Chesapeake Bay State and Local Backstop Limitation Act of 2012

Chesapeake Bay State and Local Backstop Limitation Act of 2012 - Prohibits the Administrator of the Environmental Protection Agency (EPA) from: (1) modifying a permit issued under the Federal Water Pollution Control Act (commonly known as the Clean Water Act) before this Act's enactment for a point source in the Chesapeake Bay watershed to require additional reductions in discharges of nitrogen, phosphorus, or sediment; or (2) requiring lower levels of discharges of such pollutants under a national pollutant discharge elimination system (NPDES) permit for a point source in such watershed for purposes of compensating for any lack of progress in a state toward meeting the water quality goals established by the 2010 Chesapeake Bay TMDL (total maximum daily load).

Prohibits the Administrator from revising, for purposes of application in such watershed, the definitions of: (1) "storm water discharge associated with industrial activity" in regulations concerning storm water discharges in the EPA administered NPDES program, and (2) "concentrated animal feeding operation" in regulations concerning the EPA administered NPDES program.

Prohibits the Administrator from requiring a permit under the NPDES program for a discharge of stormwater in such watershed, either from a municipal separate storm sewer system or associated with an industrial activity, for which a permit has not been issued before this Act's enactment.

Prohibits the Administrator, before the date on which all of the nitrogen, phosphorus, and sediment TMDLs established in the 2010 Chesapeake Bay TMDL are met, from: (1) revising the 2010 Chesapeake Bay TMDL to establish more specific or finer scale waste load or load allocations and requiring additional reductions in loadings from point sources; or (2) issuing or enforcing regulations regarding such pollutants for any navigable waters within such watershed in Chesapeake Bay states (Delaware, Maryland, New York, Pennsylvania, Virginia, West Virginia, or the District of Columbia), other than the 2010 Chesapeake Bay TMDL, unless the chief executive of a Bay state approves of such regulation.

Prohibits the Administrator and the Secretary of Agriculture from conditioning, withholding, or redirecting grants related to water quality in Bay states under the Clean Water Act or the Food Security Act of 1985 because Bay states do not meet the water quality goals established for them in the 2010 Chesapeake Bay TMDL, unless the Administrator or the Secretary has offered technical assistance in meeting such goals and the Bay state has failed to show reasonable progress in meeting such goals after a sufficient amount of time.