ARCHIVED REPORTS XR0000354 - Laserfiche WebLink

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ARCADIS GERAGHTY&MILLER through GM-9, to enhance the oxygenation of the groundwater The air sparging system is checked monthly to ensure proper operation Infection wells are checked quarterly at the well head to ensure that the flow rate into each well is approximately equal Operational parameters including system injection rate and infection pressure for the air sparging system are included in Table 2 System Effectiveness Concentrations of petroleum hydrocarbons measured as Total Petroleum Hydrocarbons (TPH) as gas have shown significant decreasing trends in groundwater in some onsite monitoring wells Monitoring Well MW-1 has decreased from a high of 30,000 µg/L (June and September 1996) to 380 ltg/L March 1998 Monitoring Well MW-5 has shown a decrease from 38,000 gg/L in May 1997 to non detect(less than 50µg/L) in March 1998 Downgradient monitoring wells have not shown similar decreases Additional groundwater monitoring should verify that lower onsite concentrations of petroleum hydrocarbons in groundwater will be followed by a decrease in concentrations in downgradient monitoring points . Dissolved oxygen is required for the aerobic biodegradation of petroleum hydrocarbons The average level of dissolved oxygen in groundwater measured in March 1998 was over 2 2 mg/L Average dissolved oxygen concentrations measured in May and November 1997 were approximately 16 mg/L and 0 7 mg/L, respectively The higher recent dissolved oxygen concentrations suggests that future biodegradation is likely to occur at a faster rate for petroleum hydrocarbons in groundwater Recommendations Based on the continued low vapor influent concentrations to the SVE system, it is ARCADIS Geraghty & Miller's opinion that petroleum hydrocarbons are not available within the reduced vadose zone for effective SVE operation Remaining petroleum hydrocarbons are below the groundwater level Therefore, ARCADIS Geraghty & Miller recommends modifying the remediation program and emphasizing saturated zone remediation until conditions allow for vadose zone remediation approaches to be implemented 1) Continued operation of the air sparging system as the primary remediation mechanism The system injects air at approximately 14 cubic feet per minute into the subsurface through the nine air sparging wells The system will be checked monthly to ensure proper operation Injection wells will continue to be checked on a quarterly basis to ensure proper balancing Our ref Page RC000309 000911 stgtr98 2/3