1. Introduction toNon-Point Source Pollution Models
Pollution from diffuse land sources and not from a point source discharge.
50-70% NPS pollutants loads to surface waters 75 % of which are agricultural related.
Sediments are very costly
soil loss, chemical transport
reduce reservoir capacity
Characteristics:
diffuse pathways, spatially and temporally heterogeneous
intermittent
transport is important- extensive land areas
hard to monitor at the source, no standards can be set, BMPs are used.

2. Sediments ~5 billion from erosion per year in US
~2.7 billion tons reach small streams
60% from sheet & rill Ag erosion
40% from bank, gully, road, construction
~10% total erosion enters ocean
~45% deposited before streams
~45% deposited flood plains, ponds, reservoirs, channels, wetlands
Cost:
US Army Corps dredging >$300 million in1980, >$450 million now
disposal cost may average 100% of dredging, total cost ~ $1.5 billion
Reservoirs in 30 years 20% of nation small reservoirs will be 50% full.
Carrier of P and pesticides, crop loss, aquatic habitat degradation

3. Nutrient Pesticides BOD Pathogen
N and P, accelerated eutrophication of lakes and estuaries
P: 2,000,000 tons/year 71% Ag sources, 84% NPS
P sediment adsorbed, sediment control ~ P control
N dissolved nitrate NO3-
Pesticides
2179 tons / year, 95 % Ag sources
Toxicity to human and wild life
BOD
33.5 million tons/year, 91% NPS, 81% Ag sources
Oxygen depletion in rivers and streams
Pathogen
Bacterial and viral from feed lots, manure fields, pasture, range land.

4. Why Model NPS Diffuse, Intermittent Process Land use Planning
Stream monitoring may not be sufficient.
will not pinpoint source
will not predict land use changes
will not represent high load events unless continuos
Land use Planning
Assess impact of land use changes on NPS loads, example BMP
Resource Inventory and Assessment- Stream Assessment
Regional assessment of overall problems
Identifying potential problem areas
Scientific understanding
Models and process integrator
Sensitivity analysis
Error analysis
Validation

5. Kind of Models Process description Variables presented Temporal scale
Empirical vs. Physically based
Variables presented
Runoff volume, Peak discharge, Erosion, Sediment yield, Nutrients, Pesticides, …
Temporal scale
Single event, continuos simulation, Average annual
Spatial Scale
Hillslope, Field, Basin
Dynamic vs. Steady State
Deterministic vs. stochastic

6. Advection: Transport by the water current
Transport Processes
Advection: Transport by the water current
Dispersion: Mixing within the water body
Molecular diffusion induced by concentration gradient, very slow
Turbulent diffusion eddies and mixing due to microscale turbulence moderately slow
Dispersion due to velocity gradient
Transport of sediment particles, erosion, tillage, suspension and deposition
Chemical processes
Sorption
Ion exchange
Crystallization
Hydrolysis
Oxidation-Reduction
Phytochemical and Biochemical

7. Nitrogen Ballance
NAL = Nfertilizer + Nrain + Nresidual + Nnitrification
N leaching below the root zone is:
NAL(kg/ha) (1-e[(-K*WAL)/n]
N is porosity in cm
K is leaching coeficient ~ 1.2
WAL is water available for leaching (cm) = water inflow – losses – AWHC (cm) – actual water in soil (cm)

8. Contamination Problem
Uncontrolled spill of chemical; subsequently distribute in the subsurface, and create a health hazard.

9. Water-NAPL –air distribution on an initially wet scratched glass

10. Removal Processes

11. The two layer theory

12. Multiphase Transport Model
C : is the solute concentration (M/L3)
D :is the hydrodynamic dispersion coefficient (L2/T)
v : is the specific velocity (L/T).
r : represents the interphase transfer to or from phase 
: represents the loss or gain due to chemical or biochemical reactions.
J : is the flux from the non-aqueous phase (M/L3.T-1)
kf : is the first order mass transfer coefficient (T-1)
C : is the contaminant concentration (M/L3)
Keq : represents the thermodynamic equilibrium constant as
Henry’s law constant KH (dimensionless)
 ,  : denotes the phases involved

13. Random conductivity field

14. Hypothetical case study
The general layout for the hypothetical case study
Hydraulic conductivity = 3.0 m/day
Porosity =0.30
Longitudinal dispersivity = 2.0 meter

15. Sample result a b
The contaminant plume after 50 days of heterogeneous hydraulic conductivity field of variances of (a) 0.45 and (b) 1.2.

16. Preliminary Results
The contaminant plume in Bekaa basin after 300 days of instantaneous spill of 100 ppm contaminant at a point of local coordinate of X=15000, and Y=7500 m. The transmissivities were varied by +15%

17. Preliminary Results
The contaminant plume in Bekaa basin after 700 days of instantaneous spill of 100 ppm contaminant at a point of local coordinate of X=15000, and Y=7500 m. The transmissivities were varied by +15%