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i <br /> CHECKLIST OF REQUIRED DATA FOR NO FURTHER ACTION REQUESTS AT <br /> UNDERGROUND TANK SITES <br /> • Barnyard Site, 8960 W Walnut Grove Rd, Thornton, CA <br /> Page 3 <br /> Approximately 60,000 gallons of impacted groundwater were removed from the excavation <br /> pit during interim remediation activities Analysis of the groundwater prior to removal <br /> indicated that approximately 160 pounds of gasoline, 23 pounds of diesel, 1 pound of <br /> benzene, 2 6 pounds of toluene, 2 4 pounds of ethylbenzene, 1 4 pounds of xylenes, and 1 8 <br /> pounds of MTBE were removed by groundwater extraction and off-site disposal Based on <br /> groundwater analytical results from recent sampling of the monitoring wells, it is estimated <br /> that less than 0 2 pounds of MTBE remains in groundwater at the site No other VOCs have <br /> been detected in any well (Attachment D) <br /> 14 Assumptions, parameters, calculations and model used in risk assessment and fate and <br /> transport modeling Not Applicable <br /> 15 Rationale why conditions remaining at site will not adversely impact water quality, health or <br /> other beneficial uses <br /> • Primary and secondary contamination sources have been removed in the form of UST <br /> removal, interim groundwater extraction, and overexcavation, respectively <br /> • The minor mass of residual contamination in the soil is not expected to significantly affect <br /> groundwater <br /> • Petroleum hydrocarbons have never been detected in any site well <br /> • Dissolved concentrations of MTBE at the site continue to decrease All perimeter wells <br /> are below applicable primary and secondary MCLS Only well MW3 (100 ppb), which <br /> is located in the former excavation, contains concentrations of MTBE at levels <br /> exceeding the primary (13 ppb) and secondary (5 0 ppb) MCLs The most recent <br /> isoconcentration map for MTBE is included in Attachment D <br /> • Natural attenuation processes will continue to degrade the residual contaminants to non- <br /> detectable concentrations <br /> 16 WET or TCLP results Not analyzed <br /> appB_cklist doe 3 <br />