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<br /> 30November52005
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<br /> AGE-NC Project,No 96-0235
<br /> " Page9of13 ,r1
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<br /> " primarily of laterally continuous'silty sand,'sand and gravelly sand interbedded wiN stiff, fine-
<br /> grained soil,clayey silt,silt and clay HU3 is characterized by generally low pore pressures,and may ;
<br /> be classified as a flow unit Hydrogeologic Unit 4 (HU4)-extends from a minimum depth of 83 feet r
<br /> bsg to`a maximumkdepth of 170 feet bsg,HU4'is composed primanly of fine-grained soils including
<br /> r " clayey silt and silt interbedded with laterally discontinuous silty sand,sand and gravelly sand Minor, ' `
<br /> sandy silt and clay intervals`were observed`at`various depths HU4 is characterized'by generally`" r
<br /> r' moderate to high pore pressures Hydrogeologic Unit 5(HU5)extends from'a minimum depth of 166 r
<br /> feet bsg"to approximately 191'feetbsg,HU5'is composed'primarily of coarse-grained soils including I t r
<br /> sand and gravelly sand interbeddea,with minor silt and clayey'silt and silt HU5 is characterized by ,
<br /> r generally low pore pressures, an'd may be classified as a flow unit H05 was observed, in borings
<br /> CPT-12 and appears to be laterally continuousene��ath tbg site.H- ydrogeologic Unit 6 (HU6) was
<br /> encountered 1I1 CP�'O3 from°approximately 91 feet bsg to approximately 210_feet�b g The lateral �,
<br /> rF ' extent of HU6 is nofwell defined at the site, CPT-01, CPT-02'and CPT-04 were terminated prior f
<br /> F tt�encountermg'HU6 HU6 is composed primarily of fine-grained sails including clayey silt and silt
<br /> ` HU6 is characterized,by generally moderate to high pore pressures
<br /> 3 5 SITE CONCEPTUAL MODEL
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<br /> } , I The model presented is interpretational and will be modified as'more data is collected Depths are
<br /> approximate and can vary by several feet across the site Hydrogeologic units'are depicted in cross '
<br /> rsectional views A=A',(Figure 7) Based, on the data developed to date, including all soil bonngs,
<br /> 1 , I monitoring wells installed and CPTsoundings,AGE has developed a site subsurface model for the
<br /> release,migration and distribution of the varying contaminants in the subsurface as,described below
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<br /> •r The subsurface from site grade to approximiately 170,feet bsg is,composed primarily of fine- F�
<br /> r. grained soil,with a coarse-grained interval ofvariable'thickness and lateral distribution The -
<br />'J major coarse-grained sand intervals occurring betweeri�30and 40 feet below surface grader
<br /> (bsg}, a laterally continuous coarse-grained sand interval at approximately 75 feetto 80 feet.
<br /> bsg and again ata depth 100 feet bsg and a deep 1I tinuous coarse-grained sand R
<br /> r " " interval at approximately 1 SQµfeet bsg A laterally discontinu sand unit extends from 135' r R
<br />" r feet to' 140 feet'bsa'in the UST No 3 area The remaining stratigraph�f the site is',
<br /> rcomprised of silt with clay inter'lchanriel fill'areas A laterally continuousclay s present at
<br /> W I ' 65 feet to i 70 'feet bsg across most of the UST No 3.area These characteristics allowed'
<br /> z construction'of,a site Hydrogeologic om del sa described'above with the water table near,
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<br /> approximately 20 feet bsg i
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<br /> ¢ Advanced GeoEnvnronmental,Inc
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