Opinion by
Mr. Chief Justice Jones,Appellants were owners and tenants of commercial properties located on the north side of the 900 block of Market Street, which were condemned by the Redevelopment Authority of the City of Philadelphia (Authori*440ty). They seek a reversal of a Commonwealth Court decision dated April 5,1973, in which that Court, adopting the lower court’s opinion, affirmed the lower court’s order dismissing appellants’ preliminary objections to the Authority’s declaration of taking. See 8 Pa. Commonwealth Ct. 374, 302 A. 2d 907 (1973) (Mencer, J., dissenting). We granted allocatur and this appeal followed.
In 1963, the City Planning Commission (Commission) certified that the area from Spring Garden Street to South Street and from the Delaware River to the Schuylkill River was “blighted” as that term is defined in the Urban Redevelopment Law.1 In addition to certifying some new property, this certification consolidated several smaller areas which had been previously and separately certified as “blighted.”2 Pursuant to this certification, the Authority condemned appellants’ properties on May 21, 1970.
Appellants contend that the lower court erred in dismissing the following preliminary objections to the declaration of taking:
“(1) The area involved was not ‘blighted’ and that the Commission acted arbitrarily and capriciously in certifying the area as ‘blighted.’
“(2) The power and right of the Authority to dispossess appellants or to do anything further in the premises had expired by the explicit terms of the City Council Ordinance authorizing the condemnation.
“(3) The Authority’s procedures constituted an unconstitutional means of achieving a valid legislative purpose.
“(4) The activities of all the governmental and quasi-governmental bodies in any way connected with *441tie taking constituted suci a gross abuse of condemnees’ basic rights as to require a revestment of title.”
Under Section 406(a) of tie Eminent Domain Code,3 a preliminary objection is tie exclusive procedure to challenge the power or right of the Authority to condemn property. In their first preliminary objection, appellants allege that “the area involved was not blighted.” In Faranda Appeal, 420 Pa. 295, 216 A. 2d 769 (1966), this Court acknowledged that such a claim does challenge the Authority’s power or right to condemn the property in question and in remanding that case we directed the lower court to take testimony on the question of whether the area was in fact blighted. Citing Faranda as authority, appellants argue that the trial court here should have made a finding as to whether the area was in fact blighted and should not have limited itself to a review of the certification by the Commission.4 The direction in Faranda to take testimony on the question of whether the area was in fact blighted should not be read so broadly. That case dealt with a situation where no testimony was allowed by the trial court on the issue of blight. An offer of proof was deemed properly presentable there to assure judicial review of the preliminary objection.5 The scope of ju*442dicial review, however, was not affected by that decision. On review a condemnee should be given an opportunity to prove that a certification of blight is arbitrary or capricious. Faranda affords a condemnee that opportunity.6 It does not require the lower court to substitute its discretion for that of the legislatively-granted discretion of the Commission.
Appellants also maintain that certification of the entire center city Philadelphia as blighted was arbitrary.7 However, it is presumed that the Commission performed its duties in good faith, Washington Park, Inc. Appeal, 425 Pa. 349, 229 A. 2d 1 (1967), and the appellants’ burden of proving fraud or abuse of discretion is a heavy one. Pittsburgh School District Condemnation Case, 430 Pa. 566, 575, 244 A. 2d 42, 46 (1968). Appellants rely on testimony by their expert witness, a real estate appraiser, that only 15% of the area certified in 1963 was in fact blighted and that in 1972 only 10% was blighted. This witness, appellants’ only witness, admitted that he knew nothing about economics and was not an authority on traffic control. Both are among the statutory standards used to deter*443mine the existence of blight.8 While the executive director of the Commission, testifying on behalf of the Authority, admitted that the certification “does not indicate that blight is pervasive throughout the area” and that “there were large areas . . . which were not blighted,” he did testify that the Commission made its determination after eleven years of traffic studies, economic studies and studies of land value and use. At that time, center city Philadelphia was deemed a “logical planning unit.”
Appellants would have us shift the burden to the Authority to justify the certification of center city Philadelphia as a logical planning unit where their assertion of minimal blight is based on the unsupported testimony of one witness unfamiliar with economics and without expertise in traffic control. This we decline to do. These appellants have been afforded the opportunity to prove arbitrariness in the Commission’s certification and they have failed.
Even assuming the merit of appellants’ other three contentions,9 they are not properly raisable by preliminary objection. We have previously held that the scope of preliminary objections under Section 406(a) is to be limited. Commonwealth Appeal, 429 Pa. 254, 239 A. 2d 343 (1968). It is the clear intent of Section 406 to dispose of challenges to the validity of a condemnation as soon as possible after the taking as evidenced by the fact that preliminary objections must be filed *444within thirty days after service of notice of condemnation. When the Authority filed the declaration of talcing, it was in full compliance with terms of its authority and the condemnation was effective and valid as of that date. The Authority may take the land for an authorized purpose and subsequent legal or factual objections will not render that taking invalid. Upper Dublin Township Authority v. Piszek, 420 Pa. 536, 541, 218 A. 2d 328, 331 (1966). Accordingly, appellants cannot now raise by preliminary objection to the taking grievances that the Authority failed to comply with a provision of a City Council ordinance requiring the Authority to enter a Redevelopment Contract within one year thereafter, that the Authority had harassed them by demands for possession subsequent to the condemnation but prior to the one-year removal period set by City Council, and that the Authority erred in not offering the condemned land back to appellants for redevelopment.
Judgment affirmed.
Mr. Justice Eagen and Mr. Justice Manderino concur in the result.Act of May 24, 1945, P. L. 991, §§1-19, as amended, 35 P.S. §§1701-1719 (Supp. 1973).
Tlie area which includes appellants’ properties was originally certified in 1952.
Act of June 22, 1964, P. L. 84, §406, as amended, 26 P.S. §1-406 (Supp. 1973).
Regarding the function of the court below, this Court stated in Crawford v. Redevelopment Authority, 418 Pa. 549, 554, 211 A. 2d 866, 868 (1965); “The power of discretion over what areas are to be considered blighted is solely within the power of the Authority. The only function of the courts in this matter is to see that the Authority has acted not in bad faith; to see that the Authority has not acted arbitrarily; to see that the Authority has followed the statutory procedures in making its determination; and finally, to see that the actions of the Authority do not violate any of our constitutional safeguards.”
The lower court in Faranda reasoned that since bad faith or arbitrary action was not specifically asserted, a preliminary objec*442tion challenging the certification of blight was not subject to judicial review. This Court recognized that the Authority’s power or right to condemn was being raised, thus making testimony on a preliminary objection proper under Section 406(a) of the Eminent Domain Code, supra.
If no testimony is allowed, a condemnee has no opportunity to show that the action of the Authority was arbitrary. As in Crawford v. Redevelopment Authority, supra, where the court permitted testimony to he given by the condemnee to the effect that her property was not blighted, the court below considered similar testimony by appellants.
As noted earlier, the 1963 certification was a consolidation of several smaller areas which had been previously and separately certified as blighted. Appellants’ property was originally certified in 1952 and we find it significant that appellants have neither questioned that determination of blight nor regarded it as being arbitrary.
The criteria for determining whether an area is blighted are set out in Section 1702(a) of the Urban Redevelopment Law, Act of May 24, 1945, P. L. 991, §1702(a), 35 P.S. §1702(a).
Appellants’ third preliminary objection is based upon the Authority’s failure to offer the condemned land back to appellants’ for redevelopment. In Faranda, we indicated that the condemnation need only satisfy the statutory requirements and there is nothing in the statute requiring the Authority to select a redeveloper from among the condemnees.