SITE INFORMATION AND CORRESPONDENCE

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0 01 monitoring tracer concentrations in sentinel wells and manager and the site contractor. For facilitated tracer mass recovery in extraction wells over time. The review,the effluent sampling results should be presence of the tracer in sentinel wells indicates a lack presented alongside the discharge criteria. of capture,and a high mass recovery rate in extraction Exceedances should be highlighted and technical wells indicates a high degree of capture. The following explanations for the causes of the exceedances and the are some advantages of tracer tests: planned corrective action should be provided. • In fractured bedrock environments,tracers may Compare Design Parameters and Actual Parameters indicate flow along bedding planes and the for Treatment System connectivity of fractures between monitoring points. Because site conditions change over time and these changes can have implications on the cost and • A known mass of a tracer can be injected at a effectiveness of a remedy, P&T managers and their specified location and time,allowing mass contractors should routinely compare design values removal efficiency to be quantified. versus actual values for the following treatment process parameters: • Data from tracer tests can be used to calibrate ground water flow and contaminant transport influent flow rate to the treatment plant models. • influent concentrations for each contaminant • Depending on the tracer, sampling and analysis of concern can be relatively straightforward and low in cost if the proper sensors are available. contaminant mass loading to the treatment system(see Exhibit 5) However, tracer tests have the following disadvantages: • removal rates for the treatment system • Because the tracer is likely injected only at (influent mass minus effluent mass, or effluent select locations, demonstrating capture of the concentration divided by influent tracer does not confirm capture of the entire concentration) contaminant plume. • air to water ratio for an air stripper Injecting tracers may require obtaining an Underground Injection Control permit. pressure drop across granular activated carbon (GAC)units or filtration media • Due to the relatively slow movement of most ground water,tracer tests may take months or Addressing discrepancies between design and actual years to yield useful information. parameters can lead to changes that improve effectiveness and/or reduce O&M costs. Some PerformlInterpret Process Monitoring examples are provided in a later section of this fact sheet("Modify Inefficient System Components"). Process monitoring refers to measurements of Discrepancies between design and actual parameters concentrations in treatment plant influent and effluent, should be discussed with site contractors and and in some cases at intermediate points in the potentially with other technical assistance resources. treatment process. Evaluate Treatment System Components Verify that Discharge Standards are Being Achieved The performance of the treatment system and its Treated water from a P&T system must generally meet components can be evaluated by determining the mass appropriate standards prior to discharge. Fortunately, loading and removal rates. Especially during start up, most implemented treatment technologies have been determining the mass loading and removal rates for proven reliable through years of use in a variety of the individual treatment components may be merited. conditions,and treatment plants regularly meet the After system startup, however,these components discharge criteria. Nevertheless, sampling of plant should be operating reliably and evaluation of the effluent is recommended if not otherwise required, and treatment system as a whole(i.e., influent and effluent the resulting data should be scrutinized by both the site monitoring) should suffice. 7