established application depth or attainment of the applicable water clarity criteria 
throughout an established potential shallow-water habitat acreage. The available 
supporting technical information on segment-specific underwater bay grass 
acreages, application depths and potential shallow-water habitat acreages are 
described in the “Monitoring to Support the Assessment of Criteria Attainment,” 
section of this chapter and published in detail in the Technical Support Document for 
the Identification of Chesapeake Bay Designated Uses and Attainability (U.S. EPA 
2003). 
CHLOROPHYLL A CRITERIA 
Because of the regional and site-specific nature of algal-related water quality impair¬ 
ments, only narrative chlorophyll a criteria have been published here. The 
chlorophyll a concentrations tabulated in Chapter V are not numerical EPA criteria. 
Along with the documented methodologies, they are provided as a synthesis of the 
best available technical information supporting the states’ development and adoption 
of site-specific numerical chlorophyll a criteria or the derivation of numerical trans¬ 
lators for their narrative chlorophyll a criteria. 
The narrative Chesapeake Bay chlorophyll a criteria were derived to address the full 
array of possible impairments, all of which may not manifest themselves within a 
particular water body at a given time (Table VI-3). The site-specific nature of impair¬ 
ments caused by the overabundance of algal biomass supports the states’ adoption of 
the EPA-recommended narrative criteria, with application of site-specific numeric 
criteria only for localized waters addressing local algal-related impairments. 
The EPA expects states to adopt narrative chlorophyll a criteria into their water 
quality standards for all Chesapeake Bay and tidal tributary waters. The EPA 
strongly encourages states to develop and adopt site-specific numerical chlorophyll 
a criteria for tidal waters where algal-related impairments persist after the Chesa¬ 
peake Bay dissolved oxygen and water clarity criteria have been attained. 
The formulation and ultimately the assessment of numerical chlorophyll a criteria 
should be based upon seasonal dynamics and concentrations of chlorophyll a in the 
Chesapeake Bay and its tributaries. Spring and summer were chosen for these 
purposes. Any site-specific numerical impairment-based chlorophyll a criteria 
should be applied as salinity regime-based spring (March through May) and summer 
(July through September) seasonal mean concentrations. 
Table VI-3. Recommended Chesapeake Bay chlorophyll a narrative criteria. 
Concentrations of chlorophyll a in free-floating microscopic aquatic plants (algae) shall 
not exceed levels that result in ecologically undesirable consequences-such as reduced 
water clarity, low dissolved oxygen, food supply imbalances, proliferation of species 
deemed potentially harmful to aquatic life or humans or aesthetically objectionable 
conditions-or otherwise render tidal waters unsuitable for designated uses. 
I 
chapter vi • Recommended Implementation Procedures 
