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CLEARWATER G R O U P, [ N C 7 4 4 Air S_parging Systern Air sparging should be used to help accelerate remediation of dissolved hydrocarbons in the groundwater only after SPH has been removed from the site Clearwater recommends using existing sparge well SW-1 to target the portion of the plume with the highest benzene concentrations ( 1,000 ppb benzene) The sparge wells should be plumbed to the remedial compound with 1-inch diameter PVC piping in the system utility trench After the PVC 1s brought above grade in the utility trench, it will be connected to the air compressor used to run the pneumatic pumps It should be manifolded with the air supply to the pneumatic pumps, and equipped with a ball valve in order to turn the sparge well on and off as needed, a pressure gauge, and a port to measure air flowrate A schematic diagram of a sparge wellhead is shown on Figure 18 The sparge well can operate at a pressure of approximately 4 psi with a flow of 10 cfm Air sparging should only be conducted when soil vapor is being recovered from at least RW-1 and proposed RW-2 with cumulative flowrates exceeding three times the flowrate into the sparge 1 well (i a total extracted flowrate of at least 30 cfm) A wellhead schematic for the sparge well is shown on Figure 19 7 4 5 Natural Treatment System Emissions Counter Measures In order to balance the release of carbon dioxide from the operation of the emissions control system and enhance the removal of dissolved phase contamination from ' the eastern portion of the plume, Clearwater recommends planting five cottonwood trees along the southern edge of the store building, near the remediation compound Mature cottonwoods extract 50-100 gallons of water per day, and have been shown to facilitate removal of dissolved fuel constituents from the groundwater The uptake of carbon dioxide by the trees would minimize the impact of the operation of the thermal treatment system Selected articles that discuss the benefits associated with vegetative remedial measures are provided in Appendix F 7 4 6 Proposed Schedule of Remedial Action The proposed schedule for remedial action is provided to identify the sequence of key tasks to remediate soil and groundwater at the site ' 0 Pave site, 0 Plant trees, Bid out installation and monitoring of remediation system, Apply for appropriate construction and well permits, and water and air discharge permits, ' D-107,PAR/RAP 25 February 21, 1996 1