Betty and Guido Pronsolino, the Mendocino County Farm Bureau, the California Farm Bureau Federation, and the American Farm Bureau Federation (collectively the Pronsolinos) challenged the authority of the Environmental Protection Agency (EPA) under the Clean Water Act (CWA)[1] to set a Total Maximum Daily Load (TMDL)[2] for the Garcia River, polluted only by nonpoint source pollution. The Pronsolinos were private owners of forest land in Northern California who applied for harvest permits from the California Department of Forestry and the Regional Water Quality Control Board and were required by the state to comply with certain conditions to meet the requirements of the Garcia River TMDL. The district court ruled in favor of EPA and the Pronsolinos appealed. The Ninth Circuit affirmed the district court's ruling, finding that EPA's interpretation of the statute was reasonable and entitled to judicial deference.

The issue in this case was whether EPA properly interpreted section 303(d) of the CWA to allow EPA to require states to set TMDLs for rivers polluted only by nonpoint source pollution. Section 303(d) requires that states list and prepare TMDLs for "those waters within [the state's] boundaries for which the effluent limitations required by section 301(b)(1)(A) and section 301(b)(1)(B) of this title are not stringent enough to implement any water quality standard applicable to such waters."[3] The Pronsolinos argued that to trigger the need for a TMDL, the statute required that a water body be both subject to effluent limitations and noncompliant with water quality standards. Because effluent limitations apply only to point source discharges, the Pronsolinos reasoned that waters impaired only by nonpoint source pollution were excluded from the TMDL requirement. However, EPA interpreted the "not stringent enough" language of section 303(d) to mean that a water body must be listed if the use of effluent limitations would not implement applicable water quality standards.

The Ninth Circuit first determined that EPA's interpretation of the Clean Water Act embodied in its regulations was entitled to deference under Chevron U.S.A., Inc. v. Natural Resources Defense Council, Inc. (Chevron),[4] because "Congress delegated authority to the agency generally to make rules carrying the force of law, and [EPA's regulations were] promulgated in the exercise of that authority."[5] Under Chevron deference, the court must defer to the agency's interpretation of an ambiguous provision "as long as it is reasonably consistent with the statute."[6] Alternatively, the court determined that EPA's interpretation was entitled to deference under the less rigorous Skidmore v. Swift & Co.[7] standard, based on the persuasiveness of EPA's position in light of the agency's "expertise, care, consistency, and formality, as well as the logic of the agency's position."[8]

Before reaching its statutory analysis, the Ninth Circuit responded to the Pronsolinos' initial argument that EPA's regulations did not expressly interpret section 303(d) to require TMDLs for rivers polluted solely by nonpoint source pollution. The court determined that EPA's regulations provided for TMDLs for such rivers based on several sections of the agency's regulations. First, the court pointed to the agency's definition of a TMDL as the "sum of the individual WLAs [wasteload allocations] for point sources and LAs [load allocations] for nonpoint sources and natural background."[9] The court reasoned that because the waste load allocation for point sources could conceivably be zero, the regulations allowed that a TMDL could apply where there is only a load allocation for nonpoint source pollution. The court also reasoned that section 130.7 of EPA's regulations did not distinguish between sources of pollution for purposes of TMDLs because this section required states to identify rivers that required TMDLs if "[o]ther pollution control requirements (e.g., best management practices) . . . are not stringent enough,"[10] where best management practices pertained to nonpoint source pollution.[11] The court further noted that under section 130.3 of EPA's regulations, a purpose of water quality standards is to provide "federally-approved goals to be achieved both by state controls and by federal strategies other than point source technology-based limitations."[12] Thus, a distinction between point and nonpoint source pollution was not relevant in the TMDL context.

The Pronsolinos next argued that EPA's position was not entitled to deference because the agency did not consistently interpret the CWA to allow TMDLs for waters polluted only by nonpoint sources. The court rejected this argument, determining that since 1973 EPA had consistently interpreted the CWA to require the identification of waters not meeting water quality standards "'even after the application of the effluent limitations.'"[13] The court further determined that any past failures of EPA to actively require TMDLs for waters polluted only by nonpoint sources only reflected a general failure to enforce the section 303(d) requirements regardless of the source of pollution.

The court then reached its analysis of section 303(d) of the CWA, considering the parties' competing interpretations of the language "not stringent enough to implement any water quality standard."[14] The court viewed the major difference between the arguments as whether one interpreted "not stringent enough" to mean not strict enough (as the Pronsolinos argued) or not adequate enough (as EPA argued). The court reasoned that a logical reading of section 303(d) looked forward towards the section's goal of achieving water quality standards, which obviated the need for any distinction between sources of water pollution.

The court found that the statutory context of section 303(d) supported EPA's interpretation because it began with the broad requirement that states identify all waters within their boundaries. The second step was to identify those waters for which technology would not achieve any applicable water quality standards. The court reasoned that the Pronsolinos' interpretation would awkwardly require that states first establish a list of waters with point source discharges subject to effluent limitations, and only then look at whether effluent limitations were not adequate. The court reasoned that EPA's interpretation gave meaning to Congress's intent that EPA first focus on implementing effluent limitations and later look to managing water quality standards. The court notably relied on its decision in Dioxin/Organochlorine Center v. Clarke.[15] There the court held that EPA acted within its statutory authority in setting TMDLs for toxic pollutants not subject to effluent limitations under sections 301(b)(1)(A) or 301(b)(1)(B) because "since best practical technology effluent limitations do not apply to toxic pollutants, those limitations are, as a matter of law, 'not stringent enough' to achieve water quality standards."[16] This reasoning justified a similar outcome for waters polluted by nonpoint sources to which effluent limitations did not apply.

The court then looked to the purpose and structure of the statute to dismiss the Pronsolinos' argument that the CWA as a whole distinguished between point and nonpoint sources. The court reasoned that there was no such distinction with regard to the basic purpose of section 303(d), the attainment of water quality standards, nor to the placement of section 303(d) in the Water Quality and Implementation Plans section of the statute.[17] Furthermore, the court found that because the CWA is "replete with multiple listing and planning requirements,"[18] the existence of sections 208[19] and 319,[20] dealing exclusively with nonpoint sources, did not preclude treatment of nonpoint sources in section 303(d). Finally, the court determined that since section 303(d) clearly required that mixed waters be listed (those polluted by both point and nonpoint sources), it would be unreasonable to read the statute to not allow a river to be listed where there was only nonpoint source pollution.

The final argument raised by the Pronsolinos was that EPA's interpretation of section 303(d) intruded into areas of traditional state control because establishing TMDLs for nonpoint sources would allow EPA authority over land-use decisions. The Pronsolinos relied on Solid Waste Agency of Northern Cook County v. United States Army Corps of Engineers[21] to support their argument that EPA's interpretation was invalid because it "upset the balance of federal-state control established in the CWA."[22] The court found these federalism concerns irrelevant because the implementation of TMDLs remained within the states' exclusive authority. The TMDLs, the court concluded, were merely "informational" tools.[23] In short, the Ninth Circuit deferred to EPA's interpretation of section 303(d) of the CWA because it concluded that the agency's interpretation of the statute was reasonable.