OPINION
This is an appeal from the action of the Environmental Improvement Board (Board) *402denying a variance from an air quality control regulation.
The appellant has operated a sawmill at Española, New Mexico, since the early 1960’s. At the time the plant has constructed a wigwam incinerator was installed to burn all of the wood waste generated by the operation, approximately 247,000 cubic yards. Beginning in 1966 appellant began to investigate methods of utilizing this wood-waste. Since that time appellant has entered into contracts with various firms for the sale of approximately 93% of this waste. The remaining 7% is incinerated. However, because the incinerator was designed to burn a much larger volume of waste the incineration of the remaining waste results in smoke having an opacity in excess of 20%. In 1975 and again in 1977 and 1978, the appellant and appellee entered into agreements entitled “assurance of discontinuance.” The essence of these were that appellant was endeavoring to sell or utilize all*of the woodwaste and in the interim it might be in violation of air quality control regulation 402(A); that appellant would continue to use its best efforts to utilize all of the wood refuse and also seek to minimize the capacity of the omissions.
On February 8, 1979, appellant filed a petition for variance of Air Quality Control Regulation 402(A). A public hearing was held on June 28, 1979. At its meeting of October 12, 1979, the appellee denied appellant’s petition citing the following reasons for its decision:
(1) There was a great deal of community objection to emissions from the Española facility.
(2) The Board has been very patient with Duke City over the years.
(3) Although Duke City has made strides toward solving the woodwaste problem, the hearing record does not support the variance petition.
(4) The record shows that other alternatives are available.
The pertinent parts of Regulation 402(A) read as follows:
402. Woodwaste Burners [Adopted January 10, 1975] A. After May 1, 1975, except as provided in Subsection A.1, A.2, Section E and Section G, no person owning or operating a woodwaste burner shall permit cause, suffer or allow emissions from the woodwaste burner to equal or exceed an opacity of 20 per cent; and no person owning or operating a woodwaste burner which operates during night time hours shall permit the temperature of the woodwaste burner exhaust gases to be lower than 750 degrees F. during night time hours unless the owner or operator can demonstrate, to the satisfaction of the department, that a lower temperature can achieve an opacity of 20 per cent or better.
We remand for further consideration and proceedings.
There are certain preliminary matters which must be stated in order to view this matter in proper perspective. First, the hearing which developed the evidence upon which the appellee made its decision was quasi-judicial in nature.
“[Q]uasi-judicial is a term applied to administrative boards or officers empowered to investigate facts, weigh evidence, draw conclusions as a basis for official actions, and exercise discretion of judicial nature.” Thompson v. Amis, 493 P.2d 1259, 208 Kan. 658 (1972).
Second, the appellant had the burden of proving its entitlement to a variance.
“[T]he courts have uniformly imposed on administrative agencies the customary common-law rule that the moving party has the burden of proof.” International Min. & C. Corp. v. New Mexico P. S. Com’n, 81 N.M. 280, 466 P.2d 557 (1970).
However, it should be noted that in judicial and quasi-judicial proceedings:
“ ‘Burden of Proof’ is a term which describes two different concepts, (1) the burden of persuasion, which under the traditional view never shifts from one party to the other, at any stage of the proceedings, and (2) the burden of going forward with the evidence, which may shift back and forth between the parties as the trial progresses.” Ambrose v. *403 Wheatley, 321 F.Supp. 1220 (D.C.Del. 1971).
It has long been recognized that “proof” is an ambiguous word, and that any “burden of proof” has as its elements a burden of production or going forward and a burden of persuasion. It is said that although a plaintiff always has the burden of persuasion, which never shifts, he may produce sufficient evidence that his opponent’s failure to adduce contradictory proof either may lead to a decision for plaintiff, or must lead to such a ruling. Willingham v. Secretary of Health, Education and Welf., 2,11 F.Supp. 1254 (D.C., S.D.Fla.1974).
Once the party who bears the burden of proof has made a prima facie showing the burden of going forward with the evidence shifts to the opposing party. Goodman v. Brock, 83 N.M. 789, 498 P.2d 676 (1972).
By prima facie showing is meant such evidence as is sufficient in law to raise a presumption of fact or establish the fact in question unless rebutted. Goodman v. Brock, supra.
Section 74-2-8(A), N.M.S.A.1978, lists the criteria which must be considered in granting or denying variances:
The board may grant an individual variance from the limitations prescribed under the Air Quality Control Act, any regulation of the board, or any permit condition whenever it is found, upon presentation of adequate proof, that compliance with any part of that act, any regulation of the board, or any permit condition will result in an arbitrary and unreasonable taking of property or will impose an undue economic burden upon any lawful business, occupation or activity, and that the granting of the variance will not result in a condition injurious to health or safety.
Section 74-2-2(B), N.M.S.A.1978:
B. “air pollution” means the emission, except as such emission occurs in nature, into the outdoor atmosphere of one or more air contaminants in such quantities and duration as may with reasonable probability injure human health, animal or plant life, or as may unreasonably interfere with the public welfare, visibility or the reasonable use of property.
Air Quality Control Regulation 401(J)(2):
“opacity” means the degree to which emissions reduce the transmission of light and obscure the view of an object in the background; * * *
Air Quality Control Regulation 100(Z):
“smoke” means small gas-borne particles resulting from incomplete combustion, consisting predominantly, but not exclusively, of carbon, soot and combustible material; * * *
A summary of appellant’s evidence is as follows: Appellant’s sawmill is located on a 60 acre tract leased from the Pueblo of San Juan. The lease contains this specific provision: “waste materials, including sawdust, shall be burned or otherwise disposed of as they accumulate * * * and unreasonable piles of waste material shall not accumulate on the premises.” Appellant employs 94 people at its Española plant and the annual payroll is approximately $1,125,-000. When constructed, the “wigwam” burner cost in excess of $100,000.00. When the State air pollution standards were enacted appellant spent between $30,000 and $40,000 in modifying this burner to improve its efficiency and cut down on the amount of smoke produced. Since the early 1960’s it has been the policy of appellant to try and utilize, as much as possible, of the waste material produced by the plant. Currently appellant is utilizing approximately 97% of the waste materials. In order to do this appellant has entered into several contracts obligating itself to deliver all of the sawdust, green sawdust, wood chips and bark produced by the plant. Appellant’s staff engineer studied the cost and problems involved in landfill of wood waste and came to the conclusion that it was a short term expedient with serious long term consequences because of the indefinite and continuous possibility of fire and the difficulty in extinguishing such a fire. Since appellant is presently burning about 75 cubic *404yards of waste per day it would take between 10 and 12 truck loads to haul it to a landfill which entails the cost of the trucks and drivers plus the pollution produced by the trucks. Appellant asked the City Manager if it could use the city landfill for disposal of the waste that was not incinerated and was told, that on the advice of Mr. Ray Baca of the Environmental Improvement Division, it could not. Mr. Baca had written the City Manager that they should refuse such a request because of the volume of the waste and because it “may cause a major fire problem.” The capacity of a sanitary landfill is between 6,000 and 10,000 cubic yards of debris per acre. At 75 cubic yards of wood waste per day the total would be about 18,000 cubic yards per year which translates into between 2yh and 3 acres of land per year to dispose of it. Appellant’s officials testified that even though they were accumulating the wood waste in the incinerator and burning approximately once or twice a week it was not possible to remain within the 20% opacity. The only alternatives were to build several incinerators with varying capacities or to close the mill for several months out of every year or to close it completely, all of which would entail a considerable financial sacrifice.
The principal witness for the Board was Mr. David J. Duran, Program Manager for the Enforcement Section of the Air Quality Control Section of the Environmental Improvement Division. He testified that on a visit to appellant’s mill on June 18, 1979, about 80 to 90 percent of the material in the incinerator were slabs which he felt could be utilized, and if the slabs were taken out the remaining refuse would be of such a small quantity that it would be feasible to landfill it. When asked where this could be landfilled, he said, “this could possibly be done within the plant boundaries or possibly taken to the Española landfill.” It was his opinion that slabs could be taken out after the mill operations had ceased for the day. The largest part of these slabs would have to be cut and after being cut they could be bundled and sold for firewood. All of this assumed a normal functioning of the mill without a breakdown in anyone of the systems. It was also his opinion that incineration should be limited to periods of equipment breakdowns. He said the Environmental Improvement Division had supported the appellant in its efforts towards full utilization of all the wood waste.
On cross-examination he was asked if he had investigated to determine how many men it would take to remove the slabs from the incinerator. His answer was: “Well, again, I don’t have the specific information. Again, I believe that burden would be on the company to show why it wouldn’t be feasible.” When asked if he had any idea how much it would cost in terms of equipment or man hours, he replied: “No, I don’t — it doesn’t appear that it would take too many people to go through that material * * He was asked if he disputed appellant’s evidence that there was no room to conduct a landfill operation on the 60 acre mill site, he replied: “I have not investigated that particular aspect in full as far as the facilities available. Perhaps, there are facilities available nearby that could be used.” He was also asked if he disputed appellant’s evidence that their lease with the Pueblo of San Juan contained a provision that prohibited a landfill operation, his answer was: “Well, I know that that can be renegotiated or at least that it would be approached on that basis.” He was then asked: “You don’t know whether or not it could? You have not talked to' the San Juan Pueblo or the Bureau of Indian Affairs agent about it?” His answer, “No, I have not.”
Section 74-2-8, supra, provides that if an applicant has shown adequate proof of “arbitrary and unreasonable taking of property” or “undue economic burden,” the only reason permitted for refusing such a request would be that the granting of the variance would “result in a condition injurious to [human] health or safety.” It is our opinion that appellant made a prima facie showing of undue economic burden. The only evidence controverting that of appellant’s on this question was that of Mr. Du*405ran. We have quoted at length from his testimony to show that it consisted almost entirely of surmise and conjecture. “If the factual foundation for an opinion is insufficient it is nothing more than conjecture.” Hegtvedt v. Prybil, 223 N.W.2d 186 (Iowa 1974). Consequently, this testimony did nothing to rebut appellant’s showing of undue economic burden.
This brings us then to the second requirement, that the granting of the variance will not result in a condition injurious to health or safety. The appellant’s engineer testified that he knew of no studies showing that wood smoke was injurious to human health. The record shows that there were 7 written complaints received by the Board’s Española office: (1) “creating tremendous amount of smoke which threatens my health”; (2) “I feel this pollution is unnecessary. Scrap wood could be sold to the poor people in this area also particle board could be made instead of polluting”; (3) “too much pollution in the Valley”; (4) “Too much smoke, it’s hurting the air we all breath”; (5) “smoking hazards to my health”; (6) “Too much smoke”; and (7) “Too much smoke.” Mr. Ray Baca, the supervisor and environmentalist for the Española office, testified that he had received other complaints but had not written them down. Mrs. Jeanne C. Olby, Chairman of the Española Chapter of New Mexico Citizens for Clean Air and Water, wrote to the Board, in part, as follows: “the emissions from Duke City’s woodwaste burners have caused the people living in the vicinity to suffer poor visibility conditions, inconvenience (laundry cannot be hung on outside lines as it becomes covered with wood ash) and discomfort.” Ms. Jean Browman, Acting Chairman of the Los Alamos Chapter of New Mexico Citizens for Clean Air and Water wrote to the Board, in part, as follows: “From our inception [1969], air pollution from woodwaste burners in the Rio Grande Valley has been a problem of continuing concern to the members of the Los Alamos Chapter. This pollution is often especially apparent in the morning when it hangs in the air in thick layers or bands after night long emissions in the still night air with little mixing. The woodwaste pollution is one of the two or three continuing problems most often complained of by our members to Chapter Officials and it is one of the specific problems most often mentioned as a reason for joining the Chapter.” As can be seen, these were lay opinions without authoritative support of any kind.
“The general rule is ‘that witnesses must testify to facts, and not to opinions, and that whenever the question to be determined is the result of the common experience of all men of ordinary education, or is to be inferred from particular facts, the inference is to be drawn by the jury, and not by the witness.’ ” Burch v. Valley Motor Lines, Inc., 179 P.2d 47, 78 Cal. App.2d 834 (1947).
The effect of this second requirement of § 74-2-8, supra, is to impose the duty of proving a negative on the applicant for a variance. The courts have recognized the difficulty of such a task and ruled accordingly.
“[A] party is not required to make plenary proof of a negative averment. It is enough that he introduces such evidence as, in the absence of counter testimony, will afford reasonable ground for presuming the allegation is true; and when this is done the onus probandi will be thrown on his adversary.” Shumak v. Shumak, 332 N.E.2d 177, 30 Ill.App.3d 188 (1975).
“Evidence which renders the existence of the negative probable may be sufficient in the absence of proof to the contrary. Jones on Evidence, § 178. * * * ‘Full and conclusive proof, however, when a party has the burden of proving a negative, is not required, but even vague proof, or such as renders the existence of the negative probable, is in some cases sufficient to change the burden to the other party."' In re Chicago Rys. Co., 175 F.2d 282 (7th Cir. 1949).
“Where the burden of proof of a negative fact normally rests on one party, but the other party has peculiar knowledge or control of the evidence as to such matter, the burden rests on the látter to produce *406such evidence, and failing, the negative will be presumed to have been established.” Allstate Finance Corporation v. Zimmerman, 330 F.2d 740 (5th Cir. 1964).
The words “opacity of 20 per cent” as used in Regulation 402, and the word “smoke” as used in § 74-2-2, supra, in and of themselves indicate nothing as to whether the air is so polluted as to be “injurious to health or safety.” Smoke, in a given situation, may be composed of elements which at a given density or opacity may be “injurious to health or safety”, but something more than the percentage of opacity must be shown. As was stated in Portland Cement Association v. Ruckelshaus, 486 F.2d 375 (D.C.Cir. 1973): “It may be * * * that the opacity test is an important enforcement tool * * *. However, it is one thing to use a method of testing to observe possible violations of a standard; it is another to constitute that method as the standard itself.” There is also the question of whether or not the testimony of the smoke reader should be given much weight.
[A] test conducted for the National Center for Air Pollution Control (U.S. Dept. H.E.W.), where six trained smoke inspectors evaluated a white training plume known to have 0% opacity. All six inspectors rated the plume at more than 0% opacity and 3 evaluated it at more than 20%. A plume known to be at 20% opacity was rated higher than 20% by 5 of the 6 inspectors (one rated it lower) and 2 of them rated it at almost 40%.
As to whether wood smoke is injurious to human health, at least one study seems to indicate not.
In Papua New Guinea chronic lung disease is common in both sexes from middle age onwards * * *. Acute pneumonia has a high incidence and is a leading cause of hospital admissions and hospital deaths in adults and children. This picture, together with British evidence of a connection between early childhood experience and subsequent respiratory disease led to the theory that adult chronic lung disease may be caused by repeated or severe childhood chest infections.
A previous study of 1200 children aged 0-14 years sampled from 52 areas reported that highlanders had less respiratory disease than lowlanders and on this basis it was concluded that domestic wood smoke was not an important factor. * * In this study, 112 children who attended the same village school but who differed in their exposure to domestic wood smoke were examined each week over a thirty week period.
[F]our classes were examined once a week for loose cough, cough complaint and nasal discharge. * * * There were two groups: 1) 87 children from surrounding villages who were exposed each night to wood smoke from domestic fires; 2) 25 children from the adjacent Lufa Administrative Station whose parents were public servants and who lived in permanent materials houses which were free from internal pollution (except cigarette smoke). * * * Smoke concentrations were highest in the early evening when they ranged from 0.8 to 11.2 mg/m 3. Between 8 and 10 pm the range was 0.8 to 7.3 mg/m3 but by late evening samples drawn from the sleeping areas were usually under 1 mg/m3. The mean concentration in the sleeping area over the entire period 6 pm to 4 am ranged from 0.57 to 1.98 mg/m3. These results are in general agreement with those of Cleary and Blackburn (22) who, using a different method elsewhere in the highlands, found a mean smoke concentration of 0.67 mg/m 3. The mean concentration of aldehydes, an important gaseous component of wood smoke was 1.08 ppm.
Based on the smoke measurements between 6 pm and 4 am, mean 24 hour exposure is probably from 0.3 to 0.8 mg/m3. * * *
The school study in the highlands provides further evidence that exposure to wood smoke, which is the most prominent environmental difference, is not associated with respiratory disease. * * * Anderson, H. R. Respiratory Abnormalities *407in Papua New Guinea Children — International Journal of Epidemiology 1978, 7: 63-72.
This matter is remanded with instructions to the Board to conduct further proceedings to determine whether the wood smoke, in the volume being emitted from appellant’s wigwam burner is “injurious to health or safety.” If it is determined not to be injurious, the Board is ordered to grant the variance.
IT IS SO ORDERED.
LOPEZ, J., concurs.
SUTIN, J., dissents.