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CeaiogiUI hCltnics litC. Page 8 City of Escalon(Escalon) rProject No.: 1114.2 L•ir September 29,2003 4. To ensure conservative estimates each ring contains the higher estimated contaminant r concentration. 4. 5. The soil type closely resembles silts and clays. 6. It was assumed degradation of the contaminant, even with aerated stockpiled soil, does rnot occur. 4.� 7. Groundwater was not impacted with MtBE contamination. Depth to groundwater at the site is approximately 57 feet bgs and it is unlikely that any contamination, originating at this site, will reach groundwater. 8. The conversion factor of 1 gallon of MtBE equals 6.2 pounds was used.- 14. sed:14. Model Parameters The dominant soil type in the elliptical cylinder, from 5 to 18 feet bgs, is silts and clays as noted in the borehole logs included in Appendix A. Below is a summary of the lithology at L the site: Northwest • Dirty Sand—fine to medium, occasionally coarse, often silty, 0 - 5 feet • Silts and Clays—sandy and clayey, slightly plastic, 5 — 18 feet • Sand —fine to coarse grained, 18 —26 feet • Silts and Clays 26 —35 feet • Dirty Sand—fine to coarse grained, 35 - 51 feet Southeast • Dirty Sand—fine to medium, occasionally coarse, often silty, 0 - 22 feet • Sand—fine to coarse grained, 22—30 feet • Silts and Clays— 30—36 feet r • Dirty Sand—fine to coarse grained, 36 - 46 feet • Sand—fine to coarse grain, 46— 51 feet 15. Rationale For the following reasons, the conditions at this site should not adversely impact water quality,public health, or beneficial use of this property. • The tank and primary soil contamination source has been removed. • Less than 20g allons of residual contamination remain in the soil at the site. The tank sample and borehole sample data shows that the residual contaminant is at a Lshallow depth in the subsurface, with at least a 40-foot buffer between the contamination and groundwater. • The soil is primarily sand, silt and clay. Most of the contamination is in silt and clay soils. The contamination will have a tendency to sorb to the fine-grained material, thereby limiting migration.