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PRE-TANK REPLACEMENT Site Assessment Results <br />4315 WATERLOO RD, STOCKTON, CA <br />Aegis Project No. 89-047 <br />Page 9 <br />5.0 CONCLUSIONS <br />Aegis offers the following conclusions regarding petroleum <br />hydrocarbons in the existing tank basin and proposed new tank <br />location: <br />Low concentrations of petroleum hydrocarbons are present in <br />native soils adjacent to the existing tank basin. <br />Backfill soils in the existing tank basin probably contain <br />petroleum hydrocarbons. There are about 300 cubic yards of <br />backfill soil in the tank basin. A permit from the San <br />Joaquin County Health District (SJCHD) is required to remove <br />more than two feet from the bottom of an excavation from <br />which underground storage tanks have been removed. <br />3 Soils from the western portion of the proposed new tank <br />location contain petroleum hydrocarbons in low <br />concentrations (estimate 200 cubic yards). <br />4 Preliminarily, native clay soils present in borings to about <br />20 ft. of depth are not suitable for in-situ treatment <br />technologies, such as vapor extraction. <br />On-site thin-spreading and aeration of soils containing <br />petroleum hydrocarbons requires a permit from the San <br />Joaquin County Air Pollution Control District (SJCAPCD) and <br />approval from SJCHD. There are limits to the amount of soil <br />that can be aerated at a given time, depending on the <br />concentrations in soil. <br />There appears to be impact to native soils adjacent to the <br />fuel island, at soil boring location SB-6. <br />A contingency should be developed to manage a maximum 500 <br />cubic yards of soil generated during the tank closure, which <br />may contain petroleum hydrocarbons (including trench lines, <br />tank backfill, and soils from the proposed new tank <br />location).