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I[IMICIr-�-11HUB <br />Mr. Charles Leubner <br />20 January 1997 <br />Page 7 <br />Hence the gasoline tank excavation stockpile was deemed acceptable for use as backfill material. <br />Clean pea gravel and Class A/B subbase was imported for this excavation to complete backfilling. <br />CONCLUSIONS <br />Due to the presence of petroleum hydrocarbons remaining in soil beneath Tank T7 (6,150 mg/Kg of <br />TPH-D) and T1 (691 mg/Kg of TPH-G), further investigations are required before these sites can <br />be closed. A soil investigation of these areas should be conducted to evaluate the vertical extent of <br />the hydrocarbons that remain in the soil. After the vertical extent of the contamination is <br />determined, a risk based exposure assessment can be conducted to determine if further remediation <br />of the tank sites are warranted. <br />In 1990, four remote fill lines were removed near Tank T7. These lines were located near the <br />trench excavated for removing the piping for the current project. Figure 4 from Stockton Unified <br />School District Oil & Fuel Tank Project conducted in 1990 shows the locations of soil samples <br />collected during the removal of those fill lines. A copy of this Figure is included within this report.. <br />Petroleum hydrocarbons were detected at depths of 4 to 5 feet below the ground surface in the <br />trench samples ranging 17 to 5,200 mg/Kg as Total Extractable Hydrocarbons (see attached Table 1 <br />copied from that project's report). It is recommended that any investigation of Tank T7 also include <br />sampling of the areas where hydrocarbons remain beneath the remote fill lines removed in 1990. <br />We recommend that this report be submitted to the County for their concurrence with our findings. <br />If you have any questions, please call. <br />Sincerely yours, <br />HELN41CK & LERNER INC. N <br />R <br /># 39708 <br />Noel M. Lerner C11A <br />Project Manager �T� CN \3% <br />enclosures: Figure 1, 2, 3, and 4 (current report) <br />Figure 4 from Oil & Fuel Storage Tank Project (1991 Report) <br />Tables 1 and 2 (current report) <br />Table 1 from Oil & Fuel Storage Tank Project (1991 Report) <br />Attachment A - Disposal Manifests <br />Attachment B - Laboratory Analysis Reports <br />cc: Ms. Letitcia Briggs - San Joaquin County Environmental Health Division <br />ZAP\0081 I \REMOVAL.DOC <br />