Cleaning Well by Pump and Treat Dr. D.G. Zeitoun ED Technology

Groundwater contamination Potential sources of contaminants include: septic tanks landfills and illegal dumps mining operations industrial discharge (used waters) urban runoff pesticides and fertilizers underground storage tanks waste-water treatment plants saltwater, etc. About 1/2 of the people in the U.S. depend on groundwater for their domestic water supply. Groundwater may become inadequate for human or animal consumption if concentrations of undesirable materials (contaminants) exceed safe levels. Contaminants may have undesirable health or ecological effects. Once contaminants enter the groundwater systems, they disperse as a result of groundwater flow, producing an ever-growing contaminant plume, if not remediated.

Types of contaminant sources Groundwater contamination occurs when contaminants enter the groundwater system by infiltration, or injection, or any other mean. Contaminants may infiltrate from point sources (e.g., underground tank, dump) or non-point sources (e.g., pesticides, fertilization, urban runoff, etc.).

Common types of contaminants in ground and surface water: pesticides nutrients volatile organic compounds microbes trace elements, heavy metals radioactive materials These different types of contaminants are undesirable for a variety of reasons, including human and animal health risk, effects on ecosystems, poisoning of crops, etc. In accordance with the Safe Drinking Water Act, the US Environmental Protection Agency sets guidelines, including maximum contaminant levels (MCLs) for human consumption.

Microbes Various water-borne microbes which pose a threat to human and/or animal health can make their way into surface water and groundwater systems. These included cryptosporidium, giardia, cholera, forms of hepatitis, etc. cryptosporidium cyst (1 mm = .001 mm) Many of these microbes reside in human and animal excrements. When water comes in contact with these, the microbes can enter and be transported into the water system. E. coli is a fecal microbe (coliform) which is used as an indicator of the possible presence of other harmful, microbes in the water (because the concentration of E. coli is relatively easy and cheap to determine). E. coli coliform

Pesticides Pesticides (herbicides, insecticides and fungicides) are used in agriculture to curb the development of organisms that negatively impact crop productivity or quality (weeds, insects, fungi, etc.). Improper or excessive use of such products can lead to their entering the ground and surface water systems. Frequency of occurrences of atrazine (herbicide) in groundwater wells in the U.S., from National Water Quality Assessment project (NAWQA)

Trace elements, heavy metals Toxic trace elements, including heavy metals such as lead, arsenic, uranium, etc., can be released into the groundwater systems from a number of sources, including landfills, buried pipes, industrial waste, mine drainage (above), etc.

Nutrients Plants need nutrients such as nitrogen (N) and phosphorus (P) to grow. Farmers spread commercial fertilizers or animal manure to enrich their soils in these nutrients, and stimulate plant growth. These nutrients are also released after waste water treatment, and found in certain commercial products (e.g., phosphorus in detergents). Excessive addition of these nutrients have health risks for human and animals. In additions, excess nutrients can enter surface water bodies where they stimulate excessive plant growth which can significantly alter ecosystems. The nitrogen cycle

Excessive release of nutrients to streams and lakes Release of nutrients to surface water bodies either from groundwater discharge or surface runoff leads to enhanced plant and algae growth. When the plants and algae die, their decomposition takes up oxygen dissolved in the water, leaving oxygen-depleted (anoxic) conditions. Such environmental changes stress certain species (fish, shell fish, etc.) which may die out.

Nutrients in Chesapeake Bay Excessive use of fertilizers and release of waste water treatment byproducts in the Chesapeake Bay drainage has led to enhanced influx of nutrients in Bay waters. This, in turn, has led to declining populations of certain species, such as oysters, Bay crabs, striped bass, etc. A decline in these species leads to a decline of the species that feed on them (e.g., shorebirds). Overall, nutrient contamination may produce permanent destruction of ecosystems and loss of biodiversity in Chesapeake Bay.

Remediating groundwater contamination Several options exist when groundwater has been found to contain unacceptable levels of contaminants. They can generally be divided into two approaches: - Source control, e.g., remove the source, or isolate source from groundwater - Plume treatment, e.g., contaminant flushing, contaminant extraction (pump and treat), in situ degradation of contaminants by action of added biological (bioremediation) or chemical catalysts

Plume treatment: Source control In some cases, as for leaky underground tanks, it is practical to remove the source of the contaminant. Further treatment of contaminated ground may also be necessary. removal of leaky gas tank Properly designing potential sources of groundwater contamination can result in effective isolation of the contaminants from the groundwater systems. Lined landfill with collection and treatment of leachate

Plume treatment: Pump and treat In many cases, to remove, or at least contain, a contaminant plume, it is necessary to pump the contaminated water out of the aquifer. This water is typically treated and purified, than put back into the surface water system. This approach is costly and may not necessarily result in complete removal of the contaminant.

Plume treatment: bioremediation Contaminants may break down over time if left to themselves, solely by chemical reactions, or by biologically-mediated reactions (natural bioremediation). microbes breaking down oil (black) Artificial bioremediation involves the addition of appropriate microbes or microbe nutrients to the contaminant plume. Over time, these organisms break down the contaminant in-situ. Bioremediation can also be done ex-situ, in pump-and-treat schemes, or wetlands for instance. injection of air and bio-catalyst to contaminant plume

FRTR Groundwater Remediation Case Studies Ex Situ Groundwater Treatment In Situ Groundwater Treatment Bioremediation (32) Permeable Reactive Barrier (13) Pump and Treat (44) Air Sparging (11) Chemical Oxidation (8) Multi-Phase Extraction (7) Drinking Water Treatment (3) Monitored Natural Attenuation (6) Flushing (6) Other (12) In-Well Air Stripping (3) Phytoremediation (3) Thermal Treatment (3) Bioslurping (1) Constructed Wetlands (1) Membrane Filtration (1)

Soil Vapor Extraction/Air Sparging System Air sparging means pumping air into the saturated zone to help flush (bubble) the contaminants up into the unsaturated zone where the SVE extraction wells can remove them.

Electrokinetics Electroremediation Field Test of a Chromate Waste Site in New Jersey The objective of the project is to demonstrate in the field an electro-restoration process developed at MIT for sites with low and highly variable permeability. The initial field demonstration will be directed towards the removal of the Cr (VI) portion of a chromium-contaminated site in Jersey City, NJ. Estimated Cr remediation cost is $100/ton versus excavation, transport and land disposal at $250/ton. For in situ remediation of an organic contaminated site $40-60/ton, versus $125/ton ex situ thermal desorption.

Pneumatic Fracturing The pneumatic fracturing process involves injection of highly pressurized air into consolidated sediments that are contaminated to extend existing fractures and create a secondary network of fissures and channels. This enhanced fracture network increases the permeability of the soil to liquids and vapors and accelerates the removal of contaminants, particularly by vapor extraction, biodegradation, and thermal treatment. Source: EPA Innovative Technology Office (http://www.clu-in.org/remed1.htm)

Land Treatment Contaminated soil is removed from the site and applied to surface soil where natural biological action removes the contaminants or converts them to harmless chemicals Land treatment of hazardous wastes or contaminated soils involves applying the wastes to the land at controlled rates. The waste is typically mixed into the soil with some type of cultivation equipment such as a disk harrow or rototiller. The cultivation step serves two important purposes. It maximizes the contact between the waste and the bacteria in the soil. It also provides aeration needed for biological degradation of organic compounds by aerobic bacteria. The key to successful land treatment is to apply the wastes in quantities and frequencies that do not exceed the capacity of the site to degrade the contaminants. Metals may be removed from solution by adsorption to soil particles and by precipitation and ion exchange. These mechanisms can effectively immobilize metals in the soil and prevent migration into the groundwater. Control of the pH of the soil is important for the immobilization of metals. If a vegetative cover exists, plant uptake may be a removal mechanism for metals.

Groundwater circulation well systems create a circulation pattern in the aquifer by drawing water into and pumping it through the well, and then reintroducing the water into the aquifer without bringing it above ground. Depending upon the configuration of the system, the technology is also known as in-well vapor stripping, in-well air stripping, in situ vapor stripping, in situ air stripping, and vacuum vapor extraction. Source: EPA Technology Innovation Office (http://www.clu-in.org/pub1.htm)

In Situ Chemical Oxidation In situ chemical oxidation is based on the delivery of chemical oxidants to contaminated media in order to either destroy the contaminants or to change them into harmless compounds. Groundwater does not contain much oxygen. Adding oxygen to contaminated sites allows aerobic bacteria that are present in nature to break down or consume the target contaminant. Aerobic bacteria are the type of bacteria that need oxygen to grow. The oxidants applied in this process are typically hydrogen peroxide (H2O2), potassium permanganate (KMnO4), ozone, or, to a lesser extent, dissolved oxygen (DO). Adapted from: EPA Technology Innovation Office (http://www.clu-in.org/pub1.htm)

Passive Treatment Wall Water-permeable treatment walls are installed as permanent, semi-permanent, or replaceable units across the flow path of a contaminant plume, allowing the plume to move passively through while precipitating, sorbing, or degrading the contaminants. These mechanically simple barriers may contain metal-based catalysts for degrading volatile organics, chelators for immobilizing metals, nutrients and oxygen for microorganisms to enhance bioremediation, or other agents. Degradation reactions break down the contaminants in the plume into harmless by-products. Precipitation barriers react with contaminants to form insoluble products that are left in the barrier as water continues to flow through. Sorption barriers adsorb or chelate contaminants to the barrier surface. The reactions that take place in barriers are dependent on parameters such as pH, oxidation/reduction potential, concentrations, and kinetics. Thus, successful application of the technology requires characterization of the contaminant, groundwater flux, and subsurface geology. Although most barriers are designed to operate in situ for years with minimal maintenance and without an external energy source, the stability of aging barriers has not been established. Source: EPA Technology Innovation Office (http://www.clu-in.org/remed1.htm)

Pump-and-Treatment System at Commencement Bay Tacoma, Washington Groundwater pumping and treatment is a method in which contaminated ground water is extracted. The contaminants are separated from the water and treated. Techniques typically used to treat groundwater include carbon or zeolite adsorption, air stripping, biological treatment or ultraviolet light oxidation.