Definitions

Measurable Goal

BMP design objectives (goals) that quantify the process of implementation and performance. Measurable goals contain descriptions of the actions taken to implement each BMP, the frequency and dates for each action, and what is expected to be achieved. (EPA - Measurable Goals Guidance for Phase II Small MS4's - pg. 8)

Retention Pond

An area designed to hold storm water until the effects of percolation, evapotranspiration, and/or controlled release, return the area to its normally dry state. The area is designed so storm water inflow is dissipated (or slowly released) within 72 hours so that a new volume can be accommodated. Since these storm water areas are designed to be dry, they are often called "dry-retention systems."

Detention Pond

A permanent or semi-permanent aquatic system that dries out only under drought conditions. Storm water entering a detention area displaces an equivalent amount of water. The detention pond acts as a trap where pollutants picked up by the initial surge of storm water settle out before leaving the detention pond. These ponds are usually referred to as "wet-detention systems."

Municipal Separate Storm Sewer System (MS4)

A MS4 is a conveyance or system of conveyances (including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains) owned or operated by a municipality, township, or local sewer district, state or federal department of transportation, university, hospital, military base, or correctional facility.