Water Quality Analysis of Eutrophication of the St. Mary's Lake, St. Mary's County, Maryland.

摘要

Section 303(d) of the federal Clean Water Act (CWA) and the Environmental Protection Agency (EPA)s implementing regulations direct States to identify and list waters, known as water quality limited segments (WQLSs), in which current required controls of a specified substance are inadequate to achieve water quality standards. For each WQLS, the State is to either establish a Total Maximum Daily Load (TMDL) of the specified substance that the waterbody can receive without violating water quality standards, or demonstrate that water quality standards are being met. St. Marys Lake in the St. Marys River watershed (02-14-01-03) was identified on Marylands 1998 list of WQLSs as being impaired by nutrients, with an additional impairment of mercury appearing on its 2002 list. This report provides an analysis of recent monitoring data, which shows that the dissolved oxygen criterion and designated uses associated with nutrients are being met in St. Marys Lake. This analysis supports the conclusion that a TMDL for nutrients is not necessary to achieve water quality standards in this case. Barring any the receipt of contradictory data, this report will be used to support the removal of St. Marys Lake from Marylands list of WQLSs when MDE proposes the revision of Marylands 303(d) list for public review in the future. Although the waters of St. Marys Lake do not display signs of eutrophication, the State reserves the right to require additional pollution controls in the St. Marys watershed if evidence suggests that nutrients from the basin are contributing to downstream water quality problems. The mercury impairment is being addressed in a document entitled Total Maximum Daily Load of Mercury for St. Marys Lake, St. Marys County, Maryland.