The state of Texas is in EPA region 6, and instead of statewide regulation operates regionally on MS4s. Volume control and post-construction requirements come from EPA/federally legislation and may vary based on additional municiple requirements.
"The Storm Water Management Program (SWMP) is a comprehensive program to manage the quality of discharges from the municipal separate storm sewer system (MS4). TxDOT does not utilize a single statewide SWMP but rather a district-specific SWMP that is based on a standardized plan.
The Texas Commission on Environmental Quality requires that the SWMP must contain a specified number of minimum control measures (MCM). In order to meet each required minimum control measure, TxDOT utilizes best management practices."
Required Minimum Control Measures
"A Large or Phase I MS4 Permit is issued to an operator, such as a city or county, who owns or operates storm sewers or storm sewer systems that serve populations of 100,000 or more.
A Small or Phase II MS4 Permit is issued to an operator, such as a county, university or transportation authority, who owns or operates storm sewers or storm sewer systems that serve populations within urbanized areas."
Storm Water Management and Best Management Practices
Storm water is defined in the Construction General Permit (CGP) as "Rainfall runoff, snow melt runoff, and surface runoff and drainage." For TxDOT purposes, storm water includes overland flow, and flow in ditches and storm drain systems.
Storm water management includes non-structural and structural measures such as the following:
Measures intended to mitigate storm water quantity and quality problems are termed “best management practices” (BMPs). These measures include detention and retention ponds which delay storm water flow and trap sediment, rock filter dams for the same reasons, silt fences to trap sediment, various filter materials in socks or tubes, and vegetation to retard flow and trap sediment.