WORK PLANS_PRE 2019 - Laserfiche WebLink

Home Browse Search

Stantec Site History and Previous Investigations BP Stockton Terminal No. 40T June 17, 2009 was limited to a radius of a few ft from the well casing over the study period (IT, September 2001). Pacific Environmental Group (PEG) incorporated the results of the natural attenuation evaluation into the Corrective Action and Management Plan (1996). The plan recommended setting a trigger boundary at Stork Road, located down-gradient of the terminal lease area and an attenuation zone at the eastern boundary of the Port of Stockton property. Natural attenuation was proposed as the approach for addressing the petroleum hydrocarbon impacts within the attenuation zone. Impacts to groundwater within the terminal lease and up-gradient of the trigger boundary would also be addressed via natural attenuation. The plan proposed maximum contaminant levels (MCLs) as the water quality objectives at the trigger boundary and a monitoring and data evaluation plan was proposed to assess concentration trends (IT, September 2001). Stantec started an Iso-Gen feasibility test at the site on June 20, 2002. Due to safety concerns, Stantec on behalf of STTC, terminated the Iso-Gen feasibility test on July 25, 2002. It was discovered that during several Iso-Gen tests, the integrity of the wires within the wells had become compromised, causing the wires to short circuit, which created a potential explosive hazard. With this new information, the test was deemed unsafe due to the high hydrocarbon concentrations within the wells and the test being performed within an active terminal (SECOR, November 2002). URS conducted an enhanced bioremediation pilot study in 2004 and 2005. Approximately 720 gallons of an aqueous nitrate/sulfate solution were prepared at the site for each injection event. The aqueous solution consisted of 137 milligrams per liter(mg/L) of sodium nitrate, 400 mg/L of sodium sulfate, and approximately 500 grams of Miracle GRO that was added as a nutrient supplement. Once the solution was prepared, the injection system was started and the solution was injected into each well at a rate of 0.2 gallons per minute (gpm). Approximately 240 gallons of the solution were pumped into each well over a period of approximately 18 hours. The injection events began on May 25, 2004 and were performed weekly until June 22, 2004. Injections were temporarily stopped after the fifth event because the levels of sulfide exceeded the baseline limits set for monitoring well AR/MW-1A. The injections were restarted in August 2004, following a change in the baseline levels. During the course of the URS pilot study, a total of 11 nitrate/sulfate injection events were performed, during which, approximately 7,920 gallons of the nitrate/sulfate solution were injected. URS concluded that the impact of the nitrate/sulfate injections on the hydrocarbon concentrations only appeared to be significant near the injection points. GRO and benzene concentrations in groundwater monitoring well AR/MW-5A decreased compared to groundwater monitoring wells farther from the point of injection. Therefore, the pilot study indicated that nitrate/sulfate injections may be able to remediate dissolved hydrocarbons at the site (Pilot Study Evaluation Report Enhanced Bioremedation Pilot Study, URS, 2005). Stantec submitted a work plan to the RWQCB on May 7, 2007 for injection of nitrate/sulfate as part of the Enhanced Bioremediation Pilot Study (SECOR, 2007). The RWQCB developed a waste discharge requirement permit using background concentrations the previously established for groundwater based on the URS-2005 study. The problem with the background concentrations were that many of on-site wells contained groundwater with concentrations 0040T Site History and Previous Investigations.doc 3