Assessment of Designated Uses in Maryland's Water Quality Programs
The designated uses defined in the Code of Maryland Regulations are evaluated using a limited set of field and analytical measures. Key parameters include water temperature, dissolved oxygen, pH, turbidity, water clarity (Secchi depth or light extinction), acreage of estuarine grasses, ammonia levels, biological integrity, and specific bacteria levels. While measures of nitrogen and phosphorus (nutrients) are monitored, they are not yet defined in terms of criteria. However, exceedances in dissolved oxygen or chlorophyll a criteria, along with nuisance algal blooms, are often linked to elevated nutrient levels. Metals and both inorganic and organic parameters are not routinely measured due to high analysis costs and the low likelihood of finding these substances at levels exceeding criteria, except in special studies or discharge permit requirements. Specific toxins, such as mercury and PCBs, are monitored through MDE's fish and shellfish programs.
Data Review Process
Water quality datasets used for assessing designated uses are first evaluated based on the corresponding QAPP or other reports that outline monitoring objectives and quality control measures. Key steps in this review include:
- Sample Size and Distribution: Assessing whether the sample size is adequate and analyzing data distribution, including identifying outliers or errors.
- Spatial and Temporal Distribution: Evaluating how data varies over space and time.
- Censored Data: Examining any censored data and field notes for unusual events (e.g., storm events) that may impact data quality.
- Seasonality and Correlations: Analyzing data for seasonal trends and known correlations (e.g., between conductivity and salinity). Censored data may be excluded from analyses if necessary.
Alternative Assessment Approaches
Not all water quality criteria assessments follow this methodology. Some assessments are conducted by other state programs using peer reviewed or specific methods and these results are not re-evaluated. Examples include:
- Assessment of algal samples
- Maryland's probabilistic non-tidal living resource survey (MD Biological Stream Survey)
- Fish kill and bacterial assessments
- Bathing and shellfish harvesting restrictions
- Toxic contaminants in fish tissue, shellstock, and sediments
Additionally, some assessments are conducted by external agencies such as the Virginia Institute of Marine Science, MD DNR, Versar, Inc., Old Dominion University, and EPA's Chesapeake Bay Program. In these cases, assessment methods are peer-reviewed, and results are submitted to the state without further re-evaluation. Examples of such assessments for Maryland's Chesapeake Bay and tidal tributaries include:
- Benthic community criteria
- Aquatic grass coverage
- Water clarity
- Dissolved oxygen levels
Innovative Approaches and Modeling
MDE supports the integration of computer models and innovative methods in water quality monitoring and assessment. The Chesapeake Bay model plays a crucial role in developing loading allocations, evaluating the effectiveness of best management practices, and guiding implementation efforts. Various modeling approaches are also utilized in the development of Total Maximum Daily Loads (TMDLs). Given the high number of biological impairments listed in Category 5 of the Integrated Report, Maryland is increasingly relying on land use analyses, GIS modeling, data mining, and other innovative techniques to identify stressors, define ecological processes, and develop TMDLs.