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a. The methodology employed during the PWB survey project and the format of the questionnaire employed were based on the experiences of a similar project conducted for the electroplating industry by the National Center for Manufacturing Sciences (NCMS) and the National Association of Metal Finishers during 1993 and 1994 (see Reference 1). Permission to use the survey format and information gathering techniques of that study were given by the NCMS Project Steering Group.

b. In several of the exhibits subsequently presented in this report, rigid/flex combinations and flex PWBs are combined under the table heading of "Non-Rigid."

c. A use cluster is defined by EPA as a set of chemicals, processes, or technologies that may substitute for each other to perform a specific function. Traditionally, EPA assessed the potential hazards and exposure scenarios of specific chemicals, and generally left the evaluation of potential substitutes as a post-risk assessment consideration. The use cluster approach evaluates or compares the potential risk of all substitutes within a given use (ref. 3).

d. ssf = surface square feet.

e. Water conservation methods such as these were covered in Section 6 of the PWB survey form. The responses to these questions are summarized in Section 5 of this report. Individual responses can be viewed using the computer database available with this report.

f. Based on six facilities (ID#'s 25503, 3470, 43694, 37817, T1, 31838) that have installed ion exchange and have an average adjusted production-based flow rate of 5.4 gal/ssf vs. an average for all facilities of 12.4 gal/ssf.

g. A limit of 5.0 mg/l Cu was reported by one respondent. It is assumed that the actual limit for this facility is no higher than the applicable Federal limitation.

h. Although confidentiality was ensured, some respondents may have avoided listing any compliance difficulties do to the sensitivity of the subject.

i. A detailed discussion of drag-out and rinse water requirements is presented in Reference 1.

j. Ion exchange is also comonly used to soften or deionize raw water prior to use as rinse water or for bath make-up. This function of ion exchange is not discussed in this section.

k. Electrowinning can be performed on either sulfuric-peroxide or potassium persulfate; however another simple recovery method-cooling-is available for sulfuric-peroxide, which may be more efficient.

l. This description is based on information found in the literature (ref. 4) and may vary from the system used by the respondent.

m. This particular recycling company operates recycling facilities in both Arizona and Pennsylvania. Due to the confidentiality procedures employed during this project, it is not known if the two PWB manufacturers discussed send their waste to the same site.

n. Conventional treatment is a series of unit operations that is commonly installed for metals removal by facilities in the metal finishing and PWB manufacturing industry sectors. Metals removal is accomplished using hydroxide precipitation followed by separation of the precipitated metals.

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