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and embayments. EPA provided three measures for assessing attainment of the 
shallow-water Bay grass designated use for a Chesapeake Bay segment: 
1. measure SAV acreage from overflight data mapping analysis and compare with 
the targeted restoration goal acreage of SAV in a given segment; 
2. goal attainment may be achieved if sufficient shallow-water area with the water 
clarity necessary to achieve restoration of the targeted SAV exists, based on 
routine water quality mapping using data from the Chesapeake Bay shallow- 
water monitoring program. This measurement concept is defined as “water 
clarity acres” (see p. 54, U.S. EPA 2007); and 
3. if the water-clarity criteria were attained through the shallow-water designated 
use reaching to a specific contour (i.e., segment-specific water clarity criteria 
application depth) based on the cumulative frequency diagram assessment 
methodology, again based on shallow-water monitoring program data (U.S. 
EPA 2003a, 2003b, 2007). 
Assessment of either SAV acreage, water clarity acres, or a combination of both, 
serves as the basis for determining attainment or impairment of the shallow-water 
designated use (U.S. EPA 2007). In the absence of sufficient shallow-water moni¬ 
toring data to determine the available water clarity acres or assess water clarity 
criteria attainment using the CFD-based procedure, the EPA recommends that the 
states assess shallow-water bay grass designated use attainment based on the acres 
of mapped SAV (see Chapter 8 of U.S. EPA 2007). 
REVISION OF THE WATER CLARITY ACRES 
ASSESSMENT METHODOLOGY 
Revision of the water clarity acres assessment methodology involves clarification of 
the attainment method previously published in 2007 (U.S. EPA 2007). The 2007 
published attainment method recommended assessments to be made from a mean of 
annual means for three years of assessments (see p. 54). The revised methodology 
evaluates each year in the three-year cycle for a single best year attainment evalua¬ 
tion of segment restoration goals. This attainment assessment framework could be 
used when mapped SAV acres alone do not meet its restoration goal and as an alter¬ 
native to the CFD-based water clarity criteria assessment method (Table IV-1). 
The detailed standard operating procedures (SOPs) that define the detailed computer 
workstation methods used in each State from the import of data through data 
processing, regression calculations, interpolations and attainment assessment are 
available from Maryland and Virginia (Maryland Department of Natural Resources 
2008, Virginia Departments of Environmental Quality 2008). These specific SOPs 
are updated with computer coding revisions that maintain the standard baywide 
framework of the criteria assessment methodology but acknowledge such State 
specific issues as changes with new software and software updates, new data sources 
and programming efficiency updates to accomplish the tasks. 
chapter iv 
Refinements to Procedures for Assessing Chesapeake Bay Water Clarity and SAV Criteria 
