ARCHIVED REPORTS XR0003442 - Laserfiche WebLink

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Ms Marla D Guensler Exxon Company, U S A August 20, 1997 Page 5 The average vacuum applied to VEW-3 was 70 inches of water column, and the average air flow rate recorded during the test was 46 5 cubic feet per minute (cfm) The average vacuum applied to VEW-1 was also 70 inches of water column with a corresponding average air flow rate of 9 4 cfm The air flow rates from the SVE wells were calculated from measurements of the airstream velocity using an anemometer located at the discharge stack Calculations of the average air flow rate, average length of available screen, and the average flow rate per foot of screen are included in Enclosure H Calculations have been performed to estimate the soil vapor flow rates and soil vapor hydrocarbon extraction rates from each of the test wells during the pilot testing The mass flow rates from the test conducted on VEW-3 were not calculated due to nondetectable concentrations The average mass flow rate from the test conducted on VEW-I was calculated to be 0 25 pounds per day The average mass flow rate calculation is included in Enclosure H No measurable vacuums were noted in the surrounding monitoring wells during both tests Based on the results of the SVE pilot tests, an effective radius of vacuum influence could not be assessed Discussion of SVE Pilot Test Results . The SVE pilot tests performed on VEW-3 and VEW-1 both reported average vacuums of 70 inches of water column, average airflow rates of 46 5 and 9 4 cfm, and average flow rates per length of screen of 10 3 and 10 4 cubic feet per foot of screen, respectively Based on Delta's experience with SVE systems, a flow rate of 1 cfm per foot of screen is generally considered to be adequate for effective removal of petroleum hydrocarbons from soil However, based on the low influent TPPH as gasoline concentrations and the lack of a measurable vacuum in the surrounding monitoring wells, it is anticipated that a SVE system would not be economically practical for this site at this time Instead, it is recommended that a low flow bioventing/air sparging system be installed at the site as a remedial option Proposed Remedial Alternative An extended air sparging test was conducted at the site from March 13, to July 17, 1995 The results of the air sparging test are included in Delta's report dated August 15, 1995 Based on data from the SVE pilot test performed on June 5, 1997, and the air sparging test conducted in 1995, Delta recommends that a low flow bioventing/air sparging system be installed as a remedial alternative The proposed low flow bioventmg/spargmg system would initially consist of a Rotron 454 or equivalent blower, controls, existing system piping, and vapor extraction wells VEW-1 and VEW-3 Air would be injected into VEW-1 and VIEW-3 during low ground water elevation periods It is anticipated that the injected air would increase soil oxygen levels which in turn would enhance natural biological attenuation in the soil matrix With a low injection flow rate of between approximately 5 and 10 efim per well, the probability of soil vapor migration would be reduced to a minimum while still delivering an adequate amount of oxygen to the soil to enhance biological activity Additionally, during seasonal . periods of high ground water elevations, the system would be converted to a low flow sparging; system by adding a small GAST or equivalent oilless air compressor A drop tube would then be connected to a KVA or equivalent sparge point which would be installed in VEW-1 and VEW-3 approximately 3 feet below the surface of the ground water The air compressor would be used to inject air into the ground water at approximately 3 to 5 cfm per well It is anticipated that this would increase the