Water Quality Components


Up to 10 water quality components can be specified. Each column represents a separate component. Columns must be used in consecutive order (no intervening blank columns).

Component concentrations are computed from the simulated concentrations of each particle class and the particle compositions (mg/kg) specified in this screen.

The 'Scale Factor' (normally = 1) is multiplied by all of the Particle Composition.  This provides an easy way of modifying the composition of all particle fractions simultaneously.

Particle compositions refer to runoff suspended solids, not to soils or to street dust/dirt accumulations.

Up to 3 water quality criteria or standards ('LEVELS A, B, C') may be specified for each  component.  P8 computes excursion frequencies for each component, criterion, and device (see Output Tables ).

Concentration units are ppm ( = mg/liter) for each water quality component. 

The component parameters are combined with the particle parameters in the P8 particle files .  The pre-calibrated values should be edited with caution (see discussion).


Particle Composition

Particle Compositions (mg/kg) have been calibrated so that median, event-mean runoff concentrations correspond to values reported by the Nationwide Urban Runoff Program:

Component Median Site 90th Percentile Site % Dissolved
P8 Particle File NURP50.P8P NURP90.P8P
Total Suspended Solids 100 300 0
Total Phosphorus .33 0.70 30
Total Kjeldahl Nitrogen 1.50 3.30 40
Total Copper 0.034 0.093 40
Total Lead (a) 0.020 0.05 10
Total Zinc 0.16 0.50 40
Hydrocarbons (b) 2.5 b 5.0 10

 

 

 

 

 

 

 

 a - NURP lead values reduced to account for >10-fold reduction in gasoline lead content since NURP monitoring.

b - Hydrocarbons estimated from load factors reported by Hoffman et al. (1985)

 

Water Quality Criteria

The following water quality criteria are included in the NURP50 and NURP90  particle/component files .

Component Level A Level B Level C
Total Suspended Solids 5 10 20
Total Phosphorus 0.025 0.05 d 0.10 e
Total Kjeldahl Nitrogen 2.0 1.0 0.5
Total Copper 2.0 a 0.0048 b 0.02 c
Total Lead 0.02 a 0.0140 b 0.15 c
Total Zinc 5.0 a 0.0362 b 0.38 c
Hydrocarbons 0.1 0.5 1.0

 

 

 

 

 

 

 

a - USEPA primary drinking water standard (as of 1990)
b - RI standard, acute toxicity, fresh waters, hardness = 25 ppm
c - NURP threshold for aquatic life, intermittent exposure, soft waters
d - USEPA (1976) guideline for eutrophication in streams
e - USEPA (1976) guideline for streams entering lakes

Others are arbitrary benchmarks (no particular standards or criteria as of 1990).