The five outdoor samples must be collected in addition to the five indoor samples, the two field blanks, and the one sealed blank for a total of thirteen air samples. (40 CFR part 763.90(i)(3)) If the five inside samples are below 70 structures/mm2 and the volume of air used for the samples is equal to or greater than 1,199 L of air for a 25 mm filter, or greater than or equal to 2,799 L of air for a 37 mm filter, then according to 40 CFR part 763.90(i)(4), regardless of the statistical comparison between the indoor and outdoor samples, the response action is considered complete.