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MTBE soluble mass values of 2.4 kg and 0.40 kg (Sands A and B, respectively) in the source area were selected for this input parameter in the final model run (see additional discussion in Section 5.2.2 below). 5.2.2 Model Calibration and Sensitivity In an attempt to calibrate the model inputs as described above to actual field conditions observed over the nine year historic period in which data is available (February 2000 to June 2009), actual groundwater analytical data from the June 2009 were entered for the Sand A and Sand B wells, and the model was run for a nine year simulation period. For Sand A calibration, analytical data from wells MW-2 (80 feet from source), MW-13A/B (160 feet from source), MWO-3 (320 feet from source) and MW-15A (400 feet from source) were used. For Sand B calibration, analytical data from wells MWO-1x (84 feet from source) and MW-13A/B (126 feet from source) was used. The model divides the model and spaces field data in 10% increments of the full model length; therefore, field data was placed at the point nearest to the actual distance from the source area. The input data and model output for the calibration simulations in Sands A and B are included in Appendix C. Using the input parameter values described above, and adjusting those parameters where definitive values were unknown, Stratus determined the parameters/variables that most affected the length and longevity of the plume were 1) hydraulic conductivity and 2) the soluble mass of NAPL present at the source. To fine-tune the calibration of the model, these two parameters were adjusted in an attempt to match the simulated plume to the known data. �.. Hydraulic Conductivity Adjustments: Pump testing conducted in 2006 by SECOR estimated hydraulic conductivity in Sand A ranging from 2.5 x 10-2 to 8.0 x 10-3 cm/sec and in Sand B ranging from 1.8 x 10-3 to 8.0 x 104 cm/sec. During calibration of the model in both zones, Stratus adjusted (increased) the hydraulic conductivity of Sands A and B to 2.9 x 10-2 cm/sec and 1.3 x 10-2 cm/sec, respectively. Although Stratus' increasing of this parameter fit the actual behavior of the migration of the MTBE plume during the nine year period in which data has been collected, it can also be considered conservative since if measured (lower) hydraulic conductivities were to be used in modeling, slower/less migration of the MTBE plume would result. Soluable Mass NAPL Ad iustments: As discussed in the previous section, an extremely conservative source area soluble mass of 1.1 Kg was estimated by Stratus based on site-specific data. During calibration of the model in both zones, Stratus increased this value in Sand A to 2.4 Kg and decreased this value in Sand B to 0.40 Kg. These values were selected for use in the model based on the calibration runs fitting actual dissolved-phase concentrations measured, overall migration area and timeframes for migration to historic groundwater data. All estimates used are likely much higher than in reality. Page 21 STRATUS