HINKLEY The Lahontan Regional Water Quality Board has requested that Pacific Gas and Electric install more monitoring wells in order to determine the full extent of the chromium 6 plume.

Water board staff are requesting that the utility company install more monitoring wells because of information from PG&E that shows total chromium up to 10 parts per billion was found along Thompson Road in the early 2000s. The historical data shows that chromium has impacted groundwater farther north along Mountain View Road and west along Thompson Road than previously thought, according to the letter.

Lahontan also stated in the letter that further monitoring was needed in order to find out if chromium is migrating through gaps between fresh water injection wells which are designed to form a barrier to keep chromium 6 from moving on Serra Road.

The water board said that the company needs to install the wells in specific locations to the west and north of the plume, including installing wells as far north as Salinas Road and Sonoma Street.

"Board staff believes it is imperative to get out in front of the chromium plume rather than continually chase it," read the letter from Lahontan.

PG&E submitted a work plan in March that proposed the installation of several monitoring wells on private properties to the east and north of Summerset Road in order to monitor the amount of chromium 6 in the upper aquifer. PG&E will be required to submit a revised work plan by May 11.

The chromium 6 contamination began in Hinkley after PG&E used chromium 6 to prevent rusting in cooling water tower in the 1950's and 1960's and then dumped the water into unlined ponds. The chromium 6 contamination spread to the groundwater and the plume is now about three miles long and nearly a mile and a half wide.