Lecture 31

Introduction to Contaminants

Start with some introductory contaminant hydrogeology, then discuss advection, dispersion,
and reactive transport.

Build the fundamentals of contaminant transport before deriving equations of transport for
models.

We can categorize ground-water contaminants by their source (Fetter, 1993)

1. Sources designed to discharge substances
       Septic tanks/cesspools
           - Transform nitrogen, don't remove it
       Injection wells
           - Brine, hazardous waste
       Land application
           - Sludge, heavy metals (dioxins)
   
2. Sources designed to store/treat/dispose of waste
       Landfills - regulated facilities
           ~ 12,000 in the U.S.
           ~ 2,500 open dumps
           - Most generate leachate
       Surface impoundments
           - Pits, lagoons (evaporative ponds)
       Mine wastes
           - Often inorganic
       Animal burials
           - Radioactive carcasses
       Storage tanks
           - Above ground - containment system
           - Below ground ~ 2.5 million in the U.S.
       Radioactive waste disposal
   
3. Retain substances during transport
       Pipelines - Bemidji, Black Mesa coal slurry
       Transfer stations - solid waste
   
4. Discharge as a result of other activities
       Irrigation - selenium, salts
       Agriculture/Lawns
           - Pesticides
           - Fertilizer- natural and anthropogenic
       Road salt
       Urban runoff
       Water softeners
   
5. Sources as conduits to aquifers
       Poorly constructed wells (observation or monitoring)
       Excavation - dewatering
   
6. Naturally occurring that is aided by humans
       Saltwater intrusion or up(down)coning
       Coal mines

The public perceived greatest threats are

Nitrates, pesticides, volatile organic compounds, petroleum products

The most frequent contaminants by source are

	Underground storage tanks
	Septic tanks
	Agricultural activity
	Landfills

What is considered to be a hazardous waste by the U.S. EPA?

If a waste meets one of the following four criteria, it is hazardous

1. It is a listed waste, i.e., the waste material is listed as a hazardous waste in
   40 CFR, Part 261 (1990). Such wastes are designated by an alphabetic
   prefix (F, K, P, or U) followed by a three-digit number, and are considered
   hazardous regardless of concentration.
   
2. It is a characteristic waste, meaning that it exhibits any of the following
   characteristics: ignitibility, corrosivity, reactivity, and toxicity.
   
3. It is a mixture containing both hazardous and nonhazardous waste. An
   exception is if the mixture is specifically excluded or no longer exhibits
   any of the characteristics of a hazardous waste.
   
4. It is not specifically excluded from regulation as a hazardous waste.

The listed types of wastes are

F     Wastes generated by a variety of industrial processes (nonspecific sources)
        and are broken down into solvent wastes (F001-F005), electroplating wastes
        (F006-F012, F017), and dioxin wastes (F020-F023, F026-F028).

K     Wastes generated by specific sources and come from various industrial materials
        and processes: metal processing, wood preservation, petroleum products, acids
        and caustics, pesticides or related chemical: dyes, paints, printing inks, thinners,
        solvents, or cleaning fluids; explosives.

P      Acutely hazardous wastes (contain chemicals that are fatal to humans in small doses).
        Are subject to more stringent requirements for empty containers and quantify limits.

U     Non-acutely hazardous wastes.

What are the excluded hazardous wastes? (non-hazardous)

(from 40CFR, Part 261, 1990)

1. Domestic sewage.
   
2. Any mixture of domestic sewage and any other waste that passes
   through a sewer system to a publicly owned treatment works.
   
3. Irrigation return flows
4. Source, special nuclear, or by-product material as defined by the
   Atomic Energy Act.
   
5. Materials subjected to in situ mining techniques that are not removed
   from ground during extraction.
   
6. All household wastes.
   
7. Materials returned to the soil as fertilizers such as animal manure.
   
8. An many others

The bottom line of this discussion,

The waste is important to consider in contaminant transport

Some wastes may not be regulated, therefore not of concern.

Some wastes must be highly regulated in transport, disposal and monitoring.

Hazardous waste in the U.S.

Hazardous waste in the U.S. (cont.)

Return to Lectures