SITE HISTORY_FILE 2 - Laserfiche WebLink

Home Browse Search

ATC Associates Inc. (YA 1117 Lone Palm Avenue, Suite 201 Modesto, California 95351 209-579-2221 �i • SSCCI � TES INC . fax: 209-579-2225 groundwater monitoring wells, MW8 through MW 10 . Field activities and analytical results were detailed in ATC's Offsite Subsurface Investigation Report, dated April 24, 2003 . In December 2003, ATC implemented remedial activities at the site. The remedial activities consisted of SVE coupled with air sparging (AS). The SVE system was designed to utilize up to five extraction wells (VW I through V W4 and MW 1 ) and the AS system was designed to utilize up to two AS wells (AS I and AS2). The current SVE system consists of a 300 actual cubic feet per minute (ACFM) thermal oxidizer. The AS system consists of a GAST 2567-P132-T908X rotary vane, 2- horsepower, air compressor. This blower is capable of injecting at a maximum of 20 i pounds per square inch (PSI) at low flow rates. The maximum flow rate is approximately 21 standard cubic feet per minute (SCFM). Accumulated groundwater from the extraction wells is treated and discharged to the City of Stockton sewer system. I In April 2006, ATC submitted a report recommending modifications to the remediation system. The report evaluated system performance and recommended continuing operation of the SVE/AS system and adding an ozone sparge component. ill, A workplan to conduct a feasibility study for ozone pilot testing was submitted to the SJCEHD on August 6, 2008 . The workplan was requested by the SJCEHD through correspondence dated { September 25, 2007. 2.0 MASS CALCULATIONS ATC performed mass calculations to estimate the mass of TPHg remaining in soil and groundwater beneath the site. Mass calculations were not performed for the remaining analytes of interest since they were not requested by the SJCEHD. A summary of soil analytical results is presented as Table 1 . A summary of groundwater analytical results is presented as Table 2. Mass Calculations for TPHg, benzene, and MTBE associated with the vadose zone soil, saturated zone soil, and groundwater are provided in Appendix A. II 2.1 Vadose Zone Soil To estimate the lateral extent of petroleum hydrocarbon impacted vadose zone soil, ATC reviewed previous soil boring logs to evaluate which samples were collected from the vadose "- zone. Typically groundwater has been encountered at a depth of approximately 25 feet bgs!w however, on occasion groundwater has been encountered at depths as shallow as 24 feet bgs and as deep as 29 feet bgs. For all intents and purposes of this report, ATC has defined the vadose zone from 0 to 25 feet bgs. Soil samples submitted for chemical analyses associated with the vadose zone were collected from soil borings SBI (VWl ), SB2 (MW1), SB3 (VW2), SB6, SB7, ASB1 , SB13, SB14, SB15, SB16, VW3, and VW4. The distribution of TPHg in vadose zone soil is illustrated as Figure 3 . It is important to note that two or more samples were collected S:Enviro m ta1k62596\Repons\Mns Cates 2009.doc 3 '. J