amount of time a water parcel is above or below a particular concentration, but does 
not address the length of individual exposure, rate of re-exposure, or a specific event- 
duration such as daily or 7-day mean. 
WATER CLARITY CRITERIA ASSESSMENT 
'Recommended' Level of Monitoring 
Because the DATAFLOW technology is the only viable approach for assessing water 
quality conditions in shallow-water designated use areas, there is only a ‘recom¬ 
mended’ level of monitoring for assessing the water clarity criteria. Significant 
spatial and temporal variability are expected in the shallow-water designated use 
area. The DATAFLOW is best suited to address the high level of variability and 
provide data for credible assessments of criteria attainment. The only option for 
reduced costs in shallow-water monitoring is to limit either the total number of tidal 
systems assessed and/or the frequency of monitoring events for each system that are 
conducted during a single year. 
Assessing Attainment of the Shallow-Water Bay Grass 
Designated Use 
Restoring underwater bay grasses to areas supporting “the propagation and growth 
of balanced, indigenous populations of ecologically, recreationally and commer¬ 
cially important fish and shellfish inhabiting vegetated shallow-water habitats” is 
ultimately the best measure of attainment of the shallow-water bay grass designated 
use. To determine the return of water clarity conditions necessary to support restora¬ 
tion of underwater grasses and, therefore, attainment of the shallow-water designated 
use, states may: 1) evaluate the number of acres of underwater bay grasses present 
in each respective Chesapeake Bay Program segment, comparing that acreage with 
the segment’s bay grass restoration goal acreage; and/or 2) determine the attainment 
of the water clarity criteria within the area designated for shallow-water bay grass 
use. The shallow-water bay grass use designated use area may be defined by either: 
1) applying the appropriate water clarity criteria application depth (i.e., 0.5, 1 or 2 
meters) along the entire length of the segment’s shoreline (with exception of those 
shoreline areas determined to be underwater bay grass no-grow zones; see U.S. EPA 
2003 for details); or 2) determining the necessary total acreage of shallow-water 
habitat within which the water clarity criteria must be met using a salinity regime 
specific ratio of underwater bay grass acres to be restored within a segment to acres 
of shallow-water habitat that must meet the water clarity criteria within the same 
segment (regardless of specifically where and at what exact depth those shallow 
water habitat acreages reside within the segment). These approaches to assessing 
attainment of the shallow-water bay grass designated use are described below in 
more detail. 
Assessing Underwater Bay Grasses Restoration. In response to a commit¬ 
ment in the Chesapeake 2000 agreement, the Chesapeake Bay watershed partners 
chapter vi • Recommended Implementation Procedures 
