ARCHIVED REPORTS XR0001342 - Laserfiche WebLink

Home Browse Search

w 10 December 2001 AGE-NC Project No.00-0769 ,.. Page 5 of 6 and sandy silt occurs locally from surface grade to 45 feet bsg. Fine grained, silt, silty clay and clay were observed at all other depths. • AGE interprets the CPT data to identify four potential hydrogeologic units informally 'y identified as "First Water Zone" (located 25 feet to 90 feet bsg), "Second Water Zone" (located 112 feet to 125 feet bsg), "Third Water Zone"(located 140 feet to 160 feet bsg)and Fourth Water Zone" (located 160 feet to greater than 175 feet bsg) as having significant intervals of apparently porous,coarser-grained soil separated by significant intervals of finer- grained, less permeable soil. The First Water Zone was subdivided into three sub-units i.. (Upper, Middle and Lower Water Zones) that may not have significant barriers to vertical migration of contaminations. Generally, First Water- Upper Zone was identified at depths between 25 feet(first encountered ground water) and 51 feet bsg,First Water-Middle Zone was identified at depths between 48 feet and 75,feet bsg, First Water- Lower Zone was identified at depths between 60 feet and 90 feet bsg. It is not known how effectively the intervening fine grained intervals hydrologically separate the informal hydrogeologic units though substantial contamination has migrated through or around them. Geologic cross sections A A',B-B'and GC'were generated from CPT data collected at CPT-01 through CPT-06 and depict general lithology beneath the site in cross sectional view(Figures 3;4 and �• 5, respectively). • Generally,the greatest hydrocarbon-impact was reported from grab water samples collected from CPT-05, located near the former UST No. 3 location, and from CPT-06, located near the formerUSTNo. i andUSTNo.2 excavation. TPH-g,BTEX,and 1,2-DCAwere detected at various depths between 55 and 173 feet bsg in samples collected -from CPT-06 and ,o between 89 and 161.5 feet bsg in samples collected from CPT-05. The CPT-06 sample collected from First Water-Middle Zone contained the greatest concentrations of TPH-g, BTEX and 1,2=DCA. Concentrations of hydrocarbon constituents increased significantly in �. samples collected from depths greater than 160 feet bsg following a marked decrease in concentrations with depth. Constituents of concern detected in ground water samples collected during the CPT investigation are depicted in cross sectional views A A',B-B'and C-C' (Figures 6, 7-and 8). Figures 9 through 26 illustrate, by.water zone, the inferred horizontal extent of petroleum hydrocarbon-impacted ground water.' UW • Variable concentrations of TPH-g, BTEX and 1,2-DCA were reported from off-site borings CPT-01 through CPT-04 at various depths between 29 and 146 feet bsg. 4.0. RECOMMENDATIONS Based upon the results of the August 2001 CPT investigation, AGE recommends: Advanced GeoEmkonmental,Inc.