2009-05-19_REVISION - M1978039HR (28)

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• Pt. 60, App. A-4, Meth. 9 Plume appearance include: Angle of the ob- server with respect to the plume; angle of the observer with respect to the sun; point of observation of attached and detached steam plume; and angle of the observer with re- spect to a plume emitted from a rectangular stack with a large length to width ratio. The method includes specific criteria applicable to these variables. Other variables which may not be control- lable in the field are luminescence and color contrast between the plume and the back- ground against which the plume is viewed. These variables exert an influence upon the appearance of a plume as viewed by an ob- server, and can affect the ability of the ob- server to accurately assign opacity values to the observed plume. Studies of the theory of plume opacity and field studies have dem- onstrated that a plume is most visible and presents the greatest apparent opacity when viewed against a contrasting background. It follows from this, and is confirmed by field trials, that the opacity of a plume, viewed under conditions where a contrasting back- ground is present can be assigned with the greatest degree of accuracy. However, the potential for a positive error is also the greatest when a plume is viewed under such contrasting conditions. Under conditions presenting a less contrasting background, the apparent opacity of a plume is less and approaches zero as the color and lumines- cence contrast decrease toward zero. As a re- sult, significant negative bias and negative errors can be made when a plume is viewed under less contrasting conditions. A negative bias decreases rather than increases the pos- sibility that a plant operator will be cited for a violation of opacity standards due to observer error. Studies have been undertaken to deter- mine the magnitude of positive errors which can be made by qualified observers while reading plumes under contrasting conditions and using the procedures set forth in this method. The results of these studies (field trials) which involve a total of 769 sets of 25 readings each are as follows: (1) For black plumes (133 sets at a smoke generator), 100 percent of the sets were read with a positive error' of less than 7.5 percent opacity; 99 percent were read with a positive error of less than 5 percent opacity. (2) For white plumes (170 sets at a smoke generator, 168 sets at a coal-fired power plant, 298 sets at a sulfuric acid plant), 99 percent of the sets were read with a positive error of less than 7.5 percent opacity; 95 per- cent were read with a positive error of less than 5 percent opacity. ' For a set, positive error=average opacity determined by observers' 25 observations- average opacity determined from transmissometer's 25 recordings. 40 CFR Ch. 1 (7-1-07 Edition) The positive observational error associated with an average of twenty-five readings is therefore established. The accuracy of the method must be taken into account when de- termining possible violations of applicable opacity standards. 1. Principle and Applicability 1.1 Principle. The opacity of emissions from stationary sources is determined vis- ually by a qualified observer. 1.2 Applicability. This method is applicable for the determination of the opacity of emis- sions from stationary sources pursuant to §60.11(b) and for qualifying observers for vis- ually determining opacity of emissions. 2. Procedures The observer qualified in accordance with section 3 of this method shall use the fol- lowing procedures for visually determining the opacity of emissions: 2.1 Position. The qualified observer shall stand at a distance sufficient to provide a clear view of the emissions with the sun ori- ented in the 140° sector to his back. Con- sistent with maintaining the above require- ment, the observer shall, as much as pos- sible, make his observations from a position such that his line of vision is approximately perpendicular to the plume direction, and when observing opacity of emissions from rectangular outlets (e.g., roof monitors, open baghouses, noncircular stacks), approxi- mately perpendicular to the longer axis of the outlet. The observer's line of sight should not include more than one plume at a time when multiple stacks are involved, and in any case the observer should make his ob- servations with his line of sight perpen- dicular to the longer axis of such a set of multiple stacks (e.g., stub stacks on baghouses). 2.2 Field Records. The observer shall record the name of the plant, emission location, type facility, observer's name and affili- ation, a sketch of the observer's position rel- ative to the source, and the date on a field data sheet (Figure 9-1). The time, estimated distance to the emission location, approxi- mate wind direction, estimated wind speed, description of the sky condition (presence and color of clouds), and plume background are recorded on a field data sheet at the time opacity readings are initiated and com- pleted. 2.3 Observations. Opacity observations shall be made at the point of greatest opac- ity in that portion of the plume where con- densed water vapor is not present. The ob- server shall not look continuously at the plume, but instead shall observe the plume momentarily at 15-second intervals. 2.3.1 Attached Steam Plumes. When con- densed water vapor is present within the 312