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based on spatially intensive shallow-water monitoring turbidity data converted to Kd 
(light attenuation coefficient), interpolated as described in Chapter 2 and then 
compared to the corresponding Kd threshold assigned to each interpolator grid cell. 
The total acreage of an interpolator grid cell is added to the running total water 
clarity acres for a segment when the interpolated Kd for that cell is less than or equal 
to the Kd threshold assigned to that cell. 
The Kd value based on achieving the applicable water clarity criteria at the 2-meter 
depth will apply to all interpolator grid cells with centroids within the 2-meter to 1- 
meter depth contours. All interpolator grid cells with centroids that lie within the 
area bounded by the shoreline and the 1 -meter contour will be assigned the Kd value 
for the 1 -meter depth. 
If the segment's single best year of water clarity acres, as calculated above, is equal 
to or greater than the segment's water clarity restoration acreage, then that segment 
has attained the shallow-water bay grass designated use. If the segment’s single best 
year of water clarity acres is less than the segment’s water clarity restoration acreage, 
then the segment is in non-attainment of this designated use. 
The EPA recommends the states adopt one of two approaches to calculating water 
clarity acres. Both methodologies directly account for progress towards meeting the 
SAV restoration goal acreage and measurement of suitable shallow water habitat 
acreage necessary to support restoration of the remaining SAV beds needed to reach 
the goal acreage. 
The first methodology was originally published in the 2004 Chesapeake Bay water 
quality criteria addendum (U.S. EPA 2004a). This methodology assesses attainment 
of the shallow-water bay grass designated use in a segment through a combination 
of mapped SAV acreage and meeting the applicable water clarity criteria in an addi¬ 
tional, unvegetated shallow water surface area equal to 2.5 times the remaining SAV 
acreage necessary to meet the segment's restoration goal (SAV restoration goal 
acreage minus the mapped SAV acreage). In other words, a segment’s shallow-water 
bay grass designated use would be considered in attainment if there is sufficient 
acres of shallow-water habitat meeting the applicable water clarity criteria to support 
restoration of the remaining acres of SAV, beyond the SAV beds already mapped, 
necessary to reach that segment’s SAV restoration goal acreage. These measure¬ 
ments of SAV acreages and water clarity levels would be drawn from three years of 
data as previously described in the Regional Criteria Guidance (U.S. EPA 2003a). 
Here’s a hypothetical example of this first methodology for determining attainment 
of the shallow-water bay grass designated use using both mapped SAV acreage and 
shallow-water habitat acreage meeting the water clarity criteria. Segment X has an 
SAV restoration goal acreage of 1,400 acres. Over the past three years, SAV beds 
totaling 1,100 acres have been mapped within the segment. Therefore, the remaining 
SAV acreage necessary to meet the segment’s restoration goal is 1,400 acres 
(segment SAV restoration goal) minus 1,100 acres (SAV acres currently mapped) or 
300 acres. Beyond the currently vegetated shallow-water habitat, an additional 
chapter v 
Refinements to the Shallow-Water Designated Use Assessment Procedures 
