanup activities included steam cleaning the freeway and engineered drainage system and hand cleanup in the riparian section. Cleanup efforts in the downstream grassland section were complicated by the fluctuating flow rates. A site in Grapevine Creek with continual surface flow was selected for stream-flow diversion. Utilizing portable irrigation equipment, the flow from the creek was used to irrigate 40 acres of adjacent grassland. The system was operated for 21 days and required 24-hour supervision to adjust for stream flow fluctuations. Approximately 3,400 barrels of crude oil were recovered as a liquid from two primary locations: a permanent concrete containment weir and the terminus containment dike. Recovered liquids were returned to tankage for subsequent processing. An estimated 1,200 barrels of crude oil were collected in 19,000 cubic yards of excavated soil and sediment. Thus, approximately 74 percent (4,600 barrels) of the spilled oil was recovered. The soil was converted into a road-base material and used to pave pipeline system facilities for dust control, at a cost of less than $30 a ton. Water samples collected during and after cleanup activities combined with surveys of macroinvertebrates, birds, and riparian habitat indicate only short-term and localized impacts. Dissolved hydrocarbons in surface waters declined rapidly. Benthic macroinvertebrate population density and diversity were similar to reference station within five months of the initial release.