ARCHIVED REPORTS XR0002613 - Laserfiche WebLink

Home Browse Search

• The data indicated the following site conditions: transmissivity was calculated at 4,353 gallons per day/ft and a storativity value was calculated at 0.18. Based on a transmissivity ' value of 583 ft2/day and the extraction well screen thickness equal to 25 ft(screen interval at EW-1), a hydraulic conductivity value was calculated at 0.061 cm/s; a hydraulic conductivity is consistent with a screened interval located within a silt or a silty to fine sand. CPT HYDROGEOLOGIC INVESTIGATION In November 2002,seven paired soil borings were advanced on and adjacent to the site utilizing CPT technology. CPT-1 was advanced to 148 feet bsg at the former UST excavation; CPT-2 was advanced to 138 feet bsg directly east of monitoring well MW-6; CPT-3 was advanced to 152 feet bsg north of monitoring well MW-6, on the landscape strip of the southern sidewalk of Harding Way; CPT-4 was advanced to 110 feet bsg adjacent to monitoring well MW-10 on the ' landscape strip of the northern sidewalk of Harding Way, on the landscape strip of the northern sidewalk of Harding Way; CPT-5 was advanced to 120 feet bsg at 75 feet northeast of monitoring well MW-10, on the Stockton Unified School site; CPT-6 was advanced to 133 feet bsg 110 feet ' northeast of CPT-5 on the Stockton Unified School site; and CPT-7 was advanced to 113 feet bsg at 125 feet north of Harding Way, between monitoring well MW-10 and CPT-4 on the Stockton Unified School site parking area.The following conclusions were made from the CPT investigation: ' • The subsurface is composed predominantly of interbedded fine-grained soil, mainly clay, silty clay and silt; three laterally continuous clay layers were identified. Coarse-grained sediment is limited to laterally discontinuous layers of sandy silt, silty sand and sand. • Based on CPT-generated lithologic properties,AGE identified a vadose zone extending from ' surface grade to approximately 25 feet bsg and six hydrologic units. Three hydrologic units (HU1,HU3 and HU5)are clay layers of low dynamic pore pressures.Three units(HU2,HU4 and HU6) are predominantly zones of interbedded clayey silt, silt and stiff fine-grained ' sediment,with occasional, laterally discontinuous sand lenses; pore pressures within these intervals vary from medium low to high. • The highest TPH-ss-impacted soil is concentrated at between 10 and 50 feet bsg in the area of the former UST clusters and extending northwards to borings SB 1, SM and MW-3. In addition,vinyl chloride was detected in soil samples collected from boring SB 1 to a depth ' of 65 feet bsg. However, the highest concentrations of PCE, TCE and cis 1,2-DCE was detected in soil samples collected from off-site monitoring well MW-10. • The vertical extent, and lateral extent towards the northeast and southeast, of dissolved ' TPH-ss have not been defined. • The lateral extent of dissolved PCE and TCE concentrations has been defined to t concentrations below 20 µg/1 (CPT6-50); the vertical extent has been defined to concentrations below 5.0 µg11, which are within their established MCLs. • The lateral extent of the dissolved cis 1,2-DCE plume has been defined to on-site boring SB2 and off-site boring CPT4,monitoring well MW-10 and CPT5. The vertical extent has been defined, at approximately 80 feet bsg. The lateral and vertical extent of vinyl chloride has been defined. Advanced GeoEnvironmental,Inc. t