II.C.  MARKETS FOR TIRES AS FUEL

 

High energy potential makes tires an attractive alternative to many existing fuels, primarily coal and wood wastes. As a result, tires have been used as fuel since the 1970s in North America, Europe and Japan (CIWMB, 1992; 24-27).  Energy recovery from whole tires and “tire-derived fuel” (TDF)[1] is currently the largest market for waste tires both nationally and in California, and the energy is used both to generate electricity and as fuel in cement kilns. 

Tires contain 12,000 to 16,000 British thermal units (Btu) per pound, depending upon composition and whether or not steel has been removed (California Integrated Waste Management Board [CIWMB], 1992; 11-12).  An 18 lb. tire contains energy equivalent to approximately 2 gallons of gasoline.  In comparison, bituminous coal has energy values ranging from 11,000 to 13,000 Btu/lb., fuel oil (No.6) has 18,000-18,500 Btu/lb., wet wood (hogged-fuel) has 4,000-5,500 Btu/lb., and agricultural waste has 5,000-8,500 Btu/lb. (CIWMB, 1992; 11-12).  Additionally, percentage moisture by weight in tires is much lower than for all these fuels except for fuel oil.

Burning whole tires in cement kilns can also be very attractive economically  to the kiln operator.  A payback period estimated to be between one year (CIWMB, 1992; 59-60) and 2.2 years (Lindert, CIWMB, 1993, citing Franklin Associates, 1989), is possible on the kiln operator’s investment. 

In this chapter, we review national and local use of tires as fuel, and describe kiln combustion processes, emissions, and health risks.  We examine the current market trends and discuss existing or potential barriers to further use of tires as a fuel source in California.

 

Current Use of Tires as Fuel

A. National

A 1995 survey shows that in the U.S., tires have been used to supplement fossil fuels and biomass fuels at 24 cement kilns, 18 pulp and paper mills, 9 utility boilers, 12 industrial boilers, and 3 dedicated tire-to-energy plants (Scrap Tire Management Council [STMC], 1995).  These facilities burned approximately 130 million tires in 1995, roughly 40% of the amount of PTEs generated in the U.S. that year (STMC, 1995).

B. California

In 1995, approximately 10.6 million passenger tire equivalents (PTEs) were used as fuel in California. 
Of this total, 1.0 million PTEs were imported from neighboring northern states (Keller, 1996).  According to our end-use survey, 26% of California-generated scrap tires (9.65 million PTEs) were burned as fuel — 41% by cement kilns and 59% by Modesto Energy Limited Partnership (MELP) in a dedicated tires-to-energy facility.  In 1996, the amount burned (including imported tires) is expected to increase to approximately 12 million PTEs because one kiln (Riverside Cement) came on-line in 1995 and burned only a fraction of its capacity.  Projected totals for tires-as-fuel in the next few years depend on whether MELP continues to burn tires after December 1997, and whether more kilns are permitted to burn tires by local air quality boards in California. 

The Modesto Energy Limited Partnership (MELP) tires-to-energy facility has been burning whole tires to produce electricity in Westley, California, since 1987.  The facility uses a stoker-grate boiler to burn approximately 5.0 million tires (about 5.5 million PTEs) annually.  Emissions of nitrogen oxides (NOx), sulfur dioxides, and particulates are controlled using Thermal DeNOx (a limestone slurry spray scrubber) and a baghouse (TL & Associates, 1996).  The heat energy from burning the tires creates steam which is then used to power turbines to generate electricity.  The MELP facility produces approximately 14 megawatts of electrical power, enough to supply 14,000 homes (CIWMB, 1992; 35).  In December, 1997, MELP’s 10 year contract with Pacific Gas and Electric Company (PG&E) will expire.  This will lead to a large decrease in the price PG&E pays MELP for its electricity.  At this lower price, MELP may have to close the facility or look at alternative mechanisms to keep it operating. 

Limited testing of tires-as-fuel has was also conducted at a biomass facility in California in 1994 (Gauff, 1996).  Tests measured emissions when tires replaced 10% of the hog fuel, which was becoming increasingly expensive.  However, the price of hog fuel dropped and the incentive to use tires disappeared (Gauff, 1996).  Currently, only cement kilns and the MELP facility burn tires in California.

 

Cement Kiln Combustion Processes

The advantages that have been cited for using tires as fuel in cement kilns are that cement kiln processes operate at high temperatures and with high residence times and kiln turbulence—conditions that usually favor the production of low levels of metal or other toxic residues.  The objective when burning tires in cement kilns is to achieve nearly complete combustion of all organic materials in the fuel so that complex organic compounds do not become part of the air emissions.  Moreover, non-combustible tire components (e.g., metals) become part of the cement ‘clinker’ and purportedly do not contribute either to air emissions or to waste ash (CIWMB, 1992; 24-27).  Another advantage cited is that oxides of nitrogen (NOx) emissions usually decrease when tires are burned (CIWMB, 1992; 24-27), a possible benefit in urban areas that have high ozone levels.

In actual operation, a variety of toxic organic compounds and metals are emitted.  The emissions produced by burning up to 20% tires (with 80% coal) in cement kilns depend on the completeness of combustion (combustion efficiency), which is determined by several factors other than the type of fuel burned: temperature, residence time, oxygen levels, and the degree of turbulent mixing within the reaction chamber.   Although the temperature and residence time are high in cement kilns, optimizing cement production dictates using the minimum amount of oxygen needed to produce the cement ‘clinker.’  These oxygen levels might not achieve adequate combustion efficiency to fully burn the tire fuel, especially the 25% of the tire composed of aromatic extender oils (refinery tank bottoms).  Incomplete combustion of these heavy aromatic components is likely to produce increased emissions of polycyclic aromatic hydrocarbons (PAHs) and other toxic air pollutants (Carman, 1996). 

The specific emissions from a given cement kiln burning tires will also depend upon some combination of the following: the type of cement process used (Long Dry, Long Wet, Preheater/Pre-Calciner); the pollution abatement methods used; the degree of substitution of whole tires/TDF for coal; the point in the process at which tires are fed; and the quality (including moisture and metal content) and form (chips or whole tires) of the tire fuel.  Additional factors that potentially contribute to producing toxic emissions include the following: the metal in the scrap tire can act as a catalyst on the chlorine that is also present in the scrap tire, to promote the production of dioxins and furans (Carman, 1996); and the very high operating temperatures can promote increased volatilization of metals, especially those with relatively low volatilization temperatures, such as mercury (Carman, 1996).  The characteristics of the limestone—the raw material for cement production—may also affect emissions.

Because of the complexity of these physical and chemical processes occurring in the kiln, each new permit request by a cement kiln operator has been reviewed on a case-by-case basis by local air pollution control authorities, who usually base their decision on test runs comparing emissions from burning up to 20% tires (whole or TDF) with coal, versus the baseline levels for coal alone (see Air Pollution and Risk Assessment section, below).

 

Facilities Other than Cement Kilns

Facilities other than cement kilns that seek to use tires for all or part of their energy requirements, such as tires-to-energy facilities like MELP or pulp and paper mills, do not offer  the same combination of very high temperatures and high residence times as do cement kilns.  Emissions from burning tires at these facilities may, therefore, be higher than those from cement kilns burning tires (Gonzalez, 1995; Flynn, 1995).  However, Carman (1996) believes that dedicated tire-to-energy facilities (such as the MELP facility) are better designed for controlling air pollution than are cement kilns.  Although the average residence times of the fuel (tire) may be shorter, incinerators designed for combustion efficiency can have several features that help minimize emissions, including dual chamber combustion, afterburners, high oxygen levels, and better abatement and control equipment.  The design of these waste-to-energy incinerators makes them better able to take care of any process upsets or malfunctions without excessive emissions, and these facilities typically have more monitoring requirements, such as for entrained metals, than cement kilns do (Carman, 1996).

 

Trends in Use of Tires as Fuel

Taking account of the late-1995 increase in capacity of cement kilns to use tires, we expect the 9.65 million PTEs of California tires burned in 1995 to increase to approximately 11.2 million PTEs in 1996.  If the three facilities currently seeking permits to start or increase their tire-burning are successful, the amount of tires burned would increase to between 15 and 16 million PTEs per year.  However, opposition from citizens groups and environmental organizations poses a barrier to such expansion.  Furthermore, the economic viability of the MELP waste-to-energy facility, which burns about 5.5 million PTEs per year, will be in doubt after its current contract with PG&E expires in December 1997.

 

Barriers to Market Growth

It appears that the most important barrier to growth in the tires-as-fuel market in California is citizen and environmental group opposition to tire-burning.  Because of public opposition, test-burning of tires at RMC Lonestar Cement in Davenport was halted, and a lawsuit requesting a full CEQA review at California Portland Cement in Mojave was successful[2].  Local opposition to burning tires has also been directed at Kaiser Cement in Cupertino.  The local air district (BAAQMD) has determined that some form of environmental review under CEQA is necessary, but as of June 1996 it had not specified the form of this review (Hall, 1996).

Citizens groups claim that full CEQA reviews of proposals to burn tires in cement kilns are necessary in order to correct what is perceived to be a lack of adequate opportunities for public participation in the decision-making process.  One air district staff member has questioned the motives behind the calls for full CEQA review, suggesting that it is a strategy to halt tire-burning altogether by increasing the cost and effort required by cement kiln operators to make the changeover from coal-only firing  (Flynn, 1995).  However, cement kiln operators do not necessarily view the CEQA process as a “stopper” in the process of gaining approval for burning tires.  In discussing the results of preliminary testing of tires as fuel, an RMC Lonestar report commented on the inherent difficulties involved in obtaining accurate stack samples and in estimating health risks and suggested that “a long term use [of tires as fuel], if proposed, would require a more extensive review of health and environmental impacts under the California Environmental Quality Act (CEQA)” (RMC Lonestar, 1992; Carman, 1995).

A. Stated Basis for Opposition

Opponents raise the following concerns when arguing against the burning of tires:

        1.  Increased levels of toxic air emissions and damaging health effects.   The core of the argument opponents use is that burning tires increases emissions of  toxic pollutants such as dioxins, furans, PCBs, and metals, in some cases by several hundred to several thousand percent, which results in serious threats to health, to human reproductive systems, and to the normal development of fetuses and infants.  They cite recent reviews of the health hazards of dioxin by scientific panels, especially the U.S. EPA’s (1993) dioxin reassessment report, which indicate that dioxin may be much more dangerous than previously believed, that it can disrupt hormone systems at very low levels, and that there may be no safe threshold of exposure  (Angel, 1996; Carman, 1995; I-35 Cement Kiln Pollution Corridor Network, 1996; Rachel’s #479, 1996).  The opponents’ emphasis on dioxin is especially strong, and they note that cement kilns are the third largest source of dioxin emissions in the U.S. (I-35 Corridor Network, 1996).  Grass-roots environmental groups recently launched a National Dioxin Campaign (Rachel’s # 479, 1996).

        2. Flaws in methods used by District Air Boards to determine the health threats posed by air emissions.  Because District Air Boards rule on permits to burn tires, several objections by opponents focus on the methods by which the Boards assess the risks.

        ·  Opponents assert that risk assessments ignore the dangers resulting from combinations of pollutants, which can be synergistic (much larger than the sum of individual risks), and also ignore important non-cancer risks, such as risks from disrupting  hormone systems (Angel, 1996; Carman, 1995; I-35 Corridor Network, 1996; Rachel's #470, 1995).

·  Opponents argue that it is important to consider the existing background levels of potentially damaging emissions, because increased emissions (from burning tires) that may not be dangerous by themselves could cause damage if they react synergistically with existing background chemicals.  The Sierra Club analysis (Carman, 1995) faults the California Portland Cement risk assessment because it assumes background levels of zero.  It also cites a study showing that the Mojave-Rosamond area has had childhood cancer rates six times those of other areas in California, which many residents attribute to three local cement kilns (including National Cement, the only kiln with a permit to burn hazardous wastes), as well as several local toxic dumpsites (Carman, 1995).

        ·  Opponents claim that current regulations governing cement kiln emissions are too lax, and that some of the current pollution abatement equipment is inadequate, permitting emissions of high levels of particulates from the kilns (I-35 Corridor Network, 1996).

        ·  Communities for a Better Environment (formerly Citizens for a Better Environment), the Sierra Club, and others have criticized the sampling protocols used in some of the test studies, claiming that they underestimate the emitted levels of small particulates and vapor-phase metals (Carman, 1995; I-35 Corridor Network, 1996).

        3. Disagreements with  decision-making philosophy.  Opponents disagree with the philosophy of allowing increases in highly toxic pollutants as long as the increased health risk is below a preset “significant threshold.”  They argue instead for the principle that there should be no increase in risk if the risk is avoidable.  They oppose using risk assessment for decision-making, not only for reasons cited above, but also because “risk assessment NEVER asks whether a particular risk can be avoided” (emphasis in original; Rachel’s #470, 1995).

        4. Test burns do not mirror actual operating conditions.  Critics argue that equipment and procedures are at their best during closely observed and controlled test runs, which does not reflect the range of emissions found in day-to-day operations, especially when “upset conditions” occur.  As a result, they say, risk assessments underestimate the true risk (Angel, 1996).  Cement kilns are subject to process-disrupting malfunctions during combustion that lead to emitting much more air pollution than is produced during normal operation.  For example, a fused ring of cement material can form in the kiln and subsequently break loose, causing large swings in operating pressures and even reversal of process flow (Carman, 1996).

        5. The manner in which tires are introduced into kilns.  Several analyses (Carman, 1995; I-35 Corridor Network, 1996) state that burning whole tires reduces combustion efficiency and increases the emission of dioxins and other pollutants.  To prevent this drop in efficiency, they say, tires should be ground very finely and fed into the hottest section of the kiln, along with the pulverized coal, rather than fed as whole tires into the cooler sections (Carman, 1995; I-35 Corridor Network, 1996).  At least some of the emissions results reviewed from test burns support this claim (see Canadian Test Burn Results section, below).  RMC Lonestar, in its proposal for further testing, also suggested that exposing the TDF to more zones of combustion and to higher initial temperatures should result in more complete combustion and hence lower emissions (RMC Lonestar, 1992).  Another promising approach would involve converting the tires to a gaseous state by pyrolysis, then burning the gas in a cement-kiln incinerator designed for maximum combustion efficiency (Carman, 1996).

 

        B. Air Pollution and Risk Assessment

In order to better understand the opponents’ arguments, we now present data about the emissions of pollutants from cement kilns burning tire/coal combinations, and information about possible health consequences and risk assessment methods.

 

1. California Test-Burn Results 

Results of tests at four California cement kilns burning up to 20% tires (with two tests at one kiln) are summarized as follows (note that not all pollutant types were reported for all tests) (CIWMB, 1992, App. B; California Portland Cement, 1995; Carnot, 1996; RMC Lonestar, 1992; Bateman, 1996):

• Dioxins and furans showed increases of between 53% and 100% in four tests;

• polycyclic aromatic hydrocarbons (PAHs) increased in three tests (between 296% and 2230%) but decreased by 68% in a fourth test;

• nitrogen oxide (NOx) emissions increased by less than 10% at Kaiser Cement (Bateman, 1996), but decreased by 22% in two other tests;

• sulfur oxides (SOx) increased by 7.5% in one test, but decreased in two tests by 45% and 90%;

• lead emissions increased in three tests, by 59%, 388%, and 475%, respectively, and decreased in one test, by 94%;

• hexavalent chromium increased in one test by 727%, and decreased in two tests by 36% and 87%, respectively.

 

2. Canadian Test-Burn Results

A review of test-burning of tires at five Canadian cement kilns also showed a wide variation in emissions levels, similar to the results for California test burns.  Dioxins and furans increased (when burning tires, compared to coal-only firing) by 37% and 247% in two of the tests, and decreased by 54% and 55% in the other two reported tests.  Four of the five Canadian kilns experienced decreases in nitrogen oxides (NOx) ranging from 6% to 44%, while the a fifth had a 21% increase.  Four tests reporting on sulfur oxides (SOx) showed increases of between 17% and 133%. 

Both of the Canadian facilities that reported decreases in dioxins use the long, dry process in which whole tires are injected at the midsection of the kiln.  The plant reporting the 247% increase in dioxins also reported an increase in NOx emissions.  This facility uses the preheater process, and reportedly had been converted to burn whole tires that were injected into the preheater riser duct (the last and coolest combustion zone)  (Proctor and Redfern, 1995).

While the data is insufficient to make definitive conclusions about the effects of process type and burn conditions on emissions, it does indicate that the way in which the tire fuel is introduced into the kiln may be important in maximizing combustion efficiency and minimizing toxic emissions levels (see point 5, under Stated Basis for Opposition, above).

3. NOx and SOx Emissions

The prospect of reducing NOx emissions by burning tires is appealing to cement kiln operators because the kiln’s NOx emissions typically are close to the limits specified in operating permits (Flynn, 1995).  Increases in NOx, as occurred at the Kaiser Cement facility, are viewed as “disappointing” (Bateman, 1996).  Meeting SOx emissions limits has generally been less problematic for cement kiln operators because the raw material from which cement is made acts as a “scrubber” to reduce sulfur below permit levels.  Based on the material balance alone, we would expect higher SOx emissions from burning tires that contain sulfur levels higher than the low-sulfur coal the tires replace in California.1  However, SOx increased in only one of the three California tests, although it increased in all four Canadian tests (Proctor and Redfern, 1995). 

4. Chlorine Content and Dioxins 

Public interest groups have long called for the regulation of burning wastes that contain chlorine because of their concern about resultant dioxin emissions.  A content comparison indicates that tires may contain as much as two to five times the chlorine level of western coal, with an average of 0.04 weight percent for western coal, and a range of 0.07 to 0.2 weight percent for tires (CIWMB, 1992; 69).  One major source of chlorine in tires is their halogenated butyl rubber liners.  The addition of chlorine or bromine (the latter used more widely for truck tires) to the butyl rubber gives liners the air-impermeability required to maintain proper tire inflation. 

5. Health Risk Assessment

California law (1987’s “Air Toxics ‘Hot Spots’ Information and Assessment Act,” AB 2588) requires owners or operators of facilities such as cement kilns to prepare a health risk assessment when applying for a permit to burn tires.  The kiln operator’s contractor uses the test-burn emissions results in risk assessment models to estimate the resulting changes in health risk due to burning tires along with coal, as compared to burning coal alone.  Dispersion models predict ambient concentrations in populated areas near the facility; population exposure and risk of death are calculated from guidelines that contain risk factors. 

The risk assessment must be reviewed by the state Office of Environmental Health Hazard Assessment (OEHHA) and approved by the local air pollution control district.  If the district judges that potential significant health risks are associated with emissions from the facility, operators must notify all exposed individuals and must also reduce toxic emissions below the level of significance2 (California Air Resources Board, 1994).

For tire-burning in cement kilns, the risk calculations have typically shown increases in risk that are
still below the levels that local air pollution control districts consider “significant.”  However, opponents have not been convinced by determinations that risk is not significant, and point to important sources of uncertainty, some of which are acknowledged by kiln operators and risk assessors.

        a. Uncertainties in risk assessment.  Many uncertainties and potential sources for error exist in the risk assessments.  The RMC Lonestar preliminary evaluation identified several “deficiencies” and “omissions” in the company’s original risk assessment calculation (RMC Lonestar, 1992).  Some of these error sources underestimated the risks from burning tires, whereas others caused risks to be overstated.  One major source of underestimation of risk was a sampling error in formaldehyde emissions during coal-only firing; another source of underestimation was the omission of non-inhalation cancer risks arising from arsenic, cadmium and PCBs (RMC Lonestar, 1992).  One staff member of the Bay Area Air Quality Management District indicated that some staff believe that the current risk assessment methodology is too conservative (i.e., it overstates risks), and he expects the basic methodology to be revised (Bateman, 1996). 

        Although some staff find the methodology too conservative, the document containing the risk assessment guidelines they use  (issued by the California Air Pollution Control Officers Association [CAPCOA, 1993]), identifies important flaws in the methodology that lead to underestimating risks:  1) “Effects of exposure to more than one carcinogen or toxicant are also not quantified in the risk assessment.  Many examples of additivity or synergism (effects greater than additive) are known” (CAPCOA, 1993; p. I-3).  2) “Additionally, there may be chemicals which pose health risks but are not considered in a given risk assessment for a number of reasons, including lack of information on toxicity” (CAPCOA, 1993; p. I-3).    3) “The estimates of cancer potency in humans contain many sources of uncertainty. . . .  Differences in these factors . . . cannot be easily quantified and incorporated into risk assessment . . . .  Other uncertainties arise in the assumptions underlying the dose-response model used.” (CAPCOA, 1993; p. I-4). 

        Other critics of risk assessment state that 1) risk assessment considers primarily the risk of death from cancer, but consequences other than death, such as disruption of human immune and hormone systems, can cause serious health, social, and economic damages (Rachel’s #470, 1995); and, 2) models of cancer causation are controversial, and risk estimates can vary enormously depending on the model used (Ricci and Molton, 1986; pp. 85-86).1

        In addition to the specific sources of error cited above, the CAPCOA guidelines further state that because of the uncertainty inherent in risk assessment, risk numbers should be “used as a yardstick” and “should not be construed as the expected rates of disease in the exposed population” (CAPCOA, 1993; p. I-4).  This statement implies that the specific risk number calculated by the risk assessments should not be compared to a criterion of “significant risk” as a basis for making decisions.

 

        b.  Recent evidence of health risks. In the most thorough assessment of the hazards of dioxin yet undertaken, the U.S. EPA’s scientific advisory panel concluded that dioxins are more dangerous than previously believed and pose not only a risk of cancer but also a risk of disrupting reproductive processes (U.S. EPA, 1993).  The Erice Statement,1 issued by an international group of scientists in November 1995, further warns of the serious threat posed by chemicals that disrupt human hormone systems.  The statement2 says that research since 1991 has reinforced these concerns, and that “new evidence is especially worrisome because it underscores the exquisite sensitivity of the developing nervous system to chemical perturbations.” Furthermore, according to the Erice statement, these chemical changes can undermine neurological and behavioral development of fetuses and infants, which could cause “reduced intellectual capacity and social adaptability, impaired responsiveness to environmental demands,” or a variety of other functional problems. Compounding that threat, it continues, is the fact that many hormone-disrupting contaminants, even if less potent than natural products, occur in living tissue at concentrations millions of times higher than the natural hormones; and that humans and wildlife exhibit adverse health effects at existing environmental concentrations of synthetic chemicals that act as hormone disrupters (Rachel's #499, 1996).  Thus, evidence exists that dioxins, furans, and PCBs disrupt hormone systems at extremely low levels, levels that are already found in human tissues.  Furthermore, it is believed that there is no safe threshold below which disruption of the hormone system does not occur (Silbergeld, 1993).

Several recent studies have also shown that children exposed to relatively low levels of PCBs via their mothers’ diets exhibited impairment of neurological and mental functioning that was correlated with the level of exposure (Jacobson and Jacobson 1996a and 1996b). This impairment occurred even though the mothers’ PCB levels were within the normal range (i.e., there were no extreme exposures).

Furthermore, recent experimental results show that synthetic chemicals (pesticides) that are mildly estrogenic by themselves—that is, they mimic the effect of estrogen on the hormone system—produce a much greater effect when acting in combination.  The researchers introduced a human estrogen receptor into yeast cells, then tested the estrogenic effects of four different chemicals, alone and in pairs. When the chemicals were applied in pairs, they elicited an estrogenic effect at concentrations between 160 and 1600 times smaller than the dose required to elicit a response by each chemical alone, thus indicating that these chemicals are much more potent in combination (Arnold, et al., 1996).  Even though the chemicals tested were pesticides, the dioxins, furans, and PCBs produced when tires are burned can disrupt hormone systems in similar ways. 

 

Assessment

Opponents to tire-burning focus on the resulting increases in some toxic emissions from burning tires and the effects of those chemicals, and may discount any reductions in other emissions.  They have access to, and rely on, emission data from test burns, and they use recent scientific evidence about the potentially damaging effects of toxic pollutants when arguing their case. 

Given their concern with dioxins and their critique of traditional risk assessment, opponents are not likely to be persuaded by arguments that the risks from increased toxic emissions are insignificant, and that they should respond to risk more rationally.  That strategy failed in the cases of nuclear power and incineration of hazardous waste.  We believe that a more fruitful policy response involves supporting research to reduce toxic emissions via improved control technology, process modification, and altered operating procedures.  Because several tests have shown reductions in some toxic emissions from burning tires, research should attempt to identify and create the conditions under which no toxic emissions increase.

II.C. REFERENCES

 

 

Angel, Bradley. Greenpeace, San Francisco, CA. Personal communication with S. I. Schwartz, June 14,             1996.

 

Arnold, Steven F., et al. “Synergistic Activation of Estrogen Receptors with Combinations of Environmental                 Chemicals.” Science, Vol. 272, (June 7, 1996), pp. 1489–1492.

 

Bateman, Brian. Bay Area Air Quality Management District. Personal communication with S. I. Schwartz,        June 14, 1996.

 

CAPCOA (California Air Pollution Control Officers Association).  Air Toxics “Hot Spots” Program:               Revised 1992 Risk Assessment Guidelines. (Place of publication not listed), 1993.

 

California Air Resources Board, California Environmental Protection Agency. Overview of the Air Toxics “Hot Spots” Information and Assessment Act. Sacramento, CA, (June 3, 1994).

 

California Integrated Waste Management Board, (CIWMB). Tires as a Fuel Supplement: Feasibility Study. Sacramento, CA, (1992).

 

California Portland Cement Company. Modify Pyroprocessor: Add Whole Tire Handling System and               Allow Use of Whole Tires as Supplementary Fuel to Kiln. Application to Kern County Air Pollution Control District, (March 28, 1995).

 

Carman, Neil J. Clean Air Programs Director, Sierra Club, Lone Star Chapter, Austin, TX. Letter to     Citizens for a Better Environment and Desert Citizens Coalition regarding California Portland Cement Co. Proposal to Burn TDF, (November 14, 1995).

 

-----. Personal communication with M. Lycan, July 12, 1996.

 

Carnot Technical Services, Inc., and Radian International, LLC, Tustin, CA. Kaiser Cement Corporation        TDF Demonstration Program. Volume I, Executive Summary, (April, 1996), pp. 1–15.

 

Flynn, Mary. Kern County Air Pollution Control Board. Personal communication with M. Lycan, July 25,        1995.

 

Franklin Associates, Ltd., and Robert L. Hershey. Market Development Study for Tires (draft). Prepared for   the Office of Solid Waste, U.S. Environmental Protection Agency, (August 30, 1989).

 

Gauff, Nate. Waste Management Engineer, California Integrated Waste Management Board, Sacramento,       CA. Personal communication with M. Madison, June 20, 1996.

 

Gonzalez, Narci. Stationary Sources Division, California Environmental Protection Agency, Sacramento,         CA. Personal communication with M. Lycan, July 19, 1995.

 

Hall, Douglas. Bay Area Air Quality Management District, San Francisco, CA. Personal communication          with S. I. Schwartz, June 14, 1996.

 

I-35 Corridor Cement Kiln Pollution Network. Consensus Statement of 15 citizens, environmental, and public health groups in Texas; available from Sierra Club, Lone Star Chapter, P.O. Box 1931, Austin, TX, (512) 477-8526 (fax). (July, 1996.)

 

Jacobson, Joseph L., and Sandra W. Jacobson, “Intellectual Impairment in Children Exposed to Polychlorinated Biphenyls in Utero.” New England Journal of Medicine, Vol. 335 No. 11 (September 12, 1996a), pp. 783–789.

 

-----. “Dose-Response in Perinatal Exposure to Polychlorinated Biphenyls (PCBs): The Michigan and North Carolina Cohort Studies.” Toxicology and Industrial Health, Vol. 12, Nos. 3/4 (1996b), pp. 435–445.

 

Keller, Bill. Loomis, CA. Personal communication with M. Madison, June 5, 1996.

 

Lindert, Lin. Market Development Status Report: Tires. California Integrated Waste Management Board, Sacramento, CA, (July, 1993), p. 27.

 

Proctor and Redfern, Ltd. A Review of Emissions Performance of Cement Kilns Using Tire-Derived                 Fuel. Don Mills, Ontario, Canada, (July, 1995), pp. 5, 16–23.

 

Rachel's Environment and Health Weekly, #470. Environmental Research Foundation, P.O. Box 5036, Annapolis, MD 21403; electronic copy available via ftp from ftp.std.com/periodicals/rachel and from gopher.std.com. November 30, 1995.

 

-----. #479. February 1, 1996.

 

-----. #499. June 20, 1996.

 

-----. #501. July 4, 1996.

 

Ricci, Paolo, and Lawrence F. Molton. “Health Risk Assessment: Science, Economics, and Law.” Annual       Review of Energy, Vol. 11, (1986), pp. 77–94.

 

RMC Lonestar Cement. Preliminary Evaluation and Proposal to Conduct Testing on the Use of Whole         Tires as a Supplementary Fuel in the Cement Manufacturing Process. Davenport, CA, (May 1, 1992),    pp. 6, 29.

 

Serumgard, John. “Scrap Tires in Cement Kilns.” Second Biennial Tire Recycling Conference, California          Integrated Waste Management Board, Sacramento, CA, (May 15, 1995).

 

-----. Chairman, Scrap Tire Management Council, Washington, DC. Personal communication with M.                Madison, February 16, 1996.

 

Scrap Tire Management Council. “Scrap Tire Use/Disposal Study.” (February, 1995), p. ii.

 

Silbergeld, Ellen. Testimony on the Health Risks of Dioxin. In: U.S. Congress, House Human Resources and Intergovernmental Relations Subcommittee of the Committee on Government Operations. Hearing: The Health Risks of Dioxin. 102nd Congress, 2nd session, June 10, 1992. Washington, DC.: GPO, (68-058 CC) (1993).

 

TL & Associates. California Tire Report. Vol. 2, No. 1, (January, 1996), p. 7.

 

U.S. Environmental Protection Agency, Office of Research and Development. External Review Draft,

        Health Assessment Document for 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and Related   Compounds. (Pub. No. EPA/600/BP-92/100), Washington, DC, (1993).