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cha pter IX 
Determining Where Numerical 
Chlorophyll a Criteria Should 
Apply to Local Chesapeake Bay 
and Tidal Tributary Waters 
As published in Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity 
and Chlorophyll a for Chesapeake Bay and Its Tidal Tributaries (U.S. EPA 2003): 
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 impair¬ 
ments are expected to persist even after the Chesapeake Bay dissolved 
oxygen and water clarity criteria have been attained. 
The Chesapeake Bay Program partners developed a general methodology for 
possible use by the jurisdictions with tidal waters to determine consistently which 
local tidal waters will likely attain the published Chesapeake Bay dissolved oxygen 
and water clarity criteria yet algal-related water quality impairments will persist. The 
methodology is for application by Maryland, Virginia, Delaware and the District of 
Columbia to assist in their future determinations of where they need to derive and 
apply numerical chlorophyll a criteria for localized tidal waters. 
RECOMMENDED METHODOLOGY 
The jurisdictions should evaluate the available Chesapeake Bay Water Quality Moni¬ 
toring Program’s time series of spring and summer chlorophyll a concentrations on 
a station by station, segment by segment basis and compare these concentrations to 
a range of season and salinity regime-based target chlorophyll a concentrations. 
Target concentrations, examples given in Table IX-1, should be derived from 
published chlorophyll a concentrations associated with an array of water quality and 
biological community effects and impairments. The jurisdictions should then iden¬ 
tify those stations/segments that are persistently higher than the applicable target 
chlorophyll a concentrations with the individual jurisdictions developing their own 
chapter ix 
Determining Where Numerical Chlorophyll a Criteria Should Apply 
