books/references introduction to environmental engineering third edition by davis & cornwell,...

Books/References

• Introduction to Environmental Engineering Third Edition by Davis & Cornwell, McGraw Hill

• Introduction to Environmental Engineering Second Edition by Davis & Cornwell, McGraw Hill

• Environmental Engineering Laboratory, by Dr. Khurshid Ahmad

• Wastewater Engineering Treatment and Reuse by Metcalf & Eddy

• Environmental Assessment in Practice by D. Owen Harrop & J. Ashley Nixon

• Integrated Solid Waste Management by George Techobanoglous, Hilary Theisen & Samuel A. Vigil

Environmental Systems

Environmental SystemsSystem

A regularly interacting or independent group of items forming a unified whole as:

a. a group of interacting bodies under the influence of related forces

b. a group of body functions that together perform one or more vital functions

c. a group of related natural objects or forces

d. a group of devices or artificial objects or an organization forming a network

Characteristics of Systems

• All systems have some structure or organization

• They are all to some extent generalizations or idealizations of the real world

• They all function in some way

• There are, therefore, functional as well as structural relationships between the units

Characteristics of Systems

• Function implies the flow and transfer of something

• Function requires the presence of some driving force, or source of energy

• All systems show some degree of integration

Defining Systems

• Systems are defined by boundaries that distinguish between the elements of interest and the surroundings

• Each element has a set of attributes, states or properties

• Relationships define how the properties of two or more elements relate to each other, the surroundings, or motivation

Types of Environmental Systems

• Isolated systems – no interaction with surroundings across the system boundary. Only approximated under laboratory conditions.

• Closed systems – energy can be transferred across system boundaries, but matter can not. These are rare.

• Open systems – both matter and energy can be transferred across boundary.

Systems can be of any scale

• Global water cycle• Continental watersheds• Regional aquifer• Lake• Vadose zone of an irrigated plot• Beaker in a titration experiment• Raindrop• Bacterial cell• Monolayer of water on a particle surface

Soil Vapor Extraction Systems

Take-home message

• Systems are abstractions that provide simple descriptions of a complex real world

• As such, their usefulness depends on how they are defined relative to how the abstraction will be used

• Unfortunately, there are no rules• Fortunately, trial-and-error works pretty

well

Units (Solid)

• Concentrations most commonly expressed as mass of substance per mass of solid mixture, e.g. mg/kg, g/g

• 1 mg/kg = 1 mg-substance per kg solid

= 1 part per million by weight

= 1 ppm

Common Prefixes

Quant. Prefix Symbol Quant. Prefix Symbol

10-15 femto f 101 deka da

10-12 pico p 102 hecto h

10-9 nano n 103 kilo k

10-6 micro 106 mega M

10-3 milli m 109 giga G

10-2 centi c 1012 tera T

10-1 deci d 1015 peta P

LIQUIDS

• Concentrations most commonly expressed as mass of substance per unit volume of mixture, e.g. mg/L, g/L, g/m3

• Alternatively, mass of substance per mass of mixture, e.g. parts per million (ppm) or parts per billion

• Occasionally, molar concentrations, e.g. moles/liter (M) or equivalents/liter (N)

Perspectives on Concentration

• 1 ppm is one drop in 15 gallons

• 1 ppb is one drop in a large swimming pool

• 1 ppb is 5 people out of the Earth’s population

Conversion of Liquid Concentrations

• For solutions and mixtures that are mostly water, 1kg of mixture = 1 liter (specific gravity = 1):– 1 mg/L = 1 g/m3 = 1 ppm (by weight)– 1 g/L = 1 mg/m3 = 1 ppb (by

weight)

• For high concentrations, 1 kg 1 liter:– mg/L = ppm (by weight) × specific

gravity of mixture

ppmv 1)(by volume ppm 1

air of volumes610pollutant gaseous of volume1

GASES

• Volume:volume ratio is used because concentrations are independent of pressure and temperature changes

Volume of an Ideal Gas

• Ideal gas law: PV = nRTP = absolute pressure (atm)V = volume (m3)n = mass (moles)R = gas constant = 0.082056 L·atm·K-1

·mol-1

T = absolute temperature (K)

K = °C + 273.15

Volume of an Ideal Gas (cont.)

Example: Determine the number of moles of gas found in 1 liter at 25 °C and 1 atm.

Solution:

mol 0.04 mol 0409.0

K) )(2981-·mol 1-L·atm·K (0.082L) atm)(1 (1

PV/RT n

Converting ppm to mg/m3

atm 1(atm)

(K)K15.273

22.414 wtmolppm

m

mg3

PT

Converting ppm to mg/m3 (cont.)

Example: 1000 L of air in a bar is analyzed and found to contain 0.078 g of carbon monoxide. Is this a problem?

Solution: Look up standard for workplace air in standard Pocket Guide to Chemical Hazards -- 8 hour time-weight exposure limit = 50 ppm

Converting ppm to mg/m3 (cont.)

ppm 70 ppm 52.69

)1)(15.273)(28)(1()1)(15.304)(414.22)(78(

(atm)atm 1

K15.273(K)

wtmol22.414

m

mgppm

3

P

T

Standard is exceeded -- clear problem

Biological Agents

• Bacteria

• Viruses

• Biotoxins

• Additional Agents of Concern

• Model Microorganisms

Possible Contamination Scenarios

• Complete System Contamination– Raw Water Source– Treatment Plant– Storage Facility

• Localized Contamination

Environmental Ethics

• Ethics are discussed by Philosophers, Lawyers, Conservationists etc.

• “Sustainable Development” - growth that meets the needs of the present generation without compromising the ability of future generations to meet their needs

Environmental Ethics

• Can Economic Growth and Environmental Protection occur simultaneously?– A Business is in business to make a profit,

not usually to protect the environment. Environmental Regulations force them to care!

• Environmental Impact Statements (EIS) are required by legislature

• Prior to design stage• Impact on water quality, wetlands, and

endangered species• Long term ecological damage

Environmental Ethics

• Engineers are not traditionally trained to think in terms of ethics– Traditionally Engineers don’t deal with policy

but perform duties to society – Design, Build, and Economic Feasibility of

Public and Private Projects

• Anthropocentric– Regarding humans as the central

element of the universe.– nature is here for us to command

Environmental Ethics

• The Engineer has to have their belief system established clearly and on an individual level determine how much tampering with the Environment is acceptable.

• Long term effects vs. Short term economic gains

• For every action there will be consequences for someone or something.

What is Environmental Engineering-A Global

Perspective

The Major Environmental Problems

Environmental Groundwater Hydrology

Ground Water Resources - Quantity

• Aquifer system parameters• Rate and direction of GW flow • Darcy’s Law - governing flow relation• Recharge and discharge zones• Well mechanics- pumping for water supply,

hydraulic control, or injection of wastes

Ground Water Resources - Quality

• Contamination sources

• Contaminant transport mechanism

• Rate and direction of GW migration

• Fate processes-chemical, biological

• Remediation Systems for cleanup

Trends in Ground Water Use

Ground Water: A Valuable Resource

• Ground water supplies 95% of the drinking water needs in rural areas.

• 75% of public water systems rely on groundwater.

• In the United States, ground water provides drinking water to approximately 140 million people.

Aquifer Characteristics

Ø Porosity (n)Ø Confined or unconfinedØ Vertical distributionØ Hydraulic conductivity (K)Ø Intrinsic permeability (k)Ø Transmissivity (T)Ø Storage coefficient or Storativity (S)

Vertical Distribution of Ground Water

Vertical Zones of Subsurface Water

• Soil water zone: extends from the ground surface down through the major root zone, varies with soil type and vegetation but is usually a few feet in thickness

• Vadose zone (unsaturated zone): extends from the surface to the water table through the root zone, intermediate zone, and the capillary zone

• Capillary zone: extends from the water table up to the limit of capillary rise, which varies inversely with the pore size of the soil and directly with the surface tension

Typical Soil-Moisture Relationship

Soil-Moisture Relationship

• The amount of moisture in the vadose zone generally decreases with vertical distance above the water table

• Soil moisture curves vary with soil type and with the wetting cycle

Vertical Zones of Subsurface Water Continued

• Water table: the level to which water will rise in a well drilled into the saturated zone

• Saturated zone: occurs beneath the water table where porosity is a direct measure of the water contained per unit volume

Porosity– Porosity averages about 25% to 35%

for most aquifer systems– Expressed as the ratio of the volume

of voids Vv to the total volume V:

n = Vv/V = 1- b/m

where:b is the bulk density,

andm is the density of grains

Porosity

Water

Arrangement of Particles in a Subsurface Matrix

Porosity depends on:

• particle size

• particle packing

• Cubic packing of spheres with a theoretical porosity of 47.65%

Soil Classification Based on Particle Size

Material Particle Size, mm

Clay <0.004

Silt 0.004 - 0.062

Very fine sand 0.062 - 0.125

Fine sand 0.125 - 0.25

Medium sand 0.25 - 0.5

Coarse sand 0.5 - 1.0

Soil Classification…cont.

Material Particle Size, mm

Very coarse sand 1.0 - 2.0

Very fine gravel 2.0 - 4.0

Fine gravel 4.0 - 8.0

Medium gravel 8.0 - 16.0

Coarse gravel 16.0 - 32.0

Very coarse gravel 32.0 - 64.0

Particle Size Distribution and Uniformity

• The uniformity coefficient U indicates the relative sorting of the material and is defined as D60/D10

U is a low value for fine sand compared to alluvium which is made up of a range of particle sizes

• The uniformity coefficient of sand is defined as a ratio: the size at which 60 percent (by weight) of a sand sample passes through a sieve (in other words 60 percent of the sand is finer than a given size) divided by the size at which 10 percent of the same sample (by weight) passes through a sieve (10 percent is finer than a given size)

Cross Section of Unconfined and Confined Aquifers

Unconfined Aquifer Systems

• Unconfined aquifer: an aquifer where the water table exists under atmospheric pressure as defined by levels in shallow wells

• Water table: the level to which water will rise in a well drilled into the saturated zone

Confined Aquifer Systems

• Confined aquifer: an aquifer that is overlain by a relatively impermeable unit such that the aquifer is under pressure and the water level rises above the confined unit

• Potentiometric surface: in a confined aquifer, the hydrostatic pressure level of water in the aquifer, defined by the water level that occurs in a lined penetrating well

Special Aquifer Systems

• Leaky confined aquifer: represents a stratum that allows water to flow from above through a leaky confining zone into the underlying aquifer

• Perched aquifer: occurs when an unconfined water zone sits on top of a clay lens, separated from the main aquifer below

Darcy’s Law

• Darcy investigated the flow of water through beds of permeable sand and found that the flow rate through porous media is proportional to the head loss and inversely proportional to the length of the flow path

• Darcy derived equation of governing ground water flow and defined hydraulic conductivity K:

V = Q/A where:

A is the cross-sectional area V -∆h, and V 1/∆L

Darcy’s LawV= - K dh/dl

Q = - KA dh/dl

Ground Water Hydraulics

• Hydraulic conductivity, K, is an indication of an aquifer’s ability to transmit water

–Typical values:

10-2 to 10-3 cm/sec for Sands

10-4 to 10-5 cm/sec for Silts

10-7 to 10-9 cm/sec for Clays

Ground Water Hydraulics

Transmissivity (T) of Confined Aquifer

-The product of K and the saturated thickness of the aquifer T = Kb

- Expressed in m2/day or ft2/day

- Major parameter of concern- Measured through a

number of tests - pump, slug, tracer

Ground Water Hydraulics

Intrinsic permeability (k)Property of the medium only, independent of fluid properties

Can be related to K by:K = k(g/µ)where: µ = dynamic

viscosity = fluid densityg = gravitational

constant