Pollution Engineering, March 2011 Cover Story
By: Alan Bacock and Anthony Maggio
The Mystery of the Upgradient Contaminant
Given the PCE was in the groundwater, finding the source turned into a real detective activity
The Big Pine Indian Reservation comprises 279.08 acres of land adjacent to Big Pine, Calif., approximately 238 miles north of Los Angeles and 17 miles south of Bishop, in the central portion of the Owens Valley between the Sierra Nevada and White Mountain Ranges (see Figure 1). The terrain is relatively flat, sloping easterly towards the Owens River at grades ranging from 1 to 4 percent. The reservation's highest elevation of 4,050 feet is located at the extreme southwest corner of the property.
Two community water systems exist on the reservation. The first consists of two community-owned wells (Wells 1 and 2), which supply groundwater to 139 service connections. The second system is a privately owned well that supplies groundwater to 35 service connections in a trailer park (see Figure 2). The population of the reservation is approximately 456.
Although groundwater quality met most of the national primary and secondary standards, perchloroethylene (PCE, a chlorinated solvent) had been detected in the two water supply wells when a monitoring program began in 1995 to comply with the federal Safe Drinking Water Act. The detection of PCE was unexpected considering the location of the water supply wells. Located 0.70 miles southwest of the town, topographically the wells were 100 feet higher than the town. Likewise, the wells were located at the highest point of the area. In essence, they were higher in elevation than all of the downgradient locations where potential contaminating activities (PCAs) could have occurred.
As a result of these topographical differences, there was an immediate concern that the reservation's source water had become vulnerable to possible illegal dumping of PCE that could have been occurring somewhere within the radius of influence of the supply wells. A systematic approach was undertaken in an effort to better understand the shape of the capture zone under pumping conditions, so that potential sources of PCE could be mapped and mitigation measures might be developed.
For the full cover story, visit Pollution Engineering's March, 2011 issue.