ARCHIVED REPORTS XR0009957 - Laserfiche WebLink

Home Browse Search

DISCUSSION The results of this monitoring event indicated that the concentration levels of dissolved gasoline hydrocarbons are generally consistent with previous sampling events The groundwater gradient and direction of groundwater flow were also generally consistent with previous data Groundwater elevation decreased approximately 0 57 foot from the previous sampling event (March 1997) Because vapor wells VW-1, VW 7, VW-8, and VW-12 are used as extraction wells, dissolved hydrocarbon concentrations observed in groundwater samples collected from these wells may not represent actual groundwater conditions beneath the former UST It is EMCON's opinion that groundwater samples may have been compromised due to the condensation of hydrocarbons along the casing during SVE In addition, these wells have not been developed, due to greater slotted size casing (0 10) Therefore, EMCON will not collect groundwater samples from vapor wells VW-1, VW-7, VW-8, and VW-12 during future sampling events The SVE system is operating effectively to reduce petroleum hydrocarbon impact to sod and groundwater A total of 1,375 pounds of TPHG was removed during the second quarter of 1997 A cumulative amount of 24,269 pounds of TPHG has been removed since commencing SVE activities(see Table 4) Figures 4 and 5 present the rate of TPHG concentration over time and extraction rate and cumulative mass of TPHG removed over time, respectively EMCON recommended pulsing the SVE system due to low hydrocarbon extraction rates In a subsequent telephone conversation with Mike Infurna of the SJCPHS, this recommendation was approved, and EMCON will pulse the system in the third quarter 1997 Air sparging was initiated on September 5, 1996, and continued through second quarter 1997 Air sparge flow rates and DO concentrations are presented in Table 5 EMCON will continue to monitor the effects of air sparging during the third quarter 1997 when the system is being pulsed The DO readings were measured in the groundwater monitoring wells DO isoconcentration maps are depicted on Figure 6 Based on the data, DO concentrations have increased near the sparge points ATTACHMENTS • Table 1 Groundwater Monitoring Data • Table 2 Operational Uptime Information of the Soil Vapor Extraction System • Table 3 Flow Rates and Results of Air Sample Analyses • Table 4 Extraction and Emission Rates • Table 5 Air Sparge Flow Rates and Dissolved Oxygen Levels • Figure 1 Site Location Map • Figure 2 Generalized Site Plan • Figure 3 Groundwater Contour Map (May 20, 1997) • Figure 4 TPHG Concentration Vs Time • Figure 5 Extraction Rate and Cumulative Mass of TPHG Removed Vs Time • Figure 6 Dissolved Oxygen Isoconcentration Map • Appendix A Sampling and Analysis Procedures • Appendix B Chain-of-Custody Records and Laboratory Analysis Records • Appendix C Field Data Sheets cc Elizabeth Thayer, California Regional Water Quality Control Board Bruce Tuter, San Joaquin Unified Air Pollution Control District SACNN\PJ0\0805\08051140 8BS 96,gb 2