The known northern boundary of the plume of chromium 6 contamination in Hinkley grew one-mile in a year, according to the Lahontan Water Board. In the third quarter of 2010, the plume was touching Thompson Road. This year’s third-quarter map shows the plume slightly north of Sonoma Street (Click for a closer look at the official map documents)
Jim Steinberg, Staff Writer

Posted: 12/10/2011 02:15:51 PM PST

HINKLEY – The plume of chromium 6 contamination in this unincorporated community eight miles west of Barstow has leaped a mile in a year, according to maps released by the Lahontan Regional Water Quality Control Board.

Traditionally the plume has migrated about a foot per day, said Lisa Dernbach, senior engineering geologist with the water board.

“We surprised by the movement of the plume in the last last year,” Dernbach said during a question and answer session following a town meeting hosted by the water board at Hinkley Elementary School late last week.
Hinkley Plume Boundary Expanding

This site is the only school in this town of not quite 1,700 made famous by the year 2000 hit movie “Erin Brockovich”.

Agricultural wells in the area could be pulling the plume along more quickly, she said.

Another action coming into play, is likely the narrowing of the underground valley on the plume’s northern edge, which is naturally causing the plume to move more quickly, Dernbach said.

Imagine a wide, slow moving river that is gradually narrowing, Lauri Kemper, assistant executive officer with the water board, said in an interview.

The water travels faster and faster as the river narrows. The same thing happens to underground rivers, she said.

In the 1950s and 1960s, utility company Pacific Gas & Electric Co. emptied water containing chromium 6 from its Hinkley natural gas pumping station, which then seeped in the town’s groundwater.

At that time, before the cancer risks from chromium 6 were recognized, it was used to kill microbes and provide corrosion protection for the utility’s massive cooling towers in Hinkley.

The resulting plume now measures four miles long by about two miles wide, Dernbach told about 60 people gathered in the school’s gymnasium.

The plume map for the third quarter of 2010 showed the plume’s northern edge extending to Thompson Road. The most recent map shows it crossing Somona Street, with one well showing a concentration of chromium 6 exceeding 4 parts per billion.

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