Regional Water Quality Control Board, Lahontan Region (Regional Board) found that magnesium peroxide failed to achieve target BTEX and total petroleum hydrocarbons (TPH) cleanup levels in groundwater at several petroleum contaminated sites where applied in the Lake Tahoe Basin.
Between 1996 and 1998, Regional Board staff approved three in situ field-scale bioremediation proposals using Oxygen Release Compound (ORC). These proposals were made with the knowledge that below freezing (0C) temperatures can exist in the Lake Tahoe Basin for five months of the year or more. Two of the sites had gasoline contamination and one site had diesel contamination. The geology at the three sites consists of lacustrian and alluvial sediments. Ground water varied from 1 to 14 ft (0.3 to 4.5 m) below ground surface. ORCwas installed at sites either in a curtain of borings by direct-push technology or in socks placed inside monitoring wells.
The results indicated that magnesium peroxide failed to remediate petroleum contaminated sites to target cleanup levels. The site given the greatest concentration of magnesium peroxide points showed an initial 40% decrease in TPH concentrations in ground water after the first month.
Toluene and ethylbenzene also decreased in concentration by up to 90%. But after six months of ORCinstallation, almost all constituents returned to original concentrations before ORC, except for benzene, which increased in concentration by 80%. The results were similar at the other gasoline site, except that benzene increased in concentration by 10% from the original concentration. At the site containing diesel contamination, TPH concentrations in ground water decreased 20% from initial concentrations after 9 months of ORCinstallation.
None of the three sites came close to reaching target cleanup levels for groundwater, which are mostly secondary drinking water standards. Data show magnesium peroxide’s effectiveness is short term, followed by rebounding concentrations. The proponents did not explain why magnesium peroxide failed to restore groundwater quality, yet cold temperature likely inhibited bioremediation. Regional Board staff now only consider the remediation method for petroleum hydrocarbon sites in warm weather areas of the Lahontan Region.