Table 6.

Back-volume calculations to determine average final sample volume in UF concentrates, secondary concentrates, and total viral NA extracts

Sample type	n	Total sample volume (L)	Average concentrate in mL (range)	Total sample (mL)/average concentration (mL)	Average total secondary concentrate (mL)*	Average total sample (mL)/secondary concentrate (L)	Average total viral NA extract (μL)†	Average total sample in 5 μL NA extract (mL)
GW	4	100	338 (218–495)	328	0.42	55	93.6	699
DW	6	100	229 (86–434)	632	2.67	17	92.2	1,323
SW	9	100	232 (143–419)	493	1.05	33	95.0	629

NA = nucleic acid; GW = groundwater; DW = treated drinking water; SW = surface water.

^*Total secondary concentrate from 70 mL UF concentrate.

^†Total viral NA extract from 200-μL secondary concentrate except in two GW and one DW secondary concentrates, for which 150-μL volumes were used.