Baltimore County is required by the United States Environmental Protection Agency (USEPA) and the Maryland Department of the Environment (MDE) to take routine bacteriological samples at public bathing beaches. Baltimore County also samples in larger areas of open water subject to frequent recreational use. Various chemical parameters such as temperature, salinity, and pH are also routinely measured.
Bathing beach monitoring consists of five samples taken in a pattern designed to represent the designated swimming area at the facility. Sample runs are made every two weeks for tidal water bathing beaches and monthly at fresh water bathing beaches.
Non-regulated open areas in tidal waters typically subject to recreational uses such as boating, fishing, skiing, or wind surfing that involve only occasional full body contact and occasional accidental ingestion of water are also sampled on a bi-weekly basis.
Sampling for tidal waters is typically conducted from early April through November, weather permitting. Sampling at fresh water beaches is performed from Memorial Day through Labor Day. Additional sampling may be initiated in response to unusual conditions or events that could negatively impact water quality and public health.
Sampling Result Standards
Recreational water quality standards are used to determine the relative risk of illness for swimmers. Beach closures and associated Water Contact Alerts are based on consideration of the geometric mean of results for that beach or area and any known or suspected sewage contamination. The association of sewage contamination with elevated indicator organism concentrations is particularly important because sewage carries a significant array of human pathogens, greatly increasing the possibility of contracting a water borne illness. Elevated, naturally occurring bacteria concentrations due to water fowl, marsh decomposition, or normal ground surface runoff are, in general, not considered to have as great a public health significance.
The USEPA/MDE bacteriological standard for consideration of beach closure at tidal beaches is a geometric mean of 35 MPN, Enterococci. The USEPA/MDE bacteriological standard for fresh water beaches is a geometric mean of 126 MPN, E. coli.
Water Quality Characterization for Open Water
The results for open recreational waters are considered individually and as a geometric mean. The geometric mean beach closure standards for Enterococci and E. coli are used for comparison purposes only in conjunction with information regarding known or suspected sewage contamination to evaluate the need for a Water Contact Alert.
In cases where there is no suspected sewage overflow, there are no mandated standards for evaluation. The County, therefore, considers sampling results, other sources of possible contamination, sampling history, and environmental factors to determine the need for increased concern, investigation, or public notification regarding water quality.
This evaluation also reflects the manner in which the public uses these waters. The majority of activities, which routinely occur in these areas, seldom involve the participation of very young children or immune-compromised individuals. In addition, activities do not typically consist of constant, complete repeated immersion in, or ingestion of water. This reduces both the opportunity for exposure and pathways for bacteria to enter the body. Occasional, reduced water quality in these areas therefore poses less of a risk to the general recreational population.
Revised June 5, 2012
Revised April 6, 2016