291 F.3d 1123 (9th Cir. 2002)
Pronsolino v. Nastri is a foundational Clean Water Act (CWA) decision that defines the scope of the Environmental Protection Agency's (EPA) authority over waterbodies degraded by nonpoint-source pollution (such as runoff from forestry, agriculture, and stormwater not discharged through a discrete conveyance).
Does the Clean Water Act authorize and require the establishment of TMDLs for waters impaired solely by nonpoint sources, and may EPA approve or establish such TMDLs even though EPA cannot directly regulate nonpoint-source activities?
Under CWA § 303(d), states must identify waters for which technology-based effluent limitations are not stringent enough to implement applicable water quality standards and must establish TMDLs for those waters that account for seasonal variations and include a margin of safety. EPA must approve or disapprove the state's lists and TMDLs; if EPA disapproves, it must establish TMDLs itself. A TMDL represents the maximum amount of a pollutant a waterbody can receive and still meet standards, and is commonly expressed as the sum of wasteload allocations (for point sources) and load allocations (for nonpoint sources and natural background), see 40 C.F.R. § 130.2. The CWA does not confer direct regulatory authority upon EPA over nonpoint sources; instead, implementation of nonpoint-source controls occurs principally through state programs and planning under §§ 303(e) and 319. Where statutory language is ambiguous, EPA's reasonable interpretation is entitled to deference under Chevron.
Yes. Section 303(d) requires TMDLs for all impaired waters, including those impaired solely by nonpoint sources. EPA may approve or, if necessary, establish such TMDLs. However, TMDLs do not themselves regulate nonpoint sources or impose enforceable controls on landowners; implementation of nonpoint-source load allocations remains within state discretion.
Pronsolino is a leading case on the reach of § 303(d) and the nature of TMDLs. It clarifies that TMDLs are required for all impaired waters, ensuring no statutory gap for nonpoint-source pollution, while reaffirming the cooperative federalism model: EPA sets targets and oversees planning; states choose how to implement. For environmental and administrative law students, the case illustrates Chevron deference, textual and structural interpretation, the relationship between §§ 303(d) and 319, and the distinction between informational planning tools and enforceable regulations. It is frequently cited in Clean Water Act litigation and policy debates over watershed-based management and nonpoint-source control.