Biomass combustion should not be an approved compliance method under the Clean Power Plant because burning trees is not carbon neutral, both senators from Massachusetts told the Environmental Protection Agency (EPA) on Friday.

In a letter to EPA Administrator Gina McCarthy, Sens. Ed Markey (D-Mass.) and Elizabeth Warren (D-Mass) said that treating bioenergy as having zero emissions under the plan would undermine its purpose, which is to slash U.S. power sector carbon emissions by 30% from 2005 levels by 2030.

“As the EPA knows, wood-burning power plants emit around 3,000 pounds of carbon dioxide per megawatt-hour. A growing body of scientific evidence, including a study commissioned by the State of Massachusetts, has found that it takes decades of forest regeneration to offset these emissions,” the letter reads.

The lawmakers recommended that the EPA impose a moratorium extending to 2020 on the use of biomass combustion as a compliance method until the agency could develop a “robust method” in place “to account for facility-level emissions and a means of ensuring that emissions offsetting actually occurs in an appropriate timeframe.”

By 2020, states will have had the opportunity to apply for modifications to their implementation plans. The approach would give the EPA time to finalize a biogenic carbon accounting framework and focus on near-term state efforts on wind, solar, and other zero-carbon renewable energy technologies.

While they understood the plan is not yet final, aspects of the plan indicate that the EPA may decide to treat all bioenergy generation as having no greenhouse gas emissions, the senators wrote. “For example, the equation that EPA used to calculate state-level emissions rate goals includes all of the energy, but none of the emissions, associated with renewable generation—including bioenergy, which is not a zero-carbon technology.”

Massachusetts has already eliminated renewables energy subsidies for utility-scale wood-burning power plants, the lawmakers noted.

The EPA[can’t name the spokesperson?] told POWER in a statement on Tuesday that it had already addressed the issue in its biogenic carbon framework, which was revised last November after several years of litigation. The revision essentially declares that waste-derived materials, biogas, and forest-derived industrial products are “likely to have minimal or no net atmospheric contributions of biogenic [carbon dioxide] emissions, or [could] even reduce such impacts, when compared with an alternate fate of disposal.”

“We’ve received 4.3 million comments on the proposed Clean Power Plan, including comments on the treatment of biomass. We’re considering all of the comments we’ve received as we work to finalize the rule this summer,” said the EPA.

Sonal Patel, associate editor (@POWERmagazine, @sonalcpatel)