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EM 1110-1-4001 <br /> 3 Jun 02 <br /> be collected and analyzed for specific constituents of interest to verify contarrunant removal Leeson and <br /> Hmchee (1995)indicate that respiration rates below 1 %Oz/day represent background If in situ respiration <br /> starts significantly above 1%/day,and then drops below this value,it is indicative of a halt to biological <br /> treatment This halt may be due to a variety of factors,including <br /> • Changes in soil moisture (e g,raised water table)occluding the pore in contaminated zone, <br /> preventing the delivery of oxygen This can be investigated by observing changes in sort moisture <br /> and the local water table <br /> • Reduction in available macro or micro-nutnents,hnuting biological activity In some instances, <br /> bacterial populations"run-out" of nutrients such as phosphate necessary for respiration,even <br /> though there are adequate sources of carbon(i e ,contaminant)and oxygen In situ addition of <br /> nutrients, or collection of soil samples for bench scale tests can elucidate these limitations <br /> • Reduction in available carbon(i e ,contaminant)for respiration Rebound testing(see paragraph <br /> 9-9)can help evaluate this possibility This result may help make the case for site closure <br /> 9-6. System Shutdown Checklist <br /> A system can be automatically or manually shut down to minimize hazards and aid in decontamination of <br /> equipment and areas of the project There are several reasons for shutting down a system <br /> • There may be a power loss at the site <br /> • Equipment failure may initiate shutdown in the control systems <br /> • The control systems may identify an operating condition that warrants shutdown <br /> • A system may be shut down for maintenance <br /> • Evaluating remedial progress by perforirung rebound tests <br /> • Remediation may be complete <br /> a Emergency shutdown If the system is automatically shut down, an operator should be called to <br /> check the system Depending on the configuration of the system,there are several observations and notes <br /> an operator should make If a control system includes a FIRST OUT indication(an indicator panel with <br /> lights to identify the failure),the operator is informed of the reason for the shutdown,however, it is <br /> expensive to include FIRST OUT indication for all possible influences on a system If failure <br /> identifications are not included, the operator should check the unit for broken equipment,piping,hoses,or <br /> ducts Accumulated liquids should be checked and stored properly Check for electrical power failure If <br /> there are no apparent failures or reasons for shutdown, the system can be restarted and the operator can <br /> watch or even listen for causes of a failure <br /> b Maintenance shutdown If the process system is intentionally shut down,there are subsystems that <br /> should be checked Decontamination of the system can lessen exposure problems during maintenance and <br /> dismantling of equipment Steps include <br /> • Remove liquids from collection points <br /> • Isolate extraction well(s)and draw clean air through the entire system <br /> • Shut down vacuum pump(s)or extraction blower(s) <br /> 9-8 <br />