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There is another problem associated with using a vadose zone monitoring system at this particular site. Due to the fine-grained, low permeability nature of the native soils located at the subject site, either vapor monitoring or soil pore liquid monitoring is a highly unreliable means of vadose zone monitoring. Lysimetry is not effective in fine-grained sediments (7). Further, AEMC contends that the amount of soil pore liquid required for laboratory analyses (approximately 32 ounces) cannot be collected on a consistent basis from the native soils to effectively conduct a monitoring program based on lysimetry. In addition, clogging of the porous membrane at the lysimeter tip is very possible due to the fine-grained nature of the native soils, thereby rendering the lysimeter useless for its intended purpose (7). There is also the high probability that false positives or negatives in the lab analyses can occur through the use of lysimetry (7). Generally, soil-gas sampling is most applicable to sites at which the vadose zone is characterized by dry, coarse-grained soils containing minimal organic carbon (5). Fine- grained soils tend to have a relatively low air-filled porosity and trap moisture and organic material that can act as a sink for VOC's (5). In addition, compounds that possess low vapor pressures do not diffuse adequately in soil gas (4). For these reasons, AEMC considers soil- gas, or vapor, monitoring inappropriate for monitoring the #6 fuel oil tank. It is for this reason that AEMC proposes that, in addition to a regular groundwater monitoring program, a daily inventory reconciliation program could be carried out in accordance with California Administrative Code Title 23, Chapter 3, Subchapter 16, Article 4, Section 2644, "Inventory Reconciliation," where applicable, to fulfill the requirement for a vadose zone monitoring system and eliminate the need for a variance to Monitoring Alternative #2. Since Inventory Reconciliation is a monitoring alternative normally used for motor-fuel storage tanks, some modification of section 2644 may be required. Page 3