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Ms. Katie L. Hower Project 22560-203.002 July 2, 1997 Page 4 analyzed for PAHs by EPA Method 8310. A duplicate sample, collected from MW-3, was analyzed for TPHG, TPHD, and BTEX by the same methods. FINDINGS Site Hydrogeology On May 29, 1997, before collecting groundwater samples, the depth to groundwater was measured in the monitoring wells using an electronic sounder. The depths to groundwater were used, along with surveyed wellhead elevations, to calculate groundwater elevations in the vicinity of the wells. The groundwater elevations were used to construct a groundwater contour map (Figure 3). The data collected from the wells indicate a hydraulic gradient of 0.0012 and a groundwater flow direction to the north-northwest. Although the groundwater flow direction has fluctuated slightly since March 1997, the present flow direction is consistent with the previous flow direction. In addition, under the present hydraulic gradient, monitoring wells MW-1 and MW-3 are still directly downgradient of the petroleum-hydrocarbon impacted soils. Soils encountered within the saturated zone in the vicinity of hydrocarbon-impacted soils, identified by borings GP-6 and GP-12, consist predominantly of sandy gravels with lesser sands and silty sands. An estimate of the hydraulic conductivity for the sandy gravel can be made by comparison to tables in Driscoll, 19866. The value for hydraulic conductivity for a sandy gravel is approximately 102 ft/day. The value for effective porosity for a sandy gravel is approximately 25%. A groundwater (seepage) velocity within the sandy gravel can be estimated using Darcy's formula. v= Ki/n, where v = groundwater or seepage velocity K= Hydraulic conductivity = 102 ft/day i = Hydraulic gradient= 0.0012 ne = Effective porosity= 0.25 Using the values listed above, the groundwater velocity in the vicinity of monitoring wells MW-1 and MW-3 was calculated to be 0.48 ft/day or 180 ft/yr. If petroleum-hydrocarbon 6 Driscoll,G.F. 1986. Groundwater and wells. St. Paul,Minnesota: Johnson Division. mcon FRE:\H:\WINWORD\MP2QT97.DOC-97\jes:2