The worksheet with input decisions and output (red outline) for filtration in catchment 1 and the service life results for the input data are:
Example calculation for service life:
Service life is calculated knowing the OP media capacity (removal rate) and the amount of OP removed by the filter in a year. The OP removal capacity is the Filter Volume Provided and with typical units in cubic feet (CF) x in-place moist weight (105 pounds/CF) of media x 454 g/pound x OP removal rate of the media (mg OP/ gram of media). The OP removed is the fraction of OP in TP x mass removed (kg/yr.) x 1,000,000 mg/kg. The fraction of OP in TP is assumed at 1.0 (most conservative) and likely because of particulate settling in the ponds and in the transport ditches. The amount removed is the sum during runoff conditions as well as during non-runoff conditions at the discharge (non runoff and upstream removal is zero in this example).
Service life (years) = 0.6 mg/g x 7000 CF x 95 lbs/CF x 454 g/lb = 31.7 years.
(1.90) kg/yr x 10^6 mg/kg