4102 RUCKER AVE SAFEWAY FUELING STATION 2016-01-01 MF Import

GEOTECHNICAL ENGINEERING STUDY Inform, Inc May 9, 2002 E-8493-5 Page 3 The underlying native soil consists of silty sand (SM) with localized interbeds of poorly graded sand with silt and gravel (SP-SM), and sandy silt (ML) to the maximum exploration depth of twenty one and one half (21.5). At the boring location B-201 located in the eastern portion of the planned development area, the native soil was medium dense to approximately seven and one half feet below grade. The soil became dense from approximately seven and one half (7.5) to fifteen and one half (15.5) feet, grading to very dense to the maximum exploration depth. in Boring B-202. the native soil was genarally dense to very dense from two (2) to twenty one and one. half 121.5) feet below yrade. However, from eight and one half (8.5) to sixteen (16) feet below grade we encountered medium dense to dense silty sand with a much lower silt c,ontent. Groundwater At the time of our subsurface exploration IApril 2002i, moderate to heavy groundwater seepage was encountered at around five feet below grade to the maximum r:xploration depth at both of our boring locations. The observed seepage appears to bn occurring within interbeds of relatively permeable poorly graded sand within the surrounding lower permeability silty sand. The observed seepage is likely indicative of a seasonal high, perched groundwater condition with groundwater collecting along dense to very dense, low permeability glacial till. Based on our review of the previous boring logs for the existing Safeway Store, the groundwater seepage conditions at the proposed fueling station site appear to be heavier and more extensive. The heavier groundwater seepage conditions are likely due to the presence of the permeable sand interbeds which were not as extensive at the previous boring locations. The contractor should be made aware of the potential for seepage, and understand that groundwater levels are not static. There will Iikeiy be fluctuations in the seepage and groundwater table Ievel depending on the season, amount of rainfall, surface water runoff, and other factors. Generally, the water level is higher and seepage rate is greater in the wetter winter months Itypically Gctober through May1. The presence of groundwater seepage should be expected in the proposed excavation for the underground storage tanks, especially if the excavation is conducted during the wet season. Ennh Cnn�uhnnl�,lnc.