TABLE 3.

Assumptions used in risk calculations

Parameter	Symbol	Unit	Distribution	Reference
Fraction of organisms ingested that initiate infection (r value)
Giardia	rg	Unitless	Empirical (2.5th = 0.009798; 12.5th = 0.01336; 25th = 0.01584; 50th = 0.0198; 75th = 0.02466; 87.5th = 0.02845; 97.5th = 0.03582)	44; calculated based on likelihood confidence intervals
Cryptosporidium	rc	Unitless	Empirical (5th = 0.0074; 25th = 0.0227; 50th = 0.0539; 75th = 0.1197; 95th = 0.3044)	62
Incidental sediment ingestion rate	IRsed	mg/day	Triangular	Selected based on a
Recreator			Minimum = 25, mode = 100, maximum = 200	review of sediment
Visitor			Minimum = 25, mode = 50, maximum = 95	ingestion rates
Homeless person			Minimum = 25, mode = 200, maximum = 350	provided in regulatory guidance and recent health assessments
Exposure frequency	EF	Days/yr	Triangular	Selected based on a
Recreator			Minimum = 1, mode = 12, maximum = 95	review of sediment
Visitor			Minimum = 1, mode = 2, maximum = 12	ingestion rates
Homeless person			Minimum = 1, mode = 24, maximum = 150	provided in regulatory guidance and recent health assessments. Maximum number of days limited by meteorological factors such as precipitation and temperature
Incidental water ingestion rate, swimming (for bacterial calculations)	IRswim	ml/day	Triangular (minimum = 10, mode = 16, maximum = 100)	20