Man. Gas Processes
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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 must 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)
by Situational and Operational Factors
Direct relationship with volume of specific gas-making residuals to be
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
Use Browns and other relevant data to devise a graph of production
quantities, then make approximate computations of theoretical quantities
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
Relative pH conditions of operational waste disposal bodies may be in change
and liberating cyanides.
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
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
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.
Masses of Coal-Tar Residuals in the Subsurface
Delimit the outline ("foot print") of the potential source area
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.
Advance vertical borings or probes to the uppermost aquifer, top-of- rock
or otherwise suitable vertical distance below ground surface of source
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.
Detect or determine the vertical stratigraphic identity, character and
thickness of each geologic unit capable of influencing lateral distribution
of coal-tar compounds
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.
Assess the migration effect of each of the seven geologic parameters for
each stratigraphic horizon along the boring or probe.
the relative rate of migration and potential for lateral displacement.
Determine the relative degree of horizontal or Q -displaced down-
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.
Review frequent vertical increments of chemical analyses for Chemicals
of Concern (COC).
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.
Determine which horizons are conducive or indicative of horizontal departures.
which COCs have apparently been influenced by geologic parameters toward
lateral displacement to the normal outside of the vertically-bounded original
Select which, if any, direction appears to favor amorously- lateral migration.
Employ additional borings or probes in verification; Take and analyze
additional samples or chemical sensings required to achieve acceptable
level of assurance of maximum lateral and vertical extent of compound
Integrate the findings into the remainder of site and waste characterization
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.
Verify maximum extent of vertical migration within source volume
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
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.
Negative Environmental Conditions at FMGP Sites
over-run of commercial gas plants not otherwise detectable from entries
in Browns Directory of North American Gas Companies
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
plants generated more solid PAH residuals than could be accommodated on
the plant site.*
off-site caches of purification wastes, high-water tar emulsions,
of Plant Process Waters
amounts of cooling waters typically used for gas purification.
once through, to maintain low temperature; Generally shunted off site via
municipal or special sewers.
|Contamination at District Gas Holders
of tar wastes in basins of non-slab holders-based and to a lesser degree
all off-site holders.
neglected or written off as patently uncontaminated sites.
for Subsurface Tank Leakage.
materials commonly used for construction of subsurface tanks were
to ongoing leakage.
undisclosed sources of subsurface source areas and migrated
Accumulation in Plant Trench Works
slow, accumulation of gas manufacturing and purification wastes along subsurface
caches and source bodies for contaminant transport; Possibly connecting
to off-site migration.
Wells Used for Disposal of Ammonical Liquors
disposal method for unwanted ammoniacal liquors not otherwise convertible
to valuable by-products.
impossible to store at plants not served by tar recovery companies or
which tars were not burnable as boiler fuel.
"Pristine" Gas Works
not exist; Leakage of fluids was ordinary and common, to variable
of plant maintenance and cleanliness.
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.
by Allen W. Hatheway, from various information cited by Pankow, Feenstra,
Cherry, and Ryan,
in Pankow and Cherry, eds., 1996 (On chlorinated DNAPLs).
Prediction of Coal-Tar DNAPL Movement
in Site Remediation
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.
to move beyond/ahead of subsurface masses of accumulated accumulated mass
of vadose-zone soil-pore coal-tar residuals.
interfacial tensions with pore water
to enter water-bearing vadose-zone soil pores or displace water from pores
of the saturated zone.
move downward as gases ahead of wetted front of contamination in the vadose
to move as a drip, small mass or accumulated slug, through soil masses.
to remove, by recovery, from soil pores or rock fractures of the saturated
solubilities relative to drinking water limits
to solubilize in ground water to levels representing regulatory contamination
of water supplies
partitioning to soils
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.
low natural degradability
greater than those of chlorinated solvents, but still typical of long-chain
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