The designated uses defined in the Code of Maryland Regulations are assessed by relatively few field and analytical measures. Water temperature, dissolved oxygen, pH, turbidity, water clarity (Secchi depth or light extinction), acres of estuarine grasses, ammonia, biological integrity, and certain bacteria levels define the principal data used to assess criteria attainment. Various measures of nitrogen and phosphorus (nutrients) have not been defined in terms of criteria, although exceedance of dissolved oxygen or chlorophyll a criteria or nuisance levels of algae are attributed to high levels of nutrients. Except for special studies or as a discharge permit requirement, metals, inorganic and organic parameters defined as criteria are not routinely measured due to the high cost of analysis and few of these substances are found in ambient waters at levels exceeding criteria. Specific toxins known to be directly related to human health (i.e., mercury and PCBs) are assessed through MDE’s fish and shellfish monitoring programs.
Water quality datasets reviewed for assessing use support are first examined in terms of a QAPP or other reports that define monitoring objectives and quality control. For selected parameters, the data are reviewed for sufficient sample size, data distribution (type and outliers/errors) and spatial and temporal distribution in the field. Censored data and field comments are examined for unusual events that may affect data quality (e.g., storm event). Data are examined for seasonality and known correlations (e.g., conductivity and salinity) are reviewed. Censored data are noted and may be excluded from the analysis.
Not all water quality criteria are assessed using this approach. Some assessments are conducted by other state programs using peer-reviewed or defined methods (e.g., Maryland’s assessment methodologies) and are not re-evaluated using other approaches. Examples include; assessment of algal samples, the state’s probabilistic non-tidal living resource survey (MD Biological Stream Survey), fish kill and bacterial assessments, bathing and shellfish harvesting restrictions, and toxic contaminants in fish tissue, shellstock and sediments.
Some criteria assessments are conducted externally by other agencies and programs such as VA institute of Marine Science, MD DNR, Versar, Inc., Old Dominion University, and EPA’s Chesapeake Bay Program. In these circumstances, the assessment methods are peer reviewed and results are provided to the state. Criteria assessed in this manner are not re-evaluated. Examples include; for Maryland’s Chesapeake Bay and tidal tributaries, benthic community criteria, aquatic grass coverage, water clarity, and dissolved oxygen.
MDE supports the use of computer models and other innovative approaches to water quality monitoring and assessment. Maryland and the Bay partners have also relied heavily on the Chesapeake Bay model to develop loading allocations, assess the effectiveness of best management practices, and guide implementation efforts. Several different modeling approaches have also been used in TMDL development. With the large number of biological impairments in Category 5 of the IR, Maryland has been relying more heavily on land use analyses, GIS modeling, data mining, and other innovative approaches to identify stressors, define ecological processes, and develop TMDLs.