Aguilar, Alex M.

Thompson Engineering

State Study 225

Tech Report

Mississippi

Mississippi. Dept. of Transportation

The objective of this project was to establish baseline turbidity conditions at select construction

sites by establishing a water quality monitoring program and documenting MDOT approved

BMPs on site. In 2009 the United States Environmental Protection Agency (EPA) proposed a

numeric turbidity limit for stormwater runoff at construction sites. The proposed limit of 280

NTUs was stayed due to a miscalculation, and EPA has not released a new numeric limit for

turbidity. Current Mississippi Department of Environmental (MDEQ) Water Quality Standards

(WQS) require that turbidity 750 feet downstream from the point of discharge not exceed the

background turbidity levels upstream of the discharge point buy 50 NTU. MDOT has no method

of evaluation in place to measure turbidity at construction sites; and therefore, no background

data are available to indicate how current erosion and sedimentation BMPs are performing with

respect to potential increases in turbidity. Methods of analysis used in this report included the

collection of turbidity data from seven sites where MDOT construction posed a potential threat

to waters of the state. Prospective sites had to meet certain criteria in order to be used for the

study.

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09-2118-0034

US Transportation Collection