Dissenting Opinion by
Mb. Justice Jones:I agree with the writer of the majority opinion that the rural and suburban communities of our Commonwealth may not ignore the problems we all share with respect to population growth, and that any unjustified attempt by these communities to avoid these problems by exclusionary zoning should be resisted by our courts. However, we must bear in mind that zoning does, most often, have a legitimate and even laudable purpose, and we should not, therefore, hold a zoning ordinance to be invalid if it does have a legitimate, nonexclusionary purpose, particularly where the ordinance is part of an overall plan which is specifically designed to face the problem of population growth.
William K. Davis, who served on the Delaware County Planning Commission from 1960 to 1966 and was its Executive Director for the last four years, gave his assessment of the new Concord Township zoning plan as follows: “It was adopted by the township to *482recognize the need for change and departure from the zoning pattern that preceded this one. The township itself is in a transitory stage of development. There are growth trends, there is new housing in and around the township. This to me represents an effort to move directly into future growth patterns, to provide relief and land areas for growth to take place where the township officals think it most appropriate.” (Emphasis supplied)
I begin my consideration of this appeal by reiterating the salutary principle of judicial self-restraint in this area of the law set forth in National Land and Investment Co. v. Easttown Twp. Board of Adjustment, 419 Pa. 504, 521-22, 215 A. 2d 597, 606-07 (1965) (hereinafter cited as national Land) : “The days are fast disappearing when the judiciary can look at a zoning ordinance and, with nearly as much confidence as a professional zoning expert, decide xipon the merits of a zoning plan and its contribution to the health, safety, morals or general welfare of the community. This Court has become increasingly aware that it is neither a super board of adjustment nor a planning commission of last resort. [Citing authorities]. Instead, the Court acts as a judicial overseer, drawing the limits beyond which local regulation may not go, but loathing to interfere, within those limits, with the discretion of local governing bodies. [Citing authority]. The zoning power is one of the tools of government which, in order to be effective, must not be subjected to judicial interference unless clearly necessary. For this reason, a presumption of validity attaches to a zoning ordinance which imposes the burden to prove its invalidity upon the one who challenges it. [Citing authorities].” (Emphasis supplied) See also: Bilbar Const. Co. v. Easttown Twp. Bd. of Adjustment, 393 Pa. 62, 72, 141 A. 2d 851, 856 (1958).
*483By reason of the technical and factual nature of the issues involved in a zoning appeal, the scope of review of a reviewing court is limited to determining whether the zoning hoard of adjustment abused its discretion or committed an error of law. See, e.g., National Land, 419 Pa. 504, 523, 215 A. 2d 597, 607 (1965); Cleaver v. Board of Adjustment, 414 Pa. 367, 380, 200 A. 2d 408, 416 (1964) ; Tidewater Oil Co. v. Poore, 395 Pa. 89, 93, 149 A. 2d 636, 638 (1959). I conclude from my examination of this record that the evidence before the board amply supported its decision to uphold the minimum lot requirements, and, accordingly, I would reverse the order of the court below.
The majority has stated that a zoning ordinance may not be upheld solely because of a sewage disposal problem, that the zoning ordinance presently in question was enacted exclusively to solve such a sewerage problem and, therefore, this ordinance is invalid. If either of the majority’s first two points is incorrect, then its conclusion must also fall.
Two Pennsylvania cases have been cited as support for the proposition that sewerage problems cannot, per se, excuse minimum-acreage zoning requirements. In National Jjand, the first of these two cases, the township subdivision regulations authorized the township zoning officer to require lots larger than the minimum as stated in the zoning ordinance if the disposal of sewage so required. This Court held, therefore, that since other means were available to solve any sewerage problem, the township’s use of a minimum-lot zoning ordinance was unnecessary and improper. There is no evidence in the instant case which might indicate that Concord Township’s authorities have such power, and, accordingly, National Ijand is distinguishable on its facts.
Moreover, the position now taken by the majority, even if it were the same as in National Land, totally *484ignores intervening legislation which appears to specifically reject the broad proposition as now stated. ’National Land was handed down in 1965, when the applicable state zoning act was the Act of May 1, 1933, P. L. 103, art. XX, §2001, added by Act of July 10, 1947, P. L. 1481, §47, as amended, 53 P.S. §§67001-10. However, this Act was repealed in 1968 and replaced by the Act of July 31, 1968, P. L. , 53 P.S. §§10601-20.
The former statute listed several objectives which, collectively, delineated the proper purpose for zoning regulations under that statute. 53 P.S. §67003. The comparable section of the 1968 Act reads as follows: “The provisions of zoning ordinances shall be designed: (1) To promote, protect and facilitate one or more of the following: . . . sewerage . . . .” 53 P.S. §10604 (Pocket Parts) (Emphasis supplied). The new legislation differs from the 1947 Act in that it specifically states that any one of the listed problems may be the basis for a township’s zoning ordinance. In contradistinction to the 1968 Act, the majority opinion states that a zoning ordinance may not be upheld solely because of a sewerage problem.
The second case cited by the majority as support for the first proposition, as stated above, is Delaware County Community College Appeal, 435 Pa. 264, 254 A. 2d 641 (1969). That case, however, dealt with a situation in which the existing sewer facilities could amply handle the proposed facilities. The zoning board there merely anticipated a possible problem at some future time, as the result of other expansion which had not yet, in fact, been proposed. In the case at bar, however, the sewerage problem will be caused by this application; we do not have a “potential sewerage problem in the future.” It should also be noted, parenthetically, that in the Community College case the Executive Director of the Delaware County Planning *485Commission testified that the proposed use (the college) 'mould be consistent with the applicable comprehensive plan, supporting the position of the applicant in that case.1
The first proposition suggested by the majority is that the alleviation of a sewage disposal problem cannot, per se, justify a minimum-acreage zoning ordinance. As I have indicated above, this suggestion is not only directly contrary to the most recent state legislation, but it is also without support (as applied to the instant case) in either of the only two cases relied upon as authority in the majority opinion.
The second premise of the syllogism suggested by the majority is to the effect that the Concord Township zoning ordinance was enacted solely to solve a problem of sewage disposal. This point finds no more support in the record than does the first premise in the law. Several other factors were considered by the zoning board and were fully testified to at the hearing. One of these is that the local road network surrounding the tract in question is already taxed to its capacity at certain times of the day. There is but one bus route in the township and no train service, and, therefore, we must assume that any additional residents of the community will use their automobiles for transportation. Moreover, most of the residences surrounding the tract are built on five-acre lots. Two- and three-acre zoning would be more in conformity with the rural and historical surroundings of the neighborhood. Finally, there is no guarantee as to the source of a water supply for the new development. There is a municipal water main 1000 feet from the property but there is no evidence in the record that *486this source of water will be available for the new development.2
We note in passing that a new zoning map was adopted by the Township while the board was conducting its hearings. Land which had been zoned three acre under the old map, and which constituted 80% of the Township, was reduced in area to 10% of the Township, and the new map also substantially enlarged the one-acre and light industry areas.3 While this information is not necessarily germane to the instant litigation, it does reveal that the Township is aware of its responsibility to readjust its zoning classifications to meet the needs of an increasing population. Evidence in the record indicates that under the present zoning classification the Township can absorb adequately all population increases until the year 1980. This evidence suggests that the officials of the Township are making a conscientious effort to develop the Township according to a systematic plan, and we should be loath to upset that plan by striking down a zoning classification unless absolutely required to do so.
The real crus of the controversy in this case is indicated by the following statement in the majority opinion: “Finally, we cannot ignore the fact that in the narrow confines of the case before us, Concord Township’s argument that three-acre minimum zoning is necessary for adequate on-site sewerage is patently ridiculous.” (Emphasis supplied) If, in fact, there is no support for the Township’s contentions on this is*487sue, then it might be argued that the situation does not justify this type of zoning, and we must, therefore, consider the evidence which was offered by the Township and how that evidence is to be judged.
The general rule for determining the constitutionality of a zoning act or ordinance was set forth by this Court in Colligan Zoning Case, 401 Pa. 125, 131, 162 A. 2d 652, 654 (1960) : “It is now well settled that zoning acts and ordinances passed under them are valid and constitutional as structural or general legislation whenever they are necessary for the preservation of public health, safety, morals or general welfare, and not unjustly discriminatory, or arbitrary, or unreasonable, or confiscatory in their application to a particular or specific piece of property.”4 The burden of proof is upon the applicant attacking the constitutionality of the zoning act to prove that it does not meet these standards.5 As the majority has noted, the proper question for a reviewing court is whether the zoning board abused its discretion or committed an error of law in deciding that the ordinance in question is constitutionally sound.
In its determination that the instant petition involves no sewerage problem, the majority opinion totally and unjustifiably ignores all the evidence presented on this question by the Township and by the applicant. Whenever we are called upon to decide a complex scientific question, we must rely upon the testimony of experts and give great weight to the scientific conclusions which they reach. Where there is a conflict *488between the testimony offered by one side and that offered by the opposing side, the zoning board must consider both positions carefully to arrive at its conclusion as to which is correct. However, once the board has made its findings of fact and reached a conclusion, the function of a reviewing court is to examine the evidence before the board to determine whether the board’s results are reasonably supported by the facts and by the law. The question is not whether Ave—at the appellate level—would have reached the same result, but rather whether the zoning board’s determination was arbitrary and contrary to the weight of the evidence. Gilden Appeal, 406 Pa. 484, 487, 178 A. 2d 562, 564 (1962).
At this point, it is necessary to briefly delineate the means by which the majority has concluded that the possibility of a sewerage problem is “patently ridiculous.” I first note that there had been no reference whatsoever in the record, at any stage of these proceedings, to the Pennsylvania Department of Health Regulations until the promulgation of the majority opinion. The majority refers to the scientific opinions contained in these Regulations as determinative on the question of whether a sewerage problem exists, although the Regulations were never offered in evidence by either Concord ToAvnship or the petitioner. The patent impropriety of basing a decision on these Regulations which are beyond the scope of the record in this case is too clear to require elucidation. It should suffice to merely point out that scientists are continually questioning the opinions and conclusions of other scientists, even those opinions and conclusions which have been legislatively accepted. Therefore, it is extremely important that such evidence be subjected to cross-examination, and that the opposing party (i.e., the Township) be given the opportunity to present rebuttal evidence. These Regulations must certainly carry great *489weight in our consideration. Nevertheless, I believe it is improper to base a scientific conclusion solely upon Regulations which have not been referred to by the parties, the zoning board, or the lower court, and where a substantial amount of other evidence has been offered with all the safeguards of open-court examination.
Moreover, the Regulations themselves point out the issue which wag actually disputed by the parties. According to §7.1-1 thereof, an on-site sewerage system is impermissible if tbe percolation rate in the immediate area is over sixty minutes per inch.6 The controversy at the hearing in the instant case, and the point on which the parties differ, is whether and to what extent the 140-acre tract in question is comprised of land with a percolation rate of over sixty minutes per inch. It is clear to me that if, as claimed by the Township, a substantial portion of the land cannot support on-site sewerage systems, then we would be dangerously derelict in our duty to protect the citizens of this Commonwealth if we permit this tract of 115 one-acre lots to be built, each lot with its own system.7 Accordingly, *490we reach what should he the decisive question on this appeal: Can the evidence on the record support the conclusion of the Zoning Board that a substantial portion of this 140-acre tract cannot support on-site sewerage systems?
The only evidence offered by the applicant, Kit-Mar Builders, Inc., on the question of whether this land would be suitable for on-site sewerage systems if divided into one-acre lots, was given by David Clark. Mr. Clark is a professional engineer as well as the president of Kit-Mar Builders, Inc., the applicant. He testified as to the results of thirteen percolation tests which he personally conducted, and these tests indicated that the entire property would be satisfactory for on-site sewage disposal,8 9although Mr. Clark admitted, on cross-examination, that at least seven acres of the tract would not even be suitable for building because the ground was low and wet.
On the question of percolation rates, the Township offered the testimony of Harry H. Curtin, who has been conducting these tests for twenty years and is now the vice president of Boy F. Weston Company, an independent firm of consulting engineers. Mr. Cur-tin’s firm conducted fifteen percolation tests, under his personal supervision. He testified that five of the tests gave completely unsatisfactory results,® that seven of the tests indicated the possibility of disposal problems,10 and that three of the tests “would indicate that on-site systems might work in that particular area.”11 *491By way of summarizing Mr. Curtin’s lengthy testimony, I refer to the following exchange on direct examination : “Q. If in fact it was developed into one-acre lots with on-site sewerage systems, what in your opinion would be the results from a sanitary standpoint? A. I would predict that there would be a high percentage of failures within five to ten years after these systems were put into use. Q. And a failure consists of what? A. Failure in a clay soil of this type would probably first mean back-up of sewage into the house or the overflow of these systems into yards and streets.” The evidence, therefore, which was offered as to percolation rates was contradictory, although both parties agreed that this was the standard method of measuring the feasibility of installing on-site sewerage systems.
On the question of whether a potential sewerage problem may exist, the Township also offered the testimony of Walter Satterthwaite, a consulting geologist for Roy F. Weston Company. Mr. Satterthwaite utilized a “base map” of the area in question, which map had been prepared by the United States Department of Agriculture. On the basis of criteria established by the Department of Agriculture as guide lines to determine soil acceptability for on-site waste disposal, Mr. Satterthwaite testified as to the extent to which the tract could support on-site sewerage systems. His findings were as follows: 40% of the area would not be acceptable for on-site sewerage; 51%% of the area would normally be all right, but might cause problems at some time; and on 7%% of the area the normal oxidation process would be effective. Mr. Satterthwaite summarized his testimony as follows, on cross-examination: “Q. Now, you aren’t saying by your testimony here that any dire consequence would happen to anyone who would possibly end up living on a one-acre lot on this property, are you? A. It very likely could become quite a health hazard. Q. Would you tell me *492how, sir? A. By the inability of the soil to accept the effluent or by the altogether too rapid passage of sewage wastes through the soil into the surface of the ground or to the surface of streams and springs that are in the area.” The potential sanitation threat is compounded by a drainage problem attributable to the steep terrain in the interior of the tract where the land descends to a creek bed.
The Township also offered the testimony of Oliver Armitage, a licensed real estate broker and appraiser for fourteen years. Mr. Armitage stated his professional opinion, based upon the nature of the surrounding area and the market for houses, that “a residential subdivision of two or three acres is the most desirable method of developing this property.” In fact, he pointed out that although in a more urbanized area there would tend to be a much greater demand for one-acre lots, in an area such as this 140-acre tract, the market would be stronger for two- or three-acre lots. His testimony agreed with that of William Davis, referred to above, who also pointed out that the present zoning plan would adequately absorb all population increases through 1980. No population estimates had been made beyond 1980.
Considering all the evidence before the zoning board, I find it impossible to say that the board was guilty of either an abuse of discretion or of committing an error of law when it upheld this zoning ordinance. The fact that the majority opinion takes no notice of the evidence offered by the Township is particularly distressing because of the “presumption of validity [which] attaches to a zoning ordinance [and] which imposes the burden to prove its invalidity upon the one who challenges it” National Land, 419 Pa. 504, 522, 215 A. 2d 597, 607 (1965).
I am well aware that at times minimum-acreage requirements might be a crude way of dealing with a *493sewerage problem. Nevertheless, I feel that a potential sewerage problem may be a very important factor to be considered in evaluating a zoning ordinance, particularly in the light of the 1968 Zoning Act. Of course, if we hold that a potential sewerage problem is one factor to be considered, we might well be encouraging certain municipalities which desire to maintain high-acreage requirements to drag their feet as far as constructing municipal sewerage systems is concerned. If this appears to be the case, then in evaluating such a zoning ordinance we would be forced to discount the potential sewerage problem. On the other hand, we should not say that the sewerage problem must be overlooked entirely. Concord Township has no municipal sewerage system. If we strike down this zoning ordinance and if the sewerage problem is such that on-site systems would not be feasible, then the Township will be forced to incur the expense of installing a municipal system. Rural and suburban townships have relatively limited tax resources for the obvious reason that they are composed primarily of single-family residences, properties which do not yield high real estate tax revenues. To require these municipalities to incur the great expense of installing sewerage systems and to augment their limited municipal services to meet a population which is increasing more rapidly than anticipated, does not appear to me to be a sound way to face what is admittedly a serious problem of providing residential communities for a rapidly-growing population.
I dissent.
Mr. Justice Cohen joins in this dissenting opinion.Compare that situation with the testimony of William K. Davis in the instant case, wherein he opposes the position of the applicant. Supra at pages 481-2.
As previously noted, the 1908 Act lists several factors which, individually or collectively, may support a zoning ordinance. In addition to sewage disposal, the Act refers to “coordinated and practical community development, proper density of population, ... disaster evacuation, transportation, water . . . .” 53 P.S. §10604(1) (Pocket Parts).
By way of contrast, the zoning ordinance involved in National Land upzoned the property in question from one to four acres.
See also Exton Quarries, Inc. v. Zoning Bd. of Adjustment, 425 Pa. 43, 58-59, 228 A. 2d 169 (1967) ; National Land, 419 Pa. 504, 511-12, 522, 215 A. 2d 597 (1965) ; Binar Const. Co. v. Easttown Twp. Bd. of Adjustment, 393 Pa. 62, 72, 141 A. 2d 851 (1958).
See, e.g., Cleaver v. Board of Adjustment, 414 Pa. 367, 373, 200 A. 2d 408 (1964) ; Bilbar Const. Co. v. Easttown Twp. Bd. of Adjustment, 393 Pa. 62, 70, 141 A. 2d 851 (1958).
By way of clarification, the percolation test is the most eommonly-used means of deciding whether an on-site sewerage system may be safely installed. It tests the length of time required for the soil to absorb water. Generally speaking, if it requires more than sixty minutes for one inch of water to be absorbed, then it is likely that the system will back up and not operate—i.e., the sewage might come to the surface of the land and collect there instead of dissipating.
The majority opinion states that it is “sheer fantasy” to claim, as does the Township, that although a one-acre lot would not support on-site sewage disposal, a three-acre lot would. The witnesses for the Township have simply reasoned that because substantial portions of this 140-acre tract have high percolation rates, it would be possible to lay out three-acre lots, each lot including an area with an acceptable percolation rate, although this could not be done with one-acre lots. I find nothing fantastic about this and, in any case, would he extremely hesitant to adopt any -personal assessment over the unrebutted testimony of expert witnesses.
The percolation rates obtained by Mr. Clark ranged from 2.8 minutes per incb up to 26.0 minutes per inch.
The percolation rates ranged from 80 minutes per inch up to 160 minutes per inch.
The percolation rates ranged from 30 minutes per inch up to 50 minutes per inch.
The percolation rates ranged from 12 minutes per inch up to 24 minutes per inch.