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Other model parameters, including time step length, cell dimensions, output intervals, area of polygons, and initial soil concentrations of naphthalene are shown in Appendix B which includes the VLEACH output for the three model runs A time step of 25 years was used as being most relevant in terms of the half life or degradation rate of naphthalene in soil. This time also matches the period of record available for water levels in nearby wells ' The source area used in the model was the cross section A-A' (Figure 16) which passes through the more extensive eastern area of TPHd impact and the eastern area of remediation in a direction closely parallel to the prevalent direction of groundwater flow TPHd concentrations for samples collected from soil borings on this cross section were used to assign concentrations to cells of unit width normal to the cross section, extending half the distance vertically within a boring to an adjacent sample, and half the distance laterally to the next boring TPHd concentrations were converted to naphthalene concentrations for input to the model using a multiplier of 0 002 This multiplier was established previously(Dames &Moore, 1988) from the ratio of naphthalene to TPHd in samples which had been submitted for analysis of both analytes 5 5 MODEL RESULTS AND INTERPRETATION Leaching was simulated for a period of 25 years for each of three scenarios (35 feet, 54 feet, and 70 feet to groundwater) The model results are presented in Table 10 The VLEACH output ' represents the mass of naphthalene leaching to groundwater under the three conditions during 25 years To calculate the naphthalene concentration in groundwater for each scenario, Darcy's law was used to estimate the mass of groundwater passing beneath the site through an area of unit width and 10 feet in depth Using the hydraulic parameters discussed above in Section 5 1 the volume of groundwater was estimated to be 1 45 x 0' ml ' Based on the above input conditions and assumptions, a maximum concentration of naphthalene in groundwater of 19 2 ug/L (ppb) is predicted for the case of a water table at a depth of 35 feet bgs being maintained for 25 years For the other extreme of a water table persisting at 70 feet bgs for 25 years, a naphthalene concentration of 0 172 ppb is predicted However, as described above, neither of these extremes are likely Using an average groundwater level of 54 feet bgs, a maximum concentration of naphthalene in groundwater of 1 16 ppb is predicted This is more than an order of magnitude below the EPA "Suggested No-Adverse-Response-Level" (SNARL) of 20 ug/L (EPA, 1993) This value suggests that if left in place without further treatment, the impacted soil would not be classified as a "Designated Waste" so long as the groundwater level did not rise to 35 feet bgs SAC116 07 13 AUGUST 1994 ' DAMES &MOORE