SITE INFORMATION AND CORRESPONDENCE_FILE 2

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J � � SNITN For layer no. 1, the surface layer, the organic carbon content of 1.16% was conservatively calculatedl from the lower most range (2-5%) of organic matter reported by the Soil Conservation Service (for a depth range of 0 to 22"). Because site specific organic information is unavailable with depth, average percent organic matter are specified based on soil texture after Dragun, 1988. The mean percent organic matter in silty clay is not reported but both clay and sandy clay are reported to average 0.38% organic matter. The use of average values is probably conservative because the Soil Conservation Service information indicates that the soils near the surface contain high amounts of organic carbon. Therefore, 0.2 % (= 0.38%/1.724) is considered a conservative estimate of the subsurface organic carbon content (i.e., less than one fifth of the minimum reported 0 to 22" depth value). The dry bulk density of the soil is estimated to be 2,500 lbs/cy which is equal to 1.5 gm/cc (94 lbs/cf). The numerical results are not sensitive to the range of possible bulk density values. Program SESOIL requires the input of a soil's intrinsic permeability (k) instead of the better know saturated hydraulic conductivity (K). The intrinsic permeability of a soil is related to its saturated hydraulic conductivity as follows: k = (K) (viscosity of water)/((density of water)(gravity constant)), or k (cm2) = 1 x 10-5 (K)(cm/sec) SESOIL allows the input of separate permeabilities for each of the 4 layers but it then calculates a single depth-weighted average permeability for internal calculations. An overall intrinsic permeability of 5 x 10-11 cm2 (equivalent to a hydraulic conductivity of 5 x 10-6 cm/sec) is considered conservative since the soil type, CH, in the critical area below the residual chemicals indicates a much lower permeability. Furthermore, the silt below the fat clay is very dense as indicated by the blow counts measured during standard penetration tests. The standard penetration tests were performed while drilling the monitoring well boring MW- 1. Blow counts varied from 18 to 47 which indicates Very Stiff to Hard soils. The disconnectedness index for silt and clay, 12, is specified as recommended by the SESOIL documentation. This index is a dimensionless number, generally ranging from 3.7 to 12. Higher values indicate less-connected pore space and hence greater resistance to flow. The effective porosity for silt, 0.27, is specified as recommended by the SESOIL documentation. The effective porosity is defined as the ratio of the pore space through which flow can occur to the total volume. Cation exchange capacity is specified as zero. SESOIL determines retardation based on organic carbon content alone when the cation exchange capacity is specified as zero. Cation exchange modeling is typically utilized for heavy metal transport. lorganic carbon content = organic matter / 1.724 (Ref. 6) NA150114\model\param.doc 3