Opinion for the Court filed by Circuit Judge GINSBURG.
GINSBURG, Circuit Judge:
The Federal Power Act (FPA), 16 U.S.C. §§ 791a-823a (1976 & Supp. V 1981), directs the Federal Energy Regulatory Commission (FERC, or Commission) to supervise the development of the nation’s navigable water resources and to license the construction and operation of hydroelectric projects on all bodies of water subject to federal jurisdiction.1 Calaveras County Water District (CCWD), a political subdivision of the State of California, applied to FERC for a license to build a hydroelectric power plant near Modesto, California. CCWD’s application was supported by the Northern California Power Agency (NCPA), a joint enterprise of publicly-owned electric systems. NCPA procures electric power on behalf of its members and planned to purchase the power generated at the CCWD plant. On February 8, 1982, FERC granted CCWD a license somewhat narrower in scope than the one described in CCWD’s application.2
The construction and operation of CCWD’s plant, as licensed, will have certain adverse impacts on a hydroelectric dam and powerhouses operated by Pacific Gas and Electric Company (PG & E) pursuant to prior license grants. In separate petitions consolidated for review PG & E and CCWD present challenges to FERC’s decision. For the reasons set out below we conclude that the Commission’s action on CCWD’s application reasonably accommodated two principal goals of the FPA: promoting the comprehensive development of waterways subject to federal jurisdiction, and encouraging private investment to effect that development. We therefore affirm the Commission’s decision to grant a license to CCWD, subject to the terms and conditions FERC specified to protect PG & E’s legitimate interests.
I. Background
The North Fork Stanislaus River flows southwestward from Lake Alpine and converges with the main stream of the Stanislaus River near Modesto, California. See map infra p. 82. PG & E, under licenses granted by the Federal Power Commission (FERC’s predecessor agency, hereafter not distinguished from FERC), currently operates three hydroelectric facilities in the vicinity of that junction. PG & E maintains a dam and small reservoir at Spicer Meadow (north edge of the map) which is used to control water supplies to two powerplants— the Angels3 and Murphys4 powerhouses (shown in the southwest section of the map). PG & E’s third facility is the Stanis[317]*317laus powerhouse5 (just east of the Murphys powerhouse) which draws on a different source of water.
CCWD’s project,6 as originally proposed to FERC, would have had three adverse impacts on PG & E’s existing operations.
First, CCWD proposed to divert most of the water currently used at PG & E’s Angels and Murphys powerhouses to a new, CCWD-operated powerhouse at Collierville (situated between the Murphys and Stanislaus powerhouses, and shown in the southwest section of the map).7 CCWD asserted that it was prepared to compensate PG & E for the power PG & E would lose, but insisted that FERC had a statutory duty to license CCWD’s new project to the full extent CCWD proposed. CCWD’s projected diversion would increase the power generated from the water in question. Because CCWD’s proposal was “better adapted” to developing the waterway, CCWD claimed FERC was obliged to accept it. For this argument CCWD relied principally on section 10(a) of the FPA.8 PG & E, on the other hand, maintained that FERC may authorize no encroachment on its licensed operations without PG & E’s consent.9 PG & E placed principal reliance on section 6 of the FPA.10
Second, CCWD’s project would somewhat raise the water level downstream of the Stanislaus powerhouse, and consequently reduce the power PG & E could generate there by about 0.3% of the powerhouses current output. Again, CCWD expressed a willingness to compensate PG & E for the power lost; PG & E adhered to the position that no adverse impact on its license could be authorized by FERC without PG & E’s consent.
Third, CCWD proposed to erect a new dam at Spicer Meadow that would substantially increase the size of the existing reservoir at that location, inundate PG & E’s Spicer Meadow dam, and destroy PG & E’s associated facilities and conduits. CCWD contended that a clause in PG & E’s license for the Spicer Meadow dam permitted FERC to authorize the erection of this new dam. PG & E maintained that the clause in question permits only the raising of the old dam, not the erection of a new one.
In the license issued to CCWD, FERC resolved these three disputes as follows. First, PG & E is to retain control of the water it currently uses at the Angels and Murphys powerhouses. Second, CCWD is permitted to raise the water level downstream of the Stanislaus powerhouse, but must compensate PG & E for the power lost. The amount of compensation, and the forum for determining it, remain open questions. Third, subject to protection of PG & E’s interest in water now channeled to its powerhouses, CCWD is licensed to erect a new dam at Spicer Meadow.
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II. Discussion
The FPA was enacted to establish a systematic, orderly process for promoting the comprehensive development and full use of the nation’s navigable waters. Congress’ general statement of the FPA’s purpose appears in section 10(a), which requires projects licensed by FERC to be
best adapted to a comprehensive plan for improving or developing a waterway ... for the use or benefit of interstate or foreign commerce, for the improvement [319]*319and utilization of water-power development, and for other beneficial public uses, including recreational purposes; and if necessary in order to secure such plan the Commission shall have authority to require the modification of any project and of the plans and specifications of the project works before approval.
16 U.S.C. § 803(a).11
The FPA contemplates development through private investment. Chemehuevi Tribe of Indians v. FPC, 420 U.S. 395, 407-08, 95 S.Ct. 1066, 1074, 43 L.Ed.2d 279 (1975). Prior to the FPA’s enactment in 1919, licenses to develop hydroelectric power projects on navigable waterways were issued in one of two ways. The Secretary of the Interior could license projects pursuant to legislation enacted in 1901; these licenses were revocable at will. In contrast, individual acts of Congress were used to grant perpetual licenses for specific projects. Secure licenses were thus difficult to obtain; revocable licenses, though more readily available, were of little value to private investors. These conditions, Senator Walsh remarked during the Senate debates on the FPA, made legislation necessary. See 59 Cong.Rec. 1,440 (1920). Accordingly, the FPA was designed to insure that the licenses granted by FERC promote secure licensee expectations.
To this end, section 6 specifies:
Licenses under this subchapter shall be issued for a period not exceeding fifty years. Each such license shall be conditioned upon acceptance by the licensee of all of the terms and conditions of this chapter and such further conditions, if any, as the Commission shall prescribe in conformity with this chapter, which said terms and conditions and the acceptance thereof shall be expressed in said license. Licenses may be revoked only for the reasons and in the manner prescribed under the provisions of this chapter, and may be altered or surrendered only upon mutual agreement between the licensee and the Commission after thirty days’ public notice.
16 U.S.C. § 799. Correspondingly, the last clause of section 10(a) authorizes FERC to require licensee modifications only “before approval.” Related language restricting the licensee's power unilaterally to make changes in a licensed project appears in section 10(b).12 A final indication of the Sixty-sixth Congress’ strong concern that licensees receive reliable grants appears in FPA section 28, which purports to limit the power of future Congresses to amend the FPA in any way that would adversely affect extant licenses.13
There is some tension between section 10’s focus on comprehensive development, and section 6’s emphasis on secure licenses. Secure licenses are likely to promote the development of new projects on previously undeveloped waterways. But to the extent FERC’s power to alter or revoke licenses is narrowed, the replacement of small or antiquated facilities by larger or more efficient ones may be impeded. Congress judged that on balance secure licenses for terms not exceeding fifty years would more often further than obstruct comprehensive development.
FERC’s power to limit license agreements and to reserve the right to require future alterations enables the Commission to ac[320]*320cord section 6 the scope its terms indicate without unreasonably undermining the FPA’s broader purpose set out in section 10(a). FERC has discretion under section 6 to restrict license terms to any period not exceeding fifty years, and is also authorized by that section to impose additional license conditions at its discretion. FERC understands — and has not hesitated to exercise— this discretionary authority. In Duke Power Co., 55 F.P.C. 677, 680 n. 8 (1976), for example, the license agreement expressly reserved the Commission’s right to “issue [a subsequent] license authorizing the construction, operation and maintenance of a hydroelectric project which will more completely utilize the water resources” of the river in question.
In the case at hand we are called upon to determine first, whether FERC has misconstrued the relevant sections of the FPA, and second, whether FERC’s construction of PG & E’s Spicer Meadow license is correct. An agency’s interpretation of the statute it administers is entitled to deference, Zenith Radio Corp. v. United States, 437 U.S. 443, 450, 98 S.Ct. 2441, 2445, 57 L.Ed.2d 337 (1978), as is its construction of the license agreements it negotiates and oversees. Cf. Andrew G. Nelson, Inc. v. United States, 355 U.S. 554, 558, 78 S.Ct. 496, 498, 2 L.Ed.2d 484 (1958); Alabama Power Co. v. FERC, 584 F.2d 750, 753-54 (5th Cir.1978). But cf. Harrison v. FERC, 567 F.2d 308, 310 (5th Cir.1978) (“The issue is one of document interpretation, a field where plain meaning controls, absent ambiguity or special usage.”).
A. Diversion of the Angels and Murphys water supplies
FERC rejected CCWD’s proposal to divert to CCWD’s new Collierville powerhouse water now channeled to PG & E’s Murphys and Angels powerhouses. PG & E currently generates about 31,000 Megawatt-hours (Mwh) of energy per year using that water; CCWD would use it to generate about twice as much — 65,850 Mwh per year. CCWD Initial Brief at 15. FERC urged CCWD and PG & E to pursue negotiations on the matter,14 but ruled that section 6, applied to the licenses held by PG & E, prevented FERC from authorizing these diversions without PG & E’s consent.15 At oral argument PG & E’s counsel informed the court that negotiations have not abated.16
[321]*321As a threshold matter, CCWD has not persuaded us that “long established Commission precedents” support its view that FERC must license the better adapted project even if it interferes with a prior license. CCWD Initial Brief at 41-43. In a prior decision FERC has, indeed, stated:
The Commission’s comprehensive licensing authority is not restricted by any rights of existing licensees to be free of encroachment from a new project where the Commission finds that the resulting totality of river development, giving full consideration to any negative effects of the encroachment, is most conducive to comprehensive development.... Where the record indicates that such an encroachment will significantly impair the operational value of the existing project, the Commission has included a provision in the new license requiring it to compensate the existing licensee for the loss.
Susquehanna Power Co. & Philadelphia Electric Power Co., 32 F.P.C. 826, 831 (1964) (footnotes omitted). The Commission reiterated this view in Duke Power Co., 55 F.P.C. 677, 681 (1976). Neither of these cases, however, involved a non-consensual interference.
The quoted language from Susquehanna is pure dictum,17 as FERC itself tacitly acknowledged in that case. “We do not have any question here of compensation to [the prior licensee] for damages to its licensed operations by [the new project]; as conditioned as set forth above, there will be none.” 32 F.P.C. at 832. In Duke Power FERC overruled a licensee’s objection to a license agreement clause in which the Commission reserved the right to authorize future interference with the licensed project. Again, there was no question of a non-consensual encroachment on existing operations. At oral argument CCWD conceded that it could identify no prior case in which FERC had allowed a new license to encroach on an old one in circumstances where the old licensee did not tacitly or explicitly acquiesce in the encroachment or agree to a negotiated settlement.
On at least one prior occasion FERC has refused to license a project that would have substantially reduced water supplies to existing licensees. In North Kern Water Storage District, 16 FERC ¶ 61,082 (1981), FERC squarely addressed — and rejected — a new applicant’s assertion that under section 10(a) the Commission is obliged to license a subsequent, “better adapted” project regardless of the adverse impact on a prior licensee. The Commission’s decision with respect to the Angels-Murphys water dispute is entirely consistent with that precedent.
Turning from Commission precedent to the FPA itself, CCWD relies primarily on [322]*322FPA section 10(a) to support its claim that FERC should have licensed CCWD’s “better adapted” project in its entirety, without regard to the adverse impacts on PG & E’s existing licensed facilities. CCWD would derive from this provision a command that FERC reallocate water to a new applicant whenever the applicant demonstrates, as CCWD has, that it will make better use of the water than does the- prior licensee. FERC, according to CCWD, has not only the authority, it has a statutory obligation to license the “better adapted” project regardless of adverse impact on prior licensees, subject only a requirement that those licensees receive adequate compensation.
We do not find in section 10(a) the firm directive CCWD urges. On the contrary, we cannot gainsay FERC’s conclusion that, in the circumstances presented here, section 6 requires rejection of CCWD’s position.
CCWD overreads section 10(a) and diminishes the policy declared in section 6. Section 6 clearly states: “Licenses may be revoked only for the reasons and in the manner prescribed under provisions of this chapter, and may be altered or surrendered only upon mutual agreement between the licensee and the Commission .. .. ” This appears to dispose of CCWD’s claim to the Angels-Murphys water. But CCWD reads section 6 only to prevent FERC from unilaterally imposing on a licensee additional, affirmative obligations not specified in the license agreement. See CCWD Initial Brief at 30, 32-33. This reading finds no support in the specific language of section 6 (which restricts revocation or surrender of a license as well as alteration), no support in other provisions of the Act (which are clearly designed to promote stable licensee expectations), and none in the legislative history.18 The Act’s overarching purpose, all [323]*323parties agree, is to promote the development of the nation’s waterways. Congress determined that development should be financed largely by private investment, and sought to promote that investment by making licenses secure. Section 6 unmistakably reflects that policy.19
CCWD’s counterarguments are insubstantial. CCWD concedes that the FPA attaches importance to secure licenses,20 but suggests that the purpose of section 6 is achieved equally well, and more consistently with the FPA’s larger purpose, by a requirement that displaced licensees receive adequate compensation when a new, “better adapted” project is approved. This argument is unpersuasive. To potential investors, a right to wrangle in court over compensation is likely to be a less attractive drawing card than a hydroelectric project reasonably secure from regulatory interference. And no provision of the FPA sets up inter-licensee compensation as an alternative to the protections specified in section 6 against unilateral license revisions by FERC.- Neither section 10(c), nor section 21, both cited by CCWD in support of its compensation theory, can reasonably be read to do so.21
[324]*324CCWD insists, however, that the reading of section 6 we accept will gravely undermine section 10(a)’s focus on projects “best adapted to a comprehensive plan for improving or developing a waterway.”22 Section 6, CCWD argues, should not be read to allow a prior licensee of a tiny project to “veto” a subsequent proposal to develop a much larger project in the same location.23 The short answer to this argument is that the CCWD-PG & E dispute over the Angels-Murphys water does not present that case.24 CCWD’s project as licensed by FERC, without access to the Angels-Murphys water, has not suffered large diminution as a result of any PG & E “veto.” The project can operate at about 90% of the originally-planned capacity: without the disputed water CCWD can generate about 494,000 Mwh of energy per year; with the water, about 560,000 Mwh. CCWD Initial Brief at 15. PG & E is therefore in no position to .exploit its status as prior licensee unreasonably to obstruct CCWD’s larger proposal.
We need not decide whether section 6 affords leeway irrelevant to the present facts. We have earlier noted FERC’s ability to write consent requirements into licenses at the time of issuance, and the United States’ clear power to overcome the withholding of required consent by condemnation of the project under section 14 of the Act.25 Nonetheless, it may be that the consent requirement of section 6 is subject to a “reasonableness” safeguard against a licensee’s arbitrary refusal to consent, when that refusal would substantially impair the interest of the licensor in effective use of water power.26 To dispose of the present case, it suffices to say that we decline to enter into assessments of reasonableness where lack of consent does not affect the viability of the subsequent project.27
[325]*325B. Impact on PG & E’s Stanislaus powerhouse
CCWD’s project will raise the water level downstream of PG & E’s Stanislaus powerhouse by some sixteen feet, and thereby reduce power generated at that plant by about 0.3%. FERC estimates the resultant financial loss to PG & E will be in the range of $14,400 to $52,800.28 J.A. 740. Notwithstanding PG & E’s refusal to consent, FERC judges the 0.3% impact on PG & E’s Stanislaus license to be permissible because it is so small. FERC leaves open the possibility of requiring CCWD to compensate PG & E in an amount yet to be determined.29
PG & E insists that section 6 does not contemplate even a “de minimis” exception — FERC simply may not approve a license that will have any adverse impact on one already issued.
In our view PG & E’s interpretation of section 6 is not compelled by the language of that section, and is unnecessary to its purposes. PG & E’s interpretation would tilt the balance too far in favor of prior licensees, making it possible for PG & E and similarly situated licensees to undermine, perhaps significantly, the FPA’s broader objective of encouraging comprehensive development of the waterways.30
Section 6 states, without qualification, that licenses31 “may be altered or surrendered only upon mutual agreement between the licensee and the Commission.” But the operative term “altered” is not self-defining. It is safe to assume that any new hydroelectric project will have some impact on every other project on the same waterway or in the same geographical area. Water levels or flow rates upstream or downstream may change slightly, drainage into or out of the river may be affected, indeed rainfall in the area might change when a large reservoir is created or removed. Section 6, like most other statutory provisions, must incorporate some common sense limits.32 Without seeking to define [326]*326those limits precisely, we are persuaded that an unconsented 0.3% reduction in generating capacity does not amount to a license “alteration” prohibited by the explicit terms of section 6.33
Section 6’s goals are not eroded by this interpretation. Encouraging and protecting private investment in waterway development does not require FERC to disallow every conceivable adverse impact, no matter how slight, on existing licensees. Investor confidence can remain unshaken under a rule that allows the Commission to authorize de minimis interferences with the operation of an existing plant. Small encroachments on a license, comparable in their adverse impact to variations in conditions that investors might expect from other causes such as, for example, annual fluctuations in water supply, should be within FERC’s authority to grant in implementing the design of Congress to promote, at the same time, development and stable investment incentives.34 It is implausible to suggest that a 0.3% reduction in generating capacity precipitated by FERC’s approval of a new license constitutes interference of an order that will undermine investor confidence.35 PG & E’s interpretation of the Act, FERC argues and we agree, “would inflate the rights of existing licensees far beyond any needs for protecting their investment or ensuring the continued operation of their projects.” Brief for Respondent FERC at 21.36
[327]*327Since CCWD agrees that as an encroaching licensee it must compensate PG & E, the adversely affected prior licensee, even for the de minimis adverse impact in question, and since it is premature for us to decide in what forum that compensation should be fixed or what standards should govern its determination,37 we need not now decide whether and to what extent compensation is mandated by the FPA, other law, or equitable considerations.
C. Expansion of the Spicer Meadow reservoir
The dam CCWD proposes to build at Spicer Meadow will flood PG & E’s existing dam and reservoir at that location. PG & E argues that the terms of the Spicer Meadow dam license issued by the Commission to PG & E in 1951 do not allow FERC to permit construction of a new dam. FERC disagrees. It approved CCWD’s proposed dam, but protected PG & E’s interest in water currently channeled from the Spicer Meadow reservoir to PG & E powerhouses by issuing CCWD’s license “subject to” the provisions of Article 32 of PG & E’s Spicer Meadow dam license. J.A. 744.
Article 32 provides, in pertinent part: In order that this project shall not unreasonably interfere with any other project or part thereof which may hereafter be developed ... the Commission expressly reserves the right at any time ... to grant another license ... authorizing [the new] applicant alone or jointly with the licensee for this project to raise a dam or the dams of this licensed project and to increase the storage capacity of any or all of the reservoirs; provided, that any such authorization shall require: (i) that the licensee for this project shall be adequately protected from or recompensed for any damage, temporary or permanent, which may be caused by the raising of said dam or dams or by the construction of any other works or structures within the area of the project for which license is issued ... (iv) the licensee for this project shall at all times have complete control over storage and release therefrom of any of its waters, whether stored in reservoirs constructed at its own expense, constructed jointly with such other applicant or constructed at [the] expense of such other applicant; ... provided that the licensee for this project shall be indemnified from liabilities and costs involved as in (i), (ii), and (iii) above and shall retain control of its water as in (iv) above.
10 F.P.C. at 1186 (emphasis supplied). . PG & E points to the first italicized phrase and argues that FERC thereby reserved the right to authorize only the “raising” of existing dams, not the construction of an entirely new one. We think PG & E’s reading is crabbed. The three italicized sections of Article 32, sensibly read, indicate that FERC retained authority to permit enlargement of the Spicer Meadow reservoir “to increase the storage capacity,” by any appropriate means, means that could include but were not restricted to appropriating and raising PG & E’s existing dam.
First, the language of Article 32 itself gives little support to PG & E’s narrow reading. The most obvious way to “increase the storage capacity” of a reservoir, action authorized by the first italicized passage in Article 32, is to build a higher dam [328]*328downstream. PG & E’s argument would exclude this interpretation by implying the following bracketed word in that passage: “to raise a dam or the dams of this licensed project and [thereby] to increase the storage capacity of any or all of the reservoirs.” Such an interpretation renders the last portion of the passage superfluous.38 It is not readily compatible, moreover, with other portions of Article 32. Both of the other italicized passages, since they form part of a proviso, relate only to actions that increase storage capacity in the manner permitted by the principal provision. Thus, the second italicized passage, when it anticipates “construction of any other works or structures within the area of the project for which [a new] license is issued,” must have in mind works or structures for the purpose of increasing reservoir capacity; and the most likely of these is a dam downstream. Similarly, the third italicized passage’s reference to “reservoirs ... constructed at [the] expense of [the new licensee],” must allude to reservoirs that “increase the storage capacity of [the existing licensee’s] reservoirs” — and this most likely refers to a reservoir that inundates the existing licensee’s present dam. Finally, the proviso that the existing licensee “shall at all times have complete control over storage and release ... of any of its waters [whereever stored]” hardly seems necessary if the increase of storage capacity is only to be achieved behind the existing licensee’s own raised dam.
Elsewhere in the license agreement the parties reiterated their expectation that a subsequent increase in storage capacity effected by another licensee might be authorized, but made no reference to any limitation on the means that might be used to accomplish that purpose. FERC announced in the license its finding that
[ujnder present circumstances and conditions ... the project is best adapted to a comprehensive plan for the improvement and utilization of water-power development, and for other beneficial public purposes, including recreational purposes.
10 F.P.C. at 1184 (emphasis supplied). In Article 25, which deals with PG & E’s duty to clear the bottom of its reservoirs, the parties anticipate, in general terms, an “addition to the reservoir storage capacity by others under a license issued by the Commission.” Id. at 1185. Finally, Article 30 of the license provides:
In order not to interfere with future comprehensive development of the water power resources of the Stanislaus River watershed, waters stored in project reservoirs shall not be released for use or permitted to be used in the development of power except in existing powerhouses and by existing installations, without the prior approval of the Commission.
Id. (emphasis supplied).
The body of the license agreement thus reflects the parties’ understanding that FERC retained broad authority to permit future development at Spicer Meadow. In sum, we are convinced that Article 32’s reference to the raising of PG & E’s existing dams was an alternative the license agreement specifically kept open to facilitate future development, not an exclusive means that the parties anticipated PG & E might invoke to impede it.39 This squares precisely with FERC’s interpretation of the license, an interpretation to which we owe deference. Accordingly, we hold that FERC retained the power to authorize CCWD’s erection of a new dam, subject to a [329]*329requirement that PG & E retain its present control40 over water supplied to the Angels and Murphys powerhouses.41
III. Conclusion
For the reasons stated, the Commission’s orders challenged in the PG & E and CCWD petitions for review are
Affirmed.
A companion decision, issued today, resolves No. 82-2022, Friends of the River v. FERC, 720 F.2d 93. Judge Bazelon, for the reasons stated in his dissenting opinion in Friends of the River, would order a remand, and therefore would not reach the issues raised in the petitions consolidated for decision in this opinion. He has noted, however, that “[w]ere the issues to be reached, [he] would agree with the majority’s reasoning.” Friends of the River v. FERC, at 110 n. 3 (Bazelon, J., dissenting).