WORK PLANS - Laserfiche WebLink

Home Browse Search

Stantec , Addendum Remedial Action Plan — Former Tosco Bulk Terminal No. 10013 July 21, 2010 estimate of the TDS levels beneath the site can be derived (Freeze, R.A., and J. A. Cherry. 1979. Groundwater). During the first quarter monitoring and sampling event completed at the site, the average specific conductance (final reading prior to sampling) from all sampled wells was approximately 2,350 pmhos/cm, and when that average is multiplied by the conversion factor of 0.65 an estimated TDS of 1,525 mg/I is yielded. Applicable California drinking water standards list 500 mg/I TDS as a recommended value, 1,000 mg/I TDS as the upper limit, and 1,500 mg/I TDS as the short- term limit. This comparison suggests that groundwater at the site is largely non-potable. Due to these factors, basing the remedial objectives/site clean-up goals on California primary or secondary maximum contaminant levels is believed to be questionable. Stantec proposes to complete risk based modeling (ASTM E2081) to determine the appropriate site specific remedial objectives/clean-up goals. If approved by the CRWQCB-CVR, Stantec will perform the required risk modeling and present the results prior to the proposed end date of the ongoing oxygen injection activities in December 2010. Present background concentrations on which the proposed remedial objectives are based. If deemed warranted by the CRWQCB-CVR, Stantec proposes to collect groundwater samples from monitoring wells MW-6 and MW-10 to determine if results are deemed appropriate for use as background constituent of concern concentrations. If groundwater sampling results show non- detectable concentrations for the site related COCs, Stantec will perform additional sampling of MW-6 and MW-10 to assess select drinking water quality constituents and parameters including TDS, salinity, total coliforms, bromate, chlorite, chlorine, antimony, arsenic, barium, total chromium, lead, mercury, nitrate, nitrite, sulfate, iron, and selenium. If groundwater beneath the site is deemed not suitable for drinking water quality based on State of California criteria, Stantec proposes to move forward with case closure protocols based on a low risk criteria. Define the magnitude of the rebound that would tripper the contingency measures. Contingency measures are proposed to be implemented if the dissolved concentrations of the site related constituents of concerns (CDCs), including total purgeable hydrocarbons as gasoline (TPHg), total purgeable hydrocarbons as diesel (TPHd), benzene, methyl tertiary butyl ether (MtBE), or tert- butyl alcohol (TBA), rebound to concentrations five times greater than the site-specific risk-based clean- up goals for groundwater (to be determined through proposed risk modeling). Present a contingency plan should constituents of concern (COCs) rebound once the injections are discontinued. Following the conclusion of oxygen injection activities at the close of 2010, dissolved petroleum related concentrations will be tracked for rebound analysis along with monitored natural attenuation. If dissolved concentrations for TPHg, TPHd, benzene, MtBE, and TBA rebound to concentrations five times greater than the site specific risk based clean-up goals, bi-weekly oxygen injections will be reinitiated for six-months. After six months of oxygen injection activities, the dissolved concentrations will be reevaluated to determine whether continuation of remedial activities is necessary. 2