According to Table 6-4 , if the retrofit of the FGD , SCR , and ACI systems for 2005 occur over thirty-one months prior to 2005 and over a three-year period for each five-year increment after 2005 to 2020 , the maximum demand would be about 23 percent of the journeyman boilermakers or about 19 percent for journeymen and apprentices combined .
During the period of maximum demand for boilermakers , costs would be the highest .