FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

Underground Storage Tank Delinean Sampling Using Cone Penetration Testing With An Ultra-Violet Optical Screening Tool Report 216 N.California Street Page 5 of 7 v 3.2 ULTRA-VIOLET SCREENING TOOL RESULTS The decay signatures included in the callout windows of each boring indicated that the type of .. hydrocarbon impact was consistent within depth intervals. Waveforms shown as callouts on the UVOST logs indicate that diesel is predominant at depths of 16 to 70 feet. The waveforms at a depth of 90 feet in CPT2 and CPT3 indicate that a gas profile is present, but waveforms are highly dependent upon soil and v weathering (see UVOST Log Reference, Appendix C). The signal intensity indicated that hydrocarbons were located at relatively higher concentrations at some locations and depths: at depths of 16 to 50 feet bgs in CPTI, 5 feet from the source area; at depths of 30 to 48 feet bgs in CPT2, 25 feet from the source .. area; at depths of 31 to 42 feet bgs in CPT3, 40 feet from the source area. The maximum signal intensity was reported as 226.0% at 46.08 feet bgs in CPTI, 18.5% at 31 feet bgs in CPT2, and 12.3% at 37.84 feet bgs in CPT3. The background or base-level signal was approximately 0.9%throughout the 100 foot sampling interval for all three borings, both above and below the depth of elevated signal intensity. A slightly elevated signal intensity o approximately 2% was reported in the top 10 feet and 58 to 62 feet bgs of CPTI, CPT2 and CPT3, and at 88 to 95 feet in CPT2. 3.3 CONE PENETRATION TEST-SOIL BEHAVIOR TYPE RESULTS Cone penetration tests indicate that, in general, the tested soils are fine grained and have a high silt content (green), but are generally mixtures with clay (blue), see Boring Logs, Appendix C. The soils from the surface to 10 feet bgs classify as silt and silty sand (yellow), which lie above clays at approximately 10 to 15 feet. Clay and silty clays predominate at depths of 15 to 35 feet bgs. Sandy silt ` and clayey silt soils predominate at depths of 35 to 100 feet. Sand (brown) and very dense or stiff soils are present in the interval between 35 and 100 feet bgs, and are important because of their relative ability to transmit or retard groundwater transport, respectively. A pore pressure test conducted in CPT3 at a depth of 98.6 feet indicated the depth to groundwater was approximately 37.3 feet bgs, compared to the 30 feet bgs that was indicated in February of 2008. Very dense, stiff soil was reported at a depth of 40 to 44 feet in CPT1 and CPT3. Sand was reported with low pore pressure at depths of 46 to 50 feet and 72 to 75 feet bgs in CPTI. The shallower sand in CPTI correlates well spatially to the sand with gravel that was identified at a depth of 43 to 48 feet bgs in SB-1 in ep g February 2008. Sand was reported with low pore pressure at depths of 60 to 65 feet and 70 to 75 feet bgs in CPT2 and CPT3. The deeper sands identified in CPT2 and CPT3 correlate well spatially to the lower sand in CPT L Thin clays and silty clay were i' reported at depths of 75 to 90 feet with relatively thin inter-layering of dense/stiff soil, overlying predominantly sandy silt and clayey silt at depths of 90 to 100 feet bgs in CPT1, CPT2, and CPT3, see Figure 5 Appendix A. 3.4 DATA QUALITY ANALYSIS CPT data and SBT classifications correlate well to spatial trends and soils identified during the advancement of continuous coring completed with SB-1, and with visual identification of soil samples collected for laboratory analysis (Boring Logs, Appendix C). Laboratory analysis included laboratory blanks with a control surrogate, matrix spikes, and laboratory duplicate analysis of each of the selected analytes. Results of laboratory quality control procedures indicate that detection limits and analyte detection quantification were supported within method guidelines of+/- 30%. BTEX analyses had an average surrogate recovery of 94%. Diesel analyses had an average surrogate recovery of 92% (Laboratory Analytical Results Appendix B UVOST data did not correlate strongly to laboratory ( rY Yt� PP )• g Y analytical data using 6 data points, see Data Quality Analysis,Chart 1, and Chart 2,Appendix B.UVOST data did not correlate well at CPT1-60, CPTI-72, and CPT3-35 where laboratory analytical results, staining and odor, all indicated that higher concentrations were present compared to UVOST output. UVOST data would be expected to vary because soil samples are collected from co-located but separate n +.� CONDOR