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Gossman Consulting, Inc

HWF NOTES©


Gossman Consulting, Inc.                                  August, 1994


REVIEW OF GUIDANCE ON TRIAL BURNS

David Constans

In the November 1993 HWF NOTES GCI reviewed EPA's draft memorandum on Implementation of Exposure Assessment Guidance for RCRA Hazardous Waste Combustion Facilities that document had been issued by the EPA in September 1993. In June 1994 the EPA issued Exposure Assessment Guidance For RCRA Hazardous Waste Combustion Facilities. A review of this document is the focus of this issue of HWF NOTES.

This document, Implementation Guidance for Conducting Indirect Exposure Analysis at RCRA Combustion Units, is a revision of the document sent out in September of 1993, and apparently supersedes that document. The risk assessment is to be performed by the Regional EPA or the State if authorized. Some states require the applicant to perform the risk analysis in which case the permit writer "...should be intimately involved in the planning and carrying out of the risk assessment and should be formally reviewing and approving the risk assessment protocols."

The permit writer is to determine the list of compounds the facility must sample for in the stack. The EPA offers similar guidance, as in the September document, regarding selection of PICs to be examined in the stack emissions. In Appendix A, attached to this document, the EPA has included two lists totalling 226 chemicals; 163 "Chemicals Recommended for Identification" and 63 "Chemicals for Potential Identification." The first list includes the ten BIF metals, selenium and nickel as well as specifically naming 15 of the PCDDs/PCDFs and PCBs as a group. The Appendix A list is derived from a number of sources within the EPA from various programs; it is certainly not representative of PIC data from tests on BIF units. The EPA devotes about two pages to defending this PIC list. There is additional guidance given in PIC selection that is repeated in more detail in Appendix B reviewed below.

As a way to account for unidentified compounds in the risk assessment the EPA proposes two options. In both cases the EPA assumes that the unidentified PICs must be similar in toxicity to the identified PICs, i.e. guilt by association. The difference between the two options is the degree of guilt. The first option increases the emission rate of each of the identified compounds by multiplying by the result of the concentration of total organic carbon divided by the concentration (carbon basis) of the identified compound. The second option assumes the unidentified organic compounds are carcinogenic and supplies a formula that adjusts the known carcinogens' emission rate upward. These adjusted emission rates would than be used in the risk assessment. No criteria are given to determine which option the permit writer should choose. No justification is given for the assumption that the unidentified compounds are in any way toxic.

It is worth noting here that not all organic compounds have the same toxicity. This is amply demonstrated in the calculation of the PCDD/PCDF TEQ values. The toxicity equivalence factors (TEF) range from 0 to 1, for the various dioxins and furans normally analyzed for in stack emissions. Interestingly the predominate factor is zero (10 out of 21 TEFs). The EPA options noted above calculates toxicity equivalence factors based solely on the inability to identify a compound. If the toxicity factors of certain dioxins and furans (all chemically related), often touted as the most toxic chemicals created, deserve TEFs as low as zero, why would unidentified compounds, possibly not even chemically related, be given toxicity equivalence factors based solely on their proportion in relation to the identified compounds they are merely associated with? No justification is given.

The permit writer is to evaluate whether compounds on the PIC list developed for the trial burn that are not detected during the sampling/analysis are "likely to pose a significant risk" at or near the detection limit. If so, the permit writer is to include those compounds at concentration values of one-half of the detection limit. GCI encourages the owner/operator to work very hard to keep the PIC list as short as possible, most especially if it is unlikely that a particular compound will be a PIC. The way this is structured, the applicant is penalized for what he can not identify equal to what he can and half as much for what is not there as for what is there.

The risk assessment is to include fugitive emissions from hazardous waste and combustion residues handling. This was previously included in the September document.

The remainder of this portion of the document is on conducting the indirect assessment based on the data supplied by the testing. GCI admittedly is not versed in risk assessment and can not adequately review this or Appendix C. Appendix C is a screening analysis for determining if a more rigorous risk analysis is required, this appendix is in excess of 130 pages. It is obvious however based on even GCI's limited experience that the risk assessment will over-estimate the risk. The risk assessment approach in conjunction with the aggressive selection of worst-worst case wastes, adjustment of PIC emission rates and the extreme operating conditions required during the trial burn, is virtually certain to produce some instances of "unacceptable risk."

Attachment B Guidance on Trial Burns

Review of Introductory Paragraphs

It is worth noting here that in the ancient document, the Preamble to BIF, specifically in Part Three, II, B, 3, a discussion is provided on PIC control through the Tier II HC/CO standard. The Science Advisory Board (SAB) had stated: "It is prudent to control PICs given the inability to show they do not pose a health risk because of limitations of sampling and analytical techniques and health and environmental impact assessment data and methodologies." The EPA Response: "The Agency agrees. Additional emissions testing cannot be used to determine if, in fact, PICs can pose significant risk because the sampling and analytical techniques are not available to identify the unknown compounds. Moreover, even if the techniques were available, health effects data are not likely to be available for the compounds so that the risk assessment could not be conducted." Later in the section the SAB states: "The risk assessment procedures are adequate, however, to show that the technology based HC limit of 20 ppmv appears to be protective of human health." EPA Response: "The Agency agrees." (Note that there were no modifying sentences following the response.) Still further along in the section the EPA discusses a health based approach to controlling the PICs then stated: "A number of commenters supported the health-based approach while several others pointed out that the approach was seriously flawed. EPA's Science Advisory Board reviewed the approach as discussed above and concluded the site-specific, health-based approach to controlling HC was not scientifically supportable." The approach proposed was similar to the method of determining the Tier IA metals emission limits. The EPA in the next paragraph stated: "Upon re-evaluation, EPA believes that basing the HC limit on a health based approach is not supportable and, thus, has not selected this approach for the final rule." This whole issue was discussed and analyzed for several years before being put into the final rule. Even then the decision was somewhat arbitrary, however, the selection of a HC/CO standard as a PIC control was at least quantifiable and enforceable.

The purpose of this document on trial burns is to provide guidance to the permit writer in setting trial burn test conditions that will provide data on PIC emissions for an indirect exposure risk assessment on PIC emissions. From this the permit writer is to set operating and other permit conditions. If the EPA could not support a health-based PIC emissions control standard for inclusion into BIF how can EPA now claim that there is a basis for pursuing a health based "indirect exposure risk assessment" for PICs that would lead to permit conditions? The EPA does not offer any data to support this new concern only stating: "...with respect to risk from indirect exposure, there is not sufficient information currently available to verify that the CO and HC emission limits...are sufficiently protective." It is interesting that the same insufficiency of evidence on one hand throws out a health-based standard for emission limits and on the other inserts a health-based risk assessment that would impose emission limits. Needless to say, EPA has changed direction again and offers no justification to account for the new direction.

The introductory paragraphs continue with a general discussion of EPA's concern and the general direction of this document. As in the September '93 document the BIF metals are of concern. In addition the EPA wants to expand metals determinations to include "data on metals which can be important for multi-pathway risk assessments (i.e. copper, aluminum, nickel, selenium and zinc)." The list of metals is footnoted with concern that some of these metals "may not have significant impact directly on the risk assessment, but may affect the formation of other toxic compounds such as dioxins/furans." No references are cited for these claims. Metals speciation, individual metal compounds versus the metal, is also discussed. This is not technically possible at this time, however the "...permit writer may consider adding metals speciations determinations to trial burns..." as methods become available. Evidently the EPA has forgotten that the RSDs and RACs assigned to the metals were based on "...the conservative assumption that soluble (i.e., bioavailable) metallic complexes are emitted, is assumed to protect health." (Preamble to BIF Part Three, III, A). It is highly unlikely, based on the data derived from feeding cattle CKD (this was reported in the CKD Report to Congress), that the metals compounds emitted from cement kilns are the extremely toxic varieties. Additionally TCLP testing has repeatedly illustrated the low solubility of the metals compounds in CKD. If such testing demonstrated that the particular metal complexes are as a whole less toxic than the assigned risk values, thereby allowing higher permit limits for metal inputs, the extra testing expense may be worth it. If however it is mere curiosity on the EPA's part and the existing risk values would be retained as "protective of human health" then the expense is not worth the trouble.

The last point made in these introductory paragraphs is that the permit writer is charged with determining that the test conditions are "representative of the permit conditions" and he "must have some assurance that the device is operated under good operating conditions." To accomplish this last item the permit writer "should use his experience and engineering judgement as well as documents such as ...CETRED." Does this mean that the permit writer must have experience and an engineering degree? Is CETRED an acceptable/defensible choice as a reference document knowing the number and extent of the errors it contains?

Review of Waste Feed Conditions

The facility is to use "real" "worst case" wastes during the testing. The method of deciding which reveal wastes begins with an exhaustive review by the permit writer of the "waste profile sheets" for the waste received at the facility, with the top ten constituents selected for each of five categories. The EPA devotes 4 pages to describing this selection process including formulas that rank constituents/wastes by quantity, RACs, RFDs, and bioaccumulation. The waste profile sheets are a poor source of this information, since they frequently contain estimates of quantities and constituents. Some facilities have constituent lists based on actual analysis and tonnage received which would be much more accurate and useful. This will be a long, tedious and technically questionable review process followed by a long negotiation process to decide what wastes are the "real" "worst case" wastes. Such wastes may not be available during the test period, or certain combinations of wastes may not be compatible, or may be physically difficult to handle.

If an insufficient amount of wastes containing "dioxin/furan precursor compounds" is not fed to the unit during the test, the permit writer may specify permit limits for such compounds. "Insufficient" is not defined. Precursor compounds are defined as, "such as chlorinated phenols and chlorinated aromatics." These same compounds "should ideally be present" in the POHC test as well. It may be advisable to add these compounds to the waste fuel.

During the testing "Batch charged wastes," usually drums, buckets, etc., are to be charged to the kiln in the largest container at the maximum rate, with waste containing the highest volatility, the maximum BTU per pound, and the highest halogen content (including the halogen in "auxiliary fuels" -a reference more applicable of incinerators than BIFs) allowed by the permit. Regardless of the type of waste the halogen content fed to the kiln must be the same for the low temperature PIC test and the high temperature PIC and metals tests. Various combinations of this requirement are conflicting. That is, the maximum input rate at maximum BTU per pound and/or volatility may not be possible. Compensating for this in order to conduct the trial burn would likely result in an operating limit at a lower mass input rate or lower heat content.

The metals: copper, iron, zinc, nickel and aluminum have been shown to catalyze PCDD/PCDF (and associated compounds) formation. This document proposes that waste streams be "doped" with copper chloride at a rate equal to 0.1-1.0 weight percent of total ash content. Such levels of copper may be a problem to some cement kilns, compromising product quality. The references cited are for incinerators. With the large amount of particulate present in cement kiln and aggregate kiln APCDs, this requirement should be unnecessary for these units.

Feed streams containing nitrogenated compounds at levels greater than 5% should conduct the low temperature PIC test with the highest level of nitrogenated compounds to determine the levels of PAHs in the stack gas. A HCN emissions test should also be conducted.

The document repeats the "difficult to atomize" viscous wastes concept seen in the earlier document. The concern is entrainment without complete combustion into the stack. This should be adequately dealt with in three ways in a cement kiln: 1) The CKD is routinely tested, 2) The CO/HC CEMs, and 3) The counter current flow in the kiln would bring large droplets/solids back into the combustion zone. Be warned that the permit writer may believe that there should be an upper viscosity limit on liquid HWF fed to the device.

Similarly, the EPA is concerned with soot formation and the subsequent formation of PCDD/PCDF and PAHs on the soot particles. The EPA is especially concerned with soot formation during the combustion of highly volatilized organic material in batch-fed or container fed wastes. "The trial burn test conditions for containerized waste should generally follow current guidance including consideration of waste volatility and container size." With all of the CKD present in cement kiln APC devices, the soot (if any) is a non-player.

The EPA recommends that the test be conducted with maximum chlorine input, maximum feed rates, etc., and for cement kilns with maximum hydrocarbon content (TOC) in the kiln raw feed. This is very difficult to achieve and even more difficult to control. The unit could easily exceed CO or THC limits. The EPA's use of the TOC test is decidedly questionable. The TOC method has been demonstrated to be a poor choice for use on this matrix (kiln raw feed). Lone Star Industries has submitted data to Region V documenting this problem. Doing a TOC on the raw feed will not necessarily predict what the THC in the stack will be, due to volatility, form, molecular weight, etc. of the organic constituents that make-up the TOC in the raw feed. This is an easy way for a facility to fail a test. Based on this guidance from EPA the permit writer may believe that it is necessary to establish a permit limit for TOC in raw feed.

Review of Development of Permitted Operating Conditions

For the minimum combustion chamber temperature test, the EPA recommends using waste with the maximum moisture content that would be "expected during the life of the permit." This may easily be a conflicting parameter with other operating conditions such as minimum P in a bag house as well as displace combustion air in a system where the gas velocity is limited.

The document discusses amount and distribution of combustion air. The low temperature POHC/PIC and the high temperature metals tests are to be run at the same gas velocity. The intent here is to demonstrate that the detention time is adequate at maximum gas velocity and that the APC device is adequate to control particulate emissions at maximum gas velocity. Presumably if the gas velocity values for these two conditions are different the lower velocity would become the permit value. Air distribution is another concern the EPA has. In incinerators air is introduced into the combustion device in a number of places to induce turbulence as well as to supply oxygen for combustion. This is necessary to prevent localized low oxygen pockets or other effects of inadequate mixing of air and fuel. Due to the nature of the cement making process, this should not be an issue for cement kilns. However, in recent trial burn plan NODs, the permit writers obviously did not understand the differences between one technology and another. Consequently, cement kiln operators may have to deal with a permit writer that wishes to set a higher O2 limit and/or minimum primary air input or possibly a minimum ID fan speed (or amperage).

As noted earlier, the PIC testing is to set an operating condition of a maximum thermal input limit in addition to all the rest of the operating limits. EPA acknowledges that "it may be difficult to simultaneously achieve a maximum thermal input rate and minimum combustion temperature for the POHC test. Adjustments to the excess air rates and waste moisture contents can help mitigate the conflicts between these two parameters." Of course the stack O2 would than be higher and/or the moisture content would be higher. Will this higher O2 concentration be pegged as the operating limit? Will the extra water create problems with the operation? It is obvious that the cement kiln cannot do all of these things simultaneously.

EPA has added a requirement of determining a particulate size distribution of the stack emissions. Ideally it would like this data to be acquired as site specific ambient monitoring as opposed to stack data. Be aware that site specific ambient monitoring would include more than what is discharged out of the stack. It's also more expensive.

A Trial Burn Example Test Matrix is attached to the end of Appendix B. These kind of things are always used as "check lists" by permit writers even if an item is inappropriately or incorrectly listed. As an example, copper chloride is noted under the column "Permit Condition (Y/N)" as "Y as appl." Frequently the permit writer does not see the "as appl." Similarly the TOC of kiln feed is listed "N?". Does this mean it is the permit writer's decision? What criteria does he use? Under the APCD section of this matrix the permit writer is to establish a permit limit for P. This is fine for bag houses (even though everyone knows that minimum P in a bag house may indicate a broken bag), but it is inappropriate for ESPs. Similarly, the "rapping or cleaning rate" is to be set at maximum during the metals test; not normal. This is the first time GCI has seen this, nor is it listed anywhere else in the document.

Concluding Comments on the Indirect Assessment Guidance

The EPA is using the "omnibus" authority to implement the Combustion Strategy set out by Ms. Browner in May 1993. This is effectively stated in the first paragraph under the heading "Authority" on page B-2 of Appendix B. "The Combustion Strategy provides no new authority for requiring monitoring and permit requirements. Permit writers should use the authority provided under...often called the "omnibus" authority..."

In writing the BIF regulations, just a few years ago, the EPA dealt with risk assessment procedures. Section III of Part Three of the Preamble to BIF is entitled "Risk Assessment Procedures." Subsection (C)(1) states:

"1. Indirect Exposure. During the proposal stages of these regulations, a few commenters recommended incorporating indirect exposure pathways into the risk assessment process. Indirect exposure is defined, in these regulations, as any exposure pathway other than direct inhalation of emissions from a boiler or industrial furnace. One commenter maintained that emissions such as metals, chlorinated dioxins, and furans would be environmentally persistent and able to enter the food chain after the deposition on the ground (including crops, pasture land, surface waters). Consequently, the commenter argued that indirect exposures should be factored into the risk assessment.

EPA recognizes that the contribution of indirect pathways may be significant. However, the Agency believes that other conservative procedures, such as apportioning 75% of exposures to either indirect pathways or other emissions sources (that can contribute to background levels) in the calculation of RACs, will help to offset the contribution of indirect pathways. Another significant source of conservatism, offsetting the contribution of indirect pathways, is represented by the inherent uncertainty, and consequent conservatism, in the models used to estimate unit risk values. Use of the MEI in the Screening Limits procedure comprises yet another conservative element in the risk assessment process which offset direct estimation of indirect pathway exposure. Therefore, the Agency has not modified the risk assessment process to address indirect pathways."

At the end of Part Three, Section III, the EPA concludes with this paragraph:

"If the facility fails to meet the screening criteria, the option of site-specific risk assessment is still available. For site-specific risk assessment, more realistic and less conservative assumptions may be incorporated, reflecting actual site or facility conditions."

There is no point in GCI arguing that an indirect risk assessment is unneeded for BIF units. The EPA did that very well in the Preamble to BIF in support of the BIF regulations as they were promulgated. In fact based on these comments the insistence on conducting a proper indirect risk assessment should be viewed as an activity that is less protective of human health than the BIF regulations as promulgated. In every case the BIF units have met the requirements of the BIF regulations. For the EPA to now maintain that the BIF regulations are inadequate to protect human health they must first refute their own words in the BIF Preamble. To persist in an indirect risk assessment of BIF units when the Preamble to BIF has made it clear that these regulations were specifically designed to preclude that necessity (that is BIF is more protective of human health than permit conditions arrived at through a proper risk assessment) is a clear abuse of the "omnibus" authority. There may be cause here for actions against permit writers who demonstrate such abuse.

The EPA is forced into assigning the permit writer to initiate this policy. EPA is using the "omnibus" authority which "gives the permit writer the authority to apply additional permit conditions as necessary to adequately protect human health."

Given that the EPA has not demonstrated that the human health is endangered, only that there is no proof that human health is not in danger, this call for protection is decidedly thin. Placing the permit writer in this position is at best a questionable management practice. The permit writers have the least experience of any of the EPA staff, especially in a field that is demonstratably as complex as risk assessment. The possibility of executing a permit in less than two years is remote.