Hazardous and toxic waste are currently properly disposed in a select few landfill facilities, however, much waste generated by municipalities and industries is still dumped on the surface or in shallow burial sites or pulped down wells. Potential contamination of aquifers continues to be a principal health oomern with such disposal methods.

In the United States, federal and coordinated state legislative acts are beginning to have an impact on proper waste management. There is still need to develop adequate system for the safe disposal of a myriad of hazardous waste projects with the proper monitoring. To do this adequately requires a thorough knowlege of the hydrogeology of the site.

Introduction

The management of hazardous and radioactive waste is currently a number one issue of the world public. It is imperative that a prudent policy concerning the disposal of these wastes be based on a thorough understanding of the scientific, technical, and social issues involved. The purpose of this paper is to provide assístance to the public, policy makers, and politicians at state and federal levels with information to better understand these issues and particularly to become fully cognizant of the, geologic and hydrologic aspects of these considerations.

Every  human and animal on the earth produces waste   but not always hazardous. Many wastes comprise an important component part of the ecological system. These wastes only beocme hazardous if:

1. It contains a toxic chemical.
2. It presents a fire hazard.
3. It is corrosive ar caustic.
4. it is explosive.
5. It reacts violently with water or air.
6. It generates a toxic liquid or gas.
7. It is biologically viral.
8. It is radioactive.

Four Important Concepts

A first basic concept nest be understood, "Hazardous waste can be properly handled, using present scientific and technological expertise."

A second basic concept is that millions of tons of sledges, solvents, acids, scull tailings, PCBs, flotation tailings, shavings, and wastewater are produced over the nation as a result of our industrial complex productivity and are "a necessary evil." Sane of these wastes have low toxicity; others are extremely dangerous in only tiny amounts.

A third basic understanding must recognize that these hazardous wastes are also generated in agriculture, and by the consumer of the products that caused the industrial waste in the first place. For example, every household disposes of trash that includes: drain cleaners, pain: thinners, medicines, chemicals, and even some radioactive materials. Every person is involved in the problem of waste management.

A fourth factor is that the complexity and volume of waste has increased sharply over the past 20 years. Much of this waste in the earlier history of the nation, because America was a frontier country with lots of land, was either dumped in remote places or in ladfills with little regard to the location of a suitable site geologically, hidrologicalle, or with relation to population centers, water supply systems, and stream runoff. Now, with the waste stream far more complex and much greater in volume, hazardous wastes are seeping into the groundwater, and from there entering private, municipal, and in others, have contaminated soils.
In some instances, because of the insidious movement of wasters in groundwater, they have contaminated water supplies for generations to come.

What has been done?

In the past, state and federal goverments have passed laws in an attempt to solve this problem. To date, no single law covers all aspects of proper waste management. Some extremely importan recent laws that have resulted in very substancial improvement include: RCRA, the Resource Conservation and Recovery Act of 1976, directed at protecting public health and the environment from hazardous waste. RCRA's concept is directed at cradle to grave management of hazardous waste, including generation, transportation, final disposal, and monitoring. RCRA sets standards for hazardous waste, for labelling, storage, and packaging. EPA has been charged with establishing the regulations and enforcing them.
A part of this program is the permiting, either through EPA or appropriate state agencies, or both, 100 percent of the nation's hazardous waste facilities by 1989.

In 1980 CERCLA, Comprehensive Environmental Response, Compensation, and Liability Act, or Superfund, was created to cover both past and present emergencies. EPA, likewise, manages superfund and this program is directed at past contaminated sities, now abandoned. Superfund allows EPA to also act immediately in the cleanup of a spill or other emergency and bill the responsible entity.

How to Get Rid of Waste

During the past few years there has evolved sore basic concepts: generate as little waste as possible, recycle and reduce the volume and toxicity, and dispose of the residual waste products safely by: (AIPG, 1984).

1. Process Modification
2. Resource Recovery, Recycling, and Waste Exchange
3. In--house Volume/Toxicity Reduction
4. Waste Fixation
5. Incineration
6. Solar Evaporation/Land Treatment
7. Chemical Treatment
8. Deep-Well Injection
.9. Secure Landfills

Of the above list of methods, several art, in disrepute in the mind of many environmentalists, regulators, and the public.
This neqative attitude is unwarranted and is primarily due to ineffective application or use of these practices in the past.
The most controversial of these are the subject of the "Hammer Clauses" in the November 8, 1984 RCRA Reauthorization Bill that may result in actions that will prohibit use of secure landfills and deep-well injection.

Hydroqeology and Monitoring

Land disposal can be performed in a manner that is both environmentally safe and cost effective. The American Institute of Professional Geologists (AIPG) has adapted the following as part of its policy: "...Secure land burial can provide safe, effective, cost-efficient, hazardous waste management in many locations...

In a position paper (1985) The Environmental Institute for Waste Management Studies (EIWhLS) at The University of Alabama stated:

... .Most regions of the United States include areas with hydrogeologic conditions suitable for containment of solid or solidified, solvent-bearing wastes in landfills for as long as those wastes remain hazardous to human health and the environment..."

Neither of the two Institutes provides total endorsement of land disposal, and each includes a disclaimer indicating that the viability of a site for safe containment of. wastes depends upon site-specific, hydrogeologic conditions. At present, USA federal regulations do not require selection of land disposal sites based on hydrogeologic conditions known to be acceptable for long term containment. EIWMS and AIPG have addressed the issues related to federal regulations.

AIPG's policy states the following: "...Federal regulations imply that engineering can overcome the geological limitations of poor sites (disregarding costs), but AIPG believes that sites must demonstrate natural capability to isolate wastes from the biosphere for hundreds or thousands of years. In fact, one areas are too risky for even the best landfill technology to secure..." (AIPG, 1985).

U.S. EPA recognizes that if a Hazardous Waste Land Treatment, Storage and Disposal (AWLTSD) facility fails then effects on human health and the environment may differ depending upon: the physical location of the facility.

"Analysis of the first submissions of FCRA Part B permit applications indicates that in the event of design and operating control failure, many new, as well as existing, HWLTSD facilities are sited in locations having hydrogeologic characteristics that favor rapid release of waste constituents and maximize the potential for adverse impact." (U.S. EPA, 1985a)

The Code of Federal Regulations (40 CFR 264) contains performance standards expected to be met by operators at hazardous waste treatment, storage, and disposal facilities (M). The performance standards implicitly involve characteristics of the hydrogeologic setting, but do not allow denial of a permit at locations where groundwater is especially vulnerable to contamination (U.S. EPA, 1985a). Howeever, permits can be denied if the applicant has not demostrated that the facility will satisfy:

1. Requirements for monitoring (Part 264.92 and 264.97)

2. Requirements for liner (Parts 264.211(a), 264.251(a), and 264.301(a)

3. Standards for closure (Parts 264.111, 264.228(x), and 264.310(x))

4. Requirements for dike integrity (Part 264.211(d))

Existing restrictions in the Federal Code of Regulations include only two prohibitions related to geology and hydrology.

1. Seismic restrictions (40 CFR 264.18(x)) prohibit location of HWLTSD facilities within 61 meters (200 feet) of a fault
    known to have been active in Holocene time (last 10,000 years).

2. The flood plain standard (40 CFR 264.18(b)) prohibits location. of HWLTSD facilities within the 100--year flood plain.

Variances can be granted under certain conditions.
Recognition of the effect the local hydrogeology has on the location of a facility is given in the U.S. EPA Permit Writers' Guidance Manual (1985a), to aid determination as to whether a proposed facility is an acceptable location.
The criteria are:

1. Site Characterization

a) Demonstration that the hydrogeologic and pedologic features can be fully characterized. Characterization must
    include groundwater flow paths and flow velocities.

b) Geologically complex locations (karst, fractured bedrock, alluvial materials, certain glaciated regions) require
    extensive investigation to demonstrate acceptability of the site.

2. High Hazard and Unstable Terrains

a) Site geology must provide a stable foundation.
    Includes consideration of:

Flood Prone Areas
Seismic Impact Zones
Volcanic Impact Zones
Landslide Susceptible Areas
Subsidence Prone Areas
       Fluid Withdrawal Zones
       Karst Terrain
       Mine Subsidence Areas
Weak and Unstable Soils

3. Ability to Monitor

a) Ability to monitor the site requires characterization of all potential flow paths for ground water in the uppermost aquifer. Physically possible to install upqradient and downqradient monitoring wells. acception granted for "minimal recharge zone" (arid climate).

4. Protected Lands
         Protected Lands include:

a. Archaeological and historic places
b. Habitats of endangered and threatened species
c. Parks, monuments, and scenic rivers
d. Wilderness areas
e. Coastal areas
f. Wildlife refuges
g. Significant agricultural lands
h. Wetlands

5. Vulnerable Hydrogeology

EPA, 1984 identifies three classes of groundwater.

I. Special groundwater (irreplaceable and/or ecologically vital

II. Current and potential sources of drinking water and waters having other beneficial uses

III. Groundwater not considered a potential source of drinking water and of limited beneficial value

U.S. EPA will, in the future, provide regulations try protect Class I and Class II groundwater. At present, the agency discourages location of HWLTSD facilities above such sources of water, but cannot now deny permits in such areas. Location of sites with proper hydrogeologic conditions for disposal to land is conceptually a simple process, provided that we remember air original goal-safe, cost-effective disposal.

Safe disposal requires hydrogeologic isolation of wastes for as long as the wastes retrain hazardous to human health and the environment. If our goal is to protect groundwater in aquifers from contamination, then perhaps we must consider laws, regulations, and guidelines that require HWLTSD facilities to be located in non-aquifers at some reasonable distance from centers of population. Deep well disposal can provide hydrogeologic isolatión by injection of wastes into Class II aquifers (greater than 10,000 ppn total dissolved solids) below the deepest occurrence of aquifers which are sources of drinking water.

A universal acceptable term "aquifer" as defined by Meinzer (1923) in USGS Water Supply Paper 489, "An aquifer is a hydrogeologic unit with sufficient porosity and permeability to store groundwater, and to yield economically significant quantities of groundwater to wells and springs," must be acted in applying rules and regulations. If it is not accepted, problems develop in permitting. For example, the operator of a hazardous waste facility is required to monitor the uppermost aquifer beneath the facility. According to the RCRA Ground-Water Monitoring Technical Enforcement Guidance Document 9a (TEGD) (U.S. EPA, 1985b, p. 1-33) "...The uppermost aquifer extends from the water table to the first confining layer (or ten feet into bedrock) and includes any overlying perched zones of saturation..." It is important to recognize that the existence of a water table and the existence of a saturated zone may not be synonymous with the presence of an aquifer. The determination of monitoring requires a thorough knowledge of the hydrogeology and the potential pollutant flow patts. See Figure 1.

Many hydrogeologic units contain groundwater and may transmit groundwater slowly, but do not have sufficient permeability to yield significant quantities of water to wells or springs. Such units are characterized by low hydraulic conductivity and must not be classed as aquifers to monitor. The most abundant sedimentary rocks are typically composed of fine-grained materials such as silt and clays, which interact with and attenuate contaminants in the groundwater. The interlocking crystalline structure of many igneous and metamorphic rocks also provide hydrogeologic systems of very low permeability and are not aquifers, except for zones that contain abundant fractures. Other nonaquifes exist.

Many sedimentary sequences of clay, shale, claystone, marl, and sore glacial tills, have maxímun hydraulic conductivities of 1 x 10 ^-7 an/sec. Under unit head, groundwater movement is approximately 0.1 foot/year at a hydraulic conductivity of X x 10^-7 cm/sec. Cartwright et al (1981) state that the actual rate of gnounwater movement in fine-grained material is 5 to 100 times less than that estimated by the unmodified form of the Darcy equation. Griffin and Roy (1985) demonstrate that dissolved, hydrophobic, organic contaminants move mare slowly than does groundwater, because of retardation by sorption on the organic matter present in many host rocks. Inorganic contaminants may be retarded by sorption on the active surfaces of clay particles in the host material.

Assuming selection of sites where the fine-grained rocks do not contain continuous layers of interbedded permeable units and have no well-developed systems of secondary permeability (such as fracture systems); then wastes may be stratigraphically isolated from potential routes of escape in direct proportion to the thickness of the host unit.

An example of such a location is Emelle, Alabama, USA, which contains landfills thát are located in a chalk and marl unit, over 800 feet thick, which can provide excellent hydrogeologic isolation of wastes. The marl is not homogeneous but has uniformly low permeability. Abundant clay in the marl readily deforms to seal fractures so that permeability does not increase appreciably along the fractures. Deep aquifers beneath Emelle are confined by the marl under artesian pressure, and have a total dissolved solids content that precludes use as a source of drinking water in the area down-dip from the site. Installation of double liner systems beneath the landfill provides an added component of hydrologic isolation. The first underlying aquifer can be monitored. Base line knowledge of the geochemistry of ground water is available and any waste placed in the facility would take 10,000 or more years to migrate downward to the first aquifer. Good engineering practices and management at such a site provides safe waste management.

Landfills can be located in areas where geologic structure can provide isolation of wastes; in areas not underlain by sources of groundwater; and in areas underlain by class III aquifers, (U.S. EPA groundwater classification, U.S. EPA, 1984), however, as much as possible. Landfills should be placed in areas underlain by hydrogeologically simple system composed of thick sequences of earth materials with low permeability.

In conclusion, incomplete or improper characterization of the site prior to installation of the disposal facility, typically postpones the expensive process until, at a later time, contaminants are detected in the system of monitoring wells. Costs for complete characterization, litigation, and clean-up belie the concept that on-site disposal in areas of hydrogeologic complexity is effective. Adherence to guidelines specified in the RCRA Groun-Water Technical Enforcement Guidance Documen (TEGD) published. by the U.S. EPA (1985b) are sufficient to provide complete characterization of site-specific hydrogeology for disposal facilities. The information obtained during the characterization process will allow design of a site-specific detection monitoring system.

References

American Institute of Professional Geologists (1985) Hazardous Waste-issues and Answers. American Institute of Professional- Geologists, Arvada, CO, 24 p.

Environmental Institute for Waste Management Studies, 1985, Disposal of Solvents and Solvent-Contaminated Wastes to land, University, Alabama, 46 p.

Griffin, R.A, and Roy, W.R., 1985, Interaction of Organic Solvents with Saturated Soil-Water Systems, Environmental Institute for Waste Management Studies Open-File Report, University of Alabama, Tuscaloosa, AL, 86 p.

Griffin, R.A. and Roy, W.R., 1986, Feasibility of land Disposal of Organic Solvents: Preliminary Assessment, Environmental Institute for Waste Management Studies (in press), University of Alabama, Tuscaloosa, Al.

Meinzer, O.E., 1923, The Occurrence of Ground Water in the United States: U.S. Geological Survey, Water Supply Paper 489, U.S. Government Printing Office, Washington, DC, 53 p.

U.S. EPA, 1985a, Permit Writers Guidance Manual for Hazardous Waste Land Storage and Disposal Facilities, Phase I, Criteria for Location Acceptability and Existing Applicable Regulations, Final Draft, Office of Solid Waste and FInergency Response, Washington, DC.

U.S. EPA, 1985b, RCRA Ground-Water Monitoring Technical Enforcement Guidance Document, Draft, Office of Solid Waste and Emergency Response, Washington, DC.

U.S.EPA, 1984, Ground-Water Protection Strategy, Office of Ground-Water Protection, Washington, DC, 56 p.

U.S.EPA, 1981, Solid Waste Data: A Compilation of Statistics on Solid Waste Management Within the United States:
NTIS PB82-107301 prepared by JRB Associates, 73 p.

Fig. 1 Cross-section -- alluvial and marginal marine sediment

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