SITE INFORMATION AND CORRESPONDENCE

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Phase VI Report Memorandum -4- 14 May 1991 Nestle Foods Corporation 8. We will inspect the site on 4 June 1991. The modelers will also be at the site on this date. GROUND WATER MODELING REVIEW 1. The assumptions of the flow and contaminant transport models generally were not discussed. The flow model assumptions for boundary conditions, leakage, static conditions, recharge, composite wells, etc. and the transport model assumptions for solubility, adsorption, dispersivity, concentration versus the unit thickness, etc. should be presented as a baseline understanding of the model conditions and limitations. 2. One of the recommendations in the Report is to investigate whether a finer degree of discretization would be beneficial for the transport model calibration. The Report should have presented the grid map as a separate graphic indicating those areas that may need to have finer discretization. 3. The Report states that the model was calibrated under "steady-state" conditions using averaged pumping rates and heads. The Report is unclear as to what conditions or time period were used to determine the averaged rates and heads. In addition, it is unclear why averaged conditions were used for the steady- state calibration rather than one period of time to calibrate the model . 4. A 24 hour flow simulation period was selected for the steady-state model calibration. The rationale for this simulation period was not presented in the Report. It is unclear how the wealth of ground water level data collected at the site has been used in the model calibration. 5. Some of the terminology used in reference to the modeling [i .e. , "target" (does this mean actual or the averaged value?) , "calculated" (does this mean the averaged or the simulated value?) and "level "] and as presented in Tables 3-10 to 3-12 needs clarification or explanation. 6. The source of the aquifer parameters used in the modeling was not discussed. Table 3-13 presents the aquifer parameters assigned to each layer after calibration. It is unclear why the value for storativity is different than specific yield for the B zone in this table. This water bearing zone is reported to be unconfined, therefore the appropriate value for this parameter should be 0.25 and not 10-6 . 7. The Report states that the transport modeling, the period from 1950 to 1990 was divided into four ten year periods and that this division was based on the data available for the regional flow field. It is unclear whether the available data was collected only for the years 1950, 1970, 1980 and 1989 or whether the available data were averaged in each ten year period. 8. The report states that the plume appears to be migrating to the north (page 3- 36) . However, the plume maps presented in the Report clearly demonstrate that the plume is moving to the south. This discrepancy needs to be clarified. 9. The Report does not state whether a sensitivity analysis will be performed once the model is calibrated.