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Broadbent & Associates, Inc. OWS System Decommissioning Report Chico, California Pilot Flying 1 Travel Center #618, Ripon, California March 11, 2020 Page 2 Fifty pounds of dry ice were added to the tank after cleaning . A Marine Chemist then employed a field measuring instrument to check the tank' s internal atmosphere for percent oxygen content and percent lower explosive level ( LEL) at the top , middle , and bottom . The tank' s internal atmosphere was certified to contain 20 . 8 percent oxygen and zero ( 0 ) percent LEL at the three ( 3 ) elevations by the Marine Chemist prior to the UST being harnessed and removed from its location using a track mounted excavator . A copy of the Marine Chemist' s field certification form is included in Appendix D . Broadbent personnel examined the UST upon removal . The UST had a diameter of four ( 4 ) feet and length of twelve ( 12 ) feet . The outer surface was observed to be solid with no holes or staining . The resulting UST depression was thirteen ( 13 ) feet below ground surface ( bgs ) . No typical hydrocarbon odors were noted during removal of the tank and no areas of apparent staining were found in the tank depression . Soil sampling beneath the UST was delayed until January 3 , 2020 due to Site space restrictions and the need to clear enough space to accommodate the use of a track mounted excavator to collect the samples . Groundwater was not observed by Broadbent within the excavation during removal and sampling field work . The concrete OWS structure was partially abandoned in place . The upper half of the unit was demolished and disposed of. The lower half was pressure washed to remove residue and then slurry filled . 3 . 1 Soil Sampling Broadbent collected compliance soil samples on January 3 , 2020 with excavating assistance from JCGI and under the direction of a SJCEHD inspector . Two ( 2 ) compliance soil samples were collected directly from the backhoe bucket in stainless steel sleeves . Sample T1 was collected from underneath the South end of the UST at an approximate depth of fifteen ( 15 ) feet bgs . Sample T2 was collected from underneath the North end of the UST at an approximate depth of fifteen ( 15 ) feet bgs . Soil sample locations are shown on Drawing 3 . Approximately 50-cubic yards of overburden soil ( pea gravel ) was excavated from above and around the OWS system and piled adjacent to and Northwest of the excavation . Broadbent collected two ( 2 ) discrete soil samples from the overburden stockpile as directed by SJCEHD . Stockpile samples were designated as SP - 1 and SP - 2 . Stainless steel sampling liners were filled with soil to preclude headspace . The ends of each liner were covered with Teflon sheets and snug fitting plastic end caps and sealed with silicon tape . Each liner was labelled and placed on ice in a cooler . Soil samples were submitted to Alpha Analytical of Sparks, Nevada ( Alpha ) , a California State - certified laboratory, under chain - of-custody protocol . Submitted soil samples were analyzed for i I E S i i