and their use might reveal additional violations (GAO 2001b). The vendors of CEM technologies are likewise reluctant to put resources into more research unless they have some assurance that EPA will require companies to install them (GAO 2001b). At the same time, EPA must be confident that potentially expensive CEM technologies will work over the long haul before it prescribes their use. Thus, the relevant actors find themselves in a cycle in which promising monitoring technologies are not developed or implemented (see discussion on advances in environmental instrumentation in Box 7-5 in Chapter 7).

Remote Sensing

Remote-sensing techniques quantify the concentrations of gases and particles emanating from a source by measuring the spectral properties of light waves that have interacted with these gases and particles. Remote sensors can be deployed at surface sites in the vicinity of a source, on aircraft, or even on satellites. They are particularly useful for detecting leaks or “fugitive” emissions, because they allow a large area to be rapidly sampled. Remote sensing has not been used widely for routine compliance monitoring (EPA 1992), although a recent report prepared for EPA identified several remote-detection technologies (see Chapter 7, Box 7-5) that, if used instead of portable monitors, could drastically reduce the costs of such programs (ICF 1999).

Off-Normal Emissions

A basic assumption underlying technology-based standards (which include EPA’s NSPS, LAER, BACT, RACT, MACT, and most SIP requirements) is that a well-operated and maintained source can achieve a specified emission standard or limit under all expected operating conditions by using control equipment that has been shown through a performance test to be capable of achieving that limit (62 Fed. Reg. 54900 [1997]). Emission-control technologies, however, are not perfect, and even the most advanced technology may experience off-normal conditions that cause emissions to spike upward. An agency seeking to regulate the emissions from a facility through the application of emission-control technologies has two alternatives: (1) set a lenient emission standard so that a facility can be expected to remain in compliance 100% of the time, including during off-normal conditions; or (2) set a stringent standard and allow for “upsets” or “excursions” in emissions during off-normal conditions identified in the relevant permits and compliance monitoring regulations. For the most part, EPA has elected the second option, often permitting an operating-emission range for a source. Determination of whether a source is in compliance then depends on the

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