Site Waste Characterization

Environmental Threat
Site Characterization
Man. Gas Processes
Plant Wastes
Contamination Threat Modes
Residuals - Components
Sources of MGP Liquid Effluent
FMG Plants in the US
Parallel MG Technologies
Think you've found a gas works?
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Site Waste Characterization

Without a competent site and waste characterization it is impossible to evaluate any former manufactured gas plant in terms of its environmental threat. The manufacture of gas was a process made complicated by numerous factors, most of which mus t now be deduced by compilation of a thorough and competent site historic technical assessment and then, taking site geologic conditions into consideration, to explore the surface and subsurface of the site for appropriate physical and chemical evidence by which the environmental threat can be evaluated. Without this information gathered and appropriately assessed, protection of residents, site and site area workers, area citizens, and the environment cannot adequately be protected.

Tar well at Fairfield Iowa, NPL FMGP Site; contains abandoned tar water emulsion of carburetted water gas process waste (courtesy U.S. EPA/Region VII)


Site Complexity Represented by Situational and Operational Factors

Factor Nature Effect
 Size of Plant Direct relationship with volume of specific gas-making residuals to be managed. Give some ruled-of-thumb on quantities generated on basis of Mcf or ton of coal/gal of oil 
Years of Operation Direct relationship with volume of specific gas-making residuals to be managed. Use Brown’s and other relevant data to devise a graph of production quantities, then make approximate computations of theoretical quantities of wastes historically generated.
Changes in Ownership Subtle to detect but possible of major influences in nature and volume of gas-making residuals and their fate. May also affect tendencies to economize, manage plant with relative differences in cleanliness, and selection of historic waste-management options. May signal a change in perceived goodwill with community over-enhanced cleanliness of the plant and waste-management options selected.
Changes in Process Gas-making residuals vary by process and with plant operational characteristics and conditions. Relative pH conditions of operational waste disposal bodies may be in change and liberating cyanides.
Site Geology Fluvial: Highly variable conditions along rivers and streams subject to relative frequent flooding. Expect significant variations in subsurface; Possibly poor foundation conditions having led to excessive settlement and foundation cracking or use of wooden piling (subject to rot and transport of residuals) & general site elevational rise to avoid flood effects; Often obscuring older works and their wastes. Levees may have been required and may obscure pockets of gas-making residuals.
Site Topography Unequal or relatively high relief Gives natural impetus to create leveled space for plant use and expansion through on-site disposal of plant debris such as brick and clay retort cast-aways, forming porous ground for sorption of gas-making residuals.
Surface Drainage Conditions Gas works required some means of relief from accumulating aqueous wastes Anticipate previous existence of open-channel and various sewered drains; Especially as oriented toward possible discharge points.
Frequency of Improvement of Plant Expansion of production and/or area of service. Increases may indicate progressive policies which may  have influenced the manner of operation with respect to quantities and fates of gas-making residuals
Historic Litigation Incidences of municipal, agency or public complaints Possible direct relationship with management and operational ethics with respect to plant residuals.


  Rational Steps in Characterizing

Once the historical chronological history of an FMGP is established, either through utility historic archives or by searching key literature references, an understanding can be developed as to how the plant likely was operated. Here are a list of rational steps by which the expected source volumes of coal-tar residuals can be characterized. 

Rational Steps in Characterizing
Masses of Coal-Tar Residuals in the Subsurface

Sequential Step Guidance
1. Delimit the outline ("foot print") of the potential source area Equivalent to the layout or fire insurance bounds of the specific plant component, plus an outward fringe equivalent to the lateral extent of angle Q of any outward-drawing geologic condition.
2. Advance vertical borings or probes to the uppermost aquifer, top-of- rock or otherwise suitable vertical distance below ground surface of source component o Utilize a minimum of four locations, positioned at the 90- degree planar angles, to cover the points of the compass, for detection of laterally-biased migration; Start from the nearest achievable lateral point to the outline of the source component; Continuously sample by borehole drive samples or chemically sensed push technology.
3. Detect or determine the vertical stratigraphic identity, character and thickness of each geologic unit capable of influencing lateral distribution of coal-tar compounds This stratigraphic sequence represents the physical-chemical controls of site geology over the relative rate of vertical and lateral migration, as well as lateral departures from verticality.
4. Assess the migration effect of each of the seven geologic parameters for each stratigraphic horizon along the boring or probe. Assess the relative rate of migration and potential for lateral displacement.
5. Determine the relative degree of horizontal or Q -displaced down- gradient movement. Q is the angle from horizontal of geologic units or interfaces that cause COCs to move in a lateral displacement from the outer vertical bounds of the area footprint origin of the source.
6. Review frequent vertical increments of chemical analyses for Chemicals of Concern (COC). o Examine the relative concentrations of each of the COC so Relate relative concentration to chronologic uses of coal-tar generating processes more or less favorable to production of each COC.
7. Determine which horizons are conducive or indicative of horizontal departures. Assess which COCs have apparently been influenced by geologic parameters toward lateral displacement to the normal outside of the vertically-bounded original footprint.
8. Select which, if any, direction appears to favor amorously- lateral migration. o Employ additional borings or probes in verification; Take and analyze addit ional samples or chemical sensings required to achieve acceptable level of assurance of maximum lateral and vertical extent of compound migration.
9. Integrate the findings into the remainder of site and waste characterization Work Plan. o Make best-estimate of depth of vertical migration; estimate potential or degree for DNAPL entry and/or presence in weathered or jointed bedrock; Consider contamination potential for second aquifer.
10. Verify maximum extent of vertical migration within source volume Employ penetration and sampling technologies designed to locate maximum depth of vertical migration, taking care not to compromise any inherent migration-constraint or obstacle-integrity of earth material directly underlying the source volume.


  Some Predictable Negative Conditions

One of the greatest challenges to site and waste characterization of FMGPs is to anticipate certain predictable negative environmental conditions that appear again and again at these sites. Here is a list of conditions and situations that faced the historic  plant owners, managers and operators. This list will help you think like the historic management as you plan and conduct the necessary site and waste characterization. Without this level of anticipation the field work may not be capable of making the key discoveries that will support an ethically accurate evaluation and assessment of FMGP site threats.

Some Predictable Negative Environmental Conditions at FMGP Sites

Condition Nature of Condition Implication for Remediation
Unrecorded Sites Significant over-run of commercial gas plants not otherwise detectable from entries in Brown’s Directory of North American Gas Companies Unrecorded sites may now be 140 percent more than those previously known to environmental regulatory agencies, plus other shown on various city maps.
Waste Generation Potential Most plants generated more solid PAH residuals than could be accommodated on the plant site.* Expect off-site caches of purification wastes, high-water tar emulsions, lampblack and cyanogens.
Excesses of Plant Process Waters Significant amounts of cooling waters typically used for gas purification. Commonly once through, to maintain low temperature; Generally shunted off site via municipal or special sewers.
Contamination at District Gas Holders Accumulation of tar wastes in basins of non-slab holders-based and to a lesser degree all off-site holders. Commonly neglected or written off as patently uncontaminated sites.
Penchant for Subsurface Tank Leakage. All materials commonly used for construction of subsurface tanks were susceptible to ongoing leakage. Commonly undisclosed sources of subsurface source areas and migrated contamination.
Waste Accumulation in Plant Trench Works Relative slow, accumulation of ga s manufacturing and purification wastes along subsurface transport network. Considerable caches and source bodies for contaminant transport; Possibly connecting to off-site migration.
Tar Wells Used for Disposal of Ammonical Liquors Alternative disposal method for unwanted ammoniacal liquors not otherwise convertible to valuable by-products. Nearly impossible to store at plants not served by tar recovery companies or for which tars were not burnable as boiler fuel.
The "Pristine" Gas Works Did not exist; Leakage of fluids was ordinary and common, to variable degrees of plant maintenance and cleanliness. Expect to encounter evidence of historic fluid leaks at all points along manufacturing, purification and storage pathway.

  Guidelines for Prediction of Coal-Tar DNAPL Movement

PAH gas-making residuals are unlike most industrial hazardous wastes. FMGPs were sites of what is known as "incomplete combustion" (pyrolysis or absence of oxygen) or organic materials, and the PAHs are a group of organic chemical compounds characteristic of the residuals of pyrolysis. PAHs also are Semi-Volatile Organic Compounds (SVOCs), meaning that they will not quickly evaporate and that they characteristically are viscous and sticky. Furthermore, the PAHs typically form is pyrolytic associations of from 500 to 3000 separate compounds, although they blend together well as what we call "tar" (not "asphalt" as that forms from petroleum original which largely are of animal life, not of plant life). PAHs form long-chair compounds built upon the hexagonal benzene ring, as their "building blocks." PAHs, strictly speaking, are of three to six benzene rings, with attached atoms oxygen and hydrogen. PAHs typically are more dense than water, hence, they are referred to as DNAPLs (Dense Non-Aqueous-Phase Liquids; those that do not mix perfectly with water). All of these physical and chemical characteristics are influential in governing the movement (="migration" or "transport") of the PAHs, particularly when associated together as masses of gas-works tar residuals. 

Guidelines for Prediction of Coal-Tar DNAPL Movement

Relative Factors Implication in Site Remediation
High densities Has the ability to be driven by gravity, in the subsurface, ahead of the leaked or spilled mass of coal tar residue. May also spread laterally at the fringes of the subsurface mass, in zones of higher permeability. 
Low liquid viscosity Able to move beyond/ahead of subsurface masses of accumulated accumulated mass of vadose-zone soil-pore coal-tar residuals.
Low interfacial tensions with pore water Able to enter water-bearing vadose-zone soil pores or displace water from pores of the saturated zone.
High volatility Can move downward as gases ahead of wetted front of contamination in the vadose zone
Low absolute solubilities Able to move as a drip, small mass or accumulated slug, through soil masses. Difficult to remove, by recovery, from soil pores or rock fractures of the saturated zone.
High solubilities relative to drinking water limits Able to solubilize in ground water to levels representing regulatory contamination of water supplies
Low partitioning to soils Not retarded by earth material characteristics typically of aquifers. Accounts for presence of masses of coal-tar residuals at depths in soil greater than might normally be appreciated. Once in fractured rock, there is essentially no natural mechanism to defeat their advance, mainly vertically, but also laterally, in directions of groundwater flow. Has the ability to move counter to groundwater flow, within rock fractures.
Relatively low natural degradability Generally greater than those of chlorinated solvents, but still typical of long-chain organic compounds.
Expanded by Allen W. Hatheway, from various information cited by Pankow, Feenstra, Cherry, and Ryan, in Pankow and Cherry, eds., 1996 (On chlorinated DNAPLs).
Copyright 2020-25 by Dr. Allen W. Hatheway    All rights reserved.
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