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<br /> ® ' 09 January 2003
<br /> AGE-NC Project No. 95-0114
<br /> Page 7 of 9
<br /> chemicals, including stoddard solvents, PCE, TCE, vinyl chloride, and cis 1,2-DCE.
<br /> Additional VOCs detected in soil samples collected in the vicinity of the USTs included
<br /> ethylbenzene, isopropyl benzene, n-propylbenzene, 1,3,5-trimethylbenzene, tert-
<br /> butylbenzene, 1,2,4-trimethylbenzene,sec-butylbenzene,p-isopropyltoluene,n-butylbenzene
<br /> and naphtalene.The highest TPH-ss-impacted soil is concentrated at between 10 and 50 feet
<br /> bsg in the area of the former UST clusters and extending northwards to borings SB 1, SB2
<br /> and MW-3. In addition, vinyl chloride was detected in soil samples collected•from boring
<br /> SB 1 to a depth of 65 feet bsg.However,the highest concentrations of PCE,TCE and cis 1,2-
<br /> DCE was detected in soil samples collected from off-site monitoring well MW-10.
<br /> • Once released to the subsurface,the contaminants migrated vertically and laterally. On-site,
<br /> stoddard solvents have been detected to total depth;off-site,stoddard solvents were detected
<br /> to total depth in borings CPT borings CPT3 and CPT4, and to a depth of approximately
<br /> 50 feet bsg in boring CPT5. On-site, VOCs have been detected only to a depth of
<br /> approximately 50 feet bsg, apparently staying within the thick clay layer of HU1; however,
<br /> VOCs have been detected to total depth in off-site CPT borings and monitoring wells. The
<br /> deeper, off-site presence of VOCs may be due to lateral changes in hydrostratigraphic
<br /> properties and/or additional off-site sources of contamination.The presence of 1,2-DCA off-
<br /> site in HU6, the deepest hydrologic unit, but not on-site suggests an off-site source for the
<br /> 1,2-DCA.
<br /> 4.0. SUMMARY AND CONCLUSIONS
<br /> Based on the findings from this investigation, supplemented with data from previous site
<br /> investigations, AGE concludes:
<br /> • The subsurface is composed predominantly of interbedded fine-grained soil, mainly clay,
<br /> silty clay and silt; three laterally continuous clay layers were identified. Coarse-grained
<br /> sediment is limited to laterally discontinuous layers of sandy silt, silty sand and sand.
<br /> • Based on CPT-generated lithologic properties,AGE identified a vadose zone extending from
<br /> surface grade to approximately 25 feet bsg and six hydrologic units. Three hydrologic units
<br /> (HU 1,HU3 and HU5)are clay layers of low dynamic pore pressures.Three units(HU2,HU4
<br /> and HU6) are predominantly zones of interbedded clayey silt, silt and stiff fine-grained
<br /> sediment, with occasional, laterally discontinuous sand lenses; pore pressures within these
<br /> intervals vary from medium low to high.
<br /> • The highest TPH-ss-impacted soil is concentrated at between 10 and 50 feet bsg in the area
<br /> of the former UST clusters and extending northwards to borings SB 1, SB2 and MW-3. In
<br /> addition, vinyl chloride was detected in soil samples collected from boring SBI to a depth
<br /> Advanced GeoEnvironmental,Inc.
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