g) For used oil, the indicator contaminants must be determined by the results of a used oil soil sample analysis. In accordance with Section 734.210(h) of this Part, soil samples must be collected from the walls and floor of the used oil UST excavation if the UST is removed, or from borings drilled along each side of the used oil UST if the UST remains in place. The sample that appears to be the most contaminated as a result of a release from the used oil UST must then be analyzed for the following parameters. If none of the samples appear to be contaminated, a soil sample must be collected from the floor of the used oil UST excavation below the former location of the UST if the UST is removed, or from soil located at the same elevation as the bottom of the used oil UST if the UST remains in place, and analyzed for the following parameters:

1. 1) All volatile, base/neutral, polynuclear aromatic, and metal parameters listed at Appendix B of this Part and any other parameters the Licensed Professional Engineer or Licensed Professional Geologist suspects may be present based on UST usage. The Agency may add degradation products or mixtures of any of the above pollutants in accordance with 35 Ill. Adm. Code 620.615.
2. 2) The used oil indicator contaminants must be those volatile, base/neutral, and metal parameters listed at Appendix B of this Part or as otherwise identified at subsection (g)(1) of this Section that exceed their remediation objective at 35 Ill. Adm. Code 742 in addition to benzene, ethylbenzene, toluene, total xylenes, and polynuclear aromatics listed in Appendix B of this Part.
3. 3) If none of the parameters exceed their remediation objective, the used oil indicator contaminants must be benzene, ethylbenzene, toluene, total xylenes, and the polynuclear aromatics listed in Appendix B of this Part.

i) An owner or operator exempt from having to address MTBE as an indicator contaminant pursuant to subsection (h) of this Section may elect to include MTBE as an indicator contaminant under the circumstances listed in subsections (1) or (2) of this subsection (i). Elections to include MTBE as an indicator contaminant must be made by submitting to the Agency a written notification of such election signed by the owner or operator. The election must be effective upon the Agency's receipt of the notification and cannot be withdrawn once made. Owners or operators electing to include MTBE as an indicator contaminant must remediate MTBE contamination in accordance with the requirements of this Part.

1. 1) If the Agency has not issued a No Further Remediation Letter for the release; or
2. 2) If the Agency has issued a No Further Remediation Letter for the release and the release has caused off-site groundwater contamination exceeding the remediation objective for MTBE set forth in 35 Ill. Adm. Code 742.