Presentation of the New Mexico Environment Department (NMED)


Mr. Walker received a B. S. in Geological Engineering, University of Missouri-Rolla. Mr. Walker is a registered professional engineer. He has over 15 years of expertise in RCRA permitting, emphasizing facility engineering and corrective action. Mr. Walker has conducted RCRA Part B permit review and analyses, RCRA Closure and Post-Closure Plan reviews, and RCRA Facility Investigation workplans and report reviews for numerous facilities, and has managed the implementation and oversight of all phases of field activities related to these reviews. Mr. Walker currently manages several large-scale RCRA Corrective Action projects. He has presented Corrective Action training to several EPA Regions. With respect to WIPP, Mr. Walker has supported the EPA Office of Solid Waste (OSW) on both the WIPP Test and Disposal Phase No Migration Variance Petitions, the EPA Office of Radiation and Indoor Air (ORIA) on the WIPP Compliance Certification Application review, and the NMED on the WIPP Test Phase and Disposal Phase permits applications.

Currently, Mr. Walker is a member of the NMED WIPP Support Program for Techlaw. Techlaw is the technical consultant for the NMED on the Applicant's Permit.

The purpose of the Confirmatory VOC Monitoring Program is to measure the concentrations of 9 VOCs of concern that could be released into the air from the operations at WIPP. [The 9 VOCs of concern are carbon tetrachloride; chlorobenzene; chloroform; 1, 1-dichloroethene; 1, 2-dichloroethane; methylene chloride; 1, 1 ,2, 2-tetrachloroethane; toluene; and 1, 1, 1-trichloroethane.]

Thirty days after the final Permit is issued, the Confirmatory VOC Monitoring Program must start. The Program will continue through the operational phase. Typically VOCs are cleaning solvents or carrier chemicals for compounds like paint. VOCs volatilize easily, allowing for rapid drying.

The total individual risk due to VOC exposure should not exceed certain acceptable risk levels. The NMED calculated the risk for both carcinogenic and non-carcinogenic VOCs for 2 receptors: a resident who lives at the site boundary and a WIPP non-waste surface worker.

The carcinogenic total individual excess cancer risk should not exceed 1 x 10-6 [0.000001] for the resident, and 1 x 10-5 [0.00001] for the non-waste surface worker. Non-carcinogenic acceptable risk level for both is the same and should not exceed 1.0 according to the hazard index.

The source of the VOC gases in the waste drums will probably be rags, soils, etc. contaminated by cleaning solvents or carrier chemicals for compounds like paint. The contaminants evaporate and become VOCs. The VOCs concentrate in the headspace of the drum.

VOCs get entrained into the air in open and closed rooms. Open rooms have mine ventilation airflow. Most of the time workers are upstream of the airflow. VOCs in the open rooms will also flow out into the exhaust drift. In closed rooms there will be no ventilation. The pressure of the VOCs will equalize to that of the average headspace gases in the closed room. The "creep" of the salt will reduce the volume of the closed room, thus increasing the pressure. This will lead to an "effective" gas generation rate. In the closed rooms, the pressure will push the gases through the ventilation barriers, and eventually the gases will end up in the exhaust drift. Closed Panels are similar to closed rooms. The VOC concentrations will equalize to the average headspace gases in the whole panel. Again, the pressure will push the gases through the panel closure systems. Gases from the Closed Panels will enter into the E-300 or Exhaust Drift (corridor).

The average measured gas concentration limits in all of the containers in the room or panel are established through risk assessment. For the maximally exposed individual, the maximum concentrations should not exceed the acceptable risks described above. Worker risk is one order of magnitude greater than public risk because the NMED balanced occupational exposure of employees with the fact that workers during normal operations are covered under Occupational Safety and Health Administration (OSHA) and Mining Safety and Health Administration (MSHA) regulations. Usually occupational exposure is not taken into consideration under RCRA.

The non-waste surface workers would get the greatest chronic dose because they could be in the vicinity of the exhaust shaft outlet. The NMED may also include employees at greater risk because of health, age, etc. than the standards set by OSHA. [Such standards are usually based on the results of studies of young, healthy, white, male medical students.] However, the potential of underground workers to get a large acute dose during a roof-fall cannot be discounted. The NMED used equations, assumptions and models from Appendix D9 of the 6.3 revision of the Application to calculate potential doses from a roof-fall. However, the NMED lowered the DOE's assumed mine ventilation rate to better replicate actual conditions and changed the reference for 1, 1, 1-trichloroethylene.

Limitations must be set for total risk for all carcinogenic and non-carcinogenic VOCs. Once the risk is set, back-calculations reveal how high the limits could be without exceeding the environmental performance levels. The initial set of concentration limits was changed in the second draft Permit.

1. Chlorobenzene and tuolene: The initial limits had to be reduced to ensure a closed room limit would not exceed lower explosive limits (LEL). A roof-fall, a spark, or static electricity could cause an explosion or fire. LELs are set for 6 of the 9 VOCs.

2. Methylene chloride: The limit was raised in the second draft Permit. The first draft Permit had set the concentration limits below the risk and LEL limits.

3. 1, 1, 1-trichloroethylene and 1, 1-dichloroethylene: The first draft Permit [?] set the concentration below the limits to ensure that the IDLH (Immediately Dangerous to Life and Health) limits would not be exceeded in an open room under a roof fall scenario. The DOE's Application said the potential for a roof-fall in Panel 1 prior to or during waste emplacement was 1/100 to 1/1000 [1 x 10 2 or 1 x 10 3].

In the open room roof-fall scenario, the biggest problem is the roof falling onto the waste drums resulting in crushed and broken waste drums. This scenario would render the assumption that VOCs diffuse through filter vents invalid. However, the increased concentration of VOCs under this scenario would not last long because the fresh air in the ventilation system would flush them out.

The VOC concentrations in the closed room air are the averages of all the drum headspace gases. Ninety percent will flow into the void of the roof fall. Ten percent will blow through the ventilation barriers--5% on each side, so a worker would get a 5% dose. The release of VOCs from a closed room roof-fall is the limiting case. This is the reasoning behind why the limits for 1,1,1 trichloroethylene were lowered.

An error was made in worker exposure calculations, and the concentration for carbon tetrachloride went from long-term risk to the IDLH limit which is why the limit was reduced (though not by much). Limits for all are based on apportioning the carcinogenic and non-carcinogenic risks equally to keep from exceeding all risk limits.

There are no specific RCRA regulations addressing this. The groundwater compliance analysis program seemed the most similar, since both regulate known releases from miscellaneous units to the environment. There are 2 monitoring locations (stations), Station VOC A and Station VOC B. Both will be in the E-300 exhaust ventilation drift. Station VOC A stays in the same place. It is upstream of Panel 1, and its location changes in such a way that it is always upstream of the active panel. It monitors the background VOCs.

The monitoring program will operate during the entire Operational Phase. Samples are taken twice a week and limits are based on the long-term risk. Minor changes over the short term will not cause problems. Several assumptions are used when calculating risks. The gas generation rate in a closed room is a key assumption. There are other assumptions, too. Without a continuous monitoring program, you could not comply with the limitations in the Permit. The monitoring program confirms that the assumptions used are correct.

Samples are analyzed using gas chromatography mass spectrometry (GCMS) and are analyzed at EPA contract labs. Grab samples and integrated samples can be taken over time. The contract labs allow the detection of low levels of VOCs.

Certain conditions were assumed when the concentration limits were set. These assumptions are:
1. The ventilation was assumed to be 260,000 standard cubic feet/minute;
2. The ventilation at Station VOC A in the E-300 Drift was assumed to be 130,000 standard cubic feet/minute; and
3. The VOC concentrations at Station VOC B are subtracted from those at Station VOC A.

This data evaluation and reporting process yields the VOC emission concentrations from the Hazardous Waste Disposal Units (HWDUs) themselves. Atypical conditions are expected to occur and do not necessarily indicate there is a problem. But changes in mine ventilation rates, for instance, can affect the calculations. A much higher ventilation rate can dilute the concentrations. The overall ventilation rate, the rate in the E-300 drift, as well as the temperature and pressure must be measured. The data must be normalized to standard conditions. There is an equation in Appendix N of the Draft Permit that will be applied to data gathered from Station VOC A and Station VOC B. The normalized concentrations are taken as Station VOC B and subtracted from the normalized concentrations from Station VOC A. This calculation reveals the VOC emissions coming from the HWDUs.

These concentrations are compared to the concentration of concern, which is calculated to limits at the top of the exhaust shaft and is also related to Station VOC A concentrations. When the concentration limits are set, the assumptions are that there are 9 closed panels full of waste and 1 open panel full of waste and that the headspace gas concentrations in each container are equal to the concentration limits found in Table IV.D.1. You then take the exhaust shaft calculation and back-calculate to the Station VOC A concentrations of concern.

If VOC emissions exceed the concentrations of concern, the DOE must notify the NMED within 5 days. If the VOC emissions exceed the concentrations of concern, a running annual average (the average for the previous 12 months) is calculated. If the running annual average exceeds the concentration of concern once disposal has ceased, the room is closed and ventilation barriers are installed in the room. If the running annual average exceeds the concentration of concern for 6 months, the entire panel is closed, and the panel closure system is then installed.


There are no specific OSHA standards for waste and non-waste surface workers, but the standards are specific for hazardous waste workers. OSHA standards are not necessarily the only standards that apply.

The assumption that the roof will fall even with roof supports is conservative. An extra margin of safety beyond conservative assumptions is not necessary.

The non-waste surface worker is the human receptor with the largest potential chronic dose. There are no occupied buildings within 120 feet from the exhaust shaft outlet, so using that location is a conservative assumption. This is based on air modeling, which determined that the highest air dispersion factor was at the location where the VOCs are least diluted.

Mr. Walker was not aware that all workers at WIPP have to pass a fitness evaluation.

The NMED wants language in the Permit to require the DOE to require hourly reporting of ventilation rates. This is a new condition and is not included in the revised draft Permit now. This condition addresses comments by the DOE to the effect that they want more flexibility for the mine ventilation rate. It is possible that reporting only changes instead of the hourly log might be sufficient and the NMED concurs that there is a need for flexibility here. But there is not enough information in the Application on how the DOE would measure and record the ventilation rate.

The revised draft Permit does not prohibit non-workers from being underground or on the surface. Exposures for non-workers (visitors) are not included in the draft permit and they are not included in the risk assessment. If certain OSHA and MSHA requirements that apply to WIPP are changed, the revised draft Permit requirements do not necessarily change too. The concentration limits, especially for the underground workers, are based on not exceeding the Immediately Dangerous to Life and Health (IDLH) limits, which is a National Institute of Occupational Safety and Health (NIOSH) measurement.

In the open room roof-collapse scenario, the assumption is that 21 drums will fall and breach. There have not been any studies to determine how many drums would actually be breached. Appendix D-9, which refers to the 1995 Safety Analysis Report, is the basis for the 21-drum assumption. In an open room there could actually be up to 11,000 drums. The roof-fall scenarios also assume that backfill will be used.

Another assumption is that each drum will be vented. However, there are no studies on how often vents fail to function normally. If a drum is visible and the vent is clogged, the drum would appear to be bulging. But most drums will not be visible in the underground due to stacking and the lack of aisle space. Mr. Walker would not be surprised to find out that there have been occasions when drum vents have failed to work or were blocked.

In an open room roof-fall containing waste drums, hazardous as well as radioactive gases and particles would be released. In a closed room roof-fall, however, Mr. Walker is not as convinced that a non-gaseous release would occur due to the ventilation barrier. The waste drums in a closed room are assumed to be breached already.

The test phase Permit (1993) required supplementary roof supports, but the revised draft Permit does not. The roof supports were necessary for the test phase so that the rooms would remain open.

The VOC risk at the Land Withdrawal Act boundary should be 1 part per million. Emissions from WIPP would be both radioactive and VOCs. The radioactive component of that release would come under a different set of regulations. Any radioactive exposures to the boundary resident are in addition to what the NMED has calculated. The NMED did not consider the carcinogenic risk from the radioactive releases for the boundary resident.

In order to account for background concentrations of hazardous constituents, the EPA has set acceptable limits for total additive exposures to individual compounds that are targets. The rates are set at conservative limits already (1 x 10-6). The limits account for all sources to which the receptor might be exposed. However, the cumulative and possible synergistic effects of radioactive exposures are not included in these total additive exposure limits.

The underground waste workers are not the limiting case for long-term exposure. It is assumed that the underground waste workers are downstream for only 33 hours/year. The non-waste surface workers are assumed to be downstream from the exhaust air from the WIPP underground for 1,920 hours/year. This is not a conservative assessment, but it is appropriate. A more detailed explanation of the rationalization for this will be given in reply to the comments later. Also, no long-term risk assessment was done for the underground worker because the OSHA standards cover this worker during normal operations.

The NMED did a deterministic risk assessment analysis, but not a probabilistic risk assessment analysis. A roof-fall was assumed to occur and the RCRA consequences were analyzed. A one in one hundred (1/100) chance of a roof-fall is a high probability. However, the risk assessment was based on assumptions for long term releases and effects. A roof-fall would increase VOC concentrations, but this would not be a problem over the long term. The NMED used the assumptions in Attachment 1 of Appendix D-9 of the DOE's Application, including the assumptions about the total dynamic loading on the drums and the type of drum used. However, the robustness of the drums is only a factor in an open room because, in a closed room it is assumed that the VOCs are already equalized to the headspace concentrations of the drums. The NMED did not take into account the irregularities of the salt and the hundreds of roof bolts supporting the roof. It was assumed that there would be no breaching of containers behind the face of the waste stack. It is possible that up to 60 waste drums could be breached and the performance standard could still be met. Beyond that, it would be necessary to reanalyze. Appendix D-9 of the DOE's Application also assumes the waste is arranged in 7-packs, stacked three high and does not take into account a different container, such as a standard waste box in the analyses. [A 7-pack is a circular arrangement of 6 drums around a center drum.]

Bulging drums are not taken into account in the accident scenarios. Out of 11,000 drums arranged in 7-packs, it would be impossible to see which ones are bulging. [It is estimated that there will be 11,000 waste drums in each room.] There is no requirement in the Permit to inspect the waste drums once they are emplaced. Scenarios in which either the ventilation bulkheads or the ventilation barriers are crushed by roof-falls have not been considered.

The overall purpose of the VOC monitoring program is to determine if the assumptions in the risk assessment are correct. If the assumptions change, the limits could change also.

Volatile radioactive off-gassings are not considered in the calculations because such off-gassings are not regulated by RCRA. The VOC lower explosive limits (LEL) are based on hazardous constituents in a closed room and on another set of regulations relating to the potential for fire and explosion in the underground.

A roof-fall accident leading to a short-term increase in VOC emissions is not likely to have an acute effect at the ground surface, though this accident was not analyzed. VOCs will be diluted once they exit the exhaust shaft. There will not be any aboveground VOC monitoring.

VOC samples are analyzed at the WIPP on-site lab and or at a suitable contract lab. If the on-site lab is used, duplicate samples from each station will be collected and 10% of those samples will also be analyzed at an off-site lab.

Workers do not use any masks or breathing apparatus. This is an OSHA issue.

The NMED never calculated how many roof-falls there could be during the life of the Permit. Effects are calculated only for a single short-term event. The NMED is considering a re-evaluation of the number of drums that could be breached in an open room roof-fall since there are 11,000 drums in a room. All the calculations are based on theoretical modeling, not on experiments based on the actual conditions at WIPP.

The effects of particulate hazardous metals are not addressed in any of the calculations. If waste drums were burning and mercury (and possibly lead) vapors were generated, these vapors would not be monitored.

If a room had to be closed because the VOC concentrations had exceeded the running annual average and a new active room was opened, a situation could occur where the new room would also exceed the running annual average. It is unclear in the revised draft Permit, if during the 6-month period of potential violation of the running annual average that could lead to the closure of a Panel, how a succession of rooms might have to be closed.

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